Enhanced condenser tube designs can significantly improve the heat rate and performance of fossil and nuclear plants. Using the optimum number of tubes and replacement tube sheets will cost more than simply replacing plain tubes. However, the investment’s simple payback is measured in only weeks, which builds a strong case for using an enhanced tube design as part of your next condenser overhaul.
The vast majority of electric utility plants operate with the Rankine cycle, which uses a turbine-generator to produce electric power. One of the limitations of this cycle is that the condenser cooling water temperature directly affects plant efficiency and the power generated. Colder water during the winter months yields a higher power output and, conversely, plant output is reduced when the condenser water temperature rises during the summer. In addition, plant output is more sensitive to high turbine backpressure (in summer months) than to low backpressure (in winter months).
As you will see shortly, the effect of condenser water inlet temperature is strongly influenced by the shape of the "turbine backpressure curve," as shown in Figure 1. Note that the smallest incremental improvement occurs at the lowest backpressure, where the curve is reasonably flat. Conversely, the greatest incremental improvement will occur at the higher condenser inlet water temperature conditions. Therefore, fossil and nuclear plants experience the greatest benefit of reduced condenser water temperature in the summer months during peak demand season.
1. Changes with temperature. This turbine heat rate correction factor curve specifies 3 in. HgA as the standard performance condition. A turbine heat rate factor must be applied when the turbine backpressure changes as a reaction to condenser cooling water temperature changes. Note the differences between the response of a typical fossil and nuclear plant. Source: Dr. Ralph L. Webb
In addition to lower cooling water temperatures, advanced technology condenser tubes with special surface geometries on the inner and outer surfaces will yield a higher overall heat transfer coefficient (U) than a plain tube condenser, increasing the heat transfer between the steam and cooling water, and thereby increasing power output and reducing plant heat rate. Such a special surface geometry tube is called an "enhanced tube."
There are practical and commercially available enhanced condenser tube geometries that will yield a U-value increase of approximately 40%. These tubes are available to any power plant that operates on the Rankine cycle using condenser water from any source (lake, river, or cooling tower). An increased U-value means that a lower turbine backpressure factor (Figure 1) is required for a given condenser water temperature, resulting in higher plant efficiency and power output.
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