Condensate collection systems

How much steam condensate is your plant recovering Seventy percent is considered pretty good, and 30 percent is, by any standard, pretty awful. As condensate collection flows are rarely metered, here is a really good way to make such an overall measmement (ST = steam TR = treated water)  

Determine TR—the Ib/h of softened or deminerahzed treated water flowing to the deaerators. 

Loss of steam condensate to the plant s sewer is environmentally wrong and wastes money for water-treating chemicals and energy. The principal reasons why steam condensate is lost to the sewer are 

Steam or water hammer (more properly called hydraulic hammer) is one process plant phenomenon familiar to the general public. I well remember trying to warm up the steam system of a large amine plant in Texas City in 1980, and feeling more than hearing the crescendo of crashes due to steam hammer. The cause of steam hammer is illustrated in Fig. 12.7. 

In general, hydraulic hammer is caused by the sudden conversion of the velocity of a liquid into pressure, causing a surge of pressure 

Operators who have problems with loss of reboiler capacity often attribute these problems to condensate backup. This is usually true. To drop the level of water out of channel head, either the steam trap or the condensate drum is bypassed by putting the condensate to the sewer. Sometimes the float of the trap is sticking, but mostly the difficulty is an erratically high pressure in the condensate collection 

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It creates steam or water hammer in the condensate collection system. 

Figure 8.8 Avoiding water hammer in a condensate collection system.

Some auxiliary equipment is required to create a vacuum and separate the methanol and water removed from the product in the vacuum and condensate collection system (see Figure 11.9). These auxiliary systems include a steam ejector vacuum system, peroxide treatment system, and tempered water system. 

The interaction of a steam reboiler with its condensate collection system can be very simple or very complex. Simple in the sense that the plant operators are satisfied to drain the steam condensate to the sewer from the channel head of the steam reboiler or feed preheater. Complex if the operators are trying to route the condensate back to the steam generation (boiler house) for recovery and reuse. 

The design of a steam condensate collection system is a complex task. It cannot be approached just as a problem in hydraulics, because it is also a problem in vapor-liquid equilibrium and in the conversion of sensible heat to latent heat. Considering these three factors together requires quite complex calculations, for which I have had to rely on the use of a computer model. These same sorts of considerations apply to multicomponent hydrocarbon systems, such as propane-butane refrigeration loops, but then the calculation complexity increases by an order of magnitude. 

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