Logs, wood chips, brush clippings and grasses all serve as woody biomass—renewable fuels suitable for producing heat and power. In the not so distant past, burning wood logs in a fireplace or wood stove was our only option for heating our homes.
From 19th Century Fireplaces to Institutional Boilers
Today, these old-fashioned fireplaces are more for ambiance than heating because they allow cold air inside and pollute the air. Modern designs of wood stoves (for burning logs) and pellet stoves (for burning compressed biomass pellets) produce less air pollution and are more energy efficient than traditional fireplaces.
On a larger scale, woody biomass can operate boilers that heat schools, offices, institutions and manufacturing facilities. The largest wood-powered facilities typically produce both heat and electricity at the same time. Such thermal and electric power “cogeneration” systems are actually the most energy efficient.
Like any power source, woody biomass has its benefits and challenges.
Pros of Wood Burning Systems
- The net fuel cost is cheaper than heating oil, natural gas, and coal.
- Woody biomass can be grown and purchased locally and promotes local economies.
- Fuel (in the form of logs, wood chips, brush clippings, grasses, and lumber yard waste) is widely available, renewable, and sustainable.
- Fuel prices are relatively stable.
- Pellet stoves, which burn pellets made of compressed woody biomass, are relatively non-polluting and approved by the EPA.
- The EPA has a certification program for wood stoves. Of the approved styles, catalytic wood stoves burn more cleanly (emitting no more than 4.1 grams of particulate per hour).
- With proper engineering, wood burning systems emit fewer pollutants into the air than coal and oil.
- Large, automated commercial-grade systems are designed to burn more cleanly and efficiently than small wood stoves.
- Over its lifecycle, biomass is carbon-neutral.
- Using forest wastes improves forest health.
Cons of Wood Burning Systems
- When wood burns it releases hazardous gasses (e.g., nitrogen oxide and carbon monoxide) and soot (also known as particulate matter). Therefore wood energy appliances and facilities must be properly designed and receive permits that meet air quality regulations and standards.
- The upfront, capital cost of building a sizeable wood energy facility can be high and it can take years to realize any savings.
- Constant use requires a continuous supply of wood chips or other biomass.
- Wood systems require more space to store bulky fuel.
- Compared with conventional boiler systems, wood systems require a larger boiler to handle the fuel.
- Waste ash that remains after burning needs proper, safe disposal.
- Automated wood chip conveyor systems and fuel-handling equipment must be monitored closely to prevent jams and system shutdowns.
- Wood chip fuel varies by size, moisture content, and energy content. Standard un-dried, or “green,” fuel contains 30-55% water, which slows combustion.
- Equipment to dry wood chips and improve efficiency is very expensive. (Note: dry wood is highly flammable and requires a sophisticated boiler system.)
- Most pellet stoves require some electricity to operate.