Four main methods for removing gaseous pollutants

1. Dust control technology

. High-voltage electrostatic precipitator technology

turns

Hz,

220

volt alternating current into

100

Direct current above kilowatts is applied to the corona electrode

(

Cathode

)

Form a non-uniform high-voltage electric field,

ionize the gas to produce a large number of negative ions and electrons,

charge the gas dust entering the electric field

Under the action of the electric field force, the charged dust tends to the opposite electrode.

Generally, the anode is the dust collecting electrode and falls into the dust hopper by rapping.

The dust hopper is discharged ,

Complete the purification and dust removal process.

The high-efficiency and low-resistance high-voltage electrostatic precipitator can be widely used in dust pollution situations in industries such as building materials,

metallurgy,

chemical industry, etc.

. It handles high dust concentration, and the dust removal effect is more obvious for

micron fine or high specific resistance dust. The series of products can meet the needs of drying with different air volumes. Dry equipment, flexible matching, suitable for dust control based on dryer exhaust gas characteristics.

. Cyclone dust removal technology

The working principle is that under the action of the fan, the dust-laden airflow enters the dust collector volute from the inlet at a high speed along the tangential

direction.

It performs a spiral rotating motion from top to bottom.

Under the action of centrifugal force, the dust particles are thrown towards the outer wall

and along the wall. Downspin,

As the cone shrinks, it turns to the axis,

returns due to resistance from the lower part,

spirals from bottom to top along the axis Rotate

and discharge through the core tube.

The dust particles on the outer wall are driven by gravity and downward movement of airflow,

fall into the ash hopper along the wall,

reaching the purpose of dust removal

Purpose. Since the cyclone dust collector relies on the inertial separation of dust particles, the dust removal efficiency is proportional to the particle size. Larger particle sizes have better dust removal effects;

Small particle sizes have poor dust removal effects and are generally treated

For dust above 20

microns, the dust removal efficiency ranges from

% to

． Bag dust removal technology

For particle

0.1

micron dust-containing gas, the dust removal efficiency can be as high as

%, Dryer exhaust gas dust removal selection

Using bag dust collector does not need to consider the problem of excessive emission concentration.

The anti-condensation fiberglass bag dust collector of the dryer is currently the ideal dust removal and purification equipment.

The equipment adopts microcomputer control, backflush in different chambers, regular dust cleaning, and is equipped with temperature detection display and over-temperature alarm device.

Adopts

CW300

—

FcA

Anti-condensation fiberglass filter bag, which can effectively prevent condensation on the filter bag and will not burn the filter bag.

. Wet dust removal technology

The dust-containing gas is sent into the lower part of the dust removal tower through the air duct by the induced draft fan. Due to the enlarged cross-section, the flow rate

reduces,

and becomes coarse. The granular dust first settles in the air flow.

The finer dust rises with the air flow.

The water droplets sprayed down move against the

direction of the dust air flow, and the dust is The wet weight continues to increase.

Under the action of gravity, it overcomes the lift of the air flow and drops into mud water.

It enters the sedimentation tank through the

lower pipe to achieve dust removal. purpose. Mud water generally undergoes

～

stages of circulation and sedimentation to become clean water, which is pumped

It can be recycled into the dust removal tower without causing secondary pollution.

． Wet dust removal technology

It consists of a settling chamber and high-voltage electrostatic dust removal process. The dust-containing exhaust gas is sent from the induced draft fan through the air duct at high speed

to the settling chamber, and collides with the wall. The air flow direction Change, causing the wind speed to decrease rapidly, the particle dust settles, and is discharged through the conveying equipment

The fine dust enters the electric field of the high-voltage electrostatic precipitator with the air flow,

in the ion Under the continuous bombardment of charged particles, they fly to the dust collecting pole and are collected and discharged. The purified gas is discharged into the atmosphere through the air duct.

． Cyclone + high-voltage electrostatic precipitator technology

This dust removal technology is that the dusty exhaust gas from the dryer enters the front-stage high-efficiency cyclone from the air duct

The dust collector performs pre-dust removal,

The dust is discharged from the ash hopper through the ash discharge equipment.

The dust concentration in the airflow is reduced.

Then it enters the secondary dust removal of the high-voltage electrostatic precipitator

The purified gas is discharged into the atmosphere by the air outlet, which improves the dust removal efficiency, makes the process flexible, and is safe and reliable.

Sulfur dioxide control technology

. Disposal method: Throw away the desulfurization products as solid waste

. Recycling method: Convert

SO2

into useful substances for recycling

. Wet removal

SO2

Technology

Limestone

Gypsum desulfurization technology

After the flue gas is first treated by the heat exchanger, it enters the absorption tower. In the absorption tower

SO2

directly mixes with the lime slurry Contact is removed by absorption. After treatment, the flue gas is processed by the demister and heat exchanger and then discharged through the chimney.

Part of the reaction liquid produced by absorption is recycled, and the other part is dehydrated and further processed to make gypsum.

