[{"data":1,"prerenderedAt":1469},["ShallowReactive",2],{"site-footer-common":3,"glossary:selective-catalytic-reduction":45,"glossary-related:selective-catalytic-reduction":232},{"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":52,"category":204,"description":205,"extension":206,"meta":207,"navigation":208,"path":209,"relatedTerms":210,"seo":219,"sources":222,"stem":229,"term":230,"__hash__":231},"glossary\u002Fglossary\u002Fselective-catalytic-reduction.md","Selective Catalytic Reduction (SCR)",[49,50,51],"SCR","SCR system","SCR reactor",{"type":53,"value":54,"toc":197},"minimark",[55,77,82,98,102,105,136,154,158],[56,57,58,61,62,67,68,72,73,76],"p",{},[59,60,47],"strong",{}," is the dominant flue-gas NOx-control technology on coal-fired and gas-fired utility boilers, ",[63,64,66],"a",{"href":65},"\u002Fglossary\u002Fheat-recovery-steam-generator","HRSGs"," in combined-cycle plants, ",[63,69,71],{"href":70},"\u002Fglossary\u002Fwaste-to-energy","waste-to-energy"," and ",[63,74,75],{"href":70},"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.",[78,79,81],"h2",{"id":80},"reactor-layout","Reactor layout",[56,83,84,85,89,90,93,94,97],{},"A typical SCR reactor is a vertical or horizontal duct containing 2–4 layers of catalyst modules. Upstream of the catalyst sits the ",[63,86,88],{"href":87},"\u002Fglossary\u002Fammonia-injection-grid","ammonia injection grid (AIG)"," that distributes the ammonia evenly into the flue gas. Most installations operate in the ",[59,91,92],{},"high-dust"," position (between economiser and air heater) where catalyst temperature is around 300–400 °C; ",[59,95,96],{},"tail-end"," SCRs sit downstream of particulate control at lower temperatures, with the trade-off of needing flue-gas reheating.",[78,99,101],{"id":100},"fouling-and-cleaning","Fouling and cleaning",[56,103,104],{},"SCR catalysts foul in two ways:",[106,107,108,127],"ul",{},[109,110,111,117,118,72,122,126],"li",{},[59,112,113],{},[63,114,116],{"href":115},"\u002Fglossary\u002Fcatalyst-pluggage","Pluggage"," — fly ash, ",[63,119,121],{"href":120},"\u002Fglossary\u002Fpopcorn-ash","popcorn ash",[63,123,125],{"href":124},"\u002Fglossary\u002Flarge-particle-ash","large-particle ash"," wedge into the catalyst cells, blocking the gas path",[109,128,129,135],{},[59,130,131],{},[63,132,134],{"href":133},"\u002Fglossary\u002Fcatalyst-masking","Masking"," — a thin layer of deposit covers the active sites; gas flow continues but catalytic activity falls",[56,137,138,139,143,144,148,149,153],{},"Both reduce NOx-reduction efficiency, raise ",[63,140,142],{"href":141},"\u002Fglossary\u002Fammonia-slip","ammonia slip",", and shorten catalyst life. Cleaning options include steam ",[63,145,147],{"href":146},"\u002Fglossary\u002Fsteam-sootblower","sootblowers",", ",[63,150,152],{"href":151},"\u002Fglossary\u002Fsonic-horn","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.",[78,155,157],{"id":156},"related-terms","Related terms",[106,159,160,166,171,176,181,186,192],{},[109,161,162],{},[63,163,165],{"href":164},"\u002Fglossary\u002Fselective-non-catalytic-reduction","Selective Non-Catalytic Reduction (SNCR)",[109,167,168],{},[63,169,170],{"href":87},"Ammonia injection grid",[109,172,173],{},[63,174,175],{"href":141},"Ammonia slip",[109,177,178],{},[63,179,180],{"href":133},"Catalyst masking",[109,182,183],{},[63,184,185],{"href":115},"Catalyst pluggage",[109,187,188],{},[63,189,191],{"href":190},"\u002Fglossary\u002Fhoneycomb-catalyst","Honeycomb catalyst",[109,193,194],{},[63,195,196],{"href":151},"Sonic horn",{"title":198,"searchDepth":199,"depth":199,"links":200},"",2,[201,202,203],{"id":80,"depth":199,"text":81},{"id":100,"depth":199,"text":101},{"id":156,"depth":199,"text":157},"scr-sncr","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.","md",{},true,"\u002Fglossary\u002Fselective-catalytic-reduction",[211,212,213,214,215,216,217,218],"selective-non-catalytic-reduction","denox","ammonia-injection-grid","ammonia-slip","catalyst-masking","catalyst-pluggage","honeycomb-catalyst","sonic-horn",{"title":220,"description":221},"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.",[223,226],{"title":224,"url":225},"Wikipedia — Selective catalytic