Final Report: A Catalytic Exhaust Purifying System for Restaurants

EPA Contract Number: EPD05022
Title: A Catalytic Exhaust Purifying System for Restaurants
Investigators: Gosau, Jan-Michael
Small Business: Clear Skies Unlimited, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2005 through August 31, 2005
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2005) RFA Text |  Recipients Lists
Research Category: SBIR - Air Pollution , Air Quality and Air Toxics , Small Business Innovation Research (SBIR)


There are more than 870,000 restaurants across the United States, nearly all of which emit particulate matter (PM) and volatile organic compounds (VOCs) that can cause adverse health effects. PM primarily affects the respiratory system and may cause coughing, wheezing, and physical discomfort in breathing. It also may alter the immune system.

Clear Skies Unlimited, Inc., was formed in 2001 to commercialize a newly patented and U.S. Environmental Protection Agency-certified wood-burning stove catalytic combustor based on a unique ceramic reticulated substrate. Test data on Clear Skies Unlimited, Inc.’s combustor, known as the CS-200, shows that it is capable of removing virtually all PM2.5 and PM10+, VOCs, and carbon monoxide from streamlined emissions in wood stoves and fireplaces (independent tests were conducted at OMNI Environmental Labs, Portland, Oregon).

The major problem for the removal of harmful substances from restaurant exhausts is the very high volumes of air that need to be treated. Large facilities have exhaust volumes of 50,000 cfm and more; even small units typically move approximately 2,500 cfm of exhaust per station. Also, the high content of oils and fats in the off-gas makes conventional filter systems either inefficient or in need of very frequent filter changes.

Filtering, or a direct thermal treatment, even if catalytically enhanced, is unlikely to succeed due to the very high air volumes involved in this application. To solve this problem, Clear Skies Unlimited, Inc., combined a filtering and thermal treatment approach using its unique catalytic reticulated ceramic substrates and combustors. The reticulated ceramic is used as a high-volume, high surface area filtering agent to collect VOCs and PM from the off-gas stream. Clear Skies Unlimited, Inc., combined this with an automatic offline filter regeneration system. During the thermal regeneration of the filter, Clear Skies Unlimited, Inc.’s catalytic combustor destroys any harmful substances from the off-gas stream.

The primary objective of Phase I was to demonstrate the feasibility of a self-regenerating air filtration system for restaurants and large kitchen operations. The system provides a significant reduction in VOC and PM emissions, will be virtually maintenance-free, and can be integrated into existing air-handling equipment for retrofit into today’s operations. This technology can be applied to numerous additional polluted airstreams, such as paint booths, printing processes, and composite processing.

Summary/Accomplishments (Outputs/Outcomes):

The Phase I project was a complete success. All three programmatic elements—demonstration of filtering, modeling of the system for suitability and safety, and demonstration of the regeneration system—were fulfilled.

The ceramic filters were shown to effectively filter grease and other side products of charbroil operations out of the air stream. The very low backpressure generated by the filters will not negatively influence the performance of existing air-handling systems retrofitted with the new system. Repeated thermal regeneration of the filters did not negatively influence the filter capabilities.

Modeling of the airflow in a system using the Clear Skies Unlimited, Inc.’s filtration system showed that it is compatible with air-handling systems currently used in restaurants. Temperatures at the filter surface stay well below the temperature needed to pose an ignition hazard. The airflow is comparable to that of conventionally filtered systems.


The potential of the catalytic converter was shown during the thermal regeneration of the filters. Although open regeneration leads to the development of large quantities of smoke, the smoke generation can be suppressed almost completely by using a preheated catalytic combustor in the exhaust stream. Temperature and positioning control of filter and catalytic combustor are vital operating parameters for successful pollution control and will be optimized in the Phase II project.

Phase II also will include work on integration into existing air-handling systems, improved catalysts specially developed for the combustion of grease, a method for verification of filter performance, and filter substrates optimized for restaurant conditions.

Supplemental Keywords:

particulate matter, PM, volatile organic compounds, VOC, carbon monoxide, restaurant exhaust, wood stoves, fireplaces, off-gas, catalytic combustor, reticulated ceramic, filter regeneration system, thermal regeneration, charbroil operations, EPA, small business, SBIR,, RFA, Scientific Discipline, Air, Waste, POLLUTANTS/TOXICS, Sustainable Industry/Business, particulate matter, Environmental Chemistry, Sustainable Environment, Chemicals, Technology for Sustainable Environment, Incineration/Combustion, Environmental Engineering, restaurant exhaust purification, air pollutants, air toxics, combustion-related pollutants, hazardous emissions, combustion emissions, air pollution control, particulate emissions, carbon monoxide (CO), VOC removal, airborne particulate matter, catalytic reticulated ceramic combustor, air pollution, emissions control, combustion technology, combustion exhaust gases, Volatile Organic Compounds (VOCs), aersol particles, restaurant emission controls, exhaust purification, ambient pollution control