CN106123632A - A kind of method utilizing residual heat of aluminum reduction cell to generate electricity - Google Patents

Abstract

The invention discloses a method for generating electricity by utilizing the waste heat of an aluminum electrolytic tank. The invention uses water as a medium to recover low-level heat energy generated in the aluminum electrolysis process through direct current heat exchange, and is used to generate steam for power generation. In the present invention, the waste heat of flue gas is recovered by arranging a vertical tube heat exchanger in the branch pipe of the electrolytic aluminum flue gas; Sensible and radiant heat at the top of the tank. The equipment of the invention has a simple structure, does not change the original structure of the aluminum electrolytic cell, has high heat recovery efficiency, reduces the amount of electrolytic aluminum flue gas by more than 60%, can save 300-400kWh of electricity per ton of aluminum, and has remarkable energy-saving and emission-reduction effects; the process is simple, Low investment and low operating costs.

Description

A method of generating electricity by utilizing the waste heat of an aluminum electrolytic cell

technical field

The invention relates to a method for recovering the waste heat of an aluminum electrolytic cell and converting low-level heat energy into electric energy, so as to achieve the purpose of saving energy, and belongs to the field of energy utilization.

Background technique

Aluminum is one of the most traded commodities in the world. In 2014, China's aluminum output increased by 14% year-on-year, hitting a record high of 28.3 million tons, and the export volume is also surging. China has become the world's largest producer and consumer of electrolytic aluminum.

The production of electrolytic aluminum needs to consume a lot of energy, and the power consumption of each ton of aluminum produced is 12200-1450kWh. The electrolytic aluminum industry is a veritable industrial energy-consuming household. In my country, the electrolytic aluminum industry is an industry with high energy consumption. Compared with foreign countries, the production cost of electrolytic aluminum per ton in my country is generally 2,000 yuan higher than that in foreign countries.

Energy saving and consumption reduction is the fundamental way for the electrolytic aluminum industry to improve economic efficiency and meet market challenges, and energy saving and emission reduction is an unshirkable economic and social responsibility of enterprises. The state has formulated relevant measures to guide and plan to reduce energy consumption per unit of GDP by 4%. Integrating the waste heat of the low-temperature flue gas generated by the aluminum electrolytic cell into the energy system can realize the efficient utilization of low-grade energy and bring economic and environmental benefits to the enterprise.

Before the 1970s, my country's aluminum electrolysis industry was mainly based on the self-baking tank production technology imported from the Soviet Union, with low efficiency, high energy consumption, backward operation and serious pollution. After the 1980s, on the basis of the introduction of foreign advanced technology, aluminum electrolytic cells have been digested and absorbed and experimentally studied. From small to large, large-scale devices have been formed, such as 400kA pre-baked anode aluminum electrolytic cells, which completely solved the traditional self-baking. The anode aluminum electrolytic cell has technical problems such as harmful smoke and dust control, environmental protection, mechanization, automation, etc., and has achieved good results such as high efficiency, energy saving and investment saving in aluminum electrolytic production, and thus formed a relatively advanced pre-baked cell technology and equipment technology in the domestic aluminum electrolytic industry And a complete technology development system. At present, my country's aluminum electrolysis process and equipment technology have reached the international advanced level. The 400kA electrolytic cell has the distinctive feature of large capacity, and the large electrolytic cell has laid a good foundation for waste heat utilization.

The invention uses water as the medium of low-level thermal energy to generate steam through heat exchange, and the steam generates electricity through a turbine generator set, and the electricity is returned to the electrolytic aluminum power system. From a single electrolyzer, the recovered heat energy is not much, but the large-scale aluminum plant has a large number of installed capacity, such as a 335kt aluminum enterprise, if the waste heat of the flue gas is recovered and utilized, it can be equipped with a 12-15Mw generator set, and the annual power generation can be Up to 10000-110 million kWh, the power generation is quite considerable.

Contents of the invention

The purpose of the present invention is to provide a method for generating electricity by using the waste heat of an aluminum electrolytic cell, in which the low-level thermal energy generated in the aluminum electrolysis process is generated through heat exchange to generate steam, the steam generates electricity through a turbine generator set, and the electricity is returned to the electrolytic aluminum power system to achieve The purpose of energy saving. The principle is to use water as the medium to convert water into steam for power through staged heat exchange from low to high in a direct current manner, and then convert the steam into electrical energy through a turbine.