Cyclone plate desulfurization and dust removal technology

According to the characteristics of the flue gas composition, the alkali liquid absorption method is adopted, and after swirling and spraying

Physical and chemical processes such as leaching, absorption, adsorption, oxidation, neutralization and reduction can achieve the purpose of desulfurization, dust removal,

dehumidification and flue gas purification through dehydration and defogging. Desulfurizer

Lime liquid method, double alkali method, sodium alkali method.

Semi-dry removal

SO2

Technology

Spray drying desulfurization technology

Using the principle of spray drying, after the absorbent (calcium oxide or calcium hydroxide) is sprayed into the absorption tower with a fixed nozzle,

on the one hand, the absorbent and A chemical reaction occurs in the flue gas,

to produce a solid product;

On the other hand,

the flue gas transfers heat to the absorbent,

The desulfurization reaction product is formed into dry powder.

The reaction product is separated at the bag dust collector

(or electric

dust collector) and further removed

SO2

Circulating

Circular fluidized bed flue gas desulfurization technology

Using the fluidized bed principle,

The desulfurizer is fluidized, and flue gas and desulfurizer undergo desulfurization reaction in a suspended state.

Dry removal

SO2

Technology

Activated carbon adsorption method

In the presence of oxygen and water vapor,

activated carbon adsorption can be used

SO2

Because activated carbon The catalytic effect on the surface

makes the adsorbed

SO2

be oxidized by the oxygen in the flue gas into

SO3

reacts with water and absorbs it to generate sulfuric acid; or it can be decomposed by heating

to generate high-concentration SO2,

This

SO2

can be used to make acid.

)

Catalytic oxidation method

Under the action of a catalyst,

SO2

can be oxidized to

SO3

and then use it.

It can be used to treat sulfuric acid tail gas and non-ferrous metal smelting

smelting tail gas.

The technology is mature and has become part of the acid-making process.

However, there are still some technical and economic problems that need to be solved when using this method to treat power plant boiler flue gas and oil refining tail gas.

Nitrogen oxide treatment technology

. Adsorption method

Uses the principle that the amount of adsorption of

NOx

by the adsorbent changes with changes in temperature or pressure

,

Control by periodically

changing the temperature or pressure in the reactor

The adsorption and desorption reaction of NOx

to achieve the purpose of removing

NOx

from the gas source

The purpose of separation. Commonly used adsorbents are molecular sieves, silica gel, activated carbon and ammonia-containing coal washing.

. Photocatalytic oxidation method

Uses

TiO2

The photocatalytic effect of semiconductor to remove

NOx

The mechanism is

: When TiO2

is irradiated by optical radiation exceeding

its band gap energy

The electrons in the valence band are excited

exceed the forbidden band and enter the conduction band

while in the valence band Produce

corresponding holes.

Electrons and holes migrate to different positions on the particle surface

The holes themselves have a strong ability to obtain electrons

can be taken away

taken

NOx

electrons in the system

It is activated and oxidized. The electrons react with water and oxygen in the air to form ·

and

O-2 < which have stronger oxidizing ability

/p>

etc.

is the final oxidation of

NOx

NO -3

The most important oxidizing agent.

． Liquid absorption method

Water absorption, acid absorption

(

Such as concentrated sulfuric acid, dilute nitric acid

)

, Absorption of alkali solution

(

Such as sodium hydroxide, hydroxide

potassium hydroxide, magnesium hydroxide

)

And molten metal salt absorption. There are also oxidation absorption methods, absorption reduction methods and complex absorption methods to treat nitrogen oxides mainly composed of nitrogen monooxide

You can first Carry out oxidation

Increase the oxidation degree of exhaust gas to

～

1. 3

After

absorb again.

. Absorption reduction method

Use sulfite, sulfide, thiosulfate, urea and other aqueous solutions to absorb nitrogen oxides

and

Reducing it to

Ammonium sulfite has strong reducing ability

can

NOx

is reduced to harmless nitrogen

while ammonium sulfite is

oxidized to sulfuric acid Ammonium

can be used as chemical fertilizer.

. Biological method

There are two mechanisms for microbial purification of nitrogen oxides: nitrification and denitrification.

Suitable denitrification bacteria can be used in the presence of external carbon sources

Use nitrogen oxides as nitrogen source

Assimilate nitrogen oxides into organic nitrogen compounds

Become part of the bacteria

(

Anabolism

)

The denitrifying bacteria themselves obtain growth and reproduction

Dissimilation and denitrification

(

Catabolism

)

will

NOx

eventually be reduced to

nitrogen.

IV.

Volatile organic pollutant control technology

. The absorption method

utilizes the characteristic that a certain VOC is easily soluble in a special solvent (or a solution with added chemicals).

This process is usually carried out in an absorption tower equipped with packing. Completed in.

． The condensation method allows high-concentration VOCs to pass through a condenser, and the gaseous VOCs are reduced below the boiling point,

condensed into liquid droplets,

and then fall to the lower part of the condensation zone by gravity. In the storage tank,

the liquid VOC is extracted from the storage tank,

can be recycled

for reuse.

． Adsorption method

Use certain porous solids

(adsorbents)

that have the ability to selectively adsorb certain components from the gas phase mixture to remove A method of VOC.

