The Design of an Instructional Cogeneration Laboratory

California State University, Sacramento has designed and constructed a cogeneration laboratory for the instruction of students in modern electrical generation. This facility serves about 100 senior level students per year. The major components are a 75 kW gas turbine generator, a waste heat boiler and a small absorption chiller. Future plans include the addition of a 50 kW steam turbine. The analytical design of this plant is described from concept to final layout with particular emphasis on cycle analysis, selection and sizing of components and instrumentation, and the layout of the equipment. A diagram showing the entire cycle on a scaled temperature entropy plot provides an interesting graphical interpretation of the plant’s operation. While the gas turbine has a relatively low pressure ratio of 3.3:1 and thus a low thermal efficiency, the addition of the other components improves the performance significantly. An aspect of the analysis of particular interest is relating the cooling of the chiller to an equivalent work term thus enabling the determination of an overall thermal efficiency. If all of the steam were to be used for cooling the plant efficiency would improve slightly from 10% for the turbine alone; when made equivalent to other types of refrigeration the improvement is more than 6%. When all of the steam is used in the proposed steam turbine the efficiency will improve to about 17%. Using the chiller to cool inlet air to the gas turbine—thus increasing performance—is discussed at length. Student use of the laboratory is discussed briefly. While the plant is quite small and intended for laboratory use, the design analysis is applicable to similar plants which might be used in remote locations, or as stand-by or peaking power supplies.