JPH01115439A - Method for reducing amount of nox in product gas containing carbon black - Google Patents

Abstract

PURPOSE:To efficiently reduce the amt. of NOX in product gas contg. carbon black produced in a furnace carbon black reaction furnace by holding the gas at >=700 deg.C for 0.5-2sec in a part behind the rapid cooling part of the furnace. CONSTITUTION:Product gas contg. carbon black produced in a furnace carbon black reaction furnace 22 by feeding oil 20 as starting material is cooled with cooling water 23 in the second halt of the reaction chamber. The gas is then held at a high temp. of >=700 deg.C for 0.5-2 sec during passing through a roundabout flue 30 and reaches an air preheater 33. In order to considerably reduce the amt. of NOX in the gas, water-cooled dampers 31, 32 are attached to the flue 30.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for reducing NOX in waste gas in a carbon black manufacturing plant. In more detail, NOx can be removed by utilizing the temperature and gas components of the gas produced in the reactor, without having to perform additional denitrification treatment on the tail gas from a carbon black manufacturing plant or the waste gas after its heat has been recovered. Regarding how to.

[Conventional technology]

Furnace carbon black is produced by burning fuel oil together with an excess amount of air at the head of a cylindrical reactor, and injecting hydrocarbon feedstock into the combustion gas for thermal decomposition. The produced carbon black passes through a quenching section along with the generated gas, is collected by a back filter, and then goes through the process steps of granulation and drying to become a product.

On the other hand, the generated gas separated from the carbon black in the bag filter chamber is called tail gas, and due to its flammability, most of it is used as a heat source for the drying process and boiler, and the remainder is burned in the flare stack. After that, it will be released to the atmosphere.

The composition of the produced gas is mainly composed of water vapor, nitrogen, carbon-monide, hydrogen, and carbon dioxide, but it also contains nitrogen oxides (hereinafter referred to as NOX) produced at the head of the reactor. ing. Since NOx does not change during the tail gas combustion process, it is contained in the waste gas released into the atmosphere, causing air pollution, and must be reduced in order to prevent pollution.

Conventionally, methods for reducing NOx in tail gas include installing a separate denitrification device for redistribution, selectively using expensive low-nitrogen fuel oil, and other measures to prevent pollution. are forced to bear an increased burden.

In addition, as conventional methods for removing nitrogen oxides (NOx) from combustion gas, the following several methods have been proposed.

■ Cleaning and removal methods that mainly use alkaline aqueous solutions such as caustic soda aqueous solutions.

■ React NOX and reducing gas in the presence of a catalyst,
A method of reducing to nitrogen, etc.

■ A method of adsorption and removal using adsorbents such as activated carbon and zeolite.

■ A method of oxidizing to NO2 in the coexistence of an oxidizing agent such as MnO2, H20□, etc. and removing it by washing with water.

■ A method of contacting with an acidic urea aqueous solution to form nitrous acid, which is then reacted with urea and converted into nitrogen and CO2.

■ By adding an ammonia source to NOX in the combustion exhaust gas,
A method of converting it into water and nitrogen without a catalyst at high temperatures of 00°C or higher has also been proposed.

[Problem that the invention seeks to solve]

Although each of the methods proposed above has some degree of effectiveness, many practical problems remain. Especially low am
It is not effective when treating large amounts of NOx-containing gas.

Although various improvements have been made to cleaning equipment and types of alkaline solutions in the cleaning method using an aqueous alkaline solution as the main method, the removal effect is generally low.

The catalytic reaction method of method (2) is used when reducing gases such as hydrogen and methane are present in the exhaust gas.

Platinum metals and metal oxides such as copper and cobalt have been proposed as catalysts, but platinum, palladium, and the like are expensive. Furthermore, since metal oxides exhibit activity in a reduced state, the presence of oxygen often oxidizes the catalyst and turns it into an inactive oxide.

Furthermore, these catalysts are generally easily poisoned by sulfur, lead, etc., and there are also problems with catalyst stabilization.

The adsorption removal method of method (2) has a problem in the desorption of adsorbed nitrogen oxides, and when water vapor is present in the exhaust gas, nitric acid is generated on the adsorbent, making regeneration of the adsorbent extremely difficult.

The cleaning removal method in the presence of an oxidizing agent (method ①) still has economical and operational problems.

The cleaning method using a urea aqueous solution (Method ①) has the disadvantage that the cleaning equipment becomes large when a large amount of processing gas is used, and the gas temperature
If the temperature is 00°C or higher, there are problems in implementation.

