[{"data":1,"prerenderedAt":829},["ShallowReactive",2],{"site-footer-common":3,"glossary:denox":45,"glossary-related:denox":255},{"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":235,"description":236,"extension":237,"meta":238,"navigation":239,"path":240,"relatedTerms":241,"seo":246,"sources":249,"stem":253,"term":47,"__hash__":254},"glossary\u002Fglossary\u002Fdenox.md","DeNOx",[49,50,51],"deNOx","NOx reduction","NOx control",{"type":53,"value":54,"toc":228},"minimark",[55,73,78,104,108,197,200,204],[56,57,58,61,62,67,68,72],"p",{},[59,60,47],"strong",{}," is the collective term for post-combustion NOx-reduction technologies on industrial flue gas. The two dominant options are ",[63,64,66],"a",{"href":65},"\u002Fglossary\u002Fselective-catalytic-reduction","Selective Catalytic Reduction (SCR)"," and ",[63,69,71],{"href":70},"\u002Fglossary\u002Fselective-non-catalytic-reduction","Selective Non-Catalytic Reduction (SNCR)",". Both rely on a reagent — ammonia or urea — that reacts with NOx to produce nitrogen and water.",[74,75,77],"h2",{"id":76},"why-denox-is-mandatory","Why DeNOx is mandatory",[56,79,80,81,85,86,85,90,85,94,98,99,103],{},"NOx is a regulated pollutant under the ",[63,82,84],{"href":83},"\u002Fglossary\u002Findustrial-emissions-directive","Industrial Emissions Directive (IED)",", ",[63,87,89],{"href":88},"\u002Fglossary\u002Fmats-us-mercury-and-air-toxics","MATS",[63,91,93],{"href":92},"\u002Fglossary\u002Fepa-nsps","EPA NSPS",[63,95,97],{"href":96},"\u002Fglossary\u002Fta-luft-2021","TA Luft 2021"," and most national emission codes. Limits for coal-fired power stations and large ",[63,100,102],{"href":101},"\u002Fglossary\u002Fwaste-to-energy","WtE"," plants are usually 100–200 mg\u002FNm³ on a 30-day average, with stricter site-specific BAT-AEL values from BREF revisions.",[74,105,107],{"id":106},"choice-of-technology","Choice of technology",[109,110,111,127],"table",{},[112,113,114],"thead",{},[115,116,117,121,124],"tr",{},[118,119,120],"th",{},"Factor",[118,122,123],{},"Favours SCR",[118,125,126],{},"Favours SNCR",[128,129,130,142,153,164,175,186],"tbody",{},[115,131,132,136,139],{},[133,134,135],"td",{},"Reduction efficiency required",[133,137,138],{},"> 70%",[133,140,141],{},"30–60%",[115,143,144,147,150],{},[133,145,146],{},"Plant size",[133,148,149],{},"Large",[133,151,152],{},"Small \u002F medium",[115,154,155,158,161],{},[133,156,157],{},"Capital available",[133,159,160],{},"Higher",[133,162,163],{},"Lower",[115,165,166,169,172],{},[133,167,168],{},"Space available",[133,170,171],{},"More",[133,173,174],{},"Less",[115,176,177,180,183],{},[133,178,179],{},"Catalyst cost tolerance",[133,181,182],{},"Yes",[133,184,185],{},"Avoid",[115,187,188,191,194],{},[133,189,190],{},"Fuel chemistry",[133,192,193],{},"Predictable",[133,195,196],{},"Variable",[56,198,199],{},"Many plants run combined systems: SNCR provides bulk reduction, SCR polishes to meet permit limits.",[74,201,203],{"id":202},"related-terms","Related terms",[205,206,207,212,216,222],"ul",{},[208,209,210],"li",{},[63,211,66],{"href":65},[208,213,214],{},[63,215,71],{"href":70},[208,217,218],{},[63,219,221],{"href":220},"\u002Fglossary\u002Fnox-reduction-efficiency","NOx reduction efficiency",[208,223,224],{},[63,225,227],{"href":226},"\u002Fglossary\u002Fammonia-injection-grid","Ammonia injection