7 replies to this topic

[NicoleS]

Hi, can anyone tell me the use of a steam trap?

I'm designing a oil storage tank which constantly heating up by a steam heating coils and the saturated condenstate is discharged to a condensate flush drum before discharging to the condensate cooler. My client want to replace the condensate flush drum by a steam trap. My question is can steam trap effectively separate the vapour flushing from the condensate?

Thanks

[Art Montemayor]

Nicole:

This question is so basic and the description given is so erroneous that I'm at a loss as to what it is that you require - an explanation of what a steam trap is or how steam is employed as a heating medium.

Steam is used as a heating medium through its latent heat. That means that the vapor is condensed as it gives up its heat content. In order to have continuous steam heat, you must continuously remove the condensate formed. It's that simple. And a steam trap is nothing more than a phase separation device: it continuously removes the condensate formed.

Your description, "the saturated condenstate is discharged to a condensate flush drum before discharging to the condensate cooler. My client want to replace the condensate flush drum by a steam trap" makes no sense. You need a steam trap or a similar device to discharge the condensate to the "flush" drum - or any other drum. Therefore, you need a steam trap or a level control device (a sort of steam trap) at the bottom of the heating coil (which could be a condensate drum).

Your description makes no sense. Draw us an accurate and legible schematic diagram; it's quicker and more accurate.

[NicoleS]

Hi Art Montemayar,

Thanks for your response.

Yes, I think my description is misleading and indeed the used of steam trap proposed by my client looks dodgy for me too. However if they found a suitable steam trap with correct capacity and pressure drop, I think the system may work. I have attached a sketch of the system.

Thanks for helping.

Attached Files

•  Steam_Condensate.pdf   428.14KB   168 downloads

[santy]

Nicole,

I can not even see why a "flush drum" is needed.
Normally what we do is to use a condensate drum to receive condesate from a steam heater,
The condensate with reduced pressure will be drained via a valve controlled by an LIC installed
on the drum. It works well on site.

Probably a steam trap has the same function than what I call condensate drum.

[JEBradley]

I would imagine that an appropriate steam strap could be used instead of the flash drum. Best thing to do is consult a Steam Trap supplier and ask them - that's their job!!

Your original question was 'what is the use of a steam trap?' I've got a couple of resources which you may find useful:-

www.spiraxsarco.com - contains a good resources section dedicated to all things steam related

Also Try M. Frankel's Facility Piping Systems Handbook - you can email me if you want a copy of the relevant exerpt.

I would also like to respond to Mr. Montemayor's comment of the question being 'so basic'. Perhaps the question has a simple answer but I am delighted people will actually ask questions such as these. I completed my studies almost 10 yrs ago now and the curriculum covered finance, economics, marketing, modern languages and other such things that are of peripheral benefit to an engineer. Unfortunately doing all this meant we had no time to discuss such things as steam traps, the merits of different welding techniques, pressure safety devices etc. (the important parts of engineering). Since starting work i've found most experienced engineers will know where a steam trap is needed - but will have no idea why ('we've always put them there').

So....Keep asking questions.

Attached Files

•  steam_traps.pdf   768.88KB   183 downloads

[dehn0045]

As mentioned above, you need either a steam trap or a level control device on the downstream side of the process heater. The way that you have your drawing arranged (depending on the pressure control used on the flash drum vent) you would be blowing steam out of the vent on the first flash drum (or flush drum as I think you called it) for absolutely no reason. Really, there is no reason for this vent line, provided your steam is reasonably free of non-condensables (really no reason it shouldn't be). The steam trap is perfectly reasonable -- I am using steam traps on heaters that are kind of small, but not lab-scale (2 MMBtu/hr). You can imagine that the condensate is saturated liquid at the steam operating pressure. But when it goes through the trap or any other control device, it will flash. So to keep the pressure drop low (the two phase flow will create sustantial pressure drop) on a large condensate system it may be worth-while to flash to the atmosphere periodically (or you could use a cooler on the downstream side of the trap, before the main collection tank).

Another important point is to not simply assume that a piece of equipment is at its capacity. You should not justify spending extra money because you didn't feel like checking whether or not the equipment was installed with spare capacity. It is my experience is that the older it is, the more likely it has spare capacity. Always remember -- just because it "was" then doesn't mean it "is" now.

I also think that talking with a company like Spirax-Sarco would be a good move. Also, they have done a lot of work on these systems. They know what works, what doesn't and why -- don't re-invent the wheel.

Attached is a schematic of how we do this type of thing where I am at. I am not saying it is necessarily right for you, but it works for me.

 Book3.xls   54KB   157 downloads

I would like to take Nicole’s thread to bring the total opposite situation.

These people have troubles with his steam traps and want to replace them with condensate drums. They say that the traps always get plugged.

The system is as follow (see attachment):

It’s a high pressure steam heater. All the condensate collected through the steam trap is sent to the low pressure condensate header. Because the trap issue they want a condensate drum to collect all the liquids.

I foresee more troubles or complications with this drum. They still are gonna need steam traps and now they would need an additional level control valve and a new low pressure steam line to dispose the vapor coming from the drum.

Is it possible to complicate the system this way when probably the solution rests is in the replacement of the steam trap?

Attached Files

•  CONDDRUM.jpg   8.01KB   54 downloads

[narendrasony]

Panda,
What you have shown in your sketch is trap followed by a flash drum (and not the condensate drum as you are referring it as). To my understanding, Condensate drum is a substitute of steam trap and it is provided just at down-stream of a steam heater or re-boiler. Condensate flows from re-boiler to condensate drum by gravity and condensate drum pressure is equalized with re-boiler side steam pressure.

I expect condensate drums should be used for Low Pressure steam (<3-4 barg) re-boilers/heaters for smooth capacity control. Or otherwise (when trap is used instead of condensate drum) re-boiler capacity will have to be controlled by steam flow only and it may reduce the re-boiler side steam pressure to such a low level that condensate may back up in the re-boiler.

For High Pressure steam (>4-5 barg), steam flow control with steam trap at condensate outlet should serve the purpose.

Narendra