Analysers FAQs

Frequently Ask Questions (FAQs)

General 1

Why install analyzers in an analyzer shelter?

2

What are the advantages of installing analyzer system in a pre-fabricated analyzer shelter?

3

Why do we need a Sample Conditioning System for a process analyzer?

4

Why do some Analyzer Systems need Atmospheric balancing control and some don't?

5

Why do we need the Double Block and Bleed Systems in the Multi-Stream Switching Systems?

6

Why do some samples need heating or tracing?

7

Why do we need a sample probe to extract sample instead of a sample tap from process lines?

8

What is Pressurization? What are the types of pressurization available to protect the electrical equipment in hazardous locations?

9

When will be the best time to put the analyzer on-line during commissioning?

10

Why most of the times the analyzer and the laboratory analysis result are different?

11

How often must the analyzers be calibrated to give a reliable reading?

12

Why the pressurization of the Analyzer shelter from the HVAC system is not achievable?

13

Can CAE Asia provide outside consultant e.g. analyzer vendor to conduct training on particular analyzer maker during project execution process?

14

Does CAE Asia provide on-the-job training after project handover ?

15

Why need a trained analyzer maintenance personnel.

1 Answer

W h y i n s t a l l a n a l y z er e r s i n a n a n a l y z er er s h e l t e r ?

Although most analyzers are designed and built to i nstall in the field without further protection, grouping of analyzers together in one shelter had become more popular. Installing equipment in an analyzer shelter protects the analyzers against adverse ambient condition that may cause errors in the analyzer readout. Grouping of analyzers in this manner also results in ease of  maintenance than analyzers that were installed separately. back to top

2

W h a t a r e t h e a d v a n t a g e s o f i n s t a l li l i n g a n a l y z e r s y s t e m i n a p r e - f a b r i c a t e d a n a l y ze ze r shelter?

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Frequently Ask Questions (FAQs)

Answer

The great advantages of choosing a pre-fabricated analyzer shelter is that the complete assembled analyzer systems are pre-piped and pre-wired to all the analyzers and sample conditioning systems. All necessary utilities and power distributions are also pre-installed at the factory. The complete assembled system are then fully tested with test gases and shipped to site as a single package. In this way, minimum site installation work is required. back to top

3 Answer

W h y d o w e n e e d a Sa m p l e Co n d i t i o n i n g Sy s t e m f o r a p r o c es s an a l y z e r ?

Sample Conditioning System that are designed and built to provide the correct process parameters to the analyzer, which can control the process at optimum efficiency to produce on specs end products. The primary objective of a Sample Conditioning System is to extract sample from the process stream and deliver it to the process analyzer to ensure that: (i) sample composition/component measured by the analyzer is representative of the process stream (ii) sample to be measured is in the correct condition samples with the analyzer measurement technique (iii) the required response time for the analyzer to detect the process condition changes in order for the analyzer to give a continous representative sample reading. back to top

4 Answer

W h y d o s o m e A n a l y z e r Sy s t e m s n e e d A t m o s p h e r i c b a l a n ci n g c o n t r o l a n d s o m e d o n ' t ?

Atmospheric balancing is a technique applied for adjusting the sample pressure to atmospheric pressure where the sample pressure is expected to fluctuate and is commonly used for process gas chromatograph analyzer applications. This can be done by installing a solenoid valve to block the sample to the analyzer and another 3-way solenoid value to vent the sample to atmosphere before sample injection. back to top

5

Answer

W h y d o w e n e e d t h e D o u b l e Bl o c k a n d B l ee d Sy s t e m s i n t h e M u l t i - St r e a m Sw i t c h i n g Systems?

As analyzers are relatively expensive such as process gas chromatograph and in order to save some cost, such analyzer systems are design using multi-stream switching system. However, possibility of cross contamination between different streams is highly possible. One way to eliminate is to incorporate "Double Block and Bleed Systems" into the Sample Conditioning Systems. This type of systems uses two air-operated valves (AOVs) for each stream. When the valves are de-energized, the tubing between them is vented to the atmosphere, thus preventing contamination. A secondary bypass is used to scavenge all sample lines, keeping all samples current. The double block valves is to prevent sample contamination to the other streams in case the first valves leaked. A good way to check whether the valves are leakage is to install a leak bubbler at the atmosphere vent tubes. Symptom of bubbling indicates a leak in one of the valves. back to top

6 Answer

W h y d o s o m e s a m p l e s n e e d h e at i n g o r t r a c i n g ?

For gas samples, Electrical or Stream Heating/tracing is applied to the sample l ines or Sample Conditioning System components to maintain the sample above its dew point to keep the sample fluid in vapor state, otherwise condensation may occur. To vaporize a liquid sample can be done by reducing the pressure or increase the temperature to a condition, which sample will change into vapor.

