Energy From Biomass

Question 1

Name the three sources, where all of the energy on our earth comes from

Answer 1

The sun through nuclear fusion
Tidal energy, due to changes in gravitational forces of attraction between the moon and the Earth as the sun spins daily
Geothermal Energy, due to the molten iron core at the centre of the earth, in which many nuclear decays provide heat.

Question 2

Define Biomass

Answer 2

Is a general term for material derived from growing plants or form animal manure.

Question 3

Define Bioenergy

Answer 3

Refers to the technical systems through which biomass is produced or collected, converted and used as an energy source.

Question 4

What are the advantages of Bioenergy

Answer 4

• Reduced dependency on energy imports, thus increased security of supply
• Reduced greenhouse gas emissions
• Employment as there are opportunities in rural areas and among small and medium sized enterprises
• Widespread resource availability
• Bioenergy makes use of wastes, avoiding their pollution and cost of removal.

Question 5

What is the most commonly used Cellulosic Material Crop

Answer 5

Miscanthus Grass
This plant originates from Asia and Africa.
They have thick stems are suitable for direct combustion since they have a low water content 20-30%
The one negative it takes up a lot of land that could be used for food crops.

Question 6

How does Starchy and Sugar crops be a form of biomass

Answer 6

Sugar and starch from the plant can be fermented to produce ethanol as liquid fuel. The remainder of the plant may then be used as per cellulosic material crops (combustion)

Question 7

How is sugar cane used as a form of biomass

Answer 7

Sugar cane is used in the ethanol production. Sugar cane also has a huge advantage in that several successive harvests of stems can be taken before field declines and the crop can be replanted.
After the fermenting process, the remaining supporting cellulosic tissue may also be used for combustion for energy generation

Question 8

How can organic material be used as a form of biomass

Answer 8

Manure from animals on farms, as well as sewage from humans, is organic material that can be used as a fuel source. Manure from cows, which falls on a field, decomposes aerobically as micro-organisms feed of the material getting their energy from respiration.

Question 9

Advantages and disadvantages of organic material

Answer 9

The process is carbon neutral, with oxygen used from the atmosphere, and carbon in the manure being transformed into co2.
It also allows the addition of plant nutrients, such as Nitrogen to infiltrate the soil
DisADV
When the manure is stored in slurry tank, the organic material decomposes anaerobically. Methane from slurry tanks is estimated to account for 8% of the total emission in the USA. Methane after a short period of time, it is 20 times more effective at trapping the earth radiation and hence raising global temperature.

Question 10

Advantages of installing Aerobic Digester on a farm

Answer 10

Generate income
Generate Power
Reducing Global Warming
Reduction in Transportation

Question 11

How is Agricultural and Municipal waste disposed

Answer 11

The main disposal method for municipal solid waste, is landfill, Using suitable holes in the ground such as old quarries etc.
40% of municipal waste is incinerated

Question 12

What are the advantages of Biomass

Answer 12

• Reduced co2 emissions through reduced fossil fuel usage, as biofuels have much less emissions, and also can be assumed carbon neutral.
• Clean energy- Using the likes of biofuels, can relate fuel taxation to haulage firms, or air craft companies
• Abundant and Renewable - Suns energy will not run out. We have seen that hundreds of times more energy absorbed by photosynthesis than the annual human energy demand every year.
• Reduced dependency on fossil fuels, and so increasing energy security.
• Reduced Landfill - Many organic wastes can be incinerated, to produce heat/electricity, or anaerobic digesters used to capture the methane, to help the environment and use this to produce energy. Also transportation costs of having to landfill are mitigated, and landfill taxes in the next few decades are set to rise substantially.
• Versatile Energy Source, can be used for heating homes privately, or locally, producing electricity, or even liquid fuel for transportation, Therefore it has the potential to impact many diverse markets.
• Concentration of new jobs to manage these biofuels plants in the current market and expanding in the future.
• Increasing fossil fuels Duration- Mitigating an energy crisis if we rely in this too much in the short term, there by giving us time to mitigate and prepare for alternative action.

Question 13

Disadvantages of Biomass

Answer 13

Costs - The costs of biofuels are generally higher than fossil fuel alternatives, especially when subsides are added from nations, to make the fossil fuels more competitive. Many of the biomass forms require additional processing for transportation, and final use, and these add to the costs, and how ‘green’ the environment biomass really is.

• Some crops also require significant land preparation prior to planning, as well as fertilisers prior to planting, and harvesting can be costly and energy intensive, all standing to increase the cost of the commodity.
• Efficiency- All biomass, derives energy from photosynthesis. This is an extremely inefficient process, between 0.6-1 % efficient. When compared to a solar PV, with efficiencies of 25%, one might ask if the installation of land could perhaps be used more effectively.
• Energy Density - We have seen previously that biomass energy yields per m3 or per ton, are extremely low when compared to oil. This has disadvantage of added transportation costs, increased storage costs.
• Food crops Land use - Quite often farmers may convert lands previously used for land crops, to use for biomass crops. This acts in reducing food suppliers and increasing food prices to retailers and thus needs to be monitored closely.
• Deforestation - Some countries can fell to many trees, in an unsustainable fashion, and this is essentially deforestation. This seriously impacts Brazil, whom have over the decades, used their trees, to try pay of extensive bank loans. Aggressive policies like this are not sustainable and government programmes have intervened to help prevent this
• External Markets - The price of fossil fuels, primarily oil, impacts on the demand of bioethanol and biodiesel. The recent oil crash may be biodiesel uneconomical and farmers may revert back to crop for food purposes

Question 14

How much does combustion contribute to all energy obtained from biomass

Answer 14

Combustion accounts for 90% of all energy obtained from biomass.

