JPS63502085A - Reduction of nitrogen-based and carbon-based pollutants - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Bae Bae ゝ゛1゛ ■J This application was filed on October 4, 1985. Concurrently pending U.S. application This is a continuation-in-part application of No. 784827.

1 plate of blood beans 1 More particularly, the present invention relates to improvements in the combustion of carbonaceous fuels.

Improvements in firing large boilers with lower emissions of carbon-based and nitrogen-based pollutants related to.

Carbonaceous fuel has a high oxygen concentration; combustion air that keeps the flame temperature at a moderately high temperature; Depending on the fuel ratio - more complete combustion with lower carbon oxide and unburned hydrocarbon emissions. If fossil fuels are used to fire large practical boilers, , the temperature is over 2000°F 1 typical value is approximately 2200°F to 3000”F also reach. However, in addition to these high temperatures, hot Due to the extremely high degree of shaving, free radicals of nitrogen and oxygen are generated and these are chemically A troublesome situation arises in which nitrogen oxides (NOx) are produced by combining with the nitrogen oxides.

Therefore, a large excess of air or fuel is used, or as is known as the multi-stage combustion method. By combining these two processes, even if the flame temperature is lowered, NOx production is reduced. growth can decline. However, all of these methods produce excessive amounts of carbon-based pollutants. result in a negative outcome. Therefore, nitrogen-based and carbon-based repollutants to acceptable levels at the same time. The combination is not yet known.

1 and above average The need to reduce nitrogen- and carbon-based emissions while maintaining economical operations This is a problem that occurs wherever carbonaceous fuels are burned. and practical In order to obtain a system, each system must consider the requirements for fuel consumption efficiency. Of course, it must be done.

US Pat. No. 3,599,427 to Jones et al. There is a description of a two-stage catalytic system that treats the exhaust gases coming from the engine. First of all At the first catalytic stage.

The exhaust gas is then cooled and passed through a separate second catalytic device to reduce the -nitrogen oxide level. decrease. Before contacting with the second stage catalyst, ammonia gas and urea, hydroxide With other compounds like ammonia, ammonia carbonate and hexamethylenetetramine is mixed with the exhaust gas. Upon contact with the second stage catalyst, the nitrogen oxides are reduced to nitrogen. It turns into element and water.

Also, in U.S. Pat. No. 3,846,981, Paczt.

Wski) describes in more detail how to control a two-stage catalyst system.

That is, the second catalytic stage, which utilizes ammonia, is heated from 275°F to 900°F. It is preferable to keep it within this range. However, this process and Johns et al. The process uses catalysts that unfortunately add additional investment and service costs. The disadvantage is that it depends on

No. 3,900,554 to Lyon, nitric oxide in combustion exhaust Non-catalytic systems have been disclosed for reducing NO. i.e. According to Lyon's explanation, ammonia and ammonia carbonate disclosed by Johns et al. Certain ammonia precursors, or aqueous solutions thereof, may also be Can be injected into the exhaust to mix with nitric oxide in the 00°F range It is said that

and in some embodiments of the disclosed process, hydrogen gas or various hydrocarbons. When mixed with exhaust gas, even a pure reducing agent can be reduced at temperatures as low as 1300°F or less. As the reaction progresses, the high temperature prevents ammonia from being oxidized to nitrogen monoxide. He says it can be done. Rion further recommends the use of ammonia at temperatures above 2000°F. point out that it has the opposite effect, increasing NO rather than decreasing it.

Unfortunately, large industrial boilers operate at temperatures much higher than 2000°F. If the temperature following the boiler flame area is below 1600° F. Reaching inside the 2000°F heat exchanger is difficult because there is a water jacket on the outside. This is not possible without major design changes due to the woodwind inside. . At the discharge end of the boiler.

much lower than the lowest usable temperature of 1300°F when using reducing agents. . This effective temperature range is therefore limited to many large industrial boilers and some other N Let's implement non-catalytic operation as taught by Rion with combustion equipment that generates Ox. Even so, it would not be easy to approach.

