What will it take to keep the coal in the hole?

They trade blows from a distance. As often as the coal lobby shouts “it takes coal to make your wind turbine” the environmental movement shouts back about coal burning driving climate change. I get it. As profiled in a recent blog, loads of stuff we use and consume depends on coal. But without a stable climate, humanity will struggle to thrive like it has during the 10,000 years or so (here is a great video that explains this concept).

With such a polarised debate going on, I find it hard to know what progress on this issue would look like. Is there an alternative to burning coal? I decided to put this question to Peter Brown of Miscanthus New Zealand—a Kiwi start-up bringing a plant-based solution to the energy problem. His short answer is yes, there are biological alternatives. But the whole answer isn’t that straightforward.

One alternative coal, for heat and as a source of carbon, is biochar. Biochar is a fancy modern name for charcoal—the black stuff left over when you burn plants. Biochar is most commonly associated with agriculture where it’s added to poor soils to improve fertility. But it can also replace coal in steel manufacture (both as heat and carbon) and be used in industrial processes where coal is used as heat.

Unfortunately, the usual ways biochar is made comes with a cost that’s out of reach for most industrial uses—at least under the current market conditions. Brown explained that this is particularly true if you’re wanting to make biochar at a large enough scale to make a dent in the amount of coal we use.

The challenge is to make coal alternatives economic. In a drive to improve the economics, Brown spent the last three years innovating different biochar manufacturing processes. His concept was to make a higher value product (renewable deiseal) using a process that created biochar as a by-product.

One method he has been part of developing produced very high-quality biochar—basically activated carbon. Because this product can be applied to higher value uses, such as carbon fibre and water filters, it turns the economics around making it a biochar producing project with renewable deiseal as a bi-product.

Creating very high-quality biochar doesn’t, however, give us an economically viable alternative to burning coal for heat in manufacturing and electricity generation.

The economic challenges aren’t the only barriers to using biochar in manufacturing. Transport and handling remain core issues when replacing coal with biochar. Coal is easily crushed and sorted in handy sized dense lumps that are easy to transport, store and move around an industrial site on conveyer belts.

Biochar, on the other hand, is so fine in its raw form that it would be blown off a conveyer belt. Most processes that make biochar have a size limit on the bits of plant material going into the system, typically somewhere between 2 and 12 mm. The biochar that comes out at least as fine as the plant matter that goes in. Manufacturing that uses coal has systems for handling, transporting it and burning it, and would need to be converted (at a cost) to handle biochar.

Turning biochar into pellets may be one way of getting around the handling issues. But palletising it can be a bit of a challenge. It can also reduce the environmentally positive nature of biochars because bitumen, a product that comes from crude oil, is typically used as a binder.

A second alternative is Miscanthus. It’s a giant woody grass that can be directly substituted for coal.

Miscanthus is a sterile perennial 4 m tall grass that can be harvested like maize and is dry enough at harvest to be burnt directly in a coal handling system. Brown presses the Miscanthus into 40 mm wood pellets with about the same density and size of coal. Even the energy density is equivalent to the coal used in some manufacturing. This is key because in the best biochar manufacturing systems about 30% of what goes in comes out as a product, in essence losing 70% of what you have grown.

Peter Brown with a stand of Miscanthus

When trading one resource for another we need to think about wider consequences.

On the positive, experiments have shown that there is reduced nitrogen leaching under Miscanthus crops. This is true even when the Miscanthus crop is sprayed with high nitrogen effluent. Water is fast becoming one of our planets key issues. Anything that reduces nitrogen leaching into the aquifers is a big bonus.

New Zealand has a history of introducing plants and animals for well-meaning reasons only to find that they have got out of control and done more damage than good. The classic example of this is gorse—from a distance, it’s pretty yellow flowers, but close up gorse is a thorny problem for landowners. Miscanthus is an introduced species, but international experience has shown that it’s sterile unlikely to spread. This has also been confirmed by New Zealand authorities.

On the negative, could be the land area required to grow enough Miscanthus to replace large volumes of coal. One dairy factory using coal for heat would need around 8,000 ha of Miscanthus per year to replace all of the coal. An area slightly larger than Lake Rotorua, New Zealand.

The area may sound dizzying, but Miscanthus can be grown in lower fertility land. It can also be grown as a shelter belt that irrigation units and cattle can be driven through. So replacing coal with Miscanthus isn’t a matter of replacing food crops. Brown has spent several years working on this issue: “What really should be done is look at what makes sense overall from a land use perspective, while considering the environmental factors along with what works commercially.”


Posted on

April 18, 2017