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  • Ethanol btu's per gallon

    Does anyone have the gross BTU's per gallon of ethanol from corn? Any difference between this ethanol and that from cellulosic material? How about methanol?

  • #2
    Re: Ethanol btu's per gallon

    I found some information.

    Energy density of ethanol
    http://hypertextbook.com/facts/2003/RoxanneGarcia.shtml

    Various fuels compared.
    http://xtronics.com/reference/energy_density.htm

    Though if you are asking if ethanol from corn has a different energy density then ethanol from some other substance, I do not know. I would guess they would be the same in its purest form.

    I can help convert energy density in megajoules/kilogram to Btu/gallon if you need that.

    Comment


    • #3
      Re: Ethanol btu's per gallon

      ethanol is 76000 btu per gallon.
      it does not matter what the source was .

      Comment


      • #4
        Ethanol btu's per gallon -- That's not the only question

        It would appear that the energy density of ethanol is somewhere between 23-27 megajoules per kilogram depending on the different levels of purity that can be achieved during the distillation process (e.g. it is the same as for vodka or gin, which can be produced at different strenghts).

        I understand that greater purity can be achieved by mainly removing water and CO2 from ethanol. The less water and CO2, the purer and the higher the BTUs.

        However, let me open the question, by stating that the key is not just the "amount of energy dispensed" by ethanol but, like with any other source of energy, the "net energy dispensed", which is what is commonly called the well-to-wheel impact. In simple terms, how much energy ethanol produces minus how much it uses for production, distillation, distribution, storage, etc.

        This is where the type of raw material used for producing ethanol (sugar cane, sugar beet, wheat, corn, cellulose, etc.) makes a significant difference. Corn is a very poor raw material: research varies but, overall, all reports seem to conclude that the "net energy dispensed" by corn-based ethanol is either marginally positive or marginally negative. On the other hand, sugar cane has a highly positive net energy balance (since alcohol results from fermented sugars, it should make sense, all things being equal), in addition to producing more than twice as much ethanol per acre cultivated vs. corn.

        Therefore, thinking simply in terms of BTUs can be correct or incorrect depending on the question that you need to answer.

        I hope this helps.

        PS: a gallon of ethanol contains approx. 80,000 BTUs. A gallons of unleaded regular contains about 119,000 BTUs. As a result, a standard barrel (42 gallons) of ethanol is worth about 28 gallons of gasoline.

        Metric tonne ethanol = 7.94 petroleum barrels = 1262 liters
        ethanol energy content (LHV) = 11,500 Btu/lb = 75,700 Btu/gallon = 26.7 GJ/t = 21.1 MJ/liter. HHV for ethanol = 84,000 Btu/gallon = 89 MJ/gallon = 23.4 MJ/liter

        LHV = Lower Heating Value; HHV = Higher Heating Value.

        (Extract from a website): "Energy contents are expressed here as Lower Heating Value (LHV - also known as "net CV" or net calorific value) unless otherwise stated (this is closest to the actual energy yield in most cases). Higher Heating Value (HHV, including condensation of combustion products - also known as "gross CV" or gross calorific value) is greater by between 5% (in the case of coal) and 10% (for natural gas), depending mainly on the hydrogen content of the fuel. For most biomass feedstocks this difference appears to be 6-7%. The appropriateness of using LHV or HHV when comparing fuels, calculating thermal efficiencies, etc. really depends upon the application. For stationary combustion where exhaust gases are cooled before discharging (e.g. certain power stations using condensed gases for pre-heat), HHV may be more appropriate. Where little or no attempt is made to extract useful work from hot exhaust gases (e.g. motor vehicles, small heating boilers), LHV is more suitable. In practice, many European publications report LHV, whereas North American publications use HHV."

        Comment


        • #5
          Re: Ethanol btu's per gallon

          I am considering buying an ethanol fireplace. I would like to compare the btus of a gas fireplace vs. an ethanol one. A gas fireplace gives off approximately 40,000-45,000 btus. Can anyone do a direct comparison of ethanol btus (other than for a gallon of ethanol which was already stated).

