Research advance on influence factors and technologies of biomass pyrolysis

Abstract: Large quantities of stalk resources are produced in China, and some of the stalks are incinerated, which wastes resources and pollutes the environment. Biomass pyrolysis is attracting a great deal of attention as a way of utilizing biomass waste. In this paper, the recent advances in fundamentals and technologies of biomass pyrolysis were reviewed, focusing on the reaction process, influencing factors and its technology development status in biomass pyrolysis. The major technology advances in biomass technology were summarized and discussed, and it was particularly noted that if the drawbacks on indirectly heated pyrolysis technology are solved well, this indirectly heated pyrolysis technology is a good way to achieve high-value utilization of biomass waste. In addition, combined with the accumulated technologies of our team, an indirectly heated high-efficient rotary kiln was proposed and a 500 kg/h demonstration project was built by integrating the technology of sealed feeding, continuous pyrolysis, and gas/fuel combustion. This process demonstrated good prospects for biomass application, which solved the problems of poor operation stability and low heat exchange efficiency of continuous pyrolysis equipment, thus realizing the high-value utilization of northern corn straw. Furthermore, based on the preceding research, a further study for direct regulation of pyrolysis products was suggested to provide theoretical guidance for the utilization of rural biomass. This paper pointed out the future direction of bio-energy development, which provided a reference for the biomass pyrolysis fundamentals, technology development, and industry application. Pyrolysis for biochar is the critical core technology to achieve high-value utilization of stalks. In this process, the pyrolysis char can be used to produce carbon-based fertilizers and soil additives; the pyrolysis gas is available for cooking and heating in rural area. Aiming at many disadvantages in the existing equipment, including poor equipment stability, low quality of pyrolysis gas and tar, the study of technology equipment of stalk pyrolysis for high-quality biochar and gas was conducted. We proposed a continuous segmented temperature-controlled pyrolysis technique on the basis of gasification reforming through in-situ pyrolysis of pyrolysis gas and coke, high-efficient heat transfer based on cascade energy utilization, uniform feeding by disturbance compaction, multi-wire spiral-plate transport, multi-cavity swirl heat exchange, jacketed sedimentation cyclone for dust removal, gas gasification reforming for decoking, gas purification and upgrading. According to the stalk resources amount, energy demand and economic development level in different regions, we put forward some application modes of stalk pyrolysis at different scales and designed the continuous pyrolysis equipment of internal heating, external heating, and tube-plate mixing heating. At pyrolysis temperature of 500 ℃ and residence time of 30 min, the yield of pyrolysis gas of peanut shell achieved 3 m3/h, and the calorific value of pyrolysis gas was 16.3 MJ/m3; the yields of pyrolysis gas, tar and biochar were 0.32 m3/kg, 1.3% and 31.8% respectively. The dust concentration in tar was 7.9 mg/m3, and the NOX in flue gas emissions was 25.1 mg/m3; the particulate matter concentration was 2.4 mg/m3, and the smoke blackness was lower than Grade 1. This study offers an effective technology path for comprehensive utilization of stalks in China.