KR0128279B1 - Automatic combustion control method for a rotary combuster - Google Patents

Abstract

According to the present invention, each of the portions A, B, and C has a conduit 34, 37, 40 immediately below it, and the conduits 34, 37, 40 have six air portions 35, 36, 38, Upper combustion portions 36, 39, 42 and lower combustion portions 35, 38, 41 forming six air portions which are adjusted by the controller 51 to regulate the supply of combustion gas to the 39, 41, 42. An improved method of automatically controlling the combustion rate in a rotary combustor with a rotary combustion cylinder 11 by controlling the supply of combustion gas to the three combustion parts A, B, C further divided into

The controller 51 is responsive to the temperature disposed in the combustion cylinder 11 and the oxygen sensor 25 disposed in the fuel to maintain the oxygen in the exhaust gas 21 within a predetermined range, and to provide clean and efficient combustion. To adjust the rotational speed of the combustion cylinder (11).

Description

Automatic combustion control method of rotary combustor

1 is a side elevational view of a cross section of a rotary combustor incorporating an improved combustion control method in accordance with the present invention.

2 is a schematic end elevation view of a cross section of a rotary combustor cut along line II-II of FIG.

3 is an enlarged view of a portion of the structure of FIG.

4a is a graph of the percentage of capacity of oxygen in the exhaust gas of a rotary combustor.

4b is a graph of the percentage of carbon monoxide (p.p.m) in the exhaust gas of a rotary combustor versus the same time as shown in FIG. 4a.

5 is a flowchart illustrating the successive steps in which combustion is taken by a controller to most effectively control combustion.

* Explanation of symbols for main parts of the drawings

11: combustion bin 15: solid waste

16: inlet end 17: discharge end

25 oxygen sensor 31 temperature sensor

FIELD OF THE INVENTION The present invention relates to rotary combustors for incineration of wet or dry solid wastes in cities, and more particularly to improved automated combustion control methods for rotary combustors.

The reduction in the usable capacity at landfills for solid waste disposal has accompanied a corresponding reduction in the volume of municipal solid waste for disposal. The main method used in this program is to burn combustible materials. While such programs have been successful in reducing urban solid waste volumes and have also shown side-effects of generating energy, emissions from these facilities have been reduced to minimize the amount of carbon monoxide and the amount of unburned hydrocarbons released. It needs to be reliably controlled.

Some countries set strict requirements on the minimum oxygen levels as well as the amount of carbon monoxide allowed in exhaust emissions. If this discharge requirement is not met, the incineration plant will be temporarily closed. By operating these incineration plants more efficiently, more complete combustion will be achieved and exhaust emissions will therefore meet statutory requirements.

One type of incineration plant is known as a water cooled rotary combustor. Examples of such combustors are described in US Pat. No. 3,822,651 to Harris et al. Generally, a water-cooled rotary combustor includes a combustion cylinder having generally cylindrical sidewalls attached to an annular support band, the annular support band being received on the rollers so that the combustion cylinder can rotate about its longitudinal axis. do. The combustion bin has an open inlet end to receive the material to be combusted, such as municipal solid waste which may change into a moisture component. Opposite or discharge ends of the combustion cylinders are disposed in the flue. The furnace is inclined from the horizontal and the inlet end is above the outlet end. When the waste is combusted, it moves along the longitudinal axis of the furnace so that solid combustion products are discharged at the lower discharge end of the furnace. Exhaust gases and solid combustion products are discharged at the discharge end of the furnace.

The combustion cylinder is cooled by cooling tubes connected with a gas porous interconnect forming its cylindrical sidewalls.

Since the composition of the waste varies, it can be difficult to maintain a constant supply rate of solid waste into the furnace, so that the strength of the thermal power varies over time. In addition, the heat of combustion of the solid waste for each charge to the combustor changes significantly.

