Bitumen and Asphalt Producer

A North Queensland-based manufacturer processes raw bitumen and waste products into its bitumen and asphalt products. Most electricity on site is consumed by electric heaters, electric motors and air compressors. Diesel is also used for the burner on the asphalt drum. In 2019, the site consumed 43,265 gigajoules (GJ) of energy and emitted 3,778 tonnes of carbon dioxide equivalent (t-CO2-e).

An energy assessment identified efficiency opportunities that would reduce energy by 329.7 GJ per year and achieve annual cost savings of $11,940. It would also cut emissions by 74.2 t-CO₂-e.

A 100 kilowatt (kW) solar PV system is also recommended, which would reduce energy by more than 470 GJ a year and greenhouse (GHG) emissions by 105.9 t CO₂-e.

Summary of Opportunities

Compressed Air Leak Repair

Leaks in the site’s compressed air system were found to contribute to 25% of the compressed air energy consumption, representing a significant portion of the site’s energy costs. Many leaks were observed to be on old tubing and plastic push in fittings.

It is recommended that the manufacturer conduct a compressed air leak survey using an ultrasonic leak detector to identify the leaks, and repair any leaks found. It is estimated that this would result in more than 74 GJ of energy savings and $2,492 in annual energy cost savings.  This option would have a payback period of 3.4 years.

Compressed Air Energy Reduction

The site’s air compressor is operating at load and unload setpoints that are higher than the industry standard, at 8.4 bar and 9.0 bar, respectively. To realise an annual saving of 20.9 GJ of energy and GHG emissions reduction of 4.7 t co₂-e, these setpoints could likely be reduced by 7% per 1.0 bar of pressure reduction.

At a capex of $600, this option would have a simple payback period of 0.4 years.

Asphalt Plant Shutdown Optimisation

The asphalt plant uses a series of belt and bucket conveyors to transfer product to the central processing area where the final civil product is heated using a diesel furnace, and then mixed and loaded onto trucks. Currently, when the asphalt plant shuts down, all conveyors and belts continue to run for 10 minutes to allow the plant’s furnace to cool down so that the load conveyor (which loads the furnace) isn’t hot spot heated.

The load conveyor is the only conveyor that needs to run through the shutdown process. The programmable logical controller (PLC) could be upgraded to stop all conveyors while keeping the load conveyor running, significantly reducing the energy consumption of the system.

The optimisation project would cost $10,000 and offer total energy cost savings of $2,134 with a payback period of 4.3 years. It is estimated the project would save 63.9 GJ of energy.

Asphalt Plant Conveyor Sensors

The asphalt plant conveyors run continuously during the shift, even when there is no product on an individual conveyor. Modern production line systems are fitted with laser sensors to recognise when the conveyor is loaded, switching the motor off when it’s not required. 

The recommended project would see several laser sensors installed on each production line. A PLC upgrade (see previous option) would be required to realise the energy savings. This project would achieve $4,539 in energy cost savings and could access $1,714 in rebates. It would also offer a significant energy saving of 136 GJ and reduce emissions by 30.6 t co₂-e.

Fast-track Office LED Lighting Upgrade

While the majority of external lights in the processing plants have been changed to LEDs, many fluorescent lights remain in the site office. The manufacturer is gradually upgrading the existing T5 fluorescent lights with LEDs as they fail. In recent years, LED lighting technology has improved in quality, reliability, lifetime and cost.

It is recommended that the site fast track this upgrade to take advantage of the energy savings and emissions reduction earlier than expected. This would result in 34 GJ in energy savings, 7.7 t co₂-e in emissions reduction, and offer a payback period of 5.8 years.

Battery storage can help manufacturers more effectively participate in demand management opportunities, save on energy and be more energy independent.

Two 50 kilowatt (kW) / 100 kWh batteries (for separate site lots), would provide combined annual cost savings of more than $17,000. Based on the current market price of batteries, this option would cost $142,000, making it financially unviable. Battery prices are changing rapidly, however, so the current use cases that are uneconomical will likely change in coming years. This option should be revisited at this time.

Electric Tank Heater Demand Management

Other opportunities were also considered to improve energy performance on site. One project - to install a PLC on each electric heater in the existing tank heating system - has a capital cost of $25,000 with a highly favourable payback period of just 1.3 years. This option would save the manufacturer $18,888 per year in energy costs.

“Currently, solar PV connected batteries are only financially viable as a storage device for excess PV production if they can be effectively utilised in managing network tariff thresholds (allowing the site to remain on a cheaper network tariff), managing peak demand costs (the battery discharges when the site is nearing its peak demand threshold to reduce peak demand costs) or when the battery system is sufficiently large (>1 MW) to participate in demand response events.“