5. Use CHi4Oo7 as the simplified formula for dry, ash-free biomass to solve the

Question

5. Use CHi4Oo7 as the simplified formula for dry, ash-free biomass to solve the following problems a. Calculate the heat of reaction (HR, k]/kmol, 25°C) of the char formation from biomass: CHiAO07C+0.7 H2O (g) Is this reaction endothermic or exothermic? Equivalence ratio (ER) is a concept that is widely used in the study of hydrocarbon fuel combustion. It is also used in gasification equilibrium calculations. What is the definition of ER? What does it imply? Calculate the stoichiometric oxidant mass ratio for biomass oxidation b. CHI4007 + O2 CO2 + 0.7 H2O ()

Explanation / Answer

a.) The the heat released or absorbed (the heat change) q, in joules (J), for the reaction is calculated:

heat change = mass × specific heat capacity × temperature change

q = m × cg × ?T

so

CH1.4O0.7 ---> CO2 + 0.7 H2O ?H= -17.5 MJ/kg

Here, the ?H is negative for the reaction so the reaction releases heat. Hence it is exothermic.

b.) Equivalence ratio - The equivalence ratio is defined as the ratio of the actual fuel/air ratio to the stoichiometric fuel/air ratio. Stoichiometric combustion occurs when all the oxygen is consumed in the reaction, and there is no molecular oxygen(O2) in the products.

If the equivalence ratio is equal to one, the combustion is stoichiometric. If it is < 1, the combustion is lean with excess air, and if it is >1, the combustion is rich with incomplete combustion.

Equivalence ratio is commonly used to indicate quantitatively whether a fuel oxidizer mixture is rich, lean or stoichiometric.

CH1.4O0.7 + O2 ---> CO2 + 0.7 H2O(g) or

CH1.4O0.7 + 1.05 O2 ---> CO2 + 0.7 H2O(g) ?H=-17.5 MJ/kg

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