The following is a list of questions and answers that provide some guidelines to determine if the addition of a steam turbine is justified.
1. Where is the steam that is leaving the turbine going to? If the steam is going to a process for use as a heat source, then proceed. If the steam is entering a condenser and the steam cycle is used to produce power only, then the project should be reconsidered. This is not cogeneration and the economics are generally bad.
2. What is the source of the steam? Burning high-quality fuel like natural gas to generate steam is convenient and practical but not very economical. Combined cycles are recommended in this case. Burn the gas in a gas turbine and use the exhaust (waste) heat to make steam. The capital cost has increased significantly, but the efficiency of the combined cycles is much higher (around 60 percent for power generation only). Low-grade, cheap fuels (e.g., waste coal, groundwood, and municipal garbage) are very attractive. However, plants using these cheap fuels tend to have a very high investment in fuel handling.
3. Is it a waste heat steam generator? In general, these are installed with new gas turbines. However, they can be retrofitted to many exothermic processes with suitable choices in materials and construction. The cost of steam produced is exceptionally low.
4. What is the turbine arrangement required? Until recently, the complexity, poor accuracy, and high maintenance of...
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