pyrolysis of biomass producing bio-oil, and usually we will check the heating value for the bio-oil.
The following information may be useful for your research
Heating value is the amount of heat produced by a complete combustion of fuel and it is measured as a unit of energy per unit mass or volume of substance (e.g., kcal/kg, kJ/kg, J/mol and Btu/m³). The heat of combustion of fuels is expressed by the higher and lower heating values (HHV and LHV). The higher heating value is also known as the gross calorific value. The higher heating value (HHV) is measured using a bomb calorimeter; and defined as the amount of heat released when fuel is combusted and the products have returned to a temperature of 25°C. The heat of condensation of the water is included in the total measured heat. The lower heating value (LHV) is defined as the net calorific value and is determined
by subtracting the heat of vaporization of water vapor (generated during combustion of fuel) fromthe higher heating value (Meriçboyu et al., 1998). Same types of fuels can usually be compared according to their HHV, whereas the different types of fuels are usually compared according to their LHV. Becausehydrogen contents of the different types of fuels are different from each other (e.g. oil and coal);
therefore, it is necessary to determine the hydrogen content of the fuel for calculating the LHV. The heating values of the various types of fuels are determined according to the ASTM E 711,ASTM D 240, ASTM D 3523, ASTM D 5865. The heating values for various biochar samples were presentedin Table 1. As can be seen from Table 1, the heating values of biomass derived biochars in the literature vary between 11.83 and 44.2 (MJ/kg), whereas the values for coal and charcoal vary between 14 and 35 (MJ/kg) (Speight, 2005). Generally, the high heating values of biochars make them attractivefeeds for clean energy production instead of fossil-based solid fuels
Ref:An Approach to the Characterization of Biochar and Bio-Oil
Didem Özçimen
https://www.iconceptpress.com/download/paper/12012321442701.pdf
The following information may be useful for your research
Heating value is the amount of heat produced by a complete combustion of fuel and it is measured as a unit of energy per unit mass or volume of substance (e.g., kcal/kg, kJ/kg, J/mol and Btu/m³). The heat of combustion of fuels is expressed by the higher and lower heating values (HHV and LHV). The higher heating value is also known as the gross calorific value. The higher heating value (HHV) is measured using a bomb calorimeter; and defined as the amount of heat released when fuel is combusted and the products have returned to a temperature of 25°C. The heat of condensation of the water is included in the total measured heat. The lower heating value (LHV) is defined as the net calorific value and is determined
by subtracting the heat of vaporization of water vapor (generated during combustion of fuel) fromthe higher heating value (Meriçboyu et al., 1998). Same types of fuels can usually be compared according to their HHV, whereas the different types of fuels are usually compared according to their LHV. Becausehydrogen contents of the different types of fuels are different from each other (e.g. oil and coal);
therefore, it is necessary to determine the hydrogen content of the fuel for calculating the LHV. The heating values of the various types of fuels are determined according to the ASTM E 711,ASTM D 240, ASTM D 3523, ASTM D 5865. The heating values for various biochar samples were presentedin Table 1. As can be seen from Table 1, the heating values of biomass derived biochars in the literature vary between 11.83 and 44.2 (MJ/kg), whereas the values for coal and charcoal vary between 14 and 35 (MJ/kg) (Speight, 2005). Generally, the high heating values of biochars make them attractivefeeds for clean energy production instead of fossil-based solid fuels
Ref:An Approach to the Characterization of Biochar and Bio-Oil
Didem Özçimen
https://www.iconceptpress.com/download/paper/12012321442701.pdf
That depends on the state of water in the product of combustion. We refer to HHV when liquid water exists in the combustion products and LHV when water vapor exists in the combustion products. Numerically the difference between the two values is the latent heat of vaporization times the mass of water produced by the combustion process.
so for pyrolysis oil, is it important for us to check the HHV and LHV value?what can we see from these both result?
Basically it depends on how much hydrocarbons in pyrolysis oil. For instance, natural gas has high share of hydrogen, which in turn produce more water in combustion (buring). Thus natural gas has a large difference between the HHV and LHV. For diesel or gasoline, it is not very significant compared to natural gas, even lower for coal. So, you should have decomposition of the pyrolysis oil to figure out the difference between HHV and LHV.
