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

What is Biomass?

Biomass is called a renewable source of energy because it is replenished on a day-to-day timeframe through the process of photosynthesis.

Biomass examples include wood waste from commercial forestry processes, sugar cane residues and agricultural residues.[1]

The collection and storage of the sun’s energy in Biomass is through photosynthesis. This stored energy is released on direct burning (full or partial combustion) to yield heat for generating electricity/power and supplementary heat, e.g. in the form of hot water or low pressure steam.

The figure below illustrates how not only burning/combustion (i.e. Thermal Processing) but also other energy conversion technologies or routes can be applied to various biomass feedstocks to produce specific 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 when it is converted through combustion into another form of energy. The CO2 produced in this process is reabsorbed during the regrowth or new growth of vegetation (biomass) through the photosynthesis process[2].

As a result Biomass to Power generation is 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

In terms of carbon emissions from electricity generation, assuming Bin Wood based reciprocating engine electricity generation basis, biomass compares favourably with:

  • Hydro (Biomass at 27 gCO2e/kWh carbon emissions is 2.7 times that of Hydro at 10, assuming a 3.1MWe reservoir)
  • Wind (Biomass at 27 gCO2e/kWh is 2.7 times that of Wind at 10, assuming 1.5 MWe onshore)
  • Solar PV (Biomass at 27 gCO2e/kWh is 2 times that of Solar PV at 13, assuming 80 MWe parabolic trough)

Biomass to Power emissions contrast significantly to 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 renewable power source, dependent on feedstock supply not on sunlight and weather systems as for solar and wind. The figure below illustrates these major carbon emissions differences compared to coal and natural gas.

Biomass Carbon Comparison

What is cogeneration?

Cogeneration (Combined Heat and Power or CHP) is the simultaneous production of energy in the form of electricity and heat for usage. Different feedstocks e.g. natural gas, biomass, coal, energy pellets, liquid fuel can be used for cogeneration 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, 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.