7. Energy From Biomass

Question 1

Explain the term Biomass;

Answer 1

Biomass is a general term for material derived from plants or animals.

Question 2

Identify two crops that are commercially grown to produce biomass. {2}

Answer 2

Any two from the following;
• Willow
• Poplar
• Elephant grass
• Maize
• Sugar Cane

Question 3

Give an example of a crop that can be commercially grown to produce biomass. {1}

Answer 3

Any one of the following;

Willow / poplar / elephant grass / maize / sugar cane.

Question 4

Question; Briefly describe the global debate that surrounds farmers growing crops for energy. {2}

Answer 4

Answer to outline the global debate around ‘food versus fuel’. {1}
Global population increasing at a dramatic rate. This is increasing demand for food for basic human survival. Should farm land be used to grow energy crops instead of food produce? {1}

Question 5

The figure below shows the UKs largest power station. It is converting three of its six 660 MW electricity generating units to burn biomass. The remaining units will continue to use coal. Identify two different advantages of replacing coal with biomass at this power station.

Answer 5

Biomass fuel is a renewable energy source / can be replaced in a human lifetime whereas coal takes millions of years to form / cannot be replaced in a human lifetime.
• Combustion of biomass contritubes much less to atmospheric carbon dioxide levels (than coal / fossil fuels) / is carbon neutral / does not contribute (as much) to global warming.

Question 6

State one disadvantage of converting all six units to burn biomass instead of coal. {1}

Answer 6

Any one of the following;
• Biomass is more expensive to use compared to coal.
• Biomass is less efficient compared to fossil fuels.
• Biomass requires more land for production.

Question 7

State the typical (%) of energy from combustion that is obtained from biomass. {1}

Answer 7

% in the range of 90% {1}

Question 8

Explain the term energy density. {1}

Answer 8

Energy density is the amount of energy stored in a given system or region or space per unit volume or mass. {1}

Question 9

State two properties which could be compared and contrasted when assessing different types of woodchip for use as biomass fuel. {2}

Answer 9

Any two of the following;
• Moisture content.
• Porosity,
• Bulk density
• Energy density

Question 10

Outline the process of gasification in relation to biomass. {2}

Answer 10

Gasification is a process that converts organic or fossil based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. {1}
This is achieved by reacting the material at high temperatures, without combustion, with a controlled amount of oxygen and / or steam to produce
syngas.
{1}

Question 11

Describe the process of gasification of biomass.

Answer 11

Biomass is converted into a mixture of carbon monoxide {1} And hydrogen {1} Commonly known as syngas. {1}

Question 12

Question; State three applications in which the main product of the gasification of biomass can be utilised. {3}

Answer 12

Used in the production of ammonia. {1}
• Used in the production of methanol. {1}
• Used as an intermediate in producing synthetic petroleum. {1}
• Or can be used as lubricant in chemical processes. {1}
• Syngas is combustible and often used as a fuel of internal combustion engines. {1

Question 13

State one advantage and one advantage of using commercial anaerobic digesters. {2}

Answer 13

Treats waste and reduces greenhouse gases.
• Produces a biogas that can be used as a fuel.
• AD can take place at a location local to where waste or energy crop is produced – therefore reduces the need for transportation.
Answer to include any one of the following disadvantages; {1}
• Requires a steady supply if a consistent feedstock.
• Quality of the gases produced will vary, therefore potentially increasing he need for a gas cleansing process to protect the combustion equipment.
• The process can be slow, particularly during the winter months and may require the addition of extra heat.

Question 14

Define what is meant by the term biomass.

Answer 14

Material that is derived from growing plants or animal manure.

Question 15

State the main process used to obtain energy from biomass.

Answer 15

Combustion/burning.

Question 16

Woodchip is a form of biomass that can be commercially produced.
Explain the effect of moisture content on one property of woodchip fuels.

Answer 16

Higher moisture content results in woodchip with lower energy density [1]
as energy must be used to evaporate the water before combustion
occurs. [1)

Question 17

Certain types of biomass can undergo anaerobic digestion. Describe
the process of anaerobic digestion.

Answer 17

Anaerobic digestion is a biological process that results in the breakdown
of organic matter [1] by naturally occurring bacteria in an environment that
has an absence of oxygen. [1]

Question 18

Name the main product of anaerobic digestion and state its use.

Answer 18

Methane/biogas [1] fuel/electricity generation. [1]

Question 19

Outline three advantages of using commercial anaerobic digesters.

Answer 19

AD offers an option to treat waste and produce biogas that can be
used as a fuel. [1]
• AD diverts the methane that would be released from a landfill into the
generation of electricity, thereby reducing atmospheric methane
levels/greenhouse gas emissions. [1]
• AD can take place at a location close to where organic/farm waste is
produced therefore reducing the need for transportation/providing local
jobs/providing electricity supply/providing waste management options. [1]

Question 20

Explain what is meant by the term biomass.

Answer 20

Biomass is material derived from growing plants or from animal manure.
Award [2] for a detailed explanation and [1] for a limited explanation

Question 21

Woodchip is a specific example of a commercially available biomass
from the wood category.
List two properties of woodchip which are important in determining its
effectiveness as a fuel.

Answer 21

Percentage moisture content; [1]
• Calorific value/energy density; [1]
• Particle size. [1]

Question 22

Identify another category of biomass.

Answer 22

Organic materials; [1]
• Agricultural crops; [1]
• Agricultural and municipal wastes. [1]

Question 23

Biogas is a mixture of gases produced by the anaerobic digestion of
certain types of biomass.
(i) Define the term anaerobic digestion.

Answer 23

The biological breakdown of organic matter [1] in the absence
of oxygen [1]

Question 24

List the two main gases that are present in biogas.

Answer 24

methane; [1] carbon dioxide.[1]