WO1991006506A1 - System for the efficient reduction of nitrogen oxides in an effluent - Google Patents

Abstract

The invention presented comprises a system for the efficient reduction of nitrogen oxides in the effluent from the combustion of a carbonaceous fuel, the system comprising means for effecting a treatment regimen (10); means for generating a signal (60) representative of the condition of the effluent; and controller (70) responsive to such signal for adjusting the treatment regimen in response to such signal in order to achieve substantial nitrogen oxides reductions while minimizing the production of other pollutants.

Description

DESCRIPTION

SYSTEM FOR THE EFFICIENT REDUCTION OF NITROGEN OXIDES IN AN EFFLUENT

Technical Field

The present invention relates to an apparatus for the reduction of nitrogen oxides (NO_χ) in the effluent, especially the oxygen rich effluent, from the combustion of a carbonaceous fuel while minimizing the production of other pollutants, such as ammonia (NH₃) and/or carbon monoxide (CO) .

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 high flame temperatures. When fossil fuels are used in suspension fired boilers such as large utility boilers, temperatures above about 2000°F and typically about 2200°F to about 3000°F are generated. Unfortunately, such high temperatures tend to cause the production of thermal NO_χ, the temperatures being so high that free radicals of oxygen and nitrogen are formed and chemically combine as nitrogen oxides. Nitrogen oxides can form even in circulating fluidized bed boilers which operate at temperatures which typically range from 1300°F to 1700°F, as well as gas turbines and diesel engines.

Nitrogen oxides are troublesome pollutants which are found in the co ^ns-inn effluent streams of boilers when fired as described above, and comprise a major irritant in smog. It is further believed that nitrogen oxides can undergo a process known as photo-chemical smog formation, through a series of reactions in the presence of some hydrocarbons. Moreover, nitrogen oxides comprise a significant contributor to acid rain, and have been implicated as contributing to the undesirable warming of the atmosphere, commonly referred to as the "greenhouse effect".

Recently, many processes for the reduction of N0_χ in combustion effluents have been developed. They can generally be segregated into two basic categories: selective and non-selective. Among the selective processes, which are believed in the art to be the more desirable, there is a further division between selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) processes. Although SCR processes are believed to be capable of achieving higher levels of nitrogen oxides reductions, SNCR processes are often preferred because of their greater economy and flexibility.

SNCR processes, which are temperature dependent, generally utilize a nitrogenous substance such as urea or ammonia as well as non-nitrogenous substances and proceed in the gas phase by a complex series of free radical- mediated chemical reactions involving various nitrogen, hydrogen, oxygen and carbon-containing species and radicals. Under ideal conditions, a reaction set involving 31 species and 92 individual reactions has been postulated as a model for the overall nitrogen oxides reduction process when SNCR is utilized.

In practice, though, essentially all commercial combustion systems deviate from the ideal state by some degree. Factors which can cause such deviation include non-uniform temperature gradients, non-uniform gas velocity gradients, non-uniform gas phase chemical composition, differences in furnace or boiler geometry and fluctuations with time. The introduction of NO_χ-reducing chemicals into the combustion gasses introduces still another dimension of uncertainty into the overall system. This uncertainty can be caused by droplet size and distribution of droplets, the rate of droplet evaporation and chemical decomposition, the distribution of chemical throughout the effluent (through injector spray angle adjustment and penetration) , residence time of the NO_χ-reducing chemicals (the critical residence time is usually the time before the temperature is quenched rapidly by heat exchange surfaces) and the baseline (or initial) nitrogen oxides level and desired NO_χ reduction.

Although various models can be utilized to simulate conditions inside a combustion system, they generally do not account for many of the deviations noted. Accordingly, it is difficult, if not impossible, to predict the optimum NO_χ reducing treatment regimen to be effected in order to most efficiently reduce nitrogen oxides without generating other, secondary pollutants such as ammonia and carbon monoxide.

Background Art

Processes and compositions for the reduction of nitrogen oxides in an effluent from the combustion of a carbonaceous fuel have been developed extensively over recent years. With the increased attention to the health risks and environmental damage caused by agents such as smog and acid rain, it is expected that N0_χ reduction research will continue to be pursued.

In the past, most processes for the reduction of nitrogen oxides levels have concentrated on achieving maximum NO_χ reductions without addressing the problems raised by the production of other pollutants such as ammonia and carbon monoxide. More recently, in a unique application of NO_χ-reducing principles, Epperly, Peter- Hoblyn, Shulof, Jr. and Sullivan, in U.S. Patent No. 4,777,024, disclosed a method of achieving substantial nitrogen oxides reductions while minimizing the production of other pollutants through a multiple stage injection process. Moreover, Epperly, O'Leary and Sullivan, in U.S. Patent No. 4,780,289, have disclosed a complementary process for achieving significant, and potentially maximized, N0_χ reductions while minimizing the production of other pollutants by utilizing the nitrogen oxides reduction versus effluent temperature curve of the treatment regimen being effected at each NO_χ reduction introduction in a combustion system.

What is desired, though, is a system whereby the maximization of nitrogen oxides reductions and minimization of the production of other pollutants can be automated such that substantial operator intervention in the introduction of NO_χ-reducing chemical agents can be avoided.

Disclosure of Invention

The present invention meets this need and provides the ability to control NO_χ in concert with other pollutants under varying as well as constant load conditions automatically. According to one aspect, the invention comprises a means for effecting a treatment regimen; means for generating a signal representative of a condition of the effluent; and means responsive to the signal by adjusting the parameters of the treatment regimen in response to changes in the condition of the effluent in order to maintain or maximize N0_χ reductions while minimizing the production of other pollutants.

