Research On Catalytic Mechanism Of Coal Black Liquor Slurry Gasification And Numerical Simulation Of Entrained Flow Coal Gasifier

Coal water slurry(CWS) gasification technology is a new clean coal utilization. The coal black liquor slurry (CBLS) gasification is part of pressurized entrained bed technology,which also develope based on the technology of CWS gasification. CBLS is made up of coal and black pulping liquor, which has plenty of sodium compounds,lignin and cellulose. The sodium compound has catalytic effect in the process of coal black liquor slurry gasification,while lignin and cellulose enhances heat value.In this paper,some research works were performed to study the catalytic mechanism of sodium compounds in black liquor during the gasification of CBLS. A mathematical model was established to predict the characteristic of fluid flow of pulverized coal gasifier; A nozzle-heat-transfer model and slag model have been established based on the temperature distribution in hot condition in gasifier.The pyrolysis gas of CBLS and Xinwen coal were analysed by Gas chromatography. The gaseous products were mainly consisted of CO, CO₂, H₂ and CH4, while the concentration of CO₂ in CBLS was higher than that of Xinwen coal. These results indicated that the CO₂ can be easily separated out from oxygen-containing groups in coal(like carbosylic acid groups) in the effect of sodium compounds in CBLS. The gaseous products of CBLS mostly released in 400-500℃,which intensified the combustion capability of CBLS.The gasification reaction of CBLS was studied on the thermobalance,which indicated that the carbon conversion of CBLS was determined by the reaction temperature .When the reaction temperature was 1200℃in gasification,the carbon conversion was the highest than other temperatures. The activation energy of CBLS and CWS in gasification were 181.12KJ/mol and 206.71KJ/mol.With the increase of the gasification pressure,the activation energy of CBLS would decrease to some extent .This results showed that the characteristic of gasification of CBLS in higher pressure was better than lower pressure.The research on fixed bed reaction equipment showed that inner diffusion had effect on the gasification process of CBLS. When the particle size of CBLS decrease to around 0.075mm,the effect of inner diffusion would be eliminated.In order to improve the output of hydrogen ,CaO was used in the gasification of CBLS. While the propotion of CaO was 5% in the sample of CBLS,the hydrogen output was the most. Due to the catalytic reaction in the CBLS,the hydrogen output was higher than that of CWS.This paper first put forward the method that adding liquid carbon dioxide in the coal water slurry could strengthen the gasification process in the gasifier ,which also increased the coke burnout rate. Mathematical simulation analysis about adding liquid carbon dioxide on both carbon conversion and cold gas efficiency were conducted ,also the effect of the o/c ratio in the coal-water-slurry(CWS) in CWS gasification was considered. The results showed that the concentration of CO and CO₂ increased ,but H₂ reduced with the increase of liquid carbon dioxide concentration;at the same time ,the carbon conversion and cold gas efficiency enhanced sharply,up to the maximum of 98.58 %,76.74% respectively,which were 3.7 %,6.1 % higher than that of before;the temperature of gasifier declined in the beginning , then changed slowly. The C-H₂O-CO₂ gasification reaction of CBLS were performed in fixed bed equipment ,which showed that the availability gasous (CO+H₂) in gasification was up to the maxmum when the CaO propotion was 8%.The C-CO₂ gasification experiments of CBLS char and CWS char were performed by the thermobalance. The XRD analyses of the dry samples of CBLS and CWS indicated that the alkali metal salts in CWS and CBLS existed in the form of NaCl and sodium silicates mainly, and after gasification,they turned into nepheline (Na6K1.2Al7.1Si8.9O32) and microclion (KAlSi₃O₈).The C-H₂O gasification of different CBLS made by different coal were carried out,which indicated that there were different catalytic effect on different coal. While C_daf changed between 72%-82%,the availability gaseous products generated in CBLS gasification were higher. There were more oxygen containing groups existing in lower rank coal,which acted as the active site in CBLS gasification.Lastly,mathematical model was established to predict the characteristic of fluid flow of pulverized coal gasifier in this paper. In this model, Eulerian and Laglange model were performed to analyse the characteristics of granule phase flow and continuous phase flow in cold condition ,and non-premixed combustion model was employed to analyse the hot condition of gasifier. Results showed that the velocity ratio to particle phase and continues phase was 0.828 in cold condition; axial torque made particles spiral ascent,and prolong the residence time. In hot condition, there were some "low temperature area" in the middle of turbulent flame. The maximum concentration gradient of oxygen occured in the flame male cone,where the temperature were higher than other areas. The coal gas distribution calculated by numerical simulation were in accord with design value.A nozzle-heat-transfer model had been established based on the temperature distribution in hot condition in gasifier , which suggested that the temperature in the head area of nozzle decrease by adding whirling cooling water and increasing the roughness of the inside tube wall. At the same time, the lower temperature among the nozzle orifice would redound to prolong the operation life of nozzle. Another slag model indicated that the solid thickness around combustion area was less than those of other areas due to the high temperature. The slag thickness would decrease, when the ratio of O/C, H₂O/C increased, as well as coal supply. These results could give an important guide to experiment, design and operation of the pulverized coal gasification.