grid",{"title":229,"searchDepth":230,"depth":230,"links":231},"",2,[232,233,234],{"id":76,"depth":230,"text":77},{"id":106,"depth":230,"text":107},{"id":202,"depth":230,"text":203},"scr-sncr","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.","md",{},true,"\u002Fglossary\u002Fdenox",[242,243,244,245],"selective-catalytic-reduction","selective-non-catalytic-reduction","nox-reduction-efficiency","ammonia-injection-grid",{"title":247,"description":248},"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.",[250],{"title":251,"url":252},"Wikipedia — NOx","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FNOx","glossary\u002Fdenox","VgFeaJejynSvoxZt9xXRFXJSI6fE03o5ewbcMFuDDJA",[256,418,546,727],{"id":257,"title":66,"aliases":258,"body":262,"category":235,"description":396,"extension":237,"meta":397,"navigation":239,"path":65,"relatedTerms":398,"seo":405,"sources":408,"stem":415,"term":416,"__hash__":417},"glossary\u002Fglossary\u002Fselective-catalytic-reduction.md",[259,260,261],"SCR","SCR system","SCR reactor",{"type":53,"value":263,"toc":391},[264,281,285,300,304,307,336,353,355],[56,265,266,268,269,273,274,67,277,280],{},[59,267,66],{}," is the dominant flue-gas NOx-control technology on coal-fired and gas-fired utility boilers, ",[63,270,272],{"href":271},"\u002Fglossary\u002Fheat-recovery-steam-generator","HRSGs"," in combined-cycle plants, ",[63,275,276],{"href":101},"waste-to-energy",[63,278,279],{"href":101},"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.",[74,282,284],{"id":283},"reactor-layout","Reactor layout",[56,286,287,288,291,292,295,296,299],{},"A typical SCR reactor is a vertical or horizontal duct containing 2–4 layers of catalyst modules. Upstream of the catalyst sits the ",[63,289,290],{"href":226},"ammonia injection grid (AIG)"," that distributes the ammonia evenly into the flue gas. Most installations operate in the ",[59,293,294],{},"high-dust"," position (between economiser and air heater) where catalyst temperature is around 300–400 °C; ",[59,297,298],{},"tail-end"," SCRs sit downstream of particulate control at lower temperatures, with the trade-off of needing flue-gas reheating.",[74,301,303],{"id":302},"fouling-and-cleaning","Fouling and cleaning",[56,305,306],{},"SCR catalysts foul in two ways:",[205,308,309,327],{},[208,310,311,317,318,67,322,326],{},[59,312,313],{},[63,314,316],{"href":315},"\u002Fglossary\u002Fcatalyst-pluggage","Pluggage"," — fly ash, ",[63,319,321],{"href":320},"\u002Fglossary\u002Fpopcorn-ash","popcorn ash",[63,323,325],{"href":324},"\u002Fglossary\u002Flarge-particle-ash","large-particle ash"," wedge into the catalyst cells, blocking the gas path",[208,328,329,335],{},[59,330,331],{},[63,332,334],{"href":333},"\u002Fglossary\u002Fcatalyst-masking","Masking"," — a thin layer of deposit covers the active sites; gas flow continues but catalytic activity falls",[56,337,338,339,343,344,85,348,352],{},"Both reduce NOx-reduction efficiency, raise ",[63,340,342],{"href":341},"\u002Fglossary\u002Fammonia-slip","ammonia slip",", and shorten catalyst life. Cleaning options include steam ",[63,345,347],{"href":346},"\u002Fglossary\u002Fsteam-sootblower","sootblowers",[63,349,351],{"href":350},"\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.",[74,354,203],{"id":202},[205,356,357,361,365,370,375,380,386],{},[208,358,359],{},[63,360,71],{"href":70},[208,362,363],{},[63,364,227],{"href":226},[208,366,367],{},[63,368,369],{"href":341},"Ammonia slip",[208,371,372],{},[63,373,374],{"href":333},"Catalyst