JP2013017956A - Method for controlling additive rate of chelating agent to fly ash - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the consumption of a chelating agent and the load to a final disposal site by minimizing the additive rate of the chelating agent in an incinerated fly ash treatment.SOLUTION: The supply amount of slaked lime from a slaked lime supply device 4 is controlled corresponding to an acidic gas concentration in an exhaust gas, and the additive rate of the chelating agent added to a kneader 10 is decided in an arithmetic unit 7 based on the relation between the slaked lime supply amount and a necessary additive rate of the chelating agent.

Description

  The present invention relates to a method for controlling the rate of addition of a chelating agent to fly ash that controls the amount of addition to an appropriate amount when adding a chelating agent to incinerated fly ash collected at a garbage incineration facility or the like.

  Conventionally, in exhaust gas treatment facilities that treat combustion exhaust gas discharged from waste incinerators, industrial waste incinerators, etc., after adding slaked lime into the combustion exhaust gas to capture acidic components such as hydrogen chloride, bag filters, etc. The dust collector is designed to collect fly ash. The collected fly ash is generally composed of dust from incineration of garbage, slaked lime fly ash (unreacted slaked lime and reaction products), chemicals such as auxiliary agents and activated carbon. One of the methods for stabilizing lead contained in the collected fly ash is fly ash treatment with a chelating agent.

FIG. 3 shows a flow chart of this type of conventional exhaust gas treatment system.
In this exhaust gas treatment system 50, exhaust gas generated in a combustion furnace such as a garbage incinerator (not shown) is reduced in temperature to a predetermined temperature by a temperature reducing tower or the like and reaches the bag filter 51. Immediately before entering the bag filter 51, the slaked lime powder stored in the slaked lime storage tank 52 is added to the exhaust gas by the slaked lime supply device 53 and the chemical supply blower 54. The addition rate of slaked lime is determined by the arithmetic unit 56 based on the HCl concentration and SOx concentration of the treated exhaust gas detected by the HCl and SOx analyzer 55 disposed on the bag filter 51 outlet side.

  In the bag filter 51, dust, heavy metal compounds and the like in the exhaust gas are filtered and removed. Further, the hydrogen chloride gas in the exhaust gas is absorbed by the added slaked lime powder, turns into calcium chloride, and is similarly removed by the bag filter 51. The exhaust gas from which harmful substances have been removed in this way is discharged into the atmosphere by the induction fan 57 through the chimney.

  On the other hand, fly ash composed of dust, slaked lime fly ash and the like containing heavy metal compounds collected by the bag filter 51 cannot be discarded as it is. For this reason, after being stored in the fly ash storage tank 58, a fixed amount of fly ash is supplied to the kneading machine 59 as much as possible, and an amount of chelating agent and water set according to the supply amount of the fly ash is mixed with the kneading machine 59. By adding to the fly ash and kneading and curing and solidifying the fly ash after kneading, elution of heavy metals from the fly ash is prevented. Here, the chelating agent (liquid) is supplied from the chelating tank 60 by the chelating pump 61, and the water is supplied from the adding water tank 62 by the adding water pump 63.

  In this conventional system, the addition rate control of the chelating agent added to the fly ash from the chelate tank 60 sets a chelate addition rate of, for example, 3 to 4% during the trial operation, and the amount of fly ash cut out and the output of the chelate pump 61 are controlled. Driving is carried out while keeping constant.

  By the way, as prior arts related to the present invention, there are those disclosed in Patent Documents 1 and 2. Among them, the technique disclosed in Patent Document 1 analyzes the concentration of Pb and Cu in fly ash by atomic absorption analysis, inductively coupled plasma emission analysis, fluorescent X-ray analysis, etc. The amount of liquid chelating agent added for immobilization is determined. The technique disclosed in Patent Document 2 mixes incinerated fly ash from a combustion furnace with an alkaline aqueous solution, heats it to elute lead in the incinerated fly ash, and measures the lead concentration in the obtained aqueous solution. The amount of the chelating agent added is determined by the lead concentration in the incinerated fly ash determined by the above.

Japanese Patent No. 3843551 Japanese Patent No. 3907949

  However, since the conventional exhaust gas treatment system shown in FIG. 3 does not correct the lead concentration in the dust by slaked lime spray, for example, the concentration of acidic gases such as HCl and SOx from the furnace outlet temporarily increases. When a large amount of slaked lime is blown, the chelating agent addition rate is constant with respect to the amount of generated fly ash even though the lead concentration in the generated fly ash is low, so the amount of chelating agent exceeds the required amount. Therefore, there is a problem in that running costs such as drug costs are increased.

