Method for predicting moisture content of dewatered cake in belt press dehydrator and method for dewatering sludge

Abstract

To provide a method for predicting a moisture content of dewatered cake in a belt press dehydrator capable of easily and accurately predicting a moisture content of dewatered cake.SOLUTION: A method for predicting a moisture content of dewatered cake from a belt press dehydrator of dehydrating sludge includes: measuring the amount of mud supplied to the belt press dehydrator (m3 / h), a concentration of suspended solids in the supplied mud (wt.%), filter cloth belt speed (m / h) and dewatered cake thickness (m); and predicting the moisture content of the dewatered cake using these measurements, the dewatered cake width (m), and the specific weight of the dewatered cake, based on the following equation. The moisture content of dewatered cake (wt.%)=[1-{mud feed rate (m3 / h)×concentration of suspended solids (wt.% / 100)}] / [filter cloth belt speed (m / h)×dewatered cake width (m)×dewatered cake thickness (m)×dewatered cake specific weight]×100.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for predicting the moisture content of dehydrated cake produced by a belt press dehydrator, and also to a method for dehydrating sludge using a belt press dehydrator, utilizing the moisture content prediction method. [Background technology]

[0002] In the dehydration process of sludge using a belt press dehydrator, it is very important to reduce the moisture content of the dehydrated cake because it leads to reducing waste disposal costs. Therefore, during the operation of the belt press dehydrator, the moisture content of the dehydrated cake is measured periodically and the operating conditions such as the amount of sludge fed, the amount of coagulant fed, and the filter cloth speed are often adjusted so that the moisture content does not increase.

[0003] Conventionally, in order to measure the moisture content of a dehydrated cake, the dehydrated cake is sampled, dried, and the weight is measured before and after drying. In this moisture content measurement method, it takes a long time to dry the dehydrated cake, so there is a time lag in detecting the deterioration of the moisture content. In addition, since this measurement method is performed by a measuring operator, the measurement interval becomes long, continuous measurement is not possible, and there is a risk of overlooking the change in moisture content over time.

[0004] Patent Document 1 describes that in the gravity filtration section (gravity dewatering section) of a belt press dewatering machine, the thickness of sludge on the filter cloth is measured, the dewatering state is monitored, and the operating conditions of the belt press dewatering machine are controlled. However, although it is possible to continuously measure the sludge thickness in the gravity filtration section, it is not possible to determine whether the cause of a change in the thickness in the gravity filtration section is a change in the amount of solids supplied or a change in the dewatering state, making it difficult to predict the moisture content of the dewatered cake.

[0005] Patent Document 2 describes that the dewatering conditions (sludge feed amount, drug injection amount, and filter cloth speed) are controlled in consideration of the sludge thickness in the gravity filtration section, filter cloth speed, sludge feed amount, etc. In this method, as in Patent Document 1, only the dewatering state in the gravity filtration section is measured. Since the sludge that has passed through the gravity filtration section is squeezed in the squeezing section and then discharged as a dewatered cake, the moisture content of the dewatered cake cannot be detected by only measuring the dewatering state in the gravity filtration section. In addition, in Patent Document 2, the suspended solids concentration in the gravity filtration section is treated as a constant value, assuming that it can be made almost constant by appropriately performing drug injection using a high-precision drug injection control device, and the suspended solids concentration of the sludge is not actually measured. It is necessary to accurately grasp the amount of solids to be supplied by measuring the suspended solids concentration in the slurry state before the drug injection point.

[0006] Patent Document 3 describes a method for measuring the coarse suspended matter, net organic matter, amount of mucilage, chemical-free centrifugation water content, and suspended solids colloid equivalent value of digested sludge, and predicting the water content of the dehydrated cake based on these.

[0007] Patent Document 4 describes a method for predicting the moisture content of a dehydrated cake based on measurements of the suspended matter, net organic matter, amount of viscous matter, water content after centrifugation without chemical addition, colloid equivalent value of suspended solids, colloid equivalent value of supernatant, and colloid equivalent value of supernatant after addition of an inorganic coagulant.

[0008] However, the methods of Patent Documents 3 and 4 require the measurement of many items, and it is not possible to quickly predict the moisture content of the dehydrated cake.

