Emission Sources in the Asphalt Production Process

What is the emission factor of asphalt?

During the production process, a significant amount of dust is released during the crushing, screening, transport, drying, mixing and loading processes that must be done in asphalt plants. Outdoor aggregate storage areas, conveyor belts and aggregate transfer points can also be a source of high amounts of dust due to wind effect in open areas.
In dryers where the aggregate is heated, undesirable gases such as sulfur dioxide, carbon monoxide and nitrogen oxides originating from combustion, along with dust, and harmful organic substances that may arise by heating the bitumen material are also formed.
Depending on the fuel type, dust and gaseous pollutants originating from combustion are formed from the hot oil boilers used while heating the bituminous material.
Dust will be released as a result of crushing-sieving processes in integrated facilities where aggregate production is also carried out. In other words, drilling, blasting operations, loading-unloading, crushing-sieving operations in the quarry and open transport and storage of materials are also sources of dust emission.

Ways To Reduce and Control Emıssıons

The main pollutant for both integrated asphalt plants and non-integrated plants is dust. Dust emission can be reduced by collecting dust with dust collection systems and passing it through a dust filtering system. The most preferred filtration system is bag filters. Apart from this, electrostatic filters and aqueous dust control systems can also be used.
Apart from this, dust emissions that will occur on the aggregate conveyor belts can be reduced by using closed belt systems. The dust retained in the dust filtering system is reused as filler material in production and provides an economic contribution.
In order to reduce gas emission, drying and heating processes in dryer rotary kilns should be done with quality fuels and combustion systems. The heat energy of the waste gases must be recovered and used in the drying system. Dust emissions that will occur in these furnaces should also be filtered with the existing dust collection system or an independent dust control system should be established.
In mixers where aggregate, bitumen and other additives are mixed, it is recommended to collect and treat the organic compounds that evaporate during loading on the truck and during the bitumen filling.
Organic harmful substances will be formed as a result of heating the bituminous material in drum mix (continuous mix) asphalt plant dryers and facilities using recycled asphalt. Depending on the amount of oscillations, control techniques can be applied.
In addition, in-plant roads should be covered, cleaned and dust suppression applied in order to reduce dust emission in production areas. In addition, windbreak curtains and dust suppression systems should be used in storage areas. Thin materials should be stored indoors as much as possible.
It is recommended to carry out crushing-screening activities in completely closed areas in order to reduce dust emission and to be easily controlled.
Electrical energy may be preferred as an option for heating insulated bitumen tanks.
Environmentally friendly technologies are used to reduce the emission sources that occur during the production of Polygonmach asphalt.
EMISSION, Dust collection systems, bag filters, electrostatic filters, aggregate

Asphalt Production Process in Creating Quality Roads

Asphalt (bitumen);

It is obtained by precipitation of crude oil in nature in natural processes or by human distillation. This substance has a hydrocarbon composition and a color ranging from dark brown to black. Sometimes bitumen is modified with polymers to improve performance.
Asphalt, which is used as a superstructure material especially in road construction works; It is an adhesive bituminous binder mixture produced by incorporating minerals and aggregates. Aggregates in asphalt mixtures to be used in asphalt road construction are hard minerals selected according to the characteristics of the superstructure to be produced. These are materials such as crushed stone, gravel and sand.
The most produced asphalt road types are divided into three as hot mix asphalt, cold asphalt and surface coating.

1-Hot mix asphalt:

Aggregate at 145-160°C and bitumen liquefied by heating at almost the same temperature are mixed in desired proportions. Aggregate and bitumen ratios in the mixture vary according to the characteristics of the product to be produced. However, almost 95% of the mixture is aggregate and 5% is bitumen.
In hot mix asphalt production facilities, aggregates in 3 different sizes are generally used. The aggregates are dried in a dryer at a temperature of 145-160°C and then mixed with the bitumen heated at 155-160°C in a mixer. Additives such as fillers, stone mastic can also be added to the mixture. Each batch mixing time is approximately 45 seconds. Bitumen and aggregate must be completely homogenized with each other. Fine mineral fillers are also added to the mix and help bind the bitumen onto the aggregate. Asphalt production facilities produce asphalt at approximately 160°C. Two types of asphalt plants are used, fixed and mobile.

2-Cold asphalt:

It is a mixture formed with fine aggregate, asphalt emulsion, mineral fillers and water. It is used in the maintenance and repair of the asphalt pavement surface. Its cost is lower than hot asphalt and other coating applications.
For those who drive in traffic, cold asphalt is very effective in eliminating ruts, bumps, potholes on the road that affect driving performance and in cases where surface smoothness is aimed. It is also economical and easier to manufacture.
The bitumen mixture is usually applied to the road surface with the paving machines mounted on the truck and designed accordingly. Additional additives can be added to the mixture mortar if desired.

3-Surface coating:

It is the application where the binder and the aggregate are laid on the surface one after the other. Asphalt emulsions are sprayed on the road surface with the asphalt distributor, then gravel is laid on it and the material is compacted with a roller. Surface coating can also be applied as one or more layers. It is easy to lay and the cost is low. However, maintenance and repair costs are high because it is affected by changing climatic conditions.

Asphalt Production

The shorter the distance from the asphalt production facilities to the work area, the faster the production and the completion of the work.
Asphalt plants are of three types: Batch plants, Drum mix (continuous mix) plants and Integrated asphalt plants. All three types can be produced as fixed and mobile.

1-Batch Type Asphalt Plant:

It is the most used plant in the world. High quality production can be made in this type of plant. After all components are weighed separately according to the desired properties in a production process, they are included in the production process and each production period is completed in approximately 40-50 seconds. The production amount in such plants is lower than drum mix plants.

