RU2132219C1 - Method of and device for cleaning of gases - Google Patents

Abstract

FIELD: civil engineering and other industries. SUBSTANCE: device is designed for cleaning gases from dust and harmful gaseous compounds by passing gases to be cleaned through flow of loose filtering material moving under gravity. Gas is passed through vertically directed layers of loose filtering material moving in waves. Size of material particles in layers is different. Device has housing with gas inlet and outlet branch pipes and filtering grainy material, dust outlet branch pipe, unions to deliver vapors of reactive substances, and vibrosieves. System of louvered members is arranged inside housing. This system ensures wavy movement of freely passing layers of filtering grainy material. EFFECT: provision of high efficiency of cleaning. 3 cl, 2 dwg

Description

 The invention relates to the field of gas purification from dust and various harmful gas compounds by passing the gas to be cleaned through a stream of gravitational moving filtering bulk material and can be widely used in construction industry enterprises, especially in asphalt concrete plants, as well as in any other industry.

 A number of methods are known for cleaning gas from dust by passing through a layer of granular material (ed. St. N 323881, class B 01 D 46/00, 1971; ed. St. N 488601, class B 01 D 46/32). This layer can be located both on a horizontal surface and vertical. A known method of cleaning gases through a horizontally located filter material located on perforated plates for gas passage and through a vertical layer placed in a cone-shaped hopper with a perforated side surface for passage of gas flow through it into the housing in which the granular material moves. The flow of dusty gas flows from bottom to top, passes through the horizontal and vertical layers of granular filter material, is cleaned of dust, while the granular material is gradually mixed from top to bottom (see Lukin V.D., Kurochkin M.I. Purification of ventilation emissions in the chemical industry. L .: Chemistry, 1980, p. 153, Fig. 2-28 and V. Lukin and other authors St. St. N 516415 (USSR), 1976, BI N 21). Perforated surfaces are often clogged with a granular filter material, on which dust is accumulated when it is in a stationary state and the dust cleaning efficiency drops sharply.

 Closest to the invention is a method of gas purification by passing it through a stream of freely falling filter material in the form of gas-permeable curtains, and the same size granular ball material is used as the filter material, in addition, a wet filter material is used, and chemical solutions are used as a humidifier of the material (absorbers) (see RF patent N 2064328, IPC B 01 D 46/30 - prototype).

 This known method does not provide a sufficient degree of purification taking into account the entire range of the fractional composition of dust contained in a dusty gas stream. The degree of perfection of one or another cleaning method can be judged by the values achieved with its help of all fractional (or partial) dust-cleaning coefficients. The fractional coefficient of dust cleaning shows the ratio of the captured amount of dust of a given fraction to the amount of incoming dust of the same fraction. Therefore, the proposed cleaning method using a granular filter material with grains of the same size is effective for collecting dust particles in a range of, say, 10 to 20 μm, which is determined by the mechanism for collecting granular filters and the size of grains used in it. But it is not at all effective for collecting dust of dispersed composition in the range from 30 to 100 microns. Thus, this cleaning method is effective only when cleaning gas streams from dusts of a certain narrow fractional composition close to monodisperse, which is practically rare.

 In addition, it is possible to significantly increase the efficiency of cleaning gas passing through the curtains (curtains) of a freely falling filter material, if you give them a wavy character, because this increases the number of grains of the filter material and, of course, the total area of grains in contact with the purified gas when it passes through wave-like veils.

The use in a known method (prototype) of a wet filter material and humidifiers that enter into a chemical reaction with the components (CO, CO ₂ , Cl, etc.) of the gas to be purified and having water as the reaction product, affects the gas permeability due to adhesion particles and thereby reduces the cleaning efficiency, and yet there is the problem of removing the sludge formed in such a situation.

 The technical task of the invention is to increase the efficiency of gas purification and classification (separation of dust into fractions) of captured dust.