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faq

FAQs 7

Answer

W h y d o w e n e e d a sa m p l e p r o b e t o e x t r a c t s a m p l e i n s t e a d o f a sa m p l e t a p f r o m process lines?

As the process line has the higher fluid velocity at the center, by installing a sample probe to at least one third of the pipe diameter will have a turbulent mixing. Such way of sampling will likely to give a more representative process data and rapid responses to the process changes to the analyzer. With a sample probe, it also eliminates the possibility of suspended solids from the sample, which tends to travel from the pipe walls. back to top

8

Answer

W h a t i s Pr e s su r i z a t i o n ? W h a t a r e t h e t y p e s o f p r e s su r i z a t i o n a v a i l a b l e t o p r o t e c t t h e e l e ct r i c a l e q u i p m e n t i n h a z ar d o u s l o c a t i o n s ?

Pressurization is a process of supplying an enclosure with a protective gas with or without continuous flow at sufficient pressure to prevent the entrance of a flammable gas or vapor, a combustable dust or an ignitable fiber. Basically, there are three types of pressurization as below: (i) Type Z Pressurization: To maintain a positive pressure within an individual protected enclosure and shall be detected by an alarm or indicator, but not necessary to de-energized the protected equipment. (ii) Type Y Pressurization: Basic Requirement as type Z pressurization must be satisfied except that the protected enclosure shall be approved for Division 2 locations. (iii) Type X Pressurization: Basic requirement as type Z pressurization must be satisfied and in addition, a cut off switch shall be incorporated to de-energized power automatically from all circuits within the protected enclosure not approved in Division 1 upon failure of the protective gas supply. The cutoff switch shall supply an alarm signal output from the protected enclosure. (Information extracted from NFPA496 "Standard for Purged and Pressurized Enclosure for  Electrical Equipment) back to top

9 Answer

W h e n w i l l b e t h e b e s t t i m e t o p u t t h e a n a ly z e r o n - l i n e d u r i n g c o m m i s si o n i n g ?

Normally prior to commissioning phase, a pre-commissioning activity is carry out to demonstrate that all analyzers are calibrated and providing reliable data with the certified test standards. During the plant initial start-up, the process sample should not be introduced immediately into Sample Conditioning System since it may not cope with unstable plant conditions. When the plant condition is reasonably stable, before putting the sample into the Sample Conditioning System. it is good practice to commission the fast-loop system first to flush the sample back to the return lines. Then commissioned the system to prevent the possibility of analyzer failure and downtime. back to top

10

W h y m o s t o f t h e t i m e s t h e a n a ly z e r a n d t h e l a b o r a t o r y a n a l y s i s r e s u l t a r e d i f f e r e n t ?

http://www.caeasia.com.sg/faqs2.html(1 of 2)8/17/2011 10:51:05 AM

faq

Answer

The Plant Laboratory has always been the Quality Control benchmark point and it is difficult to convince people to change their mindset. It is unfortunate that operations team is likely to believe the laboratory results even though the on-line analyzer may be correct. In such circumstances, the following uncertainty are to be evaluated: (i) location of the laboratory sample point should be taken where the representative of the process sample being monitor by the analyzer. (ii) personnel taking the laboratory sample must follow the correct procedure such as ASTM method (iii) adequate flushing of sample bomb or container to rid of residue before taking new sample (iv) the injection of the sample to the laboratory analyzer is consistent and should not effect the operation of the analyzer. back to top

11 Answer

H o w o f t e n m u s t t h e a n a l y z er s b e c al i b r a t e d t o g i v e a r e l i ab l e r e a d i n g ?

As analyzer calibration is one of the criteria for maintaining a high reliability and confidence to the operation personnel in operating a process plant; a calibration schedule is usually established after plant start-up. For a initial start-up, analyzer may be calibrated with test standards at least twice a month and drop to once a month when operation is confident on the reliability of that analyzer. back to top

12

Answer

W h y t h e p r e s s u r i z at i o n o f t h e A n a l y z er s h e l t e r f r o m t h e H V A C s y st e m i s n o t achievable?

Usually the HVAC pressurization fans are sized to achieved the required shelter pressure as specified. A common problem is due to heavy leaks of pressurization through the analyzer doors and panels. This leak is normally significant for small shelters and needs rectification immediately before pressurization is achievable. The second common problem lies in the oversizing of the shelter louver, which can be eliminated by adding weights to limit the air flowing out of the shelter. Precaution must be taken to ensure that the required Air Changes inside the shelter is maintained. back to top

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