RU2175031C1 - Method for blowing gas ducts of aluminum cells with system for automatic supply of alumina - Google Patents

Abstract

FIELD: aluminum production, possibly designs of cells having system for automatic supply of alumina. SUBSTANCE: method comprises periodical supply of compressed air through branch pipes inclined by acute angle relative to lengthwise axis of pipeline of gas duct in several points along direction of gas suction; impulse feed of compressed air at using waste compressed air from pneumatic cylinders of punches of systems for automatic supply of alumina. EFFECT: enhanced efficiency for keeping gas duct in working state, lowered acoustic noise in shop. 3 cl, 1 dwg

Description

 The invention relates to the production of aluminum and can be used in the construction of electrolyzers equipped with automated alumina feed systems.

 Reducing the technogenic impact on the environment is one of the most urgent tasks for aluminum plants. There are a large number of inventions that solve various aspects of this problem and concerning the elimination of harmful emissions. So, some inventions relate to the designs of the gas collection bell (see the overview of the prior art in the invention RU 2151825 C1, LLC ALKORUS ENGINEERING, C 25 C 3/22, 06/27/2000) [1], burner devices that can effectively burn anode gases ( RU 2080421 C1, AOOT Siberian Research Institute of Aluminum and Electrode Industry and others, C 25 C 3/22, 05/27/1997; RU 2125124 C1, OJSC Krasnoyarsk Aluminum Plant, C 25 C 3/22, 01/20/1999) [2], special forms of covering the electrolyzer with the supply of raw materials through the gap (RU 2098520 C1, AOOT "Bratsk Aluminum Plant" and others, C 25 C 3/22, 12/10/1997) [3 ].

 A promising direction for a significant reduction in harmful emissions is the introduction of automated alumina feed systems for electrolysis cells (APG). The most widespread are APG systems with pneumatic drive of punches for punching cryolite-alumina crust. As a drive, they use pneumatic cylinders that consume compressed air with a pressure of 0.35 - 1.0 MPa. To penetrate the crust, a punch mounted on the rod of the pneumatic cylinder must perform the following working cycles: downward movement 2 - 6 s, delay below 1 - 15 s, upward movement 1 - 6 s. The intervals between duty cycles depend on the type of feeder, dose, melt temperature, location of the feed points and last from 60 to 1400 s (mainly 120 - 200 s) (see, for example, RU 2121529 C1, Kontsur, C 25 C 3 / 14, 11/10/1998) [4].

 The control is carried out by supplying compressed air pulses to the pneumatic cylinder through electro-pneumatic switches, alternately to the upper and lower working cavity (chamber) of the cylinder. In this case, the switch simultaneously discharges compressed air into the atmosphere from the cylinder chamber filled in the previous cycle. The free discharge of exhaust compressed air creates intermittent broadband acoustic noise with a sound pressure level significantly exceeding the maximum permissible levels. Depending on the pressure in the compressed air line and the diameter of the air distribution pipes through the electrolyzer, the measured sound pressure level during the movement of the APG punch reaches 100 - 120 dBA and higher.

 Noise reduction to 80-85 dBA from APG pneumatic cylinders is carried out in various ways: by installing sound absorbers, by venting air under the electrolyzer, or by venting air outside the electrolysis housing. These measures reduce the noise level at the workplaces of staff with greater or lesser efficiency, however, they lead to an obvious increase in the cost of the APG system, and in the case of filters, to a decrease in the power of pneumatic cylinders.

 The closest in technical essence is the method of blowing gas ducts of aluminum electrolysis cells, which consists in the periodic supply of compressed air through pipes installed at an acute angle to the longitudinal axis of the gas duct at several points in the direction of gas suction, implemented in the device (SU 1121323 A, Novokuznetsk Aluminum Plant , C 25 C 3/22, 10.30.84) [5].

 However, this method is characterized by increased costs of compressed air and does not solve the problem of increasing the acoustic comfort of the personnel serving the cells.

 The main technical result of the invention is to increase the efficiency of maintaining gas ducts in working condition while reducing maintenance costs by disposing of the exhaust air of an automated alumina feed system.

 An additional technical result consists in reducing the acoustic noise that occurs during the operation of the pneumatic cylinders of punch, to a level that provides acoustic comfort for personnel.

 The technical result is ensured by the fact that the method of blowing gas ducts of aluminum electrolysis cells, including the periodic supply of compressed air through nozzles installed at an acute angle to the longitudinal axis of the gas duct at several points in the direction of gas suction, consists in performing a pulsed supply of compressed air using exhaust compressed air from the pneumatic cylinders of the punches of the automated alumina feed system.

 The method may be characterized in that the first pipe in the flue with the burner device is placed at a distance equal to or greater than 10 diameters of the flue pipe from the air inlet holes of the burner device, and air is supplied through the pipes simultaneously.

The method may also be characterized in that the nozzles are installed at an angle of 10-35 ^o .

 The method, in addition, can be characterized by the fact that when using burner devices with precipitation chambers, the nozzles are installed in groups in front of the chambers and after them, with the number of nozzles in the group two or more.

 The patented method is based on the following premises.