The present invention is realized through the following technical solutions:

A method for generating electricity by using the waste heat of an aluminum electrolytic cell, the equipment used includes: an aluminum electrolytic cell 1, a boiler water supply device 2, a metering pump 3, an annular heat absorber 4, an evaporator 5, a steam-water separator 6, a steam main pipe 7, Condensing steam turbine generator set 8, flue gas branch pipe 9, flue gas butterfly valve 10, flue gas main pipe 11, water volume regulating valve 12, flue gas purification system 13, flue gas heat exchanger 14.

The flue gas discharged from the aluminum electrolytic cell 1 enters the pipe of the flue gas heat exchanger 14 from the top of the flue gas heat exchanger 14 through the flue gas branch pipe 9. The flue gas branch pipe 9 is provided with a flue flue butterfly valve 10 for controlling the flow of flue gas , the flue gas flow rate is 2000-3000Nm ³ /h, the flue gas passes through the flue gas heat exchanger 14 from top to bottom, is discharged from the bottom of the flue gas heat exchanger 14 after heat exchange, and enters the purification system 13 through the flue gas main pipe 11 upwards ;

The metering pump 3 draws water from the boiler water supply device 2 and pressurizes it to 0.9-1.0 MPa, sends it into the lower part of the flue gas heat exchanger 14 and enters the tubes of the flue gas heat exchanger 14, and controls the water volume through the liquid level of the steam-water separator 6 The regulating valve 12 controls the water intake to 160-170L/h; the water passes through the flue gas heat exchanger 14 from bottom to top, uses the heat provided by the flue gas to heat the water temperature to 100-110°C, and then passes the water into the annular heat absorber 4. The ring-shaped heat absorber 4 is arranged in a ring close to the side wall of the aluminum electrolytic cell 1, and uses the heat of the side wall of the aluminum electrolytic cell to heat the water temperature to 150-160°C, and then passes the water into the top space of the aluminum electrolytic cell. The evaporator 5 uses the heat from the top of the tank to generate a mixture of water and steam and enters the steam-water separator 6 to separate the liquid water from the steam. The 0.8MPa steam is sent to the condensing steam turbine generator set 8 to generate electricity, and the electricity generated is returned to the electrolytic aluminum for electricity system, the condensed water is returned as boiler feed water.

Preferably, the flue gas heat exchanger 14 is a vertical tube heat exchanger.

Advantage and effect of the present invention:

1. The temperature of the flue gas discharged from the aluminum electrolytic cell is 100-110°C, and the low-level heat energy is exchanged by a vertical tube heat exchanger to obtain heat from the boiler feed water. The vertical tube heat exchanger has two functions: (1) heat exchange function: the boiler feed water passes through the tubes from bottom to top, absorbs the heat in the flue gas, and increases the temperature of the boiler feed water from normal temperature to 100-110 ° C; (2 ) Dust removal function: the flue gas passes through the pipe from top to bottom, is discharged from the bottom, and suddenly changes direction and enters the flue gas purification system upwards. The flue gas is deposited in the ash hopper with gravity and discharged. The dust after the device is reduced by 30%.

2. After the side wall of the aluminum electrolytic cell passes through the carbon-silicon heat-insulating brick, the temperature of the outer surface of the steel plate is as high as 300-350°C, and this part of the heat loss is quite large. The heat-absorbing tube arranged in a ring close to the side wall is used to absorb the heat from the side , raise the boiler feed water temperature from 100-110°C to around 150-160°C;

3. The melting temperature of the aluminum electrolytic cell medium is 945-950°C, and the temperature of the upper crust is as high as 700°C. The CO ₂ gas precipitated from the anode will bring out a large amount of sensible heat through the crust, and there is a large space between the crust and the anode cover plate. For heat, the tank top evaporator is used to absorb the sensible heat and radiant heat of the tank top, and evaporate the boiler feed water into 0.8MPa water vapor;

4. The boiler feed water is a direct current water supply method, and the water volume regulating valve is controlled by the liquid level of the steam-water separator to adjust the boiler water intake;

5. Use the flue flue butterfly valve to adjust the amount of flue gas discharged from the flue. Under the condition of not affecting the operation, the amount of flue gas can be reduced as much as possible. Reduced by more than 60%;

