How Can You Calculate the Energy Content of Waste Steam in Industrial Processes?

[vespak]

I don't know if anyone can help but I have a friend who wants to capture his waste steam and convert it to energy - that's the easy bit - the difficulty is how to work out how much energy he has in the first place. He is drying wood by heating a container to 160^oC over a period of approx 40 hours which produces 16,000 litres of water in the form of steam. That exits the container (2.4 x 2.4 x 6m) through a 400mm flue. In order to capture this I want to put a shell and tube heat exchanger in the flue (I don't mind if this converts the steam back to water, we have another use for that) In order to make this work effectively I need to know what the likely pressure and or velocity does the steam emerge at. I appreciate that there will be a gradual build up in pressure. Its the last 24 hours I am interested in where there is a constant temperature and so presumably a reasonably constant velocity. We already know the saturated steam heat is around 120^oC. The only motive power causing the steam to exit the container is the expansion of the air & water vapour/steam inside the container. Fans circulate the heated air inside the container and the flue is sited at the base of the container half way up its length. Any thoughts?

 

[russ_watters]

Welcome to PF.

You don't really need velocity and even the pressure isn't all that important unless it is very high. The vast majority of the energy to be recovered comes from condensing the steam unless you can cool it well below boiling temp, so by multiplying the mass of steam by the latent heat of vaporization of 2200 kJ/kg you get yourself in the ballpark.

 

[vespak]

Many thanks that's got me going in the right direction.