Sulfuric acid mist

Another concentration method involves passing an inert gas such as N2 or CO2 through the reaction medium (12). As the gas passes through, it becomes humidified and carries captured water with it. Most of the energy required for the gas humidification comes from the heat of reaction. An advantage is that expensive drying equipment is not needed. Also, the sulfuric acid mist formed in typical concentrators is minimized. Du Pont uses a similar process in its nitrobenzene production faciUty. 

Figure 9 shows the sampling train for sulfuric acid mist collection (13). The first impinger contains 80 wt % isopropyl alcohol and the second and third contain 3 wt % H2O2. The first impinger and filter retain the acid mist and SO the next two retain the SO2. After sampling, the filter is added to the contents of the first impinger and the total acid is titrated and reported as sulfuric acid. 

The sulfur trioxide produced by catalytic oxidation is absorbed in a circulating stream of 98—99% H2SO4 that is cooled to approximately 70—80°C. Water or weaker acid is added as needed to maintain acid concentration. Generally, sulfuric acid of approximately 98.5% concentration is used, because it is near the concentration of minimum total vapor pressure, ie, the sum of SO, H2O, and H2SO4 partial pressures. At acid concentrations much below 98.5% H2SO4, relatively intractable aerosols of sulfuric acid mist particles are formed by vapor-phase reaction of SO and H2O. At much higher acid concentrations, the partial pressure of SO becomes significant. 

Small amounts of sulfuric acid mist or aerosol are always formed in sulfuric acid plants whenever gas streams are cooled, or SO and H2O react, below the sulfuric acid dew point. The dew point varies with gas composition and pressure but typically is 80—170°C. Higher and lower dew point temperatures are possible depending on the SO concentration and moisture content of the gas. Such mists are objectionable because of both corrosion in the process and stack emissions. 

More recentiy, sulfuric acid mists have been satisfactorily controlled by passing gas streams through equipment containing beds or mats of small-diameter glass or Teflon fibers. Such units are called mist eliminators (see Airpollution control methods). Use of this type of equipment has been a significant factor in making the double absorption process economical and in reducing stack emissions of acid mist to tolerably low levels. 

Process air in sulfur-burning plants is dried by contacting it with 93—98 wt % sulfuric acid in a countercurrent packed tower. Dry process air is used to minimise sulfuric acid mist formation in downstream equipment, thus reducing corrosion problems and stack mist emissions. 

Packed fiber bed mist eliminators can be designed to operate at almost any desired particle collection efficiencies, depending on the allowable pressure drop and cost. A good discussion of sulfuric acid mist generation, control, and mist eliminator design is available (109,110). 

S. M. Horvath and co-workers. Effects of Sulfuric Acid Mist Exposure on Pulmonary Function, EPA-600/S1-81-044, issued as PB81-208977 by NTIS, Washington, D.C., June 1981. 

Safety. Chlorosulfuric acid is a strong acid and the principal ha2ard is severe chemical bums when the acid comes into contact with body tissue. The vapor is also ha2ardous and extremely irritating to the skin, eyes, nose, and respiratory tract. Exposure limits for chlorosulfuric acid have not been estabhshed by OSHA or ACGIH. However, chlorosulfuric acid fumes react readily with moisture in the air to form hydrochloric and sulfuric acid mists, which do have estabhshed limits. The OSHA 8-h TWA limits and ACGIH TLV—TWA limits are sulfuric acid = 1 mg/m hydrochloric acid = 5 ppm or 7 mg/m (ceiling limit). 

SpiHs can also be diluted with large volumes of water. Care should be taken, however, because chlorosulfuric acid reacts violentiy with water Hberating heat, hydrochloric acid, and sulfuric acid mists and steam. The water should be appHed from a safe distance upwind of the spiH using a fog no22le. Remaining traces of acid should be neutrali2ed with soda ash, caustic soda, or lime before disposal. 

The oxidation catalyst (OC) operates according to the same principles described for a TWO catalyst except that the catalyst only oxides HC, CO, and H2. It does not reduce NO emissions because it operates in excess O2 environments. One concern regarding oxidation catalysts was the abiUty to oxidize sulfur dioxide to sulfur trioxide, because the latter then reacts with water to form a sulfuric acid mist which is emitted from the tailpipe. The SO2 emitted has the same ultimate fate in that SO2 is oxidized in the atmosphere to SO which then dissolves in water droplets as sulfuric acid. 