reduction","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FSelective_catalytic_reduction",{"title":227,"url":228},"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",[233,364,546,649,782,938,1084,1240],{"id":234,"title":165,"aliases":235,"body":238,"category":204,"description":348,"extension":206,"meta":349,"navigation":208,"path":164,"relatedTerms":350,"seo":354,"sources":357,"stem":361,"term":362,"__hash__":363},"glossary\u002Fglossary\u002Fselective-non-catalytic-reduction.md",[236,237],"SNCR","SNCR system",{"type":53,"value":239,"toc":343},[240,251,255,278,282,285,308,314,316],[56,241,242,244,245,247,248,250],{},[59,243,165],{}," 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 ",[63,246,49],{"href":209}," but achieves lower reduction (typically 30–60%) and produces higher ",[63,249,142],{"href":141},".",[78,252,254],{"id":253},"where-sncr-is-used","Where SNCR is used",[106,256,257,260,268,275],{},[109,258,259],{},"Smaller industrial and utility boilers where SCR capital cost is unjustified",[109,261,262,72,265,267],{},[63,263,264],{"href":70},"Waste-to-energy",[63,266,75],{"href":70}," plants — often as the primary DeNOx with optional SCR polish",[109,269,270,274],{},[63,271,273],{"href":272},"\u002Fglossary\u002Fpreheater-tower","Cement preheater towers"," where the gas temperature window is naturally available",[109,276,277],{},"As a retrofit on units where space prevents SCR installation",[78,279,281],{"id":280},"fouling-implications","Fouling implications",[56,283,284],{},"SNCR does not have a catalyst to foul, but the reagent injection itself creates downstream deposit risks:",[106,286,287,302],{},[109,288,289,292,293,297,298],{},[59,290,291],{},"Ammonia salt deposits"," — un-reacted ammonia combines with SO₃ and ash to form ",[63,294,296],{"href":295},"\u002Fglossary\u002Fammonium-bisulphate","ammonium bisulphate"," on cold-end heat-transfer surfaces, particularly the ",[63,299,301],{"href":300},"\u002Fglossary\u002Fair-heater","air heater",[109,303,304,307],{},[59,305,306],{},"Urea \u002F ammonia deposits on lance tips"," — injection lances can plug with urea solids or carbon deposits",[56,309,310,313],{},[63,311,312],{"href":151},"Sonic horns"," on the cold-end air heater address ABS fouling that follows SNCR operation.",[78,315,157],{"id":156},[106,317,318,322,328,334,338],{},[109,319,320],{},[63,321,47],{"href":209},[109,323,324],{},[63,325,327],{"href":326},"\u002Fglossary\u002Fdenox","DeNOx",[109,329,330],{},[63,331,333],{"href":332},"\u002Fglossary\u002Furea-sncr-aqueous-ammonia-sncr","Urea SNCR \u002F aqueous-ammonia SNCR",[109,335,336],{},[63,337,175],{"href":141},[109,339,340],{},[63,341,342],{"href":295},"Ammonium bisulphate",{"title":198,"searchDepth":199,"depth":199,"links":344},[345,346,347],{"id":253,"depth":199,"text":254},{"id":280,"depth":199,"text":281},{"id":156,"depth":199,"text":157},"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.",{},[351,212,352,214,353],"selective-catalytic-reduction","urea-sncr-aqueous-ammonia-sncr","ammonium-bisulphate",{"title":355,"description":356},"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.",[358],{"title":359,"url":360},"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":365,"title":327,"aliases":366,"body":370,"category":204,"description":533,"extension":206,"meta":534,"navigation":208,"path":326,"relatedTerms":535,"seo":537,"sources":540,"stem":544,"term":327,"__hash__":545},"glossary\u002Fglossary\u002Fdenox.md",[367,368,369],"deNOx","NOx reduction","NOx control",{"type":53,"value":371,"toc":528},[372,382,386,410,414,503,506,508],[56,373,374,376,377,72,379,381],{},[59,375,327],{}," is the collective term for post-combustion NOx-reduction technologies on industrial flue gas. The two dominant options are ",[63,378,47],{"href":209},[63,380,165],{"href":164},". Both rely on a reagent — ammonia or urea — that reacts with NOx to produce nitrogen and water.",[78,383,385],{"id":384},"why-denox-is-mandatory","Why DeNOx is mandatory",[56,387,388,389,148,393,148,397,148,401,405,406,409],{},"NOx is a regulated pollutant under the ",[63,390,392],{"href":391},"\u002Fglossary\u002Findustrial-emissions-directive","Industrial Emissions Directive (IED)",[63,394,396],{"href":395},"\u002Fglossary\u002Fmats-us-mercury-and-air-toxics","MATS",[63,398,400],{"href":399},"\u002Fglossary\u002Fepa-nsps","EPA NSPS",[63,402,404],{"href":403},"\u002Fglossary\u002Fta-luft-2021","TA Luft 2021"," and most national emission codes. Limits for coal-fired power stations and large ",[63,407,408],{"href":70},"WtE"," plants