[{"data":1,"prerenderedAt":920},["ShallowReactive",2],{"site-footer-common":3,"glossary:ammonia-slip":45,"glossary-related:ammonia-slip":217},{"id":4,"extension":5,"footer":6,"meta":40,"navbar":41,"stem":43,"__hash__":44},"common\u002Fcommon.yml","yml",{"tagline":7,"links":8,"sections":9},"Acoustic cleaning intelligence for industrial fouling, soot, ash, dust and build-up.",[],[10,19,31],{"title":11,"links":12},"Product",[13,16],{"label":14,"to":15},"How it works","\u002F#product",{"label":17,"to":18},"Cost assessment","\u002F#hero",{"title":20,"links":21},"Company",[22,25,28],{"label":23,"to":24},"What we build","\u002F#about",{"label":26,"to":27},"Careers","\u002F#careers",{"label":29,"to":30},"Contact","\u002F#contact",{"title":32,"links":33},"Resources",[34,37],{"label":35,"to":36},"Blog","\u002Fresources\u002Fblog",{"label":38,"to":39},"Glossary","\u002Fglossary",{},{"links":42},[],"common","YocmZRy1AYfBbpgGVms-zhdiABlF8VTxHx6h4rDmZBA",{"id":46,"title":47,"aliases":48,"body":51,"category":196,"description":197,"extension":198,"meta":199,"navigation":200,"path":201,"relatedTerms":202,"seo":208,"sources":211,"stem":215,"term":47,"__hash__":216},"glossary\u002Fglossary\u002Fammonia-slip.md","Ammonia slip",[49,50],"NH3 slip","ammonia breakthrough",{"type":52,"value":53,"toc":188},"minimark",[54,72,77,121,125,143,147,158,162],[55,56,57,60,61,66,67,71],"p",{},[58,59,47],"strong",{}," is the concentration of unreacted ammonia (NH₃) in the flue gas leaving an ",[62,63,65],"a",{"href":64},"\u002Fglossary\u002Fselective-catalytic-reduction","SCR"," or ",[62,68,70],{"href":69},"\u002Fglossary\u002Fselective-non-catalytic-reduction","SNCR"," system. It is the single most important operational KPI after NOx reduction itself: slip is regulated (typically capped at 2–10 ppm in permits), represents wasted reagent, and drives downstream fouling.",[73,74,76],"h2",{"id":75},"causes-of-high-ammonia-slip","Causes of high ammonia slip",[78,79,80,91,104,110,115],"ul",{},[81,82,83,86,87],"li",{},[58,84,85],{},"Poor NH₃\u002FNOx mixing"," at the ",[62,88,90],{"href":89},"\u002Fglossary\u002Fammonia-injection-grid","AIG",[81,92,93,66,99,103],{},[58,94,95],{},[62,96,98],{"href":97},"\u002Fglossary\u002Fcatalyst-masking","Catalyst masking",[62,100,102],{"href":101},"\u002Fglossary\u002Fcatalyst-pluggage","pluggage"," reducing active surface area",[81,105,106,109],{},[58,107,108],{},"Catalyst age and de-activation"," towards end of life",[81,111,112],{},[58,113,114],{},"Operating temperature outside the catalyst window",[81,116,117,120],{},[58,118,119],{},"Over-injection of ammonia"," to compensate for falling NOx-reduction efficiency",[73,122,124],{"id":123},"downstream-consequences","Downstream consequences",[55,126,127,128,132,133,137,138,142],{},"Slipped ammonia combines with SO₃ in cooling flue gas to form ",[62,129,131],{"href":130},"\u002Fglossary\u002Fammonium-bisulphate","ammonium bisulphate (ABS)",", a sticky low-melting deposit that fouls ",[62,134,136],{"href":135},"\u002Fglossary\u002Fair-heater","air heaters",", ",[62,139,141],{"href":140},"\u002Fglossary\u002Feconomiser","economisers"," and downstream catalysts and filters. Excessive slip can therefore destroy the cold end of a boiler within months.",[73,144,146],{"id":145},"sonic-horns-and-slip-reduction","Sonic horns and slip reduction",[55,148,149,153,154,157],{},[62,150,152],{"href":151},"\u002Fglossary\u002Fsonic-horn","Sonic horns"," reduce slip indirectly by keeping the catalyst face clear of ",[62,155,156],{"href":97},"masking"," deposits, which preserves active surface area, which lets the catalyst convert ammonia to nitrogen instead of