Final Report: Nano-Enhanced Composite Electrodesfor Electrostatic Precipitators

EPA Contract Number: EPD09014
Title: Nano-Enhanced Composite Electrodesfor Electrostatic Precipitators
Investigators: Burton, David
Small Business: Applied Sciences, Inc.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: February 1, 2009 through July 31, 2009
Project Amount: $69,955
RFA: Small Business Innovation Research (SBIR) - Phase I (2009) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air Pollution

Summary/Accomplishments (Outputs/Outcomes):

Electrostatic precipitators (ESPs) are a key pollution control element in air pollution control devices for small oil and coal-fired industrial boilers. ESPs currently use specially designed all-metal electrodes that are relatively complex and expensive compared to thermoplastic materials. In this project, Applied Sciences, Inc. (ASI) and Ohio University (OU), with assistance from industrial partner Southern Environmental, Inc. (SEI), investigated the use of carbon nanofiber to fabricate electrically conductive thermoplastic composites to reduce the complexity and cost of manufacturing and installation, and to decrease the power consumption of electrodes used to generate charged particles in electrostatic precipitators.
 
ESPs can operate with an efficiency of 98 to 99 percent for the removal of solid particulate from the gas exhaust stream. Within the electrostatic precipitator, particulates are charged electrically as the flue gas passes near an electrode held at high voltage, allowing the charged particles to be collected on oppositely charged plates. Metallic electrodes used in ESPs are extremely heavy, with a high installed cost, and they are easily corroded, especially in wet ESP systems typically used in smaller pollution control units. Polymer nanocomposite electrodes are less expensive to produce, easier and cheaper to install, and corrosion resistant, resulting in a longer service life. Polymer electrodes, however, must be made sufficiently conductive to allow dry collection within an ESP.
 
Incorporating carbon nanofiber (CNF) into polymers at moderate loadings is known to create composites that can carry electrical currents while simultaneously increasing mechanical properties of the host polymer.[1] The addition of randomly oriented CNF into a composite at loadings above the electrical conductivity percolation threshold results in exposed nanofibers that can act as field emission sites. This unique characteristic is believed to play a significant role in generating emissions at lower voltages. The observation of high electrical conductivity and field emission from low-cost polymer composites demonstrates feasibility of using such composites for electrostatic precipitators having reduced installation and maintenance costs over metal electrodes.
 
This project focused on the development of nanocomposites with sufficient electrical conductivity and similar or superior voltage-current characteristic as the current state-of-the-art ESP components, yet less expensive to produce, easier to install, and having a longer operating life. To achieve this goal, composites containing nanofibers (nanocomposites) were produced in the form of tapes by thermoplastic pultrusion and in the form of thin films by casting. These two composite forms were supported by a polymer pipe to form the electrode and then tested in small- and large-scale ESP chambers to determine the discharge or corona current with and without air flow. Tests also were conducted with fly ash in the airflow.
 
The performance of the nanocomposite electrodes were compared with a commercial high performance electrode. All test results demonstrated that the nanocomposite electrodes performed at least as well as the commercial electrode; and typically, the nanocomposite electrode provided 10 to 20 percent improvement in the corona current as compared to the metal electrodes.
 
Because wet ESPs must use stainless steel or different grades of Hastelloy to protect against the highly corrosive environment, the electrodes are expensive. Polymer nanocomposite electrodes are a less expensive alternative for wet ESPs, particularly because of their corrosion resistance. The lower mass of the polymer nanocomposite electrodes also provides an advantage because the supporting structure can be designed for a lower weight.
 
The project team included ASI, one of the world’s leading developers of carbon nanofibers and nano-enhanced products; OU, which is a leading testing facility for ESPs; and SEI, a leading ESP builder and retrofitter, which provided technical support to the project team.
 
Overall, the program was successful in demonstrating that composites made conductive with the addition of CNF can outperform traditional electrodes made of metal in terms of enhanced corona generation efficiency and increased capture of entrained particulate by 10 to 20 percent. Based on these findings of lower power consumption and higher efficiency, SEI has expressed great interest in this technology and plans on testing the composite electrodes in an industrial setting.
 
Commercialization
 
The composite electrode technology developed by ASI and OU is applicable to both large- and small-scale ESPs. The largest market for this technology is anticipated to be in large-scale ESP units for the coal-fired power plant industry. By the year 2030, 29 percent of the world energy production will be derived from coal, and coal will continue to be the lowest-cost electric source in the United States for the foreseeable future. [2][3]
 
According to a study by the McIlvaine Company, the market for ESPs was estimated to be $3.9 billion in 2007.[4] Based on the industry average of 10 percent of the total cost of an ESP going toward the electrodes, the electrode market is estimated to be $390 million annually. Although the ESP market is mature in the United States, it still is growing rapidly in China. China is the world’s largest consumer of coal and represents more than 30 percent of the market for new ESPs.
 
