JPS6026934B2 - Sludge incineration method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a sludge incinerator.

Traditionally, vertical multi-stage incinerators incinerate sludge at an air ratio of approximately 2.0 to 2.2, but in recent years it has been found that it is preferable to operate the sludge at a lower air ratio instead. ing.

In other words, when the air ratio is lowered to approximately 1.1 to 1.5,
In addition to reducing the amount of exhaust gas and making it possible to save energy,
Generation of hexavalent chromium in ash can be prevented. Furthermore, it is desirable for efficiency to increase the load on the hearth that can perform drying and incineration per unit area of the hearth. For these reasons, conventional Tsubaki Seki 54-3197
As described in Publication No. 6, a method of circulating part of the exhaust gas into the furnace is being explored. This method simply uses an air ratio of 2.0~
A constant amount of cake was circulated so that the hearth load equivalent to 2.2 (the amount of cake that can be dried and incinerated within a unit time per unit area of the hearth) was obtained.

In other words, in general, when this method does not circulate the exhaust gas, the amount of gas passing through the furnace is small, and the drying/incineration rate is reduced, which reduces the hearth load capacity and reduces the processing capacity. In view of the need to increase the ratio, part of the exhaust gas is circulated to increase the amount of gas passing through the furnace and to improve the permissible hearth load. However, since the amount of circulating exhaust gas is constant in this method, it is not possible to cope well with feed sludges having various moisture contents. For example, when incinerating a cake with a high water rate, the amount of gas passing through the furnace is small compared to the required amount, so the drying speed of the cake in the furnace decreases, the allowable hearth load decreases, and the amount of gas passing through the furnace decreases. may be discharged from the lower part of the furnace. On the other hand, in the case of a cake with a low moisture content, we operated with a small amount of cake input, and sometimes the amount of gas passing through the furnace exceeded the required amount, so the drying rate of the cake was too fast and the rice bran was burned in the upper stage. , the exhaust gas temperature rises, causing problems such as damaging exhaust gas treatment and exhaust gas circulation equipment. In addition to circulating the exhaust gas in the furnace as in the conventional example above, the method of adjusting the temperature of the combustion stage as shown in the Tokkō Sho 52-1 Senppi No. (Tokukō Akihiro No. 1162 Y) publication etc. was applied. However, from the perspective of adjusting the hearth load, when incinerating a cake with a low moisture content, the combustion stage temperature increases and the amount of exhaust gas circulation is adjusted to increase, so the drying and combustion speed becomes slower. , which may lead to problems such as damage to equipment as described above. On the other hand, as shown in FIG. 2, the hot air temperature has been adjusted together with the furnace temperature.

That is, a temperature sensor 52 is provided at the combustion stage of the multistage incinerator 51, and a temperature sensor 54 is also provided at the outlet of the hot blast furnace 53.
The amount of heavy oil from the heavy oil pump 55 and the amount of combustion air from the air fan are controlled by the control valves 57 and 58 using the furnace temperature controller 56 so that the temperature of the combustion stage is approximately 800 qo.
Proportionally adjust the air ratio to 1.3 to 1.9 degrees Fahrenheit through a hot air temperature controller, and adjust the hot air temperature to 1000 to 1100oC, usually around 1000oC, to prevent clinker generation. 59, a control valve 60 is adjusted to add an appropriate amount of dilution air. In this case, the total air ratio will be 2.5-3.0. In this way, when diluting with air, the total amount of air introduced into the furnace increases, and no reduction in the air ratio can be expected. In particular, when incinerating sludge with high water content such as sewage sludge, a large amount of heavy oil is used for auxiliary fuel, so even though it is desirable to set the air ratio to 1.1 to 1.5 as mentioned above, The amount of air intake is greater than the amount of air required for combustion of the cake, raising the air ratio in the entire furnace. As a countermeasure to this problem, if exhaust gas is used to dilute the hot air, the amount of air supplied from the hot blast furnace can be reduced to an air ratio of 1.3 to 1.0 compared to the auxiliary fuel combustion. Since it becomes the mother wall degree, there is no need to increase the combustion air ratio of the incinerated material.