The most commonly used adsorbents currently used to treat VOCs are activated carbon and activated carbon fiber. The device used is a valve-switching two-bed (or multi-bed) adsorbent.

. Biological methods

Use microorganisms to decompose VOCs and are generally used to treat low-concentration VOCs.

. Plasma method

Non-equilibrium plasma is obtained at normal temperature and pressure through high-voltage pulse corona discharge with steep front and narrow pulse width (ns level),

That is to say, a large number of high-energy electrons and active particles such as O

are produced,

contaminate VOCs molecules

Carry out oxidation and degradation reactions to convert VOCs into harmless substances.

. Oxidation method

For toxic,

harmful,

VOCs that do not need to be recycled,

Thermal oxidation method is a more thorough method Processing methods.

The basic principle is that VOC reacts with O2 to produce CO2 and H20.

The chemical equation is as follows:

xHyOz＋bO2→cCO2＋dH2O

Generally, the following two methods are used to make the oxidation reaction proceed smoothly:

The first is heating,

The exhaust gas containing VOC reaches the temperature required for the oxidation reaction;

The second is to use a catalyst, and the oxidation reaction

should be carried out on the surface of the catalyst at a lower temperature.

Odor control technology

. The microbial decomposition method

uses circulating water flow to contain pollutants in malodorous gases in water, and then cultivates microorganisms in water culture beds

and removes the pollutants in the water. Pollutants are degraded into low-harm substances,

The deodorization efficiency can reach

70%

But it is affected by microbial activity,

culture The microorganisms that come out can only process one or several gases with similar properties.

In order to improve the processing efficiency and stabilize the operation,

must add chemicals frequently, Controlling

values, temperature, etc. will cause relatively high operating costs and a lot of labor input, and

it will take a long time for organisms to die. Reculture

. Plasma method

Uses the developed internal void structure of activated carbon and the principle of huge specific surface area to adsorb the odorous gas molecules passing through the activated carbon

pool.

The initial treatment efficiency can reach

65%

But it is very easy to saturate,

usually expires within a few days,

needs frequent replacement,

And it is necessary to find a way to deal with waste activated carbon.

The operation and maintenance costs are very high.

It is suitable for low concentration and large air volume gases.

For alcohol

The effect is more obvious for sulfate and fat, but the effect is not obvious for exhaust gas with high humidity, and it is easy to cause secondary environmental pollution.

． Plasma method

The principle of using high-voltage electrodes to emit ions and electrons to destroy the structure of odor molecules and bombard the odor molecules in the exhaust gas

Thereby cracking the odor molecules,

The purification effect of low-concentration odorous gases is obvious,

under normal operation conditions, it can reach

80%

The above can handle mixed gases composed of a variety of odors, is not affected by humidity, and has no secondary pollution; but it uses a lot of electricity

and requires cleaning, operation and maintenance. The cost is high, and high concentrations of flammable and explosive gases can easily cause explosions.

. The plant spraying liquid deodorization method

sprays plant extract liquid into the space where the odorous gas is generated to neutralize and absorb the odorous gas

to achieve the purpose of deodorization. The deodorization effect is low concentration It can reach

50%

. Different spray liquids are selected for different odors.

Plant spray liquids need to be added frequently, and equipment maintenance and operation maintenance are required. The cost is high and it is easy to cause secondary pollution.

．

Photolysis purification method

Using high-energy

ultraviolet light in photolysis purification equipment Within, it cracks and oxidizes the molecules of odorous substances

chains, changes the material structure, and cracks and oxidizes high-molecular pollutants into low-molecular harmless substances. Its deodorization efficiency can be

99%

The deodorization effect greatly exceeds the odorous substance emission standards promulgated by the country

in 1993

(

GB14554-93

)

Can handle ammonia,

hydrogen sulfide,

methyl mercaptan, methyl sulfide, benzene, styrene, carbon disulfide , trimethylamine, dimethyl disulfide and other high-concentration mixed gases, the internal

light source can be used for three years,

the equipment life is more than ten years,

Purification technology is reliable and very stable.

Purification equipment does not require daily maintenance.

It can be used normally by just connecting the power supply. It has low operating cost and no secondary pollution.

Halide gas control technology

. Consider its recycling value first.

For example, hydrogen chloride gas can be recycled to produce hydrochloric acid.

Fluorine-containing waste gas can produce inorganic fluoride

substances and white carbon black.

. Physical and chemical methods such as absorption and adsorption are relatively mature in resource recycling and advanced halide treatment.

Priority is given to using physical and chemical methods to treat halide gases.

． Alkali liquid absorbs chlorine or hydrogen chloride (hydrochloric acid mist) waste gas; water, lye or sodium silicate absorbs fluorine-containing waste gas; lime water washes low-concentration hydrogen fluoride waste gas;

Water absorbs hydrogen fluoride to generate hydrofluoric acid,

at the same time, silica gel is generated.

Be sure to clean it at any time to prevent system blockage.

. The alumina powder adsorption method should be used to control fluorine-containing waste gas in the electrolytic aluminum industry.