According to another aspect of the present invention, a plurality of treatment regimen are effected, each at a different effluent temperature zone, and adjusted by the control means in response to changes in the condition of the effluent.

Brief Description of the Drawincrs

These and other objects will be described and the present invention better understood and its advantages more apparent in view of the following detailed description, especially when read with reference to the appended drawings wherein:

FIGURE 1 is a schematic illustration of the system of the present invention; and

FIGURE 2 is a schematic illustration of an alternate embodiment of the system of the present invention.

FIGURE 3 is a flowchart illustrating a set of operating instructions for controller 70.

Definitions

For the purposes of this description, the following definitions shall apply:

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

"amino acid" refers to any organic compound containing an amine group and a carboxylic acid group; ¹¹ammonium salt of an organic acid" refers to a salt 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 carboxyl group, they may be partially or completely neutralized by ammonium hydroxide.

"baseline nitrogen oxides level" refers to the level of nitrogen oxides present in the effluent immediately prior to the treatment being discussed;

"curve plateau" refers to that region of a nitrogen oxides reduction versus effluent temperature curve where the NO_χ reduction is substantially maximized over a range of temperatures and preferably encompasses at least two data points (of course a skilled artisan will recognize that a curve plateau will not necessarily be flat due to "data scatter" and other practical data generation effects) ;

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

"effluent condition" or "condition of the effluent" refers to the existing state of any one or more parameters which can be used to characterize the effluent, such as temperature, nitrogen oxides level, ammonia level, carbon monoxide level, excess oxygen level, sulfur oxides level, etc. ;

"enhancer weight ratio" (EWR) refers to the weight ratio of enhancer to N0_χ as N0₂ for a non-nitrogenous treatment agent;

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

"five or six-membered heterocyclic hydrocarbon having at least one cyclic nitrogen" refers to a cyclic five- or six-membered hydrocarbon in which one or more of the atoms in the ring is nitrogen. The cyclic compounds can be either saturated or unsaturated;

"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;

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

"high temperature side" or "right side" refer to any point on the subject nitrogen oxides reduction versus effluent temperature curve which represents the reduction achieved when a treatment regimen is effected at a higher temperature than the original temperature at which the treatment regimen was effected;

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

"nitrogen oxides reduction versus effluent temperature curve" refers to a plot of the data points generated when a treatment regimen is effected by introducing a treatment agent into an effluent over a range of effluent temperatures and the nitrogen oxides reduction at each introduction temperature is measured (and usually expressed in terms of percent of baseline) ;

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

"normalized stoichiometric ratio" (NSR) refers to the ratio of the concentration of reducing-radicals such as NH_χ radicals (NH_χ radicals, with x being an integer, are believed to be the moiety contributed by a nitrogenous treatment agent which facilitates the series of reactions resulting in NO_χ breakdown) to the concentration of nitrogen oxides in the effluent and can be expressed as [NH_χ]/[NO_χ] (alternatively, the molar ratio of the treatment agent to the NO_χ concentration can be used in place of NSR when the chemistry of reduction is not well defined; the term NSR as used herein will also be understood to encompass molar ratio when appropriate) ;

"oxygenated hydrocarbon" refers to a substituted and unsubstituted, straight or branch-chain aliphatic and cyclic, heterocyclic and aromatic hydrocarbon having at least one oxygen either in or bonded directly to the ring or a substituent group, and mixtures thereof, typical substituent groups of which include carboxylic acid groups (COOH) , peroxide groups (-0-0-) , carbonyl groups (C=0) , hydroxyl groups (OH) , ether groups (-0-) , ester groups (COOR) , etc. ; "pollution index" refers to an index which indicates the presence and level of all of the pollutants in the effluent;

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

"sugar" refers to a number of useful saccharide materials which are capable of decreasing the NO_χ 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 maltose, 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;

"temperature zone" refers to a locale wherein, under steady state conditions, the effluent temperature is within a certain range, more particularly a range wherein one or more treatment agents is known to be effective, such as 1600°F to 2100°F, 1350°F to 1750^βF, below 1300°F, etc;

"treatment agent" refers to a composition comprising at least one reductant chemical (also referred to as a treatment agent component), i.e., a pollution reducing chemical capable of reducing NO_χ, sulfur oxides (SO_χ) or other pollutants by facilitating a reaction (the term "reaction" will be understood to refer to a single reaction or a series of reactions) , and, preferably, with a solvent;

"treatment regimen" refers to the introduction (such as by injection) of a treatment agent into an effluent and the conditions under which the treatment agent is introduced, such as treatment agent components (by which is meant the ingredients of the treatment agent) , treatment agent dilution (by which is meant the concentration of treatment agent components when the treatment agent used comprises a solution) , relative presence of treatment agent components (by which is meant the relative weight ratio or fractions of the components which form the chemical formulation which makes up the treatment agent) , treatment agent introduction rate, etc. ; and

"urea" and "ammonia" refer, respectively to the compounds urea and ammonia themselves, as well as compounds equivalent in effect. Among those compounds are ammonium carbonate, ammonium oxalate, ammonium hydroxide and various stable amines, and their solutions in water.

