1. Direct combustion of biomass for power generation
Biomass direct combustion power generation refers to the direct combustion of biomass raw materials into a specific boiler suitable for biomass combustion, generating steam to drive steam turbines and generators to generate electricity. There are many types of biomass boilers that have been developed and applied, such as wood boilers, bagasse boilers, rice husk boilers, straw boilers, etc. The key technologies for biomass direct combustion power generation include raw material pretreatment, anti-corrosion of biomass boilers, improving the applicability and combustion efficiency of various raw materials for biomass boilers, and steam turbine efficiency.
The biomass combustion methods in biomass direct combustion power generation technology include fixed bed combustion or fluidized bed combustion. Fixed bed combustion requires low pre-treatment requirements for biomass raw materials, and biomass can be put into a grate furnace for combustion after simple treatment or even without treatment. Fluidized bed combustion requires pre crushing large biomass raw materials to a particle size that is easy to fluidize, with higher combustion efficiency and intensity than fixed beds.
In addition, due to the large variety and complex composition of biomass in China, collection and transportation difficulties, and the impact of agricultural production and seasonality on the main agricultural wastes, which cannot ensure the annual supply, unlike coal-fired boilers, which require fuel uniformity, biomass boilers are required to be able to adapt to a variety of biomass raw materials to ensure the stability of fuel supply.
The technology of biomass boilers and small steam turbines in China has been basically mature, but the equipment scale is small, the parameters are low, and the efficiency is lower compared to imported equipment. Biomass direct combustion power generation technology is relatively mature and has high efficiency under large-scale production conditions. This technology is rarely used in China because it requires concentrated biomass resources and a large amount. If biomass is collected or transported on a large scale, it will increase the cost of raw materials. Therefore, this technology is more suitable for waste treatment in modern large farms or large processing plants.
2. Biomass gasification for power generation
Biomass gasification power generation refers to the gasification of biomass in a gasifier to generate combustible gas, which is purified to drive an internal combustion engine or small gas turbine for power generation. Gasifiers have strong adaptability to different types of biomass feedstock. Internal combustion engines are generally modified from diesel or natural gas engines to meet the requirements of low calorific value of biomass gas; The gas turbine requires a small capacity and is suitable for burning biomass gas with high impurities and low calorific value.
Biomass gasification power generation includes two modes: small-scale gasification power generation and medium-sized gasification power generation: small-scale gasification power generation uses a simple gasification internal combustion engine power generation process, with a power generation efficiency of generally 14% - 20%, and a scale of generally less than 3MW. In addition to adopting the gasification internal combustion engine (or gas turbine) power generation process, medium-sized gasification power generation also adds a waste heat recovery and power generation system. The total efficiency of the gasification power generation system can reach 25% - 35%.
In addition, as an advanced biomass gasification power generation technology, large-scale gasification gas turbine combined cycle power generation systems have lower energy consumption and overall efficiency higher than 40% compared to conventional systems. However, key technologies are still immature and are still in the demonstration and research stage.