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

Abstract

The main aim of this study was to find out the available heat of the exhaust gas stream that is bypassed through the raw meal department at Norcem Brevik cement plant, Norway which produces about 1 million ton of clinker per year. The study has been conducted for different process conditions in order to recover the available heat. Mass and energy balance was performed for the raw meal department with the use of plant process database and manual measurements to calculate the available heat. Available heat is presented in two different end temperatures, 130 °C for LP steam generation and 50 °C for hot water generations. Sankey diagrams have been used to illustrate the available heat graphically. It has been found that waste heat varies in between 4.2 MW to 1.5 MW for LP steam generation and 2.2 MW to 5.8 MW for hot water generation at the bypass line. The available heat is low when STD type is running compared to other process conditions. Approximately a heat of 20 MW for LP steam generation and 6 MW for hot water generation is available at the conditioning tower before the raw meal department when AFM is not running. A network of heat exchangers is suggested to recover heat. The heat loss from the system and power inputs from fans and motors is negligible compared to the available heat. It has been found that there is no gas recycling via the bypass line. Furthermore, the total false air coming into the system from different locations has been estimated as 40-50% of total air going out from the raw meal department. In addition, the behavior of moisture content, oxygen content and dust content of the gas streams have been discussed.