DK202200308A1 - A process for selective catalytic reduction (SCR) of sulfur-containing gases - Google Patents

Abstract

Process for selective catalytic reduction (SCR) of sulfur compounds containing gases, wherein the SCR is operated at a temperature below the dew point of ammonium bisulfate and the catalyst is periodically regenerated contacting the SCR catalyst with ozone.

Description

DK 2022 00308 A1 1

Title: A process for selective catalytic reduction (SCR) of sulfur-containing gases

The present invention relates to a process for selective catalytic reduction (SCR) of sulfur-containing gases. In particular, the process comprises periodical regeneration of spent catalyst with ozone.

It is known that when conventional SCR catalysts are in op- eration in sulfur-containing flue gases at low tempera- tures, formation of ammonium bisulfate (NH HSO;) is an im- portant issue regarding operation time.

SCR is primarily a means of converting NOx (nitrogen ox- ides) into N; and HO. A gaseous reductant, typically anhy- drous ammonia, aqueous ammonia or urea, 1s added to a stream of flue gas or exhaust gas and then adsorbed onto a catalyst.

SCR catalysts are made of various ceramic materials used as a carrier, such as titanium oxide, and active catalytic components usually oxides of base metals (such as vanadium, possibly promoted with molybdenum and/or tungsten), zeo- lites, or various precious metals, such as palladium and platinum.

The NOx reduction reaction takes place as the gases pass through the SCR catalyst. Prior to contact with the SCR catalyst the ammonia, or other reductants, such as urea, is injected and mixed with the gas to be treated.

The chemical equations for a stoichiometric reaction using

DK 2022 00308 A1 2 either anhydrous or aqueous ammonia for a selective cata- lytic reduction process are as shown below:

ANO + 4NH3 + 02 + 4N> + 6H,0 2NO, + 4NH3 + 02 —+ 3N> + 6H0

NO + NO, + 2NH3 + 2N; + 3H,0 and several secondary reactions: 250, + O2 > 25803 2NH3 + SO3 + H20 — (NH) 2504

NH; + SO; + H20 — NH,H50O4

During the combustion process in e.g. a power plant, sulfur compounds are concurrently formed with CO and hydrocarbons in form of sulfur oxides (SOx), typically about 97% SO, and up to 3% S03. Thus, gases with a higher sulfur content tends to produce higher amounts of SOs.

As shown above, S03; can react with ammonia to produce ammo- nium sulfate ((NH4)2S50,) and ammonium bisulfate (NH:HS804).

Certain SCR catalysts, such as vanadium-based catalysts, are particularly sensitive to contamination from ammonium sulfate and especially ammonium bisulfate, which is con- densed in the pore structure of the catalyst at lower tem- peratures, thereby physically blocking the pores and deac- tivating the catalyst.

On the other hand, operation of the SCR at low temperatures is desirable because it can provide higher efficiency in

DK 2022 00308 A1 3 power production in the plant.

Thus, SCR catalysts are often operating at low tempera- tures. For sulfur-containing gases, formation of ammonium bisulfate becomes a major cause of concern.

The issue concerning formation of ammonium bisulfate when

SCR catalysts are operated in sulfur-containing flue gases at low temperatures is known from the prior art.

Thus, WO 2016/028290 describes an exhaust after-treatment system in which a sulfur trioxide trap, configured to se- lectively capture SOs from the exhaust gas, is included and the formation of ammonium bisulfate is counteracted.

KR 2016 0102691 describes an apparatus and a method for re- generating an SCR system catalyst, which is performed by controlled increase of the system temperature up to or above the temperature, at which ammonium bisulfate captured in the catalyst pores becomes removable.

Further, various Chinese documents address the ammonium bi- sulfate removal issue. Thus, CN 1039 53420 (A) describes a method and a device for the clearing of SCR catalyst sedi- ment particles in the exhaust aftertreatment of a diesel engine, and CN 1039 20540 (A) describes a method and a de- vice for regenerating an SCR denitration catalyst applied to aftertreatment of diesel engine exhaust.

The idea underlying the present invention is to operate a

SCR catalyst below the dew point of ammonium bisulfate and periodically regenerating the SCR catalyst by means of

DK 2022 00308 A1 4 ozone injection, thereby removing ammonium bisulfate from the catalyst pore structure.

From CN 1021 33547 (A) it is known to use an ozone treat- ment to regenerate a vanadium-titanium based flue gas deni- tration catalyst. The treatment method comprises filling an inactivated flue gas denitration catalyst into a catalyst regeneration reaction bed, introducing a mixed gas of ozone and air into the reaction bed and finishing the catalyst regeneration after oxidation.

