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Opting for ORC

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World Cement,

Turboden explains how cement plants could achieve better energy efficiency while reducing production costs and CO2 emissions through ORC technology for waste heat recovery.

Cement production is one of the most energy-intensive industries in the world, and the thermal and electric demand of the clinker process is the dominating cost factor. Furthermore, besides the CO2 produced through fuel combustion, the cement process produces CO2 through the chemical reaction inside the kiln, meaning the cement industry is responsible for 8% of global CO2 emissions. The pressure on CO2 reduction is increasingly strong, and the industry has been looking for various ways to both increase energy efficiency while reducing production costs and CO2 emissions to be more sustainable.

Why WHR?

Within the several options a cement plant has, Waste Heat Recovery (WHR) from cement production process exhaust gas is a proven technology with a long track record of improving the energy efficiency of cement plants. In the cement production process, there are two main hot gas streams where heat can be recovered: The pre-heater tower (PH) and the clinker cooler (CC). WHR means allowing the waste heat at a medium/high temperature (higher than 250°C) to leave the process, but converting this into useful electricity before it is discharged at a lower temperature level (below 120 – 200°C) to the environment.

After the efficiency of a cement plant has been driven to the optimum, the remaining waste heat is converted into electricity which can be used inside the cement plant, reducing the cost related to the energy purchased by the grid. Electricity produced by WHR plants is carbon free, as it does not need fuel to be produced.

Besides the lower cost for electricity, there are often other benefits for cement plants. In fact, in many plants, the gas from both pre-heater and clinker cooler has to be cooled down before entering the filtration system. Nowadays the cooling of the gas is carried out using quenching towers in the PH side and air-to-air heat exchanger in the CC gas. Cooling the gas temperature in the heat exchangers instead of these systems allows further reduction of the electric consumption of air-to-air exchanger fans and does not require water to be sprayed in the quenching tower, saving significant resources that can be very valuable in dry countries.

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