Volatile Organic Compounds & Odor Treatmet

General

VOCs are those organic liquids or solids whose room temperature vapor pressues are greater than about 0.0007atm and whose atmospheric boiling points are up to about 260. VOCSs arecontributors to the problem of photochemical oxidants and also powerful infrared absorbers and thus contribute to the greenhouse problem. Some our know to be toxic or carcinogenic

VOCs are widly used as liquid fuels, solvent, or chemical intermediates

The Kinds of VOCs

1. Alkanes (CnH2n+2) 2. Alkenes (CnH2n) 3. Alkynes (CnH2n-2) 4. Aromatics (ArH, ArR) 5. Haloalkane (R-F, -CI, etc.) 6. Alcohol (R-OH) 7. Ketones (RCOR) 8. Aldehyde (RCOH) 9. Carboxyl Acid (RCOOH) 10. Amines (RNH2) 11. Mercaptane (RSH)

Soures of VOCs

Chemical plants Petroleum refinerles Pharmaceutical plants Automobile manufactures Food processors Fiber manufactures Textiles manufacutres Printing plants Can coating plants Electronic component plants Painting facilities Wood stoves

Emission Control Technologes

• Thermal Incinerators
  Thermal incineration is the direct application of combustion to destory exhaust gases. It is a rapid, high - temperature, gas-phase reaction in which the pollutants are oxidized. The constituents of the waste stream, excluding halogenated compounds, theoretically can be converted to carbon dioxide and water in the pressure of sufficient heat, oxygen, and residence time.
  
  • Regenerative Thermal Oxidizer (RTO)
    In a RTO the process exhaust is preheated through use of a ceramic heat exchange bed before entering the central combustion chamber. Large ceramic beds are used as massive heat sinks. When cool these beds first absorb heat energy from the exhaust gases exiting the central oxidation chamber; when hot they release this energy to the new incoming air stream. This continuous cycle of alternately storing and releasing heat permits an uninterrupted flow of contaminated gas through the system at all times. It is made possible by sequencing the gas flow through the beds via valve controls and by utilizing and add number of chamber

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  • Recuperative Thermal Oxidizer
    Waste gas stream is preheated before entering the combustion chamber through use of heat exchangers that recover heat energy from the combustion chamber exhaust in a cotinuous, steady state process. Plate-to plate and shell-and-tube heat exchangers typically are used for recuperative heat recovery
    
• Catalytic Incinerators
  Catalytic Incinerator is similar in design and operation to thermal incineration except that a catalyst is used to enhance the oxidation of air contanminats at much lower temperatures. Catalysts increase the rate of reaction to occur at more favorable pressures. As preheated exhaust gases enter the catalytic bed, they are adsorbed onto the surface of the catalyst.
  
  The catalyst bed initiated and promotes the oxidation of the air toxics without being permanently altered itself
  
  Difference between catalytic Oxidizer and Thermal Oxidizer

• Carbon adsorption
  Vapor phase adsorption is a surface-related phenomenon that occurs when a gas is brought into contact with a solid substance, resulting in collection,capture, and retention of the contaminat from the gas phase by the adsorbing granular solid
  
  Adsorption can be used on waste gas streams of extremely low pollutant concentration and for contaminat gases that are noncombustible. Activated carbon is the most versatile of the solid adsorbents
  
• Absorption
  Absorption is gas-liquid contacting process that utilizes the prefernential solubility of a contaminated gas in a liquid solvent where one or more of theconstituents of the gas dissolve in a nonvolatile liquid-solid slurry
  
• Condensation
  Condensation is an operation in which one or more volatile components of a vapor mixture are separated from the remaining vapor by being changed to the liquid phase through extraction of the heat of condensation. Condenser can be located ahead of absorbers, incinerators,or carbon beds to reduce the contaminant loading to the more expensive control device. Condenser also can remove vapor componets that might adversely affect the operation of other equipment or cause corrosion problems, or they can be simply to recover a valuable material that otherwise would be destroyed
  

Consuderations of Design Emission Control Technologles

• Thermal Incinerator
  
  • Residence time
    Residence time is the timerequired for the initiation and completion of the oxidation reactions thermal incinerator are designed for a minimum residence time of 0.5 to 1 second in the combustion chamber
    
  • Operating temperature
    Operation temperature depends on the residence time,the oxygen concentration,the type and concentration of the contaminant involved, the type and amount of auxiliary fuel, and the degree of mixing.Thermal inclineator for general use operate at a temperature ranging from 800-850℃
    
  • Lower expiosive level (LEL)
    Concentrations of flammable compounds typically cannot exceed 25 percent of the LEL for safety and insurance reasons. If the concentration of flammable compounds is greater than 25 percent, the gas stream should be diluted with air to reduce the potential for expiosion.
    
  • Turbulent mixing
    There must be sufficient turbulent mixing of the fuel, air and waste for obtaining high efficiency of VOCs removal
    
• Catalytic incinerator
  
  • Space velocity
    The volume of gas entering the catalyst bed divided by the volume of the catalyst bed
    
  • Catalyst poison
    The poision or fouling of catalyst surfaces decreases performance and increase maintenance; spent catalyst replacement cost is significant. Catalyst posion is caused heavy metals, halogen, sulfur,silicon etc.
    
  • Heat value
    Generally, structure deformation of catalyst takes place at more than 500
    
  • Catalyst selection
    Performance of catalyst depends on kinds of activity material contenten amount, addition and microsocopic porosity. Selection of catalyst is very imporant to reprove the system performance
    
• Factors selecting the VOCs Removal System
  Selection parameters based upon volume flow and contamination level

RTO :Regenerative thermal oxidizer
RCO : Regenerative Catalytic Oxidizer
TO : Recuperative Thermal Oxidizer
Compact TO : Compact Recuperative Thermal Oxidizer

• Critical Selection Factors
  • Gas stream composition and concentrations
  • Process exhaust volume (i.e., maximum, average, and minimum flow rate), temperature, pressure, humidity, and reactivity
  • Number of individual emission sources
  • Existence of problem pollutants (e.g., particulate matter, chorinated compounds, and heavy hydrocarbons)
  • Hours of annual operation (i.e., percent operating time)
  • Equipment location (e.g., indoors, outdoors, ground level, roof, and available space)
  • Auxiliary fuel or energy costs
  • Overall economics (i.e., capital and annual operating costs)

• Advantage of TYME & KEU(Germany)` RTO
  • We have many references work for mainfold process in world wide
  • RTQ performance efficency depends on damper.As we have kinds of dampers, our damper apply to different process.(i.e. normal damper, high-temp. damper, anti-abrasive damper etc.)
  • The tar in waste gas is removed by burn-out system
  • We have much know-how at manlfold process