JPH0470554B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for limiting the presence of nitrogen oxides in the exhaust gases emitted by a thermal storage heating device, and also to a method for limiting the presence of nitrogen oxides in the exhaust gases emitted by thermal storage heating devices, and also to a method for limiting the presence of nitrogen oxides in the exhaust gases emitted by thermal storage heating devices, and also to a process which is suitable for this purpose and which tends to block the pores of thermal storage beds. The present invention relates to a heat storage device adapted to remove harmful substances from a heat storage bed.

A thermal storage heating device usually includes two or more thermal storage devices,
These regenerators are connected to a furnace containing a charge to be heated by combustion products fed through the furnace wall in the vicinity of the regenerators. This storage heating device is characterized in that the combustion products supplied by one regenerator in the so-called combustion stage emit waste heat in the form of waste gases leaving the furnace, and this waste heat is in the heat collection or recovery stage. It is designed to be recovered by another heat storage device.

Each regenerator typically includes a shaft housing a regenerator bed located between two openings.

One opening communicates directly with the furnace and serves as an outlet for discharging combustion products to the furnace during the combustion phase of the regenerator, and as an inlet for receiving waste gas from the furnace during the heat collection phase of the regenerator. The other opening serves as an inlet for receiving combustion air to combust the fuel in the combustion chamber during the combustion phase of the regenerator, and as an outlet for discharging the waste gas as exhaust gas to the atmosphere during the heat collection phase of the regenerator. work.

The thermal storage bed recovers heat from the waste gas during the heat collection phase before the waste gas is discharged from the thermal storage heating device as waste gas. The thermal storage bed then releases its stored heat to preheat the combustion air as it passes through the thermal storage bed before reaching the combustion chamber during the combustion phase.
The storage bed itself is permeable to fluids such as waste gases and of course air, and often consists of a porous structure of individual particles of heat collecting refractory material.

A combustion chamber is located between the regenerator bed and an opening in direct communication with the furnace and serves to effect combustion of the fuel and preheated combustion air during the combustion phase, thereby producing combustion products. During the combustion phase, fuel is injected into the combustion chamber and a device is provided to ignite the fuel so that combustion occurs.

The combustion chamber may form part of a burner incorporated into a regenerator forming part of a thermal storage heating device. Representative such storage heating devices are disclosed in US Pat.
8527894.

Preheating combustion air in the manner described above has now become a well-established technique for improving the efficiency of high temperature furnaces by recovering heat from the waste gas.

One effect of preheating the combustion air is generally to increase the temperature of the flame resulting from the fuel combustion process. This performs a combustion reaction, but tends to increase the formation of nitrogen oxides, mainly NO and _NO2 .
In fact, when the fuel is natural gas, the formation of these oxides increases significantly with flame temperature and is overwhelmingly caused by thermal fixation of the atmospheric nitrogen present in the combustion air. The amount of oxide produced is also determined by the amount of time the flame is held at these high (peak) flame temperatures (residence time).

As a result of the combustion of fuel and air, nitrogen oxides (abbreviated as _NO
It is now known that _NOX in the exhaust gases flowing from thermal storage heating devices causes air pollution that contributes to the acidification of rain, and the interaction of _NOX with hydrocarbons in the atmosphere produces photochemical oxidants. and undesirable in terms of environmental impacts such as reduced visibility if high concentrations of _NOx are released.

In some countries, for example Japan, there are
Legislation already exists to limit _the presence of _NO It is essential to limit the

A known method of reducing the concentration of NO _x produced by a burner is to supply water vapor at the combustion point. The water may be supplied in the form of liquid water that is injected into the flame, or the water vapor may be provided in the form of steam that is injected into the flame. Water, when in liquid form, forms steam on contact with a flame.

The actual presence of water vapor in the combustion chamber increases the volume and heat content of the gas in the combustion zone. As a result, the concentration of _NOx in the combustion gas decreases. However, injecting water or steam at the combustion point removes heat from the flame, which unfortunately cannot be recovered from the subsequent waste gas. As a result, the overall efficiency of the process is reduced.

It is an object of the present invention to provide a technique for limiting the presence of nitrogen oxides in the exhaust gases leaving the regenerator, with an associated reduction in overall process efficiency that is less than that obtained with the previously described methods.

It is also an object of the invention to provide a regenerator which is suitable for the above-mentioned purpose and which is thus also adapted to remove treatable substances from the regenerator bed that tend to block the pores of this regenerator. It is.

According to one aspect of the invention, during the combustion phase of the regenerator,
In the exhaust gas leaving the regenerator, characterized in that water or steam is injected into the regenerator and during the preheating collection phase the water or steam reaches the combustion chamber of the regenerator via the regenerator bed of the regenerator which is preheated. A method of limiting the presence of nitrogen oxides is provided.

According to another aspect of the invention, a shaft containing a heat storage bed and a shaft during combustion are arranged in such a way that water or steam enters the combustion chamber of the heat storage unit through the heat storage bed, which is generally preheated in a preheat collection stage. , and a device for injecting water or steam into the regenerator.

The normal temperature for preheating the heat storage bed of the heat storage device, e.g.
At 1200 °C, water (if water is injected instead of steam) is vaporized as it passes through the heat storage bed, and the resulting steam is also preheated before entering the combustion chamber. If steam, for example steam, is injected instead of water, the steam is simply preheated as it passes through the heat storage bed and then flows into the combustion chamber.

With both methods, during combustion, water vapor is present in the combustion chamber of the regenerator, increasing the volume and heat content of the combustion gases, thereby limiting the concentration of _NOx in the gases. However, since the steam was already preheated by the heat storage bed, and most of this heat is collected when the steam leaves the device via another heat storage bed, the temperature of this water vapor can be reduced to the process temperature. Little additional heat supply is required to raise the temperature. Therefore, the overall efficiency of the process is not unduly reduced.

The storage bed is cooled, especially when water or steam passes through it, but surprisingly this has been found to have only a minimal effect on reducing overall process efficiency. Ta.

If steam has to be generated, for example because it has been found to be more efficient to generate the steam in the regenerator as a result of heat release from the regenerator bed rather than by operating a steam generating boiler separately, It is recommended to inject water instead of steam.
However, if steam is freely available as a waste product of a parallel process, it is recommended to inject this steam instead of water in order to save the heat released from the heat storage bed used to vaporize the water.

Preferably, water or steam is injected into the combustion air at a point upstream of the heat storage bed with respect to the direction of movement of the combustion air, and the heat storage bed is arranged such that its surface furthest from the combustion chamber is at the top. . This surface is always the coldest part of the storage bed, thus ensuring that heat removal from the storage bed does not reduce the peak air preheat temperature below a level that is a natural consequence of heat removal in the cold zone of the storage bed. .

In a preferred embodiment of the invention, during the combustion phase of the regenerator, the temperature of the preheated combustion air is sensed by a temperature sensing device before the preheated air reaches the combustion chamber of the regenerator, and the temperature of the combustion air is preset. Stop injecting water or steam into the heat storage if the level is below the specified level.

The value of this threshold temperature is determined by the nationally approved concentration of _NO It is known that the concentration of _NOx in the air increases. As can also be seen, it is generally desirable to operate at as high a flame temperature as possible to increase the heating efficiency of the process from a user's perspective.

By monitoring the temperature of the preheated combustion air,
It is possible to maintain the flame temperature at a certain level necessary to meet the legislation for approved NO _x concentrations.

According to a still further aspect of the invention, a generally upwardly oriented shaft containing a thermal storage bed and a device for injecting water or steam onto the uppermost surface of the thermal storage bed when the shaft is in the generally upward position. and,
an inlet for supplying water or steam to the injector and an outlet for discharging water that has permeated into the heat storage bed from the heat storage, the outlet being at the lowest position when the shaft is in a substantially upward position; A heat storage device is provided, characterized in that it is arranged below the surface of a heat storage bed.

Apart from being able to reduce the concentration of _NO ing. By "processable" material is meant a material that is water-soluble or, if not water-soluble, capable of being transported by water, such as a small or in any case lightweight particulate material. Such materials are carried out of the furnace by the waste gases and deposit in the holes in the floor of the regenerator.
Such materials are fluxes and heated dust from the filling, for example metal or glass dust. In use, when the regenerator is not operating, water or steam sprayed onto the top surface of the regenerator bed will leach down the regenerator bed and dissolve any water-soluble materials or dissolve any lightweight particulate matter. The material is also washed away, and this material and the conveyed water are also discharged from the outlet. This avoids the need to remove the thermal storage bed to clean particles and effectively extends the useful life of the thermal storage bed.

Preferably, the inlet has a valve that controls the supply of water or steam from this inlet to the injector, during the combustion phase of the regenerator if the temperature of the combustion air sensed after preheating is higher than a preset level. , a device is provided for controlling said valve so that said valve is open.

Suitably, the device for controlling the inlet valve is also adapted to open this valve when the regenerator is neither burning nor collecting heat.