letting it slip. They also keep the AIG decks clean, preserving the designed spray pattern.",[73,159,161],{"id":160},"related-terms","Related terms",[78,163,164,169,174,179,184],{},[81,165,166],{},[62,167,168],{"href":64},"Selective Catalytic Reduction (SCR)",[81,170,171],{},[62,172,173],{"href":69},"Selective Non-Catalytic Reduction (SNCR)",[81,175,176],{},[62,177,178],{"href":89},"Ammonia injection grid",[81,180,181],{},[62,182,183],{"href":130},"Ammonium bisulphate",[81,185,186],{},[62,187,98],{"href":97},{"title":189,"searchDepth":190,"depth":190,"links":191},"",2,[192,193,194,195],{"id":75,"depth":190,"text":76},{"id":123,"depth":190,"text":124},{"id":145,"depth":190,"text":146},{"id":160,"depth":190,"text":161},"scr-sncr","Ammonia slip is the concentration of unreacted ammonia (NH₃) in the flue gas leaving an SCR or SNCR system. It is the single most important operational KPI after NOx reduction itself: slip is regulated (typically capped at 2–10 ppm in permits), represents wasted reagent, and drives downstream fouling.","md",{},true,"\u002Fglossary\u002Fammonia-slip",[203,204,205,206,207],"selective-catalytic-reduction","selective-non-catalytic-reduction","ammonia-injection-grid","ammonium-bisulphate","catalyst-masking",{"title":209,"description":210},"Ammonia slip — unreacted NH3 leaving an SCR or SNCR system","Ammonia slip is unreacted ammonia leaving the DeNOx system in the flue gas. It is regulated, expensive in lost reagent, and causes ammonium-bisulphate fouling downstream.",[212],{"title":213,"url":214},"Power Engineering — Selective Catalytic Reduction: Operational Issues","https:\u002F\u002Fwww.power-eng.com\u002Fenvironmental-emissions\u002Fselective-catalytic-reduction-operational-issues-and-guidelines\u002F","glossary\u002Fammonia-slip","BU6p3qY3enI-T7Yz_rpYjEbWD0YUtLcL2fA38Y4iZN0",[218,374,498,602,758],{"id":219,"title":168,"aliases":220,"body":223,"category":196,"description":353,"extension":198,"meta":354,"navigation":200,"path":64,"relatedTerms":355,"seo":361,"sources":364,"stem":371,"term":372,"__hash__":373},"glossary\u002Fglossary\u002Fselective-catalytic-reduction.md",[65,221,222],"SCR system","SCR reactor",{"type":52,"value":224,"toc":348},[225,244,248,263,267,270,297,312,314],[55,226,227,229,230,234,235,239,240,243],{},[58,228,168],{}," is the dominant flue-gas NOx-control technology on coal-fired and gas-fired utility boilers, ",[62,231,233],{"href":232},"\u002Fglossary\u002Fheat-recovery-steam-generator","HRSGs"," in combined-cycle plants, ",[62,236,238],{"href":237},"\u002Fglossary\u002Fwaste-to-energy","waste-to-energy"," and ",[62,241,242],{"href":237},"biomass"," boilers, cement plants and major refining furnaces. Ammonia or aqueous urea is injected upstream of a catalyst bed; the catalyst lowers the activation energy for the reaction NOx + NH₃ → N₂ + H₂O, achieving 80–95% NOx reduction across the reactor.",[73,245,247],{"id":246},"reactor-layout","Reactor layout",[55,249,250,251,254,255,258,259,262],{},"A typical SCR reactor is a vertical or horizontal duct containing 2–4 layers of catalyst modules. Upstream of the catalyst sits the ",[62,252,253],{"href":89},"ammonia injection grid (AIG)"," that distributes the ammonia evenly into the flue gas. Most installations operate in the ",[58,256,257],{},"high-dust"," position (between economiser and air heater) where catalyst temperature is around 300–400 °C; ",[58,260,261],{},"tail-end"," SCRs sit downstream of particulate control at lower temperatures, with the trade-off of needing flue-gas reheating.",[73,264,266],{"id":265},"fouling-and-cleaning","Fouling and cleaning",[55,268,269],{},"SCR catalysts foul