          Thanks.

          Comment


          • #6
            Re: Ethanol btu's per gallon

            Originally posted by Unregistered
            I am considering buying an ethanol fireplace. I would like to compare the btus of a gas fireplace vs. an ethanol one. A gas fireplace gives off approximately 40,000-45,000 btus. Can anyone do a direct comparison of ethanol btus (other than for a gallon of ethanol which was already stated).

            Thanks.
            Not sure I understand your question completly.

            40,000 Btus from gas fireplace would need 40,000 Btus from an ethanol fireplace. It wont matter what the source is, a Btu is a Btu.

            Comment


            • #7
              Re: Ethanol btu's per gallon

              So how does Ethanol increase octane by 2 to 3 points.?

              Comment


              • #8
                Re: Ethanol btu's per gallon

                Octane rating is not about more energy per gallon, it is about tolerating higher compression ratio. Compressing any gas heats it. In the case of an air-fuel charge, it can reach a temperature at which it spontaneously combusts from the heat; this leads to the engine knocking. Diesel engines are designed to operate in this mode, spark ignited engines are not.

                Like octane, an ethanol air-fuel charge needs a higher ignition temperature. If the fuel tolerates the compression ratio, higher compression ratios produce more power from a given weight engine and convert a larger portion of the thermal energy to mechanical. Since the fuel is typically more expensive, it may not lead to more economical operation.

                Comment


                • #9
                  Re: Ethanol btu's per gallon

                  Octane in gasoline is not a measurement of energy, but is a measurement of resistance to pre-ignition. Gasoline is made up of HC (Hydrocarbon) molecule chains and those HC chains having 7 carbon atoms are called Heptane and those that have 8 carbon atoms are called Octane. Gasoline fuel rated @ 87 Octane contains 13% Heptane HC chains and 87% Octane HC chains.

                  Octane can be (and has been by practice) increased by artifical means (addition of special additives and/or improved refinement technologies) and is today (by the American Petroleum Institute or API) more a measurement of fuel rapid oxidation rate @ a specific temperature and pressure (as determined by the API and American Society of Testing Materials or ASTM test procedures) rather than the actual percentage of Octane HC chains.

                  The reaction in an internal combustion engine is that the higher the Octane rating, the slower the fuel burns and the greater the resistance to pre-ignition. Using a fuel of a higher Octane (on the modern computer controlled engine), higher than what the manufacturer designed their engine for, will not only reduce that engine's fuel economy, but it will also reduce that engine's performance.

                  As far as fuel for heating, most home heating fuel suppliers will rate their fuel in BTUs based on what appears the most advantagous to their fuel sales. For example: 1 BTU is the heat required to raise 1 lb of water 1F. Gasoline has a BTU rating of 18,400 BTUs/lb, whereas ethanol is actually 47% less @ 9,750 BTUs/lb. Because of this, ethanol fuel suppliers display their fuel BTU ratings as BTUs per gallon (giving the consumer a perceived higher heat value). For comparison; heating oil has a BTU rating of 20,400 BTUs/lb and diesel (#2) has a rating of 24,840 BTUs/lb.

                  For those considering ethanol as an alternative due to enviornmental concerns (ethanol has near zero greenhouse gas emissions when burned), it should be noted that between 0.5 and 1.5 gallons of fossil fuel (depending on who you talk to) is used to produce a single gallon of ethanol.

                  Steve C.

                  Comment


                  • #10
                    Re: Ethanol btu's per gallon

                    I have to take issue with a few of the numbers in post #9.
                    It is unclear whether they are higher or lower heating values or the source.

                    Not sure if this link will post www . eere . energy . gov/afdc/pdfs/fueltable . pdf
                    but source is a Department of Energy table. Qutoing from it. lower heating values (LHV) are given for several fuels in format:
                    Fuel, BTU/lb, BTU/gallon
                    Gasoline, 18676, 116090
                    #2 diesel, 18394, 129050
                    Ethanol, 11585, 76330
                    Propane, 19900, 84500
                    Methane, 20263, 19800
                    Hydrogen, 52217, N/A

                    LHVs are clearly the right choice for a motor vehicle fuel as present technology has no way to recover the heat in the water vapor as mechanical energy. For high efficiency furnaces to heat homes, the correct choice is debatable.

