JPH07502194A - Aqueous ammonia injection scheme - 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] Aqueous ammonia injection scheme field of invention The present invention relates to a non-catalytic method for reducing nitrogen oxide concentrations in combustion exhaust.

More specifically, the present invention injects ammonia-rich vapor into such combustion exhaust. A method of converting the nitrogen oxides contained therein into less harmful compounds, water-based This invention relates to an improved method for producing ammonia-rich vapor from an ammonia solution.

Background of the invention Combustion emissions and waste from various machinery and equipment contribute to air pollution when discharged into the atmosphere. Becomes the main source. One particularly troublesome source of pollution found in many combustion exhaust streams is the primary This is NO2, which is extremely powerful. Furthermore, NO2 undergoes photochromication in the presence of sunlight and hydrocarbons. It is believed that this process undergoes a series of reactions known as smog formation. No□ The main source is NOx, mostly fueled by gas and oil for power plants. steam boilers, process heaters, incinerators, coal-fired boilers, Occurs in stationary mechanical equipment such as glass furnaces, cement kilns, and oil field steam generators. .

Various methods have been developed to reduce nitrogen oxide concentrations in combustion emissions. . One such method is described in Lyon U.S. Patent No. 3,900,554. This is a non-catalytic method. This US patent is incorporated herein by reference. Disclosed in the patent The proposed method converts Now to N2 by injecting ammonia into the combustion exhaust stream at high temperatures. It teaches how to reduce In general, the following two equations describe the overall process: Shows the dominant reaction: NOX 10NH3+02 + (N2) ---1 →N2+H2ONH3+ 02 −−−−−→ NOx + 820 in the first equation As shown, hydrogen (N2) was injected together with NH3 to reduce the effect of the first reaction. The properties can be extended, for example, at lower temperatures. Of course, NO according to the second equation It is desirable to minimize the production of x.

U.S. Patent No. 3,900,554 describes ammonia as a pure substance or as a precursor. Teach to use either form. A useful precursor form of ammonia is ammonia carbonate. Compounds include ammonium ammonium, ammonium formate, and ammonium oxalate.

All these substances produce ammonia when vaporized, while formic acid precursors produce ammonia. The oxalic acid precursor also produces oxalic acid. Vaporization of ammonia or its precursors is a separate process. Achieved by injecting it as a step or into the hot effluent to be treated You may. Ammonium formate or ammonium oxalate, or their aqueous solutions If vaporization of the formic acid, oxalic acid, or both by either thermal or catalytic means before may be decomposed.

Since the issuance of U.S. Patent No. 3,900,554, the concentration of NOx (nitrogen oxides) Patents or publications relating to the injection of ammonia into combustion exhaust streams to reduce continues to rapidly increase. This invention is disclosed in Patent No. 3.900.554.4, 115,515. 4,423°017.4,507,269.4,624,840 and 4,63 It is based on the teachings of No. 6,370 and further improves those teachings. Anmo that Nia or its precursors may be stored and/or used in an aqueous solution. Although generally described, the method defined in the above-mentioned patent typically involves the use of vaporized anhydrous It is carried out by injection of Monia. However, for this method anhydrous ammonia There are some recognized problems with using . Anhydrous ammonia is usually However, there are environmental concerns regarding the storage of large amounts of ammonia at factory sites. Safety concerns are growing. The use of aqueous ammonia eliminates these concerns. The reason is that aqueous ammonia can be stored at atmospheric pressure and if In the event of a spill, the release of anhydrous ammonia would pose a significant threat to human health. This is because ammonia release will be delayed to such an extent that it will almost never be shown. .

Although posing less of a risk to the environment, liquid ammonia in its aqueous form is problematic. There is a problem. This is because conventional ammonia injection in such form To solve the inherent incomplete distribution of ammonia resulting from the rapid vaporization of ammonia solution. This is because excessive ammonia is required for this purpose. As a result, the ammonia flow rate Additional chemicals are required to degrade and/or gas purification systems further ammonia to reduce excess ammonia to an acceptable level. Monia removal equipment is required.