As you know, gas exhaust systems from electrolyzers work in very harsh conditions. The gases emitted by electrolytic cells consist mainly of CO ₂ , CO, HF, CF4, and contain alumina dust and soot. Electrolyzers with self-baking anodes (BT, BT) also emit resinous coking products of the anode mass. The parameters of gas exhaust systems during operation change, which leads to the need for periodic cleaning. More often it is necessary to clean the flues from electrolytic cells with self-baking anodes, since resinous substances with dust, precipitating quickly, clog them. On each electrolyzer, sections of pipelines from burners to the common collector are cleaned by blowing with compressed air. This operation is performed at least once a day. In most aluminum smelters, the number of installed electrolytic cells is more than 600, and in some it exceeds 2000. Accordingly, labor costs and the consumption of compressed air for purging are high. It is possible to partially or completely replace the operation of cleaning gas exhaust pipelines to prefabricated collectors by connecting to them exhaust compressed air from the APG system. The specified connection allows you to simultaneously reduce noise from the discharge of compressed air, which can improve the requirements of sanitary standards for personnel.

 The drawing shows a block diagram of a device explaining the principle of the patented method and revealing the essence of the invention.

 The cell 10 is equipped with a gas collection bell 12 connected through a gas duct 14 to the case gas pipeline 16. The gas duct 14 is equipped with a burner 18 and a dust chamber 20. The gas duct is cleaned through nozzles 22, 24 located at an angle to the axis of the gas duct 14 by supplying them with compressed air from the pneumatic cylinder 26 through the standard pneumatic distributor 28 of the APG system. The first pipe 22 (and there may be several) should be located at a distance "a" from the holes 30 of the burner 18, equal to or greater than 10 diameters of the duct.

 The noise level was measured after connecting the discharge of the exhaust compressed air to the exhaust gas system from the BT electrolyzers at 130 kA, consisting of two burner devices (without precipitation chambers) on one side of the electrolyzer and exhausting gases from them by two pipelines to the collecting manifold. The APG system consisted of 4 pneumatic cylinders connected in pairs to two two-way pneumatic switches of type B64-25a, commuting compressed air with a pressure of 0.5 - 0.55 MPa. The duration of the downward stroke was 5.5 s, the delay at the bottom was 1 s, and the upward stroke was 3.5–4 s for each pair. The interval between the operation of each pair is 180 s. The sound pressure level measured by the standard method from the compressed air discharged into the gas ducts did not exceed 68 dBA, which is significantly lower than the maximum permissible (80 dBA) at workplaces in production facilities of this purpose in accordance with Sanitary Norms CH 2.2.4 / 2.1.8.562-96. Noise reduction was practically independent of the number of connected branch pipes.

 It was experimentally established that on electrolyzers with a top current lead (BT), with burner devices without a dust precipitation chamber, the connection of the first discharge point to the gas suction pipelines with a diameter of "d" = 0.159 m should be made at a distance of "a" no closer than 1.5 m from the openings for air intake into the burner. A connection made closer than 1.5 m causes a pulse ejection of flame from the openings of the burner during pulsed air injection into the gas duct and often leads to the extinction of the torch, which is unacceptable. For pipelines with a diameter d = 0.219 m, the effect of separation and extinction of the torch of the burner caused the discharge to be connected closer than 2 m from the holes. Thus, to discharge the exhaust air into the exhaust gas system from the VT electrolysis cells, it is necessary to observe the ratio a / d≥10.

 On VT electrolyzers having burners with dust precipitation chambers (see, for example, RU 2149224, OJSC Krasnoyarsk Aluminum Plant, C 25 C 3/22, 3/10, 05/20/2000 [6], Barantsev AG, Tsymbalov SD "Strategy for reducing emissions of pollutants into the environment" // f. Non-ferrous metals, N 6, 1999, pp. 27-28 [7]), the connection of discharge points to the exhaust gas pipelines is performed before and after the dust precipitation chamber, with the obligatory use of at least two nozzles and at least 10 pipe diameters removed from the burner openings. In this case, the purge of the gas duct with discharged air does not interfere with the effective functioning of the chamber.

It was experimentally established that the placement of compressed air nozzles at an angle of 35 ^o and 10-15 ^o to the flues of BT and BT electrolysis cells provides surface cleaning in the duct sections of 2 - 2.4 m and 2.8 m, respectively, that is, the efficiency increases with a more gentle entry air. By changing the number of nozzles and the angle of their installation, you can achieve a significant reduction in the period of cleaning the flue.

 Connection to the flues is made taking into account their electric potential. At various potentials, it is necessary to provide for electrical insulation breaks in the pipes of the discharged air.

 Thus, the invention allows, due to the pulsed discharge of compressed air from the pneumatic cylinders of the punches into the gas duct, to ensure both the maintenance of the gas duct in working condition and to reduce noise in the production room.

Claims (2)

 1. The method of purging the flues of aluminum electrolysis cells, including the periodic supply of compressed air through nozzles installed at an acute angle to the longitudinal axis of the duct at several points in the direction of suction of the gas, characterized in that they provide a pulsed supply of compressed air using exhaust compressed air from the punch pneumatic cylinders alumina automated feed systems.  2. The method according to claim 1, characterized in that the first pipe in the flue with the burner device is placed at a distance equal to or greater than 10 diameters of the flue pipe from the air inlet holes of the burner device, and air is supplied through the pipes simultaneously.

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