Treatment Agents

Appropriate treatment agents known as being effective at the reduction of nitrogen oxides include nitrogenous compositions like ammonia such as disclosed by Lyon in U.S. Patent No. 3,900,554 and urea such as disclosed by Arand et al. in either of U.S. Patent Nos. 4,208,386 and 4,325,924, the disclosures of each of which are incorporated herein by reference.

Additional appropriate treatment agents known as being effective for the reduction of nitrogen oxides include those disclosed by International Patent Application entitled "Reduction of Nitrogen- and Carbon-Based Pollutants Through the Use of Urea Solutions," having Publication No. WO 87/02025, filed in the name of Bowers on October 3, 1986; U.S. Patent No. 4,751,065 in the name of Bowers; U.S. Patent No. 4,719,092, also to Bowers; International Patent Application entitled "Process for the Reduction of Nitrogen Oxides in an Effluent Using a Heterocyclic Hydrocarbon," having Publication No. WO 88/07497, filed in the names of Epperly and Sullivan on March 11, 1988; U.S. Patent No. 4,877,591 to Epperly and Sullivan; U.S. Patent No. 4,803,059 to Sullivan and Epperly; U.S. Patent No. 4,863,705 to Epperly, Sullivan and Sprague; U.S. Patent Patent No. 4,844,878 to Epperly, Sullivan and Sprague; U.S. Patent No. 4,770,863 to Epperly and Sullivan; International Patent Application entitled "Composition for Introduction into a High Temperature Environment," having Application No. PCT/US89/01711, filed in the names of Epperly, Sprague and von Harpe on April 28, 1989; copending and commonly assigned U.S. Patent Application entitled "Process for Nitrogen Oxides Reduction With Minimization of the Production of Other Pollutants", having Serial No. 07/207,382, filed in the names of Epperly, O'Leary, Sullivan and Sprague on June 15, 1988; U.S. Patent No. 4,863,704 to Epperly, Peter- Hoblyn, Shulof, Jr., Sullivan and Sprague; and copending and commonly assigned U.S. Patent Application entitled "Hybrid Process for Nitrogen Oxides Reduction," having Serial No. 07/395,810, filed in the names of Epperly and Sprague on August 18, 1989, the disclosures of each of which are incorporated herein by reference.

These patents and applications contemplate the use of treatment agents which comprise urea or ammonia, optionally enhanced by other compositions 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-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, a peroxide, an aldehyde, an ether, an ester, a ketone, glycerin, tetrahydrofuran, furfuryla ine, n-butyl acetate, methylal, furan, fish oil, furfury1 acetate, tetra¬ hydrofuran tetrahydrofurylamine, tetrahydropyran, mannitol, hexamethylenediamine and acetic anhydride) , an ammonium salt of an organic acid (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 formate, ammonium and diammonium fu arate, ammonium heptanoate, ammonium linolenate, ammonium and diammonium malate, ammonium mono butyrate, ammonium oleate, ammonium and diammonium phthalate, 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, pyridine, pyrazine, pyrazole, imidazole, oxazolidone, pyrrole, pyrrolidine) , hydrogen peroxide, guanidine, guanidine carbonate, biguanidine, guanylurea sulfate, melamine, dicyandiamid , calcium cyanamide, biuret, l,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 and various other compounds which are disclosed as being effective at the reduction of nitrogen oxides in an effluent. Most preferred among these enhancers are the oxygenates, such as the oxygenated hydrocarbons, heterocyclic hydrocarbons having at least one cyclic oxygen, sugar and molasses. In fact, certain of the ammonium salts, can function as NO_χ-reducing treatment agents in an independent introduction without urea or ammonia.

When the treatment agent comprises urea, ammonia or another nitrogenous treatment agent, without a non-nitrogenous hydrocarbon component, it is preferably introduced at an effluent temperature of about 1600°F to about 2100°F, more preferably about 1700^βF to about 2100°F. When the treatment agent also comprises one of the enhancers discussed above, it is preferably introduced at an effluent temperature of about 1200°F to about 1750°F, more preferably about 1350°F to about 1750°F or higher. In addition, certain treatment agents including some of the ammonium salts such as triammonium citrate and ammonium formate can function to reduce nitrogen oxides at temperatures below about 1300°F, as disclosed by U.S. Patent No. 4,873,066 to Epperly, Sullivan and Sprague and U.S. Patent No. 4,877,590 to Epperly, O'Leary, Sullivan and Sprague, the disclosures of each of which are incorporated herein by reference.

These effluent temperatures at ^• the point of introduction can be varied depending on the particular components of the treatment agent and other effluent conditions, such as the effluent oxygen level, as discussed in the referenced disclosures. When an enhancer is introduced alone, the temperature of introduction can vary from about 900°F or about 1100°F up to about 1450°F or higher.

Nitrogenous treatment agents are generally introduced into the effluent at a molar ratio of the nitrogen in the treatment agent to the baseline nitrogen oxides level in the effluent of about 1:10 to about 10:1. More preferably, the molar ratio of treatment agent nitrogen to baseline NO_χ level is about 1:5 to about 5:1. When a non-nitrogenous treatment agent is being utilized, it is generally introduced at a weight ratio of treatment agent to baseline NO_χ of about 1:10 to about 10:1, more preferably, about 1:5 to about 5:1.

