JP2011201717A - METHOD FOR REDUCING NOx IN COMBUSTION EXHAUST GAS FROM CEMENT FIRING EQUIPMENT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for economically and efficiently reducing NOx in a combustion exhaust gas generated from a cement combustion device by positively using a waste oil being a waste.SOLUTION: In the method for reducing NOx in the combustion exhaust gas generated from the cement combustion device, a waste oil-based solid fuel composed of a mixture of a waste oil and a waste oil-absorbing material is charged into a calcining furnace of an NSP kiln being the cement combustion device and subjected to reduction combustion in the calcining furnace.

Description

  The present invention relates to a method for reducing NOx in combustion exhaust gas of cement firing equipment, and more specifically, NOx in combustion exhaust gas discharged from cement firing equipment is economically and efficiently reduced using waste. It is about the method.

In cement burning facilities, fossil fuels such as pulverized coal, heavy oil, and oil coke are used. These fossil fuels contain a large amount of nitrogen.
By the way, the nitrogen content contained in the fuel is oxidized in the combustion process and becomes NOx. This NOx is pointed out as one of pollution sources (air pollution sources), and there is a strong demand for suppression of NOx generation amount. Even in the cement industry, the suppression of NOx generation is being pushed forward strongly.

For example, in the cement firing process, it has been conventionally performed to suppress the amount of NOx generated by employing a low NOx burner or a kiln operation.
However, in the case of this method, NOx is often not stable due to the recent diversification of fuel blending ratios, varieties, etc., and in order to comply with NOx emission regulations, efficient combustion is not possible, and cement burning is not possible. There was an inconvenience.

In addition, as a method for reducing NOx in the exhaust gas generated when the cement raw material calcined by the preheater is fired in the dry cement kiln, between the lower part of the preheater and the kiln bottom of the dry cement kiln, Patent Document 1 discloses a NOx reduction method for cement kiln exhaust gas in which organic sludge containing ammonia is introduced.
The proposal disclosed in Patent Document 1 uses organic sludge as waste, which is preferable in terms of cost. However, according to the tests by the present inventors, the organic sludge is disposed under the preheater. However, there is a limit in suppressing the amount of NOx generated, and a sufficient effect cannot be obtained only by introducing it between the furnace bottom of the dry cement kiln.

Also, a solid reducing agent that generates NH ₃ gas during pyrolysis is connected to a suspension preheater, an upper part of the calcining furnace, a lower part of the calcining furnace, a rotary kiln raw material inlet, or an inlet connected to the rotary kiln raw material inlet. Patent Document 2 discloses a method for removing nitrogen oxides in combustion exhaust gas introduced from at least one location selected from the hood.
According to this method, the charged solid reducing agent heads to the downstream side while gradually decomposing and volatilizing NH ₃ gas from the surface, so that the decomposed and volatilized NH ₃ gas and combustion exhaust gas are uniformly distributed. In addition, although it will be in contact for a long time and a high denitration effect can be expected, urea, ammonium bicarbonate, ammonium carbonate, ammonium oxalate, melamine, etc., which are exemplified as the solid reducing agent to be used, are all expensive. It is not an economical method because it is a new drug and does not serve as a fuel.

On the other hand, waste oil such as crude oil sludge, waste paint, and waste solvent has high energy, and is expected to be effectively used as fuel without being incinerated as waste.
However, waste oil has high viscosity, has no fluidity at room temperature, and has solid content that settles and settles, and has poor handling properties during transportation, etc. It was difficult to use.

JP-A-10-194800 JP 2004-24971 A

  The present invention has been made in view of the problems of the background art described above, and its purpose is to actively use waste oil as waste, and to generate economically and efficiently from cement firing equipment. An object of the present invention is to provide a method for reducing NOx in combustion exhaust gas.

As a result of earnest research to achieve the above-mentioned object, the present inventors have found that a mixture obtained by mixing waste oil such as crude oil sludge and waste paint and waste oil absorbent such as waste crushed waste has moderate flammability. When the mixture is put into a calcining furnace of an NSP kiln, which is a cement firing facility, the mixture is slowly reduced and burned by the generated reducing gas (CO). It has been found that NOx in exhaust gas can be efficiently reduced and denitrated (2NO + 2CO → N ₂ + 2CO ₂ ), and the present invention has been completed.

