JPS59215504A - Method and device for reducing discharge of nitrogen oxide from calciner - 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 The present invention provides a new and advanced method and apparatus for reducing nitrogen oxide emissions from incineration systems. More specifically, one invention relates to the reduction of nitrogen oxide emissions from installations for the calcination of solid carbon-containing materials, such as petroleum coke and anthracite.

Petroleum coke is a very pure form of carbon and is the main raw material for the production of calcined carbon and graphite products. Anthracite is also a raw material for certain carbon products. Both petroleum coke and anthracite are also widely used in the production of electrodes for the aluminum industry. However, petroleum coke and jIiE smoky coal.

It contains a significant amount of volatile components, for example in the case of petroleum coke, from 5 to 15%, typically about 10%. Therefore, calcination is necessary before using coke or coal as a raw material for the production of calcined carbon products or graphite products or for other uses.
Calcination is the heating of carbon-containing materials in a rotary kiln, vertical shaft, or electric calciner to a temperature of the order of 1200 to 1800°C, depending on the final use of the product. achieved by. Most petroleum coke is calcined in rotary kilns, and in the manufacture of electrodes the calcination temperature for petroleum coke is usually about 1250°C. During the calcination stage, moisture, hydrocarbons, and other volatile components are removed and the density of the coke increases.

The hot waste gases from rotary kiln calcifiers contain hydrocarbon vapors and entrained carbon-containing solids or coke particles, which cannot be released into the atmosphere under current environmental regulations. do not have. Instead of being released, the 101-temperature gas stream is mixed with combustion air and combusted in a thermal incinerator.

It is common practice to remove carbon-containing solids or coke particles entrained with hydrocarbon vapors before the gases are released into the atmosphere. However, the operating conditions of lightning in thermal incinerators, including a large excess of oxygen and high combustion temperatures, favor the formation of nitrogen oxides (NOx), adding another problem. That's why. Nitrogen oxides are considered one of the major sources of air pollution in many regions, and current government regulations require reducing emissions of this pollutant from stationary industrial sources.

Various attempts have been made to suppress nitrogen oxide emissions by controlling thermal incinerators.

For example, this includes injecting combustion air at various locations in the incinerator to reduce excess oxygen used to produce nitrogen oxides. These attempts have generally been unsuccessful and unreliable due to the difficulty of mixing and distributing cold combustion air with the hot gas stream being incinerated.

It is therefore a general object of the present invention to provide a new and advanced method and apparatus for reducing nitrogen oxide emissions during the incineration of gas streams containing combustible components. .

A more specific object of the present invention is to provide a novel and advanced method for reducing nitrogen oxide emissions from incineration systems used in equipment for calcining carbon-containing solids, particularly petroleum coke and anthracite. A method and apparatus are provided.

In general, the above objective is to provide a staged combustion zone between the rotary kiln calcinator and the thermal incinerator, so that the entrained carbon-containing solids or coke particles are not burned, but the gas This is accomplished by supplying the population of this combustion zone with the substantially stoichiometric air volume required to combust only the hydrocarbon vapors contained in the combustion zone. High temperature selective combustion of hydrocarbons is achieved in this staged combustion zone because hydrocarbon vapors are easily oxidized in a short time compared to carbon-containing solids or coke particles. This product gas introduced into the thermal incinerator still contains entrained carbon-containing solids or coke particles, but is essentially free of hydrocarbons and excess oxygen. 5 The required additional combustion air is then added and mixed with the gas at the exit of the staged combustion zone, and the combustion of the carbon-containing solids or coke particles takes place in the thermal incinerator at lower temperatures and longer residence times. make sure that you are By eliminating the harmful combination of high temperatures and abundant excess oxygen, incinerator power and NO
x emissions are significantly reduced.

A detailed description of the features and advantages of the present invention will be provided in conjunction with Figure 1, which is a schematic diagram of a conventional petroleum coke calcination apparatus; and Figure 2. 1 is an enlarged schematic diagram showing a modification of the apparatus of FIG. 1 according to the present invention; FIG.

