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Air Pollution Control Systems for Boiler and Incinerators.Unique control problems_3

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Nội dung Text: Air Pollution Control Systems for Boiler and Incinerators.Unique control problems_3

  1. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM CHAPTER 5 MEASURING TECHNIQUES 5-1. Criteria standards. For the determination of possible violations of air quality, the continuous monitoring of pollutant In order to evaluate the nature and magnitude of air concentrations is normally required for a one-year pollution, establish remedial measures, and determine period. Air quality measurements are a function of the control programs, it is necessary to test for the exist- sampling site, the local meteorology, the methods used, ence of pollutants. In the upgrading of existing installa- and the existing pollutant concentration in the tions, compliance is determined through "point source atmosphere. Personnel knowledgeable and experienced emission rate tests." Revisions to the regulations in meteorology and air quality testing are needed to regarding air pollution test requirements for federal conduct and evaluate air-quality measurements. installations appear in the Federal Register. b. Sampling technique. The criteria for instrumen- tation, calibration, and use of EPA-approved sampling 5-2. Stack and source measurement tech- techniques are covered under 40 CFR 53 niques Environmental Protection Agency Regulations on The point source emission rate test methods and Ambient Air Monitoring Reference and Equivalent requirements are covered under Environmental Pro- Methods. See table 5-2. tection Agency Regulations on Standards of Perform- ance for New Stationary Sources, 40 CFR 60 and subsequent revisions. The techniques are listed in table 5-1. (1) Continuous sampling is the recommended technique for obtaining the most reliable information concerning the variation of pollutant concentration in the real atmosphere. Discrete sampling can be used for plume tracking and random checking. Discrete sampling should be used with caution, however, when measuring any of 5.3 Meteorological and ambient air mea- several pollutants that have daily variations. surement (For example, ozone has very low con- a. Measurements. Air quality measurements are centrations at night.) In addition, use of used to trace emission sources and determine if these discrete sampling methods will often result sources comply with federal, state, and local air quality 5-1
  2. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM CHAPTER 5 MEASURING TECHNIQUES 5-1. Criteria standards. For the determination of possible violations of air quality, the continuous monitoring of pollutant In order to evaluate the nature and magnitude of air concentrations is normally required for a one-year pollution, establish remedial measures, and determine period. Air quality measurements are a function of the control programs, it is necessary to test for the exist- sampling site, the local meteorology, the methods used, ence of pollutants. In the upgrading of existing installa- and the existing pollutant concentration in the tions, compliance is determined through "point source atmosphere. Personnel knowledgeable and experienced emission rate tests." Revisions to the regulations in meteorology and air quality testing are needed to regarding air pollution test requirements for federal conduct and evaluate air-quality measurements. installations appear in the Federal Register. b. Sampling technique. The criteria for instrumen- tation, calibration, and use of EPA-approved sampling 5-2. Stack and source measurement tech- techniques are covered under 40 CFR 53 niques Environmental Protection Agency Regulations on The point source emission rate test methods and Ambient Air Monitoring Reference and Equivalent requirements are covered under Environmental Pro- Methods. See table 5-2. tection Agency Regulations on Standards of Perform- ance for New Stationary Sources, 40 CFR 60 and subsequent revisions. The techniques are listed in table 5-1. (1) Continuous sampling is the recommended technique for obtaining the most reliable information concerning the variation of pollutant concentration in the real atmosphere. Discrete sampling can be used for plume tracking and random checking. Discrete sampling should be used with caution, however, when measuring any of 5-3. Meteorological and ambient air mea- several pollutants that have daily variations. surement (For example, ozone has very low con- a. Measurements. Air quality measurements are centrations at night.) In addition, use of used to trace emission sources and determine if these discrete sampling methods will often result sources comply with federal, state, and local air quality 5-1
