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1WASTE UTILIZATION IN KOREAN CEMENT PLANTS
Geun Seong LEE Zebo BABAKHANOVA and Mastura ARIPOVA
Dept. "Technology of Silicate Materials, and Rare, Noble Metals" Tashkent Institute of Chemical Technology, Tashkent, Uzbekistan https://doi.org/10.5281/zenodo.10822499
Cement production is a very material and energy-intensive process. Cement production is similar all over the world. After the natural raw materials such as limestone, silica sand, clay, and iron ore, are mined, they undergo various steps of mechanical treatment such as crushing, grinding, and homogenization to produce in the raw mill the so-called raw meal. The raw meal enters the cement kiln system where the thermal processes (drying, preheating and cooling) and chemical reactions (calcination, clinkerization) take place to produce the intermediate product clinker. Finally the clinker is milled together with gypsum and other constituents to produce a fine and homogeneous powder of the so-called Portland cement. The thermal energy required for raw material drying, calcination and sintering reactions has traditionally been provided by fossil fuels such as oil, natural gas, coal and petroleum coke.
"Waste" means materials, that are not products or by-products, for which the generator has no further use for the purpose of production, transformation or consumption. The use of waste as alternative fuels reduces the use of non-renewable fossil fuels such as coal, oil and natural gas. The waste utilization in cement kilns maximizes the recovery of energy from waste. All the energy is used directly in the kiln for clinker production, so that various types of waste derived alternative
fuels can be used to replace traditional fuels. Table 1 shows the widely used wastes as alternative fuel options in cement plants.
The material temperature in cement kiln can be higher than 1,450oC and the residence time in the kiln itself can be more than 30 min. The gas temperature can be even higher than 2,000oC, the residence time of gas in high temperature zone which no less the 1,300oC is more than 10 seconds. Therefore, because of the fundamentally high temperature of long residence time in cement kilns, all organic compounds, even the most resistant chlorinated hydrocarbons are completely and efficiently destroyed. Even the most stable organic compound cannot survive at temperatures exceeding slightly more than 800oC. Combustible toxic compounds found in some hazardous waste, such as halogenated organic substances, need to be destroyed through proper temperature and residence time. Hazardous and other wastes fed through the main burner, where conditions will always be favorable, decompose under oxidizing conditions at a flame temperature of >1800°C.
Cement plants have intrinsically played a role as emission barriers from the point of view in the environmental aspect, in which barriers prevent toxic substances from being emitted or becoming harmful to the environment (Fig.1).
1. High incineration temperature: In the sintering zone flame temperatures of some 2,000oC are required for the clinkerization, where even very stable organic compounds (e.g. PCB) are completely destroyed.
2. Intensive contact with the raw meal: Intensive contact of gas and raw meal is required for heat transfer. Preheater system acts as 'scrubbing station' in series, working at different temperatures
Table 1. Various wastes as alternative fuels in cement plants.
• End-of-life tyres
• Industrial, commercial and municipal solid wastes, construction and demolition wastes - RDF and SRF
• Biomass (animal meal, logs, wood chips and residues, recycled wood and paper, agricultural residues like rice husk, sawdust, sewage sludge and biomass crops)
• Plastics, textiles and paper residues
• Waste oils and solvents
f toxic compounds while contact
3. Low_temperature:
Condensation or absorption on surface active raw meal reduces the concentrations of toxic elements according to the physical/chemical equilibrium. The lower stack temperature the lower will be the equibrium concentrations of the vapors of toxic compounds.
4. Efficient dedusting equipment: The higher absortion capacity of the kiln system avoids emissions. An
efficient dedusting prevents enriched dust from getting into the atmosphere. 5. Incoporation of trace elements in clinker: A cement kiln with complete dust reintroduction offers the unique possibility to incorporate trace elements in the clinker production in diluted and immobile form, and they are not leachable.
Table 2 shows the annual utilization of wastes in Korean cement plants. Even clinker production in Korean cement plants gradually is decreased, waste utilization is rather increased. Substitution ratios of argillaceous-siliceous raw materials and total fuels are 30% and 36% in 2022, respectively.
Summary & Prospective
The utilization of alternative fuels in cement plants is a proven technology due to the complete and safe destruction for wastes by the high temperature, long residence time, and oxidizing conditions, and the insoluble form binding of trace elements with the mineral components of clinker. Therefore, wastes as alternative fuels can be replaced to the conventional fuels such as coal, gas, and liquid fuels. Intrinsic characteristics of cement plants give no effects on emission and clinker quality during the combustion of alternative fuels.
To use waste utilization in cement plants with effectively continuous and reliable availability is needed to the effective waste management, which contributes the overall carbon reduction in the country. Waste utilization in cement plants should be as an environmentally sound supply by proper sorting and pretreatment of waste, clearly ensuring quality of wastes. Even though alternative fuels are environmentally best results of the utilization of wastes as well as the CO2 reduction, some customers and inhabitants, for psychological reasons, may not accept cement which is produced by using "waste". Realization of waste utilization applied to cement plants may be time-consuming at the level of public discussion and should be supported by government for the level of the greenhouse gas reduction.
(900~300oC). This produces gas purification through absorption o occurs in counter-current pattern.
Fig. 1. Emission barriers in cement kiln.
Table 2. Annual utilization of wastes in Korean cement plants
(unit: 1,000 ton)
Items
2017 2018 2019 2020
2021
2022
Clinker production
48,657
45,391
45,932 41,894
42,890 43,430
Raw mat'I
Argillaceous
Siliceous
Fly ash (local) 2,804
3,151
3,179 2,792
2,856 3,116
Sludge 2,083 Tailings 190 Foundry sand 654
Sub-total
5,731
2,051 308 563 6,073
2,315 2,957 591 330 606 610 6,691 6,359
2,762 476 708 6,802
2,804 503 811 7.234*
Fuel
Waste tires Waste plastics
Waste rubbers Waste woods, etc.
263 858
115 30
291 915
70 50
275 186
1,016 1,407
76 88
35 40
165 1,952
112 16
199 2,402
140
22
Sub-total Total
1,266 6,997
1,326
7,339
1,402 1,720 8,093 8,079
2,245 9,047
2,763** 9,997
30% substitution of argillaceous-siliceous raw materials. 36% substitution of total fuels._