  In addition, the methods proposed in Patent Documents 1 and 2 require a large and expensive device as a device for measuring the concentration of heavy metals, and control the amount of chelating agent added in real time during system operation. There is a problem that cannot be performed.

  The present invention has been made in view of the problems as described above, and in the incineration fly ash treatment by controlling the addition rate of the chelating agent to the generated fly ash in accordance with the change in the amount of slaked lime blown into the exhaust gas. It is an object of the present invention to provide a method for controlling the rate of addition of a chelating agent to fly ash that minimizes the rate of addition of the chelating agent and enables reduction of the amount of chelating agent used and the load on the final disposal site.

In order to achieve the above object, the method for controlling the rate of addition of a chelating agent to fly ash according to the present invention comprises:
A slaked lime supply device that blows slaked lime into a flue that guides exhaust gas from the combustion furnace, a dust collector that is provided downstream of the slaked lime supply point of the flue and collects fly ash in the exhaust gas, and the dust collector In an exhaust gas treatment system equipped with a kneader that adds water and a chelating agent to the fly ash collected and kneaded,
While controlling the amount of slaked lime supplied from the slaked lime supply device according to the acid gas concentration in the exhaust gas, the addition rate of the chelating agent added to the kneader based on the relationship between the amount of slaked lime supply and the required rate of addition of the chelating agent It is characterized by determining.

  In the present invention, it is preferable to perform a dissolution test by sampling the generated fly ash during the trial operation of the exhaust gas treatment system, and obtain the relationship with the required chelating agent addition rate with respect to the ratio of slaked lime fly ash.

  According to the present invention, based on the relationship between the amount of slaked lime supplied to the exhaust gas and the required rate of addition of the chelating agent to the generated fly ash, the rate of addition of the chelating agent to the fly ash is determined. An appropriate chelating agent addition rate can be obtained with respect to the amount of fly ash in consideration of fluctuations. Therefore, it is possible to minimize the addition rate of the chelating agent in the incineration fly ash treatment, and to reduce the amount of the chelating agent used and the final disposal site load.

1 is a flowchart of an exhaust gas treatment system according to an embodiment of the present invention. Graph showing the relationship of the required chelating agent addition rate to the mixing ratio of slaked lime fly ash Flow chart of conventional exhaust gas treatment system

  Next, specific embodiments of the method for controlling the rate of addition of a chelating agent to fly ash according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a flow chart of an exhaust gas treatment system according to an embodiment of the present invention.

  In this exhaust gas treatment system 1, the exhaust gas generated in a combustion furnace such as a waste incinerator (not shown) is cooled to a predetermined temperature by a temperature reducing tower or the like, and then a bag filter (dust collecting) that collects fly ash in the exhaust gas. Apparatus) 2. The slaked lime powder stored in the slaked lime storage tank 3 is added to the exhaust gas from the inlet flue of the bag filter 2 by the slaked lime supply device 4 and the chemical supply blower 5, whereby harmful HCl gas in the exhaust gas is solid and It is changed to harmless calcium chloride. At this time, the addition rate of slaked lime is determined by the arithmetic unit 7 based on the HCl concentration and the SOx concentration of the treated exhaust gas detected by the HCl and SOx analyzer 6 disposed in the exit flue of the bag filter 2.

  In the bag filter 2, chlorides such as dust and dioxins, heavy metal compounds, calcium chloride chemically changed from HCl gas, unreacted slaked lime with calcium chloride attached to the surface, and the like are collected. The exhaust gas from which harmful substances have been removed in this way is discharged into the atmosphere by the induction fan 8 through the chimney.

  On the other hand, fly ash including dust, slaked lime fly ash and the like containing heavy metal compounds collected by the bag filter 2 is introduced into the fly ash storage tank 9 and then supplied to the kneader 10. In order to prevent elution of heavy metals from the fly ash, the kneading machine 10 is added with an amount of chelating agent and water set according to the amount of fly ash supplied and kneaded. Cured and solidified. Here, the chelating agent (liquid) is supplied from the chelating tank 11 by the chelating pump 12, and the water is supplied from the adding water tank 13 by the adding water pump 14.

