Biomass

Biomass definitions:

• Plant material, vegetation, or agricultural waste used as a fuel or energy source
• Biomass is all plant and animal matter on the earth’s surface
• Biomass is a sustainable resource – it is constantly being formed by the interaction of air, water, soil and sunlight

A major advantage of using biomass as a source of fuel or chemical is its “renewability”. Plants metabolize carbon dioxide during photosynthesis to make biomass. The planet Earth produces about 140 billion metrics tonnes of biomass annually.

Biomass is considered carbon neutral as the CO2 released into the atmosphere during combustion is used by plants of a new forest.

Drawbacks of biomass:

1. handling/logistical difficulties
2. lack of portability

Research underway to address these drawbacks and convert biomass into liquid and gaseous fuels through chemical means including pyrolysis and gasification and biological means specifically fermentation.

Common sources of biomass

1. old heritage piles – bark beside sawmills
2. slash – tree harvest residues – tops and branches
3. crop residues – corn stalks, wheat straw, seed hulls, etc
4. wood materials – mill residue, sawdust, etc
5. municipal wastes – waste paper, yard waste, etc
6. salvage and residuals – by-passed forests, or those damaged by natural occurrences
7. energy crops – willow, poplars, switchgrass, etc

A wet tonne of biomass is about a cubic metre by volume. The average household stove is about one cubic metre.

To produce one megawatt of electricity requires 20 bone dry tonnes (BDt) of biomass per day with plant in operation 300 days per year.

In small heat and power plants typically 2 MW of heat produce as 1 MW of electricity generated

Cost of transportation

Rule of Thumb – the cost of transportation exceeds the value of energy if the biomass is transported more than 100 km.

Success factors for small heat and power plants –

• Local consumer for heat i.e. industrial, greenhouse or community
• Consistent source of biomass
• Covered or moisture controlled storage
• Understanding and minimizing supply, handling, transportation and processing costs

Willow, poplar and switchgrass provide about 10 BDt of biomass per hectare per year.

The Ontario Power Authority indicate that the key to viability as a source of electricity is the ability to grow, harvest, process, transport, and convert biomass for under 11cents per kilowatt hour (Standard Offer Program). 

Another key contributor would be finding a valuable end-use for heat co-product such as greenhouse, industrial or municipal.

Crop Residues – finding the delicate balance between valuable harvest and soil health

Resource Efficient Agriculture Production (REAP) Canada suggests:

Crop	Suggested Removal Rates
Winter wheat	60-75%
Other cereals	70-75%
Corn	50%

• Sufficient supply
• Cost effective harvesting
• Harvest/storage losses
• Pre-processing costs (cutting, drying, etc)
• Transportation costs

Three types of thermal conversion technologies exist to use biomass to create heat and electricity:

• Combustion
• Pyrolysis
• Gasification

The Pyrolysis Challenge:  Lack of established markets or standards for pyrolysis liquid

The Gasification Challenge:  Gas cleaning and conditioning is challenging and expensive. Capital and engineering costs for gasification plants under 10 MW is reported to be in the $2.5-4 million per MW range.