are usually 100–200 mg\u002FNm³ on a 30-day average, with stricter site-specific BAT-AEL values from BREF revisions.",[78,411,413],{"id":412},"choice-of-technology","Choice of technology",[415,416,417,433],"table",{},[418,419,420],"thead",{},[421,422,423,427,430],"tr",{},[424,425,426],"th",{},"Factor",[424,428,429],{},"Favours SCR",[424,431,432],{},"Favours SNCR",[434,435,436,448,459,470,481,492],"tbody",{},[421,437,438,442,445],{},[439,440,441],"td",{},"Reduction efficiency required",[439,443,444],{},"> 70%",[439,446,447],{},"30–60%",[421,449,450,453,456],{},[439,451,452],{},"Plant size",[439,454,455],{},"Large",[439,457,458],{},"Small \u002F medium",[421,460,461,464,467],{},[439,462,463],{},"Capital available",[439,465,466],{},"Higher",[439,468,469],{},"Lower",[421,471,472,475,478],{},[439,473,474],{},"Space available",[439,476,477],{},"More",[439,479,480],{},"Less",[421,482,483,486,489],{},[439,484,485],{},"Catalyst cost tolerance",[439,487,488],{},"Yes",[439,490,491],{},"Avoid",[421,493,494,497,500],{},[439,495,496],{},"Fuel chemistry",[439,498,499],{},"Predictable",[439,501,502],{},"Variable",[56,504,505],{},"Many plants run combined systems: SNCR provides bulk reduction, SCR polishes to meet permit limits.",[78,507,157],{"id":156},[106,509,510,514,518,524],{},[109,511,512],{},[63,513,47],{"href":209},[109,515,516],{},[63,517,165],{"href":164},[109,519,520],{},[63,521,523],{"href":522},"\u002Fglossary\u002Fnox-reduction-efficiency","NOx reduction efficiency",[109,525,526],{},[63,527,170],{"href":87},{"title":198,"searchDepth":199,"depth":199,"links":529},[530,531,532],{"id":384,"depth":199,"text":385},{"id":412,"depth":199,"text":413},{"id":156,"depth":199,"text":157},"DeNOx is the collective term for post-combustion NOx-reduction technologies on industrial flue gas. The two dominant options are Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR). Both rely on a reagent — ammonia or urea — that reacts with NOx to produce nitrogen and water.",{},[351,211,536,213],"nox-reduction-efficiency",{"title":538,"description":539},"DeNOx — the family of post-combustion NOx-reduction technologies","DeNOx is the collective term for post-combustion NOx-reduction technologies. SCR and SNCR are the dominant options; both rely on reaction of NOx with ammonia or urea.",[541],{"title":542,"url":543},"Wikipedia — NOx","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FNOx","glossary\u002Fdenox","VgFeaJejynSvoxZt9xXRFXJSI6fE03o5ewbcMFuDDJA",{"id":547,"title":548,"aliases":549,"body":552,"category":204,"description":637,"extension":206,"meta":638,"navigation":208,"path":87,"relatedTerms":639,"seo":640,"sources":643,"stem":647,"term":170,"__hash__":648},"glossary\u002Fglossary\u002Fammonia-injection-grid.md","Ammonia injection grid (AIG)",[550,551],"AIG","ammonia injection grids",{"type":53,"value":553,"toc":632},[554,573,577,603,607,612,614],[56,555,556,557,559,560,562,563,72,565,567,568,572],{},"An ",[59,558,88],{}," is an array of injector nozzles that distributes ammonia (or vaporised aqueous-ammonia \u002F urea) evenly across the flue-gas duct upstream of an ",[63,561,49],{"href":209}," catalyst bed. The quality of the NH₃\u002FNOx mixing at the catalyst inlet is the single biggest determinant of ",[63,564,523],{"href":522},[63,566,142],{"href":141},": under-mixing leaves NOx-rich zones unreacted ",[569,570,571],"em",{},"and"," causes locally over-stoichiometric ammonia in other zones.",[78,574,576],{"id":575},"common-failure-modes","Common failure modes",[106,578,579,585,591,597],{},[109,580,581,584],{},[59,582,583],{},"Nozzle plugging"," — ash, ammonium-salt deposits or carbon block individual nozzles",[109,586,587,590],{},[59,588,589],{},"Lance fouling"," — deposits accumulate on lance bodies and disturb spray patterns",[109,592,593,596],{},[59,594,595],{},"Erosion"," — abrasive ash wears injector tips, distorting the spray pattern",[109,598,599,602],{},[59,600,601],{},"Maldistribution"," — uneven gas flow at the AIG inlet means even a perfect AIG delivers uneven mixing",[78,604,606],{"id":605},"sonic-horns-on-the-aig-deck","Sonic horns on the AIG