Steam Boilers v Steam Generators: The Differences

With the two types often being confused, Carl Knight discusses the differences between shell and tube fired steam boilers and steam generators.

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Raising Steam
The objectives of a steam raising plant are simple. To release the energy in the input fuel as efficiently as possible; to transfer the released energy to the water and raise steam as efficiently as possible; and to separate the steam from the water ready for export to the plant, where the steam energy (heat) can be transferred to the process.

Steam generators typically contain low water content with water being pumped into one end of a continuously wound steel tube (coils) and a mixture of steam and water being produced at the outlet. The coils are contained in an insulated jacket and normally wound into a tight helix, with the burner being fired through the centre, normally from the top down, with the hot flue gasses passing between the coils and up the outside to the flue exit. By the very nature of their design and due to their very low water content, steam generators are unable to deliver steam when the burner is not firing. Because water can be drawn through the coils and passed to the process load, steam generators are also not suitable for varying steam loads.

It&#;s not all bad news for steam generators though. One advantage is that they can very quickly reach working pressure from a cold start. However, during normal operation, a water purging cycle is required before firing, which can delay steam availability.

Shell and tube steam boilers &#; such as Fulton&#;s all-new VSRT or renowned J Series &#; are, by definition, constructed as a pressure vessel with a definitive water level that is evaporated into the boiler steam space for delivery into the process. Compared to steam generators, steam boilers have a large water content relative to their output and are therefore able to release flash steam to meet system demands, even when the burner is switched off.

This increased water content also enables steam boilers to respond to varying steam loads, an advantage that usually outweighs the longer cold start-up time associated with steam generators. Additionally, during normal operation, burner firing on a steam boiler is also achieved quickly as no water purging is required.

Feedwater & Water Treatment
One complication of a steam generator is that it is impossible to match exactly the burner output to the steam requirement. As a result, the pumps normally deliver more feedwater than is actually required as steam by the process, with the excess water usually re-circulated back to the heater feed pump for mixing with water from the feed tank system. A consequence of re-circulating the excess, high-temperature water is that the cost of maintaining the feed pump on a steam generator can be high due to premature failure.

It should also be noted that, due to the complexity of the control system and pump for a steam generator, a high level of technical ability is required for both servicing and maintenance. Steam boilers however, use multistage centrifugal pumps, which are very common and require little or no setup.

In order to provide acceptable quality dry steam from a steam generator, the outgoing steam and water mixture is passed through a sophisticated separator, with the separated water generally being sent to drain. In some cases, due to high total dissolved solids (TDS), the separated water is discarded, which is costly. Additionally, if water separation is not fully effective, high TDS water droplets can be exported into the steam system, which can...

The main and most critical issue with steam generators is that the change of phase from water to steam always occurs over the same length of tube in the coil. As a result, any hardness salts or deposits that are liberated by the boiling process are always deposited in this area, which can lead to overheating of the coil. Water treatment is therefore critical if continual expensive coil replacements are to be avoided.

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Control of TDS levels is also required for shell and tube steam boilers. However, TDS is usually controlled within the shell, by an automated TDS blow-down system, which prevents high TDS water droplets being exported into the steam system.

Feedwater quality control is still essential with steam boilers, but to a lesser degree than with steam generators. This is because steam boilers are far more robust and better able to cope with variations in feedwater quality and lower levels of maintenance. Additionally, the type of control systems and burner used are such that they can be more easily understood by maintenance operatives, meaning emergency repairs to occasional breakdowns can be dealt with quickly.

If you own an industrial boiler, you understand that it is a significant investment. Because a boiler represents a considerable financial commitment, you should make every effort to ensure that it lasts as long as possible. How long should you expect your industrial boiler to last? There are several important points to know, so keep reading for more information. Then, don&#;t forget to contact a reputable business to aid you with industrial boiler maintenance.

What Factors Affect the Lifespan of Your Boiler?

In average, your industrial boiler should last 10 years or more. Simultaneously, there is great diversity in the lifespan of an industrial boiler. Some of the things that will influence the longevity of your boiler are as follows:

&#;The Correct Size: You need to get a boiler that is the right size for your business. If you get one that is too small, it will have to work overtime to meet your needs.

&#;The Proper Installation: To improve your boiler&#;s performance, ensure sure it is properly installed. If you work with a professional to correctly install your boiler, it should last longer.

&#;Maintaining a Maintenance Schedule: You should also invest in routine maintenance. Your boiler should last for many years if you follow your maintenance routine.

These are just a handful of the many elements that will affect the lifespan of your boiler. If you want your boiler to last as long as possible, you must take adequate care of it.

&#;Get in touch with Ross Boilers for further clarification