Carbon neutrality in cement industry requires' disruptive 'fuel technology (Industry Frontier)

Data show that in 2020, China's cement production of 2.38 billion tons, accounting for more than 50% of the global cement production, cement and clinker products production and sales ranked first in the world for many years. At the same time, the cement industry is also a key industry in China's carbon emissions, accounting for more than 13%. Therefore, under the vision of carbon peak and carbon neutrality, how to further reduce pollution and carbon, improve quality and efficiency in the cement industry has become the focus of attention from all walks of life。

Save coal and increase raw fuel

And waste substitution ratio is the focus of emission reduction

Cement production and sales are closely related to national economic and social development, and its market demand is rigid. In the past 20 years, China's cement industry has basically completed the technical structure adjustment, and has made substantial progress in energy conservation and consumption reduction, and the potential and flexibility of further carbon dioxide emission reduction under the existing technical conditions are very limited. Therefore, the cement industry needs to apply "disruptive" technologies to achieve carbon neutrality.

At present, the state has clear requirements for enterprises that purchase emission rights through the carbon trading market to fulfill their emission reduction responsibilities, and their proportion cannot exceed 5% of emissions. Therefore, for cement enterprises, either control and reduce carbon emissions from the source, or reduce production capacity, in order to meet the requirements of carbon neutrality. At present, the cement industry to control carbon emissions from the source, in addition to large-scale large-scale use of disruptive technologies such as bioenergy, there is no other mature and feasible technical path.

Cement industry carbon emissions mainly from clinker production, a ton of clinker emissions about 0.85-0.90 tons of carbon dioxide, the main raw fuel is limestone, sandstone, aluminum and iron raw materials and coal. About 50-65% of the CO2 in clinker production comes from the decomposition of limestone, a non-renewable resource, and about 35% comes from coal burning. For a long period of time in the future, it is expected that there is no economically feasible raw material that can replace limestone in a large scale and a large proportion. Therefore, the focus of the cement industry from the source control, carbon reduction is to save coal and improve the replacement ratio of raw fuel and waste. Practice has proved that it is feasible to replace coal burning with renewable bioenergy.

For example, in the 2000 t/d cement production line and 3000 t/d cement production line implemented by a large European cement group in Africa, biofuels enter the decomposition furnace to replace part of the coal, and the replacement rate is about 20%; Conch Zongyang Cement Factory, a leading enterprise in China's cement industry, uses crop straw to achieve partial coal replacement in the decomposer, processing 200 tons of straw waste per day, and theoretically achieving 20% biofuel to replace coal. However, due to the imperfect operation mechanism and the lack of biofuel engineering technology and other problems, the supply of biofuels is not available, and the actual operation replacement rate of the above projects is only about 10%.

Biogas in rotary kilns

Firing temperature of 1700℃ is the key

At present, the biogas obtained from the gasification of conch waste, the direct combustion technology of biofuels in Europe and China, due to the insufficient combustion temperature, the material balance of the cement production line and the imperfect professional operation of bioenergy, biofuels only try to replace some fossil energy in the decomposition furnace (about 900 ° C), and there is no precedent for cement rotary kiln bioenergy to replace coal in the world.

Therefore, the use of high temperature biogas (above 400℃, through industrial pyrolysis production) in cement rotary kiln combustion (up to 1700℃), the technical problems to be solved are mainly concentrated in the rotary kiln firing temperature and cement production line material balance, etc., which requires cement enterprises and technical institutions and biogas enterprises to work together to solve the following technical and operational problems:

In the technical scheme, the use of high temperature biogas should be considered, and the heat recovered from cement clinker should be used to preheat the air used for combustion in the kiln head, and the secondary air combustion air at 900 ° C should be used to increase the firing temperature of the rotary kiln to about 1700 ° C.

The comprehensive replacement of coal involves the material balance of cement production lines such as cement decomposition furnaces and rotary kilns, and the redesign of material balance and the redesign of cement production temperature field (belt), bio-gas and combustion smoke and material flow, as well as the redesign of gas-solid liquid phase reaction and mass and heat transfer, process equipment, etc.