Perhaps, this website may be useful http://www.world-petroleum.org/index.php?/Technology/alternative-transport-fuels-courtesy-of-aip.html
It is so important to know HHV and LHV for any hydrocarbon fuel. The importance of HHV and LHV comes from whether we permit to have water liquid in the product of combustion or not. If not, then part of the liberated heat is used to evaporate the liquid, and the rest is considered as a useful heat. The useful heat in this case is the mass of the fuel times LHV. If no harm and we permit the existence of liquid water in the products of combustion, then the whole liberated heat is considered as a useful heat and equal to fuel mass time HHV.
The main difference between these two values is related to the state of the water resulting from the combustion process. If the water leaves the equipment as a liquid, you should consider the HHV; nevertheless, this is not so common to real systems. Commonly, the water embedded in the exhaust gases leaves as a gas. Likewise, you will find that HHV and LHV are employed during the design stage of combustion systems. In some countries, HHV is used while in another LHV is the preferable option. In my opinion, it is better to use the LHV resulting in a more accurate value of the real energy that the fuel will release and the quantity of fuel you will require to supply and energy demand.
The heating value of a fuel is the amount of heat released during the combustion of a specified amount of it. It is a characteristic for each fuel.
HHV (higher heating value) takes into account the latent heat of vaporization of water in the combustion products. HHV assumes all the water component is in liquid state at the end of combustion (in product of combustion).
LHV (Lower heating value) is determined by subtracting the heat of vaporization of the water vapor from the higher heating value. LHV assumes that the latent heat of vaporization of water in the fuel and the reaction products is not recovered. LHV calculations assume that the water component of a combustion process is in vapor state at the end of combustion, as opposed to the HHV which assumes that all of the water in a combustion process is in a liquid state after a combustion process.
HHV of bio-oil derived from hydrothermal treatment of microalgae has been reported as 30.1 MJ kg-1[1] - 39.7 MJ kg-1[2].
1. Yang, C.; Jia, L.S.; Chen, C.P.; Liu, G.F.; Fang, W.P. Bio-oil from hydro-liquefaction of Dunaliella sauna over ni/rehy catalyst. Bioresource Technology 2011, 102, 4580-4584.
2. Demirbas, A. Hydrogen from mosses and algae via pyrolysis and steam gasification. Energy Sources Part A-Recovery Util. Environ. Eff. 2010, 32, 172-179.
I agree with the above answers. In a commercial plant, the water produced escapes with the flue gas and thus the amount of heat generated by a given fuel for steam production, for example, is the LHV.... and so the question becomes, why would one bother with HHV since LHV is more descriptive of the heat that can be generated during combustion. The reason is that the calorific measurement is made in an enclosed bomb in which water produced during combustion is unavoidably condensed, thereby reducing the increase in temperature being measured. Thus measuring the HHV is both simpler, as it doesn't require that the H content be measured, and more accurate, as it only introduces errors from the calorific measurement whereas the LLV carries potential errors in measuring the calorific value as well as errors from sampling and determining the H content.
thank you so much for all the answers. its so helpful and now i know the difference between LHV and HHV and the importance of this value. tq again =)
The quantity known as higher heating value (HHV) (or gross energy or upper heating value or gross calorific value (GCV) or higher calorific value (HCV)) is determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced. Such measurements often use a standard temperature of 15 °C (59 °F). This is the same as the thermodynamic heat of combustion since the enthalpy change for the reaction assumes a common temperature of the compounds before and after combustion, in which case the water produced by combustion is liquid.
The higher heating value takes into account the latent heat of vaporization of water in the combustion products, and is useful in calculating heating values for fuels where condensation of the reaction products is practical (e.g., in a gas-fired boiler used for space heat). In other words, HHV assumes all the water component is in liquid state at the end of combustion (in product of combustion) and that heat below 150 °C (302 °F) can be put to use.
The quantity known as lower heating value (LHV) (net calorific value (NCV) or lower calorific value (LCV)) is determined by subtracting the heat of vaporization of the water vapor from the higher heating value. This treats any H2O formed as a vapor. The energy required to vaporize the water therefore is not released as heat.
LHV calculations assume that the water component of a combustion process is in vapor state at the end of combustion, as opposed to the higher heating value (HHV) (a.k.a. gross calorific value or gross CV) which assumes that all of the water in a combustion process is in a liquid state after a combustion process.