[0009] Patent Document 5 describes a method in which a dehydrated cake to be measured is passed between an oscillator and a detector of a microwave transmission type moisture meter, the attenuation voltage before and after the microwave irradiated on the dehydrated cake passes through is measured, the attenuation amount of the irradiated microwave is input to a controller, and the moisture content of the dehydrated cake is calculated by comparing it with calibration curve data that has been input in advance to the controller as a calibration curve showing the relationship between the microwave attenuation voltage and the moisture content of the cake. However, this method requires that the dehydrated cake is extracted from the dehydrator by a sampling device and then pressed into a measurement die of the microwave transmission type moisture meter by a pressure pump to collect measurement data, which requires expensive measuring equipment and a large-scale sampling device and sample pressing device, resulting in high facility costs. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 59-133996 [Patent Document 2] Japanese Patent Application Publication No. 7-148595 [Patent Document 3] JP 2001-334297 A [Patent Document 4] JP 2001-334299 A [Patent Document 5] JP 2003-177105 A Summary of the Invention [Problem to be solved by the invention]

[0011] An object of one aspect of the present invention is to provide a method for predicting the moisture content of dehydrated cake in a belt press dehydrator, which can easily and accurately predict the moisture content of the dehydrated cake.

[0012] Another object of the present invention is to provide a sludge dehydration treatment method in which the operating conditions of a belt press dehydrator are controlled based on the prediction results obtained by this method for predicting the moisture content of dehydrated cake of a belt press dehydrator. [Means for solving the problem]

[0013] The method for predicting the moisture content of dehydrated cake of the present invention is a method for predicting the moisture content of dehydrated cake from a belt press dehydrator that dehydrates sludge, the method comprising the steps of: 3 The water content is predicted based on the following formula [1] using the measured values, the width of the dehydrated cake (m) and the specific gravity of the dehydrated cake.

[0014] Dehydrated cake moisture content (wt%) = [1-{Sludge supply amount (m 3 / h) × suspended solids concentration (weight % ÷ 100) [Filter belt speed (m / h) × dehydrated cake width (m) × dehydrated cake thickness (m) × dehydrated cake specific gravity] × 100 …[1]

[0015] In one embodiment of the present invention, the specific gravity of the dehydrated cake is an actual value measured periodically or a predetermined value (for example, a value known empirically).

[0016] In one embodiment of the present invention, the sludge is such that the moisture content of the dehydrated cake from the belt press dehydrator is 50 to 95% by weight.

[0017] The sludge dehydration method of the present invention is a sludge dehydration method using a belt press dehydrator, in which at least one of the amount of sludge fed to the belt press dehydrator, the amount of coagulant injected into the sludge, the filter cloth belt speed, and the agitation speed in the coagulation tank is controlled based on the moisture content value predicted by the method for predicting the moisture content of the dehydrated cake of the present invention. Effect of the Invention

[0018] According to the method for predicting the moisture content of a dehydrated cake of the present invention, the moisture content of the dehydrated cake can be accurately predicted from the amount of mud fed to the belt press dehydrator, the suspended solids concentration of the fed mud, the filter fabric belt speed, the thickness of the dehydrated cake, the width of the dehydrated cake, and the specific gravity of the dehydrated cake.

[0019] According to the sludge dehydration method of the present invention, the operating conditions of the belt press dehydrator, such as the amount of sludge fed, the amount of coagulant fed, the filter cloth belt speed, the stirring speed of the coagulation tank, etc., can be appropriately controlled based on the predicted moisture content. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram of a sludge dewatering device having a belt press dewatering machine. [Diagram 2] 1 is a graph showing changes in moisture content over time. [Diagram 3] 1 is a graph showing experimental measurement results. [Figure 4] 1 is a graph showing experimental measurement results. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The present invention will be described in detail below with reference to the drawings. Fig. 1 is a schematic side view showing an example of a sludge dewatering apparatus having a belt press dewatering machine to which the method of the present invention is applied.

[0022] Raw sludge is introduced into a coagulation tank 3 by a sludge feed pump 1 and a raw sludge pipe 2. A coagulant is injected into the coagulation tank 3 by a chemical injection pump 4 and a chemical injection pipe 5.

[0023] The flocculated sludge that has been subjected to flocculation treatment in the flocculation tank 3 is supplied to a gravity filtration section (gravity dewatering section) A on a lower filter cloth belt 11 of a belt press dewatering machine 10 through a sludge supply pipe 6. The lower filter cloth belt 11 and the upper filter cloth belt 12 are respectively stretched over a drive roller and a guide roller, and are rotated endlessly by the drive roller being rotated by a motor.

[0024] In the gravity filtration section A, the flocculated sludge is gravity filtered to produce a gravity dewatered cake. This gravity dewatered cake is squeezed and dewatered by filter cloth belts 11 and 12, and taken out as a dewatered cake.