As a result, the composition of the exhaust gas can also change with time. By controlling the combustion rate of the combustion cylinder, more efficient incineration is achieved, producing exhaust gases with a more stable composition and less producing unburned hydrocarbons. In particular, it is important to keep the carbon monoxide level below 100 ppm, because this level is required by most national legislation. Another requirement imposed on the operators of municipal waste incineration plants is that the oxygen level in the exhaust gas does not drop below 3%.

Another problem associated with inefficient combustion of municipal solid waste in rotary combustors is the problem of clinker formation. Clinkers, which generally consist of molten ash, softened glass material, and the like, can form in the combustor and cause problems with combustor performance. The main cause of clinker form is localized hot spots in the combustor. Due to the various nature of solid waste in the city, it is not necessarily possible to have a fuel bed that burns completely and consistently in the combustor.

Thus, a first object of the present invention is to most accurately control the amount of carbon monoxide and unburned hydrocarbons present in the exhaust gas of a rotary combustor in order to provide the most efficient combustion of solid waste in the city.

A second object of the present invention is to compensate for the change in combustion rate that occurs in rotary combustors due to the various properties of solid waste in the city.

A third object of the present invention is to automatically control the rate of combustion in the rotary combustor to maintain the temperature in the rotary combustor at a stable level that is high enough to complete combustion but lower than the level at which clinker formation begins.

These objects are achieved by the improved method of the present invention for controlling combustion in a rotary combustor by precisely controlling the combustion gas supply to the six combustion zones of the rotary combustor used to combust solid waste in the city.

The improved method of the present invention not only senses the amount of oxygen present in the exhaust gas to produce an oxygen sensor signal, but also senses the temperature in the combustor to produce a temperature sensor signal, and in response to the signals Automatically controlling the combustion gas, or air, supplied to the three different combustion zones to most accurately maintain the oxygen level of the exhaust gas at a predetermined value. By confining the furnace to three zones, each with two combustion gas supply zones, the most efficient combustion of solid waste in the city is achieved by separating and individually controlling the amount of combustion gas supplied to each of these six zones.

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

As shown in Figs. 1, 2 and 3, a typical rotary combustor generally has a cylindrical combustion cylinder 11 as an incineration chamber, with the combustion cylinder 11 alternately extending longitudinally. It consists of a tube 12 and a porous web structure 13. The web structure 13 is preferably formed of rod steel and has an opening 14 for supplying combustion gas, preferably air, to the combustion cylinder through itself. Solid material, in particular municipal solid waste 15, is combusted in a rotary combustion cylinder 11.

The communication 11 rotates around a central axis of rotation that is slightly inclined from horizontal, with its inlet end 16 slightly higher than its outlet end 17. As can be seen at the discharge end 17 along the cut plane of line II-II, the combustion bin 11 is clockwise, as shown by arrow 18, to continuously mix the waste 15. Rotate. (Example) This facilitates the drying of the waste by continuously exposing relatively wet waste to the surface of the fuel layer where combustion normally occurs.

The inlet end 16 and the outlet end 17 of the combustion bin 11 are generally surrounded by a support band 19 received on a rotating means, preferably roller 20.

In this way, the combustion cylinder 11 rotates.

When the waste is incinerated, the exhaust gas (illustrated by arrow 21) generated thereby is discharged from the combustion cylinder 11 and contained in the exhaust region 22 in the seal 23 (see FIG. 2). .

The exhaust gas 21 is discharged from the seal 23 through the tube 24 disposed at the discharge end 17 of the combustion cylinder 11 and flows through the oxygen sensor 25. On the other hand, solid combustion products or ash 26 are also discharged at the discharge end 17 of the combustion cylinder 11. Due to the slightly inclined combustion chamber 11, this solid combustion product, or ash 26, is easily discharged.

The cooling tube 12 is typically circulated with a cooling liquid such as water, and the cooling liquid enters into the cooling tube from the annular header 27 disposed at the discharge end 17 of the combustion cylinder 11. The coolant flows to the return means (not shown) toward the inlet end, and the return means returns the heated coolant to the header 27 by incineration of the waste. The high energy coolant is discharged from the header 27 to the heat exchanger or the boiler 28 through the supply pipe 29. The heat exchanger 28 is connected to a medium-term driven power generation system (not shown), as is well known in the art. The low energy coolant from the heat exchanger 22 enters the cooling tube 12 again through the annular header 27 and a closed cycle is formed.

