We are playing our part in the supply of food for Pakistan... yesterday, today and tomorrow
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Table of Contents Acknowledgement ..................................................................... ................................................................................................................................. ............................................................ 3 Preface ................................................................. ....................................................................................................................................... ................................................................................... ............. 5 Training Program ............................................................ ............................................................................................................................... ........................................................................ ..... 7 An Introduction to FFC .............................................................. ........................................................................................................................... ............................................................. 8 Learning at the Safety Orientation ................................................................... ......................................................................................................... ...................................... 9 Safety Training ............................................................... ..................................................................................................................................... ......................................................................1 0 An overview to Production & Process Engineering ............................................................... ............................................................................. .............. 20 20 Production Department ............................................................. ....................................................................................................................... ...........................................................25 25 Ammonia Section ............................................................ .............................................................................................................................. ...................................................................... ... 26 Ammonia PFD Front End ............................................................ ...................................................................................................................... ...........................................................45 45 Ammonia PFD Back End ............................................................. ........................................................................................................................ ...........................................................46 46 Utilities Section ............................................................... ..................................................................................................................................... ......................................................................4 7 Utilities Cooling Tower Diagram ........................................................... ........................................................................................................... ................................................ 5 6 Urea Section .................................................................... ......................................................................................................................................... ......................................................................6 0 Bagging &Shipping ...................................................................... ................................................................................................................................ ..........................................................69 69 Basic Interlock System ............................................................... .......................................................................................................................... ...........................................................71 71 Equipment / API Study ............................................................... .......................................................................................................................... ...........................................................72 72 Glossary................................................................ ...................................................................................................................................... ................................................................................. ........... 73 Suggestions / Feedback ............................................................. ........................................................................................................................ ...........................................................76 76 Appendices...................................................................... ............................................................................................................................................ ......................................................................7 7
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Acknowledgement
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ltimately, I have completed my report with all the hard work which I have been doing for the last six weeks. First and foremost, thank you Allah S.W.T for giving me the strength to finish up this report. Without Your Willingness I would not have been able to complete any work. It would be impossible to acknowledge adequately all the people who have been influential, directly or indirectly in providing me with a great assistance in understanding the process and the working of the plant. I would never forget to mention the names, which played a great role in the successful completion of this project, and helped me, whenever I required any guidance from them, provided me with books for assistance and gave me ideas on different thoughts. I would like to take this opportunity to express my deepest gratitude to the unit managers, Mr. Mehmood Raza Gillani and Mr. Akbar Fida Hussain who have given me their constant encouragement constructive advises and their patience in monitoring my progress.
I am very much thankful to FFC which provided a chance for me to integrate my classroom knowledge with industrial practical knowledge in a 6 weeks internship program. I am grateful to these persons who were a great help for me by monitoring my learning and helping me understand the process in numerous interactions. A special thanks to Mr. Syed Mehmood Raza Gillani, excellent guidance on Industrial awareness. I thank Mr. Mushtaq Ahmed of Safety Unit, for his excellent guide on industrial safety awareness. I also want to thank all the Shift Engineers, especially Engr. Saad, Engr. Ramzan, Engr. Adeel, Engr. Waheed Ahmed Bhatti, Engr. Shehzad Yousuf, Engr. Rizwan, Trainee Engr. Ali Zulqarnain, Trainee Engr. Jawad Khan, Trainee Engr. Sanaullah, Trainee Engr. Tahir, Trainee Engr. Saeed, Trainee Engr. Kashif, and Process Engineers. I would not forget to mention about all the kind panel boardmen and operators who had been a very useful guide in the Central Control Room and on the plant site, respectively. Besides my project, I really enjoyed my stay at the FFC MM, appreciated all the people I worked with and spent good moments with them. My gratitude towards them is extremely of high regard. At last, I can say that my work was just an effort but wouldn’t have been an effort discernibly without the support of all acknowledged people.
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Preface Howdy, Assalamualaeikum Warahmatullahi Wabarakatuhu,
You would think those 7 semesters of engineering school, dozens of engineering fundamental and core courses would prepare someone pretty well for a chemical engineering internship at a fertilizer industry such as Fauji Fertilizer Company. While I will admit that I may have missed a few classes, I consider my time at FFC MM taught me more about chemical engineering operations than anything I have taken in school. I had a huge variety of experiences and was fortunate to get the opportunity to learn from so many different and extremely talented people. That is what made my internship special – FF C will challenge you to take on as much as you can, even if it means making mistakes or not knowing the answers to simple questions for the first time around. With little over a week under my belt at FFC MM, I realized that it wasn’t just an internship experience, but an institute helping me in knowing the actual philosophy of what chemical engineering was all about. As I learned, issues came up that needed an experienced technocrat, Engr. Syed Mehmood Raza Gillani just told me to go asking about any issues I had on my own. I thought it was really trusting of him to let the new intern just ask what I felt was appropriate, and while it may shock those with cubes near mine, I became a bit unsure about myself raising issues about the plan with an engineer who had experiences of years almost equaling my age. Yet again I found myself learning quite a bit about an area (Instrumentation) that I lesser knew practically about before coming to FFC MM! My internship was not all work and no play though. The outdoor and indoor sports at the Mathelian Club together were well planned, well executed, and very beneficial to me personally. "How things are supposed to be done" to "How things are actually done”. That is what a producti production on engineering experiences teaches.
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This report is about the learning outcomes of internship at Fauji Fertilizer Company Mirpur Mathelo, covering details of its environment, process, operations and other technical information information.. Most of the Information was collected from personnel, datasheets and the on-job training manuals of every department, and is written according to training schedule provided by FFC MM. This helps to understand various steps involved in achieving certain efficiency or the quality of the product. Undoubtedly there is so much to learn from this industry and this is a small effort to compile as much information that has been collected in a six weeks span. The principle knowledge of unit operations, heat transfer and mass transfer operations, combustion, fluid dynamics, catalyst and chemistry was very much useful while the study at the plant and complex. The critical equipments like high temperature large furnaces, boilers, fixed & fluidized bed reactors, molecular sieve driers, heat exchangers, stacks, compressors, steam turbines, pumps, fans, etc. were practically studied. Every morning I came to the plant site, entered the CCR Room, I had a feeling of not knowing anything. That day I used to keep working on overcoming that feeling. And by the end of the day, I tried to convince myself that at least I learnt something today. A sense of self-satisfaction appreciated me by the end of the day somehow. And again, the next day the same daily morning feeling gave me a feeling in retrospect. That was what I believe to be my somehow success. This summer program was an introduction towards a fertilizer industry in general and to the work environment. I thank you for having patience while reading the preface to the following report.
Muhammad Yasser Ramzan BEC-SP08-124
[email protected] BS Chemical Engineering ‘11
Department of Chemical Engineering COMSATS Institute of Information Technology, Lahore
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Summer Internship 2011 Name of Summer Trainee
: Muhammad Yasser Ramzan
Host Department
: Production
Training Duration
: 6 Weeks
Day
Date
Training Activities/ Subject
Time
Activity Sponsor
1st & 2nd
20 & 21-06-2011
Reception & Introduction / SHE Orientation
2 Day
SE/CE/UM
Ammonia Utilities Urea Bagging & Shipping Process Engineering
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An Introduction to FFC For an agricultural country like Pakistan, Urea carries a paramount importance. Fauji Fertilizer Company Ltd. It is the leading urea producing company in the Pakistan. FFC start ed its production in 1982. First plant of the FFC is located at GOTH MACHI in SADIQABAD. After the excellent performance and the successful achievements of the first plant, FFC installed the second plant at the same place in the year 1993. First plant is called the BASE UNIT and the second plant is called the EXPANSION UNIT. In order to fulfill the increasing demand and importance of urea, FFC thought for another plant. Therefore, Therefore, FFC got another plant in 2001 at MIR PUR MATHELO from Govt. of Pakistan NFC (NATIONAL FERTILIZER COMPANY) and is called FFC-3. This internship report is concerned with the plant of FFC-3. This plant was previously named as PAK SAUDI Fertilizers when it was under the provision of Govt. of Pakistan NFC (NATIONAL FERTILIZER COMPANY). The plant is designed to process natural gas which comes from the MARRI GAS FIELD to produce Ammonia (NH 3) and carbon Dioxide (CO 2) which then reacts to produce UREA.
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Learning at the Safety Orientation Orientation In the operation of any type of chemical industrial plant, there are many hazards involved. No matter, what type of plant is considered, the only goal before the workers and the management is to achieve desired production without causing any accident, loss of human life and damage of machinery. Therefore it is very important that the operation of the chemical plant should be carried out in a safe manner, following the safe procedures as guidance. The hazards involved may vary in degree or type but all damages must be rated equal. In fertilizer industries, almost all types of hazards are possible. By nature of the process used, there are involved natural gas (methane), air, hot flue gas, gases under very high pressure, steam at low pressure to very high pressure, toxic chemicals and toxic gases, various types of pumps for high and low pressure, pressure vessels, reactors and other moving machinery, high pressure compressors, etc. Only by correct control of all these things, a fertilizer plant can continue operate without injury to personnel or damage to equipment.
PLANT SAFETY POLICY Fauji Fertilizer Company recognizes the significance of maintaining an injury free environment at plant and therefore must strive to avoid any injury to personnel and any damage to equipment etc. in order to achieve this, management spells out the plant safety policy and expects all employees to comply. The management shall always remains strongly committed to the cause of safety. Safety shall be given at least the same importance as production. Safety shall have a due consideration in performance appraisal appraisal of each employ. Management believes that God willing most accidents can be prevented since most of them are caused by human errors and omission. As and when an accident occurs, the investigation shall be carried out on high priority. The company shall provide the safety training and facilities to all employees, whereas they are responsible for working safely. Adequate personnel protective shall be provided to employees against hazards at plant and full compliance shall be demanded. The management shall formulate safety regulations/procedures while employees shall comply with these regulations and procedures. The contractors shall also follow company’s safety discipline. A good standard of h ousekeeping shall be maintained at the plant. Off-the-job safety shall be promoted among employees and their families Employees are expected to maintain pollution free environment and hygienic conditions throughout the plant.
