1 overview

 

Although aluminum production in China has been for five consecutive years the highest in the world, but in aluminum industry production technology and compared to the United States, Japan, Germany, Italy and other countries, there is a larger gap task significant energy saving and emission reduction. Mainly manifested in the following aspects:

 

(1) the energy consumption and pollutant emissions in aluminum industry

 

The average production 1 ton aluminum industrial water consumption about 16 ~ 18 tons; Surface treatment of wastewater containing a variety of metal impurity ions; High energy consumption; Produce a large amount of waste residue, only an annual output of 2400 tons of aluminum oxide coloring production lines, annual produce about 150000 tons of sludge, and 2000 tons of waste residue, the quantity is great. Wastewater sludge composition is more complex, at present the most factories adopt the method of landfill deal with the sludge. This not only takes up the limited land resources, and waste of resources, environmental pollution.

 

(2) the cause of the high energy consumption and high pollution aluminum industry

 

(1) melting and recycling: currently, aluminum melting furnace in electric furnace is occupied 5%, 91% oil furnace, gas furnace (4%), 1 ton extrusion on remelting production of pellet fuel consumption than 55.17% higher than that of developed industrial countries, and the actual ingot casting, rolling flat ingot and extruding round ingot) than the average energy consumption of smelting industry in developed countries is much higher. In addition, the overall condition of aluminium melting furnace energy consumption or in the middle and lower levels.

 

(2) casting, rolling and extrusion: lack of high-grade products. Small machine, extrusion equipment is backward, low efficiency; Equipment of the low automatic degree to realize isothermal extrusion quickly, the production of precision profile; The mould in poor quality.

 

(3) surface treatment: surface treatment is high power consumption in the process of aluminum processing, high water consumption and high pollution.

 

Energy conservation and emissions reduction to become today's aluminum processing enterprises urgently need to solve problems, this article from the molten aluminum rod furnace, furnace, holding furnace, extruder and oxidation treatment sludge processing utilization, put forward some new methods and strategies, so that the aluminum processing enterprises achieve the goal of energy conservation and emissions reduction and clean production.

 

2 the melting aluminium furnace energy conservation and emissions reduction and clean production technology

 

2.1 the working process of the melting aluminium furnace

 

Melting aluminium furnace smelting process can be roughly divided into four stages, namely burden load visiters to soften, soften the hotel to charge, charge to all melting (phase the scum oxide), liquid aluminum heating up. Heating of aluminum material is through the burner flame convection heat transfer, fire and radiation heat transfer of furnace walls and conduction heat transfer between the aluminum material.

 

In the whole process, the ratio of three is constantly changing. Solid is aluminum blackness small, heat conduction ability. As the melting process, furnace charge into liquid and solid critical state, the loss of heat conduction, fundamental changes have taken place in thermodynamic properties. The ability of thermal conductivity of liquid aluminum, only 40% of the solid aluminium molten pool to the bottom of the conduction heat transfer process is slow. Metal mirror loose scum floating on a heat transfer thermal barrier layer. The molten pool surface oxidation film melt, lost protection, oxidation, inspiratory tend to increase. For flame melting aluminium furnace in aluminium smelting period, the general control of furnace temperature at 1200 ℃, at this time of flue gas temperature is the furnace temperature, flue gas heat away about accounts for 50 ~ 70% of the furnace heat load, considering the other 10% of heat loss, the effective heat utilization only 30 ~ 40%, if we do not make full use of this part of the waste heat, will inevitably caused great waste and make the furnace thermal efficiency is very low.

 

To sum up, choose to effectively strengthen the heating mode and flue gas waste heat recovery to preheat combustion air is to improve the furnace thermal efficiency, to ensure the smelting process is an effective means of the least amount of fuel consumption directly.

