CN113198301A

CN113198301A - Deep purification method for VOCs and particulate matters in dry tail gas of artificial board industry

Info

Publication number: CN113198301A
Application number: CN202110609616.9A
Authority: CN
Inventors: 刘伟
Original assignee: Jiangsu Environmental Engineering Technology Co Ltd
Current assignee: Jiangsu Environmental Engineering Technology Co Ltd
Priority date: 2021-06-01
Filing date: 2021-06-01
Publication date: 2021-08-03
Anticipated expiration: 2041-06-01
Also published as: CN113198301B

Abstract

The invention relates to a deep purification method for VOCs and particulate matters in dry tail gas in the artificial board industry. Firstly, spraying an adsorbent with the function of adsorbing VOCs into the flue gas from a flue by using an adsorbent spraying device to perform adsorption reaction on a large amount of high-temperature flue gas generated in the production and drying process of the artificial board; then removing particles in the flue gas by a wet electric precipitator, simultaneously removing more than 30% of formaldehyde, and reducing the temperature of the flue gas to about 40 ℃; then the wastewater enters a biological trickling filter to deeply remove the residual VOCs such as formaldehyde and the like; and discharging the purified flue gas to the atmosphere. Filtering the waste water containing VOCs generated by wet electric dust removal, mixing the waste water with the washing liquid of the biological trickling filter, and flowing into the activated sludge reactor for biodegradation. The purified liquid returns to the trickling filtration tower for recycling, and the sawdust and the waste activated sludge generated by filtration are conveyed to a heat energy center for incineration treatment. The invention can deeply remove particulate matters and VOCs in the flue gas, eliminate peculiar smell, solve the environmental protection problem of tail gas and does not generate high-concentration organic wastewater and waste residue.

Description

Deep purification method for VOCs and particulate matters in dry tail gas of artificial board industry

Technical Field

The invention relates to an industrial flue gas purification method, in particular to a deep purification method for VOCs and particulate matters in dry tail gas in the artificial board industry.

Technical Field

China is a large world for producing artificial boards, and the high yield is the first place of the world. With the steady improvement of national economy, the demand of production and consumption of artificial boards in China will continuously increase. Plywood, density board and shaving board are used as three major components in the field of artificial boards in China, and a large amount of high-concentration dust-containing VOCs waste gas is generated in the drying section in the production process, so that great pressure is caused to the ecological environment. In addition, the wood has peculiar smell, and the generated peculiar smell still affects the surrounding environment under the adverse diffusion climates such as low air pressure, rainy weather and the like. The peculiar smell mainly comes from low-concentration volatile organic matters of the wood, such as acidity, special sweet taste, pungent and pungent odor and the like.

The maximum emission concentration limit values of particulate matters, formaldehyde and VOCs required by the emission standard of the industrial pollutants of the artificial boards in China are 120, 25 and 120 mg/m respectively³In 6 months in 2020, the ministry of environmental protection issues technical guidelines (revised edition in 2020) made by emergency emission reduction measures in the key industry of heavily polluted weather, and the requirements of indexes of dry exhaust emission of class a enterprises in the guidelines are as follows: the emission concentrations of the dry and hot-pressing tail gas particles, formaldehyde and VOCs are respectively not higher than 10, 5 and 50mg/m³. It is expected that the environmental protection requirements of the artificial board production process will be gradually improved in the future, and artificial board production enterprises must take effective measures to reduce the pollutant emission. At present in industry generally adopt cyclone control tail gas pollutant, but because the granule is mostly low-density fine fiber in the tail gas, cyclone's entrapment ability has obvious limitation, also has the enterprise to begin to try to adopt wet-type electrostatic precipitator control dust to discharge to utilize the characteristic of the formaldehyde easy soluble in water, realize the function of entrapment formaldehyde in coordination, but the formaldehyde purifying effect of reality still remains further observation, and is basically not effectual to the getting rid of the peculiar smell.

The purification method for low-concentration formaldehyde mainly comprises a photocatalysis method, an adsorption method, an ozone oxidation method and the like, but the methods have the problems of unstable treatment efficiency, high treatment cost, secondary water pollution and the like and cannot meet industrial application, and the biological method is a new waste gas treatment technology and is more and more concerned due to the characteristics of low investment, low operation cost, simple management, no secondary pollution and the like. The method is mainly used for treating low-concentration industrial waste gas without recycling price at home and abroad.