Ozone is a strong oxidant that can also increase the reac- tivity of catalysts to convert heavy hydrocarbons at room temperature. Ozone (trioxygen, 03) is a strong oxidizing agent for waste and drinking water treatment, sterilization and deodoration. Ozone is an allotrope of oxygen that is much less stable than the diatomic allotrope 02, breaking down in the lower atmosphere to normal dioxygen. Since ozone is a powerful oxidant, it has many industrial appli- catlons related to oxidation. However, due to the fact that ozone itself is toxic, the residual ozone from these oxida- tion processes must be removed.

Moreover, being quite harmful to animal and plant tissue even in concentrations as low as around 100 ppb, ozone is a pollutant that cannot be emitted. For these reasons, much research is devoted to find suitable catalysts for oxida- tion reactions using ozone and to find effective means of removing residual ozone following such oxidation reactions.

In the presence of ammonia, acid gases in the sulfur-con- taining flue gas form ammonium salts, such as ammonium

DK 2022 00308 A1 chloride (NH4C1), ammonium nitrate ((NH4)>NO3) and ammonium bisulfate (NH HSOs). In most cases, NH4HSO04 has the highest dew point, but in waste incineration units with HCl concen- trations of several hundred ppm NH4C1, condensation deter- 5 mines the minimum temperature.

SCR installations in coal fired power plants are normally operated at temperatures between 330 and 430°C with typical ammonium bisulfate catalyst dew points between 280 and 320°C. Below the dew point, ammonia and sulfuric acid con- dense as liquid ammonium bisulfate in the catalyst pore structure, which will inhibit the catalyst performance. At sufficiently high temperatures, gaseous sulfuric acid is in equilibrium with SO:3, and the ammonium bisulfate dew point therefore depends on water content, ammonia content and SO; concentration.

Ammonium bisulfate has a melting point of 147°C. Formation of ammonia sulfate ((NH1)2S50,4) is thermodynamically more fa- vorable, but analysis of condensed salts has shown that the sulfate is only formed in limited amounts due to kinetic limitations.

The inhibition of ammonium bisulfate is reversible, and the ammonium bisulfate is readily evaporated by increasing the catalyst temperature. The bulk dew point at the SCR reactor inlet is typically around 290°C, but the observed dew point is higher due to capillary forces in the micropore struc- ture. The ammonium bisulfate dew point decreases through the SCR reactor since ammonia is consumed in the SCR reac- tion.

DK 2022 00308 A1 6

The catalyst activity is directly related to the extent of pore condensation, which means that the ammonium bisulfate increases gradually as the temperature drops towards the bulk dew point. Operation below the bulk dew point is usu- ally not an option, except for very low SO; concentrations in a low dust SCR installation. This is because ammonium bisulfate will condense, not only inside the catalyst pores but also at the catalyst surface, thereby creating a sticky surface which - over time -leads to plugging of the cata- lyst.

In contrast to the general concept in the art, the process of the invention for selective catalytic reduction (SCR) of sulfur-containing gases 1s operated below the dew point of ammonium bisulfate.

Accoringly, the present invention provides a process for for selective catalytic reduction (SCR) of sulfur compounds containing gases in presence of an SCR catalyst composition comprising one or more catalytic materials active in the

SCR, comprising the steps of operating the SCR catalyst at a temperature below the dew point of ammonium bisulfate; periodically contacting the SCR catalyst with ozone; and regenerating the one or more catalytic active materials and removing ammonium bisulfate from the pore structure of the one or more catalytic active materials by reaction with the ozone.

DK 2022 00308 A1 7

In an embodiment of the invention, the one or more cata- lytic active materials are selected from the vanadium ox- ides VO, V>03, VO» and V.0s and a titania carrier.

In further an embodiment, the catalytic active materials can additionally comprise other compounds, such as W and/or

Mo oxides.

In still an embodiment, the one or more catalytic active materials further comprise Pd in metallic or oxidic form.

In further an embodiment, the SCR catalyst composition is arranged within a porous and gas permeable substrate, pref- erably a filter substrate.

Filters are well suited for the removal of dust and partic- ulate matter from gas streams. Catalytic filters have the double utility of being able both to remove particulates from a gas stream and to catalyze one or more desired reac- tions in the gas. Dust and other particulate matter will settle on the dispersion side of the filter, from where it can easily be removed. The gas flows from the dispersion side to the permeation side of the filter in contact with the catalytic active material contained in the pore struc- ture of the filter.

As mentioned above, ozone is harmful to animal and plant tissue even in concentrations as low as around 100 ppb, and should not be emitted to the environment.

