Mercury Control with Regenerative Activated Coke Technology

Mercury Control with Regenerative Activated Coke Technology H. James Peters, Hamon Research-Cottrell, Inc., Somerville, NJ

Many issues face coal fired utilities with respect to environmental demands, some based on regulations and others based on local pressures. These include increasingly stringent control of criteria pollutants, anticipated federal and state requirements for mercury control, issues revolving around water use and water disposal, plume visibility, overall plant thermal efficiency and the future considerations for climate change issues. For utilities that burn PRB and other low sulfur coals, an exemplary reference project is the re-construction of the Isogo Power Station by J-Power. This project replaced two vintage coal fired units, and within the same site limits, more than doubled generation capacity to 2x600MW with ultrasupercritical boilers fitted with SCR, ESPs, and advanced generation ReACT technology. The controls provide low emissions from the high efficiency coal fired boiler plant and allow the plant to operate as the cleanest coal fired power plant in the world in terms of emissions intensity, at emissions levels that are equivalent to natural gas fired power plants. Isogo Unit #1 has been in operation since 2002 and Unit #2 started operation in mid 2009. J-Power EnTech has recently licensed the Regenerative Activated Coke Technology (ReACT ) to Hamon Research-Cottrell.

The multi-pollutant control ReACT technology is a completely dry scrubbing system based on adsorption of SO2, SO3, and Hg and reduction of NOx to N2 on activated coke in a moving bed, with regeneration of the coke for return to the adsorber, and production of saleable byproduct, such as sulfuric acid, from desorbed sulfur rich gases.

The basic process concept originated with Bergbau Forschung in Germany the 1950s, saw additional development by Foster Wheeler in the 1970s in conjunction with their Resox process, and commercialization with activated coke by Mitsui Mining in the 1980s, and subsequent full

commercialization by EPDC (now J-Power) in the 1990s as an advanced generation multipollutant control technology for coal fired boilers. J-Power, acquired the technology from Mitsui in 2005, now operates three full scale units at Takehara (1995), Isogo #1(2002) and Isogo #2 (2009), and has provided units for refinery, incineration, and sinter applications through its subsidiary J-Power EnTech.

J-Power’s Isogo #1 and Isogo#2 burn low-sulfur coal and incorporate high efficiency

ultrasupercritical boilers, combustion NOx control, primary SCR, ESPs and ReACT . Isogo has been recognized for emissions intensity levels for SOx and NOx that are the lowest worldwide for coal fired power. Isogo typically operates in the single digit ppm concentration range for SO2 and NOx (against permit levels of 10ppm and 13 ppm at Isogo #2), particulate at less than 5 mg/Nm3 (0.005 lb/mmBTU) and with well over 90% control of both elemental and oxidized forms of mercury.

The ReACT process has also been already been successfully demonstrated for U.S. coal

applications as an EPRI project, hosted by Sierra Pacific Power at its North Valmy Station, where the expected high levels of SO2, NOx, and Hg performance were readily demonstrated, consistent with commercial results at the full scale units in Japan.

This paper focuses on aspects of the activated coke technology as related to mercury control.

ReACT involves a three stage process. Flue gas is contacted with a slowly moving bed of

activated coke. Fresh activated coke is fed to the top of an adsorption column and flows by gravity. The activated coke removes SO2, SO3, NOx, Hg and other species through adsorption, chemisorption and catalytic reactions which are enhanced in the presence of ammonia. Particulate is also reduced across the moving bed by impaction on the coke pellets.

Pollutant laden activated coke is transferred to a thermal regeneration stage, where reactions are completed and pollutants are desorbed as a sulfur rich gas stream. The regenerated activated coke stream is cooled and fines are separated before return to the adsorber. Make-up coke in pellet form is added to replace the separated fines. The third stage receives the sulfur rich gas stream for saleable byproduct production.

This process offers advantages for utilities, as requirements for mercury control are being added to increasingly stringent SO2 and NOx regulation, and where issues related to water use, downstream plume visibility, and solid waste disposal have become major factors. These advantages derive from: ‐ Adsorption does not require any water use

‐ Adsorption of SO3 along with no humidification resolves downstream plume visibility issues ‐ Regeneration of sorbent greatly reduces site logistics for reagent make-up, processing and waste handling compared with other FGD processes

‐ Marketable byproduct is produced.

‐ Primary particulate is upstream (existing), preserving beneficial use of ash.

‐ Mercury control is obtained at >90% levels for both elemental and oxidized forms.

‐ Mercury laden disposal streams are minimized.

The present practice for mercury control at utility power plants typically involves the injection of powdered activated carbon into flue gas.

Activated carbon is injected into the flue gas stream upstream of particulate collection equipment as a once-through adsorbent. For target mercury removal of 90% activated carbon injection rates range from 2 to 10 lb per million acfm with some sensitivity to coal, combustion, SO3 levels and on the type of particulate control in place. Injection rates are generally lower with fabric filters.

Contacting conditions for activated carbon in a fabric filter include short in-flight time (1-2 seconds) followed by fixed bed …… 此处隐藏：14228字，全部文档内容请下载后查看。喜欢就下载吧 ……