50 MAKALE / ARTICLE IGCC Operation with SCR. GE says limiting syngas SOx to 12 Pı>l1l or reduc ing ammonia slip to 0.12 ıııım can reduce tlıe HRSG water wash reqı.ıiremeııt to orıce a year. Accoıdiııg to Aııor, deeper sullur ıemoval to 12 ıııım is moıe practi cal than ıeduciflg ammonia slip to 0.12 ıııım. -2.00 -2.05 -2.10 ';,: -2.15 ı -2.20 -2.25 -2.30 -2.35 -2.40 NH4HS04 GE e�timrıttd I HRSG wash ,,.,y,ıar / . .... · -: 01>''1,. . ...- ı,. , 'o-cY;:ı .' 0.1 1 ppm Ammonla Slip GEettimat9d1HRSG washperyHr GEestimated13HRSG woshes peryea, 10 ppm Gem Conccpt. Singte gasification enalıling mo<kıle facility can fuel many oom bined cyde planlS at� locations or be dedicated to a wıgıe plaot. ·------------------------------------------------------· ' ' ' ' ' ' i - 1 !.l i � ' ' ' ' ' ' ' �------------------------------------------------------· ConocoPhillips, which announced at the US gasification meeting lası year that it had purchased Global Energy, also signed a worldwide cooperative agreement with Fluor Corp. recently to develop, design and build E-Gas technology gasification projects. Japan IGCC plant Takuya Ono of JGC Corp. reported on the performance of Japan's !irsi commercial IGCC plant, Negishi, which began commercial service in June 2003. The facility operates with singletrain Chevron Texaco direct quench gasifier technology (since acquired by GE) to provide syngas fuel for electric power generation. The 1x1 combined cycle planı is designed around a Mitsubishi Heavy lndustries M701 F gas turbine, vertical flow HRSG, and MHI steam turbine. it has a net design output rating of 342 MW and % 36 thermal efficiency on syngas fuel, Ono says, although it has achieved 348 MW in commercial operation. At 15 C ambient site conditions, on syngas with nitrogen diluent, the Negishi IGCC planı generates 301 .6 MW from the gas turbine and 1 29.4 MW from the steam turbine lor a total of 431 MW gross at % 46.9 efficiency. Same basic 1 x1 M701 F combined cycle operating on Natura! gas is rated at 397 MW and % 57 efficiency with 266.1 MW generated by the gas turbine and 136.6 MW by the steam turbine. Negishi began commercial operation on June 30, 2003. As of this May, Ono reports, the planı was operating with % 93 power availability and %77.9 syngas availability. SCR for NOx control One distinctive design feature of the Negishi IGCC plant is the use of selective catalytic reduction for NOx control. As noted by Fluor engineers, Dave Heaven and Brian DeSousa, the API Falconara facility in ltaly is the only other gasification combined cycle plant that uses selective catalytic reduction. The ISAB gasification planı in ltaly also has SCR, they point out, but it is used only when operating on backup oil fuel and otherwise bypassed during syngas operation. Several years ago, at a Gasification Technology Council meeting, the subject of using SCR vs. other diluent techniques lor NOx control came up for discussion. At the time, gas turbine and process engineers participating in leh discussion did not think it a good idea and not worth considering. They argued that SCR "was not economically feasible without deep sulfur removal" and that steam or nitrogen injection were far more preferable for IGCC projects. Not necessarily so This may not be the case, say the Fluor engineers, who suggest the industry may want to re-examine the issue. They agree that the typically higher sulfur content of the gas turbine exhaust in an IGCC plant (compared to natura! gas fireci combined cycle) can produce ammonium bisulfate salt deposition on the cold surfaces of the HRSG. And, admittedly, this does lead to corrosion, loss of heat transfer, and eventually a forced outage lor water wash cleaning. But they point to the Negishi planı operating experience as proof that today's technology can cope with the problem. General Electric has evaluated the use of selective catalytic reduction with a Fr ?FA gas turbine in an IGCC configuration, they report, to assess the severity of the deposition problem and treatment options. Continuous operating with 40 ppm SOx in the gas turbine exhaust and 5 ppm ammonia slip from the SCR catalyst, lor example, would require an estimated 13 outages per year lor HRSG water washing. To reduce the number of water washes required to once a year. General Electirc recommends either limiting the syngas SOx content to 12 ppm or reducting the ammonia slip to 0.12 ppm. Giventhe state of current technology, Fluor recommends thatthe deeper sulfur removal to 1 2 ppm SOx would be more practical than reducing ammonia slip to 0.12 ppm. No problems at Negishi To the besi of everyone's knowledge, tne Negishi plant has not run into any problems with ammonium bisulfate fouling in the HRSG. With SCR treatment, the plant operators are able to keep NOx emissions below 3 ppm. Treated syngas !rom the Shell acid gas removal unit has a sulfur content of 8 ppmv, with a design maximum of 25 ppm. The stack gas temperature is 120 oC, which selective catalytic reduction. Other design considerations, such as changes in the tube arrangements of the HRSG, have also been made in order to minimize fouling problems. it appears that limiting syngas sulfur content to the 5-12 ppm range is adequate lor minimizing down time for HRSG water washing or even avoiding fouling problems completely (at the lower level). Sulfur removal in this range is possible with such technologies as Selexol and Rectisol. However, a number of additional factors other than HRSG fouling must be taken into account, Fluor cautions, when considering the use of SCR in an IGCC planı. 1 ENERJi & KOJENERASYON DÜNYASI • "Kojenerasyon: Yüksek Verim, Temiz Çevre, Enerjide Yeniden Yapılanma"
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