A typical prior art petroleum coke calcination operation using a tilted rotary kiln is shown in FIG.

The kiln numbered IO is connected to a spillover chamber 11 at its upper high end and to a firing hood 12 at its lower end. burner 1
3 is attached to the hood 12.

The fuel inlet line 14 and the primary air intake line 16 connected to the outlet of the blower 17 are connected (411).

Another blower 18 supplies secondary air to the hood 12 through a line 19. In some cases, tertiary air is supplied by blower 21 and line 22.

It is introduced into a plurality of bows 1- (not shown) of the shell of the kiln 10.

Finely powdered or finely ground raw petroleum coke is
As illustrated by line 23, rotary kiln 1
It is thrown at the end of the high position of 0.

The coke moves downward in the kiln 10 (to the left in FIG. 1), and then moves through the hood 12 and kiln
The high-temperature combustion gas generated inside the coke moves upward (toward the right in FIG. 1) and forms a counterflow relationship with the coke. As the coke moves downwards inside the kiln.

Moisture and volatile hydrocarbons are removed from the coke and the chemical structure of the coke is changed to produce a product of the intended quality. The gas streams exiting the two ends of rotary kiln 10 contain not only the moisture and hydrocarbon vapors removed from the coke (but also a significant amount of entrained coke particles).

Hot calcined coke exits the lower end of kiln 10 and passes through line 24 from hood 2 to rotary cooler 2.
Enter 6. Cooling water is connected to line 27 and spray nozzle 2
8 and into cooler 26 where the coke is cooled to approximately 300 degrees Fahrenheit (150 degrees Celsius) in direct contact with water.

The cooled calcined coke product is removed from discharge line 29.

High temperature flue gas exits from the top of kiln 10.

It passes through the spillover chamber 11 and a short communication passage 30 and enters the harrassle 31 of the thermal incineration chamber 3Z.

Combustion air is supplied to the harrassle 31 by a line 33 communicating with the outlet of the blower 34.

In the incinerator chamber 32, the hydrocarbon vapors and entrained coke particles in the calciner exhaust gas stream are completely combusted, and the resulting gases are discharged into the atmosphere through the connected exhaust stack 3G. be done. Large particles of coke that emerge from the top of kiln 10 without being directed into the hot flue gas stream are collected in spillover chamber 11 and returned to the raw coke supply via line 37 for recycling or otherwise. It is collected and used in the following manner.

The thermal incineration system requirements of a petroleum coke calcination plant are more complex than those of a conventional fuyum incinerator. This is because the incineration system must perform the following functions: viz.

(1) Oxidation of volatile hydrocarbons.

(2) Retention of large entrained coke particles until the particle size is reduced by oxidation.

(3) Rapid oxidation of small-sized coke particles.

These multiple functions are achieved in conventional petroleum coke incineration systems by using high temperatures, in excess of about 2000 degrees Fahrenheit (1095 degrees Celsius), excess #1, and long residence times.

The volatile hydrocarbon components of the calciner exhaust gas are oxidized rapidly (e.g., residence time of about 0.5 seconds) if sufficient oxygen is present. The entrained coke particles in the gas stream, however, require a fairly long residence time for complete combustion because of the limited oxygen dispersion of the combustion reaction. To achieve the desired performance of the incineration system, all combustion air is generally introduced from the harrassle 31. This configuration allows the hot kiln exhaust gases to mix well with the cold combustion air, producing a relatively hot flame5, but because the volatile hydrocarbon material is relatively easily oxidized.

That is, it is burned. however.

As a result, the combination of excess oxygen, high combustion temperatures, and long residence times within the incinerator 32 promotes the formation of nitrogen oxides.

According to the invention, a staged combustion zone is placed between the hot exhaust gas outlet from the kiln and the gas inlet of the incinerator chamber, and by controlling the introduction of air into this zone, the incinerator exhaust gas is Pre-combustion of only the hydrocarbon components takes place without significant oxidation, ie combustion, of the entrained coke particles.

More specifically, applicant's staged combustion zone is located at the location represented by passageway 30 in FIG.

