Part 2 CCT Overview
Environmental Protection Technologies (Flue Gas Treatment and Gas Cleaning Technologies)

5B4. Particulate Treatment Technology and Trace Element Removal Technology
Technology overview

1. Background
Like NOx, emissions of particulate matter are regulated, withfollowed suit. To improve power generation efficiency, theacceptable concentration levels set according to the type of fueldevelopment of pressurized-bed combustion and coal gasificationand size of boiler. At present, however, some regions are subject

combined-cycle

to a "total amount control," which provides for a region-wideceramic/metal precision-removal filters is underway.

overall emissions level as is the case with sulfur and nitrogen

On the other hand, trace element control is now being intensified,oxides. To comply with the regulations, the world’s firstsuch as through the addition of boron (B) and selenium (Se) toelectrostatic precipitator was employed in a Yokosuka thermal

the regulated wastewater materials, and through the application

power plant in 1966 and many other thermal power plants haveof U.S. regulations for mercury (Hg).

technologies

thatuse

cyclones

2. Technology(1) Electrostatic precipitators

Research and development:
Mitsubishi Heavy Industries, Ltd.; Hitachi, Ltd.; Sumitomo Heavy Industries, Ltd.; others
Overview
Electrostatic precipitators remove particulate matter in exhaust
High-voltage DC

gas in accordance with the theory that dust charged by anegative corona at a discharge electrode adheres to a positive

Power supply

dust-collecting electrode.
The particulate matter that adheres to the electrode is removed
and falls when the cathode is tapped with a hammering device.
Discharge electrodeThe effectiveness of the dust removal depends upon theelectrical resistance of the particulate matter, and is mostCollectedparticulatemattereffective in an electrical resistivity range of particles 104-1011 cm insize. Pulverized coal, where the thermal electrical resistance ofDust collecting
electrodemany particles is high, requires various countermeasures betaken against such particles.
One such measure involves adjusting the temperature conditions
for dust collection; electrical resistance changes are shown in

Flue gas(from boiler)

Figure 2. Those successfully developed and commercializedbasedonsuchcharacteristics

areahigh-temperature
Fig. 1 Theory behind electrostatic precipitatoroelectrostatic precipitator operated at 350 C, a higher temperature
thanthatof

conventional

low-temperatureelectrostatic
Low-alkali/
high-sulfur coalresistance, and an advanced low-temperature electrostatic
precipitator, with its electrical resistance lowered by operating it

Low-alkali/
low-sulfur coalat a dew point or lower temperature of 90-100oC. Other thanelectrode method, which brushes off particulate matter by moving
the electrode to prevent back corona due to dust accumulation at
the electrode, and a semi-wet electrostatic precipitator where aliquid membrane is applied to wash away dust. Other methods
are commercialized electric discharge technologies, including anintermittent charge system to supply a pulsed voltage of several
milliseconds, and a pulse charging system for several tens of
microseconds.
At present, leading pulverized coal-fired plants built in and after
1990 employ very low-temperature electrostatic dust collection

Advanced low-temperature ESPConventional low-temperature ESP

Electrical resistivity ( -cm)

these, successful commercialized technology includes a moving

High-temperature ESP

precipitators (130-150oC), in order to lower the electrical

High-alkali/
high-sulfur coal
High-alkali/
low-sulfur coalprocesses that can treat particulate matter with various
properties and shapes.

Temperature (OC)Fig. 2 Temperature effects on electrical resistance of coal ash91

andClean Coal Technologies in Japan(2) High-temperature dust collection method

Research and development: Mitsubishi Heavy Industries, Ltd.; Hitachi, Ltd.; Kawasaki Heavy Industries Co., Ltd.; othersOverview
The

underpilot plant but also under the EAGLE project. These technologies

development as a technology to remove particulate matter fromhigh-temperature

dust

collection

methodisare also expected to be used at a 250MW IGCC demonstration

hot gas for pressurized-bed combustion and integrated

unit slated for initial operation in 2007.

gasification combined-cycle (IGCC) power generation processes.
This technology utilizes a multi-cyclone, a ceramic- or metalbased filter and a granular-bed method using silica or mullite toremove particulate matter. Multiple cyclones are mainly used forcoarse, imprecise removal. Those used for precision removal
include ceramic or metal filters of a cylindrical porous body into
which SiC and other inorganic materials and iron-aluminumalloys are formed (Photo 1). The filters used for this method weredeveloped by Nihon Garasu Kogyo or overseas by Paul
Schumacher.

Suchtechnologies,

evaluation/demonstration,

are

now

usedforunderdurability

pressurized-bed

combustion power generation at Hokkaido Electric Power’s
Tomatoh-Atsuma thermal power plant, with their verification tests

Photo 1 SiC ceramic filter

conducted not only for IGCC at 200-tons/day at the Nakoso IGCC

(3) Trace element removal method

Research and development: Japan Coal Energy Center
Project type: Subsidized coal production/utilization technology promotion project
Overview
Among the trace elements of coal, mercury is cited as theresearch, selected active carbon, natural inorganic minerals, andmaterial released into the atmosphere at the highest rate, andlimestone as materials that can absorb mercury. Their absorption

approximately 30% of the mercury not removed by thecharacteristics are now being evaluated. The research results

precipitators/desulfurizers is thought to be released. However,prove that if a method to inject active carbon or an FCC ash

nearly all bivalent mercury (Hg2+) is removed, leaving behindcatalyst into the flue for the removal of metal/mercury isnonvalent mercury (Hg) as the discharge matter. A method tocombined with removal at the flue gas desulfurizer, 90% or more

remove this nonvalent mercury is being actively reviewed. Theof the mercury can be easily removed.

Japan Coal Energy Center, though still in the process of basic

References1) "Thermal/Nuclear Power Generation Companion, 6th edition," Thermal/Nuclear Power Generation Association, 2002.
2) Sato, "Design and Actual Operations of High-Temperature Electrostatic Precipitators," Thermal/Nuclear, Vol. 34, No. 4, 1983.
3) Tsuchiya et al., "Technology Development of Low Low-Temperature EP in Coal Thermal-Purpose High-Performance Flue Gas
Treatment System," MHI Technical Journal Vol. 34, No. 3, 1997.
4) "Toward the Realization of Integrated Gasification Combined-Cycle Power Generation," CRIEPI Review, No. 44, 2001.
5) Coal-Based Next-Generation Technology Development Survey/Environment-Friendly Coal Combustion Technology Field(Trace Element Measurement/Removal Technology), NEDO results report, 2003.

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