JP2010078242A - Method of melting incineration residue of waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce Pb content in generated molten slug and NOx generation amount while suppressing generation of CO when incineration residue etc. of waste is molten by using plasma. <P>SOLUTION: This method for melting incineration residue of waste by using plasma includes: a process of melting incineration residue supplied to inside of a melting furnace 10 by plasma generated by a plasma generating device 30 using gas including oxygen as operation gas; a process of discharging the molten slug 12 generated by the melting treatment to outside of the melting furnace 10 and collecting the slug 12; and a process of adding a carbon source to the molten residue supplied to inside of the melting furnace 10. The addition amount is determined so that oxygen concentration within the melting furnace 10 is 4-10% due to absorption of oxygen within the melting furnace 10 by the carbon source. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for melting municipal waste, industrial waste incineration residue, and the like using a plasma generator such as a plasma torch.

2. Description of the Related Art Conventionally, as a method for melting municipal waste, industrial waste incineration residue, or the like, a method using plasma as described in Patent Document 1, for example, is known. In this method, the incineration residue or the like is put into a melting furnace equipped with a plasma torch, and the incineration residue or the like is melted in the melting furnace. The exhaust gas generated by this melting is sent to an exhaust gas treatment device outside the melting furnace, and the molten slag is carried out of the melting furnace separately from the exhaust gas.
Japanese Patent Publication No. 7-52006

  The molten slag discharged from the melting furnace is preferably used for reuse, but if the content of Pb (lead) in the molten slag is large, the reuse is significantly limited. Therefore, reduction of the lead content in the molten slag becomes an important issue.

  Further, in a melting furnace using plasma as described above, heating at an extremely high temperature (for example, 1300 ° C.) is performed. Therefore, generation of NOx due to a chemical reaction of oxygen contained in a working gas for generating the plasma is not generated. Inevitably, its suppression is an important issue.

  As a means for reducing the Pb content and the NOx generation amount in the molten slag, it is considered that a carbon source is separately added to the melting furnace to reduce the furnace atmosphere as described in Patent Document 1. It is done. This reduction promotes volatilization by reduction of lead in the slag and leads to suppression of NOx generation.

  However, the decrease in the oxygen concentration in the furnace due to the reduction promotes the generation of CO (carbon monoxide). When the amount of CO generated is large, it is necessary to provide a secondary combustion chamber in the melting furnace, and this causes a new problem that the secondary combustion chamber is easily clogged with dust.

  In view of such circumstances, the present invention reduces the Pb content and NOx generation amount in the generated molten slag while suppressing the generation of CO when melting incineration residues of waste with plasma. The object is to provide a melt processing method which makes it possible to achieve.

  The present inventor paid attention to the relationship between the oxygen concentration in the melting furnace and the amount of CO generated in order to solve the above problems. As a result, by setting the oxygen concentration to 4% or more, the CO generation amount can be significantly reduced as compared with the case where the oxygen concentration is less than 4%, while the region where the oxygen concentration exceeds 10%. Then, the knowledge that the reduction of the amount of CO generation accompanying the increase in the oxygen concentration was hardly observed was obtained. On the other hand, regarding the relationship between the oxygen concentration, the Pb content in the molten slag, and the NOx generation amount, it was confirmed that the Pb content and the NOx generation amount increase as the oxygen concentration increases.

  The present invention has been made from such a point of view, and is a method for melting incineration residue of waste using plasma, in a melting furnace equipped with a plasma generator using an oxygen-containing gas as a working gas. Supplying the incineration residue to, melting the incineration residue with the plasma generated by the plasma generator in the melting furnace, and discharging and recovering the molten slag generated thereby, While adding a carbon source to the incineration residue supplied into the melting furnace, the amount of addition is such that oxygen concentration in the melting furnace is 4% or more and 10% or less due to absorption of oxygen in the melting furnace by the carbon source. And so on.

  According to this method, when the oxygen concentration in the melting furnace is set to 4% or more by adding a carbon source to the incineration residue, the oxygen concentration is set to less than 4% (that is, the atmosphere in the furnace is almost completely set). The amount of CO generated in the furnace is significantly reduced as compared with the case of reducing the oxygen concentration in the furnace, while reducing the atmosphere in the furnace until the oxygen concentration is reduced to 10% or less. The Pb content in the molten slag can be reduced by the promotion, and the NOx generation amount can also be reduced.

  In this invention, the carbon source may be added to the incineration residue in the melting furnace, but is added to the incineration residue outside the melting furnace and mixed with the incineration residue in the melting furnace. More preferably, it is supplied. In this way, the carbon source supplied into the melting furnace in a state of being mixed with the incineration residue in advance can intensively reduce the atmosphere around the incineration residue, so the amount of carbon source is suppressed while suppressing It is possible to effectively promote volatilization of Pb in the incineration residue. That is, while reducing the Pb content in the molten slag by adding a carbon source, it is possible to further reduce the amount of CO generated by suppressing the added amount of the carbon source.

