Maryborough Foundry

A foundry on the Sunshine Coast is a large energy user that produces a range of mining products to order. Through an energy assessment, valuable energy and cost saving opportunities have been identified, including improving the efficiency of the energy-intensive combustion systems, different methods for improving pre-heating processes and improving low voltage (LV) power factor correction.

Combustion Air Pre-Heating

The site’s combustion systems are its largest energy consumers, with stoves using 31.4 gigajoules per hour (GJ/hour) and gas-fire ladle pre-heaters consuming 4.5 GJ/hour.

Through an energy assessment, it was identified that the manufacturer could achieve a 6.5% fuel saving and more than $34,700 in estimated annual energy savings by installing a combustion air pre-heating system on the two largest stoves.

This is the highest energy saving option for the manufacturer and offers a payback period of just 2.4 years.

Oxygen Trim System

The installation of variable speed drive (VSD) controls on the burners of two stoves is recommended, removing the need for mechanical controls. Mechanical linkage wears over time and impacts a burner’s ability to keep tight control of the air to fuel ratio.

Once VSDs are installed on the burner fans, it is recommended to then install an oxygen trim system, which adjusts the oxygen and gas supply levels for the most efficient combustion and without any excess oxygen. This would typically achieve a 5% reduction in fuel and by reducing the amount of excess oxygen and fuel fed to the burner, resulting in $26,745 in annual energy savings.

LV Power Factor Correction

The site’s low voltage supply electricity data shows a mean power factor for the site of 0.85, sometimes reaching a low of 0.74. By installing a 525 kilovolt amps reactive (kVAr) power factor correction unit, the Manufacturer will increase the mean power factor to 0.95.

Power factor correction would be of significant value for the site. Bringing the power factor closer to unity would reduce demand charges (with estimated savings of $15,109 per annum) due to a reduction in the peak demand cost. It would also promote increased load carrying capabilities in existing circuits with the reduction in overall power system losses.

Proximity Sensors and Cabinet Based Pre-Heating of Work-Pieces

During the site visit, engineers observed that operators pre-heat pieces of mild steel, generally keeping them over the burner flame. It was noted that a part of the steel was not covered by silicon blanket during this time, which is highly inefficient and leads to convection losses.

Two options were identified to reduce these losses:

1. Proximity sensors – the lowest cost option.
2. Container / cabinet pre-heating – a more expensive but preferred option.

Proximity Sensors

Installation of proximity sensors, at a cost of about $1,000, would prevent an operator leaving the work station without putting the silicon cover over the part. If the sensor does not detect a cover while the burner is on, an alarm sounds after a fixed time has elapsed. This option would result in energy savings of 85 GJ each year.

Cabinet Based Pre-Heating of Work-Pieces

A more efficient way to achieve this pre-heating would be to contain the heat within a cabinet. A relatively low cost packaged industrial oven could contain several mild-steel pieces, heating them to 300^oC and providing a much more even application of heat. This would result in less wasted energy given these ovens are about 85% efficient. This option is estimated to cost $9,950, with annual cost and energy savings of $2,642 and 105 GJ per year.

Solar

The site currently consumes 4.75 gigawatt hours (GWh) of low voltage energy for operations and almost 2 GWh of high voltage energy for arc furnaces. The installation of solar on site would help the business decarbonise their energy consumption. Two options are recommended for consideration:

• Install a 99 kilowatt (kW) solar PV system, which would generate electricity to be used behind the meter, even on non-production days. This offers the shortest payback period due to the availability of small-scale technology certificate (STC) rebates for a system of this size, and would deliver more than $25,000 in annual energy cost savings.
• Install a larger solar photovoltaic (PV) system, up to 1000 kilowatt peak (kWp) in size, which would better suit the load profile of the site and would result in over 87% of generated energy being used on site and less than 13% fed into the grid (mostly on Sundays). This would present a sizeable decarbonisation opportunity for the site.

The site’s roof size is suitable for both options.