Steam trap bypass

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. 

The incident occurred soon after the main had been brought back into use after a turnaround. It was up to pressure, but there was no flow along it. The steam trap was leaking and had been isolated. An attempt was made to get rid of condensate through the bypass valve. But steam entered the condensate header, and the line was isolated, as shown in Figure 9-9. Condensate then accumulated in the steam main. 

In this case a manual drain valve is fitted at each drain point on the steam system, bypassing the trap... 

A pipeline that passes around an injection point, valve, control point, heater, steam trap, or other device in order that repairs or other work can be carried out on the bypassed item of equipment as and when required. 

Figure 3.9. Steam heaters, (a) Flow of steam is controlled off the PF outlet temperature, and condensate is removed with a steam trap or under liquid level control. Subject to difficulties when condensation pressure is below atmospheric, (b) Temperature control on the condensate removal has the effect of varying the amount of flooding of the heat transfer surface and hence the rate of condensation. Because the flow of condensate through the valve is relatively slow, this mode of control is sluggish compared with (a). However, the liquid valve is cheaper than the vapor one. (c) Bypass of process fluid around the exchanger. The condensing pressure is maintained above atmospheric so that the trap can discharge freely, (d) Cascade control. The steam pressure responds quickly to upsets in steam supply conditions. The more sluggish PF temperature is used to adjust the pressure so as to maintain the proper rate of heat transfer.

Steam traps install trap below condensate exit (or with a water seal if the trap is elevated), use a strainer before all traps, use a check valve for bucket traps. Slant pipes to the trap. Use a downstream check valve for each trap discharging to a common header. Pipe diameter > trap inlet pipe diameter. Prefer to install auxiliary trap in parallel instead of a bypass. Do not group thermodynamic traps because of their sensitivity to downstream conditions. 

Opened bypass valves, opened steam-bleed valves, steam leaking out of steam traps, visible waste condensate, and system water hammers are the signs that steam consuming equipment are not optimal. An opened bypass valve usually indicates equipment limitation, so operators open bypass valves to compensate. Bleeders are often visible at turbines and in steam jacket tracing applications. This could be a sign that operators may not have confidence in the installed CDL, so they bleed valuable steam to achieve the required operation. 

Purchaser may provide a bypass line on the discharge side to check the flow by measuring it separately before feeding in to the process unit Provision of Internal safety and rupture dise (on the discharge side) along with instantaneous trip for drive motor if excessive disehatge head is encormteied due to closed valves and ehoked lines (e.g. solidified sulphur in pipes due to failure of steam traps)... 

Hi Norman. We have a distillation tower that floods. Delta P on trays below feed point is stable delta P above feed (trays 16-22), increase from 9 to 19 KPA. Condenser and reflux drum is internal in tower, and we cannot measure the reflux rate. Yesterday, bypassed steam trap on reboiler outlet, and flooding stopped. Conclude that flooding tower due to defective steam trap. What s your opinion Note tower fractionation also improved after trap bypassed. 

Dear Jon You re quite wrong. When you bypassed the steam trap, you blew the condensate seal on the reboiler outlet. This permitted uncondensed steam to blow through the reboiler. 

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... 

Back pressure too high and trap is hot] return line too small/other traps blowing steam/obstruction in return line/bypass open/pressure in header too high. 

Traps should be installed with no bypass valves. These valves tend to leak and waste energy. They also present an easy means to increase capacity by opening them. When the load later decreases, they will result in steam being wasted at a high rate. The proper way to solve the capacity problem is to install a trap having a higher capacity. 

FIG. V-33 Process vaporizer with controls factory mounted. Note float and float-operated valve, liquid level gauge, thermostatic steam valve, condensate traps, bursting disc relief valves, and miscellaneous hand valves, including bypasses and strainers. (Source Armstrong Engineering Associates.)... 

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