ISA | Managing industrial power

ISA | Managing industrial power: "Co-generation economics
There are essentially three types of steam turbine generators at work in power generation: backpressure turbines, condensing turbines, and extraction turbines.
There are a multitude of combinations of these turbine types including backpressure units with extractions and units with multiple extractions with or without condensing stages.
How can a co-generation plant produce power cheaper than a large modern central station utility? Comparing heat utilization in a utility plant versus a co-generation plant can see the answer.
The thermal efficiency of a utility plant can be about 39% or a heat rate of @ 8750 Btu/kWh. Adding transmission and distribution losses of 5%, the net output to customers' costs is about 9200 Btu/kWh.
However, in an industrial plant where power generates from a non-condensing turbine, the heat in the low-pressure steam can also go for process use. In fact, heat utilization in an industrial plant can be, up to 85%. Thus, the ratio of heat utilization in an industrial plant to that of the utility is at least 2 to 1.
However, in general, the cost of power produced by condensing turbines in an industrial plant is higher than the incremental cost of power from the utility. Only in cases where the utility rates are high and the industrial plant's incremental fuel cost is extremely low does power produced via condensing turbines cost less than utility generated power.
Condensing power is expensive because of the large proportion of the heat in the throttle steam is lost in the condenser. Ideally, condensing turbines should not run at all, or if they must be for some reason, their loading should be at a minimum."