                    #2 diesel has a higher energy content ONLY on a per gallon basis; it is less per pound. Ethanol is a highly oxygenated fuel which is the reason for its lower energy content. In general fuels with higher C/H ratio have higher energy content per gallon. less per pound.

                    Of course for economy, what really matters is the BTU/$.

                    Comment


                    • #11
                      Re: Ethanol btu's per gallon

                      BTU'S in a gallon of ethanal compared to a gallon of diesel?

                      Comment


                      • #12
                        Re: Ethanol btu's per gallon

                        Originally posted by Unregistered
                        BTU'S in a gallon of ethanal compared to a gallon of diesel?
                        Do you want HHV or LHV? HHV assunes the water in exhaust is condensed and the heat from the condensed water is useful, LHV assumes it isn't. LHV is always used for engines, either may be used in looking at furnaces.

                        Per Department of Energy Table:
                        Diesel: 128450 BTU/gal LHV, 137380 BTU/gal HHV
                        Ethanol: 76330 BTU/gal LHV, 84530 BTU/gal HHV

                        That figure is for pure ethanol. E85 is 15% gasoline for cold start and would be higher.

                        Comment


                        • #13
                          Re: Ethanol btu's per gallon -- That's not the only question

                          You're an idiot! There are two products made when ethanol is produced in a dry grind ethanol plant. Yes, there is ethanol but the other product is distillers grains. Most corn in this country is grown to feed cattle. Ethanol is made by extracting the sugars from the corn and sending the protein to the animals such as cattle, poultry and swine. These crops would be grown anyway to feed the cattle. The ethanol process removes the sugar component not well used by the animals and still provides a high quality grain feed to the animals. The same exact crop makes ethanol and feeds the cattle instead of the crop just feeding the cattle. The byproduct is so popular there is actually a shortage of it versus supply.

                          So how can you include the BTU's used to grow the corn, harvest the corn and transport the corn? You give no value to the co product that is used around the world not only as animal feed but as a food source. This product transports and stores much better than corn. It improves the ability ship grains to third world countries.

                          You have 80,000 BTU's output and it takes about 25,000 BTU's with today's technology to make a gallon of ethanol. Further, it burns cleaner and reduces our dependance on foreign oil. The fact is gasoline contributes to global warming and ethanol reduces that carbon foot print compared to gasoline.

                          Just a note from someone who actually knows what they are talking about.

                          Have a nice day!



                          Originally posted by Unregistered
                          It would appear that the energy density of ethanol is somewhere between 23-27 megajoules per kilogram depending on the different levels of purity that can be achieved during the distillation process (e.g. it is the same as for vodka or gin, which can be produced at different strenghts).

                          I understand that greater purity can be achieved by mainly removing water and CO2 from ethanol. The less water and CO2, the purer and the higher the BTUs.

                          However, let me open the question, by stating that the key is not just the "amount of energy dispensed" by ethanol but, like with any other source of energy, the "net energy dispensed", which is what is commonly called the well-to-wheel impact. In simple terms, how much energy ethanol produces minus how much it uses for production, distillation, distribution, storage, etc.

                          This is where the type of raw material used for producing ethanol (sugar cane, sugar beet, wheat, corn, cellulose, etc.) makes a significant difference. Corn is a very poor raw material: research varies but, overall, all reports seem to conclude that the "net energy dispensed" by corn-based ethanol is either marginally positive or marginally negative. On the other hand, sugar cane has a highly positive net energy balance (since alcohol results from fermented sugars, it should make sense, all things being equal), in addition to producing more than twice as much ethanol per acre cultivated vs. corn.

                          Therefore, thinking simply in terms of BTUs can be correct or incorrect depending on the question that you need to answer.

                          I hope this helps.

                          PS: a gallon of ethanol contains approx. 80,000 BTUs. A gallons of unleaded regular contains about 119,000 BTUs. As a result, a standard barrel (42 gallons) of ethanol is worth about 28 gallons of gasoline.