  Regarding the addition rate of the chelating agent to the fly ash, if this is constant with respect to the generated fly ash, the chelating agent is excessively used when the amount of slaked lime supplied from the slaked lime supply device 4 is large. If the amount is too small, the amount of chelating agent added is insufficient and the risk of lead elution occurs. Therefore, in the present embodiment, calculation is performed by the calculation device 7 using the slaked lime supply amount by the slaked lime supply device 4 as an input condition, and the supply amount of the chelating agent and the added water is controlled based on the calculation result. .

  This means that the inventors mixed pure dust and slaked lime fly ash (unreacted slaked lime and reaction products) at an arbitrary ratio, and what is the chelate addition rate that is less than the lead elution standard value for each sample? This is based on the results of testing what happens. That is, according to this test result, as shown in FIG. 2, it is clear that the required chelating agent addition rate decreases as the mixing ratio of slaked lime fly ash increases.

  For this reason, as shown in FIG. 2, the arithmetic unit 7 inputs and stores the relational expression of the ratio of the slaked lime fly ash to the soot and the necessary chelate addition rate, and the addition rate of the chelating agent is calculated based on this relational expression. By determining and controlling the supply amount of the chelating agent and the added water, it becomes possible to add an appropriate amount of the chelating agent and water to the fly ash amount in consideration of the slaked lime supply amount.

  At the on-site plant, sampled fly ash under multiple slaked lime blowing rate conditions during trial operation, etc., and conducted an elution test on each fly ash, and the amount of slaked lime blown into the exhaust gas and chelating agent to the generated fly ash By determining the relationship with the addition rate, inputting and storing this relationship in the calculation device 7, and adding this relationship to the calculation, an appropriate chelating agent addition rate for the amount of fly ash that takes into account fluctuations in the amount of slaked lime is determined. be able to.

  In the exhaust gas treatment system 1 shown in FIG. 1, the fly ash discharged from the bag filter 2 is temporarily stored in the fly ash storage tank 9 and then supplied to the kneader 10. When the fly ash storage tank 9 is interposed, a time delay occurs until the fluctuation of the amount of slaked lime blown into the exhaust gas affects the properties of the fly ash supplied to the kneader 10. When this time delay becomes large, it becomes difficult to determine an appropriate chelating agent addition rate. Therefore, it is important to perform an operation so that fly ash is not stored in the fly ash storage tank 9 as much as possible before the chelating agent is processed.

  In contrast, an embodiment in which the fly ash storage tank 9 is eliminated and the system is configured to directly supply the fly ash discharged from the bag filter 2 to the kneader 10 is also possible. In such a case, it is possible to determine an appropriate chelating agent addition rate in accordance with the temporal fluctuation of the slaked lime blowing amount.

  The method for controlling the rate of addition of a chelating agent to fly ash according to the present invention is to treat the incineration fly ash collected at a garbage incineration facility, etc., taking into account the fluctuation of the slaked lime supply amount contained in the fly ash, Since the addition rate of the chelating agent can be determined simply and inexpensively in real time, it can be widely used for the treatment of various solid wastes, and the industrial utilization effect is great.

1 Exhaust gas treatment system 2 Bag filter (dust collector)
DESCRIPTION OF SYMBOLS 3 Slaked lime storage tank 4 Slaked lime supply apparatus 5 Chemical supply blower 6 HCl, SOx analyzer 7 Arithmetic apparatus 8 Induction fan 9 Fly ash storage tank 10 Kneading machine 11 Chelate tank 12 Chelate pump 13 Addition water tank 14 Addition water pump

Claims (2)

A slaked lime supply device that blows slaked lime into a flue that guides exhaust gas from the combustion furnace, a dust collector that is provided downstream of the slaked lime supply point of the flue and collects fly ash in the exhaust gas, and the dust collector In an exhaust gas treatment system equipped with a kneader that adds water and a chelating agent to the fly ash collected and kneaded,
While controlling the amount of slaked lime supplied from the slaked lime supply device according to the acid gas concentration in the exhaust gas, the addition rate of the chelating agent added to the kneader based on the relationship between the amount of slaked lime supply and the required rate of addition of the chelating agent A method for controlling the rate of addition of a chelating agent to fly ash, characterized in that   2. The chelating agent addition rate according to claim 1, wherein an elution test is performed by sampling generated fly ash during a trial operation of the exhaust gas treatment system, and a relationship with a necessary chelating agent addition rate with respect to a ratio of slaked lime fly ash is obtained. Control method.

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