Method for incinerating dewatered sludge

Abstract

To enable proper operation of a fluid incinerator.SOLUTION: An incineration method for sludge in which dewatered sludge is fed into a fluid incinerator 1 to be incinerated, includes carrying out an adjusting operation for a sand amount in the fluid incinerator with time based upon information including information on water fed into the incinerator 1, information on temperature of the dewatered sludge, and information on the amount of sand in the incinerator.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for incinerating dewatered sludge using a fluidized bed incinerator. [Background technology]

[0002] Fluidized bed incinerators are used to incinerate sewage sludge, as well as municipal waste, waste from food factories, and industrial waste. In addition, since it is possible to accommodate fluctuations in the moisture content of the material being incinerated, it is suitable for incinerating sewage sludge after dehydrating it.

[0003] Patent Document 1 discloses a method for operating a circulating fluidized bed incinerator in which the pressure difference between the furnace top and the furnace bed is controlled to be within a predetermined range, thereby keeping the amount of sand circulation constant. Patent Document 2 discloses that the amount of air supplied to the furnace is variably controlled according to the moisture content of the material to be combusted.

[0004] The incinerator disclosed in Patent Document 1 is merely a circulating fluidized bed incinerator, and is based on the premise that the temperature of the dewatered sludge supplied to the incinerator is approximately constant, so the operation of the incinerator does not take into consideration fluctuations in the moisture content or temperature of the dewatered sludge.

[0005] The incinerator disclosed in Patent Document 2 is also merely a circulating fluidized bed incinerator, and no consideration is given to its relationship with the amount of sand. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2002-122305 A [Patent Document 2] JP 2001-227731 A Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, a main object of the present invention is to provide a method for incinerating dewatered sludge that enables proper operation of a fluidized incinerator. [Means for solving the problem]

[0008] Means for solving the above problems include the following aspects. In a sludge incineration method, dewatered sludge is put into a fluidized bed incinerator and incinerated, Based on information including information on the moisture content of the sludge fed into the incinerator, temperature information on the dewatered sludge, and information on the amount of sand in the incinerator, The amount of sand in the fluidized incinerator is adjusted over time. A method for incinerating dewatered sludge in a fluidized incinerator. Effect of the Invention

[0009] According to the present invention, it is possible to operate a fluidized incinerator properly. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of an example of a fluidized incinerator and its associated equipment. [Diagram 2] FIG. 4 is an explanatory diagram of an example of control of various elements. [Diagram 3] FIG. 13 is an explanatory diagram of an example of the correlation between the moisture content of input sludge and the amount of sand in a control example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present invention will be described below. The embodiment is merely an example and does not define the outer edge of the present invention.

[0012] FIG. 1 is a schematic diagram of an example of a fluidized incinerator and its associated equipment, and is equipped with a fluidized incinerator (bubbling fluidized bed furnace) 1 and a dehydrator 2. The dewatering machine 2 receives sludge from the previous facility and dehydrates it, and the treated dehydrated sludge is supplied to the fluidized bed incinerator 1 through a supply line 3.

[0013] In the fluidized incinerator 1, while the dewatered sludge is received, fluidized air is blown in through the fluidized air blowing means 4 installed at the bottom of the furnace, so that the dewatered sludge is blown up together with the sand used as a fluidizing medium, and is incinerated by the combustion heat. Combustion (incineration) exhaust gas is discharged from the top of the furnace and sent to an exhaust gas treatment facility (not shown).

[0014] Various known configurations of exhaust gas treatment equipment can be used. For example, a configuration can be adopted in which the exhaust gas passes through a preheater (heat exchanger), is introduced into a dust collector, and, if necessary, is subjected to appropriate treatment, and the purified air is then released into the atmosphere. Also, as shown in, for example, Japanese Patent No. 4831309 as a representative example, a configuration can be adopted in which a turbocharger is provided, the exhaust gas from the turbocharger is passed through the preheater, and the exhaust gas is heated by heat exchange with the heat of the exhaust gas, and then used as the fluidizing air for the fluidizing air blowing means 4. It has been demonstrated that the provision of a turbocharger enables spontaneous combustion in the fluidized bed incinerator 1, and also significantly reduces the amount of energy used.

