CN103104920B - Method for trapping heavy metal and ultrafine particles in solid waste incineration process - Google Patents

Abstract

The invention relates to a method for trapping heavy metals and ultrafine particles in the incineration process of solid waste, which comprises the following steps: (1) pulverizing zeolite into zeolite powder; (2) mixing the zeolite powder and the percolate and then spraying the mixture into a solid waste incinerator; (3) the zeolite powder absorbs heavy metal and ultrafine particles in the solid waste incinerator, and then enters the bag type dust collector along with the flue gas to be collected by the bag type dust collector. The zeolite powder is firstly efficiently adsorbed to heavy metal ions in the percolate, then the zeolite powder and the percolate enter the solid waste incinerator together, the heavy metal ions on the surface of the zeolite powder react with the zeolite powder to generate eutectic substances, eutectic melting is generated, the potential energy of the zeolite surface reaction is reduced, the reaction of the zeolite powder and metal steam in smoke is further promoted, meanwhile, the melted surface also promotes the adhesion of the zeolite powder to ultrafine particles, so that the comprehensive performance of zeolite is improved, and finally, the adsorbed zeolite powder is trapped by the bag-type dust collector.

Description

Capture method of heavy metals and ultrafine particles in the process of solid waste incineration

technical field

The invention relates to the fields of solid waste incineration technology and air pollutant control, in particular to a method for trapping heavy metals and ultrafine particles in the process of solid waste incineration.

Background technique

Solid waste incineration can reduce the volume of solid waste by 90%. At the same time, it has the advantages of resource utilization of solid waste and large daily processing capacity. It is expected to become the main method of solid waste treatment in the future. Solid waste incineration usually results in the emission of highly toxic fumes, such as heavy metals, dioxins, SO ₂ and NO _x , etc. Most of these toxic pollutants are emitted in the form of particulate matter, among which submicron ultrafine particulate matter has the highest toxic content and is the most toxic. The current bag filter has a good trapping effect on ultra-micron (particle size greater than 1 μm) particles, but poor on sub-micron (particle size less than 1 μm) ultra-fine particles, so how to capture ultra-fine Particulate matter and other pollutants have become a difficult point in solid waste incineration technology.

As the waste liquid of solid waste incineration plant, leachate has the characteristics of high pollution and high toxicity. The Ministry of Environmental Protection of the People's Republic of China [Huanfa (2008) No. 82 Notice] clearly pointed out: "...the treatment of landfill leachate should give priority to re-spraying...". Incineration can effectively remove organic matter in leachate, but it will cause a high concentration of heavy metals to enter the flue gas, which will aggravate the emission of heavy metals and particulate matter from solid waste incineration.

Zeolite can physically and chemically adsorb heavy metal vapors at high temperatures. During high-temperature incineration, heavy metal vapors (such as Zn, Cu, Pb, Cd, Cr, etc.) diffuse to the surface of zeolite with a porous structure, resulting in physical adsorption, and then react with the surface of zeolite to form silicate, aluminate, aluminosilicate Salt and other non-volatile substances, such reaction products are easy to form low-temperature eutectics, resulting in the melting of the surface area of the reaction, heavy metals diffuse into the interior of the zeolite and cannot escape, so that the heavy metals are solidified in the zeolite, and finally captured by the bag filter , and not easy to leach. Zeolites also react with alkali metals by a similar mechanism, thereby suppressing the emission of ultrafine particles formed after condensation nucleation of alkali metals. At high temperature, zeolite particles can physically and chemically adhere to the formed ultrafine particles in the flue gas, thus forming large particles that can be captured by the bag filter. At the same time, as a non-metallic mineral, zeolite also has excellent cation exchange performance, which can effectively absorb heavy metal ions in sewage, and then filter or precipitate them to achieve heavy metal removal.

However, the two excellent properties of the above-mentioned zeolite are embodied in two completely different media of high-temperature flue gas and normal-temperature aqueous solution. Traditional zeolite applications are limited to the adsorption of heavy metal ions in leachate. Although the adsorption efficiency is high, the zeolite is subsequently filtered out. In fact, the heavy metal content in leachate only accounts for a small amount of the total heavy metal emissions from solid waste incineration. Some, most of it is produced by solid waste incineration. Previous studies have also sprayed zeolite directly into the incinerator, although it can absorb heavy metal vapor and particulate matter at high temperature, but the efficiency is low.

