In recent years, the co-processing of solid waste in cement kilns has become the focus of industry research and application. In 2012, the “Catalogue of Advanced Applicable Technologies for Energy Conservation and Emission Reduction in the Building Materials Industry” will use the precalciner kiln to co-process hazardous waste technology, the precalciner kiln to co-process urban sewage plant sludge technology, and the precalciner kiln to co-process waste incinerator fly ash technology Include it. In December 2014, the Ministry of Industry and Information Technology, the Ministry of Science and Technology, and the Ministry of Environmental Protection jointly issued the “Catalogue of Major Environmental Protection Technologies and Equipment Encouraged by the State (2014 Edition)”, which included cement kiln coordinated harmless disposal equipment as a solid waste treatment equipment promotion project. In 2015, six ministries and commissions including the Ministry of Industry and Information Technology jointly issued a notice on the pilot work of co-processing domestic waste in cement kilns.
Cement kiln co-processing technology has long become the main processing method in Germany, Japan and other countries. As my country is still in the development stage, cement kiln co-processing technology is facing major problems such as high initial investment costs, high operating costs, and low government subsidies. This article intends to discuss three co-processing technologies in cement kiln co-processing solid waste technology, namely cement kiln co-processing municipal solid waste (RDF), cement kiln co-processing municipal solid waste (combined gasifier) and cement kiln co-processing municipal sewage. Mud (drying), based on the 5 000 t/d production line, comprehensively consider the emission reduction and emission reduction cost indicators, analyze the potential and cost of technology energy saving and emission reduction, and give policy recommendations for technological development.
1 Overview of the co-processing of solid waste in cement kilns
1.1 Cement kiln co-processing of municipal solid waste (RDF) technology
Cement kiln co-processing municipal solid waste (RDF) technology, that is, the municipal solid waste is processed into a higher calorific value and more stable refuse-derived fuel (RDF) through pretreatment processes such as screening, crushing, fermentation, drying, and processing. , Combining the combustion characteristics of the cement decomposing furnace, to achieve the technology of resource disposal and utilization. It is suitable for the technical transformation of the co-processing of municipal solid waste in the new dry-process cement production line. It should be noted that the distance between the garbage treatment station or RDF pretreatment station and the cement production enterprise should not be too far; the harmful elements introduced by the garbage will affect the normal production of cement kilns and other issues. F.L.Sth’s “hot plate” technology and Polysius’ pre-combustion chamber technology belong to the scope of RDF co-processing technology. Domestic Huaxin Cement and Sinoma International have developed such related technologies, and process pre-combustion technology and equipment are also in the process of research and development. The commercial operation model of Huaxin cement kiln co-processing is an innovative model that integrates the collection and transfer of domestic waste, the pretreatment of waste and the co-processing of cement kilns. It is estimated that if a 5 000 t/d cement clinker production line uses this technology to process 200-500 tons of domestic waste per day, coal consumption per ton of clinker can be reduced by 3% to 6%, and electricity consumption can be increased by 3 to 5 kWh, which is converted into CO2 emissions per ton of clinker are reduced by 4.02~13.23 kg, and NOx emissions per ton of clinker are reduced by 0.02~0.06 kg. The initial investment has increased by about 80 million yuan on average, and the unit clinker operating cost has been reduced by 3.36 to 6.72 yuan/t. The subsidy fee for domestic waste is not uniform due to local government standards (50~200 yuan/t). Assuming a subsidy of 100 yuan per ton of domestic waste, the estimated investment recovery period is more than 10 years.
