RU2321687C2 - Thermal neutralizing method of aluminum cell anode gases - Google Patents

Abstract

FIELD: procedures used thermal neutralizing of anode gases of electrolytic production of aluminum.

SUBSTANCE: method comprises steps of introducing anode gases from gas collector of each aluminum cell and air heated in heat exchanger for after-burning in burner due to evacuation in gas suction-off system including inertia dust sedimentation chamber, descending outlets and gas conduit for removing created flue gases. Before feeding anode gases to burner device, anode gases from gas collector of each aluminum cell are supplied to said dust sedimentation chambers mounted on sections of gas collectors. Then anode gases through heat insulated descending outlets are fed into heat insulated gas conduit for centralized after-burning in burner or in furnace. Flue gases generated after anode gases afterburning before feeding them to gas conduit are directed to heat exchanger for heat recovery. Invention allows decrease by 1.4% penetration of benzapyrene to system of organized suction-off.

EFFECT: enhanced efficiency of neutralizing.

2 cl, 1 dwg, 1 tbl

Description

The invention relates to non-ferrous metallurgy, in particular, to the electrolytic production of aluminum, namely to thermal neutralization of the anode gases of an aluminum electrolyzer.

A known method of afterburning of anode gases in the gas collector of an aluminum electrolyzer. The gas exhaust system creates a constant vacuum in the combustion chamber. Gases from the annular space continuously enter the combustion chamber. The air is heated due to the heat lost by the surface of the anode, and enters the combustion chamber [USSR copyright certificate, No. 1023005, C25C 3/22, 1983].

The disadvantage of this method is the impossibility of cleaning the combustion chamber of the gas collector from deposits of dust and resinous substances and reducing the service life of the gas collector.

The closest in technical essence and the achieved result is a method of purification of the anode gases of an aluminum electrolyzer in a burner device [patent RU No. 4666296, C22D 3/02, 1973].

The method of purification of the anode gases of an aluminum electrolyzer includes the input of anode gases from the gas collector of each electrolyzer and the air preheated in the heat exchanger from the environment into the burner device by means of a vacuum in the afterburning system. Air is supplied to the burner device preheated in the heat exchanger due to heat recovery from the walls of the combustion chamber. The gas exhaust system includes an inertial dust precipitation chamber, descents and a gas duct to remove flue gases.

The disadvantages of this method are the instability of the combustion process and, accordingly, thermal neutralization due to the uneven flow of anode gases into the burners when the poplitear space is clogged with dusty deposits, due to the decay of the torch during processing of the electrolysis bath, and the lack of regulation of air flow, which reduces the temperature level in the volume of the burner, since each burner operates at a different vacuum, depending on its distance from the vacuum source and, therefore, at different x air consumption.

When aluminum plants switched to “dry” anodes, the content of combustible components in the anode gas sharply decreased. The content of carbon monoxide and resinous substances in the anode gas decreased by almost 2 times. The heat of combustion of the anode gas decreased by 1.5 times. Under these conditions, the operation of the burner devices is extremely unstable, accompanied by frequent attenuation, the temperature level in the burner is low. The afterburning efficiency of the harmful components of the anode gas decreases sharply with large and small air flow rates.

The objective of the invention is to increase the efficiency of thermal neutralization of anode gases and the stability of the combustion process due to a more complete afterburning of carbon monoxide, tarry substances and benzo (a) pyrene.

The technical result consists in increasing the stability of the burners by increasing the temperature level while ensuring continuous centralized supply of anode gases from a group of electrolytic cells to high-capacity burners or a furnace.

This problem is achieved by the fact that in the method of thermal neutralization of the anode gases of an aluminum electrolysis cell, which includes the intake of anode gases from the gas collector of each electrolytic cell and heated air in the heat exchanger for afterburning in the burner due to rarefaction in the gas extraction system, consisting of an inertial dust collecting chamber, slopes and a gas duct for removal the resulting flue gases, according to the claimed method, before being fed into the burner, the anode gases from the gas collector of each electrolyzer are fed into inertial dust The precipitation chambers are installed on the sections of the gas collectors, then the anode gases are sent through the insulated slopes to the insulated gas duct and centrally burned in the burner or furnace, and the flue gases formed after the anode gases are burned before being fed into the gas duct are sent to the heat exchanger for heat recovery.

