7/21/2019 Uhde Publications PDF en 10000009.00 http://slidepdf.com/reader/full/uhde-publications-pdf-en-1000000900 1/2 30tce apri 2006 Nitric acid – without the emissions Meinhard Schwefer and Rolf Siefert iNOx N O and NOx abatement process rac ca y a o e wor s n r c ac s pro uce us ng t e Ostwa process see F gure 1 , w c nvo ves t e cata yt c ox aton o ammona n a r over a p at num a oy gauze cata yst n t e so- ca e ammona urner. T e ma n react on pro uct s n tr c ox e NO , w c s converte to n trogen ox e NO an a sor e n water to orm n tr c ac HNO . Some o t e ammon a, owever, s converte to n trous ox e N O , w c ta es no urt er part n t e n tr c ac process an s emtte to atmosp ere n t e ta gas toget er w t t e n trogen o t e reacton a r an some res ua NOx NO an NO t at was not converte to ntrc ac n t e a sor er. T e amount o N O generate s cut to pre ct exact y ut s nown to e n uence y t e operat ng parameters o t e ammon a urner an t e con ton o t e cata yst gauzes. T e operat ng pressure, w c s set urng t e es gn o a p ant, as a part cu ar y strong n uence. Ammon a urners operat ng at atmosp er c pressure ave t e owest emssons o aroun 3–4 g N 2 O t HNO for medium pressure somew at g er at w e g pressure t 10 ar an a o ve ons up to 20 g tinum alloy catalyst during use and need terva s rang ng rom r some g pressure nt s or me um an re urners. As t e ns of N O usually rise. most important n ouse gas GHG a ter an met ane CH 4 an t e most power u o t ese, w t 310 t mes t e e ect on g o a warm ng o CO . With current world nitric acid production at around 55m t/y and an overall average N 2 O emission factor estimated at 7 kg N O/ t HNO , annua em ss ons o N 2 O rom n trc ac p ants are ~400,000 t N O, equ va ent to 120m t CO y. For compar son, t s s a out one-t r o t e sze o t e European Union’s GHG emission reduction commitment under the Kyoto Protocol. process development programme U e as ong een nvo ve n n tr c ac tec no ogy as a part o ts ert ser process portfolio. During the 1990s, Uhde formed the view that nitrous oxide em ss ons rom n tr c ac p ants were go ng to ecome a matter o concern an egan an R&D programme a me at test ng an eve op ng a catayst an a process to lower these emissions. Under this programme, Uhde extended its laboratory ac t es or cata yst c aracter sat on an per ormance test ng. Re a e conc usons a out t e su ta ty o any part cu ar can ate cata yst can on y e o ta ne by carrying out long-term measurements in an industrial production facility. U e t ere ore es gne a cata yst test un t or t at purpose an was ortunate n n ng a partner n Austr an- ase Agro nz Me am ne Internat ona AMI , which permitted the test unit to be installed in its 1000 t/d nitric acid p ant n L nz. T e catayst test un t s operate y a str ute contro system t at a so per orms ata ogg ng. T e temperature, pressure an owrate can be set individually for each of the two parallel reactor trains. The composition o t e ta gas rawn rom t e n tr c ac p ant can e mo e y supp y ng ot er gases rom cy n ers. Gas ana ys s s y a multi-component FT-IR analyser and a c em um nescence etector or ow NOx concentrat ons. A ter over ve years o operat on, t e catalyst test unit is still in use to identify promising catalytic materials, evaluate process concepts an o serve t e ong- term e avour o cata ytc matera s. T e ata o ta ne s o su c ent qua ty to allow scale-up to full size industrial app c at ons w t out requ r ng any nterme ate p ot p ant stage. We oun t at certa n spec c ron z eo te mater a s are very su ta e or N 2 O and NOx abatement in the tail gas of nitric ac p ants. T ese mater a s ave some nterest ng propert es, w c n uence t e c on guraton o t e process. One o t e materials investigated readily decomposes N 2 O, especially in the presence of high concentrat ons o NOx. A erent ron z eo te matera catayses t e re uc t on o N 2 O w t y rocar ons. Surpr s ng y, here, the rate of N O reduction is greatly acce erate NOx s remove . NOx s a consttuent o n trc ac p ant ta gas, ut ue to reguatons or client demand has to be reduced to a low concentration, typically less than 50 ppm or sc arge to atmosp ere. A no t er ron zeo te t at we oo e n our nvest gat ons was very e ect ve as a NOx reduction catalyst if ammonia was added. These observations have resulted in t e eve opment o two process var ants – mar ete un er t e name Env NOx – w c ot nvo ve t e com ne remova o N 2 O and NOx from the tail gas. N 2 O decomposition T s two-stage process F gure 2 exp o ts the observation that high levels of NOx enhance the rate of N 2 O decomposition. T e NOx concentrat on n untreate ta gas epen s on t e es gn an per ormance o t e a sor er an ranges from about 150 ppm up. The first catalyst e estroys a arge proport on o t e N O y ecompos t on nto n trogen an oxygen. In t e secon e t e NOx concentration is lowered to below Tail gas to stack HP steam Ammonia gas Air Condensate EnviNOx N 2 O & NOx abatement Ammonia burner Pt/Rhgauzes Boiler NO Gas Absorber Water Nitric acid product Figure 1: Simp i ie o ws eet o t e Ostwa nitric aci process Picture (top): T e process was teste at AMI's Linz nitric aci p ant F rst pu se n tcewww.tceto ay.com News & v ews rom t e process n ustr es, pu s e mont y y t e Inst tut on o C em ca Eng neers
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