Air emissions

Air emissions include point and nonpoint sources (Chapter 4). Point sources are emissions that exit stacks and flares and thus can be monitored and treated. Nonpoint sources are fugitive emissions that are difficult to locate and capture. Fugitive emissions occur throughout refineries and arise from the thousands of valves, pumps, tanks, pressure relief valves, flanges, and so on. Although individual leaks are typically small, the sum of all fugitive leaks at a refinery can be one of its largest emission sources. 

The numerous process heaters used in refineries to heat process streams or to generate steam (boilers) for heating or steam stripping can be potential sources of SOj , NO, CO, particulates, and hydrocarbon emissions. When operating properly and when burning cleaner fuels, such as refinery fuel gas, fuel oil, or natural gas, these emissions are relatively low. If, however, combustion is not 

Sulfur is removed from a number of refinery process off-gas streams (sour gas) to meet the sulfur oxide emissions limits of the Clean Air Act and to recover salable elemental sulfur. Process off-gas streams, or sour gas, from the coker, catalytic cracking unit, hydrotreating units, and hydroprocessing units can contain high concentrations of hydrogen sulfide mixed with light refinery fuel gases. 

Current methods for removing sulfur from the hydrogen sulfide gas streams are typically a combination of two processes, in which the primary process is the Claus process, followed by the Beaven process, the SCOT process, or the Welhnan-Lord process. 

The catalyst is necessary to ensure that the components react with reasonable speed, bnt unfortnnately, the reaction does not always proceed to completion. For this reason, two or three stages are nsed, with sulfur being removed between the stages. For analysts it is valuable to know that carbon disulfide (CS2) is a by-product from the reaction in the high-temperature furnace. The carbon disulfide can be destroyed catalytically before it enters the catalytic section proper. Generally, the Clans process may remove only about 90% of the hydrogen sulfide in the gas stream, and as already noted, other processes, such as the Beaven process, SCOT process, or Wellman-Lord process are often used to recover additional sulfur. 

In the past, coal gained notoriety because of emissions of hazardous substances from combustion plants into the atmosphere (e.g., sulfur, nitric oxides, mercury. 

As a consequence, the routine operation of coal-based syngas plants has successfully proven cleaning of most difficult gas streams for a broad range of employed technologies [27]. 

Special attention should be paid to emissions from pressurization (coal feeding system) and depressurization of the solids (ash or slag discharge). The proper design of equipment and consequent monitoring are required to avoid syngas 

In the special case of IGCC power plants, where the syngas is combusted in a gas turbine, the thermal formation of NO takes place as in other systems 

If present in the used coal, mercury and arsenic may require special attention. They can be accumulated in certain streams or locations depending on the employed process steps, and parts of them may even be emitted. 

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As the economic value of coproducts has decreased, it has become more difficult to provide capital for environmental controls on air emissions and wastewater streams such as toxic phenoHc effluents from chemical recovery operations. Some former coke and manufactured gas sites may require remediation to clean up contaminated soil and groundwater. These difficulties will force the shutdown of some operations and discourage recovery of coproducts in future installations. 

The need to meet environmental regulations can affect processing costs. Undesirable air emissions may have to be eliminated and Hquid effluents and soHd residues treated and disposed of by incineration or/and landfilling. It is possible for biomass conversion processes that utilize waste feedstocks to combine waste disposal and treatment with energy and/or biofuel production so that credits can be taken for negative feedstock costs and tipping or receiving fees. 

Air Pollution. Particulates and sulfur dioxide emissions from commercial oil shale operations would require proper control technology. Compliance monitoring carried out at the Unocal Parachute Creek Project for respirable particulates, oxides of nitrogen, and sulfur dioxide from 1986 to 1990 indicate a +99% reduction in sulfur emissions at the retort and shale oil upgrading faciUties. No violations for unauthorized air emissions were issued by the U.S. Environmental Protection Agency during this time (62). 

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. 

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. 

Air Emission Tests at Commerce Refuse to Energy Facility, May 26—June 5, 1987, Vol. I, ESA 20522 449, Energy Systems Associates, Pittsburgh, Pa., July 1987. 

