CN102240500A - System and process for desulfuration and denitration by pure oxygen dielectric barrier discharge in flue - Google Patents

Abstract

The pure oxygen dielectric barrier discharge desulfurization and denitrification system and process in the flue belong to the technical field of flue gas desulfurization and denitrification in thermal power plants. The air is separated by the air separator, and the separated oxygen enters the dielectric barrier discharge reactor. In the reactor, _O2 molecules are activated, cracked or ionized to generate strong oxidizing free radicals O or _O3, etc., and the oxidation after discharge treatment The reactive gas is quickly and fully mixed with the flue gas through the injection device and then reacted to oxidize the NO and SO ₂ in the flue gas into high-valence nitrogen oxides and sulfur oxides. The oxidized flue gas enters the lye absorption tower and passes through the lye Flue gas is washed to achieve the purpose of removing nitrogen oxides and sulfur oxides. This process is aimed at pure oxygen discharge, the cost of generating free radicals is low, the free radicals mix with flue gas early, the removal efficiency of pollutants is high, and it has higher economic benefits, and nitrate, nitrite and sulfate are used as products Recycling also enables green recycling of pollutants.

Description

Pure oxygen dielectric barrier discharge desulfurization and denitrification system and process in flue

technical field

The invention belongs to the technical field of flue gas desulfurization and denitrification in thermal power plants, and in particular relates to a pure oxygen dielectric barrier discharge desulfurization and denitrification system and process in a flue.

Background technique

SO ₂ and NOx in the flue gas of thermal power plants are the main gas pollutants in the atmosphere, which not only bring various hazards to the human body, but also have a great impact on the growth of animals and plants, as well as on the weather and climate , so measures must be taken to control it. An excellent flue gas purification technology not only needs to meet the high-efficiency removal rate, but also considers the technical economy and the simple operability of the system. At present, many researchers agree that the integration of SO ₂ and NOx chemical removal.

At present, thermal power plants generally use two sets of devices to desulfurize and denitrify the flue gas. The flue gas desulfurization mainly adopts the wet flue gas desulfurization process (Wet-FGD), and the flue gas denitrification uses _NH3 as the reducing agent. The Selective Catalytic Reduction (SCR) technology, in which the wet flue gas desulfurization process uses limestone or lime as the desulfurization absorbent, the limestone is crushed and mixed with water, and ground into powder to make the absorption slurry. In the absorption tower, the SO ₂ in the flue gas reacts with the CaCO ₃ in the slurry and the blown oxidizing air to form calcium sulfate dihydrate, that is, gypsum, so that the SO ₂ in the flue gas can be removed. The main reaction equation in the wet desulfurization process is:

2CaCO ₃ +H ₂ O+2SO ₂ →2CaSO ₃ 1/2H ₂ O+2CO ₂ ↑

2CaCO ₃ 1/2H ₂ O+O ₂ +3H ₂ O→2CaSO ₄ 2H ₂ O

Selective catalytic reduction technology refers to the reduction of NOx to harmless NOx at the flue gas temperature between the economizer and the air preheater in the presence of _O2 and a heterogeneous catalyst, using _NH3 as a reducing agent nitrogen and water. The main reaction equation is as follows:

4NO+4NH ₃ +O ₂ →4N ₂ +6H ₂ O

2NO ₂ +4NH ₃ +O ₂ →3N ₂ +6H ₂ O

NO+NO ₂ +2NH ₃ +O ₂ →2N ₂ +3H ₂ O

The invention patents with publication numbers CN1768902 and CN1923341 respectively introduced a method for ozone oxidation and denitrification of boiler flue gas and a device and method for simultaneous desulfurization and denitrification of coal-fired boiler flue gas by ozone oxidation. In the patents, the ozone generator is placed outside the low-temperature flue , the generated ozone is sprayed into the flue and mixed with the flue gas to oxidize nitrogen oxides and sulfur oxides, and the tail is absorbed by lye. This process can obtain a relatively ideal removal efficiency, but in the process of industrial application, the generated Ozone needs to go through a long distance to react with flue gas, resulting in a large amount of ozone loss and increasing the cost of desulfurization and denitrification.

At present, the desulfurization and denitrification system of thermal power plants in my country basically adopts the wet desulfurization process combined with SCR denitrification. Although the simultaneous installation of the two systems can guarantee the desulfurization and denitrification efficiency, it also brings inevitable shortcomings:

(1) The system is complex and requires a large amount of operation and maintenance;

(2) The initial investment cost is high, and the equipment cost is high;

(3) Due to the high sulfur content in coal combustion in my country, it is easy to cause catalyst poisoning in the SCR system and dust accumulation and blockage of the air preheater;

(4) It is not conducive to the transformation of old power plants.

