RU2291738C2 - Method of the wet ash-trapping with the help of venturi tube - Google Patents

Abstract

FIELD: chemical industry; metallurgy industry; methods of the wet ash-trapping with the help of Venturi tube.

SUBSTANCE: the invention is pertaining to the method of the wet ash-trapping with the help of the Venturi tube intended for trapping of the fly ash from the flue gases of the boilers burning the solid fuel, and also may be used for trapping of the cement kiln dust in production of the cement and for the dust trapping in the metallurgical, chemical and other industries, where the ash-and-dust catchers use the Venturi tubes. The purpose of the invention is to increase the degree of trapping of the fly ash from the flue gases of the boilers with the Venturi tubes and burning the solid fuels as well as the reduction of the specific consumptions of the water and steam to increase the boilers efficiency by sprinkling of the Venturi tube with the flue gases transiting in it, the acoustic injector giving more thin and uniform atomization of the water at the decreased consumption both of the water and the steam of the sprinkler, where the acoustic field is characterized by the strictly determined frequency, intensity and the variable acoustic pressure and the steam is in the narrow temperature interval. The flue gases passing in the Venturi tube are sprinkled by the acoustic injector using the steam with the temperature of 250-350°C and forming in the volume of the tube the acoustic field, which is characterized by the frequency of 20-22, 36-38 or 44-48 kHz, the variable sound pressure of no less than 140 dB and the acoustic field intensity of no less than 0.5 W/cm². The offered method, unlike the methods applied now, allows to act on the flue gases transiting in the Venturi tube simultaneously by several methods of deposition of the ash: - the acoustic method (coagulation - under action of the oscillations of the certain frequency, intensity and the variable sound pressure); humidification of the ash particles of ash in the steam-water aerosphere of the very finely sprinkled water with the full spectrum of the drops dimensions for all the sizes of the ash particles). This considerably increases the degree of trapping of the fly ash from the flue gases of the boilers at the simultaneous reduction of the specific consumptions of the water and steam and increases the efficiency of the boilers.

EFFECT: the invention ensures the increased degree of trapping of the fly ash from the flue gases of the boilers at the simultaneous reduction of the specific consumptions of the water and steam and the increased efficiency of the boilers using the solid fuel.

2 dwg, 1 tbl

Description

The invention relates to the field of energy, in particular to a method for wet ash collection in energy boilers (with Venturi pipes) burning solid fuel. In addition, the invention can be used for dust collection in the chemical, metallurgical and other industries.

The most effective (up to 99%) methods of wet ash collection with Venturi pipes, currently recommended but very limited in practice, are as follows. One of them is the intensive irrigation regime (Uraltehenergo). Another method involves remaking existing wet ash collectors into emulsifiers - developing Yuzhmash software [3].

The first method involves an increase in water consumption of 2.6-2.8 times. At the same time, the cost of electricity for pumps, smoke exhausters, blowers increases by 0.1-0.2%, the gross efficiency of the boiler decreases by 1.1-1.4%. An increase in water consumption causes a decrease in the temperature of the gases after the ash collector to 52 ° C (permissible - 67 ... 68 ° C), therefore, it is necessary to heat the gases to 67 ° C.

To implement the method requires significant costs:

a) for the replacement or reconstruction of smoke exhausters due to the increase in hydraulic resistance of ash collectors;

b) the construction of gas ducts for supplying hot air;

c) to increase the water supply cycle.

The second method is also associated with a decrease in the temperature of the flue gases after cleaning and the need to heat them, i.e. requires significant capital expenditures.

The following method (analog) is used more widely. Today, most TPPs burning solid fuel have adopted the wet method of collecting ash with a Venturi pipe and a droplet eliminator [1, 2, 3], the technology of which has long been reliably mastered, adapted to the equipment manufactured in the Russian Federation, has a satisfactory overhaul cycle and relatively low costs.

The main disadvantage of this commonly used method is the low efficiency of ash collection, not exceeding 95-97%.

When the gas velocity in the neck of the Venturi pipe is 46-53 m / s, the hydraulic resistance of the pipe is 1000 Pa, the ash collector is 1400 Pa, the final dust content of the gases is 1.2-2.0 g / m ³ . In this method, at a specific water flow rate of 0.25 l / m ^{3, the} final temperature of the gases after ash collection is 67-68 ° C.

As can be seen from the characteristics, a low degree of ash capture leaves dust content of gases too high in modern scales, when for every 0.1% there are hundreds of tons of uncoated ash. The percentage of capture can be slightly increased by the specific consumption of water, but then all the problems mentioned in the first two methods arise, associated with lowering the temperature of the flue gases after cleaning and the need to heat them, i.e. significant capital investments are required.