in two ways:",[78,271,272,289],{},[81,273,274,279,280,239,284,288],{},[58,275,276],{},[62,277,278],{"href":101},"Pluggage"," — fly ash, ",[62,281,283],{"href":282},"\u002Fglossary\u002Fpopcorn-ash","popcorn ash",[62,285,287],{"href":286},"\u002Fglossary\u002Flarge-particle-ash","large-particle ash"," wedge into the catalyst cells, blocking the gas path",[81,290,291,296],{},[58,292,293],{},[62,294,295],{"href":97},"Masking"," — a thin layer of deposit covers the active sites; gas flow continues but catalytic activity falls",[55,298,299,300,303,304,137,308,311],{},"Both reduce NOx-reduction efficiency, raise ",[62,301,302],{"href":201},"ammonia slip",", and shorten catalyst life. Cleaning options include steam ",[62,305,307],{"href":306},"\u002Fglossary\u002Fsteam-sootblower","sootblowers",[62,309,310],{"href":151},"sonic horns"," and offline campaigns (vacuum \u002F water wash \u002F regeneration). Sonic horns are increasingly favoured because they continuously dislodge ash before it cements onto the catalyst face, without the steam erosion of mechanical sootblowing.",[73,313,161],{"id":160},[78,315,316,320,324,328,332,337,343],{},[81,317,318],{},[62,319,173],{"href":69},[81,321,322],{},[62,323,178],{"href":89},[81,325,326],{},[62,327,47],{"href":201},[81,329,330],{},[62,331,98],{"href":97},[81,333,334],{},[62,335,336],{"href":101},"Catalyst pluggage",[81,338,339],{},[62,340,342],{"href":341},"\u002Fglossary\u002Fhoneycomb-catalyst","Honeycomb catalyst",[81,344,345],{},[62,346,347],{"href":151},"Sonic horn",{"title":189,"searchDepth":190,"depth":190,"links":349},[350,351,352],{"id":246,"depth":190,"text":247},{"id":265,"depth":190,"text":266},{"id":160,"depth":190,"text":161},"Selective Catalytic Reduction (SCR) is the dominant flue-gas NOx-control technology on coal-fired and gas-fired utility boilers, HRSGs in combined-cycle plants, waste-to-energy and biomass boilers, cement plants and major refining furnaces. Ammonia or aqueous urea is injected upstream of a catalyst bed; the catalyst lowers the activation energy for the reaction NOx + NH₃ → N₂ + H₂O, achieving 80–95% NOx reduction across the reactor.",{},[204,356,205,357,207,358,359,360],"denox","ammonia-slip","catalyst-pluggage","honeycomb-catalyst","sonic-horn",{"title":362,"description":363},"Selective Catalytic Reduction (SCR) — how the dominant NOx-control technology works","SCR is the dominant NOx-control technology on industrial combustion plant. Ammonia is injected upstream of a catalyst that converts NOx to nitrogen and water.",[365,368],{"title":366,"url":367},"Wikipedia — Selective catalytic reduction","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FSelective_catalytic_reduction",{"title":369,"url":370},"Power Engineering — SCR Catalyst Cleaning: Sootblowers vs. Acoustic Horns","https:\u002F\u002Fwww.power-eng.com\u002Foperations-maintenance\u002Fscr-catalyst-cleaningsootblowers-vs-acoustic-horns\u002F","glossary\u002Fselective-catalytic-reduction","Selective Catalytic Reduction","fmMCMd4NY3eZdSk_UYlbZ9ryi-9CR2Os6DivQjXEPCU",{"id":375,"title":173,"aliases":376,"body":378,"category":196,"description":484,"extension":198,"meta":485,"navigation":200,"path":69,"relatedTerms":486,"seo":488,"sources":491,"stem":495,"term":496,"__hash__":497},"glossary\u002Fglossary\u002Fselective-non-catalytic-reduction.md",[70,377],"SNCR system",{"type":52,"value":379,"toc":479},[380,391,395,418,422,425,446,451,453],[55,381,382,384,385,387,388,390],{},[58,383,173],{}," reduces NOx in flue gas by injecting ammonia or aqueous urea directly into the furnace at high temperature (850–1100 °C), where the reagent reacts homogeneously with NOx