As shown in FIG. 1, the combustion cylinder 11 generally consists of three combustion zones A, B and C, which are arranged in series in the longitudinal direction along the combustion cylinder 11. The main function of Zone A is to dry the waste, although combustion starts here.

The combustion of most of the waste 15 is accomplished in the intermediate zone B. In Zone C, the combustion of the solid waste is essentially complete. In general, the thermocouple temperature sensing device 13 is preferably located in zone A in the combustion vessel 11. The temperature sensor 31 senses the temperature in the combustion cylinder 11, which will be described in detail later.

Under each of the three combustion zones A, B, C are conduits or wind boxes 34, 37, 40 are arranged, respectively. Each wind box consists of a lower combustion air and an upper combustion air zone, which will be readily understood.

Combustion gas, or air, is supplied to the combustion cylinder 11 through the openings 14 of the porous web structure 13 through these wind boxes 34, 37, 40. In order to supply combustion gas or air to the zone B portion of the combustion bin 11, the zone B wind box 37 is separated by seal box edges 43, 44, 45, as shown in FIG. 2. Lower combustion air zone 38 and upper combustion air zone 39, the seal box edges 43, 44, 45 extending longitudinally adjacent the combustion cylinder and the zone of the wind box 37. It is arranged to cooperate with a plurality of folded seal strips 46 to seal the various portions of the B portion. Combustion starts at about five o'clock on the combustion cylinder 11 and the upper combustion air zone 39 is limited by the wind box edges 43, 44 along the clockwise direction, and the lower combustion air zone 38 is closed. Constrained by wind box edges 44 and 45. When the solid waste 15 is completely combusted by the fire, generally indicated at 47, the exhaust gas 21 exits the combustion bin 11 and passes through the plumbing 24.

Combustion gas is supplied to each wind box 34, 37, 40 by an air blower 48 through an air pipe 49. The combustion gas is connected to the upper combustion and lower combustion air zones 35 by corresponding conduits 35 ', 36', 38 ', 39', 41 ', 42' which are connected between the air pipe 49 and the six zones. 36, 38, 39, 41, and 42, each of which has a damper 50 disposed therein. Conduit damper 50 is the main control means described in accordance with the present invention.

The upper combustion air is defined as the air flowing from the air zones 36, 39, 42 through the opening 14 region of the furnace 11, mostly due to the rotational movement of the waste 15. Since the exposed opening is the path with the least resistance, it is called upper combustion air because the combustion gas naturally flows through the exposed opening onto the waste 15. At the same time, the bottom combustion air is defined as the air flowing from the air zones 35, 38, 41 through the area of the opening 14 of the furnace 11, covered by the waste 15. Since the waste 15 is generally made of an irregularly shaped object, the lower combustion air leaks through the waste 15 to the surface where combustion takes place. This facilitates the drying of the wet waste 15, especially in zone A. Since combustion occurs mainly in zone B, the distinction between bottom combustion air and top combustion air does not generally apply to zone C.

The importance of this point is easy to understand.

Referring to FIG. 2 in accordance with the present invention, the damper 50 and the rotation means 20 are controlled by the control device 51.

The control device 51 consists of a microprocessor 52, a wind box damper controller 53, and a rotation drive controller 54. The signals from the oxygen sensor 25 arranged in the plumbing 24 and preferably the temperature sensing device 31 arranged in the zone A of the combustion chamber 11 are inputs to the control device 51. After combustion is initiated and self-maintained, the control system operates to maintain a constant combustion rate.

When the solid waste 15 is combusted, the exhaust gas 21 is discharged through the plume 24 and sensed by the oxygen sensor 25.

