CA1334476C

CA1334476C - Multi-stage process for reducing the concentration of pollutants in an effluent

Info

Publication number: CA1334476C
Application number: CA 610667
Authority: CA
Inventors: William Robert Epperly; Jeremy Deeble Peter-Hoblyn; George Ferdinand Shulof Jr.; James Christopher Sullivan; Barry Normand Sprague; John Henry O'leary
Original assignee: Fuel Tech Inc
Current assignee: Fuel Tech Inc
Priority date: 1989-09-07
Filing date: 1989-09-07
Publication date: 1995-02-21
Anticipated expiration: 2012-02-21

Abstract

A process is presented for reducing the concentration of pollutants in an effluent from the combustion of a carbonaceous fuel. The process comprises introducing a first treatment agent into the effluent at a first temperature zone to reduce the concentration of a first pollutant and introducing a second treatment agent into the effluent at a second temperature zone to reduce the concentration of either the first pollutant or a second pollutant, wherein the first and second treatment agents are introduced under conditions effective to reduce the effluent pollution index.

Description

_ -- 3 Technical Field The present invention relates to a process for reducinq the concentration of pollutants, especially pollutants such as nitro~en oxides (NOX) in the effluent from the combust~on of a carbonaceous fuel. Preferably, the effluent is the oxyqen-rich effluent from the combustion of a carbonaceous fuel.

Carbonaceous fuels can be made to burn more completely, and with reduced emissions of carbon monoxide and unburned hydrocarbons, when the oxygen concentrations and air/fuel ratios employed are those which permit hlgh flame temperatures. When fossil fuels are used to fire large utility bo.ilers, temperatures above about 200 0Q F. and typically about 2200F. to about 30000F. are ~enerated. Unfortunately, such h:Lqh temperatures, as well as hot spots of hlgher temperatures, tend to cause the production of thermal NOX, the temperatures bein~
so high that free radicals of oxygen and nitrogen are formed and chemically combine as nitroqen oxides. Even in circu~ating fluidized bed boilers that operate at temperatures of 1300~F. to 1600F., siqnificant amounts of nitrogen oxides can be formed.
Moreover, such high temperatures, as well as hot spots of hlgher temperatures, tend also to cause the production of *

` - 4 - 1 334476 pollutants such as S03, the temperatures being so high that oxidation of sulfur dioxide (S02) occurs wherein sulfur dioxide and atomic oxygen (O) combine to form sulfur trioxide. This effect is amplified when high sulfur fuels are used. Additionally, sulfur trioxide can form at lower temperatures by the catalytic reaction of sulfur dioxide with molecular oxygen (2) brought about by catalytic metals such as vanadium oxide and iron oxides which can be in the boiler interior at lower temperatures. Sulfur trioxide, therefore, can be formed even in circulating fluidized bed boilers.

Nitrogen oxides are troublesome pollutants which are found in the combustion effluent streams of large utility and circulating fluidized bed boilers when fired as described above, and comprise a major irritant in smog. It is further believed that nitrogen oxides often undergo a process known as photo-chemical smog formation, through a series of re,actions in the presence of sunlight and hydrocarbons. Moreover, nitrogen oxides are a significant contributor to acid rain.

Sulfur oxides, especially S03, are also considered to be troublesome pollutants. Sulfur trioxide can combine with ammonia (NH3) in the effluent stream (such as ammonia present as a byproduct generated in a nitrogen oxides reducing process utilizing urea or the like) to form ammonium bisulfate (NH4HS04) which can form undesirable deposits on the walls and heat transfer surfaces, particularly the air heater, of the boiler.
.
Unfortunately, the high temperatures within boilers render most common methods of reducing NOx ` _ 5 _ l 334476 .
and/or so3 concentrations, such as effluent scrubbing or catalyst grids, uneconomical, infeasible, or both.

Backqround Art Many different processes and compositions have been proposed for chemically reducing nitrogen oxide levels in an effluent. These proposals call for adding chemicals, dry or in solution, directly to the effluent and can achieve significant N0x reductions. However, none have been identified which add a number of different chemicals at defined, distinct temperature zones to achieve N0x reductions of greater than 50%, and preferably greater than 75%, with commercially practical residence times.
Moreover, some of the techniques are capable of reducing N0x only at the expense of creating undesirable levels of other pollutants such as ammonia and/or carbon monoxide. Additionally, none of the prior processes is capable of achieving both reductions in nitrogen oxides as well as significant reductions in sulfur trioxide in a single unified process.

In U.S. Patent No. 3,900,554, Lyon discloses reducing nitrogen monoxide (N0) in a combustion effluent by injecting ammonia, specified ammonia precursors or their aqueous solutions into the effluent for mixing with the nitrogen monoxide at a temperature within the range of 1600F. to 2000F.
Lyon also suggests the use of reducing agents, such as hydrogen or various hydrocarbons, to permit the effective -use of ammonia at effluent temperatures as low as 1300F. Although the patent suggests staged injection of the ammonia composition, there remains no 1 33~47~

teaching of the efflcacy of lniecting distinct compositions at different temperature zones to optlmlze NOX reductlon w~thout producing a substantial amount of other pollutants.

In U.S. Patent No. 4,20~,386, Arand et al. disclose t.hat, for oxygen-rich effluents, the temperature of the effluent should be in the range of 1300F to 20~0F. for reduclng the nltrogen oxides concentratlon using urea added dry or in aqueous solutlon. Alkanoic solvents are said to be reducing agents which, like hydrogen, carbon monoxlde, etc., enable the effectlve operatlng temperature to be lowered to below 1600F.
Disclosed again is the suggestion to in~ect in incremerlts, but these incremental in.jections are of the same urea composition and must all be at positions meeting the same temperature and oxygen concentration conditions. The same holds true for U.S.
Patent No. 4,325,924 to Arand et al.

Although the prior art discloses in~ection of a composition for reducing nltrogen oxides at a number of spaced positions in, for instance, Bowers, in copending and commonly assigned U.S.
Patent No. 4,751,065, and Boers, in copending and commonly assigned U.S. Patent No. 4,719,092, each disclosure is related to the in~ection of the same composltion at locatlons in which the same conditions, such as temperature and oxygen concentration, exist.

Furthermore, althou~h the reduction of the concentration of nitrogen oxides in an effluent to as ~. .~

- 7 - ~334476 great an extent as posslble is hlghly deslrable, prlor art systems for reduclng NOx concentratlons are llmlted, not only by the amount of NOx reductlon that can be achleved utlllzlng them, but also by the amount of other pollutants, such as ammonla or carbon monoxlde, generated as byproducts of the NOx-reducing process.

What is desired, therefore, is a process for substantlally reducing the concentratlon of nltrogen oxldes and/or sulfur trloxlde in an effluent whlle malntalnlng a sultably low level of other pollutants.

Deflnltlons For the purposes of thls descrlptlon, the followlng deflnltlons shall apply "temperature zone" refers to a locale whereln, under steady state conditions, the effluent temperature is withln a certaln range;

"treatment agent" refers to a composltlon comprlsing a reductant chemical, l.e., a pollutlon reducing chemical capable of reducing NOx, sulfur oxides (SOx) or other pollutants, and, preferably, a solvent;

"urea" and "ammonia" refer to the compounds urea and ammonia themselves. Among those compounds are ammonium carbonate, ammonium formate, ammonium oxalate, ammonium hydroxlde and varlous stable amines, and their solutlons ln water;

"pollutlon lndex" refers to an index whlch lndlcates the presence of all of the pollutants in the effluent;

"oxygenated hydrocarbon" refers to substituted and unsubstituted, straight or branch-chain aliphatic and cyclic, heterocyclic and aromatic hydrocarbons having at least one oxygen either in or bonded directly to the primary hydrocarbon chain or in or bonded directly to a substituent group, and mixtures thereof, typical substituent groups of which include carboxylic acid groups (COOH), peroxide groups (-O-O-), carbonyl groups (C=O), hydroxy groups (OH), ether gtoups (-O-), ester groups (COOR), etc.;

"hydroxy amino hydrocarbon" refers to any cyclic, heterocyclic, aromatic, straight or branched chain, substituted or unsubstituted hydrocarbon having at least one substituent comprising a hydroxy or a carboxy group and at least one primary, secondary or tertiary amino group;

"a~mmonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1" refers to salts which can be formed by the neutralization of ammonium hydroxide with an organic acid, preferably a carboxylic acid (i.e., an acid having one or more carboxyl (COOH) groups). If the acid has more than one carboxylate group, they may be partially or completely neutralized by ammonium hydroxide. The ratio of carbon to nitrogen in the salt is greater than 1:1, meaning that there is more than one carbon per each nitrogen in the compound, most preferably there are at least two carbons per each nitrogen in the compound;
.
"five or six-membered heterocyclic hydrocarbon having at least one cyclic nitrogen" refers to a cyclic five g or six member hydrocarbon in which one or more of the atoms in the ring is nitrogen. The cyclic compounds can be either saturated or unsaturated;

"heterocyclic hydrocarbon having at least one cyclic oxygen" refers to a ringed hydrocarbon compound having at least one ring oxygen;

"alcohol" refers to a hydrocarbon derivative in which one or more hydrogen atoms have been replaced by a hydroxy group;

"sugar" refers to a number of useful saccharide materials which are capable of decreasing the NOx concentration in an effluent under conditions as described herein, including non-reducing and reducing water soluble mono-saccharides and the reducing and non-reducing polysaccharides and their degradation products, such as pentoses including aldopentoses, methyl pentoses, keptopentoses like xylose and arabinose, deoxyaldoses like rhaminose, hexoses and reducing saccharides such as aldo hexoses like glucose, galactose and mannose, ketohexoses like fructose and sorbose, disaccharides like lactose and malt~se, non-reducing disaccharides like sucrose and other polysaccharides such as dextrin and raffinose, hydrolyzed starches which contain as their constituents oligosaccharides, and water dispersible polysaccharides;

"furfural" refers to furfural itself as well as substituted furfural. Typical substituents include side chains comprising straight and branched-chain, substituted and unsubstituted aliphatic groups, oxygenated hydrocarbon groups and amino groups;

lo - 1 334476 .
"amino acid" refers to any organic compound containing an amine group and a carboxylic acid group;

"NH4-lignosulfonate'l and 'Icalcium lignosulfonatell refer respectively to the ammonium and calcium salts of lignosulfonic acid, which are sulfonate salts made from the lignin of sulfite pulp-mill liquors;

1l1,3 dioxolane'l refers to a five-membered heterocyclic hydrocarbon having oxygen at the 1 and 3 positions (also ethylene methylene dioxide);

"fish oil" refers to a drying oil obtained chiefly from menhaden, pilchard, sardine and herring, extracted from the entire body of the fish by cooking and compressing;

"solution" refers to any solution, mixture or dispersion, with "solvent" referring to solvent, carrier or dispersant.

