Combined Heat and Power Supply in Industrial Plants
Authors: Ryan W. F. 
Published: April 2023

The ever-increasing demand for cheap power—the foundation of American industry—has been ably met by the public utilities in the past, and the industrial power engineer is now taking his part in promoting the productiveness of human labor.

The use of high steam pressures has been the most noteworthy development in the industrial power field during the past few years. There are now about 200 industrial plants in the United States operating at pressures above 300 lb. gage, almost all of which have been built since 1925. The industrial plant which has a large demand for process steam has a natural advantage over the condensing central station, in that the latent heat in the exhaust is utilized, and the cycle efficiency of the prime movers is 100 per cent. The quantity of power which can be generated so economically is limited by the demand for exhaust steam, but can be materially increased by raising the throttle pressure.

There are few industries which can generate their entire power requirements, at all times, in all seasons, as a by-product of their process steam. There are still many such plants which generate power in condensing prime movers, but the vast majority purchase their requirements from public utilities. There is rarely any economic justification for the private generation of steam power in condensing units, although under certain conditions internal-combustion engines may be used advantageously. There is a growing tendency in this country to use the Diesel engine as an adjunct to an industrial steam-power plant; when the electric-power demand exceeds the relative demand for exhaust steam, the deficiency is supplied by the Diesel engine.

There are many plants which have large demands for process steam, but relatively little demand for electric power. The most significant trend in the industrial power field today is the cooperation of public utilities with manufacturing plants to develop “by-product” power to its economical limit. An example of such cooperation is cited in which the power output of an industrial plant is increased from 5500 kw. to 25,500 kw., the surplus power being distributed to other consumers, over the transmission lines of the public utility. The fuel cost of the additional 20,000 kw. is less than 4500 B.t.u. per kw-hr. The combination results in a decrease of 10 per cent in capital cost and a decrease of 20 per cent in fuel consumption, as compared with the separate generation of electricity by the public utility and of power and heat by the industrial plant.

Gratifying progress has been made in the conservation of fuel by developing the high-temperature end of the industrial power and heat cycle. An enormous quantity of potential energy is still being dissipated in the relatively low-temperature wastes from our manufacturing plants. For the present, the high-temperature field offers more attractive return on investment, but the future will undoubtedly see much progress in the recovery of heat at low temperatures. This source of energy will become economical long before such projects as the generation of power from the tides, which have greater appeal to the imagination, but which inherently involve enormously greater capital outlay.