JPH0230752B2 - - Google Patents

Description

[Detailed description of the invention]

a. Industrial Application Fields The present invention is designed to detoxify the incineration dust (fly ash) in the exhaust gas generated when municipal waste, sewage sludge, human waste sludge, industrial waste, etc. are incinerated. The present invention relates to a method of granulation. b. Prior Art The incineration dust contained in the exhaust gas from incineration of the wastes is concentrated with various salts and heavy metals, which are fine and light and easily scattered, posing the risk of polluting the environment. Therefore, after collecting these incineration dusts, a method is used to granulate and solidify the incineration dust to render it harmless and dispose of it. FIG. 7 is an explanatory diagram of a conventional granulation system for processing such incineration dust. In other words, in a waste incineration facility, after the waste is first incinerated in incinerator a, the incineration dust (hereinafter abbreviated as dust) generated here is guided along with the exhaust gas to gas cooling room b, where it is cooled and further collected. The dust is collected by a container c and stored in a dust storage tank d from there by a conveyor. After collecting the dust, the exhaust gas is released from the chimney s. A fixed amount of the dust stored in the storage tank d is fed into the kneading device g via the collection chute f by the dust quantitative supply device e. On the other hand, a fixed amount of cement is supplied from a separately provided cement storage tank h to a cement quantitative supply device i and a collection chute f, and simultaneously to a kneading device g.
The dust and cement are mixed together with water supplied from water tank j. The kneaded mixture is sent to a granulator l by a conveyor k, where it is granulated into a predetermined shape. The granulated material granulated by the granulator l is dropped onto a curing conveyor m, cured while moving on the curing conveyor m, and finally transferred to a curing bunker n.
The material is then put into a container where it is cured for a predetermined period of time. Note that q is a slaked lime storage tank, and a supply device r supplies slaked lime to the exhaust gas passage between the gas cooling chamber b and the dust collector c to remove CHl from the exhaust gas. c Problems to be Solved by the Invention The conventional method has the following problems.
In other words, since it is a wet process, the aluminum contained in the dust reacts with water, generating H ₂ gas, which poses the risk of explosion. Since granulation is performed by adding cement and water, it is necessary to clean the kneading device g and the granulation device l each time the work is completed before solidification, which requires a great deal of labor. Since cement does not have quick hardening properties, granulation equipment is required.
The granulated material requires a long-stroke curing conveyor m and a curing bunker n for curing. The process is complicated because additives such as cement and water are required for the dust. Skill is required to operate the granulation equipment in order to maintain a constant addition rate of cement and water. Because the dust is granulated by adding cement and water, the apparent density is small (porosity approximately 39%).
Therefore, the volume of the granules becomes large, which increases disposal costs. d. Means for Solving the Problems In view of the above circumstances, the present invention aims to provide a granulation method that eliminates the problems. That is, the present invention supplies slaked lime to exhaust gas and incineration dust generated by incineration of waste to remove HCl in the exhaust gas, and further, in the incineration dust collected by a dust collector, by the treatment, Incineration dust containing at least 10% of residual slaked lime is sent as it is to a high compression granulation device without adding additives such as cement or water, and is
By applying a high pressure of 4ton/ ^cm2 , slaked lime is forced into a matrix between the dust particles, creating a highly dense (empty)
This is a method for granulating incineration dust, which is characterized by forming granules with high crushing strength at a ratio of 5 to 10%). Generally, the properties of dust differ depending on the type of incinerator and each type of municipal waste, but based on the published composition list and the test results of the test dust adopted by the inventor, which will be described later, we can conclude as follows. was completed. First, when slaked lime for HCl removal is not added, the dust mainly contains SiO ₂ and Al ₂ O ₃ , and is also contaminated with Na ₂ O, K ₂ O, SO ₃ , and unburned organic matter. However, these vary greatly depending on the type of incinerator and the nature of the municipal waste. In general, hard inorganic substances such as SiO ₂ and Al ₂ O ₃ do not adhere to each other due to particle deformation, or dissolve or stick at contact points, even if a compression pressure of 3 to 4 t/cm ² or less is applied during granulation. Therefore, it was found that it was difficult to produce strong granules using only this molding pressure. On the other hand, NO ₂ O, K ₂ O, SO ₃ and unburned organic matter are relatively soft, and the particles deform and stick together under a pressure of 2 to 3 t/cm ² , and the particle surfaces are activated. Strong interparticle bonding force. That is,
Dust containing 25 to 30% or more of Na ₂ O, K ₂ O, etc. can be combined under a molding pressure of about 3 to 4 t/cm ² to obtain a hard granulated product. However, since salts such as Na and K are deliquescent substances, tests have shown that they disintegrate when immersed in water, making them undesirable as granules that are required to be rendered harmless. Therefore, the inventor has solved the above problems by using the method of the present invention. That is, 2 to 4 tons of the dust containing at least 10% or more, preferably about 30%, of slaked lime is mixed into the dust.