The present invention overcomes the limitations of conventional or existing practices, but substantially reduces Make it less. This is used to create ammonia-containing steam that is injected into the combustion exhaust. This is achieved by using an aqueous solution of ammonia. The use of steam causes significant mixing This makes it possible to reduce the amount of excess ammonia to a minimum.

However, the vaporization of aqueous solutions of ammonia to create ammonia-containing vapors Although the concentration of monia is low, it can be removed directly without treatment and in an environmentally acceptable manner. Creates a blowdown stream that may contain too much ammonia to handle.

Yet another feature of the invention is to direct this blowdown flow in an environmentally acceptable manner. including methods of processing.

Summary of the invention According to the present invention, the concentration of nitrogen oxides contained in combustion exhaust can be reduced in a non-contact manner. An improved method is provided. This method involves injecting ammonia into the combustion exhaust. and the ammonia is obtained by partial vaporization of an aqueous ammonia solution. It exists in the form of an ammonia-rich vapor stream. This partial vaporization is rare It also creates a blowdown stream of aqueous ammonia, which can be vaporized or not vaporized. May be applied anywhere within the runt or injected into the combustion exhaust. .

In one preferred embodiment of the invention, the operating conditions within the partial vaporization means are such that is adjusted to maintain the desired ammonia concentration in the liquid and gas phases. .

Brief description of the drawing The invention will be more clearly understood by the detailed description below taken in conjunction with the drawings. There will be.

FIG. 1 is a schematic diagram of one embodiment of the invention, in which ammonia-containing An aqueous solution containing steam and ammonia is used to treat combustion emissions. There is.

FIG. 2 is a schematic diagram of a second embodiment of the invention, in which the ammonia-containing steam is used to treat combustion emissions. .

FIG. 3 is a graph showing the evaporator operating conditions of the method of the present invention, where ammonia vs. The NOx ratio is 1.5, the ammonia feed is a 25% aqueous solution, and this graph A variety of raw materials were used to maintain a constant 30 Vppm ammonia flow rate in the effluent. shows how the evaporator temperature needs to be changed for a NOx concentration of .

FIG. 4 shows one embodiment of a control scheme for carrying out the method of the invention. FIG.

Detailed description of the invention As mentioned above, the present invention is a gas and oil fueled steam generator for power plants. Combustion of steam boilers, process furnaces, municipal incinerators, coal-fired boilers, etc. Concerning an improved non-contact method for reducing the release of nitrogen oxides (NO) from sources into the atmosphere .

As is well known, combustion is usually carried out in a device called a firebox. In part, it is commonly accomplished within combustion devices such as boilers, furnaces, and incinerators.

Combustion generally involves igniting a suitable fuel in the presence of air using one or more burners. It is achieved by doing. The main combustion products are carbon dioxide and water vapor. other combustion The products are carbon monoxide and various oxides of nitrogen and sulfur with excess oxygen and unconverted of nitrogen. - Together, these combustion products are also referred to here as combustion emissions. Configure the.

The method of the invention uses ammonia in the form of an aqueous solution. This aqueous solution is partially The vaporization creates a vapor stream enriched with ammonia, which in turn reduces Not emissions. Mixed with a carrier gas for final injection into the combustion exhaust for the purpose of reducing be done. Partial vaporization of the aqueous ammonia solution also produces a dilute aqueous ammonia stream; It may be vaporized or injected without vaporization into the same or another combustion exhaust. . Alternatively, a dilute aqueous ammonia stream, e.g. If diluted, such flow would be diverted to another part of the plant, e.g. in a scrubber. It could be used.

