Due to a highly energy-intensive manufacturing process, enormous consumption of natural resources and substantial contribution to greenhouse gas emissions, the cement industry has a significant impact on society and environment. At the same time, cement companies have to compete in a highly price-driven market. In order to conserve natural resources, fulfil legal requirements and cut down on costs, the Mannersdorf cement plant continues its efforts to increase the use of alternative fuels while decreasing the specific heat consumption for clinker burning and enhancing clinker quality. This Master thesis has the target to assess the thermal energy efficiency of the existing preheater, precalciner, rotary kiln and clinker cooler, analyse process stability issues related to fuel input and reveal potential for improvement. Analyses are carried out based on a kiln audit, online data and an energy balance that was created as part of the audit. The outcome of the subsequent discussion is summarized in a conclusion and optimization strategies are formulated.