Ozone generator


Ozone generators Ozone hole  [c.715]

O ne. Air pollution (qv) levels are commonly estimated by determining ozone through its chemiluminescent reaction with ethylene. A relatively simple photoelectric device is used for rapid routine measurements. The device is caHbrated with ozone from an ozone generator, which in turn is caHbrated by the reaction of ozone with potassium iodide (308). Detection limits are 6—9 ppb with commercially available instmmentation (309).  [c.276]

Commercial production and utilization of ozone by silent electric discharge consists of five basic unit operations gas preparation, electrical power supply, ozone generation, contacting (ie, ozone dissolution in water), and destmction of ozone in contactor off-gases (Fig. 1).  [c.497]

Ozone Generation from Oxygen. Oxygen is dissociated iato atoms by iaelastic coUisions with energetic electrons (6—7 eV) (89,90).  [c.498]

Ozone can be destroyed thermally, by electron impact, by reaction with oxygen atoms, and by reaction with electronically and vibrationaHy excited oxygen molecules (90). Rate constants for these reactions are given ia References 11 and 93. Processes involving ions such as 0/, 0/, 0 , 0 , and 0/ are of minor importance. The reaction O3 + 0( P) — 2 O2, is exothermic and can contribute significantly to heat evolution. Efftcientiy cooled ozone generators with typical short residence times (seconds) can operate near ambient temperature where thermal decomposition is small.  [c.498]

Ozone Generation from Air. Although the use of air for ozone generation has the advantage that air, unlike oxygen, is readily avaHable, the concentration of ozone produced with air is lower than that produced with oxygen. In addition, the presence of moisture ia air iaterferes with discharge formation and reaction kinetics and creates potential for corrosion that can adversely affect the performance of the ozone generator and iacrease the need for maintenance. The basic chemistry of ozone generation from oxygen is more complex when air is employed because of formation of nitrogen atoms, vibrationaHy excited nitrogen molecules, and nitrogen oxides (89,94). Nitrogen atoms are formed by the dissociation of nitrogen molecules by electron impact they can generate oxygen atoms via the foHowiag reactions N-HO2 — NO-HO and N -H NO — N2 +0. Oxygen atoms also can be formed by the dissociation of molecular oxygen by vibrationaHy excited nitrogen molecules. Thus, atomic nitrogen and excited nitrogen molecules enhance the formation of ozone by increasing the atomic oxygen concentration.  [c.498]

Suppression of Nitrogen Oxides. The concentration of nitrogen oxides during preparation of ozone from air increases linearly with the energy density in the discharge, causing a decrease in the formation rate of ozone. Most commercial ozone generators produce 0.5 kg of nitrogen oxides for every 100 kg of ozone generated. The formation of nitrogen oxides at a given energy density is minimized by decreasing the residence time and temperature, increasing the pressure, and reducing the dew point of air.  [c.498]

Feed Gas Preparation. The use of oxygen for industrial ozone generation is significant and increasing. Oxygen provides a higher ozone concentration and more efficient ozone dissolution than air, and does not add nitrogen oxides to the water. It is prepared from dry, filtered air by hquefaction and fractional distiHation. Liquid oxygen (LOX) can be prepared on-site or purchased from vendors. Oxygen is sometimes used to enrich air-fed systems. Although oxygen-rich off-gases from ozone contactors can be recycled, more often they are discarded to avoid redrying costs.  [c.498]

Cooling Requirements. Since the majority of the electrical energy input to the electric discharge is dissipated as heat, cooling is necessary to minimize decomposition of ozone and extend dielectric life. Double-sided cooling is more effective than single-sided cooling in removing heat from the ozone generator. The gas exiting an efftcientiy cooled ozone generator normally is near ambient temperatures where the rate of decomposition is low.  [c.498]

Electrical Characteristics. The basic features of an electric discharge ceH are depicted in Eigure 2. Electrical energy to the ozone generator is provided by a power supply, a frequency converter, and a transformer. Ozone formation is directiy proportional to the power consumed in the discharge at constant concentration, temperature, and pressure. The average discharge power consumption P (W) is given by (96)  [c.498]

