US3850569A

US3850569A - Process for reducing nitric oxide emissions from burners

Info

Publication number: US3850569A
Application number: US00395112A
Authority: US
Inventors: H Alquist
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1971-12-29
Filing date: 1973-09-07
Publication date: 1974-11-26
Anticipated expiration: 1991-11-26

Abstract

This invention resides in an improved process for mixing a fuel with air and steam to form a combustible mixture and combusting said mixture in a combustion zone. In the process, the mixing of the fuel and steam is maintained in a steam to fuel ration in the range of about 0.4 to about 0.95 pound steam/pound fuel for reducing the amount of nitrogen oxides emitted during combusting of the mixture.

Description

tlited States Patent 11 1 Alquist Nov. 26, 1974 I5 PROCESS FOR REDUCING NITRIC OXIDE 3.238.719 3/1966 11111510111 60/DIG. 11 EMISSIONS FROM BURNERS 3,657,879 4/1972 Ewbank at 211.... 60/3905 5 l H E A B l 1] 0k] 3,693,347 9/1972 Kydd et aI. OO/DIG. II 7 nventor: enr uist, art es'vi e, a. A PH P C OTHER PUBLICATIONS 1 sslgnee' g bfig ompany Inlet Manifold Water Injection for Control of Nitrogen Oxides-Theory and Experiment, J. E. Nicholls et [22] Filed: Sept. 7, 1973 al., SAE Transactions, Vol. 78 Paper No. 690018 21 Appl. No.: 395,112 l Primary ExammerW1ll1am F. ODea Related Appllcatlon Data Assistant Examiner-William C. Anderson [63] Continuation of Ser. No, 213,440, Dec. 29, 1971,

abandmd; 57] ABSTRACT 52 U.S. c1 431/4, 60/DIG. 11 60/3905 Thisinventk)" resides in an improved PromS 511 1111. C1 T23 7/00 ing a fuel with air and Steam to form a combustible f Search u mixture and combusting said mixture in a combustion 451/190 3 zone. In the process, the mixing of the fuel and steam is maintained in a steam to fuel ration in the range of [56] References Cited about 0.4 to about 0.95 pound steam/pound fuel for reducing the amount of nitrogen oxides emitted during UNITED STATES PATENTS combusting of the mixture. 2922,408 l/I960 Humphries et al. OOIDIG. ll 3.013.383 I2/l96l Malick 60/DIG. 11 4 Clalms, 1 a ng gure INLET AIR TEMPERATURE MEASUREMENT LOCATION SPLASH COOLING RINGS COMBUSTOR HOUSING BUSTIO AIR UST IN MIXING CYLINDER QUENCH, AIR

PIPE FLAME TUBE SECONDARY COMBUSTION AIR PRIMARY COMBUSTION AIR AIR IN TO SPLASH COOLING RINGS FUEL NOZZLE SHIELD COMBUSTOR DOME FUEL IN STEAM TO COMBUSTOR PRIMARY ZONE INVENTOR. H E ALQUIST wzoo "6539200 0 min MSNNOZ 55. woz ozjoou 12 5w 0+ z m2 12 20.5528 E525. E zoiwamzou m azoumw um? M23. NEE m2 zuzmna A 7' TORNEVS PROCESS FOR REDUCING NITRIC OXIDE EMISSIONS FROM BURNERS This application is a continuation of application Ser. No. 213,440 filed Dec. 29. 1971, and now abandoned.

In the combustion of a mixture of fuel, air, and steam in a burner, nitrogen oxides are emitted. These nitrogen oxides are toxic and are sometimes of a sufficient concentration in the atmosphere that persons are detrimentally affected thereby.

This invention therefore resides in a process for reducing the amount of nitrogen oxides emitted during combusting of a steam, air, and fuel by controlling the steam to fuel ratio of the mixture in the range of about 0.4 to about 0.95.

Although the process is particularly adaptable for use with stationary burners such as burners of an electrical power plant generating station or other power generation facility as known in the art, said process can be used in other burners for reducing the amount of nitrogen oxide emission therefrom.

These power plants generally combust a mixture of air, steam, and fuel such as heavy oil, including fuel oil containingpowdered coal or coke, residual fuels, all of which normally require some steam for proper atomization. Also No. 2 heating oil and other lighter hydrocarbons through liquid propane which do not'require steam for proper atomization can be utilized.

