Part load operation and heat recovery optimization in cogeneration units with diesel engines

This paper investigates the optimization possibilities of different co-generation units with diesel engines - especially applied in small and middle-size biogas power plant installations. The first subject of the publication is the analysis of total energy units using gaseous and liquid fuels (first of all biogas) and the main goal is to simulate and calculate the part load operation of co-generation systems and to investigate the interaction of varying parameters. Generally, the total energy units are planned for the coverage of base load and constant power but there are more and more application areas in which heat and power plants (co- generation systems) are supposed to work with variable power. The elaborated quasi-steady calculation procedures of combustion and heat transfer enable the analysis of numerous operation and optimisation issues for typical circuit schemas. The paper also offers a comparison between the chosen theoretical calculation data and the real measuring results from a biogas power plant. The comparison shows a good degree of accuracy. Aside from the fundamental calculation procedures some additional issues were examined, for example hydraulic optimisation and economical questions. The second matter of the presented research results is the possible application of organic-rankine-cycles in biogas installations. An analysis of the working fluid characteristics was carried out in order to select the most suitable fluid for the special applications. Furthermore, the thermodynamic optimization based on a special original calculation procedure was implemented, which enables the investigation of the influence of different operating parameters on the efficiency of the heat recovery. Afterwards the chosen application variants of the ORC-processes for waste heat recovering in the existing biogas power plants were analysed and carried out.