In the process of construction and production cannot avoid the emission of air pollution into the environment. Therefore, the need to have the remedy in a timely manner to avoid affecting the environment in both the stage.
During the construction phase:
- The construction area, building materials are separated from the surrounding area by building a temporary wall (wooden boards or corrugated iron), the minimum height of the temporary wall is 3m.
- Carefully cover the trunk when carrying building materials.
- Machinery and equipment participating in the construction ensure the elements meet the emission standards.
- Periodically moisten the vehicle ramp that runs through the project area, with a frequency of 2 days/times…
- Construction of temporary barriers (brick, wood, ...) in the construction area to limit dust spread to outside.
- Education of consciousness of environmental protection for workers, showing them the benefit of protecting the environment associated with the protection of the health of themselves and the community.
During the production stage:
During operation, the air environment is mainly polluted by dust and emissions from the following four main sources: Transportation, Factory area and storage of materials, Emissions from the boiler.
• Transportation
- Selection of quality assurance supplies, close to the project area.
- Transportation vehicles and internal roads of the concrete batching plant need to be cleaned to minimize the level of dust emission into the air environment.
- Set up cleaning teams, sweeping the road with minimum frequency once a day, especially in the hot dry weather, the company will proceed to spray water 2 times/day on several areas to minimize the amount of dust emission.
• Factory area and storage of materials + Storage of materials:
Material storage area comprises the raw material for the plant's manufacturing process. The majority of raw materials as cement, iron, sand, ... will the emission of polluting gases. To reduce pollution using the following measures:
- Use shields measures in gathering materials’ area to limit the dispersal of dust into the environment around.
- Restrictions contain too much material at the same time.
- Installation of sprinklers (rain spray form) in the area of material transfer conveyor.
- Growing trees around the project to limit the spread of dust.
Factory layouts are airy and clean, there are doors, Windows, ... sure enough conditions such as lighting, ventilation, ... for factory. The factory design model is shown in the picture below:
Figure 3.4: Factory model
The conveyor system of concrete mixing
Cement was transported up the silo by the aerodynamic compression method, then transported from the hopper into the mixing chamber, where the cement mix was mixed with compressed gas line pressure has about 1.2-1.6 Kg/cm2. This gas mixture goes into the silo, then cement is retained and the gas is drained out by the sleeve filter.
Besides, mixing materials and raw materials to the system of mixing will often apply measures such as water spray on the material before shipping to the mixing system to minimize the amount of dust spread into the air environment.
Use of the technology and equipment for the control of air pollution, such as:
Systems project Biofiltration, Control Of Gases, Electrostatic precipitators, Wet Heat
source
Wind Wind
Wind Wind
Scrubbers, Flexible Pulse Jet Filters.
Emissions from the boiler
Emissions (harmful gases like CO, SO2, and NOx) from coal combustion to operate the boiler and dust of the impurities will go into Cyclone dust filter system, then it will be put into the tank of lime water solution and ultimately discharged to the environment.
Boiler
Dust filtration
Exhaust fans
Lime water solution tank
Lime water solution Chimney
Emissions
The emissions go through the cyclone dust filter to remove ashes, carbon black by centrifugal force and gravity. Ashes and black carbon has a greater weight than the air, which is retained at the bottom of the cyclone dust filter, then the gas line continue to be lead through the lime water tank. The pollutants (SO2, NOx) will combine with the solution and create form salts, small dust particles are also retained and settled to the bottom. After passing through the absorption tank system, clean emissions are discharged into the air by chimneys. The waste will be processed in common with solid waste and the solution will be added periodically.
The process of absorbing the emissions occur as follows:
CO2 + Ca(OH)2 ----> CaCO3 + H2O
CaCO3 + SO2 + H2O + O2 ----> CaSO4 + CO2 + H2O Ca(OH)2 + 4NO2 ----> Ca(NO3)2 + Ca(NO2)2 + 2H2O
In fact, much concrete production factories in Vietnam and around the world have also used the aforementioned systems, 90-95% of the amount of dust, CO, NOx
and SO2 will be retained in the solution. Make sure the air after through the absorption system will be located within the limits of QCVN 19:2009/BTNMT column B.
(QCVN 19:2009/BTNMT: National Technical Regulation on Industrial Emission of Inorganic Substances and Dusts)