Contents of the invention

In view of the fact that solid waste incineration will produce highly toxic submicron ultrafine particles, and the existing bag filter cannot effectively remove ultrafine particles, a method for collecting heavy metals and ultrafine particles in the process of solid waste incineration is proposed , the combined use of zeolite and solid waste incineration leachate backspray can break through the single effect of zeolite and realize the comprehensive utilization of multiple effects of zeolite, which is better than the effect of zeolite in a single medium, so as to achieve efficient removal of heavy metals and superoxides in the process of solid waste incineration The purpose of fine particles.

Concrete technical scheme of the present invention is as follows:

A method for collecting heavy metals and ultrafine particles in a solid waste incineration process, comprising the steps of:

(1) Crushing zeolite into zeolite powder;

(2) Mix zeolite powder and leachate and spray them into the solid waste incinerator;

(3) The zeolite powder absorbs the heavy metals and ultrafine particles in the solid waste incinerator, and then enters the bag filter with the flue gas, and is collected by the bag filter.

The particle size of the zeolite powder in step (1) is 300-400 mesh; the zeolite powder is prepared by using a micro-powder mill. The particle size is controlled between 300-400 mesh.

The amount of zeolite powder mixed with leachate in step (2) accounts for 1-5‰ of the total mass of solid waste in the solid waste incinerator; zeolite powder can effectively remove heavy metals and ultrafine particles in flue gas within this range of addition , while ensuring the smooth flow of leachate.

In order to mix the zeolite powder with the leachate uniformly, the zeolite powder described in step (2) is injected into the leachate injector through the powder injection device and mixed with the leachate.

In step (2), the zeolite powder is mixed with the leachate and then sprayed into the solid waste incinerator where the temperature range is 850-1050°C; the temperature range of 850-1050°C is the optimal temperature for the reaction of metal vapor and zeolite powder, which ensures It prevents the occurrence of the reaction between the metal vapor and the zeolite powder, and prevents the zeolite surface from eutectic melting to complete melting at too high a temperature and thus loses the pore structure.

The powder injection device is a Venturi jet.

In step (2), the zeolite powder is transported to the cyclone separator through a dense-phase pneumatic conveying device, separated by the cyclone separator, weighed by a disc-type metering feeder, and then enters a Venturi jet. Use dense-phase pneumatic conveying device to convey zeolite powder to ensure sealed conveying and prevent dust pollution.

The air outlet of the cyclone separator is connected with the Venturi ejector. Because the wind at the air outlet of the cyclone separator entrains the unseparated fine zeolite powder, the wind is blown into the Venturi jet and provides power for the Venturi jet, thereby improving the utilization rate of the zeolite.

In the present invention, the heavy metal ions in the leachate are first efficiently adsorbed by the zeolite powder, and then the zeolite powder and the leachate are put into the solid waste incinerator together, and the heavy metal ions on the surface of the zeolite powder react with the zeolite powder to form a eutectic, and eutectic melting occurs, reducing The surface reaction potential energy of the zeolite further promotes the reaction between the zeolite powder and the metal vapor in the flue gas. At the same time, the melted surface also promotes the adhesion of the zeolite powder to ultrafine particles, thereby improving the comprehensive performance of the zeolite. Dust collector captures.

The present invention has following characteristics and advantages:

(1) After the zeolite powder is mixed with the leachate, the heavy metals in the leachate are adsorbed to the surface of the zeolite, sprayed into the solid waste incinerator, react with the zeolite at high temperature, and are finally captured by the bag filter, avoiding the leakage of the leachate Medium and heavy metals form ultrafine particles and are discharged into the atmosphere.

(2) The zeolite powder sprayed into the solid waste incinerator continues to react with the heavy metal vapor and alkali metal vapor in the flue gas generated by solid waste incineration to reduce the generation of ultrafine particles such as heavy metal and alkali metal.

(3) The zeolite powder sprayed into the solid waste incinerator and the formed ultrafine particles bond and adsorb each other, and are finally captured by the bag filter, reducing the emission of many harmful substances in the form of particles, such as dioxins , heavy metals, Hg, etc.

(4) The method is simple to implement, does not affect the operation of solid waste incineration, and does not need to modify the original incineration and tail gas treatment processes.

(5) The zeolite powder of the present invention absorbs the heavy metal ions in the leachate and then enters the solid waste incinerator to absorb the heavy metal vapor in the flue gas; it not only improves the trapping efficiency of the zeolite powder to absorb the heavy metal vapor in the flue gas, but also The zeolite powder is reused, saving energy and reducing costs.

Description of drawings

Fig. 1 is a process flow chart of the method for trapping heavy metals and ultrafine particles in the solid waste incineration process of the present invention.