As shown in Figure 2, the applicant's staged combustion zone is.

It is generally indicated as 50. Long, horizontally placed.

It is provided using a cylindrical or circular container lined with refractory material. The main part 5I of this container is.

It has a large diameter and frames the combustion zone 52. A small diameter artificial section 53 is connected to the spillover chamber 11 at the high end of the kiln 10, and the vessel sections 5I and 53 are connected together by a tapered section 54. A plurality of primary air injection nozzles 56 are attached to the tapered container portion 54, and the nozzles 56 include:
It is oriented at an angle so that the airflow is directed angularly inwardly and forwardly relative to the longitudinal axis of the container 50. - A secondary air vasosle 57 is placed in an annular manner around the container, surrounding the air nozzle 56.

- air for combustion is supplied to the vanosl 57 through line 58;

At the opposite end of the main body portion 51, i.e. at the outlet, the container 50 has an outwardly tapered portion 59;
and a vertical flange or wall section 61 attached to the inlet of the thermal incineration chamber 32. A plurality of secondary air injection nozzles 62 are mounted in tapered portion 59 such that the air flow from the nozzles is directed angularly inwardly and forwardly with respect to the longitudinal axis of container 50 . One annular secondary air bathosle 63 surrounds the air nozzle 62.

Secondary air is supplied to the air outlet 63 by line 64.

The calciner exhaust gas from the kiln IO has a salinity of approximately 1600 to 2200 degrees Fahrenheit (870 to 1205 degrees Celsius);
As already mentioned, unburned hydrocarbon vapors and unburned entrained coke particles, and.

Often contains small amounts of carbon monoxide. Furthermore.

The gas stream does not contain any oxygen. Immediately after passing through the reduced diameter artificial vessel section 53 of the vessel 50, the hot gas stream is mixed and directly mixed with the primary combustion air introduced through the nozzle 56.

According to the principles of the invention, the amount of primary combustion air injected at this location oxidizes all hydrocarbon material (and carbon monoxide, if present) contained in the calciner exhaust gas to carbon dioxide. limited to the substantial septic air volume required for Thus, as the mixture of calciner exhaust gas and primary combustion air passes through the combustion zone 52, the hydrocarbon components of the gas stream (and any carbon monoxide present) are removed without significant oxidation of the entrained coke particles. to preferentially oxidize, ie.

be burned. What makes this preferential oxidation possible?

Since hydrocarbon materials (and carbon oxides) burn more easily than coke particles, limiting the residence time of the gas stream in the combustion zone 52 can result in significant combustion of the entrained coke particles. Virtually complete combustion of hydrocarbons (and carbon oxides) is achieved without

At a point downstream of the primary air nostle 56, after the calciner exhaust gas stream has been completely oxidized, secondary combustion air exits the nozzle 62 to provide the oxygen necessary for combustion of the entrained coke particles. Injected into the gas stream. As shown in FIG. 2, the preferred location for the injection of secondary combustion air is near the outlet of the single stage combustion vessel 50, as the gas stream enters the incineration chamber 32.

In this way, the secondary combustion air is mixed directly with the gas stream before or during its entry into the incinerator, thereby eliminating the stratification often found in conventional system incinerators. Avoid problems with proper mixing. The amount of secondary combustion air injected through the nozzle 62 is controlled so that the entrained coke particles in the gas stream are completely combusted inside the incinerator chamber 32 . It is desirable to provide sufficient secondary combustion air so that the available oxygen slightly exceeds the stoichiometric amount required for complete combustion of the coke particles.

The gas velocity in the staged combustion vessel 50 must be at least the same as the velocity of the waste stream from the kiln 1° to prevent precipitation of entrained coke particles. The internal diameter of the 5 vessel 5o is therefore selected to ensure the necessary gas velocity to prevent the entrained coke particles from falling out.

Additionally, the length of vessel 50 is selected to ensure the residence time within zone 52 necessary to effect complete combustion of the hydrocarbon component of the gas. Since hydrocarbons are more easily oxidized than coke particles, a relatively short residence time within the zone 52 is sufficient, for example about 0.3 to 0.7 seconds, typically about 0.7 seconds. It is 5 seconds. However, since the combustion reaction of the entrained coke particles proceeds more slowly, the incineration chamber 32 is designed to provide a much longer residence time than the residence time within the staged combustion zone 52.