1.2 Cement kiln co-processing of municipal solid waste (combined gasifier) technology
Cement kiln co-processing municipal solid waste (combined gasifier) technology, that is, the municipal solid waste is fermented, homogenized, crushed, weighed and other processes are first sent to the gasifier, and after vaporization, the combustible gas is sent to the cement decomposing furnace Internal incineration, the bottom slag of the gasification furnace is separated and used as a cement ingredient. This technology is a new environmental protection technology that combines the dual advantages of cement kilns and gasifiers, and harmlessly treats the resulting waste gas, furnace bottom slag and leachate. It is suitable for the technical transformation of the co-processing of municipal solid waste in the new dry-process cement production line. It should be noted that the distance between the garbage disposal station and the cement production enterprise should not be too far; the harmful elements introduced by the garbage will affect the normal production of the cement kiln and other issues. Japan’s Kawasaki, Germany’s RÜDERSDORF Cement, etc. have mastered this type of technology, Anhui Conch CKK system technology and Nanjing Kaibeng Energy environmentally friendly gasification incineration system technology, etc. belong to the scope of this co-processing technology. With CKK system technology, the main specification of a single gasifier is 100-400 t/d, and it is equipped with cement kiln systems of different specifications such as 2 000-12 000 t/d. After investigation, when the amount of garbage fed accounts for less than 10% of the amount of cement clinker produced, it has no effect on the normal production of cement. It is estimated that if the 5 000 t/d cement clinker production line uses this technology to process 300 tons of domestic waste per day, the coal consumption per ton of clinker can be reduced by about 4%, and the power consumption can be increased by 2 to 4 kWh, which is converted into ton of clinker CO2. Emissions are reduced by 7.34~8.82 kg, and NOx emissions per ton of clinker are reduced by 0.03~0.04 kg. The initial investment increased by about 100 million yuan on average, and the unit operating cost was reduced by about 4.48 yuan/t. Assuming a subsidy of 100 yuan per ton of domestic waste, the estimated investment payback period is about 10 years.
1.3 Cement kiln co-processing of municipal sewage sludge (drying) technology
Cement kiln co-processing of municipal sewage sludge (drying) technology, that is, the municipal sewage sludge is sent to the sludge drying system, and the waste heat of the cement plant is used to directly or indirectly dry the wet sludge (with a moisture content of about 80%) to dry sludge Mud (moisture content below 30%, part of the drying technology can reach below 5%). The waste gas obtained from drying is treated again; the dried sludge obtained is in the form of loose particles (part of the drying technology can achieve a particle size of less than 10 mm and a calorific value of up to 12 540 ~ 14 630 kJ/kg). It is sent to the cement kiln and can be used as an alternative fuel to directly participate in the combustion. In addition, dry sludge contains SiO2, CaO, etc., which can be used as alternative raw materials for cement production. The core of sludge drying technology lies in heat exchangers and dryers. The sludge drying system is divided into calcium-increasing thermal drying technology, direct contact drying technology, heat transfer oil drying technology, sludge fueling technology, etc. due to the difference in heat source and sludge contact method and drying efficiency. It is suitable for the technical transformation of the co-processing of urban sewage sludge in the new dry-process cement production line. It should be noted that the distance between the municipal sewage sludge station and the cement production enterprise should not be too far; the influence of the introduced harmful elements on the normal production of the cement kiln; the airtightness of the urban sewage sludge transportation process; the monitoring and control of odor . Japan’s Japanese company, Italy’s voron company, etc. have mastered the technology of co-processing sewage sludge (drying) in related cement kilns; the domestic Beijing cement plant introduced Italy’s “VOMM high-efficiency turbine thin-layer drying technology” (referred to as turbine thin-layer technology/process) ), using heat transfer oil to dry the sludge; the swirl nozzle developed by Guangzhou Yuebao Cement Co., Ltd. directly dries the sludge. The kiln tail gas is used to dry the wet sludge, and the moisture content of the sludge can be reduced to about 30%. [1], is a typical semi-drying technology; Huaxin Environmental Engineering Co., Ltd., Hefei Cement Research and Design Institute and other production, education and research units also have corresponding technology application cases. It is estimated that the 5 000 t/d cement clinker production line processes 500-600 tons of sludge per day. One ton of clinker reduces standard coal consumption by about 6 kg, increases power consumption by 3 kWh, and reduces waste heat power generation by about 20%. This can be achieved by ton of clinker. The CO2 emission is reduced by 11.5 kg, and the NOx reduction is between 40% and 60%. Assuming that the original ton of clinker NOx emission is 1.6 kg (“The First National Pollution Source Survey”), the NOx reduction is 50%. A ton of clinker can reduce NOx by 0.8 kg. The initial investment increased by about 80 million yuan on average, and the unit clinker operating cost increased by 4.55 yuan/t. The sludge subsidy fee is not uniform due to local government standards (50-300 yuan/t). Assuming a ton of sludge subsidy of 100 yuan, the estimated investment payback period is about 6 years.