Detailed ways

The following is a specific embodiment of the present invention, but the embodiment of the present invention is not limited thereto.

Referring to Fig. 1, first, the zeolite enters the micropowder mill through a screw feeder, and is crushed into zeolite powder with a particle size of 300-400 mesh; the pulverized zeolite powder is transported to a cyclone separator through a dense phase pneumatic conveying device, After being separated by the cyclone separator, it is weighed by a disc-type metering feeder, and then enters the Venturi jet; the amount of zeolite powder entering the Venturi jet accounts for 1-5‰ of the total mass of solid waste in the solid waste incinerator; the cyclone The air outlet of the separator is connected with the Venturi ejector. The jet wind of the Venturi jet comes from: ①Roots blower; ②The separation wind of the air outlet of the cyclone separator. The mixing air mixed with zeolite powder enters the leachate injector from the Venturi jet and mixes with the leachate in the leachate injector. When the leachate and zeolite powder are mixed, the cations such as sodium and potassium on the surface of the zeolite powder are not tightly bound to the lattice, so they can exchange with the heavy metal cations in the leachate, and the heavy metal ions in the leachate are thus attached to the surface of the zeolite powder . The leachate mixed with zeolite powder is sprayed into the flame in the solid waste incinerator by the leachate injector at 850-1050°C, and the heavy metal ions on the surface of the zeolite powder in the solid waste incinerator react with the zeolite powder to generate heavy metal silicon zeolite and aluminosilicate, thus preventing the formation of submicron particles in the low temperature section after the gasification of heavy metals in the leachate; at the same time, the zeolite powder also causes heavy metals, alkali metals, etc. Metal vapor is adsorbed in the pores of zeolite, and reacts with zeolite to form heavy metal silicates and aluminosilicates, thereby preventing the incineration of metal vapor that has been produced to form submicron particles at low temperature; and the reaction of zeolite particles with metal ions Eutectic melting will occur on the surface, so that the surface of the zeolite has a certain degree of adhesion, so as to bond with the formed submicron particles to achieve the effect of trapping submicron particles. When the zeolite powder that has captured heavy metals and ultrafine particles leaves the solid waste incinerator with the flue gas and finally enters the bag filter, since its particle size is above 38 μm, it can be efficiently collected by the bag filter without Exhaust to atmosphere.

The equipment used in the technical process of the method for collecting heavy metals and ultrafine particles in the solid waste incineration process of the present invention is all existing.

The solid waste incineration test was carried out on a circulating fluidized bed incinerator with a daily waste processing capacity of 0.5 t. The incineration temperature was above 850°C. The solid waste was selected as simulated municipal solid waste. The specific components are shown in Table 1. Heavy metal acetate was added to simulate heavy metals in municipal solid waste, and the added components are shown in Table 2. The simulated leachate was sprayed into the hearth of the circulating fluidized bed incinerator, the injection volume was 1L/h, and the temperature of the injection position was 900°C±5°C. The concentration of heavy metal ions in the simulated leachate was shown in Table 3.

Table 1 The components in the simulated municipal solid waste (mass percentage, %)

name flour Vegetable leaves the paper sawdust plastic cotton pvc NaCl content 40 15 15 12 12 3 1.5 1.5

Table 2 Addition amount and composition of heavy metals in simulated MSW (percentage of total dry weight of MSW, mg/kg)

heavy metal Amount added Add ingredients Zn 8000 (CH ₃ COO) ₂ Zn 2H ₂ O Cu 2000 (CH ₃ COO) ₂ Cu H ₂ O Pb 1500 (CH ₃ COO) ₂ Pb 3H ₂ O Cd 500 (CH ₃ COO) ₂ Cd 2H ₂ O Cr 500 (CH3COO _{) 3Cr}

Table 3 Concentration of heavy metal ions in simulated leachate (mg/L)

heavy metal Zn Cu Pb Cd Cr concentration 1.50 0.18 0.14 0.09 0.10

Example 1

First, the zeolite enters the micropowder mill through the screw feeder, and is crushed into zeolite powder between 300-400 mesh; the pulverized zeolite powder is transported to the cyclone separator through the dense phase pneumatic conveying device, separated by the cyclone separator and passed through the disc Type metering feeder weighs, and then enters the Venturi jet; the amount of zeolite powder entering the Venturi jet accounts for 3‰ of the total mass of municipal solid waste in the circulating fluidized bed incinerator; the mixed air of the mixed zeolite powder flows from the Venturi The leachate injector enters the leachate injector in the inner jet, and is mixed with the leachate and injected into the furnace of the circulating fluidized bed incinerator. The temperature of the injection position is 900°C±5°C; The gas leaves the circulating fluidized bed incinerator and finally enters the bag filter, which is efficiently collected by the bag filter and then discharged to the atmosphere.

