What is bioenergy and biomass?
Bioenergy is stored energy from the sun contained in materials such as plant matter and animal waste, known as biomass. Biomass is plant matter and animal waste that can be harvested to create bioenergy in the form of electricity, heat, steam and fuels from processes such as pyrolysis and gasification. Biomass is considered renewable because it is replenished more quickly when compared to the millions of years required to replenish fossil fuels.
What the difference between gasification and pyrolysis?
Pyrolysis and gasification are thermal processes that use high temperatures to break down waste to create gas, solid and liquid residues. Pyrolysis involves heating the feedstock in the absence of oxygen until volatiles are released, either as a “fast pyrolysis” or “slow pyrolysis”.
Fast pyrolysis occurs at moderate temperatures (~500°C to 815°C) with a short residence time resulting in a primarily low pH, liquid product with some char and gaseous products formed. Slow pyrolysis occurs at low to moderate temperatures (325°C to 500°C) with a longer residence time resulting in primarily char and gaseous products formed.
If a limited amount of oxygen is available during the processing of the feedstock, gasification occurs rather than pyrolysis. Gasification is a process using heat to convert carbonaceous feedstock into a gaseous mixture composed of primarily carbon monoxide (CO) and hydrogen (H2) typically at temperatures above 850°C.
The main product of gasification and pyrolysis is syngas, which is composed mainly of carbon monoxide and hydrogen (85 per cent), with smaller quantities of carbon dioxide, nitrogen, methane and various other hydrocarbon gases. Syngas has a calorific value, so it can be used as a fuel to generate electricity or steam or as a basic chemical feedstock in the petrochemical and refining industries.
What is Biochar and what are the benefits?
Biochar is a type of charcoal produced by the conversion of biomass to a charred product under oxygen-limited conditions in a reactor, a process known as pyrolysis. Due to its chemical structure biochar is very difficult for microbes in the soil to break down which prevents the carbon sequestered in the char to be released back into the atmosphere. For the benefits of biochar click here
Do I lose nutrients when I remove or burn stubbles?
Yes, plants store nutrients in the grain, stem, roots and leaves. If stubbles are left in the paddock they break down overtime and release these nutrients back into the soil. Nitrogen and sulphur and some potassium are lost when stubbles are burnt however, most of the potassium will remain in the ash and if not blown away by wind will leach back into the soil over time.
What is biogas
Biogas is a gas, produced from a process called Anaerobic Digestion (AD) and comprised largely of methane is produced from the digestive action of microorganisims living off organic material in the absence of oxygen.
In principle, all organic materials can ferment or be digested. Biogas is a mixture of gases that is composed mainly of:
- methane (CH4): 50-70 vol.%
- carbon dioxide (CO2): 30-50 vol.%
- other gases: 1-5 vol.% including:
- hydrogen (H2): 0-1 vol.%
- hydrogen sulphide (H2S): 0-3 vol.%
The biogas produced can be fed into generators to produce electricity and heat, a bi-product of the AD process (digestate) can be used as a nutrient rich soil conditioner.