The ammonia addition and high temperature reduction method of method (2) has the problem of ammonia cost.

As described above, conventional NOx removal methods have advantages and disadvantages, and no method has been found that is suitable for processing a large amount of low-concentration NOX-containing gas at low cost.

The object of the present invention is to provide separate reducing agents, oxidizing agents,
Without the use of neutralizers, catalysts, adsorbents and without the use of selective low nitrogen fuel oils.

An object of the present invention is to provide a method for reducing NOX in carbon black produced gas.

(Means for Solving the Problems) The present inventors have conducted extensive research to solve the above problems.The carbon black produced gas has a temperature of 1.600°C or higher in the reaction chamber of the reactor. The carbon black is rapidly cooled to improve the quality of the produced carbon black, but since it contains hydrogen gas and the carbon black itself is carbon and is a reducing agent, it is possible to reduce the impact on the quality of the carbon black. The present inventors have discovered that it is possible to significantly reduce NOX in the produced gas by maintaining the temperature after quenching at a high temperature within a range that does not affect the production of gas, and by maintaining the residence time within a certain range, and have arrived at the present invention.

That is, the present invention is characterized in that carbon black-containing product gas generated during carbon black production in a furnace carbon black reactor is maintained at a high temperature of 700 ° C. or higher for 0.5 to 2 seconds after the cooling section of the furnace. This is a method for reducing NOx in carbon black produced gas.

A high-temperature combustion gas atmosphere is formed by combustion of fuel oil in the reactor, and carbon black-containing gas produced by the thermal decomposition reaction of the hydrocarbon feedstock injected into the atmosphere is provided in the downstream region of the reactor. Approx. 1 due to rapid cooling by water injection
It is cooled to a temperature of 100°C and enters the air preheater from the furnace head through the flue duct.

The maximum temperature that enters the air preheater is determined by the material of the air preheater, and immediately before the air is cooled down again, water is blown in to cool it down to below that temperature.

In the present invention, the temperature of the carbon black produced gas is maintained at a high temperature of 700° C. or higher, preferably between 900 and 1100° C., for 0.5 to 2 seconds between the first water-cooled quenching section and the second water-cooled quenching section. For this purpose, the flue duct is characterized by having a large cross-sectional area or a long length.

When the temperature is 700° C. or lower, the NOX reduction reaction becomes slow, and the denitrification rate decreases to 70% or less at the above residence time.

Also, if the residence time is less than 0.5 seconds, even if the temperature is
Even when the temperature is 0 to 1100°C, the denitrification rate decreases to 70% or less. In order to increase the residence time to more than 2 seconds, considering the large amount of gas m, it is necessary to make the flue extremely long or to make the cross-sectional area extremely large, which is not practical and also Depending on the type of carbon black, there is a risk of quality deterioration.

The residence time between the conventional reactor and air preheater is less than 0.2 seconds.

As will become clear from the examples below, in an actual reactor, the denitrification rate could be greatly improved by setting the n-retention time at 700° C. or higher to 0.5 seconds or longer.

Moreover, no deterioration in quality of carbon black was observed as a result of this.

[Effect]

Unlike ordinary combustion waste gas, carbon black generated gas contains hydrogen gas and carbon black particles. The reaction No + C = 1/2N2 + C0 N0 + H - 1/2N2 + 820 occurred due to both of these, and by keeping the temperature above 700°C, the reaction rate increased, and the reaction time fell within the extended residence time in the flue. It is presumed that this is due to the incident.

〔Example〕

The present invention will be specifically explained below using test examples and examples, but the invention is not limited to these examples in any way.

(Example 1) A test was conducted in which tail gas (TG: carbon black produced gas) was retained in a high-temperature atmosphere and NOx was reduced by the reducing action of the hydrogen gas it contained.

The flowchart of the experimental apparatus is shown in Figure 4 (However, in Test Example 1, there is no carbon black capsule 18. It is supplied from the TGj lower 10.The TG passes through the It!I tank 11 and the blower 12.
After adjusting the flow rate with the flow meter 14, it is supplied to the quartz tube 16 inserted into the electric furnace 15, and! ! After passing through tank 17,
Dissipated into the atmosphere. Measurement of NOX was performed before entering the quartz tube (S
l) and after the buffer tank 17 has flowed out (S2), NOx is measured using the NOx automatic measurement method, and the JIS
It was converted into the NOX measurement value according to the method.

The test results are shown in Table 3.