  In particular, if the mixture of the incineration residue and the carbon source is supplied into the melting furnace by a screw feeder, the mixing of the incineration residue and the carbon source is promoted by the stirring function of the screw feeder, and the carbon source This further enhances the Pb volatilization promoting effect.

As the carbon source added to the incineration residue, coke having a particle size of 0.5 mm or more and less than 4 mm is suitable. Thus, coke having a particle size of less than 4 mm has a larger contact area with the incineration residue to be melted than that of a large particle size, and thus more effectively promotes volatilization of Pb in the incineration residue. be able to. In addition, unlike dusty particles having a particle size of less than 0.5 mm, it hardly reacts with O ₂ in the furnace before promoting the volatilization of Pb, and the majority contributes to the volatilization of Pb. it can.

  As described above, according to the present invention, by optimizing the amount of carbon source added to the incineration residue of the waste supplied to the plasma melting furnace, the generation of CO is suppressed while suppressing the generation of CO. There is an effect that the lead content and the NOx generation amount can be effectively reduced.

  FIG. 1 shows a plasma melting apparatus for carrying out the method for melting a waste incineration residue according to the present invention. This apparatus includes a melting furnace 10, a supply device 20 for supplying waste incineration residue (for example, main ash, fly ash, or a mixture thereof) to the melting furnace 10, and the incineration residue in the melting furnace 10. And a plasma torch 30 that generates plasma for melting.

  The supply device 20 supplies the incineration residue from the side wall of the melting furnace 10 into the melting furnace 10. The hopper 22 accommodates the incineration residue and lowers it by an appropriate amount. And a screw feeder 24 that carries the incineration residue descending horizontally into the melting furnace 10. The screw feeder 24 includes a main body screw 26 having spiral blades and a supply pipe 28 for accommodating the main screw 26, and the main body screw 26 rotates the incineration residue through the supply pipe 28 through the supply pipe 28. 10 into.

  The plasma torch 30 is assembled to the top wall of the melting furnace 10 and generates plasma in the melting furnace 10 using an oxygen-containing gas (for example, air) as a working gas. The plasma heats and melts the incineration residue supplied from the supply device 20 at a high temperature (for example, 1300 ° C.) to generate a molten slag 12.

  The melting furnace 10 has a slag outlet 14 for discharging the molten slag 12. The slag outlet 14 is formed at a height position substantially equal to the supply device 20 on the side wall opposite to the side wall to which the supply device 20 is connected. Therefore, the molten slag 12 generated in the melting furnace 10 is accumulated in the bottom of the furnace below the slag outlet 14 and the excess is continuously discharged from the slag outlet 14 to the outside of the furnace. The The overflowing molten slag 12 is carried into a slag processing apparatus (not shown), and cooled and solidified. The solidified product is appropriately carried out and reused.

  The melting furnace 10 is provided with a gas discharge port (not shown), and this gas discharge port is connected to the exhaust gas treatment facility 32 through an appropriate pipe. The gas generated by melting the incineration residue in the melting furnace 10 is sent to the exhaust gas treatment facility 32 as exhaust gas, where it is subjected to appropriate treatment and then discharged out of the system.

  Next, an incineration residue melting method performed in this melting processing apparatus will be described.

  The incineration residue to be melted is put into the hopper 22 of the supply device 20 and supplied into the melting furnace 10 by the screw feeder 24. As a feature of this method, an appropriate amount of incineration residue in the hopper 22 is previously stored. Of carbon source is added.

  Any carbon source may be used as long as it contributes to the reduction of the atmosphere in the melting furnace 10 (that is, the oxygen concentration is reduced). For example, coke, wood residue, charcoal, and waste plastic are preferably used. In particular, coke having a particle size of 0.5 mm or more and less than 4 mm is added to the incineration residue in advance to effectively promote volatilization of Pb contained in the incineration residue in the furnace as described later. be able to.

The amount of carbon source added is set so that the O ₂ concentration in the melting furnace 10 is 4% or more and 10% or less. Specifically, the addition amount Ca [kg / h] per unit time of the carbon source can be calculated as follows.

Now, the amount of O ₂ substantially entering the melting furnace 10 per unit time (substantial O ₂ introduction amount) is Qo [m ³ N / h], and the total amount of gas entering the furnace per unit time (air inflow amount) ) Is Qt [m ³ N / h], the furnace O ₂ concentration Do is expressed by the following equation.

Do = 100 × Qo / Qt [%] (1)
Among them, the total gas inflow amount Qt includes the amount Qp of plasma gas (air) supplied into the melting furnace 10 per unit time and the flow rate (leakage amount) Q _{L of} air leaking from the outside of the melting furnace into the furnace. equal to the sum (= Qp + Q _L) of the plasma gas supply amount Qp is detected by the flow meter, the latter is determined from the calculation results of the account balance of the amount of air around the melting furnace 10.