As in common practice, the present invention shows that the NOX reduction reaction is the most effective. ammonia is injected into the combustion exhaust for a sufficient residence time within a temperature range. Consists of things. Achieving maximum NOx reduction while minimizing ammonia flow The optimal amount of ammonia is a function of many variables, the main ones being temperature and residence time. It is. Determine the optimal amount and location of ammonia injection and ensure that ammonia and combustion emissions are closely With a carrier gas that has sufficient velocity through the nozzle to achieve proper mixing Injection of ammonia-containing steam is preferred.

In general, any suitable means will permit the injection of ammonia into the combustion exhaust. It may be used for In the simplest embodiment, a suitable Tubes that are insulated or cooled allow the injected ammonia to burn out It can be arranged to cover substantially the entire cross-sectional area of the gas flow region.

Generally, the volume of combustion emissions under the conditions in which reducing gas is injected is the desired NOx considerably higher than the amount of ammonia required to achieve reduction, in fact 1 It could be 0,000 times or even more. Therefore, this capacity of ammonia Ammonia is usually combined with a diluent to achieve the desired mixing and contacting of ammonia. will be done. In general, any non-toxic gaseous substance may be used as a diluent. These include steam, nitrogen, helium, etc. The preferred carrier is compressed air. It is mind.

The temperature of combustion emissions is typically highest at or near the point of combustion, but until it is released into the atmosphere or otherwise loses its properties as combustion emissions. , as the exhaust moves along the flow path from the point of combustion, its temperature increases axially (flow along the path) and radially (outward). In addition, which combustion equipment The temperature at which the fuel is burned also determines the type of fuel being burned, the amount of such fuel burned, and the type of fuel being burned. depending on the number of burners used to It will vary depending on operating conditions such as the cooling rate applied.

Effective NOx reduction can be achieved over a relatively wide temperature range by changing the reducing gas composition. can be achieved across the range. However, the above changes in temperature as well as the discharge flow Using a single reducing gas injection means at a fixed location as a result of changing the flow rate through the NOx to the atmosphere in all possible operating modes of a given combustion device when It is generally not possible to achieve the maximum reduction in emissions. This drawback is different from Multiple variations for injection into the discharge stream within different temperature and/or flow rate ranges This can be avoided to some extent by providing a composition that Furthermore, multiple Injection means may be provided along the combustion exhaust flow path.

The reaction between ammonia and nitrogen oxides in combustion exhaust is approximately 0.1 atm to 100 atm. It may also be carried out under pressure. Ammonia in the temperature range from 1300’ to 1600° There is an effective residence time to allow NOx to be removed from the combustion exhaust stream. Adjust the rate of combustion emissions as well as the mixing of ammonia in the post-combustion zone to do. Residence times may suitably be in the range 0.001 to 10 seconds.

In the practice of the invention, ammonia is contacted with combustion exhaust in the presence of oxygen. . Combustion exhaust usually contains a moderate amount of oxygen. However, the oxygen content is very low If not, air may be used to dilute the combustion emissions, increasing the oxygen content to the total volume of the emissions. The amount is about 0.1% by volume or more, preferably about 1 to 15% by volume.

The amount of ammonia suitable for the practice of the present invention is usually approximately 0.0% of the N OK concentration in the combustion exhaust. ．． It is in the range of 4 to 50 times. The minimum amount of ammonia is usually 1 of the NOx removed. at least 1 mole per mole of ammonia, depending on the amount of ammonia used; The physical amount can be selected from the viewpoint of economical operation and N2Ox removal rate.

1 mole or more per mole of NOx removed to achieve high conversion of NOx. It is desirable to use ammonia in the above ammonia amount. However, such a large The amount of ammonia is such that even if the temperature exceeds the temperature range where NOx is reduced, ammonia will burn. This causes it to remain unreacted in the effluent. Combustion released into the atmosphere Unreacted ammonia in the effluent is referred to herein as ammonia breakthrough. a Ammonia breakthrough often has to be minimized, so combustion emissions Both the ammonia concentration range and the allowable residence time range for Now in the feedstock have been reduced. Commercial applications will be limited by the need to Tolerable amount of NOx reduction Related government regulations will be relevant.