Comparative example 1

The leachate is sprayed into the hearth of the circulating fluidized bed incinerator, and the temperature of the spraying position is 900°C±5°C; the flue gas generated by waste incineration leaves the hearth of the circulating fluidized bed incinerator, and finally enters the bag filter, and passes through the bag dust collector. It is efficiently captured by the filter and discharged to the atmosphere.

Comparative example 2

First add the zeolite powder into the leachate, the concentration of the zeolite powder in the leachate is 62.5g/L, filter after standing for 24 hours, spray the filtrate into the hearth of the circulating fluidized bed incinerator, and the temperature of the injection position is 900°C±5°C; the flue gas produced by waste incineration leaves the circulating fluidized bed incineration furnace, and finally enters the bag filter, which is efficiently collected by the bag filter and then discharged to the atmosphere.

Comparative example 3

The zeolite powder and leachate are sprayed into the hearth of the circulating fluidized bed incinerator respectively, and the amount of zeolite powder sprayed into the circulating fluidized bed incinerator accounts for 3‰ of the total mass of municipal solid waste in the circulating fluidized bed incinerator; The position temperature is 900°C±5°C; the flue gas produced by waste incineration leaves the circulating fluidized bed incineration furnace, and finally enters the bag filter, which is efficiently collected by the bag filter and then discharged to the atmosphere.

The fly ash at the outlet of the bag filter in Example 1, Comparative Example 1 to Comparative Example 3 was subjected to 8-level aerodynamic diameter classification sampling, and the emission concentration of heavy metals (Zn, Cu, Pb, Cd, Cr) and PM1 ( Ultrafine particles with a particle size of less than 1 μm) emission concentration, as shown in Table 4 and Table 5. It can be seen from Table 4 that spraying zeolite powder into the circulating fluidized bed incinerator can effectively control the discharge of heavy metals and ultrafine particles in the circulating fluidized bed incinerator, and the zeolite powder mixed with leachate and then sprayed into the furnace can reduce the heavy metal The trapping effect of zeolite powder and ultrafine particles is obviously better than spraying zeolite powder directly into the furnace.

Table 4 Emission concentration of heavy metals in flue gas from municipal solid waste incineration (μg/Nm ³ )

heavy metal Comparative example 1 Comparative example 2 Comparative example 3 Example 1 Zn 2435 2434 1043 764 Cu 1253 1254 960 783 Pb 741 737 573 214 Cd 421 423 397 196 Cr 294 289 162 105

Table 5 Emission concentration of ultrafine particulate matter in flue gas from municipal solid waste incineration (mg/Nm ³ )

Comparative example 1 Comparative example 2 Comparative example 3 Example 1 PM1 71.4 71.4 32.8 19.7

Claims (8)

1. A method for trapping heavy metals and ultrafine particles in a solid waste incineration process, characterized in that it comprises the steps: (1) Crushing zeolite into zeolite powder; (2) Mix zeolite powder and leachate and spray them into the solid waste incinerator; (3) The zeolite powder absorbs the heavy metals and ultrafine particles in the solid waste incinerator, and then enters the bag filter with the flue gas, and is collected by the bag filter. 2. The trapping method according to claim 1, characterized in that the particle size of the zeolite powder in step (1) is 300-400 mesh. 3. The capture method according to claim 1 or 2, characterized in that the amount of zeolite powder mixed with leachate in step (2) accounts for 1-5‰ of the total mass of solid waste in the solid waste incinerator. 4. The capture method according to claim 3, characterized in that the zeolite powder described in step (2) is injected into the leachate injector through the powder injection device and mixed with the leachate. 5. The capture method according to claim 4, characterized in that in step (2), the zeolite powder is mixed with the leachate and sprayed into the solid waste incinerator at a temperature range of 850-1050°C. 6. The trapping method according to claim 5, characterized in that said powder injection device is a Venturi jet. 7. The collection method according to claim 6, characterized in that in step (2), the zeolite powder is transported to the cyclone separator through a dense-phase pneumatic conveying device, and is weighed by a disc-type metering feeder after being separated by the cyclone separator. volume, and then into the Venturi ejector. 8. The collection method according to claim 7, characterized in that the air outlet of the cyclone separator is connected with a Venturi jet.