Also, in US Pat. No. 3,961,018, Williamson 7 , discloses the purification of gas streams containing acid gases at low temperatures, such as near room temperature. There is. According to Williamson, the partial pressure of the gas stream should be at least 5% of the total pressure. A corresponding method of contacting an amine vapor with a gas stream is disclosed. Therefore the book The system requires large amounts of process gas and is immediately removed from the exhaust air once the process is complete. Equipment is required to separate this gas.

Although in a slightly different setting, Goldstein et al. No. 4,061,597 describes the diacid produced when exhaust gas undergoes catalytic treatment. For the reduction of yellow vapors of nitrogen oxides (NO2), In one example of this patent, which shows that the use of FFc is effective in the % aqueous solution is used. However, the temperature range of 1000°F to 1300°F , is impractical for the treatment of exhaust gas from many types of combustion equipment.

In U.S. Pat. No. 4,325,924, Arand et al. A method for non-catalytic reduction of nitrogen oxides in exhaust gas using urea is disclosed.

That is, under fuel-rich conditions, the concentration is 10% or more, preferably 20% or more. Aqueous solutions of urea are effective reducing agents for nitrogen oxides at temperatures above 1900°F. It is said that However, in this exhaust gas produced by multi-stage combustion, the level of carbonaceous pollutants is low. The disadvantage is that the bell is high.

Also, in U.S. Pat. No. 4,208,386, Arashido et al., in the case of oxygen-rich exhaust, Urea in dry form or as an aqueous solution only.

Or suitable for adding together with an Alkanoic solvent. The temperature is disclosed to be between 1300°F and 2000°F. arcanoic It is said that by using a solvent, the effective working temperature can be lowered to below 1600°F. It is.

Water has no disclosed function other than serving as a urea carrier, and is a fuel. When operated under rich conditions, the FA feed is incomplete and carbon-based contaminants The disadvantage is that an excessive amount of dyeing substance is produced. thus reducing nitrogen-based pollutants. Despite claims that the fuel is heated at temperatures above 1900°F, Fuel-rich operations come with economic and environmental handicaps; Operating in rich conditions will ensure that fuel is used economically and as desired, while reducing carbon emissions. Although carbon-based pollutants can also be reduced, it is difficult to reduce carbon oxide pollution levels. Add urea, ammonia or other useful There will be practical difficulties in supplying the material. Furthermore, from the present invention, nitrogen oxidation It turns out that urea is not as effective as desired in reducing the levels of urea.

Therefore, under oxygen-rich conditions that are effective in reducing carbon-based pollutants. Processes that are operationally more effective at reducing nitrogen-based pollutants are available today. It is molded.

1 plate brother The present invention aims to reduce the concentration of nitrogen oxides in the oxygen-rich exhaust produced by the combustion of carbonaceous fuels. The process that provides the process of reducing the degree of guanidine, guanidine carbonate salt, biguanide, guanylurea sulfate, melamine, dicyandiamide, calci Um cyanamide, biuret, 1.1'-azohisformamide, methylo lurea, methylolurea-urea condensate, dimethylolurea, methylurea, dimethylene at least one selected from the group consisting of lurea and hexamethylenetetramine. Means is provided for injecting a solution of one additive compound into the exhaust gas. i.e. Exhaust temperature at the injection point, droplet size when the concentration of compound added to the solution is dispersed, etc. 9 Preferred implementations of the present invention to reduce the level of nitrogen oxides in exhaust gas by selecting In one embodiment, an aqueous solution of hexamethylenetetramine and urea is injected. ing. It is preferable to spray from multiple locations separated from each other to ensure uniform droplets. The size of the Salator average diameter falls within the range of about lO to about io, ooo microns. Even if there is a variation in particle size within this range, it is better to Effective for uniformly mixing exhaust gases and additive compounds at temperatures above 300°F It turned out that.

