WPCA/PCUG NOx Round Table 2009Cleveland, OhioHans Hartenstein Ed HealyComparison of Deactivation Rates ofDifferent Catalyst TypesThree different types of catalyst deactivation mechanisms:•Thermal deactivation due to rutilization as a result ofoverheating the catalyst – same for all catalyst typesand makes that use TiO2as ceramic substrate.•Physical deactivation by means of:•Cell and/or pore pluggage, i.e. fly ash, LPA, etc.•Surface blinding layers i.e. CaSO4, eutectics, etc.Same for all catalyst types and makes as caused byflue gas and/or fly ash characteristics.•Chemical deactivation as a result of the reaction offlue gas constituents with the catalyst’s catalyticallyactive centers mostly consisting of V2O5.Catalyst Deactivation BasicsChemical catalyst deactivation is primarily caused by thereaction of cation species in the flue gas with catalyticallyactive V2O5. The main catalyst poisons in coal are:• Non-metals, mainly phosphorus (P) as gaseous P4O6• Alkali metals, mainly sodium (Na) and potassium (K)• Alkaline earth metals, mainly calcium (Ca) magnesium(Mg) and to a lesser extent barium (Ba)• Metalloids, mainly arsenic (As) as gaseous As2O3Chemical Catalyst DeactivationChemical deactivation follows the same principle regardlessof type and make of SCR catalyst containing catalyticallyactive V2O5as the main ingredient. All known SCR catalystscommercially used in coal-firedunits fall in this category.Chemical deactivation ofthe catalytically activeV2O5sites by e.g. arsenic.Chemical Catalyst DeactivationIn conclusion, theory suggeststhat all commercially usedSCR catalyst regardless of type and make deactivateschemically the same way and also at the same rate whenexposed to the same conditions including:• The same flue gas composition and temperature.• The same basic SCR reactor design (same Lv).• The same location (layer) within the SCR reactor.However, various claims to the contrary were made over theyears, especially related toarsenic poisoning including:• “Arsenic resistant” catalyst, e.g. through addition of MoO3.• “Arsenic tolerant” catalyst, e.g. through migration ofarsenic to center of thin wall.• “Arsenic proof” catalyst, e.g. by means of tri-modal porestructure.Chemical Catalyst Deactivation•Southern Company has 14 high-dust SCRs in Alabama,Florida and Georgia operational since the early 2000’s.•Evonik has 17 high-dust SCRsin Germany operationalsince 1987.•Evonik has managed more than 30 high-dust SCRs inFlorida, Illinois, Indiana, Kentucky, Maryland, NewJersey and New York some operational since 1993.These units have / had all types (corrugated, honeycomb,plate) and makes (Argillon, BASF, CERAM, Cormetech,Haldor Topsœ, Hitachi, IHI, KWH) of regenerated and/ornew catalystinstalled withinthe same reactorat the same time.Database for Actual DeactivationDifferentiation according to catalyst poisons can results inthe following categories:•low arsenic, mid calcium – e.g. Northern Appalachian•mid arsenic, mid calcium – e.g. Eastern Kenntucky•high arsenic, low calcium – e.g. Southern Illinois Basinand Northern Alabama•high calcium, high alkali – e.g. PRB•high alkali, high phosphorus – e.g. biomass, ligniteDatabase for Actual DeactivationDatabase for Actual DeactivationEastern Bituminous - Low Arsenic, Mid Calcium1618202224262830323436384042440 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000SCR operating hours

activty K [m/h]layer 1, new plate Xlayer 2, new plate Xlayer 3, new plate Xlayer 4, new plate Xlayer 5, new plate Xlayer 6, new plate Ylayer 1, new plate YDatabase for Actual DeactivationEastern Bituminous - Mid Arsenic, Mid Calcium0.81.01.21.41.61.82.02.22.42.62.80 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000SCR operating hours

