The regenerative thermal oxidizer (RTO) is a very durable, well-proven technology suitable for treating a wide variety of emission streams. However, The RTO may not be the most economical technology available. Two very common systems for treating emissions from coating and finishing processes are the RTO and the concentrator/ oxidizer system. To determine which system is best suited for a given application, the capabilities and life-cycle costs of each must be evaluated and compared.
Below is a summary of the RTO and the concentrator/ oxidizer system, how each operates, how their characteristics affect both plant operation and life-cycle costs, and details on actual life cycle costs and performance data.
ADD-ON CONTROL OPTIONS- CATALYTIC, RECUPERATIVE, AND REGENERATIVE OXIDIZERS, ROTARY CONCENTRATOR
Emissions limits established by the Clean Air Act forced the finishing industry to greatly reduce the solvents exhausted from coating and finishing facilities. Production and quality demands eliminate any chance of reducing emissions through reduced production or alternate coatings. Thus finishers are forced to install an add-on solvent emission control system. MACT standards require that any add-on solvent control system exceed 95% DRE; future requirement of 99% DRE is also possible.
The evaluation by most industry plants to determine the most economical control system takes into account the following factors.
- Capital and operating costs
- Expandability- Can the system be expanded when production increases?
- System down time- Will the entire system shut down if one component requires maintenance?
- Ability to increase system efficiency- Can the system meet possible future requirements of 99% DRE
- Ability to handle widely varying solvent loads- The efficiency must remain essentially constant over the wide range of inlet solvent loadings
- Ability to handle a solvent stream containing 100% ketones- The hazards of readily-oxidizing ketones must be adequately addressed
- Footprint- Site constraints
- Noise Levels- Surrounding offices and residential areas may mean noise is a concern
Several solvent control technologies can be considered, including solvent recovery, recuperative, catalytic, and regenerative oxidation, and rotary solvent concentration. The recuperative and catalytic oxidizers are quickly eliminated because at large air volumes and relatively low solvent levels the operating cost were prohibitive.
The evaluation for the most economical and efficient solvent emission control system therefore focuses on: a) a large stand-alone regenerative thermal oxidizer (RTO); and, b) a rotary solvent concentrator followed by a small RTO.