Energy audit and waste heat recovery from kiln hot shell surface of a cement plant

In this study, a cement rotary kiln is taken as centre of discussions where thermodynamics of rotary kiln, energy losses, refractory selection and their impact, temperature profile of rotary kiln with various examples of recovering losses of high kiln shell temperature are investigated. The data are referred from a cement plant and modeling is done with related calculations and SEIDER TATE analysis using MATLAB code 45 tool. In a cement rotary kiln, high temperature heat is directly dissipated into atmosphere by means of exhaust flue gases and radiation energy through hot kiln shell surface. Heat loss through hot kiln surface by means of radiation and convection mode of heat transfer has a major contribution among all considerable heat losses (average 7-8%) in the rotary kiln system. Selection of refractory materials as per the operating condition of rotary kiln can help in optimization of shell temperature profile of cement kilns. In this paper, various profile sets of energy transfer are analyzed between hot air and cold water used in a heat exchanger designed for kiln shell heat recovery. A cement plant with 1.5 million tonnes/annum capacity has been taken up as a case study in this paper. A concept of installing a Vapor Absorption Machine (VAM) chiller application (by utilizing recovered waste heat energy from kiln shell surface) is discussed where the potential of energy saving is calculated to be 0.79 MJ/ tonne and equivalent CO2 emission savings of 4.61 tonnes CO2 per year. A VAM chiller in cement plant is used for space cooling and other process-related applications like cooling of heavy gear assemblies etc.