WO1996006674A1 - Process for the selective catalytic reduction of nitrogen oxides - Google Patents

Process for the selective catalytic reduction of nitrogen oxides Download PDF

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Publication number
WO1996006674A1
WO1996006674A1 PCT/US1995/010585 US9510585W WO9606674A1 WO 1996006674 A1 WO1996006674 A1 WO 1996006674A1 US 9510585 W US9510585 W US 9510585W WO 9606674 A1 WO9606674 A1 WO 9606674A1
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WO
WIPO (PCT)
Prior art keywords
carbamate
effluent
ammonia
urea
ammonium
Prior art date
Application number
PCT/US1995/010585
Other languages
English (en)
French (fr)
Inventor
John E. Hofmann
Original Assignee
Nalco Fuel Tech
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nalco Fuel Tech filed Critical Nalco Fuel Tech
Publication of WO1996006674A1 publication Critical patent/WO1996006674A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8621—Removing nitrogen compounds
    • B01D53/8625—Nitrogen oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/80—Organic bases or salts

Definitions

  • the invention relates to selective catalytic reduction (SCR) of nitrogen oxides (NO x ) in combustion effluents.
  • SCR selective catalytic reduction
  • NO x nitrogen oxides
  • the invention provides a process which avoids problems with urea at low injection temperatures and achieves the advantages of ammonia as a NO x -reducing agent without requiring its use.
  • the invention eliminates reagent deposit on SCR catalysts while enabling improved ease and safety of transportation.
  • SCR selective catalytic reduction
  • SNCR selective noncatalytic reduction
  • SCR processes generally involve passing NO x -laden effluent with added ammonia across a catalyst bed, and are capable of achieving relatively high NO x reductions, but require the use of ammonia.
  • Ammonia is costly and can be dangerous.
  • ammonia is required to be transported and stored in the form of ammonia water, which in its most commonly utilized form is only about 25% ammonia and is sometimes as dilute as 10% ammonia.
  • the use of ammonia water for providing ammonia to facilitate catalytic NO x reduction can be impractical because of the increased costs of storage and transportation. In its anhydrous form, moreover, it requires pressure vessels and special handling. And, it is prudent to avoid the introduction of risk factors to facilities not familiar with them.
  • Urea is safer than ammonia, and has found wide acceptance in SNCR processes. Most SCR processes, however, operate at temperatures so low that the urea cannot enter the gas phase as either free radicals or simple gas molecules. It has been found that urea injected at low temperatures ahead of an SCR catalyst, can form deposits on the catalysts. These deposits reduce catalytic activity and can cause reduced NO x -reducing activity and the creation of ammonia slip.
  • What is desired is a process for the selective catalytic reduction of nitrogen oxides which is able to economically achieve significant NO x reductions with ease of reagent transportation and storage, no catalyst fouling, high chemical utilization, and practical safety.
  • urea has been widely used since the disclosure by Arand, Muzio, and Sotter in U.S. Patent 4,208,386 and Arand, Muzio, and Teixeira in U.S. Patent 4,325,924.
  • ammonia Lion, U.S. Patent 3,900,554
  • urea hydrolysates e.g., von Harpe, et al., U.S. Patent 5,240,688
  • carbamate Hofmann, etal., U.S. Patent 4,997,631
  • carbamate as an intermediate in urea hydrolysis
  • the invention provides a process for the catalytic reduction of nitrogen oxides in a combustion effluent comprising: (a) directing the effluent through a passage including a catalysis zone containing a catalyst effective for reducing NO x in the presence of ammonia and oxygen; (b) introducing into the passage, an aqueous solution of a NO x -reducing agent consisting essentially of - ammonium carbamate, of the following formula 0
  • the solution is introduced into the effluent at a temperature of less than 1300°F but sufficient to essentially completely dissociate the carbamate and form gaseous ammonia prior to entrance into the catalysis zone and the effluent containing the ammonia enters the catalysis zone at a temperature effective to reduce the concentration of nitrogen oxides by selective catalytic reduction.
  • the carbamate is produced in equipment conventional for urea synthesis, but under conditions effective to maximize the production of ammonium carbamate and minimize the production of urea.
  • the carbamate will consist essentially of ammonium carbamate and contain no more than minimal amounts of urea.
  • the combined amount of urea and other nitrogenous species such as ammonium carbonate, ammonium bicarbonate, and the double salt of ammonium carbonate (often called commercial ammonium carbonate, NH 4 HCO 2 NH 2 COONH 4 ), is maintained at a level of less than about 10%, more preferably less than 6%, and most preferably less than 2%.
  • the carbamate is recovered from the process in the form of a solid.
  • the catalytic destruction of nitrogen oxides can be effected in the presence of ammonia while reducing or eliminating the need for the undesirable storage, handling, and transport of ammonia, ammonia water or other dilute aqueous chemical.
  • Figure 1 is a schematic representation of one embodiment of the invention wherein an aqueous solution of ammonium carbamate is introduce into a NO x -containing combustion effluent in a passage leading from a boiler and leading to a catalysis section; and
  • Figure 2 is an enlarged schematic view of a representative container means employed to transport the ammonium carbamate in dry or aqueous form, sealed from the atmosphere and to then receive make-up water and deliver a solution of the desired concentration to the effluent.
  • the invention which relates to the catalytic reduction of nitrogen oxides in a combustion effluent in the presence of ammonia by introducing into the NO x -laden effluent an aqueous solution of ammonium carbamate, to generate ammonia in the effluent, will be described with reference to the large utility boiler of the type shown as 100 in Figure 1 having a combustion zone 110 and a preferably skid-mounted container 10 as shown in Figure 2.
  • the source of NO x -containing effluent can be any combustor of any carbonaceous fuel - including an internal combustion engine such as those for fixed and mobile use powered by a suitable fuel such as gasoline, diesel fuel, heavy oil, alcohol, natural gas, or like fuel.
