JP3750379B2 - Waste gasification and melting treatment system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a treatment system for treating combustible waste, and in particular, municipal waste is burned and melted at a high temperature to make it harmless, and the heat of combustion exhaust gas at that time is recovered and used for power generation and the like. The present invention relates to a waste gasification and melting treatment system that can be used.
[0002]
[Prior art]
In recent years, environmental problems have been highlighted, and a refuse gasification and melting treatment system has attracted attention as a new waste treatment technology that is an environmental conservation alternative to conventional incineration treatment. This treatment system combusts and gasifies garbage under a low temperature / low air ratio, introduces the generated high calorie combustible gas and unburned char into the ash melting furnace, and heats the ash at a high temperature of 1300 ° C. It burns and melts at slag. According to this treatment system, the volume of waste can be reduced, so that the life of the landfill can be extended, and since the combustion temperature in the ash melting furnace is high, dioxins can be completely decomposed, and further, combustion There is an advantage that heat can also be used for power generation.
[0003]
Here, the air ratio is a ratio of an air amount (theoretical air amount) necessary for completely burning garbage and an actually supplied air amount (supply air amount). Since the theoretical air amount is calculated from the amount of combustible matter in the garbage, there is a correlation between the combustible amount and the air ratio. That is, when the supply air amount is fixed, the air ratio changes when the amount of combustible matter in the garbage changes. If this air ratio is 1 or more, the waste is completely combusted. Conversely, if the air ratio is less than 1, the waste is incompletely combusted, and high-calorie combustible gases such as CO and CH ₄ are generated. Further, when the air ratio is low, the amount of supplied air is small, so that the amount of exhaust gas can be greatly reduced, and the exhaust gas treatment device can be made compact.
[0004]
FIG. 6 is a system diagram of a conventional garbage gasification melting treatment system. Garbage in the dust feeder 1 is put into the gasification furnace 2 and burned in the gasification furnace 2 under a low air ratio to generate combustible gas G1 and unburned char C. The combustible gas G1 and the unburned char C are introduced into the ash melting furnace 3 and are combusted at a high temperature in the ash melting furnace 3 to generate molten slag and a high-temperature combustion exhaust gas G2. At this time, fuel is supplied to the burner 4, and the fuel also burns inside the ash melting furnace 3. The molten slag is discharged from the lower part of the ash melting furnace 3.
[0005]
The combustion exhaust gas G2 is introduced into the boiler 5 and heats the circulating water W. The heated circulating water W rotates the steam turbine 6, and the generator 7 is rotationally driven by the rotation. On the other hand, the combustion exhaust gas G <b> 2 that has heated the circulating water W in the boiler 5 is introduced into the air preheater 8, and heats the air A that is sent from the forced air blower 9. Further, the combustion exhaust gas G2 is discharged from the air preheater 8 and slaked lime (Ca (OH) ₂ ) is blown from the slaked lime silo 10 by the pushing blower 11 and further introduced into the bag filter 12 to be desalted. Then, the combustion exhaust gas G2 that has been desalted and cleaned is sucked by the induction blower 13 and discharged outside the system through the chimney 14. Air A heated by the air preheater 8 is sent to the gasification furnace 2 and the burner 4.
[0006]
Fly ash containing slaked lime gradually accumulates on the surface of the bag filter 12, but as the amount increases, the filter 12 becomes clogged and the flue gas G2 becomes difficult to flow, so high-pressure air is bugged every few minutes. It is necessary to cause the solid particles (fly ash) adhering to the filter surface to flow away by flowing back into the filter 12. This operation is called backwashing. Thus, the solid particles (fly ash) removed from the bag filter 12 are stably rendered harmless.
[0007]
[Problems to be solved by the invention]
By the way, when the temperature inside the gasifier and the air ratio change, the properties of the generated combustible gas and unburned char change, and it becomes difficult to perform high-temperature combustion in the subsequent ash melting furnace. Therefore, in the waste gasification and melting treatment system, maintaining the target temperature and air ratio in the gasification furnace is very important in supplying high-calorie combustible gas and unburned char to the subsequent ash melting furnace. It is. However, the above-described conventional technology has the following problems.