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Safety Training FFC produces about 60 % of market’s urea production. Not preparing for plant safety may
not only result in decrease of company production and sale but also in shortage of fertilizer in market. This may affect the country’s agriculture growth and thus shortage of food for
public followed by price hiking. FFC ensures safe work environment by providing safety training to all personnel on plant. As per the company policy all news personnel on plant receive safety training prior taking charge of their responsibilities. Safety training was provided to the group comprised of author and two other internee engineers by Mr. Mushtaq Ahmed (Safety Sub-Engineer) on June 21, 2011 at Safety Section, FFC MM. Training introduced with the plant safety policy and rules and regulations, while functioning of safety section was also briefed. The training comprised of: Importance of Safety at Plant Use of Personal Protective Equipment Use of Fire Extinguishers Ammonia Disaster
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FFC BELIEVES IN “SAFETY FIRST” FFC Management is committed to cause of safety and believes that it is everyone's responsibly. The objective is to improve the working culture through effective safety program. Zero lost work days are the target (FFC Safety Section, 2010). Details are enclosed in Appendix II (FFC MM Plant Safety Policy) and Appendix III (FFC Plant Safety Rules and Regulation). Recognition for safe work is arranged in collaboration with NSC, USA. Till July 2010, 8.3 million safe hour operations have been carried out, i.e. no Lost Time Accident (LTA) has taken place since last 8.3 million hours. h ours. FFC MM has also received IMS 2009 certification for safe working other than ISO 9001, ISO 14001 and ISO 18001. Safety Section of FFC MM performs various functions and activities for running an effective safety program through the following hierarchy of section: Deputy Manager(01) Engineers (01) Safety Sub-Engineer (01) Supervisor (01) Safety Operators (08)
Activities FFC Safety section works in both planning ad execution phases to implement safe work conditions at plant, with improved working standards and safety. This includes multidimensional efforts team. Key activities (FFC Safety Section, 2010) of unit are as follows:
Managing Safety Program Main object is to plan, organize, budget, and track execution of activities to achieve safety objectives of our plant laid down in FFC MM Safety Policy (Appendix II). Through prudent planning and effective resource management safety section cater for all the needs of personal and process safety. Motivation Safety section is committed to achieve excellence in the field of safety. All projects related to safety are given top priority and good safety and housekeeping standards are appreciated appreciated through token rewards. This include slogan of the year, best housekeeping award, safe man of the year award and safe men hours’ award. Hazard Recognition It ensures the identification of conditions or actions that may cause injury, illness or property damage, is a routine activity carried out at all levels in plant areas. Plant safety
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committees are formed all hazards of the plant are highlighted and engineering solution are evolved. Safety section also carries out routine audits of the plant and points out hazards to concerned units.
Inspection /Audits Appraise of safety and health risk is associated with equipment, materials, processes and facilities. It is monitored through routine audits. Fire Protection It reduces fire hazards by inspections of facilities and processes. It arranges all type of fire extinguishers as per need and facilities requirement. It also oversees the design and operational fire safety of the complex and suggests and coordinates requirement-based developments. Regulatory Compliance It ensures that mandatory plant rules and regulations (Appendix II) and International Safety standards are satisfied. Health Hazard Control It conducts audit and control hazards such as noise, chemical or radiation exposure. Hazardous Material Management It creates awareness that dangerous chemicals and other products are procured, stored and disposed of in ways that prevent exposure or fire. Display of MSDS in areas to increase consciousness, are ensured. Training Safety Section provides management and employees with the information and skills necessary to recognize hazards and perform their job effectively and safely. All safety inspectors are trained as fire fighters and work permit procedure auditors. Section also maintains training record of all manpower. Accident and Incident Investigation It determines the facts related to an accident or incident based on witness interviews, site inspection and collection of other evidences. The focus of this activity is to stop reoccurrence. Record Keeping All data related to accidents/ incidents is recorded and maintained. Safety section reports it to government and NSC if required. It also maintains safe man-hours data of the company and reports it to NSC. Evaluating It evaluates the effectiveness of our program through various indices like accident/ incident rate, use of personal protective equipment, quality of job safety. It also considers reporting of near miss as an effective system to avoid occurrence of a real risk.
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Work Permit Procedure
The requirement may either be from maintenance, technical services or production unit itself, the permit is issued by production unit.
Shift engr. Asks area operator to make all required preparation for safe handover of job.
Shift engr. Will physically verify the preparation.
Fill in the specific permit and sign.
Get it approved by coordination. coo rdination. Engr. where required.
After that he hands over the permit to area operator.
Area operator checks the conditions again & explains to the executing agency.
Signs on permit and handover to executing agency.
Area engr. Double checks, signs the permit and retains the hard copy.
Area engr./his designate gives safety instruction to his team.
On completion of job executing agency carries out housekeeping and ask operator to take over job.
Area operator verifies job, gets acceptance of his shift engineer about proper completion of the job including housekeeping after that permit copies are exchanged. NOTE: CHECKS ON MACHINES/EQUIPMENT ARE CARRIED OUT AFTER EXCHANGE OF WORK PERMIT.
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Marshalling Points In the event of a heavy fire or gas leak, disaster siren will be sounded. All personnel will go directly to their nearest/ designated Marshalling Points, (across wind) and await further instructions or until all clear is sounded.
Emergency Procedures (Siren) F IR E A L A R M 1 0
0 5
1 0
0 5
1 0
1 0 0 5
1 0 0 5
1 0 0 5
0 5
1 0
1 0 0 5
S E C O N D S
D IS A S T E R (H E AV Y A M M O N IA L E A K A G E )
30
10
30
10
30
10
30
10
30
10
30
10
30
10
30
S E C O N D S
E VA C U AT I O N A L A R A M
R e R e p p e e a a t t e e d d a b a b o o v v e e d i d i s a s a s s t t a r a r a l a l a r a r m m END OF EM ERGENCY
90 S E C O N D S
On the sounding of siren, all personnel other than those directly involved in the emergency, will take the following actions:
Stop all work and shutdown all mobile equipment. Advise and give assistance to personnel working in confined spaces. Proceed across wind to the nearest safe Marshalling Point. Await further instruction. Drivers of all vehicles in the Plant area must stop their vehicle at the side of the road and leave the ignition key in the vehicle so that it can be moved by the Emergency Services, if required. Residential Area When the sirens are activated, all personnel in the residential areas should follow instructions already circulated. Fire Drill Siren It is sounded on every Wednesday at 15:00 hrs. - No action is required (do not go to a Marshalling point)
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PERSONAL PROTECTIVE EQUIPMENT Personal protective equipment (P.P.E) must not be regarded as a substitute for safe working practices. Minimum personal protective equipment equipment is as follow. -
-
-
-
Safety Helmet Safety boot/shoes Escape respirator (Half Face Mask) Ear protection (designated areas)
Safety Spectacles. The correct use, care and regular cleaning of the above equipment is the
-
responsibility of each individual. Head Protection Safety helmets are intended to protect the person against impact and penetration damage and are so designed that they will not fracture when struck, or transfer the force of the blow to the wearer’s skull
below the point of impact.
Caution: Any unauthorized alternations to helmets including drilling of holes or painting, will compromise the protection of the helmet and therefore are not permitted. Eye and Face Protection Clear safety spectacles/ eye shields are to be worn at all times in operating areas as a minimum requirement. Safety spectacles/ eye shields are only adequate for relatively low energy projectile e.g metal swarf. Goggles and face shields/ visors are designed to protect the wearer from hazards such as high energy impact, exposure to dust or splashing of toxic/ corrosive substances.
Select the correct protection for the work to be carried out. Noise The exposure to high levels of noise can seriously damage the hearing and subsequently lead to permanent deafness. Hearing protection is provided by FFC for its employees. Two types of protection are provided, ear muffs and ear plugs. When correctly used, both types offer sufficient protection against the noise levels normally encountered in FFC. No other type of hearing protection is acceptable.
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Chemical Protection When handling any corrosive or toxic chemicals, only use the correct designated chemical clothing and equipment designed to prevent contact with the skin. Where relatively low concentrations of toxic gases or vapours are present, specific respirator must be used. When exposed to large amounts of gases or vapors, breathing apparatus must be worn. Only trained and competent personnel must attempt to handle toxic materials. Breathing Apparatus All personnel employed on any work which requires the use of breathing apparatus shall be trained in the correct use and care of the equipment. Under absolutely no circumstances shall anyone wear breathing apparatus without training. Breathing Apparatus is designed to provide an effective seal between the facemask and the wearer’s face when the personnel is clean shaven. Personnel with heavy
facial hair will be unable to obtain a satisfactory face seat, preventing the apparatus from functioning correctly and subjecting the wearer to a greater risk of potential fatal accident. DON’T BE A TARGET FOR AN ACCIDENT, WEAR PROTECTIVE EQUIPMENT
BE SAFE THINK SAFE!
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Fire Combustion is a chemical reaction in which heat and light is evolved. For combustion to occur three factors are necessary: Fuel, Oxygen and a source of ignition. Combustion will continue as long as these three factors present. These are known as the “fire elements ” and
removal of any of the elements will prevent combustion. Fire extinction, in principle consists in the limitation of one or more of the above elements. Classification of Fires
There are four main categories, based upon the fuel and the means of extinction. These are:
Class A
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Fires which involve solid materials mainly an organic type such as paper, wood and cloth. These are extinguished by cooling, by the use of water.
Class B
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Fires which involve liquids or liquefiable solids such as oil, petrol, paint or grease. These can be extinguished by dry powder and carbon dioxide (CO 2).
Class C
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Fire which involve gases or liquefied gases such as Methane or butane. These can be extinguished by dry powder and carbon dioxide (CO2).
Class D
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Fires which involve combustible metals such as Magnesium and sodium. Sand or similar substances and special dry powder extinguisher type should be used.
Electrical Fires Which involve the electricity supply to live equipment can be dealt with by extinguishing agents such as dry powder and carbon dioxide. Electricity is a cause of fire not a category of fire.
DO NOT USE WATER ON ELECTRICAL FIRES!!
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Fire Class
Water Class A Wood Paper, Cloth Class B Flammable Liquid Class C Flammable Gases Class D Combustible Metals Electrical Hazards
Fire Extinguisher to be used Foam CO2
Powder
Use Sand or Special Dry Powder
Discovery of a Fire On discovering a fire, your prompt action could save lives: -
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-
-
-
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Break glass Inform Coordination Engr. / Safety Section Identify location, the type of fire, and wind direction. If it can be extinguished immediately, select the correct extinguishing agent. Approach the fire from upwind to avoid inhaling gases produced by the fire. If the fire is not extinguished immediately, vacate the area closing all doors on your way out. Report to the assembly point.
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An Overview to what Production & Process do Production Department The overall responsibility rests with Production Department. Unit Managers are responsible for their respective units. Day Engineers assist their respective Unit Managers for unit matters. Coordination Engineers are responsible for coordination among the units in shifts. Shift Engineers / Sub Engineers / Staff employees are responsible for safe and smooth day-to-day operation of the plant.
Description Urea plant has a name plate capacity of 1740 MeT/day. The plant started its commercial production on October-1980. The Urea Process is designed on Snamprogetti Process Technology. Plant was uprated to 2175 MeT/day in November, 2008. The main raw materials used for urea manufacturing is natural gas which is first converted into Ammonia as an intermediate product. product. The ammonia plant is designed on process technology of Haldor Topsoe, has name plate capacity of 1000 MeT/day and uprated to 1250 MeT/day. Some utilities like power, steam, instrument air, cooling water and nitrogen are required in the manufacturing process. Production Department who is custodian of the entire plant is responsible for smooth, safe and efficient plant operation. To ensure quality of Process / Product and safety of equipments and machines, the following activities are considered: 1. Plant Monitoring 2. Plant startup/ shutdown 3. Emergency Handling 4. Exercise safe operating practices 5. Prepare / execution of plant turnaround. 6. Maintain lube oils and chemicals inventories. 7. Prepare production plan / budget. 8. Prepare / evaluate energy conservation schemes. 9. Environmental pollution control 10. Continuous monitoring of Product Quality 11. Coordination with maintenance 12. Plan and execute training of personnel. 13. Plant performance review
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Senior Production Manager
Production Manager
Coordination Engineer
CA
Unit Manager Ammonia
Unit Manager Urea
Unit Manager Utilities
Unit Manager Bagging & Shipping
Section Head
Section Head
Section Head
Supervisor
Shift Engineer
Shift Engineer
Shift Engineer
Boardmen
Boardmen
Boardmen
Boardmen
Organization Chart for Production Department
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Process Engineering Unit Relevant area Process Engineers (PEs) visit the plant regularly and monitor various operational activities through available records. Performance indices of various plant equipments/ machines are periodically evaluated through Technical Monitoring Program, TMP, Records of the TMP evaluations are maintained in the form of charts and tables. Inputs for urea product quality report sent to Process Engineering Goth Machi generally on quarterly basis. Urea production verification is done through direct bagging tests, DBT, generally on monthly basis, provided plant conditions and bagging activity is normal. Process modifications in the plant schematic with respect to capacity enhancement, energy conservation, safety or efficiency improvement and to address operational/ maintenance problems are carried out against service requests. Any incident or load limitation at plant resulting in production loss is analyzed critically. Detailed Production loss report is issued, covering all aspects of the incident / load limitation, according to PLR qu alifying criteria. Primary Reformer tube metal temperatures are monitored, generally on monthly basis and detailed report is issued. Newsletter inputs are sent to Process Engineering Rawalpindi on monthly basis. Assistance to operation and maintenance is provided as per requirement, to troubleshoot various plant problems affect production. During turnarounds, shutdowns or available opportunities, catalyst replacement and skimming are the main responsibilities of PEMM. Plant performance and major issues are discussed in Production Department meeting.