 

2.2 using high temperature air combustion technology

 

High temperature air combustion has changed the traditional way of burning, or fuel furnace flue gas recycling way direct injection combustion way, main show is after ceramic honeycomb body of combustion air is preheated to 1000 ℃ above, sprayed into the furnace at the appropriate speed, air entrainment at high speed, mixing and combustion in the furnace under the influence of product mix, the dilution of 21% of the oxygen in the air at low oxygen concentration (5% ~ 6.5%) lowest fluid in combustion, under the condition of high temperature air combustion can realize low coefficient of combustion air, reduce the oxidation burning loss of aluminum.

 

Regenerative combustion system mainly includes a pair of burner with regenerator, a swap into the device, a control system and pipeline system.

 

When the furnace temperature is 1000 ~ 1200 ℃, the temperature of combustion air is preheated to 800 ~ 1000 ℃, and the use of air heat exchanger wall between fuel melting aluminium furnace can save fuel by 50% or so.

 

Export mixed gas burner actual jet velocity at around 60 m/s, the flame length is about 2.5 ~ 3 m, flame diameter is about 0.5 ~ 0.7 m. Pairs of burner in the furnace the reversing operation, high frequent swaps, the evenness of temperature in furnace, not form low temperature area.

 

2.3 high speed burner

 

For in the old stove, spend 300000 yuan of new a pair of regenerative burner, difficult to accept for the enterprise.

 

Adopts high speed burner nozzle, gas to above 100 m/s high speed spray to the chamber of a stove or furnace, combustion air at a speed of 90 m/s involved in combustion, have a strong impact on the aluminum, accelerate the melting, in order to prevent fire, the fuel gas nozzle placed a long out of firing gun.

 

We in high-speed burner products through the digestion, absorption, the United States, on the basis of developed a performance of high speed burner, gas flow rate can reach 180 m/s, ratio of load adjusting 1:20, excess air coefficient can be adjusted between 0.65 ~ 10.8.

 

The technical features of high-speed gas burner is as follows:

 

A) precise organization combustion, the combustion efficiency 99.9%;

 

B) wide operation condition: heat load adjustment to 1:20, 0.5 ~ 10 air coefficient;

 

C) USES hierarchical burning, harmful gases (NOx) emissions in line with national environmental standards;

 

D) with flue gas ejector return functions, can be taken after the flue gas from the furnace back into back into furnace;

 

E) all metal structure, the service life of 3 years in a row.

 

2.4 melting aluminium furnace automatic control technology

 

Control system is to improve the combustion, reducing energy consumption, ensure process requirement, the important guarantee of improving product yield and yield, the ultimate goal is to realize combustion equipment parameters such as flow, temperature, pressure, atmosphere of automatic detection and process control.

 

Against 2.4.1 furnace pressure automatic adjustment control

 

Reasonable flame furnace should realize micro positive pressure operation.

 

3 extrusion press rod furnace energy saving technology

 

The energy consumption of aluminum extrusion press rod furnace 12 ~ 20% of total energy consumption of processing enterprises. Extrusion press rod furnace can be divided into three kinds, single rod furnace, furnace and short rod furnace. Images, respectively, as shown in figure 3, 1, 2, figure 3, figure 3, 3.

 

According to the theoretical calculation, the 1 t bar heated to 450 ℃, need only 13 m3 natural gas (furnace thermal efficiency is 100%), considering the furnace thermal efficiency and production process of intermittent heating, the heating furnace thermal efficiency is assumed at 60%, up to natural gas consumption and 22 m3 / t aluminum rods, converted into product energy consumption of 26 m3 / t. However, the energy consumption of aluminum rod furnace products are converted into gas for 45 m3 / t products, some even as high as more than 70 m3 / t products. Energy saving space is still large.

 

3.1 single rod furnace energy saving technology

 

3.1.1 reforming furnace

 

According to the theoretical calculation, the furnace volume heat intensity is much lower than the standard industrial furnace, the furnace is too large, low temperature in the furnace, for burning, reach a certain volume of hot strength requirements must strengthen the power of burning, it is bound to increase gas consumption per unit product. We take the reduce furnace volume and increase the brick arch ways of reforming furnace.

 

3.1.2 replace the burner

 

Will all existing dc burner replacement for flammable product patent - vortex burner (second generation). Increase the stiffness of flame, raise flame temperature, strengthening heat transfer effect.