Chinese patent CN 1973968B discloses a gas-liquid phase combined biological purification process for formaldehyde waste gas, which is a combined process of a biological trickling filtration tower and an activated sludge process, wherein the formaldehyde waste gas firstly passes through a filler rich in a biological membrane, wherein a part of formaldehyde is captured and degraded by microorganisms in the biological membrane, and the other part of formaldehyde is blended into a washing liquid and enters activated sludge aeration treatment. The aim of removing formaldehyde by gas-phase and liquid-phase dual biodegradation in an enhanced manner is fulfilled. The above patent is not applicable to waste gases of VOCs containing dust.

Disclosure of Invention

The invention aims to overcome the defects of the dry tail gas treatment technology in the current artificial board industry, and provides a method for deeply purifying dry tail gas formaldehyde and particulate matters. The purpose of the invention can be realized by the following technical scheme:

a method for purifying VOCs and particulate matters in dry tail gas of artificial board industry comprises the following steps:

firstly, after wood fibers are recovered from a large amount of high-temperature flue gas generated in the artificial board production and drying process through two-stage cyclone dust removal, an adsorbent spraying device is utilized to spray adsorbent powder with the function of adsorbing VOCs into the flue gas through a flue to perform adsorption reaction;

secondly, a wet electric precipitator is used for cooling and dedusting to remove the adsorbent and other particles in the flue gas, and meanwhile, the high solubility (4.0 multiplied by 10) of formaldehyde in water is used⁵mg/L) is sprayed and washed to remove more than 30 percent of formaldehyde, the temperature of flue gas is reduced to about 40 ℃, and wastewater generated by a wet-type electric precipitator enters a filtering device;

and thirdly, enabling the flue gas to enter a biological trickling filter, further deeply removing residual VOCs (volatile organic compounds) such as formaldehyde and the like, and discharging the purified flue gas to the atmosphere.

And fourthly, dissolving the VOCs which are not completely decomposed in the biological trickling filter in the washing liquid, mixing the washing liquid with the filtrate generated by the filtering device, and then entering an activated sludge reactor to carry out biodegradation of the VOCs such as formaldehyde in the liquid phase.

The purified washing liquid returns to the packing tower through a circulating pump for recycling, and the sawdust particles and the waste activated sludge generated by filtering are conveyed to a heat energy center for incineration treatment.

The dry tail gas contains dust particles and VOCs, wherein the VOCs comprise one or more of aldehydes and ketones, phenols, aromatic hydrocarbons, terpenes and saturated alkanes, and mainly comprise formaldehyde.

The adsorbent is a powder adsorbent with the granularity of 100-400 meshes, and the using amount of the adsorbent in the flue gas is that 50-5000mg is sprayed into each cubic meter of the flue gas.

The adsorbent is one or a mixture of more of activated carbon, molecular sieve, clay, metal organic framework material and resin.

The wet electric dust removal device is one of a conductive glass fiber reinforced plastic type or a metal polar plate type.

The bottom of the wet electric dust collector is provided with a spray cooling layer, clear water is adopted for spraying, and the gas-to-gas ratio of spray cooling liquid is 1-2L/m³。

The biological trickling filter adopts circulating spray liquid to absorb VOCs in the waste gas and to contact and react with a biological film on the surface of the filler, the spray liquid contains nutrient substances required by microbial production, and the gas-to-gas ratio of the circulating liquid is 2-5L/m³。

1-5% of activated carbon powder with the granularity of 200-400 meshes is added into circulating liquid spray in the biological trickling filter.

The biological trickling filter filler is one or a combination of more of biological carbon, bark, ceramsite, polyurethane, glass fragments, diatomite, resin and foam.

The formaldehyde VOCs which are not completely decomposed are dissolved in the washing liquid and enter an activated sludge reactor (operated according to an activated sludge aeration treatment mode) to carry out biodegradation of the VOCs such as formaldehyde in the liquid phase.

The technical principle of the invention is to highly integrate and couple an adsorption method, a wet-type electric dust removal technology and a biological method technology, firstly, VOCs in flue gas are pre-trapped by using an adsorbent, then, dust particles in the flue gas are removed by using a wet-type electric dust remover, meanwhile, the temperature and the humidity are reduced and adjusted to the ideal operation conditions of the biological method, then, VOCs such as formaldehyde in waste gas are trapped by using the biological method, and finally, the formaldehyde dissolved in water is further degraded by using the biological method.

Compared with the existing washing and wet-electricity combined process, the invention has the following advantages:

1. the technology integrates multiple technologies of dry adsorption, wet absorption, wet electric precipitation and biodegradation, can effectively remove dust, formaldehyde and other VOCs in the flue gas, deeply purifies peculiar smell components in the tail gas, does not produce waste water and waste residues, and has no secondary pollution.