2-Drum mix (continuous mix) asphalt plant:

In this type of plants, unlike batch plants, bitumen and other additives are added to it while the aggregate leaves the dryer. Since there is no mixer, waiting times (mixing, opening and closing the mixer cover, material discharge, etc.) do not occur as in batch type plants. Therefore, production amounts are higher than batch type plants.

3-Integrated asphalt plant:

An integrated asphalt plant, also known as a compact asphalt plant, is a sophisticated facility that combines various components of the asphalt production process into a single unit. Unlike traditional asphalt plants where the individual modules (such as feed silos, dryer drum, mixer, etc.) are separate entities, an integrated asphalt plant houses all these components in a compact and self-contained structure. This design offers several advantages, including a smaller footprint, reduced setup time, and enhanced mobility. Integrated asphalt plants are highly efficient and cost-effective, making them ideal for temporary projects or locations where space is limited. The integrated nature of these plants streamlines the production process, allowing for seamless operation and easy maintenance. Additionally, they often feature advanced automation systems that improve overall control and monitoring of the plant, leading to consistent and high-quality asphalt production. Integrated asphalt plants have become increasingly popular in the industry for their versatility, efficiency, and ability to meet the demanding requirements of modern asphalt production.

Modules in Asphalt Plant and Asphalt Production Stages

asphalt plants; It consists of feeding silos, conveyor belts, dryer, automatic weigher, mixer and loader modules.

Feeding silos:

In an asphalt plant, the feed silos play a crucial role in the production process. These silos are used to store various raw materials such as aggregates, filler materials, and sometimes recycled asphalt pavement (RAP). The aggregates are typically stored in different compartments within the silos based on size and type to ensure a precise mix is achieved during the production of the asphalt mix. The feed silos are equipped with systems for controlled discharge of materials to maintain a continuous and consistent flow to the mixing unit. Proper maintenance and monitoring of the feed silos are essential to prevent material segregation, ensure proper material flow, and ultimately produce high-quality asphalt mixtures. The design and capacity of the feed silos are important considerations in the overall efficiency and productivity of an asphalt plant, making them a critical component in the production of asphalt.

Conveyor Belts:

Conveyor belts are a fundamental component in the asphalt production process, facilitating the movement of various materials within the plant. These belts are used to transport aggregates, filler materials, RAP (recycled asphalt pavement), and other components from one part of the plant to another. Conveyor belts are designed to handle heavy loads and are equipped with mechanisms to control the speed and direction of material flow. They play a key role in ensuring a continuous and efficient operation by delivering materials to the mixing unit at the right time and in the right proportions. Proper maintenance of conveyor belts is crucial to avoid downtime and ensure the smooth running of the asphalt plant. Various types of conveyor belts are utilized in asphalt plants, tailored to specific needs such as incline belts for transferring materials to elevated components or troughed belts for handling bulk materials. Overall, conveyor belts are indispensable in optimizing the production process and enhancing the overall productivity of an asphalt plant.

Dryer:

The dryer drum in an asphalt plant is a critical component responsible for drying and heating the aggregates used in the asphalt mixture. Aggregates, such as gravel, sand, or stone, are fed into the dryer drum where they are heated to the required temperature. The heat not only removes moisture from the aggregates but also preheats them, allowing for better adhesion with the asphalt binder during mixing. The rotating design of the dryer drum ensures that the aggregates are evenly heated and dried, promoting a uniform and consistent asphalt mix. The efficiency of the dryer drum directly impacts the overall quality of the asphalt mix, making it a crucial element in the production process. Proper calibration and control of the temperature and speed of the dryer drum are essential to achieve the desired level of drying and heating for optimal asphalt mixture production.

Sieve and hot aggregate bunker:

The hot aggregate coming from the dryer is separated according to their size in the sieves and the hot aggregate comes to the regabunker. The sieve material is sent back to the crusher. The materials coming to the hot aggregate bunkers are taken to the mixer in the desired amount with the automatic weighing system according to the production recipe.

Mixer:

In an asphalt plant, the mixer is a crucial component responsible for combining the heated aggregates with asphalt binder to produce the final asphalt mixture. The mixer unit typically consists of a twin-shaft pugmill or a drum mixer where the aggregates and asphalt binder are thoroughly mixed to create a homogenous and well-coated asphalt mix. The rotating motion of the mixer ensures that the aggregates are evenly coated with the asphalt binder, resulting in a high-quality asphalt mixture. The mixing process is carefully controlled to achieve the desired temperature and mixing time, ensuring the proper blending of materials. Proper calibration and maintenance of the mixer are essential to ensure consistent mix quality and production efficiency in an asphalt plant. The design and efficiency of the mixer significantly impact the overall performance and quality of the asphalt mix produced.

Dust control system:

The dust control system in an asphalt plant is a crucial component designed to minimize and control the emission of dust particles during the production process. It consists of various mechanisms and equipment aimed at capturing and containing dust generated from activities such as aggregate handling, drying, conveying, and mixing. The primary goal of the dust control system is to improve air quality, meet environmental regulations, and create a safer working environment for plant personnel. Common components of a dust control system include dust collectors, filters, scrubbers, and ventilation systems. Dust collectors such as baghouses or cyclones capture airborne particles, while filters trap finer particulate matter. Scrubbers help remove dust from exhaust gases, and ventilation systems ensure proper airflow and containment of dust within the plant premises. Regular maintenance and monitoring of the dust control system are essential to ensure its effectiveness in reducing dust emissions and promoting environmental sustainability in asphalt plant operations.

Bitumen system:

It consists of bitumen storage tanks and heating system. Bituminous materials brought to the plant from the refinery by heat-insulated vehicles are stored in bitumen tanks. There is a heating system in the tanks to prevent the bituminous material from freezing. Generally, liquid or gas fueled hot oil boilers are used.