Advantageously, the outlet has a valve for controlling the discharge of water or steam from this outlet, which valve is closed during the combustion or heat collection phase and opened if the regenerator is neither burning nor collecting heat. A control device is provided to allow this to occur.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, a regenerator 1 comprises a shaft 2 constructed of refractory material and having a main portion 3 and a side portion 4, the main portion 3 being oriented substantially vertically. It forms a main bore 5 and the side part 4 forms a bore 6.

The main bore 5 has a cylindrical uppermost part 7 which opens into a frusto-conical lowermost part 8 which tapers downwardly.

Side bore 6 has an upwardly sloping cylindrical portion 9 leading from the lowermost region of portion 7 and a generally horizontal portion 10 leading from this portion 9.

The inclined portions 9 of the main bore 5 and the side bores 6 accommodate a heat storage bed 11 which is connected to the heat storage 1
During the heat collection phase of , it serves as a means of collecting heat from the waste gas and during the combustion phase of the regenerator 1 as a means of preheating the combustion air. The bed 11 consists of a large number of refractory particles, in this example balls 12 of a known type, which almost completely fill the main bore 5 and partially occupy the bore part 9. A hood 15 is secured to the shaft 2 by means of a flange 13 above the top surface 14 of the bed, through which combustion air is fed during the combustion phase and flows into the main bore 3 to store heat. Preheated by the bed 11, during the heat collection cycle the waste gas imparts its heat to the bed 11 and leaves the main bore 3 before passing in the opposite direction through the hood 15.

Hood 15 has a cylindrical wall 16 adjacent flange 13 through which a pipe 17 extends horizontally along top surface 14 .
This pipe 17 is equipped with a number of spray nozzles facing the top surface of the floor 11. These nozzles 1
8 serves to spray the water onto the top surface 14 of the floor 11 once it is supplied to the pipe 17 from the inlet 19 . It will be appreciated that, alternatively, if waste steam is available, steam can also be supplied to the inlet 19 and discharged from the nozzle 18.

The inlet 19 is provided with an adjustable regulating valve 20 for regulating the flow rate of water to the pipe 17 and a solenoid-type on-off valve 21 for controlling the supply of water to the pipe in a manner described below.

The base of the shaft 2 is centrally drilled with a hole in which a refractory insert 22 is positioned.

This insert 22 is also centrally drilled to receive a downwardly extending outlet pipe 23 for water that has permeated the heat storage bed 11. Outlet pipe 23
is provided with an open/close solenoid valve 24, and this valve 24 is controlled by a method described below.

A refractory burner 25 of a known type is fixed to the side portion 4 of the shaft 2.
5 forms a cylindrical combustion chamber 26, and this combustion chamber 26
A transverse bore 27 communicates with the side bore via. Although not shown, the burner 25 is
A fuel inlet is provided for injecting fuel into the combustion chamber 26 for combustion with the preheated combustion air leaving the thermal storage bed 11 and entering the side bore 6. Although again not shown, the burner is conventionally equipped with an ignition device, such as a pilot burner, for adding fuel to the combustion chamber 26.

Typically, a burner 25 is secured to the wall of a furnace (not shown) to provide combustion products for heating the charge within the furnace during the combustion phase. During the heat collection phase, the burner serves as an inlet for receiving waste gas from the furnace, which provides waste heat for the regenerator 1 to store in the regenerator bed 11 .

For the above purpose, a temperature sensing device 28 is inserted through the side portion 4 into the side bore portion 10 in order to sense the temperature of the preheated combustion air before it enters the combustion chamber 26 during the heat collection phase. It is extending.

Referring to FIG. 2, the same components as shown in FIG. Components bearing the suffix A and forming part of the other regenerator have the suffix B after their respective numbers.

The illustrated heat storage and heating device operates in a conventional manner, with the operation of the two heat storages 1A, 1B being as follows:
A combustion sequencer 40 of a known type ensures that when heat storage 1A is burning, heat storage 1B is collecting heat, and when heat storage 1B is burning, heat storage 1A is collecting heat. controlled.

In operation, the regenerator alternates between a combustion phase and a heat collection phase, with the changeover from one phase to the other being conventionally time- or temperature-controlled.

Each heat storage device 1 is a known type reversible valve 41A, 41B.
and each valve 41 connects the hoods 15A, 15B of the heat accumulators 1A, 1B to the combustion air supply 43 during the combustion phase or to the exhaust ejector 44 connected to the exhaust duct 45 during the heat collection phase. The connection can be activated by command signals from a combustion sequencer 40 located in the appropriate lines 42A, 42B. When valve 41A connects its hood 15A to air supply 43, valve 41B connects its hood 15B to exhaust ejector 44, and valve 41A connects its hood 15A to exhaust ejector 44. when the valve 41B connects the hood 15B to the air supply section 4.
You can see that it is connected to 3.