Another and most effective method of wet ash collection with a Venturi pipe was proposed by NIPI Energostal - a prototype that provides for a new Venturi pipe irrigation system, which includes two irrigation zones: the first - using water nozzles (sprayers); the second - with the help of vapor-liquid nozzles of Laval. Finer atomization of water allows, according to the authors of [3, p. 48], to significantly increase the contact surface with cleaned gases, reduce the amount of water supplied and increase the efficiency of trapping ash particles to 99%.

However, the main disadvantages of the prototype, as well as the considered analogue, are the following:

1. The final dust content is still very high, because, firstly, in the boiler examined, the consumption of flue gases is up to 1 million m ³ / h, i.e. up to 660 kg / h of uncaught ash, and in boilers of maximum power these figures will be incomparably higher. Secondly, the tests were conducted in a boiler where only 20% of coal was burned (8% of fuel oil, 72% of gas), and the boiler, if necessary, can only work on coal (1-10% of fuel oil in illuminated nozzles). The initial dust content will be significantly higher, and the final dust is generally unknown, but higher than that given in the prototype, because the effectiveness of ash collection methods and systems should be determined in extreme conditions, then for milder modes it can be foreseen by simple extrapolation.

2. The specific water consumption is also large, because the prototype has two irrigation zones. The first - sprayers, the second - Laval vapor-liquid nozzles. Sprayers (low-pressure water nozzles) produce a very coarse and inhomogeneous film spray with a particle diameter of water from 1000 μm and above, therefore the contact area of water particles with flue gases is insignificant and a large amount of water is required to capture a certain fraction of ash, as the authors expected. introducing sprayers.

Laval's vapor-liquid nozzles (high-pressure nozzles) provide finer atomization of water (with a diameter of 150 μm and above), which the prototype does not report, and the contact area with flue gases increases dramatically. From the table of the prototype [3] indeed, it can be seen that with increasing steam pressure in front of the nozzles, the specific water flow rate and final dust content decrease. However, the obtained contact area of water with flue gases, corresponding to the achieved dispersion, is still very far from optimal, because today it is possible to obtain a more developed contact surface of water with flue gases, having a dispersion of 0.05 microns or higher or creating the desired (for maximum capture of fly ash) dispersion interval. Then the final dust content and the specific consumption of water will significantly decrease, and the degree of capture of fly ash will increase markedly.

3. The specific steam consumption for spraying water through Laval nozzles is very high. Given that about 50% of the water passes through the nozzle, the specific steam flow rate is 0.31074 kg per 1 kg of water.

Today, in the energy sector, the permissible rate of steam consumption is 0.01-0.03 kg per 1 kg of sprayed medium, for example fuel oil, i.e. the prototype has a specific steam consumption 10 times higher than normal.

The main objective of the invention is to increase the degree of capture of fly ash from the flue gases of solid fuel boilers.

Another goal is to reduce the specific consumption of water (l / m ³ flue gas) and steam (kg / kg of sprayed water) to increase the efficiency of the boiler and the efficiency of the method.

This goal is achieved by the fact that in the known method (prototype) of capturing fly ash from flue gases with wet ash collectors with venturi pipes instead of coarse atomizing water nozzles in the first zone and Laval vapor-liquid nozzles with finer atomization in the second zone, for irrigation of the passing flue gases is installed by the axis of the Venturi pipe one steam-mechanical nozzle with an acoustic stage (acoustic nozzle), for example, according to patent 1241022 [8], with the necessary flow of water and steam, creating an acoustic field with emymi varying sound pressure, intensity and frequency of promoting coagulation of ash particles.

Figure 1 presents the acoustic nozzle.

Figure 2 shows a longitudinal section of a venturi pipe with an acoustic nozzle, where it is seen that the pipe is in a vertical position and consists of a tapering part 1 (confuser), a cylindrical part 2 (neck) and an expanding part 3 (diffuser).

Along the axis of the pipe is one acoustic nozzle 4 with nozzles 5 and 6 for supplying water and steam, respectively. Water is supplied, as already emphasized, unlike the prototype, only through one nozzle, its flow rate is determined by the volume of irrigated flue gases at the inlet to the venturi and the need for maximum ash collection.

Steam is supplied at a pressure of not lower than 0.3 MPa (operating conditions of the acoustic unit), which also differs from the prototype, where the optimum pressure is much higher (1.1 MPa) and hence a higher specific steam consumption.

In the acoustic nozzle, a higher vapor pressure can also be used. Its consumption will not increase, because the outflow of steam from the nozzle of the nozzle is always supersonic.