This generates the oxygen gas sensor signal input to the control device 51. The microprocessor 52 of the control device 51, which can be programmed by those skilled in the art, generates an output signal based on the percentage of oxygen present in the exhaust gas in response to the oxygen sensor signal. Different output signals are generated depending on whether the oxygen level is above or below any predetermined value in the range between about 4% and 10%, preferably between about 5% and 8%, by volume. The most desirable setpoint is a function of the material to be incinerated and is different for each installation.

There is a correlation between the amount of oxygen in the exhaust gas 21 and the amount of carbon monoxide. This relationship is shown graphically in Figures 4a and 4b. As long as the oxygen level is maintained at a level between 4% and 10% per volume, the amount of carbon monoxide present in the exhaust gas 21 does not actually exist. Since this represents the most efficient combustion of the solid waste 15, a method for more precisely controlling the amount of carbon monoxide present in the associated gas is preferred. By monitoring the amount of oxygen present in the associated gas to determine how much combustion air will be supplied to the combustion bin 11, the most efficient combustion of the municipal waste 15 can be achieved regardless of its nature.

When the percentage of oxygen gas in exhaust gas 21 is not a predetermined value of about 5% to 8%, the first step when attempted is to adjust the air flow into zone C wind box 40. If below a certain range, the air flow increases into zone C, and if the oxygen content is above 8%, the air flow decreases. The air distribution between the upper combustion and lower combustion air zones is essentially the same in zone C. In zone C, the combustion of solids hardly occurs, and since only gas is burned or further combined with oxygen, the effect of increasing or decreasing the amount of air introduced into zone 41 or 42 is not critical. Preferably, air control into zone C is effected by adjusting the wind box damper 50 opening. Preferably, the damper openings for the lower combustion air zone 41 and the upper combustion air zone 42 of the wind box 40 should have a minimum opening rate of about 10% and a maximum opening rate of about 100%. In the second embodiment it can also be achieved by changing the speed of the fan in the blower 48 or adjusting the blower damper opening, but this is also supplied to the zone A wind box 34 and the zone B wind box 37. Will change the amount of combustion gas.

This selection step requires simultaneous adjustment of the wind box 34, 37 damper openings to maintain a constant air flow to these two zones. When the second embodiment is selected, the controller operates the zone A wind box 34 and zone B wind if the adjustment of the combustion gas into the zone C wind box 40 is performed by adjustment of the blower 48 fan speed or damper opening. It must be further programmed to maintain air flow into the box 37.

The control of the air flow into zone C should be sufficient to bring the oxygen level of the exhaust gas 21 to a setpoint between about 4% and 10% per volume in the intake 24. If the combustion rate in the combustion bin 11 is too high or too low to control the oxygen level by controlling the combustion gas supply to zone C only, the wind box controller 53 proceeds to the next step. Ordered by

The following steps, described below, are designed to reduce the oxygen demand in the combustion vessel 11 by limiting the combustion gas supply into the zone where active combustion is occurring.

In general, gaseous combustion is actively occurring in zone B, but sometimes waste 15 may be burned in zone A. In particular, by limiting the combustion gas supply in zones A and B, such as between the lower combustion air zones 35 and 38 and the upper combustion air zones 36 and 39, the combustion rate decreases very quickly and the demand for oxygen Decreases immediately, thereby increasing the oxygen percentage level in the exhaust gas 21. Conversely, when additional combustion gas is supplied to zones A and B, the combustion rate of the solid waste 15 increases, and as a result the percentage of oxygen in the exhaust gas 21 decreases.

Using signals from the oxygen sensor 25, the microprocessor 52 instructs the wind box controller 53 to automatically control the combustion gas supply to the zone B wind boxes 38 and 39 as follows: exhaust The combustion gas supply to this zone should be reduced if the oxygen level of the gas 21 is below about 5% (preferably about 4.5%), and if the oxygen level is above 8%, the combustion gas supplied to the zone B will increase. Should be.