2. The dry-type pre-trapping method can effectively remove VOCs such as formaldehyde in the flue gas, remarkably reduce the content of formaldehyde in the washing liquid, reduce the treatment difficulty of subsequent formaldehyde wastewater, and simultaneously trap partial peculiar smell VOCs.

3. The wet-type electric dust collector can effectively remove particles, cool the flue gas, fully moisten the flue gas and be beneficial to improving the gas-liquid mass transfer rate of a biological method.

4. The washing liquid is added with the activated carbon powder, so that the adsorption of VOCs can be enhanced, the retention time of VOCs is prolonged, the mass transfer efficiency is promoted, and a favorable space surface can be provided for the growth of microorganisms.

5. VOCs such as formaldehyde in the flue gas is washed and purified by the biological trickling filter, and VOCs such as formaldehyde in the liquid phase is degraded by the biological treatment device, so that purification of VOCs such as formaldehyde is really realized, and pollutants are not transferred in the multi-media.

6. Waste residues and sludge generated by the filtering device and the activated sludge reactor can be sent to a heat energy center for incineration treatment, so that the whole treatment process does not generate secondary pollution.

Drawings

FIG. 1 is a schematic diagram of the process employed in the present invention.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

Example 1

A method for purifying VOCs and particulate matters in dry tail gas of artificial board industry adopts a process shown in figure 1, and comprises the following steps:

The adsorbent is a 400-mesh powder adsorbent with the granularity of 100 meshes, and the using amount of the adsorbent in the flue gas is that 50-5000mg is sprayed into each cubic meter of the flue gas. The adsorbent is one or a mixture of more of activated carbon, molecular sieve, clay, metal organic framework material and resin.

Secondly, a wet electric precipitator is used for cooling and dedusting to remove more than 99 percent of adsorbent and other particles in the flue gas, and meanwhile, the high solubility (4.0 multiplied by 10) of formaldehyde in water is used⁵mg/L) is sprayed and washed to remove more than 30 percent of formaldehyde, and the temperature of the flue gas is reduced to about 40 ℃;

the wet electric dust collector is one of a conductive glass fiber reinforced plastic type or a metal polar plate type. A spraying cooling layer is arranged in the wet electric dust removal device, and clear water is adopted for spraying. The gas-to-liquid ratio of the spray cooling liquid is 1-2L/m³。

In order to enhance the mass transfer rate of VOCs gas and biological membrane, 1-5% of activated carbon powder with the granularity of 200-400 meshes is added into the circulating liquid spray.

And fourthly, dissolving the VOCs which are not completely decomposed in the biological trickling filter in the washing liquid, mixing the washing liquid with the wastewater generated by wet electricity, and then feeding the mixture into an activated sludge reactor to carry out biodegradation of the VOCs such as formaldehyde in a liquid phase.

Through the treatment, the concentration of discharged dust and VOCs can be obviously reduced, tail gas has no peculiar smell, washing liquid can be recycled, and the generated sludge and wood chips can be burned on the spot, so that harmless treatment is really realized.

Example 2

The method takes simulated formaldehyde and peculiar smell VOCs waste gas as treatment objects, and performs adsorption removal experiments on VOCs in the flue gas by using dry adsorption, wherein the simulated experiment gas flow is 1L/h, and the formaldehyde concentration is 50mg/m³20mg/m of non-methane total hydrocarbons³The flue gas temperature is 100 ℃, and the specific steps are as follows:

1. weighing 50mg of activated carbon adsorbent, placing the activated carbon adsorbent in a fixed bed reactor, and controlling the temperature of the reactor to be 100 +/-5 ℃ through a tubular furnace;

2. and (3) introducing the simulated flue gas into a fixed bed reactor, and detecting the concentration of formaldehyde at the inlet and the outlet of the reactor by using an acetylacetone spectrophotometry, wherein the result shows that the removal efficiency of the formaldehyde reaches 90% and the removal efficiency of the non-methane total hydrocarbon at the outlet is 99% within one hour.

Therefore, the method has better removal performance on formaldehyde and off-flavor VOCs.

