JPS6346386A - Method of controlling pressure in industrial kiln - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Technical field to which the invention pertains The present invention relates to the opening and closing of charging doors and extraction doors in industrial kilns such as heating furnaces and heat treatment furnaces in which a heat exchanger is installed as an exhaust heat recovery device. This invention relates to a method of controlling the pressure inside the furnace to reduce the blowout of exhaust gas and the intrusion of outside air.

Prior art industrial furnaces are generally provided with a chimney for exhausting the exhaust gases burned within the furnace. A damper is provided in the flue between the furnace and the chimney, and its opening is adjusted to control the furnace pressure, as disclosed in, for example, Japanese Patent Laid-Open No. 59-182927. By the way, when charging the object to be heated into the furnace or conversely extracting it out of the furnace, it is naturally necessary to open and close the charging door and the extraction door.

If the pressure inside the furnace is too high at this time, although the amount of air entering the furnace will be reduced, the combustion exhaust gas will blow out of the furnace, causing equipment around the outer wall and the steel frame, steel shell, and refractories that make up the furnace wall to burn out. This also results in a loss of energy. On the other hand, if the pressure inside the furnace is too low than the atmospheric pressure, a large amount of air will enter from outside the furnace, and the cold air will absorb heat from inside the furnace, potentially causing a drop in the temperature inside the furnace. In addition, the oxygen concentration in the furnace increases due to air entering the furnace, and oxides increase more than necessary on the surface of the object to be heated, which adversely affects quality and reduces product yield. In addition, as in the furnace, the amount of air entering the flue increases and the temperature of the exhaust gas passing through the flue also decreases.

Maintaining the appropriate pressure in the furnace is a matter of quality of the material to be heated.

This is also important in terms of yield, equipment life and energy.

By the way, the furnace pressure setting value is not always a constant value, and is generally set by the operator who operates the furnace who periodically goes around the furnace and visually checks the blowing of combustion gas from the furnace wall space. The value is often determined. Further, even if the pressure inside the furnace is set constant, it changes not only depending on the temperature inside the furnace and the amount of fuel used, but also depending on the state of damage to the furnace walls and doors, the arrangement of the objects to be heated, etc. It is also considered that the optimum value of the furnace pressure varies depending on these conditions.

The present invention eliminates the drawbacks of conventional industrial kiln pressure setting methods and provides an improved method.

The gist of this is to optimize the ratio of the amount of flue gas passing through the heat exchanger to the flow rate of the heat recovered material in industrial furnaces equipped with a heat exchanger, and to recover the heat recovered material relative to the calorific value of the flue gas at the bottom of the furnace. We will explain in detail how to optimally modify the furnace pressure control target value so as to maximize the heat ratio.

In the present invention, when operating an industrial kiln equipped with a heat exchanger, the flow rate ratio between the amount of flue gas passing through the heat exchanger and the amount of heat recovered material is the ratio of the amount of heat recovered from the heat recovered material to the amount of heat amount of the flue gas at the bottom of the furnace. The heat recovery rate is high (
They also found that the ratio of the amount of combustion exhaust gas passing through this heat exchanger to the amount of heat recovered can be controlled by changing the pressure inside the furnace.

The present invention was made based on this new knowledge, and aims to set the target value of the furnace pressure so as to maintain an appropriate ratio of the amount of combustion exhaust gas passing through the heat exchanger of an industrial kiln and the amount of heat recovered, such as air. By making modifications, it is possible to minimize the blowing of combustion exhaust gas from inside the furnace and the intrusion of outside air into the furnace and flue, and to maximize the amount of heat of the recovered material in the heat exchanger, making it possible to The furnace can be operated using the minimum amount of fuel.

Next, one embodiment of the present invention will be described.

FIG. 1 is a schematic diagram of a kiln, such as a heating furnace, showing the implementation state of the present invention, together with a block diagram showing the flow of signals. First, the heating furnace 1 is provided with a charging door 2 and an extraction door 3. Burner 6 is supplied with fuel 4 and combustion preheated air 5.
The furnace is filled with combustion exhaust gas. The combustion exhaust gas passes through the flue 7 and gives heat to the heat exchanger 8, and the combustion exhaust gas that has passed through the heat exchanger 8 passes through the chimney 9 and is released into the atmosphere. The heat exchanger 8 is provided with a flow pipe 10 through which a heat recovery substance such as air for recovering heat passes. By the way, when the furnace pressure setting target value is set by the pressure setting device 11, the furnace pressure setting signal 12 is inputted to the pressure calculator 13.