The LHV assumes that the latent heat of vaporization of water in the fuel and the reaction products is not recovered. It is useful in comparing fuels where condensation of the combustion products is impractical, or heat at a temperature below 150 °C (302 °F) cannot be put to use.
Link: https://en.wikipedia.org/wiki/Heat_of_combustion#Higher_heating_value
what is the expected range for calorific value of bio-briquette combustion?
One alternative way to calculate HHV is the Dulong's correlation based on the elemental analysis.
HHV(MJ/kg)=0,3383C+1,422(H-O/8)
There are other correlations that take into account N, S and ashes.
Deal all,
Referring to the HHV @ calorific value, does this analysis significant for the activated carbon material?
Your feedback is truly appreciated. Thank you.
If by significant you mean do HHV and LHV have the same meaning for activated carbon, then yes but the difference between HHV and LHV will be less for AC than for coal or bio-oil because the activated carbon contains less H and so less H2O is formed during combustion. The carbon in the AC forms CO2 during combustion which does not condense following combustion. So, if you have an activated carbon that is all C and no H, then LHV and HHV would be the same.
The higher heating value is also known as the gross calorific value. The higher heating value (HHV) is measured using a bomb calorimeter; and defined as the amount of heat released when fuel is combusted and the products have returned to a temperature of 25°C. The heat of condensation of the water is included in the total measured heat.
To have scrupulous distinction between the two, LHV (net calorific value) is heat volume through combustion process, quantitative elucidation is at 25 °C, and final return will be at 150 °C, with the assumption that unused heat of water vaporization in reaction response would not be recovered. HHV (gross calorific value) is a heat deliver, quantitative elucidation is at 25 °C, when combusted and the products returned to though this time of 25°C, that take into consideration latent heat of vaporization of water in the combustion process. As regards bio heat value released though the value is less than fossil counterparts. Accordingly, emission is lower, hence, to the importance of usage, one can respect the usage of that or not.
There are two kinds of heat of combustion, called higher and lower heating value, depending on how much the products are allowed to cool and whether compounds like H2O are allowed to condense. The values are conventionally measured with a bomb calorimeter. They may also be calculated as the difference between the heat of formation ΔHof of the products and reactants (though this approach is somewhat artificial since most heats of formation are calculated from measured heats of combustion). For a fuel of composition CcHhOoNn, the (higher) heat of combustion is 418 kJ/mol (c + 0.3 h – 0.5 o) usually to a good approximation (±3%),[1] though it can be drastically wrong if o + n > c (for instance in the case of nitroglycerine (C3H5N3O9) this formula would predict a heat of combustion of 0). The value corresponds to an exothermic reaction (a negative change in enthalpy) because the double bond in molecular oxygen is much weaker than other double bonds or pairs of single bonds, particularly those in the combustion products carbon dioxide and water; conversion of the weak bonds in oxygen to the stronger bonds in carbon dioxide and water releases energy as heat.
By convention, the heat of combustion is defined to be the heat released for the complete combustion of a compound in its standard state to form stable products in their standard states: hydrogen is converted to water (in its liquid state), carbon is converted to carbon dioxide gas, and nitrogen is converted to nitrogen gas. That is, the heat of combustion, ΔH°comb, is the heat of reaction of the following process:
CxHyNzOn (std.) + O2 (g, xs.) → xCO2 (g) + (y/2)H2O (l) + (z/2)N2 (g)
When the products of combustion are cooled to 25o C, all the water vapour resulting from the combustion process is condensed. This heating value is called Higher calorific value or gross calorific value. If the heat released when water vapour in the products of combustion is not condensed and remains in vapour form, this is called lower calorific value or net calorific value. Calorific value has other names as heating value or heat of combustion. Hence, heating value (calorific value) has units as kJ/kg.
the difference lies in the fact of how is water considered (in the flue gases): vapors or liquid.
the difference between the two values is the latent heat value of water.
The method of experimental makes the difference.
Dear,
The lower heating value (LHV) might be conveniently calculated relating HHV and LHV, the standard heat of vaporization of water and the water content in the products of complete combustion.
Regards,
EMELO
only fuels with hydrogens content have differences between LHV and HHV. if the water procuces by hydrogens combustion is steam then the heating values is lower (LHV) but if the water is condensated then the heating value is higher(HHV).there are combustion system which permit use the latent heat of condensation of the water.
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