Method of removing so2and noxfrom combustion flue gases and a device for its implementation

 

(57) Abstract:

The invention can be used for removal of acid pollutants from flue gases by radiation exposure. The method is carried out by irradiation of flow of the combustion gases electron beam, as well as the influence of microwaves in the form of a continuous or pulsed stream. The device comprises a reactor, provided with at least one source of an electron beam and at least one source of microwaves. The invention improves the cleaning efficiency and reduce energy costs. 2 C. and 7 C. p. F.-ly, 4 Il., table 4.

The invention relates to methods for removal of acid pollutants such as SO2and NOxfrom flue gases by radiation exposure, particularly from industrial flue gases emitted heating plants and power plants, as well as to a device for the removal of SO2and NOxfrom industrial flue gases.

Air pollution caused by gaseous products of combustion of coal and fossil fuel power plants, represents a serious global problem. A typical thermal power plant capacity of 500 MW throws 3 - 5 is. For the treatment of industrial flue gases developed a number of effective ways.

The removal of acid pollutants from flue gases by chemical methods based on absorption of acidic pollutants in alkaline solutions, i.e., in the lime sediment. Such wet cleaning methods lead to the formation of huge amounts of sediment. Besides, this way you can only remove SO2. In the combustion gases remain significant amount of NOxin particular NO, which together with freon affect the formation of the ozone hole, so there is a need to build a separate installation for removal from flue gases NOx. Such installations are based on different principles, mainly in the catalytic reduction.

A known method of removing SO2and NOxfrom the stream of industrial flue gases, comprising the irradiation by the electron beam in the reaction zone.

It is also known a device for implementing such a method that contains the reactor, provided with at least one source of a beam of electrons (PL, A, 284996).

The method using irradiation can destroy 95% of SO2and 80% of NOxin one setting. However, in this method, full the high efficiency reach due to the introduction of moisture and some quantities of ammonia before irradiation. This known method is based on the simultaneous reactions that are initiated by radiation and lead to the formation of solid products. These products are then used as fertilizer.

Irradiation of flue gas in the presence of water vapor leads to the formation of atomic and molecular radicals and free electrons. The radicals OH., O.and H2O.oxidizes SO2and NOxto SO3and NO2and further in the presence of water formed H2SO4and HNO3. Finally, these compounds react with ammonia, resulting in the formation of solid products NH4NO3and (NH4)2SO4that can be used as fertilizer. The process is carried out at a temperature of from 65 to 100oC.

Optimization of temperature, degree of hydration and the ammonia content in accordance with the gas composition and flow rate has a negligible effect on the removal efficiency of acid pollutants from flue gas.

When this research was conducted, aimed at improving the efficiency of methods based on the use of radiation. At the core of these methods is the use of electrostatic and electromagnetic who himicheskoi reaction.

In particular, in the method described in patent DD-243-216A1, proposed use (in addition to the electron beam having an energy of 50 - 500 Kev) of the electrostatic field strength of 100 V/cm in order to reduce the energy consumption during the process. This method can improve the cleaning efficiency.

However, the disadvantage of this method is that in the reactor it is necessary to apply an additional grid of electrodes. These electrodes are located at a distance of 16 cm from each other in order to form the electric field in the reaction zone. Solid reaction products and fly ash formed during irradiation and after irradiation ceased, tend to Deposit on the electrodes and to block the reactor.

The above disadvantage can be overcome by using the method described in the patent JO-1099-633-A, in which irradiation of the reactor used a laser beam (ArF Laser with a wavelength of 193 nm) and in addition enter CH3OH. CH3OH excite with the help of light for the formation of radicals OH.that link NO and SO2in solids that must be removed. The use of a laser beam yields positive results, but industrial is m high due to the fact, the presence of water limits the penetration of ultraviolet radiation inside the reactor. In addition, it is difficult to ensure that the action of the light beam distributed in space uniformly, and this is necessary when using connection CH3OH.

The problem of energy saving is especially important in industrial settings, as 2 to 4 percent of all energy produced by the power plant is used for cleaning flue gases from the acid pollutants.

The basis of the invention is to create a method of removing SO2and NOxfrom the stream of industrial flue gases, which would reduce energy consumption to improve the efficiency of the process of cleaning the flue gases, as well as to create a reliable and easy to use device for implementing this method.

The objective of the invention is solved in that in the method of removing SO2and NOxfrom the stream of industrial flue gases, comprising the irradiation by the electron beam in the reaction zone, according to the invention, the flow of these flue gases is exposed to microwaves applied in a continuous or pulsed stream.

However, alsoobe the P CLASS="ptx2">

The reaction product may be obtained in solid or liquid form and used as fertilizer.

Thus preferably in the area of electron beam irradiation to enter the flow of pulsed microwave energy having an electric field strength Ei> 300 V/cm in the length () of the pulse is between 10-7and 10-3and the repetition frequency f > v/kwhere v is the velocity of the gas stream,k- the length of the irradiation zone, and the pressure inside the reactor is close to atmospheric pressure, and the pulse frequency microwave energy is 200 - 10000 MHz.

