部分气化煤焦燃烧动力学的活化能分布模型研究

运用两段DAEM模型分析了部分气化煤焦的燃烧动力学．结果表明，两段DAEM模型能准确地描述部分气化煤焦的燃烧行为这是因为部分气化煤焦随着气化率的增加，其燃烧曲线的二次峰越来越显著，而两段DAEM模型正好从理论上考虑了部分气化煤焦燃烧曲线的二次峰特性．同时由两段DAEM模型计算结果发现，随着3种煤焦气化率的增加，其活化能与指前因子增加，代表易反应物质量m的减小，这说明了实验与理论结果一致，随着气化反应的进行，难反应物质的比例增加．     

生物质气化低热值燃气窑炉燃烧温度特性

通过生物质气化低热值燃气在工业窑炉上燃烧的中试试验研究,得到不同燃烧条件下生物质燃气的窑炉燃烧温度特性。试验结果表明:常温空气助燃情况下,经低温净化的冷燃气的窑炉燃烧温度约1100℃,经高温净化的热燃气的窑炉燃烧温度约1200℃;如果回收燃烧烟气的余热,将助燃空气预热至400℃时,燃气窑炉燃烧温度可提高100~150℃。生物质气化低热值燃气基本能达到工业窑炉生产对温度的要求。     

两段粉煤气化在热电联供技术上应用探讨

两段粉煤循环流化床气化燃烧技术是石油大学吸收国内外先进煤气化技术开发的,将产生的煤气经过处理,作为燃气发电机组燃料发电,进行热电联供,提高能源的利用效率,降低燃油费用,实现清洁生产.本文以一台煤气发动机为例,进行热电联供以及余热计算.     

两段粉煤气化在热电联供技术上应用探讨

两段粉煤循环流化床气化燃烧技术是石油大学吸收国内外先进煤气化技术开发的，将产生的煤气经过处理，作为燃气发电机组燃料发电，进行热电联供，提高能源的利用效率，降低燃油费用，实现清洁生产。本文以一台煤气发动机为例，进行热电联供以及余热计算。     

流化床气化炉稀相段反应模拟(1)——模型建立

本研究根据流化床稀相段内的气固流动特点，采用随机理论描述稀相段内单颗粒运动，并具体使用Ｍｏｎｔｅ－Ｃａｒｌｏ方法建立了相应的数学模型；在此基础上，结合有关的气化反应动力学方程建立了流化床气化炉稀相段气化反应的数学模型。同时使用中试实验数据与模拟结果进行了比较，结果表明模型能较好地反映稀相段的反应情况。     

飞灰循环流化床悬浮段颗粒的燃烧模型

在流化床锅炉中,悬浮段不仅可以作为传热区段,而且也有燃烧作用。以往的资料中,对于其燃烧的计算比较粗糙,本文考虑到悬浮段具体情况建立了数学模型,进行了数值计算。实验证明,理论计算与实验结果吻合较好。     

基于数值模拟的链条锅炉煤层燃烧分区特性分析

链条锅炉大颗粒煤的层燃过程与煤粉燃烧差异很大,为了对燃煤链条锅炉煤层燃烧特性和机理进行深入分析,本文应用二维稳态层燃模型对链条锅炉燃烧过程进行了模拟计算,并与实验结果进行了比较。对比发现模拟计算值与实验值符合较好,说明模型能准确反映床层的燃烧特性。同时对不同煤种的水分析出线、挥发分析出线、焦炭氧化区、焦炭气化区和灰渣区进行分析对比,发现不同煤种燃烧分区的差异性与煤质特性及燃烧工况等因素有关系。     

专利介绍

专利名称:耦合旋转锥体给料器的两段燃烧系统及燃烧污染控制方法专利申请号: 02157779.X　公开号: 1421639申请人:上海交通大学本发明涉及耦合旋转锥体给料器的两段燃烧系统及燃烧污染控制方法,在单台炉体上实现燃气蒸汽联产和燃烧污染控制,通过锥体的旋转实现煤颗粒的输送给料,并将旋转锥体给料器设置在燃烧床内,通过间壁加热和渗流传热方式对给料器内的煤实现热解干馏或气化。本发明采用两段燃烧方法实现低NOx排放,给料器产生的半焦进入燃烧床燃烧,可燃气体进入燃烧炉可燃气体燃烧段燃烧,同时配合两级脱硫实现低SOx排放,一级脱硫段设置…     

