JP3678596B2 - Sludge treatment method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sludge treatment method and apparatus for dewatering and incinerating sludge, for example, a sludge treatment method and apparatus for treating sludge discharged from a sewage treatment plant.
[0002]
[Prior art]
As a method for treating sludge discharged from a sewage treatment plant, conventionally, a method in which sludge is dehydrated with a dehydrator and then incinerated with an incinerator has been used. In order to make the incinerator and subsequent treatment equipment such as exhaust gas compact, it is preferable to reduce the moisture content of the dehydrated dehydrated cake as much as possible.
[0003]
[Problems to be solved by the invention]
If the content of combustible materials such as organic matter in the sludge increases, the amount of heat generated by the sludge increases, the in-furnace temperature during incineration increases, the thermal load on the incinerator increases, and a portion of the sludge increases. The problem of melting and sticking to the wall of the furnace occurs. Conventionally, the temperature rise in the furnace was suppressed by injecting water or air directly into the furnace. However, when water or air is injected into the furnace in this way, the amount of exhaust gas increases, which causes a problem that the exhaust gas treatment facility is increased in size.
[0004]
In view of this problem, the present invention is a sludge treatment method and apparatus capable of suppressing the temperature rise in an incinerator without increasing the amount of exhaust gas and making the incinerator and subsequent exhaust gas treatment equipment compact. It is an issue to provide.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, a sludge treatment method of the present invention is a sludge treatment method comprising a dehydration step of dewatering sludge to form a dehydrated cake, and an incineration step of incinerating the dehydrated cake in an incinerator. By adjusting the mixing ratio of sludge or dehydrated cake and incinerated ash after incineration based on the furnace temperature and the moisture content of the dehydrated cake, the calorific value of the dehydrated cake put into the incinerator is adjusted to the temperature of the incinerator. Is further provided with an adjustment step of adjusting the temperature to a target temperature .
[0006]
On the other hand, the sludge treatment apparatus of the present invention is a sludge treatment apparatus comprising a dehydrator for dewatering sludge to form a dehydrated cake, and an incinerator for incinerating the dehydrated cake. Of the incinerator ash and control to adjust the input amount by the input device so that the incinerator temperature becomes the target temperature based on the incinerator temperature and the moisture content of the dehydrated cake And a device.
[0007]
By introducing and mixing incinerated ash after incineration to sludge or dehydrated cake, the ash content of the sludge or dehydrated cake after addition increases, while the combustible content and water content both decrease. As a result, the calorific value per unit weight and unit volume also decreases. That is, it is possible to adjust the calorific value of the incinerated ash mixed dehydrated cake finally obtained by controlling the input amount of the incinerated ash. It can control so that the temperature of an incinerator may not rise by adjusting the calorific value of the incinerated ash mixing dehydrated cake to incinerate in this way. Since ash does not contribute to the combustion reaction during incineration, the exhaust gas does not increase regardless of whether or not the incineration ash is mixed, and it is not necessary to increase the size of the exhaust gas treatment facility. Moreover, since the influence of the volume increase by ash mixing is small, an incinerator can also be made compact.
[0008]
This adjustment process may be performed prior to the dehydration process or between the dehydration process and the incineration process. That is, the charging machine may be arranged before the dehydrator or may be arranged between the dehydrator and the incinerator. It is more preferable to incinerate the incinerated ash into the sludge before dehydration because the sludge and the incinerated ash can be easily mixed and the dewatering efficiency can be increased.
[0009]
Note that the temperature of the incinerator can be measured at any time with an in-furnace thermometer, and the moisture content of the dehydrated cake can be measured by sampling. It is possible to estimate the composition of the dehydrated cake from the temperature of the furnace and the moisture content of the dehydrated cake, and to adjust the composition so that the in-furnace temperature of the incinerator becomes a calorific value that becomes the target temperature.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. FIG. 1 is an overall flow diagram of a sludge treatment apparatus according to the present invention.
[0011]
This apparatus includes a dehydrator 1 for dewatering sludge, an incinerator 2 for incinerating and reducing the amount of combustible material in the sludge, an exhaust gas treatment facility 3 for treating incinerator exhaust gas, and treated exhaust gas into the atmosphere. A chimney 4 to be discharged and an ash collection facility 5 for collecting incinerated ash from the exhaust gas are provided. The dehydrator 1 and the incinerator 2, the incinerator 2 and the exhaust gas treatment facility 3, the exhaust gas treatment facility 3 and the chimney 4, the exhaust gas treatment facility 3 and the ash recovery facility 5 are connected by lines L2, L3, L4, and L5, respectively. The line L1 for introducing sludge into the dehydrator 1 is connected to a line L6 for mixing a part of the incinerated ash recovered by the ash recovery facility 5 with the sludge.
[0012]
Here, a filter press dewatering device, a belt press dewatering device, a centrifugal dewatering device or the like can be suitably used as the dehydrator 1. Moreover, although various incinerators can be used for the incinerator 2, a fluidized bed type or a circulating fluidized bed type incinerator is suitable. The exhaust gas treatment facility 3 is configured by combining a heat recovery facility such as an exhaust heat boiler and an air preheater, a quenching tower, a denitration / desulfurization facility, and a dust collector.
[0013]
Next, the operation of the apparatus, that is, the sludge treatment method according to the present invention will be described with reference to FIGS. FIG. 2 shows the material balance in this apparatus.
[0014]
Sludge Ms (kg) containing a large amount of water generated at a sewage treatment plant or the like is supplied to the dehydrator 1 via the line L1. As shown in FIG. 2 (a), the composition of this sludge has a moisture content of γs, a combustible fraction of Vs, and an ash fraction of As. Therefore, if the calorific value per unit weight of combustible is Qv (kcal / kg), the calorific value per unit weight of the sludge is QvVs (kcal / kg). Ma (kg) is mixed into the sewage sludge by the subsequent incineration process and the incinerated ash recovered by the ash recovery facility 5 through the line L6. That is, the line L6 functions as an input device to the line L1. The setting of the mixing ratio will be described later. As shown in FIG. 2B, the composition of the input incineration ash is entirely composed of nonflammable ash. Therefore, the calorific value is 0 (kcal / kg). The composition of the sludge before dehydration in which the sewage sludge and the incinerated ash are mixed in this way decreases as shown in FIG. On the other hand, the ash content increases as (AsMs + Ma) / (Ms + Ma). As a result, the calorific value per unit weight also decreases to {QvVsMs / (Ms + Ma)} (kcal / kg).
[0015]
This pre-dewatered sludge is guided to the dehydrator 1, and W (kg) of water is dehydrated. In addition, when using a centrifugal dewatering machine such as a decanter type, the sludge is stirred in the dewatering machine 1, so both sludge and incinerated ash are dehydrated even if they are put into the dewatering machine 1 on separate lines. It can be mixed in the machine 1. That is, the dehydrator 1 also serves as a charging machine. By mixing incinerated ash with sludge before or during dehydration, the dewatering efficiency can be increased.
[0016]
FIG. 2 (d) shows the composition of the sludge after the dehydration treatment, that is, the dehydrated cake. When the weight of the dehydrated cake obtained is Mc (kg), Mc = Ms + Ma-W is established, and the moisture ratio (moisture content) is reduced to (γsMs-W) / Mc compared to before dehydration, while combustible component The ash content increases to VsMs / Mc and (AsMs + Ma) / Mc, respectively, compared to before dehydration. As a result, the calorific value per unit weight also increases (QvVsMs / Mc) (kcal / kg) before dehydration, but as the amount of incinerated ash increases, the calorific value per unit weight of the dehydrated cake becomes the original sewage. Lower than sludge. Therefore, the calorific value can be adjusted by adjusting the addition amount Ma of the incinerated ash described above.
[0017]
The dehydrated cake is put into the incinerator 2 and burned at about 800 to 900 ° C. for incineration. It is possible to adjust the furnace temperature by adjusting the heat generation amount of the dehydrated cake. Further, the incineration ash addition amount Ma may be adjusted by feedback control so that the furnace temperature becomes the target temperature.
