Physical Study of a Steam Generating Unit

REPORT NO. 5 PHYSICAL STUDY OF A STEAM GENERATING UNIT

OBJECTIVE

To make a thorough study of a steam generating units and all accessories associated in it.

BRIEF BACKGROUND

A steam generating unit is composed of a boiler furnace and some of all various accessories essential to its efficiency of steam generation. These accessories are fuel burning equipment, superheater, reheater coil economizer, an air heater. The boiler from which water or other liquid vaporizer may be classified according to: 1. Methods of firing, as internally and externally fired 2. Water tube or fire tube 3. Vertical, horizontal, and inclined arrangement of tube 4. Stationary, marine and locomotive 5. Straight tube and curve tube 6. Return tabular and through tube 7. Vertical-baffle and horizontal-baffle 8. High pressure and low pressure 9. Longitudinal-drum and cross-drum

APPARATUS

The package type boiler in the ME laboratory

ACTIVITY

1.

Make a multi-view sketches of the boiler in the ME laboratory. Label all important

 parts and indicate complete specification of the equipment or vessels.

RESEARCH ACTIVITIES

1.

What is meant by boiler horsepower and boiler capacity?

Boiler horsepower measures boiler's capacity to produce steam. One BHP denotes ability to produce 34.5 pounds of dry steam per hour at 100°C (212°F), and corresponds to 10 square feet of heated surface, 33479 British thermal units (BTU), or 9.809 kilowatt per hour (equal to more than 13 mechanical horsepower). Boiler capacity or bo iler load is the steam boilers' maximum output, which can be expressed in Boiler Horsepower or in Pounds of Steam delivered per hour.

2.

Define and illustrate through drawings the different classifications of boilers as

enumerated above. -Methods of firing, as internally and externally -the furnace is located inside the boiler shell (internally)

-the fire is outside the shell (externally)

-Water Tube - A water tube boiler is such kind of boiler where the water is heated inside tubes and the hot gasses surround them. This is the basic definition of water tube boiler. Actually this  boiler is just opposite of fire tube boiler where hot gasses are passed through tubes which are surrounded by water.

-Fire Tube - It is a type of boiler in which hot gases pass from a fire through one or more tubes running through a sealed container of water.

-Vertical -vertical axis boiler

-Horizontal -horizontal axis boiler

-Inclined - inclined axis boiler

- Stationary These boilers are used for power plants or proc esses steam in plants

- Marine - a design of steam boiler best known for its use on ships

-Locomotive -is a type of railway locomotive that produces its pulling power through a steam engine.

-Straight Tube Straight tube boilers have straight water tubes

-Curve Tube -Curve tube boilers have bent water tubes

-Return Tubular - Horizontal return tubular boiler (HRT) has a horizontal cylindrical shell, containing several horizontal flue tubes, with the fire located directly below the boiler's shell, usually within a brickwork setting

-Through tube This boiler is made up of the same parts as the return tube, the main difference is that of arrangement. The rear plate of the combustion chamber forms one tube sheet and the end plate

forms the other. The top of the combustion chamber is stayed to the shell by sling stays which are bars having forked ends fastened to the shell and to the combustion chamber. -Vertical-baffled  boilers are usually installed in boilers with horizontal tubes. -Horizontal -baffled  boilers are usually installed in boilers with Vertical tubes. - High pressure and low pressure A boiler can be considered as high-pressure boiler if its generated steam is above 15  psig while boilers with pressures of 15psig and below care called low-pressure boilers -Longitudinal-drum and cross-drum Longitudinal - It consists of a drum connected to a series of front end and rear end header by short riser tubes Cross-drum - the steam drum is placed at cross ways to the heat source as shown in the figure. Here, the down-comer is fitted on the bottom of the drum and riser is fitted on the top of the drum via a horizontal tube as shown in the figure. 5o to 15o inclined water tubes are connected with down-comer and riser tubes in same manner of longitudinal drum

3.

What are the importance and uses of an industrial boiler?

Industrial hot water boiler systems for generating thermal heat are very similar to the household heating boilers in our cellars. The main difference is that industrial boilers are dimensioned significantly larger, so their heating capacity is not only sufficient for a family home but also for hotels, hospitals, skyscrapers, industrial buildings or entire districts. When using process heat generated by steam boiler systems the individual applications are far more versatile. They are used in many industry sectors.

4.

What is an air vent, how important is it and how it is done?

Air vent valve is very necessary and comes under one of the boiler mounting. These are fitted to the upper parts of the boiler as required to release air from drums and headers, either when filling the boiler or raising steam. Air vent valve also plays a significant role in  preventing the boiler to collapse while draining the boiler.it prevents the vacuum to be developed during draining. However, it is to be kept in mind that vent valve is opened only when the boiler is cooled.

5.

What is purging?

Purging is required before ignition of the first burner to clear any combustibles that may have accumulated in the boiler and components. This is a critical time before the lighting of the first burner.

6.

Define the following: de scaling, back firing, water hammer. De scaling A chemical substance used to remove lime scale from metal surfaces in contact with hot water, such as in boilers, water heaters, and kettles. Descaling agents are typically acidic compounds such as hydrochloric acid that react with the alkaline carbonate compounds present in the scale, producing carbon dioxide gas and a soluble salt. Back firing -A back-fire or backfire is combustion or an explosion produced by a running internal combustion engine that occurs in the air intake or exhaust system rather than inside the combustion chamber. Unburnt fuel or hydrocarbons that are ignited in the exhaust system can produce loud sounds even if flames are not present at th e tailpipe. A visible flame may momentarily shoot out of the exhaust pipe where the exhaust system is shortened. Fire may also travel into the air intake piping. Either condition may cause a loud popping noise, together with possible loss of power and forward motion Water Hammer -Is a pressure surge or wave caused when a fluid, usually a liquid but sometimes also a gas, in motion is forced to stop or change direction suddenly, a momentum change. A water hammer commonly occurs when a valve closes suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe.