Although the removal efficiency of the ozone desulfurization and denitrification process is high, because the ozone generator is set outside the flue, after the ozone is generated, it takes a certain distance to enter the flue and mix with the flue gas, and the strong oxidizing ozone is mixed with the flue gas. Before the mixed reaction, it will partially react with other substances, and the ozone itself will also partially decompose, resulting in unnecessary consumption of ozone, corrosion of equipment and pipelines, and high operating costs.

Contents of the invention

The invention provides a pure oxygen dielectric barrier discharge desulfurization and denitrification system and process in a flue that can realize the recovery and utilization of nitrogen oxides and sulfur oxides and improve the economic benefits of desulfurization and denitrification.

The structure of the system described in the present invention is as follows: the inlet end of the electrostatic precipitator is connected with the flue gas outlet, the outlet end of the electrostatic precipitator is connected with the original flue gas side inlet of the gas-gas heater through the flue inlet, and the gas-gas heater is originally The flue gas side outlet is connected to the flue gas inlet at the lower part of the lye absorption tower through the flue exhaust duct; the dielectric barrier discharge reactor is arranged in the flue inlet duct or the flue exhaust duct, and the inlet end of the dielectric barrier discharge reactor is connected to the air separator The bottom of the lye absorption tower is communicated with the lye liquid storage tank by pipeline, and the top of the lye absorption tower is provided with a spray device, and the liquid outlet of the lye liquid storage tank is communicated with the spray device by a pipeline and a peristaltic pump; The top of the lye absorption tower is provided with a gas outlet, which is connected to the inlet port of the net flue gas of the gas-gas heater through a pipe, and the outlet port of the net flue gas of the gas-gas heater is connected to the chimney.

In the lye absorption tower, a demister is arranged above the spraying device.

The outlet of the dielectric barrier discharge reactor is connected to the nozzle through a Venturi tube. The nozzle has a gradually expanding structure along the axial direction, and the head of the nozzle is a spherical cap structure, and 5 ball caps are evenly distributed in a "ten" shape. The five injection pipes are respectively located at the four endpoints and the center of the "ten" character, which are perpendicular to the spherical crown surface and reduce towards the exit direction.

The divergence angle α of the outlet nozzle is 25°-60°, and the axial length L is 30-50mm.

The length of the injection pipe is 10-20mm, the diameter of the outlet of the "ten" central injection pipe is 8-15mm, and the diameter of the outlets of the four injection pipes around is 5-10mm.

The present invention also provides a flue gas desulfurization and denitrification process based on the system, which is divided into the following steps:

(1) The flue gas enters the flue after being dedusted by the electrostatic precipitator; the treated flue gas is heat-exchanged with the clean gas absorbed by the lye through the gas-gas heater, and the temperature is lowered to 40-60°C, and then passed through The exhaust flue enters the lye absorption tower;

(2) After the air is separated by the air separator, the oxygen enters the dielectric barrier discharge reactor placed in the flue inlet or exhaust duct, and the discharge power in the reactor is controlled by adjusting the voltage and frequency of the high-voltage power supply. A uniform and stable discharge occurs in the reactor, where the voltage adjustment range is 6-20kV, the frequency adjustment range is 7-15kHz, and the flow rate of oxygen in the dielectric barrier discharge reactor is 20%-60% higher than the flow rate of flue gas in the flue ;The discharge produces a large number of high-energy electrons, which are ejected from the nozzle of the dielectric barrier discharge reactor;

(3) Under the action of high-energy electrons, O ₂ and H ₂ O molecules are activated, cracked or ionized, producing highly active oxidizing particles including O, O ₃ , OH, and HO ₂ , making the smoke in the flue gas NO, SO ₂ oxidation, the oxidation product of NO is mainly NO ₂ and a small amount of HNO ₃ , HNO ₂ and other high-valence nitrogen oxides, the oxidation product of SO ₂ is mainly SO ₃ , in the case of high water vapor content will further generate sulfuric acid;

(4) lye is configured, and lye enters the lye absorption tower from the upper part of the absorption tower through the spray device through the peristaltic pump, and is discharged from the lower part of the tower after reacting with flue gas in the lye absorption tower, and enters the lye liquid storage tank; The flue gas treated by the dielectric barrier discharge reactor enters from the lower part of the lye absorption tower, and is discharged from the top of the lye absorption tower after reacting with the lye;

(5) The low-temperature flue gas discharged from the lye absorption tower is sent to the gas-gas heater, exchanged heat with the high-temperature flue gas, and then sent to the chimney for discharge.

