Zhanjun Cheng

Air gasification of biogas-derived digestate in a downdraft fixed bed gasifier

Digestate is a byproduct from biomass anaerobic digestion process. Gasification of dried digestate to produce gasesous product might be a promising route. In this work, air gasification of digestate with high ash content was performed in a downdraft fixed bed gasifier at temperature varying from 600°C to 800°C and air equivalence ratio (ER) ranging from 0.25 to 0.30. The ash melting properties were firstly detected by the Intelligent Ash Melting Point Test, and the by-products (biochar and ash) were analyzed. The results showed that no ash slagging was observed and therefore it is feasible to operate digestate gasification under 800°C and ER ranging from 0.25 to 0.30. High temperature favored gas production, 800°C is proposed for digestate gasification in the present study. ER with a medium value improved gas quality and cold gas efficiency (CGE), and the optimal LHV of 4.78MJ/Nm3 and CGE of 67.01% were obtained with ER of 0.28. High ER favored the increase of gas yield and decrease of tar concentration, and the optimal gas yield of 2.15 Nm3/kg and tar concentration of 1.61g/Nm3 were achieved with ER of 0.30. Improved molar ratio of H2/CO varying from 1.03 to 1.08 was obtained at 800°C, indicating gaseous product has the potential for chemical synthesis processes (1

Environmental, energy, and economic analysis of integrated treatment of municipal solid waste and sewage sludge: A case study in China

Incineration is well used to treat municipal solid wastes (MSW) but is difficult to treat sewage sludge (SS) because it requires a large amount of heat to remove high content of moisture in SS. Over 50u202fbillionu202ftons of SS are discharged annually in China, and the need for a better waste treatment strategy is urgent. This paper is to introduce a waste disposal technology referring to the integrated treatment of MSW and SS. Four scenarios were analyzed including Mono-incineration of MSW (Case 1) and SS (Case 2), co-incineration of SS and MSW by traditional (Case 3) and integrated ways (Case 4), in terms of environment, energy and economic impact by means of LCA, CED and TEA method. From the environmental perspective, the top four mid-point categories involving the largest effect on four cases are N-C (non-carcinogens), OLD (Ozone layer depletion), TET (Terrestrial eco-toxicity), and GWP (Global warming potential). Case 4 has the most positive effect on climate change and resources (-1.44u202fkgu202fCO2u202feq and -18u202fMJ, respectively) according to end-point categories. From the view of energy, Case 4 shows the best performance of energy efficiency, and significantly saves the non-renewable energy (0.21u202ft coal per ton feedstock compared with Case 3). From the economic part, Case 4 is preferentially potential with the best profit, cutting down 79.08% of cost in coal than that in Case 3. These results provide understandings of developing an effective approach for co-treating MSW and SS in the near future.

Catalytic cracking of model compounds of bio-oil over HZSM-5 and the catalyst deactivation

The catalytic cracking upgrading reactions over HZSM-5 of different model compounds of bio-oil have been studied with a self-designed fluid catalytic cracking (FCC) equipment. Typical bio-oil model compounds, such as acetic acid, guaiacol, n-heptane, acetol and ethyl acetate, were chosen to study the products distribution, reaction pathway and deactivation of catalysts. The results showed: C6-C8 aromatic hydrocarbons, C2-C4 olefins, C1-C5 alkanes, CO and CO2 were the main products, and the selectivity of olefins was: ethylene>propylene>butylene. Catalyst characterization methods, such as FI-IR, TG-TPO and Raman, were used to study the deactivation mechanism of catalysts. According to the catalyst characterization results, a catalyst deactivation mechanism was proposed as follows: Firstly, the precursor which consisted of a large number of long chain saturated aliphatic hydrocarbons and a small amount CC of aromatics formed on the catalyst surface. Then the active sites of catalysts had been covered, the coke type changed from thermal coke to catalytic coke and gradually blocked the channels of the molecular sieve, which accelerated the deactivation of catalyst.

Estimation and emissions from crop straw and animal dung in Tibet

Based on the statistics data, this paper estimated the quantity of biomass resource, and then the distribution of emissions from its combu3stion and gasification was analyzed in Tibet in 2015. The main conclusions are as follows: (1) biomass energy is rich in Tibet and its geographical distribution and quantity mainly depends on the relationship between ecological zones and the climate conditions. Crop straw is mainly distributed in Xigazê, Lasha, Qamdo and Shannan with the total quantity of 3.29×106t/year; while animal dung is mainly distributed in Nagqu, Qamdo and Xigazê with the total quantity of 1.69×107t/year. For the acquirable quantity of crop straw and animal dung is 7.27×106t/year, mainly distributed in Nagqu, Qamdo and Xigazê. (2) The energy production potential of crop straw and animal dung in Tibet for combustion (thermal efficiency: 22.5%), HLG (system efficiency: 28.75% based on our investigation) and VLG (system efficiency: 38.75%) is 2.56×1010J/year, 3.28×1010J/year and 4.42×1010J/year, respectively. (3) Compared to the household combustion, the reduction of SO2 is 72% with HLG and 97% with VLG, and the NOx reduction is 79% with HLG, 96% with VLG and 72% with gasification-combustion case.