Abstract:
Cement is finely ground material having composition of various minerals which, when
mixed with water, sand and aggregate materials form concrete. Cement provides the
chemical bonds that hold the other materials together to form a dense rocklike substance.
Among the minerals, clinker is the main ingredient, which is converted to cement by
grinding with gypsum, and natural pozolana mainly pumice. To produce this highly
consumed good it requires an enormous amount of energy both thermal (fuel) and
electricity. Researches show that up to 40% of the total production cost of cement is
attributed by energy and a significant source of greenhouse gas, accounting for about 5%
of the annual global anthropogenic carbon dioxide emissions and process energy loss
during the clinker production.
Clinker production needs enormous amount of thermal energy and it is in this process
where various energy losses occur so that it gives opportunity to evaluate energy
conservation opportunities. This can be accomplishing by conducting Energy Audit for
estimation of process thermal loss and calculation of the amount of heat that can be
trapped for waste heat to energy conversion.
To accomplish these objectives, data is collected from several sources, including plant
instrumentation, field measurements (using a portable stack gas analyzer, infrared
thermometer, anemometer etc.), and plant records. These data are surface temperature in
preheater, kiln and cooler, hourly consumption of coal and hourly feeding of raw meal,
kiln feed to clinker factor, exit gases temperature and pressure and air flow to cooler from
forced draught fans.
Kiln system is a unit which consumes thermal energy in cement industry. Habesha
Cement Factory uses coal to produce the required thermal energy. And using the
collected data a detail audit conducted such as performing an energy and mass balance on
the system and the specific energy consumption was 800kcal/Kg clinker. From the
energy balance the main area of heat losses are the exhaust gas, the hot air from clinker
cooler and from kiln surface, which are 824.34, 345.71 and 162.47KJ/Kg of clinker
respectively.
To minimize the energy loss waste heat recovery (waste heat to power) conversion from
exhaust gas and clinker cooler hot air exhaust are taken as the conservation measures.
The waste heat is utilized using waste heat recovery boiler for production of steam which
will expand in steam turbine for power generation. A total of 20325960Kwh will be
saved annually and emission reduction of 17465tCO
2
annually will be achieved.