That is, the present invention provides the following [1] to [4] methods for reducing NOx in combustion exhaust gas of cement burning facilities.
[1] A waste oil-based solid fuel composed of a mixture of waste oil and a waste oil absorbent is charged into a NSP kiln calcining furnace that is a cement burning facility, and the waste oil-based solid fuel is reduced and burned in the calcining furnace. NOx reduction method in combustion exhaust gas of cement firing equipment.
[2] The method for reducing NOx in combustion exhaust gas of cement firing equipment according to [1] above, wherein the waste oil-based solid fuel has an average particle size of 30 to 100 mm.
[3] The method for reducing NOx in combustion exhaust gas of a cement burning facility according to [1] or [2], wherein the waste oil-based solid fuel has a water content of 10 to 60% by mass.
[4] Any one of [1] to [3] above, wherein the waste oil-based solid fuel is adjusted to at least a minimum handling property capable of being mechanically transported and mechanically charged. A method for reducing NOx in combustion exhaust gas of the cement burning equipment described.

According to the above-described method for reducing NOx in combustion exhaust gas from a cement firing facility according to the present invention, waste oil as waste is actively used without affecting the quality of cement clinker at all, and it is economical and efficient. In addition, NOx in the combustion exhaust gas generated from the cement firing facility can be reduced.
More specifically, when waste oil-based solid fuel is introduced into the NSP kiln calcining furnace, which is a cement calcining facility, as in the method of the present invention, the inside temperature of the calcining furnace is higher than the front temperature of the rotary kiln kiln. Although there is a possibility that unburned parts may come out due to lowness, etc., even if some unburned parts come out from the calciner, it will eventually enter the rotary kiln and gradually move toward the front of the kiln as the rotary kiln rotates. Combustion is completed while moving, so there is no fear of affecting the quality of cement clinker. Further, as described above, the combustion of the waste oil-based solid fuel charged into the calciner becomes combustion in a slow reducing atmosphere (reduction combustion), and NOx in the combustion exhaust gas is generated by the generated reducing gas (CO). Can be efficiently reduced and denitrated (2NO + 2CO → N ₂ + 2CO ₂ ). Furthermore, the combustion temperature of the fuel blown from the calciner burner is suppressed by charging the waste oil-based solid fuel into the calcining furnace, thereby suppressing the generation of thermal NOx and the amount of heat generated by the combustion of the waste oil-based solid fuel. Naturally, this contributes to the saving of fossil fuel such as pulverized coal supplied to the burner of the calciner, and NOx in the combustion exhaust gas can be reduced economically.

It is the figure which showed notionally the whole cement baking equipment which implements the NOx reduction method in the combustion exhaust gas which concerns on this invention. It is the figure which showed notionally the RSP type calciner which throws in waste oil type solid fuel in this invention. It is an expanded sectional view of the part which follows the II line | wire of FIG. It is an expanded sectional view of the part which follows the II-II line of FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram conceptually showing the whole cement firing facility for carrying out the NOx reduction method in combustion exhaust gas according to the present invention.

The waste oil-based solid fuel used in the present invention is a mixture of waste oil and waste oil absorbent.
Waste oil includes waste wire saw oil, oil sludge (for example, heavy oil sludge, crude oil sludge, etc.), waste oil regeneration residue (residue that remains after waste oil is regenerated using distillation equipment, etc.), waste cutting oil, waste polishing oil, waste ink, Examples include waste solvent, waste grease, waste vegetable oil, waste edible oil, and the like. These may be used singly or as a mixture of two or more thereof.
As waste oil absorbers, waste crushed materials, wood chips, waste polymers, waste sponges, paper scraps, various sludges, etc. can be used, and these waste oil absorbers and the above waste oils are mixed, combustibility and handling properties. The waste oil-based solid fuel is adjusted.