However, even if exhaust gas is simply used to dilute hot air, the exhaust gas is about 300 degrees Celsius, which is higher than normal room temperature air.
Compared to dilution with about 20 oo of cold air, the amount of high-temperature exhaust gas required for dilution of hot air is greater than in the case of cold air, and more hot air is supplied into the furnace. As a result, the amount of circulating gas passing through the incinerator increases, and regardless of the intention to adjust the combustion rate, the amount of gas that contributes to drying the cake at the top of the furnace increases, and the exhaust gas temperature at the furnace outlet increases. However, there is a problem in that the amount of facial heat released from the exhaust gas to the outside of the system increases and the thermal efficiency of the furnace decreases. The present invention solves the above-mentioned problems in one fell swoop, and its purpose is to prevent incomplete combustion with a constant thermal efficiency against fluctuations in load and incinerated materials, to ensure a stable temperature inside the furnace, and to provide auxiliary fuel. The purpose of this invention is to provide a method that can significantly reduce the amount of energy used.

The first invention to achieve this object is to circulate a part of the exhaust gas from the drying stage of the sludge incinerator back into the incinerator without diluting it with air, and to measure the temperature by an exhaust gas temperature detector installed in the exhaust gas path. This system is characterized in that the temperature of the exhaust gas from the incinerator is controlled by adjusting the amount of exhaust gas circulation based on the signal, and the air ratio in the furnace is set to 1.1 to 1.6.

In addition, the second invention circulates a part of the exhaust gas from the drying stage of the sludge incinerator back into the incinerator without diluting it with air, and generates a temperature signal based on a temperature signal from an exhaust gas temperature detector installed in the exhaust gas path. The temperature of the exhaust gas from the incinerator is controlled by adjusting the amount of exhaust gas circulated, and a part of the exhaust gas is guided to the hot blast furnace, and the temperature of the hot air from the hot blast furnace is controlled by adjusting the amount of exhaust gas supplied to the hot blast furnace. At the same time, the furnace air ratio is set to 1.1 to 1.6.

That is, the main points of the present invention are as follows.
{1' The air ratio in the furnace is set to 1.1 to 1.6, and a part of the exhaust gas is circulated in order to reduce the amount of exhaust gas, save energy, and increase the hearth load.

Furthermore, the temperature of the exhaust gas from the incinerator is controlled by adjusting the amount of circulation. The invention described in Hakama Seki No. 54-31976 has the same purpose in that it improves the hearth load, but is different in that it does not have a means for controlling the amount of circulation.

As mentioned above, if the circulation amount is constant as in this conventional example, there is a problem. The invention is based on the finding that, for example, as the moisture content of the cake increases, the furnace outlet exhaust gas temperature decreases.

Therefore, if the temperature of the exhaust gas at the furnace exit has fallen and it is necessary to increase the drying/combustion rate, increase the amount of circulating gas, raise the exhaust gas temperature, increase the drying/combustion rate, or conversely, increase the drying/combustion rate. - When it is desired to slow down the combustion rate, by reducing the amount of circulation, it is possible to maintain a combustion state that accurately corresponds to the properties of the cake in the furnace, such as the moisture content and calorific value of the cake. Generally, as shown in equation [1}, the drying rate Q becomes more distant as the contact gas amount G increases and the contact gas temperature T rises. k and n are positive constants.
Q=KG×(10Tn)...[11[2} As in the above-mentioned Japanese Patent Publication No. 54-11629, it does not rely solely on adjusting the temperature of the combustion Z stage to a constant level, but rather depends on the exhaust gas temperature. Considering that this is an indicator of the combustion and drying conditions in the furnace,
Controls the amount of exhaust gas circulation.

