In Situ Reforming of the Volatile by Char during Sewage Sludge Pyrolysis

Abstract

In this study, the volatile from sewage sludge (SS) pyrolysis is passed through the hot char from the same source in a fixed bed reactor. The reforming effect of the sewage sludge char (SSC) on the quality and energy distribution of liquid and gas products is studied. In comparison to dolomite, SSC presents a better tar-eliminating effect from 450 to 650 °C. The production of combustible products, including CH4, H2, and CO, is significantly increased by both the catalytic cracking on the SSC surface and the volatile–char reaction. After the reforming effect at the pyrolysis temperature of 650 °C, the gas yield is increased from 17.19 to 34.27 wt % and the fraction of combustible components is increased by 54.28 vol %. The quality of the oil is also upgraded by reforming of SSC, with the escalation of the light components, and nitrogen-containing and oxygenated fractions are greatly reduced. When the pyrolysis temperature is fixed at 650 °C and the reforming temperature is increased from 450 to 650 °C, the liquid yield is decreased from 18.76 to 10.67 wt %. In addition, the combustible fraction in the gaseous product is greatly increased. The calculation of the energy distribution indicates that, via the reforming process, a lot more heating value will concentrate on the gas product and the overall high heat value of the pyrolysis volatile and SSC will be significantly promoted.

Upscaling of Thermo-Catalytic Reforming Process from Lab to Pilot Scale

“…In accordance to previous studies, 18,19,24,25 the yield of gaseous fraction is increased, with higher post reforming temperatures, with the opposite effect on the amount of carbonisate and bio-oil.…”

“…A similar trend is observed by Yu G. et al 19 , in which the catalytic reforming process was carried with sewage sludge carbonisate as a catalyst. The results show that the total condensate (mixture of oil and aqueous phase) yield is reduced from around 20wt.% at 500°C to 10.6wt.% at 650°C by raising the reforming temperature.…”

“…In comparison to Yu G. et al 19 , the valuable gas components H2, CO, and CH4 are increased with reforming process and with temperature, it is around 14%, 2%, and 5.5% at 500°C…”

“…The upgrading can be done by filtration, emulsification, solvent addition, catalytic pyrolysis, hydrogenation processing, or steam catalytic reforming. [15][16][17][18][19] A study on microwave catalytic pyrolysis reports a reduction in the bio-oil yield and an increase in the carbonisate yield by using a commercial zeolite (ZSM-5) catalyst. The catalytic cracking reactions are improved and causing an increase of the conversion rate of volatile components to gas.…”

Thermochemical conversion of sewage sludge: A critical review

“…Sewage sludge char impregnated with activation agents such as KOH and ZnCl2 are promising for reducing NOx, in addition, activated carbon can also be produced. Comparison of char with dolomite and quartz, show that char has more effective reforming efficiency to produce bio-oil with less oxygenated compounds and nitriles, and improved heating value of the product gas [166]. Addition of active metals on sewage sludge char gives enhancement in the catalytic activity for improved results compared with metal oxides and zeolites [167,168].…”