We stood on a high platform looking out over the surrounding fields, with a light breeze blowing. Both nearby and in the distance were huge mounds, each the size of a football field. A truck moved along a far away road, eventually reaching one of the mounds and emptying its cargo.
‘One of those mounds lasts us about a month’, Paul said, referring to burning it as a fuel source to power the entire mill, like coal but a sandy yellow colour. It was difficult to comprehend the huge quantities being produced and renewed each year.
Paul had emailed me a government report a few days earlier saying that this was the largest source of renewable energy in Australia, at 26% of total renewable energy use in 2017-18. It had made me even more keen to come and see it for myself.
I had cycled into the region the day before, passing endless canefields as I reached the town of Ayr. The harvest was in full swing, with harvesters in the fields and cane trucks and trains regularly passing me on the road, transporting the cane to the nearest mills. I couldn’t help but wonder what happened to it.
The big sugar mills around Ayr could be seen from miles away, and I simply needed to ride in the direction of the tall smoke stack to the west to find my way out to ‘Pioneer Mill’, the largest in the area.
Leaving my bike propped outside and signing in at the front office, I met with Paul in the kitchen where we sat down for lunch together. Originally a chemical engineer, Paul worked with sugar companies in the Carribean, East Africa, China and the UK, and was now in charge of the power generation portfolio for Wilmar Sugar in northern Queensland.
He’d offered to give me a tour of the facility, but we had a time limit. After washing up our plates we donned safety helmets, gloves and earplugs and set off into the sugar mill, the huge structure looming over us and the smokestack towering above.
Paul suggested we start at the beginning of the process, taking me around the side to where a cane train was sliding along tracks up to the mill. It looked like a chain of giant open-topped shopping baskets, each loaded high with sugarcane. The train’s baskets were being rotated one at a time by a giant wheel, tipping their load onto the conveyor belt below.
We stood watching as the conveyor carried the fire blackened cane up into the mill. Burning the canefields is still a common practice in the region, Paul told me, and I’d seen the evidence of this in the columns of black smoke on the Ayr skyline.
The harvesters cut the cane up into short pieces called ‘billets’, Paul explained, to fit more on the trucks and trains. Once the cane is cut and the sugar inside is exposed to the air it will start to degrade, so it’s brought to the mill as soon as possible. It’s a huge logistical exercise transporting all the fresh harvest kfrom around the region.
We followed the conveyor up a staircase into a vast hall filled with billowing steam, machinery, girders, pipes and raised metal gangways, like something out of a steampunk novelist’s fantasy. It had a sweet grassy smell and the noise was tremendous. I followed Paul’s example sticking my earplugs in, which somehow still allowed us to hear each other.
The conveyor stopped at a machine which Paul said was the shredder, smashing up the billets before sending them on to the first mill.
The Number 1 Mill is the most important one in the whole plant, Paul said as we approached it. Not only does it have the job of extracting most of the juice out of the cane, it also determines the quality of the cane and the price paid to the farmer.
It was made up of two sets of three enormous rollers with metal ridges that interlocked with each other, and the shredded cane was being fed between them. A worker sat keeping an eye on it all.
Coming out the other side was a frothy brown mess of juice and pulped fibre. Paul pointed to a channel that piped the juice away to another part of the mill and we headed over to see what happened to it.
A lot of the process was hidden away inside large vats and machines, but Paul explained that the juice is first clarified to remove dirt and impurities and then put through an evaporator, where about 80% of the water is evaporated off to create a syrup.
He pointed into the bowels of one machine and explained how the syrup is seeded with raw sugar crystals in a vacuum pan and boiled until sugar crystals have formed and grown. Walking up a flight of metal stairs revealed the tops of these vacuum tanks. He pulled out a cartridge from the side of one of them, giving it a few solid whacks to dislodge what was inside. It was full of the newly crystallised sugar, which he offered me to taste. Rich and caramelly.
Our next stop was at the centrifuges. Peering through a metal grate, we could see sugar being pushed up against the walls of a circular tub as it spun at high speed. It turned from brown to shades of white as water flushed off the molasses. Paul explained that the resulting sugar would later be sent to a refinery to be processed into things like white table sugar, which he said was mostly about removing the colour.
We returned to the mills where the juice was being squeezed from the cane, and continued along the gangway past mill numbers 2, 3 and 4. It was hot, humid and steamy around each of them.
It was a repeating pattern: a conveyor carried the cane pulp from the previous mill and dropped it into the next one, which squeezed out yet more juice, which was fed back to be mixed with the juice from the previous mills. Meanwhile, the pulp continued on. Having been squeezed and flushed several times, the residue that came out of the last mill was called ‘bagasse’ and had a vital role still to play.
Paul took me to an adjoining structure several storeys tall with enormous pipes running up it. The level we arrived at had sparks flying out the sides of a line of oven-like doors and heat radiating off them, enough to make my skin smart with sweat.
Around the corner it was marginally cooler and Paul showed me a series of viewports. ‘Don’t worry, it’s not too hot’, he said, encouraging me to pull down on a handle, which I did with some trepidation. It revealed a window into a hellish inferno. The flames seemed close enough to reach out and touch, and it was hard to believe that the wall of metal was able to protect us from that intense heat.