Therefore, optimal combustion corresponding to the cake properties can be achieved. J Note that the exhaust gas according to the invention in the same publication means gas in an excess air state containing additional air, according to the description thereof. In contrast, the present invention circulates exhaust gas that is not diluted with air.
2 In the invention disclosed in the same publication, the circulating gas amount is adjusted in the first place in order to maintain the temperature in the combustion compartment at a constant temperature by replenishing the gas from the furnace with air and displacing relatively low-temperature gas with excess air. The system detects the temperature of the compartment stage and adjusts the amount of circulating gas before supplying it to the combustion section of the furnace, and its purpose is to incinerate the sludge at a constant temperature.

If there is excess heat in the combustion zone, the amount of exhaust gas is increased and the temperature is lowered by absorbing the excess heat with low-temperature exhaust gas, and if there is insufficient heat, fuel and fuel from the outside are added without adjusting the amount of exhaust gas circulation. It increases the amount of air. Thus, although the two methods may not seem to have much difference at first glance, they not only have significant differences in purpose and substantive structure as described above, but also have clear differences in operation as follows. .

Reference example Invention '31 In the second invention, a part of the exhaust gas is guided to the hot air stove, and the temperature of the hot air in the hot air stove is adjusted by adjusting the temperature of the hot air in the hot air stove, instead of adjusting the amount of dilution air as in the example in Fig. 2 of the subchapter. It is controlled by adjusting the combined amount of exhaust gas supplied to the furnace.

Therefore, for example, when the amount of exhaust gas led to the hot-air stove increases and the drying/combustion speed becomes faster, the increase in exhaust gas temperature is detected, and the amount of circulating gas that does not pass through the hot-air stove is reduced, resulting in upper stage combustion and high-temperature combustion. This can prevent combustion.
The present invention will be described below with reference to a concrete example shown in the drawings. Reference numeral 1 denotes a vertical multi-stage sludge incinerator, in which the incinerated material S is supplied from the supply port 2 at the top, and the exhaust gas G is supplied from the exhaust gas furnace outlet 3 at the top. The exhaust gas is discharged through the exhaust gas path 4.

The incinerated ash A is discharged from the incinerated ash outlet 5 at the bottom. Reference numeral 6 denotes a rotary furnace shaft that supports blades (not shown), and this furnace shaft 6 is cooled by cooling air (hereinafter referred to as shaft air) from a cooling fan 7.

The chilled air is heated indirectly in the furnace 1, and is passed through a shaft-cooled air duct 8 to a secondary air inlet 9 so that the oxygen concentration in the exhaust gas, that is, the sludge combustion air ratio, is kept constant.
The other shaft-cooled air is supplied to the furnace 1 from the shaft-cooled air, and the other shaft-cooled air is sent to an exhaust gas treatment device (not shown). This control is performed in the exhaust gas path 4
The oxygen concentration detector 1 installed in the furnace detects the oxygen concentration, and the oxygen concentration (furnace air ratio) controller 11
The cooling air duct damper 12 and the exhaust damper 1
This is done by controlling the opening and closing of 3. On the other hand, the exhaust gas in the exhaust gas path 4 passes through the suction circulation duct 14 to the circulation fan 1.
5, the air is circulated to the hot blast stove 18 and the incinerator 1 via the hot blast stove side circulation duct 16 and the incinerator side circulation duct 17, respectively.

Fuel ○i made of heavy oil is suitably supplied to the hot stove 18 through a fuel pipe 19, and air Ai is supplied via an air pipe 20 by a combustion fan 21. Fuel pipe 1
9 is provided with an oil amount regulating valve 22, and an air pipe 201 is provided with an air amount damper 23, respectively. In addition, a temperature detector 24 is arranged at the relevant stage of the competition furnace 1, and the temperature of the combustion stage is taken into the combustion stage temperature control and auxiliary fuel/air ratio controller 25, and sent to the air/fuel ratio setting device 26 to adjust the oil amount. A combustion stage temperature control signal by adjusting valve 22 is output. Furthermore, a damper 27 is provided in the duct 16, and the opening degree is controlled by a hot air temperature controller 29 based on a temperature signal from a hot air temperature detector 28 provided at the supply portion of the hot air stove 7, and the hot air temperature is adjusted. Ru.

