Fume Exhaust System

Besides the air handling system, the cleanroom will have one or more fume exhaust systems. These will vent organics, corrosive oxidizers, and heat from the tools in a cleanroom and prevent their contaminating the clean air within the room. Many fabs have separate exhaust for each of the categories of chemicals. Since one of the objectives of the fume exhaust system is to prevent reaction of chemicals within the system, this is the most desirable means of exhausting the chemicals. 

Dedicated exhausts used for flammable vapors should be of ferrous construction. Flammable liquids do not have an adverse effect on materials so there is no reason to use plastic ducts. Flammable vapors could condense and the duct should be sprinklered. This condensation of the material could occur where the duct is subject to change in temperature or the solvent stream is subject to a change in velocity. 

The most desirable means of transporting the flammable liquids is to assure that the concentration of flammable vapors never exceeds 25% of the lower flammable limit. This can be designed into the system and then checked with a flammable vapor detector. 

Where corrosive chemicals are used, the fume exhaust or ordinary ferris construction would not stand up to the atmosphere. The duct should be of a special metallic duct designed for the specific atmosphere. Many corrosive atmospheres can be handled by stainless steel or other metal ducts. 

Metal ducts are also available with various plastic linings. These are effective for many additional chemicals but have some adverse characteristics. The thickness of the coating on the interior of the duct is extremely 

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Caution The digestion should be conducted in a fume hood, or the digestion apparatus should be equipped with a fume exhaust system. 

Copper Roasting S02, particulates, fume Exhaust system, settling chambers, cyclones or scrubbers and electrostatic precipitators for dust and fumes and sulfuric acid plant for S02... 

Reverberatory furnace Smoke, particulates, metal oxide fumes, Exhaust system, settling chambers,... 

Many derivatizing reagents are highly corrosive or toxic and the procedure is usually carried out using a simple spray in a spraying chamber or fume cupboard. The spraying-chamber must be made of some appropriate corrosion resistant material, usually a suitable plastic and connected directly to the laboratory fume exhaust system... 

Microwave digestion systems have become very popular for decomposing samples. The photo shown is a closed-vessel microwave digestion system for high-pressure digestions. A microwave oven with a built-in fume exhaust system is shown along with sample trays that contain up to 1 2 samples. Teflon sample vessels can be operated at temperatures up to 2300 C and 625 psi. 

Denning - The fluid material from the mixer goes to a den where it solidifies. Solidification results from the continued reaction and crystallization of monocalcium phosphate. The process is faster than-with SSP, and denning times of 10-30 minutes are suitable for TSP as compared with 30 minutes to 2 hours for SSP. Special belt conveyors are sometimes used for TSP rather than conventional dens. In any case, the belt or den must be enclosed and connected to a fume exhaust system to direct fluorine-containing gases to a scrubber. 

Diazomethane. CA UTION. Diazomethane is highly toxic its pre paration should be carried out only in a fume cupboard (hood) provided with a powerful exhaust system. The use of a screen of safely glass is recommended. 

A filter cake from the wringer is washed to remove absorbed acid, transferred to a slurry tank of water, and quickly submerged, after which the nitrocellulose is pumped to the stabilization operation as a diluted water slurry. Exhaust systems are installed to protect personnel and equipment from acid fumes, and water sprays and cyclone separators are used for acid fume recovery before venting to the air. 

J. L. Alden and J. M. Kane, Design of Industrial Exhaust Systems for Dust and Fume Eemoval, 4th ed.. Industrial Press, New York, 1970. 

Design considerations and costs of the catalyst, hardware, and a fume control system are direcdy proportional to the oven exhaust volume. The size of the catalyst bed often ranges from 1.0 m at 0°C and 101 kPa per 1000 m /min of exhaust, to 2 m for 1000 m /min of exhaust. Catalyst performance at a number of can plant installations has been enhanced by proper maintenance. Annual analytical measurements show reduction of solvent hydrocarbons to be in excess of 90% for 3—6 years, the equivalent of 12,000 to 30,000 operating hours. When propane was the only available fuel, the catalyst cost was recovered by fuel savings (vs thermal incineration prior to the catalyst retrofit) in two to three months. In numerous cases the fuel savings paid for the catalyst in 6 to 12 months. 