On the other hand, the furnace pressure detected by the furnace pressure detection end 14 passes through a pressure detector 15, and its pressure detection signal 16 is input to the pressure calculator 13. The pressure calculator 13' compares it with the above-mentioned furnace pressure setting signal 12, and sets the furnace pressure control signal 1 according to the difference.
7, and a damper 19 is driven by a driving surface 18 to control the pressure inside the furnace. This result is detected by the furnace pressure detection end 14 and fed back to the pressure calculator 13 through the pressure detector 15. At the bottom of the furnace, the oxygen concentration in the combustion exhaust gas is detected by the oxygen concentration detection end 20a, passes through the oxygen concentration detector 21a, and the oxygen concentration signal 22a is input to the arithmetic processing unit 23. Further, the temperature signal 26a of the combustion exhaust gas temperature at the bottom of the furnace is inputted to the arithmetic processing unit 23 from the thermocouple 24a through the thermometer 25a. The oxygen concentration at the combustion exhaust gas inlet of the heat exchanger 8 is determined by the oxygen concentration detection end 20b.
The temperatures of the combustion exhaust gas and the heat recovery material passing through the heat exchanger 8 are detected by thermocouples 24b, 24c, 24d, and 24e, and are manually input to the processing unit 23. The fuel 4 supplied for combustion in the furnace is measured by a flow rate needle, for example, an orifice 27, and the measured signal is inputted to the arithmetic processing unit 23 as a flow rate signal 29 by a flow rate detector 28. This arithmetic processing device 23 uses the above-mentioned input signals to perform arithmetic operations to be described later, and inputs the results to the pressure setting device 11 to correct and change the furnace pressure setting target value according to the operating state.

The flow balance between the heating furnace 1 and the heat exchanger 8 and the energy balance model will be explained using FIG. 2. First, the amount of air Fa required for the amount of fuel used Ff to be combusted in the furnace is determined using the following equation.

F a =F f xA o xmf-・-■Here A
o is the theoretical air amount determined by the fuel components,
Indicates the amount of air required for unit fuel consumption. m( is the excess air ratio. When burning fuel in a furnace, if only the theoretical amount of air Ao is supplied, actual combustion may generate soot or unburned matter due to problems with the structure of the burner. Therefore, in order to supply excess air and achieve efficient combustion, an excess amount of air is supplied, but this is the excess air ratio.

If the oxygen concentration measured in the combustion exhaust gas at the bottom of the furnace is 02f, the excess air ratio mf described above can be found by the equation 0.

m(=21./(21,02f) −
-■Furthermore, the amount of combustion exhaust gas Fgf generated by combustion of the fuel 4 supplied to the heating furnace 1 can be determined by equation 0, assuming that there is no air entering the furnace and no air blowing out of the furnace.

Fgf=FfX (GoX <mr 1.)X
Ao)...■ Here, Go is the theoretical amount of combustion exhaust gas determined by the fuel components, and indicates the amount of exhaust gas theoretically generated with respect to the unit amount of fuel used. However, in actual cases, fluctuating pressure in the furnace or opening/closing of the charging door 2 or the like may cause combustion exhaust gas to blow out or air to enter. Therefore, if the amount of combustion exhaust gas blown from inside the furnace to the outside of the furnace is Fo, the amount of intruding air entering from the charging door 2 etc. and entering the flue 7 is Fi, and the actual amount of combustion exhaust gas passing through the heat exchanger 8 is Fgx. A flow balance equation such as equation 0 is established between the heating furnace 1 and the heat exchanger 8.

Fgl=Fgf−F o +F i −
...■On the other hand, consider the heat balance formula around heat exchanger 8.

Qgl is combustion exhaust gas human body heat, Qg2 is combustion exhaust gas outlet RA heat, Qa1 is heat recovery product such as air human body heat, Qd
Considering that 2 is the sensible heat at the air outlet and Qd is the heat dissipated from the heat exchanger body, the heat balance formula 2 is established.

