Pouvoir calorifique

Résumé

Le pouvoir calorifique ou chaleur de combustion ( ou heat of combustion) d'une matière combustible est l'opposé de l'enthalpie de réaction de combustion par unité de masse dans les conditions normales de température et de pression, notée ΔH (< 0). C'est l'énergie dégagée sous forme de chaleur par la réaction de combustion par le dioxygène (autrement dit la quantité de chaleur). Le plus souvent, on considère un hydrocarbure réagissant avec le dioxygène de l'air pour donner du dioxyde de carbone, de l'eau et de la chaleur. Elle est exprimée en général en kilojoules par kilogramme (noté kJ/kg ou kJ·kg), mais on rencontre également le pouvoir calorifique molaire (en kilojoules par mole, kJ/mol) ou le pouvoir calorifique volumique (en kilojoules par litre, kJ/L). Pour le gaz naturel, il est exprimé en kilowatts-heures par normo mètre cube (noté kWh/Nm). Définition Selon la norme NF EN ISO 15112, le pouvoir calorifique inférieur (PCI) d'un gaz est : La température de référenc

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Publications associées (27)

Formulation reproducing the ignition delays simulated by a detailed mechanism: Application to n-heptane combustion

This article is part of the project to model the kinetics of high-temperature combustions, occurring behind shock waves and in detonation waves. The "conventional" semi-empirical correlations of ignition delays have been reformulated, by keeping the Arrhenius equation form. It is shown how it polynomial with 3(N) Coefficients (where N is an element of [1, 4] is the number of adjustable kinetic parameters, likely to be simultaneously chosen among the temperature T, the pressure P, the inert fraction X-Ar, and the equivalence ratio Phi) can reproduce the delays predicted by the Curran et al. [H.J. Curran, P. Gaffuri, W.J. Pitz. C.K. Westbrook, Combust. Flame 129 (2002) 253-280] detailed mechanism (565 species and 22538 reactions), over it wide range of conditions (comparable with the validity domain). The deviations between the simulated times and their fits (typically 1%) are definitely lower than the Uncertainties related to the mechanism (at least 25%). In addition. using, this new formalism to evaluate these durations is about 10(6) times faster than simulating them With SENKIN (CHEMKIN III package) and only 10 times slower than using the classical correlations. The adaptation of the traditional method for predicting delays is interesting, for modeling. because those performances are difficult to obtain simultaneously with Other reduction methods (either purely mathematical, chemical, or even mixed). After a physical and mathematical justification of the proposed formalism, some of its potentialities for n-heptane combustion are presented. In particular, the trends of simulated delays and activation energies are shown for T is an element of [1500 K, 1900 K], P is an element of [10 kPa, 1 MPa] X-Ar is an element of [0, 0, 7], and Phi is an element of [0.25, 4.0]. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

2008

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Process design of Synthetic Natural Gas (SNG) production using wood gasification

Alexis Joseph Duret, Claude Friedli, François Maréchal

The process design of a 10 to 20MWth Synthetic Natural Gas (SNG) production process from wood has been performed. Combining process modeling and process integration techniques, this study proceeds via the following stages: • thermodynamic modeling: mass, energy balances and simulation of the wood gasification, the methanation and the purification units; • process integration that identifies the energy saving opportunities and prepares a thermo economic optimization. This work demonstrates that the process can transform wood into pipeline quality methane with a thermal efficiency of 57.9% based on the Lower Heating Value (LHV). The process integration study shows that the heat surplus of the process can be used to almost satisfy the mechanical work required by the process; only 7% of the mechanical needs should come from an external source.

Elsevier2005

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Biomass-to-electricity or -chemical via power-to-x can be potential flexibility means for future electrical grid with high penetration of variable renewable power. However, biomass-to-electricity will not be dispatched frequently and becomes less economically-beneficial due to low annual operating hours. This issue can be addressed by integrating biomass-to-electricity and -chemical via ‘‘reversible’’ solid-oxide cell stacks to form a triple-mode grid-balancing plant, which could flexibly switch among power generation, power storage and power neutral (with chemical production) modes. This paper investigates the optimal designs of such a plantconcept with a multi-time heat and mass integration platform considering different technology combinationsand multiple objective functions to obtain a variety of design alternatives. The results show that increasing plant efficiencies will increase the total cell area needed for a given biomass feed. The efficiency difference among different technology combinations with the same gasifier type is less than 5% points. The efficiency reaches up to 50%–60% for power generation mode, 72%–76% for power storage mode and 47%–55% for power neutral mode. When penalizing the syngas not converted in the stacks, the optimal plant designs interact with the electrical and gas grids in a limited range. Steam turbine network can recover 0.21–0.24 kW electricity per kW dry biomass energy (lower heating value), corresponding to an efficiency enhancement of up to 20%points. The difference in the amounts of heat transferred in different modes challenges the design of a common heat exchange network.

2020

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