From cellulose to tar: Analysis of tar formation pathway with distinguishing the primary and secondary reactions.

Tar problem seriously hinders the development of biomass gasification. The tar formation of biomass is greatly influenced by cellulose. In this work, PY-GC/MS was employed for providing a precise insight into the formation of primary and secondary products, and a tar contribution index was introduced to evaluate the potential of tar formation from different origins. Combined with statistical analysis and corroboration by DFT analysis, key intermediates for tar formation are recognized, and corresponding influence is confirmed. A new framework from cellulose to tar was built. The secondary reaction acts a more important role for tar formation. The aromatic precursors and high-activity small-molecular gases are two key compounds responding to tar formation, and the existence of high-activity small-molecular gases could significantly reduce the energy barrier during tar formation. For furans, the energy barrier can be reduced from 100.2 kcal/mol to 74.2 kcal/mol in the presence of ethylene.

Environmental, economic, and energy analysis of municipal solid waste incineration under anoxic environment in Tibet Plateau.

The first Municipal solid waste incineration (MSWI) plant in Lhasa, Tibet, the plateau region of China, started its operation in 2018. Considering the elevation and extreme climate (low pressure and low oxygen content) in Tibet, noticeable differences may be envisaged compared to MSWI elsewhere. The aim of this study is to evaluate the environmental impacts, economic benefits, and energy efficiency of this MSWI project with three representative MSWI case in plain region using Life cycle assessment (LCA), Cost-benefit analysis (CBA), and energy analysis methods. The result showed that enhancing blast volume and cross-sectional area of the boiler help adapt to the oxygen-deficient environment. GaBi model was employed based on the CML 2001 methodology to perform LCA. LCA shows that the Lhasa MSWI project has lower positive environment impacts than the projects in plain region. More attention is needed for the deficiencies in flue gas emissions of MSWI in the plateau region. CBA shows that the payback period is 11.97 years and the internal rate of return is 8.75%. The energy analysis indicates that the boiler energy efficiency is up to 81.92%. MSWI subject to minor changes seems suitable to Tibetan plateau, and can be deployed further.

Characterization of municipal solid waste incineration and flue gas emission under anoxic environment in Tibet Plateau.

Waste incineration is a process of full combustion reaction between waste and oxygen at high temperature. It is a new problem whether the special natural environmental conditions of Tibet Plateau, such as low air pressure, low oxygen content, and low temperature, will affect the waste incineration in the plateau area. In this work, the influence of different parameters on MSW incineration efficiency and flue gas emission were investigated. The results showed that the temperatures exhibited a significant impact on the flue gas emission. Under the lower temperature, CO was determined to be the main pollutant. With the increase of temperature, NOx became the main pollutant. The optimal temperature range of flue gas emission was between 800 and 900°C. A slight negative pressure in incinerator was benefit for incineration system safety and flue gas emissions. The optimal range was -50 to 0Pa. Lower oxygen content (3-6%) in the incinerator affected the incineration efficiency and flue gas emission. Meanwhile, the high oxygen content had no obvious impact on the flue gas emission, but the cost increased and the service life of the incinerator was affected. The optimal oxygen content in the incinerator was controlled at 6-8%. Furthermore, the air temperatures, pressures, and oxygen content in the natural environment had no significant effect on MSW incineration process. Increasing the air volume would bring about the increase of N2 in the incinerator. This work provides the basic data support for MSW incineration technology in plateau area.