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Hot Mix Asphalt is an expensive construction material. High cost of hot mix asphalt is dependent on expensive bitumen (binder material), high fuel consumption in production process and high investment cost of facilities. Return of the investment takes a long time period. Because of the mentioned causes, asphalt plants must be operated efficiently for highest performance.

There are many ways to increase asphalt plant’s efficiency through a combination of thorough cleaning, equipment maintenance, moisture control, and energy conservation. Regular deep cleaning of the plant may cost a little down time. But the savings in decreased energy use and increased equipment service life can greatly offset the cost of a periodic plant system shutdown.

Fuel Consumption

Fuel costs are driving most asphalt plant operations today and many producers are looking to reduce costs in any way they can. One of the best ways to cope with volatile fuel costs is to reduce consumption at the plant. Some of the measures for reducing fuel consumption are:

Tuning the Burner

The very first step to reduce the fuel consumption and improving the efficiency of asphalt plant is to improve the efficiency of burner, and the very first step to doing that is to tune the burner. With proper burner tuning, proper burner calibration and adjustment, the fuel is atomised very finely – which means it burns efficiently and easily. A considerable amount of fuel can be lost if the dryer flame does not burn out completely.

If the burner does not operate efficiently and unburnt fuel is passed to the bag filter, this can cause bag blinding or a bag filter explosion or burn out, resulting in the plant being put out of operation.

Insulation

Effective insulation of dryer, asphalt tank, hot mix storage silo, and hot oil and asphalt pipelines can greatly reduce fuel consumption and cost. Insulation around equipment and pipes reduce heat loss by millions of BTUs a day. That can add up to considerable cost saving over the course of a year.

Insulation not only reduces the fuel consumption but also protects the plant components and increases their life. Insulating dryer drum protects the motors, reducers, bearings and wiring that are all around the drum from heating. By protecting those elements from high temperatures, they will ultimately end up lasting longer.

Painting the silos and other asphalt plant components, such as drag slats, in black retains more of the sun’s natural heat inside the facility, saving energy.

Reducing Moisture in Aggregates

The majority of fuel savings associated with asphalt plants relate to moisture content in the aggregate feed to the dryer. Higher the moisture content in the aggregates higher the fuel consumption. If there is water on the rock, bitumen won’t stick to it, so it is essential to dry the stone – evaporating all the water off of it. So, additional fuel is required to remove the moisture from the aggregates. A 1% decrease in stockpile moisture can reduce costs by about 12%.

There are two ways to reduce the moisture of stockpiles: cover or slope. A cover reduces moisture and dust emissions. Sloping the stockpile (ideally at 4%) will also reduce moisture by draining water away from the aggregate. Also, covering feeder belts and conveyors will keep dust down and moisture out.

Dryer Flights

The purpose of dryer flights is to create dense veil of aggregates in front of burner flame for efficient transfer of the heat from the flame to the aggregate. If the flights are not designed and placed well in dryer they will be ineffective and high-temperature exhaust gases will escape from stack or will enter the bag filter without imparting the heat to aggregates. It is important, therefore, that the flights should be designed well or a serious loss of fuel and production will ensue.

Maintenance and Upkeep

Two key drivers of asphalt plant efficiency are reducing energy use i.e. fuel consumption and keeping equipment in good working order. Just keeping the facility, equipment, and fuel clean can increase the asphalt plant’s efficiency.

Keeping the overall asphalt production facility clean helps reduce the amount of stuff – dust, dirt, and grime – that can get into the equipment. Oil build-up in asphalt machinery may not cause them to breakdown. They just work less efficiently. For example, dirty burner components require the burner to work harder to turn the fuel to vapour. Which will in turn uses more fuel.

If there is a build-up on bitumen tank heating coils, that build-up is carbon and it cannot dissipate heat from the thermal fluid into the asphalt so the heater has to run longer to get the same temperatures.

Cleaning the drum and internal flights is another regular maintenance practice followed for build-up aggregates within a drum. Aggregate build-up end up with gaps in the “curtain” of stone falling down through the drum, and that leads to inefficiencies heating the aggregate.  Instead of having an even curtain there will be a gap down one side – and instead of hot air going through stone and heating it, it will race down the side of drum where there is no restriction.

Bag filters must be inspected to confirm no undue leakage. The ducting between the dryer and the fan inlet should also be inspected for leakage, as any leakage or excess air will increase the power consumption of the exhaust fan and reduce the production rate of the dryer. Exhaust fan blades need to be inspected frequently to avoid out-of-balance operation and fan impeller disintegration.

It’s possible that replacing certain components of older asphalt plant can decrease its energy consumption. In some cases buying new (or newer) equipment can increase energy efficiency enough to cover the cost. In addition to lower energy consumption, high-quality new equipment, such as an industrial heating system, typically needs less repairs. This also reduces downtime, saving money.

Keeping the plant well-maintained can extend its service life. It can also increase its energy efficiency. Of course equipment that breaks can lead to plant shutdowns that cost money.