Disclosure of Invention This invention relates to a process for reducing the concentration of at least one pollutant in the effluent from the combustion of a carbonaceous fuel.
One of the objectives of the invention is to achieve the desired level of pollutant control, such as a significant reduction in nitrogen oxides or sulfur trioxide concentration, while minimizing other harmful emissions such as ammonia and carbon monoxide, and m~;mi zing the utilization of the chemicals employed.

More particularly, the present invention comprises a process which serially treats the effluent from the combustion of a carbonaceous fuel by introducing different treatment agents at different effluent temperatures. For example, a first treatment agent is introduced into the effluent at a first temperature zone to reduce the effluent concentration of a first pollutant, a second treatment agent is introduced into the effluent at a second temperature zone to reduce the effluent concentration of either the first pollutant or a second pollutant, and the process is repeated, if desired, to achieve the desired level of pollutant control. The composition of each treatment agent is formulated to be effective at reducing the concentration of the target pollutant, especially nitrogen oxides or sulfur trioxide, in the effluent when introduced into the effluent at the designated temperature zone.

It has been found that nitrogen oxide and/or sulfur trioxide reduction can be improved by increasing the amount of reductant chemical employed in the treatment agent. However, a point is reached where emissions of other pollutants such as ammonia are experienced. The emission of such other pollutants is undesirable. For instance, the emission of ammonia can lead to harmful deposits of ammonium bisulfate, especially when there is sulfur trioxide in the effluent. Furthermore, carbon monoxide, another undesirable pollutant, can also be produced. This limits the amount of pollutant control possible in any one treatment step. It has also been found that different chemical formulations are effective at reducing nitrogen oxides or sulfur trioxide concentrations at different temperatures.

Moreover, it is not possible to introduce chemicals in every location in a boiler, because of design considerations. The introduction must occur in a location where space is available inside the boiler for distribution of chemicals. Introduction directly on heat exchange tubes could lead to harmful deposits and ineffective use of chemicals. As a practical matter, adequate space for introduction may typically exist in a boiler at two to four locations, and these will be at different temperatures because of the heat transfer taking place.

In the practice of this invention, nitrogen oxides reduction can be r~Y;~;zed by selecting the locations at which introduction is possible, formulating treatment agents that are effective at reducing the nitrogen oxides level at the temperature at each location, injecting the chemicals at each location to maximize reduction while avoiding other emissions such as ammonia and carbon monoxide, and controlling the introduction process as boiler load varies. For example, if boiler load drops from 100% to 50%, temperatures at each location may be lowered and changes in introductions (amount, composition, or both) may be needed.

This invention can be used to achieve a given levet of nitrogen oxides control and also to minimize the chemical cost of doing so. To accomplish this, use of the least expensive treatment agent is preferably r~;r; zed first, followed by the next least expensive treatment agent, etc., until the desired level of control is achieved.

The present invention can also be used to reduce the amount of nitrogen oxides in the effluent while also reducing the concentration of SO3 in the effluent by introducing a first, N0x-reducing treatment agent into the effluent at a first effluent - 13 - 1 334~76 temperature zone and then introducing a second, S03-reducing treatment agent into the effluent at a second effluent temperature zone. Most preferably, nitrogen oxides reductions are maximized by providing a second treatment agent which is capable of reducing both sulfur trioxide and nitrogen oxides.

Although this description is written in terms of the reduction of the concentration of nitrogen oxides and/or sulfur trioxide in the effluent, the skilled artisan will recognize that the process of this invention may be equally applicable to the reduction of other pollutants which may be found in the effluent from the combustion of a carbonaceous fuel.
Furthermore, although written in terms of utilization in a suspension-fired boiler, the description should be understood to be equally applicable to other types of units such as circulating fluidized bed boilers and moving grate boilers, both firing a variety of fuels including refuse. The description is also applicable to gas turbines.

The presence of pollutants in an effluent may be referred to as the pollution index. It will be understood that reducing the concentration of one pollutant, such as nitrogen oxides, in the effluent in a process which simultaneously leads to the generation of an equal or greater amount of another pollutant does not lower the pollution index. Likewise, reduction of the effluent concentrations of two different pollutants, such as nitrogen oxides and sulfur trioxide, leads to a reduction in the effluent pollution index greater than the reduction obtained when only one pollutant is reduced. The present invention accomplishes the reduction of nitrogen oxides while substantially avoiding the production of other pollutants such as ammonia or carbon monoxide, and/or also accomplishes the reduction of sulfur trioxide, thus effecting a net lowering of the pollution index of the effluent, by a step-wise or multi-stage process wherein a plurality of treatment fluids are introduced into the effluent at a plurality of temperature zones.

The use of the terms "first", "second" and "third"
treatment zones in this description is meant to denote relative locations of the treatment zones. For instance, the second temperature zone can be any zone where the effluent temperature is lower than the effluent temperature of the first temperature zone.
Similarly, the third temperature zone can be any zone where the effluent temperature is lower than the effluent temperature in the second temperature zone, etc. This description should not be read as indicating that any specific temperature zone for introduction must in all cases be in a location where the effluent is in a specific temperature range (i.e., the first temperature zone does not in all cases have to be in a location where the effluent temperature is in the range of about 1700F. to about 2000F., and as high as about 2100F.). Moreover, the terms "first", "second", "third", etc. are meant to be relevant with respect to the present invention only and do not exclude other effluent treatments performed either "before" (in time or location) the first treatment or "after" the third or final treatment, whether for the same or different pollutants, combust:Lon enhancement, etc.

The treatment agent to be introduced at any particular temperature zone is preferably chosen to be most effective at the effluent temperatures existing within that zone. For lnstance, if the flrst available temperature zone for introduction is in an upstream location comprising a temperature zone where the effluent temperature is in the range of about 1700F. to about 2000F or even as high as 2100F., the treatment fluid can be chosen to be that which ~s most effective in that temperature range, such as an aqueous solutlon of urea, as disclosed hy Arand et al. ln U.S. Patent No. 4,208,386, and by Bowers ln U.S. Patent No. 4,719,092 entitled "Reduction of Nitrogen-Based Pollutants Through the Use of Urea Solutions Containlng Oxygenated Hydrocarbon Solvents", or an a~ueous solutlon of ammonla, or gaseous ammonia itself, as dlsclosed by Lyon ln U.S. Patent No. 3,900,554. Although the mechanlsm by which ammonia or urea decrease the concentration of nltrogen oxldes is not fully understood, lt ls believed that they function by facilltatln~ a series of reactlons lnvolvin~
NHX radicals (x belng an lnteger) and NOX. The molar ratio of the concentration of NHX radlcals to the concentratlon of NOX
([NHX]/[NOx]) is often referred to as the normalized stoichlometrlc ratlo (NSR).

If the ~eometry of the boller permlts, two introductions can be made ln an upstream location. The first can be further upstream ln a temperature zone where the effluent temperature ls about 1850QF. to about 2000QF. and the second at a locat~on downstream from the first locatlon ln a temperature zone where the effluent temperature ls about 1700CF. to about 1850F. As lndlcated by the referenced disclosures, the urea or ammonia solution can be more concentrated (e.g., about 10% to about 50%
urea or ammonia by weight) ln the lower temperature locatlon J

and more dllute ~e.g., preferably about 5% to about 10% urea or ammonia by weight and as low as about 2%) in the higher temperature location.