When molded in ^cm2 , slaked lime is formed between hard dust particles in a matrix shape. This slaked lime is soft and the dust particles deform and stick together, and because it has particularly high surface activity, it creates interparticle attraction (intermolecular attraction).
is strong. Furthermore, if there is a slight amount of moisture on the surface of the particles, high pressure and frictional heat will cause a portion of the particles to melt, precipitate, or stick together at the contact points, creating a strong cohesive force. In addition, when the molding pressure is 4t/ ^cm2 or more,
This is not desirable in terms of cost as it requires equipment costs. Also
If it is less than 2t/cm ² , granules with the desired properties cannot be obtained. It can also be estimated from the experimental results that hydration reactions and hydraulic reactions occur with other components in the dust. In other words, slaked lime (Ca(OH) ₂ ) in the granules reacts with CO ₂ in the air over time and changes to CaCO ₃ as shown in the equation below, resulting in highly water-sealing,
Moreover, it becomes a granulated material with a large cohesive force. That is, it hardens over time. Ca(OH) ₂ +CO ₂ →CaCO ₃ +H ₂ O Also, when slaked lime alone is molded under high pressure, it becomes so strong that it hardly dissolves even in water after 24 to 48 hours. Therefore, in high-pressure granules of dust containing slaked lime, the slaked lime enters between the dust particles in a matrix form, enveloping the particles and solidifying, which reduces the contact between the dust particle surface and water and prevents the elution of the dust. It is thought that this will significantly reduce the
However, if the addition of slaked lime is 10% or less, the hardening is small. A similar effect can be obtained even if the amount of slaked lime is 30% or more, but in consideration of economic efficiency, it is most preferable to add slaked lime to about 30%. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In Figure 1, 1 is a waste incinerator, 2 is a gas cooling room, 3 is a dust collector, 4 is a dust storage tank for the dust collected in the dust collector 3, and 5 is the lower part of the dust storage tank 4. 6 is a high compression granulation device, 7 is a classification device, 8 is a curing device,
9 is a return conveyor connected from the classification device 7 to the dust storage tank 4; 10 is a slaked lime storage tank; 11 is a slaked lime storage tank 10 that supplies slaked lime to the exhaust gas passage between the gas cooling chamber 2 and the dust collector 3; 12 is a fan for supplying exhaust gas, and 13 is a chimney for discharging exhaust gas. After the waste is incinerated in the incinerator 1, the dust generated here is guided along with the exhaust gas to the gas cooling chamber 2, where it is cooled, and further collected by the dust collector 3, from which the dust is collected by a conveyor. It is stored in the storage tank 4. On the other hand, slaked lime is blown from the slaked lime storage tank 10 through the supply device 11 into the pre-process of the dust collector 3 to remove HCl contained in the exhaust gas. Therefore, the dust stored in the dust storage tank 4 contains some slaked lime. The stored dust is sent from the dust storage tank 4 to a high compression granulation device 6 by a feeder 5. This high-compression granulation device 6 is provided with a feeder 6a consisting of, for example, a cone-shaped rigid screw in the upper part, and forcibly feeds the dust between press rolls 6b below. For example, the press rolls 6b are provided with recesses for granulation, that is, master molds, on the surfaces of the rolls that rotate relative to each other.
A pressure of cm ² is applied to form granules into a predetermined shape. The granulated material is sent to a curing device 8 via a separator 7. Further, burrs and small pieces generated around the granules are separated by the classifier 7, and returned to the dust storage tank 4 by the return conveyor 9 for reuse. Next, we will discuss the results of a comparative test regarding the volume reduction effect due to pressurization and curing over time in the molding of granules. () Comparative volume reduction test Dust generated from an incinerator installed at Higashiban Sanitary Treatment Association in Iwate Prefecture (hereinafter referred to as Sample A),
The test was conducted on dust generated from an incinerator at the Megasaki Beautification Center in Kanagawa Prefecture (hereinafter referred to as Sample B). Figure 2 shows the test equipment, with a diameter of 25 mm.
A sample is filled into a cylinder 31 with a depth of 25 mm, and while it is pressurized by a piston 32 at a pressure P, the table 3 is measured for each compression force.
The change in thickness of Tablet 33 was measured, and the apparent density of Tablet 33 was calculated, and an apparent density ρ-compressive force P curve was created. Note that samples A1 and B1 contain only dust, and samples A2 and B2 each contain 30% slaked lime. The test results are shown in Table 1 and FIGS. 4 and 5.

[Table] Volume after compression
(Note) Volume reduction rate =

Claims (1)

[Claims] 1. Slaked lime is supplied to the exhaust gas and incineration dust generated by waste incineration to remove HCl in the exhaust gas, and the remaining slaked lime is removed from the incineration dust collected by the dust collector through the above treatment. Incineration dust with a content of at least 10% is sent as it is to a high compression granulation device without adding additives such as cement or water, and is subjected to high pressure of 2 to 4 tons/ ^cm2. , slaked lime is inserted between the dust particles in a matrix form to create a high density (5 to 10% void ratio)
A method for granulating incineration dust, characterized by forming granules with high crushing strength.