Energetic and Exergetic analysis of waste heat recovery boilers in the cement industry
Waste heat recovery boiler is an efficiency way to gain energy from the exhaust gases in a cement plant. In a typical cement producing procedure, 25% of the total energy used is electricity and 75% is thermal energy. However, the process is characterized by significant heat losses mainly by the flue gases and the ambient air stream used for cooling down the clinker. About 35% - 40% of the process heat is lost by those waste heat streams. Approximately 26% of the heat input to the system is lost by dust, clinker discharge, radiation from the kiln and pre-heater surfaces, and convection from the kiln and pre-heaters. A waste heat recovery boiler could be used to increase the efficiency of the cement plant and thus lower the CO2emissions. Moreover, it would reduce the amount of waste heat to the environment and lower the temperature of the exhaust gases. Waste heat can be captured from combustion exhaust gases, heated products, or heat losses from systems. This study aims at the identification of a best practice example for energy utilization in an existing commercial cement production plant with a waste heat recovery boiler as a new component. Firstly, a water-steam Rankine cycle will be analyzed and then an Organic Rankine Cycle (ORC) with an intermediate pressurized water circuit will also be investigated.
Waste heat recovery boilers
The identification of the waste heat sources in the cement industry is thus of high importance for the improvement of the process efficiency. The two main waste heat sources are:
1. The exhaust gases from the rotary kiln, which after passing through the raw material preheater are at a temperature in the range of 380°C
2. The waste heat from the clinker cooler, in the form of hot air, at an average temperature of about 360°C.
These waste heat sources can be efficiently used in a waste heat recovery boiler to produce electricity....