deck",[56,608,609,611],{},[63,610,312],{"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.",[78,613,157],{"id":156},[106,615,616,620,624,628],{},[109,617,618],{},[63,619,47],{"href":209},[109,621,622],{},[63,623,175],{"href":141},[109,625,626],{},[63,627,185],{"href":115},[109,629,630],{},[63,631,196],{"href":151},{"title":198,"searchDepth":199,"depth":199,"links":633},[634,635,636],{"id":575,"depth":199,"text":576},{"id":605,"depth":199,"text":606},{"id":156,"depth":199,"text":157},"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.",{},[351,214,216,218],{"title":641,"description":642},"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.",[644],{"title":645,"url":646},"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":650,"title":175,"aliases":651,"body":654,"category":204,"description":770,"extension":206,"meta":771,"navigation":208,"path":141,"relatedTerms":772,"seo":773,"sources":776,"stem":780,"term":175,"__hash__":781},"glossary\u002Fglossary\u002Fammonia-slip.md",[652,653],"NH3 slip","ammonia breakthrough",{"type":53,"value":655,"toc":764},[656,667,671,708,712,727,731,740,742],[56,657,658,660,661,663,664,666],{},[59,659,175],{}," is the concentration of unreacted ammonia (NH₃) in the flue gas leaving an ",[63,662,49],{"href":209}," or ",[63,665,236],{"href":164}," 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.",[78,668,670],{"id":669},"causes-of-high-ammonia-slip","Causes of high ammonia slip",[106,672,673,681,691,697,702],{},[109,674,675,678,679],{},[59,676,677],{},"Poor NH₃\u002FNOx mixing"," at the ",[63,680,550],{"href":87},[109,682,683,663,687,690],{},[59,684,685],{},[63,686,180],{"href":133},[63,688,689],{"href":115},"pluggage"," reducing active surface area",[109,692,693,696],{},[59,694,695],{},"Catalyst age and de-activation"," towards end of life",[109,698,699],{},[59,700,701],{},"Operating temperature outside the catalyst window",[109,703,704,707],{},[59,705,706],{},"Over-injection of ammonia"," to compensate for falling NOx-reduction efficiency",[78,709,711],{"id":710},"downstream-consequences","Downstream consequences",[56,713,714,715,718,719,148,722,726],{},"Slipped ammonia combines with SO₃ in cooling flue gas to form ",[63,716,717],{"href":295},"ammonium bisulphate (ABS)",", a sticky low-melting deposit that fouls ",[63,720,721],{"href":300},"air heaters",[63,723,725],{"href":724},"\u002Fglossary\u002Feconomiser","economisers"," and downstream catalysts and filters. Excessive slip can therefore destroy the cold end of a boiler within months.",[78,728,730],{"id":729},"sonic-horns-and-slip-reduction","Sonic horns and slip reduction",[56,732,733,735,736,739],{},[63,734,312],{"href":151}," reduce slip indirectly by keeping the catalyst face clear of ",[63,737,738],{"href":133},"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.",[78,741,157],{"id":156},[106,743,744,748,752,756,760],{},[109,745,746],{},[63,747,47],{"href":209},[109,749,750],{},[63,751,165],{"href":164},[109,753,754],{},[63,755,170],{"href":87},[109,757,758],{},[63,759,342],{"href":295},[109,761,762],{},[63,763,180],{"href":133},{"title":198,"searchDepth":199,"depth":199,"links":765},[766,767,768,769],{"id":669,"depth":199,"text":670},{"id":710,"depth":199,"text":711},{"id":729,"depth":199,"text":730},{"id":156,"depth":199,"text":157},"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.",{},[351,211,213,353,215],{"title":774,"description":775},"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.",[777],{"title":778,"url":779},"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",{"id":783,"title":180,"aliases":784,"body":788,"category":204,"description":924,"extension":206,"meta":925,"navigation":208,"path":133,"relatedTerms":926,"seo":928,"sources":931,"stem":936,"term":180,"__hash__":937},"glossary\u002Fglossary\u002Fcatalyst-masking.md",[785,786,787],"SCR catalyst masking","catalyst fouling","face plugging",{"type":53,"value":789,"toc":918},[790,799,803,858,861,865,879,883,893,895],[56,791,792,794,795,798],{},[59,793,180],{}," is the deposition of a thin blanket of fine ash on the face of an ",[63,796,797],{"href":209},"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.",[78,800,802],{"id":801},"how-masking-differs-from-related-failure-modes","How masking differs from related failure modes",[415,804,805,818],{},[418,806,807],{},[421,808,809,812,815],{},[424,810,811],{},"Failure mode",[424,813,814],{},"Mechanism",[424,816,817],{},"Reversible?",[434,819,820,832,844],{},[421,821,822,826,829],{},[439,823,824],{},[59,825,134],{},[439,827,828],{},"Ash blanket on the active surface",[439,830,831],{},"Yes — cleaning restores