  3. TM 5-815-1/AFR 19-6 Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com (1) Total suspended particulates. The high in economically unacceptable manpower volume air sample is the federal reference requirements. In these cases, sampling with method for measuring total suspended continuous instruments and recording on particulates. Air is drawn (at 40 to 60 data charts provides a lower cost solution. ft3/min) through a glass fiber filter by means (2) Air quality regulations require the measure- of a blower, and suspended particles having ment of extremely small pollutant con- an aerodynamic diameter between 100 and centrations (1/100 of a part per million by 1.0 micron are collected. The suspended volume). Sensitive instruments capable of particulate is calculated by dividing the net detecting small concentrations are needed. weight of the particulate by the total air c. Sampling method for carbon monoxide. The fed- volume samples and is reported in ug/m3. eral reference method for measuring carbon monoxide (2) Coefficient of haze (C OH). A few states is the instrumental nondispersive infrared technique. A have standards for a particulate measurement typical instrument consists of a reference cell filled called the coefficient of haze. This measure- with CO free air, and a sample, or detector, cell. The ment is reported in units of COH/1000 linear difference in transmittance of infrared radiation passing feet of sampled air. In this method, air is through the sample cell and the reference cell is sensed drawn through a small spot on a circle of by a photon detector. The difference is a measure of filter paper until the equivalent of a 1000 feet the optical absorption of the CO in the sample cell and long column of air of the diameter of the spot is proportional to the CO concentration in the sample. has passed through the filter paper. The signal from the detector is amplified and used to Transmittance through this spot then serves drive an output meter as a direct measure of CO as a measurement of particulate material concentration. This method is precise and accurate. collected on the filter. There are considerable d. Sampling method for sulfur dioxide. The West- doubts as to the usefulness and true meaning Gaeke sulfuric acid method is the Federal reference of COH data, since the transmittance method for measuring sulfur oxides. The West-Gaeke recorded is a function of the nature of the method is a discrete bubbler technique which involves particulate as well as the total weight bubbling ambient air through an impinger for 24 hours. sampled. Sulfuric acid is added to the absorber to eliminate (3) Dustfall (settleable particulates). Several interferences from oxides of nitrogen. SO2 is collected states have standards for the amount of par- in a tetrachloromercurate solution. When acid bleach ticulate that settles out of the air over a given pararosaniline is added to the collected SO2 together length of time (one common unit is grams/ with formaldehyde, a red-violet compound is formed square meter/30 days). The method of collection is generally the dust bucket. A dust which is then measured spectrophotometrically. This bucket is a 15-inch deep metal or plate con- method is a discrete instrumental sampling method, but tainer with a 6-inch opening that is exposed may be modified for continuous use. to the air generally for a period of one month. e. Sampling method for oxidants and ozone. The Dust buckets should be partially filled with instrumental-chemiluminescence method is the federal distilled water (or antifreeze) which prevents reference method for measuring ozone. Upon mixing the transporting of dust out of the buckets by ambient air and ethylene in the testing instrument, strong winds. This water also acts as a wash ozone reacts with the ethylene to emit light. This light at analysis time. After evaporating the water, is measured by a photomutiplier. If the air and ethylene the remaining material is weighed and the flow rates are constant, and the proportion of air and residues are converted to the required units. ethylene therefore known, the resulting signal can be i. Traceable compounds. Test methods for com- related to ozone concentration. Analyzers are cali- pounds other than those for which standards exist are brated with a known ozone concentration. often useful in evaluating stack dispersion. If unusual f. Sampling method for nitrogen dioxide. The fed- fuel additives are used, or if incinerators are used to eral reference method for NO2 is the indirect measure- dispose of specialized materials, laboratory chemists ment of the concentration of nitrogen dioxide by can often devise sampling methods to measure these photometrically measuring the light intensity of wave- compounds in the atmosphere. lengths greater than 600 nanometers resulting from the j. Ringelmann standards. Particulate matter such as gas phase chemiluminescent reaction of nitric oxide soot, fly ash, and droplets of unburned combustibles (NO) with ozone (O3). present in exhaust gases tend to impart blackness or g. Sampling method for total hydrocarbons. Gas opacity to a plume. It is assumed that the darker the chromatography flame ionization is the federal refer- shade of gray or black, the greater the concentration of ence method of measuring total hydrocarbons. particulate matter present in a plume. The Ringelmann h. Sampling method for particulates. 5-2