2 Cement kiln co-processing technology emission reduction potential and cost
In order to more comprehensively analyze the emission reduction potential and emission reduction costs of the co-processing of solid waste technology in major cement kilns, the 5 000 t/d cement clinker production line was used as a benchmark, and the marginal emission reduction cost curve (MAC) method was used to carry out the related technology. Evaluation analysis.
2.1 Marginal abatement cost curve
The marginal abatement cost curve (MAC), from the perspective of technological development trends, focuses on considering the potential and cost of technological abatement relative to the baseline scenario, and ranks the target annual abatement costs for technical evaluation and analysis. The main advantage is low data requirements and easy operation. The main analysis steps include:
1) The emission reduction potential and emission reduction cost of the collection technology.
2) Analysis of synergistic control effect. In the two-dimensional coordinate system, the horizontal axis reflects the NOx emission reduction effect of technical measures, and the vertical axis reflects the CO2 emission reduction effect of technical measures. The spatial position of the technical measure in the coordinate system can intuitively reflect its reduction. The effect of discharge and its disposal status.
3) Cost-effectiveness evaluation. The unit pollutant emission reduction cost is a comprehensive consideration of the emission reduction effect and emission reduction cost of emission reduction measures, and reflects the cost that must be paid to reduce the unit quantity of pollutants.
4) Sort technologies from low to high long-term marginal cost, and draw a marginal abatement cost curve (see Figure 1).
5) According to the emission reduction target, draw a straight line through the abscissa (its value is the target emission reduction amount), and the left side of the straight line is the technology combination to be screened.
2.2 Analysis of Cooperative Control Effect
According to the “China Cement Yearbook”[2] and “The First National Pollution Source Survey”[3], the NOx emissions per unit of standard coal in the cement industry are calculated; according to the “China Cement Yearbook” and the “China Cement Industry CO2 Emission Coefficient” Data” [4], calculated the CO2 emissions per unit of standard coal in the cement industry; according to “Energy Data” [5], the NOx and CO2 emission coefficients of the power industry were obtained. The relevant emission parameters are shown in Table 1.
The weight of each pollutant is determined on the basis of market transaction prices. When the price of pollutants changes, the weight will change accordingly, which will affect the value of the air pollutant coordinated emission reduction equivalent APeq, the unit pollutant emission reduction cost of technical emission reduction measures, and Prioritize the results. Before the “Twelfth Five-Year Plan” period, NOx is not an indicator of total emission control, and there is no case of emissions trading. According to the “Administrative Measures for the Collection of Pollutant Emission Fees”, the transaction price of NOx is 5,000 yuan/t; the average price of CDM projects in my country’s market in 2008 About 10~12 Euro/tCO2, this article temporarily uses 100 yuan/t as the CO2 price parameter. In order to investigate the impact of price, a sensitivity analysis is carried out: (N and C are the NOx and CO2 emission reduction potential or emission reduction script respectively).
According to the basic data described in Sections 1.1 to 1.3 above, the two-dimensional coordinate system of the NOx and CO2 synergistic control effect of the main cement kiln co-processing solid waste technologies is shown in Figure 2. The emission reduction potential of each technical measure and the coordinated emission reduction equivalent index are shown in Figure 2. Table 4. Cement kiln co-processing municipal solid waste (RDF) technology, cement kiln co-processing municipal solid waste (combined gasifier) technology, cement kiln co-processing municipal sewage sludge (drying) technology, these three technologies can reduce CO2 while reducing CO2 It can synergistically reduce NOx and has a better synergistic control effect. From the perspective of the total emission reduction effect, the cement kiln co-processing municipal sewage sludge (drying) technology has a better overall emission reduction effect.
Post time: Jul-16-2021