activity",[421,833,834,838,841],{},[439,835,836],{},[63,837,116],{"href":115},[439,839,840],{},"Particles physically block catalyst channels",[439,842,843],{},"Sometimes (depends on hardness)",[421,845,846,852,855],{},[439,847,848],{},[63,849,851],{"href":850},"\u002Fglossary\u002Fcatalyst-poisoning","Poisoning",[439,853,854],{},"Chemical species bind to active sites",[439,856,857],{},"Usually no — catalyst replacement",[56,859,860],{},"Masking is the most operationally manageable of the three because it responds to cleaning.",[78,862,864],{"id":863},"what-deposits-cause-masking","What deposits cause masking",[106,866,867,870,873,876],{},[109,868,869],{},"Calcium-rich fly ash (Western US sub-bituminous, biomass)",[109,871,872],{},"Ammonium-salt films on tail-end SCRs",[109,874,875],{},"Sub-micron silica from biomass fuels",[109,877,878],{},"Iron-oxide carry-over from blast-furnace or sinter-plant SCR applications",[78,880,882],{"id":881},"sonic-horns-and-masking-control","Sonic horns and masking control",[56,884,885,887,888,892],{},[63,886,312],{"href":151}," positioned upstream of each catalyst layer continuously dislodge the developing ash blanket before it consolidates. Combined with periodic steam ",[63,889,891],{"href":890},"\u002Fglossary\u002Fsonic-sootblower","sootblowing",", this two-tier cleaning typically restores catalyst activity by 10–30% within months of installation.",[78,894,157],{"id":156},[106,896,897,901,905,910,914],{},[109,898,899],{},[63,900,47],{"href":209},[109,902,903],{},[63,904,185],{"href":115},[109,906,907],{},[63,908,909],{"href":850},"Catalyst poisoning",[109,911,912],{},[63,913,191],{"href":190},[109,915,916],{},[63,917,196],{"href":151},{"title":198,"searchDepth":199,"depth":199,"links":919},[920,921,922,923],{"id":801,"depth":199,"text":802},{"id":863,"depth":199,"text":864},{"id":881,"depth":199,"text":882},{"id":156,"depth":199,"text":157},"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.",{},[351,216,927,217,218],"catalyst-poisoning",{"title":929,"description":930},"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.",[932,933],{"title":227,"url":228},{"title":934,"url":935},"Integrated Global Services — SCR Fouling Solved","https:\u002F\u002Fintegratedglobal.com\u002Fen\u002Fcase_studies\u002Fscr-performance\u002F","glossary\u002Fcatalyst-masking","WbNY355NxnwGZ3FW-bDAalSFTSrruJrjYN-62Fgc5Ig",{"id":939,"title":185,"aliases":940,"body":944,"category":204,"description":1070,"extension":206,"meta":1071,"navigation":208,"path":115,"relatedTerms":1072,"seo":1075,"sources":1078,"stem":1082,"term":185,"__hash__":1083},"glossary\u002Fglossary\u002Fcatalyst-pluggage.md",[941,942,943],"catalyst plugging","catalyst channelling","SCR catalyst pluggage",{"type":53,"value":945,"toc":1065},[946,958,962,995,999,1036,1038],[56,947,948,950,951,953,954,957],{},[59,949,185],{}," is the physical blockage of ",[63,952,797],{"href":209}," channels by particulate material. Unlike ",[63,955,956],{"href":133},"catalyst masking"," (a thin surface blanket), pluggage fills the catalyst channels themselves, stopping gas flow through affected cells. The result is ΔP rise across the SCR, gas-flow maldistribution into the remaining open cells, and channelling effects that reduce overall NOx reduction.",[78,959,961],{"id":960},"sources-of-pluggage-material","Sources of pluggage material",[106,963,964,972,980,989],{},[109,965,966,971],{},[59,967,968],{},[63,969,970],{"href":124},"Large-particle ash (LPA)"," — slag fragments and agglomerated ash carried over from the boiler",[109,973,974,979],{},[59,975,976],{},[63,977,978],{"href":120},"Popcorn ash"," — porous low-density ash particles that wedge into honeycomb cells",[109,981,982,985,986,988],{},[59,983,984],{},"Ammonium-salt deposits"," — ",[63,987,296],{"href":295}," on tail-end SCRs at lower temperatures",[109,990,991,994],{},[59,992,993],{},"Refractory debris"," — fragments from upstream furnace or duct repairs",[78,996,998],{"id":997},"prevention","Prevention",[106,1000,1001,1007,1013,1019,1028],{},[109,1002,1003,1006],{},[59,1004,1005],{},"LPA screens"," — coarse mesh screens upstream of the catalyst trap large particles",[109,1008,1009,1012],{},[59,1010,1011],{},"Guard layers"," — sacrificial top catalyst layer with larger pitch absorbs the initial particulate",[109,1014,1015,1018],{},[59,1016,1017],{},"Larger pitch on the top layer"," — wider