Qgl+Qal=Qg2+Qa2+Qd...
・−・−■Here, Tgl is the combustion exhaust gas inlet temperature, Tg2
is the combustion exhaust gas outlet temperature, Tal is the air inlet temperature, Ta2
is the air outlet temperature, Cpgl is the combustion exhaust gas specific heat, C9g
2 is the combustion exhaust gas outlet specific heat + Cpa+ is the air inlet specific heat, C
If pa2 is the air outlet specific heat, the 0 equation becomes the 0 equation.

FglXTglXCI)gl +FaXTalXCp
a, =FglXTg2XCpg2 +F a XTa2
XCpa2 +Qd...■ From equation 0, the combustion exhaust gas itFgl passing through the heat exchanger 8 is expressed by equation 0.

That is, the air flow rate Fa obtained by calculating the above equation 0.

Dissipated heat Qd from the heat exchanger body is input separately.

In addition, the heat exchanger inlet combustion exhaust gas temperature 'r''gt, the heat exchanger outlet combustion exhaust gas temperature 'rg2, the heat exchanger inlet air temperature T al, and the heat exchanger outlet air temperature Ta2 are measured, and these are sent to the arithmetic processing unit 23. Heat exchanger 8 is input and calculated.
The combustion exhaust gas fFg1 passing through can be determined. Here, the specific heat is known in advance depending on the temperature of the combustion exhaust gas and the heat recovery material, such as air. Therefore, by measuring the flow rate and temperature of the combustion exhaust gas and the heat recovery material, the amount of heat of each can be calculated and determined by the arithmetic processing device 23. The flow rate of heat recovery material, such as air, passing through the heat exchanger 8 is detected by a flow rate detection device 30 and input to the arithmetic processing device 23 . Instead of this flow rate detection, the air iFa determined by the above equation 0 may be used.

FIG. 3 shows the influence of the ratio of the amount of combustion exhaust gas passing through the obtained heat exchanger 8 to the flow rate of the heat recovery material, such as air, on the ratio of the amount of heat recovered from the heat recovery material to the amount of heat of the combustion exhaust gas at the bottom of the furnace. As can be seen from this figure, the ratio of the combustion exhaust gas and air flow rate passing through the heat exchanger is set appropriately, for example, 1.1 in this example.
It can be seen that when the temperature is set to 1.2, the amount of recovered heat is maximized.

As shown in Figure 4, we have discovered that the ratio between the amount of combustion exhaust gas passing through this heat exchanger and the flow rate of heat recovered material, such as air, can be controlled by changing the pressure inside the furnace.Based on this knowledge, the amount of recovered heat The set target value of the furnace pressure is changed so that the flow rate ratio of the combustion exhaust gas 9 and the air amount becomes the maximum ratio.

If for some reason the flow rate ratio of combustion exhaust gas and heat recovery material passing through the heat exchanger 8 deviates from the flow rate ratio that maximizes the recovered heat ratio of the heat exchanger 8, correct it and replace the heat exchanger 8. By changing the furnace pressure target set value so as to maximize the recovered heat ratio and maintaining the optimum furnace pressure, it is possible to reduce the heat consumption unit of the industrial kiln.

In this embodiment, a gas-gas heat exchange example was adopted for the heat exchange, but a gas-liquid heat exchange may also be used. Also, the arithmetic processing unit 2
As for calculation method 3, not only the amount of fuel used is significantly reduced, but also the amount of scale generated on the heated material is reduced, quality improvement 6. Yield is improved, and damage to equipment is also reduced.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram illustrating the state of implementation in a heating furnace of the present invention, with a block diagram illustrating the flow of signals superimposed, and Figure 2 is an exhaust gas flow balance model from the heating furnace to the heat exchanger of the present invention. Figure 3 shows the flow rate ratio of both fluids passing through the heat exchanger and the heat exchange for the heat loss of the flue gas at the bottom of the furnace. Figure 4 is a graph showing the relationship between the flow rate ratio of both fluids passing through the heat exchanger and furnace pressure under the same conditions as Figure 3. be. In FIG. 1, 8 is a heat exchanger, ■ is a heating furnace, 4 is fuel, and 5 is preheated air.

Claims (1)

[Claims] In controlling the furnace pressure of an industrial kiln equipped with a heat exchanger, the combustion exhaust gas passing through the heat exchanger and heat recovery are 1. A furnace pressure control method for an industrial kiln, characterized by modifying a set target value of furnace pressure in order to adjust the flow rate ratio of a material.