Thus, in an embodiment of the invention the porous and gas permeable substrate or filter substrate is provided with a

DK 2022 00308 A1 8 catalyst layer for catalytic reducing or abating ozone.

The catalyst for reducing or abating ozone, comprises pref- erably manganese oxide and copper oxide supported on cerium oxide.

During regeneration of the SCR catalyst, the ozone is passed through wall of the filter substrate from permeation side thereof. Then, the dispersion side, i.e. outer wall of the filter can be provided with the catalyst serving the primary purpose of reducing residual ozone.

The operation temperature of the process of the invention is preferably above the solidification temperature of ammo- nium bisulfate.

Typically, the solidification temperature of ammonium bi- sulfate is above 147°C.

The SCR catalytic active material is a catalyst composition comprising a vanadium oxide and titania.

The preferred vanadium oxide for use in the process of the invention is vanadium pentoxide (V>05).

The catalytically active material can further comprise pal- ladium or platinum in metallic and/or oxidic form.

These catalysts are active both in the removal of VOCs and carbon monoxide and in the removal of nitrogen oxides (NOx) by the SCR reaction with NH.

DK 2022 00308 A1 9

The Pd/V/Ti catalyst is a preferred catalyst because (i) it has a dual functionality (removal of NOx and removal of

VOCs), (ii) it is sulfur-tolerant, and (iii) it has a lower

SO, oxidation activity compared to other catalyst composi- tions.

It is known that the oxidation activity of a Pd-containing catalyst is reduced in the presence of a few ppm of NH3. It is also known that, besides being an active catalyst in the

NH3-SCR of NOx, vanadium oxide is also an active oxidation catalyst. Compared to the precious metal catalysts, like the Pd catalyst, the vanadium oxide catalyst is less selec- tive in the formation of CO, and some CO is produced dur- ing the oxidation reactions. CO cannot be oxidized to CO, at a feasible reaction rate by contact with the vanadium oxide catalyst, but requires presence of a noble metal cat- alyst, such as Pd.

Any dust and particles present in the process gas will be deposited on dispersion side, i.e. the outer surface of the outer filter wall facing dirty gas. Thus, the catalysts loaded within the filter wall are effectively protected against potential catalyst poisons present in the particles contained in the dirty gas.

In the process of the invention, the catalyst is periodi- cally regenerated with ozone, whereby ammonium bisulfate is removed from the pore structure of the catalyst.

In a specific embodiment of the invention, the regeneration is preferably conducted in reverse flow through the cata- lytic filter during catalyst regeneration with ozone, i.e.

DK 2022 00308 A1 10 from the permeation side through the filter wall and into the filter house or chamber, housing the filters.

The ozone to be injected can come from various sources, such as an ozone generator. Ozone generators are available in full industrial size, and they are widely used, such as in the pulp and paper industry.

Claims (10)

DK 2022 00308 A1 11 Claims:

1. A process for selective catalytic reduction (SCR) of sulfur compounds containing gases in presence of an SCR catalyst composition comprising one or more catalytic mate- rials active in the SCR, comprising the steps of operating the SCR catalyst at a temperature below the dew point of ammonium bisulfate; periodically contacting the SCR catalyst with ozone; and regenerating the one or more catalytic active materials and removing ammonium bisulfate from the pore structure of the one or more catalytic active materials by reaction with the ozone.

2. Process according claim 1, wherein the one or more catalytic active materials comprise the vanadium oxides VO, V,03, VO, and V.0s and a titania carrier.

3. Process according to claim 2, wherein the one or more catalytic active materials further comprise oxides of tungsten and/or molybdenum.

4, Process according to claim 2 or 3, wherein the one or more catalytic active materials further comprise Pd in metallic or oxidic form.

5. Process according to any one of claims 1 to 3, wherein the SCR catalyst composition is arranged within a porous and gas permeable substrate.

DK 2022 00308 A1 12

6. Process according to claim 5, wherein the porous and gas permeable substrate is a filter substrate.

7. Process according to 5 or 6, wherein the porous and gas permeable substrate is provided with a catalyst layer for catalytic reducing or abating ozone.

8. Process according to claim 7, wherein the catalyst layer comprises manganese oxide and copper oxide supported on cerium oxide.

9. Process according to any one of claims 6 to 8, wherein the ozone is passed through wall of the filter sub- strate from permeation side thereof.

10. Process according to any one of claims 1 to 9, wherein the SCR is operated at a temperature above the so- lidification temperature of ammonium bisulfate.

SEARCH REPORT - PATENT Application No. PA 2022 00308

1.U] Certain claims were found unsearchable (See Box No. I).

2.[] Unity of invention is lacking prior to search (See Box No. ID.

