Simulation Of Coal Gasification Process Research Articles

Investigation of radiation models in entrained-flow coal gasification simulation

Adequate modeling of radiation heat transfer is important in CFD simulation of coal gasification process. In an entrained-flow gasifer, the non-participating effect of coal particles, soot, ashes, and reactive gases could significantly affect the temperature distribution in the gasifier and hence affects the local reaction rate and life expectancy of wall materials. For slagging type gasifiers, radiation further affects the forming process of corrosive slag on the wall which can expedite degradation of the refractory lining in the gasifier. For these reasons, this paper focuses on investigating applications of five different radiation models to coal gasification process, including Discrete Transfer Radiation Model (DTRM), P-1 Radiation Model, Rosseland Radiation Model, Surface-to-Surface (S2S) Radiation Model, and Discrete Ordinates (DO) Radiation Model. The objective is to identify the pros and cons of each model’s applicability to the gasification process and determine which radiation model is most appropriate for simulating the process in entrained-flow gasifiers.The Eulerian–Lagrangian approach is applied to solve the Navier–Stokes equations, nine species transport equations, and seven global reactions consisting of three heterogeneous reactions and four homogeneous reactions. The coal particles are tracked with the Lagrangian method. Six cases are studied—one without the radiation model and the other five with different radiation models. The result reveals that the various radiation models yield uncomfortably large uncertainties in predicting syngas composition, syngas temperature, and wall temperature. The Rosseland model does not yield reasonable and realistic results for gasification process. The DTRM model predicts very high syngas and wall temperatures in the dry coal feed case. In the one-stage coal slurry case, DTRM result is close to the S2S result. The P1 method seems to behave stably and is robust in predicting the syngas temperature and composition; it yields the result most close to the mean, but it seems to underpredict the gasifier’s inner wall temperature.

Water–gas shift modeling in coal gasification in an entrained-flow gasifier – Part 2: Gasification application

Water–gas-shift (WGS) reaction is one of the major reactions in the industrial gasification process. Using an adequate WGS reaction rate is vital to predicting correctly syngas composition in a gasification process. In Part 1, three different WGS reaction rates from Jones, Wade, Sato were modified to match the experimental data of raw syngas undergoing water quench process. It is not clear if these calibrated WGS reaction rates are adequate in a gasification process. Hence, the objective of this study in Part 2 is to apply both the three original published WGS rates and the calibrated rates derived in Part 1 to simulate experiments performed in the Japanese CRIEPI research gasifier. The CFD model incorporates 3-D Navier–Stokes equations and nine species transport equations with seven global gasification reactions (three heterogeneous and four homogeneous,) and a two-step thermal cracking model for volatiles. The Chemical Percolation Devolatilization (CPD) model is used for the devolatilization process. Similar to the result in Part 1 for water quench process, the result in this study further shows that the three originally published rates cannot be directly applied to the simulation of coal gasification process, due to different temperature and pressure range. Even the modified rates obtained from a water quench process in Part 1 also appear faster in the gasification process. The pre-exponential rate constant value (A) of each reaction rate is therefore further slowed down, while the activation energy is kept the same as the original value to match the experimental data. The results show that all three WGS reaction rates can be modified to match the experimental data reasonably well. The exit temperature can be matched within 2% (20K). The mole fractions of CO and H2O can be matched fairly well within 4 percentage points (or 10%); however, the simulated H2 mole fractions are always 7–9 percentage points higher than the experimental data. It needs to be emphasized that the calibrated WGS reaction rates in this study can only be applied in the range of water quench and gasification operating conditions for which they have been validated.

Modelling and simulation of coal gasification process in fluidised bed

A one-dimensional steady state mathematical model and a numerical algorithm have been developed to simulate the coal gasification process in fluidised bed. The model incorporates two phases, the solid and the gas. The gaseous phase participates in the emulsion (with the solid phase) and forms the bubble. The solid phase is composed of carbonaceous material, limestone and/or inert bed material. The model can predict temperature, converted fraction, and particle size distribution for the solid phase. For the gaseous phase, in both emulsion and bubble, it can predict profiles of temperature, gas composition, velocities, and other fluid-dynamic parameters. In the feed zone, a Gaussian distribution for the solid particle size is considered. This distribution changes due to attrition, elutriation, consumption and drag inside the reactor. A system of 29 differential and 10 non-linear equations, derived from the mass, energy and momentum balances for each phase, at any point along the bed height, are solved by the Gear and Adams Method. Experimental data from the Universidad de Antioquia and Universidad Nacional-Medellin have been used to validate the model. Finally, the model can be used to optimise the gasification process by varying several parameters, such as excess of air, particle size distribution, coal type, and geometry of the reactor.