Liquid scrubber system

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

A typical emergency scrubber system consists of a scrubbing column (often filled with packing), recirculating liquid pumps, solvent cooler, and in some cases (where the entering effluent gas/vapor is at a low pressure) exhaust blowers (see Fig. 23-57). Redundant equipment and instrumentation is usually provided to ensure reliable scrubber operation at all times. 

In 1974 Midwest Research Institute operated a pilot-scale multiple chamber incinerator to evaluate for EPA the operational variables for pesticide incineration (8). The system included a. pilot-scale incinerator, a three-stage scrubber system, and a scrubber water treatment system. Nine pesticides (aldrin, atrazine, captan, DDT, malathion, mirex, picloram, toxaphene, and zineb) in 15 liquid and solid formulations were studied. Destruction efficiencies generally exceeded 99.99% over a range of temperatures and retention times ( 950 to 1100°C, 1.2 to 6 s, and 80 to 160% excess air). This study also documented the generation of measurable quantities of cyanide in the incinerator off-gas during the incineration of organonitrogen pesticides. 

Almost all particle-separating devices can be converted into wet scrubbers by adding liquid spraying systems. Three types of commonly used scrubbers are the spray chamber, cyclonic scrubber, and venturi scrubber. Figure 7.18 shows a simple spray chamber in which water is sprayed through a series of nozzles into a settling chamber. The dust-laden gas is fed from the bottom of the chamber and exits from the upper portion of the chamber. 

What of the death toll The most conservative estimates were 3,000 at the time, with about 200,000 injured. More recent estimates suggest that 16,000 people may have died as a result of the accident. How did it happen The factory, which was owned by the American Union Carbide company, was making Sevin, or carbaryl, an insecticide. Methyhsocyanate was one of the components of the synthesis, of which a large amount was stored in a tank. It seems that water was able to enter the tank via a newly fitted pipe because of a faulty valve. The water caused a reaction when it mixed with the methyhsocyanate, producing heat, which raised the temperature to such an extent that the liquid chemical boiled and was converted into a gas, which overwhelmed the containment system. It seems there was no trap to contain the excess, no flare system, and the scrubber system was overloaded. It was clear that the safety systems were inadequate. 

The solids concentration of the underflow from the clarifier-thickeners is between 20 and 40 wt % and is not concentrated enough for transportation by either trucks or railroad cars to the disposal areas. For this reason vacuum filters are usually used to concentrate the underflow to 60-80 wt % solids. Ponds are also being used to store solids and to accomplish solid-liquid separation. C-E is doing developmental work to determine the leaching characteristics of the sulfur compounds present in the sludge and also to determine the most suitable filtration system for lime/limestone wet scrubber systems. 

Total liquid in the scrubber system in the pilot equipment is maintained at about 16 liters. The raw solution in the scrubber is recycled to the distribution plate at rates from 0.2 to 0.7 gal/min. The filtered portion that flows through the monitoring instruments and the cooling spray are maintained constant at a rate of 0.2 gal/min. Flow of solution to the regenerator is controlled from 0 to 4.2 liters/hr, depending on the rate at which ammonia is needed for the vapor-phase reaction. 

Contact power theory is an empirical approach relating particulate collection efficiency and pressure drop in wet scrubber systems. The concept is an outgrowth of the observation that particulate collection efficiency in spray-type scrubbers is mainly determined by pressure drop for the gas plus any power expended in atomizing the liquid. Contact power theory assumes that the particulate collection efficiency in a scrubber is solely a fimction of the total power loss for the unit. The total power loss, is assumed to be composed of two parts the power loss of the gas passing through the scrubber, q, and the power loss of the spray liquid during atomization, The gas term can be estimated by... 

In this gas scrubber system the liquid absorbs particulate contaminants and also removes any electrolyte aerosols that flow out of the electrolyzer with the gas. Distilled water is very effective at removing the electrolyte from the gas, but the addition of vinegar also neutralizes the KOH, which enhances the scrubbing process greatly. 