[0018]
In the incinerator 2, the dehydrated cake is burned by adding air of A (kg) as shown in FIG. 2 (e), and as shown in FIGS. {(1-As) Ms + A−W} (kg) exhaust gas and (AsMs + Ma) (kg) dust (incineration ash) are generated. The exhaust gas and dust are sent to the exhaust gas treatment facility 3 via the line L3, and the exhaust gas is processed by the facility and then discharged from the chimney 4 to the atmosphere via the line L4. On the other hand, the incineration ash is separated by the exhaust gas treatment facility 3 and sent to the ash recovery facility 5 through the line L5, and Ma (kg) is returned through the line L6 as described above.
[0019]
The amount of exhaust gas sent to the exhaust gas treatment facility 3 is irrelevant to the amount of incinerated ash that is input, and does not increase by injecting incinerated ash. Since the amount of dehydrated water is reduced, the exhaust gas volume is reduced, and the processing equipment can be made compact. On the other hand, dust increases with the addition of incineration ash, but the volume of dust is extremely small compared to the volume of exhaust gas, so the increase in load on the processing equipment due to the increased amount is not large. In this device, only a part of the incineration ash circulates, so unlike the case where the additive is added from the outside, the storage facility for the additive is not required and the cost of the additive is not required. Can be realized.
[0020]
Here, the amount control of the incineration ash for adjusting the temperature of the incinerator 2 will be described in detail with reference to FIG. FIG. 3 is a diagram showing a self-combustion limit line indicating the furnace top temperature (temperature of the top portion in the circulating fluidized bed incinerator) with respect to the ash content and water content of the sludge charged into the incinerator.
[0021]
Since the calorific value per unit weight of the dehydrated cake is almost constant and the heat capacity of the incinerator 2 is known, in a given incinerator 2, if the composition of the dehydrated cake to be burned is known, auxiliary fuel is used. The temperature inside the furnace when the combustible component is completely burned without being used can be calculated. Further, if the moisture content, combustible fraction, and ash fraction of the dehydrated cake are γc, Vc, and Ac, respectively, γc + Vc + Ac = 1 holds, so if any two are known, the other one can be calculated. FIG. 3 shows the moisture content at which the temperature at the top of the incinerator becomes constant when a predetermined amount of sludge is charged and completely burned without supplying auxiliary fuel in a circulating fluidized bed incinerator. The relationship between the ash content and the ash content is obtained as a diagram. Calculation was made assuming that the incinerator had an inner volume of 97 m ³ , the amount of dehydrated cake charged was 100 t / day, and the higher calorific value of the combustible component was about 5600 kcal / kg.
[0022]
In the figure, the lines indicated by (1), (2), and (3) indicate lines at which the furnace top temperatures are 800 ° C., 850 ° C., and 900 ° C., respectively, and the higher the ash content or moisture content, that is, the combustible content. It can be seen that the furnace top temperature decreases as the rate decreases. And in each curve of (1) (2) (3), the ash content and water content are
γc = aAc ² + bAc + c
It was found to satisfy the relationship. This formula calculates several points of sludge components that become the self-combustion limit based on the furnace shape, operating conditions, furnace top temperature, etc. of the incinerator, and obtains an approximate curve of these points by the least square method. That is, a, b, and c are constants.
[0023]
Next, when the furnace top temperature when a certain dehydrated cake is burned is higher than the target, the amount of incinerated ash Ma1 to be added to 1 kg of dehydrated cake required to adjust the furnace top temperature to the target temperature ( kg) will be described. The moisture content, flammable fraction, and ash content of the dehydrated cake before adjustment are γc1, Vc1, Ac1, respectively, and the moisture content, flammable fraction, and ash content of the dehydrated cake after adjustment are γct, Vct, and Act, respectively.
γct = aAct ² + bAct + c (1)
A, b, and c satisfying the condition are known. Because incinerated ash Ma1 (kg) with 100% ash is added to 1 kg of dehydrated cake before adjustment.
γct = γc1 / (1 + Ma1) (2a)
Vct = Vc1 / (1 + Ma1) (2b)
Act = (Ac1 + Ma1) / (1 + Ma1) (2c)
Each holds. Substituting (2a) and (2c) into (1) and rearranging,
AMa1 ² + BMa1 + C = 0 (3)
However, A = a + b + c
B = 2aAc1 + b (1 + Ac1) + 2c-γc1
C = aAc1 ² + bAc1 + c-γc1
Is established, and Ma1 can be obtained from equation (3).