 The technical problem is achieved by the fact that a stream of dusty gas is passed through gravitationally moving layers of bulk filter material in the form of wave-like curtains, forming at least two vertically directed layers of filter material, and from the first layer along the dusty gas stream to the subsequent vertical layers use filter particles material in decreasing size, which are saturated with vapors of a gaseous reactive substance. For example, grains (crushed stone) are used as grains of various sizes, in the first layer the size of grains of gravel is from 10 mm to 20 mm, in the second layer from 3 to 7 mm; in addition, the grains of the filter material are impregnated with a gaseous reactive substance, for example, vapors of bromine, iodine, lead acetate or others; after which they (grains) act as adsorbents (absorbers of harmful impurities). For example, gravel grains impregnated with bromine are used to remove ethylene impurities from the air, iodine - to trap mercury vapor, lead acetate - to trap hydrogen sulfide and sodium silicate - to trap hydrogen fluoride.

 As a result of giving a freely falling layer of loose filtering material the appearance of wave-like curtains with an increase in their number from two or more, it provides increased cleaning efficiency and dust separation into fractions (classification). The number of vertical layers is determined by the optimal value of the hydraulic resistance of the entire filter, which uses the proposed cleaning method. From the conditions of the hydraulic resistance of the receiving room for practical purposes, the minimum size of granules (grains) is determined at least 2.5 mm. It was found that the degree of dust removal depends on the granulometric composition of the granular layer, the degree of purification of a layer with grains of 5-10 mm in size exceeds 80% on average; the degree of purification of the layer with 10-20 mm grains is much lower. Thus, the cleaning efficiency depends on the particle size distribution of the filter material. In addition, high cleaning efficiency can be achieved only by filtering gases through several layers of different particle size distribution. (see Proceedings of NIPIOTSTROM, issue 6, Novorossiysk. 1972, p. 34, 37). In addition, the undulating nature of the movement of freely falling grains of the filter material turbulates the flow of dusty gas passing through their layer, creating favorable conditions for the deposition of dust on them and thereby increasing the cleaning efficiency.

 It should be noted that the high-speed flight of particles unambiguously increases the cleaning efficiency (see RF patent 2064328), it cannot be said. There is an optimal value for the speed of movement of the granular material, since both inertial forces and adhesive forces affect the degree of dust removal, and it all depends on the ratio between them. As soon as the speed of movement exceeds the limit value for these specific conditions, the dust particles that have already been caught will break down and the cleaning efficiency will decrease. Such interrelation of inertial and adhesive forces during cleaning of particles of a granular filtering material moving in a wavy layer can be taken into account by the amplitude of the waves.

 There are also a number of devices for filtering gases passing through a gravitationally moving stream of filter material (ed. St. 644508; Volobuev V.E. et al. "The use of granular filters for cleaning gases from harmful impurities", 1983). The device includes a housing with inlet and outlet nozzles for gas, fittings for loading and unloading of spent grains of filter material and a regeneration unit. A common disadvantage of all these devices is the low dust cleaning efficiency and increased energy costs for overcoming the hydraulic resistance of the layers of granular material, selected without taking into account the interconnection of grain size distribution of grains in different layers and their total hydraulic resistance.

 Closest to the invention is a device that represents a granular filter with a moving filter layer (Balabekov OS, etc. "Purification of gases in the chemical industry", M. Chemistry, 1991, Fig. 5.3.2, p. 208). Dusty gas is passed through layers of continuously falling grains and already cleaned is removed through the outlet pipe, and the spent granular material is freed from dust by sifting through a grid. Low cleaning efficiency and the inability to classify trapped dust is also characteristic of this device.

 In the proposed device for gas purification, comprising a rectangular housing with inlet and outlet nozzles of the gas stream, with inlet and outlet nozzles of a granular filter material, with fittings for supplying vapors of a reactive substance uniformly distributed on a load of granular filter material freely moving inside the housing from two or more systems of louvre elements assembled from flat parallel plates providing wave-like movement of the granular mat rial in the vertical direction, wherein the first downstream dust-laden gas stream vertical layer must move a larger particle size distribution than in the next and so on, and the ratio between the thicknesses of adjacent granular layers is 1: 0.5.

 Since the cleaning efficiency depends on the grain size and the filtration rate, in the case of using several layers, it is advisable to obtain the best cleaning with a minimum hydraulic resistance. As noted above, each layer separately and each layer in combination with one or two other layers work differently, but good efficiency can be achieved only by filtering gases through several layers of different particle size distribution.

