Waste heat availability in the raw meal department of a cement plant

The main aim of this study was to determine the available heat in the cement kiln exhaust gas subject to different process conditions. A Norwegian cement plant producing about 1.3 million tons of cement per year was used as a case study. A mass and energy balance was made for the raw meal department, and process data available from the plant process database as well as manually measured gas flow rates were used to calculate the available heat. The available heat can be utilized by a combination of low pressure (LP) steam generation and hot water generation. It was found that waste heat is 1.5-4.2 MW for LP steam generation and 2.2-5.8 MW for hot water generation. The variation in available heat is due to different raw meal types being produced, requiring different gas inlet temperatures to raw meal mill. In cases when no raw meal is produced (in maintenance shutdown periods), all the gas will bypass the mill, and approximately 20 MW of LP steam and 6 MW of hot water can be generated. The heat loss from the system was estimated based on measurements, and the fan power inputs were calculated. Both were found to be negligible compared to the available heat. Furthermore, the total false air coming into the system was estimated as 40-50% of the total gas flow rate going out from the raw meal department.