For example, a residence time of at least about 12 seconds is usually required to ensure combustion of the largest of the entrained coke particles.

The highest temperatures obtained in this process occur in the two-stage combustion zone 52, where the hydrocarbon material is combusted.

However, by controlling the injection of primary air into the nozzle 56, the situation of excess oxygen is avoided when maximum 10j temperatures prevail. In this way, the production of nitrogen oxides is controlled even though the kinetics and equilibrium of NOx production are dominated by high temperatures.

Because there is no excess oxygen needed for nitrogen oxidation.

suppressed. Since the combustion reaction of the entrained coke particles proceeds much more slowly, the initial release of heat at the point of secondary air injection through nozzle 62 is comparatively less than that obtained at the point of primary air injection through nozzle 56. low. As a result, peak temperatures of about 2600 degrees Fahrenheit to about 3000 degrees Fahrenheit (1430 degrees Celsius to 1650 degrees Celsius) may be obtained within combustion zone 52;
At the point where the gas mixes with the secondary combustion air injected through nozzle 62, the gas temperature actually decreases;
The peak temperature inside the incineration chamber 32 has been reduced to a lower level 9
For example, from about 2200 degrees Fahrenheit to about 2500 degrees Fahrenheit (1205 to 1370 degrees Celsius).

By using the present invention, nitrogen oxide emissions are significantly reduced due to the elimination of the high temperature and abundant excess oxygen in conventional petroleum coke incinerators. be.

The actual emissions of nitrogen oxides from the system depend on the nature of the raw coke input, the operating conditions of the kiln.

Depends on incinerator design and other factors.

However, in either case, the production of NOx is less than in conventional systems.

Of course, the chemical mass amount of air required for complete combustion of the hydrocarbons (and carbon oxides) in the calcination furnace exhaust gas.

It depends on the hydrocarbon content in the gas, which depends on various factors, such as the hydrocarbon content of the green coke, the feed rate of the green coke, the hydrocarbon composition, and the amount of fuel gas and air injected into the kiln. Any suitable means can be used to control the primary air injection from nozzle 56 so that the amount of oxygen does not significantly exceed the stoichiometric requirement. For example, the control system
Means may also be provided for measuring the NOx content or unburned hydrocarbon content of the gases exiting the air supply system 2 and adjusting the primary air injection accordingly. In many cases, effective control of secondary air injection involves continuously measuring the exit temperature of the gas from the first stage combustion zone 52 and automatically controlling the air injection to achieve a set maximum temperature. This is achieved through control. For example, in typical driving, approximately 2 degrees Fahrenheit
A maximum temperature of 950 degrees (1620 degrees Celsius) is achieved by using 100% of the stoichiometric air requirement. The amount of secondary combustion air injected through the nozzle 62 is preferably controlled by monitoring the oxygen content of the flue gas from the incinerator stack and adjusting the injection of secondary air to reduce the amount of flue gas. to the desired level of excess oxygen inside. Generally, the injection of secondary combustion air will increase the oxygen content to between about 1% and about 10%, preferably between about 2% and about 5%.
Control to keep it between %.

Although only two primary air nozzles 56 and two secondary air nozzles 62 are shown in FIG. 2, the size, quantity, and placement of the air injection nozzles may vary between the hot process gas and the cold combustion. (selected to be mixed with air for use).

Generally, the degree of mixing increases with increasing number of nozzles and decreasing nozzle diameter to increase gas velocity.

Although the foregoing description of FIG. 2 relates to a petroleum coke incineration process, the present invention is also applicable to anthracite calcinations.

The following is a hypothetical operating example of the present invention based on design calculations of a petroleum coke calcination plant such as that of FIG. 2 with a capacity of 50 tons/15 green coke.