Bagasse was being fed into the bottom of the chamber inside, and I could see it being consumed by jets of flame erupting out of pinholes in the floor. Pure bagasse burns quite clean, Paul told me, but there were also contaminants in there that I could see fallen to the bottom plate.
The burning bagasse was heating the main boiler to produce superheated steam, up to 800 degrees Celsius, much of which was used for the sugar-making process. Some, however, was directed to our next stop.
Paul took me to another semi-detached building and we entered through a side door into a chamber full of enormous blocks of machinery, valves and pipes, no doubt carrying all that steam. A sign read ‘Danger: 11,000V’
He pointed out the two huge turbines, each connected to an equally huge generator or alternator, their metal casings concealing what was inside.
Superheated steam was piped here and rapidly expanded through the blades of the turbines, causing them to spin at high speed. These then spun the alternators, which produced electricity. One of the turbine-alternator units had the capacity to generate 36MW of electricity and the other 32MW. The larger unit here was apparently the most efficient biomass generator in Australia.
It seemed suspiciously similar to how a coal power station worked, and when I mentioned this to Paul he said that they’re basically the same; this one could burn coal, but it’s tuned for bagasse. Some other companies switch their biomass cane mills to coal in the off-season to keep the supply of power going.
Generating electricity and utilising the steam left over at the same time (in this case for sugar making) is called ‘cogeneration’, or ‘cogen’ for short. Sugar mills have been burning their crop residue for energy for a long time, but there’s been a move to upgrade to more efficient machines to export more electricity. Wilmar have recently upgraded their cogen plants at their Invicta, Pioneer and Victoria mills and now have the capacity to export about 140MW of renewable electricity across all their mills; enough to power about 80,000 homes. This one here at Pioneer Mill was Australia’s largest cogeneration plant running only on biomass.
‘Does your bike have a name?’, ‘Does it have a motor?’ We had entered the control room for the entire mill and I’d been introduced to two of the operators, Peter and Steve, sitting on wheelie chairs in front of a bank of computers. On one of Peter’s computer screens was a schematic of the mill showing sensor readouts for the various parts.
One number on the screen he was particularly keeping an eye on was the price of electricity on the spot market. This was the price they would be paid for electricity they exported into the grid, but it changed every thirty minutes. Peter was monitoring this market price so as to be ready to ramp up or down their generators to capitalise on it.
As with most markets, the price of electricity was determined by supply and demand, with power stations in the region bidding how much electricity they’d sell at each price. Sometimes the price even went negative, meaning that it would cost them to dispatch electricity to the grid. This happened when there was an oversupply of electricity, such as when all the large solar farms being built in the area flooded the market with cheap electricity during the day.
Peter and I started chatting about what it was like to work the night shifts here, but Paul called me away as we were running out of time. There was one last thing he wanted to show me.
Returning to the bagasse conveyor, we followed it through a long, upwards-slanting tunnel, eventually emerging onto a platform high above the mill and the surrounding countryside. We were standing on top of an enormous multi-storey storage silo where the freshly produced bagasse was held for short-term use. Beyond were the series of mounds, each the size of a football field. These were the bagasse stockpiles, some with bulldozers on them, moving and compacting it.
As with grain or hay, bagasse was liable to explode if it wasn’t stored carefully. Each of the stockpiles was apparently compacted to make it denser and reduce oxygen from entering. It also made it easier to cover with the giant tarpaulins that they pulled over the top ready for the wet season and cyclones.
It was currently the harvest or ‘crush’ season and the mills were working around the clock. There were four in the region and we could see two of the others in the distance, each burning bagasse for their energy needs.
Paul explained how the cane becomes drier as the weeks and months of the crush proceed, and thus the bagasse derived from it burns more efficiently. This means that less is needed and there’s more excess leftover each week. This excess is brought to Pioneer Mill to be stockpiled, coming in faster near the end of the crush.
The crush will finish in seven weeks, at which point they’ll reach maximum stockpile and the bagasse will stop coming in. One of the massive stockpiles lasts about one month and they’ll consume about four piles by Christmas. The whole lot will last them until about March, at which point they’ll shutdown, do maintenance and wait until the next crush.
Some other companies will switch to burning coal when they run out of bagasse, to keep the power going.
A major part of Paul’s job was overseeing the transport and storage of bagasse between the mills. It was its own logistical challenge, with 60 to 70 people working in the region in bagasse transfer and 12 trucks moving it to where it was needed.
Wilmar was the largest biomass user in Australia, and with their Pioneer Mill stockpiling more than all their others, it occurred to me that I was looking out over the largest store of this renewable fuel in the country.
We were out of time, and Paul led me down a stairwell to the ground, ready to take me back to the front office. ‘Can I touch some?’, I asked. He did an about face and took me across to the nearest bagasse stockpile. Picking up a handful, it felt light and fluffy, releasing a fine dust that blew away in the breeze. I could see how easily combustible it was — it made so much sense to use it as a fuel.
It was time for Paul to dash — he needed to pick up his daughter from school — so we made a hasty return to the front office and said our farewells. I collected my bike and cycled back through the canefields to Ayr, thinking of how this massive rural industry was using its own waste to meet its energy needs and provide renewable energy to the grid, in the process reducing Australia’s greenhouse gas emissions by over 1.5 million tonnes each year.
Huge thanks to Paul for taking the time to show me around Pioneer Mill and their biomass operation.