[0008]
Unlike municipal fuel and waste, such as coal and oil, the properties of municipal waste and waste always change. For example, if there is a large amount of high molecular weight compounds such as vinyl, the amount of combustibles in the garbage will increase, and if there is a large amount of garbage, the amount of combustibles in the garbage will decrease and the amount of moisture will increase. . When the supply air amount is constant, if the property of the dust changes, the theoretical air amount changes, so the air ratio in the gasifier changes. In order to maintain the target air ratio, the amount of supplied air must be changed. In this way, the air ratio must be controlled according to the nature of the waste, but it is difficult to always know the nature of the waste carried into the waste combustion facility, and the real-time air ratio in the gasifier is known. Since there is no means, it is difficult to maintain the air ratio at the target value in the conventional refuse gasification and melting treatment system.
[0009]
Furthermore, since the air ratio is determined by the amount of combustible matter regardless of the amount of water and the amount of ash in the waste, the gasifier temperature changes when the amount of water in the waste changes even if the air ratio is kept constant. For example, when raw garbage contains a large amount of moisture, the furnace temperature decreases due to heat absorption due to the heat of vaporization of water in the gasification furnace, even if the air ratio is maintained at a target value. In such a case, it is necessary to raise the temperature in the furnace by performing auxiliary combustion. However, in the conventional waste gasification and melting treatment system, the real-time air ratio in the gasification furnace cannot be known as described above. It was difficult to properly control the furnace temperature.
[0010]
An object of the present invention is to provide a refuse gasification melting treatment system capable of knowing a real-time air ratio in a gasification furnace and thereby appropriately controlling the air ratio and the temperature in the gasification furnace. That is.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a gasification furnace for combusting combustible materials under a low air ratio to generate combustible gases and combustible solids, and combusting the combustible gases and combustible solids at a high temperature. An ash melting furnace that melts the combustible solids and discharges it as slag, in a waste gasification and melting treatment system, from the temperature in the gasification furnace and the composition of the combustible gas, Control means for controlling the amount of air supplied to the gasification furnace based on the estimation result is provided.
[0012]
The control means measures the CO concentration and CO ₂ concentration in the combustible gas at a certain temperature in the gasification furnace to obtain the ratio CO / CO ₂ of the two concentrations, and estimates the air ratio from the result.
[0013]
The control means detects the temperature inside the gasification furnace, the surface of the fluidized bed, and the inside of the fluidized bed, and when the detected temperature is lower than a predetermined temperature, the temperature in the gasification furnace is increased. It has a function to make it. Specifically, the control means performs auxiliary combustion to increase the temperature in the gasification furnace.
[0014]
In the gasifier, when garbage is burned under conditions of a low air ratio, CO and CO ₂ are generated. The concentration of CO and CO ₂ when the temperature in the gasifier was 700 ° C. and the air ratio was 0.2, 0.4, and 0.6 was obtained by experiments. The result is shown in FIG. Similarly, the CO and CO ₂ concentrations were determined by experiments when the temperature in the gasifier was 600 ° C. and the air ratio was 0.2, 0.4, and 0.6. The result is shown in FIG. As can be seen from FIG. 2 and FIG. 3, the concentration of the produced CO and CO ₂ is different if the temperature in the gasification furnace is different. Further, as the air ratio increases, the CO concentration decreases, and conversely, the CO ₂ concentration increases, and the CO and CO ₂ concentrations are affected by the air ratio. This is because CO and CO ₂ are generated by the combination of carbon in the combustible carbon and oxygen in the air, so if the air ratio, that is, the amount of air increases, more carbon binds to oxygen. is there.
[0015]
However, if the waste quality changes, the concentration of CO and CO ₂ also changes (for example, if the moisture content of the waste increases, the amount of gas generated increases due to the addition of water vapor and the concentration of CO and CO _{2 in} the generated gas decreases. Therefore, the measured values of the CO and CO ₂ concentrations are not a guideline for knowing the actual air ratio in the gasifier.
[0016]
FIG. 4 shows the relationship between the air ratio and CO / CO ₂ for each gasification temperature based on the data in FIGS. 2 and 3. Here, CO / CO ₂ is the ratio of the CO concentration to the CO ₂ concentration. As can be seen from FIG. 4, the value of CO / CO ₂ increases as the gasification temperature increases and decreases as the air ratio increases. That is, the proportion of CO and CO ₂ produced from the carbon contained in the combustible matter in the garbage is almost determined by the gasification temperature and the air ratio, and even if the amount of ash and moisture in the garbage changes, CO / CO ₂ does not change. As a result, since the value of CO / CO ₂ with respect to the air ratio is known in advance, the concentration of CO and CO ₂ produced when gasifying the waste is measured to obtain CO / CO _2, thereby obtaining the gas The actual air ratio in the furnace can be estimated. Utilizing this, the amount of air supplied to the gasifier is changed so that the CO / CO ₂ of the generated gas becomes a predetermined value, and the target air ratio is maintained in response to the change in the waste quality. Can do. In FIG. 4, S <b> 1 is a region where tar is generated, and S <b> 2 is a region where the furnace temperature cannot be maintained only by the amount of heat generated by the dust.
