Overview of advances in emission control technologies for nitric oxides from biomass boilers

Currently, fossil fuels such as oil, coal, and natural gas are the world's primary energy sources. However, it is anticipated that these energy sources will be depleted in less than 100 years. As such, the development of new energy technologies is urgently needed. Biomass is one of the earliest sources of energy, and is used especially in rural areas where it is often the only one that is accessible and affordable. With the depletion of fossil fuels and increasing environmental degradation, biomass energy is attracting increasing attention around the world. Compared with fossil fuel, biomass is carbon neutral and sustainable, and has a smaller greenhouse gas footprint and lower SO₂ emission levels. In addition, biomass energy remains the only renewable green energy that can be stored and transported. A number of countries have developed mature and proven combustion technologies, but these technologies are mainly based on wood biomass fuels. Unlike these developed countries, China is a large agricultural country with a limited amount of available firewood. As such, foreign experience cannot be fully applied in China. Although biomass fuels typically have relatively low fuel-N contents, this fuel-N between 70%-100% mass fraction is converted to NO_x during combustion. In addition, the combustion of straw and other biomass fuels emits more NO_x than wood fuels. In recent years, the air quality in China has become a serious public health concern, and NO_x is a widespread atmospheric pollutant with significant impacts on human health and the economy. In this paper, an overview of biomass combustion technologies and NO_x control systems in China and around the world was presented, and their advantages and disadvantages were summarized. The main bottleneck was identified in NO_x control technologies with respect to biomass boilers in China and the development of new technologies in this field was predicted.