Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/54—Nitrogen compounds
  • B01D53/56—Nitrogen oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/00049—Controlling or regulating processes
  • B01J2219/00051—Controlling the temperature
  • B01J2219/00054—Controlling or regulating the heat exchange system
  • B01J2219/00056—Controlling or regulating the heat exchange system involving measured parameters
  • B01J2219/00058—Temperature measurement

Definitions

• the present invention relates to a process for the reduction of nitrogen oxides (NO ⁇ ) in the* effluent, especially the oxygen-rich effluent, from the combustion of a carbonaceous fuel by injection of a treatment agent comprising a heterocyclic hydrocarbon having at least one cyclic oxygen into the effluent.
• a treatment agent comprising a heterocyclic hydrocarbon having at least one cyclic oxygen into the effluent.
• 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.
• temperatures above about 2000°F. and typically about 2200°F. to about 3000°F. are generated.
• thermal NO ⁇ 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.
• Nitrogen oxides are troublesome pollutants which are found in the combustion 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 sunlight and hydrocarbons. Moreover, nitrogen oxides comprise a major portion of acid rain.
• Sullivan discloses the use of hydrocarbons to reduce NO ⁇ levels in effluents at low temperatures (i.e., below 1450°F., especially below 1300°F.).
• the present invention relates to a process for reducing nitrogen oxides in the effluent from the combustion of a carbonaceous fuel. More particularly, the present invention relates to a process which comprises injecting into the effluent from the combustion of a carbonaceous fuel a treatment agent comprising a heterocyclic hydrocarbon having at least one cyclic oxygen under conditions effective to reduce the nitrogen oxides concentration in the effluent. Most preferably, the heterocyclic hydrocarbon comprises furfural.
• FIGURE 1 is a graphic representation of the results of Example I, illustrating the broadened range of 0. effectiveness with respect to temperature dependency elicited by use of the present invention.
• FIGURE 2 is a schematic representation of a circulating fluidized bed boiler used to perform Example m.
• the present invention relates to the reduction of nitrogen oxides in the effluent, especially the oxygen-rich . effluent, from the combustion of a carbonaceous fuel using a treatment agent which 2QP comprises a heterocyclic hydrocarbon having at least one cyc i ⁇ oxygen, preferably furfural.
• heterocyclic hydrocarbon having at least one cyclic oxygen refers to a ringed hydrocarbon compound having at least one ring oxygen.
• furfural as used in this description is meant to include furfural itself as well as substituted furfural. Typical substituents include side chains 5 comprising straight and branched-chain, substituted and unsubstituted aliphatic groups, oxygenated hydrocarbon groups and amino groups. Preferred substituted furfural compounds include hydroxymethyl furfural and furfural acetone.
• the treatment agent of this invention most preferably further comprises urea.
• urea as used in this description includes the compound urea itself, as well as compounds equivalent in effect. Thus, unless otherwise specified, reference in this disclosure to urea should not
• the treatment agent of this invention is injected into the effluent in solution or as a dispersion or mixture in a suitable solvent.
• Water is a 5 preferred solvent due to the economy of aqueous solutions, dispersions and mixtures and the fact that they can be employed with suitable effectiveness in most situations.
• the term "mixture" will be used to denote mixtures, dispersions and solutions.
• the 0. effective mixture comprising the treatment agent of this invention will range from saturated to dilute. While water is an effective solvent for most applications, it will be recognized that 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 heterocyclic hydrocarbon present in the mixture is advantageously in the range of about 0.5% to about 25% by weight, preferably about 5% to about 15% by weight. Where urea is employed in the treatment agent, it should preferably be present in the mixture in the range of about 2% to about 60%, most preferably about 5% to about 30% by weight.
• the weight ratio of heterocyclic hydrocarbon to urea when urea is used with the heterocyclic hydrocarbon as the treatment agent in mixture, should advantageously be about 1:10 to about 4:1, more preferably about 1:5 to about 3:1. The most preferred weight ratio of heterocyclic hydrocarbon to urea in the mixture is about 1:4 to about 2.5:1.
• the temperature of the effluent at the point .of injection will have an influence on the concentration of the mixture.
• the mixture will tend to operate effectively at high concentration, e.g., about 10% to about 65% by weight treatment agent.
• the solution will tend more towards dilute.
• the treatment agent of this invention is preferably injected into the effluent in an amount effective to elicit a reduction in the nitrogen oxides concentration in the effluent.
