Saturday, December 2, 2023

Full steam ahead towards carbon neutrality

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A Victorian-era tram will run on wood waste in Scion trial.
The briquettes, designed to replace coal, are made using forest residues such as bark, branches and low-quality stem wood.
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It’s out with the coal and in with the biofuel for steam tram No 100.

The tram, which was built in the United States in 1891, will operate on a renewable energy source made from trees when it appears at the Museum of Transport and Technology (MOTAT) live day in Auckland on August 20.

Developed by Crown Research Institute Scion, the biofuel will undergo its largest trial to date when 250kg of briquettes supplied to MOTAT keep the tram running all day.

The briquettes are made using forest residues such as bark, branches and low-quality stem wood – all woody biomass that is currently seen as a waste product in the industry. 

Scion is attempting to unlock the potential of this “waste”, seeing opportunities in the estimated 4 million tonnes of harvest and thinning residues that currently remain in production forests.

Over 2 million tonnes of coal was burned in New Zealand in 2022 and Scion believes forestry may hold the solution for providing coal burners with a clean and renewable energy source.

Scion integrated bioenergy portfolio lead Paul Bennett said a biofuel future is essential for NZ to meet its global climate change commitments.

“Energy use contributes to around 90% of New Zealand’s carbon dioxide emissions. If Aotearoa is going to achieve its net zero target, it needs to address emissions from energy use.

“This is currently the most achievable target for New Zealand to reduce carbon emissions. However, it’s not a target that can be achieved only by Scion. It requires connections with the industry and the public. 

“To bring biofuel to the market and successfully replace coal, the technology needs to be tested at a range of scales. This partnership with MOTAT is the ideal first step to demonstrate the effectiveness of biomass briquettes at a larger scale, with a like-minded company that wants to reduce its environmental impact,” Bennett said.

MOTAT collection workshops manager Graham Anderson said the museum is committed to reducing its carbon footprint and the trial is another step toward becoming carbon neutral.

“However, we acknowledge the challenges to this objective when it comes to operating many of our heritage collection objects that require burning coal, such as the Pumphouse and Beam Engine, steam trains and steam tram. 

“It’s a balancing act between sharing with our visitors how these magnificent examples of science and technology work, while keeping carbon emissions to a minimum.” 

 Anderson said steam tram No 100 has a fascinating history.

 Built in the United States in 1891, it was shipped to Sydney where it operated on the New South Wales Government Tramway system until 1905, when electric trams replaced steam services. It was briefly used by the private Saywells Tramway at Rockdale and then brought to Whanganui, New Zealand in 1910 for construction of the Gonville and Castlecliff Tramway Board’s electric tramway extensions to the Wanganui system. 

This work was completed in 1912 and the tram was then placed in storage. It was briefly pressed into service hauling passengers between July and October 1920 when the electric tramway power supply failed. It was restored to operational condition by MOTAT in 1971, and today runs on MOTAT’s tramway from Great North Road to Motions Road.

Although MOTAT has a licence to burn coal and complies with all legislation, it is investigating options for more sustainable, clean, or cleaner, fuel alternatives. The collaboration with Scion is an opportunity to further this research.

Scion scientists have been developing the biofuel since the early 2000s, but have made significant breakthroughs in the past 12 months.

Scion scientist Dr Bing Song said the success to date is a culmination of more than 20 years’ work.

“The project team are experts in this field. While the machinery is not new and the concept of continuous briquetting has been around for decades, the magic is really in the method. Our deep knowledge and understanding allow us to see results not yet recorded in scientific journals.

“We have been excited to be seeing positive developments of the biofuel in the past 12 months. And with further engineering innovations in the pipeline, we’re feeling confident about the future of this project.”

To produce a briquette, forest residues are first dried, and their size reduced to fine particles smaller than 3mm. These particles are then heated to approximately 100degC and pressed into briquettes.

For a true coal replacement, forest residues must be densified and upgraded to a heating value comparable with coal. The resulting briquettes must also be durable, meaning they can hold their shape and not break or crumble during transportation and handling.  

Thermal coal’s average bulk density is approximately 700 to 800kg per cubic metre. To date, Scion has achieved a density of around 550kg per cubic metre with a durability greater than 91%, qualifying the briquettes as a coal replacement for medium/low process heat supply.

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