Meanwhile, the substantially _{O 2} introduction amount Qo is actually from the flow rate of _{O 2} entering per unit time in the melting furnace 10 (actual _{O 2} flow ^{rate) Qi [m 3 N / h} ], melt per unit time the amount of _{O 2} absorbed by the carbon source the furnace 10 (i.e., reducing the ^{amount) Qr [m 3 N / h} ] minus the (= Qi-Qr) equally, the actual _{O 2} inflow Qi, the This is equal to the air inflow amount Qt (= Qp + Q _L ) multiplied by the O ₂ concentration in air (21%). Therefore, the equation (1) is as follows.

Do = 100 × [0.21 (Qp + Q _L ) −Qr] / (Qp + Q _L ) (2)
Here, the absorption of O ₂ by the carbon source means combustion of C + O ₂ = CO ₂ . Since the molar ratio of C and O _{2 that} react with each other is 1: 1, the reduction amount Qr is equal to the amount of free carbon supplied into the furnace per unit time. This free carbon refers to carbon in a form capable of consuming oxygen, and means carbon excluding carbon fixed as an inorganic substance such as CO ₂ . Therefore, when the amount of free carbon introduced into the furnace per unit time (hereinafter referred to as “the amount of free carbon introduced”) is Ci [kg / h], the following relationship is established.

Qr = Ci × 22.4 / 12 (carbon element amount) (3)
The introduced free carbon amount Ci includes the unburned carbon amount Co [kg / h] contained in the incineration residue supplied into the furnace per unit time and the free carbon amount Ca [ kg / h], which is equal to the sum (= Co + Ca), the treatment amount of the incineration residue supplied into the furnace per unit time is As [kg / h], and the ratio of unburned carbon contained in this (this ratio) Can be determined by chemical analysis) Rc (%), the amount of carbon source added to the furnace per unit time is At [kg / h], and the ratio of free carbon contained in each carbon (each carbon Depending on the source, for example, 80% for coke) and Rd (%), the above equation (3) becomes as follows.

Qr = (As × Rc + At × Rd) × 22.4 / 12 (4)
By substituting the equation (4) into the equation (2), the addition amount At [kg / h] of the carbon source for obtaining the target furnace O ₂ concentration Do (for example, 7%) can be calculated backward. it can.

  By heating and melting the incineration residue by plasma in the melting furnace 10 in which the oxygen concentration is controlled by adding such a carbon source, the molten slag 12 having a low Pb content is generated and recovered. In addition, both the NOx generation amount and the CO generation amount in the furnace can be effectively reduced. The reason is as follows.

1. FIG. 2 shows the relationship between the measured value of the O ₂ concentration in the furnace and the measured value of the CO concentration when the apparatus shown in FIG. 1 is operated at an operating temperature of 1350 ± 50 ° C. Is. As shown in this figure, the CO concentration in the region where the O ₂ concentration in the furnace is 4% or more is significantly lower than the region where the concentration is less than 4%. Therefore, controlling the O ₂ concentration in the furnace to 4% or more is extremely effective in reducing the amount of CO generated. On the other hand, if the in-furnace O ₂ concentration reaches 10%, almost no CO is generated, and even if the in-furnace O ₂ concentration is increased, the effect of reducing the CO concentration does not change.

2. 3. Reduction of Pb content in molten slag FIG. 3 shows the relationship between the measured value of the O ₂ concentration in the furnace and the measured value of the Pb concentration in the molten slag when the apparatus is operated under the same conditions as described above. It is. Here, the Pb concentration in the molten slag was measured by the same method as the bottom sediment survey of the water bottom. Specifically, nitric acid, hydrochloric acid and perchloric acid were added to the crushed sample and heated and concentrated on a hot plate, and nitric acid and hydrochloric acid were added to the ground sample and heated and dissolved on the hot plate. Thereafter, the measured value can be obtained by a method in which the volume of the treated sample is made constant and the Pb content is measured by ICP emission spectrometry.

As shown in FIG. 3, the Pb concentration in the molten slag increases almost in proportion to the O ₂ concentration in the furnace. In other words, it is possible to reduce the Pb content of the molten slag as the O ₂ concentration in the furnace is kept low. This is because reduction of the oxygen concentration around the incineration residue promotes reduction of PbO (lead oxide) contained in the incineration residue and promotes volatilization of Pb as, for example, PbCl _2. it is conceivable that.

3. FIG. 4 shows the relationship between the measured value of the in-furnace O ₂ concentration and the in-furnace NOx concentration when the apparatus is operated at the same temperature. As shown in the figure, the in-furnace NOx concentration increases in proportion to the in-furnace O ₂ concentration, similar to the Pb concentration in the molten slag. In other words, the amount of NOx generated can be reduced as the furnace O ₂ concentration is kept lower.

