RU2023478C1 - Method of and device for gas cleaning - Google Patents

Abstract

FIELD: gas cleaning. SUBSTANCE: method involves heating of gas to be cleaned, its passage through vertical channel from top downward, cooling while it comes in contact with vertical channel walls, and removal of separated impurities. Channel height is to be not smaller than its equivalent diameter; gas flow conditions in channel should be such that inequality ≅ of thermal velocity < 1000 for largest fragments is satisfied. EFFECT: enlarged functional capabilities. 5 cl, 1 dwg, 2 tbl

Description

 The invention relates to the purification of gases from suspended solid and liquid fine particles and can be used in non-ferrous and ferrous metallurgy, chemical industry, building materials industry.

 Currently, two methods are used to clean gases from mechanical impurities: wet and dry. Despite the high degree of purification achieved by the use of wet gas purification, this method is less widely used than dry (due to the need for a water supply, a sufficiently high energy intensity of the process, clogging of the apparatus with wet dust, high hydraulic resistance, etc.). Much more common are various implementations of the dry gas purification process.

 A known method of purification of gases from mechanical impurities [1], in which the heated cleaned gas is passed through a vertical pipe, impurities are informed of an electric charge, deposited on the walls of the pipe and removed beyond it. This method allows to achieve a high degree of purification (the size of the deposited particles is a fraction of a micrometer). However, it requires significant energy costs for its implementation. In addition, the need for periodic cleaning of the walls of the pipe from settled dust reduces the productivity of the process.

 The closest in technical essence to this invention is a gas purification method [2], in which the heated cleaned gas is passed through a vertical pipe from bottom to top, cooled by interaction with the walls of a vertical pipe, and the separated impurities are removed.

 The specified method, based on the phenomenon of thermophoresis, provides a sufficiently high degree of gas purification, however, it decreases with the deposition of impurities and the formation of a layer of particles on the walls of the vertical pipe. In this regard, the thermal resistance of the walls of the vertical pipe increases, which means that the efficiency of the method is reduced. To maintain the required degree of purification, it is necessary to lower the temperature of the walls of the vertical pipe, which significantly increases the energy intensity of the process. As described in the analogue, this method is periodic, which reduces its performance.

 The aim of the invention is to reduce energy intensity and increase the productivity of the process by ensuring its continuity.

 The goal is achieved by the fact that in the gas purification method, in which the heated gas to be purified is passed through a vertical pipe from the bottom up, it is cooled by interacting with the walls of a vertical pipe and the separated impurities are removed, the pipe height is chosen not less than its equivalent diameter, and the gas is passed at a speed at which for particles of the largest size, the Reynolds criterion corresponds to the following relation: 10 ≅ Re solenoid ≅ 1000. Moreover, in a gas purification device comprising a housing with nozzles for supplying the gas to be cleaned and outlet about cleaned gas and a cooled vertical pipe installed in the casing, the height of the vertical pipe is not less than its equivalent diameter, the casing is equipped with an additional pipe located outside the vertical pipe, forming a pressurized cavity from the last one and equipped with refrigerant inlet and outlet pipes, while in the lower part of the casing an additional pipe made a window for the removal of separated impurities. In a preferred embodiment of the device, the vertical pipe is movable along its longitudinal axis; the upper section of the additional pipe is made conical, converging to the corresponding end of the vertical pipe, in addition, the upper section of the vertical pipe is equipped with an annular visor, bent from the outside in the direction of the additional pipe.

 Distinctive features of the proposed technical solution are: the choice of pipe height not less than its equivalent diameter; ensuring the gas velocity at which for the largest particles the Reynolds criterion corresponds to the inequality: 10 ≅ Re soaring ≅ 1000; placement of an additional pipe in the housing; the location of the latter outside the vertical pipe; the formation of the indicated tubes in a sealed cavity and supplying it with pipes for supplying and discharging refrigerant; supplying the housing in the lower part from the side of the additional pipe with a window for discharging the separated impurities; the implementation of a vertical pipe with the ability to move along its longitudinal axis; the implementation of the upper section of the additional pipe conical, converging to the corresponding end of the vertical pipe; supplying the upper section of the vertical pipe with an annular visor, bent from the outside in the direction of the additional pipe.