6. In order to generate more power, the steam turbine generator set adopts the condensing type, and the condensed water is returned as boiler feed water, reducing boiler feed water treatment equipment and costs;

7. The structure of the low-level heat recovery equipment is simple, without changing the original structure of the aluminum electrolytic cell, just add heat exchange equipment to the original structure, the transformation is easy to implement, and does not affect the operation and equipment maintenance;

8. The flue gas volume is reduced by more than 60%, and at least one set of dry purification system is reduced, which can save 13-15 million kWh of electricity every year, and reduce the power consumption per ton of aluminum by 40-50kWh;

9. The electrolytic aluminum flue gas and the side wall of the electrolytic cell are collected and utilized, and the low-level heat energy generated in the aluminum electrolysis process is converted into high value-added electric energy. The heat is recovered in stages, the heat recovery efficiency is high, and the energy saving effect is obvious. Aluminum can save 300-400kWh of electricity, making the energy consumption per unit of aluminum reach an advanced level.

Description of drawings

Figure 1 is a flow chart of the waste heat direct current heat exchange steam power generation of the aluminum electrolytic cell;

Figure 2 is a flow chart of the steam production test of the aluminum electrolytic cell waste heat direct current heat exchange.

In the figure: 1-aluminum electrolytic cell, 2-boiler water supply device, 3-metering pump, 4-annular heat absorber, 5-evaporator, 6-steam water separator, 7-steam main pipe, 8-condensing vapor transmission Flat generator set, 9-flue gas branch pipe, 10-flue gas butterfly valve, 11-flue gas main pipe, 12-water volume regulating valve, 13-flue gas purification system, 14-flue gas heat exchanger, 15-flow meter.

specific implementation plan

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to the content described below.

Example 1: Aluminum electrolytic cell waste heat direct current heat exchange to produce steam

The steam production test process of aluminum electrolytic cell waste heat direct current heat exchange is shown in Figure 2. The 400kA electrolytic cell 1 is used as the test cell. The soft water is drawn from the boiler water supply device 2 by the metering pump 3, pressurized to 0.9-1.0 MPa and sent to the flue gas Between the tubes of the heat exchanger 14, the liquid level of the steam-water separator 6 controls the flow rate of the soft water to 160-170 L/h by the water volume regulating valve 12. After absorbing heat, the temperature of the soft water rises to 100-110°C and enters the annular heat absorber 4 After absorbing the heat from the side wall of the aluminum electrolytic cell, the water temperature rises to 150-160°C, and then enters the evaporator 5 in the top space of the electrolytic cell, uses the heat on the top of the cell to generate a mixture of water and steam, enters the steam-water separator 6, and separates water droplets and steam, 0.8 The MPa steam is vented to achieve the purpose of the test.

The flue gas discharged from the aluminum electrolytic cell 1 enters the pipe of the flue gas heat exchanger 14 from the flue gas branch pipe 9. The flue gas branch pipe 9 is provided with a flue gas butterfly valve 10 to control the flue gas discharge, and recover as much as possible under the operating conditions. Heat, the flue gas after heat absorption enters the flue gas main pipe 11 after being measured by the flow meter 15, and then enters the purification system 13.

Example 2: Aluminum electrolytic cell waste heat direct current heat exchange power generation

For an enterprise with a scale of 300kt/a aluminum, there are 288 sets of 400kA aluminum electrolytic cells, the water supply pressure is 1.0MPa, and the flow rate is 170L/h. 110°C, enters the annular heat absorber 4 to absorb the heat from the side wall of the aluminum electrolytic cell, and the water temperature rises to 150-160°C, then enters the evaporator 5 in the top space of the electrolytic cell, uses the heat from the top of the cell to generate a mixture of water and steam and enters the steam-water separation The device 6 separates the water droplets from the steam to obtain 0.8MPa saturated steam, which is collected in the steam main pipe 7. The total steam volume is 40t/h, which drives a 15Mw condensing steam turbine generator set to generate electricity, and the electricity generated is returned to the power consumption system.

The flue gas discharged from the aluminum electrolytic cell 1 enters the pipe of the flue gas heat exchanger 14 from the flue gas branch pipe 9. A flue gas butterfly valve 10 is installed on the flue gas branch pipe 9 to control the flue gas flow rate to 3000Nm ³ /h, and the flue gas transfers heat After being passed to water, it is discharged from the bottom, and enters the purification system 13 through the flue gas main pipe 11. The steam power generation process of waste heat in aluminum electrolytic cell is shown in Figure 1.