All temperatures herein were measured with a single thermocouple without a sheath. Drops for use again The size is based on the Franhofer diffraction racer base. ・Measured using a Malvern 2200 device using the system did.

and unless otherwise specified, all copies and bases used alone or in combination. In addition to the above additive compounds that can be used, urea and the following substances are added: ammonia carbonate. ammonium, &ammonium acid, ammonia, hydrazine, ammonium hydroxide and A variety of amines can be used with the additive compounds described above.

According to the invention, aqueous solutions are preferred, but this is because of economical reasons and most There are advantages that can be used effectively. Effective liquid concentration varies from saturated liquid to dilute liquid. Ru.

Although water is an effective solvent in most cases, other solvents from about 1300” F. In the range of about 2000°F2, highly concentrated solutions, e.g. 25 to 40% by weight, are more effective. It tends to work. On the other hand, if the temperature exceeds 2000'F, the concentration should be lowered.

In other words, at such high temperatures, the water content per weight of the liquid is 80%.

85% or even 90%, the concentration of added soluble compounds ranges from about 0.5 to about 80% by weight of liquid. It decreases to 10%.

Urea within the above temperature range, especially above 1800°F when finely atomizing the solution. If two conditions are appropriate, N It was found that almost the entire amount was consumed in the reaction with Ox. Furthermore, when used in combination with urea , When urea reduces NOx, hexamethylenetetramine reduces the utilization of urea. The improvement is astonishing. Therefore, hexamethylenetetramine is The combination of the above-mentioned additive solution metals can be used to optimize NOx reduction and improve economic efficiency. This is an essential condition for Hexamethylenetetramine itself and other active substances such as urea. presence of at least about 25% based on the total amount of NOx and other NOx reducing agents. A typical weight ratio of hexamethylenetetramine to urea is preferably about 1. :3 to 3:1.

The solution of the additive compound is heated to a temperature of 1300°F, preferably 1500'F or higher. Evenly distributed within the exhaust gas stream at the location. Power generation plants in use and Large industrial boilers of the type used in other large installations usually have a water supply. 0 Typical cases where the reach of one hand is restricted due to the included jacket. In this case, access to the inside of the boiler is through the frame area and the top of the frame. When operating at full capacity, this will reach temperatures in the range of approximately 2200°F to approximately 2600’F. It is normal to In boilers that operate efficiently with gas, this reaching point (A The temperature of

Usually between about 2100°F and about 2600°F2, coal- or oil-fired It typically falls between 2050'F and 2400°F.

At these temperatures, the addition compound solution must be introduced at lower concentrations and more dispersed. It is effective to make the droplets larger when they are mixed.

The solution of the additive compound according to the invention is fluidized in order to achieve homogeneous mixing. The U Preferably, the droplet size is from about 10 to about 100 mm. It is preferable to be in the range of 0.000 mm, with an average diameter of about 50 to 10,000 mm. At temperatures below 2000°F, the droplet size is more preferably in the range of If the temperature is higher than 150 microns or less.

It is preferable that the droplet size is larger than this9, e.g. 500 microns or more. .

What is the concentration of the additive compound or compounds in the exhaust gas?

The concentration should be sufficient to reduce nitrogen oxide levels. If so, increase the rate of additive compound used relative to the baseline nitrogen oxide level. The molar ratio of nitrogen in the addition compound is adjusted to be from about 1=lO to 2:1, and about l: It is more preferable to take the range from 4 to 3=2.

II'''T The examples below are based on a small burner and a commercially available scale bottle. operational details about the nitrogen oxide system and the reduction in nitrogen oxides emitted. I will explain.

菟-Taneichi■-Yu Home heating with a 1.25 gallon per hour nozzle that burns with a slight excess of oxygen An initial period of test runs was conducted to establish baseline operating conditions for the burner. Roll around.

Oxygen (02) and nitrogen oxides (NO) obtained in two independent tests as shown in the table below. x) was recorded. For testing with rFc, operating temperatures reached 1550°F. Add 7.2% (v/v) rfc base liquid at a rate of 240ml/h to the burner nozzle. 02 and NOx at the specified temperature. Ta. When testing with hexamethylenetetramine (HMTA), the 155 After reaching 0'F, add 9.5% (K/v) hexamethylenetetramine solution again. into the exhaust air at the same rate and at the same point as in test 1, and then add 02 and NOx again. Recorded at the specified temperature. For each test, the fluid supply reached the specified temperature of 2000°F. Then it stopped. The results are shown in Table 1.