Best Mode for Carrying Out the Invention

As previously noted, the present invention relates to a system for the efficient reduction of nitrogen oxides in combustion effluents, by which is meant significant NO_χ reductions without the generation of substantial amounts of other pollutants such as ammonia or carbon monoxide. The inventive system comprises a means for effecting a treatment regimen, a means for generating a signal representative of a condition of the effluent and a controller means responsive to the signal by adjusting the parameters of the treatment regimen in response to changes in the condition of the effluent in order to achieve substantial NO_χ reductions while minimizing the production of other pollutants by utilizing the nitrogen oxides reduction versus effluent temperature curve for the treatment regimen being effected.

The nitrogen oxides reduction versus effluent temperature curve for a treatment regimen comprises a curve plateau which indicates where the N0_χ reduction elicited by the treatment regimen is maximized and that such maximum level is substantially maintained over a range of effluent temperatures. Merely maximizing the nitrogen oxides reduction obtained with a treatment regimen, though, is not enough, since the level of other pollutants such as ammonia and carbon monoxide are also important in reducing the overall pollution index for the effluent and not just the nitrogen oxides. The levels of ammonia and carbon monoxide, for instance, are important because when NO_χ reduction is achieved by using a treatment agent which comprises urea or ammonia, ammonia is often produced or remains in the effluent, whereas when NO_χ reduction is achieved by the use of a treatment agent which comprises a hydrocarbon enhancer either alone or in combination with urea or ammonia, carbon monoxide is present.

The presence of ammonia in the effluent should be minimized because, among other things, it can react with S0₃ to form ammonium bisulfate which can foul heat exchange surfaces in a boiler. Moreover, ammonia has detrimental effects on ambient air quality, as has carbon monoxide. If the reduction of nitrogen oxides levels brings about the production of significant amounts of other pollutants, then such reduction can, in fact, be counterproductive, since the effluent pollution index is not substantially lowered and can in certain circumstances actually be raised.

Surprisingly, as disclosed in U.S. Patent No. 4,780,289 to Epperly, O'Leary and Sullivan, and International Patent Application entitled "Process for Nitrogen Oxides Reduction and Minimization of the Production of Other Pollutants," having Publication No. WO 89/02781, filed in the names of Epperly, Sullivan, Sprague and O'Leary on August 12, 1988, the disclosures of each of which are incorporated herein by reference, operation on the high temperature or right side of the nitrogen oxides reduction versus effluent temperature curve of a treatment regimen substantially reduces the production of other pollutants such as ammonia and carbon monoxide.

In fact, as disclosed, it has been found that operation on a nitrogen oxides reduction versus effluent temperature curve plateau at any point further to the right of present operation will reduce the production of other pollutants while maintaining maximum NO_χ reduction. If moving to the right leads to operation off the curve plateau, further reductions in secondary pollutants will be achieved, but nitrogen oxides reductions will no longer be maximized. This may be desirable depending on the level of NO_χ reductions required as well as maximum allowed levels of the secondary pollutants.

This "translation or shifting to the right" can be achieved by either l) translating the position on the curve at which the treatment regimen being used is being effected by effecting that treatment regimen at a higher effluent temperature (usually by utilizing an injector upstream from the original point of injection) ; or 2) by varying one or more of the parameters of the treatment regimen being effected, for instance the particular components of the treatment agent, the introduction rate of the treatment agent, the dilution of the treatment agent when in solution (usually with a concommitant variation in treatment agent introduction rate to maintain the NSR or EWR of the treatment regimen) the relative presence of treatment agent components, or combinations of the above in order to replace the current treatment regimen with one which is operating further to the right on its nitrogen oxides reduction versus effluent temperature curve.

In order to be able to achieve significant NO_χ reductions with minimum production of other pollutants automatically, it is important that the system be able to effect a treatment regimen and alter either the location for introduction of that treatment regimen (and thereby the temperature at which the treatment regimen is being effected) or treatment regimen parameters in response to the condition of the effluent. The system of the present invention accomplishes this.

As illustrated in Figures 1 and 2, the inventive system comprises apparatus 10 which in turn comprises means for effecting a treatment regimen. Such means can be made up of any components effective at supplying and introducing a treatment agent into the effluent at a specified introduction rate. More preferably, the means for effecting a treatment regimen can comprise a mixer 40 which functions to mix a plurality of chemical treatment agent components; a plurality of feeders 20a, 20b, etc., each of which is operatively connected to mixer 40 for feeding chemical treatment agent components from a source 30a, 30b, etc. to mixer 40 in variable amounts and an introduction means 50 operatively connected to mixer 40 which functions to introduce the mixed chemical treatment agent into the effluent (or flue gas) in the effluent path 110 of the boiler 100 from mixer 40.

In a preferred embodiment, as illustrated in Figure 1, the plurality of feeders 20a-20d each comprise a series of conduits, tubes, pipes or other suitable like members, 22a, 22b, 22c and 22d, each of which is connected to a source of a treatment agent component, 30a, 30b, 30c, 30d (such as a stationary tank, vat, tank car, etc. or in the case of diluent component such as water, from the water system) and to mixer 40. Although Figure 1 illustrates the embodiment where four treatment agents are available, for instance, urea or ammonia from source 30a, an enhancer such as an oxygenated hydrocarbon from source 30b, a low temperature chemical such as triammonium citrate from source 30c and dilution water from source 30d, it will be recognized that any number of sources and treatment agents can be used ranging from two (such as urea and water) upwards.

Feeders 20a-20d can each further comprise suitable elements needed for physically feeding the treatment agent components to mixer 40 as well as regulating the amount of each treatment agent component fed. Such suitable elements can include pumps 24a, 24b, 24c and 24d and valves 26a, 26b, 26c and 26d.

