Progress in the application of biomass energy power generation technology at home and abroad

1.5.3 Pollutant discharge problem

At present, China has no specific provisions for the emission of pollutants from pure burning biomass generators, and can only refer to GB 13223-2011 "Air pollutant emission standards for thermal power plants", and NOx and SOx emissions are required to be less than 100 mg/ m3. With the increasingly stringent pollutant emission requirements for coal-fired power plants, the future pollutant emission control of pure burning biomass power plants should also be strictly implemented in accordance with the ultra-low emission standards for coal-fired power plants, with NOx below 50 mg/ m3 and SOx below 35 mg/ m3.

In biomass fuel, the sulfur content is low, and the alkali metal content is high, which has a good self-desulfurization performance. On the basis of optimized design, the original SOx emission of most boilers can meet the requirements of ultra-low emission. For individual biomass fuels with high sulfur content, the method of adding limestone in the furnace can be used to desulphurize, which has low investment and operating cost, and can also easily achieve ultra-low emission of SOx.

Regarding NOx emission, the original generation of NOx can be effectively controlled by strengthening the local reducing atmosphere on the surface of coke particles through the adjustment of the flow pattern in the furnace, adjusting the ratio of primary and secondary air and the setting of secondary air, and increasing the reducing atmosphere space in the furnace. On this basis, the addition of non-selective catalytic reduction (SNCR) method to further reduce nitrogen oxide emissions can achieve ultra-low emissions.

Whether it is desulfurization or nitrogen removal, in order to further achieve the requirements of ultra-low emissions, it is necessary to increase a certain amount of investment and operating costs. The power generation cost of pure biomass power plants has further increased, and the survival difficulty of power plants has increased in the case of inadequate policy subsidies.

2 Biomass mixed combustion technology

2.1 Technical Advantages

Due to the regional nature of biomass energy, it is difficult to expand the scale of pure burning biomass power plants. In addition, considering the high temperature corrosion caused by biomass combustion, the improvement of steam parameters is limited, and the thermal efficiency of pure biomass power plants is low. If the existing boilers, steam turbines and auxiliary systems of coal-fired power plants can be used to replace part of coal as boiler fuel with biomass fuel, the initial investment in pure biomass power generation can be greatly reduced. Relevant studies have shown that processing the same amount of biomass fuel can save about 50.0% of the initial investment. In addition, the parameters of the coal-fired boiler units in operation are high, and the power supply efficiency is generally about 40.0%. Relying on high-efficiency coal power units, the power supply efficiency can be improved by about 10.0% compared with pure burning biomass power plants.

The most prominent advantage of biomass co-firing technology is that when biomass is co-fired with coal, the content of alkali metal and Cl in biomass fuel is diluted by the addition of coal, and a series of problems such as ash and slag deposition in boiler operation can be effectively solved, and the boiler availability rate can reach the level of coal-fired boilers.

Due to the above-mentioned advantages of coal-fired coupled biomass power generation, it is widely used around the world, and the proportion of biomass power generation in some countries is as high as 15.0% to 20.0%.

2.2 Application status of biomass mixed firing abroad

At present, EU countries have taken various measures to reduce CO2 emissions from coal-fired power generation in terms of regulations, policies and technologies, and one of the main technical measures is coal-fired coupled biomass power generation. With specific carbon emission reduction indicators, coupled with the government's policy drive to promote coal-fired coupled biomass power generation, coal-fired coupled biomass power generation in EU countries has been well promoted and applied for more than 30 years, and valuable experience has been gained in policies, regulations and coal and biomass co-burning technology in large coal-fired power plants.

DONG Energy 2× 430.0MW supercritical combustion of a variety of fuels/biomass power plant in Copenhagen, Denmark, through the mixed burning of a variety of fuels and biomass, including a biomass reciprocating furnace boiler dedicated to burning straw, can burn 170,000 t of straw per year, the generated supercritical parameter steam and steam generated by pulverized coal furnace mixed power generation. At the same time, in the supercritical pulverized coal furnace, the mixed burning of waste wood molding particles can consume 160,000 tons of waste wood and 500,000 tons of coal every year.

Japan already has 20 coal-fired power plants planned for biomass cogeneration, with a total installed capacity of about 1 GW. The policy target for biomass power generation in 2030 is 5 GW. In 2017, Japan imported 500,000 t of wood pellets and 1.4 million t of palm kernel shells (PKS). It is estimated that by 2023, Japan's wood pellet imports will exceed 5 million tons.