Redesign of Thermal Oxidizers – Five Success Stories

Many thermal oxidizer systems are almost "catalog" type items, supplied to handle common waste situations. Solid waste incinerators, land fill flares, and pulp mill waste gas incinerators are examples of incinerators that differ primarily in size rather than performance.

Thermal oxidizers that are custom designed for a specific application are very common. The waste streams generated by petrochemical plants are often unique, so trying to use an incinerator from one site at another usually involves changes to avoid unstable operation or poor emission performance. Differences in waste flow, heating value, nitrogen content, temperature, oxygen demand, etc. all require careful attention when preparing an existing thermal oxidizer design for new use.

Banks Engineering has redesigned a number of thermal oxidizer systems for use in new situations. Here are a few typical ones:

A metal recovery company needed a thermal oxidizer to dispose of fumes generated by their process to recycle computer circuit boards and other hardware. Budget constraints lead to purchase of an existing thermal oxidizer from a wood treatment operation. Banks Engineering designed new waste gas injection hardware, verified the air blower and natural gas burner suitability and specified an extension to the furnace to handle the larger flue gas flow from the new waste stream. Fabrication shops near the new site then made the required changes and the company enjoyed a savings of about 50% vs. a newly designed thermal oxidizer system.

A geothermal power plant needed larger capacity to handle acid waste gases from their turbine exhaust. They purchased a thermal oxidizer from a similar plant and Banks Engineering checked the waste gas handling system, combustion air system and wet quench hardware for the new use. With small changes to the stainless steel waste injectors and relocation of some quench water guns, the system was reinstalled in its new location and put into service. The savings, again, were at least 50% of the price of new.

A petrochemical plant was being enlarged due to an increased demand for its product. The existing thermal oxidizer was too small – increased flow rates would increase backpressure on the process too much and emissions were likely to rise. In addition, the furnace was already showing signs of unstable operation, causing "breathing" which aged the expansion joints too fast. Banks Engineering upgraded the heat & material balances for the new conditions, and working with an outside firm to generate computerized fluid dynamic models, settled on new waste gas delivery hardware, new fuel gas injectors and new air delivery equipment. Changes were made in conjunction with a scheduled shutdown and the thermal oxidizer was brought back up with increased waste flow, better stability and almost no increase in emissions. No change in the existing air permit was needed and the plant avoided purchase of a new system – over $1,000,000 savings.

A pesticide manufacturer had installed a small thermal oxidizer system for disposal of waste gases containing chlorinated compounds. Over the years, the waste gas mix had changed enough that the burner had become unstable enough to cause nuisance shutdowns every few weeks. Banks Engineering generated new heat & material balances, determined that several aspects of the waste handling system were likely causing the problems and designed changes that were built and installed by the plant maintenance shop. At the same time, the system instrumentation was examined to determine why flow measurements had become unreliable in the flue gas stream to the scrubber. Some simple changes to eliminate liquid impingement were recommended and installed. The system was restarted with good results.

A natural gas processing plant was using a thermal oxidizer to dispose of tail gases from their Claus sulfur plant. Flame-outs had been a problem from the start, but increased throughput forced a careful analysis. The waste was being injected directly into the natural gas flame, resulting in high carbon monoxide from incomplete combustion, as well as flame loss due to premature quenching. Banks Engineering worked with a local burner company to design baffle plates to delay contact of the waste gas with the flame, solving the problem with a very small change at a critical point. Later, Banks Engineering designed a flare gas diversion system to replace part of the natural gas used for the burners with gases that were being sent to an adjacent elevated flare. A specialized flare gas control system combined with changes to the existing thermal oxidizer combustion air flow control logic, resulted in considerable savings. Natural gas that had been used to operate the thermal oxidizer was instead routed to the plant product line and sold for a profit.

Banks Engineering Inc. – Tulsa

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