Government regulations on particulate emissions and competition from alternative pollution control technologies, such as dry scrubbers and baghouses, are driving ESP manufacturers to develop more efficient ESPs. With the increased emphasis on clean coal technology, coal-fired power plants utilizing ESPs comprised of this electrode will contribute to their plant's overall filtration efficiency.
 
Following the recommendations of industry experts[5], ASI and OU are performing preliminary testing of prototype electrodes at OU prior to the installation and testing at one of SEI’s pilot-scale facilities. SEI is an international, full service ESP provider and repairs all makes and models of precipitators. SEI services all sizes of ESPs used in coal fired power plants to small industrial shops. In Phase II, an aggressive program is planned to fabricate and test a full-scale prototype electrode at SEI. ASI and OU will use data developed from prototype testing to generate a set of working electrodes and provide them to SEI for testing in an operating environment. Successful testing will provide the platform for commercial production and sales of composite electrodes for ESPs.
 
Conversion to composite electrodes at a unit price of $100/piece is estimated to result in cost savings of $15,000 per installation for time and materials to replace traditional metallic precipitator electrodes; this represents a total industry-wide savings of $260 million annually. The improved efficiency provided by the composite electrodes also will reduce emissions and power consumption. OU has filed a suite of patent applications to protect the developed technology and is negotiating with companies to license the technology. ASI is working closely with OU to support the licensing effort.
 

Conclusions:

There is a need to develop cost efficiencies for small-scale electrostatic precipitators used in enhanced emission control for clean coal utilization. Metallic electrodes used in electrostatic precipitators are easily corroded, especially in wet ESP systems, leading to high maintenance costs. The goal of materials research in this area is to provide cost advantages to the wet ESP technology so that smaller units can be built at reduced cost and with the potential of addressing multiple emissions.
 
In this Phase I effort, ASI demonstrated the feasibility of producing light-weight, low cost, and longer life electrodes for electrostatic precipitators with higher current (corona) generation at lower operating voltages using polymer composites containing nanomaterials. The best performing electrode tested under this effort was the composite tape produced with carbon fiber and polypropylene that was pre-loaded with 20 weight percent carbon nanofiber. This composite composition generated a 10 to 20 percent higher corona current than state-of-the-art metal electrodes when operated at the same voltage. This superior performance increases the particulate capture efficiency of the electrostatic precipitator and lowers power consumption. There also was no detectable damage to the tapes from the electrode function tests, indicating that consistent performance can be expected over the lifetime of the composite electrode.
 
The superior performance of the carbon fiber tape over the metal electrode is attributed to the nanofiber that provides connectivity between the microfibers and a conductive path to the surface where the corona current is generated. Additionally, each carbon nanofiber exposed at the surface of the composite acts a potential source of charge emission. Interaction between the carbon fiber and carbon nanofiber not only enhances the electrical conductivity, but also the thermal conductivity of the tape. While thermal conductivity of the electrode has not been raised as an important parameter, it should be noted that improvement in thermal conductivity will enhance dissipation of thermal effects due to sparking of the electrode and prevent softening or melting of the polymer matrix.
 
Future work will focus on the generation of more tapes containing carbon fiber/carbon nanofiber/ polypropylene tapes for larger scale testing and prototype electrode production. Once built, the prototype electrode will undergo laboratory-scale testing prior to testing in the field by SEI, a full service ESP provider to coal-fired power plants and small industrial shops.

References:

[1] Tibbetts GG, Lake ML, Strong KL, Rice BP. A Review of the Fabrication and Properties of Vapor-Grown Carbon Nanofiber/Polymer Composites. Composites Science and Technology 2007;67:1709-1718.
[2] “International Energy Outlook 2008,” Energy Information Administration Web Site, June, 2008, http://www.eia.doe.gov/oiaf/ieo/world.html (accessed March 12, 2009).
[3] “Clean Coal Technology & The Clean Coal Power Initiative,” U.S. Department of Energy Office of Fossil Energy Web Site, http://www.fossil.energy.gov/programs/powersystems/cleancoal/ (accessed March 12, 2009).
[4] McIlvaine R. Environmental Markets: The Future of Electrostatic Precipitators. Pollution Engineering, November 2006.
[5] Foresight Science and Technology, Technology Niche AnalysisTM, Nano-Enhanced Composite Electrodes for ESPs, March 18, 2009.

Journal Articles:

No journal articles submitted with this report: View all 2 publications for this project

SBIR Phase II:

Nano-Enhanced Composite Electrodes for Electrostatic Precipitators  | Final Report