[0024]
Specifically, in the diagram of FIG. 3, in the curve (2), a = 0.015, b = −0.81, and c = 0.77. Here, assuming that the ash content and moisture content of the dehydrated cake before adjustment are 5% and 70% (P point), respectively, A, B and C in the formula (3) are -0.034 and -0.0013, respectively. 0.034, and Ma1 = 0.98. As a result, the ash content and water content of the dehydrated cake after adjustment are 52.1% and 35.3% (Q point), respectively, as shown in the figure.
[0025]
In actual control, for example, the furnace top temperature of the incinerator 2 that can be easily measured online with an in-furnace thermometer and the moisture content of the dehydrated cake that can be measured by sampling at the outlet of the dehydrator 1 are measured. 3 is used to estimate the ash content of the cake from the curve in FIG. 3, find the optimum amount of incineration ash input using equation (3), and supply the amount from the ash recovery facility 5 to the line L 6 so as to obtain this input amount Can be controlled. Furthermore, when adjusting precisely, there will be a slight time delay, but the dehydrated cake or sludge is sampled to measure the ash content, combustible content, and calorific value. You may adjust.
[0026]
In the above description, the apparatus and method for injecting the incineration ash into the sludge before the dehydrator 1 have been described. However, the incineration ash is added to the dehydrated cake after the dehydrator 1 via the line L6 ′ shown by the dotted line in FIG. May be input. In this case, it is preferable to provide a device for mixing and stirring the dewatered cake and the incineration ash. Alternatively, a necessary amount of incineration ash may be charged directly into the incinerator.
[0027]
【The invention's effect】
As described above, according to the sludge treatment method and apparatus according to the present invention, incineration ash is mixed with sludge or dewatered cake to adjust the heat generation amount. However, the furnace temperature can be kept low. Further, since the amount of exhaust gas does not increase, the subsequent exhaust gas treatment facility does not increase in size and can be made compact.
[0028]
Furthermore, it is preferable to add incineration ash to the sludge before dehydration because dehydration efficiency is improved.
[Brief description of the drawings]
FIG. 1 is an overall flow diagram of a sludge treatment apparatus according to the present invention.
FIG. 2 shows a material balance in the apparatus of FIG.
FIG. 3 is a diagram showing the furnace top temperature with respect to the ash content and water content of sludge charged in the circulating fluidized bed incinerator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Dehydrator, 2 ... Incinerator, 3 ... Exhaust gas treatment equipment, 4 ... Chimney, 5 ... Ash recovery equipment, L1-L6 ... line.

Claims (6)

In a sludge treatment method comprising a dehydration step of dewatering sludge into a dehydrated cake, and an incineration step of incinerating the dehydrated cake in an incinerator,
Based on the temperature of the incinerator and the moisture content of the dehydrated cake, the heat generation of the dehydrated cake put into the incinerator by adjusting the mixing ratio of the sludge or the dehydrated cake and the incinerated ash after the incineration treatment A sludge treatment method further comprising an adjustment step of adjusting the amount so that the temperature of the incinerator becomes a target temperature .   The sludge treatment method according to claim 1, wherein the adjustment step is performed prior to the dehydration step.   The sludge treatment method according to claim 1, wherein the adjustment step is performed between a dehydration step and an incineration step. In a sludge treatment apparatus comprising a dehydrator for dewatering sludge into a dehydrated cake, and an incinerator for incinerating the dehydrated cake,
A charging machine for charging and mixing incinerated ash after incineration to the sludge or the dewatered cake;
A control device that adjusts the input amount by the input device so that the in-furnace temperature of the incinerator becomes a target temperature based on the in-furnace temperature of the incinerator and the moisture content of the dehydrated cake ;
A sludge treatment apparatus characterized by further comprising: The sludge treatment apparatus according to claim 4 , wherein the charging machine is disposed in front of the dehydrator. The sludge treatment apparatus according to claim 4 , wherein the charging device is disposed between the dehydrator and the incinerator.

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