Performance criterion of a steam power plant:
Sol.: The design of power plant can be determined largely by the consideration of capital cost and operating cost; the former depends mainly on the plant size and latter is primarily a function of overall efficiency of the plant. Generally the efficiency can be improved, but only by increasing the capital cost of the plant, thus a suitable compromise should be reached between capital costs and operating costs.
l. Specific steam consumption (S.S.C.). The plant capital cost is mainly dependent upon the size of the plant components. These sizes will depend on the flow rate of the steam themselves which is passed through them.
Hence, an indication of relative capital cost of different steam plant is given by the mass flow rate m of the steam required per unit power output, which means by the specific steam consumption (s.s.c.) or steam rate In M.K.S. system.
1 horsepower hour ≈ 632 k cal
1 kilowatt hour ≈ 860 k cal. Work ratio can be defined as ratio of net plant output to gross (turbine) output.