Enhancing Cement Industry Sustainability through Biomass Co-Combustion in Precalciners

The cement industry, known for its energy-intensive operations, has long been associated with substantial resource consumption and high pollutant emissions. In particular, the energy demands for clinker production and the resulting NO_x emissions have posed significant environmental challenges. Moreover, as global carbon dioxide (CO₂) concentrations continue to rise, finding alternative fuels, improving combustion efficiency, and reducing pollutant emissions have become critical priorities for the cement industry. A new study conducted by Professor Shangyi Yin from Nanjing Normal University, in collaboration with Dr. Ruidan Gao, Tao Song, and Dr. Ping Lu, published in the Journal Fuel. The study investigated the feasibility and benefits of co-combusting biomass with coal in the precalciner of cement production, shedding light on a promising avenue for enhancing sustainability in this energy-intensive industry.

The cement industry relies heavily on fossil fuels, primarily coal, for clinker production. This reliance accounts for approximately 15% of the total coal consumption in many countries. Additionally, NO_x emissions from the cement industry constitute a notable portion of industrial emissions, posing a significant environmental concern. To address these issues, researchers have explored alternative energy sources, including plant biomass, municipal solid waste, solid recovered fuel, and others. Among these alternatives, biomass stands out as one of the most promising renewable energy sources. China, being an agricultural powerhouse, possesses abundant biomass resources, making it particularly suited for biomass utilization. Recent research indicates that China’s bioenergy potential from residues and energy crops is expected to reach significant levels by 2100. Furthermore, biomass energy offers environmental advantages, such as carbon neutrality, low carbon emissions, and reduced nitrogen and sulfur dioxide emissions. Hence, harnessing China’s vast biomass resources for co-combustion with coal in cement production represents a compelling opportunity to mitigate energy shortages and environmental issues. While previous studies have investigated various aspects of fuel combustion and raw meal decomposition in cement precalciners, there are several critical gaps in the existing literature, for example the existing research on alternative fuels in cement precalciners, especially when considering biomass, remains relatively scarce. Secondly, there is a lack of detailed co-combustion analysis. Although some studies have examined the co-combustion of biomass and coal, they have not provided sufficient detail on the combustion characteristics and their impact on the decomposition of calcium carbonate in the precalciner. Moreover, many studies have focused on volatile nitrogen without adequately addressing nitrogen present in the fuel, leading to oversimplified models of NO_x formation. In light of these research gaps, Professor Shangyi Yin’s study aims to comprehensively investigate the co-combustion of pulverized coal and biomass in TTF precalciners. This research incorporated multiple factors, including fuel composition, heat and mass transfer, combustion characteristics, raw meal decomposition rates, and NO_x emissions, to offer a more holistic understanding of the complex interplay between biomass co-combustion and cement production.

To achieve their research objectives, Professor Yin and associates employed numerical simulation techniques. Specifically, they utilized the Euler-Lagrange method, a widely accepted approach for studying multiphase flow phenomena in engineering problems. This method treats the fluid phase as a continuum and tracks particle movement using Lagrangian equations while solving the Navier-Stokes equation for the gas phase. It also accounts for the coupling between the particle and gas phases through appropriate source terms. The study involved modeling a TTF precalciner with a complex geometric structure, including multiple cylinders, necks, and cones. Various biomass types, such as corn straw, cotton stalks, and wheat straw, were considered alongside pulverized coal. The team carefully characterized the physical properties and chemical composition of both the fuels and the raw meal used in the simulations. Additionally, they established boundary conditions and grid sizes to ensure the accuracy of their numerical calculations.

The authors’ numerical simulations yielded several crucial findings.  First, enhanced Raw Meal Decomposition. The co-combustion of biomass and coal in the precalciner led to the formation of multiple recirculation zones near the raw meal inlets. These zones increased the residence time of particles, improved heat exchange between gas and solid materials, and ultimately enhanced the decomposition rate of raw meal. Secondly, biomass co-combustion resulted in a reduction in the average gas temperature within the precalciner. This temperature reduction is attributed to the lower heating value of biomass compared to coal. However, the temperature profiles remained suitable for cement production. Thirdly, the introduction of biomass as a substitute for coal contributed to reduced NO_x emissions in the precalciner. NO_x concentrations at the precalciner outlet fell significantly below regulatory limits, showcasing the potential of biomass co-combustion for environmental benefit. The researchers compared the performance of different biomass types (corn straw, cotton stalks, and wheat straw) in the precalciner. It revealed that the choice of biomass had minimal influence on temperature distribution, raw meal decomposition, and NO_x concentration, emphasizing the representativeness of using corn straw for these investigations.

It is noteworthy to mention that the authors has several important recommendations and strategies can lead to improved environmental performance and reduced reliance on fossil fuels. Continued Research: Further research is needed to explore different biomass types and their specific impacts on precalciner performance. This will help refine strategies for optimizing biomass co-combustion in cement production. They recommended for the cement manufacturers to consider implementing biomass co-combustion in their precalciner processes as a means of reducing environmental impact and increasing sustainability. Moreover, governments and environmental agencies should recognize the potential of biomass co-combustion as a sustainable solution for the cement industry and align regulations accordingly. Furthermore, academic institutions, industry associations, and research organizations should disseminate the knowledge and findings from this study to encourage wider adoption of biomass co-combustion practices.

In conclusion, the study led by Professor Shangyi Yin and colleagues provided important information into the feasibility and benefits of co-combusting biomass with coal in cement precalciners. The study successfully addressed critical gaps in the existing literature and offers a comprehensive understanding of the complex interactions between biomass co-combustion and cement production processes. The findings highlighted the potential for significant environmental and sustainability improvements within the cement industry through the adoption of biomass co-combustion strategies. As the global community strives to address climate change and reduce carbon emissions, such innovative approaches hold great promise for a more sustainable future in energy-intensive sectors like cement production.