Fig. 2. Basic configuration of ozone generators. Fig. 2. Basic configuration of ozone generators.
The potential and frequency employed in commercial ozone generators varies with the type of design and can range from 5—20 kV and 50—3000 Hz, respectively. Typically, high frequency ozone generators operate at lower voltages, where the expected lifetime of the high voltage electrode is virtually unlimited. Although lower voltage decreases the ozone production rate, when combined with high frequency it can produce more ozone per unit electrode area. Modem ozone generators operating at 10 kV rms and 600—1000 Hz employ power densities of 3—4 kW/m, resulting in production densities of 0.2—0.25 kg/hm in air and 0.35—0.45 kg/hm in oxygen (97).  [c.499]

Ozone Concentration and Yield. The output of an ozone generator can be increased by raising the power input at constant temperature and feed gas flow rate, but the increase in output is less than proportional unless the gas flow is increased to maintain a constant ozone concentration. Raising the flow rate at constant power input decreases the ozone concentration but increases the ozone and energy yields. At low flow rates, although the ozone concentration is high, the yield is low because the specific energy is high. At higher flow rates, the ozone concentration decreases the yield approaches a limiting value because the specific energy does not change much at low ozone concentrations.  [c.499]

Most ozone generators currently in operation produce ozone in concentrations of 1—1.5 wt % (12—18 g/m ) in air and 2—3 wt % (27—40 g/m ) in oxygen. However, modem, weU-cooled ozone generators can produce ozone efficiently at double these concentrations, ie, 2—3 wt % (24—37 g/m ) in air and 4—6 wt % (54—81 g/m ) in oxygen (97). The required ozone concentration depends on the appHcation concentrations as high as 16 wt % have been produced in oxygen. Commercial ozone generators are available that have different ozone production rates from air, ranging from 10 g/h to 90 kg/h higher production capacities are obtained by combining multiple units.  [c.499]

Energy Requirements and Efficiency. The thermodynamics of ozone synthesis require the expenditure of 142.7 kj/mol (34.1 kcal/mol) thus the formation of 1 kg of ozone requires 2.97 MJ (711 kcal) or 0.85 kWh/kg at 100% efficiency. The more concentrated the ozone, the higher the specific energy (kWh/kg) and the lower the efficiency. The specific energy for ozone production from dry oxygen varies from 7—14 kWh/kg over the 1—6 wt % range. For dry air, the specific energy (15—22 kWh/kg for 0.5—3.0 wt % ozone) is lower than expected due to the contribution of atomic nitrogen to ozone formation. The higher-than-theoretical specific energy requirements are due to the fact that most of the suppHed energy is converted to heat resulting from ozone formation and decomposition reactions. These specific energy requirements correspond to ozone synthesis efficiencies from oxygen and air of 6—12% and 4—6%, respectively. Thus, the portion of the input synthesis energy dissipated as heat is 88—94% for oxygen and 94—96% for air. In addition to the power requirements for the ozone generator, the air-preparation unit requires 4.4—7.7 (kWh)/kg ozone, and the oxygen-recycle unit an additional 2—7 (kWh) /kg ozone.  [c.499]

Ozone Generator Design. A better understanding of discharge physics and the chemistry of ozone formation has led to improvements in power density, efficiency, and ozone concentration, initiating a trend toward downsizing.  [c.499]

The basic configuration of an electric discharge cell consists of two closely spaced electrodes (one of which is coated with a dielectric), suppHed with high voltage ac and filled with a flowing oxygen-containing gas. The gap width varies from 1 to 3 mm, depending on whether oxygen or air is employed. The purpose of the dielectric, usually made of glass or ceramic, is to limit current flow, resulting in the formation of a relatively cold plasma. A thin dielectric with a high dielectric constant faciUtates heat removal and improves ozone-generating efficiency. The higher the appHed voltage, the thicker the electrode should be to prevent failure by electrical arcing. The dielectric must be strong enough to withstand mechanical shock and prevent puncturing by the apphed voltage. High peak voltages induce dielectric failure, as do high power densities, the latter on account of its dielectric heating.  [c.499]

The electric discharge ozone generator is equivalent to a gas-phase reactor having internal heat generation its design also bears some similarity to heat exchangers such as shell and tube. The gap width influences both the voltage requirement and the back pressure and should be uniform to avoid hot spots. Small gap widths typically are employed to faciUtate heat removal the smaller the discharge gap, the greater the power efficiency.  [c.499]

Types of Ozone Generators. Since 1906, a number of different ozone generators have been developed, including the plate-type (water- or air-cooled), the horizontal tube (water-cooled), and the vertical tube (water- or oil- and water-cooled) generators. Originally introduced in 1906, plate-type ozone generators have experienced operational problems and have been discontinued for use in some countries, even though many installations remain operational and the technology is stiU being promoted by some manufacturers.  [c.499]