It has been discovered that these burners can be efficiently and economically operated while reducing the amount of nitrogen oxides emitted during combustion of the fluid mixture if the ratio of the steam to fuel in the combustion zone is carefully controlled and maintained in the range of about 0.4 to about 0.95 pound steam/pound fuel and more particularly in the range of about 0.5 to about 0.7 pound steam/pound fuel. At ratios less than about 0.4 the nitric oxide emissions are not reduced to a. desirable low value and at ratios greater than about 0.95 the process approaches a value at which expenditures for providing the steam are not compensated by corresponding additional nitric oxide emission reductions.

At ratios less than about 0.4 the amount of nitrogen oxides emitted is objectionable and at ratios greater than about 0.95 the efficiency of the burner is less than desirable. This invention therefore sets forth a-precise combustion mixture for the combustion process which markedly reduces the amount of nitrogen oxide pollution discharged therefrom while maintaining the efficiency.

EXAMPLE Combustion was carried out in the combustor shown in the drawing which is representative of a high-heat output burner in which combustion takes place slightly downstream from a nozzle forming a heterogeneous mixture of primary air and droplets of liquid fuel. Provision was made to provide varying quantities of steam into the combustor primary zone through openings immediately surrounding the fuel nozzle. This is essentially the same point at which steam is introduced with large powerplant steam assisted fuel spray nozzles. As a matter of convenience the fuel used in this experiment was a kerosene having the physical properties described in Table I. Although this fuel is somewhat lighter than the heavy fuels frequently used in powerplants, it is well known to those skilled in the art that fuel characteristics of gas or liquid fuels have only a minor influence on burner NO, emissions, i.e., NO is fixed at elevated temperatures in the primary burning gas zone of the combustor.

The variables controlled in this experiment with this combustor are described in Table II. At each of four inlet temperatures (500, 700, 900 and 1,100 P) representative of various powerplant air preheat levels, and at the fuel flow and air flow conditions shown, the steam flow around the fuel nozzle was varied between 0 and 191.2 lb/hr. This permitted steam/fuel ratios of from 0 to 2.48. At each condition a measurement was made of the NO, and hydrocarbons in the exhaust from the combustor. The method for measuring NO, was the standard Saltzman wet chemical technique. Analysis of the unburned hydrocarbons was made by the standard flameionization technique. In order to avoid bias in the results, the emission data were obtained in duplicate at each of the 40 conditions in a statistically designed experiment.

The NO emission data from this experiment are described in Table III and the exhaust hydrocarbon emission data are shown in Table IV. It will be noticed in comparing Tables III and IV that substantially all of the NO, emissions can be eliminated without significant increases in hydrocarbon emissions (Table IV).

There are certain other aspects of the data shown in Tables III and IV that deserve comment. First, it is apparent that the amount of steam used to achieve proper atomization in a heavy liquid fossil .fuel powerplant has an important benefit on NO, emissions, i.e.-, compare the NO, emissions with no steam to the NO, emissions when 02 lb. steam/lb.fuel is used. If it is desired to make a 50 percent reduction of NO emissions from present powerplants, these data suggest that such a reduction can be achieved by increasing the steam/fuel ratio from the present level of 0.2 to approximately 0.8-0.9 lb. steam/lb. fuel (see mean values on Table III). It can be seen in Table IV that this reduction in NO, does not compromise burner efficiency by an increase in exhaust hydrocarbons.

TABLE l-Contmued Gum, m g/ 1()0 ml 0.0

Composmon, vol 7?.

Paraffins 52.8 Physical and Chemical Prooerties of Test Fuel Cycloparamns Kerosene Olefins (H 80 vol 7r evaporated 442 5 xfi fi 6 5 90 1 Stoichiometrie Fuel/Air Ratio. lb/lb 0.0676 95 vol 7r evaporated 474 End Point 496 Residue, vol 7:. 0.8 Aw 7 V 7 W l 7 HM Other mod1ficat1ons and alterat1ons of th1s 1nvent1on Gravny, dcgrccs API 46.6 b h d h f Density lbs/gal M 0 w1 eeome apparent to t ose s 1 e 1n t e art rom H6111Combustion.ncLBtu/lb 1 the foregomg C11SCUSS1OI1, example, and accompanying gydmgcwcomclw drawing, and 1t should be understood that th1s mvenmokc Pomt. mm 27.2 Sulfur. wt "/7 0.001 tlon 15 not to be unduly l1m1ted thereto.