FIG. 1 shows one embodiment of the invention. Used to treat combustion emissions The ammonia source, an aqueous ammonia solution, is preferably placed in tank 1 at near atmospheric pressure. Saved. In operation, pump 3 transports ammonia to the ammonia vaporization means. This means is an ammonia evaporator 5.

This evaporator has two streams: an ammonia-rich first stream in line 7; Create a dilute aqueous ammonia stream in 23. Ammonia evaporator 5 performs the necessary separation. Any conventional means may be used. As will be understood by those skilled in the art, This can be either an evaporator drum or a stripping tower. evaporator drum Typically, indirect heat is provided by steam to achieve the desired vaporization.

The stripping tower is equipped with vacuum and/or heat and/or stripping gas. Vaporization is achieved using a Suitable stripping gases include steam and air. steaming Qi may be introduced directly into the stripping tower.

The ammonia-rich vapor stream in line 7 is fed to line 1 from carrier gas supply means 9. 1 carrier gas. Typically the carrier gas is vapor or compressed It's air. Pulp 13 and valve 15 provide flow regulation and ammonia and capillary It is used for rear gas ratio adjustment, and the automation of this system requires a normal process. It will be understood by those skilled in the art that control devices may also be used. ammonia The combined gas mixture in line 17 consisting of steam and carrier gas is is injected into the combustion device 21 via a , through which combustion emissions flow. The dilute aqueous ammonia flow in line 23 is diverted to valve 25. into the combustion exhaust by one or more spray nozzles 27. .

Alternatively, the dilute aqueous ammonia stream 23 is preferably supplied with a carrier gas. In stream 11, a carrier gas, e.g. For example, it may be combined with water vapor or compressed air. For compressed air, carrier gas The gas is exposed to high temperatures (typically 350-400°F) caused by the heat of compression. Since dilute aqueous streams can be easily vaporized by injecting them into a carrier gas stream, There will be. A conventional nozzle is used to introduce the dilute aqueous stream into the carrier gas transport conduit. A nozzle may be used and the nozzle may be aligned with the flow of the carrier gas. stomach. Of course, to achieve vaporization of the dilute aqueous ammonia stream into the carrier gas stream It is within the scope of this invention to utilize additional heating means or other means.

The operating conditions of the ammonia evaporator 5 are such as to provide suitable concentrations and quantities of the two streams. May be adjusted; these concentrations and amounts are based on the total amount of ammonia injected (steam and NO! concentration and required to achieve the required N Ox reduction. The generally accepted model is equal to the product of the ammonia to NOI molar ratio. N using ammonia injection.

Determined by evaluation of x reduction. However, ammonia injected in liquid form Acceptable ammonia from reaction along with unreacted ammonia from steam injection Limit the flow rate so that it does not exceed the flow rate.

An alternative embodiment of the method of the invention is shown in FIG. Atmospheric pressure or An aqueous solution of ammonia stored nearby is pumped to evaporate the ammonia. (Stripping Tough-35 in this case). This tower 35 has two streams, namely the ammonia-rich first stream in line 37 and the diluted aqueous stream in line 43. Creates an ammonia flow. In this example, tower 35 is driven by water vapor in line 36. Vaporization is achieved and this water vapor is introduced directly into the bottom part of the tower 35.

A dilute aqueous ammonia stream in line 43 is drawn from the bottom of tower 35 and After passing through line 39, it is typically sent to combustion device 50 via line 44. . Alternatively, since the aqueous ammonia stream is dilute, it can be valved. 39 may be used in another part of the plant, e.g. in a scrubber. .

The ammonia-rich vapor stream 37 mentioned above is taken from the top of the tower 35, which carrier gas through line 54 from carrier gas supply means 52 and valve 5; 6. Mixed afterwards. Ammonia vapor and carrier gas combined in line 45? A gas mixture consisting of 50 into which the combustion exhaust flows.

