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Going Regenerative
(An Article from Pollution Online)
How much is yesterday’s oxidizer costing you today?
When one manufacturer of coated products in central New York looked at its natural gas bill, it decided that enough was enough. The destruction efficiency of their outdated, recuperative thermal oxidizer was slipping and the annual cost for repairs was increasing. The constant roar of the burners was a reminder of the wasted dollars of fuel consumption. The equipment of the past was no longer acceptable in the heavily regulated and competitive market of today.
This is when they turned to Alstom Air Preheater Company and the TechNO-VOC™ oxidizer for a more practical solution to their pollution.
The Problem
 Recuperative oxidizers rely on shell and tube heat recovery. These heat exchangers are traditionally stainless steel, which is susceptible to loss of structural strength at temperatures in excess of 1000°F. This limit’s the technology’s oxidation temperature to no more than 1500°F. Furthermore, there is a law of diminishing returns in recuperative technology. Each additional pass in a shell and tube heat exchanger will approximately double the pressure drop and capital investment, but the increase in thermal effectiveness will increase at a less than proportional rate. For this reason, many such oxidizers are only 60-70% thermally efficient.
Besides the limitations in heat recovery, many existing recuperative oxidizers are inefficient by design. In past decades, many facilities purchased their recuperative oxidizers based on high solvent loading, and even worse, theoretical "future" conditions that never materialized. In many cases, processes were changed to include less solvent because of EPA regulations, economic concerns or even changes in the process or product. Recuperative oxidizers have only one corrective measure to adapt to these changes – fire the burners at a higher rate.
A manufacturer of goods that use solvent coatings are caught in a crossfire between burners firing at rates higher than anticipated and the ever-increasing cost of natural gas.
A New Solution
Consider all the things that one would look for in an oxidizer:
» High Destruction Efficiency
» Self-Sustaining Operation (high thermal effectiveness)
» Low Unit Pressure Drop
» Unit Reliability
» Ease of Service and low maintenance
The TechNO-VOC™ oxidizer is the culmination of Alstom Air Preheater Company’s decades of experience in VOC destruction and the manufacturing of oxidation equipment. The innovative design is distinguishable by several features.
 Each of the two heat transfer beds is a layer of ceramic sub-straight. The specially formulated material is is chemically inert and unfazed by temperatures over 2000°F. This structured geometry provides the same heat transfer, but lower pressure drop than random packed media beds of other designs. This type of heat exchanger is much more thermally efficient than the shell-and-tubes of the past. With 95% thermal recovery, the TechNO-VOC™ oxidizer becomes self-sustaining at approximately 3-1/2% LEL.
The impact of this increased thermal efficiency is that for many common applications, the TechNO-VOC™ oxidizer is completely self-sustaining on the heat released from the VOCs themselves. In applications of extremely low solvent loading, an automatic system of natural gas injection (NGI) is employed as a supplemental heat source. The benefit of using NGI is that there is no formation of NOx, as there would be if a burner was used for additional heat.
The direction of flow alternates to keep the oxidation zone centered between the two heat exchanger layers. This is accomplished by a vertical poppet valve. Vertical poppet valves are industry proven to be a low leakage answer to the issue of flow redirection. The placement and easy access of the valve assembly makes servicing the poppet valves less timely than other arrangements.
The Satisfied Customer
 Recuperative technology was clearly not a ideal solution for the coating line in central New York State. A new TechNO-VOC™ oxidizer replaced the direct-fired unit. . Testing revealed that the TechNO-VOC™ oxidizer was performing with a destruction efficiency in excess of 99% -- exceeding the requirements of the EPA.
As predicted, the increase in thermal efficiency of the new oxidizer began to immediately pay dividends. For the first time in a dozen years, the natural gas meter stopped turning as the VOC itself became the fuel for the oxidizer, accounting for an annual savings of $140,000. |