514 Fermentation and Biochemical Engineering Handbook In a compression evaporation, a part or all of the evaporated vapor is compressed by a compressor to a higher pressure level and then condensed, usually in the heating element, thus providing a large fraction of the heat required for evaporation. 23] Energy economy obtained by multiple-effect evaporation can sometimes be equalled in a single-effect compression evaporator. Compression can be achieved with mechanical compressors or with steam jet thermo-compressors. To achieve reasonable compressor costs and power requirements, compression evaporators must operate with fairly low temperature differences, usually from 5to 10 C. This results in a large heat transfer surface, partially offsetting the potential energy economy When a compression evaporator of any type is designed, the designer must provide adequate heat transfer surface and may decide to provide extra area over that required to anticipate reduced heat transfer should fouling occur. If there is inadequate surface to transfer heat available after compression, the design compression ratio will be exceeded causing a thermo-compressor to break or backfire or a mechanical compressor to exceed the horsepower provided Mechanical compression evaporation(Figs. 19 and 20)is general limited to a single effect. All of the vapor is compressed and condensed eliminating the cooling water required for conventional or steam jet thermo compression evaporators; an advantage when cooling water is costly. Me- chanical compression is ideally suited for locations where power is relatively expensive and fuel is expensive. The greatest advantage of mechanical compression is thehigh energy economy. Compressors may be reciprocating, rotary positive displacement, centrifugal, or axial flow. Single stage positive displacement compressors appear to be better suited to compression evapo ration because oflower cost and their characteristic fixed capacity, dependent nly on speed or discharge pressures developed compression ratios and material of construction. The c may be driven with a diesel unit, a steam turbine, a gas turbine or an electric motor. Selecting the compressor drive requires analysis of all factors present at a particular location. One disadvantage of mechanical compression is that most systems require a heat source to initiate evaporation during start-up Because the vapor is frequently water, which has a low molecular weight and a high specific volume, compressors are usually quite large and costly. Compressors require high purity of the vapor to avoid buildup on the blades of solids that result from evaporation of liquid as the vapor is superheated by compression. Liquids having high boiling point elevations are514 Fermentation and Biochemical Engineering Handbook In a compression evaporation, a part or all of the evaporated vapor is compressed by a compressor to a higher pressure level and then condensed, usually in the heating element, thus providing a large fraction of the heat required for evaporation.[23] Energy economy obtained by multiple-effect evaporation can sometimes be equalled in a singleeffect compression evaporator. Compression can be achieved with mechanical compressors or with steam jet thermo-compressors. To achieve reasonable compressor costs and power requirements, compression evaporators must operate with fairly low temperature differences, usually from 5" to 10°C. This results in a large heat transfer surface, partially offsetting the potential energy economy. When a compression evaporator of any type is designed, the designer must provide adequate heat transfer surface and may decide to provide extra area over that required to anticipate reduced heat transfer should fouling occur. If there is inadequate surface to transfer heat available after compression, the design compression ratio will be exceeded causing a thermo-compressor to break or bacwre or a mechanical compressor to exceed the horsepower provided. Mechanical compression evaporation (Figs. 19 and 20) is generally limited to a single effect. All of the vapor is compressed and condensed, eIiminating the cooling water required for conventional or steam jet thermo￾compression evaporators; an advantage when cooling water is costly. Me￾chanical compression is ideally suited for locations where power is relatively inexpensive and fuel is expensive. The greatest advantage of mechanical compression is the high energy economy. Compressors may be reciprocating, rotary positive displacement, centrifugal, or axial flow. Single stage positive displacement compressors appear to be better suited to compression evapo￾ration because of lower cost and their characteristic fixed capacity, dependent only on speed or discharge pressures. They are, however, limited in developed compression ratios and material of construction. The compressor may be driven with a diesel unit, a steam turbine, a gas turbine or an electric motor. Selecting the compressor drive requires analysis of all factors present at a particular location. One disadvantage of mechanical compression is that most systems require a heat source to initiate evaporation during start-up. Because the vapor is frequently water, which has a low molecular weight and a high specific volume, compressors are usually quite large and costly. Compressors require high purity of the vapor to avoid buildup on the blades of solids that result from evaporation of liquid as the vapor is superheated by compression. Liquids having high boilingpoint elevations are