稻壳旋风空气气化器的数值模拟

在计算流体力学软件FLUENT的平台上,以稻壳旋风空气气化器为原形,选择了合理的数学模型,对稻壳旋风气化器的气化过程进行了模拟.模拟再现了反应温度及5种主要气体在气化器中的分布规律,讨论了风量对最终燃气成分的影响.通过对计算结果和试验数据的比较分析,验证了计算结果的正确性,为进一步开展生物质气化方面的研究提供了理论依据.     

喷油冷却活塞传热过程的流固耦合分析

应用ANSYS Fluent软件建立发动机活塞及其冷却结构三维瞬态流-固-热耦合模型,通过燃烧计算得到燃气平均温度与平均传热系数,作为燃烧室壁面热边界;活塞及其冷却结构采用流固耦合计算,使用两相流流体体积(VOF)模型与动网格模拟活塞喷油冷却过程;通过瞬态传热数值仿真,得到活塞振荡油腔流场云图、油气分布云图、冷却油腔传热系数及活塞温度分布,与标定工况下活塞温度测试数据对比分析,研究结果表明:仿真结果与测试数据误差在5%以内,由此说明应用活塞流-固-热耦合仿真方法可以较好模拟柴油机活塞及其冷却结构瞬态传热。     

A comprehensive mathematical model of a serial composite process for biomass and coal Co-gasification

A comprehensive mathematical model to simulate a serial composite process for biomass and coal co-gasification has been built. The process is divided into combustion stage and gasification stage in the same gasifier, it is a new process for the co-gasification of biomass and coal. The model is based on reaction kinetic, hydrodynamics, mass and energy balances, it is a one-dimensional, K-L three-phase, unsteady state model. The model is divided into two sub-models, one is the combustion sub-model, the other is the coal-biomass serial gasification sub-model. Combustion sub-model includes coal pyrolysis, dense phase combustion, and dilute phase combustion model. Gasification sub-model includes biomass pyrolysis, dense phase coal gasification, dense phase biomass gasification, and dilute phase gasification model. The model studies the effects of key parameters on gasification properties, including gasification temperature, S/B, B/C, and predicts the composition of product gas and gas calorific value along the reactor's axis at different time. The model predictions agree well with experimental results and can be used to study and optimize the operation of the process.     

Experimental Study on Coal Multi-generation in Dual Fluidized Beds

An atmospheric test system of dual fluidized beds for coal multi-generation was built.One bubbling fluidized bedis for gasification and a circulating fluidized bed for combustion.The two beds are combined with two valves:one valve to send high temperature ash from combustion bed to the gasification bed and another valve to sendchar and ash from gasification bed to combustion bed.Experiments on Shenhua coal multi-generation were madeat temperatures from 1112 K to 1191 K in the dual fluidized beds.The temperatures of the combustor are stableand the char combustion efficiency is about 98%.Increasing air/coal ratio to the fluidized bed leads to theincrease of temperature and gasification efficiency.The maximum gasification efficiency is 36.7% and thecalorific value of fuel gas is 10.7 MJ/Nm3.The tar yield in this work is 1.5%,much lower than that of pyrolysis.Carbon conversion efficiency to fuel gas and flue gas is about 90%.     

