HOT TOPIC HOUR

Precipitators can compete with Fabric Filters – Hot Topic Hour Thursday October 22, 2015

The Hot Topic Hour yesterday reviewed options to improve precipitator operations. There are ways to reach very high efficiency levels equal to fabric filters. A Route Map and Summary was quickly reviewed slide by slide with stops for discussions where participants were so inclined.

Route Map and Summary Slides Precipitator Improvements

This Route Map and Summary will be updated continually from contributions and questions received.

Most precipitator decisions will be made in Asia. The challenge will be to eliminate language barriers. There are 10,000 precipitators operating at coal-fired power generators around the world. New regulations and new technology meet to determine the fate of these units. Will they be replaced by fabric filters or will they be upgraded?  Upgrading can employ, new power supplies, new processes, such as lower inlet air temperatures, new designs, such as hybrid filters or internal modifications.

A recent refinery cat cracker precipitator explosion raises the question of whether more can be done to improve precipitator safety.

Should the industry move to “Total Solutions”? Companies such as B &W can supply complete systems and then all the repair parts as needed. Remote monitoring can allow suppliers to provide continuous advice and support. The ultimate is the service offered by FLS which includes total operation of a cement plant. What are the trends and what should they be?

Power is the main but not only application for precipitators. What is the latest in oil mist collection?  Clarcor and KLEAN (a Chinese company) have new precipitator designs for this application. Fabric filters have supplanted precipitators for many applications in many countries.  Where are precipitators being applied today?  Steel mill BOF furnaces in India, nickel smelters in Zimbabwe, pulp mills in Canada and wood-fired boilers in the U.S. are examples. Will precipitators continue to be used for these applications?

Emissions: The future emission limits is a big variable in determining whether to upgrade or replace a precipitator.

• In Germany an ELV of 30 mg/m³ is enforced.
  

• The Near Zero Emissions (NZE) limits recently imposed in certain Chinese provinces and cities limit particulate to 5 mg/NM³.
  

• In 2012 in the UK, existing PCC plant are limited to 50 mg/m³ and new build have a limit of 30 mg/m³.
   

• In some advanced economies, ELV are reduced to 1 mg/m³ in some urban areas.
  

• Public opinion can also drive the emission limit value below legislative requirements.
  

• In 2011, Units 1 and 2 of Isogo PCC plant (Japan) had particulate emissions of 1 mg/m³. Isogo is equipped with a state-of-the-art electric catalytic reduction, dry regenerable activated coke multi-pollutant system (ReACT) and a modern ESP (cold-side, dry, parallel plate).
  

• Depending on where a PCC plant is located, it may well be the case that flue gas leaving it will have fewer particulate than the ambient air.

Process Improvements: One of the options for precipitator improvement is lowering the inlet gas temperature. Most plants can justify extending the air heater and injecting sorbent ahead of it to pick up a 2 percent efficiency increase.  The outlet gas at 200°F instead of 350°F will make the precipitator more efficient as described by Kyle Nicol of IEA.

Power Supplies: One option for improvement is switch mode power supplies as available from Stock, NWI and Alstom.

The hybrid HF power supply from LongKing has been installed in many precipitators in China.

• Discharge Electodes: In India ESP Technologies (P) Ltd has improved efficiency with specially designed spiral emitters. The electrostatic precipitators of Chinese-design installed in many of the coal-fired power plants in India are invariably fitted with spike/barbed type emitting electrodes in the fields located at the inlet sections of electrostatic precipitators. The electrical performance of these types of electrodes had been observed to be far from satisfactory due to many reasons like the defective design and mounting arrangement, faulty erection, etc., resulting in poor availability of the fields and the overall performance of the electrostatic precipitator. The plant engineers had also faced serious problems in the operation and maintenance of the electrostatic precipitators fitted with such type of emitters.
  

• ESP Technologies (P) Ltd, Chennai had successfully replaced these spike/barbed emitters of the Chinese–make electrostatic precipitators with specially engineered spiral emitters in a large operating plant. The electrical performance of the fields replaced with spiral emitters had been excellent both on air-load as well as on gas-load as shown in the Voltage–Current (V-I) curves below. The conversion had been tailor-made to suit the plant requirements without the need to carry out any major modifications to the emitting system frame-work and its suspension systems including the rapping mechanisms and their drives.
  

Multiple Capture Zones: A double zone ESP is another option. LongKing has installed the double zone design in many Chinese power plants.

