3-3: The process of exhausting smoke and gases from fuel in the asphalt factory
dryer
Turbojet heat dust separation
Dust extraction
cyclone
Rotary separation of filler
Dust extraction
ventilation
His tail is dust
Blue filter
Water shower to separate dust from gases
mud
The smoke and gases from the fuel of the factory burner and the dust caused by the drying of the materials are sucked through the suction and transferred into the cyclone, where after the separation of the filler, the dust and the resulting smoke and gas are also separated by the exosphene. The factory filter, which is blue, is transferred.
And with the use of a water shower, dust and dirt are turned into sludge and sent to the factory pool together with water to settle, and vapors, smoke and purified gas are sent to the environment from the outlet of the filter.
4-3: Bitumen preparation process in asphalt factory
Bitumen pool
Pump or gravity transfer
Falx
Hot oil, heating
hot bitumen
Transfer pump
Top of the tower (three-way valve)
Adjustable drain valve
Bitumen weighing tank
Drain pump
mixer
Drain valve
Asphalt silo
Drain valve
Compress
The bitumen purchased by the contractor is transported from its production site in the refinery by bitumen trucks to the asphalt factory, where it is poured and stored in metal bitumen tanks or bitumen pools.
The bitumen inside the tanks is liquefied using indirect heat (heat of oil heating coils) or indirect heat (torch) and by using a bitumen pump or by gravity if the tanks are located at a height compared to the bitumen flux. It is transferred into the bitumen phalax.
In Falx Bitumen, by using oil heating coils, the bitumen temperature has reached about 200-250 °C and is ready for use. It is used in the production of asphalt. Then, using a bitumen pump, the heated bitumen is transferred to the top of the factory tower where a three-way valve is installed.
And from there, after the command to open the bitumen path in the three-way valve, bitumen is sent to the bitumen weighing tank, and after weighing the appropriate amount according to the design, inside the mixer, where the materials have already been entered, by means of the bitumen pump with pressure on It is sprinkled on the materials and after mixing with the materials along with the filler, the resulting mixture, which is asphalt, is emptied into the asphalt silo and from there it is emptied into the asphalt truck to be sent to the project for spreading.
4- Asphalt factory equipment:
Cold bins: 1-4
Belt conveyor: 4-2
Dryer: 3-4
Turbo jet: 4-4
(Cyclone) Cyclone: 4-5
(Fan) ventilation: 4-6
(Filter) Filter: 4-7
Elevator: 4-8
(Screen) Serand: 4-9
Hat bins: 4-11
(Electronic weighing) (scale) tank weighing: 11-4
(Mixer) Mixer: 4-12
(Finished product silo) gram asphalt silo: 13-4
(Control cabin) Control cabin: 4-14
(Compressor Pneumatic) Compressor wind: 15-4
(Flask) Flask: 4-16
(Oil heater) Oil heater: 4-17
4-18: Bitumen tanks
In the following, explanations and how each part works along with their forms are provided
Cold bins: 1-4
Usually, in each asphalt factory, there are four silos for cold materials next to each other, with the capacity corresponding to the production capacity of the asphalt factory, which is made of steel sheet in the shape of an incomplete inverted pyramid, and it is possible to increase the capacity of the silos from their upper part.
Under each of the silos, there is a discharge valve system with feed control of a strip feeder with AC variable speed electromotor and adjustable speed of the strip feeders with potentiometer control from the steering room by the operator to control the flow percentage of feed according to the workshop formula and asphalt plan.
Belt conveyor: 2-4
The conveyor belt is made of a rubber band with strong and flexible fibers that is placed on rollers mounted on a tubular or chute chassis and is moved by an electric motor, and it moves and transfers the load placed on it.
In the asphalt factory, conveyor belts are used to transfer materials from cold tanks to dryers.
Dryer: 3-4
The dryer is one of the main components in the asphalt factory, which is the place to dry and heat the materials to the appropriate temperature (about 200-220 °C).
Asphalt factory dryer consists of a rotating double-walled steel cylinder with internal diagonal blades for moving materials, which is installed horizontally with a low slope (about 2-3 degrees) on its chassis.
In the external environment of this cylinder, there are usually two cast iron or steel belts to support the dryer on the idle rollers mounted on the chassis.
