5lb Superheated Steam Blowoff Concern

[joejoe23]

I have a potential problem that I'm hoping someone can shed some light on. Our client has directed us to vent to roof the steam exhaust from a steam turbine driving an air compressor. The Owner does not have sufficient capacity of service water (river water) to condense the exhaust to recover the condensate, and does not mind blowing off to atmosphere. My concern is that with 17,000 lbs/hr exhaust rate of 5lb steam at 408F, I will have a snowmaking stack in the winter (Detroit area), or ice up the roof and adjacent building walls. Is this a legitimate concern? Is there some way to look at the psychrometrics and determine if the winter air can prevent the moisture from falling out, and just how often or likely that this will be a problem? Thanks in advance for any help you can be.
Joe

 

[pmover]

will the steam venting to atmosphere be continuous or temporary?

up here in alaska where temps remain below freezing for 6-months, there are locations of occasional venting of steam taking place (not at rates you stated). once the steam mixes with atmosphere and if atmospheric conditions are ideal, teeny tiny ice crystals are formed and carried away by the atmosphere. however, some steam does condense onto vent piping and gravity then commands the direction of condensate. if condensate collects onto a surface below the freezing temp, then ice may very well form.

yes, venting of steam is a waste of money. so perhaps you could incorporate an air-cooled condenser for this vent IF there is that much concern.

good luck!
-pmover

 

[joejoe23]

thanks pmover! Yes, unfortunately that exhaust rate will be continuous, which makes me very uneasy based on your experience. Thanks for the tip about condensing with air as well. I will look into that.

Joe

 

[tommy75]

Joe,

It sure seems that there could be somewhere in the process you could use that energy!! Maybe installing a desuperheater spray valve using boiler feedwater for attemperation and sending it back to feedwater supply or a feedwater heater, or possibly attemperate to a plate and frame have for hot water supply. I'm not sure what your process is other than the driven air compressor but 17000#/Hr is a lot of energy and being that it is superheated for turbine operation the expansion property could give you alot more energy.

Just some ideas to ponder.
Tommy

 

[joejoe23]

Thanks Tommy, and I agree that it is a huge energy waste. I will look into an air cooled condenser since they are low on service water capacity. Thanks again,
joe

 

[rmw]

What is the rest of the steam system like? Is this air compressor located far away from the boiler? What is the turbine inlet conditions? Does the boiler house have a deaerator? Is the feedwater heated in any form prior to the boiler or deaerator? What is the ratio of returned condensate to total boiler requirement (we know that he will be making up 17K pph.)

An air cooled condenser was mentioned in another thread you posted, but it would be expensive, but a heat exchanger to heat make up water wouldn't.

This client must have lots of money or really cheap fuel.

rmw

 

[joejoe23]

Thanks rmw for the feedwater heating tip. Unfortunately, they are a long way from the boiler. And yes...you are right about the cheap fuel. They are making steel, and apparently the coke oven gas is used in the boilers, and is very inexpensive.

Thanks again,
joe

 

[tommy75]

The fuel may be cheap but 17 KPPH of water and chemical is NOT!! That is a substantial amount of makeup and like RM stated, air cooled condensers are high rent!! Where the compressors are located is there anything around that area that requires hot water or a condensate return heading back to the power block? A heat xchanger be it plate and frame, or tube and shell as said previous would be the best bet and probably easy to sell seeing as water and chemicals are not free!!

 

[joejoe23]

Thanks Tommy,

the boiler is about 300 ft away, and we will try to convince the owner to route that turbine exhaust back to potentially the deaerator or feedwater heating.

thanks again.

 

[MJCronin]

joejoe.....

I am trying to understand the overall concept of your plant's steam system and the way the the backpressure turbine fits into it.

Recall that many engineering texts discuss the specification and use of backpressure turbines "as they fit into" a multipressure process steam system. The backprssure turbine "makes sense" both thermally and economically because it can be used to ballance massflow between the various steam systems and generate power at the same time.

Backpressure turbines are sized and selected "for the plants needs"......not the other way around.

Was your turbine part of the original plant's design.....or was it a "great idea" developed by the management of the mill and all details were to be worked out by others.

Now, I have been working with steel industry "great ideas" for a few years now and have seen many that get "sent off to an outside engineering firm" when they begin to look bad.
This is the typical MO of the industry.

I know that I am guessing here... but is this the real story behind your problem ????

Regards

-MJC