Although the skilled artisan would be aware of different types of pumps and valves which can be utilized in each of feeding means 20a-20d, most preferably pumps 24a-24d comprise centrifugal, gear or progressive cavity pumps. Although many different kinds of pumps are suitable, including diaphragm pumps, screw pumps, piston pumps and plunger pumps, most preferred are centrifugal, gear and progressive cavity pumps because of their simplicity and uniform (non-pulsating) flow.

It will be recognized that, when the treatment agent component is gaseous, such as gaseous ammonia or a gaseous enhancer such as hydrogen, a compressor is used in the respective feeding means. The use of the term "pump" herein will be understood to encompass compressors when appropriate.

Additionally, although virtually any kind of valve is suitable for use in the present invention, provided it is capable of variable flow, including needle valves, globe valves, diaphragm valves, plug cocks, butterfly valves and motor operated valves, it is desired that the valves used have the ability to stepwise regulate flow to small degrees since the possibility exists that extremely small amounts of some of the treatment agent components will be needed in certain situations.

It will also be recognized by the skilled artisan that the particular arrangement of pumps 24a-24d and valves 26a-26d in Figure 1 is not critical to operation of the present invention, but that any suitable pump and valve arrangement can be utilized, although the embodiment of Figure I is considered to be the most efficient.

As noted, each of the treatment agent components are fed to mixer 40 in order to be mixed into a single treatment agent in the appropriate proportions for introduction into the effluent. Devices suitable for use as mixer 40 include any line or flow mixers which can accomplish this including jet mixers and centrifugal pumps which can also function to mix the treatment agents. Most preferred is a static mixer because of its simplicity. Of course, it will be recognized that the treatment agent components can also be mixed in certain injectors by the way they are fed to such injectors. Mixer 40 can also, therefore, comprise the mixing segments of such injectors.

After mixing, the treatment agent is then fed from mixer 40 to a suitable introduction means for introducing the treatment agent into the effluent. Most preferably, such means comprises at least one injector 50 which injects the treatment agent as droplets of a desired size into the effluent (in fact, droplet size can, in certain circumstances, comprise one of the treatment regimen parameters adjusted in response to the condition of the effluent since droplet size affects penetration and, hence, N0_χ reduction) . Moreover, injector 50 advantageously comprises suitable pumps, valves, etc. (not shown) to facilitate injection of the treatment agent into the effluent, as well as a source of atomization fluid when required.

Preferred for use as injector 50 are those injectors disclosed by Burton in U.S. Patent No. 4,842,834 and DeVita in International Patent Application entitled "Process and Injector for Reducing the Concentration of Pollutants in an Effluent," International Publication No. WO 89/07982 filed 24 February 1989, the disclosures of each of which are incorporated herein by reference, although other injectors known to the skilled artisan may also be utilized with acceptable results.

In the most preferred embodiment, the system of the present invention comprises a plurality of injectors, illustrated in Figure 1 as injectors 50a, 50b and 50c, each of which is disposed in a different effluent temperature zone and each of which is capable of introducing into the effluent treatment agents fed from mixer 40, as will be discussed in more detail below.

Moreover, although only one injector, 50a, 50b, 50c, respectively, is illustrated as being disposed in each temperature zone in boiler 100, it will be recognized that each injector 50a, 50b and 50c can represent a set or plurality of injectors disposed about boiler 100 in their respective temperature zones in order to achieve the desired distribution of treatment agents throughout the effluent.

As illustrated in Figure 1, apparatus 10 further comprises a means for generating a signal representative of a condition of the boiler as noted above, and transmitting that signal to a controller 70 through, for instance, transmission line 66. Such generating means 60 either detects the condition of the effluent by detecting at least one of effluent temperature at (at least) one location, effluent nitrogen oxides level at (at least) one location, effluent oxygen concentration at (at least) one location, effluent carbon monoxide concentration at (at least) one location and effluent ammonia concentration at (at least) one location, or receives inputted data such as data which represents current boiler load (from, for instance, the boiler operation or control panel or by having boiler load manually inputted) , which can provide information concerning the boiler condition such as temperature, NO_χ level, etc.

Because of the temperature dependency of most N0_χ reduction processes, temperature is the most important parameter detected by generating means 60. It is preferred, though, that generating means 60 receive data concerning boiler load, which, with knowledge of boiler 100, can provide the necessary temperature information (as well as information on the other parameters, including N0_χ, ammonia, oxygen and carbon monoxide levels) .

As will be discussed in more detail below, controller 70 which forms an element of apparatus 10 regulates the treatment regimen being effected in response to the condition of the effluent. Accordingly, generating means 60 need only generate a signal representative of that parameter which controller 70 is using to effect the treatment regimen. In other words, if controller 70 is effecting a treatment regimen based on boiler load, then it is only a signal representative of boiler load which must be generated by generating means 60, although for informational purposes generating means 60 may also generate a signal representative of other boiler parameters.

Preferably, generating means 60 comprises a central processing or analytical unit 62 which can advantageously comprise what is popularly referred to as a personal computer (PC) and which receives data from at least one sensor 64 (and often a plurality of sensor 64a, 64b, 64c, 64d, etc.), through, for instance, data transmission lines 68a, 68b, 68c, 68d, etc. Alternatively, processing unit 62 can have data inputted directly from the boiler control panel or manually, through, for instance, input 67. Generating means 60 then transmits a signal represent¬ ative of such data to controller 70. This signal can be transmitted constantly or, most advantageously, at selected intervals, such as minute intervals. Preferably, processing unit 62 is also capable when necessary of converting data into a form which controller 70 is capable of utilizing; for instance, the conversion of analog data to digital values.

