Plant air

The most overlooked hazard and contaminant is water (99). Water reacts with isocyanates at room temperature to yield both ureas and large quantities of carbon dioxide. The presence of water or moisture can produce a sufficient amount of CO2 to overpressurize and mpture containers. As Httle as 30 mL of water can result in 40 L of carbon dioxide which could result in pressures of up to 300 kPa (40 psi). For these reasons, the use of dry nitrogen atmospheres is recommended during handling. If a plant air system must be used, purification equipment, such as oil traps and drying beds, should be installed between the source and the isocyanate vessel. 

The OSHA limits, regulations, and recommendations apply to in-plant air quaUty. Improperly filtered exhaust air may cause a plant to be in violation of the EPA standard, therefore these data should not be confused with the EPA limit for airborne lead, 1.5 fig lead/m, measured over a calendar quarter, which pertains to the exterior plant environment and emissions. The installation and proper maintenance of exhaust filtration systems enables most plants to comply with the EPA limits for airborne lead (see Lead compounds, industrial toxicology). 

In the early 1970s, air pollution requirements led to the adoption of the double contact or double absorption process, which provides overall conversions of better than 99.7%. The double absorption process employs the principle of intermediate removal of the reaction product, ie, SO, to obtain favorable equiUbria and kinetics in later stages of the reaction. A few single absorption plants are stiU being built in some areas of the world, or where special circumstances exist, but most industriali2ed nations have emission standards that cannot be achieved without utili2ing double absorption or tad-gas scmbbers. A discussion of sulfuric acid plant air emissions, control measures, and emissions calculations can be found in Reference 98. 

Pneumatic controllers are made of Bourdon tubes, bellows, diaphragms, springs, levers, cams, and other fundamental transducers to accomplish the control function. If operated on clean, diy plant air, they offer good performance and are extremely reliable. Pneumatic controllers are available with one or two stages of pneumatic amphfi-cation, with the two-stage designs having faster dynamic response characteristics. 

Membrane separation Medium to high purity Na, 95to 99.9% Small typical module produces 855 scfh at I75lb/in and 77°F Can use plant air as air source simple and safe to operate stable output maybe economical for low-capacity medium- to high-purity requirements excellent when some oxygen is required with the nitrogen temperature and pressure sensitive... 

Instrument and Plant Air Systems. A typical setup for a large plant could include three to four 50% instrument air compressors and two 100% plant air compressors, with steam drives for normally operated units and electrical drives for spares. Common practice would provide an interconnection to allow makeup from plant air into instrument air, but not vice versa, and two sets (two 100% driers per set—one on-stream and one regenerating) of 1007c instrument air driers. Two main receivers on instrument air near the compressors with several minutes holdup time and satellite receivers at process trains would be likely and proper for feasibility cost estimating. 

The compressors to be covered in this book are those using mechanical motion to effect the compression. These types of compressors are commonly used in the process and gas transport/distribution industries. A partial list of these industries includes chemical, petrochemical, refinery, pulp and paper, and utilities. A few typical applications are air separation, vapor extraction, refrigeration, steam recompression, process and plant air. 

A plant air system could resemble Figure 8-40(d) where a motor-dn-ven centrifugal compressor is used. 

Assume that a plant air system requires 10,000 fti/min of dry air measured at 14.7 psia and 60°F. The air is required at 100 psia. Intake conditions are... 

Figure 12-39D. Oil-free air compressor with two impellers, Elliott Company. Plant Air Package , Plus, gear driven. (Used by permission Bui. P-51 B. Elliott Company.)...

In reverse-pulse applications, most plants rely on plant-air systems as the source for the high-velocity pulses required for cleaning. In many cases, however, the plant-air system is not sufficient for this purpose. Although the pulses required are short (i.e., 100 milliseconds or less), the number and frequency can deplete the supply. Therefore, care must be taken to ensure that both sufficient volume and pressure are available to achieve proper cleaning. 

From the bottom of the extractor, the caustic solution, containing sodium mercaptide, enters the regenerator. Plant air supplies oxygen to react with the sodium mercaptide to form disulfide oil (Equation 1-11), which is insoluble in caustic. The oxidizer overhead stream... 

Generation of clarified water for deinking plants (air flotation). 

Unfiltered Brine, f Filtered Brine, Sludge, ( ) Plant Air, Valve Open, Valve Closed... 

It was stated that the chromatographic analysis of the flavonoid profde may help the determination of taxonomic relationships between these species [125], The optimization of the separation of flavonoid glycosides of Mentha piperita (Laminaceae) was carried out on silica, amino, cyano and C18 HPTLC statinoary phases. The investigation was motivated by the spasmolytic, carminative and cholagogue characteristics of the plant. Air-dried and powdered leaves of peppermint (300 g) were extracted with methanol-water 1 1 v/v at ambient temperature. The suspension was filtered, concentrated to 200 ml acidified to pH 3 with formic acid and separated in an ODS column (400 X 40 mm i.d. particle size 40 pm). 

All solids resulting from processing are loaded (under automatic or remotely operated control) into process bins for transport to Area 400 for decontamination to a 5X condition. Gases released from the operations in this area, with the exception of those from the COINS (which are swept to Area 400 for destruction), are swept into the standard cascade air system utilized to control and condition the plant air in baseline system facilities. 

Steam-generating plants, air compressor plants, and similar plants should be provided with potassium bicarbonate dry chemical extinguishers (120-B C) for Class B or Class C fires in the areas containing hydrocarbons or other flammable liquids. For fires in electrical equipment, at least one extinguisher (10-B C) should be provided. If Class Afire hazards exist, multipurpose dry chemical extinguishers (20-A 80-B C) or water extinguishers should be provided. 

As a reference document and an educational tool by any individuals who want to review important aspects of in-plant air quality, water quality, safety, and health protection at industrial sites having hazardous substances. 

Ferrante, L.M. Indoor/in-plant air quality. Natl. Environ. J. 1993, March-April, 36-40. 

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