Gaseous emission

Disposal of exhausted soHds can be easily overlooked at the plant design stage, particularly when these have no intrinsic value alternative disposal methods might include landfiU of inert material or incineration, hydrolysis, or pyrolysis of organic materials. Liquid, soHd, and gaseous emissions are aU subject to the usual environmental considerations. 

There are four chemical-engineering unit operations commonly used for the control of gaseous emissions ... 

Petroleum products are obtained from crude oil. In the process of getting the crude oil from the ground to the refinery, many possibilities for emission of hydrocarbon and reduced sulfur gaseous emissions occur. In many cases, these operations take place in relatively remote regions and affect only those employed by the industry, so that little or no control is attempted. 

A widely used system for the control of organic gaseous emissions is oxidation of the combustible components to water and carbon dioxide. 

Most petrochemical processes are essentially enclosed and normally vent only a small amount of fugitive emissions. However, the petrochemical processes that use air-oxidation-type reactions normally vent large, continuous amounts of gaseous emissions to the atmosphere (10). Six major petrochemical processes employ reactions using air oxidation. Table 30-5 lists the atmospheric emissions from these processes along with applicable control measures. 

Hydrogen fluoride accounts for about 907o of the gaseous fluoride emitted from the electrolytic cell. Other gaseous emissions are SO2, COj, CO, NO2, HjS, COS, CS2, SFg, and various gaseous fluorocarbons. Particulate fluoride is emitted directly from the process and is also formed from condensation and solidification of the gaseous fluorides. 

Wood-fired power boilers are generally found at the mills where wood products are manufactured. They are fired with waste materials from the process, such as "hogged wood," sander dust, sawdust, bark, or process trim. Little information is available on gaseous emissions from wood-fired boilers, but extensive tests of particulate matter emissions are reported (19). These emissions range from 0.057 to 1.626 gm per dry standard cubic meter, with an average of 0.343 reported for 135 tests. Collection devices for particulate matter from wood-fired boilers are shown in Table 30-21. 

EPA Proposed Revisions to Gaseous Emissions Rules for Aircraft and Aircraft Engines. Fed. Regist. 43, 12615 (1978). 

All chemical operations produce waste either as solid wastes (including pastes, sludge and drummed liquids), liquid effluents, or gaseous emissions (including gases, particulate solids, mists and fogs). Relevant data are summarized in Chapters 16 and 17. 

Waste treatment prior to disposal may introduee phase ehanges whieh result in quite different pollution eontrol eonsiderations. For example, the gases generated by ineineration of a solid waste ean be serubbed with liquid in order to meet an aeeeptable diseharge eriterion henee, in addition to ash for disposal, a liquid effluent stream is produeed and requires treatment. Other waste treatment proeesses may result in the liberation of flammable or toxie gaseous emissions as exemplified in Table 16.5. 

Ail the parameters on which various consents (or permissions to dispose of, waste streams) are based must be reliably measured and recorded. This is easier to achieve with gaseous emissions (Chapter 10) and liquid effluents than with heterogeneous solid wastes. Systematic analysis of solid wastes will cover as a minimum the information in Table 17.15. 

Wet scrubbers rely on a liquid spray to remove dust particles from a gas stream. They are primarily used to remove gaseous emissions, with particulate control a secondary function. The major types are venturi scrubbers, jet (fume) scrubbers, and spray towers or chambers. Venturi scrubbers consume large quantities of scrubbing liquid (such as water) and electric power and incur high pressure drops. Jet or fume scrubbers rely on the kinetic energy of the liquid stream. The typical removal efficiency of a jet or fume scrubber (for particles 10 g. or less) is lower than that of a venturi scrubber. Spray towers can handle larger gas flows with minimal pressure drop and are therefore often used as precoolers. Because wet scrubbers may contribute to corrosion, removal of water from the effluent gas of the scrubbers may be necessary. 

Other methods for removing scale include salt pickling, electrolytic pickling, and blasting blasting is environmentally desirable, where feasible. EAFs produce metal dusts, slag, and gaseous emissions. 

The following are some typical questions to address when developing the material balance around the gaseous emissions components. 

O Are there certain times when gaseous emissions are more prominent - are they linked to temperature ... 

O Are gaseous emissions from confined spaces (including fugitive emissions) vented to the outside ... 

A variety of containment strategies employ floating solid objects to control the rate of gaseous emissions from surface impoundments. These include synthetic membrane covers, rafts, and hollow plastic spheres. Synthetic membrane covers are feasible where the out-gassing of volatiles due to biological activity is not expected. Selection of the liner material must be... 

Example 2,2 Recovery of benzene from a gaseous emission... 

Example 2.2 Recovery of Benzene from a Gaseous Emission... 

A countercurrent moving-bed adsorption column is used to remove benzene from a gaseous emission. Activated carbon is employed as the adsorbent. The flowrate of the gas is 1.2 kg/s and it contains 0.027 wt/wt% of benzene. It is desired to recover 99% of this pollutant. The activated carbon entering the column has 2 X 10 wt/wt% of benzene. Over the operating range, the adsorption isotherm (Yaws et al., 1995) is linearized to... 

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