It is desirable in the pulse stream additionally to introduce a continuous flow microwave energy having an electric field intensity of 300 V/cm and a frequency of 200 to 10000 MHz.

In addition, preferably e-beam is realized in the form of a pulsed electron beam with duration) of the pulse is between 10-8and 10-5c, and to the pulses of the electron beam and microwave were synchronized so that preferably the pulses of the electron beam was ahead of pulses of microwaves, and the combustion gas passing through the reaction zone first contactor the I removal of SO2and NOxfrom the stream of industrial flue gases containing reactor, provided with at least one source of a beam of electrons, according to the invention the reactor is further provided with at least one source of microwaves.

While it is desirable that the source of microwaves represented a means to enter the flow of microwave energy into the reactor through its wall at a right angle to the direction of the electron beam through the input and output rectangular waveguides, each of which is attached to the reactor end area with its narrow side.

In addition, it is preferable to equip the device with two additional waveguides attached to the wall of the chamber emitter is located between the reactor and accelerator, by means of the microwave window is permeable to microwave energy, formed on end parts of the narrow side walls of the additional waveguides, and these waveguides should connect each to the appropriate of the two branches 3-DV device, with one tap is connected to the microwave load, and the other to attach to a microwave generator and a microwave load adapted to poglosheniya from 3-DV device.

An important feature of the method according to the invention, is a secondary use of free electrons that excite during irradiation and injected into the system in the form of a beam of accelerated electrons with the aim to create oxidizing radicals, as well as the application of microwave energy to increase the number of free electrons and to maintain their energy at an optimal level. This leads to a decrease in the average dose rate of absorption of the electron beam and reduces the cost of the accelerators at the same effective cleaning.

The maximum used in the present invention, the dose absorption of the electron beam is 1 to 20 kGy. In practice, this dose is established in accordance with the desired results. For example, when you need approximately 50% reduction of pollutants, the dose may be 5 to 10 kGy.

The amount of ammonia added to the flue gas in the reactor depends on the content SO2and NOxand approximately corresponds to the stoichiometric amount. The water content should preferably be 8 - 12% vol. and can be optimized in accordance with the situation in the system.

Further izopet>Fig. 1 depicts schematically shown in example a reactor with a concentrated electron beam according to the invention;

Fig. 2 - the same as in Fig. 1, a view in plan;

Fig. 3 is schematically shown in the example reactor electron accelerator in the form of a linear scanning system mounted on the reactor in accordance with the present invention;

Fig. 4 is a block diagram of the experimental setup, according to the present invention.

Before entering the reactor according to the standard procedure applied during irradiation, residual gas processed (filtered particles of fly ash, produce hydration, introducing ammonia). Additional introduction of microwave energy frequency 200 - 10 MHz in the reaction zone, which already is irradiated by an electron beam, increases the number of free electrons and free radicals in this area. By this measure increases the removal efficiency of acid pollutants from flue gases. The resulting process of the solid products collected on the filters. Electric flow component of the microwave energy is involved in the process, occurring in the reaction zone, where it is exposed to flue gases. Microwave energy is injected to the accelerated electrons. Connecting elements are arranged on the narrow sides of the waveguide and are shaped like rectangles. The device, which can be equipped with two additional waveguides increases the cleaning efficiency. In an optimal embodiment, microwave energy is introduced into the reactor perpendicular to the axis of the reactor, but may be directed at any other angle, depending on the geometric shape of the reactor design. As shown in Fig. 1 to 3, the flow of microwave energy is introduced into the reactor 4 through the side wall in the same manner as the above-mentioned electron beam through the input and output rectangular waveguides 5, the connecting elements are made in the narrow walls of the waveguide. The presence of pulses of microwave energy leads to an increase in the number of free electrons and free radicals in this volume, which helps to make the cleaning process more effective.

In order to maintain the energy of the free electrons, two additional rectangular waveguide 3 set the camera emitter 2 electrons between the reactor 4 and ucitelem 1 and 1'. Fasteners are in the narrow walls of the waveguide, and the waveguide is attached to the two outlet branches 3-dB device prisposoblencev load (in this device, the microwaves are absorbed without reflection), and the other outlet is attached to the generator of microwaves. A steady stream of microwave energy supports energy of free electrons involved in the process. Generation of free radicals and the cleaning process is more efficient than the known method (DD243218 A1), despite the fact that no additional electrodes in the reactor is not set.

According to the invention in addition to the electron beam in the reactor using a flow of microwave energy of a frequency of 200 to 10000 MHz. Flue gas at the inlet of the reactor must be cleaned of fly ash and hydrated as using other methods of exposure. The use of microwave energy increases the number of radicals OH.due to the presence of a greater number of free electrons that are expressed by the following formula:

,

where

Neo- the number of free electrons to the application of microwave energy; vi- the number of ionizing collisions, depending on the strength of the electric field inside a pulse of microwave energy; t is the time.