('F) 02 NOX ZNOx 02 NOX ZNOx (2:) (pp m) * Decrease (X) (ppm) * Decrease 1550 4.7 132 4.8 1321600 - - - 4.7 85 361700 4.9 98 26 4.6 70 471800 - 107 19 4.6 87 342 000 4.9 110 17 4.9 86 35 *Supplementary to 3χ excess oxygen in exhaust gas Corrected.

Residuals from 10 Peabody burners in a utility boiler Output of 80 MW by burning residual fuel oil issued. Forms medium to coarse droplets at 7 locations 48 feet above the top bar A series of atomizers were installed to direct the process liquid to the exhaust air at an average temperature of approximately 1600'F. Injected zero-order operation, i.e. (1) Perform baseline operation without using treatment liquid; (2) Hexamethylene A 15 wt% aqueous solution of tramin (HMTA) was added to The molar ratio of TA is maintained at 0.125 and the average salator diameter is approximately 150. (3) (2) Same conditions, but now injecting just a 6% solution of xamethylenetetramine: (4) Same as (3), but using a 15% by weight aqueous solution of HMTA, Tests were conducted keeping the molar ratio of HMTA to NOx at 0.5.

The test results are summarized in Table 2.

Experiment HMTA Mono V ratio NONO decrease Number (% by weight) (HMTA vs. NO) (ppm) (%) (2) 15 0 ．． 125 184 17 (3) 6 0.125 187 16 (4) 15 0.5 101 55 *Corrected to 3z″!A surplus oxygen in exhaust Act-1 example 1-1 The solution was injected into the exhaust air, which had an average temperature of about 2100°F. NO levels in combustion products corresponded to about 10 moles per hour.

The next operation, viz. (5) Perform baseline operation without using treatment liquid; (6) Urea in 3.5% water The solution was delivered at a baseline urea to NO ratio of 0.20. , 5p to produce droplets with an average diameter of about 150 to 200 microns. Inject with sig so that the urea supply amount of the liquid at that time is 2 moles per hour; (7) Same as (6), but with urea and hexamethylenetetramine (HMTA) combinations such that the ratio of chemical agent to baseline NO was 0.18. At that time, the amount of urea supplied to the liquid was approximately 1 mol per hour, and the amount of HMTA supplied was approximately 0. ．． It was added so that it became 8 mol.

The test results are summarized in Table 3.

Table--1 Experiment HMτAr; Fc element molar ratio NONO reduction number (weight Z) (weight (vs. No) (ppm)” (%) (6), + 3.5 0.2 226.4 5 24.5 (7) 1,75 1,75 0.18 174 41.9 Table 3 data shows that using urea reduces NO by 24.4% (sic); In this case, only about half of the urea is used, but when used in combination, it decreases by 41.9%. , from which both urea and HMTA are almost completely utilized. The additive compounds shown in Table 4 below, their concentrations and supply ratios are as shown in Table 4. This was different from Example 1.

Table--4 Addition concentration Supply temperature - NOX (ppm) - Compound (V/V) Ratio (°F) base after treatment % (ml/hr) line decrease Flyer 11.4K 280 1800-123 77 37.4 let 18 50 Seam f port 20Z 2808 1800-122 75 38.6-lu urea 1 850 Gua-shi 10Z 2B0 1800-120 80 33.3 carbonate 18 50 7=7k14.1Z 280" 1800-121 71 41.4 Urea sulfur Acid acid 1850 HMTA 122 280 1800-120 79 34.2 Methyl-15 2280 pieces 1800-122 70 42. Fluurea 1850 Urea 1oz 280 1800-122 72 41 Dimethyl 14.7z4 20 1790-42i element Methyl 12.3χ 420 1785-43 Urea Urea + 7χ & 3$ 420 1780 −− −− 37.5) IMTA 1.1'-A 18.5χ 420 1790 -52 Melamine 3.5χ 56 0 1800 115 90 21.8 *Additives are not completely added under the conditions of this test. It did not dissolve, and the NOX level fluctuated, but the level after the treatment indicated by 9 was low.

