Biomass direct combustion power generation emissions are not "pure and clean"



Biomass power generation 'not so clean'

China is a big agricultural country, straw, bagasse and other agricultural and forestry waste power generation can effectively solve the problem of straw open burning, promote the comprehensive utilization of biomass, and help to achieve carbon peak and carbon neutrality. The implementation of the Renewable Energy Law has promoted the rapid development of the biomass direct combustion power generation industry in the central and eastern regions. In recent years, the structure of China's thermal power plants has changed greatly, and the installed capacity and power generation of renewable energy plants such as biomass have increased significantly, accounting for an increasing proportion.

"Most of the previous studies on thermal power plant emission inventories focused on coal-fired power plants. The rapid development of biomass power plant emissions in recent years and their possible environmental impacts have not received enough attention." Tian Hezhong said.

In 2013, China issued the "Announcement on the implementation of Special Emission Limits for Air Pollutants", which stipulates that since July 1, 2014, coal-fired units in the thermal power industry shall implement special emission limits for smoke and dust (ultra-low emission). Since then, coal-fired power plants have installed or upgraded pollution control equipment, which has significantly reduced the emissions of harmful air pollutants.

"The introduction of ultra-low emission limits for coal-fired power plants has helped China build the world's largest clean coal power generation system." "Previously cleaner biomass power generation has become relatively 'not so clean', with some emissions even exceeding ultra-low emission coal power generation," Tian Hezhong told the Chinese Journal of Science.

Particulate emission outburst

Based on the distribution and development trend of biomass power plants in China, the researchers established refined activity level data sets, combined with relevant testing and online monitoring results, and constructed localized emission factors. The emission trends, regional distribution characteristics and future development scenarios of conventional and unconventional air pollutants (heavy metals, etc.) from biomass power plants in China were evaluated and analyzed in detail.

"Because most biomass power plants have not implemented ultra-low emission transformation, the average emission performance of inhalable particulate matter, sulfur dioxide and nitrogen oxide among the pollutants emitted by biomass power plants in 2017 was about 0.103g/kWh, 0.357g/kWh and 0.742g/kWh, respectively. It is several times higher than the ultra-low emission retrofitted coal-fired power plants (approximately 0.028g/kWh, 0.165g/kWh and 0.239g/kWh, respectively), where particulate emissions are relatively more prominent." "In addition, due to soil pollution in some areas, the content of harmful elements such as arsenic and cadmium in biomass fuels such as crop straw is high, so the pollution of harmful elements emitted by biomass power plants burning such straw cannot be ignored," Tian said.

At present, the technical equipment, operation and maintenance management level of biomass power plants in China is quite different, and the distribution of harmful air pollutants in different regions of biomass direct combustion power plants is not uniform. The emission problem is mainly concentrated in the eastern, northeastern and central regions where biomass power generation is developing rapidly.

In the past five years, Shandong, Heilongjiang and Anhui have ranked the top three in terms of emissions of harmful air pollutants and installed capacity, the study showed. In terms of the characteristics of biomass fuel distribution, Anhui, Jiangsu, Hunan and other places use straw as the main fuel, affected by the accumulation of heavy metals in the soil in the straw, arsenic, cadmium and other heavy metals emissions are high.

Ultra-low emissions will become an inevitable requirement

The study suggests that the combination of pollution control technologies proven in the past 7 years of ultra-low emission transformation of coal-fired power plants, combined with the actual situation of biomass fuel and power generation boilers, optimize and upgrade the emission control facilities of biomass power plants, and promote the healthy development of biomass power plants in China.

"CFB combustion will dominate biomass direct combustion power generation in the future, and accordingly, furnace pollution control technology will also become a priority choice to reduce flue gas emissions." In the future, the integrated dry flue gas purification technology that simultaneously removes multiple pollutants (particulate matter, sulfur dioxide, nitrogen oxides and heavy metals, etc.) may become the development trend of pollutant emission reduction in biomass power plants." Tian Hezhong said.

With China's proposal to achieve carbon peak before 2030 and carbon neutrality before 2060, biomass power generation is expected to usher in a new round of development boom. "There is still a gap between the current emission levels of biomass power plants and the ultra-low emission limits." "As the goal of future pollution control, ultra-low emissions will become an inevitable requirement for the biomass power generation industry to reduce emissions," Tian Hezhong said.