Water wash processes

Figure 10-12 Toluene water wash process before formal safety review.

A toluene water wash process is shown in Figure 10-12. This process is used to clean water-soluble impurities from contaminated toluene. The separation is achieved with a Podbielniak centrifuge, or Pod, because of a difference in densities. The light phase (contaminated toluene) is fed to the periphery of the centrifuge and travels to the center. The heavy phase (water) is fed to the center and travels countercurrent to the toluene to the periphery of the centrifuge. Both phases are mixed within the centrifuge and separated countercurrently. The extraction is conducted at 190°F. 

Ammonia removal is the next step in the gas cleanup process. A typical approach is to contact the coke-oven gas with a solution of sulfuric acid to form ammonium sulfate, which is then recovered by crystallization, dried, and sold as fertilizer. More modem processes for ammonia removal include the water wash process, in which the coke-oven gas is scrubbed with water that dissolves the ammonia along... 

The process of extraction of oil with hot water was originally designed by K. A. Clarke and called the hot-water washing process for exploitation of Arthabasca bituminous tar sand [1, 2, 3 ]. The term hot water is used instead of steam or water vapor , because tbe operating temperature (around 90 °C) was maintained near tha water boiling point without ever reaching it [ 4 ]. 

There are basically two options in the purification, that is, the water washing process and adsorbent treatment process (water-free process). In the water washing process the main drawbacks are the amount of wastewater produced and the energy costs to evaporate and recover water for re-use. In the adsorbent treatment process the problems are the high cost of adsorbent (e.g., Mg-silicate) and the disposal of the spent adsorbents. A potential cleaner process should thus eliminate the catalyst cleanup step and simplify biodiesel and glycerol purification. The options are (i) the use of heterogeneous solid catalysts, (ii) the use of an enzymatic transesterification processes and (iii) a catalyst-free process, using, for example, supercritical methanol. 

Among various processes used for carbon dioxide removal, the Giam-marco-Vetrocoke, a hot potassium carbonate and water wash process, is the most efficient when the inlet C02 concentration was about 50% and the exit gas contained 2%. It was also found that when the exit stream contains a higher C02 level, the propylene carbonate process becomes the most economical. An amine-cleanup process was recommended for units where very low exit carbon dioxide concentrations are required. 

The temperature during cold water washing process is 20-25 °C, the time is 6 min. The temperature during warm water washing process is 30-35 °C, the time is 6 min. The stability temperature during washing process is 40-45 °C, the time is 6 min. 

In the cold water washing process the ratio of glycerinum and water is 1 1.2-1.5. 

Table 5.56 Parameters of stability treatment of pentaerythritol trinitrate in water-washing process...

Not all components are compatible with the water-wash process. Circuit board mounted switches are notable in this regard. Even some switches sold as environmentally sealed or water-wash-compatible have been found to leak during the high-pressure wash spray or submersion steps of aqueous cleaning. This can result in failure of the switch to work properly (the water causes an electrical short within the switch) or, if there is enough ionic content in the wash water or in the switch itself, switch contact corrosion may occur in the long term. 

IVpical Stream Compositions for Water-Wash Process for Ammonia Removal from Coke-Oven Gas... 

When any of the previously mmitioned irtqRnities are absorbed from a gas stream, smaU amounts of the primary gaseous components are also absorbed. This effect is particularly noticeable in high-pressure operations and can materially affect the economics of the water-wash process for such cases. Water-solubility data for components, which typically make up... 

The absorption of carbon dioxide in water at elevated pressure was formerly an important industrial process, particularly for the purification of synthesis gas for ammonia production. The process has now generally been replaced by more efficient systems which employ chemical or physical solvents with much higher capacities for carbon dioxide than water. Such systems are described in Chapters 2, 3, 3, and 14. A description of the water wash process for carbon dioxide removal is included in this chapter because of its historical interest, its technical value as a classical liquid film-controlled operation, and the hope that the extensive work done on the process will prove usefril in the development of new processes or applications. 

No nitrogenous solvent vapors introduced into the gas stream The principal disadvantages of the water-wash process are... 

In view of these disadvantages, the water-wash process is rarely used today for carbon dioxide removal. 

Although the water-wash process is simple, it has the drawback of producing a dilute sulfuric acid product, which is difficult to store, ship, or market. Concentration can be troublesome. There appears to be no further development of the Hitachi process (Behrens et al., 1984). 

Basically a water-washing process, the crude desalter must accomplish intimate mixing between the crude oil and water, then separate them sufficiently so that water will not enter subsequent crude-oil distillation heaters. 

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