The above specification is for the purpose of teaching those skilled in the art how to carry out the present invention. −°Details all changes and improvements that will be obvious to the technically savvy person upon reading. However, such modifications and improvements are also covered by the following claims. Of course, it is included within the scope of the present invention.

Claims (21)

[Claims] 1. Guanidine, quanidine carbonate, biguanide, guanylurea sulfate, mela Min, dicyandiamide, calcium cyanamide, biuret, 1,1'-a Zobisformamide, methylol urea, methylol urea-urea condensate, dimethyl Group of dimethylurea, methylurea, dimethylurea and hexamethylenetetramine A liquid containing at least one additive compound selected from carbonaceous fuel with means for injecting it at a concentration and temperature effective to lower the A product that reduces the concentration of nitrogen oxides in the oxygen-rich exhaust produced by combustion. Seth. 2. The process of claim 1, wherein the exhaust temperature at the point of injection is greater than 1300°F. 3. Process according to claim 1, wherein the solvent comprises water. 4. In claim 1, the additive compound includes hexamethylenetetramine and nitrogen The molar ratio of hexamethylenetetramine to oxides goes from 1:6 to 2:1. The process of injecting enough liquid into the exhaust gas to 5. Claim 4 states that the ratio of hexamethylenetetramine to nitrogen oxides is A process in which the ratio is 1:4 to 1:1. 6. Claim 1 provides a process in which the solution contains hexamethylenetetramine and urea. vinegar. 7. Claim 6 provides that the weight ratio of hexamethylenetetramine to urea is 1. :3 to 3:1 process. 8. In claim 1, the solution is injected from multiple locations to generate dispersed droplets. A process in which the average outer diameter ranges from about 10 to about 10,000 microns. 9. 9. The process of claim 8, wherein the droplets are larger than about 50 microns. 10. In claim 1, the temperature is distributed to the exhaust gas from 2000°F to 2500°F. The process of spraying liquid. 11. Claim 10 provides that, based on the weight of the solution, the solution contains at least Process containing 80% solvent. 12. Claim 11 provides that, based on the weight of the solution, the solution contains at least Process containing 90% solvent. 13. An aqueous solution of urea and hexamethylenetetramine is prepared at a location where the exhaust temperature is effective. Maintain a certain concentration of urea and hexamethylenetetramine in the solution, and keep nitrogen in the exhaust gas. provided with means for injecting a solution effective in the exhaust gas to reduce the level of elemental oxides; The goal is to reduce the concentration of nitrogen oxides in the oxygen-rich exhaust produced by the combustion of carbonaceous fuels. The process of lowering. 14. Claim 13 provides that the exhaust temperature at the injection point is 1300°F and 1800°F. process in between. 15. Claim 14 states that hexamethylenetetramine for nitrogen oxides; The process of injecting enough solution to give a molar ratio of 1:6 to 2:1. 16. Claim 14 states that hexamethylenetetramine for nitrogen oxides; A process in which the ratio of is from 1:4 to 1:1. 17. Claim 13 provides that the solution contains hexamethylenetetramine and urea. Roces. 18. Claim 17 states that the weight ratio of hexamethylenetetramine to urea is A process in which the ratio is 1:3 to 3:1. 19. In claim 13, the solution is sprayed at multiple locations to form dispersed droplets. A process in which the Souter mean diameter ranges from about 10 to about 10,000 microns. 20. 20. The process of claim 19, wherein the droplets are larger than about 50 microns. 21. Claim 19 provides that the melt in the exhaust gas has a temperature of 2000°F to 2500°F. A process in which a liquid is injected and the solution contains at least 90% solvent.