Caustic soda scrubber

Pressure Water Scrubber CO2 HaS almost entirely absorbed. Caustic Soda Scrubber (NaOH 30°/ ), last traces COj HaS absorbed. 

Caustic soda scrubber Spent caustic solution High pH, alkalinity, and color. Extremely low average flow rate... 

In the steam-reforming process (Fig. 1), the hydrocarbon feedstock is first desulfurized by heating to 370°C in the presence of a metallic oxide catalyst that converts the organosulfur compounds to hydrogen sulfide. Elemental sulfur can also be removed with activated carbon absorption. A caustic soda scrubber removes the hydrogen sulfide by salt formation in the basic aqueous solution. 

Equipment designed to handle an MIC release included a recirculating caustic soda scrubber tower and a flare system designed for 10,000 lb/hr, which would be moderate flows... 

In the case of Bhopal, water entered into pipes on the floor of the factory during routine cleaning but safety slips had not been placed at the joints. Water reached Tank E-610. The exothermic reaction between water and MIC increased the temperature of the tank converting liquid MIC into gas. The increase in pressure forced open the vent valve letting most of the MIC escape to the outside as gas. Various safety measures to neutralize MIC, such as caustic soda scrubbers, were not functional or unserviceable. Even if safety measures had been in perfect workig order, they could not have handled such a big leak. Fortunately, MIC stored in the other two tanks (E-611 and E-619) was not affected it was later converted to pesticide in what was... 

Unconverted SOj, SO3 (mainly as sulphuric acid mist) and entrained organic acid are present in the exhaust gas and are the main potential atmospheric pollutants. The recommended practice is to use an electrostatic precipitator (ESP) to trap any particulate material in the form of mist or aerosols and a caustic soda scrubber which absorbs SO2 and small amounts gaseous SO3 that will pass the ESP. 

SO2 concentrations in exhaust gas leaving the sulphonation system will be, during steady-state operation, of the order of 2 000 mg/m assuming 98% conversion in the SO2-SO3 converter tower. However, during plant start-up, concentrations of the order of 50 000 mg/m may occur (see 5.9.2.). The level should be reduced to less than 5 mg/m SO. in the exhaust gas leaving,the caustic soda scrubber under steady-state conditions and about 15 mg/m during initial start-up PQnditions>... 

Sulphuric acid mist levels are directly related to the dew-point of the dried air (see 5.2.2.). Ihe sulphuric acid mist is effectively removed in the ESP and levels smaller than 10 mg/m ar guaranteed by ESP suppliers (see also 5.9.1. and 5.9.3.). Very small amounts of gaseous SO3 will pass the ESP but will be trapped in the caustic soda scrubber. 

Sodium hydroxide, caustic soda Electrolytic Chlorine Mercury Alkaline scrubbers Chemical scrubbing and adsorbers... 

Both scrubbers will be supplied with three sources of electrical power - the main grid supply, a back-up grid supply from a different substation and an emergency diesel generator. In the emergency chlorine scrubber, critical equipment items will be backed-up by automatic start-up of stand-by equipment. A gravity head tank of caustic soda and a nitrogen ejector will also be provided to allow safe neutralisation of chlorine vents in the event of total power failure. 

The abatement of chlorine vents and the subsequent destruction of the resulting sodium hypochlorite has been the subject of many studies. There are a variety of approaches to the waste hypochlorite destruction including chemical dosing, homogeneous and slurry catalysis as well as fixed-bed catalysis. For the most part these processes treat the hypochlorite at its natural strength the stoichiometric equivalent strength of the caustic soda fed to the scrubber. 

The schematic shown in Fig. 43(a) is a commercial example of this technology. Stack gas is scrubbed with an alkaline solution of sodium hydroxide, sodium sulfite, and sodium sulfate. The sodium sulfite reacts with SO2 in the stack gas to form sodium bisulfite. This salt solution is processed in a bipolar membrane unit [Type (I) shown in Table IX] to generate an alkaline solution and an acidic solution. The alkaline solution contains regenerated caustic soda and sodium sulfite, and can be recycled to the scrubber, while the sulfurous acid can be further processed to sulfur or sulfuric acid for sale. 