masking",[208,376,377],{},[63,378,379],{"href":315},"Catalyst pluggage",[208,381,382],{},[63,383,385],{"href":384},"\u002Fglossary\u002Fhoneycomb-catalyst","Honeycomb catalyst",[208,387,388],{},[63,389,390],{"href":350},"Sonic horn",{"title":229,"searchDepth":230,"depth":230,"links":392},[393,394,395],{"id":283,"depth":230,"text":284},{"id":302,"depth":230,"text":303},{"id":202,"depth":230,"text":203},"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.",{},[243,399,245,400,401,402,403,404],"denox","ammonia-slip","catalyst-masking","catalyst-pluggage","honeycomb-catalyst","sonic-horn",{"title":406,"description":407},"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.",[409,412],{"title":410,"url":411},"Wikipedia — Selective catalytic reduction","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FSelective_catalytic_reduction",{"title":413,"url":414},"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":419,"title":71,"aliases":420,"body":423,"category":235,"description":531,"extension":237,"meta":532,"navigation":239,"path":70,"relatedTerms":533,"seo":536,"sources":539,"stem":543,"term":544,"__hash__":545},"glossary\u002Fglossary\u002Fselective-non-catalytic-reduction.md",[421,422],"SNCR","SNCR system",{"type":53,"value":424,"toc":526},[425,436,440,463,467,470,493,499,501],[56,426,427,429,430,432,433,435],{},[59,428,71],{}," 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 ",[63,431,259],{"href":65}," but achieves lower reduction (typically 30–60%) and produces higher ",[63,434,342],{"href":341},".",[74,437,439],{"id":438},"where-sncr-is-used","Where SNCR is used",[205,441,442,445,453,460],{},[208,443,444],{},"Smaller industrial and utility boilers where SCR capital cost is unjustified",[208,446,447,67,450,452],{},[63,448,449],{"href":101},"Waste-to-energy",[63,451,279],{"href":101}," plants — often as the primary DeNOx with optional SCR polish",[208,454,455,459],{},[63,456,458],{"href":457},"\u002Fglossary\u002Fpreheater-tower","Cement preheater towers"," where the gas temperature window is naturally available",[208,461,462],{},"As a retrofit on units where space prevents SCR installation",[74,464,466],{"id":465},"fouling-implications","Fouling implications",[56,468,469],{},"SNCR does not have a catalyst to foul, but the reagent injection itself creates downstream deposit risks:",[205,471,472,487],{},[208,473,474,477,478,482,483],{},[59,475,476],{},"Ammonia salt deposits"," — un-reacted ammonia combines with SO₃ and ash to form ",[63,479,481],{"href":480},"\u002Fglossary\u002Fammonium-bisulphate","ammonium bisulphate"," on cold-end heat-transfer surfaces, particularly the ",[63,484,486],{"href":485},"\u002Fglossary\u002Fair-heater","air heater",[208,488,489,492],{},[59,490,491],{},"Urea \u002F ammonia deposits on lance tips"," — injection lances can plug with urea solids or carbon deposits",[56,494,495,498],{},[63,496,497],{"href":350},"Sonic horns"," on the cold-end air heater address ABS fouling that follows SNCR operation.",[74,500,203],{"id":202},[205,502,503,507,511,517,521],{},[208,504,505],{},[63,506,66],{"href":65},[208,508,509],{},[63,510,47],{"href":240},[208,512,513],{},[63,514,516],{"href":515},"\u002Fglossary\u002Furea-sncr-aqueous-ammonia-sncr","Urea SNCR \u002F aqueous-ammonia SNCR",[208,518,519],{},[63,520,369],{"href":341},[208,522,523],{},[63,524,525],{"href":480},"Ammonium