Sensor 64 can comprise any sensor capable of performing its intended function. In other words, if generating means 60 generates a signal representative of effluent temperature, then sensor 64 should be capable of receiving information concerning effluent temperature from boiler 100 such as comprising a thermocouple extending into the effluent, and transmitting that data back to processing unit 62. Although not illustrated in Figures 1 or 2, sensor 64 can also comprise a nitrogen oxides sensor which extends into the effluent, an oxygen sensor which extends into the effluent or sensors for the other effluent parameters being detected.

Most preferably, generating means 60 also, assuming suitable sensors are in place, provides data concerning other parameters of apparatus 10 including status of the various elements of apparatus 10, such as degree of opening of valves 26a-26d, mixer 40 status (such as on or off) and pump 24a-24d activity. Moreover, generating means 60 can also provide information concerning alarm or fail data and chemical levels in treatment agent component sources 30a-30d.

As noted, apparatus 10 further comprises controller 70, illustrated in Figure 1, which serves to determine the appropriate treatment regimen to be effected in response to the signal received from detector 60 and variably regulate any of pumps 24a-24d, valves 26a-26d, mixer 40 and/or injectors 50a-50c (such as through the agency of regulation the appropriate signals sent via transmission lines 74a, 74b, etc.) to feed the appropriate treatment agent components in the appropriate combinations and introduce the mixed treatment agent into the effluent to effect the appropriate treatment regimen.

Most preferably, controller 70 is managed by a central processor or computer 72 which, in a preferred embodiment, also comprises a PC and which operates according to a program, instructions or operating table which permits it to determine the parameters of the treatment regimen to be effected in response to the signal representative of boiler condition generated by generating means 60.

Such program, instructions or operating table (referred to hereafter as primary operating instructions) is preprogramed into controller computer 72 and is based upon the boiler condition for which generating means 60 is generating a signal. In other words, if boiler load is the operative boiler condition, then the operating instructions will indicate how much of each treatment agent component and the introduction rate is appropriate for the temperature or other conditions existing at injector 50 (which can be derived from boiler load) . Controller 70 then regulates at least one of valves 26a-26d, pumps 24a-24d and mixer 40 to provide and mix to appropriate treatment agent components. Most advantageously, controller 70 regulates valves 26a-26d to accomplish this, since this would be most efficient. Moreover, controller 70 also regulates injector 50 to set the appropriate introduction rate. A flowchart illustrating the operating instructions for controller 70 is set out in Figure 3.

For instance, if the boiler condition being utilized is boiler load, and the operating instructions for controller 70 indicate that when boiler load is x (such as 75%) , then the treatment regimen being effected at injector 50a should comprise χ-"-% of the treatment agent component from source 30a (such as 10% urea) , x²% of the treatment agent component from source 30b (such as 2% enhancer) , x³% of the treatment agent component from source 30c (such as 0% low temperature chemical such as triammonium citrate) , and x⁴% of diluent component from source 30d (such as 88% water) , controller 70 can then regulate valves 26a-26d and injector 50a to provide and mix the indicated treatment agent components in the indicated proportions and feed them to injector 50a to be introduced into the effluent. The desired introduction rate for the treatment regimen can be achieved by either adjusting the overall flow of pumps 24a-24d, valves 26a-26d or mixer 40 through injector 50a, or, most preferably, the pumping system of injector 50a, to achieve that introduction rate. In addition, droplet size can be adjusted by adjusting the rate of flow of atomization fluid (such as air, steam or water) through injector 50a.

Alternatively, controller 70 can regulate mixer 40 and/or injectors 50a-50c such that the treatment regimen is introduced through a different one of injectors 50a-50c (and therefore into the effluent at a different temperature zone, one which is more appropriate for the treatment regimen being effected) by, for example, regulating valves 52a, 52b and/or 52c. This can be done if the operating instructions indicate that, under the indicated conditions, there is no appropriate treatment regimen for the injector in question. The operating instructions then cause controller 70 to repeat the process illustrated in Figure 3 with another injector.

In a preferred embodiment of apparatus 10, controller 70 has a secondary set of operating instructions which uses feedback information concerning boiler conditions such as N0_χ level, ammonia level, carbon monoxide level, etc. to fine-tune the introduction of the treatment agent. For instance, as noted above, each of injectors 50a, 50b and 50c advantageously comprise a set or plurality of injectors within the respective temperature zones. Because of non-uniform flow gradients in the effluent, one or more of these injectors can be injecting the treatment agent into "cold" spots, or areas where the effluent is at a temperature below that needed for efficient reduction of nitrogen oxides. In such situations, secondary pollutants such as ammonia can be generated in undesirable amounts.

If ammonia levels downstream are measured as being higher than expected based on the treatment regimen being effected, the secondary operating instructions can cause controller 70 to transmit a signal to disengage or "turn off" each of the set or plurality of injectors in the temperature zone sequentially until ammonia levels return to the expected values. The disengaged injectors are thereby identified as those located in the "cold" spots.