[0015] A sand excavation equipment 5 is provided at the bottom of the fluidized incinerator 1. The sand excavation equipment 5 includes a excavation valve 5a, a screw transfer section 5b, a sieving section 5c, and the like. When necessary, a command to extract sand is received from the sand extracting equipment 5, and when a command to supply sand is received, a predetermined amount of sand is returned to the temporary storage tank 7 via the conveyor 6. In the temporary storage 7, a command to supply sand is received and a predetermined amount of sand is supplied into the fluidized incinerator 1 via the supply valve 7a.

[0016] The fluidizing air blowing means 4 receives air from a blower 8 via a fluidizing air header 4a. If necessary, heated air can be received from a hot stove 9 using auxiliary fuel and blown into the fluidizing air blowing means 4.

[0017] In this embodiment, there are provided means 11 for detecting the moisture content of the dewatered sludge, means 12 for detecting the amount of dewatered sludge introduced into the fluidized incinerator 1, and means 13 for detecting the temperature of the dewatered sludge. Signals from these detection means are input to the arithmetic processor 20. The detection signals to the arithmetic processor 20 may be input automatically or manually by an operator.

[0018] A known means for detecting the moisture content of the dewatered sludge 11 can be used. For example, when the dewatering machine 2 is a screw press type dewatering machine, a form can be selected in which a signal is taken in from a torque detector that detects the torque of the drive motor M that rotates the screw, similar to the drive motor indicated by reference numeral 50c in FIG. 1 in Patent No. 6696020. In this case, the moisture content of the dewatered sludge is predicted from the detected torque. Other examples of using the drive torque as a detection signal include Patent No. 6489444 and JP 2019-107628 A. On the other hand, a detection signal from a microwave transmission type moisture meter as disclosed in JP-A-2003-177105 may be used.

[0019] The moisture content of the dewatered sludge is predicted using a model capable of outputting the moisture content of the dewatered sludge. For example, the moisture content of the dewatered sludge is predicted using a trained model. The trained model is a trained model that has learned the relationship between the dewatering condition information and the moisture content of the dewatered sludge through machine learning. In other words, when dewatering condition information is input as input data, the trained model is capable of outputting the moisture content of the dewatered sludge as output data. Here, the dehydration condition information is information that indicates the conditions for dehydration in the dehydrator 2. The dehydration condition information is information that indicates, for example, the torque of a drive motor that rotates a screw when the dehydrator 2 dehydrates sludge, the sludge temperature of the dehydrated sludge, the sludge properties of the sludge, etc. The dehydration condition information includes at least the torque of a drive motor that rotates a screw when the dehydrator 2 dehydrates sludge, and the sludge temperature of the dehydrated sludge.

[0020] The trained model used to predict the moisture content of the dewatered sludge may be any machine learning method, such as linear regression, support vector machine regression, Gaussian process regression, decision tree, or neural network. In addition, the model capable of outputting the moisture content of the dewatered sludge is not limited to a machine-learned trained model. For example, the model capable of outputting the moisture content of the dewatered sludge may be a regression model, a regression formula, a classification model, or the like.

[0021] A known means can be used as the sludge input amount detection means 12 for detecting the amount of dewatered sludge fed into the fluidized incinerator 1. For example, the amount of dewatered sludge fed per hour through the feed path 3 or by a feeder into the fluidized incinerator 1 can be used as the detection signal.

[0022] A known device can be used as the temperature detection means 13 for detecting the dewatered sludge temperature. As an example, the applicant disclosed in Japanese Patent No. 6696020 that the moisture content of the dewatered sludge can be adjusted and fluctuations can be suppressed by heating the sludge. However, the temperature detection means 13 for the dewatered sludge temperature can be based on the amount of heat medium to be controlled, as in the said patent, or can be based on the detection signal from a temperature sensor (not shown) provided in space 50A2 to detect the temperature of the heat medium in heating section 50A4 in Figure 1 of Patent No. 6696020. In addition, when detecting the temperature of the dewatered sludge discharged from the dehydrator 2, for example, a non-contact thermometer such as a thermometer can be used as the temperature detection means 13 for detecting the temperature of the dewatered sludge. On the other hand, when steam is blown in to heat and dehydrate the sludge, as in JP 2020-157261 A, the temperature of the steam, for example, can be used as the temperature detection means 13 for the dehydrated sludge temperature.