Process Engineers Ammo Am moni nia a - 02 Unit Manager
`
Process Enginees Urea -02 Process Engineers Utiliti Uti lities es - 02
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Unit Manager Plan, coordinate, supervise and control all activities performed in PEMM. Assign Jobs to process engineers. Plan training of process engineers as per requirement and keep record. Review and issuance of all process engineering documents. Performance appraisal of process engineers and administrative activities.
Urea Process Engineer Visit urea plant regularly and monitor various operational activities through available records. Arrange performance evaluation of various plant equipment / machines periodically through Technical Monitoring Program (TMP). Provide inputs for urea product quality report to Process Engineering Goth Machi (PEGM) generally on quarterly basis. Verify Urea production through direct bagging tests (DBT), generally on monthly basis. Perform studies for process modifications in the plant schematic with respect to capacity enhancement, energy conservation, safety, environment and efficiency improvement against service requests. Analyze any incident or load limitation at plant resulting in production loss and issue production loss report (PLR) covering all aspects of the incident / load limitation, according to PLR qualifying criteria. Provide assistance to operation and maintenance as per requirement to troubleshoot various plant problems affecting directly or indirectly the production or product quality. Discuss Plant performance, major issues and plant modifications in Sub PPRC meetings, held generally as per requirement.
Ammonia Process Engineer Visit Ammonia plant regularly and monitor various operational activities through available records. Arrange performance evaluation of various plant equipment / machines periodically through Technical Monitoring Program (TMP). Monitor Primary reformer tube metal temperatures generally on monthly basis and issue report. Perform studies for process modifications in the plant schematic with respect to capacity enhancement, energy conservation, safety, environment and efficiency improvement against service requests.
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Analyze any incident or load limitation at plant resulting in production loss and issue production loss report (PLR) covering all aspects of the incident / load limitation, according to PLR qualifying criteria. Provide assistance to operation and maintenance as per requirement to troubleshoot various plant problems affecting directly or indirectly the production or product quality. Review specifications of chemicals and catalyst used at Plant site prior to procurement. Discuss Plant performance, major issues and plant modifications in Sub PPRC meetings, held generally as per requirement.
Utilities Process Engineer Visit Utilities plant regularly and monitor various operational activities through available records. Arrange performance evaluation of various plant equipment / machines periodically through Technical Monitoring Program (TMP). Perform studies for process modifications in the plant schematic with respect to capacity enhancement, energy conservation, safety, environment and efficiency improvement against service requests. Analyze any incident or load limitation at plant resulting in production loss and issue production loss report (PLR) covering all aspects of the incident / load limitation, according to PLR qualifying criteria. Provide assistance to operation and maintenance as per requirement to troubleshoot various plant problems affecting directly or indirectly the production or product quality. Review specifications of chemicals, lube oil and resins used at Plant site prior to procurement. Discuss Plant performance, major issues and plant modifications in Sub PPRC meetings, held generally as per requirement.
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Production Department Production Department of an industry manages product production in field in coordination with process unit (which does the desk job for same). The sole responsibility of the unit is to ensure maximum production through overcoming the problems and issue coming up on daily routine on plant. The unit manages process parameters like temperature, pressure, flow rate etc to achieve production targets, while guaranteeing the safety of personnel and plant. The plant is monitored / controlled through a controlling centre (CCR at FFC MM) where shift engineers work under the supervision of a coordination engineer and achieve the set goals. At FFC MM, production unit works under a Production Manager and is sub-divided into four sub-units, as per their working goals. These include: 1. Utilities Unit; provides utilities like instrument air, cooling water, electricity to other units 2. Ammonia Unit; provides raw materials i.e. ammonia and carbon dioxide for urea section 3. Urea Unit; produces the product urea (trade name: Sona Urea) 4. Bagging and Shipment Unit; bags urea and dispatch it to consumer market Each of the unit has a UM which works with a team of engineers and other technical staff to manage smooth run of unit. Shift starts with a coordination meeting of production manager, Unit Managers, staff engineers and engineers; discussing and addressing the problems to be encountered. Shift engineers coordinate with board men (operators of DCS monitoring facility at CCR) and operators (at respective areas) areas) for following the agreed plan of action for the shift or day.
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A M MO N I A
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Training at Ammonia 22 & 23-06-2011
Reforming Section (02 Area)
2 Days
Syed Mehmood Raza Gillani
th
24 & 26-06-2011
Carbon Dioxide Removal Section (03 Area)
3 Days
Syed Mehmood Raza Gillani
8 to 11
th
27 to 30-06-2011
Compression Section (04 Area)
4 Days
Syed Mehmood Raza Gillani
12th to 13th
01 to 02-07-2011
Ammonia Synthesis & Refrigeration 2 Days
Syed Mehmood Raza Gillani
rd
th
3 &4
5
th
to 7
th
th
13
02-07-2011
Closing Meeting
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Ammonia Process Steam
Primary Fuel
Reformer
Refrigeration
Combustion Air
[
Secondary Process Air
NH3 Synthesis
Reformer
Product Ammonia
CO Shift Methanation
Converters
CO2 Removal C O
Ammonia (NH3, melting point –77.7°C, boiling point –33.4°C, and density 0.817 at –79°C and 0.617 at 15°C) is a colorless gas with a penetrating, pungent- sharp odor in small concentrations that, in heavy concentrations, produces a smothering sensation when inhaled. Ammonia is soluble in water and a saturated solution contains approximately 45% ammonia by weight at the freezing temperature of the solution and about 30% ammonia by weight at standard conditions. Ammonia dissolved in water forms a strongly alkaline solution of ammonium hydroxide (NH4OH) and the aqueous solution is called ammonia water, aqua ammonia, or sometimes Ammonia (although this is misleading). Ammonia burns with a greenish-yellow flame. The importance of ammonia is growing worldwide because of its uses as a fertilizer and an intermediate product for urea production.
Processes and Catalysts Desulphurization o
Absorption
Reforming Section o
Primary Reformer
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o
Secondary Reformer
Gas Purification o
Shift Converter
HT Shsift Converter
LT Shift Converter
o
CO2 Removal (Benfield Unit)
o
Methanation
Ammonia Synthesis o
Chemistry Involved
o
Process Conditions
Gas Composition
Ammonia Concentration at Converter Inlet
Inert Gases
Hydrogen/Nitrogen Ratio
Reaction Temperature
Circulation Rate
Operation Pressure
General Ammonia is produced from a mixture of hydrogen and nitrogen where the ratio of H 2 to N 2 should be 3:1. Besides there two compounds the mixture will contain inert gases to a limited degree, such as argon and methane. For the ammonia plant in Pakistan the source of H 2 is hydrocarbons in the form of natural gas. The source of N 2 as in all ammonia plants is the atmospheric air. The processes which are necessary for preparing ammonia from the above mentioned raw materials are as follows: Hydrocarbon feed is completely co mpletely desulphurized in the desulphurization section. The desulphurized hydrocarbon is reformed together with steam and air to raw synthesis gas. This gas contains: o
Hydrogen
o
Nitrogen
o
Carbon Monoxide
o
Carbon Dioxide
The reforming takes place at 30 kg/cm
2
In the gas purification section, CO is first converted to CO 2 and H2 with steam in order to increase the H 2 yield. CO2 is then removed in the CO 2 removal section, and the remaining CO and CO 2 is afterwards removed in the methanator.
29
In the ammonia synthesis section, the purified synthesis gas is, after compression to 2
a pressure of about 260 kg/cm , converted into ammonia by a catalytic reaction.
Desulphurization Desulphuriza tion Unit The desulphurization unit consists of two absorbers. The natural has feedstock contains sulphur compounds, which have to be removed in order not to poison the reforming catalyst in the primary reformer, and the low temperature shift catalyst in the CO-converter. Particularly the latter is sensitive to deactivation by sulphur and sulphur-bearing compounds. Passing through the desulphurization unit the suplhur contained in the natural gas will be reduced to a very low level i.e. about 0.1ppm sulphur by weight. Natural gas coming from Maripur Gas field through Natural Gas Station contains:
H2 N2 CO2 CH4 C2H6
0.1% 19.5% 9% 71% 0.2%
Absorption The natural gas passing to the process is compressed in the natural gas compressor, to 40 2
o
kg/cm and preheated to 400 C in the waste heat section of the primary reformer. A small amount of recycle gas from the main compressor is added to the natural gas before entering the waste heat section. The hot mixture is then passed through one of the two absorption vessels and the other vessel is kept as a spare. The absorption vessels contain each 21m
3
of HTZ-3 catalyst
(specially prepared zinc oxide). Each vessel contains 2 beds with a bed height of 2.15m. o
o
The normal operation temperature will be 330 C to 440 C, but also at low temperatures the catalyst will react with hydrogen sulphide according to the following reaction. ZnO + H 2S ZnS + H2O o
Above 310 C, the catalyst will react with carbonyl sulphide. ZnO + COS ↔ ZnS + CO2 At normal operating temperatures also sulphides and disulphides will react with the sulphur absorption Catalyst.
30
Reforming Section In the reforming section, a gas containing the necessary compounds for preparation of the ammonia synthesis gas is produced by catalytic reforming of a mixture of hydrocarbon and steam and addition of air. CH4
+
2H2O
↔
CO2
+
4H2
o
The reactions start at 600 C for methane. The section produces synthesis gas containing necessary compounds (hydrogen and nitrogen in ratio 3:1) for ammonia synthesis by catalytic steam reforming of natural gas and addition of atmospheric air to give nitrogen content to mixture. Endothermic reactions consuming great deal of energy, govern the process economics.
In the primary reformer, the heat is supplied indirectly by firing. In secondary reformer it is supplied by mixing air into the gas resulting in auto-ignition temperature conditions. The burning gas provides heat for the rest of the reforming. The reforming taking place in the primary reformer is so adjusted that the air supplying the reaction heat in the secondary reformer will give the required hydrogen/nitrogen of 3:1. It is desired to keep the methane content of syn gas as low as possible to keep the inert level minimum. Methane content is governed by reforming reaction which is promoted by high temperature, low pressure and more steam. On the other hand, high pressure reforming can give considerable savings in power consumption for syn gas compression and equipment size could be reduced as well. An economic compromise has been achieved by 2
keeping operating pressure at 35 kg/cm . The third reaction consumes important hydrogen and therefore is minimized with excess steam to carbon ratio is increased to 3.75:1.