The particle size of the waste oil-based solid fuel is preferably set to an average particle size of 30 to 100 mm by adjusting the particle size of the waste oil absorbent such as waste crushed material and wood chips to be mixed. In the case of a small waste oil-based solid fuel having an average particle size of less than 30 mm, it is likely to burn when put into a calcining furnace and a reducing atmosphere may not be formed. On the contrary, in the case of a large waste oil-based solid fuel having an average particle size exceeding 100 mm, the handling property is poor and it is difficult to put into a calcining furnace.
The average particle size of the waste oil-based solid fuel can be measured using a standard sieve conforming to JIS Z 8801.

Moreover, it is preferable that the water content of the waste oil-based solid fuel is adjusted to 10 to 60% by mass. In the case of a dry waste oil-based solid fuel having a moisture content of less than 10% by mass, it is likely to burn when put into a calcining furnace, and there is a possibility that a reducing atmosphere cannot be formed. On the contrary, in the case of a waste oil-based solid fuel having a moisture content exceeding 60% by mass, the calorific value is low and the utility value as a fuel is reduced. The adjustment of the moisture content takes into account the moisture content of the waste oil by mixing the waste water and other waste water in consideration of the moisture content of the waste oil absorbing material such as waste wood and wood chips and the moisture content of the waste oil. This can be done by adjusting the rate.
The water content of the waste oil-based solid fuel can be measured by a method based on JIS K 2275 “Crude oil and petroleum products—moisture test method”.

  In addition, the handleability of the waste oil-based solid fuel can be at least transported by mechanical conveyors such as screw conveyors, bucket elevators, belt conveyors, etc., and can be handled by mechanical feeders such as double flap dampers and rotary feeders. What is necessary is just to set it as the mixture provided with handling property, such as the minimum fluidity | liquidity and adhesiveness which can be thrown in.

  1 uses waste tatami A and wood waste B as waste oil absorbers, and these waste oil absorbers are crushed to an appropriate particle size by a crusher 1 and then crushed waste oil absorbers and waste oil absorbers. Are mixed with the mixer 2 to obtain a waste oil-based solid fuel X having the above-described particle size, water content, and handling properties.

The waste oil-based solid fuel X, whose properties are adjusted by mixing waste oil and waste oil absorbent, is loaded into a vehicle, preferably a sealed vehicle 3 with a canopy, and is carried to the vicinity of a cement firing facility. The waste oil-based solid fuel X transported to the vicinity of the cement firing facility is put into the hopper 4 and transported to a calcining furnace of the cement firing facility by a mechanical transport device such as a screw conveyor 5, a bucket elevator 6 or a belt conveyor 7. Is done.
In addition, when the mixing facility of the said waste oil and a waste oil absorber and the cement baking facility are close, it is not necessary to carry by the vehicle.

In the present invention, the position where the waste oil-based solid fuel X is introduced is a calcining furnace of an NSP kiln that is a cement burning facility.
As shown in FIG. 1, the NSP kiln 10 includes a suspension preheater 11 composed of a plurality of stages, for example, four stages of cyclones C1, C2, C3, and C4, a calcining furnace 12 attached to the suspension preheater 11, The rotary kiln 14 is connected to the calciner 12 and the lowermost cyclone C <b> 1 via the inlet hood 13, and the cooler 15 is connected to the outlet of the rotary kiln 14. The cement raw material charged from the raw material charging port 16 is sequentially preheated in a cyclone of the suspension preheater 11 and then introduced into the calcining furnace 12 to perform a calcining reaction such as decarboxylation. And is baked as a cement clinker in the rotary kiln 14. The cement clinker discharged from the rotary kiln 14 is rapidly cooled in the cooler 15 and becomes the final cement clinker. In addition, KB is a burner provided in the rotary kiln 14.