 In FIG. 1 shows the proposed device / end view /, in FIG. 2 - node 1 in FIG. 1 / louvre elements, vertical section.

 A device for gas purification consists of a housing 1 with an inlet pipe 2 and an exhaust pipe 3 for a gas stream; with inlet 4 and outgoing 5 nozzles for granular filter material. On the body there are nozzles 6 for supplying vapors of the reactive substance and the incoming bulk granular material, as well as dust extraction nozzles 7 for removal of the corresponding dust fractions. Systems 8 / from two or more / louvre elements 9 are placed inside the housing. Each element is composed of flat parallel plates 10, which ensures the gas permeability of the louvre element.

 Each system of louvre elements is configured to provide wave-like movement of the granular material in the vertical direction. The offset value "c" of the elements, equal to the distance from the end part of one element to the surface of another element, determines the thickness of the vertical layer. In two neighboring systems, the ratio between the displacement "c" of the louvre elements / thickness of adjacent granular layers / is 1: 0.5. Moreover, in the first vertical layer along the dusty stream, granular material of a larger particle size distribution moves than in the second vertical layer. In the lower part of the housing 1 are placed vibrating screens 11 for separating dust from the granular filter material.

The proposed method of gas purification in the device is implemented as follows. The filtering granular bulk material continuously enters through the inlet pipes 4 of the housing and, under the action of gravity, moves in the systems 8 of the louvre elements 9, forming wave-like curtains directed downward. The flow of dusty gas entering the housing 1 through the nozzle 2 passes through the louvre elements 9 and the vertical layer of filtering granular material, is cleaned of dust and through the nozzle 3 is removed by the smoke exhauster outside the device. The spent grains on the vibrating screen 11 are freed of dust and sent through the outlet pipe 5 to the circulation system for loading through the inlet pipe 4. The dust is discharged through the nozzles 7. To ensure the purification of gas from harmful impurities through the nozzle 6, pairs of a reactive substance are fed to impregnate the incoming granular filter material , and giving it the properties of an adsorbent of harmful impurities. The degree of gas purification can be controlled by choosing the number of wave-like curtains formed by systems of louvre elements, by changing the material and the intensity of the flow of granular material. A jump-like increase in the pressure drop associated with the presence of a sequential series of filter layers, and, consequently, an increase in energy costs can be eliminated by choosing the hydraulic resistance of each layer equal to one value p = const. If the empirical dependence of the hydraulic resistance / p / on the filtration rate / w /, the grain diameter / d / and the layer thickness / S / has the form p = 18w ^1.8 • d ^-0.6 • S / cm. Proceedings of the NIPIOSTROM, vol. Xv. Novorossiysk, 1978 /, then the ratio between the thicknesses of adjacent granular layers / if the average grain diameter in the first layer is d ' _f. = 15 mm, and in the second d '' _cf. = 5 mm at p, w = const / is S _I : S _II = 1: 0.5, because h = 1 / d ^-0.6 .

Claims (2)

 1. A method of cleaning gases from dust by passing a stream of dusty gas through gravitationally moving layers of bulk filter material, characterized in that the movement of the filter material is carried out in the form of wave-like curtains forming at least two vertically directed layers of filter material, and from the first vertical layer, along the dusty gas stream, to the subsequent vertical layers use particles of filter material in decreasing size, which are saturated with gaseous vapors reactive substances.  2. A device for cleaning gases, comprising a housing with inlet and outlet nozzles of the gas stream, with inlet and outlet nozzles of the granular filter material, dust extraction nozzles and a mesh for dedusting the granular material, and also vertical systems of louvres installed from flat parallel plates placed inside the housing characterized in that the housing is equipped with fittings for supplying vapors of a reactive substance, the mesh for dedusting the granular material is made in the form of a vibrating screen, and the system Volumes of louvre elements are placed in the housing in an amount of two or more, each system of louvre elements made with the possibility of providing wave-like movement of the granular material in the vertical direction, and the ratio between the thicknesses of adjacent granular layers is 1: 0.5, while in the first direction a dusty gas stream in a vertical layer moves granular material of a larger particle size distribution than in the second vertical layer.

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