[0025] In this embodiment, the raw sludge pipe 2 is provided with a sludge supply amount measuring sensor 21 and a suspended solids concentration measuring sensor 22. Although not shown in the figure, the belt press dehydrator 10 is provided with a speed measuring sensor for the lower filter fabric belt 11 and a thickness measuring sensor for the dehydrated cake.

[0026] The detection signals from these sensors are input to the control device 20, which performs calculations and controls the mud supply pump 1, the agitator in the coagulation tank 3, the chemical injection pump 4, and the drive motor for the filter cloth belt 11 according to the results.

[0027] Examples of sludge to be treated include excess sludge and coagulated sedimentation sludge, but are not limited thereto. The sludge is preferably one in which the moisture content of the dehydrated cake from the belt press dehydrator 10 is 50 to 95% by volume. The lower limit of the moisture content of the dehydrated cake is preferably 50%, more preferably 70%, and even more preferably 78%. The upper limit of the moisture content of the dehydrated cake is preferably 95%, more preferably 90%, and even more preferably 82%.

[0028] The sludge supply pump 1 may be of any type as long as it can supply sludge.

[0029] As the mud supply amount measuring sensor 21, a flow meter or the like is used.

[0030] As the suspended solids concentration measuring sensor 22, a sludge concentration meter or the like is used.

[0031] The flocculant fed from the chemical feed pump 4 reacts with the sludge to form flocculated flocs. The flocculant may be an inorganic flocculant, a polymer flocculant, or a combination of both. As the inorganic flocculant, the inorganic flocculants described in JP-A-2001-334299 and JP-A-2001-334297 may be used. As the polymer flocculant, the polymers described in JP-A-2001-334299 and JP-A-2001-334297 may be used.

[0032] As the speed measuring sensor for the filter cloth belt, a sensor that measures the speed of the filter cloth belt based on the number of revolutions of a motor for driving the filter cloth belt is suitable.

[0033] As a dehydrated cake thickness measurement sensor at the dehydrator outlet 13, a non-contact distance sensor such as a laser distance meter or an ultrasonic distance sensor can be installed at the dehydrator outlet 13 of the compression section of the belt press dehydrator or immediately before the dehydrator outlet 13 to measure the thickness of the dehydrated cake discharged from the dehydrator.

[0034] In the present invention, the amount of mud fed (m 3 The water content of the dehydrated cake is predicted based on the following formula [1] using the measured data, the width of the dehydrated cake (m) and the specific gravity of the dehydrated cake.

[0035] Dehydrated cake moisture content (wt%) = [1-{Sludge supply amount (m 3 / h) × suspended solids concentration (weight % ÷ 100) [Filter belt speed (m / h) × dehydrated cake width (m) × dehydrated cake thickness (m) × dehydrated cake specific gravity] × 100 …[1]

[0036] This equation [1] is derived from the solid mass balance, which assumes that the amount of solids in the sludge per unit time supplied to the gravity filtration section A of the belt press dehydrator 10 through the sludge supply pipe 6, Min, is equal to the amount of solids in the dehydrated cake removed from the belt press dehydrator 10 per unit time, Mout.

[0037] The amount of solids in the sludge supplied to the belt press dewatering machine 10 per unit time is expressed as Min. Min = mud supply amount per unit time (m 3 / h) × suspended solids concentration (weight % ÷ 100) …[2] The suspended solids concentration (weight % ÷ 100) is the weight part of solids in 1 weight part of feed mud.

[0038] The solid content (Mout) of the dehydrated cake taken out from the belt press dehydrator 10 per unit time is expressed as follows, assuming that the moisture content of the dehydrated cake (i.e., the weight part of water in 1 weight part of dehydrated cake) is β: Mout = filter belt speed (m / h) × dehydrated cake width (m) × dehydrated cake thickness (m) × dehydrated cake specific gravity × (1-β) …[3] Here, (1-β) is the weight part of solids in 1 weight part of dehydrated cake.

[0039] By substituting equations [2] and [3] into the material balance equation Min=Mout, which equates the supply solids amount Min and the discharged solids amount Mout, and solving for the moisture content of the dehydrated cake, the above equation [1] is derived.

[0040] [Specific gravity of dehydrated cake] The specific gravity of the dehydrated cake is set to an actual measurement value obtained by periodically (e.g., once a month) collecting and measuring samples, or a preset value (e.g., 1.0). As the preset value, an empirically understood value is preferable. In the case of excess sludge or coagulated sedimentation sludge, the specific gravity of the dehydrated cake is usually about 1.0 to 2.0.