Further, a damper 30 is disposed in the duct 17, and the exhaust gas path 4
The opening degree is adjusted by the furnace outlet exhaust gas temperature controller 32 based on the temperature signal from the exhaust gas temperature detector 31 provided at the furnace outlet, thereby controlling the exhaust gas temperature at the furnace outlet. That is, when the oxygen concentration detector 10 in the exhaust gas path 4 detects that the oxygen concentration in the exhaust gas has risen above the predetermined upper limit of the adjustment range, the cooling is performed so that the supply of secondary air is reduced from the shaft-cooled air duct 8 in the furnace. The air duct damper 12 operates in the "close" direction according to the instruction from the oxygen concentration controller 11, and similarly, when the oxygen concentration falls below the predetermined lower limit value, the shaft air duct damper 12 operates in the "close" direction.
By operating in the “open” direction, the air ratio in the furnace is 1.1~
1.6.

The adjustment range of the oxygen concentration may be indicated by a median value.
Note that the exhaust damper 13 is the same as the cold air duct damper 1.
2 and the oxygen concentration controller 11 to provide the required air resistance to the exhaust duct, thereby operating for good adjustment of the amount of secondary air. The damper 27 of the duct 16 operates to open the damper 27 via the hot air temperature controller 29 when the hot air temperature detector 28 detects a rise in the hot air temperature to a predetermined temperature or higher. The exhaust gas from the passage 4 is supplied to the hot air stove 18, and when the hot air temperature falls below a predetermined temperature, the opening degree is operated in the "closed" direction to reduce or stop the amount of exhaust gas supplied to the hot air stove 18, and the secondary air To manage the hot air temperature of a hot blast furnace without interfering with the function of adjusting the air ratio in the furnace in a supply system. In the apparatus configured in this way, the amount of exhaust gas G is adjusted by the furnace air ratio controller 11, and is controlled to the amount of exhaust gas corresponding to a predetermined air ratio (1.1 to i.6). Furthermore, when the exhaust gas temperature at the furnace outlet 3 changes due to changes in the load and the properties of the incinerated material, the temperature controller 32 adjusts the amount of exhaust gas circulating through the duct 17, and the furnace exit temperature is controlled to about 300°C. When the hot air temperature fluctuates, the hot air temperature controller 29
The dilution force by the exhaust gas passing through the furnace 1 is adjusted, and the temperature of the hot air is controlled within the range of 1000 qo to 1100 qo, which does not generate clinker in the furnace 1 and has good thermal efficiency. As described above, in the first invention, since the exhaust gas circulation amount is adjusted so that the furnace outlet temperature is within a predetermined temperature (range), a constant thermal efficiency can always be obtained with respect to fluctuations in load and incinerated material. At the same time, incomplete combustion can be reliably prevented and a desired furnace temperature can be achieved.

In addition to the effects of the first invention, the second invention can significantly reduce the amount of auxiliary fuel used.

To further explain the reason for this, when circulating the exhaust gas, the amount of koji-cooled air supplied into the furnace 1 is adjusted so that the oxygen concentration in the exhaust gas is 2 to 8%, but air is used to dilute the hot air. If used, when incinerating sludge with a high moisture content, even if the amount of cold air supplied to the furnace 1 is reduced to zero, the amount of oxygen supplied from the hot blast furnace 18 will be excessive, and the oxygen in the exhaust gas will exceed a predetermined value. The amount of hexavalent chromium that remains in the hot stove is more likely to be generated, which increases the amount of exhaust gas and reduces the thermal efficiency of the furnace. However, if the hot air is diluted by the circulating exhaust gas as described above, Since the oxygen concentration is reduced to that extent, the above-mentioned situation can be avoided, and the sludge air can be used exclusively as air for sludge combustion, so the heat of the sludge air itself heated in the furnace can also be used to assist sludge combustion. This is because it can be effectively used as a heat source. In the above example, the circulating gas inlet into the furnace, the secondary air (bag cooling air) inlet 9, the air ratio measurement point, etc. can be selected as appropriate.

