Carbon neutrality in the cement industry requires "disruptive" fuel technologies

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.

In addition, it is necessary to promote the innovation of traditional production and management mode of cement enterprises to adapt to the industrial technological revolution; Promote and solve a series of problems such as biofuel engineering technology, cement industry value engineering technology, biomass gasification technology upgrading and efficiency improvement, and large-scale industrial application.

Among them, the most important is to achieve the technical breakthrough of high temperature biogas firing temperature at 1700℃ in rotary kiln. Previously, the team of Wu Chuangzhi, director of the Guangzhou Energy Research Institute of the Chinese Academy of Sciences, successfully realized the industrialization breakthrough of the open push steel heating furnace using biological gas burning 1300℃ rolling steel in the steel project of Shenzhen Disen Huamui, and stable operation for 3 years.

CCUS technology is still difficult to be industrialized

Bio-gas technology to reduce carbon burden:

On May 18, the International Energy Agency (IEA) released its annual report proposing a roadmap for carbon-neutral technologies: most of the CO2 reductions in global net zero emissions in 2030 will come from technologies that are actually available today (existing technologies), and nearly half of the reductions in 2050 will come from technologies that are currently in the demonstration or prototype stage (future technologies).

The report makes clear that CCUS technology (carbon capture, utilization and storage technology) can be used to address emissions from existing energy assets, such as cement, which is difficult to reduce carbon. Support the rapid expansion of low-emission hydrogen production and removal of some carbon dioxide from the atmosphere, in areas such as electricity where fossil fuels cannot be easily or economically replaced, and where limited supplies of sustainable bioenergy cannot meet demand, hydrogen and hydrogen-based fuels will fill the gap.

The energy utilization of biomass resources by human beings has experienced three generations of technologies. The traditional fire cooking and heating in rural areas is the first generation of bioenergy technology, and the average energy utilization efficiency is about 13%. Direct combustion of biomass for power generation or heating is the second generation of bioenergy technology, and the energy utilization efficiency is about 30%. Biomass gasification is the third generation of bioenergy technology, and the energy utilization efficiency is about 85%. At present, the biomass direct combustion power generation and heating industry of the second generation of bioenergy technology is gradually withdrawing from the market, and its maturing biofuel market is giving way to the third generation of bioenergy technology - bio-gas technology.

Although the IEA report has clarified that CCUS technology can be used in industries that are difficult to reduce carbon, such as cement, and conch cement has also achieved CCUS technology breakthroughs, it will take time to truly realize industrialization. Therefore, the cement industry cannot rely on the uncertain CCUS technology to achieve carbon neutrality. In the era of wind and light power generation has achieved parity Internet access, about 3 billion tons of limited biomass resources in China should not be used for direct combustion power generation or heating, applied to the development of biomass gasification technology, and priority for cement, steel and other industries that are difficult to achieve carbon neutrality.