There are various types of calcining furnaces 12 attached to the suspension preheater 11, but in the cement burning equipment shown in FIG. 1, an RSP type calcining furnace [swirl (S) furnace] is used. It is installed.
In this RSP type calcining furnace 12, the cement raw material collected by the cyclone C2 is put into the calcining furnace 12, and is efficiently heated by the swirling combustion system in the calcining furnace 12, and decarboxylation proceeds. Then, it is discharged downward from the calcining furnace 12 and put into the mixing chamber 17 where it is mixed with high-temperature kiln exhaust gas, and the cement raw material reaches a decarboxylation rate of 85% or more, and then collected by the cyclone C1. And is put into the rotary kiln 14.

  The configuration of the calcining furnace 12 will be described in more detail. As shown in FIG. 2, the calcining furnace 12 is provided with a combustion furnace 12a with a burner SB in the upper part, and is squeezed below the combustion furnace 12a. A calciner main body 12c is provided via the portion 12b. The diameter of the combustion furnace 12a is formed smaller than the diameter of the calcining furnace main body 12c. As shown in FIGS. 1 to 4, bleed ducts 18 a and 18 b branched from the air delivery pipe 18 connected to the cooler 15 are connected to the combustion furnace 12 a and the calcining furnace main body 12 c in the tangential direction, respectively. ing. Further, a raw material chute 19 for feeding the cement raw material to be calcined into the calcining furnace 12 is connected between the lower end of the cyclone C2 and the bleed duct 18b of the calcining furnace main body 12c. In the combustion furnace 12a, pulverized coal as fuel is burned in the burner SB, and the combustion of the pulverized coal is in a good and stable state by the air blown tangentially into the combustion furnace 12a via the bleed duct 18a. Maintained. The cement raw material collected by the cyclone C2 is introduced into the extraction duct 18b of the calciner main body 12c through the raw material chute 19, suspended in hot air, blown into the calciner main body 12c, and swirled. It gets on and disperses in the furnace and is heated so that decarboxylation proceeds efficiently. The mixing chamber 17 is provided by enlarging a part of the riser pipe of the suspension preheater, and the high temperature kiln exhaust gas coming from the lower part and the cement raw material and exhaust gas discharged from the calciner 12 from the side part are introduced. Here, the cement raw material which has been reheated and decarboxylated to 85% or more is collected by the cyclone C1 and put into the rotary kiln 14 through the inlet hood 13. In each drawing, the solid arrow indicates the flow of the cement raw material, and the broken arrow indicates the gas flow.

In the present invention, for example, the waste oil-based solid fuel X is introduced from the calcining furnace ceiling 12d above the fuel outlet of the burner SB installed in the combustion furnace 12a of the RSP calcining furnace 12 having the above-described configuration.
The waste oil-based solid fuel X is introduced into the waste oil-based solid fuel X that has been transported to the calciner 12 of the cement firing facility by a mechanical transport device such as a screw conveyor 5, a bucket elevator 6, or a belt conveyor 7. It is preferable to carry out by natural fall from the calcining furnace ceiling portion 12d into the calcining furnace through a mechanical charging device having a sealing function such as the flap damper 20 of the above.

  In addition, when the waste oil-based solid fuel X is introduced into the calcining furnace through the mechanical charging device having a sealing function such as the double flap damper 20, the chute 20a of the mechanical charging device is provided with a waste oil-based solid fuel. It is preferable to be installed in the calcining furnace ceiling portion 12d so that the charging angle α of X is 57 degrees or more, more preferably 60 degrees or more. This is because, when the charging angle α of the waste oil-based solid fuel X is less than 57 degrees, the falling speed of the waste oil-based solid fuel X is slow and may accumulate in the chute 20a and ignite in the chute 20a. This is because there is a concern that the

Further, it is preferable to dispose a dispersion rod 21 for dispersing the charged waste oil-based solid fuel X in the calcining furnace immediately below the chute 20a of the mechanical charging device. By disposing the dispersing rod 21, it becomes possible to decompose and disperse the waste oil-based solid fuel X that is highly viscous and lumps or lumps.
Note that a rotary feeder or the like can be used instead of the double flap damper 20 as a mechanical charging device having a sealing function.

