Chapter 3 - Single Effect Evaporation-Vapor Compression

Abstract

This chapter focuses on evaluation of the single effect evaporation system combined with various types of heat pumps. The single-effect thermal vapor-compression desalination process is of very limited use on industrial scale. However, thermal vapor compression is used with the multiple effect evaporation (MEE) system, which is known as MEE-thermal vapor compression (TVC). TVC system design and analysis provides the basis for the more complex system of multiple effect evaporation with thermal vapor compression. The mathematics for the TVC system includes material and energy balance equations for the condenser and evaporator. Also, the model includes heat transfer equations for the condenser and evaporator as well as an empirical equation for the steam jet ejector. The analysis of the system is made as a function of variations in the thermal performance ratio, the specific heat transfer area, and the specific flow rate of cooling water. The analysis is performed over a range of the boiling temperature, the motive steam pressure, and the compression ratio. The analysis of the system performance by the mathematical models shows consistency of predictions and industrial practice. The specific power consumption is found to vary over a similar range, 9-17 kWh/m3 at 60 ºC. In addition, the predicted evaporator specific heat transfer area is close to the industrial practice, with values between 400-600 m2/(kg/s) at 60 ºC. The temperature values predicted by the model are also found consistent with reported industrial data. Further, the absorption heat pump combined with the single effect evaporation desalination process is analyzed as a function of the design and operating parameters.