A number of regulatory issues were raised by the Army s test results for the MCG/PLASMOX technology that must be resolved before it could be permitted in the United States. These include improvements to the gas scrubber system, more complete knowledge of the fate of key components of the non-stockpile CWM (e.g., phosphorus), and better characterization of the solid, liquid, and gaseous secondary waste streams. 

The scrubber system consists of the scrubber, a liquid recirculating system, and sometimes a mist... 

When the demand for vapor is higher, apparatus designed for this purpose becomes necessary. This section discusses design and operation of such vaporizers. Not all plants operate vaporizers, but these units still account for a large fraction of the releases of chlorine that producers and users report. Vaporization is relatively a more frequent operation among users who do not produce chlorine. In many cases, vaporization becomes a batch operation, which lacking a steady state can be more hazardous. Many incidents have resulted from overloading a scrubber system with liquid [75]. The relative lack of experience and sophistication on the part of some operators may help to account for... 

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. 

Carbon monoxide and methanol from the scrubber unit are fed to the reactor containing the catalyst and the solvent. The liquid product stream is depressurized in a flash vessel and divided in a gas and liquid phase. In this step the rhodium catalyst is separated from the crude acetic acid and is recycled to the reactor. It is critical for the process economics to avoid any rhodium metal loss in this step that could occur by precipitation and vaporization. The gas stream is scrubbed with methanol to recover the toxic and volatile methyl iodide and the off-gas of the scrubber system is flared. The liquid phase is sent to the light ends column (separation of light compounds, e.g., methyl iodide and methyl acetate). The bottom of this column (catalyst, water, and acetic acid) is recycled to the reactor. Wet acetic acid is sent to the drying column and dried acetic acid is obtained as bottom product. The overhead (mixture of acetic acid and water) is recycled back to the reactor. In the product column heavy by-products (major liquid by-product propionic acid) are removed from the dried acetic acid. The overhead is sent to the finishing column, where ultrapure acetic acid is obtained as a side-stream. 

A fixed roof tank contains liquid with a vapor space above it, as illustrated in Figure 12.1. When the tank is being filled, vapors are discharged through the vent. If the vapors are hazardous or detrimental to the environment, they will be discharged to a scrubber system and/or a flare. The vent must be big enough to handle the maximum flow of liquid into the tank, as demonstrated by two Process Safety Beacon reports CCPS (2002) and CCPS (2003) in which the vents were not big enough and tank rupture occurred. 

Figure 4.5 Some Effluent Removal Systems (a) Liquid Scrubbers, (b) Thermal Decomposition-Pyrolisis Scrubber, (c) Combustion, Liquid, Catalysis Scrubber System...

Table 14-2 illustrates the observed variations in values for different packing types and sizes for the COg-NaOH system at a 25 percent reactant-conversion level for two different liquid flow rates. The lower rate of 2.7 kg/(s-m ) or 2000 lb/(h-ft ) is equivalent to 4 (U.S. gal/min)/ft and is typical of the liquid rates employed in fume scrubbers. The higher rate of 13.6 kg/(s-m ) or 10,000 lb/(h-fU) is equivalent to 20 (U.S. gal/min)/ft and is more typical of absorption towers such as are used in CO9 removal systems. For example. We note also that two different gas velocities are represented in the table, corresponding to superficial velocities of 0.59 and 1.05 m/s (1.94 and 3.44 ft/s). 

RooBng plants (asphalt saturators) Felt or paper saturators spray section, asphalt tank, wet looper Crushed rock or other minerals handling Asphalt vapors and particulates (liquid) Particulates (dust) Exhaust system with high inlet velocity at hoods (3658 m/s [>200 ft/min]) with either scrubbers, baghouses, or two-stage low-voltage electrostatic precipitators Local exhaust system, cyclone or multiple cyclones... 

Fhix-force-condensation scrubbers combine the effects of flux force (diffiisiophoresis and thermophoresis) and water-vapor condensation. These scrubbers contact hot, humid gas with subcooled liquid, and/or they inject steam into saturated gas, and they have demonstrated that a number of these novel devices can remove fine particulates (see Fig. 25-24). Although limited in terms of commercialization, these systems may find application in many industries. 

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