7.

What is a water softener? Give details on its operation and standards. Is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted mopping up calcium ions. Soft water also extends the lifetime of plumbing by reducing or eliminating scale build-up in pipes and fittings. Water softening is usually achieved using lime softening or ion-exchange resins

8.

What are the dangers associated in boiler ope ration? Dangers associated with steam are due to pressure and temperature. The super high-pressure steam normal operating temperature is 510 ℃. Physical contact with any equipment or piping that is not insulated with this steam or any other steam source will

cause severe burns. Personnel working around steam systems should wear long sleeve shirts at all times to lessen the exposure of burns Steam and hot condensate pose severe burn potentials for the operators in the  performance of this job. Temperatures of the various system range from 160 to 510 ℃. Burns may occur at temperatures above 46 ℃. Equipment damage is also to be avoided by preventing eater hammer during heating and cooling the systems. The heaters and drums containing steam and condensate have to be heated up slowly and cooled slowly to prevent water hammer from occurring.

9.

What is the difference between economizers and pre heaters? Economizer The feed water from the high pressure heaters enters the economizer and picks up heat from the flue gases after the low temperature superheater. Many types of economizer are designed for picking up heat from the flue gas. These can be classified as an inline or staggered arrangement based on the type of tube arrangement. The staggered arrangement is compact and occupies less volume for the same amount of heat transfer when compared to the inline arrangement. Economizers are also designed with  plain tube and fined tubes. The fins can be longitudinal or spiral. All these types are suitable for clean fuels like gas, oil, and low ash c oals. For high ash coals, only the plain tube inline arrangement is used. This is mainly to reduce ash erosion and thus reduce erosion failures. These economizers pick up about 50 to 55 degrees centigrade in a large capacity boiler, which will reduce the flue gas temperature by about 150 to 170 degree centigrade. The boiler designers always keep the economizer water outlet temperature to about 25 to 35 degrees below the drum saturation temperature. This is done to mainly avoid steaming in the economizer. A steaming economizer generally is less reliable. As a rule of thumb, for every one degree pick up of economizer water temperature, there will be a drop of about 3 to 3.5 degrees. Air pre heaters Air pre-heaters are provided in boilers to preheat the combustion air. There are two main types: recuperative and regenerative air heaters. Tubular or recuperative air  pre-heaters are provided in boilers of medium and small range of steam generation. This type of air pre-heater becomes very large in size if they have to be used in very high capacity boilers like 600 tons/hr. of steam production and above. In these cases, regenerative air pre-heaters are used. The arrangement of all these air pre-heaters differ with the design and, in large, the way they are combined for very high capacity boilers. Regenerative air per-heaters are compact and can have a stationary or rotating hood. A combination of tubular and regenerative type of air pre-heaters is used in very high capacity boilers. The tubular being used for primary air heating and the regenerative used for the secondary air heating. In case the boiler designers do not want to go for a

combination of tubular and regenerative air pre-heater, then they have a choice of trisector regenerative air heater. Normally the ambient air is heated to about 300 to 350 degree centigrade. This results in a flue gas temperature drop of around 230 to 250 degree centigrade. So for each degree pick up in air temperature, roughly 0.8 degree drop in flue gas temperature is achieved.

10. What is the difference between design pressure and operating pressure? -In designing equipment, it is seen that it sustains the stress imposed on it from the external and the internal pressures, and this pressure is termed as d esign pressure. -MAWP is the maximum pressure at which the vessel or equipment is allowed to function at a specific temperature. -Design pressure is the condition of coincident temperature and pressure that is expected in a normal condition. -Maximum Allowable Working Pressure is the maximum pressure that is p ermissible at the top of the equipment or vessel in normal operating conditions. -One of the main differences between Maximum Allowable Working Pressure and design pressure is that the latter one is always equal or less than MAWP of the vessel or equipment. -The MAWP will be changing with time because of corrosion and vessel fatigue. Design  pressure depends on the kind of system (fuel, water, steam, etc.) that is used in the vessels.

REFERENCES

http://banksengineering.com/blrsafety.htm https://en.wikipedia.org/wiki/Back-fire https://en.wikipedia.org/wiki/Descaling_agent https://en.wikipedia.org/wiki/Water_hammer https://en.wikipedia.org/wiki/Water_softening http://setxind.com/downstream/the-importance-of-industrial-boiler-maintenance/ http://www.answers.com/Q/What_is_the_need_of_Purging_in_boiler http://www.differencebetween.net/science/difference-between-mawp-and-design-pressure/ https://www.dli.mn.gov/ccld/PDF/guide2saferboiler.pdf https://www.brighthubengineering.com/power-plants/34240-economizer-and-air-preheaters-are-provided-for-heat-recovery/ http://www.hse.gov.uk/pubns/indg436.pdf https://www.quora.com/What-is-the-use-of-an-air-vent-valve-in-a-boiler https://www.scribd.com/document/280624893/Principles-of-Boiler-Operations https://www.scribd.com/presentation/299865327/Introduction-to-Boiler