Biomass Energy Questions and Answers

Answer: A

The constituent is CO, carbon monoxide.

Producer gas from a wood or charcoal gasifier is typically about 20-25% CO, 12-18% H₂, 1-3% CH₄, 8-12% CO₂ and roughly half nitrogen. Nitrogen is the largest constituent but is inert, so among the gases that add heating value, carbon monoxide occupies the largest volume and contributes most of the calorific value.

CO₂ is an incombustible diluent that lowers the calorific value. Hydrogen is combustible but present in a smaller share than CO. Methane has the highest heating value per cubic metre, but there is only a few per cent of it.

Answer: C

The combustible constituents are CO and \(H_{2}\).

Producer gas from a gasifier is typically about 20% carbon monoxide, 15 to 20% hydrogen, a few percent methane, around 10% carbon dioxide and roughly half nitrogen. Its heating value comes from the combustible gases, chiefly CO and \(H_{2}\).

\(CO_{2}\) is already fully oxidised and, like nitrogen, only dilutes the gas, so every option containing \(CO_{2}\) names a non-combustible component.

Answer: B

The process is pyrolysis.

Pyrolysis heats biomass in the absence, or near absence, of oxygen. At around 450-600 °C it breaks the biomass down into a solid char (biochar), a condensable liquid (bio-oil or tar) and non-condensable gases; slow pyrolysis favours char and fast pyrolysis favours bio-oil.

Gasification uses a controlled amount of oxygen or steam at higher temperatures, around 800-1000 °C, to make syngas. Anaerobic digestion is a biological process at 35-55 °C that makes biogas. Steam reforming converts hydrocarbons such as methane into hydrogen.