[0023] The amount of sand required in a fluidized bed incinerator is determined by the moisture content of the material fed into the incinerator (sand layer moisture load x input moisture content). For example, a large amount of sand is required when feeding high moisture content sludge. If the amount of sand is small and the input moisture content exceeds the design moisture load, it becomes difficult to maintain the temperature of the sand layer, making it difficult to continue operation.

[0024] On the other hand, by subjecting the dewatered sludge to pretreatment such as heating before feeding it into a fluidized incinerator, particularly by using waste heat from incineration to heat the sludge, it is possible to economically produce dewatered sludge with a low moisture content.

[0025] The inventors have confirmed that the dewatered sludge with a low moisture content obtained by such heating treatment has good dispersibility in a fluidized bed incinerator, and that diffusion, drying, pyrolysis, and combustion proceed in a short period of time after being charged into the incinerator. When the dewatered sludge with a low moisture content obtained by such a heating treatment is incinerated, if the amount of sand is large, the agitation property becomes poor and the temperature of the sand layer tends to decrease. As such, there is an optimal amount of sand depending on the properties of the sludge fed into the furnace. In the past, however, in anticipation of the possibility that the sludge properties may change significantly in a short period of time, operation was carried out with an amount of sand determined based on representative sludge properties, and if the sludge properties deviated significantly from the representative properties, measures such as adding auxiliary fuel to prevent the temperature of the sand layer from dropping were taken.

[0026] If sludge with low moisture content and high dispersibility is added, the sand layer temperature can be maintained by adding auxiliary fuel, but the upper freeboard section will have excessive heat, which may pose risks such as the generation of clinker and thermal impact on downstream equipment. Furthermore, the input of auxiliary fuel has been a factor in increasing fuel costs.

[0027] In an embodiment of the present invention, the amount of sand in the fluidized incinerator is adjusted over time based on information including information on the moisture content of the water charged into the incinerator, temperature information on the dewatered sludge, and information on the amount of sand in the incinerator.

[0028] Information on the amount of sand in the incinerator can be substituted, for example, by the pressure difference (hereinafter, the pressure difference will be represented as ΔP) between the indicated pressure gauge 15A of the fluidizing air header 4a of the fluidizing air blowing means 4 in Figure 1 and the in-furnace pressure gauge 15B installed at the top of the furnace.

[0029] The moisture input into the incinerator (input moisture information) is the amount of sludge input multiplied by the moisture content of the sludge. However, continuously changing the input moisture information, dewatered sludge temperature information, and sand amount information in the incinerator will not only result in unstable control but also lead to heat loss, so it is desirable to use step control (stepwise operation) in two to three stages.

[0030] For example, as shown in Figure 3, the input moisture information (= sludge input amount x sludge moisture content) is set to three levels for the sludge moisture content, and the sludge temperature is set to two levels, unheated and heated, and then the amount of sand in the incinerator is adjusted. In this example, sand is automatically extracted by the sand cutting equipment 5 or supplied from the temporary storage tank 7 via the supply valve 7a in accordance with a control signal from the calculation processor 20 so that the current differential pressure from the differential pressure indicator 14 becomes the target differential pressure ΔP.

[0031] (Example) Next, an example of operation (driving example) in the above embodiment will be shown with reference to FIG. 2 and FIG. This embodiment shows an example of the transition from high moisture content sludge to heated / warmed dehydrated sludge (highly dispersible, low moisture content).

[0032] (1) Dewatered sludge with a high moisture content of about 78 to 82% is fed into the incinerator. Check the torque of the dewatering machine, predict the moisture content of the dewatered sludge, and calculate the amount of moisture to be fed. Since the amount of sand is small when the SV value of the sand layer ΔP is 20 kPa, the SV value of the sand layer ΔP is rewritten to SV1 = 25 kPa. Sand supply is started because PV=20kPa for SV1=25kPa of the sand layer ΔP. Sand supply is stopped when PV=25kPa. As a result, the sand layer temperature rises with the increase in sand amount, and the auxiliary fuel input amount is optimized.