31
Primary Ref Reformer ormer Primary reformer has a total of 288 reforming tubes installed in two radiant chambers with a common flue gas channel and 648 burners on side walls. The side-fired tubular reformer offers: Uniform and higher heat flux Fewer tubes and longer tube life No risk of flame impingement Safer and more reliable operation
o
The catalyst should not be exposed to liquid water or steam below 350 C, because this might cause weakening of the catalyst carrier. The catalyst (in oxidized form) must therefore o
be heated up by air to above 350 C before steam is added. On the other hand, during starto
up the catalyst should not be exposed to air at a temperature above 600 C. Special care must be taken to avoid water drops on hot catalyst, as this would disintegrate the catalyst. Potential sources of liquid water on hot catalyst are boil-over from a steam boiler or water condensed in a cold preheat coil in the hairpins.
When the activated catalyst is cooled by steam, it will be reoxidized and the catalyst must be activated before being taken into operation again. Full oxidation of the catalyst is o
expected after a continuous flow of steam for 5 hours at a temperature of 600 C and at a rate of 5-15kg steam/kg catalyst. After complete oxidation of the catalyst, the subsequent
32
start-up should comprise a full reactivation procedure. After a stand-by steaming at essentially shorter time and lower temperature than required for full oxidation has taken place, the reactivation during the subsequent start-up is greatly facilitated. 3
The reformer is loaded with 31.8m RKS catalyst in the form of ceramic rings 16/6.5mm by 16mm high, impregnated with nickel. Excessive steaming at high temperatures should be 2
avoided for RKS. If steaming is necessary, the pressure should be reduced to below 3kg/cm , o
o
and the temperature to below 700 C but above 350 C. The magnesia-alumina-spinnel catalyst with 17% nickel oxide has stable pore system, high thermal resistance and a 2
negligible content of silica and other volatile compounds. The crush point is 300 kg/cm and fusion is 2000°C. Catalyst is activated by reducing the oxide to nickel by steam – hydrocarbon mixture. Deactivation is done through cooling by steam that re -oxidizes it. The natural gas mixture is pre-heated to approximately 52°C and the passed downward through the vertical tubes of filled with catalyst; placed inside a fired heater, primary reformer F-201. Sensible heat is transferred by radiation from a number of wall burners to the tubes. Methane is reformed through steam yielding an incr ease in hydrogen and carbon dioxide content of mixture. Almost 90% of reforming takes place in primary reformer. The gas leaves the primary reformer at 927°C. H2 N2 CO CO2 CH4
65.5 % 7.14 % 10.13 % 11.44 % 5.77 %
It is possible that during operation, carbon might deposit on the catalyst bed. This would lead to an increase in pressure drop for outside deposition and reduction in activity and mechanical strength of catalyst for inside deposition. Carbon formation is avoided by maintaining equilibrium for each reaction step. Other reasoning for carbon formation includes: Catalyst poisoning by sulfur; reducing activity and increasing carbon deposition High contents of olefins, aromatics or naphthenes in hydrocarbon f eed Low steam to carbon ratio
33
Secondary Reformer
Secondary Reformer is used to separate nitrogen from air by burning the oxygen with it and 3
reforming the remaining methane. 35 m of RKS-2 catalyst in the form of ceramic rings placed on the lower portion of reformer. The combustion of air will give high gas temperature at the top of catalyst bed. The reaction mixture contacts with catalyst at the temperature about 1100°C – 1200°C. Some of the catalyst activity is lost during the first high temperature interaction, but continuous operation decreases the rate to very slow. The sintering temperature of the catalyst is 1400°C – 1500°C. Activated catalyst should not be exposed to air at temperatures above 100°C, which would cause spontaneous heating and destruction of catalyst.
34
The gas from primary reformer then enters the upper portion of secondary reformer where 2
a pre-heated stream of 28167 Nm3/h compressed process air at 150°C and 35.5 kg/cm is mixed with the gas. High temperature results in auto ignition and an exothermic reaction that consumes the oxygen from air. The gas is then passed to the catalyst bed in lower section of the reformer, where reforming reaction is completed with simultaneous cooling 2
of gas. The outlet gas leaves the chamber at 972°C and 31 kg/cm . 3
In the secondary reformer is installed 35m of RKS-2 catalyst in the form of ceramic rings, which is 19/9 mm by 19mm high. In the secondary reformer the combustion of air will give high gas temperature at the top of the catalyst bed. The reforming reaction of methane will o
lower the temperature and at exit of the reformer the temperature will be about 970 C. The o
reaction mixture will contact the catalyst at about 1100 -1200 C. In the temperature range of o
1100 to 1350 C some catalyst activity will be lost during the first period of time. This will, however, only be significant if the catalyst is operated for some time at high temperatures, the further activity decrease will be very slow. In the temperature range of 1400-1500oC the catalyst begins to sinter. Catalyst activation, oxidation and behavior to air are as mentioned for the primary reformer. The catalyst can be affected by poisons in the effluent gas from the primary reformer or by the process air, which could be contaminated contaminated (sulphuric acid fog). The fresh catalyst contains when delivered some minor amounts of sulphate (about 50mm sulphur), which by the activation will be reduced to H 2S and released. The absence of silica is a special feature of this catalyst. In the high temperature service a silica containing catalyst would give off gaseous silicon monoxide which may be deposited at lower temperatures and cause troubles in the units downstream of the reformer by fouling of waste heat boiler of by partial blocking of the upper layer of the shift catalyst.
35
The activated catalyst in the secondary reformer should never be exposed to air at o
temperatures above 100 C, as this would cause spontaneous heating which, due to “snowballing” affect, may essentially lead to overheating and destruction of the catalyst.
H2 N2 CO CO2 Ar CH4
55.93 % 22.15 % 12.14 % 9.02 % 0.20 % 0.30 %
Gas from secondary reformer is cooled in a waste heat boiler E-208, to 380°C. As the stream contains considerable amount of carbon mono and dioxides, there is a probability of carbon formation, when the gas is cooled. 2CO → CO2 + C (soot)
The reaction is only possible with the range of 650°C – 720°C because of equilibrium conditions. At temperatures below 650°C, the rate of reaction is too slow to have any practical importance. Therefore, a waste heat boiler is employed to provide a rapid cooling. The boiler rapidly decreases the temperature by converting water into high pressure steam, without a contact between process gas and hot surface.
Gas Purification Section The section prepares a syn gas containing hydrogen and nitrogen in ratio of 3:1 by purification. Only inert gases like methane and argon are permissible in lowest possible concentrations. Carbon monoxide is converted in two shift convertors R-204 and R-205 according to the following reaction to reduce the concentration concentration to (0.4 % on dry basis). CO + H2O ↔ CO2 + H2 + (heat) Reaction increases the hydrogen yield with formation of carbon dioxide which is more easily removable. After cooling of gas and condensation of water content, carbon dioxide is removed up to 0.1 %, which is then converted to methane methanator R-311, at the cost of expensive hydrogen. CO + 3H 2 ↔ CH4 + H2O + (heat) CO2 + 4H2 ↔ CH4 + 2H2O + (heat) Inert levels in ammonia synthesis loop are controlled via purging of inerts to keep the level low and obtain higher production. p roduction.
36
Shift Conver Co nversion sion Shift conversion of carbon monoxide to carbon dioxide is an equilibrium reaction with low temperature and more water supporting the forward move. However, higher temperature will give a higher reaction rate. More water can apparently give a lower reaction rate due to bigger total volume giving a shorter contact time. An optimum temperature is therefore needed to give the best conversion. Keeping in view the activity and quantity, conversion is performed in two steps: High temperature shift (HTS); to increase the rate of reaction Low temperature shift (LTS); to favor equilibrium conditions
HTS – Convertor The HTS convertor R-204 is installed with 61 m3 of SK conventional chromium oxide promoted iron oxide catalyst, distributed on two beds, each 2.1 m high. Fresh catalyst has highest oxidized level of iron oxide and therefore is not affected by air, steam carbon dioxide or inerts at elevated temperatures. Catalyst should not be exposed to heating above 400°C. Methane is not an inert for the catalyst and reduces it to be spoiled by carbon deposits. Catalyst is therefore not exposed with reducing agents like hydrogen or carbon monoxide unless absolutely cold. Catalyst is activated by reduction at 250°C with a mixture of hydrogen and carbon monoxide after being preheated with steam (inert for catalyst). It is sensitive to salts in water and chlorine level in gas, while inert to sulfur. Gas stream from the secondary reformer enters the HTS convertor R -204 after being cooled by waste heat boiler. The main part of reaction takes place here causing a temperature increase of 59°C. The outlet stream temperature is 435°C. The gas from HTS convertor is then cooled in trim heater E-205, HP waste boiler E-210 and BFW pre-heater E-211 to 220°C before being sent to LTS convertor. H2
59.66 %
N2
20.28 %
CO
2.87 %
CO2
16.73 %
Ar
0.19 %
CH4
0.127 %
37
LT S – Convertor The LTS convertor R-205 consists of specially prepared zinc and chromium oxides catalyst with much higher activity and therefore is used at lower temperatures of 220°C – 240°C. Catalyst loses its activity if temperature is higher than 250°C – 270°C. 85 m3 of LSK catalyst is distributed on two beds each 2.8 m high. The catalyst which is in the form of small pellets is sensitive to sulfur, chlorides and gaseous silicon compounds. Activity is diminished by 0.2 wt % sulfur and 0.1 wt % chlorine. Catalyst is activated through reduction reduction with natural gas at 150°C – 200°C including 0.1 % hydrogen. Reduced catalyst is pyrophoric and is oxidized before unloading. Stream from HTS Convertor enters the LTS convertor R-205 where remaining reaction is completed. The gas leaves the vessel at 235°C and 29 kg/cm2. H2
50.54 %
N2
19.78 %
CO
0.08 %
CO2
18.75 %
Ar
0.18 %
CH4
0.27 %
Carbon dioxide Removal (Benfield Unit) The section removes the carbon dioxide formed in shift conversion section by absorption in hot aqueous Benfield solution containing about 30 wt % potassium carbonate (potash) partly converted in to bicarbonate and 3 % di-ethanolamine (DEA) as an activator. The solution is kept hot to increase the absorption rate and maintain bicarbonate content in solution. High temperature is also an advantage for regeneration which requires the same temperature. Both in absorber and in De-absorber the Demister pad are use to avoid the Benfield solution particles goes with the gas stream. Section has a Benfield Absorber C-302 and a Benfield Regenerator C-301. The absorber C302 contains four beds of steel pall rings arranged in four beds in a column. The two upper 3
beds with bed height 7.7 m and dia 2.5 m contains a total of 75 m of 1.5’’ rings. The lower two beds same bed height but dia 3.50 m contains a total of 148 m3 of 2’’ rings. The 4.5m diameter regenerator C- 301 contains four beds of 450 m3 2’’ pall rings with a total height of 28.20 m. The gas from LTS convertor R-205 is passed through the LP steam boiler E-301 where water in the stream is condensed, while the temperature is dropped to 160°C. Passing through the
38
separator V-305, process condensate is withdrawn and gas is further cooled through passage from Benfield re-boiler E-302 and BFW pre-heater E-304 to minimize the temperature to 110°C and 27.7 kg/cm2. Separator V-304 removes the further traces. Gas is then passed to the bottom of Benfield absorber C-302, where it flows countercurrently against the potash solution. A quarter of the solution flows from the top of the column at 70°C, where as the remainder three fourth flows after the two top beds at 119°C. Process stream leaves the column at 70°C for methanation. The reason for splitting the streams before entering the absorber is to reduce the partial pressure, in order to help reduce to the lowest carbon dioxide traces in process stream. H2