  The amount of waste oil-based solid fuel X input to the calciner 12 is not particularly limited, but is appropriately determined according to various processing conditions such as the scale of the cement firing facility and the firing temperature. In a normal Portland cement firing facility using an NSP kiln with a maximum daily volume of 4,000 tons, 2-8 t / hr is appropriate.

Next, the operation of the cement firing equipment configured as described above will be described.
First, as shown in FIG. 1, the cement raw material charged into the suspension preheater 11 from the raw material charging port 16 is gradually heated by exchanging heat with the kiln exhaust gas while passing through the cyclones C4, C3, etc. The raw material heated to ˜750 ° C. is separated from the kiln exhaust gas in the cyclone C2. The separated raw material is introduced into the extraction duct 18b through the raw material chute 19, suspended and suspended in hot air at 300 to 700 ° C., and blown into the calcining furnace main body 12c, as shown in FIG. Become.

  On the other hand, the waste oil-based solid fuel X introduced into the calcining furnace from the calcining furnace ceiling 12d through the mechanical charging device having a sealing function such as the double flap damper 20 falls to the vicinity of the burner SB. As shown in FIG. 3, it is dispersed in the swirling air (bleeding air) blown into the combustion furnace 12a from the bleed duct 18a, flows while swirling around the burner SB, and burns gently.

  Part of the combustion heat is lost to the swirling flowing waste oil solid fuel X, the combustion temperature of the fuel blown from the burner SB is suppressed, and combustion (reduction) of the waste oil solid fuel X in a moderate reducing atmosphere Combustion) generates CO gas (reducing gas) and unburned carbon in the combustion furnace 12a. Therefore, the amount of NOx generated in the combustion furnace 12a is reduced, and the NOx generated in the combustion furnace 12a is partially reduced and denitrated by the reducing gas, so that the amount of NOx further decreases.

  The cement raw material supplied into the calciner main body 12c swirls and flows along with the flow of air blown in the tangential direction, and the combustion heat of the fuel blown from the burner SB and the combustion heat of the waste oil-based solid fuel X It is calcined by. At this time, since the waste oil-based solid fuel X, the reducing gas, and the unburned carbon flow from the combustion furnace 12a into the central portion of the calcining furnace main body 12c in a turbulent state, the combustion flame does not rapidly become high temperature. . Subsequently, the cement raw material in the calcining furnace main body 12 c flows down the inclined duct while being calcined, and is introduced into the lower portion 17 a of the mixing chamber 17. At this time, the cement raw material reaches the lower portion 17a of the mixing chamber 17 in a mixed state with unburned carbon.

  Then, the mixture of the cement raw material and unburned carbon in the mixed state merges with the kiln exhaust gas discharged from the rotary kiln 14 in the mixing chamber lower portion 17a to form a fluidized bed of a high-concentration mixture. At this time, NOx in the kiln exhaust gas is mixed with NOx generated in the calciner 12 and diluted. Moreover, since the unburned carbon in the fluidized bed is combusted by surplus oxygen in the kiln exhaust gas, the fluidized bed becomes 800 to 900 ° C. suitable for the decarboxylation reaction, and becomes a further reducing atmosphere. Therefore, NOx in the kiln exhaust gas is reduced and denitrated, and the exhausted NOx of the entire kiln is greatly reduced.

  Subsequently, the cement raw material is mixed and heat-exchanged with the high-temperature combustion gas in the mixing chamber 17, and is uniformly mixed and stirred at 830 to 900 ° C., then enters the cyclone C1, and enters the inlet hood 13 as a cement raw material at 820 to 900 ° C. Through the rotary kiln 14. The cement raw material thrown into the rotary kiln 14 moves while rolling toward the outlet, and is heated to 1450-1500 ° C. by combustion heat of heavy oil or the like sown in the kiln burner KB during that time, and fired as a cement clinker. . The cement clinker discharged from the rotary kiln 14 is rapidly cooled in the cooler 15 and becomes the final cement clinker.