This adjustment is made by changing the damper 50 opening. This is especially true if the adjustment to air to zone C has been made by adjusting the blower 48 fan or damper. Preferably, the control of the combustion gas supplied to zone B is more than 60% to 40% lower in the lower combustion air zone 38 than the upper combustion air zone 39 because the lower combustion air has more influence on the combustion rate. Supplying a large percentage of the combustion gases.

The minimum and maximum damper openings for zone B lower combustion air zone 38 and upper combustion air zone 39 should preferably be about 10% and 80%, respectively.

If the two preceding steps did not bring the oxygen level to the set point, the wind box controller 53 is commanded by the microprocessor 52 to perform the following steps: The oxygen level indicated by the oxygen sensor 25 is weak. If it is 8.5% or more, the supply of combustion gas to Zone A is increased, and if the oxygen level is about 4% or less, a reduced amount of combustion gas or air is supplied to Zone A.

Preferably, the wind box controller 53 performs this step by adjusting the combustion gas supply to the zone A upper combustion air zone 36 in accordance with the oxygen sensor signal. Zone A upper combustion air zone 36 preferably has a maximum damper opening rate of about 50% and a minimum limit of about 0%. The combustion gas supply to zone A lower combustion air zone 35 is controlled by a signal received by microprocessor 52 from temperature sensing device 31. The purpose of this step is to introduce combustion gas into the zone A bottom combustion wind box 35 to facilitate drying of very wet solid waste 15. The zone A lower combustion air zone 35 damper opening rate should have a minimum and maximum opening rate and correspondingly have a combustion gas flow rate inversely proportional to the value of the furnace temperature sensing device 31. Therefore, when the temperature sensing device 31 generates a signal above a predetermined set value (the set value is different for each facility), the combustion gas supply to the lower combustion air zone 35 is reduced, and automatically when the signal is below the predetermined temperature set value. Is increased. In general, the temperature should be maintained at a set point in the range of 1100 ° C. (2000 ° F.), otherwise it should be understood that the set point depends on the size of the combustor itself as well as the location of the temperature sensing device in the combustor 11.

As a further step, the rotational speed of the combustion cylinder 11 can also be adjusted. This step is necessary if the steps do not allow the oxygen level in the exhaust gas 21 to be maintained within a predetermined range between about 5% and 8% (most preferably about 6.5%) by volume.

This may occur in the case of very wet waste 15 with an oxygen level of 8% or higher or when the rotational speed shown by arrows 18 is first increased, and now the dry waste 15 is burned in the furnace 11. Can be incinerated at and oxygen levels below 5%. Since combustion occurs at the surface of the continuously rotating waste 15, the combustion rate is increased because the new material 15 is continuously exposed to the fire 47 due to the faster rotational speed. In the case of very wet waste 15, the material may not burn at the surface 47 due to the faster rotational speed, combined with the drying action achieved by the additional air previously introduced through the Zone A lower combustion air zone 35. Dries faster when exposed.

The control of the rotational speed of the combustion cylinder 11 is based on the output signal from the temperature sensing device 31. Dry waste will burn at higher temperatures than wet waste. When the temperature in the combustion cylinder 11 is above a predetermined temperature set point as determined by the temperature sensing device 31, the rotation controller 54 reduces the rotational speed of the rotation means 20 and thus the combustion cylinder 11. Instructions are received by the microprocessor 52 in order to do so. The slower rotational speed results in less material 15 being exposed to the surface, whereby the burn rate is reduced, so that combustion occurs mainly in zone B. Conversely, if the temperature in the combustion vessel 11 is too low (indicating the presence of the wet waste), the rotation controller 54 increases the rotational speed of the combustion vessel 11 to dry the wet waste and increase the combustion rate. This is because more waste 15 is exposed to the surface, whereby the wet waste is dried and the combustion rate is increased.