[0033] (2) Based on the above (1) sludge characteristics, the sludge was heated and dehydrated to gradually reduce the moisture content. As a result, the dehydrated sludge had a moisture content of 75% and a sludge temperature of 45°C. In this case, when the amount of water added was calculated in the same manner as above, the amount of sand was found to be sufficiently large, so the SV value of the sand layer ΔP was rewritten as SV2 = 20 kPa. Sand extraction was started because PV=25kPa for SV2. Sand extraction was stopped when PV=20kPa. The reduction in sand volume increased the mixability, the sand layer temperature rose, and the auxiliary fuel injection amount was optimized.

[0034] (3) Based on the sludge properties in (2) above, the sludge continues to heat up, and becomes dehydrated sludge with a moisture content of 70% and a sludge temperature of 60°C. At this time, the amount of water input is calculated in the same manner as above, and as a result, the amount of sand is sufficiently large, and due to the sludge characteristics of high dispersibility and low moisture content, the sand layer temperature drops and the freeboard temperature rises. The SV value of the sand layer ΔP is rewritten to SV3 = 15 kPa. Since PV = 20 kPa for the same SV3, sand extraction begins. Sand extraction stops when PV = 15 kPa. As the amount of sand decreases, the mixability increases and the sand layer temperature rises, so auxiliary fuel input is stopped and self-combustion operation is performed.

[0035] Optimizing the amount of sand for each sludge property provides the following benefits: The amount of auxiliary fuel input required to maintain the temperature of the sand layer can be minimized. By optimizing the combustion ratio in the sand layer, abnormal temperature increases in the freeboard area can be suppressed, which contributes to preventing clinker and reducing NOx. In the case of a bubbling fluidized bed furnace in which combustion air is pushed in by a fluidized bed blower, the sand layer ΔP can be kept to a minimum by optimizing the amount of sand, which contributes to reducing the power consumption of the blower. In the case of a turbocharged fluidized bed furnace, in which the combustion air is forced in by a turbocharger, there is more room for the turbocharger to operate, making it easier to operate independently at low loads. [Explanation of symbols]

[0036] 1...fluidized incinerator, 2...dehydrator, 4...fluidized air blowing means, 4a...fluidized air header, 5...sand cutting equipment, 7...temporary storage tank, 7a...supply valve, 11...moisture content detection means, 12...sludge input amount detection means, 13...temperature detection means for dewatered sludge temperature, 15A...indicating pressure gauge, 15B...inner furnace pressure gauge, 20...calculation processor.

Claims

1. In a sludge incineration method, dewatered sludge is put into a fluidized bed incinerator and incinerated, Based on information including information on the moisture content of the sludge fed into the incinerator (the product of the amount of sludge fed and the moisture content of the sludge), temperature information on the dewatered sludge, and information on the amount of sand in the incinerator, The amount of sand in the fluidized incinerator is adjusted over time. A method for incinerating dewatered sludge in a fluidized incinerator.

2. 2. A method for incinerating dewatered sludge in a fluidized incinerator as described in claim 1, wherein the input moisture information is obtained based on the amount of dewatered sludge input into the fluidized incinerator over time and the moisture content of the dewatered sludge.

3. 3. The method for incinerating dewatered sludge in a fluidized bed incinerator according to claim 1 or 2, wherein the operation over time is a stepwise operation.

4. 3. The method for incinerating dewatered sludge in a fluidized bed incinerator according to claim 2, wherein the moisture content of the dewatered sludge is obtained based on the torque of a screw press type dewatering machine for obtaining the dewatered sludge.

5. A method for incinerating dewatered sludge in a fluidized incinerator as described in claim 2, wherein the moisture content of the dewatered sludge is obtained based on information from a moisture content meter installed in the supply path of the dewatered sludge from a dehydrator obtaining the dewatered sludge to the fluidized incinerator.

6. The method for incinerating dewatered sludge in a fluidized incinerator as described in claim 2, wherein the moisture content of the dewatered sludge is obtained using a trained model that has been machine-learned to determine the relationship between the dewatering condition information of the screw press dewatering machine that obtains the dewatered sludge and the moisture content of the dewatered sludge.

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