Examples 3 to 5

The actual dry tail gas of a certain artificial board production enterprise is taken as a treatment object, and 1000m of the actual dry tail gas is led out from a flue³The actual smoke gas has the formaldehyde concentration of 50mg/m³50mg/m of non-methane total hydrocarbons³Dust concentration 80mg/m³The flue gas temperature is about 120 ℃, the flue gas enters a conductive glass fiber reinforced plastic type wet electric dust remover, a layer of spraying washing is arranged at the wet electric bottom, and the circulating liquid-gas ratio is 1L/m³At the moment, the temperature of the flue gas is reduced to about 40 ℃, and the flue gas at the outlet of the system is sampled and analyzed after the system is stabilized, and the result shows that the outlet dust is concentratedDegree of 8mg/m³Formaldehyde concentration 35mg/m³50mg/m of non-methane total hydrocarbons³。

Spraying activated carbon powder with the particle size of 300 meshes into an inlet flue of a wet electric precipitator, wherein the spraying amount of the adsorbent is 50-5000mg/h, sampling and analyzing the flue gas at the outlet of the system, and the result is shown in the table, wherein when the spraying amount of the adsorbent is 50mg/h, the concentration of the outlet dust is 3mg/m³Formaldehyde concentration 30mg/m³40mg/m of non-methane total hydrocarbons³. When the spraying amount of the adsorbent is further increased to 500mg/h, the outlet dust concentration is 5mg/m³Concentration of formaldehyde 10mg/m³10mg/m of non-methane total hydrocarbons³。

Therefore, the dry-wet combination method can achieve the function of cooperatively removing VOCs such as formaldehyde, and the addition of the adsorbent does not cause the dust concentration at the outlet of the wet electric dust collector to be obviously increased.

TABLE 1 examples 3-5 Process parameters and treatment Effect

	The usage amount of the adsorbent is mg/h	Outlet concentration of formaldehyde mg/m³	Outlet non-methane total hydrocarbon concentration mg/m³	Outlet dust concentration mg/m³
					Example 3	0	35	50	3
Example 4	50	30	40	3
					Example 5	500	15	10	5

Examples 6 to 8

The actual dry tail gas of a certain artificial board production enterprise is taken as a treatment object, and 1000m of the actual dry tail gas is led out from a flue³The actual smoke gas has the formaldehyde concentration of 50mg/m³The amount of non-methane total hydrocarbons was 50mg/m³Dust concentration 80mg/m³Spraying 300-mesh activated carbon powder into flue at flue temperature of about 120 deg.C, spraying adsorbent at 500mg/h, passing through a wet electric dust collector of conductive glass fiber reinforced plastic type, spraying and washing with a layer of spray washing at wet bottom, and circulating liquid-gas ratio of 1L/m³And at the moment, the temperature of the flue gas is reduced to about 40 ℃, the residual VOCs such as formaldehyde in the flue gas are treated by using the bio-trickling filter, and the treated flue gas returns to the main flue through the induced draft fan.

Adopting domesticated activated sludge to carry out biofilm formation on a biological trickling filter, wherein the diameter of the biological trickling filter is 60cm, the height of filler is 50cm, inert filler made of ceramsite is adopted, and the specific surface area is 70cm²(g) the flow of the spray liquid is 5m³H is used as the reference value. In order to enhance the mass transfer rate of VOCs gas and biological membrane, 1-5% of activated carbon powder with the granularity of 200-400 meshes is added into the circulating liquid spray. The incompletely decomposed VOCs in the biological trickling filter are dissolved in the washing liquid, mixed with the wastewater generated by wet electricity and then enter an activated sludge reactor for liquid phaseBiodegradation of VOCs such as formaldehyde.

The activated sludge reactor is manufactured by processing a polyvinyl chloride clinker cylinder, the inner diameter is 20cm, the height is 50cm, the total volume is about 160L, the effective liquid volume is 125L, a sludge discharge port is formed in the bottom of the reactor, aeration is provided by an air pump, the flow is controlled at 100L/min, and 50L of activated sludge containing formaldehyde purification flora is taken and put into the reactor.

After the system is finished, sampling and analyzing pollutants such as the smoke at the outlet of the biological trickling filtration tower and the formaldehyde in the wastewater discharged by the activated sludge reactor, wherein the results are shown as the following table: when the washing liquid of the biological washing tower is not added with the activated carbon powder, the concentration of the dust in the outlet flue gas is 8mg/m³Formaldehyde concentration 4mg/m³The amount of non-methane total hydrocarbons was 6mg/m³The concentration of formaldehyde in the wastewater is 0.5 mg/L; when the adding amount of the activated carbon powder is 1 percent, the dust concentration of the outlet flue gas is 8mg/m³Formaldehyde concentration 3.5mg/m³The amount of non-methane total hydrocarbons was 5mg/m³The concentration of formaldehyde in the wastewater is 0.5 mg/L; when the adding amount of the activated carbon powder is 5 percent, the dust concentration of the outlet flue gas is 8mg/m³Formaldehyde concentration 1mg/m³The amount of non-methane total hydrocarbons is 2mg/m³The concentration of formaldehyde in the wastewater is 0.5 mg/L; the tail gas has no peculiar smell.

