Why use Biomass? ………. And what is Cogeneration?

What is Biomass?

Biomass is called a renewable source of energy because it is replenished on a daily timeframe, through the process of photosynthesis.

Biomass examples include wood waste from commercial forestry processes, waste from business activity e.g. packaging and from new home construction and sugar cane residues and agricultural residues.[1]

The collection and storage of the sun’s energy in Biomass takes place through photosynthesis. This stored energy is released on direct burning (full or partial combustion) to yield the heat to generate electricity/power and thermal energy namely heat, in the form of hot water or steam.

The figure below illustrates how not only burning or combustion or “Thermal Processing but also other energy conversion technologies can be applied to various biomass feedstocks to produce value added products.

Figure 1: Bio-energy conversion routes

110405 Bioenergy conversion routes v3 inc sewage and combustion

Source: Extract from Annual Forest Growers Conference 2006

Biomass releases carbon dioxide (CO2) and small amounts of other greenhouse gases depending on the technologies used when it is converted through combustion into another form of energy. The CO2 produced in this process is reabsorbed during the photosynthesis process[2].

As a result Biomass to Power generation is called net zero carbon emission, excluding carbon emissions related to feedstock supply and preparation.

 

[1] Geoscience Australia – BioEnergy web page.
[2] Geoscience Australia – BioEnergy web page.

Carbon Comparisons for Biomass

In terms of carbon emissions from electricity bioenergy generation e.g. Bin Wood, based on a reciprocating steam engine electricity generation approach, biomass compares favourably with:

  • Wind (Biomass at 27 gCO2e/kWh is around 2.7 times the carbon emissions of Wind at 10, assuming 1.5 MWe onshore)
  • Solar PV (Biomass at 27 gCO2e/kWh is around 2 times the carbon emissions of Solar PV at 13, assuming an 80 MWe parabolic trough)

Importantly Biomass to Power emissions are significantly better than the carbon emission levels from:

  • Coal at 960 gCO2e/kWh with scrubbing and 1,050 gCO2e/kWh without scrubbers (Coal based electricity generation emissions are between 35 and 39 times the carbon emissions of Biomass); and
  • Natural gas at 443 gCO2e/kWh using various combined cycle turbines (Gas based electricity generation emissions are 16 times the carbon emissions levels of Biomass)

 
A further advantage of Biomass is it is an non-intermittent or continuously 24/7 available renewable power source, unlike solar or wind. It depends on feedstock supply not on sunlight and weather systems. The figure below illustrates the major carbon emissions differences referenced above for coal and natural gas.

Biomass Carbon Comparison

What is Cogeneration?

Co-generation (Combined Heat and Power or CHP) is the simultaneous production of energy in the form of electricity and heat for use typically in industrial processes. Different feedstocks e.g. natural gas, biomass, coal, energy pellets, liquid fuel can be used for co-generation depending on the technologies used.

The central and most fundamental principle of cogeneration is that, in order to maximise the many benefits that arise from it, systems need to be based on the heat demand/requirements of the application/end use, that is, customised to the offtakers needs[3] Read more

The figure below shows the types of energy efficiency benefits achievable through cogeneration and why they are achieved.

Hero-Images-1

 

[3] Adapted The European Association for the Promotion of Cogeneration (COGEN Europe) web page.