A Breakthrough in "In-Situ" Filter Cleaning
By Dick Nixdorf, President & CEO, Industrial Ceramic Solutions, LLC

Today's global economy has placed industry in developed countries at a competitive disadvantage with developing countries in the areas of labor costs and environmental regulations. The answer to maintaining market share and reasonable profit margins is reducing manufacturing costs and minimizing environmental compliance expense. Industrial process efficiency improvements usually require higher operating temperatures. Lower emission control expenses require a need to replace outdated pollution control systems with innovative filtration technologies. Temperature dependent industrial manufacturing requires increasing the process exhaust temperature beyond the limits of the current cellulosic or polymeric filtration equipment. The standard solution in moving to a higher temperature exhaust is a thermal oxidizer system. This technology is similar to a catalytic converter on a car. A ceramic or metal honeycomb is coated with a precious metal catalyst that converts emissions to harmless gas products at a temperature above the catalyst reaction temperature. Most industrial process exhausts do not reach this catalyst reaction temperature. Therefore, additional heat must be added by burning large volumes of natural gas to increase the process exhaust stream to the catalyst reaction temperature as it passes through the ceramic honeycomb. These costs for natural gas can range from $100,000 to $5 million/year, depending on the size of the exhaust stream. An additional penalty is high CO2 emissions.

One answer to these high operating costs is a patented, dual-layer, wet-laid, nonwoven ceramic fiber filtration media trademarked ThermoPore™.

How "In-Situ" Cleaning Works
This alternative, commercially available, ceramic fiber filter media and its ceramic frame components will operate to temperatures up to 1,200°C to accommodate high processing and exhaust temperatures. The filter media shown in Figure 1 is 95% efficient at removing organic and carbonaceous particles down to 0.1 microns. The ceramic filter media can, further, be coated with a precious metal catalyst to destroy all combustible hydrocarbons and VOC's at temperatures above 400?C. In circumstances where industrial exhaust steams operate below this temperature at the filtration equipment location, the ceramic fiber media can capture the particulate over a period of time, regardless of the exhaust temperature. When the filter cartridge(s) reach a designed particulate loading, as determined by backpressure measurements, the filter cartridge(s) are cleaned in a periodic mode to combust the captured particulate to a harmless CO2 and H2O gasses at an elevated temperature.

The clean filter is then returned to its filtering task in the process stream. In many cases the filter cartridges can be individually cleaned, in place, without moving to a separate filter cleaning station. The natural gas expense required for this cleaning is less than 5% of that consumed by a thermal oxidizer.

The preferred concept is to trap particulate over a long period of time without applying auxiliary heat to the exhaust stream, followed by cleaning at a high temperature for a short period. A typical operating sequence for a ceramic fiber cartridge emission system is filtration for eight hours, followed by a 30 minute high temperature cleaning cycle. The filter systems are designed to trap a given quantity of particulate to reach a designated backpressure. Upon reaching the selected backpressure, the cartridge assembly is exposed to a high-temperature cleaning cycle. During the cleaning cycle, the temperature of the filter cartridges is raised to the particulate oxidation state. The filter is cleaned. Any pollutant exhaust gases evolved from the filter system, during this cleaning cycle, are directed through an auxillary catalyst coated ceramic fiber exhaust chimney filter to assure that no hydrocarbons or VOC's escape to the atmosphere.

Other Advantages
The ceramic fiber filter media is very efficient at removing particulate from the exhaust stream. There usually is no visible smoke from the plant exhaust. Figure 2 shows the efficiency of a filter cartridge servicing a high particulate diesel engine application. The light color bar is the particle count prior to the filter and the dark bars represent the particle count after the ceramic fiber filter. 95% to 99% particle removal efficiency is typical. Figure 3 illustrates the degrees of freedom in filter cartridge shapes. Ceramic fiber filter cartridges can be fabricated into any shape available to polymer fiber media cartridges, e.g. flat or round pleats. Filter systems can be designed to accommodate exhaust streams from 10 to 250,000 cfm, with clean filter media backpressure at 0.3 inches of water. Therefore, ceramic fiber media can accommodate exhaust systems that demand a low backpressure from the filtration system. The weight of the filter cartridge is approximately 1/3rd that of competing ceramic honeycomb products. The weight benefit is a meaningful cost reduction of large systems. A complementary option is a secondary polymer fiber filter coated with a special organic absorbent material that will remove VOC's after the ceramic fiber filter.

The Applications
The US EPA Clean Air Act of 1990 and the emerging regulations from the California Air Resources Board are changing the requirements for commercial, industrial and vehicle exhaust emissions. The transition from PM10 to PM2.5 regulations will leave many exhaust emissions in a non-compliance situation. If the current Cap and Trade regulations become law, the established practice of using gas burners and thermal oxidizers will become more expensive. An energy efficient technology is needed to overcome these issues. The ceramic fiber filter media will comply with the PM2.5 regulations. It will reduce the operating expense of gas burner thermal oxidizers to less than 5% of their current operating costs.

The following are four common end-use applications for in-situ cleaning:

Thermal Oxidizers are used in most smoke, odor and VOC control applications in industry today. The ceramic fiber filter media can provide a cost-effective replacement for many of these units.

Coal-Fire Steam Plants currently comply with PM10 emission regulations. The existing equipment, such as scrubbers and electrostatic precipitators, need to be replaced to comply with PM2.5. Ceramic fiber filters provide PM2.5 filtration efficiency at lower capital and operating costs.

Restaurant, Coffee Roaster and Volume Food Cooking Emissions are facing smoke and odor regulations in California and subsequently across the US. There is no reliable low-cost emission control system to bring these applications into compliance.

Wood-Burning Boilers and Waste Oil Incinerators are a rapidly growing industry in colder climates in the Northeast and Midwest. Their emissions are a nuisance to the environment. However, their cost savings on energy bills is significant. Ceramic fiber filtration may provide a solution to their pollution problems.

Summary
High-temperature ceramic fiber filtration products are now commercially available due to processing breakthroughs in binders, pleating and filter cartridge manufacturing technology. This product technology provides advantages in many existing manufacturing and new processing applications. The use of ceramic fiber filter systems opens previously unavailable high-temperature filter system design opportunities to application and process development engineers. The ceramic fiber filter technology also offers significant energy cost savings compared to existing emission control systems with high operating costs.

Mr. Nixdorf is a material scientist at Industrial Ceramic Solutions experienced in converting new materials ideas to commercial products in exhaust emissions control systems.

For more information contact:
Dick Nixdorf
Tel: 1-865-482-7552 Ext.2
Email: rnixdorf@indceramics.com | Website: www.indceramics.com