| In this paper, pyrolysis performance of a weakly reductive Shendong (SD) coal was investigated by using thermogravimetric analyzer (TG), thermogravimetric analyzer - mass spectrometer (TG-MS), a fixed bed reactor and a semi-continuous apparatus with sub- and supercritical solvent. The characteristic of residues from coal extraction with sub- and supercritical solvent was also characterized by different methods. Pingshuo (PS) coal, a reductive coal was used as reference coal in comparison with SD coal. Main research works and results are as follows:Kinetic characteristics of two coals during pyrolysis were investigated by TG. The results showed that the pyrolysis of SD coal mainly takes place in the temperature range between 365 and 650℃. The temperature corresponding to the maximum weight loss rate appears at about 450℃. In comparison with PS coal, SD coal has a high weight loss and low temperature corresponding to the maximum weight loss rate and another peak of weight loss rate appears at the temperature between 600 and 700℃. with the increase of heating rate, the temperature corresponding to the maximum weight loss rate shifts to high temperature. Activation energy of SD coal and PS coal during pyrolysis at the temperature of 300-650℃are 118-265kJ·mol-1 and 196-280kJ·mol-1, respectively.TG-MS was used to investigate the pyrolysis behaviours of two coals. The results showed that The evolution intensity of H2 and CO2 from SD coal is higher than that from PS coal between 600 and 700℃.It means that weight loss peak of SD coal between 600-700℃is attributed to the second reaction of the pyrolysis product and the mineral matter decomposition. The H2S evolution of PS coal mainly comes from the rupture of sulfur containing bond in coal macromolecule. The SO2 evolution of PS coal attributed to decomposition of pyrite and the evolution of organic sulfur. The H2S and SO2 evolution of SD coal mainly attributed to decomposition of pyrite, and partly come from the evolution of organic sulfur.The effect of end temperature on product distribution of two coals was investigated in a fixed bed reactor under N2 and H2 atmosphere. With the increase of the temperature, the tar yield of SD coal increases, gets a maximum and then decreases with further increase of the temperature under N2 atmosphere. The maximum, 10.5%, appears at about 650. Under H2 atmosphere, the tar yield of SD coal increases with a increasing of the temperature. The maximum, 12.1%, appears at about 700℃. The tar yield of PS coal has a similar trend as that of SD coal pyrolysis under both N2 and H2 atmosphere. The maximum, 17.1 % and 19.8%, respectively, appears at about 650℃, higher than that of SD coal. The gas evolution rule of two coals during pyrolysis and hydropyrolysis shows a similar trend. The total gas volume of SD coal is higher than that of PS coal. The char yield of two coals decreases with an increase of the temperature. At the same final temperature, the char yield of SD coal is higher than that of PS coal.On a semi-continuous apparatus, SD coal and PS coal were non-isothermally extracted with sub- and supercritical solvent to explore the differences between the two coals. The effect of temperature on extract formation rate, conversion and product composition under different pressures was investigated. Water, toluene, and toluene-tetralin (9:1, V/V) were used as solvent. When the solvent is water, the results indicate that the liquid formation rate of two coal samples increases to a maximum at temperature about 400℃and then decreases with further increase of the temperature. With increasing pressure, the liquid yield increase. At a pressure of 30MPa, the liquid yield of SD coal and PS coal is 16.3% daf, 21.3% daf respectively. The conversion and the liquid formation rate also increases and the temperature corresponding to maximum of liquid formation rate moves to higher temperature. In comparison with PS coal, SD coal has high conversion, low liquid yield and low temperature corresponding to the maximum formation rate: The main fraction in liquid product from PS coal is asphaltene, while that from SD coal has relatively higher content of oil fraction. The yield of gas formed during coal extraction increases with the increase of the pressure and the main gas components are CO2, CH4 and H2. In comparison with PS coal, SD coal has a high gas yield. The main product in coal extraction is extraction residue, about 65-75% of coal. SD coal has lower residue yield than PS coal.When the toluene is solvent, the results indicate that the rule of the liquid and gas product with the change of the temperature and pressure is similar with that using water as solvent. The difference is the change intensity and composition. For example, the liquid yield of PS coal is 35.3% daf and that of SD coal is 33.8% daf at the pressure of 30MPa. The main fraction in liquid product from two coals is oil. The liquid formation rate and the maximum liquid formation rate are smaller than that using water as solvent, while the temperature corresponding to the maximum liquid formation rate is higher than that using water as solvent. SD coal has higher gas yield than PS coal, although the main gas components change to CH4 and H2. About 70-80% of coal became the extraction residue. SD coal has higher residue yield than PS coal. When the toluene-tetralin (9:1, V/V) is used as solvent, the results indicate that with increasing pressure, the liquid yield increase. At a pressure of 30MPa, the liquid yield of SD coal and PS coal is 64.0% daf, 68.2% daf respectively. The main fraction in liquid product from two coals is also oil. The liquid formation rate under the low pressure has the similar as that using water and toluene as solvent, while that under the high pressure increases with an increase of the temperature. The main gas components are CH4 and H2, although the content of H2 has a small increment. About 65-75% of coal became the extraction residue. SD coal has lower residue yield than PS coal.The residues, obtained from extraction of SD coal and PS coal with sub- and supercritical solvent were characterized by proximate analysis, ultimate analysis, calorific value analysis, FTIR analysis and combustion experiment. The results indicate that the residues from the extraction of two coals with sub- and supercritical water have higher carbon content, lower hydrogen, oxygen content and higher calorific value than coal samples. In compared with the extraction residues of PS coal (PSER), the extraction residues of SD coal (SDER) has a high calorific value and carbon, hydrogen content and a low volatile matter and ash yield. The results of the FT-IR comparison between raw coal and the extraction residues indicate that the main part of mineral matter is not involved in extraction. The results of combustion indicate that the extraction residues of SD coal are more reactive and can be more easily burned than that from PS coal. The characteristics of the residues using the toluene and toluene-tetralin (9:1, V/V) as solvent have the similar trend, the difference is the change intensity and the actual value.The residues from extraction of two coals with sub- and supercritical water were characterized by XPS analysis and N2 adsorption. The results indicate that the average pore diameter has a decrease after extraction, and the surface area of residue becomes larger with the increase of pressure. The sub- and supercritical water extraction has an activation effect to the samples, although this effect is limited. In compared with PSER, SDER have high surface area and small average pore diameter, which shows the character of mesopore materials. C-C and C-0 are the main form of carbon, oxygen element on the surface of coal samples and extraction residues. Pyridinic nitrogen (N-6) and pyrrolic nitrogen (N-5) are the main form of nitrogen element on the surface of coal samples. Pyridinic nitrogen (N-6) is the main form of nitrogen element on the surface of extraction residues. In comparison with PS coal, SD coal has a high C-C content and a low C-H content. |
PDF Full Text Request