The increase / decrease in the amount of air or rotational speed to be drawn into each zone required to maintain a more stable combustion rate depends on how large a deviation is detected from a predetermined set of sensors. Since these parameters are also a function of the combustor size, each incineration plant needs to set its own parameters. However, by performing these precise steps in accordance with the present invention as shown in the flowchart of FIG. 5 based solely on the output signals generated by the oxygen sensor 25 and the temperature sensor 31, the municipal solid waste 15 ), The rate of combustion can be controlled most efficiently regardless of the composition of the waste, especially the moisture content, and it is possible to keep the level of monoxide and unburned hydrocarbons in the exhaust gas below statutory requirements. The improved control method is high enough to complete combustion, but can maintain the temperature in the combustor at a level below the level at which clinker formation begins, regardless of the size of the combustion.

In addition, in the case where combustion is self-maintaining in the combustor, the method of the present invention minimizes temperature fluctuations that can cause clinker formation to begin. In addition, a more stable combustion rate is independent of the feed rate, whereby clinker formation is prevented. In this way, the volume of solid waste can be reduced by more than 90% in a complete and efficient manner.

While the present invention has been described with reference to specific implementations, it will be apparent to those skilled in the art that various modifications, changes and variations are possible in light of the above teaching.

Accordingly, the claims herein are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the invention.

Claims (7)

An inlet portion A, which is supplied to the combustion cylinder 11 through a hole disposed throughout the length and circumference of the combustion cylinder, and disposed adjacent to an end portion at which the solid waste 15 is introduced into the combustion cylinder 11; An exhaust portion C disposed adjacent the end portion at which the exhaust gas 21 and the ash 26 are discharged from the combustion cylinder 11, and an intermediate portion disposed between the inlet portion and the discharge portions A, C ( Divided into supplying the lower combustion air (35, 38, 41) and the upper combustion air (36, 39, 42), respectively, into the three parts (A, B, C) of the combustion cylinder (11) consisting of B). Automatically initiate combustion in a rotary combustor having a rotary combustor (11) in which solid waste is combusted by air (35, 36, 38, 39, 41, 42) supplied through a plurality of conduits (34, 37, 40). In the control method, the upper combustion flows into the respective portions (A, B, C) of the combustion cylinder (11) in response to the temperature change in the combustion cylinder (11) and the oxygen percentage change in the exhaust gas (21). Air and bottom Individually changing the combustion air 36,39,42 and 35,38,41 and at a temperature that prevents clinker formation in the combustion cylinder 11 in response to temperature changes in the combustion cylinder 11. Varying the speed of rotation of the furnace (11) to completely burn the solid waste (15). The method of claim 1, wherein the step of individually changing the air flowing into the respective parts (A, B, and C) of the combustion cylinder (11) is performed in response to the temperature change in the combustion cylinder (11). Varying the rotational speed of the combustion cylinder (11) to maintain a predetermined temperature in the combustion cylinder (11). Combustion control method. The method of claim 2, wherein the predetermined temperature is generally 1100 ° C. The method of claim 1, wherein the step of individually changing the air (35, 36, 38, 39, 41, 42) introduced into the respective parts (A, B, C) of the combustion cylinder (11) is exhaust gas (21). The upper combustion air 42 to the discharge part C of the combustion cylinder 11, the lower combustion air 38 to the middle part B of the combustion cylinder 11, and the combustion cylinder in order to make oxygen in inside into the predetermined limit value fall. Changing the air flow (35, 36) to the inlet (A) of the (11) to a predetermined level. 5. Method according to claim 4, characterized in that the predetermined limit of oxygen in the exhaust gas (21) is between 4% and 10% per volume. The method of claim 1, wherein the step of individually changing the air (35, 36, 38, 39, 41, 42) flowing into the respective parts of the combustion cylinder (11) is to bring the oxygen in the exhaust gas (21) to within a predetermined limit. To change the upper combustion air 42 to the outlet C of the combustion cylinder 11 and then to the lower combustion air 38 to the middle portion B of the combustion cylinder 11 and then to the combustion cylinder 11 Varying air (35, 36, 38, 41, 42) sequentially by varying the air flow (35, 36) to the inlet (A) of (11). Control method. 7. A method according to claim 6, characterized in that the predetermined limit of oxygen in the exhaust gas (21) is generally between 4% and 10% by volume.

Images