74.58 %
N2
24.29 %
CO
0.48 %
CO2
0.10 %
Ar
0.23 %
CH4
0.33 %
The rate of reaction for absorption is kept high by the combined effect of relative high temperature and the activator. K2CO3 + CO + H 2O ↔ 2KHCO3 The reversible reaction enables the regeneration of potash solution and recovery of carbon dioxide by disturbing the equilibrium conditions. The solution is sent to the top of Benfield 2
regenerator C-301, where pressure is reduced to 5 kg/cm to flash the carbon dioxide off. Remaining is removed from the solution by flowing it downwards through the packed tower 2
in a counter-current flow with LP steam at 138°C and 0.5 kg/cm . Regenerated solution from the bottom of the tower is pumped back to absorber through circulation pump P-301. The main part of solution is introduced in the absorber under the upper two beds, while the rest is cooled in LP BHW pre-heater E-307 and split stream cooler E-303 to 70°C and introduce top of the absorber. 2
The steam – carbon dioxide mixture from the top at 105°C and 0.5 kg/cm is cooled in BFW pre-heater E-305 and condenser E-306 before separation in separator V-301. Here 7874 3
2
Nm /h carbon dioxide is separated and sent to the urea unit at 45°C and 0.29 kg/cm , while the condensed steam is through condensate pumps P-302 A/B to sewer. H2
1%
N2
0.5 %
CO2
98.5 %
39
Methanation The traces of carbon dioxide are poison to reactor catalyst and therefore are converted to methane (inert) in methanator R-311. Methanation is just the reverse of reforming, supported by lower temperatures. CO + 3H 2 ↔ CH4 + H2O + (heat) CO2 + 4H2 ↔ CH4 + 2H2O + (heat) The reaction is based more upon the activity of catalyst rather than other parameters. Efficiency is increased through higher temperature conditions but also reduces the life of the catalyst. The reactor reduces the combined carbon mono and dioxides compositions to less than 10 ppm with a temperature rise of 30°C. 3
Methanator R-3111 contains 30 m of PKR catalyst in the form of spheres in a single bed of 3.1m height. The catalyst has approximately similar characteristics as reforming catalyst but great activity due to reaction at lower operating temperatures. Process gas stream from the top of the Benfield absorber C-302 passes through separator V302 to remove the traces of potash solution. Passing through the shell of gas-gas exchanger E-311 and trim heater E-205, its temperature is increased increased to 320°C and fed to methanator R311. Methanated gas at 351°C is passed through the tubes of gas -gas exchanger E-311 and final gas cooler E-312, it is fed to a separator V-311; from where it leaves for ammonia 2
synthesis section at 39°C and 25 kg/cm . H2
74.4 %
N2
24.74 %
Ar
0.23 %
CH4
0.92 %
40
Ammonia Synthesis Section (Area 05) The ammonia synthesis takes place in the ammonia convertor R-501 with a catalyst bed, according to the reaction: 3H2 + N2 ↔ 2NH3 + (heat) The synthesis being the equilibrium reaction does not reach completion and only a part is converted to ammonia. Conversion is supported by high pressure and low temperature, but high rate of reaction demands high temperature. Therefore, a compromise has been made between theoretical conversion and approach to equilibrium in a single pass over to catalyst. This gives an optimum level for catalyst temperatures to ensure maximum production. The synthesis loop consists ammonia synthesis reactor R-501, re-circulating compressors (integrated with synthesis gas compressor), BFW pre-heat; for cooling the syn gas and condensation and separation of ammonia. The synthesis loop is operated at 380°C – 2
520°C and 270 kg/cm , with promoted iron catalyst containing small amounts of nonreducible oxides. Reaction liberates about 750 kcal/kg ammonia produced, part of which is utilized to pre-heat the HP boiler feed water. The convertor R-501 is a radial type convertor with the gas flowing through the two catalyst 3
beds in a radial direction. It contains a total of 33m catalyst, distributed in three beds with 3
3
3
bed height 5m , 10m and 18m respectively. Catalyst size decreases downward in beds, increases the catalytic activity of smaller particles. The catalyst is stable in air below 100°C, while above 100°C it reacts and spontaneously heat up. The catalyst is activated by reducing the iron oxide surface layer to the free iron, by circulating syn gas. Catalyst activity decreases slowly during normal operation, with a catalyst life of 5 – 8 years. Catalyst life is much influences by process conditions like temperature in the catalyst bed and concentrations of catalyst poisons in syn gas convertor. Lower temperatures temperatures reduce catalyst activity and prolong lifetime. Therefore lowest possible temperatures are maintained observing a stable operation. The catalyst temperature ranges 500°C – 530°C. Compounds like water, carbon monoxide, and carbon dioxide, sulfur or phosphorous compounds are all poisons to the catalyst. The gas compositions for ammonia synthesis loop are characterized by any one of the following: Ammonia content Inert gases content (argon and methane) Hydrogen to nitrogen ratio Purity
41
The hydrogen to nitrogen ration in synthesis loop is of great importance. A small change of ratio in fresh feed will result in a much bigger change in the ratio in circulating synthesis sy nthesis gas. Decreasing the ratio in circulating synthesis gas decreases the efficiency of convertor, leading to an increased ammonia concentration at convertor inlet. Temperature conditions at the reactor inlet are also an important governing factor. At the top of the convertor, where has enters the catalyst layer, a certain minimum temperature of 380°C - 400°C is required to ensure a sufficient reaction rate. If the temperature at the catalyst inlet is below 370°C – 380°C, the reaction rate will become so low that the heat liberated by the convertor and the reaction will quickly extinguish itself, if proper process adjustments are not made properly. The reactor is so designed to increase the temperature of an inlet gas through exchangers up to 400°C, where it enters the first catalyst bed from bottom. As the gas passes through the catalyst bed, the temperature is increased to a maximum temperature at the outlet from the first bed. The temperature here is about 520°C, which is normally the highest in the convertor and is called “The Hot Spot”. The gas from the first bed is quenched with cold gas to 400°C – 420°C before the second bed. After the second bed, the outlet temperature is about 500°C. The syn gas from methanator R-311 is compressed in synthesis re-circulation compressor K2
431/432 and fed to the synthesis loop at 39°C and 261 kg/cm . The gas is having a maximum carbon monoxide and dioxide concentration up to 10 ppm and water vapor concentration in order of 330 ppm, depending upon synthesis pressure. Therefore, this large amount of water is removed by absorption in the shell side of condensing ammonia chiller E-506 before the gas enters the convertor. H2
74.11 %
N2
24.74 %
CO
10 ppm
CO2
10 pm
Ar
0.3 %
CH4
0.92 %
GAS COMPOSITIONS AFTER COMPRESSOR K-431/432 The carbon dioxide contained in make-up gas will also be removed by absorption in condensing ammonia. The carbon dioxide will further more react with gaseous or liquid ammonia with formation of ammonium carbamate. In case of no liquid ammonia, carbamate will separate from the gaseous phase as a solid which will tend to plug the system. Therefore, make-up gas is introduced between the ammonia chillers E-505 and E506, so that carbamate remains dissolved in liquid ammonia. The carbon monoxide content of gas does not react with ammonia as dioxide does, neither is it absorbed by the condensing ammonia. The total amount of carbon dioxide is therefore
42
fed to the catalyst, where it is hydrogenated to water and methane. This reduces the a ctivity of the catalyst and hence the monoxide concentrations concentrations are kept as low as possible. NH3
3.60 %
H2
63.31 %
N2
21.09 %
Ar
2.44 %
CH4
9.56 %
GAS COMPOSITIONS OF CIRCULATING SYNTHESIS GAS BEFORE CONVERTOR R-501 The circulation syn gas separated by ammonia separator V-501 at 0°C is passed through the shell of cold heat exchanger E-504 and compressed; to be fed to the convertor R-501 at 2
150°C and 269 kg/cm . The gas contains up to 3.6% of ammonia (function of operating temperature and pressure conditions), which is of importance for the conversion obtained. A low ammonia concentration at convertor inlet gives a high reaction rate and thus a high production capacity. In convertor R-501, only about 25 % of hydrogen and nitrogen (obtained in syn gas at convertor inlet) are converted to ammonia therefore it is necessary to recycle the unconverted syn gas to convertor. NH3
15 %
H2
52.94 %
N2
17.62 %
Ar
2.74 %
CH4
10.70 %
GAS COMPOSITIONS AFTER CONVERTOR R-501 2
Convertor effluent gas from the convertor exit at 325°C and 265 kg/cm is cooled to 195°C in BFW pre-heater E-501 A/B, then in the hot heat exchanger E-502 to 79°C and in the water cooler E-503°C, where condensation of ammonia starts. Further cooling and condensation takes place in the cold heat exchanger E-504 to 25°C, in the first ammonia chiller E-505 to 11°C , and finally in the second ammonia chiller to 0°C. The condensed ammonia is separated from the circulating syn gas in the ammonia separator V-501. Make-up gas is introduced between the two chillers. The circulating syn gas contains about 12% inerts (argon and methane) which do not go any chemical reaction in convertor. As syn gas is recycled, the inerts level is increased until constant addition of inerts with fresh feed is counter-balanced by a constant removal of the 3
same quantity of inert gases from the synthesis loop. At designed conditions, 7437 Nm /h of synthesis gas is constantly purged from the loop after the first ammonia chiller E-505 (inert level is high after the first chiller). However, purge rate is so adjusted to keep the inerts level 12% in the loop. With catalyst age and decrease in activity, purge should gradually be
43
increased to maintain the constant production. Dissolved inerts flash off in the let-down 2
vessel V-502, where pressure is decreased to 25 kg/cm . Ammonia liquid stream from ammonia separator V-501 goes to a let-down vessel V-502 to for further removal of gaseous contents, from where it is further directed to ammonia spheres S-501 and S-502 or the Urea Unit. NH3
99.94 %
H2
0.015 %
N2
0.015 %
Ar
0.015 %
CH4
0.015 %
AMMONIA COMPOSITIONS AFTER LET-DOWN VESSEL V-502
44
UTILITIES
47
Training at Utilities th
04-07-2011
Pretreatment Section
1 Day
Akbar Fida Hussain
16
th
05-07-2011
Demin Lines
1 Day
Akbar Fida Hussain
17th
06-07-2011
Waste Water Disposal / Cooling Tower
1 Day
Akbar Fida Hussain
th
07 to 09-07-2011
Instrument Air Compressors / Natural Gas Station / Inert Gas Unit
3 Days
Akbar Fida Hussain
22nd & 23rd
11 to 12-07-2011
Auxiliary Boilers / Steam Network
2 Days
Akbar Fida Hussain
24th & 25th
13 to 14-07-2011
Turbo Generators / Gas Turbine
2 Days
Akbar Fida Hussain
15
th
18 to 20
48
Industrial Water Water used in industries comes from natural sources like rivers, lakes and wells. This water is likely to contain both dissolved and suspended solids even though they may appear perfectly clear. Because water circulates many times through pipes, exchangers, cooling towers and basins, it picks up more/less solids. When water evaporates, dissolves solids are left behind, increasing their concentration in the remaining supply. Solubility of these solids varies with temperature. For example, calcium and magnesium carbonates are less soluble in hot water than in cold water. When cooling water goes through a heat exchanger, these become suspended solids. When water containing these salts is boiled in a vessel, it deposits or scales on the sides and the bottom of the vessel. Scaling decreases the efficiency of equipments and causes fouling which makes periodic cleaning necessary. Suspended particles also cause erosion in narrow passages or turns in the flow. Microbiological growth in water can also plug the narrow passages in the system. Similarly, oxygen content in water can become a cause of corrosion and reduces equipment life. In order to secure the equipment and maintain its smooth operation, water is treated and them used by the plant. Water treatment reduces turbidity, TDS, DS, DO, organic matter, hardness and color of water. Different unit operations are applied often in series to make water usable by plant.
