Vapor compression mechanical

Fig. 2-17. Steam distillation unit with heat recovery by mechanical vapor compression [2.12]. Representation according to the data of GEA Wiegand GmbH.

A general discussion of the economic efficiency of mechanical vapor compression is found in [2.13]. The use of vapor compressors is already of economic benefit if... 

Solvent evaporation has to be carried out with a minimum total cost. This implies minimal energy consumption with respect to the evaporation rate, but also investment costs, maintenance and service costs have to be in an acceptable range. Solution concentration by evaporation of solvent, is carried out in single or multistage evaporation units with or without thermal or mechanical vapor compression, or in multistage flash evaporation units. Common evaporation units include circulating evaporators, continuous (single pass) evaporators or flash evaporators. 

With mechanical vapor compression (Fig. 7-14 see also Table 2-12) the vapor from the solution is removed from the vapor space of the evaporation unit slightly superheated due to the rise in boiling point (1 -> 2), polytropically compressed (2 3)... 

Fig. 7-15. Nomogram to find the specific energy costs for each ton of water evaporated from an aqueous solution for the case of mechanical vapor compression and multistage evaporation. Representation according to Mannesmann-Engineering AG, Messo-Chemietechnik [7.29].

Compressor technology and availability has permitted the application of mechanical vapor compression. 

For falling film evaporators, disentrainment apparently occurs in the tubes. Droplets ejected from the film on one side of the tube are absorbed by the film on the opposite side. Consequently, falling film units are well suited for mechanical vapor compression systems. 

Perhaps the highest thermal vapor compression technology in any field can be found in the water desalination industry. Technology in that industry has advanced to designs with more than eight successive effects with steam economies over 12. Thermal compression evaporators beyond seven effects In process industries does not appear to be economical because mechanical vapor compression systems offer a better alternative. 

Compressor power is proportional to the increase in saturation temperature (AT) produced by the compressor. An evaporator designer must optimize power consumption and heat transfer surface. Mechanical vapor compression achieves the highest possible energy savings these energy savings are reached at the expense of much higher investments and, in most cases, increased electrical power consumption. 

Many of these disadvantages may also be present for any evaporator system. Mechanical vapor compression systems can ba operated under vacuum, and many times ara the bast economical choice. 

Mechanical vapor compression can oftan ba used in preconcentrators where tha major portion of tha avaporation is accomplishad. The remaining concentration can then be done in some other evaporator system. 

Tha availability of cooling water should be determined. Mechanical vapor compression has no cooling-water requirements. This may be important where expansion of existing facilities is required or whan water is axpansiva. 

Seawater or brackish water is used for process applications or as potable water when fresh water is scarce. Six techniques are used for desalination. Five are evaporation processes multiple-effect thermocompression mechanical vapor compression once-through multistage flash and multistage flash with brine recirculation. The sixth process, reverse osmosis, uses membrane technology for desalination. 

Seawater Supply Seawater required per unit of water produced varies from 2 for mechanical vapor compression to 3 for reverse osmosis and 8-10 for the other processes. Seawater requirements may dictate more or larger equipment. 

Maintenance requirements could be listed in the following order, from lowest to highest maintenance thermocompression once-through multistage flash multistage flash with brine recirculation reverse osmosis multiple-effect evaporation mechanical vapor compression. Several factors are important ... 

Mechanical Vapor Compression Scaling and acid treatment problems can also occur. The mechanical compressor and its motor, gearbox, and lubrication system require considerable maintenance. 

There are several types of heat pumps that are currently feasible for industrial applications, including mechanical vapor-compression systems, closed-cycle mechanical heat pumps, absorption heat prnnps, heat transformers, and reverse Brayton-cycle heat prnnps. 

Preliminary concentration of the whey to 50-55% dry matter in falling-film evaporating systems (thermal or mechanical vapor compression), followed by spray drying (one step or two step with subsequent vibraton fluid bed). 

---