Dispensing chemicals

Control is exercised by binary logic gates. These will prevent steps from being set in motion until the conditions under which they should become operative have been established. Thus, for example, the chemical dispense tanks cannot be opened until a specified temperature has been reached, irrespective of the time called for in the programme. 

BOC Edwards special gases vacuum, abatement and chemical dispensing systems all mainly for semiconductors ... 

Chemical dispensing areas can be protected with automatic sprinklers. The room should have sprinklers on an extra hazard density. They should be 286°F heads and have separate control valves. 

Finish removers are manufactured in open or closed ketdes. Closed ketdes are preferred because they prevent solvent loss and exposure to personnel. To reduce air emissions from the solvents, condensers are employed on vent stacks. Mild steel or black iron ketdes are used for neutral or basic removers stainless steel (316 or 317) or reinforced polyethylene ketdes are used for acidic removers. The ketdes are heated to increase dispersion of paraffin waxes and aid in the mixing of other ingredients. Electric or air driven motors drive either sweeping blade or propeller mixers that give sufficient lift to rotate and mix the Hquid. Dispenser-type mixers are used to manufacture thick and viscous removers. Ketde, fittings, mixer, and fill equipment must be fabricated with materials resistant to the chemicals in remover formulas. 

Sanitizer and Chemical Feeders. Eeeders dispense the chemicals in gaseous, Hquid, and soHd (both granular and compacted) forms. Many health departments require that pubHc pools have approved feeding devices for the daily appHcation of all chemicals, including saniti2ers. A slurry feeder for diatomaceous earth (DE) on diatomite filter installations may also be required. 

Provision of a defined quantity for dispensing and metering, as in agricultural chemical granules or pharmaceutical tablets. 

Other, more recently developed, uses include microwave oven parts, transparent pipelines, chemical plant pumps and coffee machine hot water dispensers. One exceptional use has been to produce, by an extrusion moulding process, very large rollers for textile finishing for use where cast nylons cannot meet the specification. Also of growing interest are medical equipment applications that may be repeatedly steam-sterilised at 134°C, filtration membranes and cartridges for ink-jet printers. 

In batch operations, mixing takes place until a desired composition or concentration of chemical products or solids/crystals is achieved. For continuous operation, the feed, intermediate, and exit streams will not necessarily be of the same composition, but the objective is for the end/exit stream to be of constant composition as a result of the blending, mixing, chemical reaction, solids suspension, gas dispension, or other operations of the process. Perfect mixing is rarely totally achieved, but represents the instantaneous conversion of the feed to the final bulk and exit composition (see Figure 5-26). 

Typically, chemical formulations were supplied as balls or briquets and dispensed through bypass feeders or hanging baskets. Alternatively, pulverized or powdered treatments were dissolved in water and pumped to FW tanks or added via drip-feed arrangements. 

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