Problems Hardness Water becomes hard due to the presence of carbonates, bicarbonates, chlorides and sulfates of metal ions like calcium, magnesium, iron, manganese, aluminum and barium. The former two cause temporary hardness and the later two are reason for permanent hardness. . Since the concentration of calcium and magnesium salts is usually much higher than concentrations of other compounds which impart hardness, it is customary to consider only the hardness caused by these salts (Utilities Unit, 2009). Calcium is dissolved as it passes over and through lime stone deposits. Magnesium is dissolved as it passes over and through dolomite and other magnesium bearing formations. Hardness is reason for scaling or deposition of salts inside water pipes, eventually reducing their capacity. Scaling within appliances, pumps, valves causes wear on moving parts. This also creates insulation problems inside boilers, water heaters and hot water lines and increases heating cost. Hardness is expressed in ppm or mg/l. Calcium carbonate is one of the most common causes of hardness ,total hardness i.e. reported in terms of calcium carbonate (mg/l as CaCO 3), using either of two methods.
49
a) Ca and Mg hardness b) Carbonate and non carbonate hardness Hardness caused by calcium is called calcium hardness regardless of the salts associated with it similarly hardness caused by magnesium is called magnesium hardness. Total hardness=carbonate hardness + non carbonate hardness. The amount of carbonate and non carbonate hardness depends on the alkalinity of water. D EGR E E
OF
H AR DN E SS
Ppm 75
Hardness Soft
75 – 150
Moderate
150 – 300
Hard
Above 300
Very hard
Softening is the term which refers to the process of hardness removal.
Alkalinity In water chemistry, the carbon dioxide (CO 2)/Carbonic Acid (H 2CO3), bicarbonate (HCO 3), carbonate (CO 3), and hydroxide (OH) content affect the pH of the water. The amount of bicarbonates, carbonates, and hydroxides in water are usually expressed as equivalent concentration of CaCO 3. Total alkalinity is that obtained by titration with standard acid with methyl orange as a pH sensitive color indicator; hence it is also called
Methyl Orange, MO, or M-Alkalinity. It may also be referred to as the total alkalinity, as it measures all alkalinity above 4.3. In the like manner, titration to a phenolphthalein indicator endpoint provides the Phenolphthalein or P alkalinity, which represents all alkalinity above pH above 8.3.
Alkalinity is the capacity of water to neutralize acids. This is determined by the content of carbonate, bicarbonate, and hydroxide. Expressed in ppm of calcium carbonate, it is a measure of how much acid can be added to a liquid without causing any significant pH change. It has two types: P – alkalinity and M – alkalinity. As already mentioned, P – value is the measure of hydroxyl and carbonate alkalinity while M-value is the measure of total alkalinity. Phenolphthalein indicator enables the measurement of alkalinity contributed by hydroxide ions and half of carbonate ions. Any indicator responding in pH range 4 – 5 can be used to measure the total M – alkalinity. P value and M – value determinations are useful for calculations of chemical dosage required in the treatment of natural water supplies.
50
A L K AL I N IT Y I ND I C AT I O N
Alkalinity 2P=M
Indication All alkalinity is due to carbonat es.
2PM
Carbonates and hydroxyl are present.
P=M=0
M – Alkalinity id due to bicarbonates only. Carbonates and hydroxyl are not present.
P=0
Carbonates, bicarbonates and hydroxyl all are absent. Hardness is permanent.
Treatment Water is treated to meet certain specifications before use in equipments. It is obtained from surface and underground sources. Surface water with a higher turbidity is generally rich in microorganism and contains fewer dissolved solids. It has high concentrations of oxygen and low concentrations of carbon dioxide. Whereas the underground water is harder than surface water and contains more alkalinity and dissolved solids. It is clearer and less sensitive to microbiological contamination contamination than surface waters. Canal water is preferred due to low hardness despite of high turbidity. This is because turbidity reduction is less costly than hardness removal. A mixture of both could also be used to make process more economical, if one alone does not give desired process optimization. Tube wells are only used when canal is nonfunctional, due to water shortage in country. W A T E R Q U A L I T Y C O M P A R I S O N
Surface Water High Turbidity Low
Underground Water Low Turbidity High
Hardness
Hardness Low
High TDS
TDS Basic pH
Acidic pH
Low Dissolved Gases
Clarification Clarification is carried out in a cone-shaped clarifier clarifier that clarifies the source water through the addition of chemicals like lime, ferrous sulfate, chlorine and polyelectrolyte. Clarifiers purify water by precipitating and coagulating the impurities and removing them by sedimentation filtration. This results in removal of temporary hardness, turbidity and organic matter. It involves three steps: 1. Coagulation 2. Flocculation 3. Sedimentation Colloidal particles have large surface area that keeps them in suspension and a negative
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charge through which they repel each other and do not form flocs to settle under gravity.
Coagulation is the process of destabilizing the small particles by neutralizing their charge and mixing them thoroughly to enable their contact. In case of low turbidity, previously settled particles (also referred as sludge) are recycled in order to increase the number of particle collisions and promote the thickness of sludge. Coagulants (e.g. ferrous sulfate) are used to destabilize the colloidal particles in waste water so that floc formation can result. Their dosage varies with respect to turbidity of the source water.
Flocculation is the bridging together of the coagulated particles. Flocculants (e.g. polyelectrolyte) gathers together floc particles in a net bridging from one surface to another and binding the individual particles into larger flocs that could settle down under gravity. It is favored by gentle mixing and a fast pace can destroy the flocs formed. Flocculants work under the principle that a high molecular wt polymer can attach itself to many suspended particles creating a low density floc with an increase in the overall size of suspended material.
Sedimentation is the settling of suspended particles to the bottom of the structure leaving behind clear water. Chlorine is added to water in order to kill the organic matter and oxidize the iron ions in water enabling their reaction with lime and settling. Lime removes temporary hardness caused by presence of bicarbonates salts. Lime reacts with dissolved carbon dioxide soluble bicarbonates to convert them into carbonates and hydroxyl salts are insoluble and therefore settle at the bottom of the tank. CO2 + Ca(OH)2 → CaCO3 ↓ + H2O 3+
2 Fe + 3 Ca(OH) 2 → 2 Fe(OH)3 ↓ + 3 Ca
2+
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 ↓ + 2H2O Mg(HCO3)2 +Ca(OH) 2 → MgCO3 ↓ + CaCO3 ↓ + 2H2O MgCO3 + Ca(OH) 2 → Mg(OH)2 ↓ + CaCO3 ↓
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C L AR IF I C A T I O N T A N K
Filtration
Suspended solids are removed from water by filtering the solids in gravity or pressure filter. These filters have sand and gravel for limiting the flow of suspended particles. Installed in batteries of two or more, these filters are often backwashed by forcing water in reverse direction. This flushes the solids trapped in and on the filter bed into waste disposal system. The flow of other cells is continued through when one cell of the filter is being backwashed.
Ion Exchange Demineralization is based on ion exchange process. process. Ion exchange is the displacement of one ion by another. It may also be defined as a reversible exchange of ions between a liquid and a solid phase (resin). This exchange does not involve any radical change in physical structure of the solid (resin). The ion exchange or solid body must have its own ions to exchange for others. In demineralization two types of exchange take place a cation exchange and anion exchange. Cations like calcium magnesium, sodium, potassium, aluminum iron etc are removed in cation exchanger. Replacement of these cations is carried out with hydrogen ions. Anions such as chlorides, nitrates, sulfates, bicarbonates and carbonates are replaced with hydroxyl ions in the anion exchanger after the water has been treated by the cation exchanger. Most ion exchange units are simple vessels containing a bed of ion exchange resin operated down flow on cyclic basis. In demineralization process, there are four different types of ion exchange resins: Strongly acidic cation Weakly acidic cation
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Weakly basic anion Strongly basic anion
Strong Acid Cation (SAC) resins are used in softening and demineralization applications. In softening applications, it is used in the sodium form (regenerated with salt) and in demineralization applications in the hydrogen form (regenerated with acid). A strong acid cation exchanger will exchange all cations of both neutral and alkaline salts with the hydrogen ion.
Weak Acid Cation (WAC) resins remove only cations associated with alkalinity. While WAC resins can remove mono-valent ions such as sodium associated with hydroxide alkalinity, in most water treatment applications they are used to remove divalent ions such as calcium associated with carbonate alkalinity. A weak acid cation exchanger will exchange cations of mainly alkaline salts, and to a very small extent, the cations of neutral salts. Most commercial ion exchange resins are synthetic plastic materials materials such as co-polymers of styrene and divinyl benzene.
Strong Basic Anion (SBA) resins have strongly basic ammonium groups as the functional +
groups either with tri methylamine {(-CH 2N (CH3)3)} OH- or with di-methylethanol amine {(+
-
CH2N (CH3)2 C2H4OH) OH )} Groups both these types of strong base resins are used in the hydroxide form for de-mineralizing systems. Since strong base resins are highly ionized, they will exchange practically all anions which are present as both strong and weak acids, e.g. hydrochloric acid, sulfuric acid, nitric acid, carbonic acid and silicic acid. They will also split salts which remain unconverted in the cation exchanger. They are of two types of SBA resins: Type I SBA resins are used where low levels of silica leakage are important operating criteria or in warmer climates where source water temperatures may be quite warm for a significant part of the year. They operate at improved efficiency when warm caustic (120º F) is used to regenerate the resin bed; Type II SBA resins have an exchange site that is chemically weaker than Type I resins. Therefore, they must be regenerated at lower temperatures (95º F.) and normally are not used in climates where warm water temperatures are experienced for a good part of the year. However, Type II SBA resins have the advantage of a higher initial exchange capacity. They can be the resins of choice in applications that do not have heated caustic regenerant or where a low silica level is not a critical operating specification.
