What is Biomass Combined Heat and Power (CHP) Systems?
In a biomass CHP system, the input fuel is biomass, typically wood chip or wood pellets.
Biomass CHP is particularly useful when the site is off the mains gas grid and where biomass fuel is readily available.
How does Biomass Combined Heat and Power (CHP) Systems work?
Small-scale biomass CHP boilers usually rely on pyrolysis (heating the fuel in the absence of air).
This produces syngas which is a mixture of hydrogen and carbon monoxide with a little carbon dioxide.
This gas is fed through a spark ignition engine, which in essence is the same as a gas-powered CHP unit.
The goal is to produce ‘clean’ gas as the carbon released from burning the biomass is roughly equal to what was absorbed during its growth.
Maintenance of small-scale biomass CHP is far greater than with mains gas powered CHP. Medium and large- scale biomass CHP systems tend to use steam to drive a turbine or Organic Rankine Cycle (ORC) that uses a
turbine driven by gas which boils at a lower temperature than water.
Both are mature technologies with excellent durability and reliability, which call for far less maintenance than is required for gasification CHP.
While most gas-powered CHP units can ‘modulate’ (respond to reduced electrical or heat load, usually to around 50% of peak output), biomass CHP boilers will run at maximum output consistently – they cannot run on part load. As a result, the ideal biomass CHP project is for the unit to provide a base load of electricity and heat, with the unit running for as close to 8,000 hours as possible.
How are Biomass Combined Heat and Power (CHP) Systems applied to a building?
Small scale (<100kW) and micro-scale (<15kW) biomass CHP are particularly suitable for applications in commercial buildings, such as hospitals, schools, industrial premises, office building blocks, and domestic
Optimum system design and implementation is crucial for cost-effective operation and it is established that the best economic performance come about with high load factors when the maximum amount of both electricity and heat sold on-site is maximised.
Biomass CHP systems need to have access to a reliable fuel supply, like a managed woodland or sawmill, as well as the ability for vehicles to deliver the fuel to the site. It is important that the fuel provided is of high quality with a very low moisture content to achieve the best results (wood chip typically has less than 15% moisture content).
Fuel costs are central since when considering the levelled cost of electricity and heat production, ongoing running costs far outweigh capital investment. Thus, it is imperative before considering investment in a biomass CHP system to ensure that the right fuel can be sourced locally.
Space is also a consideration, as the site will not only need space for the boiler, but also space to store the fuel.