without needing a catalyst. SNCR is cheaper to install than ",[62,386,65],{"href":64}," but achieves lower reduction (typically 30–60%) and produces higher ",[62,389,302],{"href":201},".",[73,392,394],{"id":393},"where-sncr-is-used","Where SNCR is used",[78,396,397,400,408,415],{},[81,398,399],{},"Smaller industrial and utility boilers where SCR capital cost is unjustified",[81,401,402,239,405,407],{},[62,403,404],{"href":237},"Waste-to-energy",[62,406,242],{"href":237}," plants — often as the primary DeNOx with optional SCR polish",[81,409,410,414],{},[62,411,413],{"href":412},"\u002Fglossary\u002Fpreheater-tower","Cement preheater towers"," where the gas temperature window is naturally available",[81,416,417],{},"As a retrofit on units where space prevents SCR installation",[73,419,421],{"id":420},"fouling-implications","Fouling implications",[55,423,424],{},"SNCR does not have a catalyst to foul, but the reagent injection itself creates downstream deposit risks:",[78,426,427,440],{},[81,428,429,432,433,436,437],{},[58,430,431],{},"Ammonia salt deposits"," — un-reacted ammonia combines with SO₃ and ash to form ",[62,434,435],{"href":130},"ammonium bisulphate"," on cold-end heat-transfer surfaces, particularly the ",[62,438,439],{"href":135},"air heater",[81,441,442,445],{},[58,443,444],{},"Urea \u002F ammonia deposits on lance tips"," — injection lances can plug with urea solids or carbon deposits",[55,447,448,450],{},[62,449,152],{"href":151}," on the cold-end air heater address ABS fouling that follows SNCR operation.",[73,452,161],{"id":160},[78,454,455,459,465,471,475],{},[81,456,457],{},[62,458,168],{"href":64},[81,460,461],{},[62,462,464],{"href":463},"\u002Fglossary\u002Fdenox","DeNOx",[81,466,467],{},[62,468,470],{"href":469},"\u002Fglossary\u002Furea-sncr-aqueous-ammonia-sncr","Urea SNCR \u002F aqueous-ammonia SNCR",[81,472,473],{},[62,474,47],{"href":201},[81,476,477],{},[62,478,183],{"href":130},{"title":189,"searchDepth":190,"depth":190,"links":480},[481,482,483],{"id":393,"depth":190,"text":394},{"id":420,"depth":190,"text":421},{"id":160,"depth":190,"text":161},"Selective Non-Catalytic Reduction (SNCR) reduces NOx in flue gas by injecting ammonia or aqueous urea directly into the furnace at high temperature (850–1100 °C), where the reagent reacts homogeneously with NOx without needing a catalyst. SNCR is cheaper to install than SCR but achieves lower reduction (typically 30–60%) and produces higher ammonia slip.",{},[203,356,487,357,206],"urea-sncr-aqueous-ammonia-sncr",{"title":489,"description":490},"Selective Non-Catalytic Reduction (SNCR) — DeNOx without a catalyst","SNCR injects ammonia or urea directly into the furnace at 850–1100 °C to reduce NOx without a catalyst. Cheaper than SCR but lower efficiency and higher slip.",[492],{"title":493,"url":494},"Wikipedia — Selective non-catalytic reduction","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FSelective_non-catalytic_reduction","glossary\u002Fselective-non-catalytic-reduction","Selective Non-Catalytic Reduction","IXdCJcIAQIaUzfIpBXuWLUA2b5T-pTWfhvZ703VsbdA",{"id":499,"title":500,"aliases":501,"body":503,"category":196,"description":590,"extension":198,"meta":591,"navigation":200,"path":89,"relatedTerms":592,"seo":593,"sources":596,"stem":600,"term":178,"__hash__":601},"glossary\u002Fglossary\u002Fammonia-injection-grid.md","Ammonia injection grid (AIG)",[90,502],"ammonia injection grids",{"type":52,"value":504,"toc":585},[505,526,530,556,560,565,567],[55,506,507,508,510,511,513,514,239,518,520,521,525],{},"An ",[58,509,253],{}," is an array of injector nozzles that distributes ammonia (or vaporised aqueous-ammonia \u002F urea) evenly across the flue-gas duct upstream of an ",[62,512,65],{"href":64}," catalyst bed. The quality of the NH₃\u002FNOx mixing at the catalyst inlet is the single biggest determinant of ",[62,515,517],{"href":516},"\u002Fglossary\u002Fnox-reduction-efficiency","NOx reduction efficiency",[62,519,302],{"href":201},": under-mixing leaves NOx-rich zones unreacted ",[522,523,524],"em",{},"and"," causes locally over-stoichiometric ammonia in other zones.",[73,527,529],{"id":528},"common-failure-modes","Common failure modes",[78,531,532,538,544,550],{},[81,533,534,537],{},[58,535,536],{},"Nozzle plugging"," — ash, ammonium-salt deposits or carbon block individual nozzles",[81,539,540,543],{},[58,541,542],{},"Lance fouling"," — deposits accumulate on lance bodies and disturb spray patterns",[81,545,546,549],{},[58,547,548],{},"Erosion"," — abrasive ash wears injector tips, distorting the spray pattern",[81,551,552,555],{},[58,553,554],{},"Maldistribution"," — uneven gas flow at the AIG inlet means even a perfect AIG delivers uneven mixing",[73,557,559],{"id":558},"sonic-horns-on-the-aig-deck","Sonic horns on the AIG deck",[55,561,562,564],{},[62,563,152],{"href":151}," mounted near the AIG deck keep ash from accumulating on the injection lances, on the inlet duct walls and on the gas-distribution turning vanes upstream. Maintaining clean lances preserves the design spray pattern and the NH₃\u002FNOx mixing quality on which the entire SCR depends.",[73,566,161],{"id":160},[78,568,569,573,577,581],{},[81,570,571],{},[62,572,168],{"href":64},[81,574,575],{},[62,576,47],{"href":201},[81,578,579],{},[62,580,336],{"href":101},[81,582,583],{},[62,584,347],{"href":151},{"title":189,"searchDepth":190,"depth":190,"links":586},[587,588,589],{"id":528,"depth":190,"text":529},{"id":558,"depth":190,"text":559},{"id":160,"depth":190,"text":161},"An ammonia injection grid (AIG) is an array of injector nozzles that distributes ammonia (or vaporised aqueous-ammonia \u002F urea) evenly across the flue-gas duct upstream of an SCR catalyst bed. The quality of the NH₃\u002FNOx mixing at the catalyst inlet is the single biggest determinant of NOx reduction efficiency and ammonia slip: under-mixing leaves NOx-rich zones unreacted and causes locally over-stoichiometric ammonia in other zones.",{},[203,357,358,360],{"title":594,"description":595},"Ammonia injection grid (AIG) — even reagent distribution upstream of SCR","An AIG is the array of nozzles that distributes ammonia evenly into flue gas upstream of an SCR catalyst bed. Poor AIG performance is the leading cause of high ammonia slip.",[597],{"title":598,"url":599},"Power Engineering — AIG Upgrades Slash HRSG Ammonia Usage and Tube Fouling","https:\u002F\u002Fwww.power-eng.com\u002Foperations-maintenance\u002Finjection-grid-upgrades-slash-hrsg-ammonia-usage-and-tube-fouling\u002F","glossary\u002Fammonia-injection-grid","stRYue3vgASPZCX_uw4T7aiGWPWb-G1ACGgJf6kKlP0",{"id":603,"title":604,"aliases":605,"body":610,"category":196,"description":744,"extension":198,"meta":745,"navigation":200,"path":130,"relatedTerms":746,"seo":749,"sources":752,"stem":756,"term":183,"__hash__":757},"glossary\u002Fglossary\u002Fammonium-bisulphate.md","Ammonium bisulphate (ABS)",[606,607,608,609],"ABS","ammonium bisulfate","ammonium sulphate","NH4HSO4",{"type":52,"value":611,"toc":739},[612,630,634,637,673,677,713,715],[55,613,614,617,618,620,621,624,625,627,628,390],{},[58,615,616],{},"Ammonium bisulphate (NH₄HSO₄, ABS)"," — sometimes written ",[522,619,607],{}," in US technical literature — is a sticky, low-melting deposit formed when ",[62,622,623],{"href":201},"slipped