Example 3: Aluminum electrolytic cell waste heat direct current heat exchange power generation

For an enterprise with a scale of 200kt/a aluminum, there are 255 sets of 300kA aluminum electrolytic cells, the water supply pressure is 0.9MPa, and the flow rate is 160L/h. 110°C, enters the annular heat absorber 4 to absorb the heat from the side wall of the aluminum electrolytic cell, and the water temperature rises to 150-160°C, then enters the evaporator 5 in the top space of the electrolytic cell, uses the heat from the top of the cell to generate a mixture of water and steam and enters the steam-water separation The device 6 separates the water droplets from the steam to obtain 0.8MPa saturated steam, which is collected in the steam main pipe 7. The total steam volume is 35t/h, which drives a 12Mw condensing steam turbine generator set to generate electricity, and the electricity generated is returned to the power consumption system.

The flue gas discharged from the aluminum electrolytic cell 1 enters the pipe of the flue gas heat exchanger 14 from the flue gas branch pipe 9. The flue gas branch pipe 9 is provided with a flue flue butterfly valve 10 to control the flue gas flow rate to 2000Nm ³ /h, and the flue gas transfers heat After being passed to water, it is discharged from the bottom, and enters the purification system 13 through the flue gas main pipe 11. The steam power generation process of waste heat in aluminum electrolytic cell is shown in Figure 1.

Claims (11)

1. utilize the method that residual heat of aluminum reduction cell generates electricity, with water as medium, utilize electrolytic aluminum smoke, aluminium cell sidewall, Aluminium electrolysis cell top provides heat, water is heated to be steam, then by turbine generators, steam is converted into electric energy.

Method the most according to claim 1, it is characterised in that the equipment that described method uses includes: aluminium cell (1), Boiler water-feeding device (2), dosing pump (3), ring-type heat extractor (4), vaporizer (5), steam-water separator (6), main steam range (7), Turbine power generation unit, flue gas arm (9), flue gas house steward (11), water regulating valve (12), flue gas purification system (13), flue gas change Hot device (14)；

The flue gas that aluminium cell (1) is discharged, enters flue gas heat-exchange unit (14) by flue gas arm (9), and flue gas carries out heat exchange After from flue gas heat-exchange unit (14) bottom discharge, by flue gas house steward (11) enter flue gas purification system (13)；

Dosing pump (3) pulls water out and is forced into 0.9～1.0MPa from boiler water-feeding device (2), sends into flue gas heat-exchange unit (14), Utilize the heat that flue gas provides by water temp. heating to 100～110 DEG C, then water is passed through ring-type heat extractor (4), utilizes aluminium electroloysis Water, by water temp. heating to 150～160 DEG C, is passed through vaporizer (5) by groove sidewall heat the most again, utilizes groove top heat, generate water, Entering steam-water separator (6) after vapour mixture, by aqueous water and vapor removal, steam is sent to the generating of turbine power generation unit.

Method the most according to claim 2, it is characterised in that flue gas heat-exchange unit (14) is vertical tubular heat exchanger.

Method the most according to claim 2, it is characterised in that flue gas arm (9) is provided with flue butterfly valve (10), controls cigarette Throughput is 2000-3000 Nm³/h。

Method the most according to claim 2, it is characterised in that flue gas is discharged, to enterprising from flue gas heat-exchange unit (14) bottom Enter flue gas purification system (13).

Method the most according to claim 2, it is characterised in that boiler feedwater mode is direct cooling water supply.

Method the most according to claim 2, it is characterised in that the pressure of boiler feedwater is 0.9～1.0MPa.

Method the most according to claim 2, it is characterised in that dosing pump (3) is other is provided with water regulating valve (12), control into The water yield is 160～170L/h.

Method the most according to claim 8, it is characterised in that described water regulating valve (12) is steam-water separator (6) Liquid level water regulating valve.

Method the most according to claim 2, it is characterised in that turbine generators is condensation steam turbine electromotor, cold Solidifying water returns is used as boiler feedwater.

11. methods according to claim 2, it is characterised in that the steam pressure being sent to the generating of turbine power generation unit is 0.8MPa。