When generating means 60 transmits a signal to controller 70 which differs from a previous signal and, therefore, indicates that a change in effluent condition has occurred (i.e., a change in boiler load, nitrogen oxides content, temperature, etc.), controller 70, through application of its operating instructions, then regulates feeders 20a-20d, especially valves 26a-26d and injector 50 to alter parameters of the treatment regimen, including composition (i.e., more or less of each treatment agent component and/or diluent component) or introduction rate into the effluent, in other words, to effect a "new" treatment regimen which operates as efficiently as possible under these new conditions to maximize N0_χ reductions and minimize the production of other pollutants (i.e., to operate on the right side of its nitrogen oxides reduction versus effluent temperature curve) .

Most advantageously, apparatus 10 functions to control the effecting of a plurality of treatment regimen in a multiple stage injection process. As taught by U.S. Patent No. 4,777,024 and International Patent Application entitled "Multi-stage Process for Reducing the Concentration of Pollutants in an Effluent", International Publication No. WO 89/02780, filed in the names of Epperly, Peter-Hoblyn, Shulof, Jr. , Sullivan, Sprague and O'Leary on August 12, 1988, the disclosures of which are incorporated herein by reference, the reduction of nitrogen oxides in an effluent while maintaining low levels of secondary pollutants, can be effectively accomplished by serially treating the effluent by introducing different treatment agents at different effluent temperatures.

For instance, a first treatment agent can be introduced into the effluent at a first temperature zone, a second treatment agent introduced at a second temperature zone, and the process repeated with subsequent treatment agents and temperature zones to achieve the desired level of pollution control. In this way, and by using the technology for maximizing NO_χ reduction and minimizing secondary pollutants by utilizing the nitrogen oxides reduction versus effluent temperature curve for each introduction, treatment regimen can be effected that are most efficient at reducing nitrogen oxides at the temperature at each temperature zone in which treatment agents are introduced.

In other words, the treatment agent to be introduced at each of the plurality of temperature zones is chosen to be the most effective at the effluent temperatures existing within that zone. For instance, if the first available temperature zone for introduction is an upstream location at a temperature zone where the effluent temperature is in the range of about 1700"F to about 2000°F, i.e., in the area of injector 50a in Figure I, the treatment agent can be chosen to be that which is most effective in that temperature range, such as an aqueous solution of urea.

Likewise, if another temperature zone is located where the effluent temperature is in the range of about 1350°F to about 1750°F, i.e., in the area of injector 50b, the appropriate treatment agent may be an aqueous solution of urea along with an enhancer such as sugar, molasses, or furfural. If a third location for introduction is available at a zone where the effluent temperature is below about 1300°F, i.e., in the area of injector 50c, a third treatment agent may be injected at that location which comprises an aqueous solution of, for instance, triammonium citrate In this way, each of the treatment agents introduced is effective at substantially reducing nitrogen oxides without the generation of other pollutants, and the additive effect of the three introductions of treatment agents can lead to greater NO_χ reductions then previously thought possible without the undesirable generation of secondary pollutants.

Of course, it will be recognized that it is not possible to introduce treatment agents 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 can lead to harmful deposits and ineffective use of chemicals (potentially to the creation of pollutants such as ammonia and carbon monoxide because of temperature differentials) . As a practical matter, adequate space for introduction of treatment agents 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.

Apparatus 10 can be utilized to make most efficient use of the introduction locations available by "tailoring" the treatment regimen introduced at any or all of these locations. This is illustrated in Figure 2. Furthermore, one of the downstream locations for introduction can be used primarily to reduce secondary pollutants present after an upstream introduction has caused the generation of substantial amount of such secondary pollutants in order to achieve the desired nitrogen oxides reductions. Such an introduction can be performed according to the technology disclosed in U.S. Patent No. 4,830,839 to Epperly, Peter-Hoblyn and Sullivan, the disclosure of which is incorporated herein by reference.

In practicing the multiple stage injection permitted by apparatus 10 to maximize the reduction of the concentration of nitrogen oxides in the effluent, it is preferred to first "tune" or "tailor" the introduction of the first treatment agent into the first temperature zone to optimize the introduction (i.e., maximize reduction of NO_χ concentration 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 (where a third treatment agent and a third temperature zone are used) is advantageously "tuned" third, and so forth, until the desired number of introductions and low level of pollutants is reached.

The identity of other pollutants which can be limiting factors can vary from boiler to boiler 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 injection at each temperature zone. Rather, it may be desirable to achieve maximum possible reduction at earlier temperature zones irrespective of the production of other pollutants, provided that the level of such other pollutants can be reduced at later, or the last, temperature zones. In other words, it is the pollution index after the final injection that is most significant, not the pollution index at intermediate levels.

As illustrated in Figure 2, apparatus 10 accomplishes this by utilizing a plurality of mixers 40a, 40b and 40c, each of which is operatively connected to an introduction means, 50a-50c respectively, and also operatively connected to each of feeders 20a-20d, which utilizes valves 26a-26d for mixer 40a, valves 26^,a-26^,d for mixer 40b and valves 26"a-26"d for mixer 40c. By this arrangement the treatment agents being introduced by each of introduction means 50a-50c can be regulated and varied so that the treatment regimen being effected at each temperature zone is the most efficient (i.e., capable of maximizing NO_χ reduction and minimizing the reduction of other pollutants for that temperature zone) . Alternatively, the different introductions can be utilized to maximize N0_χ reductions at one introduction and then eliminate secondary pollutants in downstream introductions, such as disclosed above with respect to U.S. Patent No. 4,830,839.

