FAQ



Ans : Forbes Marshall provides on-line monitoring solutions for the boiler feed water. The old method of laboratory analysis is now being replaced by on-line instrumentation. Many times, one needs to take samples of boiler feed water at different locations such as deaerator, feed water to economizer, boiler drum, superheater, condenser & so on. It exists at different temperature & pressures & thus, may not be suitable for sensors of the on-line analyzers. To take care of this problem, Forbes Marshall offers a complete solution, which is called “Steam & Water Analysis System (SWAS)”. In SWAS, the sample is first conditioned to bring it to temperature / pressure conditions acceptable to the analyzer sensors and then feeds it to the analyser. We are one of the largest manufacturers of SWAS in the world & supply these systems to more than fifteen countries.
Ans : There are several good methods available. If the water is hard, one needs to use softeners. For high salt contents, a Reverse Osmosis (RO) method would be essential. A De-Mineralised (DM) Water treatment plant would be required to get ultra pure water as boiler feed water. There would also be a primary treatment with filtration systems before the water undergoes the above mentioned treatment processes.
What is the need of boiler water treatment for industrial and process application?

Ans : Boiler water treatment is very crucial for industrial and process applications, as the life & efficiency of the plant equipment depend on it. Properly treated boiler water brings down issues related to corrosion, deposition and erosion. Corrosion and erosion are amongst the main reasons of plant equipment failure & loss in production hours. Well-treated boiler water ensures trouble free operation of the plant, in addition to increasing the life of the plant equipment.
7/14/2015 7:09:33 PM

Why do sample coolers fail?


One of the main reasons for sample cooler failure has been observed to be the failure of the sample coil due to stress corrosion cracking. Here is a detailed analysis of this problem :
       
Root Cause:
If the chloride content of cooling water is high as per cooling water specifications (i.e. more than 35ppm), we don’t recommend use of SS316 material for sample cooler coil. The reason being, sample steam entry is at a higher temperature and pressure. In such cases sample coil may be subjected to inter-granular corrosion resulting in stress corrosion cracking. Due to high hardness of cooling water there is formation of sludge and scales on sample cooler coils causing the above problems. Scales and sludge in the sample cooler is a non conductive layer formed on the water side of sample cooler coil causing reduced heat transfer efficiency
Symptoms: Failures in the coil are characterized by a thick wall, brittle-type crack. This may be found at locations of higher external stresses, such as near attachments.
Causes: SCC is most commonly associated with austenitic (stainless steel) materials and can lead to either transgranular or intergranular crack propagation in the tube wall. It occurs where a combination of high-tensile stresses and a corrosive fluid are present. The damage results from cracks that propagate from the ID. The source of corrosive fluid may be carried over into the super heater from the steam drum or from contamination during boiler acid cleaning, if the super heater is not properly protected. Other sources include scaling, deposition, mud and impurities that can travel in the pipelines during startups
Problems faced by the user:
1.      Scaling and sludge formation on  the water side of sample cooler
2.      Loss in sample cooler efficiency causing higher sample temperature at outlet of sample cooler
Solution offered:
We recommend use of alloy steels like “MONEL400”/ “INCONEL 625” for sample cooler coil. We can offer “Inconnel 625 coils” in our “DHx Series” high efficiency sample coolers. We have supplied such coolers in the Middle East and coastal areas of India where chloride content in cooling water is major problem. These coolers are available with IBR approval and certification.
Use of special material like Inconnel 625 reduces formation of non conductive layer, but, it cannot avoid it 100%. Thus following are remedies to this problem:
1.      D M Water is recommended for use as cooling water
2.      If it is not possible, softened water with very low hardness (CaCO3 & MgCO3) can be used, to reduce scaling problems
3.      Proper maintenance and periodic cleaning of sample cooler coils is must in cases where D M Water is not used for cooling purposes
To make maintenance easy:
1.      All coils in our coolers are removable – so if there is damage, you don’t have to replace the entire cooler – just coil replacement is possible
2.      The shell is removable without the need to dismantle the sample cooler. This facilitates cleaning of coils in a very simple way
3.      For routine maintenance, a drain plug is provided at the bottom of the shell. This facilitates quick cleaning of the shell, as the mud / sediments settled at the bottom can be easily removed
We believe that a good SWAS package is one that is engineered properly by people who have domain knowledge on (a) Steam engineering as well as (b) Control Instrumentation. The SWAS supplier should have enough strength in R&D to support the technology and to innovate (an ISO 9001 company). A good SWAS would effectively cool the sample with minimum cooling water requirement. It will reduce and regulate it’s pressure (using a well engineered pressure regulator – and not a pressure reducer) and it will also maintain the flow characteristic constant. The analyzers should be from a single source and with proven technology. User friendliness and ease of maintenance should be given due importance in selecting these analyzers. Analyzers that can measure parts per trillion (ppt) levels are available for parameters like sodium – such analyzers should be preferred. The analyzer should be chemist friendly and should have grab sampling feature for parameters like sodium, silica and phosphate. Non hazardous chemicals should be used wherever possible. Auto calibration feature should be insisted on, so as to reduce the hassle of maintenance. In short, SWAS should be selected looking into the end user requirements in mind.
Sample Cooler :
This should be preferably a coil-in-shell type of heat exchanger that provides contra-flow type of heat exchange. It should achieve an approach temperature within + 50 C. The pressure drop on the c.w. side should be minimum. Should have necessary blow-down arrangement for the coolant for periodic maintenance. There should be provision of shell relief valve on the cooler itself.

