Bioenergy is renewable energy produced from recently living biological material or organic matter, termed biomass. Conversion of biomass into energy takes a number of forms including direct heat from burning wood or other plant material or electricity produced from burning of those same materials. Biomass can be converted into biogas through a biological conversion known as anaerobic digestion or a synthetic gas (syngas) produced by a partial combustion system called gasification. These biogases can replace natural gas and LPG, both fossil fuels. It can also be a transport fuel including compressed biogas, ethanol from fermented biomass and biodiesel from vegetable oils and fats. Newly developed cellulosic biofuels (green petrol and diesel) can be produced directly from plant matter. For any fossil fuel-based product there’s an equivalent replacement product that can be derived from biomass.
Pyrolysis of wood residues in mobile automated system to produce charcoal and potentially power and heat.
Biochar is based on the technology of slow pyrolysis, where biomass is heated in absence of oxygen to 250–300 degrees celsius. The wood breaks down to release volatile gases, which can be used in an external process to produce heat and power. What is left is the carbon that makes up about half the dry weight of the wood. This is termed either charcoal or biochar, depending on the process and the end use of the carbon.
Slow pyrolysis can be used to just produce charcoal from wood (about 5 million tonnes per year of charcoal is produced in large kilns in Brazil alone – mainly for ore smelting – and tens of millions of tonnes per year elsewhere in the world). The process can utilise a mix of other feedstocks, including straw, chicken litter and crop residues from hothouse vegetable production.
Slow pyrolysis is used to produce charcoal and biochar, while fast pyrolysis is used to produce bio-oil (the condensate of the volatile gases) plus non-condensible flammable gases and ash. Flash pyrolysis is used to break down fine particles of dry biomass to produce synthesis gas, which can be reformed into advanced biofuels, or base industrial biochemicals, or used as a gas fuel for power and high temperature heat – including for firing bricks, or in cement production.
Images taken at Lal Lal near Ballarat in 2014.
The harvester can be set to leave straw that has gone through the machine along with heads either in a windrow, or spread widely. If it is a heavy crop it may be necessary to remove some of the straw to allow sowing of the next crop without problems due to excess straw being collected by the sowing tines.
If straw is left in a windrow this is then pressed into big square bales later to be picked up and put in stacks off the paddock. Usually over half the straw is left as a standing stubble. This gives shelter to the next crop that is sown into it.
Barley and oat straw do have some markets already – but wheat straw and canola stalk do not yet have consistent markets, and so in the more southern higher yield cropping country in Victoria this is normally burned in the paddock (as is most barley straw).
A market for straw for energy, including in anaerobic digestion or for production of biofuels, will assist farmers to move away from burning stubbles.
In Europe and elsewhere silage made from green maize, other leafy green crops or grass is used as a feedstock for making biogas in anaerobic digesters.
Leafy spring growth that is not prime feed, including unpalatable species (like capeweed, silver grass, yorkshire fog, barley grass, thistles and soft brome) can be made into silage.
This process can both improve the palatability of these species and prevent them seeding, preserving maximum nutritional value in the conserved fodder while allowing a second growth of better fast growing pasture species to grow on and stay green further into summer.
At a bioenergy development located near Ballarat, Victoria, the manure slurry from approximately 300 internally housed dairy cows is collected by a scraper system along the barn alleyways.
This slurry is then transferred to a tank, then into the modular containerised anaerobic digester. This is a prototype of a highly efficient system developed by the company Gekko in Ballarat. More of these are being produced to go out to other companies that produce a stream of putrescible wastes that had previously been a costly disposal issue.
A large amount of biomass resources exist in rural areas, particularly in currently under-utilised derelict trees, which have no present use and would likely be pushed up and burnt due to no market for chip.
A market for biomass would be important in prompting the planting of more multipurpose shelter belts, with the benefits of carbon sequestration, shelter, shade and habitat as well as biomass to energy from removed heads and possibly stems.
Located at Smithton in North west Tasmania, a Herz (Austrian-made) woodchip fired heat system at the brand new Aquatic Centre was found to be the most cost-effective way to heat both water and the enclosed aquatic centre air space out of about 6-7 various options.
The system is able to produce 300 kW of heat with about 200 kW being needed for the actual heating job and 100 kW available for drying chip as it arrives. Smithton is a big timber processing town, so there is no shortage of chip. Wet chip is usually very cheap so this installation of a drier is financially economical.
European Case Studies
In Denmark, the national target is for 100% of energy to be from renewable sources by 2050, with about half of this to be from biomass.
Presently Denmarks aim to cease all use of coal for energy by 2023, along with progressive conversion of many large coal-fired plants to being fired with biomass.
By 2022 Denmark aims to have 100% of gas in the Copenhagen city grid converted to biomethane. By 2020, 50% of all city food waste in Greater Copenhagen city area is to be diverted into anaerobic digestion, with the biogas mainly to be upgraded to biomethane and injected into the national gas grid.
Almost all mixed municipal solid wastes goes to production of heat and power, and this is at least 50% ‘green’.
The new waste to energy plant using non-recylable municipal solid waste from the 5 municipalities of inner Copenhagen provides about 20% of the power and 30% of the heat needs of this population of about 800,000.
It is common for city buses in Sweden to be fueled by biomethane, or often a mix of about 70% biomethane and the balance natural gas. The Swedes say that the putrescible wastes of a city (including sewage) will produce enough biogas to power the city public transport.