 A thermal oxidiser and heat exchanger designed and manufactured by GCD. The equipment was built to address a serious odour problem at a liquid waste treatment plant near the Sydney 2000 Olympic Games Village. |
The US Clean Air Act (CAA) amendments of 1990 required that the EPA establish Maximum Achievable Control Standards (MACT) for major sources of Hazardous Air Pollutants (HAP) emissions. The EPA identified 174 major industry categories which are subject to MACT standards. Some MACT standards have already been promulgated while others are imminent. A list of 189 specific chemical compounds were identified as HAPs. Nineteen (19) of the 189 HAPs account for nearly 75 percent of the total air toxics emissions. Most of these 19 compounds can be controlled effectively with thermal oxidation technology.
GCD, with over 1000 reference sites worldwide, is the world leader in the supply of custom designed low NOx thermal oxidation (incineration) systems for the destruction of industrial waste gases and liquids containing organic compounds. Applications cover a wide range of industries including chemical, petrochemical, pharmaceutical, petroleum, oil & gas, man made-fibres and general processing.
Thermal oxidisation systems are available for projects anywhere in the world from the following companies within the GCD: Process Combustion Corporation, Pittsburgh USA; PCC Sterling Ltd, Aylesbury UK; and GCD International Pty Ltd, Melbourne Australia.
Destruction levels of organics higher than 99.99% can be achieved.
Typical Industries
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Typical Waste Steams
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 Waste condensate incinerator for PNG oil field |
A Thermal Oxidiser sometimes described as an incinerator is a reactor designed to oxidise certain chemical species in a liquid or gaseous waste stream, e.g. methane (CH's), hydrogen sulphide (H2S), carbon monoxide (CO), to less harmful components, e.g. carbon dioxide (CO2) water vapour (H2O) and sulphur dioxide (SO2).
Most thermal oxidation, combustion and burning processes consist of the following three (3) reactions:C + O2 è CO2 + 32,852 kJ/kg of C
2H2 + O2 è 2H2O + 120,337 kJ/kg (LVH) of H2
S + O2 è SO2 + 9,285 k J/kg of S
The waste stream containing these, or other components, is introduced into a combustion chamber (oxidiser) which has already been heated to a temperature above the minimum required to initiate the oxidation reaction. This minimum temperature depends on the chemical species being oxidised. For example, H2S might require a minimum of 650oC whilst CO may need 900oC. In order for the reaction to take place, the containments must be mixed with air to provide oxygen for the reaction.
 Diagram: typical fully integrated thermal oxidation system |
There are three essentials for effective oxidation to take place:
Temperature: to achieve the correct temperature required to break the molecular bones of the individual chemical species in the waste stream into their basic elements to allow oxidation to take place.
Turbulence: to ensure that all the chemical species in the waste stream are brought to the correct temperature by thorough mixing with the products of combustion (P.O.C.) in a turbulent environment. Thorough mining is critical when the concentration of the chemical species is diluted and/or the waste stream is inert. The GCD uses proprietary mixing technology to ensure turbulence and thorough mixing.
Time: to maintain the temperature required for oxidation for sufficient length of time to ensure that mixing and oxidation is fully completed.
The degree of oxidation for each chemical species in a thermal oxidiser is measured as "destruction efficiency". This is defined as:
(inlet concentration of species - outlet concentration of species) x 100 / inlet concentration of component
and is measured in %.
Targeted DRE's are normally 99% or greater and may be 99.9999% for "nasties" such as PCB's and furans.
In order to achieve the required destruction efficiency for a particular compound (e.g. H2S) a residence time must be chosen. The longer the residence time, the greater the destruction efficiency. Also, the residence time required is inversely and exponentially proportional to the temperature - i.e. the higher the temperature, the shorter the residence time required for a particular compound.
The temperature and residence time are therefore selected for a particular situation, to achieve the required destruction efficiency for a particular chemical species in the waste stream. The incinerator is designed and controlled to always operate above the minimum temperature and to give greater than the required residence time to achieve the required destruction efficiency for that chemical species.
As mentioned above, the destruction efficiency depends on the temperature and residence time. To make sure destruction efficiency is maintained, it is necessary to make sure the oxidiser temperature is controlled so that it is always above the minimum, that there is sufficient oxygen for the reaction and that the residence time is not reduced. Oxidiser temperature control is achieved by varying the flow of fuel into the unit. Sufficient oxygen may be achieved by controlling the air flow to the unit (by setting the draught on a natural draught unit, or by air fuel ratio control on a forced draught unit). Sufficient residence time is achieved by making sure that the oxidiser is sized to accept the largest possible flow of waste gas.
To ensure that the thermal oxidiser always meets the destruction efficiency requirements it is necessary to design the unit correctly, to control the temperature and to set up (natural draught) or control (forced draught) the oxygen level in the thermal oxidiser.
Optimise effectiveness
Optimise efficiency
Maximise reliability
Minimise Capital costs
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© 2002 GCD International Pty Ltd. |