bisulphate",{"title":229,"searchDepth":230,"depth":230,"links":527},[528,529,530],{"id":438,"depth":230,"text":439},{"id":465,"depth":230,"text":466},{"id":202,"depth":230,"text":203},"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.",{},[242,399,534,400,535],"urea-sncr-aqueous-ammonia-sncr","ammonium-bisulphate",{"title":537,"description":538},"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.",[540],{"title":541,"url":542},"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":547,"title":221,"aliases":548,"body":552,"category":235,"description":715,"extension":237,"meta":716,"navigation":239,"path":220,"relatedTerms":717,"seo":718,"sources":721,"stem":725,"term":221,"__hash__":726},"glossary\u002Fglossary\u002Fnox-reduction-efficiency.md",[549,550,551],"DeNOx efficiency","SCR efficiency","NOx conversion",{"type":53,"value":553,"toc":709},[554,568,572,632,636,676,680,689,691],[56,555,556,558,559,561,562,564,565,567],{},[59,557,221],{}," is the percentage of NOx removed from the flue gas by a ",[63,560,47],{"href":240}," system, calculated as (NOx_in − NOx_out) \u002F NOx_in. It is the headline KPI for any ",[63,563,259],{"href":65}," or ",[63,566,421],{"href":70}," installation and the figure permit compliance is measured against.",[74,569,571],{"id":570},"typical-performance","Typical performance",[109,573,574,589],{},[112,575,576],{},[115,577,578,581,584],{},[118,579,580],{},"System",[118,582,583],{},"Reduction range",[118,585,586,587],{},"Typical ",[63,588,342],{"href":341},[128,590,591,602,613,622],{},[115,592,593,596,599],{},[133,594,595],{},"SCR (high-dust)",[133,597,598],{},"80–95%",[133,600,601],{},"2–5 ppm",[115,603,604,607,610],{},[133,605,606],{},"SCR (tail-end)",[133,608,609],{},"90–98%",[133,611,612],{},"1–3 ppm",[115,614,615,617,619],{},[133,616,421],{},[133,618,141],{},[133,620,621],{},"5–10 ppm",[115,623,624,627,630],{},[133,625,626],{},"Combined SNCR + SCR",[133,628,629],{},"up to 99%",[133,631,601],{},[74,633,635],{"id":634},"what-erodes-efficiency-over-time","What erodes efficiency over time",[205,637,638,645,654,661,670],{},[208,639,640,644],{},[59,641,642],{},[63,643,374],{"href":333}," — fine ash blanket reducing active surface area",[208,646,647,653],{},[59,648,649],{},[63,650,652],{"href":651},"\u002Fglossary\u002Fcatalyst-poisoning","Catalyst poisoning"," — chemical de-activation",[208,655,656,660],{},[59,657,658],{},[63,659,379],{"href":315}," — channel blockage and gas channelling",[208,662,663,669],{},[59,664,665,668],{},[63,666,667],{"href":226},"AIG"," distribution drift"," — uneven NH₃\u002FNOx mixing",[208,671,672,675],{},[59,673,674],{},"Operating outside the temperature window"," — too cool or too hot for the catalyst",[74,677,679],{"id":678},"how-cleaning-preserves-efficiency","How cleaning preserves efficiency",[56,681,682,684,685,688],{},[63,683,497],{"href":350}," and steam ",[63,686,347],{"href":687},"\u002Fglossary\u002Fsonic-sootblower"," attack masking and pluggage directly. A well-cleaned catalyst maintains 85–90% of its initial efficiency for 30,000 operating hours, against 60–70% for a poorly cleaned catalyst of the same age. The economic case for active cleaning is therefore measured in deferred catalyst replacement and avoided ammonia-over-injection cost.",[74,690,203],{"id":202},[205,692,693,697,701,705],{},[208,694,695],{},[63,696,66],{"href":65},[208,698,699],{},[63,700,71],{"href":70},[208,702,703],{},[63,704,369],{"href":341},[208,706,707],{},[63,708,374],{"href":333},{"title":229,"searchDepth":230,"depth":230,"links":710},[711,712,713,714],{"id":570,"depth":230,"text":571},{"id":634,"depth":230,"text":635},{"id":678,"depth":230,"text":679},{"id":202,"depth":230,"text":203},"NOx