The temperature of the exhaust gas stream from kiln 10 is 1800 degrees Fahrenheit, and the materials in this stream are listed in Table 1 below.
°−1 Bottom 1) Top/Verse SCFM-Carbon Oxide
4.309 972 carbon dioxide 26
,873 3.858 ni $, 127,5
20 28.768 Oxygen OQ Sulfur dioxide 987 -97 Volatile hydrocarbon 7,489 7.883 Water 2
9. 811-10. 4.62 Carbon fine particles
7.014 ~ Ash content 28
~Total 204.031 52.040 The stoichiometric amount of air necessary to combust all the carbon monoxide and volatile hydrocarbons in the kiln exhaust gas to carbon dioxide and water is added through nozzle 56. . -The list of substances in the airflow is shown in the table "-4" L4 SCFM Oxygen
30.4,21 6,005 Nitrogen 100,16
7 22.597 Moisture 566
199 Total 131.154 28,801 The gas velocity in the kiln is 3000 ft/min, and to prevent the entrained particulate carbon from falling off, the gas velocity in the 9-stage combustion zone must be 3000 ft/min. must exceed the limit.
The agglomerator 50 is designed such that the combustion zone 52 has an internal diameter of 13.3 feet, thereby allowing a combustion zone of 3500 feet/ft.
yielding a gas velocity of minutes. The length of the strip is 29.2 feet, giving a dwell time of 0.5 seconds.

The exhaust gas stream from staged combustion zone 52 has a temperature of 2980 degrees Fahrenheit.
degree (1640 degrees Celsius), this flow of material -1-----
---211--1 ~Table 2'' - 4 bases j top/poem SCFM carbon dioxide 55,611 7.984 nitrogen
227.688 51.365 oxygen
0 0 sulfur dioxide
985 97 Moisture 43.860
15.391 Carbon fine particles 7,014
=Ash 28 -Total 335.186 74.837 Secondary air is introduced through the nozzle 62 and mixed with the exhaust gas from the refrigerating zone 52 in the 9th stage l') V m, in the amount.

This amount is sufficient to combust all particulate carbon to carbon dioxide and provide 2% excess oxygen in the exhaust gas from the incinerator 32. Secondary air flow material 54 o'clock Bar 1 Carbon dioxide 81,431 11.690 Nitrogen 3
23,691 73.023 Oxygen 10,
381 2.04.9 Sulfur dioxide 98
5 97 Moisture 44,401
15.581 Ash content 28 -
Total 460.917 102.440 The gas emitted from the incinerator chimney is approximately 120 ppm or less NOx
NOx levels using prior art calcining and incineration systems of the type shown in FIG.
It is more than PPM.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a conventional petroleum coke filling device, Figure 2
The figure is an enlarged schematic diagram showing a modification of the apparatus of figure 1 according to the invention. 10...kiln, 11...spillover chamber. 12... Baking hood, 13... Burner, 14
...Fuel inlet line, 16...-Next air intake line, 17.18.21.34...Blower, 19.2
2.24.27.33.37.58.64...Line, 23...Line, 26...Rotary cooler, 2
8...Spray nozzle, 29...Discharge line,
30... Connecting passage, 31... Hasosul, 32...
Thermal incineration chamber, 36... Chimney, 50... Container, 51
．． 53... Container part, 52... Combustion zone + 54,5
9...Taper part, 56...Air injection nozzle, 5
7... Secondary air basosulu, 61... Flange or wall portion, 62... Secondary air injection nozzle, 63...
Yo next air hasosul.

Claims (1)