Appropriate temperature zones for introduction accordlng to the present invention may also be found downstream from the zones discussed above, where the effluent temperature is in the range of about 1350~F. to about 1750~F. Suitable treatment agents for introduction into a temperature zone havlng such effluent temperatures are dlsclosed in those patent discussed above and also by Bowers in U.S. Patent No. 4,751,065 entitled "Reduction of Nitrogen- and Carbon-Based Pollutants"; copending and commonly assigned Canadian Patent Application Serial Number 558,753 entitled "Process for the Reductlon of Nltrogen Oxides in an Effluent" filed in the names of Epperly and Sullivan on February 11, 1988; copending and commonly assigned Canadian Patent Application Serial Number 560,683 entitled "Process for the Reduction of Nitrogen Oxides in an Effluent Using Sugar"
filed ln the names of Epperly and Sullivan on March 7, 1988;
copending and commonly assigned Canadlan Patent Appllcation Serlal Number 561,235 entitled "Process for the Reduction of Nitrogen Oxides ln an Effluent Using a Heterocyclic Hydrocarbon"
filed in the names of Epperly and Sullivan on March 11, 1988;
copending and commonly asslgned Canadian Patent Application Serial Number 563,g55 entitled "Process for the Reduction of Nltrogen Oxldes ln an Effluent Uslng a Hydroxy Amino Hydrocarbon" filed in the names of Sullivan and Epperly on April 12, 1988; copending and commonly assigned Canadian Patent Appllcation Serial Number 578,080 entitled "Process for the Reductlon of Nltrogen Oxides in an Effluent" filed in the names of Epperly, Sullivan and Sprague on September 21, 1988; and copending and commonly asslgned Canadian Patent Application Serlal Number 580,105 entitled "Process for the Reductlon of Nitrogen Oxldes in an Effluent" filed ln the names of Epperly, Sullivan and Sprague on October 12, 1988; copendin~ and commonly assigned Canadlan Patent Appllcatlon Serial Number 602,128 entitled "Multi-Stage Process for Reducing the Concentration of Pollutants in an Effluent Using an Ammonium Salt" filed in the names of Epperly, Peter-Hohlyn, Shulof, Jr., Sullivan and Sprague on June 8, 198g;
and copending and commonly assigned Canadian Patent Appllcatlon Serial Number 602,390 entitled "Process for Nitrogen Oxides Reduction Wlth Minimization of the Production of Other Pollutants" filed in the names of Epperly, O'Leary, Sullivan and Sprague on June 8, 1989. The disclosed treatment agents include aqueous solutions of ammonia or urea, enhanced with suitable enhancers such as hexamethylenetetramine ~HMTA), a paraffinic hydrocarbon, an olefinic hydrocarbon, an aromatic hydrocarbon, an oxygenated hydrocarbon (such as acetone, sugar, especially sucrose, d-galactose and molasses, an alcohol, especially ethylene glycol, methanol, furfurylalcohol, 1,3 butylene glycol, tetrahydrofuryl alcohol, 2,5-furandimethanol, a lignin derivative, especially NH4-lignosulfonate and calcium lignosulfonate, a carboxylic acid, especially 2-furolc acld, gluconlc acid, citric acid, formic acid, coumalic acid, 2,3,4,5-tetracarboxylic acid, furylacrylic acld, barbituric acid, oxalic acid and muclc acid, a peroxlde, an aldehyde, an ether, an ester, a ketone, glycerln, tetrahydrofuran, acetone, 1,3 dioxolane, 1,4 dioxane, tetrahydrofuran, furfurylamine, n-butyl acetate, methylal, furan fish oil, furfuryl acetate, tetrahydrofurantetrahydrofurylamine,tetrahydropyran, mannitol, hexamethylenediamine and acetic anhydride), an ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1 (such as ammonium acetate, ammonium and diammonium adipate, ammonium benzoate, ammonium binoxalate, ammonium caprylate, ammonium, diammonium and triammonium citrate, ammonium crotonate, ammonium and diammonium dodecanoate, ammonium and diammonium fumarate, ammonium heptanoate, ammonium linolenate, ammonium and diammonium malate, ammonium mono butyrate, ammonium oleate, ammonium and diammonium pthalate, ammonium propionate, ammonium salicylate, ammonium and diammonium succinate ammonium and diammonium tartarate, and ammonium, diammonium and triammonium trimellitate), a hydroxy amino hydrocarbon (such as alkanolamines, amino acids and protein-containing compositions), a heterocyclic hydrocarbon having at least one cyclic oxygen (such as furfural and derivatives of furfural), a five or six membered heterocyclic hydrocarbon having at least one cyclic nitrogen (such as piperazine, piperidine, py~ridine, pyrazine, pyrazole, imidazole, oxazolidone, pyrrole, pyrrolidine), hydrogen peroxide, guanidine, guanidine carbonate, biguanidine, guanylurea sulfate, melamine, dicyandiamide, calcium cyanamide, biuret, 1,l' azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea and mixtures thereof, as well as aqueous solutions of the enhancers themselves.

The geometry of the boiler may also permit more than one temperature zone for introduction within the effluent temperature range of about 1350F. to about 1750F. For example, an introduction can be made at a location in a temperature zone where the effluent temperature is in the range of about 1550F. to about 1750F. A second location for introduction can be in . lg a temperature zone where the effluent temperature ls in the range of about 1350~F to about 1550F. The treatment agent introduced ln the second of the indlcated temperature zones can be slmilar to that of the flrst or can be less dllute, or comprise a different enhancer concentration, etc., as would be famillar to the skllled artlsan upon readlng the referenced dlsclosures.

Another temperature zone ln a boller at whlch introductlon may be made ls at the locatlon where the effluent temperature ls below about 1400~F. As dlsclosed by copendlng and commonl~
asslgned Canadian Patent Application Serlal Number 560,672 entitled "Process for Nitrogen Oxides Reductlon with Mlnlmlzatlon of the Productlon of Other Pollutants" flled ln the names of ~pperl~, O'Leary, Sulllvan and Sprague on March 4, 1988, a sultable treatment agent for lntroductlon lnto the effluent at such effluent temperatures comprises a hydrocarbon, especlally an oxygenated hydrocarbon such as ethylene glycol, sugar or furfural, or hydrogen peroxide. More than one temperature zone for lntroductlon of a treatment agent can also be located wlthln the lower effluent temperature locatlons ln the boller.

In a preferred embodlment, the process comprises J.n~ectin~
a first treatment agent lnto the effluent at a flrst temperature zone. For lnstance, in a large suspension-fired utlllty boiler, the location of f`
` .~

-introduction of the first treatment fluid can be upstream from the superheater, such that the effluent temperature in the first temperature zone is greater than about 1700-F. The composition and amount of the first treatment agent can then be chosen to provide effective reduction of NOX concentration in an effluent which is at temperatures greater than about 1700F. while minimizing the production of ammonia.
Suitable formulations for use as the first treatment agent are those comprising aqueous solutions of urea or ammonia, or gaseous ammonia.

The urea or ammonia aqueous solution functioning as the first treatment agent is preferably introduced at a number of spaced positions within the first temperature zone from nozzles or other apparatus which are effective to uniformly form and disperse droplets of the solution within the flowing effluent stream to achieve uniform mixing.

The rate of introduction of the first treatment agent into the effluent at the first temperature zone is preferably that rate which achieves m~imum N0x-concentration reduction up until the point of "ammonia breakthrough". "Ammonia breakthrough" is a term used in the art which refers to the point where a significant increase in the NH3 concentration with rate of introduction is observed. The actual rate of introduction of the first treatment agent is determined experimentally by "tuning" the ratè of introduction to achieve the conditions described above, because the actual rate will vary with effluent stream flow rate, as well as the particular temperature at that temperature zone, which can vary within the given range due to the load at which the boiler is fired. Advantageously, in the situation where the temperature range within the first temperature zone is greater than about 1700F., and the first treatment agent is a solution comprising urea or ammonia, the molar ratio of the nitrogen in the first treatment agent to the baseline nitrogen oxides level is about 1:5 to about 5:1, more preferably about 1:3 to about 3:1, and most preferably about 1:2 to about 2:1.

The temperature of the effluent will have an influence on the concentration of urea or ammonia in the solution. At temperatures of between about 1700~F. and about 1850F., the solution will tend to operate most effectively at concentrations of about 10 to about 50 weight percent. Contrariwise, at temperatures of greater than about 1850F., the concentration of the solution will typically be more dilute, such as about 2 to about 10 weight percent.
Alternatively, when the effluent temperature is in the range of about 1700F. to about 1850F., the urea or ammonia solution which comprises the first treatment agent may be enhanced by the addition of hexamethylenetetramine. Other enhancers which may be suitable for use include oxygenated hydrocarbons as described above, guanidine, guanidine carbonate, biguanidine, guanylurea sulfate, melamine, dicyandiamide, calcium cyanamide, biuret, 1,1'-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea, and mixtures thereof. It is also understood that the first treatment agent can comprise gaseous ammonia. In addition, depending on boiler configuration, it is anticipated that at least two temperature zones (e.g., one at a location where the effluent temperature is about 1850F. to about 2000F. and another at a location where the effluent - 22 - l 3344~6 temperature is about 1700-F. to about 1850F.) may be possible and/or desired upstream from the superheater, as discussed above.

The process of this invention preferably further comprises injecting a second treatment agent into the effluent at a second treatment zone located downstream from the first temperature zone. For instance, in a large suspension-fired utility boiler, the second temperature zone can advantageously be at a location downstream from the superheater, where the temperature in the second temperature zone will typically be in the range of about 1350F. to about 1750~F. However, as discussed above, the second temperature can be any defined zone having temperatures lower than the first temperature zone, e.g., it may be above or below the temperature of about 1350F. to about 1750 F. so long as it is below that of the first temperature zone.
The composition of the second treatment agent is then preferably chosen to achieve optimal nitrogen oxides reduction without ammonia breakthrough in this temperature zone. Advantageously, the second treatment agent for use under these conditions comprises a mixture of urea or ammonia and an enhancer, or the enhancer alone. Suitable enhancers which may be used include HMTA, a paraffinic hydrocarbon, an olefinic hydrocarbon, an aromatic hydrocarbon, an oxygenated hydrocarbon, as described above, an ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than l:l, as described above, a hydroxy amino hydrocarbon, as described above, a heterocyclic hydrocarbon having at least one cyclic oxygen, as described above, a five or six membered heterocyclic hydrocarbon having at least one cyclic nitrogen, as described above, hydrogen peroxide, guanidine, guanidine carbonate, biguanidine, ~ - 23 - 1 334476 guanylurea sulfate, melamine, dicyandiamide, calcium cyanamide, biuret, 1,1'-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea and mixtures thereof, as well as aqueous solutions of the enhancers themselves. The most preferred enhancers under these conditions are ethylene glycol, ammonium acetate, pyridine, methanol, sugar and furfural.