  • the container is illustrative of one means for transporting ammonium carbonate, while other forms and constructions are possible.
  • the container can be a replaceable cartridge which can be simply removably inserted in the supply line for NO x - reducing chemical between a source of water and means for injecting the solution into the effluent.
  • ammonium carbamate is produced in equipment conventional for urea synthesis, but under conditions effective to maximize the production of ammonium carbamate and minimize the production of urea and urea hydrolysis products other than the carbamate.
  • the carbamate will consist essentially of ammonium carbamate and contain no more than minimal amounts of urea.
  • the amount of urea and other nitrogenous species such as ammonium carbonate, ammonium bicarbonate, and the double salt of ammonium carbonate (often called commercial ammonium carbonate, NH 4 HCO 2 NH 2 COONH 4 ), is maintained at a combined level of less than about 10%, more preferably less than 6%, and most preferably less than 2%.
  • the carbamate is produced by combining liquid ammonia and liquid carbon dioxide at a pressure preferably above the critical pressure of ammonia, e.g., of from about 120 to about 200 atmospheres at a temperature of from about 135° to about 200° C, and then recovering the ammonium carbamate. Under these conditions, the reaction goes very rapidly and evolves large amounts of heat. When water is essentially excluded from the system, the production of urea and carbonates can be controlled to the low amounts preferred according to the invention.
  • ammonium carbamate can be shipped in dry form and, thereby, achieve savings in transportation costs because it is not necessary to ship it with large amounts of water.
  • One particularly advantageous procedure is to store the ammonium carbamate in dry form, such as in sealed container 10 as shown in the drawings.
  • water from a source 12 enters the container 10, preferably from the bottom, to take the carbamate 11 into solution for delivery via line 14 to passage 16.
  • the concentration of the solution can be controlled by suitable metering valves and, if desired, mixing elements within the container.
  • the solubility of the carbamate in water increases with temperature, varying from about 35% at O°C to about 75% at just under the boiling point.
  • the solution (aqueous solution) is introduced into the effluent at an effluent temperature wherein the ammonium carbamate readily converts to ammonia in order to facilitate the catalytic reduction of nitrogen oxides.
  • Acceptable temperatures are those where the ammonium carbonate is not oxidized to NO x , e.g., as high as about 1950°F, but are preferably lower.
  • the effluent temperature is preferably less than 1300°F, and preferably within the range of from about 230° to about 1200°F at the point of introduction. More preferably, the effluent temperature is between about 500°F and about 1100°F. Most preferably, the effluent temperature at the point of introduction of the ammonium carbamate should be between about 550°F and about 950°F.
  • the point of introduction of the carbamate solution into the effluent should also be chosen so as to achieve essentially complete conversion of the ammonium carbamate to ammonia. This is assured by the provision of sufficient residence times and good mixing at the temperatures involved. Preferably, residence times of from about 0.5 to about 2 seconds are employed. If necessary, baffling or other structures can be added to assure good mixing.
  • the ammonia produced in situ is then utilized to selectively catalytically reduce the nitrogen oxides remaining in the effluent by passing the ammonia-containing effluent through a catalysis zone 18 comprising one or more catalyst sections 20 comprising a catalyst material effective for the reduction of nitrogen oxides in the presence of ammonia to further reduce the concentration of nitrogen oxides.
  • the ammonium carbamate solution may be at ambient temperature prior to introduction or, alternatively, it may be at or above its boiling point. In this way, the ammonium carbamate can flash off immediately upon introduction into the effluent, which might provide advantages in minimizing air requirements for atomization, etc.
  • the ammonium carbamate is introduced into the effluent in an amount sufficient to provide a molar ratio of the ammonia generated to the baseline nitrogen oxides level (by which is meant the pre- treatment level of NO x in the effluent) of about 0.8:1 to about 1.5:1. More preferably, treatment solution is introduced into the effluent to provide a molar ratio of ammonia to baseline nitrogen oxides of about 1 :1 to about 1.2:1 , most preferably about 1 :1.
  • the catalyst used is one capable of reducing the effluent nitrogen oxides concentration in the presence of ammonia.
  • These include, for instance, activated carbon, charcoal or coke, zeolites, vanadium oxide, tungsten oxide, titanium oxide, iron oxide, copper oxide, manganese oxide, chromium oxide, noble metals such as platinum group metals like platinum, palladium, rhodium, and indium, or mixtures of these.
  • Other catalyst materials conventional in the art and familiar to the skilled artisan can also be utilized. These catalyst materials are typically mounted on a support such as a ceramic substance, a zeolite, or a homogeneous monolith, although other art known supports can also be used.
  • Patent 4,393,031 disclose the catalytic reduction of NO x using platinum group metals and/or other metals such as titanium, copper, molybdenum, vanadium, tungsten, or oxides thereof with the addition of ammonia to achieve the desired catalytic reduction.
  • Ginger in U.S. Patent 4,268,488, discloses exposing a nitrogen oxides containing effluent to a first catalyst comprising a copper compound such as copper sulfate and a second catalyst comprising metal combinations such as sulfates of vanadium and iron or tungsten and iron on a carrier in the presence of ammonia.
  • a first catalyst comprising a copper compound such as copper sulfate and a second catalyst comprising metal combinations such as sulfates of vanadium and iron or tungsten and iron on a carrier in the presence of ammonia.
  • the ammonia-containing effluent is most preferably passed over the catalyst while the effluent is at a temperature between about 230°F and about 950°F, preferably at least 550°F. In this manner, the ammonia present in the effluent by the introduction of the ammonium carbamate solution most effectively facilitates the catalytic reduction of nitrogen oxides.
  • the effluent will preferably contain an excess of oxygen, e.g., from about 1 to about 10%.

