Sewage sludge pyrolysis coupled with self-supplied steam reforming for high quality syngas production and the influence of initial moisture content
2020
Mei, Zhenfei | Chen, Dezhen | Zhang, Jixuan | Yin, Lijie | Huang, Zhen | Xin, Qianfan
A technology of sewage sludge (SS) pyrolysis coupled with self-supplied steam reforming of the volatile is developed to utilize the latent heat of the steam vapor released in the SS drying & pyrolysis process. An integrated reactor consisting of a vertical free-falling pyrolysis section and a horizontal screw-moved reforming section is designed for this purpose. The performance of the reactor shows that by changing the moving speed of the char in the reforming section, high quality syngas with an H₂/CO ratio of 4.37 and a percentage of H₂ + CO up to 66.58 vol% can be obtained at approximately 570–600 °C for the dry SS. There is an optimum moving speed of the screw for producing the highest volume of the syngas. A higher moving speed of the screw also results in a higher concentration of the aromatic compounds in the final pyrolysis oil. When the initial moisture content of SS increases from 0 to 65.50%, the H₂/CO ratio and H₂/CO₂ ratio in the syngas increase from 4.37 to 30.87 and from 2.1 to 2.6 correspondingly, and the final oil yield decreases from 24.03 wt% to 14.16 wt%. Moreover, the total energy recovery efficiency decreases from 88.85% to 61.92%, while the energy portion of syngas shows a peak of 44.18% of the total energy input when the initial moisture content is 41.26%. The integrated reactor also provides a good opportunity for adding a catalyst such as dolomite to make the process more effective. The technology developed in this paper provides an approach to deal with SS with a relatively high moisture content.
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