Also, a large gear wheel is installed in the outer environment of the dryer to transfer power to rotate the dryer. This gear is engaged with the pinion gear (small) connected to the gearbox, and thus the rotary power of the electric motor is transferred to the gearbox.
After reducing the speed and increasing the torque by the gearbox, the rotation is transferred to the belt gear of the dryer by the pinion gear and causes the dryer to rotate.
The cold material enters the dryer from the beginning, and from the other side where the turbojet burner is installed, after heating and losing moisture, it comes out and is transported to the top of the factory tower by the elevator.
The materials brought into the dryer during the dryer contact with the flame of the turbojet burner reach a suitable temperature of 200-220 °C and are ready to produce asphalt.
Asphalt factory dryers have different dimensions (length and diameter) according to the production capacity of the asphalt factory, and the higher the production capacity of the factory, the greater the diameter and length.
The installation angle of the dryer on the chassis and the rotational speed of the dryer also affect the production capacity. Usually, the angle of inclination of the dryer is 2-3° towards the end of the dryer (place where the burner is installed) and its rotation speed is 20-22 RPm.
By increasing the slope and rotational speed of the time, the length of the dryer is reduced by the material, as a result, the production capacity increases, but on the other hand, with the decrease of the remaining time of the material in the dryer, the possibility of the temperature of the material reaching the desired temperature will be faced with a problem. It is necessary to increase the thermal power of the burner, and as a result, there will be a need for a burner with a higher thermal efficiency.
For this reason, according to the production capacity of the factory and the thermal power of the burner on it, the angle of installation of the dryer and its rotation speed, which directly affects the time the materials stay inside the dryer, are determined.
One of the factors that should be taken into account in the maintenance of the dryer is cooling the dryer at the end of the daily work of the factory, and the internal temperature of the dryer should be reduced to about -80 °C by blowing fresh ambient air through a turbojet whose fuel has been cut off. This action prevents the dryer from warping and deforming as a result of turning off the dryer at high temperatures.
In addition, it is necessary to avoid oiling the cast iron or steel belts of the drier, which are resting on the round garbage rollers and moving, because the oily surface of the belts causes the dust and fillers around the factory to sit and stick on them. It turns out that the aforementioned dust causes the contact surface of rollers and belts to corrode with sanding action.
In order to prevent heat loss and increase thermal efficiency, the outer wall of the dryer is usually double-walled and insulated with a layer of glass wool and a steel sheet.
Turbojet is also used at the end of the dryer to heat the input materials to the expected level, and also to send pure air at the end of the work to cool the dryer.
Turbo jet: 4-4
The turbojet is installed at the end of the dryer to provide heat, or in other words, to heat the materials and help to separate the dust from the materials, and it performs its task by producing trailing heat throughout the dryer. Its fuel is gas, diesel or diesel fuel.
A turbojet burner usually consists of a high-speed electric motor, a compressor, a turbine, a nozzle, an anti-heat hood and a body.
The thermal power of turbojet burners used in asphalt factories varies according to the asphalt production capacity (h/ton) of the factory, so that the higher the hourly production capacity of the factory, the higher thermal capacity turbojet burners are used.
As a general rule, a burner with a heat capacity of 200,000 h/kcal is needed to produce one ton of asphalt per hour. For example, for an asphalt factory with a capacity of 0-0, producing asphalt 250 h/ton, a burner with a heat capacity of 25,000,000 h/kcal is needed.
One of the important issues in the maintenance of burners, especially burners that work with diesel and fuel oil, is the daily cleaning of the coke resulting from the combustion of the burner fuel, which sticks and settles in the inner environment of the burner's refractory cap.
Failure to clean these cakes causes incomplete flame and deformation, damage and unusability of the cone.
If the fuel of the burner is diesel, the diesel must be brought to the desired temperature (around 200-250 °C) before consumption and then sent to the burner for consumption.
To heat fuel oil, the best method is to use indirect heating of oil using an oil heater and fuel oil tank with a coil.
To prevent the bearing of the burner's ventilation vanes from seizing, which disrupts the operation of the burner and prevents control.
The heat of the burner is controlled by the operator from inside the cabin. After finishing the daily work, the dust sitting on the bearings and joints of the fan should be removed using the air hose.