The second treatment agent is introduced into the effluent to provide a molar ratio of nitrogen in the agent to the baseline nitrogen oxides concentration suitable to maximize the reduction of NOx concentrations in the second temperature zone while minimizing the production of other pollutants, such as ammonia or carbon monoxide. Preferably, the mixture, when comroced as described above, is introduced so as to provide a molar ratio of nitrogen in the mixture to the baseline nitrogen oxides level of about 1:5 to about 5:1, more preferably about 1:3 to about 3:1 and most preferably about 1:2 to about 2:1. The enhancer is present in the agent in a weight ratio of enhancer to urea or ammonia of, preferably, about 1:10 to about 5:1, more preferably about 1:5 to about 3:1. Most preferably, the weight ratio of enhancer to urea or ammonia in the ammonia/enhancer agent is about 1:4 to about 2.5:1. In the instance where the treatment agent does not contain any nitrogen-containing compounds, the weight ratio of treatment agent to the baseline nitrogen oxides level should be about 0.5:1 to about 10:1.

Typically, the agent is prepared by dissolving a water-soluble enhancer in water at a concentration of about 5 to about 25 weight percent, more preferably about 10 to about 20 weight percent, and the desired amount of urea or ammonia mixed in. The resulting mlxture ls then lntroduced lnto the effluent at a number of spaced posltlons wlthln the second temperature zone from nozzles or other apparatus whlch are effective to unlformly form a dlsperse droplets of the solutlon wlthin the flowlng effluent stream to achleve uniform mixing. As discussed above, there can be at least two temperature zones, if desired and boiler conflguration permlts, within the indlcated effluent temperate range with at least two treatment agents lntroduced therelnto.

Addltlonally, the second treatment agent can be used to perform ammonla scrubbing, as dlsclosed by copendlng and commonly asslgned Canadian Patent Application Serial Number 584,625 entltled "Ammonla Scrubblng" flled ln the names of Epperly, Peter-Hoblyn and Sulllvan on November 30, 1988.
Ammonla scrubblng lnvolves the lntroductlon of a non-nltrogenous treatment agent such as a hydrocarbon, especlally an oxygenated hydrocarbon, at an effluent temperature of greater than about 1350F. Under condltlons effectlve to reduce the amount of ammonla ln the effluent, whlle also achlevlng further nltrogen oxldes reductlons. Generally, the non-nltrogenous treatment agent ls lntroduced into the effluent at a welght ratlo of treatment agent to effluent ammonla level of about 2:1 to about 200:1.

A more preferred embodiment of the present invention comprlses lntroductlon of a thlrd treatment agent lnto the effluent at a third temperate zone, wherein the third temperature zone ls located sequentlally downstream from the flrst and second temperature zones. For instance, ln a - 25 - l 334476 suspension-fired utility boiler, the third temperature zone can advantageously be located after the economizer where the effluent temperature will be within the range of about 800~F. to about 1400-F.
Under these conditions, the third treatment agent preferably comprises a hydrocarbon or hydrogen peroxide. The most preferred hydrocarbons suitable for use in the third treatment fluid under the indicated conditions are oxygenated hydrocarbons such as low molecular weight ketones, aldehydes, mono, di or polyhydric alcohols of aliphatic hydrocarbons and hydroxy amino hydrocarbons such as monoethanolamine and amino acetic acid (glycine). Ethylene glycol, methanol, furfural, sugar and glycerol are preferred oxygenated hydrocarbons for this purpose, with ethylene glycol, methanol and sugar being most preferred. Other hydrocarbons . which can advantageously be employed include nitrogenated hydrocarbons such as monomethylamine, triethylene tetramine, hexamethylenediamine, tetraethylene pentamine, bis-hexamethylene triamine, polyamine HpA, 1,2-diaminopropane, N,N-dimethylethylenediamine, tetramethylethylenediamine, 2-methylaziridine, bis (3-aminopropyl) ethylenediamine, tetramethyl-dia~inomethane, ethylenediamine and diethylene-triamine. Mixtures of polyols, such as those mixtures of low molecular weight polyols known as hydrogenated starch hydrosylates, can also be advantageously employed. Additional hydrocarbons which are suitable for use in the present invention include paraffinic, olefinic and aromatic hydrocarbons, including naphtha-based hydrocarbons, and mixtures thereof.

~ The hydrocarbon can be used alone in its pure form, in dispersions, preferably aqueous dispersions or in solution, preferably aqueous solution due to the - 26 - l 334476 economy of aqueous solutions, although there may be instances where other solvents may be advantageously used, either alone or in combination with water, as would be known to the skilled artisan. The level of the hydrocarbon employed should be that level necessary to elicit optimal reductions in the concentration of nitrogen oxides in the effluent while also minimizing the presence of other pollutants, such as ammonia and carbon monoxide. Advantageously, the hydrocarbon is employed at a weight ratio of hydrocarbon to the third baseline nitrogen oxides level of about 1:5 to about 5:1, most preferably about 1:2 to about 2:1. The exact amount of hydrocarbon employed may vary depending upon the overall economics of the process.

A hydrocarbon, when utilized as the third treatment agent according to this invention, is preferably introduced into the effluent at a number of spaced positions within the third temperature zone from nozzles or other apparatus which are effective to uniformly form and disperse droplets of the hydrocarbon, either alone or in a dispersion or solution as discussed above, within the flowing effluent stream to achieve uniform mixing. Depending on boiler configuration, there can be two zones of introduction in the temperature range of about 800F.
to about 1400F.

Advantageously, the process of the present invention can be used to reduce the concentration of sulfur trioxide in the effluent in addition to the N0x reductions and ammonia scrubbing obtained. The introduction of a treatment agent which comprises hydrogen peroxide or a hydrocarbon, especially an oxygenated hydrocarbon such as alcohols, sugars, lignin derivatives, carboxylic acids, peroxides, aldehydes, ethers, esters, ketones, and mixtures thereof, into the effluent at a temperature zone where the effluent temperature is below about 1700-F., especially no greater than about 1450-F. will significantly reduce the S03 content of the effluent. The most preferred oxygenated hydrocarbons for this purpose include methanol, ethylene glycol, molasses, glycerin, tetrahydrofuran, acetone, citric acid, sucrose, and mixtures thereof, which can be introduced as an aqueous solution at a ratio of hydrocarbon to sulfur trioxide of about 3:1 to about 8:1 by weight. The reduction of S03 in the effluent is in addition to the N0x reduction and/or ammonia scrubbing achieved with the disclosed treatment agents.

It will be recognized that the use of the terms "first", "second" and "third" herein is merely for the sake of convenient description. The actual numbering sequence will vary depending on the actual number of temperature zones chosen and the number of treatment agents introduced in each situation. This number can vary depending on boiler geometry (as discussed above) and the particular pollutant level desired.

The effluent from the combustion of a carbonaceous fuel into which the treatment agents disclosed herein according to the present invention are introduced is generally oxygen-rich, meaning that there is an excess of oxygen in the effluent. Typically, the excess of oxygen is about 15% by volume or less. In conventional utility boilers, the excess of oxygen is in usually the range of about 1% to about 10% by volume.

- 28 - ~ 334476 In practicing the process of the present invention to m~x;~;ze the reduction of the concentration of nitrogen oxides in the effluent or to achieve a specified level of NOx, it is preferred to first "tune" the introduction of the first treatment agent into the first temperature zone to optimize the introduction (i.e., m~;m;ze pollutant concentration reduction and minimize production of other pollutants). The introduction of the second treatment agent into the second temperature zone is then "tuned", the introduction of the third treatment agent into the third temperature zone (when a third treatment agent and third temperature zone are used) is advantageously "tuned" third, the introduction of the fourth treatment agent into the fourth temperature zone (when a fourth treatment agent and fourth temperature zone are used) is preferably "tuned"
fourth, etc., until the desired number of introductions or level of pollutants is reached.

Once the introduction of treatment agents is optimized, it is also possible to "adjust" the treatment agents, by altering the dilution, relative concentration or particular components of the chemical formulation of the treatment agent, to compensate for changes in boiler operating load, which results in changes of effluent temperature at the locations at which treatment agents are introduced. Adjusting the treatment agents in response to boiler operating load changes ensures that the treatment agent introduced at each location is appropriate to maintain nitrogen oxides at specified levels or to maximize NOx reductions for the effluent temperature existing there. Otherwise, inefficient and non-optimized introduction of treatment agents may occur, resulting in lowering of pollutant reductions achieved and, ~ potentially, the generation of substantial amounts of other pollutants.

The identity of other pollutants which comprise the limiting emissions can vary from boiler to boiler, situation to situation, or temperature zone to temperature zone. For instance, at temperature zones where the effluent temperature is relatively high, the limiting emission can be ammonia, whereas at temperature zones where the effluent temperature is relatively low, the limiting emission can be carbon monoxide. Furthermore, it may not be necessary in each case to "tune" the introduction at each temperature zone. Rather, it may be desirable to achieve maximum possible target pollutant reduction at earlier temperature zones irrespective of the production of other emissions, provided that the level of such other emissions can be reduced at later, or the last, temperature zones, especially when a process step involving ammonia scrubbing is utilized. In other words, it is the pollution index after the final introduction that is most significant, not the pollution index at intermediate levels.