Weak base anion (WBA) resins do not exchange any ions but removes by adsorption only those anions associated with strong acids like hydrochloric, sulfuric and nitric acids (as shown in the above equation). These resins do not remove carbon dioxide and silica since carbonic and silicic acids are weak acids. Therefore, they cannot be used to make demineralized water without a SBA resin bed following in the train to remove the carbonate/bicarbonate and silica. The exhausted resin is when regenerated with any alkali;
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this simply neutralizes the adsorbed acid and releases it as a neutral salt. Because the weakly basic exchanger is regenerated simply by neutralization of the adsorbed mineral acids, so a variety of alkalis can be used for this purpose. The advantage of using the WBA resin is its efficiency. It is fully regenerated using only about 120 percent of stoichiometry. Like their WAC counterparts, WBA resins can be regenerated using the spent caustic from the SBA resin bed making their use very efficient especially when used on water having a high percentage of anion loading from sulfate, chloride or nitrate.
Mixed Beds provide optimum conditions for the ion exchange process and produces completeness of exchange with resultant treated water quality much better than could be realized in a multi bed deionizer. Polishing is carried out when it is necessary to get on high purity water. Resin structures classified according to their operating properties are: Styrene-divinyl benzene copolymer bead structure. structure. Acrylic resin structure. Physical classification of resins is: Gel resins; have smaller pores in the resin structure, higher initial exchange capacity and a lower purchase price Macro porous resins; have ability to elute foulants easier due to the larger pore structure, stand up better in harsher operating environments.
Cooling towers There are ten cooling towers in equipment utilities that are used for cooling of water. The cooled water is used for cooling of machineries, fluids etc. There are two types of cooling towers Cross flow cooling towers Mixed flow cooling towers
The cooling towers used in utilities plant are of cross flow type. In cross flow cooling towers hot water splashes from the top of the cooling water, fan present at the top of the cooling tower suck air from the bottom, an induced draught is created and in this way heat transfer take place to cool the water. The water is also purified by using chemical dosing. The water in the cooling tower also passes through the side way filters to remove turbidity. After the cooling of water, water is supplied to the plant where it is needed.
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Moist Warm Air Out
Hot Water In
Fan
Hot Water In
Dry Air In
Dry Air In
Cold water out
Cooling Tower
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Chillers Two chillers are installed in utilities to supply comfort and air conditioning system for the fertilizer complex. The main functions of the chillers are to cool the water before ambient temperature. Actually a chiller is a type of heat exchanger in which cooled fluid transfer heat with the water. The chilled water is used in centrally air conditioning systems.
Steam generation Auxiliary boiler The auxiliary boiler is used to produce steam which is used in steam turbines. The auxiliary boiler is a water tube bottom supported designed for firing natural gas. The auxiliary boiler shall operate continuously in parallel with a Heat Recovery Generator to produce steam for use in the complex. There are two main types of boilers i)
Fire tube boiler
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The flame and hot gases are confined within the tubes arranged in a bundle with in a water drum. The hot combustion gases are passed through a series of tubes and act as the medium of heat transfer to water which circulates outside the tubes. As the water changes to steam, it rises and collected there at the top of the boiler drum. ii)
Water tube boilers
The flame and hot combustion gases flow across the out side of the tubes and water is circulated within the tubes. Heat transfer takes pl ace and water is converted in to steam.
Heat recovery steam generation It is installed to recover heat from gas turbine flue gases. Flue gases, from two gas turbines combine in a duct and exchange heat to the boiler feed water flowing in HRSG tubes to produce steam. HRSG is a non-reheat and natural circulation boiler with horizontal gas flow vertical fin tubes in all sections.
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Instrument & service air ai r system Instrument air is the air free of impurities, moisture, and oil and dust particles. Instrument air make possible the functioning of pneumatic valves installed over multiple locations on plant. The area is of extreme importance because in case of its failure, plant might lead to shut down. Air is first passed through through the dryers to remove any water content content present in it. After that air is passed through the dryers to remove the dust contents of the air. Then the air is stored in the storage vessel, which is further provided to the plant where it is needed. Three air compressors supply the instrument & service air demands of the plant. The air compressors and their auxiliaries are designed to automatically respond to the compressed air demand. Two compressors are arranged so that the two compressors are continuously compressing the gas. The third compressor is on standby condition, ready to operate at any shut down condition. INSTRUMENT AIR PLANT
To Plant Air Header
Air Dryers
Instrument Air Storage Tank
From Main Compressor
capacity 1300 NMC
Filters
After Cooler
After Cooler
2nd Stage
2nd Stage
Air
Inter Stage Cooler
Air Inter Stage Cooler
1st Stage
To Instrument Air Compressor Air Header
1st Stage
Air Compressor
Inert Gas Uses Purging of vessels, v essels, tanks, pipelines, heat exchangers To maintain inert atmosphere in oil consoles Consumption during Shutdown/Turnaround Blanketing of catalysts
Generation Processes Natural Gas Combustion (Process Employed at Base Unit) Air Liquefaction Process (Process Employed at Expansions Unit)
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UREA
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Training at Urea 26th th
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Visit of Plant / Study of PFD Operational Parameters / Utilities Available at Urea Plant Compressor, Turbines, Pumps (Centrifugal, Reciprocating) Synthesis Loop Ammonia Recovery Section Low Pressure Section Waste Water Treatment and Hydrolyser Section Vacuum System Instrumentation, Control Valves, PSVs, Transmitters, Control Loops, Alarm & Trip Securities Interlocking Logics & Working of Instruments, Product Quality Standards Bagging & Shipping Process Engineering
1 Day 1 Day 1 Day 1 Day 1 Day 1 Day 1 Day 1 Day 1 Day 1 Day 1 Day 1 Day
Muhammad Aslam Muhammad Aslam Muhammad Aslam Muhammad Aslam Muhammad Aslam Muhammad Aslam Muhammad Aslam Muhammad Aslam Muhammad Aslam Muhammad Aslam
Farooq
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Urea The nature has its own nitrogen fixing bacteria in the soil to rejuvenate the fertility of the soil for the growth of the plants in different crop pattern known as nitrogen cycle. Organic manures through the natural biodegrading used to enhance the fertility further. But the human population growth has been much faster needing larger and larger food grain for its living, necessitating higher and higher food grain output. Invention and use of chemical fertilizers played a key role in this area. Chemical fertilizers provides the three primary nutrients i.e. nitrogen (N 2), phosphorous (P 2O5) and potash (K 2O). In the use of Nitrogenous fertilizers starting from Ammonium Sulphate, Ammonium Chloride, Ammonium Nitrate etc. the inventions of urea made a revolutionary change.
Most Conc. Dry source of Nitrogen (46%). N2 promotes protein formation in plants, major component of chlorophyll which helps promote healthy growth, high yields and keep plants green. Usages are fertilizer, resins, glues, fiber glass insulation, animal feed supplement and as de-ice to melt snow.
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Process description Manufacturing of urea has five steps
Urea Synthesis
Recovery & Decomposition
Vacuum Concentration Concentration
Waste Water Treatment
Urea Prilling
Urea Synthesis Urea is produced by synthesis from liquid ammonia and gaseous carbon dioxide. In the urea reactor R-101 the ammonia and carbon dioxide react to form ammonium carbamate, a portion of which dehydrate to form urea and water. The reactions are as follows: 2 NH3
+
CO2
NH2 COONH 4
NH2 COONH 4
NH2CONH2
+
(Exothermic Reaction)
H2O
(Endothermic Reaction)
At the synthesis conditions (T = 190 °C, P=150 kg/cm 2 residence time 45 min) the first reaction occurs rapidly and goes to completion while the second reaction occurs slowly and determines the reactor volume. The mole ratio of ammonia to carbon dioxide is around 3.6 to 1. The mole ratio of water carbon dioxide is around 0.67 to 1. NH3 32.13 % CO2 15.82 % H2O 19.67 % Urea 32.38 Total 280403 kg/h SOLUTION COMPOSITION AFTER REACTOR R-101
The liquid ammonia, coming directly from the ammonia plant is collected in the ammonia receiver V-101. By means of centrifugal pump P-105 part of this ammonia is sent to medium pressure absorber C-101; the remaining part enters the high-pressure synthesis loop. The ammonia to the synthesis loop is pumped by two reciprocating pump P-101 A/B to a pressure of about 240 ata. Before entering the reactor ammonia is used as driving fluid in the
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carbamate ejector ejector EJ-101, where the carbamate carbamate coming from the bottom of the carbamate carbamate separator MV-101 is pumped up to the synthesis pressure. The liquid mixture of NH 3 and carbamate enters the reactor where it reacts with compressed carbons dioxide. The carbon dioxide drawn at urea plant battery limits at 1 ata and about 45°C enters the centrifugal compressor K-101 and leaves it at pressure of about 155 ata. A small quantity of air is added to the carbon dioxide at the compressor’s su ction in order to
passivate the stainless steel surfaces to protect them from corrosion. The products leaving the reactor enter in stripper, E-101 where 75% un-reacted components are recycled back to reactor. Heat in the stripper is supplied by 26ata saturated steam. NH3 CO2 H2O Urea Inets Total
25.03 % 6.75 % 24.53 % 43.69 % 0.1% 207641 kg/h SOLUTION CONCENRTATION AFTER STRIPPER E-101
Recovery & Decomposition Urea purification takes place in two stages: Medium Pressure Section Low Pressure Section
1. Medium Pressure Section The solution, with a low residual CO 2 content, leaving the bottom of the stripper is expanded to the pressure of 18 ata and enters the medium pressure decomposer MV102 where residual carbamate is decomposed and the required heat is supplied by means of 26 ata steam condensate flowing out from the stripper. The NH3 and CO2 rich gases leaving the top separator are sent to the medium pressure condenser E-107 where they are partially absorbed in aqueous carbonate solution coming from the low pressure recovery section at 4.5 ata. Solution from E-107 fed to C101 where remaining CO2 is absorbed with ammonia from ammonia receiver. Ammonia (NH3) with minimum CO 2 residue (20-100 ppm) and small amount of inerts send to V-101 through a condenser. The solution from the bottom of C-101 is recycled by centrifugal pump P-102 to mixer ME-106 in the synthesis section.
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NH3 6.83 % CO2 1.86 % H2O 28.97 % Urea 62.34 % Total 145530 kg/h SOLUTION CONCENTRATIONS AFTER MPD E-102
2. Low Pressure Section The solution leaving the bottom of medium pressure decomposer is expanded at 4.5 ata and enters the low-pressure decomposer MV-103 where the residual unconverted carbamate is decomposed. The gases leaving the top separator are sent to the lowpressure condenser E-108 where they are absorbed in an aqueous carbonate solution coming from the wastewater treatment section and send to carbonate vessel V-103 from here the carbonate solution is recycled back to medium pressure section by pump P-103. NH3 1.67 % CO2 0.76 % H2O 28.71 % Urea 68.87 % Total 131729 kg/h SOLUTION COMPOSITIONS AFTER LPD E-103
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Vacuum Concentration The solution leaving the low-pressure decomposer bottom, having urea concentration of 72% by wt is sent to the first stage pre-heater E-114, operating at a pressure at 0.3 ata. The mixed phase coming out from first first stage pre-heater E-114 enters the gas-liquid gas-liquid separator MV106, wherefrom the vapors are extracted by the first vacuum system ME- 104, while the solution enters the second stage vacuum pre-heater E-115 operating at the pressure of 0.03 ata. The mixed phase coming out from E-115 enters the gas-liquid separator MV-107 from where the vapors are extracted by the second system ME-105 while the melted urea is separated in the holder ME-107. NH3 CO2 H2O Urea Total
0.38 % 0.1 % 16.24 % 83.28 % 108928 kg/hr SOLUTION COMPOSITIONS AFTER PRE-CONCENTRATOR E-150 Urea 99.62 % H2O 0.38 % Total 90291 kg/hr SOLUTION CONCENTRATIONSS AFTER VACUUM SEPARATOR MV-106 AND MV-107
The water coming from first and second vacuum systems containing ammonia and carbon dioxide is collected in the waste water tank T-102. From here it is pumped to the waste water distillation tower, C-102. Before entering the top of the column the solution is preheated in the heat exchanger E-118A/B by means of the distilled water flowing out of the tower. In column ammonia and carbon dioxide are stripped by means of vapor produced in the reboiler E-116. The vapor coming from the top of the tower is condensed in the overhead condenser, E-117. Solution from E-117 is collected in the accumulator, V-110. A part of this solution recycled back to the top of the tower as reflux, the remaining part to the low-pressure low -pressure condenser E-108 with the help of centrifugal pump P-115. The distilled water containing only traces of ammonia after cooling in E-118 is sent to urea battery limits by means of the centrifugal pumps P-114.