The use of microwave pulses leads to the multiplication of the free electrons, while a steady stream of microwave energy podderjivaet eneonatal in Fig. 4. Installation for removal of SO2and NOxfrom flue gases was established on the basis of corites ILU 6 [1] and supplemented by two independent microwave generators. This design allowed us to test the effectiveness of sanitation concepts based on the simultaneous use of the electron beam and the flow of microwave energy to generate free radicals in the reactor.

Two heating furnace 6, each of which was equipped with a water-tube boiler, used for the production of gaseous products of combustion. Test the flue gas composition was obtained by introducing into the gas stream components, such as SO2, NO, and NH3.

The installation consisted of an introductory system (two boilers with a heating stove, a pressure regulator in the boiler, the dosing system of SO2, NO, and NH3analytical equipment), the reactor in which it can simultaneously or separately to enter the electron beam from the accelerator 1 [1] and microwave flows from the pulse generator 7 generator 8 of the carrier frequency, and output system (sump 9, the filtration system 10 (e.g. bag filter), the fan 11, and a discharge pipeline 12 and analytical equipment). Sensors the installation, was 400 Nm3/h gas Temperature in the reactor can be maintained in the range 70 - 100oC using a water cooling system of the boiler.

The main parameters of the sources of accelerated electrons and the flow of microwave energy are presented in table. 1.

The composition of the flue gas in the reactor are presented in table. 2.

The combustion gas fed into the reactor having the form of a cylinder with a diameter of 200 mm Microwave threads passed through the axis. The electron beam was injected into the reactor perpendicular to the axis of the reactor, through a titanium window thickness of 50 μm. More than 75% of the microwave energy is concentrated in the pressurized volume, an inlet and an outlet for flue gas was located on the side wall of the reactor. The gas stream can flow directly or in a spiral. Flue gas temperature at the outlet of the reactor did not exceed 100oC.

Tests were conducted to determine the removal efficiency of SO2and NOxfrom flue gases and to determine the amount of reduction of the energy consumption at the same level of treatment, comparing the results obtained when using a single electron beam, with the results obtained when using a combination of electron beam and microwave the new thread and the electron beam in the gas phase.

The cleaning efficiency of the combustion gas with the same energy consumption shown in the table. 3.

Energy demand in the combined method of cleaning using e-beam and microwave:

SO2a 95% absorption of the energy of 5.5 kGy

NOx80% absorption of 7 kGy

Reducing electricity demand per dose in kGy under the same conditions shown in the table. 4. The expression "the same conditions" means that during the experiment, all parameters related to the quantity and composition of the applied gas, and the temperature and pressure were the same.

The results show that the cleaning efficiency, and reducing energy consumption are the advantages of this method.

The invention is defined by the attached claims. On the basis of the claims, it is possible to implement the invention in various modifications, but departing from the basic concept of the invention.

Industrial application of the invention is that in the process of removing acidic pollutants such as SO2and NOxfrom combustion flue gases, particularly gases from heating ustanovke efficiency and reduce energy costs.

1. Method of removing SO2and NOxfrom the stream of industrial flue gases, comprising the irradiation by the electron beam in the reaction zone, characterized in that the flow of these flue gases is exposed to microwaves applied in a continuous or pulsed stream.

2. The method according to p. 1, characterized in that the flow of the combustion gases dedust and before it is fed into the reaction zone moisturize and give him the ammonia.

3. The method according to PP. 1 and 2, characterized in that the reaction product get in solid or liquid form and used as fertilizer.

4. The method according to p. 1, characterized in that the area of irradiation of the electron beam is injected stream of pulsed microwave energy having an electric field strength Ei> 300 V/cm in the length () of the pulse is between 10-7and 10-3and the repetition frequency f > v/towhere V is the velocity of the gas stream,to- the length of the irradiation zone, and the pressure inside the reactor is close to atmospheric pressure, and the pulse frequency microwave energy is 200 - 10000 MHz.

5. The method according to p. 4, characterized in that in the pulse stream is additionally introducing a continuous stream is CLASS="ptx2">

6. The method according to any of paragraphs. 1 to 5, characterized in that the electron beam is realized in the form of a pulsed electron beam with duration) of the pulse is between 10-8and 10-5C, and the pulses of the electron beam and microwave synchronized so that preferably the pulses of the electron beam is higher than the pulses of microwaves, while the flue gas when passing through the first reaction zone in contact with an electron beam, and then with microwaves.

7. Device for removal of SO2and NOxfrom the stream of industrial flue gases containing reactor, provided with at least one source of a beam of electrons, characterized in that the reactor is further provided with at least one source of microwaves.

8. The device according to p. 7, characterized in that the source of microwaves is a means for input stream of microwave energy into the reactor through its wall at a right angle to the direction of the electron beam through the input and output rectangular waveguides, each of which is attached to the reactor end area with its narrow side.

9. The device according to PP. 7 and 8, characterized in that it has two additional waveguides, etc the new Windows permeable to microwave energy, formed on end parts of the narrow side walls of the additional waveguides and waveguides each connected to the corresponding two taps 3-DV device, with one tap is connected to a microwave load, and the other connected to a microwave generator and a microwave load is adapted to absorb microwave energy with capability suppress any reflected microwave energy coming from 3-DV device.

 

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