Regenerative activated coke technology (ReACT) is an integrated multipollutant control approach that removes SOx, NOx, and Hg from coal-fired plants by adsorption with activated coke to attain emissions levels found at natural gas–fired plants. One big advantage of this technology is that it uses only a fraction of the water used by conventional wet flue gas desulfurization. A recent license agreement brings this technology to the U.S.
Routine reductions in air emissions limits are a fact of life for power generators around the globe. In the U.S., adding wet flue gas desulfurization (wFGD) to remove SO2 and selective catalytic reduction (SCR) for NOx control are de rigueur for new plants, and these systems also have been retrofitted onto hundreds of operating coal-fired plants. The future will likely bring increasingly stringent control of criteria pollutants such as mercury and other hazardous air pollutants, plume visibility, disposal issues, as well as new greenhouse gas emission controls.
The conventional approach to controlling SO2 is by using either wFGD or a dry spray dryer absorber (SDA). Another option is regenerative activated coke technology (ReACT), an integrated multipollutant control approach that not only can remove SO2 and NOx from the flue gas stream but also removes mercury (Hg) through adsorption using activated coke. The activated coke sorbent is regenerated in the process while using only 1% of the water required by conventional wFGD systems. ReACT is fully commercial on coal-fired projects up to 600 MW in Japan and is now available in the U.S. through a recent license agreement between J-POWER Entech and Hamon Research-Cottrell Inc.
World-Class Performance
Japan’s Electric Power Development Corp. (EPDC) first negotiated pollution control permits for its 2 x 265-MW Isogo Thermal Power Station (Isogo) with the city of Yokohama City in 1964. EPDC launched a number of initiatives in the following years, including installing the first wFGD system in Japan.
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| 1. Best-in-class performance. The Isogo repowering project replaced two 265-MW conventional pulverized coal boilers and pollution control equipment (ESP and wFGD) with two 600-MW ultrasupercritical boilers fitted with ReACT advanced multipollutant controls. The newly repowered plant claims the title as the world’s lowest emissions-intensity coal-fired power plant. Design of the plant, located in Yokohama harbor, also considered plant aesthetics, including visibility of the stack. Courtesy: J-POWER |
After operating Isogo for more than 30 years, EPDC (now J-POWER) committed to replace the plant and negotiated with the city of Yokohama for a major repowering project, which would more than double generation capacity at the site yet further reduce emissions with more stringent environmental controls. The J-POWER/Isogo repowering project replaced the two vintage coal-fired units while more than doubling the generation to two 600-MW units within the same site limits. J-POWER’s newly repowered Isogo burns low-sulfur coal and incorporates high-efficiency ultrasupercritical boilers, low-NOx burners and controls, primary SCR, electrostatic precipitators (ESPs), and ReACT (Figure 1).
After more than eight years of operating experience at Isogo Unit 1 (the plant entered service in 2002), the ReACT system performance has been exceptional:
- Less than 5 ppm of SO2 at the stack with an SO2 inlet concentration of 200 ppm–400 ppm. SOx removal efficiency is over 98%.
- Greater than 90% mercury removal.
- An additional 20%–40% NOx reduction provided by ReACT as a co-benefit, dropping stack NOx concentrations to <10 ppm. An SCR is installed upstream as the primary NOx control.
Based on this record of Unit 1 performance, J-POWER agreed to a more stringent permit level for the second unit. Unit 2 began commercial operation in mid-2009.
Today, Isogo ranks as the cleanest coal-fired power plant in the world in terms of emissions intensity, with emissions comparable to those from natural gas firing. Isogo typically operates in the single-digit ppm concentration range for SO2 and NOx (against Unit 2 permit levels of 10 ppm and 13 ppm), at less than 5 mg/Nm3 (0.005 lb/mmBtu) for particulates, and with well over 90% control of both elemental and oxidized forms of mercury (Figure 2).
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| 2. Small environmental footprint. ReACT is a regenerative activated coke–based technology that produces saleable by-products (sulfuric acid or gypsum) and, as a dry process, does not require water. The technology should be of special interest to U.S. utilities burning lower-sulfur western fuels, especially at locations where there are significant water supply concerns. J-POWER reports that SO2 and NOx emissions at the Isogo plant are both at single-digit ppm concentration levels—emissions that are on par with a natural gas–fired plant. Data for Japan represent combined data for Japan’s 10 regional electric utilities and J-POWER. Figures for Isogo represent actual performance for fiscal 2008. Country figures represent combined emissions intensity for coal-, oil-, and gas-fired thermal power plants. Source: Federation of Electric Power Companies of Japan |
Development History
The basic process concept originated with Bergbau Forschung in the 1950s in Germany. Additional development was provided by Foster Wheeler in the late 1960s in conjunction with its Resox process. Commercialization with activated coke was achieved by Mitsui Mining in the 1980s. Full commercialization by EPDC as an advanced generation multipollutant control technology for coal-fired boilers followed in the 1990s.
Process development efforts in the late 1970s focused on high-efficiency (98%) SO2 removal efficiency, but researchers quickly recognized that ReACT also provided NOx removal. The ReACT process design for SO2 control routinely removes 20% to 40% NOx as a co-benefit, and the process can be configured to achieve 50% to 70% NOx removal or higher by adding secondary injection of ammonia into the regenerator.
EPDC, which had faced serious difficulties in obtaining water from local government water agencies when siting earlier projects, began developing ReACT as an alternative to wFGD because the process used a fraction of the water required by a wFGD system. Reducing the water demand of the Isogo site post-repowering was a key project requirement, making ReACT a natural selection for that project. J-POWER subsequently acquired the rights to the technology from Mitsui in 2005 and has since provided units for refinery, incineration, and sinter plant applications through its subsidiary J-POWER EnTech.
The ReACT process has been successfully demonstrated in the U.S. over a period of five months as part of an Electric Power Research Institute project hosted by Sierra Pacific Power at its North Valmy Station. Valmy reported the following outstanding removal rates: 97.6% to 99.9% for SO2, 25.7% to 48% for NOx, and 97.1% to 99.6% for Hg removal. (The data were reported in “ReACT Process Demonstration at Valmy Generating Station,” C. Dene, et al., MEGA Symposium, Paper 123, 2008.) The expected high levels of SO2, NOx, and Hg removal were entirely consistent with commercial results at the full-scale units in Japan.
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