[0041] [Suspended solids concentration] The suspended solids concentration of sludge is the concentration of insoluble matter with a particle size of 2 mm or less in the sludge.

[0042] In the present invention, the suspended solids concentration of the sludge is preferably about 0.3 to 6.0% by weight. If the suspended solids concentration is less than 0.3% by weight, it may be difficult to perform coagulation and dehydration treatment, which is not preferable. On the other hand, if the suspended solids concentration exceeds 6.0% by weight, the sludge may not spread uniformly in the gravity filtration section A, which may make it difficult to perform dehydration treatment, which is not preferable.

[0043] [Sludge supply amount] The sludge supply rate is the flow rate of sludge fed into the coagulation tank.

[0044] The sludge supply amount is 0.1 to 400 m 3 / h is preferable. The mud supply amount is 0.1m3 If the amount of mud fed is less than 400 m / h, the amount of mud fed to the dewatering process will be reduced, which may be undesirable. 3 If the rate exceeds 100 / h, the amount of flocculation treatment increases, which may make it difficult to carry out the dehydration treatment, which is not preferable.

[0045] The solids throughput of a dehydrator can be calculated by multiplying the mud feed rate by the suspended solids concentration (mud feed rate x suspended solids concentration = solids throughput). The solids throughput per 1 m of filter fabric belt width x hour is preferably about 20 to 300 kgDS / m·h. If the solids throughput is less than 20 kgDS / m·h, the amount of mud fed to the dehydration process will be small, which may not be desirable. On the other hand, if the solids throughput exceeds 300 kgDS / m·h, the amount of flocculation processing will increase, making dehydration difficult, which may not be desirable.

[0046] [Filter belt speed] The filter cloth belt speed is the speed of the filter cloth belt used in the belt press dewatering machine.

[0047] In the present invention, the filter cloth belt speed is preferably about 12 to 720 m / h. If the filter cloth belt speed is less than 12 m / h, the load on the device increases and dehydration treatment may become difficult. On the other hand, if the filter cloth belt speed is more than 720 m / h, sufficient squeezing time may not be secured and good dehydration effect may not be obtained.

[0048] [Dehydrated cake width] The dehydrated cake width is the width of the filter fabric belt used in the belt press dehydrator that is actually used for dehydrating sludge.

[0049] In the present invention, the width of the dehydrated cake is preferably about 0.3 to 4 m. If the width of the dehydrated cake is less than 0.3 m, the amount of dehydration may be reduced, which is not preferable. On the other hand, if the width of the dehydrated cake is more than 4 m, the load on the device may be increased, which may make it difficult to dehydrate the cake, which is not preferable.

[0050] [Dehydrated cake thickness] The dewatered cake thickness is the thickness of the dewatered cake produced by the belt press dewaterer.

[0051] In the present invention, the thickness of the dehydrated cake is preferably 0.001 to 0.02 m. If the thickness of the dehydrated cake is less than 0.001 m, the thickness of the dehydrated cake is reduced, which may make it difficult to dehydrate the cake, which is not preferable. On the other hand, if the thickness of the dehydrated cake exceeds 0.02 m, the thickness of the dehydrated cake is increased, which may make it difficult to dehydrate the cake, which is not preferable.

[0052] According to the present invention, it is possible to predict the moisture content of the dehydrated cake by measuring the sludge condition (sludge feed amount and suspended solids concentration), the operation condition of the belt press dehydrator (filter cloth belt speed), and the dehydration condition of the sludge (dehydrated cake thickness).Then, by controlling the sludge feed amount, the amount of coagulant injected, the filter cloth belt speed, and the agitation speed of the coagulation tank based on the prediction results, it is expected that the dehydration treatment of the belt press dehydrator can be optimized.

[0053] In the method of the present invention, since the moisture content can be predicted in real time, it is possible to detect the deterioration of the moisture content as soon as possible. Therefore, when the moisture content (predicted value) of the dehydrated cake becomes high, the amount of mud feed is reduced, the amount of coagulant fed is increased, and the filter cloth belt speed is controlled to be lowered, thereby preventing the moisture content from deteriorating. Conversely, when the moisture content (predicted value) is sufficiently low, the amount of mud feed is increased, the amount of coagulant fed is reduced, and the filter cloth belt speed is controlled to be increased, thereby increasing the amount of processing and reducing the amount of feed.