For a period of time just after startup, the piping upstream of this compressor operated under a vacuum. This upstream piping was equipped with a set of double block and bleed valves to a scrubber that circulated diluted caustic soda. During this unusual startup configuration, moisture was sucked into the system and the wet chlorine completely dissolved the stainless steel ball within the 3-inch (7.6 cm) quarter-turn valves. 

The most intriguing question is why the plant s safety equipment and controls, which should liave been designed to cope with a chemical tliat is known to be subject to violent reactions, did not work. Tlie MIC tank liad tliree safety devices. A pipe leading from tlie tank contained a valve tliat was set to rupture if the pressure in the tank e.xceeded 40 psi. Beyond the valve there were two other safety devices. One was a flare (tower) to bum escaping gas. The other was a vent gas scrubber, a tower packed with loose niaterial tlirough wliich a solution of caustic soda could be poured onto rising MIC to decompose it. On December 3, 1984, tlie operator of the factory s control room noticed tliat the pressure in tlie MIC tank (see Figure 1.3.2) luid risen from 2 to 30 psi, and in a... 

Eight of the Bahco scrubbers are located on oil-fired boilers in pulp mills. The boilers range in size from 50,000 to 375,000 Ibs/hr of steam and produce 10,000-145,000 ACFM of oflF-gas at about 340°-360°F. Each of these units operates with caustic soda as the scrubbing reagent. The units operate at a controlled pH of 6.5 which maximizes the production of sodium bisulfite and limits unwanted sulfate oxidation. The soluble bisulfite product is utilized in the pulping operation. Particulate and mist concentrations are held to about 0.02 grain/SCFW and SO levels are reduced by 97-99% from about 1500 to about 30 ppm. These units have operated continuously without any operational upsets. 

Venturi scrubbers are designed on the basis of the venturi flow-metering device. The flow channel is narrowed down so that the velocity will greatly increase at the throat. Then, as in the flow-metering device the flow channel widens ouf. For ease of fabricalion venturi scrubbers are designed with a rectangular cross section. The absorption fluid is injected into the Venturi at the throat where the velocity is the greatest. For particulate removal plain water could be used. As in the plate columns discussed above, for the simultaneous removal of particulate matter and sulfur dioxide, soda ash or caustic soda slurries could be used for absorption of the gas. Venturis are frequently used in conjunction with plate towers. They also serve as stand-alone removal devices in some cases. 

Natural gas from a gas well can be passed through an alkali scrubber to remove H2S gas and the alkali solution in the scrubber fed to an electrolyzer to recover caustic soda as catholyte and to precipitate sulfur in the anode compartment together with the generation of hydrogen gas.157... 

In this process, oxides of sulfur are absorbed in caustic soda. The reactions in the scrubber (29.4-29.7) produce soluble reaction products. The solution from the sump of the absorber is treated in a separate reaction vessel with lime (Fig. 29.2). 

Carbon tetrachloride wastes may be destroyed by mixing with vermiculite, caustic soda, and slaked lime, followed by burning in a chemical incinerator equipped with an afterburner and scrubber. Incomplete combustion may produce chloroform (Thumau... 

As shown in Figure 4.21, the salt that is formed from tertiary amine (e.g. DMEA, DMIA and triethanolamine (TEA)) in the acid scrubber, and the scrubbing acid (e g. sulphuric acid) are retransformed by reaction with a strong base (e.g. caustic soda solution), thereby forming free amine and e.g. sodium sulphate. The amine is expelled with water vapour and is then cleaned and concentrated in a column, to an extent that allows it to be re-used. The sodium sulphate solution (together with polluted scrubbing solution) can be recovered or may be disposed of. 

Venturi scrubbers followed by packed towers is the most common system used for sulfuric acid wherein the level of pH of the scrubbing liquor is automatically maintained at around 8.0-8.5 by addition of caustic soda solution at a controlled rate. An online pH meter is employed with a control valve for this purpose. 

A number of metallic ions were identified including chromium and nickel, which suggested that the stainless steel had been attacked by the reaction. This would have released catalytic material and accelerated the reaction still further. There were also significant quantities of sodium which indicated that some caustic soda from the scrubber had found its way into the tank. 

Provide induced draught fans and scrubbers for necessary equipments to suck out any toxic and inflammable vapours in working areas (e.g. electrolysis cells for chlorine/caustic soda plants). 

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