On Sat, Jan 7, 2012 at 07:49, Robert Kana <[email protected]> wrote:
> We need some help calculating the amount of fuel needed to generate enough > power for 160 Kwe every hour. Suggestions are welcomed. > Are you looking for an approximate quantity (so you know how big to build your gasifier)? That's pretty straightforward (to get an estimate within say +/-15%). If all you need is a rough estimate, mine is that you'll need 160-240 kg/hour of fuel input, with 190kg/hour being my best first guess. ***** some detail on how to do the calculations yourself, better. You need to know your overall system efficiency (electricity output per unit of fuel energy input), then you multiply that by 160kW (your electrical power output). Your overall system efficiency is the product of three subsystems: - gasifier - engine - generator A conventional gasifier might have a 70% "cold gas efficiency" (which means the fuel energy of its cooled, ready-to-use output gas, divided by the fuel energy of its input feed). A typical small spark ignition engine might give 20% efficiency (shaft power out divided by fel energy in). But there could be quite a big range here, this figure could easily be 15%-30% so the best idea is to lookup the data of that engine and find out the manufacturer's ratings (if they give a specific fuel consumption "sfc" for natural gas or gasoline/petrol, you can convert that). Electrical generators are pretty efficient. For this calculation let's use 90% (but for better results, look up the specs on the generator you are using). Now we can calculate your overall system efficiency: OverallEfficiency = GasifierColdGassEfficiency * EngineEfficiency * GeneratorEfficieny OverallEfficiency = 70% * 20% * 90% OverallEfficiency = 12.6% The final thing you need to know is then energy content of your input fuel. You know your fuel better than I do but I will assume that it is "standard wood": InputFuelEnergyContent = 20,000,000 Joules / kg (in Imperial units 8612 BTU/lb) You want your generator to produce 160kWe. This is 160,000 Watts of electrical power output, which is 160,000 Joules / second. Because your overall efficiency is 12.6%, to get 160,000 Watts out you will need to feed: FuelInputRate(power) = OutputPower / OverallEfficiency FuelInputRate(power) = 160000 Watts / 0.126 FuelInputRate(power) = 160000 Watts / 0.126 FuelInputRate(power) = 1,269,841 Watts So you need 1269841 Watts (which is Joules/ sec) of fuel input. How much is that? FuelInputRate(massflow) = FuelInputRate(power) /InputFuelEnergyContent FuelInputRate(massflow) =1,269,841 Joules/sec / 20,000,000 Joules / kg FuelInputRate(massflow) =1,269,841 Joules/sec / 20,000,000 Joules / kg FuelInputRate(massflow) = 0.0634921 kg/sec If you want an hourly rate, multiply it by one hour (which is 3600 seconds/hour): FuelInputRate(massflow) = 0.0634921 kg/sec * 3600 sec/hr FuelInputRate(massflow) = 230 kg/hour So my estimate is that you will need 230 kg/hour fuel input in order to produce 160 kWe (this is a system end-to-end Specific Fuel Consumption of 1.4 kg wood per kWh of electricity output) The accuracy of this calculated result depends directly on the accuracy of the input data. If your engine actually has 28% efficiency rather than the 20% I assumed/used in my calculation, your fuel consumption will be 20/28= 71% of what I've calced (so that would be 160kg/hour). -- - Daniel Fredericton, NB Canada
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