Although not shown, the combustion sequencer 40 also injects fuel into the burner 25 for each regenerator in a known manner to inject fuel into the burner 25 only when that particular regenerator is in the combustion phase for mixing with preheated combustion air and combustion. Controls injection of fuel into burners 25A and 25B of No. 1.

The combustion sequencer 40 has two switches 46A,
46B, each heat storage device 1A, 1
A switch 46 is provided at B. To energize the combustion sequencer 40 to operate the thermal storage heating device, the combustion sequencer 40 is activated by moving each of the switch members 47A, 47B into engagement with the respective contacts 48A, 48B in the "combustion" position. 40 must be able to be energized by power lines 49A, 49B.

To shut down the storage heating device, each of the switch members 47A, 47B must be moved into engagement with the respective "clean" position contacts 49A, 49B. In this position, the heat storage beds 11A, 11B of each heat storage 1 can be cleaned by removing treatable substances with water.

Water is supplied to the water inlets 19A, 19B from respective water supply sections 50A, 50B under the control of respective water inlet solenoid valves 21A, 21B and regulating valves 20A, 20B.

The solenoid valves 21A and 21B are not energized unless the OR gates 51A and 51B are energized, respectively.
1A and 21B are closed, and the respective OR gates 51A and 51B are controlled so that when these gates are energized, the valves 21A and 21B are opened.

If each switch member 47A, 47B engages a contact 49A, 49B in its "clean" position, or if the appropriate AND gate 52A, 52
If B is energized, OR gates 51A and 51B are energized.

A signal instructing the heat storage units 1A and 1B to perform combustion is sent from the combustion sequencer 40 to each line 53.
A, 53B, and if the temperature of the combustion air in that regenerator is still above its preset level or limit when sensed by the appropriate temperature sensor 28A, 28B.
AND gates 52A and 52B are activated. In the latter case, the sensed temperature is compared to a temperature preset value in comparators 54A, 54B, and if the temperature is still above the preset level, an energizing signal is activated.
It reaches AND gates 52A and 52B.

Unless the respective switch members 47A, 47B are in contact with their "clean" position contacts 49A, 49B, the water outlet solenoid valves 24A, 24B are always closed and the respective switch members 47A, 47B are not in contact with the contacts 49A, 49B in their "clean" position.
47B is the contact 49A, 49 in its "clean" position
B, the valves 24A, 24B open and the water is drained from the outlets 23A, 23B to the drains 55A, 55B by the drain ducts 56A, 56B.
Discharge to.

If the heat storage heating device is operating to apply heat to the furnace filling, the switch members 47A, 47B
each has a contact 48 in its respective "burn" position.
A, 48B to energize the combustion sequencer 40. In this case, sequencer 40 causes one of the regenerators to perform combustion and the other to collect heat. Thus, in a regenerator undergoing combustion, the combustion air is preheated by a preheated regenerator bed. If the temperature of this air sensed by sensor 28 is higher than a preset limit;
AND gate 52 is energized and energizes OR gate 51, thus opening water inlet solenoid valve 21.
Thus, water is supplied to the pipe 17 and the nozzle 1
8 onto the top surface 14 of the bed 11.
This water is converted to steam at the bed level where the temperature of bed 11 is sufficiently high. Under normal circumstances, the temperature in this part of the bed is above 200°C, so water evaporation occurs immediately. This vapor is captured and carried by the combustion air stream as it passes through bed 11 and preheats. Combustion air vapor tends to reduce the concentration of _NOx produced by combustion of the fuel and preheated air in the combustion chamber 26 of the burner 25. The resulting combustion material flows into the furnace and heats the charge contained therein.
This waste gas then flows into the other regenerator to preheat the cold storage bed of this regenerator for the next combustion stage. This process occurs when the temperature of the preheated combustion air in the burning regenerator falls below its preset level, AND gate 52 is deenergized, and as a result valve 21 closes and sprays water. continues until the end. In either case, at the end of the combustion phase, AND gate 52 is deenergized in switching to the heat collection cycle, even though water is supplied to the still burning regenerator. This process continues for as long as the storage heating device is in operation.

When the storage heating devices are shut down for cleaning, the switch members 47 switch their respective “clean”
It is engaged with the contact 49 at the position. Therefore, in this case, each OR gate 51 can be energized to open the water inlet solenoid valve 21 and spray water onto the thermal storage bed 11 for cleaning. In addition, outlet valve 2
4 is also opened to drain the water from the heat storage device 1. As this water leaches through the thermal storage bed 11, it contains water-soluble lightweight particulates that are carried away from the furnace charge and tend to plug the pores in the bed 11, thus cleaning the bed.