ammonia"," reacts with SO₃ in cooling flue gas. ABS condenses between roughly 150 °C and 250 °C, coating the cold end of any ",[62,626,439],{"href":135}," downstream of an ",[62,629,65],{"href":64},[73,631,633],{"id":632},"why-abs-is-the-most-feared-cold-end-deposit","Why ABS is the most-feared cold-end deposit",[55,635,636],{},"ABS is uniquely problematic because it is:",[78,638,639,645,655,661,667],{},[81,640,641,644],{},[58,642,643],{},"Sticky"," — bonds tenaciously to air-heater baskets and economiser tubes",[81,646,647,650,651],{},[58,648,649],{},"Hygroscopic"," — picks up moisture and accelerates ",[62,652,654],{"href":653},"\u002Fglossary\u002Fcold-end-corrosion-dew-point-corrosion","cold-end corrosion",[81,656,657,660],{},[58,658,659],{},"Hard to remove"," — resists steam sootblowing once consolidated",[81,662,663,666],{},[58,664,665],{},"Self-reinforcing"," — coated surfaces trap more ash, accelerating fouling",[81,668,669,672],{},[58,670,671],{},"Concentrated in a narrow temperature band"," — predictably plugs the same air-heater rows",[73,674,676],{"id":675},"mitigation","Mitigation",[78,678,679,687,693,699,707],{},[81,680,681,686],{},[58,682,683,684],{},"Minimise ",[62,685,302],{"href":201}," at the SCR (the single biggest lever)",[81,688,689,692],{},[58,690,691],{},"Manage SO₃ formation"," — fuel sulphur control, catalyst formulation",[81,694,695,698],{},[58,696,697],{},"Avoid the dew-point window"," — keep cold-end gas temperature above the formation band",[81,700,701,706],{},[58,702,703,705],{},[62,704,152],{"href":151}," on the cold end"," — continuous cleaning prevents ABS from consolidating before periodic water-washing",[81,708,709,712],{},[58,710,711],{},"Water-washing campaigns"," — periodic offline washes restore air-heater performance",[73,714,161],{"id":160},[78,716,717,721,725,730,735],{},[81,718,719],{},[62,720,47],{"href":201},[81,722,723],{},[62,724,168],{"href":64},[81,726,727],{},[62,728,729],{"href":135},"Air heater",[81,731,732],{},[62,733,734],{"href":653},"Cold-end corrosion \u002F dew-point corrosion",[81,736,737],{},[62,738,347],{"href":151},{"title":189,"searchDepth":190,"depth":190,"links":740},[741,742,743],{"id":632,"depth":190,"text":633},{"id":675,"depth":190,"text":676},{"id":160,"depth":190,"text":161},"Ammonium bisulphate (NH₄HSO₄, ABS) — sometimes written ammonium bisulfate in US technical literature — is a sticky, low-melting deposit formed when slipped ammonia reacts with SO₃ in cooling flue gas. ABS condenses between roughly 150 °C and 250 °C, coating the cold end of any air heater downstream of an SCR.",{},[357,203,747,748,360],"air-heater","cold-end-corrosion-dew-point-corrosion",{"title":750,"description":751},"Ammonium bisulphate (ABS) — sticky deposit from SCR slip plus SO3","Ammonium bisulphate is a sticky low-melting deposit formed when slipped ammonia reacts with SO3 in cooling flue gas. The dominant cold-end fouling species on SCR-equipped boilers.",[753],{"title":754,"url":755},"POWER Magazine — SO3's impacts on plant O&M","https:\u002F\u002Fwww.powermag.com\u002Fso3s-impacts-on-plant-om-part-ii\u002F","glossary\u002Fammonium-bisulphate","eVfkw0arMYLXvUn7Eb2ZquRKgct13PXCySe8Iclt3GY",{"id":759,"title":98,"aliases":760,"body":764,"category":196,"description":906,"extension":198,"meta":907,"navigation":200,"path":97,"relatedTerms":908,"seo":910,"sources":913,"stem":918,"term":98,"__hash__":919},"glossary\u002Fglossary\u002Fcatalyst-masking.md",[761,762,763],"SCR catalyst masking","catalyst fouling","face plugging",{"type":52,"value":765,"toc":900},[766,775,779,840,843,847,861,865,875,877],[55,767,768,770,771,774],{},[58,769,98],{}," is