[Scope of Claims] (11) A hot exhaust gas containing hydrocarbon vapors and entrained carbon-containing solid particles is removed from the calciner and introduced into a thermal incinerator for combustion of said vapors and said particles. In the calcination process of carbon-containing solids, a 5-stoichiometric amount of combustion air is used to pre-combust only the hydrocarbon vapor in the aforementioned gas, without pre-combusting the carbon-containing solid particles, and in effect A method of introducing a hydrocarbon- and oxygen-free product gas into a thermal incinerator in which the aforementioned carbon-containing solid particles are combusted with additional combustion air, thereby reducing nitrogen oxide emissions from the incinerator. (2) A method according to claim 1, characterized in that said improvement consists of the following steps: (i) burning the carbon-containing solid particles while sufficient to burn the volatile hydrocarbons; In the first zone, said gas is mixed with a substantially stoichiometric amount of air for a relatively short residence time, which is not long enough to cause combustion, and thereafter the gas is mixed with excess combustion air. introducing this mixture into the second zone of said incinerator for a relatively long residence time sufficient to effect the combustion of said particles. (3) The method of claim 1. and, furthermore, said improvement is characterized in that it consists of the following steps: namely: transferring said exhaust gas comprising hydrocarbon vapors and entrained carbon-containing solid particles to a method having one inlet and one outlet; A staged combustion zone is passed through. Combustion air is introduced into said zone near said inlet, the amount of which is sufficient to effect most complete combustion of the hydrocarbons in said gas. The stoichiometric requirements shall not be significantly exceeded. The combustion air as mentioned above shall be mixed with the gases as mentioned above within the said zone;
providing a limited residence time within said zone sufficient to effect nearly complete combustion of said hydrocarbon vapor without burning said particles, whereby the gas produced is a hydrocarbon vapor and Excess oxygen becomes virtually indestructible. Mix excess combustion air with the above-mentioned product gas. 1. By introducing this mixture into an incinerator and providing sufficient residence time to said mixture to effect combustion of said particles within said incinerator. Avoid the combination of high temperatures, excess oxygen, and long residence times in the incinerator mentioned above, which promote the formation of nitrogen oxides. (4) The method of claim 3, further comprising: a peak temperature within said staged combustion zone of about 2600 degrees Fahrenheit to about 30 degrees Fahrenheit;
00 degrees Fahrenheit, and the peak temperature within said incinerator is about 2200 degrees Fahrenheit to about 2500 degrees Fahrenheit. (5) The method of claim 3, further comprising a residence time in the staged combustion zone of about 0.3 to 0.7 seconds;
and a method characterized by a short residence time in the incinerator (both about 12 seconds). (6) The method of claim 3, further comprising: (7) The method of claim 3, further characterized in that the staged combustion zone is characterized in that the gas passing through the zone is a velocity sufficient to prevent precipitation of entrained carbon-containing solid particles, and sufficient to provide preferential combustion of said hydrocarbon vapors, but insufficient to burn said carbon-containing solid particles; (8) one calcination furnace, one incinerator, and a method for transporting hydrocarbon vapor from the above-mentioned calcination furnace to the above-mentioned incinerator; and a passageway for passing the high-temperature calciner exhaust gas containing the entrained carbon-containing solid particles.In an apparatus for calcining carbon-containing solids, said passageway has one inlet and one inlet. means for defining a staged combustion zone having an outlet and through which the incinerator exhaust gas passes before entering the incinerator; and the combustion of said carbon-containing solid particles in said incinerator exhaust gas. means for introducing a controlled amount of combustion air into said zone near said inlet to effect preferential combustion of said hydrocarbon vapors but not said carbon-containing solid particles; and means for mixing additional combustion air with the gases entering said incinerator from said outlet to effect combustion. said means for defining an incinerator having an inlet end portion configured to receive and take hot exhaust gases from the incinerator, an intermediate combustion zone portion and an outlet end portion configured to discharge gases to the incinerator. a long cylindrical combustion vessel having a plurality of nozzles mounted at the inlet end portion for injecting the controlled amount of combustion air into the combustion zone portion, and an incineration vessel from the aforesaid outlet; 8. The apparatus of claim 8, characterized in that it comprises a plurality of additional nozzles attached to said outlet end portion for injecting said additional combustion air to be mixed with the gases entering the furnace. , furthermore, said staged combustion zone has a velocity sufficient to prevent precipitation of entrained carbon-containing solid particles through which said staged combustion zone passes, and sufficient to effect preferential combustion of said hydrocarbon vapors. but characterized in that the two dimensions are determined so as to maintain an insufficient residence time to burn the carbon-containing solid particles mentioned above.