The inventive method complements a particular distinguishing feature, also aimed at achieving the task.

The flow of anode gases from each cell is controlled by a throttle, which allows the cells to work with the same volumes of gas exhaust.

The analysis conducted by the applicant showed that the set of essential features is new, and the method itself satisfies the inventive step condition due to the novelty of the causal relationship “distinctive features - technical result”.

Anode gases are transported at temperatures below their ignition temperature. The main problem when transporting the anode gases of electrolytic cells to a device for centralized thermal neutralization is the deposition of condensed resinous substances on the walls of the flues while lowering the temperature of the gas stream.

The study of the sublimation of resinous substances trapped on a “cold” probe at the outlet of the aluminum electrolyzer from the gas collector showed that the bulk of the deposits sublimate in the temperature range 300–400 ° C. Therefore, the condensation of resinous substances and, accordingly, their deposition on the walls of the flues most intensively occurs in the same temperature range.

To prevent or minimize the fouling of gas ducts with tarry deposits, it is necessary to ensure the temperature of the anode gases at the inlet to the burner or furnace for centralized thermal neutralization above 400 ° C or less than 300 ° C. In this regard, thermal insulation of the slopes and the gas duct is necessary.

Calculations show that taking into account heat losses from the surface of a thermally insulated gas duct, anode gases can be transported for 90 m, i.e. within the brigade of electrolyzers. Due to the limited size of the subcasing space at the zero mark, it is advisable to centrally anode gas afterburning in the intercase courtyard. After thermal neutralization of the anode gases, the heat of the exhaust flue gases is disposed of in heat exchangers.

In the inventive method for thermal neutralization of anode gases, gases are collected simultaneously from all electrolyzers into the sub-duct, which ensures the continuity of the centralized supply of anode gas to the furnace or burner and the stability of their operation, regardless of the technological processing of electrolysis baths. This eliminates the thermal effect of the device on the angles of the anode, since all the burners are replaced by a furnace or one high-capacity burner installed in the thermal anode neutralization unit located between the electrolysis body and the gas cleaning system.

Thermal neutralization is carried out at the highest possible temperatures, since a forced control of the heated air flow is provided in the burner or furnace.

The drawing shows a variant of the device for implementing the method. The device consists of a mixing chamber and partial afterburning 1 with nozzles for the tangential supply of anode gas 2 and air 3, a afterburning chamber 4 with a flue gas outlet 5. The afterburning chamber 4 is closed by a removable cover 6 with a cleaning flap 7. The afterburning chamber 4 is covered with a gap air box 8. Air box 8 and the mixing chamber and partial afterburning 1 using the flanges 9 are connected by a riser 10, inside which a throttle valve 11 is installed to control the flow of heated air. The chamber 1 at the bottom is equipped with a hatch for removing tarry deposits and dust 12. An opening 13 is made in the lower part of the chamber 1 for visual control of the combustion process and ignition of the gas-air mixture.

The results of thermal disposal of anode gases by the present method are shown in the table.

Table Indicators The proposed method Prototype Air flow coefficient, α 2-4 2-4 Air heating temperature, ° С 180 180 Maximum torch temperature, ° С 1020 870 The efficiency of thermal neutralization of benzo (a) pyrene η,% 99,2 97.8

The data in the table show that, with the same air flow rates and air heating temperature, the proposed method for thermal neutralization of anode gases can increase the efficiency of thermal neutralization of anode gases by benz (a) pyrene by 1.4% due to the regulation of heated air flow, ensuring high-quality gas mixing and air, increase the stability of the combustion process.

Claims (2)

1. The method of thermal neutralization of the anode gases of an aluminum electrolyzer, including the input of anode gases from the gas collector of each electrolyzer and heated air in the heat exchanger for afterburning in the burner due to rarefaction in the exhaust system, consisting of an inertial dust-collecting chamber, slopes and a flue for removing the generated flue gases the fact that before being fed into the burner, the anode gases from the gas collector of each electrolyzer are fed into inertial dust precipitation chambers, setting nye on the sections of the gas plenum, and then insulated by anodic gases slopes directed to a thermally insulated and afterburning flue centrally in the burner or furnace, and the resulting flue gases after the anodic afterburning gases before entering the gas duct to a heat exchanger for heat recovery. 2. The method according to claim 1, characterized in that regulate the flow of anode gases from each cell using a throttle.