cell openings on the first catalyst layer pass LPA through to a removable screen below",[109,1020,1021,1027],{},[59,1022,1023,1024,1026],{},"Periodic ",[63,1025,218],{"href":151}," cleaning"," — dislodges accumulating ash before it cements",[109,1029,1030,1035],{},[59,1031,1032,1033],{},"Steam ",[63,1034,891],{"href":890}," — for harder deposits",[78,1037,157],{"id":156},[106,1039,1040,1044,1049,1053,1057,1061],{},[109,1041,1042],{},[63,1043,47],{"href":209},[109,1045,1046],{},[63,1047,1048],{"href":124},"Large-particle ash",[109,1050,1051],{},[63,1052,978],{"href":120},[109,1054,1055],{},[63,1056,180],{"href":133},[109,1058,1059],{},[63,1060,191],{"href":190},[109,1062,1063],{},[63,1064,196],{"href":151},{"title":198,"searchDepth":199,"depth":199,"links":1066},[1067,1068,1069],{"id":960,"depth":199,"text":961},{"id":997,"depth":199,"text":998},{"id":156,"depth":199,"text":157},"Catalyst pluggage is the physical blockage of SCR catalyst channels by particulate material. Unlike catalyst masking (a thin surface blanket), pluggage fills the catalyst channels themselves, stopping gas flow through affected cells. The result is ΔP rise across the SCR, gas-flow maldistribution into the remaining open cells, and channelling effects that reduce overall NOx reduction.",{},[351,1073,1074,215,217,218],"large-particle-ash","popcorn-ash",{"title":1076,"description":1077},"Catalyst pluggage — channel blockage that reduces SCR gas flow","Catalyst pluggage is the physical blockage of SCR catalyst channels by large-particle ash, popcorn ash or ammonium-salt deposits. It causes ΔP rise and gas-flow maldistribution.",[1079],{"title":1080,"url":1081},"Airflow Sciences — SCR Catalyst Pluggage Reduction at Roxboro Unit 3","https:\u002F\u002Fwww.airflowsciences.com\u002Fsites\u002Fdefault\u002Ffiles\u002Fdocs\u002F2010_MEGA_Symposium_Roxboro_U3.pdf","glossary\u002Fcatalyst-pluggage","m2viiLe19KKcTBiDWhyUc38xPIzoOiMpL15r0i_ayHg",{"id":1085,"title":191,"aliases":1086,"body":1089,"category":204,"description":1227,"extension":206,"meta":1228,"navigation":208,"path":190,"relatedTerms":1229,"seo":1233,"sources":1236,"stem":1238,"term":191,"__hash__":1239},"glossary\u002Fglossary\u002Fhoneycomb-catalyst.md",[1087,1088],"honeycomb SCR catalyst","extruded catalyst",{"type":53,"value":1090,"toc":1221},[1091,1100,1104,1153,1157,1160,1174,1178,1192,1194],[56,1092,1093,1094,1097,1098,250],{},"A ",[59,1095,1096],{},"honeycomb catalyst"," is a monolithic extruded ceramic block containing a dense grid of parallel square channels through which flue gas flows. The active catalytic material — typically vanadium pentoxide and tungsten trioxide on a titanium-dioxide carrier — is incorporated into the bulk ceramic. Honeycomb is the most common form of ",[63,1099,797],{"href":209},[78,1101,1103],{"id":1102},"strengths-and-weaknesses","Strengths and weaknesses",[415,1105,1106,1116],{},[418,1107,1108],{},[421,1109,1110,1113],{},[424,1111,1112],{},"Strength",[424,1114,1115],{},"Weakness",[434,1117,1118,1129,1137,1145],{},[421,1119,1120,1123],{},[439,1121,1122],{},"Very high geometric surface area per unit volume",[439,1124,1125,1126,1128],{},"Channels susceptible to ",[63,1127,689],{"href":115}," by ash",[421,1130,1131,1134],{},[439,1132,1133],{},"Low pressure drop in clean condition",[439,1135,1136],{},"Brittle — handle with care during install \u002F replacement",[421,1138,1139,1142],{},[439,1140,1141],{},"Mature, large supplier base",[439,1143,1144],{},"Channels are harder to clean than open structures",[421,1146,1147,1150],{},[439,1148,1149],{},"Wide range of pitch options (3.5–7.4 mm typical)",[439,1151,1152],{},"Smaller pitch = more risk of pluggage",[78,1154,1156],{"id":1155},"pitch-selection","Pitch selection",[56,1158,1159],{},"Pitch (centre-to-centre channel spacing) trades surface area against pluggage risk:",[106,1161,1162,1168],{},[109,1163,1164,1167],{},[59,1165,1166],{},"Smaller pitch (3.5–4.5 mm)"," — high surface area, used on clean gas streams (NGCC HRSGs, gas-fired duty)",[109,1169,1170,1173],{},[59,1171,1172],{},"Larger pitch (6–7.4 mm)"," — used on dusty coal, biomass and WtE duty where pluggage risk dominates",[78,1175,1177],{"id":1176},"layer-assembly","Layer assembly",[56,1179,1180,1181,1185,1186,1188,1189,1191],{},"Individual honeycomb blocks are loaded into a ",[63,1182,1184],{"href":1183},"\u002Fglossary\u002Fcatalyst-layer-module","catalyst