TABLE II 2-1nch Combustor Operating Conditions Combustor Inlet Air Data Combustor and Steam Point Pressure, Air Flow, Fuel Flow, Steam Flow, Temperature Numin. Hg abs lb/sec 1b/hr 1b/hr F ber (a) Use following schedule:

Steam Flow. Test lblhr TABLE III Effect of Steam Atomization on Nitric Oxide Emissions 2-1nch Combustor Inlet Steam[Fuel Ratio. lb/lb Air, F 0.00 0.20 0.44 0.69 0.95 1.22 1.51 1.81 2.14 2.48

First Test With Values of Nitric Oxide in Parts ger Million on a Mole Basis Second Test 1100 338 237 208 153 111 101 55 53 39 11 1100 338 247 227 175 111 98 59 49 39 16 900 234 185 173 101 44 42 26 13 900 235 174 182 99 78 65 42 42 28 13 700 159 107 120 65 52 46 33 29 15 13 700 166 101 110 65 49 42 39 24 16 10 500 97 71 87 71 33 36 23 16 15 0* 500 94 68 72 45 36 33 23 21 16 0* Mean of Two Tests 1100 327 248 204 171 114 95 669 53 38 15 900 238 174 154 69 61 42 41 23 13 700 156 107 93 78 48 38 34 29 17 10 500 98 74 64 63 36 31 24 19 14 0* Mean of Two Tests With Values of Nitric Oxide in Pounds per 1000 Pounds Fuel Flame Out.

Effect of Steam Atomization on Hydrocarbon Emissions 2-lnch Combustor Inlet SteamlFuel Ratio. lb/lb Air, "F 0.00 0.20 0.44 0.69 0.95 1.22 1.51 1.81 2.14 2.48

First Test With Values in Terms of Parts r Million Carbon 1100 6.0 5.0 14.0 4.3 13.0 5.0 2.5 3.8 5.0 4.0 900 33.0 4.0 13.0 3.0 6.4 4.8 3.6 8.1 10.0 5.0 700 7.0 10.0 l0.0 l6.0 4.3 l 1.0 [9.3 7.5 6.8 l8.8 500 4.0 21.0 3.0 9.0 24.8 9.0 2.7 18.0 23.0 33.000

(Flame Out) Second Test 1100 3.0 5.0 32.0 6.0 3.9 4.7 9.0 7.0 2.7 2.5 900 12.0 30.0 25.4. 4.0 4.2 6.3 7.0 3.6 3.7 2.4 700 2.0 8.0 12.7 4.0 6.6 3.8 6.0 9.0 7.0 7.4 500 7.0 5.0 5.1 4.0 3.7 3.3 5.7 3.0 17.0 (33,000)

' (Flame Out) Mean of Two Tests 1100 4. 5.0 23.0 5.1 8.5 4.9 5.7 5.8 3.9 3.3 900 22.5 17.0 19.2 6.0 5.3 5.6 6.8 5.9 6.9 3.7 700 4.5 9.0 11.3 10.0 5.5 7.4 12.7 8.3 6.9 13.1 500 5.5 13.0 4.1 6.5 14.3 6.l 4.2 10.5 20.0 (33.000)

(Flame Out) What is claimed is: V 2. A process. as set forth in claim 1, \vl'ierein the ratio 1. In a process for mixing a fuel with air and steam of steam to fuel of the mixture is maintained at values to form a combustible mixture and combusting said in the range of about 0.5 to about 0.7 pound steam/- mixture in a combustion zone, the improvement compound fuel. Pnsmg: 3. A process. asset forth in claim l 6116361111116 fuel controlling the mixing of the fuel and steam for mamis oil and including atomizing the Steam and Oil taining the ratio of steam to fuel of said mixture in gether into the combustion Zone said combust1on zone at values in the range of about 0.4 to about 0.95 pound steam/pound fuel for reducing the amount of nitric oxide emitted during combustion of the mixture.

a stoichiometric amount of air in injected.

' I) process, as set forth in claim '1', wherein atleast

Claims

1. IN A PROCESS FOR MIXING A FUEL WITH AIR AND STEAM TO FORM A COMBUSTIBLE MIXTURE AND COMBUSTING SAID MIXTURE IN A COMBUSTION ZONE, THE IMPROVEMENT COMPRISING: CONTROLLING THE MIXING OF THE FUEL AND STEAM FOR MAINTAINING THE RATIO OF STEAM TO ALL OF SAID MIXTURE IN SAID COMBUSTION ZONE AT VALUES IN THE RANGE OF ABOUT 0.4 TO ABOUT 0.95 POUND STEAM/POUND FUEL FOR REDUCING THE AMOUNT OF NITRIC OXIDE EMITTED DURING COMBUSTION OF THE MIXTURE.

2. A process, as set forth in claim 1, wherein the ratio of steam to fuel of the mixture is maintained at values in the range of about 0.5 to about 0.7 pound steam/pound fuel.

3. A process, as set forth in claim 1, wherein the fuel is oil and including atomizing the steam and oil together into the combustion zone.

4. A process, as set forth in claim 1, wherein at least a stoichiometric amount of air in injected.