Pressure Regulator (PR) :
This should provide not only pressure reduction but pressure regulation also, irrespective of upstream fluctuations. Especially at low flow rates or low inlet sample pressures, the PR should still give regulated output. If the pressure reducing device is not capable of doing so, it is possible that some of the analyzers will starve, which defeats the purpose of having a sampling system. The GDCD 234 / 163 standards can be referred for this.

The pressure regulator also should provide tight shut-off if downstream blockage arises.

The pressure reducing device should not have large dead volume in the body which can entrap particulate and other species, causing ionic exchange and degradation of sample and therefore leading to incorrect readings.
6/23/2009 4:36:10 PM

What codes should one refer to?


Naturally the latest codes from the countries who are pioneers in 'Steam Power Plants' such as CEGB of Great Britain, Vereinjgung der Grossgrosskraftwerks Betreiber ( VGB ) of Germany & the Central Research Institute of Electric Power Industry ( CRIEPI ) of Japan ( Refer : the guidelines set by Electric Power Research Institute, Chicago, USA ). e.g.The latest British Standard BS2486 - Treatment of Water for Steam Boilers : 1997 or BS3285 - Sampling Steam & Water. The ASTM D1192 is now withdrawn & there is no substitute to this code now as per our knowledge. Currently we refer to CEGB 164 & CEGB 234 when it comes to SWAS
Simple. Based on the internationally accepted 'Codes and Standards'.
Why not ?

When one can get solutions that are reliable, cost effective, technically sound…and that too from people who have years of experience in both the fields of 'Steam Engineering' & 'Control Instrumentation' why should one look at costly alternatives.

The basic components of the sampling system such as 'Sample Cooler', 'Pressure Regulator' (and not a pressure reducer !), ' Back Pressure Regulator' play a vital role in deciding accuracy and reliability of the system. Incidentally, these components also have a bearing on the price of the system.
6/23/2009 4:39:54 PM

So what makes 'GOOD' SWAS?


SWAS that comes as a package from a renowned supplier who,

a) Has experience both in 'Steam Engineering' & 'Control Instrumentation'
b) Can offer all 'On-Line' analyzers under one brand
c) Has capabilities to manufacture the system in-house with vital components that are proven theoretically on the field as well as approved by recognized authorities.
d) Can get technical support from experts both in 'Steam Engineering' & 'Control Instrumentation'
e) And….. many more other reasons
  
6/23/2009 4:56:54 PM

Who should look after SWAS?


Since the SWAS package mainly comprises of sample conditioning equipment as well as on-line analyzers, it needs the supplier to have technical knowledge and expertise in the areas of mechanical design, thermodynamics, steam engineering and also be aware of the latest trends in this industry. Such a supplier can provide the necessary support and help the plant chemist to obtain results from analyzers in a accurate and dependable way.
Do you know that 50% of forced power plant shutdowns can be attributed to impurities and other cycle chemistry problems?

A well designed SWAS package directly attacks these problems. People with good knowledge, experience and expertise prefer on-line monitoring of all the necessary parameters involved in plant cycle chemistry. You will always find a properly maintained SWAS in all power plants that are running at 95+ PLF / PAF
The very reason to have SWAS package in a thermal power station is to have a constant watch on problems associated with corrosion, impairment of heat transfer, dosing optimization, plant effluents, scaling, boiler blow down etc. It is important for the health of a power plant
6/23/2009 4:47:23 PM

Where is it used?


Anyone who is using steam for his or her process and the quality of steam is critical, one should look for SWAS to provide a good solution. Apart from Power industry there are many other industries which are dependent on quality of steam for their end product. All these can benefit from SWAS
6/23/2009 4:50:41 PM

What is SWAS?


SWAS stands for Steam & Water Analysis System. This system is useful for Power Plants that run on steam. The quality of steam that is used by these power plants is of utmost importance – it is like monitoring cholesterol in human body. Various contaminants that might exist in steam can prove very harmful to the turbine, to the boiler, to the piping etc. SWAS effectively monitors these parameters (such as pH, Conductivity, Silica, Sodium, Phosphates, Dissolved Oxygen etc.) and thus helps in maintaining healthy operation of a power plant. In all power plants in India that work with more than 90% efficiency – you will always find a well engineered, well maintained SWAS. A typical SWAS comprises of (A)  a Sample Conditioning System (some call it Sampling System) where the Temperature, Pressure & Flow of sample if conditioned and regulated and (B) an analyzer panel where all the on-line analyzers are located. The sensors of these analyzers receive the sample conditioned by the sample conditioning system and send signals to analyzers. The analyzers in turn send these signals to respective parameters in 4 to 20mA signal which is finally delivered to the plant DSC or PLC