Final Report: Surface Plasma Electrode for Electrostatic PrecipitatorsEPA Contract Number: EPD08037
Title: Surface Plasma Electrode for Electrostatic Precipitators
Investigators: Alexander, Jeffrey
Small Business: Johansson Industries Inc.
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2008 through August 31, 2008
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2008) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air Pollution
The Plasma Discharge Electrode (PDE) is a technology for use with electrostatic precipitators in coal-fired power plants. Implementation of the PDE technology promises to significantly reduce emissions of particulate matter from coal-fired power plants in a cost-effective manner. Previous laboratory testing has demonstrated several innovative operational characteristics, specifically:
- Ability to independently control voltage and current in a precipitator field.
- Ability to operate with very low current levels while maintaining high voltage levels.
As testified by various industry experts, the impact of these technical advantages will be higher precipitator collection efficiencies with a broader range of fuel and process dust characteristics.
The main objectives of the research program were to:
- Find an optimum design for the PDE, the two main variables being:
- Choice of dielectric material and associated fabrication techniques.
- Electrode shape as it determines precipitator current distribution.
- Find an optimum design for the PDE AC power supply.
- Demonstrate the optimum design in a pilot precipitator at a coal-fired power plant:
- Verify increased current density.
- Verify ability of dielectric material to withstand temperatures and rapping.
- Investigate dust fouling of PDE and its effect on performance.
A laboratory precipitator was built to measure the distribution of current generated by the discharge electrode. It was first operated with a conventional spike pipe electrode design. The highly non-uniform current distribution can be seen in the diagram below. About 24 percent of the collection plate area has negligible current.
Various shapes of the PDE were then fit into the laboratory precipitator and tested. The optimum configuration was found to be a three-pipe design, where three PDEs, each of round pipe design, replaced a single conventional spike pipe electrode. Significantly improved current distribution was measured. In fact, 0 percent of the collection plate area had negligible current. The variance coefficient of the current distribution for the pipe spike electrode was 98 percent, while for the PDE it was 43 percent. These results are innovative and offer substantial improvement to conventional precipitator design.
An optimum electrode design was determined: a set of three 1.5” Ø pipes coated with borosilicate porcelain enamel. Stainless steel strips (1/8” wide x 5 mil thick) are wrapped around the OD of the coated pipes. The three PDEs would replace a single conventional electrode of spike pipe design. A three-coat process for the application of the porcelain enamel was developed in order to ensure adequate electrical insulation strength of the dielectric. This design met the criteria of cost and function. Other electrode designs using Teflon and alumina as the dielectric materials failed to meet the criteria. Teflon was not sufficiently robust (periodic electrical failures), while alumina was too expensive and difficult to fabricate into the desired electrode shapes. A significant amount of time was spent determining that these other electrode designs were not feasible. With the porcelain enamel, good electrical insulation strengths could be achieved, several times greater than the anticipated operating voltages. Long-term testing yielded no failures in the porcelain enamel.
Design of the electrode power supply turned out to be a straight-forward engineering task, using commercially available equipment. Measurement of voltage and current for the electrodes was made to allow design of full-scale power supplies.
PDEs were fabricated, installed, and operated in a precipitator pilot unit installed at a coal-fired power plant (burning PRB coal). The purpose of the field testing was to demonstrate electrode function and identify potential problem areas. The innovative results were:
- Effective operation of the electrode power supply with the precipitator HVTR set was demonstrated.
- The porcelain enamel PDE was proven to generate precipitator current levels (92 nA/cm2) 42 percent greater than the conventional electrode (65 nA/cm2) and withstood all precipitator environmental challenges (temperature, acids, dust, and thermal cycling).
- The precipitator rapping system in the pilot unit was not effective at preventing dust deposits from fouling the PDE and defeating precipitator current generation.
Subsequent to the field tests, a proprietary modification to the design was developed to achieve a self-cleaning electrode. A prototype was built and successfully tested in the laboratory precipitator. A dust-fouled electrode was shown to clean itself upon energisation of the AC power supply and precipitator HVTR. This will be the subject of a patent application.
The research program was successful at developing a commercially feasible configuration of the PDE technology. Many approaches were rejected due to either technical failures or excessive projected cost, but one approach, borosilicate porcelain enamel coated pipe, was successful. Significantly improved uniformity of precipitator current distribution was verified. Testing in a pilot unit at a coal-fired power plant demonstrated function of the technology in an actual operating environment and identified a new problem: dust fouling. A modified design to address the dust fouling issue was developed and successfully tested in the laboratory.
The PDE could provide material improvement in utility and industrial electrostatic precipitator performance by providing adjustable voltage/current relationship. This relationship is now primarily dependent on electrode geometry, which is fixed with the precipitator original design. The variable voltage/current capability of the PDE design will help optimize powering and collection, especially under conditions of back corona and low spark-over voltages. This is an exciting development and the recent pilot work has moved the concept closer to commercial reality.
A commercialization plan is proposed whereby a leading U.S. supplier (Neundorfer, Inc.) of precipitator aftermarket services will be the licensee of the technology. The remaining steps necessary for commercialization are:
- Completely equip both fields of the pilot unit with PDEs and operate.
- Verify improved performance of the pilot precipitator compared to that with conventional electrodes.
- Execute a beta site project where a complete field of a full-scale precipitator is fit with PDEs and operated for an extended period of time.
These tasks could be completed via an EPA SBIR Phase II project with verification and commercialization options.