[Brief explanation of drawings]

Figure 1 is a vertical cross-section of a regenerator that produces low concentrations of NO _x and is adapted to remove treatable substances from the storage bed; Figure 2 shows two regenerators of the type shown in Figure 1. 1 is a schematic diagram of a suitable control device for a thermal storage heating device, FIG. 1... Regenerator, 2... Shaft, 3... Main part, 4... Side part, 5... Main bore, 6... Side part, 11... Heat storage bed, 12... Ball, 14...
Top surface of heat storage bed, 15... hood, 17... pipe, 18... nozzle, 19... inlet, 20...
Regulating valve, 21... Opening/closing valve, 25... Burner, 26
... Combustion chamber, 28 ... Temperature detection device, 40 ... Combustion sequencer.

Claims (1)

[Claims] 1. Water or steam is injected into the regenerator during the combustion stage of the regenerator, and the water or steam reaches the combustion chamber of the regenerator through the heat storage bed of the regenerator that is preheated during the preheat collection stage. but detect the temperature of the combustion air after it leaves the heat storage bed and before it enters the combustion chamber, and only if the detected temperature of the combustion air exceeds a predetermined level does the water or steam enter the heat storage inject into;
and water or steam is injected into the combustion air at a point upstream of the heat storage bed with respect to the direction of movement of the combustion air, so that water vapor enters the combustion chamber of the heat storage and flows out of the heat storage during the combustion phase. A method of limiting the presence of nitrogen oxides in exhaust gases. 2. A method according to claim 1, characterized in that the heat storage bed is arranged such that its surface furthest from the combustion chamber is the top. 3. A heat storage bed, and an injection device for injecting water or water vapor into the heat storage, such that the water or water vapor flows into the combustion chamber of the heat storage through the preheated heat storage bed. and a control valve for controlling the supply of water or steam from said inlet to the device for injecting water or steam into the heat storage, during combustion. A temperature detection device is provided between the heat storage bed and the combustion chamber to detect the temperature of the combustion air before it reaches the combustion chamber, and the inlet valve is controlled according to the detected temperature. and a control device provided for opening an inlet valve when the detected temperature exceeds a predetermined level and closing the inlet valve when the detected temperature is lower than the predetermined level, Regenerator, characterized in that the device for injecting water or steam into the regenerator is arranged to inject water or steam into the combustion air at a point upstream of the regenerator bed with respect to the direction of movement of the combustion air. 4. The heat storage device according to claim 3, wherein the heat storage bed is arranged such that the surface farthest from the combustion chamber is the top. 5. The heat storage bed has a top and a bottom, and an openable and closable outlet is located directly below the bottom of the heat storage bed for discharging water from the heat storage bed when opened, and the control device is connected to the outlet. The control device is arranged to control the opening and closing of the control valve, so that when the regenerator is not burning or collecting heat, the control device can open the control valve and the outlet so that water or steam can be released. The heat storage device according to claim 3, characterized in that the water that is injected into the heat storage device through an injection device and has permeated into the heat storage bed is discharged through an open outlet. 6. Claim 5, characterized in that the injection device is arranged above the top of the heat storage bed.
The heat storage device described in section. 7. The heat storage device according to claim 6, wherein the outlet includes an outlet valve device and a control device that controls opening and closing of the outlet valve device for opening and closing the outlet. 8. A heat storage bed and an injection device for injecting water vapor into the heat storage so that the water or water vapor flows into the combustion chamber of the heat storage through the preheated heat storage bed and water or water vapor injected into the heat storage. and a control valve for controlling the supply of water or steam from said inlet to the device for injecting water or steam into the heat storage, during combustion. A temperature detection device is provided between the heat storage bed and the combustion chamber to detect the temperature of the combustion air before it reaches the combustion chamber, and the inlet valve is controlled according to the detected temperature. and a control device provided for opening an inlet valve when the detected temperature exceeds a predetermined level and closing the inlet valve when the detected temperature is lower than the predetermined level, The device for injecting water or steam into a regenerator is a regenerator arranged to inject water or steam into the combustion air at a point upstream of the regenerator bed with respect to the direction of movement of the combustion air; two or more of the regenerators, wherein when at least one of the regenerators is burning, at least one other regenerator receives heat from the combustion products of the at least one burning regenerator. A heat storage heating device characterized in that the heat storage and heating device is connected so as to collect.