A comparative analysis of the proposed solution with the prototype shows that the claimed method differs from the known one in that, firstly, there is a fundamentally new device - an acoustic nozzle - for more dispersed atomization of water and irrigation of flue gases. Secondly, it combines several factors (mechanisms) of the deposition of fly ash, including acoustic (the imposition of fluctuations of certain parameters on the passing flue gases), which has never been used for trapping fly ash.

Consider the effect of each of these differences on the objectives of the invention: increasing the degree of ash collection and reducing specific consumption of water and steam.

Acoustic nozzle, Fig. 1, differing from sprayers (working without steam, where the particles of sprayed water have a diameter above 1 mm) and Laval vapor-liquid nozzles (water and steam are fed through one nozzle, where the steam condenses completely and does not actually participate in ash collection) , has two independent channels and an acoustic generator that is paired with a temperature in the range of 250-350 ° C. The steam spent in the generator, dispersing water due to variable sound pressure (up to 163 dB), then participates in the collection of ash, wetting its particles, which then stick together faster and easier, forming easily trapped aggregates.

Water passing through the swirl, at the nozzle exit forms (due to centrifugal force) a bell (torch) 7 with the required opening angle (adjustable gap 8) to lock the venturi neck and let the entire volume of flue gases pass through the steam-water medium activated by the acoustic field .

The degree of dispersion (0.05-300 microns) is an order of magnitude higher than the Laval nozzles and can be regulated in order to more fully collect ash. The required fraction can be increased [4]. The latter is especially important since the dusty gas stream (from tenths of a micron to 25 microns) enters a relatively short confuser, where the movement of gases and ash particles is accelerated. Moreover, the smaller the ash particles, the greater the speed they acquire, and water droplets due to the greater mass have a lower speed than the ash particles [2]. Due to the significant difference in their velocities along the entire length of the confuser, as well as in the neck and diffuser, intense coagulation of ash and water particles occurs - inertial deposition. The theory gives this mechanism a decisive role in the purification of gases, however, it is effective for ash particles of the order of 5-15 microns [2, p. 9], and below 5 microns and above 15 microns its effectiveness sharply decreases.

Particles below 5 microns in the vast majority are not captured, but they are especially dangerous ecologically, because enriched with toxic microimpurities, primarily heavy metals [2, p. 10].

This is where the decisive role of the acoustic nozzle is manifested, which not only provides fine atomization with a full range of sizes of water droplets for all sizes of ash particles for inertial deposition, but also opens up the possibility of using other mechanisms for collecting fly ash. This is with:

1) steam condensation on particles of fly ash of all sizes, which is typical for an acoustic nozzle, where the steam (at a temperature of 250-350 ° C) spent in the generator becomes saturated and continues to move through the Venturi pipe, facilitating and accelerating the formation of ash aggregates, which by themselves ("dry") do not stick together, and also maintaining the temperature of the exhaust flue gases not lower than 67 ° C. A decrease in steam temperature below 250 ° C leads to a drop in the temperature of the exhaust gases below 67 ° C, and an excess of 350 ° C gives, on the contrary, an increase in the temperature of the exhaust gases above 75 ° C, which leads to heat loss with the exhaust gases;

2) acoustic coagulation, which, as tests have shown, is an effective method of fine cleaning. Its mechanism of action is that under the influence of variable sound pressure, the variable motion of particles in an acoustic field is different for particles of different masses and depends on the frequency of sound. At low frequencies (0.5-2 kHz), particles of any size completely follow the vibrations of the medium. With an increase in the field frequency, heavier particles take an ever smaller part in the general motion. At frequencies of the order of 100 kHz, only ultramicroscopically small particles undergo complete oscillations, while large particles move along more or less complex trajectories [9] and with different speeds.

Large differences in the velocities of particles of different masses lead to the fact that, firstly, the inertial deposition of ash particles of all sizes, without exception, is significantly enhanced, in contrast to the inertial deposition considered above for a venturi without an acoustic field. Secondly, between the particles of this heterogeneous system there are hydrodynamic forces of attraction (Bernoulli forces) associated with radiation pressure, which increase with the approach of the particles [9].

Thus, in an acoustic field, the effects of separation and hydrodynamic attraction significantly accelerate the process of convergence, collision and association of ash particles into aggregates.

The use of acoustic coagulation is known, for example, for aerosols of sulfuric acid and fertilizers [5, 6], but gas-jet generators (static or dynamic sirens) were used, which differ from acoustic nozzles by inhomogeneous acoustic fields and exposure without water [5].

The most difficult choice of exposure frequency, because no acoustic field was used to trap fly ash because of the established opinion that any aggregates formed in it are immediately destroyed after leaving the acoustic field [6, 7].