The operating conditions of the stripping tower 35 provide suitable concentrations and quantities of the two streams. These concentrations and amounts are adjusted so that the total ammonia injected is NOx concentration and ammonia vs. NOx required to achieve the required NOx reduction using a generally accepted model to be equal to the product of the molar ratio of It is determined based on the evaluation of NOx reduction by injection of air.

Figure 3 shows an ammonia to Not ratio of 1.5 and an ammonia feed of 25 % aqueous solution. Is this curve based on various initial NOx concentrations? Ammonia flow rate of 30 VPPm in the effluent while having an untreated NOx concentration It shows how the evaporator temperature must be changed to keep constant.

FIG. 4 shows a possible control scheme for implementing the invention.

Aqueous ammonia in tank 60 is pumped by pump 62 to flow control valve 6 4 to the evaporator drum 66. Automatic recirculation valve 68 connects pump 62 to used for protection. This flow control valve 68 is connected to the evaporator drum. 66 to the level controller 70 required to maintain the desired liquid level. more open or closed. The heating source 72, which in this example is water vapor, is evaporative. regulated by a pressure sensing control system 74 that senses the pressure in the container drum 66. be done. Constant pressure in the evaporator drum allows precise flow control of ammonia injection rate desirable to ensure the achievement of The flow rate of steam containing ammonia is NO! to control near-containing steam injection! Control system (not shown) is adjusted in response to a request signal 76 from the.

Blowdown removed from evaporator drum 66 through adjustable valve 80 The flow rate of stream 78 is controlled by a temperature sensing controller that senses the temperature in evaporator drum 66. 82.

Flow control of blowdown stream 78 by heat sensing controller 82 is used to maintain the desired ammonia concentration in the liquid phase of the vessel drum 66. The reason is that this is a function of temperature and pressure, and pressure is regulated independently. It's for a reason. If the concentration is too high, reduce the temperature to achieve the desired temperature and concentration The system is self-regulating as the valve is closed until the on the other hand, If the temperature is too high, the concentration in the liquid will be lower than desired. the valve is the desired Open wider until concentration is achieved, with strong liquid blowdown flow and feed rate increase degree.

Example In the method according to the invention, combustion emissions containing NOX are treated with ammonia. As a result, NOx is reduced to nitrogen. This example shows 300 vpp in the combustion exhaust. It is assumed that the initial NOX is m. 671bs/hour of ammonia and 2011b An aqueous ammonia stream consisting of s/h of water is introduced into the evaporator drum. Evaporator The vaporization of aqueous ammonia in the drum is carried out using steam providing 45 KW of heat. achieved. Operating conditions in the evaporator drum are 250°F and 50 psia . From the evaporator drum there are two streams: 611 bs/hr of ammonia and 86 bs/hr of ammonia. an ammonia-rich first steam stream consisting of 1 bs/hr water and 6 lbs/hr A second blowdown liquid stream consisting of 115 Ibs/hour of ammonia and 115 Ibs/hour of water is taken up. be taken out. The second stream is for steam injection introduced into the combustion exhaust at the first location. A second stream is used for liquid injection introduced into the same combustion exhaust at a second location. It is used for The combustion exhaust treated in this way has 120 ppm of Not calculated to have a 60% decrease in the content.

Those skilled in the art will appreciate that the injector of the present invention can be applied to various types of combustion systems. will be easily understood. The invention has been described in connection with specific embodiments. However, the present invention is capable of further modifications, and this application does not cover any modifications or variations of the present invention. use or suitability, and within the scope of known or common practice in the art. and includes such modifications from this disclosure that fall within the scope of the invention. It will be further understood that it is intended to

Figure 2 combustion emissions water vapor T two international search report Continuation of front page (51) Int, C1,' Identification symbol Internal office reference number 7704-3K (72) Inventor: Creedel Donald E.

