Sustainability 2022 , 14 , 4669
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• for a specific zone, the temperature inside the reactor is uniform in all directions (radially and axially) ensuring the isothermal condition; • hydrodynamic characteristics of the reactor are neglected; • all the reactions reach an equilibrium condition; • reaction pathways to form intermediate products are not considered; • ash, sulphur, nitrogen, and halogen present in WP–DIS pellet are considered nonreactive; • char is composed of 100% carbon; • gaseous components show ideal behaviour; • gasification is completed at ambient pressure; • tar formation is neglected as commonly considered in numerical modelling of biomass gasification [24,25,41,45]. Indeed, the present analysis aims at evaluating the CHP generation potentiality of WP–DIS pellets, and this simplifying assumption does not significantly affect the goal; • among the several reactions that occur during biomass gasification, only the six reactions presented in Table 1 with their heat of the reaction [55,56] are considered. Table 1. List of chemical reactions considered for the development of air-gasification of WP–DIS pellets model with their heat of reaction [55,56].
Reaction ID
Reaction Formula C+H 2 O → H 2 +CO C+O 2 → CO 2 C+2H 2 → CH 4 CO+H 2 O → H 2 +CO 2 C 2 H 4 +3O 2 → 2H 2 O+2CO 2 2H 2 +O 2 → 2H 2 O
Reaction Name
Δ (Heat of Reaction), KJ/mol
R1 R2 R3 R4 R5 R6
Water gas
+131.0 − 393.0 − 74.0 − 41.0 − 964.0 − 242.0
Carbon combustion
Methanation Water gas shift
Ethene combustion Hydrogen combustion
Assumptions for the cogeneration model simulation [57]: • cogeneration process is steady-state; • potential and kinetic energy changes throughout the system are neglected; • pressure drops and heat loss from the combustion chamber of the ICE with surround- ings are neglected. 2.2. Gasification Model Calibration During gasification modelling, a unique temperature is set for all the reactions men- tioned in Table 1. Each reaction has a different equilibrium constant that highly depends on the temperature [58]. Therefore, all the gasification reactions do not reach an equilib- rium condition for a specific temperature. Consequently, by using this approach, results predicted in terms of syngas composition and process performances (CCE and CGE) would significantly deviate from the experimental outcomes, reducing the reliability of the model [24]. According to the available literature, the deviation should be lower than ± 20% to claim the developed model represents the experimental process [24,41,56]. This condition can be achieved by restricting the equilibrium position of the individual gasification reactions to a specific temperature. Such a temperature can be identified by calibrating the model through experimental results. Consequently, the equilibrium temperature for each reaction differs from the gasification temperature and is calculated using Equation (1): T Eqlm = T Gasf + Δ T Appr , (1) where, T Eqlm is the equilibrium temperature, T Gasf is the gasification temperature, and Δ T Appr is a specific value of temperature to which the gasification is restricted.
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