[0017]
In addition to the target air ratio, it is necessary to maintain the gasification furnace temperature at the target value for the gasification of garbage. FIG. 5 shows the experimental results, the conversion of carbon in the garbage into CO, CO ₂ , CH ₄ and the residue, and the hydrogen in the garbage into H ₂ , CH _4, H ₂ O and the residue. Results of trial calculation of gas composition, net air ratio and gasification furnace temperature when the waste weight is 100kg, the amount of air is constant 67kg, and the waste quality is gasified over time based on the conversion rate data It is. When the waste quality is 50% combustible and the water content is changed from 10% → 20% → 40%, the CO concentration and CO ₂ concentration decrease, but CO / CO ₂ is constant at 1.6. The air ratio at this time is 0.2, but the gasifier temperature cannot be maintained at 700 ° C. due to the heat of vaporization of moisture. That is, as shown in FIG. 5, the gasifier temperature changes due to a change in moisture in the waste even if the air ratio is constant. For this reason, it is necessary to measure the temperature in the gasifier and to support combustion in order to maintain the target temperature (shaded area in the figure).
[0018]
In this way, by maintaining the air ratio and temperature at constant target values, it is possible to stably obtain combustible gas and unburned char having desired properties. And if those combustible gas and unburned char are supplied to an ash melting furnace, unburned char can act as a solid fuel and can maintain the inside of an ash melting furnace in a high temperature state.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is described in the same location as a prior art, and the detailed description is abbreviate | omitted.
[0020]
FIG. 1 is a system diagram of a refuse gasification melting treatment system according to the present invention. As shown in FIG. 1, a CO / CO ₂ sensor 21 is provided in a pipe 20 for introducing the combustible gas G 1 and the unburned char C generated in the gasification furnace 2 into the ash melting furnace 3. It is possible to measure the concentration of CO and CO _{2 in} the combustible gas G1 flowing through the gas. A calculator 23 is connected to the CO / CO ₂ sensor 21, and a controller 24 is connected to the calculator 23. Furthermore, a valve 26 is provided in the pipe 25 for supplying the air A heated by the air preheater 8 into the fluidized bed in the gasification furnace 2, and the opening degree of the valve 26 is controlled by the controller 24. .
[0021]
Further, the gasification furnace 2 is provided with three thermocouples 27 for detecting the temperature of the empty column part, the fluidized bed surface part, and the fluidized bed, and each thermocouple 27 is connected to the controller 28. An auxiliary combustion burner 29 is attached to the upper portion of the gasification furnace 2, and fuel is supplied to the auxiliary combustion burner 29. A valve 30 is provided in the piping for supplying fuel to the auxiliary burner 29, and the opening degree of the valve 30 is controlled by the controller 27. In FIG. 1, reference numeral 1 </ b> A denotes a screw feeder installed at the lower part of the dust feeder 1, and 2 </ b> A denotes a garbage inlet formed in the gasification furnace 2.
[0022]
In the waste gasification and melting treatment system having the above-described configuration, the waste introduced into the gasification furnace 2 from the waste introduction port 2A is heated at a low air ratio and a low temperature. The amount of air supplied through the pipe 25 is controlled so as to maintain an air ratio with respect to the theoretical air amount obtained in advance from a general waste composition. The charged waste is gasified in the gasification furnace 2 to generate combustible gas G1 and unburned char C. Here, first, a small amount of the combustible gas G1 is extracted, and a certain standard of air ratio is always set depending on whether or not to burn.
[0023]
Although the combustible gas G1 and unburned char C is sent to the ash melting furnace 3 through a pipe 20, then the measured CO in the combustible gas G1, the concentration of CO ₂ in the CO · CO ₂ sensor 21. The measured concentration data of CO and CO ₂ is sent to the calculator 23, and the calculator 23 estimates the air ratio in the gasifier 2 based on these concentration data. For example, when gasifying garbage at 700 ° C. and an air ratio of 0.2, if the CO ₂ concentration is 8 vol% and the CO concentration is 6 vol%, CO / CO ₂ is 0.75. From FIG. 4, it can be seen that gasification is performed in the state where the air ratio is 0.4 with respect to the present garbage. Therefore, it can be readily understood that the amount of air supplied to the gasification furnace 2 may be halved.
