Case Study: Odor Elimination: Rendering


In the Rendering Industry odor control equipment has been in use since the early 1970’s about the same time the Air Pollution Control industry was formed and began servicing clients with the best available Air Pollution Control equipment available. Typical early application of air pollution control equipment in Rendering consisted of a direct fired afterburner for destruction of the organic emissions (odor, ammonia, fats, grease, and particulate being emitted from the cooker process). A properly designed afterburner was capable of providing reliable destruction of organic emissions while operating at temperatures of 1200°F or higher.

As technologies continued to be developed, fire tube boilers that utilized the waste heat of the afterburners were added to produce steam for the steam intensive plant process. The use of a waste heat boiler was the first step in heat recovery of the afterburner. The addition of the waste heat boiler and the back side of an afterburner would typically make the overall system efficiency of the two components in the high 70% to low 80% range. However, the overall system efficiency was only this high if the total production of steam from the waste heat boiler was constantly used. Intermittent use of steam production severely lowered the overall system efficiency and increased the operating cost.

Other applications of different technologies included the use of Thermal Recuperative Oxidizers, which utilize a shell and tube stainless steel heat exchanger. The Thermal Recuperative Oxidizers were not used with waste heat boilers due to their lower outlet exhaust temperatures, but still utilized Economizer units for pre-heat of make-up feed water. Typical heat recovery performance of a shell and tube heat exchanger was around 60 – 70%. The lower efficiency of the shell and tube type heat exchanger vs. a waste heat boiler still averaged to a lower annual operating cost on applications where large boilers were already existing, and steam generated by a waste heat boiler could not be utilized on a continuous basis.

The Challenge:

Rising energy costs and the social pressures for improved Environmental Social Governance (ESG) around one of the oldest recycling industries, Rendering, have led to the need for implementation of improved environmental controls.  With residential areas encroaching on Rendering Plants, high intensity odors require improved removal and the low intensity odors from storage, loading, grinding, and transport areas have become increasingly important to treat with a form of air pollution control equipment. The larger air flows associated with controlling these areas make the use of higher efficiency technologies a must in order to conserve energy and meet today’s carbon reduction goals.

The Solution:

Regenerative Thermal Oxidizers (RTOs) are becoming more common place to solve high intensity odor applications while the use of a Wet Scrubber is often deployed for low intensity odors.  However, the importance of an experienced team to supply this equipment is critical.  CleanCap Technologies has the experience to ensure stringent odors are minimized, proper materials of construction are used, and consideration has been made for particulate and high moisture processes.  Pretreatment of high intensity odors from the process equipment is often part of an integrated RTO odor control solution in Rendering due to the difficulty in treating Ammonia (NH3) and Hydrogen Sulfide (H2S), two common components of cooker exhaust.  An inlet Venturi Scrubber removes the heavy wetted particulates followed by a dual-stage Scrubber to remove the NH3 and Acid gases to prevent the formation of NOx and SO2 in the RTO.

The Result:

With the multi-stage solution, the initial Venturi Scrubber uses a centrifugal action to ready the gas stream before entering the 1st stage Scrubber that treats the Ammonia.  Leaving the top of the initial packed tower into the bottom of the Hydrogen Sulfide 2nd stage section, the waste gas is further prepared for final treatment of Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs).  A 3-Canister RTO provides a means to eliminate a short duration “puff” of untreated odors from the RTO during valve cycling.  With such high intensity odors in a Rendering application, it is vital to remove greater than 99% of any entering waste components.  Leaving the exhaust stack of the RTO, final regulated emission levels are met while minimizing CO2 production with the highly energy efficient RTO technology.

RTO equipment to help reduce odor.
Scrubber in the Odor Elimination process

Project Highlights

  • Specially designed ceramic media heat recovery bed in the RTO to better resist particulate plugging.
  • Stainless steel material used to maximize equipment life when exposed to the acidic nature of the incoming gas stream.
  • Properly sized burner and combustion chamber for maximum performance and flexibility for fluctuating operations.
  • Proven controlled bake-out program to clean RTO ceramic media to maintain optimal performance.