• the treatment agent of this invention is injected into the effluent in an amount sufficient to provide a molar ratio of the nitrogen contained in the treatment agent to the baseline nitrogen oxides level of about 1:5 to about 10:1. More preferably, the treatment agent is injected into the effluent to provide a molar ratio of treatment agent nitrogen to baseline nitrogen oxides level of about 1:3 to about 5:1, 5 most preferably about 1:2 to about 3:1.
• the injection ratio can alternatively be expressed as the normalized stoichiometric ratio (NSR) of the treatment agent to the
• Normalized stoichiometric ratio is the ratio of the concentration of NH ⁇ radicals (NH ⁇ radicals, with x being an integer, are believed to be the moiety contributed by urea which facilitates the series of reactions resulting in NO ⁇ breakdown) to the
• the treatment agent is preferably injected into the effluent gas stream at a point where the effluent is at a temperature
• the boiler interior in the area above the flame operates at temperatures which at full load approach 1900°F., even 2000°F. After subsequent heat exchange, the temperature will be lower, usually in the range between about
• the treatment agent of this invention can be effectively introduced to accomplish substantial reduction of nitrogen oxides in the effluent.
• the treatment agent utilized according to this invention is preferably injected at a number of spaced positions from nozzles or other apparatus which are effective to uniformly distribute the treatment agent through the combustion effluent.
• the effluent into which the treatment agent of this invention is injected is preferably oxygen-rich, meaning that there is an excess of oxygen in the effluent.
• the excess of oxygen is greater than about 1% by volume. Most preferably, the excess of oxygen is in the range of about 1% to about 12% or greater by volume.
• the NO ⁇ reducing treatment agents of this invention are useful not only where substantial nitrogen oxides reductions are accomplished by directly applying the disclosed method as the principal NO ⁇ reducing method, but can also be employed as a discrete step in combination with other chemical, catalytic or other procedures for reducing nitrogen oxides concentrations as well as other pollutants such as sulfur dioxide (S0 2 ) , while preferably controlling levels of residual pollutants such as ammonia and/or carbon monoxide.
• S0 2 sulfur dioxide
• Such a suitable "multi-step" process is disclosed in copending and commonly assigned U.S.
• urea when used alone or in combination with a compound disclosed in the prior art as being an enhancer for urea, such as ethylene glycol, will reduce the effluent nitrogen oxides concentration in a temperature dependent manner, with the optimal NO ⁇ -reduction within a relatively narrow range of temperatures.
• the N0 ⁇ reduction curve is significantly broader with respect to temperature.
• This broadened reduction curve is extremely desirable in practical applications, because a commercial boiler is not always operated at the same load, and, even when operated at the same load over a period of time, temperature variations are not uncommon which would take the urea curve out of its optimal range if the heterocyclic hydrocarbon were not employed.
• a further advantageous aspect of the practice of this invention is in the reduced production of other pollutants, such as ammonia and carbon monoxide, during the nitrogen oxides reduction process.
• the presence of ammonia in the effluent should be avoided because, among other reasons, it can react with 0 3 s to form ammonium bisulfate which can foul heat exchange surfaces in a boiler.
• ammonia has detrimental effects on ambient air quality, as has carbon monoxide.
• the reason f r the lower levels of ammonia and carbon monoxide is not fully understood but is probably because the series of reactions involving the heterocyclic hydrocarbon, urea and N0 ⁇ which lead to the reduction of N0 ⁇ concentrations simply does not produce substantial amounts of other pollutants as byproducts.
• the following examples further illustrate and explain the invention by detailing the operation of a treatment agent comprising a heterocyclic hydrocarbon having at least one cyclic oxygen in the reduction of nitrogen oxides emissions.
• the burner used is a burner having an effluent flue conduit, known as a combustion tunnel, approximately 209 inches in length and having an internal diameter of 8 inches and walls 2 inches thick.
• the burner has a flame area adjacent the effluent entry port and flue gas monitors adjacent 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 interest which may be present in the effluen .
• the effluent flue conduit additionally has thermocouple ports for temperature measurement at various locations. The temperature of the effluent into which the treatment agents are injected is measured at the point of injection utilizing a K-type thermocouple.
• Atomizing injectors described in copending and commonly assigned U.S. Patent Application entitled “Process and Apparatus for Reducing -the Concentration of Pollutants in an Effluent" having Serial Number 009,696, filed in the name of Burton on February 2, 1987, the disclosure of which is incorporated herein by reference, are positioned through ports in the effluent flue conduit in order to introduce and distribute the treatment agents into the effluent stream.
• the agents are injected into the effluent at a rate of 300 ml/hr.
• the burner fuel is a Number 2 fuel oil, and the burner is fired at a rate of 9.6 lbs/hr to 12.0 lbs/hr.