The lye in the step (2) is a NaOH solution containing KOH, Na ₂ CO ₃ , Ca(OH) ₂ , CaCO ₃ , wherein the sum of NaOH, KOH in the lye and SO ₂ in the flue gas and the oxidized The ratio of the molar value of the sum of NO ₂ is 1.8 to 2.6, and the ratio of the molar value of the sum of Na ₂ CO ₃ , Ca(OH) ₂ , CaCO ₃ to the sum of SO ₂ in the flue gas and the sum of oxidized NO ₂ is 0.9 ~1.3.

After the lye reacts with the flue gas, it flows into the lye storage tank to obtain a mixed solution of nitrate, nitrite, and sulfate. After evaporation, crystallization, and separation processes, the corresponding nitrate, nitrite, and sulfuric acid are obtained. Salt.

The beneficial effects of the present invention are:

(1) Simplified desulfurization and denitrification equipment and process flow;

(2) When burning high-sulfur coal, it will not cause wear of the tail flue and dust accumulation and blockage of the air preheater;

(3) Sulphate, nitrate and nitrite are recycled as products, which realizes the green recycling of resources and increases economic benefits;

(4) The cost of generating free radicals is low for pure oxygen discharge; the DBD reactor is placed in the flue, and the free radicals can quickly mix and react with the flue gas through the injection device, which improves the removal efficiency.

Description of drawings

Fig. 1 is the structural representation of dielectric barrier discharge reactor in gas-gas reactor inlet flue;

Fig. 2 is the structural representation of dielectric barrier discharge reactor in gas-gas reactor outlet flue;

Fig. 3 is the sectional view of outlet nozzle of dielectric barrier discharge reactor;

Fig. 4 is a schematic diagram of the spray pipe distribution of the nozzle.

Labels in the figure:

1-Electric precipitator; 2-Dielectric barrier discharge reactor; 3-Air separator; 4-Inlet flue; 5-Gas-gas heater; 6-Exhaust flue; liquid reservoir; 9-mist eliminator; 10-chimney.

Detailed ways

The present invention provides a pure oxygen dielectric barrier discharge desulfurization and denitrification system and process in a flue. The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

As shown in Figure 1 or Figure 2, the inlet end of the electrostatic precipitator 1 is connected to the flue gas outlet, and the outlet end of the electrostatic precipitator 1 is connected to the original flue gas inlet end of the gas-gas heater 5 through the flue inlet 4. The original flue gas outlet end of the gas heater 5 is connected to the flue gas inlet at the bottom of the lye absorption tower 7 through the flue exhaust duct 6; The inlet end of the discharge reactor 2 is connected with the air separator 3; the bottom of the lye absorption tower 7 is communicated with the lye liquid storage tank 8 through a pipeline, and the top of the lye absorption tower 8 is provided with a spray device, and the top of the spray device is provided with Demister 9; the liquid outlet of lye liquid storage tank 8 communicates with the spray device through pipeline and peristaltic pump; the top of lye absorption tower 7 is provided with gas outlet, through pipeline and gas-gas heater 5 to clean smoke The inlet end of the gas is connected, and the outlet end of the gas-gas heater 5 clean flue gas is connected with the chimney 10 .

The outlet of the dielectric barrier discharge reactor 2 is connected to the nozzle through a venturi tube. As shown in Figure 3 and Figure 4, the nozzle has a gradually expanding structure along the axial direction, and the head of the nozzle is a spherical cap structure. Five nozzles are evenly distributed on the spherical cap and arranged in a "ten" shape, respectively perpendicular to the direction of the spherical cap surface. The jet tubes are reduced in the exit direction, and the five jet tubes are respectively located at the four ends and the center of the "ten". The gradual divergence angle α of the outlet nozzle is 25°-60°, and the axial length L is 30-50mm. The length of the injection pipe is 10-20mm, the diameter of the outlet of the "ten" central injection pipe is 8-15mm, and the diameter of the outlets of the four injection pipes around is 5-10mm.

