How to calculate the pressure produced from heating logs?!?
How to calculate the pressure produced from heating logs?!?
(OP)
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 160C over a period of approx 40 hours which produces 16,000lt of water in the form of saturated 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 at what pressure and velocity steam emerges at. I appreciate that there will be a gradual build up in pressure. It's 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 120oC. The only motive power causing the steam to exit the container is the expansion of the air & water vapor/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?





RE: How to calculate the pressure produced from heating logs?!?
The steam pressure inside the container will be a function of the rate that it is being produced and the pressure drop through the flue. Adding a heat exchanger will increase the resistance to flow, so pressure inside the container should rise accordingly.
You definitely want the steam to be condensed back to water, as the latent heat is the major source of any energy recovery.
I imagine that the steam is being produced at close to atmospheric pressure. Saturated steam with a temperature of 120C would be at a pressure approaching 1 Barg under normal circumstances. It could be that in this case that it has a certain amount of superheat because of the hot air being circulated, so could be in equilibrium at a lower pressure.
Haven't really helped, but it's going to be pretty much guesswork unless you can determine the energy balance - if you can condense all the steam somehow over set time periods to determine rate, then you will be some way there.
Cheers,
John