Caustic scrubber systems

Caustic scrubber systems should be installed to control chlorine emissions from condensers and at storage and transfer points for liquid chlorine. 

This chapter has therefore shown that cost minimisation of the treatment of hypochlorite effluent streams is achieved only through consideration of a wide range of process alternatives. The optimal solution for a given plant is dependent on a number of aspects, which include not only the rate and concentration of the stream as well as its required exit concentration, but also the configuration and operational mode of the caustic scrubber and any existing treatment system. 

Compounds containing sulfur and cyanide become a potential source of air pollution when treated with this system. A caustic scrubber may be required to capture the combustion products of these compounds if sulfur and cyanide levels are high enough to exceed health and safety or applicable air quality standards. Metals that are not particularly volatile are not likely to be treated effectively by the TDS. Plastic materials are not recommended for treatment since their decomposition products could cause plugging or foul surfaces. 

Fig. 38. Caustic purification system, a, 50% caustic feed tank b, 50% caustic feed pumps c, caustic feed preheater d, amonia feedpumps e, ammonia feed preheater f, extractor g, trim heater h, ammonia subcooler i, stripper condenser j, anhydrous ammonia storage tank k, primary flash tank 1, evaporator reboiler, m, evaporator n, caustic product transfer pumps o, purified caustic product cooler p, purified caustic storage tank q, ammonia stripper r, purified caustic transfer pumps t, overheads condenser u, evaporator v, evaporator vacuum pump w, aqueous storage ammonia tank x, ammonia scrubber y, scrubber condenser z, ammonia recirculating pump aa, ammonia recycle pump. CW stands for chilled water.

It is recommended that any plant which makes or uses phosgene in large quantities should be provided with two separate scrubber systems. A fume scrubber (to handle low phosgene concentrations diluted with a large volume of inerts) and a caustic scrubber (to handle higher phosgene concentrations). The fume scrubber is a general suction service for... 

For aqueous systems such as acid gas scrubbers and caustic scrubbers (where mercaptans are removed from gasoline), hydrophobic silicas or polyglycols are used. The specific chemistries and applications for both aqueous and nonaqueous foaming situations will be discussed. 

Caustic Scrubbers and Sour-Water Strippers. Caustic scrubbers and sour-water strippers are used to remove sulfur from a variety of products, gases, and waste streams. Foaming is a fairly common occurrence in these systems because of contaminants found in the streams. 

The offgas treatment system includes a cyclone for removal of large particulates and a flameless thermal oxidizer that converts carbon monoxide and hydrogen to carbon dioxide and water. This is followed by a fast quench system to minimize dioxin and furan formation, acidic and basic (caustic) scrubbers, and an adsorber/ particulate filter system that uses Sorbalite, a mixture of calcium oxides and carbonates with activated carbon. 

Large quantities of fluorine can be disposed of with large burners and scrubbers, or charcoal systems. Turnbull reports the disposal of 125 lb of fluorine per hour in a 10-in. ring-type burner followed by 30-ft water and caustic scrubbers packed with 2-in. carbon rings. ... 

The caustic-circulating system for the scrubber has two pumps, one of which serves as a spare. The caustic solution for the scrubber is supplied from a caustic mixing tank where the solution is prepared as required to replace the depleted caustic solution in the scrubber. To provide for periodic sampling of the caustic solution a tap is provided at the bottom of the reservoir. 

Applications for coolers include caustic being transferred to Storage, low-concentration solutions prepared by exothermic dilution, circulating caustic in vent scrubber systems, and full-concentration process applications. Stainless steel plates are used frequently at temperatures up to about 60°C. Nickel or one of its alloys is the... 

Restricting the caustic concentration to improve the quality of bleach can make a scrubber system uneconomically large or unreliable in an emergency, where the available caustic may be insufficient to prevent a breakthrough of chlorine gas. 

This system is used when the sulphuric acid produced can be utilised locally or easily sold to third parties. The sulphuric acid produced is of an excellent technical grade. The SO3 absorber tower is also used in emergency situations so that the S03/air flow can be diverted immediately to the absorber tower, preventing a complete plant shut-down procedure. The SO2 in the partially converted mixture will be absorbed in the caustic scrubber, which is part of the exhaust gas cleaning system. The design of the SO2 absorber should be adequate to absorb SO2 effectively during the start-up stage. 

The SO2 in the partially converted mixture will be absorbed in the caustic scrubber, which is part of the exhaust gas cleaning system. 

The absorption efficiency of the scrubber is dramatically reduced by the presence of any active detergent. The theory is that the active forms a boundary layer between the gas-phase and the caustic, preventing or at least limiting contact. Also, foam formation will hamper normal operation of the scrubber. Hence for the efficient operation of the scrubber system, the ESP s primary function is to prevent the active contamination of the scrubber liquor, i.e. all organic acid mist and droplets should be trapped in the ESP. 

The liquid effluent leaving the SO2 scrubber consists of a solution of caustic soda, sodium sulphite, sodium sulphate and traces of active matter. At 98% SO2 SO3 conversion (steady-state running conditions) about 80 kg/h of a 10% sodium sulphite solution will leave the scrubber system, based on a 10(X) kg/hr sulphonation plant (see table 19). The alkaline solution is collected in an acid/caustic-resistant pit. It is common practice to dilute this liquid stream with other effluent streams (ex slurry-making and powder manufacture) and to re-use it in the detergent powder manufacturing plant as dilution water. 

Disposal of boron trifluoride may be accomplished by slowly discharging the gas into a countercurrent flow caustic scrubber or other suitable vessel containing approximately 15-35 percent potassium hydroxide or other caustic solution. The system must contain a vacuum break, reverse flow trap, or check valve to prevent caustic solution from drawing back into the cylinder. 

In order to examine the hydrocarbon contaminant problem in an air separation plant, we may refer to Figure 1, Some contaminants in the entering air will be removed in the prepurification system, in the compressor interstage separators, in the caustic scrubber or other carbon dioxide removal system, in the adsorptive driers, and in the heat exchanger circuit, or in the regenerators of a low-pressure cycle. Those contaminants which pass these points will enter the high-pressure column where they will be washed into the enriched air stream and pass to the hydrocarbon adsorbers. The adsorbers will have substantial capacity for all hydrocarbons except methane. Most of the methane and traces of other hydrocarbons will pass on to the low-pressure column. They will be scrubbed down the column to the reboiler-condenser and, in a cycle as pictured, be continuously removed with the product oxygen. 

In the feed preparation step, uranyl sulfate solution from the reactor core and thorium oxide from the blanket system, freed of D2O and suspended in ordinary water, are fed into the dissolver tank. The di.s.solvent is 13 N nitric acid to which has been added catalytic amounts (0.04 N) of sodium fluoride. When short-cooled thorium is being processed, potassium iodide is added continuously to the dissolver to provide for isotopic dilution of the large amount of fission-produced which is present. The dissolver solution is continuously sparged with air, and the volatilized iodine is removed from the off-gases in a caustic scrubber. 

A scrubber has a closed-loop recycle of caustic. The make-up caustic solution is added continuously on an ORP (oxidation-reduction potential) controller. The caustic concentration will typically be 20 wt% and thus the blow-down stream will contain approximately 15 wt% hypochlorite. Such a system will typically be provided with a large reservoir of caustic that is released on a once-through basis for containment of emergency relief streams or operated with a permanent excess of caustic, resulting in a hypochlorite concentration in the blow-down stream in the range of 6-12 wt%. 

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