DeNOx potential P = K/Avlayer1, new platelayer 2, new platelayer 3, new platelayer 4, regenerated honeycomblayer 1, regenerated platelayer 2, regenerated platelayer 3, regenerated plateDatabase for Actual DeactivationEastern Bituminous - High Arsenic, Low Calcium202224262830323436384042444648505255,000 65,000 75,000 85,000 95,000 105,000 115,000SCR operating hours

activty K [m/h]layer 1, new plate Ylayer 2, regenerated plate Xlayer 3, new plate Ylayer 5, new corrugated Xlayer 6, new corrugated Xlayer 2, new plate XDatabase for Actual DeactivationEastern Bituminous - Various Coals0.450.550.650.750.850.951.050 5,000 10,000 15,000 20,000 25,000 30,000 35,000SCR operating hours

relative activitylow arsenic, mid calcium, new plate Xmid arsenic, mid calcium, regenerated plate Yhigh arsenic, low calcium, new plate Y•Central and Southern Appalachian coals with mid arsenicand mid calcium contents.•Deactivation is about what was initially expected.•Arsenic deactivation seems to have reached saturationas deactivation appears to have leveled out.•Peculiarity: Inverse deactivation was noted initially,which means that the deactivation is greater on lower(downstream) layers than onhigher (upstream) layers.This is unusual for bituminouscoal units but is supportedthrough data showing higher deactivation at the lowerlayers initially. The trend reversed to what would beconsidered normal now.Mid Arsenic Case Study – Wansley 1Mid Arsenic Case Study – Wansley 1Mid Arsenic Case Study – Wansley 1Mid Arsenic Case Study – Wansley 1Mid Arsenic Case Study – Wansley 1Database for Actual DeactivationSouthern Illinois Basin - High Arsenic, Low Calcium2025303540450 5,000 10,000 15,000 20,000 25,000SCR Operating Hours

activty [m/h]layer 1, new plate Xlayer 1, new plate Xlayer 3, new plate Xlayer 1, new corrugated Xlayer 1, new corrugated Xlayer 1, regenerated plate Xlayer 3, new plate XDatabase for Actual DeactivationSouthern Illinois Basin Coal - High Arsenic, Low Calcium0.450.550.650.750.850.951.051.150 2,000 4,000 6,000 8,000 10,000 12,000 14,000SCR operating hours

activity [m/h]plate X, plant A, coal 1plate X, plant A, coal 1honeycomb X, plant B, coal 1corrugated X, plant C, coal 1plate Y, plant D, coal 2plate Y, plant D, coal 2corrugated X, plant E, coal 2honeycomb Y, plant F, coal 2honeycomb Z, plant G, coal 2•Important trends in Northern Alabama coal burned:•Increasing variability of the As/Ca ratio.•Increase in absolute arsenic concentration.•Deacrease in heating value and increase in ash content.•Observations:•Plate catalyst shows a greater and/or quicker uptake ofarsenic update than honeycomb(same as in Europe).•Arsenic uptake appears to reach saturation since K/K0isnow about the same on all layers regardless of catalysttype and make (same as in Europe).•SEM shows arsenic gradient across wall of catalyst withhigher [As] on walls and lower in the middle regardlessof catalyst type and make (same as in Europe).High Arsenic Case Study – Gorgas 10High Arsenic Case Study – Gorgas 10High Arsenic Case Study – Gorgas 10High Arsenic Case Study – Gorgas 10High Arsenic Case Study – Gorgas 10High Arsenic Case Study – Gorgas 10High Arsenic Case Study – Gorgas 10High Arsenic Case Study – Gorgas 10High Arsenic Case Study – Gorgas 10Database for Actual DeactivationPRB - High Alkali, High Calcium15202530354045500 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000operating hours

K-value [m/h]layer 1layer 2layer 3layer 4•PRB fuel – high calcium, high alkali, high phosphorus.•Deactivation significantly better than initially expected(although, Miller was designed conservatively).•Deactivation due to gypsum layer deposition on surface ofcatalyst.•Inverse deactivation noted – deactivation greater on lowerlayers than on higher (top) layer. This is not unusual forPRB units and has been observed elsewhere also.•Also significant is gross versus effective/available DeNOxpotential due to fly ash plugging. Southern Company istrending towards larger pitch whereas the industryappears to be going to smaller pitch.PRB Case Study – Miller 1, 2, 3 & 4PRB Case Study – Miller 1, 2, 3 & 4PRB Case Study – Miller 1, 2, 3 & 4– 8.2 mm pitchPRB Case Study – Miller 1, 2, 3 & 4– 9.3 mm pitchConclusions•Theory suggests that chemical deactivation mechanismsand deactivates rates should be essentially the same forall catalyst types and makesas they are primarilydependent on the composition of the coal burned.•Actual field data confirms theory as all makes and typesof catalyst deactivate chemically at essentially the samerate when exposed to the sameflue gas in the same SCRreactor. This is also true for regenerated catalyst.•Catalyst make and type canbe selected only based on:•Suitable geometry (pitch,mechanical strength, etc.).•Lowest price per DeNOx potential unit.•There is no such thing asarsenic resistant SCR catalyst.Questions?