In the present invention, this was not confirmed and the authors found that the process of acoustic coagulation is affected both by the characteristics of fly ash (concentration, dispersion, cohesion) and field characteristics (frequency, variable sound pressure, sound intensity, exposure time), which can be set and adjust for specific conditions of a state district power station (CHP).

So, given that the prototype method does not capture particles of fly ash up to 5 μm, the authors tested and selected an interval of certain frequencies at which, firstly, these particles of fly ash could oscillate with a frequency and amplitude close to these parameters acoustic field, when the number of collisions of particles and the formation of aggregates sharply increase.

Secondly, the frequency of the field impact on the particles of fly ash should be such that the formation of aggregates in the exhaust flue gases can be completed even at maximum speeds in the neck of the Venturi - from 40 m / s and above. For example, at a field frequency of 20 kHz, each liter of the moving mass of exhaust gases is exposed to a variable sound pressure 800 times.

Thirdly, the frequency of the field should provide not only the efficiency of coagulation of fly ash with a size of 5 microns or less, but also the dispersion range of the sprayed water, discussed above. Moreover, the higher the frequency of the field, the more power is required to apply at equal field intensity.

In addition, the use of frequencies below 16 kHz (the area of audible sounds) requires the protection of personnel.

The authors obtained three frequency maxima, where the highest efficiency of fly ash capture was observed: 20-22 kHz, 36-38 kHz and 44-48 kHz, which is apparently associated with unequal conditions for burning solid fuel, initial dust content of exhaust gases, changing size composition of fly ash.

The proposed method of wet ash collection with a venturi is implemented as follows.

On the axis of the venturi, an acoustic nozzle is installed in the confuser, as shown in figure 1, to which water (5) and steam (6) are connected.

Pressure is measured by pressure gauges. The nozzle [8] is put into operation by supplying steam under a pressure of at least 0.3 MPa at a temperature in the range of 250-350 ° C.

The oscillation generator, where steam arrives at a supersonic speed, forms an acoustic field of the required frequency around the nozzle. In this case, it is: 20-22 kHz, 34-36 kHz or 44-48 kHz with variable sound pressure not lower than 140 dB (intensity not lower than 0.5 W / cm ² ).

The nozzle [8] works equally at any higher vapor pressure (with a constant flow rate), which is determined only by the vapor pressure available at the facility under which the nozzle structural elements are calculated.

The temperature of the steam is determined by the need to maintain the temperature of the exhaust flue gases not lower than 67 ° C.

Since the acoustic field is set simultaneously with the steam supply, then the water supply is turned on, the pressure and flow rate of which are determined by the irrigation conditions of the Venturi pipe, i.e. operating conditions: pipe dimensions, volume of passing flue gases per hour, initial dustiness, temperature of exhaust gases, etc.

The working nozzle (Fig. 2) has a torch opening angle of 60-80 ° (depending on the size of the Venturi pipes) and closes the neck of the pipe so that all the flue gases pass through the acoustic field of a finely sprayed steam-water medium in order to obtain the best ash collection efficiency. The nozzle during adjustment can be moved due to the adjustable gap 8.

Thus, the dusty gas stream enters a relatively short confuser, where the movement of gases and ash particles accelerates (the finer the ash particles, the greater the speed they get).

In the same zone of the confuser, an acoustic nozzle delivers finely dispersed water with particles of 0.05-300 microns in size and the steam spent in the generator with the necessary frequency, variable sound pressure, and intensity.

The intersection of a dusty gas stream with a sprayed water stream (torch) and steam, which bear acoustic vibrations, forms a confluent (multicomponent) diffuse field with powerful turbulence and the special effects discussed above, which are inherent only in the acoustic field.

As a result of this interaction (mainly in the confuser, neck and partly in the diffuser), intense ash particles coagulate.

Moreover, as the tests showed, not only 100% slip (incomplete deposition) of any ash fraction is not possible, but even a 30% slip for the above reasons.

Moreover, the capture of the largest particles of ash (above 15 microns) and the smallest (less than 5 microns), not possible by the prototype method, is carried out in the proposed method mainly by different mechanisms.

In the first case, for each ash particle there is a corresponding water particle with which it has a significant difference in speeds - inertial deposition.

In the second case, the coagulation of ash particles occurs (by 90%) under the influence of the separation and hydrodynamic attraction effects discussed above.

Active steam penetrating the entire volume of the confuser, neck and diffuser (due to the effects of acoustics), contributes to the coagulation of particles of fly ash of all sizes.