Numerical Simulation of Pressure Effects on the Gasification of Australian and Indian Coals in a Tubular Gasifier

This article presents a numerical study on the effect of pressure on the gasification performance of an entrained flow tubular gasifier for Australian and Indian coals. Gasification using a substoichiometric amount of air, with or without steam addition, is considered. The model takes into account phenomena such as devolatilization, combustion of volatiles, char combustion, and gasification. Continuous-phase conservation equations are solved in an Eulerian frame and those of the particle phase are solved in a Lagrangian frame, with coupling between the two phases carried out through interactive source terms. The numerical results obtained show that the gasification performance increases for both types of coal when the pressure is increased. Locations of devolatilization, combustion, and gasification zones inside the gasifier are analyzed using the temperature plots, devolatilization plots, and mass depletion histories of coal particles. With increase in pressure, the temperature inside the gasifier increases and also the position of maximum temperature shifts upstream. For the high-ash Indian coal, the combustion of volatiles and char and the gasification process are relatively slower than those for the low-ash Australian coal. The mole fractions of CO and H₂ are found to increase with increase in pressure, in all the cases considered. Further, the effects of pressure on overall gasification performance parameters such as carbon conversion, product gas heating value, and cold gas efficiency are also discussed for both types of coals.     

Laboratory studies on cavity growth and product gas composition in the context of underground coal gasification

Systematic laboratory scale experiments on coal blocks can provide significant insight into the underground coal gasification (UCG) process. Our earlier work has demonstrated the various features of the early UCG cavity shape and rate of growth through lab-scale experiments on coal combustion, wherein the feed gas is oxygen. In this paper, we study the feasibility of in situ gasification of coal in a similar laboratory scale reactor set-up, under conditions relevant for field practice of UCG, using an oxygen-steam mixture as the feed gas. By performing the gasification reaction in a cyclic manner, we have been able to obtain a product gas with hydrogen concentrations as high as 39% and a calorific value of 178 kJ/mol. The effect of various operating parameters such as feed temperature, feed steam to oxygen ratio, initial combustion time and so on, on the product gas composition is studied and the optimum operating conditions in order to achieve desired conversion to syngas, are determined. We also study the effect of various design and operating parameters on the evolution of the gasification cavity. Empirical correlations are proposed for the change in cavity volume and its dimensions in various directions. The results of the previous study on the combustion cavity evolution are compared with this gasification study.     

Clean combustion of solid fuels

A chemical-looping process is proposed for the clean combustion of solid fuels for electric power or heat generation. The process is based on coal gasification with CO₂ to produce CO. The CO then reduces CaSO₄, which is used as an oxygen carrier, in a separate reactor to give CaS and CO₂. A portion of the CO₂ is recycled for the gasification stage and the rest can be sent for sequestration. The CaS is sent to another reactor for oxidation with air and to generate heat or power. The overall thermal effect is the same as direct combustion, but separation of CO₂ and other pollutants, such as sulphur, is achieved. In comparison with conventional chemical-looping combustion of natural gas, much less water is present in the CO₂ product, and hence the loss of heat energy and corrosion of the fuel–reactor system can be reduced.     

Enhancement of hydrogen production in a modified moving bed downdraft gasifier – A thermodynamic study by including tar

A new approach on thermodynamic simulation of the gasification process is conducted by considering the formation of tar using Aspen Plus. The present model shows higher accuracy as compared to the conventional model in term of the composition of producer gas. The tar from pyrolysis process is successfully reduced with high reaction temperature in the combustion zone. A parametric study is performed by varying the split ratio of gasifying agents (steam/oxygen) through three different zones: (i) combustion zone, (ii) counter-current reduction zone, and/or (iii) co-current reduction zone. Introduction of the gasifying agents through the counter-current reduction zone has positive effects on the gasification performances in term of hydrogen concentration, cold gas efficiency, and gasification system efficiency. The effects of O₂ equivalence ratio and steam to carbon ratio (S/C) on the performance of gasification are also investigated. The gasification with oxygen provided the highest cold gas efficiency. A remarkable hydrogen production is achieved from gasification with both oxygen and steam.     

