The Utilization Of Sewage Sludge Coupled With Low Rank Coal And Sawdust Based On Pyrolysis

In this paper, a new technical route for the integrated utilization of biomass solid wastes is established based on the properties of inferior resource such as low rank coal, sawdust and sewage sludge and the technology of pyrolysis/ co-pyrolysis. The main contents in this paper are as follows:The char is prepared by pyrolysis of low rank coal and the blended sawdust and low rank coal feedstock. The influencing factors of the yield, the quality parameters and the structure characteristic of the char are investigated by proximate and ultimate analysis, FT-IR, et,al. The results show that the main factor governing the properties of char is the pyrolysis environment(pyrolysis temperature and rentention time). For the same raw material, when the temperature and retention time increased, the yield, the volatile content, the hydrogen content of char showed a decreasing trend, while the ash content, the C/H ration and the degree of aromatization showed a rising trend. The semi-coke prepared from Shaanxi coal under the condition of 600 ? /1.5 h with nitrogen atmosphere was used for sludge conditioning and deep concentration dewatering. The effects of adding amount and size distribution of semi-coke on the promoting effect were investigated by gravity concentrating method. The obtained results indicated that when the particle size of semi-coke was less than 425 ?m and the adding amount was 2.5 g/100 g sludge, the sludge dewatering performance reached the optimum. In the first 20 minutes, the average sedimentation rate of sludge increased from 2.49 mL/min to 3.48 mL/min. When it comes to 30 min, the turbidity, CODCr, SS of the concentrated sludge supernatant were reduced from 836 NTU, 258.2 mg/L, 630.1 mg/L to 14.8 NTU, 38.2 mg/L, 18.6 mg/L, respectively, which met the requirements of the national integrated wastewater discharge Grade II standard. The moisture content of concentrated sludge was reduced from 91.74% to 83.71%. And the calorific value of concentrated sludge was enhanced from 8.041 MJ/kg to 18.295 MJ/kg, which lays the foundation for the utilization of sludge as a source of energy.The TG-DTG analysis indicated that the ignition point, the peak temperature and the activation energy of concentrated sludge conditioned by semi-coke was enhanced from 181.2 ??256.9 ??19.08 kJ/mol of raw sludge to 474.0 ??548.0 ??88.36 kJ/mol, respectively. The flameout accident which may occur during the combustion of sludge can be avoided for the concentrated sludge due to the addition of semi-coke, which can transfer the separated double peaks in the DTG of raw sludge to single peak. The combustion performance of feedstock, which was prepared by blending the concentrated sludge with Zhuzhou bituminous coal at a mass ratio of 1:5, was extremely close to that of Zhuzhou bituminous coal. Therefore, the sludge-coal water slurry with the same combustion performance as coal water slurry can be prepared by blending the appropriate coal with concentrated sludge at a suitable ratio. This research paves a new way for the utilization of sludge as a source of energy.The effect of additive, size distribution and materials on slurry-ability of coal-char, blended sludge/ coal-char feedstock, co-pyrolysis char was investigated by slurry performance experiment. Results show that, the composite additive DCSA, which was independent developed by ourselves, are the best additive for enhance the slurry-ability of char, blended sludge/ coal-char feedstock. In terms of coal-char, when the particle less than 75 ?m increased, the slurry concentration showed a decreasing trend, while the stability and pseudo-plastic behavior showed a rising trend. When the particle less than 75 ?m occupied 75 % of the total char's mass, the char water slurry with good properties can be prepared with DCSA. Meanwhile, the slurry's concentration was up to 70.63 % and it had maintained good stability for 7 days and displayed good fluidity, pseudo-plastic and shear thinning behavior. In terms of blended sludge/ coal-char feedstock, the weight fraction of sludge has significant impact on the slurry-ability of blended sludge/char feedstock. The correlation between the weight fraction of sludge(x) and slurry concentration(?) could be quantitatively described with the linear function as following: ?=69.656-2.5885 x, R2=0.98013. The increase in the weight fraction of sludge would undermine the slurry-ability of the sludge/char feedstock. The shear thinning property of SCWS became more pronounced with increasing weight fraction of sludge. The slurry-ability of sawdust and Yunnan coal were significantly improved via pyrolysis process. Bio-char and semi-coke were prepared under 500 centigrade with a residence time of 1.5 hour. The solid loadings of the resulting slurry fuels derived from sawdust and coal were enhanced from 29.21 % and 54.63 % to 38.57 % and 60.19 %, respectively. Under the same pyrolysis conditions, the slurry-ability of the char prepared from the co-pyrolysis of sawdust and Yunan coal was apparently superior to that of the corresponding bio-char/coal char mixture with the same original mass ratio of feedstock. The prepared char-water slurries generally display pseudo-plastic behavior, i.e., the shear press decreases with increasing shear rate. When the mass ratio of sawdust exceeds 50%, the rheological property of char-water slurry tend to be shear thickening, exhibiting strong dilatant behavior at low shear rate, which is similar to the rheological property of biochar-water slurry. The desirable slurry-ability of the char produced from co-pyrolysis could be attributed to the synergistic effect of biomass and coal, which is likely to improve the aromaticity of the resulting hybrid char.