The horizontal tube-type ozone generator (Fig. 3a) was a significant improvement over the plate-type ozone generators. A single unit consists of two concentric tubes, an outer stainless steel tube that serves as the ground electrode, and an inner glass tube sealed at one end (which functions as the dielectric) with an inner conductive coating that acts as the high voltage electrode. Discharge occurs in the annular space between the two tubes through which the feed gas flows. A group of tubular units (eg, up to 1000) is arranged in parallel and enclosed in a cylindrical housing so that the ends protmde out of the cooling water jacket, which cools the outside stainless steel tube. Manifolds distribute the feed gas to the annular discharge spaces of the tubes at one end and collect the ozone-containing gas at the other. The tubular electrodes are suppHed with low frequency power (- 60 Hz). When higher production rates (>10 kg/h) are required, the use of soHd-state variable medium frequency (600—1000 Hz) power suppHes may be cost-effective.  [c.499]

Off-Gas Treatment. Ozone-transfer efficiencies vary with the number of stages and are typically above 90%. However, since even a 95% ozone absorption efficiency can result in a contactor off-gas containing as much as 740 ppmw ozone (based on a 1.5 wt % feed gas), treatment is required to reduce the ozone concentration to an acceptable maximum level of 0.2 mg/m. Ozone in the vent gases from water-treatment ozone contact chambers is destroyed mainly by thermal (300—350°C for <5 s) and/or catalytic means, and sometimes by wet granular-activated carbon (GAG). Another option is recycling the off-gas to points in the water-treatment system having a high ozone demand. Dilution of ozone vent gases with air has been employed whenever practical. When oxygen is used as the feed gas, it can be recycled to the ozone-generation step however, once-through operation is common in order to avoid redrying costs.  [c.501]

Ozone. Ozone generators are based on uv or silent discharge. Although uv ozone generators are marketed, they are not effective for treating  [c.296]

Figure 14-4 illustrates the analytical technique based on this principle. To determine the NO2 concentration, the NO and NO (NO -I- NO2) concentrations are measured. The block diagram shows a dual pathway through the instrument, one to measure NO and the other to measure NO. The NO pathway has an ambient air stream containing NO (as well as NO2), an ozone stream from the ozone generator, a reaction chamber, a photomultiplier tube, and signal-processing circuitry. The NO pathway has the same components, plus a converter for quantitatively reducing NO2 to NO. The instrument can also electronically subtract the NO from NO, and yield as output the resultant NO2.  [c.199]

The mechanism for ozone generation is the excitation and acceleration of stray  [c.486]

Figure 7, Types of ozone generators. Figure 7, Types of ozone generators.
Contactor design is important in order to maximize the ozone-transfer efficiency and to minimize the net cost for treatment. The three major obstacles to efficient ozone utilization are ozone s relatively low solubility in water, the low concentrations and amounts of ozone produced from ozone generators, and the instability of ozone. Several contacting devices are currently in use including positive-pressure injectors, diffusers, and venturi units. Specific contact systems must be designed for each different application of ozone to wastewater. Further development in this area of gas-liquid contacting needs to be done despite its importance in waste treatment applications. In order to define the appropriate contactor, the following should be specified  [c.488]

A typical ozone system consists of 100 g/hr at a concentration of 1.0 percent to 1.5 percent in air fed to the bottom of bleach collection tanks through ceramic spargers (pore size of approximately 100 t). The system contains air compression and drying equipment, automatic control features, and a flat-plate, air-cooled ozone generator. Regeneration of bleach wastes totaling about 10,000 gallons a year, and recovery of other chemicals can also be cost effective.  [c.490]

Ozonation systems are comprised of four main parts, including a gas-preparation unit, an electrical power unit, an ozone generator, and a contactor which includes an off-gas treatment stage. Ancillary equipment includes instruments and controls, safety equipment and equipment housing, and structural supports. The four major components of the ozonation process are illustrated in Figure 8.  [c.491]

A high level of gas preparation (usually air) is needed before ozone generation. The air must be dried to retard the formation of nitric acid and to increase the efficiency of the generation. Moisture accelerates the decomposition of ozone. Nitric acid is formed when nitrogen combines with moisture in the corona discharge. Since nitric acid will chemically attack the equipment, introduction of moist air into the unit must be avoided. Selection of the air-preparation system depends on the type of contact system chosen. The gas-preparation system will, however, normally include refrigerant gas cooling and desiccant drying to a minimum dew point of -40° C. A dew-point monitor or hygrometer is an essential part of any air preparation unit.  [c.491]