                          Metric tonne ethanol = 7.94 petroleum barrels = 1262 liters
                          ethanol energy content (LHV) = 11,500 Btu/lb = 75,700 Btu/gallon = 26.7 GJ/t = 21.1 MJ/liter. HHV for ethanol = 84,000 Btu/gallon = 89 MJ/gallon = 23.4 MJ/liter

                          LHV = Lower Heating Value; HHV = Higher Heating Value.

                          (Extract from a website): "Energy contents are expressed here as Lower Heating Value (LHV - also known as "net CV" or net calorific value) unless otherwise stated (this is closest to the actual energy yield in most cases). Higher Heating Value (HHV, including condensation of combustion products - also known as "gross CV" or gross calorific value) is greater by between 5% (in the case of coal) and 10% (for natural gas), depending mainly on the hydrogen content of the fuel. For most biomass feedstocks this difference appears to be 6-7%. The appropriateness of using LHV or HHV when comparing fuels, calculating thermal efficiencies, etc. really depends upon the application. For stationary combustion where exhaust gases are cooled before discharging (e.g. certain power stations using condensed gases for pre-heat), HHV may be more appropriate. Where little or no attempt is made to extract useful work from hot exhaust gases (e.g. motor vehicles, small heating boilers), LHV is more suitable. In practice, many European publications report LHV, whereas North American publications use HHV."

                          Comment


                          • #14
                            Re: Ethanol btu's per gallon -- That's not the only question

                            Originally posted by Unregistered
                            You're an idiot! There are two products made when ethanol is produced in a dry grind ethanol plant. Yes, there is ethanol but the other product is distillers grains. . .

                            So how can you include the BTU's used to grow the corn, harvest the corn and transport the corn? You give no value to the co product that is used around the world not only as animal feed but as a food source. This product transports and stores much better than corn. It improves the ability ship grains to third world countries.

                            You have 80,000 BTU's output and it takes about 25,000 BTU's with today's technology to make a gallon of ethanol.
                            You can make the same points without insulting other posters.

                            It is true that the energy to grow the corn and some of the intermediate processing has to be allocated between the ethanol and other products such as corn oil and distillers grains.

                            Doing so is a normal part of life cycle analysis. If you are interested in the techniques and results, I would suggest review of the papers by Dr. Michael Wang at Argonne National Lab (they are all on website.)

                            However, Wang's figures are essentially reversed from your's. About 25000 BTU of the 76330 BTU/gallon (LHV) is net renewable energy, and the rest, 51000+ BTU, is energy used to manufacture it after partitioning energies between co-products. Of course, it is always debatable how to do such partitioning. Other authors such as Pimenthal (whom I would disagree with) assert the net renewable energy is negative.

                            The roughly 33% net renewable energy yield isn't very good, and the amount of corn required to replace foreign oil would produce more distiller's grain than we could ever feed to farm animals. Until the experimental techniques to make ethanol from cellulosic material can be commercialized, ethanol is a very poor renewable energy plan. It is mostly operated to bilk tax credits from the taxpayers, and enrich farmers and ADM.

                            The Brazilian sugar cane process is also vastly superior to the US ethanol from corn process. However, this is mostly due to burning bagasse (cane residue) for the process heat required in brewing and distilling, and lower agricultural energy to grow and harvest cane. It is around 80% net renewable energy for the overall process.

                            Comment


                            • #15
                              Re: Ethanol btu's per gallon

                              Something that is being overlooked about BTU's is that this is a measurement of heat. When you run your car is it turn the heater on or is it to make it move? Gasoline burns at a much higher temperature than ethanol. Therefore a greater percent of the energy that ethanol has is going to its expansion as a gas. This is what is moving the pistons. Why do you think that there is a radiator on a car? It is bleeding off the excess heat (wasted) energy from the gas. The loss in mileage that you see when running on ethanol is also that the compression ratios in cars is designed for gas. Ethanol performs better at a higher compression ratio. So the higher the compression the better the ethanol will perfom

                              Comment

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