 

(1) the working principle of the swirl burner

 

Various types of vortex generator are installed in the burner (hereinafter referred to as cyclone). Fuel and air mixing flow occurs through the hydrocyclone rotation, from the rotary jet nozzle injection after formation. Using rotary jet to form is conducive to the burning high temperature flue gas recirculation region, and makes the flow strong mixing.

 

(2) good combustible swirl burner structure

 

Swirl nozzle, compared with traditional cut long stick hot furnace nozzle, has the flame stiffness big, heat power, high combustion efficiency, etc.

 

3.1.3 cancel the circulation fan

 

Extrusion press rod furnace with the help of circulation fan, hearth negative pressure is too high, breathing in cold air quantity, nozzle serious fire, greatly reduces the thermal efficiency of the furnace.

 

Cancel furnace can be run after the circulation fan in micro positive pressure condition, ensure the safety of the stove,

 

The economic operation. Can also save electricity 45000 ~ 66000 yuan /. Years.

 

According to the experience of our reformation, Φ 180 mm below the rod furnace can cancel the circulation fan, Φ above 180 mm rod furnace is not suitable to cancel the circulation fan, but the plate heat exchanger makes full use of flue gas waste heat heating combustion air, improve the heating furnace thermal efficiency as a whole.

 

3.1.4 add oxygen detector

 

In order to more accurate adjustment of combustion, the precise control of air-fuel ratio, get rid of the passive situation of thumb debugging, installed on the pipe behind the venturi mixer oxygen detector, oxygen detector data continuous oxygen content will be sent to the PLC, PLC according to the set of air-fuel ratio data adjustment of gas and air valve opening, keep the oxygen content is always in the right proportion, ensure accurate tissue burning.

 

3.1.5 enhance thermal insulation

 

Chamber of a stove or furnace after modification, the outside of the burner brick and roof tile with emerging insulation materials to strengthen insulation, furnace wall temperature is reduced to below 80 ℃, to reduce heat loss.

 

Since 2010, we have to more than 80 sets of single rod furnace energy saving renovation of the best energy saving 49%, the worst has reached 12%. We are promised to customers through our energy saving after modification, gas energy saving rate is above 10%.

 

3.2 how great furnace energy saving technology

 

3.2.1 the combustion chamber

 

Will be a great furnace side into the combustion chamber, cancel the original combustion system, using high speed burner as a heat source equipment, high speed air flow the high-speed burner spray directly into the combustion chamber, reduce the heat exchange process with air.

 

In order to avoid direct flame contact aluminum rods, which leads to the melt accident happened, in the burner flame

 

Laid a fireproof partition, at the bottom of the flames spread to every corner of the chamber of a stove or furnace at a high speed.

 

3.2.2 use high speed burner

 

With the melting aluminium furnace approximation.

 

3.2.3 cancel the hot air circulation system

 

Will be modified combustion chamber, the circulation fan, burning machine, the abolition of all the original combustion chamber, in order to reduce the workload, the internal structure is not change, only the original circulation duct avenues. This not only saves the fan with combustion machine investment, also saves power consumption due to circulation fan.

 

3.2.4 the furnace pressure control system

 

Control of furnace temperature, smoke temperature and furnace pressure control is inseparable. First of all, the provisions of combustion chamber pressure in the range of 10 to 20 pa, chimney is installed on a panel, furnace pressure high, the baffle opening increase, on the other hand, decrease. In the furnace pressure within the normal range, according to the chamber of a stove or furnace temperature especially the exhaust temperature damper opening. This is known as cascade control.

 

3.2.5 increase plate air preheater

 

In order to keep the exhaust temperature kept at 150 ℃ or so, make full use of flue gas waste heat, add an air preheater at the bottom of the chimney, the combustion air preheating, increase the combustion temperature, lower excess air coefficient, improve the efficiency of rod furnace, reducing gas consumption.