Electrical power supply units vary considerably among manufacturers. Power consumption and ozone-generation capacity are proportional to both voltage and frequency. There are two methods to control the output of an ozone generator vary voltage or vary frequency. Three common electrical power supply configurations are used in commercial equipment  [c.492]

The most frequently used is the constant low-frequency, variable-voltage configuration. For larger systems, the 600-Hz fixed frequency is often employed as it provides double ozone production with no increase in ozone generator size. The electrical (corona) discharge method is considered to be the only practical technique for generating ozone in plant-scale quantities. In principle, an ozone generator consists of a pair of electrodes separated by a gas space and a layer of glass insulator. An oxygen-rich gas is passed through the empty space and a high-voltage alternating current is applied. A corona discharge takes place across the gas space and ozone is generated when a portion of the oxygen is ionized and then becomes associated with nonionized oxygen molecules.  [c.492]

Figure 9 shows the details of a typical horizontal tube-type ozone generator. This unit is preferred for larger systems. Water-cooled plate units are often used in smaller operations. However, these require considerably more floor space per unit of output than the tube-type units. The air-cooled Lowther plate type is a relatively new design. It has the potential for simplifying the use of ozone-generating equipment. However, it has had only limited operating experience in water treatment facilities.  [c.492]

Power supplied to the ozone generators. The parameters measured include amperage, voltage, power, and frequency, if this is a controllable variable.  [c.494]

Flow rate and temperature of the cooling water to all water-cooled ozone generators. Reliable cooling is important to maintain constant ozone production and to protect the dielectrics in the generation equipment.  [c.494]

Discharge Characteristics. The energy for chemical reaction is transferred to oxygen molecules by energetic electrons producing atoms, excited molecules, and ions. In an ozone generator, the feed gas (oxygen or air) passes between two closely spaced electrodes (one of which is coated with a dielectric) under an appHed nominal potential of - 10 kV. A silent or dielectric barrier discharge occurs when the gas becomes partially ionized, resulting in a characteristic violet glow in air. Silent discharge consists of numerous randomly distributed, low current (but high current density) microdischarge pulses (89—92). The approximately columnar streamers or filaments (100—200 )Tm dia) emanating from the metal electrode discharge at the dielectric and extinguish within 10 ns.  [c.497]

Air is widely used as the feed gas for commercial ozone generators. The air feed gas to the ozone generator should be dry and free of foreign matter. EHtered ambient air is drawn into the plant by vacuum, blower, or compressor. The pressure of the treated air can vary from sub atmospheric to >400 kPa kPa (4 atm). Since compression heats the air, cooling is necessary. The air is filtered again to remove oH droplets that can foul the desiccant dryers and interfere with ozone generation. Any hydrocarbons in the air can be removed with activated carbon. Moisture is removed by desiccant-drying or a combination of refrigerant- and desiccant-drying. Desiccant-drying is accompHshed by using molecular sieves (qv), sHica gel, or activated alumina, aH of which are capable of regeneration. Liquid water droplets in refrigerant-dried air should be removed by filtration prior to contacting the desiccant dryers. A final filtration is necessary to remove desiccant dust particles down to 1 p.m. The efficiency of ozone generation decreases with increasing moisture content in the air (95). At high dew points, nitrous and nitric acids are deposited within the ozone generator, decreasing performance and substantiaHy increasing the maintenance frequency. The air feed to the ozone generator should have a dew point of at least —60° C, corresponding to a moisture content of <20 ppmv some systems, however, operate at a dew point of —80° C. A sensor should be placed in the air stream entering the generator that can shut the system off and sound an alarm if the dew point increases above the desired level. In high pressure systems, the pressure of the compressed air prior to entering the ozone generator is reduced by means of a pressure-reducing valve. The pressure employed depends on the ozone generator type and can vary from 100 to 240 kPa (0—20 psig). The pressure of the ozone generator feed should be maintained at a constant level to avoid affecting power draw and apphed voltage.  [c.498]