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  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Biomedical Technology (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Exhaust Gas After Treatment (AREA)
PCT/US1995/010585 1994-08-29 1995-08-21 Process for the selective catalytic reduction of nitrogen oxides WO1996006674A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US29729294A 1994-08-29 1994-08-29
US08/297,292 1994-08-29

Publications (1)

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WO1996006674A1 true WO1996006674A1 (en) 1996-03-07

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WO (1) WO1996006674A1 (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6761868B2 (en) 2001-05-16 2004-07-13 The Chemithon Corporation Process for quantitatively converting urea to ammonia on demand
US6887449B2 (en) 2002-11-21 2005-05-03 The Chemithon Corporation Method of quantitatively producing ammonia from urea
EP2551009A1 (en) * 2011-07-29 2013-01-30 Deere & Company Diesel exhaust fluid formulation having a high ammonium content and a low freezing point
CN104128090A (zh) * 2014-08-03 2014-11-05 长春市永畅实业有限责任公司 一种满足车辆低温去除氮氧化物的还原剂
CN104226108A (zh) * 2013-06-17 2014-12-24 迪尔公司 减少排气系统中的尿素沉积物的柴油机排气处理液制剂
US10695719B2 (en) 2016-12-01 2020-06-30 Loughborough University Producing ammonium carbamate and reducing nitrogen oxides

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5139754A (en) * 1989-09-12 1992-08-18 Fuel Tech, Inc. Catalytic/non-catalytic combination process for nitrogen oxides reduction

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5139754A (en) * 1989-09-12 1992-08-18 Fuel Tech, Inc. Catalytic/non-catalytic combination process for nitrogen oxides reduction

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
GRANT AND HACKH'S CHEMICAL DICTIONARY, Fifth Edition, 1987, page 612. *
KIRK OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Volume 23, October 1983, pages 551-552. *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6761868B2 (en) 2001-05-16 2004-07-13 The Chemithon Corporation Process for quantitatively converting urea to ammonia on demand
US7008603B2 (en) 2001-05-16 2006-03-07 The Chemithon Corporation Process and apparatus for quantitatively converting urea to ammonia on demand
US6887449B2 (en) 2002-11-21 2005-05-03 The Chemithon Corporation Method of quantitatively producing ammonia from urea
EP2551009A1 (en) * 2011-07-29 2013-01-30 Deere & Company Diesel exhaust fluid formulation having a high ammonium content and a low freezing point
CN102895874A (zh) * 2011-07-29 2013-01-30 迪尔公司 具有高铵含量和低凝固点的柴油机排气处理液制剂
US8518354B2 (en) 2011-07-29 2013-08-27 Deere & Company Diesel exhaust fluid formulation having a high ammonium content and a low freezing point
CN102895874B (zh) * 2011-07-29 2016-05-04 迪尔公司 具有高铵含量和低凝固点的柴油机排气处理液制剂
CN104226108A (zh) * 2013-06-17 2014-12-24 迪尔公司 减少排气系统中的尿素沉积物的柴油机排气处理液制剂
CN104128090A (zh) * 2014-08-03 2014-11-05 长春市永畅实业有限责任公司 一种满足车辆低温去除氮氧化物的还原剂
US10695719B2 (en) 2016-12-01 2020-06-30 Loughborough University Producing ammonium carbamate and reducing nitrogen oxides

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Publication number Publication date
TW278050B (enrdf_load_stackoverflow) 1996-06-11

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