Gases stripped from process water

Ammonia, H2S, HCN, phenols and oily matter commonly are stripped from process water and then are processed in by partial oxidation under carefully chosen conditions to produce a gas suitable for further Claus processing. 

B. Chlorinated Condensate. An important aspect of chlorine cooling is the composition of the condensate. The water removed from the gas, or in the case of direct cooling of the cooling water as well as that condensed, will be saturated with chlorine. This water is often a process waste, and it must be made innocuous before discharge. Usually, the bulk of the chlorine is stripped from the water after adding acid to reverse its hydrolysis. Hie basics of dechlorination of aqueous streams were covered in the chapter on brine treatment (Section 7.5.9). 

The bottoms from the stripper (40—60 wt % acid) are sent to an acid reconcentration unit for upgrading to the proper acid strength and recycling to the reactor. Because of the associated high energy requirements, reconcentration of the diluted sulfuric acid is a cosdy operation. However, a propylene gas stripping process, which utilizes only a small amount of added water for hydrolysis, has been described (63). In this modification, the equiUbrium quantity of isopropyl alcohol is stripped so that acid is recycled without reconcentration. Kquilibrium is attained rapidly at 50°C and isopropyl alcohol is removed from the hydrolysis mixture. Similarly, the weak sulfuric acid process minimizes the reconcentration of the acid and its associated corrosion and pollution problems. 

Most glycol dehydration processes are continuous. That is, gas and glycol flow continuously through a vessel (the contactor" or absorber ) where they come in contact and the glycol absorbs the water. The glycol flows from the contactor to a reboiler (sometimes called "reconcentrator or regenerator where the water is removed or stripped from the glycol and is then pumped back to the contactor to complete the cycle. 

Drizo A variation of the glycol process for removing water vapor from natural gas, in which the water is removed from the glycol by stripping with a hydrocarbon solvent, typically a mixture of pentanes and heavier aliphatic hydrocarbons. The process also removes aromatic hydrocarbons. Last traces of water are removed from the triethylene glycol by stripping with toluene in a separate, closed loop. Invented in 1966 by J. C. Arnold, R. L. Pearce, and H. G. Scholten at the Dow Chemical Company. Twenty units were operating in 1990. U.S. Patent 3,349,544. 

The GS enriching process is a counter-current gas-liquid extraction done at a pressure of 2000 kPa in a sieve tray tower with the upper half operating at 30 C and the lower at 130 C. ( 5) In the top half of the tower, feedwater extracts deuterium from the upflowing cold H2S, reaching a maximum at the centre of the tower. The recycled lean H2S entering the lower hot half of the tower strips deuterium from the water, which then leaves the system depleted in deuterium. A cascade of several stages is used to reach the desired feed concentration for the final water distillation or finishing unit. Transfer between cascades can be either by gas or liquid from the centre of the tower. 

Volatilization from surface waters is not expected to be a significant source of isophorone in the atmosphere, since this is anticipated to be a slow process (based on the Henry s Law Constant of 4.55x10 atm m mol"). Wastewater treatment plants may, however, emit some isophorone from influent water to the air, particularly if gas stripping methods are used (Hawthorne and Sievers 1984, Hawthorne et al. 1985). Drinking water plants that practice aeration of influent water may also emit small amounts of isophorone to air. 

In such processes, the creation of a permanent gas phase by means of an (inert) gas allows a low-boiling compound (often water) to be stripped from the liquid phase at temperatures lower than the reactant boiling points. 

The tar and liquor plant handles the flushing liquor that circulates between the byproduct plant and the primary cooler. It also processes the wastewater that results from recovery of the coal moisture and chemically bound water in the coal. The flushing liquor flows into tar decanters, where the tar separates from the water and is pumped to storage for later sale. Heavier solid particles separate from the tar and are removed as tar decanter sludge. After withdrawal of a bleed stream that contains ammonia, the aqueous liquor is pumped back to the primary cooler. Following removal of tar particles, the wastewater stream is steam stripped. An alkali, such as sodium hydroxide, is added to decompose ammonia compounds dissolved in the liquor. The ammonia vapor is recovered and combined with the rest of the ammonia recovered from the coke-oven gas. 

After final cooling by air or cooling water, the synthesis gas is compressed (6) and sent to the synthesis loop (7). The synthesis loop is comprised of a straight-tubed boiling water reactor, which is more efficient than adiabatic reactors. Reaction heat is removed from the reactor by generating MP steam. This steam is used for stripping of process condensate and thereafter as process steam. Preheating the... 

The volatile hydrogen sulfide (b.p. —60.7°C) is then separated as an overhead gas stream. The monoethanolamine (b.p. 170°C) and diethylene glycol (b.p. 245°C) emerge as a regenerated solution, hot, from the bottom of the stripping column. To conserve heat, the hot, H2S-lean monoethanolamine stream from the stripper is heat exchanged with the cooler H2S-rich stream from the base of the absorber, sometimes with additional cooling with process water before it enters the absorber. 

Catalytic incineration (complete air oxidation) for the purification of gas streams is now quite commonly used in many applications (1-7), being preferred in these over thermal (non-catalytic) incineration and adsorption methods. It can offer advantages over thermal incineration in terms of costs, size, efficiency of destruction, and minimization of thermal NOx by-product formation. The catalytic incineration systems are now commonly employed in such applications as exhaust emission purification from a variety of industrial processes (including manufacture of organic chemicals and polymers) and air-stripping catalytic processes used to clean contaminated water or soil. 

The sour-water stripper removes contaminants from condensed water and wash water used in various process units. The water may then be reused, for example, as desalter wash water or to water-wash light gas streams. In this process, the contaminants such as H2S are removed by stream stripping of the water. Figure 9 is a general diagram of a sour-water stripper. 

---