Selecting A Thermal Oxidizer
Various different operating facilities and processes can demand varying types of thermal oxidizers. As a result, companies may want to review which type of thermal oxidizer best suits their needs. Below, we summarize the most salient information on the relative merits of each application, addressing the following four solutions in turn:
- Direct-fired thermal oxidizers
- Regenerative thermal oxidizers
- Catalytic regenerative thermal oxidizers
- Recuperative thermal oxidizers
Direct-Fired Thermal Oxidizer (DFTO)
While presenting the lowest capital cost for design and installation, direct-fired thermal oxidizers have a principal drawback in comparison to more expensive alternatives: their significant use of fuel. The lifetime cost of a direct-fired thermal oxidizer, therefore, depends greatly on the cost of that fuel, which can be unpredictable.
On the positive side, however, DFTOs have advantages when the stream to be treated is very small, and/or the VOC concentration is high, which reduces the fuel demand, and a long-term supply of less expensive fuel gas or oil can of course make a DFTO more affordable. DFTOs are particularly well suited to destroying chlorinated compounds, such as those used in a system with acid gas treatment, or extremely dirty or dusty exhausts. A direct-fired thermal oxidizer can also be adjusted rapidly, accommodating batch and variable-load operations.
Importantly, a DFTO will have a larger exhaust gas flow when compared to other thermal oxidation technologies. The larger fuel consumption is accompanied by a need for combustion air.
In sum, systems relying on direct-fired thermal oxidizer technology may appear at inception to be cheaper, but may present less capital savings in comparison to other TO system options long-term, especially if a wet scrubber is employed for SOx removal, since the DFTO exhaust-gas has to be quenched before it enters the scrubber. And since the quencher and scrubber can each add expense for such a system, a DFTO solution may end up costing more than other TO solutions when viewed in aggregate.
Regenerative Thermal Oxidizer (RTO)
A regenerative thermal oxidizer alternately heats a bed of ceramic material, either a randomly packed or a structured media, then uses that stored heat to raise the temperature of the gas stream prior to combustion. This recovery of heat energy can reduce fuel consumption by up to 90% when compared to a DFTO for the same gas stream. Benefits of a regenerative thermal oxidizer include lower fuel cost, a high destruction efficiency, and only moderate costs for maintenance.
Catalytic Regenerative Thermal Oxidizer
When greater fuel savings are required, a standard RTO unit can be designed to introduce a catalyst as well. In this case, volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) are destroyed at ~600°F (315° C) instead of at ~1,600° F (870° C), requiring approximately 1/3 of the fuel of the conventional RTO.
This technique is attractive when the additional cost of the catalyst is offset for by a proportional savings in fuel costs. Traditionally, the catalytic thermal oxidizer is more economical at VOC loadings of less than 4% LEL.
Recuperative Thermal Oxidizer
Use of a heat exchanger to preheat the incoming gas stream from a thermal oxidizer's exhaust is a solution best suited to operations which run at a steady state for long periods of time, providing an even heat load.
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