  4. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM Chart offers a set of standards with which to measure have a removable cover. On double wall stacks the opacity of an effluent plume. By the comparison of sampling ports may consist of a 4-inch diameter pipe the blackness of a plume to the blackness of a series of extending from 4 inches outside the stack to the inner graduated light diffusers, a Ringelmann number corre- edge of the inner stack wall. Accessible sampling ports sponding to a percent opacity can be assigned to the shall be provided and located so that the cross sectional plume (see table 5-3). It should be noted that while area of the stack or flue can be traversed to sample the Ringelmann numbers give a relative indication of flue gas in accordance with the applicable current plume opacity, they bear no direct relationship to federal or state regulations for fuel burning equipment. plume particulate loading. They should supplement but 5-5. Air pollution project contacts not replace point-source emission tests. U.S. Army Environmental Hygiene Agency (AEHA), Aberdeen Proving Grounds, MD, may be contacted for the respective service air pollution projects on the fol- lowing: a. Source testing to characterize pollutants for design controls. b. Consultation on test performance standards and witnessing tests. 5-4. Flue gas sampling ports c. Testing of installed air pollution abatement equip- Sampling ports are approximately 4 inches in diameter, ment for compliance with regulatory standards. extend out approximately 4 inches from the stack, and 5-3
  5. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM CHAPTER 6 CYCLONES AND MULTICYCLONES 6-1. Cyclone be handled and high collection efficiencies are needed a multiple of small diameter cyclones are usually The cyclone is a widely used type of particulate collec- nested together to form a multicyclone. A unit of this tion device in which dust-laden gas enters tangentially type consists of a large number of elements joined into a cylindrical or conical chamber and leaves together with a common inlet plenum, a common through a central opening. The resulting vortex motion outlet plenum, and a common dust hopper. The or spiraling gas flow pattern creates a strong multicyclone elements are usually characterized by centrifugal force field in which dust particles, by virtue having a small diameter and having axial type inlet of their inertia, separate from the carrier gas stream. vanes. Their performance may be hampered by poor They then migrate along the cyclone walls by gas flow gas distribution to each element, fouling of the small and gravity and fall into a storage receiver. In a boiler diameter dust outlet, and air leakage or back flow from or incinerator installation this particulate is composed the dust bin into the cyclones. These problems are of fly-ash and unburned combustibles such as wood offset by the advantage of the multicyclone’s increased char. Two widely used cyclones are illustrated in figure collection efficiency over the single high efficiency 6-1. cyclone unit. Problems can be reduced with proper plenum and dust discharge design. A typical fractional 6-2. Cyclone types efficiency curve for multi-cyclones is illustrated in a. Cyclones are generally classified according to figure 6-6. their gas inlet design and dust discharge design, their e. Wet or irrigated cyclone. Cyclones may be oper- gas handling capacity and collection efficiency, and ated wet in order to improve efficiency and prevent their arrangement. Figure 6-2 illustrates the various wall buildup or fouling (See fig. 6-7). Efficiency is types of gas flow and dust discharge configurations higher for this type of operation because dust particles, employed in cyclone units. Cyclone classification is once separated, are trapped in a liquid film on the illustrated in table 6-1. cyclone walls and are not easily re-entrained. Water is b. Conventional cyclone. The most commonly used usually sprayed at the rate of 5 to 15 gallons per 1,000 cyclone is the medium efficiency, high gas throughput cubic feet (ft3) of gas. Wet operation has the additional (conventional) cyclone. Typical dimensions are illus- advantages of reducing cyclone erosion and allowing trated in figure 6-3. Cyclones of this type are used the hopper to be placed remote from the cyclones. If primarily to collect coarse particles when collection acids or corrosive gases are handled, wet operation efficiency and space requirements are not a major con- may result in increased corrosion. In this case, a sideration. Collection efficiency for conventional corrosion resistant lining may be needed. Re- cyclones on 10 micron particles is generally 50 to 80 entrainment caused by high values of tangential wall percent. velocity or accumulation of liquid at the dust outlet can c. High efficiency cyclone. When high collection occur in wet operation. However, this problem can be efficiency (80-95 percent) is a primary consideration in eliminated by proper cyclone operation. Wet operation cyclone selection, the high efficiency single cyclone is is not currently a common procedure for boilers and commonly used (See figure 6-4). A unit of this type is incinerators. usually smaller in diameter than the conventional cyclone, providing a greater separating force for the 6-3. Cyclone collection efficiency same inlet velocity and a shorter distance for the parti- a. Separation ability. The ability of a cyclone to cle to migrate before reaching the cyclone walls. These separate