A. CLASSIFICATION OF SUBJECT MATTER B01D 53/96 (2006.011); BO1J 23/92 (2006.011); BO1J 38/12 (2006.01i); BO1D 53/50 (2006.01i); BO1D 53/86 (2006.011); B01J 23/22 (2006.01a); BO1J 23/34 (2006.01a); BO1J 23/648 (2006.01a); BO1J 23/652 (2006.01a); BO1J 23/72 (2006.01a) According to International Patent Classification (IPC)

B. FIELDS SEARCHED PCT-minimum documentation searched (classification system followed by classification symbols) CPC & IPC: BO1D, B01J, FOIN, F23J Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched DK, NO, SE, FI: IPC-classes as above. Electronic database consulted during the search (name of database and, where practicable, search terms used) EPODOC, WPI, FULL TEXT: ENGLISH GOOGLE (Search terms: ozone, filter, regenerate)

C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant for claim No. X; A WO 2018/055162 Al (SHELL INTERNATIONALE RESEARCH 1-6, 10; 7-9 MAATSCHAPPIJ [NL] 29 March 2018 See entire document, esp. abstract; page 1, lines 5-22; page 4, line 6- page 5, line 1; example and claims 1, 2, 13-18 and 21. X; A WO 2021/089471 Al (UMICORE AG & CO. KG [DE]) 14 May 2021 1-6, 10; 7-9 See entire document, esp. abstract; page 5, line 17 - page 6, line 18; page 7, lines 1-22; examples and claims. A CN 1853920340 B (UNIV NINGBO) 25 November 2015 1-10 See abstract, EPO machine translation and figures. NI Further documents are listed in the continuation of Box C. + Special categories of cited documents: "pr Document published prior to the filing date but later than the "A" — Document defining the general state of the art which is not priority date claimed. considered to be of particular relevance. "TT" Document not in conflict with the application but cited to npn Document cited in the application. understand the principle or theory undetlying the invention. "E" Earlier application or patent but published on or after the filing date. | x Document of particular relevance; the claimed invention cannot be . Co . 0 considered novel or cannot be considered to involve an inventive "" Document which may throw doubt on priority claim(s) or which is step when the document is taken alone cited to establish the publication date of another citation or other Sr . Å . . special reason (as specified). Y Document of particular relevance; the claimed invention cannot be . . oo considered to involve an inventive step when the document is "O" Document referring to an oral disclosure, use, exhibition or other combined with one or more other such documents, such means. combination being obvious to a person skilled in the art. "&" Document member of the same patent family. Danish Patent and Trademark Office Date of completion of the search report Helgeshøj Allé 81 29 September 2022 DK-2630 Taastrup Denmark Authorized officer Hans Christian Rudbeck

Tel.: +45 4350 8000

Tel.: +45 43 50 81 25 October 2021 1/4

Application No.

SEARCH REPORT - PATENT ppricaion 0 PA 2022 00308 C (Continuation). DOCUMENTS CONSIDERED TO BE RELEVANT Citation of document, with indication, where appropriate, of the relevant passages Relevant for claim No.

A CN 182133347 A (UNIV SOUTH CHINA TECH et al.) 27 July 2011 1-10 See abstract, EPO machine translation and figures.

A CN 185521831 A (HANGZHOU HATYUN ENV PROT ENG CO LTD) 1-10 27 April 2016 See abstract and EPO machine translation.

A WO 2018/158183 Al (HALDOR TOPSØE A/S [DK]) 07 September 2018 1-10 See abstract and claims 1-9. A WO 2018/065176 A1 (HALDOR TOPSØE A/S [DK]) 12 April 2018 1-10 See abstract and claims.

A CN 187376930 A (UNIV CHONGQING) 06 July 2017 1-10 See abstract and EPO machine translation, esp. paragraphs [0001]-[0026] and claim 1. October 2021 2/4

Application No. SEARCH REPORT - PATENT PA 2022 00308 Box No. I Observations where certain claims were found unsearchable This search report has not been established in respect of certain claims for the following reasons:

1.[] Claims Nos.: because they relate to subject matter not required to be searched, namely:

2. U] Claims Nos.: because they relate to parts of the patent application that do not comply with the prescribed requirements to such an extent that no meaningful search can be carried out, specifically:

3. I Claims Nos. because of other matters, Box No. II Observations where unity of invention is lacking prior to the search The Danish Patent and Trademark Office found multiple inventions in this patent application, as follows: October 2021 3/4

Application No.

SEARCH REPORT - PATENT

PA 2022 00308 SUPPLEMENTAL BOX Continuation of Box [.] October 2021 4/4