Dear Crispin, Ron, and all,
When I now think about all this it all seems so simple and obvious as the way to do it. Not sure if others are following me in my thinking. All we need to do is have all start with the same Energy from a biomass and use that as a baseline when comparing stoves. Oven dry weight energy value minus the char in the pipe. When burning wet (real) biomass we just report that in the 6 Box reporting sheet so a lower (or higher if the water reaction) results can be explained. When the fuel is wet we have all that FREE energy from the catalyst that will evaporate it IN the stove body. In fact, if one puts a cup of water in a stove the evaporated steam hitting the pot will increase the water temperature in the pot. Unless the steam lowers the temperature of the secondary, or otherwise interferes with the secondary combustion, it will add to the energy heating the water. It cost nothing to evaporate the water. As for coal: I have not thought how this would work and know little about burning coal. I would think it much like adding char to a rocket stove? There being little secondary combustion and the stove body getting very hot(?) In my own mind I think this is what really happens in the real world and it seems clear to me this is the direction we should go. And if we can make it work it would simplify stove testing immensely. Regards Frank Frank Shields Control Laboratories; Inc. 42 Hangar Way Watsonville, CA 95076 (831) 724-5422 tel (831) 724-3188 fax [email protected] www.controllabs.com From: Stoves [mailto:[email protected]] On Behalf Of Crispin Pemberton-Pigott Sent: Monday, August 19, 2013 1:45 PM To: 'Discussion of biomass cooking stoves' Subject: Re: [Stoves] Saving the WBT Dear Frank It is a difficult question to answer. Do you want the actual energy available from a particular piece of wood or the heat theoretically available, or what it would be if it was dry? If the fuel is moist, then the gasification or the volatiles energy has to evaporate that moisture to get it out of the way. Unfortunately the amount of gas you can make from a bit of wood literally changes with the moisture level because the moisture is involved in the chemistry of what happens in the processes. With respect to coal, I was not even about to get a carbon content of the 'volatiles' let alone an energy figure. I suspect you are not going to get a good answer, and whatever answer you get is not going to be very useful in a real world problem. Regards Crispin Dear Stovers, I am trying to determine the best way to calculate the energy in the Natural Volatiles. The sample we place in the iron pipe of the oven dried biomass we can test or 'look up' the energy value. In the char remaining after 450c deg. (char-ash) we can give that a value of 34.78 kJ/g. Then for the total NV in the fuel we just subtract the total biomass from the char energy remaining. All done in the pipe. Then use the energy calculated from the increase temperature of the water to determine efficiency. I am still wondering what to do with the moisture in the fuel. Any suggestions? It is like the NV fraction but with possible varying results. As Alex reminded me in his writings there is the water-reaction that can increase the energy output or the LHV stealing energy from the NV. So depending on the stove and operator working the catalyst to control the internal body temperature the water can be a plus or minus. My thinking now is to just use the dry NV value as the total energy of the biomass. Like playing golf. You have a par 5 and you can go above or below depending on your day. The dry NV value is the value we use and we go above or below 100% efficiency depending on how good the stove and operator controls the catalyst and if water is included in with the biomass. >From the replies it's a bit hard to tell but it seems we are mostly all in agreement. : ) Regards Frank
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