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Urea Prilling The melted urea leaving the second vacuum separator is sent to the Prilling bucket ME-109 by means of centrifugal pump P-108. The urea coming out from the bucket in the form of drops d rops falls along the Prilling tower ME-108 and encounters a cold airflow, which causes its solidification. The solid prills falling to the bottom of the Prilling tower are collected on the belt conveyors ME-112 A-E. From here they are sent to screeners ME-113 A-E to separate fines, and then to belt conveyor ME-114 carries the urea to the storage section. Urea fines by means of belt conveyor ME-116 are recycled back to the underground tank T-104 where they are dissolved and solution is recycled back to vacuum section. Nitrogen content 46.3 min Biuret content 0.8 max Moisture 0.225 max Prill size range 1 mm – 2.4mm Temperature 65°C max EXPECTRED UREA Q UALITY UALITY
Urea Cooling Tower 3
It is induced draft having three cells and three 5000m /hr capacity centrifugal pumps MP800F/G/H. Three side stream filters for reducing the suspended solids in cooling water. Hot water comes at 42°C at the top in hot basin. It then showered on the packing in the three cells of cooling tower and cooled up to 32°C by the cross flow of air. Three fans MK-800K/M/L are used for air flow in the cells. Cold water is collected in the cold basin at the bottom from where MP-800F/G/H supplies this cold water to urea plant for reuse. Phosphate treatment is being used at urea cooling tower. For dosing of chemicals small PD pumps are used and also an acid pump to control CW pH. Most important parameters which monitored at Urea cooling tower are pH conductivity and scale level at different temperature.
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Bagging and Shipment Unit Urea from urea plant is transferred to bagging unit through belt conveyers. There are three areas in unit: Area 12 ( storage + fresh feed belts) Area 13 ( cleaning system or screening and recycling) Area 14 ( dispatching area , packing , stitching) Urea is fed to hoppers in area 12, there are two main kinds of hopper: Hopper for fresh feed Hopper for both fresh and recycle feed Hopper feed urea to feeders for being transferred to the belts. Bags used for packing are woven poly-propylene bags. Inside covering of bag is made of nylon to prevent incoming and outgoing of moisture. In order to remove dust there is a suction air system of cleaning. In air cleaning system SOVs operate and separate air from dust by pressure Certain securities concerned in urea transferring include: Misalignment switches Pull card Speed monitors Thermal overload Usually every belt has different capacity and speed. Fresh feed belts
have
above
90
ton
capacity.
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Interlock System The nature of chemical plants is such that there has to be some order to things else the end result will not be what is desired, or worse a very unsafe condition could exist. Thus there are interlocks to help avoid these situations. Some interlocks could be as simple as a too high or low temperature. If for example a chemical reaction is only safe at a certain temperature then the system may not allow the plant operator to start that process if the temperature is too high or too low. The same for pressure flows etc. Another example is a boiler. Every boiler should have an interlock that prevents it from being started if the water level is too low. Some gas furnaces have interlocks that prevented them from being started if there is not enough combustion air, or too much or too little gas, or if the purge sequence has not been completed.
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Equipment / API Study The following equipments were studied practically: 1) Compressors (Centrifugal, Positive Displacement) 2) Pumps (Centrifugal, Positively Displacement) 3) Urea Reactor 4) Urea Stripper 5) Refrigeration Cycle A few lectures and sittings for learning more about valves and instrumentation were taken. 1) Valves 2) Instrumentation
And the following APIs were studied on the plant. 1) Furnace 2) Cooling Tower 3) Heat Exchanger 4) Instrumentation 5) Centrifugal Compressors 6) Valves
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GLOSSARY Adiabatic Combustion: Burning fuel with no radiant heat losses. Accumulator:
A vessel for the temporary storage of a gas or liquid, usually used for collecting sufficient material for a continuous charge to some refining process.
Absorption:
Absorption is an operation in which a gas mixture is contacted with a liquid for the purpose of preferentially absorbing one or more components of the gas to provide a solution of these solutes in the liquid.
Adsorption:
Adsorption is an operation in which certain solids arrest specific substances from fluids on to their surfaces.
Available NPSH:
The difference between the pressure at the suction of a pump and the vapor pressure of the liquid.
Baffle:
A partial restriction, generally a plate located to change the direction, guide the flow or promotes mixing within the equipment in which it is installed.
Bleeder:
A connection located at a low place in a gas line by means of which condensate, water and oil can be drained from the line without discharging the gas.
Blind:
A solid plate or cover designed to prevent the flow of fluids through the opening that has been blinded.
Bubble Cap:
An inverted cup with a notched or slotted periphery to disperse the vapor in small bubbles beneath the surface of the liquid on the bubble plate in a distillation column.
Bubble Tray:
A horizontal tray fitted to the inside of a fractionating tower and used to secure intimate contact between rising vapors and falling liquid in the tower.
Boiler Feed Water (BFW): Water that has been softened or Demineralized, and deaerated. Compressor:
A device for increasing the pressure of a gas or vapor.
Convection Section:
The section of a furnace shielded from direct flame radiation, in which heat transfer takes place by conduction and convection from hot exit flue gases.
Cavitations:
Flashing of liquid in a confined space, such as nozzle.
Compression Ratio:
The discharge pressure divided by the suction pressure.
Distillation:
It is a process of separating, concentrating, or purifying liquid by boiling it and then condensing the resulting vapor.
Downcomer:
Part of a tower tray which enables the liquid phase to travel from tray to tray on its way down the tower.
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Endothermic Reaction: The chemical reactions which are accompanied by the evolving of heat are called endothermic reactions.
Expansion Loop:
A loop of pipe to take up thermal expansion and contraction.
Flooding:
In distillation, the point in the operation where increase in vapor‐liquid loading causes a noticeable reduction in the fractionation efficiency or tray efficiency of the tower.
Forced Circulation:
Circulation in reboilers which receive their liquid iced from the discharge of a pump.
Firebox:
The combustion chamber of a furnace or heater.
Flash Drum:
A Drum or Tower into which the heated outlet products of a pre ‐heater or exchanger system are conducted, often with some release of pressure. A flash drum usually has no pattern, or only simple de‐entrainment means such as disk and doughnut plates.
Floating Head:
That end of a heat exchanger into which the tubes are fitted which is so constructed as to allow for the expansion and contraction of the exchanger.
Floating Roof:
A special roof on tanks which floats on the liquid this type of roof reduces evaporation looses and minimizes tank hazards.
Furnace:
A piece of equipment which is used to supply heat to the stream flowing through the furnace tubes by the combustion of fuel fuel oil and/or fuel gas.
Heat Flux:
Heat input, per unit of time, per unit of heat ‐transfer surface area.
Holdup:
The time that liquid is restrained in a vessel; usually to promote separation or provide hold time for a downstream pump.
Humidity:
The humidity H of an air water vapor mixture is defined as the Kg of water vapor contained in one kg of dry gas or air. The humidity so defined depends depends only on the partial pressure pA of water vapor in the air and on the total pressure P.
Irreversible Reaction: When reaction is taking place plac e in forward direction only and amount of reverse reactions is undetectable, such reactions are called irreversible reactions.
Knockout Drum:
A drum or vessel constructed with baffles through which a mixture of gas and liquid is passes to disengage one from the other. As the mix ture comes in contact with the baffles, the impact frees the gases and allows them to pass overhead; the heavier substance falls to the bottom of t he drum.
Metering Pump:
Used to both pump and measure the flow rate of small chemical additive streams.
Net Positive Suction Head (NPSH): Net Positive Suction Head.
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Nozzle:
A nozzle is a flanged opening in a tower, drum or large pipe used for connecting lines.
Packed towers:
Packed towers, used for continuous cou nter‐current contact of liquid and gas, are vertical columns which have filled with packing’s or device of large surface. The liquid is distributed over and trickles down through the pa cked bed, thus exposing a large surface to contact the gas.
Percentage Humidity: The percentage humidity Hp is defined as 100 times the actual humidity H of the air divided by the humidity Hs if the air were saturated at the same temperature and pressure. Hp = 100 – H/ Hs
Prime:
Filling the case of a pump with liquid.
Reboiler:
Source of heat input to a distillation tower.
Required NPSH:
The net positive suction head needed to keep a pump fro m cavitation.
Raschig Rings:
Small cylindrical rings used in packed tower.
Riser:
A pipe or other opening to allow vapors to rise through a plate in a tower.
Slop tanks:
Tanks containing any products which are not up to quality and must by rerun.
Standpipe:
A vertical tube filled with aerated dense phase powdered catalyst, usually provided with a valve outlet at its lower end. This serves as a pressure leg for the injection of powdered catalyst into a zone wherein the pressure is lower than the hydrostatic head at the bottom of the standpipe.
Surge Drum:
Any vessel which provides sufficient holding time to smooth out fluctuations in flow.
Sensible Heat:
Sensible heat is defined as the heat that is input or removed from any material with no change of state.
Stripping:
Stripping is mass transfer operation involving the transfer of low boiling components to gaseous phase. The driving force for this process is the concentration difference of the component to be stripped from liquid to the vapor phase.
Transfer Line:
Refers to a line carrying oils and/or gases at some elevated temperature (usually from a furnace) to some other equipment, i.e. a line from the outlet of a furnace to a reactor or tower.
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Suggestions / Feedback FFC MM is efficiently utilizing all the units involved in the production of Ammonia and Urea. Though there can always a room for improvement. o
will
Log Books filled by Shift Engineers should be made computerized. This better
the
efficiency,
better
record
maintenance,
conveniently
communicated if required etc. o
Work should be done to look for an alternative to the feedstock currently
being used (i.e. Natural Gas) e.g. Coal Gasification. This is in concern with the country’s current and future energy situation. o
Complete PPE should be followed. Half sleeve shirts should be discouraged.
o
Training lectures should be given in the classroom prior to the plant visit.
o
Urea Dust Recovery.
Apart from these considerations it is very hard to find any loopholes in the processing plant. Whatever is present is being utilized at its level best.
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Appendices With respect to the order: 1) Ital Floc 2) Urea PFD 3) Natural Gas Station 4) Instrument Air Plant 5) Demineralization Plant 6) Clarified Water Distribution System
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