  From the above measurement results, in order to achieve both suppression of the amount of CO generated in the furnace and reduction of the Pb content in the molten slag and the amount of NOx generated, the O2 concentration in the furnace is controlled in the range of 4% to 10%. You can conclude that it is effective.

The control of the O ₂ concentration in the furnace is based on the carbon source addition amount based on the operating conditions (plasma gas amount Qp, leak amount Q _L , unburned carbon amount Co contained in the incineration residue, etc.) as described above. It is not limited to what is calculated. For example, the O ₂ concentration in the furnace may be sensed by a sensor, and the carbon source addition amount may be manipulated by calculation of feedback control based on the result.

The carbon source may be supplied into the melting furnace 10 independently of the incineration residue and added to the incineration residue in the melting furnace 10. However, as described above, the carbon source is added to the incineration residue outside the melting furnace 10 and supplied into the melting furnace 10 in a state of being mixed with the incineration residue, particularly in the atmosphere around the incineration residue. There is an advantage that the O ₂ concentration can be locally reduced and the volatilization of Pb can be promoted with a smaller amount of carbon source. Therefore, it is possible to reduce the amount of carbon source added to reduce the Pb content in the molten slag to a specified value or less and further reduce the amount of generated CO. In particular, when the mixture of the incineration residue and the carbon source is supplied into the melting furnace by the screw feeder 24 as in the embodiment, the screw feeder 24 mixes the incineration residue and the carbon source. By promoting the above, it becomes possible to further enhance the Pb volatilization promoting effect by the carbon source.

  In the method according to the embodiment described above, experiments were conducted using coke having various particle size ranges in order to confirm the influence of the particle size of coke used as a carbon source on the effect of reducing the Pb content in the slag. It was broken. The results are shown in Table 1.

This experiment was performed under furnace operating conditions in which the furnace O ₂ concentration was 10% and the furnace temperature was 1350 ± 50 ° C. In addition, the coke to be used is classified in advance into four groups shown in Table 1 by sieving, and experiments are performed for each group by adding coke belonging to each group to the incineration residue before in-furnace supply. , Data (Pb content in slag) were collected.

  As a result of this experiment, as shown in Table 1, the Pb content in the slag can be reduced most when a group of coke having a particle size of 0.5 mm or more and less than 4.0 mm is used as the carbon source. did it. The reason is considered as follows.

  1) The smaller the coke particle size, the larger the contact area between the coke and the incineration residue. This effectively promotes the local reduction and volatilization of Pb in the incineration residue by coke as a carbon source.

2) However, since the dusty coke having a particle size of less than 0.5 mm disappears due to the reaction with O ₂ in the furnace before contributing to the promotion of the volatilization of Pb in the incineration residue, the volatilization of the Pb A small percentage can contribute to the promotion.

  3) As a conclusion, coke having a particle size of 0.5 mm or more and less than 4.0 mm can contribute most to the promotion of Pb volatilization.

It is sectional drawing of the plasma melting apparatus which concerns on embodiment of this invention. It is a graph showing the relationship between the measurement values of the furnace CO concentration in the furnace O ₂ concentration obtained in the apparatus. Is a graph showing the relationship between the measurement values of the molten slag in Pb concentration in the reactor in the O ₂ concentration obtained in the apparatus. Is a graph showing the relationship between the measurement values of the furnace NOx concentration in the reactor in the O ₂ concentration obtained in the apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Melting furnace 12 Molten slag 14 Slag outlet 20 Feeding device 24 Screw feeder 30 Plasma torch

Claims (4)

A method of melting waste incineration residue using plasma,
Supplying the incineration residue into a melting furnace;
Melting the incineration residue supplied into the melting furnace with plasma generated by a plasma generator using an oxygen-containing gas as a working gas, and discharging and recovering the generated molten slag to the outside of the melting furnace; ,
While adding a carbon source to the molten residue supplied into the melting furnace, the amount of addition is such that the oxygen concentration in the melting furnace is 4% or more and 10% or less due to absorption of oxygen in the melting furnace by the carbon source. And a melting treatment method for waste incineration residues, comprising: In the melting processing method of the incineration residue of the waste according to claim 1,
The carbon source is added to the incineration residue outside the melting furnace, and is supplied into the melting furnace in a state of being mixed with the incineration residue. In the melting processing method of the incineration residue of the waste according to claim 2,
A waste incineration residue melting treatment method, wherein a mixture of the incineration residue and the carbon source is supplied into the melting furnace by a screw feeder. In the method for melting a waste incineration residue according to claim 2 or 3,
A method for melting a waste incineration residue, wherein the carbon source added to the incineration residue is coke having a particle size of 0.5 mm or more and less than 4 mm.

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