Sulfur Dioxide EPA Method 6 is the reference method for determining emissions of sulfur dioxide (SO9) from stationary sources. As the gas goes through the sampling apparatus (see Fig. 25-33), the sulfuric acid mist and sulfur trioxide are removed, the SO9 is removed by a chemical reaction with a hydrogen peroxide solution, and, finally, the sample gas volume is measured. Upon completion of the rim, the sulfuric acid mist and sulfur trioxide are discarded, and the collected material containing the SO9 is recovered for analysis at the laboratory. The concentration of SO9 in the sample is determined by a titration method. 

Sonic agglomerators, which have been used experimentally for sulfuric acid mists and as mist eliminators. Commercial development is not projected at this time because the energy requirements are considerably greater than those for venturi scrubbers of similar capacity. 

If your facilrty has several pieces of equipment performing a similar service, you may combine the reporting for such equipment on a single line. It is not necessary to enter four lines of data to cover four scrubber units, for example, if all four are treating wastes of similar character (e.g., sulfuric acid mist emissions), have similar influent concentrations, and have similar removal efficiencies. If, however, any of these parameters differ from one unit to the next, each scrubber must be listed separately. 

Primary copper processing results in air emissions, process wastes, and other solid-phase wastes. Particulate matter and sulfur dioxide are the principal air contaminants emitted by primary copper smelters. Copper and iron oxides are the primary constituents of the particulate matter, but other oxides, such as arsenic, antimony, cadmium, lead, mercury, and zinc, may also be present, with metallic sulfates and sulfuric acid mist. Single-stage electrostatic precipitators are widely used in the primary copper industry to control these particulate emissions. Sulfur oxides contained in the off-gases are collected, filtered, and made into sulfuric acid. 

Schlesinger, R.B., Naumann, B.D., and Chen, L.C., Physiological and histological alterations in the bronchial mucociliary clearance system of rabbits following intermittent oral or nasal inhalation of sulfuric acid mist, J. Toxicol. Environ. Health. 12, 2-3, 441, 1983. 

Fiber-bed scrubbers are used to collect fine or soluble particulate matter or as mist eliminators to collect liquid aerosols, including inorganic (e.g., sulfuric acid mist) and volatile organic compounds. Insoluble or coarse PM will clog the fiber bed with time, and VOCs that are difficult to condense will not be collected efficiently. 

Historically, the sulfur oxides have long been known to have a deleterious effect on the atmosphere, and sulfuric acid mist and other sulfate particulate matter are well established as important sources of atmospheric contamination. However, the atmospheric chemistry is probably not as well understood as the gas-phase photoxidation reactions of the nitrogen oxides-hydrocarbon system. The pollutants form originally from the S02 emitted to the air. Just as mobile and stationary combustion sources emit some small quantities of N02 as well as NO, so do they emit some small quantities of S03 when they bum sulfur-containing fuels. Leighton [2] also discusses the oxidation of S02 in polluted atmospheres and an excellent review by Bulfalini [3] has appeared. This section draws heavily from these sources. 

In the presence of water a sulfuric acid mist forms according to... 

Sulfuric acid mist was not teratogenic in mice or rabbits exposed 7 hours/day to 20mg/m during the period of major organogenesis. ... 

AmdurMO, Silverman L, Drinker P Inhalation of sulfuric acid mist by human subjects. AMA Arch Ind Hyg Occup Med 6 305-313, 1952... 

Alarie YC et al Long-term exposure to sulfur dioxide, sulfuric acid mist, fly ash, and their mixtures—results of studies in monkeys and guinea pigs. Arch Environ Health 30 254-263, 1975... 

Wet electrostatic precipitators (WESP) are used for removal of liquid contaminants such as sulfuric acid mist, aerosols, and particulate matter. The acid mist and aerosols are typically formed in a WGS by condensation of SO3. Unlike dry precipitators, wet precipitators do not require rapping to remove the dust. The collected mist and particulate matter form a liquid film that runs down a vertical collecting plate. In some cases, a continuous spray of liquid is used to prevent solids deposition on the collecting plates. 

Dust particles, water droplets, and sulfuric acid mist (and if present, ammonium salt aerosols) are electrically charged in the same way as in the dry precipitator. The negatively charged particles are collected on the positive collecting electrodes. 

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