[0024]
Thus, when CO / CO ₂ is different from the target value in the air ratio, the controller 24 changes the opening degree of the valve 26 and adjusts the amount of air supplied to the gasification furnace 2 to adjust the inside of the gasification furnace 2. Control air ratio instantly. In the above case, the controller 24 reduces the opening of the valve 26 to halve the amount of air A supplied into the gasifier 2 so that the air ratio in the gasifier 2 becomes 0.2. adjust.
[0025]
Next, the temperature in the gasification furnace 2 is measured. The temperature in the gasification furnace 2 is measured by the thermocouple 27 at the measurement positions at several locations in the empty column part, the fluidized bed surface part, and the fluidized bed. When the temperature inside the gasification furnace 2 is measured by the thermocouple 27 and the measurement result is lower than the target temperature, the controller 28 opens the valve 30 to supply the fuel to the auxiliary burner 29, and the auxiliary combustion burner 29 supplies the gasification furnace. The empty tower in 2 is heated so as to maintain the target gasification temperature. Instead of heating with the auxiliary burner 29, the air A supplied to the fluidized bed may be heated.
[0026]
According to the present embodiment, since the air ratio in the gasification furnace 2 can be known in real time based on the concentrations of CO and CO _{2 in} the combustible gas, the temperature in the gasification furnace 2 can be easily and quickly determined. It is possible to control and measure the temperature inside the gasification furnace 2, and if the temperature inside the gasification furnace 2 is lower than the target temperature, by performing auxiliary combustion, even if the waste quality changes, the target heat generation The amount of combustible gas and unburned char can be stably obtained.
[0027]
【The invention's effect】
As described above, according to the present invention, the air ratio in the gasification furnace can be known in real time, and the temperature in the gasification furnace can be appropriately controlled.
[0028]
In addition, even if the waste quality varies, the target value of combustible gas and unburned char can be obtained, so that high-temperature combustion in the ash melting furnace is possible, and the efficiency of the system can be improved.
[0029]
Moreover, CO, and detecting the concentration of CO _2, because it is configured for controlling the air ratio based on the detection result, it is not necessary to install a large-scale equipment, it is possible to reduce the equipment cost.
[Brief description of the drawings]
FIG. 1 is a system diagram of a refuse gasification melting treatment system according to the present invention.
FIG. 2 is a diagram showing a relationship between a generated gas and an air ratio at a temperature of 700 ° C.
FIG. 3 is a diagram showing a relationship between a generated gas and an air ratio at a temperature of 600 ° C.
FIG. 4 is a diagram showing the relationship between CO / CO ₂ and the air ratio.
FIG. 5 is a diagram showing estimated values of the net air ratio, generated gas composition, and gasifier temperature due to changes in waste quality over time.
FIG. 6 is a system diagram of a waste gasification and melting treatment system according to the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Dust feeder 2 Gasifier 3 Ash melting furnace 4 Burner 5 Boiler 6 Steam turbine 8 Air preheater 12 Bag filter 21 CO / CO ₂ sensor 23 Calculator 24, 28 Controller 26, 30 Valve 27 Thermocouple 29 Auxiliary burner A Air C Unburnt char G1 Combustible gas G2 Combustion exhaust gas

Claims (4)

A gasification furnace for combusting combustible materials under a low air ratio to generate combustible gas and combustible solids, and combusting the combustible solids by melting the combustible gas and combustible solids at a high temperature to slag An ash melting furnace that discharges as a waste gasification melting treatment system,
Control means for estimating the air ratio in the gasification furnace from the temperature in the gasification furnace and the composition of the combustible gas and controlling the amount of air supplied into the gasification furnace based on the estimation result is provided. Waste gasification and melting treatment system characterized by that. In the refuse gasification melting treatment system according to claim 1,
The control means measures the CO concentration and CO ₂ concentration in the combustible gas at a certain temperature in the gasification furnace to obtain the ratio CO / CO ₂ of the two concentrations, and estimates the air ratio from the result. Garbage gasification melting treatment system characterized by. In the refuse gasification melting treatment system according to claim 1,
The control means detects the temperature inside the gasification furnace, the surface of the fluidized bed, and the inside of the fluidized bed, and when the detected temperature is lower than a predetermined temperature, the temperature in the gasification furnace is increased. Waste gasification and melting treatment system characterized by having a function of causing In the refuse gasification melting processing system according to claim 3,
The said control means performs auxiliary combustion, and raises the temperature in a gasification furnace, The refuse gasification melting processing system characterized by the above-mentioned.

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