Reboilers condensate backup

Water Hammer and Condensate Backup Steam-Side Reboiler Control... 

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... 

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. 

In one instance the effect of steam condensate backup was clearly observed during a unit turnaround. As shown in Figure 12-10, the rust layer on the inside of the channel head of a reboiler showed clearly where the condensate level normally ran. This was a positive indication that 20% of the heat-transfer surface area of the reboiler was waterlogged and, therefore, useless. Steam condensate backup can be due to one of the following ... 

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. 

To suppress the evolution of steam in the drain line, the condensate must be subcooled from 320°F to 270°F as it leaves the reboiler. This can only be accomplished by condensate backup. And if the condensate is not subcooled to 270°F, then the condensate will begin to vaporize. Which will then ... 

---