the deposition of a thin blanket of fine ash on the face of an ",[62,772,773],{"href":64},"SCR catalyst"," that physically blocks ammonia and NOx molecules from reaching the underlying active sites. Gas continues to flow through the catalyst cells, but the active surface area is shadowed and reaction efficiency falls.",[73,776,778],{"id":777},"how-masking-differs-from-related-failure-modes","How masking differs from related failure modes",[780,781,782,798],"table",{},[783,784,785],"thead",{},[786,787,788,792,795],"tr",{},[789,790,791],"th",{},"Failure mode",[789,793,794],{},"Mechanism",[789,796,797],{},"Reversible?",[799,800,801,814,826],"tbody",{},[786,802,803,808,811],{},[804,805,806],"td",{},[58,807,295],{},[804,809,810],{},"Ash blanket on the active surface",[804,812,813],{},"Yes — cleaning restores activity",[786,815,816,820,823],{},[804,817,818],{},[62,819,278],{"href":101},[804,821,822],{},"Particles physically block catalyst channels",[804,824,825],{},"Sometimes (depends on hardness)",[786,827,828,834,837],{},[804,829,830],{},[62,831,833],{"href":832},"\u002Fglossary\u002Fcatalyst-poisoning","Poisoning",[804,835,836],{},"Chemical species bind to active sites",[804,838,839],{},"Usually no — catalyst replacement",[55,841,842],{},"Masking is the most operationally manageable of the three because it responds to cleaning.",[73,844,846],{"id":845},"what-deposits-cause-masking","What deposits cause masking",[78,848,849,852,855,858],{},[81,850,851],{},"Calcium-rich fly ash (Western US sub-bituminous, biomass)",[81,853,854],{},"Ammonium-salt films on tail-end SCRs",[81,856,857],{},"Sub-micron silica from biomass fuels",[81,859,860],{},"Iron-oxide carry-over from blast-furnace or sinter-plant SCR applications",[73,862,864],{"id":863},"sonic-horns-and-masking-control","Sonic horns and masking control",[55,866,867,869,870,874],{},[62,868,152],{"href":151}," positioned upstream of each catalyst layer continuously dislodge the developing ash blanket before it consolidates. Combined with periodic steam ",[62,871,873],{"href":872},"\u002Fglossary\u002Fsonic-sootblower","sootblowing",", this two-tier cleaning typically restores catalyst activity by 10–30% within months of installation.",[73,876,161],{"id":160},[78,878,879,883,887,892,896],{},[81,880,881],{},[62,882,168],{"href":64},[81,884,885],{},[62,886,336],{"href":101},[81,888,889],{},[62,890,891],{"href":832},"Catalyst poisoning",[81,893,894],{},[62,895,342],{"href":341},[81,897,898],{},[62,899,347],{"href":151},{"title":189,"searchDepth":190,"depth":190,"links":901},[902,903,904,905],{"id":777,"depth":190,"text":778},{"id":845,"depth":190,"text":846},{"id":863,"depth":190,"text":864},{"id":160,"depth":190,"text":161},"Catalyst masking is the deposition of a thin blanket of fine ash on the face of an SCR catalyst that physically blocks ammonia and NOx molecules from reaching the underlying active sites. Gas continues to flow through the catalyst cells, but the active surface area is shadowed and reaction efficiency falls.",{},[203,358,909,359,360],"catalyst-poisoning",{"title":911,"description":912},"Catalyst masking — fine-ash blanket that suppresses SCR activity","Catalyst masking is the deposition of a thin ash layer on the SCR catalyst face that blocks ammonia and NOx from reaching the active sites. Distinct from pluggage and poisoning.",[914,915],{"title":369,"url":370},{"title":916,"url":917},"Integrated Global Services — SCR Fouling Solved","https:\u002F\u002Fintegratedglobal.com\u002Fen\u002Fcase_studies\u002Fscr-performance\u002F","glossary\u002Fcatalyst-masking","WbNY355NxnwGZ3FW-bDAalSFTSrruJrjYN-62Fgc5Ig",1782613749282]