(Cyclone) Cyclone: 4-5
The dust separated from the materials from the upper channel of the dryer goes to the cyclone as a result of the suction caused by the exosphene, and according to the design inside the cyclone, it turns into a round wind and rotation, and its heavy particles (filler) are separated and gravity-wise to the end of the cyclone and from there it enters the filler storage tank, which is finally transferred to the corresponding tank at the top of the tower using the filler lift.
(Fan) ventilation: 4-6
Ventilation or exhaust fan consisting of housing, anti-wear blades, electric motor, inlet and outlet valve.
According to the location of the ventilator at the outlet of the cyclone, through the corresponding channel (above the dryer), dust particles, filler and pollutants are sucked from the dryer which is done at the same time as the filler is separated in the silicone, and then to the blue filter for Cleansing blows.
In the figure below, an example of the impeller used in the exhaust chamber of the fan is shown, which is made of wear-resistant steel and sucks the dust and fumes from the combustion of the turbojet burner inside the dryer and pushes it towards the filter with high pressure. Is.
(Filter) Filter: 4-7
In order to prevent pollution, dust and pollutants from the factory in the environment, a filter (dry or water) is used.
1-7-4: Dry filter (bag)
The metal chamber containing many cloth bags for separating dust particles along with hot air is blown by the blower (located at the silicone outlet) from the suction dryer and also after separating its filler in the cyclone, into the chamber containing the cloth bags. to be
After the cleaning operation, the dust falls to the lower part of the filter by gravity and is directed to the corresponding tank, which is transported out of the factory if it is not needed (replacement of the filler).
Blue filter: 4-7-2
The chamber is cylindrical (the top and bottom of the incomplete cone) and has a nozzle and high-pressure water showers that are fed by a water pump. As mentioned in the previous part, the dust particles are sucked by the ventilator from the dryer and cyclone and are blown to the water filter, where after hitting the water from the showers, they are weighed down and fall to the bottom of the filter by gravity. Muddy water is directed to the corresponding pool for sedimentation.
(Elevator): Elevator 4-8
A type of chain hoist on which small tanks called "kashkak" are mounted and move upwards in a metal case.
The dust-free hot aggregates are poured from the shooting (outlet) of the end of the dryer into the buckets of the elevator, and during the movement, the aggregates are transferred to the top of the factory tower and then they are discharged by gravity on the conveyors.
(Screen): Line 4-9
It includes anti-wear metal nets, shooting and vibration system.
Anti-abrasion metal mesh nets are classified according to the size of the passage holes and are installed at a certain distance in parallel on the track, so that the net with large holes is arranged in the upper part and the rest are arranged in order of size.
It should be noted that the size and dimensions of the sand depends on the capacity of the factory and the size of the holes of the nets depends on the asphalt mixing plan.
During the operation of the asphalt factory, the vibrating system shakes the gratings and separates and directs the aggregates to the respective tanks, and if there is excess or coarse aggregate, it is transferred out of the system from the shots at the ends of the gratings.
Hat bins: 4-11
There are tanks, each of which is placed under a special net, so that after separation, the hot aggregates are guided into them. At the end of the gaps, there is also a drain valve, which opens after commanding the jacks (hydraulic or pneumatic) and aggregates. They are guided to a certain amount on the scale and are closed with the next command. Usually, there are four bins with suitable capacity in each asphalt factory.
(Electronic weighing) Tank weighing: 4-11
A set of tanks, load cells (weight gauges), discharge valves that are opened and closed by pneumatic jacks.
In the asphalt factory, three separate scales are usually used to weigh bitumen, filler and materials, and based on the mixing plan, the materials are weighed and then discharged into the mixer.
(Mixer) Mixer: 4-12
The mixer is made up of a tank with a volume corresponding to the production capacity of the factory with an anti-wear inner wall, a controllable discharge valve, two rotating axes opposite to each other, on which a number of arms and claws are installed for mixing and producing asphalt.
The three materials entering the mixer (aggregate, filler and bitumen) are weighed against the asphalt plan, for 52 to 30 seconds by the arm and claws installed on the rotating shafts of the mixer, which rotate in opposite directions, they are completely mixed and the asphalt is homogeneous and It is produced uniformly and then by opening the valve under the mixer by pneumatic jacks, the produced asphalt is emptied into the asphalt storage silo.