reduction efficiency is the percentage of NOx removed from the flue gas by a DeNOx system, calculated as (NOx_in − NOx_out) \u002F NOx_in. It is the headline KPI for any SCR or SNCR installation and the figure permit compliance is measured against.",{},[242,243,400,401],{"title":719,"description":720},"NOx reduction efficiency — the headline KPI for SCR and SNCR systems","NOx reduction efficiency is the percentage of inlet NOx removed by the DeNOx system. The headline KPI for SCR (80–95%) and SNCR (30–60%) operation.",[722],{"title":723,"url":724},"Power Engineering — Selective Catalytic Reduction: Operational Issues","https:\u002F\u002Fwww.power-eng.com\u002Fenvironmental-emissions\u002Fselective-catalytic-reduction-operational-issues-and-guidelines\u002F","glossary\u002Fnox-reduction-efficiency","Xfcyi2ujLtvybPvlNwYTJpUqlszO7aEsUUq3q0gVXkw",{"id":728,"title":729,"aliases":730,"body":732,"category":235,"description":817,"extension":237,"meta":818,"navigation":239,"path":226,"relatedTerms":819,"seo":820,"sources":823,"stem":827,"term":227,"__hash__":828},"glossary\u002Fglossary\u002Fammonia-injection-grid.md","Ammonia injection grid (AIG)",[667,731],"ammonia injection grids",{"type":53,"value":733,"toc":812},[734,753,757,783,787,792,794],[56,735,736,737,739,740,742,743,67,745,747,748,752],{},"An ",[59,738,290],{}," is an array of injector nozzles that distributes ammonia (or vaporised aqueous-ammonia \u002F urea) evenly across the flue-gas duct upstream of an ",[63,741,259],{"href":65}," catalyst bed. The quality of the NH₃\u002FNOx mixing at the catalyst inlet is the single biggest determinant of ",[63,744,221],{"href":220},[63,746,342],{"href":341},": under-mixing leaves NOx-rich zones unreacted ",[749,750,751],"em",{},"and"," causes locally over-stoichiometric ammonia in other zones.",[74,754,756],{"id":755},"common-failure-modes","Common failure modes",[205,758,759,765,771,777],{},[208,760,761,764],{},[59,762,763],{},"Nozzle plugging"," — ash, ammonium-salt deposits or carbon block individual nozzles",[208,766,767,770],{},[59,768,769],{},"Lance fouling"," — deposits accumulate on lance bodies and disturb spray patterns",[208,772,773,776],{},[59,774,775],{},"Erosion"," — abrasive ash wears injector tips, distorting the spray pattern",[208,778,779,782],{},[59,780,781],{},"Maldistribution"," — uneven gas flow at the AIG inlet means even a perfect AIG delivers uneven mixing",[74,784,786],{"id":785},"sonic-horns-on-the-aig-deck","Sonic horns on the AIG deck",[56,788,789,791],{},[63,790,497],{"href":350}," 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.",[74,793,203],{"id":202},[205,795,796,800,804,808],{},[208,797,798],{},[63,799,66],{"href":65},[208,801,802],{},[63,803,369],{"href":341},[208,805,806],{},[63,807,379],{"href":315},[208,809,810],{},[63,811,390],{"href":350},{"title":229,"searchDepth":230,"depth":230,"links":813},[814,815,816],{"id":755,"depth":230,"text":756},{"id":785,"depth":230,"text":786},{"id":202,"depth":230,"text":203},"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.",{},[242,400,402,404],{"title":821,"description":822},"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.",[824],{"title":825,"url":826},"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",1782613751218]