Alternatively, to obtain a target level of NOx reduction while minimizing chemical cost, ~x;~um use of the least expensive of the treatment agents without significant production of other pollutants is first established. The use of the next least expensive treatment agent is m~x;m; zed next, and this process is repeated until the desired target level is reached.

Moreover, the introduction of each treatment agent may be performed in a manner so as to minimize the generation of other pollutants such as ammonia or carbon monoxide while maximizing the reduction of the 1 33~476 ~0 target pollutant, e.g. nitrogen oxldes or sulfur trioxlde. Thls can be accomplished throu~h use of the nitrogen oxldes reductlon versus effluent temperature curve as taught by copending and commonly assigned Canadian Patent Appllcation Serlal Number 566,246 entltled "Process for Nltrogen Oxldes Reductlon and Mlnlmizatlon of the Productlon of Other Pollutants" filed in the names of Epperly, O'Leary and Sulllvan on May 6, 1988.

It wlll be further understood that when economlcs, boiler load, target NOx levels or other conslderatlons dlctate, what was the second temperature zone ln one situation can become the flrst temperature zone in another, and what was the third temperature zone in one situation can become the second temperature zone ln another, etc. Moreover, the difference between any two consecutive treatment agents may be the dilution of the solutlons whlch comprlse the treatment agents.

It will also be recognized by the skilled artisan that the process of the present lnventlon can be comblned wlth NOx reduclng process whlch utlllzes selectlve catalytic reductlon ("SCR") to reduce nltrogen oxides. Such an SCR process utllizes compounds of catalytlc materlals such as oxldes or lron, vanadium and activated carbon to reduce the NOx content of effluents. In fact, the SCR treatment can be used as an addltional stage in the process of this invention. To do so, the process dlsclosed hereln is practlced to reduce the nltrogen oxldes concentratlon ln the effluent and also to ad~ust the ammonia remaining ln the effluent to approxlmately a 1:1 ratlo of ammonia to the nitrogen ~' '''`~
~J

oxides remalning ln the effluent by ammonla scrubbing or other means achlevable by the practice of the present invention, and then scrubbing the effluent with SCR to reduce the effluent NOx levels even further. In this way, the most advantageous aspects of both the non-catalytic, free radical reduction of nitrogen oxides disclosed herein and SCR can both be obtained, resulting in extremely hlgh NOx reductlons wlthout significant amounts of other pollutants such as NH3 or CO remaining in the effluent.

Summary of the Invention In accordance with the present invention, there ls provided a process for reducing the concentration of nitrogen oxides, sulfur trloxlde or both in the effluent from the combustion of a carbonaceous fuel, the process comprising: a) introducing a first treatment agent selected from the group consistlng of gaseous ammonla, and an aqueous solution of urea or ammonia and mlxtures thereof into the effluent at a first temperature zone in order to reduce the concentration of nitrogen oxides in the effluent; and b) lntroducing a second treatment agent selected from the group consistlng of urea, ammonla, hexamethylenetetramine, an oxygenated hydrocarbon, a parafflnic hydrocarbon, an oleflnlc hydrocarbon, an aromatic hydrocarbon, an ammonlum salt of an organic acid having a carbon to nltrogen ratio of greater than l:l, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon havlng at least one cycllc oxygen, a five or six-membered heterocycllc hydrocarbon having at least one cyclic nltrogen, hydrogen peroxlde, ~uanidlne, guanidlne carbonate biguanidlne, guanylurea sulphate, melamlne, dlcyandlamlde, calclum cyanamide, biuret, l,l~azoblsformamlde, methylol urea, methylol urea-urea condensatlon product, dlmethylol urea, methyl urea, dlmethyl urea, and mlxtures thereof lnto the effluent at a second temperature zone in order to reduce the concentration of nltrogen oxides, sulphur trioxlde, or both in the effluent, wherein said first and second treatment agents are lntroduced under condltions effective to lower the effluent pollutlon lndex.

~ ' ~....

In accordance wlth another aspect of the present lnvention, there is provided a process for the reduction of the concentratlon of nltrogen oxldes ln the effluent from the combustion of a carbonaceous fuel, the process comprising selectlng a plurallty of locatlons for lntroductlon of chemlcal formulatlons and introducing at each of said locations at least one chemlcal formulatlon, selected from the group conslstlng of urea, ammonia, hexamethylenetetraamine, an oxygenated hydrocarbon, a paraffinic hydrocarbon, an oleflnlc hydrocarbon, an aromatlc hydrocarbon, an ammonium salt of an organic acld havlng a carbon to nitrogen ratio of greater than 1:1, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon having at least one cycllc oxygen, a flve or slx-membered heterocycllc hydrocarbon havlng at least one cyclic nltrogen, hydrogen peroxlde, guanidine, guanidine carbonate, biguanidine, guanylurea sulphate, melamine, dicyandiamlde, calclum cyanamlde, bluret, l,l-azobisformamlde, methylol urea, methylol urea-urea condensatlon product, dlmethylol urea, methyl urea, methyl urea, and mlxtures thereof, effective to reduce the concentratlon of nltrogen oxides at the effluent temperature exlstlng at sald locatlon, such that optimlzatlon of the level of ln~ectlon at each of said locatlons leads to the reduction of the level of nitrogen oxides below a predetermined target level.

In accordance with another aspect of the present invention, there is provided a process for the reductlon of the concentratlon of nltrogen oxldes ln the effluent from the combustlon of a carbonaceous fuel to a predetermlned target level at mlnlmum cost, the process comprlslng selectlng a plurallty of locatlons for lntroductlon lnto the effluent;
selecting at least one chemlcal formulation selected from the group conslstlng of urea, ammonia, hexamethylenetetraamine, an oxygenated hydrocarbon, a parafflnlc hydrocarbon, an oleflnlc hydrocarbon, an aromatlc hydrocarbon, an ammonlum salt of an organlc acid havlng a carbon to nitrogen ratio of greater than 1,1, a hydroxy amlno hydrocarbon, a heterocycllc hydrocarbon ., ~
~J

~ - 31B -having at least one cyclic oxygen, a five or six-membered hetero-cyclic hydrocarhon having at least one cyclic nitrogen, hydrogen peroxlde, guanldlne, guanldlne carbonate, blguanldlne, guanylurea sulphate, melamine, dicyandlamlde, calclum cyanamide, bluret, l,l-azoblsformamlde, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea, and mlxtures thereof, for lntroductlon onto each of sald locations, each of said chemical formulations being effective at the reduction of the concentration of nitrogen oxides at the effluent temperature existing at the location into which said chemical formulation is lntroduced; and introduclng sald chemlcal formulations into the effluent, whereln the sequence of lntroductlon comprlses introduclng the least expensive formulation first, and repeating the introduction procedure with the remalnlng chemlcal formulatlons untll the predetermlned target level is attalned.

In accordance with another aspect of the present invention, there ls provlded a process for reduclng the concentratlon of nltrogen oxides, and sulphur trioxide or ammonia in the effluent from the combustion of a carbonaceous fuel, the process comprislng: a) introducing a flrst treatment agent selected from the group conslsting of urea, ammonia, hexamethylenetetramlne, an oxygenated hydrocarbon, a paraffinlc hydrocarbon, an oleflnlc hydrocarbon, an aromatlc hydrocarbon, an ammonlum salt of an organlc acld havlng a carbon to nltrogen ratio of greater than 1:1, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon having at least one cyclic oxygen, a five or six-membered heterocyclic hydrocarbon havlng at least one cyclic nitrogen, hydrocarbon peroxlde, guanidlne, guanldine carbonate, biguanldlne, guanylurea sulphate, melamlne, dlcyandlamide, calcium cyanamlde, bluret, l,l-azoblsformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea, and mixtures thereof, into the effluent at a first temperature zone to reduce the concentration of nitrogen oxides; and b) lntroducing a second treatment agent comprlslng an oxygenated hydrocarbon lnto the effluent at a second temperature zone to reduce the concentratlon of sulphur trloxlde or ammonla, whereln sald flrst and second treatment agents are lntroduced under condltions effectlve to lower the effluent pollutlon lndex.

In accordance wlth another aspect of the present lnventlon, there ls provlded a process for reduclng the concentratlon of nltrogen oxldes ln the effluent from the combustlon of a carbonaceous fuel, the process comprlslng: a) lntroduclng lnto the effluent a treatment agent whlch comprises any of urea, ammonla, hexamethylenetetramlne, a parafflnlc hydrocarbon, an oleflnlc hydrocarbon, an aromatic hydrocarbon, an oxygenated hydrocarbon, an ammonlum salt of an organlc acld havlng a carbon to nltrogen ratlo of greater than 1:1, a hydroxy amlno hydrocarbon, a heterocycllc hydrocarbon having at least one cycllc oxygen, a five or six-membered heterocyclic hydrocarbon havlng at least one cycllc nltrogen, hydrogen peroxlde, guanldlne, guanldlne carbonate, blguanldine, guanylurea sulphate, melamlne, dlcyandlamlde, calclum cyanamlde, bluret, l,l-azoblsformamide, methylol urea, methylol urea-urea condensatlon product, dlmethylol urea, methyl urea, dlmethyl urea, and mixtures thereof under conditions effective to effect a free radlcal nltrogen oxldes reduclng process; and b) contacting the effluent with a compound of catalytic material under condltlons effectlve to effect a selectlve catalytlc nitrogen oxides reducing process, whereln sald nitrogen oxldes reduclng processes are effected under condltlons effectlve to lower the effluent pollutlon index.

