7/21/2019 Uhde Publications PDF en 10000009.00

http://slidepdf.com/reader/full/uhde-publications-pdf-en-1000000900 1/230  tce  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 at on 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 acHNO . 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 em tte 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 ntr c

ac n t e a sor er. T e amount o N O

generate s cu t 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 t on o t e cata yst gauzes. T e

operat ng pressure, w c s set ur ng t ees 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

em ss ons o aroun 3–4 g N2O t HNO

  for medium pressure

somew at g er at

w e g pressure

t 10 ar an a ove

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 anre urners. As t e

ns of N O usually rise.

most important

n ouse gas GHG a ter

an met ane CH4

 

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

N2O emission factor estimated at 7 kg N O/ 

t HNO , annua em ss ons o N2O rom n tr c

ac p ants are ~400,000 t N O, equ va ent

to 120m t CO y. For compar son, t ss a out one-t r o t e s ze 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 cata yst an a process

to lower these emissions. Under thisprogramme, Uhde extended its laboratory

ac t es or cata yst c aracter sat on an

per ormance test ng. Re a e conc us ons

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 acidp ant n L nz. T e cata yst 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, evaluateprocess concepts an o serve t e ong-

term e av our o cata ytc mater a s.

T e ata o ta ne s o su c ent qua ty

to allow scale-up to full size industrial

app cat ons w t out requ r ng any

nterme ate p ot p ant stage.

  We oun t at certa n spec c ron

zeo te mater a s are very su ta e or N2O

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

con guraton o t e process. One o t e

materials investigated readily decomposesN

2O, especially in the presence of high

concentrat ons o NOx. A erent ron

zeo te mater a cata yses t e re uct on

o N2O 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 const tuent o n tr c ac

p ant ta gas, ut ue to regu at ons

or client demand has to be reduced to

a low concentration, typically less than

50 ppm or sc arge to atmosp ere.

Anot 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 N2O

and NOx from the tail gas.

N2O decomposition

T s two-stage process F gure 2 exp o ts

the observation that high levels of NOx

enhance the rate of N2O 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 rangesfrom 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 N2O& NOx abatement

Ammonia

burner

Pt/Rhgauzes

Boiler

NO Gas

Absorber

Water

Nitric acid product

Figure 1: Simp i ie ows 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 s e n tce  www.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

7/21/2019 Uhde Publications PDF en 10000009.00

http://slidepdf.com/reader/full/uhde-publications-pdf-en-1000000900 2/2apri 2006 tce  31

emissions 1

the regulatory limit for discharge to

tmosp ere y reacton w t t e ammona

e etween t e e s.

operating experience

The first reactor employing this concept

was es gne y U e or AMI an as

een n operat on n t e 1000 t L nzplant since September 2003. Of the

1000–1200 ppm N O enter ng t e reactor,

98%–99% s estroye , an t e NOx eve

is lowered from 400–500 ppm to ~10 ppm

r ess. F gure 3 s ows t e operat ng ata

or t e rst 2½ years.

process concepts: N2O reduction

The EnviNOx process variant 1 is suited

to temperatures g er t an ~425 °C,

s nce t e rate o N O ecompos t on

falls quite rapidly at lower temperatures.

However, many n tr c ac p ants ave

ta gas temperatures e ow 425 °C. To

cater for plants with tail gas temperatures

own to aroun 350 °C we eve ope

t e Env NOx process var ant 2 F gure

4) which utilises the knowledge gained

about N O reduction with hydrocarbons.

As high concentrations of NOx have

a negat ve e ect on N2O re ucton,

NOx s remove n t e rst e o t e

reactor y react on w t ammon a. A

y rocar on suc as natura gas or LPG,

epen ng on ava a ty, s a e to

t e ta gas etween t e e s an reactswith the N O in the second bed. In some

situations the two beds can be combined

and hydrocarbon and ammonia added

together upstream of the reactor. We

expect s m ary g rates o N2O an

NOx remova to t ose o process var ant

1. In act, t e ac eva e out et NOx

concentrat on s <1 ppm, ma ng t e ta

gas very c ean. Not on y s process var ant

2 use u n t e ow temperature range; at

high temperatures a variant 2 reactor is

significantly more compact than a variant

1 reactor using N O decomposition.

There is some additional emission

o GHG, s nce t e y rocar ons are

converte to CO n t e reactor an

t ere may e some CH4 s p natura

gas s use . However t e a t ona GHG

em ss on s ow, ess t an 0.5% o t e

em ss on re uct on ue to t e estruct on

of N2O.

industrial implementation

T e rst commerc a -sca e mp ementat on

o t e Env NOx process var ant 2 w e

n t e 1830 t n tr c ac p ant o A u

Q r Fert zers an C em ca s n Egypt.T s p ant s one o t e ggest n t e

wor an t e expecte GHG em ss on

reduction is also large, at 1.2m t CO2

equivalent per year. This is roughly the

same as the GHG emissions from a 250

MW gas- re e ectrc ty generaton

p ant. T e catayst or t s an uture

Env NOx systems w e manu acture y

Sü -C em e, an nternatona spec a ty

c em ca s company w t ea quarters

n Mun c , Germany, at t e r ac t es n

Sout A r ca.

