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DESCRIPTIONnh3 emission abatement technologies
EnviNOx Setting Emission Standard for Nitric Acid Plants.
Table of contents
Company profile 3
EnviNOx The Uhde N2O/NOxabatement process for nitric acid plants 4
Development of the EnviNOx process 6
The Uhde DeNOx process 7
The Uhde EnviNOx process variant 1 8
The Uhde EnviNOx process variant 2 9
The Uhde DeN2O process 10
Commercial scale implementation 11
Advantages that speak for themselves 13
Sd-Chemie Catalyst 15
The novel EnviNOx process developed by Uhde makes it possible to remove the
environmentally damaging nitrogen oxides N2O and NOX almost entirely from the
waste gases produced by nitric acid plants.
With its highly specialised workforce of more than 4,500 employees and its international network of subsidiaries and branch offices, Uhde, a Dortmund-basedengineering contractor, has, to date, successfully completed over 2,000 projectsthroughout the world.
Uhdes international reputation has been built on the successful application ofEngineering with ideas to yield cost-effective high-tech solutions for its customers.The ever-increasing demands placed upon process and application technology in the fields of chemical processing, energy and environmental protection are metthrough a combination of specialist know-how, all-round service packages, top-quality engineering and impeccable punctuality.
Uhdes head office in Dortmund, Germany
Fig. 1: Block diagramof a nitric acid plant
N2O emissions in the production of nitric acid
The industrial production of nitric acid (HNO3)involves oxidising ammonia (NH3) with air over a platinum/rhodium gauze catalyst to producenitrogen oxides. This process yields nitrogenmonoxide (NO), which then reacts with oxygenand water to form nitric acid. However, it alsoproduces nitrous oxide (N2O) a greenhousegas and ozone killer as an undesired by-product.Unlike NO, the nitrous oxide is not involved inthe HNO3 production process and is emitted into the atmosphere with the tail gas.
The N2O emissions in nitric acid plants varyfrom about 3 - 4 kg of N2O per metric ton ofHNO3 to as much as 20 kg of N2O per metricton of HNO3 depending on the type of nitric acid plant. An estimated 400,000 metric tons of nitrous oxide are emitted each year by nitricacid plants worldwide. Due to its longevity in theearths atmosphere and its special absorptionproperties for infrared radiation, N2O is a potentgreenhouse gas. One metric ton of N2O emissions
has the same effect on global warming as about300 metric tons of CO2. Consequently, nitric acidplants are now the largest single source of green-house gas emissions among industrial manufacturing facilities. Whereas limits on NOxemissions have long been in force (due to concerns about acid rain, smog, etc.), therehave been no restrictions on N2O emissionsuntil recently. However, now that N2O has beenrecognised as a major greenhouse gas (and alsodesignated as such in the Kyoto Protocol), somecountries have introduced limits on emissions ofN2O from nitric acid plants. Because the specific impact of N2O on the greenhouse effectis many times greater than that of CO2, the elimination of N2O from nitric acid plants canmake an important contribution to the protectionof the earths climate. These facts make nitricacid plants an ideal object for the implementationof a carbon trading project under the flexiblemechanisms of the Kyoto Protocol or otherEmission Trading Schemes (e.g. EU-ETS).
EnviNOx The Uhde N2O/NOxabatement process for nitric acid plants
5The 1997 Kyoto Protocol, which came into forceon February 16, 2005, commits participatingindustrialised countries, the Annex I countries, toindividual, legally-binding targets to limit or reduce their greenhouse gas emissions. Many of these Annex I countries will be unable to fulfiltheir obligations under the Kyoto Protocol withintheir own borders. The Kyoto Protocol thereforeprovides three flexible mechanisms (EmissionsTrading (ET), Joint Implementation (JI) andClean Development Mechanism (CDM)), whichallow an Annex I country to be credited withemission reductions made outside its borders.
In view of the fact that, since February 16, 2005,it has become possible to obtain Certified Emission Reductions (CERs) from CDM projects,the interest in greenhouse gas emission reductiontechnologies has increased rapidly and, withinthe 2nd phase (2008 2012) under the KyotoProtocol, it will increase further still.
Emissions Trading (ET) allows companies withinAnnex I countries to trade emission rights witheach other both nationally and across borders.The European Union Emissions Trading Scheme(ETS) became effective in 2005, but includedonly carbon dioxide in its cap and trade system.The next ETS round will start in 2013 and willinclude N2O. The installation of an N2O abatement unit is obligatory for nitric acid plantowners in the European Union due to regulationsthat will come into force in 2013 (auctioning orcap and trade system most probable).