Best Mode for Carrylng Out the Invention The followlng examples further lllustrate and explaln the lnvention by detalling the operation of the process for reducin~
nitrogen oxides concentratlon by multl-stage lntroductlon.

Example I

The burner used in this example is a burner havlng an effluent flue conduit, known as a combustlon tunnel, approxlmately 209 lnches ln length and havlng an lnternal dlameter of 8 lnches and walls 2 inches thlck. The burner hss a flame area ad~acent the effluent entry port and flue gas monltors ad~acent the effluent exit port to measure the concentration of compositions such as nitrogen oxides, sulfur oxides, ammonia, carbon monoxide, carbon dioxide, percent excess oxygen and other compounds of lnterest which may be present ln the effluent. The effluent flue condult addltlonally has thermocouple ports for temperature measurement at various locations. The temperature of the effluent into which the treatment agents are introduced ls measured at the polnt of introduction utilizing a K-type thermocouple.

,~3;~5 ", ~.f Atomlzing ln~ectors descrlbed ln copendlng and commonly asslgned Canadlan Patent Application Serial Number 557,776 entltled "Process and Apparatus for Reduclng the Concentratlon of Pollutants in an Effluent" filed in the name of Burton on January 29, 1988, are posltioned through ports in the effluent flue conduit in order to introduce (by in~ecting) and distribute the NOx-reducing agents into the effluent stream. The burner fuel is a Number 2 fuel oil, and the burner is fired at a rate of 9.6 lbs/hr to 10.9 lbs/hr.

A basellne nltrogen oxldes concentration reading is taken prior to beginning each run to calculate the ratlo of agents lntroduced and to facilitate the calculation of the reductlon in nitrogen oxides concentration, and a nitrogen oxides reading is taken durlng introduction of each of the treatment agents to calculate the reduction in the nltrogen oxides concentration in the effluent elicited by each of the agents introduced.

Seven runs were made employlng the treatment agents descrlbed below. In each, a flrst treatment agent ls introduced lnto the effluent at the lndicated temperature. The second treatment agent is introduced into the effluent flue conduit at a positlon 43 lnches downstream from the flrst treatment agent lntroductlon polnt and the thlrd treatment agent, when used, is lntroduced at a posltlon 40 lnches downstream from the second treatment agent introduction point.

1. An aqueous solution comprising 10% by weight of urea and 0.2% by weight of a commercially available surfactant is lntroduced as the flrst , I

~ 33 1 334476 treatment agent at a rate of 100 ml/hr. into the effluent which is at a temperature of 1810F.; and an aqueous solution comprising 5% by weight of urea, 25%
by weight of ethylene glycol and 0.1% by weight of a co~rcially available surfactant is introduced as the second treatment agent at a rate of 200 ml/hr. into the effluent which is at a temperature of 1600F.

2. An aqueous solution comprising 10% by weight of urea and 0.2% by weight of a commercially available surfactant is introduced as the first treatment agent at a rate of 200 ml/hr. into the effluent which is at a temperature of 1765F.; and an aqueous solution comprising 5% by weight of urea, 25%
by weight of ethylene glycol and 0.1% by weight of a commercially available surfactant is introduced as the second treatment agent at a rate of 200 ml/hr. into the effluent which is at a temperature of 1545F.

3. An aqueous solution comprising 10% by weight of urea and 0.2% by weight of a commercially available surfactant is introduced as the first treatment agent at a rate of 100 ml/hr. into the effluent which is at a temperature of 1760F.; and an aqueous solution comprising 10% by weight of urea, 30%
by weight of sucrose and 0.2% by weight of a commercially available surfactant is introduced as the second treatment agent at a rate of 200 ml/hr. into the effluent which is at a temperature of 1540F.

4. An aqueous solution comprising 10% by weight of urea and 0.2% by weight of a commercially available surfactant is introduced as the first treatment agent at a rate of 200 ml/hr. into the effluent which is at a temperature of 1765F.; and an aqueous solution comprising 7.28% by weight of urea, -3.12% by weight of hexamethylenetetraamine, 15% by weight of ethylene glycol and 0.208% by weight of a commercially available surfactant is introduced as the second treatment agent at a rate of 200 ml/hr. into the effluent at a temperature of 1545~F.

5. An aqueous solution comprising 10% by weight of urea and 0.2~ by weight of a co~m~rcially available surfactant is introduced as the first treatment agent at a rate of 200 ml/hr. into the effluent which is at a temperature of 1790-F.; an aqueous solution comprising 10% by weight of urea, 30%
by weight of sucrose and 0.2% by weight of a commercially available surfactant is introduced as the second treatment agent at a rate of 100 ml/hr. into the effluent at a temperature of 1560F.: and an aqueous solution comprising 15% by weight of sucrose is introduced as the third treatment agent at a rate of 100 ml/hr. into the effluent at a temperature of 1305F.

6. An aqueous solution comprising 10% by weight of urea and 0.2% by weight of a commercially available surfactant is introduced as the first treatment agent at a rate of 200 ml/hr. into the effluent which is at a temperature of 1790F.; an aqueous solution comprising 10% by weight of urea, 30%
by weight of sucrose and 0.2% by weight of a commercially available surfactant is introduced as the second treatment agent at a rate of 100 ml/hr. into the effluent at a temperature of 1560F.; and an aqueous solution comprising 15% by weight of glycerol is introduced as the third treatment agent at a rate of 100 ml/hr. into the effluent which is at a temperature of 130SF.

7. An aqueous solution comprising 10% by weight of urea and 0.2% by weight of a commercially available surfactant is introduced as the first treatment agent at a rate of 200 ml/hr. into the effluent which is at a temperature of 1750F.; an aqueous solution comprising 10% by weight of urea, 30~
by weight of sucrose and 0.2% by weight of a commercially available surfactant is introduced as the second treatment agent at a rate of 100 ml/hr. into the effluent at a temperature of 1530F.; and kerosene is introduced as the third treatment agent at a rate of 100 ml/hr. into the effluent which is at a temperature of 1295-F.

The results of the above-described runs are set out in Table 1.

Table 1 Run Nx NOx % reduction NH3 Baseline Final ppm ppm ppm 1 240 120 S0.0 4 2 218 75 65.6 21 3 220 92 58.2 19 4 218 83 61.9 30 -210 42 80.0 21 6 210 39 81.4 --- 36 - l 334476 ~~ Table 1 (cont.) Run Nx N0x % reduction NH3 Baseline Final ppm ppm ppm 7 210 50 76.2 --Examle II

The boiler used is a front fired coal design with a nominal 140 megawatt (thermal) per hour input. The temperature of the effluent which is measured at the first level of introduction is approximately 1900F.
with an excess of oxygen of about 4.5% and the temperature of the effluent at the second level of introduction is approximately 1750-F. with an excess of oxygen of about 8.2%.

An aqueous solution comprising 8.6% by weight of urea and 0.17% by weight of a commercially available surfactant is introduced as the first treatment agent at à rate of 754 gallons/hr. to provide a normalized stoichiometric ratio (NSR) of treatment agent to baseline nitrogen oxides level of 1.79 and an aqueous solution comprising 16.5~ by weight of urea and 0.33%
by weight of a commercially available surfactant is introduced as the second treatment agent at a rate of 91 gallons/hr. to provide an NSR of treatment agent to baseline nitrogen oxides level of 0.41.

The baseline NOX level is measured at 693 ppm and the NOX level measured during introduction of the first treatment agent, measured upstream from 37 ~ 1 334476 introduction of the second treatment agent, is approximately 251 ppm. The NOx level measured during introduction of the first and second treatment agents is 145 ppm, which is an 79.1~ reduction from the original baseline NOx level (all NOx levels are corrected so as to be standardized to 3~ oxygen).

It will be apparent that by practice of the present invention, superior NOx reductions can be elicited without significant ammonia breakthrough.

The above description is for the purpose of teaching the person of ordinary skill in the art how to practice the present invention, and it is not intended to detail all of those obvious modifications and variations of it which will become apparent to the skilled worker upon reading the description. It is intended, however, that all such obvious modifications and variations be included within the scope of the present invention which is defined by the following claims.

Claims

1. A process for reducing the concentration of nitrogen oxides, sulfur trioxide or both in the effluent from the combustion of a carbonaceous fuel, the process comprising:
a. introducing a first treatment agent selected from the group consisting of gaseous ammonia, and an aqueous solution of urea or ammonia and mixtures thereof into the effluent at a first temperature zone in order to reduce the concentration of nitrogen oxides in the effluent; and b. introducing a second treatment agent selected from the group consisting of urea, ammonia, hexamethylenetetramine, an oxygenated hydrocarbon, a paraffinic hydrocarbon, an olefinic hydrocarbon, an aromatic hydrocarbon, an ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon having at least one cyclic oxygen, a five or six-membered heterocyclic hydrocarbon having at least one cyclic nitrogen, hydrogen peroxide, guanidine, guanidine carbonate biguanidine, guanylurea sulphate, melamine, dicyandiamide, calcium cyanamide, biuret, 1,1-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea, and mixtures thereof into the effluent at a second temperature zone in order to reduce the concentration of nitrogen oxides, sulphur trioxide, or both in the effluent, wherein said first and second treatment agents are introduced under conditions effective to lower the effluent pollution index.