layer \u002F module"," and stacked 2–4 layers deep inside the SCR reactor. ",[63,1187,312],{"href":151}," and steam ",[63,1190,147],{"href":890}," are positioned between layers to keep channels clear.",[78,1193,157],{"id":156},[106,1195,1196,1200,1206,1212,1217],{},[109,1197,1198],{},[63,1199,47],{"href":209},[109,1201,1202],{},[63,1203,1205],{"href":1204},"\u002Fglossary\u002Fplate-catalyst","Plate catalyst",[109,1207,1208],{},[63,1209,1211],{"href":1210},"\u002Fglossary\u002Fcorrugated-catalyst","Corrugated catalyst",[109,1213,1214],{},[63,1215,1216],{"href":1183},"Catalyst layer \u002F module",[109,1218,1219],{},[63,1220,185],{"href":115},{"title":198,"searchDepth":199,"depth":199,"links":1222},[1223,1224,1225,1226],{"id":1102,"depth":199,"text":1103},{"id":1155,"depth":199,"text":1156},{"id":1176,"depth":199,"text":1177},{"id":156,"depth":199,"text":157},"A honeycomb catalyst is a monolithic extruded ceramic block containing a dense grid of parallel square channels through which flue gas flows. The active catalytic material — typically vanadium pentoxide and tungsten trioxide on a titanium-dioxide carrier — is incorporated into the bulk ceramic. Honeycomb is the most common form of SCR catalyst.",{},[351,1230,1231,1232,216],"plate-catalyst","corrugated-catalyst","catalyst-layer-module",{"title":1234,"description":1235},"Honeycomb catalyst — extruded SCR catalyst form factor","A honeycomb catalyst is an extruded ceramic block with parallel square channels, the most common SCR catalyst form. High surface area but susceptible to channel pluggage.",[1237],{"title":224,"url":225},"glossary\u002Fhoneycomb-catalyst","_YfmRO7jrh-yc8ZLI7n3Nr5QKYo9e0uBw4yWiXy1uho",{"id":1241,"title":196,"aliases":1242,"body":1245,"category":1444,"description":1445,"extension":206,"meta":1446,"navigation":208,"path":151,"relatedTerms":1447,"seo":1454,"sources":1457,"stem":1467,"term":196,"__hash__":1468},"glossary\u002Fglossary\u002Fsonic-horn.md",[152,1243,1244],"sonic cleaning horn","industrial sonic horn",{"type":53,"value":1246,"toc":1437},[1247,1277,1281,1289,1293,1355,1359,1395,1399,1406,1408],[56,1248,1093,1249,1252,1253,1257,1258,148,1262,148,1266,148,1269,72,1273,250],{},[59,1250,1251],{},"sonic horn"," is a pneumatically-driven sound emitter that produces high-intensity, low-frequency sound waves — typically between 60 and 400 Hz at sound pressure levels of 140 to 180 dB — used to dislodge particulate fouling from inside industrial process equipment. Sonic horns are the most common form of ",[63,1254,1256],{"href":1255},"\u002Fglossary\u002Facoustic-cleaner","acoustic cleaner"," and the default specification for cleaning ",[63,1259,1261],{"href":1260},"\u002Fglossary\u002Felectrostatic-precipitator","ESPs",[63,1263,1265],{"href":1264},"\u002Fglossary\u002Ffabric-filter","baghouses",[63,1267,1268],{"href":209},"SCR catalysts",[63,1270,1272],{"href":1271},"\u002Fglossary\u002Fsuperheater","boiler heat-transfer surfaces",[63,1274,1276],{"href":1275},"\u002Fglossary\u002Fhopper","hoppers and silos",[78,1278,1280],{"id":1279},"how-a-sonic-horn-works","How a sonic horn works",[56,1282,1283,1284,1288],{},"Compressed plant air admitted through a ",[63,1285,1287],{"href":1286},"\u002Fglossary\u002Fsolenoid-valve","solenoid valve"," drives a metal diaphragm — typically titanium or 316 stainless — into resonant oscillation at the horn's fundamental frequency. The oscillating pressure field is amplified by an exponential bell horn and projected into the vessel as a near-spherical sound wave. Particulate already deposited on internal surfaces receives an oscillating acceleration that overcomes adhesion; loosened material is then carried out with the gas flow before it can sinter, bridge or bond. Because the cleaning is acoustic and non-contact, the horn can fire while the plant is online without tube erosion, refractory damage or thermal shock.",[78,1290,1292],{"id":1291},"key-parameters","Key parameters",[415,1294,1295,1305],{},[418,1296,1297],{},[421,1298,1299,1302],{},[424,1300,1301],{},"Parameter",[424,1303,1304],{},"Typical range",[434,1306,1307,1315,1323,1331,1339,1347],{},[421,1308,1309,1312],{},[439,1310,1311],{},"Fundamental frequency",[439,1313,1314],{},"60–400 Hz",[421,1316,1317,1320],{},[439,1318,1319],{},"Sound pressure level",[439,1321,1322],{},"140–180 dB",[421,1324,1325,1328],{},[439,1326,1327],{},"Compressed-air