New Chassis, United States 38 Woodrest Drive, Convent Station, 07961 l F23J 15100A

Claims (1)

[Claims] 1. A method of reducing the concentration of nitrogen oxides contained in combustion emissions, comprising: (a) The aqueous ammonia-containing solution is partially vaporized in the separation zone to form ammonia. at least two streams, a first stream consisting of enriched steam and a second stream consisting of dilute aqueous ammonia. (b) carrying said first stream of ammonia-enriched vapor; to be mixed with Yagas; (c) A mixture of ammonia-rich vapor and carrier gas is produced by a combustion zone. (d) said second stream consisting of dilute aqueous ammonia; (i) injected into the combustion exhaust, or (ii) installed in a scrubber or other plug. be used with a client device; The method characterized by: 2. Dilute aqueous ammonia is injected with ammonia-rich steam. A method according to claim 1, including injection into the combustion exhaust at different locations. 3. Inject dilute aqueous ammonia into the carrier gas, evaporate it, and then The method according to claim (1), wherein the method is injected into the extract. 4. Claims where the carrier gas is compressed air heated to 400-500°F. Method of range (4). 5. A method of reducing the concentration of nitrogen oxides contained in combustion emissions, comprising: (a) The aqueous ammonia-containing solution is partially vaporized in the separation zone to form ammonia. at least two streams, a first stream consisting of enriched steam and a second stream consisting of dilute aqueous ammonia. (b) producing said second stream of dilute aqueous ammonia into a carrier; This is vaporized by injecting it into Yagas to create a dilute ammonia vapor stream. thing; (c) converting said dilute ammonia vapor stream to said first stream comprising ammonia-enriched vapor; (d) combining said combined ammonia vapor stream with said combined ammonia vapor stream; injecting a steam stream into the combustion exhaust produced by the combustion zone; 6. Claims where the carrier gas is compressed air heated to 400-500°F. Method of range (5). 7. The heat source supplied to the separation area is controlled by a pressure sensitive controller. The method includes: sensing pressure in the separation region; and controlling the pressure in the separation region. By holding the force constant, the flow rate of ammonia-rich vapor from the separation region is controlled as desired. The method according to claim (5), characterized in that the method is maintained within a range. 8. controlling the flow rate of the ammonia-rich vapor according to the demand signal, and The flow rate of the dilute aqueous ammonia stream was controlled in the separation zone using a temperature sensitive controller. Maintaining the ammonia concentration in the liquid phase within the desired range as a function of pressure and temperature The method according to claim (5), characterized in that: 9. Those that reduce the concentration of nitrogen oxides contained in the combustion emissions produced in the combustion zone In law, (a) Partially vaporize the aqueous ammonia-containing solution in the vaporization region to A first stream consisting of Nia-rich steam and a second stream or blow consisting of dilute aqueous ammonia. producing at least two streams of downflow; (b) ammonia-rich vapor; injecting air into the combustion exhaust at a first location in or near the combustion zone. and; (c) the same combustion emissions with or without vaporization of dilute aqueous ammonia. to inject into something; The method comprises changing the operating conditions in the vaporization region to the ammonia in the first and second streams. The heating source in the vaporization region is adjusted to provide an appropriate concentration and amount of Ensure that the desired flow rate and injection rate of the ammonia-rich vapor injectate is achieved. Sensing the pressure within the vaporization region to ensure that a constant pressure is maintained within the vaporization region. The flow of ammonia-rich steam is regulated by a pressure-sensitive controller that Adjust the flow rate of the second or blowdown stream to the evaporator according to the demand signal. vaporize so that the desired ammonia concentration is maintained in the liquid phase as a function of temperature and pressure. It is characterized by being adjusted by a temperature sensing controller that senses the temperature of the area. Said method. 10. The ammonia-rich vapor is mixed with a carrier gas before being injected into the combustion zone. The method according to claim (9).