 This method can be called continuous heat treatment of gas from mechanical impurities. It is based on the phenomenon of thermophoresis [2] and a change in the regime of gas movement in the boundary sublayer (near the walls of the channel (pipe).

 During thermophoresis, gas molecules, in contact with a hotter body, acquire greater speed and act with greater force on particles suspended in the gas stream, facilitating their movement from the core of the hot gas stream to its periphery bounded by cold walls. Here, the gas molecules are cooled, the viscosity of the flow increases, the speed of the solid particles slows down, and the latter tend to reach the cold wall due to Brownian motion. Thus, the temperature gradient between the hot gas and the cold walls of the vertical pipe facilitates the movement of particles from the core of the gas stream to its periphery. Under the action of the translational motion of the gas flow and micro-eddies that occur at the walls of the pipe, dust particles move along the cold walls, and, reaching the upper cut of the vertical pipe, are thrown out and deposited in the accumulator.

 In the known method [2], using the phenomenon of thermophoresis (and not based on the latter, as in this invention), mechanical particles released from the gas stream are deposited on the walls of the pipe, which not only reduces the productivity of the process (makes it periodic), but also reduces cleaning efficiency.

 In this invention, by ensuring the gas velocity in the pipe, at which for the largest particles 10 ≅ Re whirling ≅ 1000, the continuous movement of the selected impurities along the walls of the pipe and their removal beyond its limits is guaranteed. In this case, the Reynolds criterion is determined through the velocity of the largest particles because they have the longest travel time from the center of the gas stream to the walls of the channel (pipe) due to their inertia.

 Providing the specified regime for particles of maximum size, the movement time of smaller particles to the periphery of the gas stream will be provided. It has been experimentally proved that the height of the pipe to ensure gas cleaning efficiency must be at least its equivalent diameter (or simply the diameter when using a round pipe). When Re soiling <10, individual particles of maximum size are deposited on the walls of the pipe and are not removed beyond the latter, which reduces the efficiency of the gas cleaning process. When Re whirling> 1000, individual large particles do not have time to reach the pipe wall even at a considerable height, which can be explained by the onset of a transitional and even turbulent gas movement throughout the pipe, which leads to random mixing of gas and particles and excludes the guaranteed movement of the latter to the walls pipes.

, где V_{витания} = V_газа - V_{частицы} - скорость витания, представляющая разность скорости газа и скорости движения частицы, м/с;
d_экв - определяющий размер, равный эквивалентному (приведенному диаметру частицы наибольшего размера), м.Reynolds criterion in this case is determined by the dependence:
Re _soaring =

where V _soaring = V _gas - V _particles - soaring speed, representing the difference in gas velocity and particle velocity, m / s;
d _equiv - determining the size equal to the equivalent (reduced diameter of the largest particle size), m

= 1,24

, где М - масса частицы, кг;
ρ - плотность материала частицы, кг/м³;
ν - кинематическая вязкость газа при определяющей температуре t, равной:
t = 0,5 ˙(t_стенки +

), где t_стенки - температура стенки, ^оС;

- средняя температура газа в трубе, ^оС.The equivalent diameter of an irregularly shaped particle is calculated as the diameter of a conditional ball whose volume V is equal to the volume of an irregularly shaped body:
d _eq =

= 1.24

where M is the particle mass, kg;
ρ is the density of the particle material, kg / m ³ ;
ν is the kinematic viscosity of the gas at a determining temperature t equal to:
t = 0.5 ˙ ( _wall t +

), where t of the _wall is the wall temperature, ^о С;

- the average temperature of the gas in the pipe, ^about C.

 The drawing shows a device for implementing the method of gas purification.

 The method is as follows.

 A gas with suspended impurities (powdered solid material and a dropping liquid) is heated (or an already heated process gas, for example flue gas, is used) and fed to the lower part of the vertical pipe.

 The walls of the vertical pipe are continuously cooled (water, salt solutions, liquid nitrogen). When a gas moves along a pipe, mechanical impurities due to the phenomenon of thermophoresis and micro-eddies at the pipe walls caused by a temperature gradient move from the core of the gas stream to its periphery. The selection of impurities is carried out outside the vertical pipe due to the hydrodynamics of the wall layer, which facilitates the movement of particles at the upper section of the pipe from the latter beyond its limits.