2. The process of claim 1 wherein the effluent temperature at said first temperature zone is about 1700° F. to about 2100° F.

3. The process of claim 1 wherein the effluent temperature at said first temperature zone is about 1850° F. to about 2100° F. and the effluent temperature at said second temperature zone is about 1700° F. to about 1850° F.

4. The process of claim 3 wherein said first treatment agent comprises an aqueous solution comprising about 2% to about 10%
of urea or ammonia and said second treatment agent comprises an aqueous solution comprising about 10% to about 50% of urea or ammonia.

5. The process of claim 3 wherein said first treatment agent comprises gaseous ammonia or an aqueous solution of urea or ammonia and said second treatment agent comprises an aqueous solution of urea or ammonia, wherein said second treatment agent further comprises a composition selected from the group consisting of hexamethylenetetramine and an oxygenated hydrocarbon.

6. The process of claim 3 which further comprises introducing a third treatment agent into the effluent at a third temperature zone.

7. The process of claim 6 wherein the effluent temperature at said third temperature zone is about 1350° F. to about 1750° F.

8. The process of claim 6 wherein the effluent temperature at said third temperature zone is below about 1400° F.

9. The process of claim 1 wherein the effluent temperature at said second temperature zone is about 1350° F. to about 1750° F.

10. The process of claim 1 wherein said oxygenated hydrocarbon is selected from the group consisting of acetone, sugar, an alcohol, a lignin derivative, a carboxylic acid, a peroxide, an aldehyde, an ether, an ester, a ketone, glycerin, tetrahydrofuran, acetone, NH4,-lignosulfonate, calcium lignosulfonate, 1,3 dioxolane, 1,4 dioxane, furfurylamine, n-butyl acetate, methylol, furan, fish oil, furfuryl acetate, tetrahydrofurylamine, tetrahydropyran, mannitol, hexamethylenediamine and acetic anhydride.

11. The process of claim 10 wherein said sugar is selected from the group consisting of sucrose, d-galactose and molasses.

12. The process of claim 10 wherein said alcohol is selected from the group consisting of ethylene glycol, methanol, furfurylalcohol, 1,3 butylene glycol, tetrahydrofuryl alcohol, 2,5-furandimethanol.

13. The process of claim 10 wherein said carboxylic acid is selected from the group consisting of 2-furoic acid, gluconic acid, citric acid, formic acid, coumalic acid, 2,3,4,5-tetracarboxylic acid, furylacrylic acid, barbituric acid, oxalic acid and mucic acid.

14. The process of claim 1 wherein said ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1 is selected from the group consisting of ammonium acetate, ammonium and diammonium adipate, ammonium benzoate, ammonium binoxalate, ammonium caprylate, ammonium, diammonium and triammonium citrate, ammonium crotonate, ammonium and diammonium dodecanoate, ammonium and diammonium fumarate, ammonium heptanoate, ammonium linolenate, ammonium and diammonium malate, ammonium mono butyrate, ammonium oleate, ammonium and diammonium pthalate, ammonium propionate, ammonium salicylate, ammonium and diammonium succinate, ammonium and diammonium tartarate, and ammonium, diammonium and triammonium trimellitate.

15. The process of claim 1 wherein said heterocyclic hydrocarbon having at least one cyclic oxygen is selected from the group consisting of furfural and derivatives of furfural.

16. The process of claim 1 wherein said hydroxy amino hydrocarbon is selected from the group consisting of alkanolamines, amino acids and protein-containing compositions.

17. The process of claim 1 wherein said five or six membered heterocyclic hydrocarbon having at least one cyclic nitrogen is selected from the group consisting of piperazine, piperidine, pyridine, pyrazine, pyrazole, imidazole, oxazolidone, pyrrole, pyrrolidine, and mixtures thereof.

18. The process of claim 1 which further comprises introducing a third treatment agent into the effluent at a third temperature zone.

19. The process of claim 18 wherein the effluent temperature at said third temperature zone is below about 1400° F.

20. The process of claim 19 wherein said third treatment agent comprises a composition selected from the group consisting of hydrogen peroxide, paraffinic hydrocarbons, olefinic hydrocarbons, aromatic hydrocarbons, oxygenated hydrocarbons and nitrogenated hydrocarbons.

21. The process of claim 20 wherein said third treatment agent comprises an oxygenated hydrocarbon.

22. The process of claim 20 wherein said nitrogenated hydrocarbon is selected from the group consisting of monomethylamine, triethylene tetramine, hexamethylenediamine, tetraethylene pentamine, bis-hexamethylene triamine, polyamine, HpA(hydroxypropylacrylate), 1,2-diaminopropane, N,N-dimethylethylenediamine, tetramethylethylenediamine, 2-methylaziridine, bis (3-aminopropyl) ethylenediamine, tetramethyldiaminomethane, ethylenediamine and diethylenetriamine.

23. The process of claim 1 wherein the effluent temperature at said first temperature zone is about 1700° F. to about 2000° F. and the effluent temperature at said second temperature zone is about 1350° F. to about 1750° F.

24. The process of claim 1 wherein the effluent temperature at said second temperature zone is below about 1450° F.

25. The process of claim 1 wherein the effluent temperature at said first temperature zone is about 1350° F. to about 1750° F. and the effluent temperature at said second temperature zone is below about 1400° F.

26. The process of claim 4 which further comprises introducing a third treatment agent into the effluent at a third temperature zone.

27. The process of claim 5 which further comprises introducing a third treatment agent into the effluent at a third temperature zone.

28. The process of claim 27 wherein the effluent temperature at said third temperature zone is about 1350° F. to about 1750° F. and said third treatment agent comprises urea, ammonia, hexamethylenetetramine, a parafinic hydrocarbon, an olefinic hydrocarbon, an aromatic hydrocarbon, an oxygenated hydrocarbon, an ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon having at least one cyclic oxygen, a five or six membered heterocyclic hydrocarbon having at least one cyclic nitrogen, hydrogen peroxide, guanidine, guanidine carbonate, biguanidine, guanylurea sulphate, melamine, dicyandiamide, calcium cyanamide, biuret, 1,1-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea and mixtures thereof.

29. The process of claim 28 wherein said oxygenated hydrocarbon is selected from the group consisting of sugar, an alcohol, a lignin derivative, a carboxylic acid, a peroxide, an aldehyde, an ether, an ester, a ketone, glycerin, tetrahydrofuran, acetone, NH4-lignosulfonate, calcium lignosulfonate, 1,3 dioxolane, 1,4 dioxane, furfurylamine, n-butyl acetate, methylol, furan, fish oil, furfuryl acetate, tetrahydrofuran tetrahydrofurylamine, tetrahydropyran, mannitol, hexamethylenediamine and acetic anhydride.

30. The process of claim 29 wherein said sugar is selected from the group consisting of sucrose, d-galactose and molasses.

31. The process of claim 29 wherein said alcohol is selected from the group consisting of ethylene glycol, methanol, furfurylalcohol,1,3 butylene glycol, tetrahydrofuryl alcohol, 2,5-furandimethanol.

32. The process of claim 29 wherein said carboxylic acid is selected from the group consisting of 2-furoic acid, gluconic acid, citric acid, formic acid, coumalic acid, 2,3,4,5-tetracarboxylic acid, furylacrylic acid, barbituric acid, oxalic acid and mucic acid.

33. The process of claim 28 wherein said ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1 is selected from the group consisting of ammonium acetate, ammonium and diammonium adipate, ammonium benzoate, ammonium binoxolate, ammonium caprylate, ammonium, diammonium and triammonium citrate, ammonium crotonate, ammonium and diammonium dodecanoate, ammonium and diammonium fumarate, ammonium heptanoate, ammonium linolenate, ammonium and diammonium malate, ammonium mono butyrate, ammonium oleate, ammonium and diammonium pthalate, ammonium propionate, ammonium salicylate, ammonium and diammonium succinate, ammonium and diammonium tartarate, and ammonium, diammonium and triammonium trimellitate.

34. The process of claim 28 wherein said heterocyclic hydrocarbon having at least one cyclic oxygen is selected from the group consisting of furfural and derivatives of furfural.

35. The process of claim 28 wherein said hydroxy amino hydrocarbon is selected from the group consisting of alkanolamines, amino acids and protein-containing compositions.

36. The process of claim 28 wherein said five or six membered heterocyclic hydrocarbon having at least one cyclic nitrogen is selected from the group consisting of piperazine, piperidine, pyridine, pyrazine, pyrazole, imidazole, oxazolidone, pyrrole, pyrrolidine and mixtures thereof.

37. The process of claim 27 wherein the effluent temperature at said third temperature zone is below about 1400 F. and said third treatment agent comprises a composition selected from the group consisting of hydrogen peroxide, paraffinic hydrocarbons, olefinic hydrocarbons, aromatic hydrocarbons, oxygenated hydrocarbons and nitrogenated hydrocarbons.

38. The process of claim 18 which comprises introducing a fourth treatment agent into the effluent at a fourth temperature zone.

39. The process of claim 1 wherein each of said treatment agents is introduced so as to minimize the generation of pollutants other than nitrogen oxides while substantially maximizing the reduction in nitrogen oxides concentration by utilizing the nitrogen oxides reduction versus effluent temperature curve for each treatment agent.