  If only NOx but not N O abatement is

required, a DeNOx reactor with a single

zeolite bed and upstream ammonia

addition can be used to reduces NOx very

e ect ve y etween ~200 °C an 500 °C.

opportunities with Kyoto

W t t e 2008–2012 rst comm tment

per o o t e Kyoto Protoco approac ng,

there is increasing interest in GHG

emission reduction technology. Many

countries which are committed to

re uc ng GHG em ss ons un er t e Kyoto

Protoco – t e Annex 1 countr es – w

e una e to u t e r o gat onsw t n t e r own or ers. Kyoto t ere ore

prov es t ree ex e mec an sms t at

a ow an Annex 1 country to e cre te

w t em ss on re uct ons ma e outs e

its borders.

Emission trading allows companies

w t n Annex 1 countr es to tra e em sson

r g ts w t eac ot er ot nat ona y

and across borders. The European Union

Em ss ons Tra ng Sc eme EU ETS starte

n 2005 ut ncu e on y CO2  n ts cap

and trade system. The next round of the EU

ETS starts n 2008. Present y, t s not c ear

w et er ot er GHGs suc as N2O w e

brought into the EU ETS. If this were the

case, t e nsta at on o an N2O a atement

un t cou e an nterest ng opt on or

nitric acid plant owners in the EU.

  W t Jo nt Imp ementat on JI , t e

em ss on re uct ons o a pro ect n a

host Annex 1 country are transferred to

a secon Annex 1 country. Su ta e ost

countr es are t ose o Eastern Europe an

Russia that have already fulfilled their

Kyoto o gat ons ue to t e re ucton n

n ustr a act v ty s nce t e ase ne year

of 1990. Reductions obtained under JI onlycount t ey occur a ter t e start o 2008.

T e C ean Deve opment Mec an sm

CDM s s m ar to JI except t at t e

host country is a developing country

w t out any Kyoto o gat on an t e

em ss on re uct ons ac eve now can e

banked until the start of the first Kyoto

comm tment per o . T an s to t e EU

n ng rect ve, em ss on re uct ons

under CDM and JI can be acquired by

organ sat ons part c pat ng n t e EU

ETS n t e same way as ot er em ss on

rights within the EU ETS. CDM is subjectto very str ct ru es a me at prevent ng

CDM pro ects rom e ng un a r y cre te

with emission reductions. These rules are

set own n t e approve met o o og es

t at are su ecte to ntense scrut ny

by the public and experts before being

passe or re ecte y t e CDM execut ve

oar . A CDM pro ect w t out an approve

methodology cannot generate saleable

GHG em ss on re uct ons. T e on y

current y-approve CDM met o o ogy or

N2O abatement in nitric acid plants was

or t e A u Q r pro ect an s genera y

app ca e to a Env NOx process var ants.  Provided a GHG emission reduction

tec no ogy suc as Env NOx s ava a e,

t e Kyoto Protoco an ts ex e

mechanisms can offer process plant

owners nterest ng opportun t es to

mprove t e env ronment an t e r

balance sheet. tce

M c ae Groves (M c ae .Groves@

t yssen rupp.com) s a sen or process

ngineer in the fertiliser division of

erman- ase U e; Me n ar Sc we er

(Me n ar .Sc we er@t yssen rupp.

om) is a senior research chemist in

ts R&D v s on; an Ro S e ert (Ro .

e ert@t yssen rupp.com) a sen or

research chemist at Uhde R&D

CW

CW

 Tailgas

heating

 Tailgas

Clean Tailgas

H2O

Process gas

ith N2O and NO2

Nitric acid product

Tailgas

turbine

Ammonia (gas)

 To atmosphere Tailgas with N2O

and residual NO2

    A

    b   s   o   r   p    t    i   o   n    t   o   w   e   r

gure : nv x

N an NOx

a atment process

ariant 1 Linz

P ant: T e U e

EnviNOx N an

NOx a atement

reactor at AMI, Linzre uces green ouse

gas emissions y

over 0.5m t CO

equivalent/year and

owers stac NOx

concentrations to

e ow 10–15 ppm

(Be ow) Figure 3:

Per ormance o

EnviNOx N an

NOx a atement

reactor at , nz 

Figure 4: EnviNOx

N an NOx

abatment process

ariant 2

CW

CW

 Tailgas

heating

 Tailgas

Clean Tailgas

H2O

Process gas

with N2O and NO2

Nitric acid product

Tailgas

turbine

Ammonia (gas)

Hydrocarbon

 To atmosphere Tailgas with N2O

and residual NO2

    A    b   s   o   r   p    t    i   o   n    t   o   w   e   r