Vapor compression distillation

Seawater Distillation. The principal thermal processes used to recover drinking water from seawater include multistage flash distillation, multi-effect distillation, and vapor compression distillation. In these processes, seawater is heated, and the relatively pure distillate is collected. Scale deposits, usually calcium carbonate, magnesium hydroxide, or calcium sulfate, lessen efficiency of these units. Dispersants such as poly(maleic acid) (39,40) inhibit scale formation, or at least modify it to form an easily removed powder, thus maintaining cleaner, more efficient heat-transfer surfaces. 

Distillation processes, 26 61-73. See also Distillation(s) freeze-desalination, 26 71 materials and scaling issues in, 26 71-73 multi-effect distillation, 26 65-67 multistage flash evaporation, 26 61-65 vapor compression distillation, 26 67 Distillation reactors, 21 332 Distillation region diagrams (DRD), 22 302, 303, 331... 

The maximum number of effects in a multiple-effect evaporation system and a comparison of energy economy of multiple-effect evaporation with that of vapor-compression distillation are discussed. 

Vapor-Compression Distillation Process. This plant will operate on a highly brackish water and will be located at Roswell, N. M. It will have a design capacity of 1,000,000 gallons per day. Construction is under way. 

The work required for vapor-compression distillation may be calculated from the equation... 

Dodge, B. F., Eshaya, A. M., Economic Evaluation Study of Distillation of Saline Water by Means of Forced-Circulation Vapor-Compression Distillation Equipment, Office of Saline Water, Research and Development Progr. Rept. 21. 

Constmction of new power plants in the coal region of the western United States presents serious problems in states whose laws dictate zero effluent. In these plants, cooling-tower water withdrawn from rivers cannot be returned to them. In these situations, cooling-tower effluent is purified by distillation (vapor-compression plants have predominated) and by a combination of distillation and membrane technology. The converted water then is used as boiler feedwater the plant blowdown (effluent) is evaporated from open-air lined pools, and pool sediment is periodically buried back in the coal mine with the flue ashes. 

The compressor can be driven by electric motors, gas or steam turbiaes, or internal combustion (usually diesel) engines. The compressor can also be a steam-driven ejector (Fig. 7b), which improves plant reUabiUty because of its simplicity and absence of moving parts, but also reduces its efficiency because an ejector is less efficient than a mechanical compressor. In all of the therm ally driven devices, turbiaes, engines, and the ejector mentioned hereia, the exhaust heat can be used for process efficiency improvement, or for desalination by an additional distillation plant. Figure 8 shows a flow diagram of the vertical-tube vapor compression process. 

The saturation temperature of a vapor rises when it is mechanically compressed and its latent heat is available at a higher temperature. AppHcation of this heat to an aqueous stream evaporates part of the water, producing a distillate of pure water. AppHcation of vapor compression has grown significantly since 1960. 

FIG. 13-2 Complex distillation operations with single columns, a) Use of intermediate heat exchangers, (h) Coupling of intermediate heat exchangers with heat pump, (c) Heat pump with external refrigerant, (d) Heat pump with vapor compression, (e) Heat pump with hottoms flashing. 

Multidentate V-heterocyclic ligands, thorium and, 24 767 Multidimensional gas chromatography, 4 617-618 6 433-434 Multidrug resistant bacteria, 18 252 Multi-effect distillation (ME), 26 65—67 Multi-effect vapor-compression submerged-tube desalination plant, 26 70 Multielevation piperacks, 19 515 Multifeed fractionation, 10 616 Multifilamentary superconductor, 23 846 Multifilament sutures, 24 218 threads for, 24 207 Multifilament yarns, 11 177-178 Multifile patent searches, 18 244 Multifunctional aliphatic epoxies, 10 376 Multifunctional coatings, 1 714-716 Multifunctional epoxy resins, 10 367-373, 418, 454... 

All commercial types of processes, with the exception of freezing, namely, distillation, reverse osmosis and electrodialysis, are being applied in the above units with various kinds of distillation processes being used for seawater desalting. Two of them, horizontal tube multieffect distillation and vapor compression units were developed and manufactured locally by the Israel Desalination Engineering Ltd. Recently, two small RO units with a combined capacity of approx. 100 cu. m/day were also used to desalt seawater. The main aim of these units is to test and demonstrate the feasibility of this new technology. 

This is a process mainly used in power plants for separation of dissolved matters by evaporation of the water. Multistage flash distillation, multiple-effect vertical long-tube vertical evaporation, submerged tube evaporation, and vapor compression are effective process equipment. It may require pH adjustment. The process removal efficiency is about 100%. 

Vapor compression uses the reverse principle of multieffecl distillation. As a vapor is compressed, its temperature and pressure increase. The compressed vapor can be used instead of fresh steam as a heat source at the high-temperature end of the distillation process. 

A question that arises in connection with distillation processes is How does a vapor-compression process compare with a multiple-effect evaporation process on the basis solely of energy cost This is readily answered as follows. The work of compression as kilowatt-hours per 1000 gallons is given by a specific form of Equation VIII. 134... 

A variety of desalting technologies has been developed over the last 40 years. Based on their commercial success, they can be classified into major (viz., multistage flash distillation, MSFD multiple-effect distillation, MED vapor compression, VC ED RO) and minor (i.e., freezing, membrane distillation solar humidification) processes. 

Vapor compression stills of various sizes are commercially available and can be used to produce water of high purity when properly constructed. A high-quality distillate, such as water for injection, can be obtained if the water is first deionized. The best stills are constructed of types 304 or 316 stainless steel and coated with pure tin, or are made from chemical-resistant glass. 

The low distribution coefficients, the attendant requirement of recycling CO2 containing very little ethanol in order to achieve a high recovery of ethanol from the feed stream, and the inability to achieve the separation of ethanol from the extract stream by pressure letdown required the development of this SCF extraction-distillation process. The diagram shown in figure 8.14 pictorially summarizes that an old distillation technique can be combined with new supercritical CO2 extraction to solve the separation problem supercritical CO2 can extract the ethanol from the feed stream, distillation can separate and regenerate the solvent for recycle, and vapor compression can achieve energy efficiency. 

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

Figure 16-2 Distillation column with heat pumping by overhead vapor compression.

---