Regenerative Thermal Oxidation (RTO) Technology is the fastest growing segment of the air pollution control equipment supply market. RTO technology has emerged as the preferred technology for treating Hazardous Air Pollutants (HAP) emissions for waste gas streams with low concentrations and large volumes.
Its popularity stems from its ability to achieve very high VOC destruction with no by-product disposal and at reasonable operating costs.
Regenerative Thermal Oxidisers (RTO)
are distinguished by their ability to achieve high heat recovery
efficiencies, often as high as 95%. This is a
significant advantage for high volume, contaminated air streams with
low organic concentrations and no process waste
heat requirements.
Table 1 below compares the operating costs of an
RTO with those of a thermal oxidiser without heat recovery, and a thermal
oxidiser with recuperative heat recovery,
all of which are treating a 25,000 scfm waste gas stream containing 50ppm of
acetone. The fuel cost savings with the RTO
are very significant
TABLE 1 : FUEL COST COMPARISON
|
|
| Annual Fuel Cost | |
| Thermal Oxidiser Without Heat Recovery |
1,046,000 |
| Thermal Oxidiser With Recuperative Heat Recovery (70%
Recovery) |
345,000 |
| Regenerative Thermal Oxidiser with 95% Heat Recovery |
95,000 |
Basis for calculations:
|
|
Table 2 below shows relative
costs between capital and operating costs for RTO, thermal oxidiser with
recuperator, and basic thermal oxidiser
without waste heat recovery.
TABLE 2: RELATIVE COSTS
|
|||
| Oxidiser Type | % Heat Recovery | Capital Cost | Operating Cost |
| Basic |
0 |
1 |
18 |
| Recuperative |
70 |
2.75 |
5.5 |
| Regenerative |
95 |
3.85 |
1 |
Source, Technical papers: * Economics of heat recovery in the Thermal Oxidation of Waste.
RTO technology emerged in the
mid 1980's. Until recently, RTO designs incorporated at least three beds packed
with a heat transfer medium. However, many
suppliers are now offering two bed designs. Two bed designs offer
significant savings in capital costs with only a
minimal reduction in unit performance.
The USA Clean Air Act (CM) amendments of 1990
require that the EPA establish Maximum Achievable Control
Standards (MACT) for major sources of Hazardous Air
Pollutants (HAP) emissions. The EPA has 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 have been 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.
The EPA classifies a major source as one which emits greater than 10 tons/yr of any one HAP or 25 tons/yr of a combination of HAPs. HAP emissions are determined from a combination of concentration and waste gas flow. For example, a waste gas stream at a flow rate of 5,000 scfm must contain 50ppm of acetone to be classified as a major source. However, if the flow rate is 25,000 scfm, a concentration of only 10ppm would qualify this waste gas as a major source.
Previous to MACT standards, waste gases containing low concentrations of VOC were not regulated. However, waste gas streams that contain low concentrations may now be regulated if the volume of gas is high.
Most of the newly regulated streams are air streams contaminated with one or more HAPs. Examples are painting operations in the aerospace and automotive industries, drying operations in the wood products industry, and coating operations in the semiconductor industry.
In the USA the EPA estimates
that the aerospace industry alone emits more than 208,000 tons/yr of
Hazardous Air Pollutants plus an additional 145,000
tons/yr of Volatile Organic Compounds (VOCs).
VOCs will also be regulated in areas in which ozone
levels exceed National Ambient Air Quality
Standards (NMQS). Implementation of recently enacted MACT standards for the
aerospace industry are projected to cost the
industry between $16.5 and $25 billion.