The proposed method of wet ash collection with a venturi pipe can be implemented on any boiler unit that burns solid fuel, as well as other facilities using wet ash collectors with a venturi pipe to collect dust, cement and other solid materials.

Thus, the combination of several fly ash collection mechanisms significantly increased the efficiency of wet ash collectors with venturi tubes, as shown in the table.

Using the proposed method is most effective for trapping the finest fractions of volatile materials.

The main thing - the degree of capture of fly ash increased to 99.6%.

Steam consumption is reduced 100 times, from 0.3 kg / kg of water to 0.003 kg / kg of water due to the use of an acoustic nozzle [8], which ensures the use of steam and the optimal temperature range.

Water consumption for irrigation of the Venturi pipe is reduced 1.66 times due to finer polydisperse atomization of water and the use of an acoustic field of a certain frequency and power.

No. Parameters The inventive method Prototype Analogue 1. Fuel 1) Coal of different grades - 98%
2) Fuel oil - 2% 3) coal grade ASH - 20%
4) gas - 72%
5) fuel oil - 8% 1) coal grade ASH - 20%
2) gas - 72%
3) fuel oil - 8% 2. The consumption of flue gases at the entrance to the ash collector, m ³ / hour 600000-1200000 684000-1000000 684000-1000000 3. The initial dust content, g / m ³ 88 40 40 4. Final dust content, g / m ³ 0.352 0.25-0.35 1.2-2.0

5. The efficiency of ash collection,% 99.6 99.1-99.3 95-97 6. The gas velocity in the neck of the venturi, m / s 45-55 up to 53 46-53 7. The temperature of the gases to the ash collector, ° C 130-150 130-150 130-150 8. The hydraulic resistance of the venturi pipe, Pa 1000 1050-1100 1000 9. The temperature of the gases after the ash collector, ° C 68-70 64.5-67 67-68 10. Steam pressure, MPa 1.1 (in front of the nozzle) 1.1 (in front of Laval nozzles) No steam used 11. The temperature of the steam, ° C 280 not measured No steam used 12. Specific steam consumption, kg / kg of sprayed water. 0.003 0.31074 No steam used 13. Specific consumption of water, l / m ³ flue gases. 0.05-0.07 0.09-0.11 0.25 14. The frequency of the acoustic field, kHz 20-22 Not used Not used 15. Variable sound field pressure, dB. 150 Not used Not used 16. Field intensity, W / cm ² 0.6-0.8 Not used Not used

Verification of the invention “Wet ash collection method with a venturi” was carried out on models, as well as on boilers burning coal of various grades. Preliminary tests yielded positive results (shown in the table), confirming the correctness of the selected solution, and preparatory work is currently underway to transfer boilers at Vorkuta CHPP-2 to the indicated ash collection method.

LITERATURE

1. Guidelines for setting up wet ash collectors with venturi pipes. MU 34-70-055-83. Soyuztekhenergo, M., 1984

2. L.I. Kropp, E.N. Medik. Development and development of ash collectors SVD-VTI-UTE. All-Union Institute for Advanced Studies. Ministry of Energy of the USSR, M., 1989

3. G.M.Kanenko and others. Improving the efficiency of wet ash collectors. Industrial Energy Magazine No. 2, 1997

4. V.A. Solokha, A.V. Lizogub. Reconstruction of burner devices of boilers KVGM 20, KVGM 100, KVTS 10 with the transition to steam-mechanical nozzles with an acoustic stage. Journal "Industrial Energy" No. 2, 1992

5. M.L. Varlamov and others. “Study on the purification of exhaust gases from the production of sulfuric acid and mineral fertilizers.” Collection "Materials of the anniversary scientific and technical conference." Odessa, 1968

6. N.L. Shirokova. Coagulation of aerosols. In the book "Physical Foundations of Ultrasound Technology." M., Science. 1970 year

7. L. Bergman. “Ultrasound and its application in science and technology.” Foreign literature. M., 1957

8. V.A. Solokha, K.Ya. Kornienko, K.D. Kornilov, V.M. Karachunov, P.E. Kargin, Yu.I. Stepanov. "Acoustic nozzle." Patent No. 1.241.022.

9. I. Mataushek. "Ultrasound technology." M., 1962

Claims (1)

A method of wet ash collection with a venturi, in which the flue gases passing in the venturi are irrigated with water nozzles, characterized in that the flue gases passing in the venturi are irrigated with an acoustic nozzle operating in pairs with a temperature of steam of 250-350 ° C and creating in the volume of the pipe an acoustic field, which is characterized by a frequency of 20-22, 36-38 or 44-48 kHz, a variable sound pressure of at least 140 dB and an acoustic field intensity of at least 0.5 W / cm ² .

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