and collect particles is dependent upon the units may be used singly or arranged in parallel or particular cyclone design, the properties of the gas and series as shown in figure 6-5. When arranged in paral- the dust particles, the amount of dust contained in the lel they have the advantage of handling larger gas vol- gas, and the size distribution of the particles. Most umes at increased efficiency for the same power con- efficiency determinations are made in tests on a geo- sumption of a conventional unit. In parallel they also metrically similar prototype of a specific cyclone have the ability to reduce headroom space require- design in which all of the above variables are ments below that of a single cyclone handling the same accurately known. When a particular design is chosen gas volumes by varying the number of units in opera- it is usually accurate to estimate cyclone collection tion. efficiency based upon the cyclone manufacturer’s d. Multicyclones. When very large gas volumes must 6-1
  6. TM 5-815-1/AFR 19-6 Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com efficiency curves for handling a similar dust and gas. efficiency curve in order to determine overall cyclone All other methods of determining cyclone efficiency collection efficiency. are estimates and should be treated as such. (1) A particle size distribution curve shows the b. Predicting cyclone collection efficiency. A parti- weight of the particles for a given size range cle size distribution curve for the gas entering a cyclone in a dust sample as a percent of the total is used in conjunction with a cyclone fractional weight of the sample. Particle size 6-2
  7. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM 6-3
  8. TM 5-815-1/AFR 19-6 Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 6-4
  9. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM distributions are determined by gas sampling inlet ductwork and the outlet ductwork. This pressure and generally conform to statistical drop is a result of entrance and exit losses, frictional distributions. See figure 6-8. losses and loss of rotational kinetic energy in the (2) A fractional cyclone efficiency curve is used exiting gas stream. Cyclone pressure drop will increase to estimate what weight percentage of the as the square of the inlet velocity. particles in a certain size range will be b. Cyclone energy requirements. Energy require- collected at a specific inlet gas flow rate and ments in the form of fan horsepower are directly pro- cyclone pressure drop. A fractional efficiency portional to the volume of gas handled and the cyclone curve is best determined by actual cyclone resistance to gas flow. Fan energy requirements are testing and may be obtained from the cyclone estimated at one quarter horsepower per 1000 cubic manufacturer. A typical manufacturer’s frac- feet per minute (cfm) of actual gas volume per one tion efficiency curve is shown on figure 6-9. inch, water gauge, pressure drop. Since cyclone (3) Cyclone collection efficiency is determined by pressure drop is a function of gas inlet and outlet areas, multiplying the percentage weight of particles cyclone energy requirements (for the same gas volume in each size range (size distribution curve) by and design collection efficiency) can be minimized by the collection efficiency corresponding to that reducing the size of the cyclone while maintaining the size range (fractional efficiency curve), and same dimension ratios. This means adding more units adding all weight collected as a percentage of in parallel to handle the required gas volume. The the total weight of dust entering the cyclone. effect on theoretical cyclone efficiency of using more units in parallel for a given gas volume and system 6-4. Cyclone pressure drop and energy pressure drop is shown in figure 6-10. The increased requirements collection efficiency gained by compounding cyclones in parallel can be lost if gas recirculation among a. Pressure drop. Through any given cyclone there individual units is allowed to occur. will be a loss in static pressure of the gas between the 6-5
  10. TM 5-815-1/AFR 19-6 Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 6-5. Application other equipment or as a final cleaner to improve overall efficiency. a. Particulate collection. Cyclones are used as par- b. Pre-cleaner. Cyclones are primarily used as pre- ticulate collection devices when the particulate dust is cleaners in solid fuel combustion systems such as coarse, when dust concentrations are greater than 3 stoker fired coal burning boilers where large coarse grains per cubic foot (gr/ft3), and when collection effi- particles may be generated. The most common applica- ciency is not a critical requirement. Because collection tion is to install a cyclone ahead of an electrostatic efficiencies are low compared to other collection precipitator. An installation of this type is particularly equipment, cyclones are often used as pre-cleaners for 6-6
  11. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM 6-7
  12. TM 5-815-1/AFR 19-6 Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 6-8
  13. Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com 5-815-1/AFR 19-6 TM 6-9
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