Table 2 examples 6-8 process parameters and treatment results

	The usage amount of the activated carbon powder	Outlet concentration of formaldehyde mg/m³	Outlet dust concentration mg/m³	Non-methane total hydrocarbon amount mg/m³	Concentration of formaldehyde in wastewater is mg/L
						Example 6	0	4	8	6	0.5
Example 7	1%	3.5	8	5	0.5
						Example 8	5%	1	8	2	0.5

Claims

1. A deep purification method for VOCs and particulate matters in dry tail gas of artificial board industry is characterized by comprising the following steps:

firstly, after wood fibers are recovered from a large amount of high-temperature flue gas generated in the artificial board production and drying process through two-stage cyclone dust removal, an adsorbent spraying device is utilized to spray adsorbent powder into the flue gas from a flue to perform adsorption reaction;

secondly, cooling and dedusting by using a wet electric precipitator to remove adsorbents and other particles in the flue gas, simultaneously spraying and washing by using high solubility of formaldehyde in water to remove more than 30% of formaldehyde, reducing the temperature of the flue gas to about 40 ℃, and feeding the wastewater generated by the wet electric precipitator into a filtering device;

thirdly, the flue gas enters a biological trickling filter to further deeply remove the residual VOCs, and the purified flue gas is discharged to the atmosphere;

fourthly, dissolving the VOCs which are not completely decomposed in the biological trickling filter in the washing liquid, mixing the washing liquid with the filtrate generated by the filter device, then feeding the mixture into an activated sludge reactor, carrying out aeration treatment by an activated sludge method, and carrying out biodegradation of VOCs such as formaldehyde and the like in a liquid phase;

the cleaning solution after purification treatment is returned to the biological trickling filter as a circulating liquid for recycling, and sawdust generated by the filtering device and waste sludge obtained by the activated sludge reactor are all conveyed to a heat energy center for incineration treatment.

2. The method for deeply purifying VOCs and particulates in dry tail gas of artificial board industry according to claim 1, wherein the dry tail gas contains dust particulates and VOCs, wherein the VOCs comprise one or more of aldehydes, ketones, phenols, aromatic hydrocarbons, terpenes and saturated alkanes, and mainly comprise formaldehyde.

3. The method for deeply purifying VOCs and particulate matters in dry tail gas of artificial board industry as claimed in claim 1, wherein the adsorbent is a powder adsorbent with a particle size of 100-400 meshes, and the usage amount of the adsorbent in flue gas is 50-5000mg injected per cubic meter of flue gas.

4. The method for deeply purifying VOCs and particulate matters in dry tail gas of artificial board industry according to claim 1, wherein the adsorbent is one or a mixture of activated carbon, molecular sieve, clay, metal organic framework material and resin.

5. The method for deeply purifying VOCs and particulate matters in dry tail gas of artificial board industry according to claim 1, wherein the wet electric dust collector is one of a conductive glass fiber reinforced plastic type or a metal polar plate type.

6. The method for deeply purifying VOCs and particulate matters in dry tail gas of artificial board industry according to claim 1, wherein a spray cooling layer is arranged at the bottom of the wet electric precipitator, process water is adopted as spray liquid, and the gas-to-gas ratio of the spray cooling liquid is 1-2L/m³。

7. The method for deeply purifying VOCs and particulate matters in dry tail gas of artificial board industry according to claim 1, wherein VOCs in the waste gas are absorbed by circulating spray liquid in the bio-trickling filter and are in contact reaction with a biological film on the surface of a filler, the spray liquid contains nutrient substances required for microbial production, and the gas-to-gas ratio of the circulating liquid is 2-5L/m³。

8. The method for deeply purifying VOCs and particulate matters in dry tail gas of artificial board industry as recited in claim 1, wherein 1-5% of activated carbon powder with a particle size of 200-400 mesh is added to the circulating spray liquid in the bio-trickling filter.

9. The method for deeply purifying VOCs and particulate matters in dry tail gas of artificial board industry according to claim 1, wherein the bio-trickling filter filler is one or more of biochar, bark, ceramsite, polyurethane, glass fragments, diatomite, resin and foam.