• A combination precipitator/fabric filter is another option.  W. L. Gore has a license from DOE obtained 15 years ago and a decade ago worked with Elex to install a unit in a European cement plant. LongKing has a large number of installations in China.

• WESPs: If total particulate, including condensibles, is used as a metric, the WESP is the most efficient option. China is opting for many WESP tail-end retrofits to meet new particulate standards. One huge winner could be
  
  • Venturi scrubber for particulate and HCl capture with 30 percent acid and rare earths as byproducts.
  • SO₂ scrubber
  • WESP

The particulate and HCl are captured in the first scrubber where only the water is added. A 30 percent hydrochloric acid solution builds up and then bleed is maintained. The acid with the flyash then continues through the leaching process where rare earths and valuable metals are extracted.  The gas passes through an SO₂ scrubber and then to a WESP for final particulate cleanup.

The WESP is a very efficient particulate removal device as determined by Lundberg.

• The Chinese government is reducing the permitting PM levels of existing and new unit utility coal-fired power plants in key areas to 5 mg/Nm³. These requirements result in a large demand for WESPs. There are hundreds of utility units that will need to meet PM_2.5 limits of 5 mg/Nm³ or less within the next five years. Recognizing the need to optimize a continuous-wash system on horizontal WESP designs, Babcock & Wilcox Power Generation Group (B&W PGG) funded an ambient-air bench-scale, water wash test program.

• Continuous water washing of electrodes is a way to reduce the corrosion-resistant grade of alloy used without compromising on the operating and maintenance of the unit and thus provide a lower capital cost WESP. The water-wash bench test program was successful in determining the relationship between power and flow rate. The next step is to optimize the process design on the full-scale pilot plant. Tests are planned for this summer. The full-scale unit is 10 meters tall with two gas passages and will be energized with airflow.

Safety: Safety is a continuing problem. Over-pressurization in the ESP is reported as the cause of the explosion at the ExxonMobil’s Torrance Facility. The explosion, which injured four workers, was triggered by pressure in an electrostatic precipitator receiving exhaust from a fluid catalytic cracking unit, according to the South Coast Air Quality Management District.

Injury to workers from the high voltage is a major concern. Kirk Key has a solution.

Total Solutions: Owners of power plants with air pollution challenges are increasingly looking for suppliers who will provide a “Total Solution.” In the broadest sense, this can be the determination of how to meet the emission goals followed by a turnkey installation with operational and maintenance support.

• The most common explanation for the lack of “Total Solutions” knowledge in the industry is the retirement of experienced people and the lack of replacements. McIlvaine contends that the real reason is the explosion of knowledge. The complex technology options and support knowledge available to the young engineer are an order of magnitude greater than to his predecessor. If one does not have the same full grasp of the knowledge, it is because there is ten times as much to try to assimilate.
• This gap between user and supplier precipitator knowledge is greatest in developing countries with the exception of China which is a leader
• Indonesia, Vietnam, and India are installing large numbers of precipitators and need Total Solutions.

Babcock & Wilcox has a number of  services ranging from complete build-own-operate (BOO) to just training.

• B&W’s full-scope power plant operations and maintenance (O&M) services help plant owners maximize availability, profitability and safety performance. B&W and its subsidiary, Delta Power Services, LLC, currently operate and maintain 11 U.S. plants. ​
• DPS is the fourth-largest power plant O&M services provider in the United States. Based in Houston, Texas, DPS is a subsidiary of Babcock & Wilcox. DPS employs approximately 195 people and has O&M contracts at eight facilities. 
• The Palm Beach County Renewable Energy Park (PBREF) is a waste-to-energy facility designed to reduce the volume of the county’s wastes, generate electricity, and maximize the recovery of aluminum and ferrous metals. The park, which now includes two facilities, began operation in 1989. It is owned by the Solid Waste Authority of Palm Beach County (SWA) and is operated by Palm Beach Resource Recovery Corporation (PBRRC), a B&W subsidiary.
• B&W offers an extensive array of engaging instructor-led technical training courses conducted on-site and at various seminar locations. To meet plant-specific needs, courses are frequently modified and new courses are developed. 

Maintenance and repair services include:

• Consultations
• Inspections, condition assessment, non-destructive examination
• Outage management
• On-site engineering and evaluation
• Code compliance
• Mechanical and structural evaluation
• Chemical cleaning
• Laboratory analyses
• Air heater maintenance

The Route Map and Summary will be continually updated and available free of charge to power plants around the world. It is displayed in Power Plant Air Quality Decisions.  We encourage submission of additions to this intelligence system.