The flow of the system is as follows: first, the nitrogen in the air is separated by the air separator, and the remaining oxygen is introduced into the dielectric barrier discharge reactor placed in the flue, and by adjusting the voltage of the power supply (adjustment range: 7～15kHz) to control the discharge power in the reactor, so that a relatively uniform and stable discharge occurs in the reactor, and the discharge generates a large number of high-energy electrons. Under the action of high-energy electrons, the oxygen molecules in the reactor are activated and cracked Or ionization, producing highly active oxidizing particles such as O, O ₃ etc., quickly flow out of the nozzle and mix with the flue gas in the flue, reducing the loss of active groups along the way, and oxidizing NO and part of SO ₂ in the flue gas , the oxidation products of NO are mainly NO ₂ , NO ₃ and a small amount of other high-valence nitrogen oxides, and the oxidation products of SO ₂ are mainly SO ₃ , and sulfuric acid will be further generated in the case of high water vapor content. The dielectric barrier discharge reactor is wrapped with a wear-resistant sleeve, and the oxygen flow rate in it should be selected in an appropriate range. If the flow rate is too high, the yield of highly active free radicals will be reduced, and if the flow rate is too low, the disturbance between the outlet and the flue gas will be weakened, affecting both Therefore, the removal efficiency of nitrogen oxides and sulfur oxides will be affected if the oxygen flow rate is too high or too low. It is stipulated that the oxygen flow rate in the dielectric barrier discharge reactor is 20% to 60% higher than the flue gas flow rate in the flue. The relevant reaction equations are as follows:

NO+O+M→NO ₂ +M,

O ₃ +NO→NO ₂ +O ₂ ,

O ₃ +NO ₂ →NO ₃ +O ₂ ,

NO ₃ +NO→2NO ₂ ,

SO ₂ +O+O ₂ →SO ₃ +O ₂ ,

O ₃ +SO ₂ →O ₂ +SO ₃ ,

H ₂ O+SO ₃ →H ₂ SO ₄ ,

The fully reacted flue gas is introduced into the lye absorption tower. Configure NaOH solution containing KOH, Na ₂ CO ₃ , Ca(OH) ₂ , CaCO ₃ as lye for flue gas treatment, wherein the sum of NaOH, KOH in lye and SO ₂ in flue gas and oxidized NO ₂ The molar ratio of the sum is 1.8-2.6, and the molar ratio of the sum of Na ₂ CO ₃ , Ca(OH) ₂ , CaCO ₃ to the sum of SO ₂ and oxidized NO ₂ in the flue gas is 0.9-1.3. The lye enters the tower from the upper part of the absorption tower through the spray device through the peristaltic pump, and is discharged from the lower part of the tower after reacting with the flue gas in the tower, and enters the liquid storage tank. The flue gas treated with oxidizing gas enters from the lower part of the tower, fully reacts with the lye through the absorption tower, and then is discharged from the top of the tower. After the lye is absorbed, the nitrate, sulfate and other solutions generated are produced through evaporation, crystallization, separation and other processes. Qualified products are then packaged and installed for sale, creating economic benefits and realizing resource recycling.

In this combined desulfurization and denitrification process, oxygen is first oxidized by low-temperature plasma, and then mixed with flue gas. The oxidized flue gas is further absorbed by lye, and finally the treated flue gas is discharged into the atmosphere. The removal rate of NOx It can reach more than 80%, and the removal rate of SO ₂ can reach more than 90%.

Implementation case 1: As shown in Figure 1, the dielectric barrier discharge reactor is placed in the flue after the electrostatic precipitator, and the number of dielectric barrier discharge reactor monomers and the flow rate of oxygen passing through the reactor are selected according to different unit loads , The reactor is evenly arranged in the flue, so that the ejected oxidizing gas can fully mix and react with the flue gas. The alkali liquid in the absorption tower adopts one of NaOH, KOH, Na ₂ CO ₃ , Ca(OH) ₂ and CaCO ₃ or a mixture of several of them.

Example 2: As shown in Figure 2, the dielectric barrier discharge reactor is placed in the exhaust duct between the gas-gas heater and the inlet of the lye absorption tower, and the reduction of the flue gas temperature is conducive to the oxidation of NO. The number of dielectric barrier discharge reactor monomers and the flow rate of oxygen passing through the reactor are selected according to the different loads of the unit. The reactors are evenly arranged in the flue, so that the oxidizing gas ejected can fully mix and react with the flue gas. The alkali liquid in the absorption tower adopts one of NaOH, KOH, Na ₂ CO ₃ , Ca(OH) ₂ and CaCO ₃ or a mixture of several of them.

Claims (8)

1. pure oxygen dielectric barrier discharge system for desulfuration and denitration in the flue, it is characterized in that, the arrival end of electric cleaner is connected with exhanst gas outlet, the port of export of electric cleaner is connected by the former fume side inlet of flue and gas-gas heater, and the former fume side outlet of gas-gas heater is connected by the smoke inlet of smokejack with bottom, alkali lye absorption tower; The dielectric barrier discharge reactor is arranged in described flue or the smokejack, and the arrival end of dielectric barrier discharge reactor is connected with air separator; The bottom on alkali lye absorption tower is communicated with the alkali lye liquid storage tank by pipeline, and the top on alkali lye absorption tower is provided with spray equipment, and the liquid outlet of alkali lye liquid storage tank is communicated with described spray equipment by pipeline and peristaltic pump; The top on alkali lye absorption tower sets out gas port, is connected by the clean smoke inlet end of pipeline and gas-gas heater, and the clean smoke outlet of gas-gas heater is connected with chimney.

