Scrubber Cleanings

A scrubber cleaning process can be optimized by adjusting the brush and wafer rotation speed, the DI water/chemical flow rate, and the gap between the brush and the wafer surface. Because brush cleaning is based on the mechanical pressure applied to the wafer surface, the brush must be compressed to the wafer surface to have either direct or semidirect contact with the wafer to effectively remove fine particles. 

Figure 10-29 is an example of a commercially available system for the determination of mercury. The sample is placed in the sample bottle, diluted to about 100 ml, and treated with stannous chloride. The sample bottle is placed into the system as shown in the figure. The air pump is turned on and in about 30 sec an equilibrium concentration of mercury is produced in the absorption cell and mercury absorbance is then determined. After the absorbance is read, the T valve is adjusted so the air stream passes through the scrubber. The scrubber cleans the system to prepare it for another mercury determination. 

Despite their potential for increased collec tion efficiency, fiber-bed scrubbers have had only limited commercial acceptance for dust collec tion because of their tendency to become plugged. Their principal use has been in small units such as engine-intake-air cleaners, for which it is feasible to remove the fiber bed for cleaning at frequent intervals. 

Shared equipment Design to avoid or minimize use of (e.g. auxiliary process- common equipment for incompatible ing scrubbers ). Pos- materials sihility of incompatible, Implement proper cleaning procedure materials coming between incompatible uses to prevent together. cross contamination Prescrub or treat process streams before transfer to common equipment API RP 750 CCPS G-11 CCPS G-22 Kletz 1991 Lees 1996 NFPA-91... 

The electric arc furnace process accounted for about 25% of the 1982 U.S. steelmaking capacity (14). Most of the raw material used for the process is steel scrap. Pollutants generated by the electric furnace process are primarily particulate matter and CO. The furnaces are hooded, and the gas stream containing the particulate matter is collected, cooled, and passed to a bag-house for cleaning. Venturi scrubbers and ESPs are used as control devices at some mills. Charging and tapping emissions are also collected by hoods and ducted to the particulate matter control device. 

The power consumed to operate a wet electrostatic precipitator is much less than that required by most other methods of control. There are four areas in which power is consumed (1) electrostatic power, (2) fan power, (3) insulator heating power, and (4) pump power. The total electrostatic power input required for operation is 0.8 to 1.0 kW/1,000 ft of collection area. A comparable piece of equipment is a venturi scrubber with 50-in.wg pressure drop. The power required for this installation would be 6 to 7 kW/1,000 cfm. This would mean that approximately seven times the power would be needed to achieve the same amount of cleaning with a venturi scrubber as opposed to using a precipitator. 

Foam scrubber A cleaning device that uses foam as a collecting medium for particulate matter in a gas stream. 

Optimum droplet size The idea size of a water droplet in a centrifugal spray scrubber or spray tower to ensure the highest possible cleaning efficiency. 

Wet scrubbers have found widespread use in cleaning contaminated gas streams because of their ability to effeetively remove both particulate and gaseous pollutants. Specifically, wet scrubbing describes the technique of bringing a contaminated gas stream into intimate contact with a liquid. The types most widely used for particulate control are spray towers, packed-bed units, ionizing wet scrubbers, and venturi scrubbers. 

The high temperatures ensure that inputs like MPW are effectively destroyed. Acidic substances such as HCl and SOx are neutralised by the alkali raw materials, which act in fact as a caustic scrubber. Metals are bound in the clinker or in the fly ash. Fly ash is captured with an electrofilter and subsequently added to the clinker. In general, no other flue gas cleaning is applied. 

Methods of dust removal depend mainly on the particle size of the dust and the temperature and moisture content of the gas. The methods used are broadly divided into dry methods and wet methods. The dry methods involve the use of gravity and baffle chambers, cyclones, filters, and electrostatic precipitators, while the wet methods involve the use of spray towers and venturi scrubbers. In principle, wet cleaning is preferred to dry cleaning because of the excessive wear associated with and the difficulty in handling the fine dusty material removed in the dry methods. The wet methods, however, must be followed by such operations as filtration, drying of filter cakes, and recycling of water. 

Largest source gas cooling water and scrubber water for gas cleaning Typical water flows ... 

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