Experimental simulate on hydrogen production of different coals in underground coal gasification

Research on hydrogen production from coal gasification is mainly focused on the formation of CO and H₂ from coal and water vapor in high-temperature environments. However, in the process of underground coal gasification, the water gas shift reaction of low-temperature steam will absorb a lot of heat, which makes it difficult to maintain the combustion of coal seams in the process of underground coal gasification. In order to obtain high-quality hydrogen, a pure oxygen-steam gasification process is used to improve the gasification efficiency. And as the gasification surface continues to recede, the drying, pyrolysis, gasification and combustion reactions of underground coal seams gradually occur. Direct coal gasification can't truly reflect the process of underground coal gasification. In order to simulate the hydrogen production laws of different coal types in the underground gasification process realistically, a two-step gasification process (pyrolysis of coal followed by gasification of the char) was proposed to process coal to produce hydrogen-rich gas. First, the effects of temperature and coal rank on product distribution were studied in the pyrolysis process. Then, the coal char at the final pyrolysis temperature of 900 °C was gasified with pure oxygen-steam. The results showed that, the hydrogen production of the three coal chars increased with the increase of temperature during the pyrolysis process, the hydrogen release from Inner Mongolia lignite and Xinjiang long flame coal have the same trend, and the bimodality is obvious. The hydrogen release in the first stage mainly comes from the dehydrogenation of the fat side chain, and the hydrogen release in the second stage mainly comes from the polycondensation reaction in the later stage of pyrolysis, and the pyrolysis process of coal contributes 15.81%–43.33% of hydrogen, as the coal rank increases, the hydrogen production rate gradually decreases. In the gasification process, the release of hydrogen mainly comes from the water gas shift reaction, the hydrogen output is mainly affected by the quality and carbon content of coal char. With the increase of coal rank, the hydrogen output gradually increases, mainly due to the increasing of coal coke yield and carbon content, The gasification process of coal char contributes 56.67–84.19% of hydrogen, in contrast, coal char gasification provides more hydrogen. The total effective gas output of the three coal chars is 0.53–0.81 m³/kg, the hydrogen output is 0.3–0.43 m³/kg, and the percentage of hydrogen is 53.08–56.60%. This study shows that two-step gasification under the condition of pure oxygen-steam gasification agent is an efficient energy process for hydrogen production from underground coal gasification.     

An experimental study on air gasification of biomass micron fuel (BMF) in a cyclone gasifier

Biomass micron fuel (BMF) produced from feedstock (energy crops, agricultural wastes, forestry residues and so on) through an efficient crushing process is a kind of powdery biomass fuel with particle size of less than 250 μm. Based on the properties of BMF, a cyclone gasifier concept has been considered in our laboratory for biomass gasification. The concept combines and integrates partial oxidation, fast pyrolysis, gasification, and tar cracking, as well as a shift reaction, with the purpose of producing a high quality of gas. In this paper, characteristics of BMF air gasification were studied in the gasifier. Without outer heat energy input, the whole process is supplied with energy produced by partial combustion of BMF in the gasifier using a hypostoichiometric amount of air. The effects of equivalence ratio (ER) and biomass particle size on gasification temperature, gas composition, gas yield, low-heating value (LHV), carbon conversion and gasification efficiency were studied. The results showed that higher ER led to higher gasification temperature and contributed to high H₂-content, but too high ER lowered fuel gas content and degraded fuel gas quality. A smaller particle was more favorable for higher gas yield, LHV, carbon conversion and gasification efficiency. And the BMF air gasification in the cyclone gasifier with the energy self-sufficiency is reliable.     

Mechanisms of Thermochemical Biomass Conversion Processes. Part 2: Reactions of Gasification

Abstract

Gasification as a thermochemical process is defined and limited to combustion and pyrolysis. The gasification of biomass is a thermal treatment which results in a high proportion of gaseous products and small quantities of char (solid product) and ash. Biomass gasification technologies have historically been based upon partial oxidation or partial combustion principles, resulting in the production of a hot, dirty, low Btu gas that must be directly ducted into boilers or dryers. In addition to limiting applications and often compounding environmental problems, these technologies are an inefficient source of usable energy. The main objective of the present study is to investigate gasification mechanisms of biomass structural constituents. Complete gasification of biomass involves several sequential and parallel reactions. Most of these reactions are endothermic and must be balanced by partial combustion of gas or an external heat source.