Dear Crispin,
From: Stoves [mailto:[email protected]] On Behalf Of Crispin Pemberton-Pigott Sent: Thursday, January 31, 2013 8:59 AM To: 'Discussion of biomass cooking stoves' Subject: Re: [Stoves] WBT (never ending) Dear Frank Crispin > Whatever is happening, the numbers are required in real time. Frank> Why? Don’t all we need is energy going in – energy left to = energy used during the time of the test? Nice to have real time measurements to see how the stove performs but not needed for the WBT. Crispin> I think you need to see the SETAR test method in operation. It is not nearly as difficult as you imagine and I am beginning to have more confidence that we can get the fuel analysis as it burns from the combustion products. Frank> So many combustion products in all forms of energy bonds that need to be looked at and assembled along with accurate flow measurement, possible leaks, calibration for gas flow and equipment etc. Crispin> The chemistry is not all that complicated if you don’t go after the past 0.5%. Test methods are surprisingly inaccurate. For example given a choice between measuring what is on a scale and measure gases using a pitot tube, I will take the scale every time. Given that we are trying to get a reproducible measurement within 6.66% on each run we can’t start with a method that is ±20% before even lighting the stove. Frank> The method to estimate energy left over that have been used are very inaccurate -agree. But we can use much better equipment (CHN analyzer) that will give us the values far more accurate than needed. Crispin> The carbon balance method is used by the EPA for vehicle emissions for precisely the same reason we should: because it is convenient, simple and reasonably accurate. It is harder for wood stoves than liquid fuels, but there are a lot of stoves burning liquid fuels. So why not use methods that are really accurate for everything, forgiving the wood burners a bit because the fuel is variable? Frank> If burning liquid fuel why not just weight the fuel to Start – fuel left over? Unlike burning biomass there is no change in the chemistry of the fuel left in the pot. But wood fuels are much harder (as you know) because of burn variation and change in chemistry from start to end as char is produced. Crispin> Here is an example: if you have a fuel you know is 50% carbon, and 10% is missing (based on what you expected, based on a change in mass) what does that tell you? Quite a bit. It means char is being produced somewhere inside or on the fuel and what is burning is hydrogen. That’s not hard. Frank> Much easier if you know the CHN of the starting material and the CHN of the final material and weight of both. Very exact measurements. Moisture at the start is easy. Only problem is moisture at the end and I think that can be dealt with. Then we have only the estimated calculations for bond energy to determine the energy used. Crispin> The big variable is water vapour and when the moisture left the fuel. Frank> ‘When’ the moisture left the fuel? We need this for the WBT? Or just total water vapor during the run? Crispin> This needs to be measured directly in real time and the emissions summed to see what is hydrogen burning and what is fuel moisture evaporating. That is not nearly as difficult a calculation as FTIR requires. Frank> Seems this is all good info for researching the stove performance but overkill and introduces much more potential error for the WBT test. IMO I get the feeling people think this should be a quick test and cheap. Always nice if possible. But this is an important test –very important if a stove producer wants to compare his/her stove to others for sale. And that warrants the most accurate and reproducible test we can do. Each test may take a week+ to dry, grind and prepare samples for CHN analyzer etc. That’s typical for this type of complexity. It should all boil down to fuel quality as being the biggest variable during testing or round-robin test programs –not test procedure or test equipment. Thanks for your well appreciated comments. Frank Frank Shields Control Laboratories, Inc. 42 Hangar Way Watsonville, CA 95076 (831) 724-5422 tel (831) 724-3188 fax <http://www.biocharlab> www.biocharlab.com When you get lots of carbon per MJ and no H2O, you are burning char. You can know this from the computer screen without even looking into the stove. If you watch the computer screen you can often tell if a fire is going to go out. J Regards Crispin Dear Crispin, If we want to determine the Trees Savings that, as you mention, is different than determining energy going in and being used. That because different wood densities and components burn differently. To determine the forest savings we need to use that fuel for the different stoves tested. But for now we have our hands full just following the energy (the C and the H along with water) going in and out. Putting the stove on a balance to measure weight loss seems a very poor way because the weight left is likely much more concentrated in energy than the weight starting with the char formed and water