| Summary: | Conventionally, the thermal design a biomass power plant is aimed at maximizing the energy efficiency by using extracted steam to increase feed water temperature in feed water heaters and installing heating surface areas of heat exchangers in boiler to recover flue gas energy. The temperature of flue gas at the boiler outlet must not be so low that a risk of acid corrosion is unacceptable. The energy efficiency can also be improved by reducing fuel moisture content in steam dryer and increasing air temperature in steam-air preheater. However, both devices require extracted steam, which is already used for raising feed water temperature in an existing power plant. In this paper, it is hypothesized that retrofitting steam dryer and steam-air preheater to an existing power plant can improve the energy efficiency. Performances of the existing power plant and the retrofitted power plant integrated with steam dryer and steam-air preheater are compared. Simulation results indicate that, despite lower final feed water temperature in the retrofitted power plant, the retrofitted power plant is more energy efficient than the existing power plant. Economic assessment is carried under the condition that both power plants generate the same power output, which means that the retrofitted power plant consumes less fuel than the existing power plant. The payback period for the retrofitting investment is approximately 7 years.
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