consumption",[439,1329,1330],{},"8–14 Nm³\u002Fmin at 4–7 bar",[421,1332,1333,1336],{},[439,1334,1335],{},"Operating temperature (with appropriate materials)",[439,1337,1338],{},"−40 °C to +500 °C",[421,1340,1341,1344],{},[439,1342,1343],{},"Firing cycle",[439,1345,1346],{},"5–15 s burst, repeated every 3–15 minutes",[421,1348,1349,1352],{},[439,1350,1351],{},"Mass",[439,1353,1354],{},"15–60 kg depending on horn size",[78,1356,1358],{"id":1357},"frequency-selection","Frequency selection",[56,1360,1361,1362,148,1366,1370,1371,148,1375,1379,1380,148,1383,1386,1387,72,1391,250],{},"Lower frequencies (60–125 Hz) project longer wavelengths and penetrate further into large open vessels — ",[63,1363,1365],{"href":1364},"\u002Fglossary\u002Fpreheater-cyclone","preheater cyclones",[63,1367,1369],{"href":1368},"\u002Fglossary\u002Frecovery-boiler","recovery-boiler superheaters",", large ",[63,1372,1374],{"href":1373},"\u002Fglossary\u002Fesp-field-bus-section","ESP fields",[63,1376,1378],{"href":1377},"\u002Fglossary\u002Fsilo","silos",". Higher frequencies (230–400 Hz) carry more energy per unit volume and suit finer dust loads in ",[63,1381,1382],{"href":1264},"fabric-filter compartments",[63,1384,1385],{"href":190},"catalyst layers"," and smaller hopper geometries. See ",[63,1388,1390],{"href":1389},"\u002Fglossary\u002Flow-frequency-acoustic-cleaner","low-frequency acoustic cleaner",[63,1392,1394],{"href":1393},"\u002Fglossary\u002Fhigh-frequency-acoustic-cleaner","high-frequency acoustic cleaner",[78,1396,1398],{"id":1397},"sonic-horn-vs-steam-sootblower","Sonic horn vs steam sootblower",[56,1400,1401,1402,1405],{},"Sonic horns are increasingly specified alongside or in place of ",[63,1403,1404],{"href":146},"steam sootblowers"," because they consume no boiler-grade steam, cause no tube erosion, require almost no moving parts and can fire every few minutes without operator intervention. They are less effective on hard, fused slag than retractable steam lances, so on furnace waterwalls and high-temperature superheaters they typically complement rather than replace mechanical cleaning.",[78,1407,157],{"id":156},[106,1409,1410,1415,1420,1426,1432],{},[109,1411,1412],{},[63,1413,1414],{"href":1255},"Acoustic cleaner",[109,1416,1417],{},[63,1418,1419],{"href":890},"Sonic sootblower",[109,1421,1422],{},[63,1423,1425],{"href":1424},"\u002Fglossary\u002Fbell-horn","Bell horn",[109,1427,1428],{},[63,1429,1431],{"href":1430},"\u002Fglossary\u002Fdiaphragm-horn","Diaphragm horn",[109,1433,1434],{},[63,1435,1436],{"href":1389},"Low-frequency acoustic cleaner",{"title":198,"searchDepth":199,"depth":199,"links":1438},[1439,1440,1441,1442,1443],{"id":1279,"depth":199,"text":1280},{"id":1291,"depth":199,"text":1292},{"id":1357,"depth":199,"text":1358},{"id":1397,"depth":199,"text":1398},{"id":156,"depth":199,"text":157},"core-technology","A sonic horn is a pneumatically-driven sound emitter that produces high-intensity, low-frequency sound waves — typically between 60 and 400 Hz at sound pressure levels of 140 to 180 dB — used to dislodge particulate fouling from inside industrial process equipment. Sonic horns are the most common form of acoustic cleaner and the default specification for cleaning ESPs, baghouses, SCR catalysts, boiler heat-transfer surfaces and hoppers and silos.",{},[1448,1449,1450,1451,1452,1453],"acoustic-cleaner","acoustic-cleaning-system","sonic-sootblower","bell-horn","diaphragm-horn","low-frequency-acoustic-cleaner",{"title":1455,"description":1456},"Sonic horn — definition, frequency, SPL and industrial applications","A sonic horn is a pneumatically-driven low-frequency sound emitter (typically 60–400 Hz at 140–180 dB SPL) used to dislodge particulate fouling from boilers, ESPs, baghouses and process vessels.",[1458,1461,1464],{"title":1459,"url":1460},"Power Engineering — Sonic Horns: A User's Introduction","https:\u002F\u002Fwww.power-eng.com\u002Fcoal\u002Fsonic-horns-a-userrsquos-introduction\u002F",{"title":1462,"url":1463},"Power Engineering — Tuning in to Acoustic Cleaning","https:\u002F\u002Fwww.power-eng.com\u002Fcoal\u002Ftuning-in-to-acoustic-cleaning\u002F",{"title":1465,"url":1466},"Wikipedia — Sonic soot blowers","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FSonic_soot_blowers","glossary\u002Fsonic-horn","YzrhN0kKzqSaQo0wfn0rueNZ-V43mcg5zahqeWi3lnU",1782613751808]