Chapter 9 : Energy From Biomass

Question 1

Explain the term Biomass (1)

Answer 1

Biomass is a general term for material derived from plants or animals. {1}

Question 2

Define the term biomass (1)

Answer 2

Biomass is a general term for material derived from plants or animal manure. {1}

Question 3

Biomass can be used as a fuel. Explain what is meant by the term biomass. {2}

Answer 3

Biomass is material derived from growing plants or from animal manure. (2)

Question 4

Identify another category of biomass apart from woodchip. {1}

Answer 4

Any from:

Organic materials. {1}
Agricultural crops. {1}
Agricultural and municipal wastes. {1}

Question 5

Identify two crops that are commercially grown to produce biomass (2)

Answer 5

Any two from the following;

• Willow
• Poplar

• Elephant grass
• Maize
• Sugar Cane

Question 6

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

Answer 6

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 7

Identify two different advantages of replacing coal with biomass at this power station. {2}

Answer 7

• 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. (1)

• Combustion of biomass contributes much less to atmospheric carbon dioxide levels (than coal / fossil fuels) / is carbon neutral / does not contribute (as much) to global warming. (1)

Question 8

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

Answer 8

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 9

(i): State two advantages of using biomass as an alternative to fossil fuels. {2}

Answer 9

(i): Any two from:

Lower fossil fuel dependency [1]

Renewable [1]

Lower greenhouse gas emissions [1]

Waste may be diverted from landfill [1]

Question 10

(ii): State two disadvantages of using biomass as an alternative to fossil fuels.

Answer 10

ii): Any two from:

Requires significant quantities of land [1]

Has a lower energy density than fossil fuels/larger quantities required [1]

Biomass power plants have higher set-up costs [1]

Question 11

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

Answer 11

Approximately 90%

Question 12

Explain the term energy density. {1}

Answer 12

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

Question 13

State the main process used to obtain energy from biomass. {1}

Answer 13

Combustion (1)

Question 14

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

Answer 14

Any two of the following;
• Moisture content.

• Porosity,

• Bulk density

• Energy density

Question 15

Woodchip is a form of biomass that can be commercially produced. Explain the effect of moisture content on one property of woodchip
fuels. {2}

Answer 15

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 16

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. {2}

Answer 16

Any two from;
Percentage moisture content {1}

Energy density {1}

Particle size {1}

Question 17

Outline the biomass process of gasification in relation to biomass (2)

Answer 17

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 18

Describe the process of gasification of biomass. {3}

Answer 18

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

Question 19

Biomass can be converted into syngas. Name the two main gases present in syngas. {2}

Answer 19

Carbon monoxide {1}
Hydrogen {1}

Question 20

(ii): Explain how biomass is converted into carbon monoxide and hydrogen. {2}

Answer 20

Biomass is heated in the presence of oxygen and steam. This causes the biomass to break down into a mixture of carbon monoxide and hydrogen gas. This process is called gasification. (2)

Question 21

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

Answer 21

Any three from the following;
• 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 22

Certain types of biomass can undergo anaerobic digestion. Describe the process of anaerobic digestion. {2}

Answer 22

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 23

Define the term anaerobic digestion. {2}

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. {2}

Answer 24

Methane {1} and Carbon dioxide {1}.

Question 25

Name the main product of anaerobic digestion and state its use. Product. {1} Use. {1}.

Answer 25

Product – Methane or biogas. {1} Use – Fuel or electricity generation. {1}

Question 26

State one advantage and one disadvantage of using commercial anaerobic digesters (2)

Answer 26

Advantages include: • 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. Disadvantages include: • 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 27

Outline three advantages of using commercial anaerobic digesters. {3}

Answer 27

Any three from; • 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 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)