Similar emission trading schemes are currentlyunder discussion (e.g. in Australia, NorthAmerica).
During the period 2008 to 2012, a further kindof emission reduction project the Opt-Inwas developed in some EU countries.
With Joint Implementation (JI), the emission reductions of a project in a host Annex I countryare transferred to a second Annex I country. Suitable host countries include those of EasternEurope and Russia, which have already fulfilled
their Kyoto obligations due to the reduction inindustrial activity since the baseline year of 1990.Emission reductions obtained under JI countfrom the beginning of 2008.
The Clean Development Mechanism (CDM) issimilar to JI except that the host country is adeveloping country without any Kyoto obligation.Thanks to the EU linking directive, emissionreductions under CDM and JI can be acquiredby organisations participating in the ETS in thesame way as other emission rights within theETS. CDM and JI are subject to very strict rulesaimed at preventing CDM/JI projects from beingunfairly credited with emission reductions. Theserules are laid down in the approved methodologieswhich are subjected to intense scrutiny by thepublic and by experts before being passed bythe CDM Executive Board. A CDM project withoutan approved methodology cannot generatesaleable greenhouse gas emission reductions.The very first CDM approved methodology forN2O abatement in nitric acid plants (AM 0028)was submitted for the Abu Qir project and isgenerally applicable to all EnviNOx processvariants.
An EnviNOx system installed as a greenhousegas emission reduction project under the KyotoProtocol or under any similar emission tradingscheme can offer process plant owners interestingopportunities for improving the environment andtheir balance sheet.
Kyoto Protocol, its flexible mechanisms and other Emission Trading Schemes
6Development of the EnviNOx process
In light of the above, Uhde a world leader innitric acid technology set about developing atechnology for removing N2O from the nitric acid production process. The goal was not onlyto achieve high rates of N2O abatement but also to ensure that the technology itself couldbe safely and simply integrated into the HNO3production process without affecting it in anyway. In particular, the aim was to find a suitableway of combining the N2O removal process withthe DeNOx stage, which is also necessary for tail gas treatment. Development therefore focussedon the catalytic removal of N2O from the tail gasof HNO3 plants (so-called tertiary measures).After preliminary tests, development concentra-ted on the use of special iron zeolite catalysts,which were supplied by Sd-Chemie AG. Underlaboratory conditions, these catalysts revealed adiverse reactivity towards N2O: either by decomposing N2O into N2 and O2 - an effectincreased significantly by the presence of NOxin the tail gas (co-catalytic NOx effect), or byreducing N2O using various reducing agents,such as hydrocarbons. In addition, the iron zeo-lites also proved to be excellent DeNOx catalystsin an unusually wide temperature window, thus
allowing N2O abatement to be ideally combinedwith NOx reduction. After optimising the catalysts,the positive laboratory results were verifiedunder industrial conditions in a mini-plant installed in an HNO3 production plant operatedby AMI Agrolinz Melamine International GmbH inLinz, Austria.
The wealth of experimental results gained in themini-plant enabled Uhde to create N2O and NOxabatement solutions that are optimised for parti-cular process conditions, such as the specifictail gas temperature or tail gas composition. In particular, the following EnviNOx processvariants were developed:
. The Uhde DeNOx process(catalytic reduction of NOx). The Uhde EnviNOx process variant 1(catalytic decomposition of N2O and thecatalytic reduction of NOx). The Uhde EnviNOx process variant 2(catalytic reduction of N2O and NOx). The Uhde DeN2O process(catalytic decomposition of N2O)
Uhde mini-plant installed at the AMI nitric acid plant, Austria
7 The Uhde DeNOx process
1)Fig. 2: Uhde DeNOx process: catalytic NOx reduction withammonia over a zeolite catalyst
This NOx abatement process is unusually flexible.Very high rates of NOx reduction can be achievedover a wide range of tail gas temperatures fromsome 200C to about 520C.
The reactor contains a single catalyst bed filledwith an iron zeolite catalyst. The required reducing agent NH3 is added via a mixingsystem upstream of the DeNOx reactor.
NOx abatement by catalytic reduction
Reactions in the DeNOx stage:
6 NO2 + 8 NH3 7 N2 + 12 H2O 4 NO + O2 + 4 NH3 4 N2 + 6 H2O