 

We have done for some aluminum processing enterprises of great furnace energy saving effect is remarkable, the original tons product 53 m3 natural gas consumption, modified only 31.8 m3, energy saving rate reached 40%, and improve the uniformity of furnace temperature, heating time is greatly shortened, raise the productivity of the equipment.

 

3.3 short rod furnace energy saving technology

 

Short bar heating furnace is a kind of convection heating furnace, as shown in figure 3, 9. Using the hot gases from the burning of combustion machine for aluminum bar convection heating.

 

Thermocouples are installed the heating furnace of aluminum rod furnace, furnace temperature control to meet the demand of the heating bar, because of the control system for pulse control temperature more than set temperature, burning machine to stop working, and when the temperature is lower than the set temperature, the combustion confidential met dozens of seconds ignition, blow a cold wind over the furnace thus affects the thermal efficiency of the furnace, increased energy consumption. In addition, the burning machine to control the air-fuel ratio cannot be automatically, are generally not large air-fuel ratio operation, lead to increase of energy consumption.

 

3.3.1 high-speed burner in alternative burning machine (see how wonderful the furnace)

 

3.3.2 rainfall distribution on 10-12 increase automatic control system

 

(1) heating furnace temperature control system basic composition

 

Heating furnace temperature control system basic composition as shown in figure 3, 10, it is composed of PLC control system, the phase shift trigger module, the SCR rectifier, heating furnace, such as sensors of five parts.

 

Short rod furnace is controlled by the furnace temperature as the temperature index, preset for the corresponding temperature of furnace temperature.

 

3.3.3 cancel the circulation fan

 

Short rod furnace are general configuration 1 ~ 4 sets of circulation fan, trying to make the furnace temperature uniformity, improve the flue gas velocity.

 

(1) cancel the circulation fan

 

Replacement for high-speed burner, because of the high high speed burner jet velocity, the atmosphere inside the chamber of a stove or furnace has strong stirring effect, no fan can ensure uniform furnace temperature, therefore, can cancel the circulation fan, to save power consumption.

 

(2) at the bottom of the chamber of a stove or furnace combustion chamber

 

Narrow at the bottom of the chamber of a stove or furnace volume, keep the flue gas velocity. With special firebrick furnace, along the flue gas flow direction opening in the order since the childhood, and to ensure uniform heating of aluminum rod.

 

Through the aluminum processing enterprises of short rod furnace for energy saving effect, gas energy saving rate of more than 10 ~ 35%.

 

4 oxidation sludge processing technology

 

Aluminum surface treatment process will produce large amounts of colloidal liquid, commonly known as sludge after precipitation treatment, further after dehydration is the aluminum slag. This kind of waste residue number is great, only one

 

Annual capacity of 2400 t aluminum oxide coloring line, each year about 150000 t sludge, slag, 2000 t, therefore the comprehensive utilization is of great significance.

 

Aluminum principle of wastewater treatment process is simple, the operation and convenient management. Present problems is the processing of slag, aluminum after filter press dewatering sludge still contains more hydroxyl, casual disposal can cause secondary pollution. Actually aluminum sediment of wastewater contains large amounts of aluminum hydroxide, if to the development and utilization, activated alumina products, has extensive USES.

 

4.1 oxidation sludge activated alumina production process

 

Process as shown in figure 4-1. With fluidized roasting furnace, wet aluminum hydroxide into first, drying machine, again into the fluidized roasting furnace, fuel injection calcined alumina, after granulation, keeping in good health, activation, classification, is the final product.

 

5 conclusion

 

Through to the aluminum processing industry of melting aluminium furnace, furnace energy saving technical reconstruction, study of oxidation processing of sludge utilization, summarizes some practical experience, also achieved certain effect. However, because most of aluminum processing enterprises orders is full, few can have plenty of time to make a thorough energy saving transformation, there are a lot of energy saving space. Suggest aluminum processing enterprises improve energy saving consciousness, fully realize the energy conservation and emissions reduction is not only a country in order to complete the national convention of tough measures, and to improve the enterprise economic benefit, improve the level of enterprise management, improve the level of enterprise technology and equipment also has the vital significance.