A U.S. EPA study (41) showed that soil vapor extraction (SVE) is an effective treatment for removing volatile contaminants from the vadose zone. Sandy soils are more effectively treated than clay or soils with higher organic content because higher air flows are possible in sand and clays—organic soils tend to adsorb or retain more contaminants. Removal of volatiles is rapid in the initial phase of treatment and thereafter decreases rapidly thereafter-an important consideration in the design of air emissions control over the life of the project. 

Recent air pollution regulations limit the amount of volatile organic carbon (VOC) that can be discharged from wastewater treatment plants. Benzene is a particular case in which air emission controls are required if the concentration of benzene in the influent wastewater exceeds 10 mg/L. 

Process and environmental air is compressed and passed through activated beds to reduce air emission levels to <5 ppm. Process wastewater is air stripped to remove CCl. The solvent containing air is also passed through the activated carbon beds. The total air flow through the beds averages about 3965 mVmin (140,000 SCFM). 

Process flow diagrams for all solid waste, wastewater, and air emissions sources... 

MSC Facihties are required to meet some of the toughest environmental air emission standards in the country. Complying with these standards makes modern waste combustors among the cleanest producers of electricity—and may even provide a means of improving a community s overall air quality. 

In addition, restrictions on industrial air emissions under the Clean Air Act (CAA) as amended in 1977, the Clean Air Act Amendments (CAAA) of 1990, and other state and local statutes and regulations have universal impact on the storage of toxic materials, with direct and significant effects on the design and operation of toxic material storage facilities. Whereas the primary factors which once determined how air emissions from storage tanks were handled were fire protection and loss prevention, in recent years environmental protection concerns nearly always determine the extent and nature of the air emission controls required to be installed. 

The process of evaluating air emission permit apphcations for large sources which are subject to federal permitting requirements is called New Source Review (NSR) and can be quite complicated, taking from six mouths to four years to complete. An NSR application would be required for a new source which could emit 100 tons per year or more of any criteria pollutant, after accounting for any air pollution control equipment. 

This chapter addresses the potential for hazardous air emissions from environmental remediation sites. These emissions can occur at hazardous spill locations, at undisturbed remediation sites, and during cleanup of remediation sites under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) or the Superfund Amendments and Reauthorization Act (SARA). Air emissions may pose a potential health risk at these sites. 

Air/Superfund National Technical Guidance Study Series," Volume II "Estimation of Baseline Air Emission at Superfund Sites," EPA-450/l-89-002a, August 1990. Volume III "Estimation of Air Emissions from Clean-up Activities at Superfund Sites," EPA-450/1-89-003, January 1989. Volume IV "Procedures for Conducting Air Pathway Analyses for Superfund Applications," EPA-450/1-89-004, July 1989. 

SI 1969/1263 Clean Air (Emissions of Dark Smoke) (Exemption) Regulations... 

SI I97I/I62 Clean Air (Emission of Gnt and Dust from Eurnaces) Regulations... 

An acid dipping operation for metal parts involves the use of a 75% strength sulfuric acid solution. Develop recommendations for the Maximum Achievable Control Technology for controlling the air emissions from such an operation. Hint Take some time to look at the EPA Web sites dealing with MACT standards and pollution prevention. 

In this chapter we focus our attention on some of the point sources of air emissions within different types of plant operations, along with the methods of abatement. Although we do not make direct comparisons between prevention and control methodologies until Chapter 6, the reader should gain an appreciation for the simplicity of applying pollution prevention as opposed to incorporating engineering controls in many situations. 

Compounds considered carcinogenic that may be present in air emissions include benzene, butadiene, 1,2-dichloroethane, and vinyl chloride. A typical naphtha cracker at a petrochemical complex may release annually about 2,500 metric tons of alkenes, such as propylenes and ethylene, in producing 500,000 metric tons of ethylene. Boilers, process heaters, flares, and other process equipment (which in some cases may include catalyst regenerators) are responsible for the emission of PM (particulate matter), carbon monoxide, nitrogen oxides (200 tpy), based on 500,000 tpy of ethylene capacity, and sulfur oxides (600 tpy). 

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