2. pure oxygen dielectric barrier discharge system for desulfuration and denitration in the flue according to claim 1 is characterized in that in the described alkali lye absorption tower, the top of spray equipment is provided with demister.

3. pure oxygen dielectric barrier discharge system for desulfuration and denitration in the flue according to claim 1, it is characterized in that, the outlet of described dielectric barrier discharge reactor is connected with nozzle by Venturi tube, this nozzle is the flaring structure along axis direction, the spout head is a spherical cap structure, evenly distribute on the spherical crown 5 by " ten " font arrange, respectively perpendicular to the playpipe that reduces to Way out of spherical crown surface, 5 playpipes lay respectively at four end points and the center of " ten " word.

4. pure oxygen dielectric barrier discharge system for desulfuration and denitration in the flue according to claim 3 is characterized in that the flaring angle [alpha] of described outlet nozzle is 25 °-60 °, and axial length L is 30-50mm.

5. pure oxygen dielectric barrier discharge system for desulfuration and denitration in the flue according to claim 3, it is characterized in that, the length of described playpipe is 10-20mm, and the diameter of " ten " word central-injection pipe outlet is 8-15mm, and four playpipe outlet diameters are 5-10mm all around.

6. the flue gas desulfurization and denitration technique based on the described system of claim 1 is characterized in that, is divided into following steps:

(1) enters flue after the dedusting of flue gas process electric cleaner; After the pure qi (oxygen) of the flue gas of handling after gas-gas heater and alkali lye absorb carries out heat exchange, reduce temperature to 40～60 ℃, enter the alkali lye absorption tower by smokejack then;

(2) after air separates through air separator, oxygen enters the dielectric barrier discharge reactor that is placed in described flue or the smokejack, by the voltage of regulating high voltage source, the discharge power in the FREQUENCY CONTROL reactor, even, stable discharge takes place in reactor, wherein the voltage-regulation scope is 6～20kV, frequency-tuning range is 7～15kHz, and velocity ratio flue gas flow velocity flue in the high 20%-60% of oxygen in the dielectric barrier discharge reactor; The high energy electron that discharge generation is a large amount of, and from the ejection of the nozzle of dielectric barrier discharge reactor;

(3) under the effect of high energy electron, O ₂, H ₂The O molecule is activated, cracking or ionization, produces to comprise O, O ₃, OH, HO ₂Highly active oxidisability particle interior makes NO, SO in the flue gas ₂Oxidation, the oxidation product of NO is mainly NO ₂And a spot of HNO ₃, HNO ₂With the nitrogen oxide of other high valence states, SO ₂Oxidation product be mainly SO ₃, under the water vapour content condition with higher, can further generate sulfuric acid;

(4) configuration alkali lye, alkali lye by peristaltic pump by top, absorption tower in spray equipment enters the alkali lye absorption tower, in the alkali lye absorption tower with behind the smoke reaction, discharge by the tower bottom, enter the alkali lye reservoir; Flue gas through the dielectric barrier discharge reactor for treatment is entered by bottom, alkali lye absorption tower, and is discharged by top, alkali lye absorption tower behind the alkaline reaction;

(5) low-temperature flue gas of discharging from the alkali lye absorption tower is sent in the gas-gas heater, and delivers to chimney after the high-temperature flue gas heat exchange and discharges.

7. flue gas desulfurization and denitration technique according to claim 6 is characterized in that, the alkali lye in the described step (2) is for comprising KOH, Na ₂CO ₃, Ca (OH) ₂, CaCO ₃NaOH solution, wherein NaOH in the alkali lye, KOH's and with flue gas in SO ₂With NO after the oxidation ₂And the mole value ratio be 1.8～2.6, Na ₂CO ₃, Ca (OH) ₂, CaCO ₃And with flue gas in SO ₂With NO after the oxidation ₂And the mole value ratio be 0.9～1.3.

8. flue gas desulfurization and denitration technique according to claim 6, it is characterized in that, behind described alkali lye and the smoke reaction, flow in the alkali lye reservoir, obtain nitrate, nitrite, sulfate mixed solution, through pervaporation, crystallization, separation circuit, obtain corresponding nitrate, nitrite and sulfate.

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