In industrial air-conditioning systems, harmful environmental gases, vapors, dusts, and fumes are often encountered. These contaminants can be controlled by exhaust systems at the source, by dilution ventilation, or by a combination of the two methods. When exhaust... 

Pouring Zinc oxide fume, lead oxide fume cover high-zinc-content brass use of good combustion controls, local exhaust system, and baghouse or... 

Cadmium Roasters, slag, fuming furnaces, deleading Idlns Particulates Local exhaust system, baghouse or precipitator... 

Zinc Roasting Sintering Calcining Retorts electric arc Particulates (dust) and SO2 Particulates (dust) and SO2 Zinc oxide fume, particulates, SO2, CO Exhaust system, humidifier, cyclone, scrubber, electrostatic precipitator, and acid plant Exhaust system, humidifier, electrostatic precipitator, and acid plant Exhaust system, baghouse, scrubber or acid plant... 

Paint and varnish manufacturing Resin manufacturing closed reaction vessel Varnish cooldng-open or closed vessels Solvent thinning Acrolein, other aldehydes and fatty acids (odors), phthalic anhydride (sublimed) Ketones, fatty acids, formic acids, acetic acid, glycerine, acrolein, other aldehydes, phenols and terpenes from tall oils, hydrogen sulfide, alkyl sulfide, butyl mercaptan, and thiofen (odors) Olefins, branched-chain aromatics and ketones (odors), solvents Exhaust systems with scrubbers and fume burners Exhaust system with scrubbers and fume burners close-fitting hoods required for open kettles Exhaust system with fume burners... 

The operation of flow dampers can cause pressure fluctuations in the ductwork system. Measurements by Melin indicate that pressure oscillations in an exhaust system can cause instabilities in the airflow through a fume cupboard sufficient to give rise to outward leakage of contamination, especially when a person stands in front of the cupboard. 

Class I The Class I BSC provides personnel and environmental protection, but no product protection. It is similar in air movement to a chemical fume cupboard, but has a HEPA filter (see Chapter 9) in the exhaust system to protect the environment (Fig. 10.94). In the Class 1 BSC, unfiltered room air is drawn across the work surface. Personnel protection is provided by this inward air velocity as long as a minimum velocity of 0.37 m s" is maintained through the front opening (see the discussion on fume cupboards in Section 10.2.3.3). In many cases Class I BSCs are used specifically to enclose equipment. 

The factors affecting the performance of a local exhaust system are well known. For fume control, an added factor is the effect of heat release or buoyancy. Important design parameters are process heat release and the size and geometry of air-supply openings and their location relative to major surfaces of the enclosure, lire kxation of the fume off-take is usually only of secondary importance. 

Fume hoods must be of a type suitable for the service they are intended to perform. For many applications, minimum face velocity is specified by regulations. An installer should always check the velocity when a new hood is placed in operation. It should be rechecked whenever any modification is made to the exhaust system. It is up to the laboratory operator to make certain that a hood is not put to new uses for which it was not designed. 

Laboratory aisles must be no less than 5 feet wide and benches should have sufficient unobstructed width to accommodate modern analytical instrumentation. An overhead (filtered) exhaust system would permit small canopy hoods to be connected as necessary to scavenge fumes from areas near injection and exhaust ports of analyzers not located in hoods. Each room should have its own supply... 

Safety glasses must be worn in the laboratory at all times. Material safety and data sheets should be read prior to the start of the experiment. All chemicals should be considered hazardous from a standpoint of flammability and toxicity. Appropriate safety gloves must be worn when using organic solvents so that no skin contact is permitted. Care must be taken to use organic solvents either in a well-ventilated area or in a hood. Avoid breathing the fumes or sources of electrical sparks. The GPC instrument, including solvent reservoir and waste container, should be vented to a fume hood or other exhaust system. 

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