Final Report: Plasma Discharge Electrode for Electrostatic PrecipitatorsEPA Contract Number: EPD09043
Title: Plasma Discharge Electrode for Electrostatic Precipitators
Investigators: Alexander, Jeffrey
Small Business: Johansson Industries Inc.
EPA Contact: Manager, SBIR Program
Project Period: March 1, 2009 through February 28, 2011
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2009) Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air Pollution
Electrostatic precipitators are widely used for removal of particulate matter from boiler exhaust gases. The EPA is expected to announce new emission standards for air toxics for boilers and certain solid waste incinerators in October 2011. This will require Utility and Industrial Boilers and Process Heaters to improve the performance of their precipitators in the coming years. Emissions limits being discussed are 0.039 lb/MMBTU for existing boilers and 0.0011 lb/MMBTU for new boilers.
In the PDE Pre-Charger, particle laden exhaust gases are passed through a set of plasma discharge electrodes (PDE) upstream of the precipitator. When energized with high voltage, the plasma based corona discharged in the PDE generates ion flow at much higher current density (500-1000 nA/cm²) than that possible in the precipitator (10-100 nA/cm²). This is achieved by cooling the anode electrodes to prevent formation of micro-plasma discharges in the interstices of the accumulated dust layer.
Because of this higher ion current density, pollutant particles in the gas stream are electrically charged to very high levels, levels higher than those normally found in conventional precipitators. Then they are collected more efficiently in the existing precipitator. The compact design of the PDE pre-charger is conducive to retrofit into the inlet plenum of the precipitator, and does not require any additional plant space or system operating pressure drop. This makes the installation cost low and the project would carry little consequential risk to the boiler operator.
The Plasma Discharge Electrode (PDE) was developed under EPA SBIR Phase I research. During Phase II research, it was demonstrated to have operational characteristics (fouling) that rendered its function unacceptable over long term testing. An alternative configuration, termed the PDE Pre-Charger, was formulated, laboratory tested, and demonstrated to significantly reduce particulate emissions from a pilot electrostatic precipitator at Alabama Power’s Plant Miller coal fired boiler.
The research program comprised extensive laboratory and bench scale tests to demonstrate particle charging fundamentals and also explore practical and operational issues (such as fouling and mechanical integrity) in laboratory simulated flue gas environments. During this process, a number of candidate configurations were rejected due to mechanical failures and/or long term fouling problems. The final configuration was the PDE Pre-charger described in this summary. Its design is simple and robust, suitable for the power plant environment.
The culmination of the Phase II research program was the installation and testing of the PDE Pre-Charger at Alabama Power’s Plant Miller Power Station near Birmingham, Alabama. The test unit was installed in conjunction with a precipitator pilot unit cleaning gases from a boiler burning low sulfur Powder River Basin coal.
Particulate emissions from the pilot plant were measured using a continuous particulate monitor (BHA CPM 1000ES). With this, real time output of particulate was achieved and the test program could consist of alternately energizing and de-energizing the PDE test unit, all the while monitoring the CPM readings.
Results of typical testing are shown in figure 3 below.
The research program demonstrated that the dielectric PDE design studied under Phase I research program was not sufficiently robust to operate in the power plant environment. An alternative design, the PDE Pre-charger was shown to operate reliably under actual boiler flue gas conditions.
The research program also demonstrated the following PDE Pre-charger successes:
- Establishing ionizing field strengths 55-77% higher than conventional precipitators
- Establishing ionizing current densities 5 to 7 times higher than conventional precipitators.
- Reducing particulate emissions from a precipitator to the range of 0.003 to 0.006 grains/acf (0.007 to 0.014 lb/MMBTU).
- The same outlet emission levels can be reached with the PDE Pre-charger, even with relatively poor original precipitator performance. In essence, the PDE Pre-charger can assure optimum precipitator performance regardless of the current operating state or design of the precipitator.
The PDE Pre-charger will be able to improve particulate emissions of even a poorly designed/ underperforming precipitator to levels that satisfy new federally mandated levels (0.039 lb. MMBTU) for existing boilers. One of the key features in the development of the technology was recognition that the resulting design be relatively easy to install in most (if not all) existing precipitators at relatively low cost. The identification of the Pre-charger concept, i.e. installing the PDE in the inlet plenum of the precipitator, achieves this goal.
The next step of the development program would be installation of a full scale PDE Pre-charger on an operating precipitator. Sufficient engineering information was obtained during the research to confidently design such an installation.
The anticipated market for the PDE Pre-charger will be a retrofit to precipitators in order to reduce the particulate emissions to atmosphere. This might be required because:
- Emission regulations have become more stringent since the precipitator was originally designed.
- Precipitator has lost performance due to aging and deterioration of some components.
- Boiler load has increased.
- Type of coal has changed since the precipitator was originally designed.
It is the plan of Johansson Industries, Inc. to approach power utility companies directly with proposals for such an installation. Although this installation will be a beta site, their risk will be the cost of the retrofit, estimated to be $1 to $1.5 million (depending on the size of the precipitator), but their potential benefit would be application of the technology to the many precipitators in their group’s control. The cost of alternative approaches to improve particulate emissions is many times greater. For example, refurbishing an existing precipitator for a 500 MWe boiler would cost $10 - $15 million, while adding a downstream
baghouse dust collector would cost some $40 - $50 million.
The following situations would be candidates for installation of the PDE Pre-charger:
- Out of compliance precipitator – a site which has been identified by environmental authorities as exceeding particulate emission regulations. The cost of alternatives for the user would be tens of millions of dollars. This is the most likely scenario for the beta site, since the alternative costs are probably tens of millions of dollars.
- Boilers operating under load constraints due to particulate emission limits- Retrofit with the
- PDE Pre-charger could provide greater operational flexibility of the boiler.
- Allow coal switching – it is often desirable for a utility to change the coal being burned, for example switching to a low sulfur coal to avoid having to install expensive scrubber systems. Often this is not possible because the coal switch would cause particulate emissions to increase beyond allowed limits. Retrofit with the PDE Pre-charger could permit this coal switching.
- Performance Insurance Policy – precipitators typically consist of multiple collection fields operated in series. Typically, if one of the fields suffers a failure of some sort (rectifier, rappers, broken insulator, broken electrode, etc.), the precipitator must be taken off line for repair, an expensive proposition because of lost boiler production. Installation of the PDE Pre-charger would allow a two field precipitator to perform as well as a three field, thus allowing failure of a field without necessitating shut down of the boiler.