As described above, the waste oil-based solid fuel X introduced into the combustion furnace 12a of the calcining furnace becomes combustion (reduction combustion) in a slow reducing atmosphere, and combustion exhaust gas is generated by the generated reducing gas (CO). The NOx contained therein can be efficiently reduced and denitrated (2NO + 2CO → N ₂ + 2CO ₂ ). In addition, the combustion temperature of the fuel blown from the burner SB can be suppressed by charging the waste oil solid fuel X into the combustion furnace 12a, the generation of thermal NOx can be suppressed, and the amount of heat generated by the combustion of the waste oil solid fuel X is Naturally, this contributes to the saving of fossil fuel such as pulverized coal supplied to the burner SB of the calciner, and NOx in the combustion exhaust gas can be reduced economically. Moreover, even if some unburned matter comes out of the calcining furnace 12, it finally enters the rotary kiln 14 and completes combustion while gradually moving to the front side of the kiln as the rotary kiln 14 rotates. There is no worry of affecting the quality of cement clinker.

The preferred embodiments of the method for reducing NOx in the combustion exhaust gas of the cement firing facility according to the present invention have been described above, but the present invention is not limited to the above-described embodiments, and is described in the claims. It goes without saying that various modifications and changes are possible within the scope of the technical idea of the present invention.
For example, in the above embodiment, the RSP type calcining furnace has been described as the calcining furnace into which the waste oil-based solid fuel X is charged. However, the calcining furnace is not limited to this type of calcining furnace. The waste oil-based solid fuel X may be introduced into a calcining furnace or an SF type calcining furnace.

Test example

  When the actual cement firing equipment conceptually shown in Figs. 1 to 4 (ordinary Portland cement firing facility with NSP kiln with a daily maximum capacity of 4,000 tons) is used and waste oil-based solid fuel is introduced from the calciner And the amount of NOx generated was measured.

The properties and input amount of the waste oil-based solid fuel were as follows.
A waste oil-based solid fuel obtained by mixing crude oil sludge and a waste oil absorbing material composed of waste crushed crushed material and wood chips at a mass ratio of 1: 2 was used. The average particle diameter of the waste oil-based solid fuel was 70 mm, and the water content was 30% by mass. Further, the waste oil-based solid fuel has a handling property capable of being mechanically transported and mechanically charged.
The waste oil-based solid fuel was charged at 2.6 t / hr from the calcining furnace ceiling 12d shown in FIG.

The amount of NOx generated in the inlet gas was measured at a denitration plant (not shown) attached to the cement firing facility.
The measurement results are shown in Table 1.

DESCRIPTION OF SYMBOLS 1 Crusher 2 Mixer 3 Sealed vehicle with canopy 4 Hopper 5 Screw conveyor 6 Bucket elevator 7 Belt conveyor 10 NSP kiln 11 Suspension preheater C1, C2, C3, C4 Cyclone 12 Calciner SB Calciner burner 12a Combustion furnace 12b Preliminary furnace body 13 Inlet hood 14 Rotary kiln KB Kiln burner 15 Cooler 16 Raw material inlet 17 Mixing chamber 18 Air delivery pipe 18a, 18b Extraction duct 19 Raw material chute 20 Double flap damper 20a Chute 21 Dispersing rod A Waste tatto B Wood waste O Waste oil X Waste oil-based solid fuel

Claims (4)

  A waste oil-based solid fuel comprising a mixture of waste oil and a waste oil absorbent is charged into a calcining furnace of an NSP kiln that is a cement firing facility, and the waste oil-based solid fuel is reduced and burned in the calcining furnace. A method for reducing NOx in combustion exhaust gas from cement firing equipment.   The method for reducing NOx in combustion exhaust gas of a cement firing facility according to claim 1, wherein the waste oil-based solid fuel has an average particle size of 30 to 100 mm.   The method for reducing NOx in combustion exhaust gas of a cement firing facility according to claim 1 or 2, wherein the waste oil-based solid fuel has a water content of 10 to 60 mass%.   The cement oil burning facility according to any one of claims 1 to 3, wherein the waste oil-based solid fuel is adjusted to at least a minimum handling property capable of being mechanically transported and mechanically charged. A method for reducing NOx in combustion exhaust gas.

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