Fabric Selection for Particulate Control was the Hot Topic Hour September 5, 2013

McKenna describes the Key Issues to Consider when Selecting Bags to Achieve Optimum Bag Life

John McKenna of ETS provided a very informative discussion of fabric selection for particulate control in the Hot Topic Hour held on September 5, 2013. When a pulse jet collector is used, the most commonly chosen fabrics are PPS felt, P-84^® Felt and woven fiberglass/ePTFE. For Reverse Air baghouses the choices are woven fiberglass or woven fiberglass/ePTFE membrane. John presented the design considerations and trade-offs. The fabric should provide the required filtration. With reduced emission standards especially in the Northeast, this may be less than 0.000 x grains/ft³. There are trade-offs between capital and operating costs. Lower gas to cloth ratio gives longer bag life and lower pressure drop. Good design and preventive maintenance retains low cleaning frequency and longer bag life.

Quality control should begin with fabrication of the bags. A detailed specification is very important. Without the spec there can be no recourse. Good distribution is also critical to long bag life. Filtration performance of P-84 and PPS felt are similar and very good. The filtration performance of woven fiberglass with membrane (WFG/Membrane) is excellent. The bag life of PPS felt can exceed five years, P-84 can exceed 2 ½ years and the life of WFG/Membrane is dependent on multiple factors.

For the relative cost of bags, P-84 commands a premium of 1.7, PPS is at 1 and WFG/Membrane is 0.8. The ultimate decision is a function of site specific inlet definition and cage design.

John made clear performance of the fabric is not the critical issue. Installation and uneven dust flow are often the cause of problems. There should be a QA/QC Program to insure a new bag set conforms to the material and construction specification. The entire bag set and associated hardware must be properly installed and are the key to successful operation. All system components should be inspected before installation and again prior to initial start-up for compliance to specifications and for correct assembly. Retensioning of reverse air bags is very important.

A bag monitoring program should be in place. This will allow the user to determine the retention of strength and flow characteristics of a bag set with on-line time. It can be used as an aid in determining useful life and scheduling the replacement of a bag set. It is also a diagnostic tool in assisting the client or his agent in troubleshooting a baghouse.

Discussing some of the problems with the fabrics John said that membrane bags may be damaged from the folding when packaged for shipping. A major concern with PPS is where it comes from. There have been problems with some shipped from overseas. Needle holes were the final problem discussed. John said these problems can be solved by singing the seams or covering the seam with tape.

Ceramic Filter with embedded Catalyst and DSI achieves High SO_x, NO_x and RO_x removal

Richard Lydon of Clear Edge Filtration Group presented the case for using a ceramic media with an embedded catalyst. The result is high dust removal and high NO_x reduction. DSI ahead of the filter allows acid gas removal as well. There are many thousands of these filter elements already in operation on various industrial operations. Recent installations in the U.S. show high efficiencies.

Could this be the technology which allows small power plants to remain in operation?  It is actually possible to inject sorbents ahead of the catalytic filter. The new highly reactive hydrated lime from Lhoist (HCl capture shown below.) or the sorbent recovery technology from Neuman (NeuStream process shown below.) could be coupled with the catalytic filter to provide cost effective high efficiency capture of all the major pollutants.

Eliminate the Rotary Air Preheater and replace it with a Heat Pipe or Other Exchanger which does not Leak and can achieve even better Heat Exchange

As part of the Clean Coal Technologies IV Demonstration program at New York State Gas and Electric Company’s Milliken Station the original rotary regenerative air heaters on the Unit 2 boiler were replaced with heat pipe air heaters. Use of the heat pipe air heaters offered the potential of improving plant heat rate by: (1) allowing operation at lower flue gas outlet temperatures than the existing air heaters, and (2) elimination of combustion air leakage within the air heater which reduces the overall system fan power requirements. At full boiler load, the fan power savings averaged 778 kW or about 0.49 percent of the gross load. Cold-end fouling of the heat pipes is the main operating concern. The fouling reduces the thermal performance and increases the gas side pressure drop with time. With the catalytic filter this problem would be eliminated.  So the total increase in efficiency would be several percent, of which 75 percent would come from heat recovery.

Bios, Abstracts and Photos can be seen at BIOS, ABSTRACTS, PHOTOS - 9-5-13.htm

The individual presentation is as follows:

• Fabric Selection for Particulate Control Webinar - Hot Topic Hour September 5, 2013  (Webinar Recording  Dated:  9/5/2013)
  
   
• Achieving lower Particle Matter (PM) emissions and Hazardous Air Pollution (HAP) standards in a one-step Filtration Process by Richard Lydon, Clear Edge Filtration - Hot Topic Hour September 5, 2013  (Presentation  Dated:  9/5/2013)
• Key Issues When Selecting Fabric Filter Bags to Achieve Optimum Bag Life by John McKenna, ETS - Hot Topic Hour September 5, 2013  (Presentation  Dated:  9/5/2013)