Tar Reforming Using Recycle Charas Catalyst During Pyrolysis Of Sludge

Municipal sewage sludge is a byproduct of sewage treatment plants.In recent years, the quantity of sewage sludge has increased significantly aggravated the environmental pollution , which is deteriorated along with the development of urban and the increase of population. Meanwhile,with the environmental regulations becoming more stringent, so sludge fanning, landfill and incineration have been limited more and more. As a biomass resource, and rich in organic matter, sludge can be treat through pyrolysis and obtain the production of fuels and valuable chemical products and reduce the secondary pollution. Both tar and biomass char are byproducts of sludge pyrolysis. While the presence of tar is a key issue in the development of sludge pyrolysis gasification, char based catalysts can catalytic removal of tar. Biomass char is rich in porous structure, which is an excellent catalyst and catalyst carrier with low cost,easy to obtain, easy to handle.In this paper, the two-stage fixed bed pyrolysis device was used to explore the effect of biomass char (almond shell char, poplar char, sludge char, Ni+almond shell char, Ni+poplar char, Ni+sludge char, Fe+almond shell char, Fe+poplar char, Fe+sludge char) obtained by pyrolysis of different biomass materials on the catalytic reformation of sludge tar, and reveal the catalytic mechanism of carbon-based catalyst. The research contents are as follows:(1) The sludge were studied by thermogravimetric analysis to study the sludge pyrolysis and combustion process.lt was found that the reaction process of sludge was different in different atmosphere. The sludge first undergoes a pyrolysis reaction and then a combustion reaction takes place in the air atmosphere. The reaction temperature ranged from 170 to 650?.The sludge undergoes pyrolysis reaction in the N2 atmosphere. The reaction temperature ranged from 140 to 560?.The maximum weight loss rate of sludge pyrolysis is greater than the maximum weight loss rate of combustion.The pyrolysis process of sludge is divided into three stages.The rate of heating has little effect on the weight loss of pyrolysis. The pyrolysis of the sludge is a first-order reaction, and the activation energy is between 25.77 and 29.21 kJ mol-1,and increases with the increase of the heating rate.(2) The pyrolysis product distribution of sludge at different temperatures was investigated by single-stage pyrolysis. As the pyrolysis temperature increases, the yield of the solid product decreases, the yield of the pyrolysis gas product increases, and the yield of the pyrolyzed liquid product increases first and then decreases. High temperature can be an advantage for H2 and CO generation. High temperature promotes the transition of pyrolysis solution to more stable, ring number of polycyclic aromatic hydrocarbons. The purpose of the sludge pyrolysis experiment is to produce gas, so the pyrolysis final temperature is set to 800 °C.(3) By comparing the effects of biomass char(almond shell char,poplar char, sludge char, Ni+almond shell char, Ni+poplar char,Ni+sludge char, Fe+almond shell char, Fe+poplar char, Fe+sludge char)on the conversion of tar, gas production and gas composition obtained by pyrolysis of sludge, it was found that the catalytic activity of sludge char was better than that of poplar char and almond shell char, the catalytic activity of Ni+char is higher than that of Fe+char. The content of aliphatic compounds increased, the content of aromatic compounds compounds decreased, and the oxygen content, nitrogen content and sulfur-containing heterocyclic compounds content of tar were decreased after the catalytic reaction of tar over different catalysts.Ni+sludge char catalyst exhibited excellent catalytic activities in 900°C, 5.63s, where the tar conversion rate was 98.46%, the maximum gas yield was 940m3/tone.(4) The structural characteristics of biomass char (almond shell char,poplar char, sludge char, Ni+almond shell char, Ni+poplar char,Ni+sludge char, Fe+almond shell char, Fe+poplar char, Fe+sludge char)were studied by BET, XRD, Raman spectra and TG-FTIR mehods. The sludge char has a mesoporous structure, and the poplar wood and almond shell char have large pore and mesoporous structure. The order of the specific surface area of the three biomass carbon is: sludge char > poplar char> almond shell char. Sludge char has more abundant alkali metal content than the other two biomass char, and the sludge has solidified most of the heavy metal elements. As the specific surface area of the sludge char is larger than that of poplar and almond shell char, the sludge char is easier to load Ni and Fe than the other two biomass char. After Ni(NO3)2 impregnation, Ni0 play a catalytic role. After Fe(NO3)3 impregnation, Fe2O3 play a catalytic role. Ni + sludge shows better catalytic performance than other catalysts due to its advantages of rich metal elements, large specific surface area, and more amorphous carbon structure.