40. A process for the reduction of the concentration of nitrogen oxides in the effluent from the combustion of a carbonaceous fuel, the process comprising selecting a plurality of locations for introduction of chemical formulations and introducing at each of said locations at least one chemical formulation, selected from the group consisting of urea, ammonia, hexamethylenetetraamine, an oxygenated hydrocarbon, a paraffinic hydrocarbon, an olefinic hydrocarbon, an aromatic hydrocarbon, an ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon having at least one cyclic oxygen, a five or six-membered heterocyclic hydrocarbon having at least one cyclic nitrogen, hydrogen peroxide, guanidine, guanidine carbonate, bigianidine, guanylurea sulphate, melamine, dicyandiamide, calcium cyanamide, biuret, 1,1-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, methyl urea, and mixtures thereof, effective to reduce the concentration of nitrogen oxides at the effluent temperature existing at said location, such that optimization of the level of injection at each of said locations leads to the reduction of the level of nitrogen oxides below a predetermined target level.

41. The process of claim 40 wherein each of said formulations is adjusted in response to changes in boiler load in order to substantially maintain the nitrogen oxides reductions achieved.

42. The process of claim 40 wherein each of said formulations is adjusted in response to changes in boiler load in order to maintain the nitrogen oxides level in the effluent at a specified level.

43. A process for the reduction of the concentration of nitrogen oxides in the effluent from the combustion of a carbonaceous fuel to a predetermined target level at minimum cost, the process comprising selecting a plurality of locations for introduction into the effluent; selecting at least one chemical formulation selected from the group consisting of urea, ammonia, hexamethylenetetraamine, an oxygenated hydrocarbon, a paraffinic hydrocarbon, an olefinic hydrocarbon, an aromatic hydrocarbon, an ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1,1, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon having at least one cyclic oxygen, a five or six-membered hetero-cyclic hydrocarbon having at least one cyclic nitrogen, hydrogen peroxide, guanidine, guanidine carbonate, biguanidine, guanylurea sulphate, melamine, dicyandiamide, calcium cyanamide, biuret,l,l-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea, and mixtures thereof, for introduction onto each of said locations, each of said chemical formulations being effective at the reduction of the concentration of nitrogen oxides at the effluent temperature existing at the location into which said chemical formulation is introduced; and introducing said chemical formulations into the effluent, wherein the sequence of introduction comprises introducing the least expensive formulation first, and repeating the introduction procedure with the remaining chemical formulations until the predetermined target level is attained.

44. A process for reducing the concentration of nitrogen oxides, and sulphur trioxide or ammonia in the effluent from the combustion of a carbonaceous fuel, the process comprising:
a. introducing a first treatment agent selected from the group consisting of urea, ammonia, hexamethylenetetramine, an oxygenated hydrocarbon, a paraffinic hydrocarbon, an olefinic hydrocarbon, an aromatic hydrocarbon, an ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon having at least one cyclic oxygen, a five or six-membered heterocyclic hydrocarbon having at least one cyclic nitrogen, hydrocarbon peroxide, guanidine, guanidine carbonate, biguanidine, guanylurea sulphate, melamine, dicyandiamide, calcium cyanamide, biuret, 1,1-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea, and mixtures thereof, into the effluent at a first temperature zone to reduce the concentration of nitrogen oxides; and b. introducing a second treatment agent comprising an oxygenated hydrocarbon into the effluent at a second temperature zone to reduce the concentration of sulphur trioxide or ammonia, wherein said first and second treatment agents are introduced under conditions effective to lower the effluent pollution index.

45. The process of claim 44 wherein the effluent temperature at said first temperature zone is about 1700° F. to about 2000° F. and said first treatment agent comprises gaseous ammonia or an aqueous solution of urea or ammonia.

46. The process of claim 44 wherein the effluent temperature at said first temperature zone is about 1350° F. to about 1750° F.

47. The process of claim 46 wherein said oxygenated hydrocarbon is selected from the group consisting of sugar, acetone, an alcohol, a lignin derivative, a carboxylic acid, a peroxide, an aldehyde, an ether, an ester, a ketone, glycerin, tetrahydrofuran, acetone, NH4-lignosulfonate, calcium lignosulfonate, 1,3 dioxolane, 1,4 dioxane, tetrahydrofuran, furfurylamine, n-butyl acetate, methylol, furan, fish oil, furfuryl acetate, tetrahydrofurylamine, tetrahydropyran, mannitol, hexamethylenediamine and acetic anhydride.

48. The process of claim 47 wherein said sugar is selected from the group consisting of sucrose, d-galactose and molasses.

49. The process of claim 47 wherein said alcohol is selected from the group consisting of ethylene glycol, methanol, furfurylalcohol, 1,3 butylene glycol, tetrahydrofuryl alcohol, 2,5-furandimethanol.

50. The process of claim 47 wherein said carboxylic acid is selected from the group consisting of 2-furoic acid, gluconic acid, citric acid, formic acid, coumalic acid, 2,3,4,5-tetracarboxylic acid, furylacrylic acid, barbituric acid, oxalic acid and mucic acid.

51. The process of claim 46 wherein said ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1 is selected from the group consisting of ammonium acetate, ammonium and diammonium adipate, ammonium benzoate, ammonium binoxalatet, ammonium caprylate, ammonium, diammonium and triammonium citrate, ammonium crotonate, ammonium and diammonium dodecanoate, ammonium and diammonium fumarate, ammonium fumarate, ammonium heptanoate, ammonium linolenate, ammonium and diammonium malate, ammonium mono butyrate, ammonium oleate, ammonium and diammonium pthalate, ammonium propionate, ammonium salicylate, ammonium and diammonium succinate, ammonium and diammonium tartarate, and ammonium, diammonium and triammonium trimellitate.

52. The process of claim 46 wherein said heterocyclic hydrocarbon having at least one cyclic oxygen is selected from the group consisting of furfural and derivatives of furfural.

53. The process of claim 46 wherein said hydroxy amino hydrocarbon is selected from the group consisting of alkanolamines, amino acids and protein-containing compositions.

54. The process of claim 46 wherein said five or six membered heterocyclic hydrocarbon having at least one cyclic nitrogen is selected from the group consisting of piperazine, piperidine, pyridine, pyrazine, pyrazole, imidazole, oxazolidone, pyrrole, pyrrolidine, and mixtures thereof.

55. The process of claim 45 wherein the effluent temperature at said second temperature zone is no greater than about 1700° F. and said second treatment agent comprises an oxygenated hydrocarbon.

56. The process of claim 55 wherein said oxygenated hydrocarbon is selected from the group consisting of alcohols, sugars, lignin derivatives, carboxylic acids, peroxides, aldehydes, ethers, esters, ketones, and mixtures thereof.

57. The process of claim 56 wherein said oxygenated hydrocarbon is selected from the group consisting of methanol, ethylene glycol, molasses, glycerin, tetrahydrofuran, acetone, ammonium acetate, citric acid, sucrose, and mixtures thereof.

58. The process of claim 45 wherein the effluent temperature at said second temperature zone is no greater than about 1450° F.

59. The method of claim 45 wherein the weight ratio of said second treatment agent to sulphur trioxide in the effluent is about 3:1 to about 8:1.

60. The method of claim 45 wherein second said treatment agent comprises an aqueous dispersion.

61. The process of claim 44 which comprises introducing a third treatment agent into the effluent at a third temperature zone to reduce the concentration of a third pollutant in the effluent.

62. The process of claim 61 wherein said first pollutant comprises nitrogen oxides, said second pollutant comprises ammonia and said third pollutant comprises sulphur trioxide.

63. The process of claim 62 wherein said second treatment agent is effective at performing ammonia scrubbing.

64. The process of claim 63 wherein the effluent temperature at said second temperature zone is greater than about 1350° F.

65. The process of claim 64 wherein said second treatment agent comprises a non-nitrogenous treatment agent.

66. The process of claim 61 wherein the effluent temperature at said third temperature zone is no greater than about 1450° F. and said third treatment agent comprises hydrogen peroxide or an oxygenated hydrocarbon.

67. The process of claim 66 wherein said oxygenated hydrocarbon is selected from the group consisting of alcohols, sugars, lignin derivatives, carboxylic acids, peroxides, aldehydes, ethers, esters, ketones, and mixtures thereof.

68. The process of claim 67 wherein said oxygenated hydrocarbon is selected from the group consisting of methanol, ethylene glycol, molasses, glycerin, tetrahydrofuran, acetone, ammonium acetate, citric acid, sucrose, and mixtures thereof.

69. A process for reducing the concentration of nitrogen oxides in the effluent from the combustion of a carbonaceous fuel, the process comprising:

a. introducing into the effluent a treatment agent which comprises any of urea, ammonia, hexamethylenetetramine, a paraffinic hydrocarbon, an olefinic hydrocarbon, an aromatic hydrocarbon, an oxygenated hydrocarbon, an ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon having at least one cyclic oxygen, a five or six-membered heterocyclic hydrocarbon having at least one cyclic nitrogen, hydrogen peroxide, guanidine, guanidine carbonate, biguanidine, guanylurea sulphate, melamine, dicyandiamide, calcium cyanamide, biuret, 1,1-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea, and mixtures thereof under conditions effective to effect a free radical nitrogen oxides reducing process; and b. contacting the effluent with a compound of catalytic material under conditions effective to effect a selective catalytic nitrogen oxides reducing process, wherein said nitrogen oxides reducing processes are effected under conditions effective to lower the effluent pollution index.

70. The process of claim 69 wherein said free radical nitrogen oxides reducing process comprises:

a. introducing a first nitrogen oxides reducing treatment agent into the effluent at a first temperature zone;
and b. introducing a second nitrogen oxides reducing treatment agent into the effluent at a second temperature zone, wherein said first and second nitrogen oxides reducing treatment agents are introduced under conditions effective to lower the effluent pollution index.