Furthermore, it goes without saying that the ducts 16 and 17 do not have to be of a branched type, but may each lead the exhaust gas from approximately 4 in parallel. Further, the term sludge as used in the present invention refers to sludge mixed with municipal waste, or sludge containing sludge and the like. Next, examples of the present invention will be shown.

Example 1 In a multi-stage incinerator with a rainbow/Hr capacity that performs exhaust gas circulation, the water content is 78% and the calorific value is 2000 kcal/k.
9- When incinerating a cake of fixed objects, the conventional example is when the exhaust gas circulation rate is fixed at about 3000〆/Hr, and the present invention example is when the exhaust gas circulation rate is automatically adjusted so that the exhaust gas temperature is 30000〆/Hr. A comparison is shown in Table 1.

Table 1 As is clear from this table, the exhaust gas temperature is at the desired 30°C.
It can be stabilized at around 0:00 o'clock, and the amount of auxiliary fuel used can be significantly reduced.

Example 2 Moisture content 80%, calorific value 1800kcal/k
91 In an exhaust gas circulation type vertical multistage furnace for incinerating solid sludge, there are cases where air is used to dilute the hot air of the auxiliary heat source (A heavy oil), and cases where circulating gas is used to dilute the hot air. Table 2 shows the comparison results with the case where the change was made.

In the case of air dilution, the oxygen concentration in the exhaust gas did not decrease even if the supply of shaft-cooled air into the incinerator was reduced to zero. Furthermore, since the amount of direct circulation into the incinerator was fixed, the exhaust gas temperature increased and the proportion of auxiliary fuel used did not clearly decrease. No.
2 Table Example 3 Regarding a circulating vertical multi-stage furnace for incinerating a cake with a moisture content of 78% and a calorific value of 2000 kcal/k9, Examples), ■ When the hot air is diluted with circulating gas without adjusting the exhaust gas temperature, ■ When the exhaust gas temperature is adjusted by adjusting the amount of circulating gas, and the hot air is also diluted with circulating gas (in accordance with the present invention) Table 3 shows the comparison results for the three examples.

Table 3

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a specific example of the present invention, and FIG. 2 is a schematic diagram showing a conventional example. 1...Incinerator, 4...Exhaust gas path, 8...
... Axial cooling air duct, 16, 17 ... Circulation duct, 18 ... Hot blast furnace, 29 ... Hot air temperature controller, 30 ... Furnace outlet exhaust gas Temperature Controller. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. A part of the exhaust gas from the drying stage of the sludge incinerator is circulated back into the incinerator without air dilution, and a device installed in the exhaust gas path is installed to adjust the exhaust gas based on the temperature signal from the exhaust gas temperature detector. A sludge incineration method characterized by controlling the exhaust gas temperature from the incinerator by adjusting the circulation amount, and setting the in-furnace air ratio to 1.1 to 1.6. 2. A part of the exhaust gas from the drying stage of the sludge incinerator is circulated back into the incinerator without air dilution, and the amount of exhaust gas circulation is adjusted based on the temperature signal from the exhaust gas temperature detector installed in the exhaust gas path. In addition to controlling the exhaust gas temperature from the incinerator, a part of the exhaust gas is guided to the hot blast furnace, and the temperature of the hot air from the hot blast furnace is controlled by adjusting the amount of exhaust gas supplied to the hot blast furnace. Ratio 1.1-1.6
A sludge incineration method characterized by: