Abstract:
East African Portland Cement limited runs an energy intensive plant in terms of both
electrical and thermal energy. The average specific power consumption for EAPCC plant
is 111 KWh/ton of cement with an average peak demand of 9.7 MW. The high cost of
electric power at 0.14 USD/KWh results into very high cost of production that
significantly lowers the company's profit margin and limits its competitive advantage.
The generation of electrical power from waste heat recovery would reduce the electricity
power bill through partially substituting the power procured from the national grid.
The research thesis's main objective was to determine the thermal energy in hot waste
gases from the clinkering process and design steam generators for the waste heat
recovery plant for conversion of thermal energy to electrical energy and evaluate its
economic feasibility. The research employed gas dynamic theories and fundamentals for
quantifying the waste gases vented into the environment and their parameters after which
the thermodynamic knowledge was employed for determination of the heat energy
content and eventually employed the energy theory in converting the computed thermal
energy into potential electrical energy and utilized the obtained results in sizing and
designing the boilers for the waste heat recovery plant. The research thesis required
utilization of specific gas handling tools for field data collection and analysis.
The research thesis evaluated the potential that the plant has for generating electrical
power from the hot waste gases vented into the atmosphere. It was found out that the
plant has the net potential to generate 2.89 MWh of electrical power which reduces the
company monthly electric power bill by 32.68%. The thesis recommends the installation
of a steam rankine cycle for the generating plant. The research thesis designed the steam
boilers for the waste heat recovery plant for conversion of thermal energy to electrical
energy and selected a commercial steam turbine for the waste heat recovery power plant.
Lastly, the researcher evaluated the economic feasibility of the waste heat recovery plant
and established that the designed plant would have a simple payback period of 2.69 years.
The design steam output from the steam boilers was at 5 bars and at a temperature of
230°C with a combined production capacity of 20.44 tonnes /hour. A commercial low
parameter steam turbine (model S3-05), to suit the calculated optimum conditions of 5
bars and 230°C was selected for the waste heat recovery plant. This research work
contributed to theory by employing the various industrial engineering concepts,
thermodynamic as well as heat transfer to develop flow calculation sheets, energy
balance tools that enabled the researcher to accurately quantify the amount of thermal
energy contained in the waste gases from the kiln. This could be applied for the various
units within a cement plant and across a waste heat recovery power plant.