Australian biomass plant to improve soil, sequester carbon, & produce biofuel

CleanTechnica

A $10 million dollar pilot biomass plant will be constructed in the Western Australian Capital of Perth.

Now you may be wondering, how can there be enough pilots in Western Australia to make rendering them down into biofuel worthwhile? But rest assured, in this case the word pilot does not mean aviator, but rather means the facility will be leading the way in terms of technology, and the feedstock to be used will be plants.

The specific type of plants will be mallee crops. This somewhat broad category includes agricultural waste and crops that are not economical for farmers to bring to market, but for the most part it means mallee scrub. This scrub is composed of a variety of plant species, mostly eucalyptus, and typically grows many thin woody stems from an underground lignotuber, which is a tuber that is totally ligno. The stems grow back from this tuber after they are harvested. While it can grow up to 10 meters in height, it is normally under 6 meters. It is found in semi-arid regions of Australia with reliable winter rain and a total rainfall of around 200 to 400mm, which is an average of about a foot for the metric impaired.

Many farmers use long rows of mallee scrub as windbreaks in an attempt to stop the thin layer of dust that covers their pebbles from getting thinner. The scrub can be harvested every 3 to 5 years for use as biomass or… well, that’s really its only use. I guess you could stack it in a pile and taunt it if you wanted to, but that doesn’t seem very productive.

The biomass will be placed inside the pilot plant’s conversion chamber and heated to a high temperature in a low oxygen environment. This will result in volatile substances separating from the biomass, leaving behind solid char, also known as biochar, which is mostly carbon. This heat treatment process is called pyrolysis. To hasten the rate at which it occurs, the conversion chamber will rotate causing large balls of steel inside to pound the biomass, breaking the material up and increasing its surface area. The steel balls allow larger pieces of wood to be used in the converter so that less time and energy need to be spent processing the biomass before it is used.

Pyrolysis will result in the flammable gases hydrogen, carbon monoxide, and methane being released. These will presumably be burned to power the process. Liquids produced include wood alcohol or methanol, turpentine, and a lot of tar. While precautions need to be taken with both methanol and turpentine due to toxicity, both are relatively easy to use as fuels. Racing cars are often powered by methanol and the first Honda motorcycles were turpentine powered due to the lack of oil products in post World War II Japan.

Tar is not so suitable as a liquid fuel. In fact, it is something that’s really a good idea not to put in an internal combustion engine. To remedy this, the liquids produced will be put together in a biorefinery reactor with sulphuric acid or other acids to act as a catalyst to result in esterification. Esters are a class of chemical compounds that, while known for causing narcolepsy in Mexico, widely occur naturally in foods and our bodies. The liquids are also treated with water at high temperature which removes some of the oxygen atoms from the molecules and replaces them with hydrogen, making it more similar to hydrocarbons currently used for fuel and enabling it to be used as a replacement for diesel.

As a safety precaution, both the pyrolysis and biorefinery processes will operate at close to atmospheric pressure to vastly reduce the probability of explosions.

The biochar created by pyrolysis can be mixed into farmland dust and pebbles to make it more like soil. Biochar has a vast number of microscopic pores that help retain both water and nutrients and provide a home for microorganisms that improve the quality of dirt. Using biochar in this way sequesters carbon and makes the process carbon negative. Biochar can also be used as a solid fuel and is carbon neutral when used this way. It can be blended with coal to reduce greenhouse gas emissions from coal power stations.

Pyrolysis could take place on farms and the biochar used on site, while the liquid feedstocks could be transported to a central biorefinery for processing. Laboratory work suggests that the biofuel may cost as little as 38 US cents a liter to produce, or about 23% less than the current price of diesel in energy terms. Also, monkeys could fly out of the biorefinery reactor. But even if fuel can’t be produced at this low price, it could still become competitive if oil prices rise. A sensible carbon price, even one similar to what Australia used to have, would also help.

While farm machinery may be electrified thanks to the declining cost of energy storage and solar power, it is still good to have the option of producing biofuel with this method if needed. It is also something that could be useful for applications such as shipping or running generators.

A total of $4 million of the plant’s $10 million cost will be supplied by ARENA. Normally when the word Arena is used in an Australian context, one automatically thinks of Sir Tina Arena, the only Australian to ever earn a French Knighthood. However, ARENA actually stands for the Australian Renewable Energy Agency, which provides funding for renewable energy research and development. The Abbott government has of course dedicated itself to destroying it.

Source: CleanTechnica. Reproduced with permission.