The principle behind this is essentially the same as that described above. In other words, generating means 60' detects the condition of the effluent such as effluent temperature at introduction points (or effluent temperature at one of the introduction points which can be extrapolated to provide introduction temperature at the other introduction points by knowledge of the characteristics of the boiler in question) . This applies also for the other parameters. In addition, if boiler load is being utilized, knowledge of boiler 100 can provide the approximate temperature at each location for introduction from the particular boiler load being employed.

With this information, controller 70' can regulate pumps 24a-24d, valves 26a-26d, valves 26^,a-26d, valves 26"a-26"d, mixers 40a-40c and/or injectors 50a-50c to introduce the combination of treatment agents at the introduction rate (i.e., effect the treatment regimen) appropriate for the temperature zones where each of injectors 50a-50c is located. This is preferably done by having a set of operating instructions for each of injectors 50a, 50b and 50c which serve to provide controller 70 with the needed instructions for regulating each of valves 26a-26d, valves 26'a-26'd and valves 26"a-26"d, as well as injectors 50a-50d.

As noted above, controller 70 or 70'can have a set of secondary operating instructions used to sequentialy disengage each injector of the sets of plurality of injectors which make up injectors 50a-50c respectively in response to elevated levels of secondary pollutants. In addition, another set of secondary operating instructions can cause controller 70 or 70'to regulate feeders 20a-20d to provide increased amounts of enhancer to the treatment regimen effected, if elevated ammonia levels, beyond those expected pursuant to the primary operating instructions, are found. This "shifts" the treatment regimen such that it will be operating further to the right on its nitrogen oxides reduction versus effluent temperature curve, which leads to lower levels of secondary pollutants. This second set of secondary operating instructions can also be utilized in conjunction with the first set of secondary operating instructions, after no injector "cold" spots have been found.

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 tfc se 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

Clai s

1. A system for the efficient reduction of nitrogen oxides in the effluent from the combustion of a carbonaceous fuel, the system comprising: a. means for effecting a treatment regimen; b. generating means for generating a signal representative of a condition of the effluent; and c. controller responsive to said signal for adjusting said treatment regimen in response to changes in the condition of the effluent, whereby substantial nitrogen oxides reductions are achieved while minimizing the production of other pollutants.

2. The system of claim 1 wherein said treatment regimen comprises the introduction into the effluent of at least one chemical treatment agent at a specified concentration.

3. The system of claim 2 wherein said effecting means is capable of effecting a plurality of treatment regimen at a plurality of locations.

4. The system of claim 1 wherein said generating means is capable of generating a signal representative of at least one of boiler load, effluent temperature at at least one location, effluent nitrogen oxides concentration at at least one location; effluent oxygen concentration at at least one location; effluent carbon monoxide concentration at at least one location and effluent ammonia concentration at at least one location.

5. The system of claim 1 wherein said controller is capable of adjusting at least one of treatment regimen composition, treatment regimen dilution, treatment regimen introduction rate, concentration of treatment regimen components and treatment regimen introduction location.

6. An apparatus for the efficient reduction of nitrogen oxides in the effluent from the combustion of a carbonaceous fuel, the apparatus comprising: a. at least one mixer which mixes a plurality of chemical treatment agents; b. a plurality of feeders, each of said feeders operatively connected to said at least one mixer for feeding one of said chemical treatment agent components from a source to said at least one mixer in variable amounts; c. at least one introduction means operatively connected to said at least one mixing means to introduce mixed chemical treatment agents into the effluent from said at least one mixing means; d. a generating means for generating a signal representative of a condition of the effluent and transmitting said signal to a controller; and e. a controller operatively connected to at least one of: said mixer, said plurality of feeders and said introduction means, and which regulates the amount of each chemical treatment agent component fed by each of said feeders to said at least one mixer and introduced into the effluent by said at least one introduction means, in response to said signal, whereby effluent nitrogen oxides levels are reduced to a , desired or minimum level while minimizing or maintaining at a desired level the levels of other pollutants.

7. The apparatus of claim 6 which comprises a plurality of mixers.

8. The apparatus of claim 7 wherein each of said feeders feeds one of said chemical treatment agent components to each of said mixers.

9. The apparatus of claim 8 which comprises a plurality of introducing means operatively connected to said mixers such that mixed chemical treatment agents from each of said mixers are introduced into different temperature zones of the effluent by at least one of said introduction means.

10. The apparatus of claim 9 wherein each of said introduction means comprises a plurality of injectors arranged in groups and extending at least partially into the effluent in different effluent temperature zones.

11. The apparatus of claim 9 wherein said generating means is capable of generating a signal representative of at least one of boiler load, effluent temperature at at least one location, effluent nitrogen oxides concentration at at least one location effluent oxygen concentration at at least one location; effluent carbon monoxide concentration at at least one location and effluent ammonia concentration at at least one location.

12. The apparatus of claim 11 wherein said controller functions to control the amount of each chemical treatment agent component fed by each of said feeders to said mixers and introduced into the effluent by said introduction means by regulating the pumps and valves which govern the flow rate of chemical treatment agent components from said feeders to said mixers and to said introduction means.

13. The apparatus of claim 12 wherein said regulation of pumps and valves is performed in order to introduce chemical treatment agents into the effluent according to a preset formula or operation table.

14. The apparatus of claim 13 wherein said regulation of pumps and valves is performed according to a set of operating instructions which relates boiler load and the desired concentration of each treatment agent component and dilution of the treatment agent mixture at each different effluent temperature zone.

15. The apparatus of claim 6 wherein said chemical treatment agent components are selected from the group consisting of nitrogenous treatment agents, enhancers, low temperature chemicals, water and mixtures thereof.