Investigation stage devolatilization during thermochemical conversion of low-grade solid fuels

摘要

One of the key characteristics of the combustion process of solid fuels, particularly coal, is volatile substances, which, along with the proportion of fixed carbon, forms reactivity fuel. By reactivity is meant fuels their reactivity in the oxidation process. Most often, the reactivity of the fuel is expressed in the release of volatile, which characterizes the process of ignition and combustion of fuel in the boiler furnace. However, this index is arbitrary and approximate because it ignores several factors influencing the conversion process, such as composition and heat of combustion of the organic portion of the porosity of the particles, the amount and composition of the mineral fraction. Volatile defines mechanical incomplete combustion, ie combustion efficiency. Mechanical underburning is an important characteristic of the boiler and taken into account in their design calculations. For a more precise determination of the reactivity of the fuel along with volatile information used calorific value and volatile source of fuel, the composition of the organic mass, the number and composition of the mineral part. Also use the additional information on the properties of fuels - the ignition temperature, the maximum intensity of the process, information on the kinetics of one stage or another (eg, drying, volatile, burning coke and others). The above figures are reactive properties of the fuel and form its reactivity. Thus, the reactivity of the fuel is the aggregate indicator of the reaction process of determining the properties of the fuel thermochemical conversion. For efficient processing of the fuel, and also for the mathematical modeling is necessary to study all the stages of heterogeneous combustion, including the step of devolatilization various solid fuels. A common way to study the mechanism and kinetics of heterogeneous processes are the methods of physical and chemical analysis, including thermal analysis and surface analysis. The condition for the use of thermal analysis is that sometime after the start of heating there is a quasi-stationary state in which the heating rate of the sample is equal to the rate of heating of the environment that provides the simplest connection between the characteristics of the thermal curves with different physical and kinetic quantities. Surface analysis allows to determine the magnitude of the surface area required for modeling the kinetics of heterophase transformations since the number of adsorption sites defines a "concentration" of one of the reactants -fuels, knowledge of surface areas into account the influence of factors on the surface speed of the process in the kinetic (the most promising) modes of processing fuels. Based on the above, the aim of this work is the kinetic analysis of the stage of release of volatile coal gasification. This will vary about the size of the fuel particles. This analysis will be carried out, using a complex thermal analysis instrument (STA 449 F1, QMS 403 C, Pulse TA). To achieve this goal the following tasks: 1. Determine the probable mechanism of formation of gaseous components on the stage devolatilization. 2. To determine the kinetic coefficients of education of the individual components of the gas phase (CO_2, CH_4, H_2, H_2O, CO, etc.). 3. Determine the surface area of ??the test fuel. The results of thermal analysis and surface analysis be used in thermodynamics and kinetic modeling of the gasifier fluidized bed. This work was carried out at the Melentiev Energy Systems Institute SB RAS and financially supported by the Russian Scientific Found (project number 16-19-10227).