Question 15

Describe the properties of wood chips

Answer 15

Wood chip is produced by the shredding of willow crop or residual forest waste. It is shredded into particles in a size range of 10mm -28mm. Newly harvested woodchip can have a moisture content of up to 50%. Drying van reduce the moisture content to less than 25%.

Question 16

Describe the properties of wood pellets

Answer 16

Wood pellets are produced by mechanically compacting saw dust that has been produced when preparing timber for commercial use. Wood pellets have a moisture content of 10%. The standard size is 6-8 mm in diameter and usually 5-30mm long. Mainly dust free.

Question 17

What is thermochemical Processing

Answer 17

It involves the use of heat and possibly the use of chemical reagents, to convert biomass into energetically more useful forms. The output from such processes may be heat, or intermediate gaseous or liquid fuels

Question 18

What is gasification

Answer 18

Biomass is converted into a mixture of carbon monoxide and hydrogen commonly known as syngas
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.

Question 19

Explain the first stage of gasification

Answer 19

Stage 1 - Drying
The biomass utilised for the gasification processes will have to be dried out fully, due to the moisture content within the material. Basically the water in the biomass must be boiled, such that temperatures can raise beyond 100 degrees Celsius to the other stages can take place the resulting steam is mixed into the gas flow and may be involved with subsequent chemical reactions, notably the water - gas reaction if the temperature is sufficiently high enough.

Question 20

Explain the second stage of gasification

Answer 20

Stage 2 - Pyrolysis
A thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen. This method involves heating the biomaterial with a carefully controlled air supply, typically at 200 - 300 Degrees Celsius. That with air supplied, some oxygen will enter, so partial combustion will take place, you don’t want the fuel to burn. The resulting reactions are complex, and hard to predict, giving a range of oils, acids, water, solid char and uncondensed gases.

Question 21

Explain the third stage of gasification and combustion

Answer 21

Stage 3 - Gasification and Combustion
This char can then be gasified by burning it at an extremely high temperatures in the region of 1000 degrees Celsius, and injecting oxygen. A complete industrial gasification process using oxygen can produce a stream of carbon monoxide and hydrogen, with any other impurities such as tars, ammonia and sulphur compounds being chemically removed.

Question 22

What is syngas

Answer 22

These products h2 and co. produce a gas referred to as synthesia gas or syngas. From syngas, almost any hydrocarbon can be synthesized, including premium liquid fuels such as methanol

Question 23

What is syngas’s main use

Answer 23

The main application of syngas is electricity production, i.e. it is combusted to produce steam, to drive a turbine as per a conventional plant.
It is used to produce synthetic natural gas.
Its used to produce ammonia
Synthetic Petroleum fuel

Question 24

What are anaerobic digesters used for

Answer 24

• Treat waste biomass material and the biogas produced is a by product.
• To produce biogas crops specifically grown to produce energy.

Question 25

What factors play a part in AD process

Answer 25

• Type of material being used
• The moisture content of the digestate
• The residence time (time a particular batch of waste remains within the digester tank) temperature may need t be adjusted to suit the properties of any particular waste system.
• Temperature, we have seen that different microorganisms are adapted to differing temperatures, with higher temperature producing a higher throughput and lower process time.

Question 26

What are the stages of biological reactions in the AD

Answer 26

The first stage is known as the hydrolysis stage, when insoluble carbohydrate materials react with the water to break down more complex insoluble organic substances to form sugars and amino acids
Acidogenic bacteria then act on these substances to produce hydrogen ammonia and organic acids.
Acetonic Bacteria convert the organic acids that are produced into acetic acid, ammonia, hydrogen and carbon dioxide.
During the final stage of the process, the bacteria present convert the hydrogen, ammonia and acetic acid into methane and carbon dioxide.

Question 27

What are the advantages of an Anaerobic Digestion

Answer 27

1: It is a net energy producing process which produces renewable energy in the form of biogas
2: It produces a liquid and a fibrous fertiliser.
3: It sanitises the feedstock which is put through it, as long as the temperature is held a required temperature for a defined time.
4: Reduces odour below unprocessed waste odour levels.
5: Less likely to cause environmental pollution that spreading untreated organic waste on land
6: The effect of the fertiliser is longer lasting than for untreated organic waste.

Question 28

What are the disadvantages of an Anaerobic Digestion

Answer 28

1: When carried out at a commercial scale on farms and at a wastewater treatment works, it requires a high level of investment in large tanks and other process vessels
2: If run inefficiently AD can cause an odour nuisance

Question 29

Describe the process of anaerobic digestion.

Answer 29

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}