From these experimental results, the reaction rate constant is Arrheni
Since the formula for us follows the formula =koexp (-E/RT), when applied to this formula, we get =438exp (-1
0150/RT) is obtained.

Since this is an experimental device, the residence time is 1/1/2 of the lower limit of the present invention.
10, but recovered by 40% at a reaction temperature of 1050°C.
A denitrification result of about 60% was obtained at 1255°C.

(Test Example-2) The influence of carbon black on the NOX decomposition reaction rate constant was investigated. The experimental apparatus is shown in Fig. 4, and the difference from Test Example-1 is that 3 to 5 carbon black was added to the porous capsule 18.
The test was carried out in the same manner as in Test Example 1 except that the sample was placed in a quartz tube 16. The capsule used was made of quartz and had an inner diameter of 20 M and a length of 1501111 mm, and its surface was perforated for ventilation.

Since the contact between the gas and carbon black is only within the capsule, when calculating, use the reaction rate constant obtained in the above experiment to estimate No. 11 at the entrance of the capsule, and use that NOx value. , the NOX decomposition reaction rate constant when contacted with carbon black was calculated. The experimental results are shown in the fourth
Shown in the table.

Compared to Test Example 1, the reaction rate constant is larger when TG is brought into contact with carbon black, and the NOX decomposition reaction is clearly promoted by carbon black.

(Example-1) In an actual carbon black reactor, the flue was made long (
Then, factory experiments of Example-1, Comparative Example-1, and Comparative Example-2 were conducted under the working conditions shown in Table 1 by changing the water injection position and the produced gas cooling temperature.

[Table 1] In Example-1, water is blown from a point at tl-0,143 seconds, expressed as the residence time of the produced gas in FIG. From Figure 1 to Figure 3, 3 is a combustion chamber, 4 is a reaction chamber, and 5 is a combustion chamber.
6 is a flue, 6 is a feedstock oil inlet, 7 is a water cooling damper, and 8 is an air preheater.

In FIG. 1 (Example-1), average temperature T1 from water injection port 1 to air preheater port 1 is 1.600°C. Average temperature T2 from water injection port 1 to air preheater port 1 is 900°C, residence time t2 is 0.
It was 765 seconds. That is, the total residence time was 0.908 seconds. The amount of water blown was 1.030/9/hr.

In Comparative Example-1, in FIG. 2, the first water inlet 1 is located at t3=Q, 132 seconds in terms of the residence time of the produced gas.
From there, at a residence time of 14=0.237 seconds, the second
A water inlet 2 was provided.

The residence time up to that point was 0.369 seconds. At this time, the average temperature up to water inlet 1 was T3-1,450°C, and the average temperature T4 between water inlet 1 and water inlet 2 was 900°C. Water blowing detective is 1.030 fl/hr from 1, 2 from 2.
To 345! Injected l/hr. The temperature after water inlet 2 was less than 700°C.

In Comparative Example 2, the water inlet 1 was provided at a location where the residence time of the produced gas was ts xo, 132 seconds in FIG. 3. The average temperature up to this water inlet 1 was T5-1.450°C. In this case, the amount of water injected from water inlet 1 is 3.3
It was set to 70Kg/hr.

The temperature after water inlet 1 was less than 700°C.

Table 2 shows the NOX content in the generated gas in the reaction chamber and the NOX content in the tail gas in this case.

(Table 2) In Example 1, in which the generated gas temperature was maintained at 90°C or higher for 0.908 seconds, a denitrification rate of 98.5% was obtained, but although the temperature was 900°C or higher, the i-to-remoe time was 0.369 seconds. In the case of Comparative Example-1 in which the heating time was less than 0.5 seconds, the llI2 nitrate ratio was 65.3%.

Furthermore, in the case of Comparative Example 2 in which the temperature was 1.450°C and the holding time was 0.132 seconds, the denitrification rate decreased to 34.7%.

In addition, the reason why the NOX value in the reaction chamber is high in Example-1 is that the generated gas temperature just before the air preheater is 840°C, and the preheated air temperature is as high as 653°C, which increases the combustion gas temperature and causes thermal NOx. This is presumed to be due to an increase in

As is clear from Table 1, no influence on the quality of carbon black was observed.

(Example-2) Using an actual reactor, 1.
A new detour flue measuring 000#lIφx10m was installed and tested.

In FIG. 5, 22 is a reactor. Raw material oil 20 is preheated by an oil preheater 21 and injected into the steady state gas. Cooling water 23 is blown into the rear half of the reaction chamber. 24 is a pure tank, 25 is a pure pump, and 26 is a heat exchanger.

