Building Materials Manufacturer

A Queensland cement, lime, plaster and concrete product manufacturer is a large energy user, relying heavily on natural gas for its operations. Options have been identified to lower its natural gas consumption and cut Scope 1 and Scope 2 emissions, which would save the manufacturer 8,800 gigajoules (GJ) of energy each year and $95,000 in annual costs. Combined, these solutions would also reduce annual emissions by about 458 tonnes of carbon dioxide equivalent (CO₂-e).

Summary of Opportunities

Oxygen Trim for Calciner and Burners

Oxygen (O₂) trim has been identified as a way to improve the energy efficiency of the site’s calciner, which relies on natural gas for the hot air used in the calcination process. There is currently an over-supply of fresh air, resulting in heat loss due to the heating of air that’s not required in the process.

By trimming the amount of fresh air supplied, the manufacturer could achieve savings of $16,349 each year with a payback period of only 1.2 years. 

Three other recommended options relate to O₂ trim on the eight burners used in the drying process. There are four 0.875 MW burners, three 1.125 MW burners and a larger 2.25 MW burner in the system. By reducing air supply to the burners, this reduces the amount of moisture introduced to the system so there is less energy waste.  The O₂ trim options vary in capital cost, from $17,500 for a single burner (no. 8) to $80,000 for O₂ trims on four burners.

Together, the oxygen trim solutions for the eight burners would cut the site’s emissions by almost 150 t CO₂-e, and save close to $67,000 a year in annual operating costs.

Heat Recovery from Calciner Exhaust

The return air from the end of the calcinating process is currently fed back into the process. This air has a higher moisture content than dry, ambient air, requiring more energy to heat it.

The assessment found that an air-to-air heat exchanger could be used to pre-heat ambient air and use this for the process air stream. This improvement would offer the most significant energy, cost and emissions savings of any of the efficiency improvements, saving the manufacturer 4,499 GJ per annum in energy and more than $48,000 in annual costs. It also offers a reasonable payback period of 3.7 years.

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Exploring Alternative Energy Supply Opportunities

Two key energy supply opportunities were identified for future consideration which, when feasible, could help the manufacturer transition to cleaner energy sources and reduce greenhouse gas (GHG) emissions. These are:

• Solar: a 99 kilowatt (kW) solar PV system would likely environmentally and financially beneficial to the manufacturer, costing about $95,000 in upfront costs. This size system may be eligible for Small-Scale Technology Certificates (STCs), which would improve upon the expected 5 to 7 year payback period.
• Hydrogen: 94% of the site’s energy use is from the combustion of natural gas. Renewable hydrogen blended with natural gas would be a convenient and potentially low capex way to decarbonise a portion of the site’s gas usage. This would deliver a site-wide greenhouse gas emissions reduction of between 4 to 8%.