One of the important factors in the production of homogeneous and uniform asphalt is the health of the arms and claws of the mixer. Due to the exposure of the arm and claws to wear, in case of excessive damage and erosion of the arm and claws, the process of mixing the production asphalt is not done well and the asphalt is out of homogeneity and uniformity. Therefore, it is necessary to
At the end of daily work, check the condition of the internal parts of the mixer, especially the arms and claws.
Also, the bricks installed in the inner wall of the mixer, which protects its body, should be visited regularly and periodically, and in case of damage, they should be replaced.
(Finished product silo) gram asphalt silo: 13-4
It is a tank that holds the ready asphalt and is waiting for the command to empty the asphalt to the compressor located at the loading station. One of the important and noteworthy points is that the control room should be installed so that the silo discharge valve and the loading compressor are within the operator's vision.
(Control cabin) Control cabin: 4-14
It is a place to install the factory control devices and tools so that the operator can supervise and control the asphalt production process from the beginning to the end (zero to one hundred) and usually from a metal room attached to the factory.
(This model is almost "obsolete") or it is formed with a small distance where all the electric and electronic control panels and other control elements are also installed there.
The operator can operate the factory by using the available facilities and issuing manual, semi-automatic, automatic or intelligent commands to achieve the desired and expected output (homogeneous and uniform asphalt equal to the asphalt plan with the right temperature) from the factory.
(Compressor Pneumatic) Compressor wind: 15-4
Wind compressor consisting of pump, electric motor and storage tank with suitable capacity.
In order to provide air with suitable pressure to control the pneumatic jacks installed in different parts of the factory, such as the discharge valves between hot air, weighing system, filler tank, bitumen tank, mixer tank, asphalt tank, etc., from the air compressor with capacity and working pressure. It is used appropriately.
The production wind pressure is transferred to the required parts by metal pipes and high pressure elastic pipes.
In the asphalt factory, according to the production capacity of the asphalt factory, fixed electric compressors with suitable flow and working pressure of 8-20 bar and a suitable storage tank are used. The produced wind is transferred to the electrical pneumatic valves of each jack through metal pipes and high pressure hoses, and from there, after the command from the steering room, it is transferred to the corresponding jacks and causes the opening and closing of the jacks to perform the corresponding process.
In order to prevent damage to asphalt plant jacks and pneumatic valves, the asphalt plant operator must take action on a daily basis to empty the water and moisture accumulated in the compressor tank through its drain valve.
(Flask) Flask: 4-16
It consists of a cylindrical tank with a capacity of 20,000-20,000 liters of bitumen, spiral pipes (coil), pump with electric motor, heat insulation layer (glass wool).
Usually, bitumen is flasked from the storage place (tank or pool) by gravity or road pumping, and the temperature of the bitumen reaches the optimal level for asphalt production by the hot oil that passes through the spiral pipes. Then, by the pump coupled to the electric motor, the heated bitumen is directed to the controllable three-way above the tower and finally to the relevant weighing tank for consumption.
(Oil heater) Oil heater: 4-17
The heated oil in the heating furnace (spiral coil pipe) is pumped by a special high temperature oil pump and moves in a closed circuit or in other words circulation. On the way of moving, the oil gives its heat to the bitumen inside the tank (flask, tank, pool) and returns to the furnace for heat absorption and the cycle is repeated until the bitumen is heated to the desired temperature.
It is worth mentioning that this kind of heat exchange (indirect) prevents bitumen molecules from burning, and at the same time, the oils used are selected with a high conductivity coefficient and high flash point, so that heat transfer and heating operations can be done better and faster.
4-18: Bitumen tanks
In each asphalt factory, according to the daily production capacity and project needs, bitumen tanks with the necessary capacity are used in the form of metal tanks or bitumen pools.
A significant point in the storage and use of bitumen in the asphalt factory is to heat it using the indirect heating method in order to prevent the burning of the bitumen molecules by the direct heating method.
In the indirect heating method, using heating coils placed inside metal tanks or pool preheaters and sending hot oil to the oil heater, which has heated up to a temperature of about 280 °C, the heat of the oil through the outer wall of the coil tubes. which is in contact with the bitumen, is transferred to the bitumen and causes the bitumen to heat up and become fluid and prepare it for pumping into the bitumen flask.
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