 A device for implementing this method comprises a housing 1 with nozzles 2 and 3 for supplying a gas to be purified and removal of a purified gas, respectively. In the center of the housing 1, a vertical pipe 4 is installed, on the outside of which an additional pipe 5 is placed. Pipes 4 and 5 form a tight annular cavity 6, equipped with pipes 7 and 8 for supplying and discharging refrigerant. In the lower part of the housing 1 from the side of the additional pipe 5, a window (or pipe) is made for the removal of impurities. Vertical 4 and additional 5 pipes can be made with the possibility of moving vertically. This makes it possible to control the height of the working channel of the device, and therefore the degree of gas purification. The upper section 9 of the additional pipe 5 may be conical, converging to the corresponding end of the vertical pipe 4, and the upper section of the latter is equipped with an annular visor 10, bent from the outside in the direction of the additional pipe 5. At the inlet to the pipe 3, a bump 11 can be additionally installed, providing guaranteed and timely removal of impurities extracted from gas outside the working channel. In addition, a heater can be installed in the center of the vertical pipe 4, which increases the temperature gradient between the hot gas and the cold walls of the vertical pipe 4, which increases the efficiency of the cleaning process.

 When the channel for the gas passage in the form of a pipe is made, its equivalent diameter is equal to the inner diameter of the pipe, and when the pipe 4 is supplied with a cylindrical heater (i.e., the channel is made in the form of a ring), the equivalent diameter of the channel is equal to the difference between the inner diameter of the pipe 4 and the outer diameter of the heater. The height H of the pipe 4 is selected not less than its equivalent diameter.

PRI me R. Experimental studies carried out flue gas cleaning process of the pulverulent material up to 500 microns, at a gas temperature of 250 ^{° C} and 50 g dust / m ^3. The diameter of the vertical channel is 0.2 m, the height of the channel is from 0.15 to 0.50. The research results are given in table. 1.

 When the pipe height is less than its equivalent diameter (less than 0.2) and for any gas movement modes, as well as when Re-soaring> 1000 and any pipe height (but not less than its equivalent diameter), individual particles do not have time to reach the pipe wall and remain in the stream gas removed from the device. When Re soiling <10, particles are deposited on the walls of the pipe, which leads to an increase in thermal resistance and a decrease in the degree of gas purification. This is explained by the fact that the composition of impurities is generally polydisperse; some large particles practically do not move along the pipe wall. In this case, smaller particles, due to the identical physical nature of impurities, begin to settle on larger particles, a kind of coagulation of particles occurs, their mass grows and particles precipitate on the wall, which reduces the efficiency of the process. Sustainable gas cleaning took place during the regime of gas movement indicated in the table. 2.

 As can be seen from the table. 2, the most efficient gas purification is carried out in the range of 10 ≅ Re soaring ≅ 1000.

 Using this method provides a reliable degree of gas purification, and its implementation is a simple hardware design.

Claims (5)

1. The method of gas purification, which consists in the fact that the heated purified gas is passed through a vertical pipe from the bottom up, cooled by interacting with the walls of the vertical pipe and the separated impurities are removed, characterized in that, in order to reduce the energy intensity and increase the productivity of the process by ensuring its continuity, gas is passed at a speed at which the Reynolds criterion corresponds to the relation
10 ≅ Re soaring ≅ 1000.  2. A device for gas purification, comprising a housing with nozzles for supplying and discharging purified gas and a cooled vertical pipe installed in the housing, characterized in that, in order to reduce energy consumption and increase the productivity of the process by ensuring its continuity, the height of the vertical pipe is not less than its equivalent diameter , the housing is equipped with an additional pipe located outside the vertical pipe, forming a sealed cavity with the latter and equipped with pipes for supplying and discharging refrigerant, while the bottom of the housing from the side of the additional pipe is made a window for the removal of separated impurities.  3. The device according to claim 2, characterized in that, in order to control the size of the emitted particles, the vertical pipe is made with the possibility of movement along its longitudinal axis.  4. The device according to PP.2 and 3, characterized in that, in order to increase the degree of purification, the upper section of the additional pipe is made conical, converging to the corresponding end of the vertical pipe.  5. The device according to claims 2 to 4, characterized in that the upper section of the vertical pipe is equipped with an annular visor, bent from the outside in the direction of the additional pipe.

Images