THE ECONOMICS OF BACK-PRESSURE STEAM TURBINES

Recently, back-pressure steam turbines have become the focal point in many cogeneration applications. This is a result of the savings in operating costs associated with the generation of electrical or mechanical power coincident with the economical use of available thermal energy. The benefits and constraints of back-pressure systems, however, are not always readily apparent and may result in the misapplication of this technology. This paper, therefore, will examine new turbine installations and backpressure retrofits and will determine the most economical back-pressure turbine applications. A generalized methodology is highlighted, allowing the reader to readily evaluate and determine the economic justification of back-pressure turbines in many cogeneration applications. The impact on plant energy use and cost is calculated, and the effects of load variation and the value of high-efficiency turbines are discussed. The specific process plant case studies reviewed involve back-pressure turbines of 100 to 5000 hp for mechanical drives, for generator drives, and as pressure reducing station replacements.