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Yining Char Characteristics in Pressured Fixed Bed

Author: WangPei
Tutor: LiFan
School: Taiyuan University of Technology
Course: Chemical Engineering and Technology
Keywords: pressured fixed bed pyrolysis furnace Yining coal coal charstructure CO2atmosphere reactivity
CLC: TQ546
Type: Master's thesis
Year: 2013
Downloads: 50
Quote: 0
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Abstract


To improve the situation of short natural gas supply in China, the SNG technology has developed rapidly. Because of the higher CH4content in the gas, the pressurized dry bottom fixed bed (PDFB) has supplied the most competitive technology in various kinds of gasifier. However,, this kind of gasifier has a higher ratio of steam to carbon, controlling gasifier temperature lower than the coal ash fusion temperature, which would cause a large amounts of waste water to generate. Meanwhile, there is lots of CO2in the crude gas. In this case, CO2can be used partly in place of steam as gasification agent, with the results that as following:(1) A large amounts of steam can be saved and CO2used;(2) Enables the adjustment of the H2/CO ratio of the crude gas produced as required by downstream processes. As a typical coal used in this gasifier, studying on Yining coal char characteristics is scarce, so it is necessary to investigate the char structure in the PDFB conditions.Yining lump sized coal sample (5～7mm) is used in this study and three char samples are prepared under pyrolysis temperatures of900℃,1000℃and1100℃respectively in a self-made pressurized tube furnace. The structure of the char samples was characterized and the char gasification reactivity was investigated in mixtures of CO2and H2O. And pyrolysis tests were conducted at pressures of0.1,0.5,1.0,1.5MPa in pure Ar and CO2atmosphere respectively from room temperature to700℃at a constant heating rate of10℃/min to prepare eight different chars. The structure of char samples prepared in Ar and CO2atmosphere under different pressures were characterized by FT-IR, XRD, SEM and nitrogen adsorption instrument. The main results are as following:(1)When the pyrolysis temperature increases from900℃to1100℃in pressurized pyrolysis tube furnace, the-CH3disappear gradually, the crystallite size of char become larger and the-OH on char surface decreases. The surface structure of chars changes from loose and porous to compact and regular. The secondary reactions was enhanced and more deposited carbon was generated, which lead to the decrease of char reactivity with the increasing pyrolysis temperature.(2) The effects of CO2co-feed with steam as gasification agents on the gasification reactivity of Yining char prepared between900～1100℃can be divided into two kinds. On one hand, the overall reaction rate of char with steam/CO2mixture was lower than that of pure steam gasification rate because the reaction rate of char-CO2is lower than that of char-steam. On the other hand, CO2can promote the char-steam reaction and the promotion effect is more evident in a relative lower pyrolysis temperature.(3) When the pyrolysis temperature is700℃, the chars prepared in CO2atmosphere have more amounts of functional groups, Hydrogen and higher H/C mass ratio comparing with that prepared in Ar atmosphere. When the pressure is higher than1.0MPa, the O/C mass ratio of chars prepared in CO2atmosphere is lower than that prepared in Ar atmosphere. The reason is that the pyrolysis process of Yining coal in CO2atmosphere releases more CO than that in Ar atmosphere over the pressure of1.0Mpa.(4) When the pyrolysis temperature is700℃, with the increase of pressure, the aromaticity of chars prepared in Ar or CO2atmosphere increases, and the aromatic layer distance of the chars decrease, but the stack height of the chars increase first and then decrease, while the crystallite size of the chars decrease first and then increase. The chars prepared in Ar atmosphere have higher aromaticity and shorter aromatic layer distance than that prepared in CO2atmosphere.(5) When the pyrolysis temperature is700℃, the specific surface area and pore volume of chars prepared in CO2atmosphere decrease with increasing pressure within1.5MPa, but these parameters of chars prepared in Ar atmosphere decrease first and then increase when the pressure is higher than0.5MPa. The specific surface area and pore volume of chars prepared in CO2atmosphere are higher than that prepared in Ar atmosphere.

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