The pure water is cooled by a heat exchanger 26 using water that is circulated through a water cooling tower 27 by a pump 28 . The carbon black generated gas is cooled to 1000°C by this water injection, and conventionally reaches the air preheater 33 within 0.45 seconds of sowing time, and the temperature was 850 to 900°C immediately before the air preheater.

By providing a bypass flue 30 of 1.0OOs+φ×10TrL to this, the temperature in front of the air preheater did not change, but the residence time of the generated gas became 1.3 seconds. 31.3
2 is a water-cooled damper, 34 is air, and 35 is preheated air.

NOX in conventional tail gas is measured by JIS method and is 17
The NOx in the tail gas was 0 to 190 ppm, barely passing the regulation value of 200 Dial, but by installing a bypass flue, the generated gas was held at 850°C or higher for 1.3 seconds, and the NOX in the tail gas was 80 ~100 Dl)l, which was able to be reduced to about 1/2.

Rapid cooling of the carbon black production gas is related to the specific surface area of carbon black and the size of stractures, and has been required from this point of view. The specific surface area of carbon black is measured by iodine adsorption ff1 (IA), and carbon black with a low IA is unsuitable for imparting reinforcing properties. In addition, the size of the strafture is measured by the DBP (Dave Tilphthalate) oil absorption, and the larger the strafture, the larger the strafture.The tinting power (TINT) is determined by the electron microscopic average particle diameter and particle diameter distribution of carbon black, the size of the stracture, and its It is an optical measure of particle physical properties such as distribution, structuring morphology, colloidal properties, etc., and is a factor related to rubber reinforcing properties.

No changes were observed in the iodine adsorption amount, DBP oil absorption amount, or coloring power due to the provision of the detour flue.

(Effects of the Invention) The present invention does not use new reducing agents, oxidizing agents, neutralizing agents, catalysts, adsorbents, etc. that are costly to reduce NOx, and selectively uses low nitrogen content fuel oil. We have developed a method to significantly reduce NOx in tail gas without deteriorating the quality of carbon black products by utilizing the temperature of carbon black generated gas, the hydrogen gas it contains, and the reducing properties of carbon black. This makes a great contribution to environmental conservation and the carbon black manufacturing industry.

[Brief explanation of the drawing]

Figure 1 shows that the generated gas is 700°C or higher from the reactor raw material injection position to the air preheater of the present invention. Reactor in which cooling water 1 was adjusted to maintain the temperature for 0.5 seconds or more.
It is a diagram showing a part of a flue. FIG. 2 is a cross-sectional view of a comparative example in which the cooling water 1 is the same as that in FIG. 1, but a larger amount of water than the cooling water 2 is injected, and the subsequent temperature is set to less than 700°. Figure 3 is a cross-sectional view of a comparative example in which a large amount of water was blown from the same water injection position as in Figure 1, and the subsequent temperature was below 700°C.
Figure 4 shows hydrogen in the produced gas and NO in carbon black.
1 is a flowchart of the experimental apparatus of Test Example-1 and Test Example-2 for understanding the X reduction reaction and the reaction rate coefficient. FIG. 5 shows a block diagram corresponding to Embodiment 2 in which a detour flue is provided in order to secure residence time in the conventional reactor-flue device. 1...First water inlet, 2...Second water inlet, 3...
・Combustion chamber, 4... reaction chamber, 5... ff way, 6...
Raw material oil charging inlet, 7...Water cooling damper, 8...Air preheater, 10...TG blower-111...Buffer tank, 12...Blower-113...Nitrogen cylinder,
14... Flow meter, 15... Electric furnace, 16... Quartz tube, 17... a% I tank, 18... Carbon black capsule, 20... Raw material oil, 21... Oil Preheater, 22... Reactor, 23... Water inlet, 24... Pure water tank, 25... Pure water pump, 26
... Heat exchanger, 27 ... Water cooling tower, 28 ... Water cooling tower circulation pump, 29 ... Flue, 30 ... Detour flue, 3
1... Water-cooled damper, 32... Water-cooled damper, 33
...Air preheater, 34...Air, 35...
Preheat air.

Claims (1)

[Claims] Carbon black-containing product gas generated during carbon black production in a furnace carbon black reactor is heated to a high temperature of 700°C or more after the quenching section of the furnace by 0.5~
A method for reducing NOx in carbon black generated gas, which is characterized by holding the gas for 2 seconds.