Economics solvent recovery

Put in the necessary hooding, ducting, and equipment for a solvent recovery system which will decrease the atmospheric pollution and also result in some economic solvent recovery,... 

Begin with a single solvent, if possible, since it simplifies the separation system and permits economical solvent recovery. 

The component C in the separated extract from the stage contact shown in Eigure 1 may be separated from the solvent B by distillation (qv), evaporation (qv), or other means, allowing solvent B to be reused for further extraction. Alternatively, the extract can be subjected to back-extraction (stripping) with solvent A under different conditions, eg, a different temperature again, the stripped solvent B can be reused for further extraction. Solvent recovery (qv) is an important factor in the economics of industrial extraction processes. 

DifficultSepa.ra.tions, Difficult separations, characterized by separation factors in the range 0.95 to 1.05, are frequentiy expensive because these involve high operating costs. Such processes can be made economically feasible by reducing the solvent recovery load (260) this approach is effective, for example, in the separation of m- and -cresol, Hnoleic and abietic components of tall oil (qv), and the production of heavy water (see Deuteriumand TRITIUM, deuterium). 

Economic Aspects. The 1992 MEK nameplate capacity for the United States, East Asia, and Western Europe is Hsted in Table 5. During the period 1980—1989 MEK achieved a negative growth rate as demand dropped from 311,000 (48) to 228, 000 t/yr (49). Stricter VOC regulations were largely responsible for the decline, and the trend will continue as solvent recovery and recycling, as well as substitution away from MEK, take effect. 

Solvent Recovery. Most of the activated carbon used in gas-phase applications is employed to prevent the release of volatile organic compounds into the atmosphere. Much of this use has been in response to environmental regulations, but recovery and recycling of solvents from a range of industrial processes such as printing, coating, and extmsion of fibers also provides substantial economic benefits. 

Engineering Considerations To effect the good engineering design of an activated carbon adsorption system, it is first necessary to obtain information on the following the actual cubic feet per minute (ACFM) of air to be processed by the adsorber, the temperature of gas stream, the material(s) to be absorbed, the concentration of the material to be adsorbed, and if the intended application is air pollution control such as odor control - then the odor threshold of the material to be adsorbed. In addition, data is needed on the presence of other constituents in the gas stream, and whether or not solvent recovery is economical. 

Skladany, G.J., J.M. Thomas, G. Fisher and R. Ramachandran. The Design, Economics and Operation of a Biological Treatment System for Ketone Contaminated Ground and Solvent Recovery Process Waters. Presented at the 42nd Annual Purdue Industrial Waste Conference, Purdue University, West Lafayette, Indiana, 1987. 

Many of these disadvantages may be overcome by modifications to the design, although these increase the cost, and often an indirectly heated dryer may prove to be more economical. This is especially the case when thermal efficiency, solvent recovery or maximum cleanliness is of paramount importance and, with indirectly heated dryers, there is always the danger of overheating the product, since the heat is transferred through the material itself. 

Solvent recovery is extremely important from the economic point of view. The solvents are recovered by various methods, dealt with in a separate section (p. 599). From the time the strips or tubes are extruded until they are loaded into the predriers a certain period of time elapses depending upon the type of plant, the method of operation etc. 

Extraction efficiency is not the only factor to be examined in the choice of solvent or reagent for a particular application. Environmental, as well as economic considerations must be taken into account. Solvents such as benzene and chloroform (which have solubilities of 0.07 and 0.82 parts per 100 parts of water) might be preferred for extractive efficiency, but their use would result in large losses to the aqueous phase. Not only would this be expensive, but it would be undesirable for reasons of health the toxic organo lead salts would be removed, but an equally toxic organic solvent would be added to the effluent. Addition of a solvent recovery unit subsequent to the extraction step might render the technique uneconomic (relative to alternative effluent treatment techniques). 

It is not practicable from an economic standpoint to reduce the solvent content of the proplnt to the desired degree in one opn, such as solvent recovery hence, the final drying is accomplished as a separate opn... 

Solvent recovery. The green powder contains a large amount of ether and alcohol which presents a twofold problem (1) the recovery of as much of the valuable volatile solvent as is economically feasible, and (2) the removal of the solvent to such an extent that the finished powder will not be disposed either to give off or to take up much volatile matter or moisture under changing atmospheric conditions. For the recovery of the solvent, the pow-... 

In the absence of a solvent-recovery method, entrainment is expected to be the major solvent-loss factor in all solvent-extraction applications [94], including CSSX [89], potentially amounting to several hundred ppm of the aqueous effluent. Solvent loss is known to be the economic determinant in most commercial solvent-extraction systems... 

Solvent recovery systems would also necessitate the specification of condenser duties, distillation tower sizes, holding tanks, piping, and valves. It is important to note that the engineering design of an adsorption system should be based on pilot data for the particular system. Information can usually be obtained directly from the adsorbent manufacturer. The overall size of the unit is determined primarily by economic considerations, balancing the operating costs against the capital costs. 

If the top product (water) from the solvent recovery column is to be discarded, the two distillation columns would be operated to reduce ethanol and ethylene glycol to low concentrations, as illustrated in the calculations shown here. However, where the overall plant scheme is such that the water product might be recycled and used—e.g, as solvent to an aqueous extractive distillation, it might under some conditions be more economical to leave more ethanol in the water product. The ethanol would be recovered in the series of separation steps which follow in the flow scheme. Water might be rejected at a more suitable point in the flow scheme than from the top of the solvent recovery column. The best operating conditions can be determined only when the entire plant flow scheme is known. 

Recovery of the solvent, sometimes by chemical means but more often by distillation, is almost always required, and the recovery system ordinarily is considered an integral part of the absorption-system process design. A more efficient solvent-stripping operation normally will result in a less costly absorber because ofa smaller concentration of residual dissolved solute in the regenerated solvent however, this may increase the overall cost of solvent recovery. A more detailed discussion of these and other economic considerations is presented later in this section. 

After operation and sales have been proven, the solvent recovery may be brought back in-house. A cost analysis of doing this in the third year improves the economic analysis. The estimate showed that the in-house solvent recovery could be done for 2M and would improve the profitability in the fourth year to 4.0M. The revised project, done in two phases, has an overall IRR of 42%, a payback of 2 years, and an NPV of 13.0M. 

---