Condensate backup problems

We can see, then, that either condensate backup, or blowing the condensate seal, will cause a steam reboiler to lose capacity. If you think either of these two problems could cause a loss in reboiler duty, try opening the bypass around the steam trap. If the reboiler duty goes up, the problem was condensate backup. If the reboiler duty goes down, then the problem might be a blown condensate seal. If it looks like a blown condensate seal problem, close the steam trap bypass. Then, partially close the valve downstream of the steam trap. If this increases the reboiler duty, a blown condensate seal failure is proved. 

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... 

Air-cooled surface condensers. Figure 8.11 shows a surface condenser elevated above the steam turbine. This creates an additional problem, in that moisture from the turbine exhaust steam will accumulate in the bottom of the turbine case. A special drain line from the turbine s case is needed to prevent condensate backup from damaging the spinning wheels. 

Surface condenser problems. These include undersized surface condenser area, water-side fouling, lack of water flow, condensate backup, and excessive cooling-water inlet temperature. To determine whether a poor vacuum in a surface condenser is due to such heat-transfer problems, plot the same point on the chart shown in Fig. 18.4. If this point is on or slightly below the curve, it is poor heat transfer in the surface condenser itself that is hurting the vacuum. 

To determine if this problem exists on a reboiler, establish a definite condensate seal by restricting the condensate effluent line. If the tower bottom s temperature increases, the reboiler has a blown condensate seal. This wastes steam and reboiler capacity. The correction is the same for condensate backup installation of a steam condensate seal drum. 

Steam reboilers are subject to a wide variety of serious capacity problems. The most common is steam condensate backup into the channel head. This is checked by manually draining the steam condensate to a nearby sewer and observing if the reboiler duty increases or the steam inlet control valve closes. 

The opposite problem to steam condensate backup is blowout of uncondensed steam through the reboiler and out the condensate drain line. This phenomenon causes a loss in heat transfer entirely out of proportion to what might be expected. Literally half of a reboiler s duty can be lost by an apparently small amount of steam blowing out the condensate drain line. 

The problem with condensate backup and subcooling is the very low heat transfer coefficient (U) for subcooling vs. condensation. Typical heat transfer coefficients (Btu/hr/fb/°F) are ... 

The problem with the precondenser is condensate backup. Something, perhaps a partially plugged drain line, is restricting... 

Condensate backup is also caused by a large number of problems associated with the barometric drain line, and especially with the seal drum, shown in Fig. 23.2 ... 

The most common problem with reftigeration condensers is condensate backup, rather than fouling (see Chap. 16). This may happen if the condenser outlet line is imdersized. Let s say that the pressure drop due to piping friction losses in this line is 10 psig. The refrigerant is isobutane. The isobutane cannot flash as it enters the refrigerant receiver. 

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