[0054] The objects to be controlled based on the change in the moisture content of the dehydrated cake (predicted value) are not limited to the four items of the mud feed amount, the coagulant dosage amount, the filter cloth belt speed, and the agitation speed of the coagulation tank, but may be one of the four items, or any two or three items. EXAMPLES

[0055] [Example] An embodiment of the moisture content prediction method according to the present invention will be described below.

[0056] The flocculated sludge from the biological treatment process was dewatered using the sludge dewatering apparatus shown in FIG. 1, and the moisture content of the dewatered cake from the belt press dewatering machine 10 was predicted based on the above formula [1].

[0057] The main conditions are as follows:

[0058] Average suspended solids concentration of raw sludge: approx. 2.5% by weight Average amount of raw sludge fed: approx. 11 m 3 / h Mud supply amount measurement sensor 21: Electromagnetic flow meter Suspended solids concentration measurement sensor 22: Sludge concentration meter manufactured by JFE Advantech Co., Ltd. Belt press dehydrator 10 dehydrated cake width: 2.0m Filter belt speed: 72~108m / h Length of gravity filtration section A: approx. 3m Dehydrated cake thickness measurement device: Laser distance meter (Keyence IL-300) Dehydrated cake specific gravity: Set value 1.0

[0059] Sludge was dehydrated under the above conditions, and the results of predicting the moisture content of the dehydrated cake at one-minute intervals (changes in predicted moisture content over time) are shown in Figure 2. Additionally, the results of manually measuring the moisture content of the dehydrated cake approximately once every 30 minutes are also shown in Figure 2.

[0060] FIG. 3 shows the relationship between the predicted moisture content at the time when the moisture content was actually measured and the measured moisture content.

[0061] [Consideration] As shown in Figures 2 and 3, the predicted values ​​and the actual measured values ​​were almost identical, demonstrating the high accuracy of the predicted values.

[0062] In this embodiment, the moisture content of the dehydrated cake can be predicted by collecting the necessary information with a sensor. In contrast, in the method of sampling the dehydrated cake and measuring the moisture content by manual analysis, the moisture content can only be known at the time of sampling by hand, and since it takes at least 30 minutes from sampling the dehydrated cake to obtaining the results, there is a risk of overlooking a deterioration in the moisture content.

[0063] [Reference example] During the operation of the above embodiment, the sludge thickness was measured in the gravity filtration section A. The relationship between the sludge thickness in the gravity filtration section at the time of the above moisture content measurement and the measured moisture content is shown in FIG.

[0064] As shown in Figure 4, no correlation was found between the sludge thickness in the gravity filter section and the moisture content of the dehydrated cake. Therefore, it was found that the moisture content of the dehydrated cake cannot be predicted from the sludge thickness in the gravity filter section. [Explanation of symbols]

[0065] 1 Mud pump 3 Coagulation tank 10 Belt press dehydrator 11 Lower filter cloth belt 12 Upper filter cloth belt 20 Control device 21 Mud supply amount measurement sensor 22 Suspended solids concentration measurement sensor A Gravity filtration section

Claims

1. 1. A method for predicting the moisture content of a dewatered cake from a belt press dewatering machine that dewaters sludge, comprising: Amount of mud fed to the belt press dewatering machine (m ３ The method for predicting the moisture content of a dehydrated cake comprises measuring the mud flow rate (m / h), the mud supply rate (wt %), the filter cloth belt speed (m / h), and the dehydrated cake thickness (m), and using these measured values, the dehydrated cake width (m), and the dehydrated cake specific gravity based on the following formula [1]: Dehydrated cake moisture content (wt%) = [1-{mud supply volume (m ３ / h) × suspended solids concentration (weight % ÷ 100)] / [Filter belt speed (m / h) × dehydrated cake width (m) × dehydrated cake thickness (m) × dehydrated cake specific gravity] × 100 … [1]

2. 2. The method for predicting the moisture content of a dehydrated cake according to claim 1, wherein an actual value measured periodically or a predetermined value set in advance is used as the specific gravity of the dehydrated cake.

3. 2. The method for predicting a moisture content of a dehydrated cake according to claim 1, wherein the sludge is such that the moisture content of a dehydrated cake from a belt press dehydrator is 50 to 95% by weight.

4. A method for dehydrating sludge using a belt press dehydrator, comprising controlling at least one of an amount of sludge fed to the belt press dehydrator, an amount of coagulant fed to the sludge, a filter cloth belt speed, and an agitation speed in a coagulation tank, based on a moisture content value predicted by the method for predicting the moisture content of a dehydrated cake according to any one of claims 1 to 3.

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