• a baseline nitrogen oxides concentration reading is taken prior to beginning each run to calculate the injection ratio of treatment agent to baseline nitrogen oxides and the NSR, and a final nitrogen oxides reading is taken during and downstream from injection of the treatment agents to calculate the reduction in the nitrogen oxides concentration in the effluent elicited by each of the treatment agents injected.
• the treatment agent injected is an aqueous solution which comprises 10% by weight of urea, 15% by weight of furfural, and 0.1% by weight of a commercially available surfactant.
• the injection temperature, % excess oxygen, NSR, baseline NO x , final N0 ⁇ and % reduction of N0 ⁇ for each run is set out in Table 1 and reproduced • graphically in Figure 1.
• Example II The procedure of Example I is repeated except that the treatment agent which is injected is an aqueous solution comprising 10% by weight of urea and 0.1% by weight of a commercially available surfactant.
• the results are set out in Table la and reproduced graphically in Figure 1.
• Example I The procedure of Example I is repeated except that the treatment agent injected is an aqueous solution comprising 10% urea by weight, 15% ethylene glycol (disclosed as being an enhancer for urea in copending and commonly assigned U.S. Patent Application having serial Number 784,828, filed on October 4, 1985, the disclosure of which is incorporated herein by reference) by weight and 0.1% of a commercially available surfactant.
• the treatment agent injected is an aqueous solution comprising 10% urea by weight, 15% ethylene glycol (disclosed as being an enhancer for urea in copending and commonly assigned U.S. Patent Application having serial Number 784,828, filed on October 4, 1985, the disclosure of which is incorporated herein by reference) by weight and 0.1% of a commercially available surfactant.
• Table lb The results are set out in Table lb and reproduced graphically in Figure 1.
• the following example illustrates the ability of treatment agents which comprise a heterocyclic hydrocarbon having at least one cyclic oxygen to reduce N0 ⁇ concentrations in an effluent without producing a substantial amount of other pollutants, such as ammonia and carbon monoxide.
• the procedure is similar to that of Example I, except that the treatment agent injected is an aqueous solution comprising 10% by weight of urea, 0.1% by weight of a commercially available surfactant and furfural at the concentrations shown in Table 2.
• the fuel supply rate is 9.6 lbs/hr. and the excess oxygen is 3.0%.
• the results of each run are set out in Table 2.
• the boiler used is a circulating fluidized bed boiler having a configuration substantially as schematically illustrated in Figure 2.
• the boiler has a heat input of 1.2 mbtu/hr., firing bituminous coal.
• the effluent 0 temperature is measured using a K-type thermocouple at the point of injection, which is at a location at the top of the cyclone.
• the boiler also has flue gas monitors inserted in a sampler located between the gas duct and the heat exchangers to measure the concentration of compositions such as nitrogen oxides, sulfur oxides, ammonia, carbon monoxide, carbon dioxide, percent excess oxygen and other compounds of interest which may be present in the effluent.
• a baseline nitrogen oxides concentration reading is taken prior to beginning each run to calculate the injection ratio of treatment agent to baseline nitrogen oxides and the NSR, and a final nitrogen oxides reading is taken during and downstream from injection of the treatment agents to calculate the reduction in the nitrogen oxides concentration in the effluent elicited by each of the treatment agents injected. All nitrogen oxides level are corrected to 3.0% oxygen.
• An aqueous solution comprising 25% by weight of urea, 10% by weight of furfural and 0.1% by weight of a commercially available surfactant is injected into the effluent at an effluent temperature of 1596°F. and an excess of oxygen of 7.0%.
• the rate of injection is 11.0 ml/min. to provide an NSR of 1.5.
• Table 3 The results are set out in Table 3.
• An aqueous solution comprising 25% by weight of urea, 10% by weight of furfural and 0.1% by weight of a commercially available surfactant is injected into the effluent at an effluent temperature of 1596°F. and an excess of oxygen of 3.1%.
• the rate of injection is 7.0 ml/min. to provide an NSR of 1.9.
• Table 3 The results are set out in Table 3.

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• 1988
  • 1988-03-11 WO PCT/US1988/000780 patent/WO1988007497A1/en not_active Application Discontinuation
  • 1988-03-11 EP EP88903538A patent/EP0305503A1/en not_active Withdrawn
  • 1988-03-11 AU AU15935/88A patent/AU1593588A/en not_active Abandoned
  • 1988-03-11 JP JP50317888A patent/JPH01503126A/ja active Pending
  • 1988-11-10 FI FI885167A patent/FI885167A/fi not_active IP Right Cessation

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