Cases have occurred in which companies have spent millions of dollars to legitimately, and in popular opinion, effectively solve the odor problem - only to be at the mercy of the public that suspects a phantom odor, perhaps due to being exposed to such for so long. This danger of variability makes it incumbent on the industrial facility that the issue be solved effectively on the first attempt. Piecing together a solution by papering over it will inevitably lead to recurrence. Further complaints, bad press, and monetary fines are likely to result.
Because of tighter budgets annually for most companies, the piecemeal approach often occurs due to the tendency to find the lowest cost option instead of the most effective one. Initial capital investments into solutions that are prematurely low inevitably fail due to either inadequacy or subsequent crippling costs of ongoing operation in the form of consumables or parts replacement. The informed owner would do well to consider both the spectrum of available solutions as well as their documented history in solving the odor problem in a similar application. Most common technologies for industrial odor problems include:
• Carbon or other sorbent filtration
• Maskants or perfumes
• Tall stack dilution / dispersion
• Chemical or bio scrubbing
• Biofiltration
• Regenerative thermal oxidation
Of these options, thermal oxidation has often proven to be most effective, particularly from the very beginning of operation – there is no need to add consumables, or adjust chemistries. Destroying odors with high temperatures is rarely a question of effectiveness. Use of high temperatures –typically in excess of 1500 F – in a thermal oxidizer proves effective. It also proves a slightly more expensive option to operate compared to less effective odor control systems, unless the RTO is designed with maximum possible heat recovery to minimize use of purchased fuel to operate. The typical argument against using thermal oxidation has come with costs of ownership. However, because of new advancements in equipment, a prudent purchasing agent can find the perfect balance of cost efficiency and effectiveness with the right thermal oxidation technology.
Ongoing maintenance costs can dim initial positive experiences of performance. The main culprit is the valve sealing system that RTOs all employ to direct air from chamber to chamber, to take advantage of ceramic heat exchanger beds for maximum fuel efficiency. The more of these flow reversal valves on an RTO, the greater the chance for odor leakage as well as maintenance upkeep and cost.
About fifteen years ago RTO technology was revolutionized by the introduction of the rotary diverter valve design. This single, heavy duty diverter replaces the multiple valves and actuators found on typical RTOs. The result is fewer moving parts, less wear and tear, and considerably less downtime and maintenance costs.
Even better, the single rotary diverter valve on these RTOs never truly opens or closes by “making” a seat or seal – the diverter indexes across an open air path and methodically seals it off by reaching the next set position. A continuous air purge captures any scavenging dirty air in the switch and returns it for treatment in the RTO. This operation results in near-zero leakage of odor or dirty air, and allows rotary RTOs to routinely remove odor to below threshold detection levels in most cases.
Installation of these systems is greatly simplified by pre-engineered, skid-mounted design that reduces site assembly time and cost. Nearly all electrical wiring and piping is completed on the unit prior to arriving on site, where just a few utility connections are required.
For the purpose of illustrating the effectiveness of regenerative thermal oxidizers, specifically those with rotary valve technology in controlling odor from an industrial facility, the following case study from a pet food manufacturer in California will be presented.
When the pet food manufacturer opened its production plant in California, the company began receiving complaints from residents and neighbors that lived near the facility because of an increasingly worsening odor that was being emitted from their process exhaust. Complaints began coming in at a rapid pace. Threats of fines and sanctions from local government agencies were real possibilities.
Recognizing the need to control the emissions coming from their facility and the desire to remedy this unfortunate issue with their neighbors, the company invested nearly $4,000,000 to solve the issue. Despite the investment in some of the above listed odor control systems, specifically carbon canisters for adsorption and tall stack dilution, the company hired the Environmental and Energy Systems business unit of Dürr Systems, located in Plymouth, Michigan, to hopefully and completely solve their odor control issues. Dürr’s past experience with not only food manufacturing applications, but specifically with pet food manufacturing, uniquely positioned them into providing an effective and cost efficient solution for this issue.
Dürr’s solution was installing their Ecopure® RL single rotary valve regenerative thermal oxidizer at the end of each of the pet food manufacturer’s new process stream ducts. The confidence in this system, specifically the zero leakage single valve technology, allowed Dürr to offer a series of guarantees concerning odor reduction that came along with the purchase of these systems. If these guarantees were not met, Dürr would be contractually liable for creating a new solution at their own expense. While concerns about the cost of thermal oxidation technology to control their odor issue were discussed initially, Dürr designed a system to maximize fuel efficiency, specifically with the use of a proprietary heat exchange ceramic media block internally installed within the RTO. For even more specific applications, the use of secondary heat recovery equipment can be seamlessly integrated at the end of the RTO to capture wasted energy to be used in other parts of the customer’s facility
As soon as the RL RTO system was commissioned and started for process, people from the plant and surrounding neighborhoods began noticing an immediate and dramatic difference. Not only was there an increased reduction, most importantly, there was no longer any odor at all coming from the plant. The complaints stopped and the threat of fines was eliminated. The systems have been in use since 2008 and there have been no reports of system downtime.
The goal in odor control is to effectively eliminate the problem. If the system process can not be changed, the use of odor control equipment will need to be instituted. While initial capital and system maintenance costs for regenerative thermal oxidizers may be more than other methods, the use of RTOs, specifically single rotary valve technology, to eliminate odor is clearly above all others.