loss. I don’t like the idea of sitting there and trying to determine the char from the wood from the ash as from my experience there is torrefied wood that looks like char. And I don’t like basing fuel used on carbon in gas stream with dilution, mixing, other hydroCarbons, exact flow determination -all prone for very large errors. For the high quality of testing we must insist on achieving we need advanced equipment; like a Leco CH analyzer and stay with testing fuel going in and out IMO. We are saying ‘my stove is better than yours’. If you think the water left over in the fuel is important and cannot be reduced by specifying a moisture in the starting fuel to be less than 15% and not adding fuel closer to 5 minutes before concluding then we need another step. Perhaps weigh the bucket of water / add the flaming mass to the water and re-weigh / increase water temperature determined / suspended solids weight and CH determined / dried fuel weight determined along with CH. The sum of the dried mass from suspended solids and dried settled material is subtracted from the total flaming mass presented to the water to determine moisture (real iffy). But I don’t think this important and more chance for error. At this point we are in charge of this test and can specific anything we want regarding fuel (oven dry?). But soon we will want to use real fuel with water and pine resins, bark, all mixed with corn cobs – This is when we can calculate in tree savings and must factor in water for Out fuel. The CHN analyzer is not a big expense for labs that are going to get into this business, useful for many other tests they likely do and needed for this testing. I don’t see any other way around it. Thanks Frank <and then pot of water part of the test> Frank Shields Control Laboratories, Inc. 42 Hangar Way Watsonville, CA 95076 (831) 724-5422 tel (831) 724-3188 fax www.biocharlab.com From: Stoves [mailto:[email protected]] On Behalf Of Crispin Pemberton-Pigott Sent: Wednesday, January 30, 2013 1:44 PM To: 'Discussion of biomass cooking stoves' Subject: Re: [Stoves] WBT (never ending) Dear Frank You are on the right track with this approach. The details are not important but let’s see what you have: Energy available when going in [moisture, LHV, mass of fuel standing by] Energy still available when finished the task (if it is a task-based test) [moisture, LHV or all remaining fuel. That is the way to get the thermal efficiency (heat transfer efficiency). Because many stoves burn stick-fuel the moisture is definitely not gone and as the influence on the final energy number is strongly affected by the moisture remaining, we have to measure it. It is not difficult at all. Weigh everything that is left. Put the char aside from the ash and homogenise it with a blender (take a sample of it). Cut off the obviously undried fuel and weigh the burned bit. Put it in a dryer for 24 hours. That gives you the moisture content of fuel remaining. Get an LDV for the dried wood and the char remaining (LHV). Calculate what heat was available to begin with and what remains. That gives you the energy offered by the fire (not necessarily offered to the pot). Some things are calculated from that energy number, but not the fuel consumption. Energy released is not the same as fuel consumed. (Please note, UNFCCC, this important fact.) Please edit any spreadsheet you have to correct this misunderstanding. You have to decide what to do with the heat in the charcoal first. Regards Crispin Stovers, Unless I’m missing something (probably am) it seems we are approaching the WBT trying to make accurate readings using simple equipment that does not measure the components we need. The components needed are: IN Fuel: total weights of 1) carbon, 2) hydrogen and 3) moisture. OUT Fuel: total weights of 1) Carbon, 2) hydrogen, 3) moisture and 4) heat in the fuel. Following these main energy constituents of the fuel we determine the amount used in the process. The procedure could go like this: Determine the weight of CH and moisture of the fuel added. AFTER Add spent fire mix to water to determine heat within (increase water temperature). Mix then drain water into a container where 100 mls filtered through a glass fiber filter and measure the CH to determine the carbon and hydrogen in the total fines drained. Then dry, grind and subsample for carbon and hydrogen in the solid material left. We still lack a moisture reading in the left over fuel but I think starting with low moisture fuel and timing the last fuel addition to the fuel box there will be none left. As for the Simmer and Boiling part of the test: The microwave oven I have has a setting for baked potatoes. Wash and pat dry. When the oven detects moisture vapor(?) the timer starts for cooking. What is the detector (?) and is this something we could use to standardize the process? Perhaps located above the pot of water? Thanks Frank Frank Shields Control Laboratories, Inc. 42 Hangar Way Watsonville, CA 95076 (831) 724-5422 tel (831) 724-3188 fax www.biocharlab.com
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