Significant changes are likely to occur ia the eaergy self-sufftcieacy of the iadustry, resultiag ia an iacreased depeadeacy oa purchased power. Whereas aew iastallatioas and retrofits of existing technologies can result ia greater eaergy efftcieacy, demands from process changes, oxygen/ozone generation requirements, and iacreased environmental regulatioas may create evea greater demand (84). Industry efforts ia the area of eaergy use are expected to focus oa iacreased eaergy coaservatioa, greater utiliza tion of biomass and other renewable energy sources, and process improvements such as better drying efficiency. Emerging technologies are most likely to have a great impact on energy use and generation. Black Hquor and biomass gasification designs are likely to play a significant role ia the future. Many expect these systems to operate at considerably greater efficiency than conventional boilers. In this type of gasification system, black Hquor and other types of biomass are fed directly iato the gasifier, where cleaned steam exits to drive gas turbiaes and produce process steam and more power further downline (84).  [c.284]

Charged particles are collected in the water film, neutralized, and drained off at the bottom of the unit. This type of unit is commonly used on scarfing operations, detarring, and sulfuric acid mist collection.The two-stage precipitator is used where low ozone generation is required. It is frequently applied in the cleaning of recirculated ventilation. The particles are charged in the first field and collected in a second noncorona stage. Intermittent-flush mechanical flushing is used to clean  [c.427]

The mechanism for ozone generation is the exeitation and aeceleration of stray eleetrons within the high-voltage field. The alternating eurrent causes the electron to be attracted first to one electrode and then to the other. As the electrons attain sufficient velocity, they beeome capable of splitting some oxygen moleeules into free radical oxygen atoms. These atoms may then eombine with Oj moleeules to form O3.  [c.454]

A typical ozone treatment plant consists of three basic subsystems feedgas preparation ozone generation and ozone/water contacting. Commercially, ozone is generated by producing a high-voltage corona, discharge in a purified oxygen-containing feedgas. The ozone is then contacted with the water or wastewater the treated effluent is discharged and the feedgas is recycled or discharged.  [c.485]

Basic configurations of ozone generators are shown in Figures 6 and 7. The thre designs are the Otto plate, the tube, and the Lowther plate. The least efficient of these generators is the Otto plate, developed at the turn of the century. The tube and Lowther plate units include modern innovations in material and design. The Lowther plate generator is the most efficient configuration due in large measure to advantages in heat removal. In addition to ozone yield, the concentration of ozone is an important consideration. Ozone concentration from a generator is usually regulated by adjusting the flow rate of the feedgas and/or voltage across the electrodes.  [c.487]

Conversion efficiencies can be greatly increased with the use of oxygen. However, the use of high-purity oxygen for ozone generation for disinfection is, cost effective. The Duisburg plant and the Tailfen plant of Brussels, Belgium, are the only operational municipal water treatment plants known which use high-purity oxygen instead of air as the ozone generator feedgas.  [c.492]

Several parameters should be measured to provide a fully operable ozonation system. There should be a means of providing full temperature and pressure profiles of the ozone generator feedgas from the initial pressurization (by fan, blower, or compressor) to the ozone generator inlet. Moisture content is also important. There should be a means of measuring the moisture content of the feedgas to the ozone generator. This procedure should be conducted with a continuously monitoring dew-point meter or hygrometer. Other parameters that require monitoring include  [c.494]

Temperature, pressure, flow rate, and ozone concentration of the ozonecontaining gas being discharged from all the ozone generators. This is the only effective method by which ozone dosage and the ozone production capacity of the ozone generator can be determined.  [c.494]

Analytical measurements of ozone concentrations must be made in the ozonized gas from the ozone generator, the contactor off-gases, and the residual ozone level in the ozonized water. Methods of ozone measurement commonly used are the simple "sniff" test, Draeger-type detector tube, wet chemistry potassium iodide method, amperometric-type instruments, gas-phase chemiluminescence, and ultraviolet radiation adsorption. The use of control systems based on these measurements varies considerably. The key to successful operation is an accurate and reliable residual ozone analyzer. Continuous residual ozone monitoring equipment may be successfully applied to water that has already received a high level of treatment. However, a more cautious approach must be taken with the application of continuous residual ozone monitoring equipment for water that has only received chemical clarification because the ozone demand has not yet been satisfied and the residua] is not as stable. Ozone production must be closely controlled because excess ozone cannot be stored. Changes in process demand must be responded to rapidly. Ozone production is costly underozonation may produce undesired effects and overozonation may require additional costs where off-gas destruction is used.  [c.494]


See pages that mention the term Ozone generator : [c.21]    [c.1043]    [c.497]    [c.198]    [c.483]    [c.485]   
Fundamentals of air pollution (1994) -- [ c.198 ]