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CPE406 Energy from Biomass and Waste > Introduction to Biomass and Biomass Combustion > Flashcards

Introduction to Biomass and Biomass Combustion Flashcards

1
Q

Up to when did we use biomass as the primary source of energy and why did this stop in the UK?

A

Wood was the primary source of energy until the 1800s and caused much deforestation in England at the beginning of the industrial revolution, but then coal was discovered.

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2
Q

How is biomass formed?

A

Through the conversion of CO2 in the atmosphere into carbohydrate by the Sun’s energy in the presence of chlorophyll and water

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3
Q

What are important ingredients for the growth of biomass?

A

A living plant, visible spectrum solar radiation, CO2, chlorophyll (serves as a catalyst promoting absorption of CO2 from the atmosphere), water

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4
Q

Why is biomass CO2 neutral?

A

Because the CO2 released into the atmosphere is only that which it absorbed to grow.

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5
Q

What is the most common use of biomass as fuel?

A

Direct combustion, followed by gasification and pyrolysis

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6
Q

How much of the biomass on Earth can be used for energy and how much of the world’s energy consumption would this provide?

A

5%, 26% (6 billion tonnes eqv)

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7
Q

What are the three motivations for using biomass for energy?

A

Renewability benefits - fossil fuels are finite, biomass is not likely to be depleted with consumption
Environmental benefits - reduce human-made GHG emissions, no net contribution to CO2 emissions, very low SOx and NOx emissions
Socio-political benefits - generally locally grown, biomass source needs to be close to the conversion plant to be viable, development of associated industries for biomass growth (collecting and transporting) therefore more local jobs, energy security for countries that need to import fossil fuels

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8
Q

What are the two key controversies surrounding using biomass for energy?

A

Food vs Fuel: agriculture production diverted away from food crops, especially in developing countries, competition in numerous areas (agriculture, rural investment, infrastructure, water, fertilisers, skilled labour), may cause food shortages and price increases
Availability of Land and Water: biomass requires land to grow and is subject to factors governing how and by whom the land should be used, therefore improving biomass productivity per hectare is key

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9
Q

Define biomass

A

A non-fossilised and biodegradable organic material originating from plant, animals and micro-organisms. This shall also include products, by-products, residues and waste from agriculture, forestry and related industries as well as the non-fossilised and biodegradable fractions of industrial and municipal wastes.

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10
Q

Does biomass include gases and liquids?

A

Yes, recovered from decomposition of non-fossilised and biodegradable organic materials

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11
Q

List the 5 common sources of biomass

A

Agricultural (food grain, sugarcane, corn stalks, straw)
Forest (trees, wood waste, sawdust, timer slash)
Municipal (RDF, food waste, waste paper)
Energy crops (poplars, willows, switchgrass, corn, soybean)
Biological (animal waste, aquatic species and biological waste)

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12
Q

What are the 4 classifications of biomass under the Quality Assurance for solid biofuels?

A

Woody biomass: trees, bushes and shrubs
Herbaceous biomass: those plants that die at the end of the growing season such as grains and cereals
Fruit biomass: fruits (derived from woody biomass)
Blends and mixtures: blends are the intentional mixing of biomass, while mixtures are unintentional mixing of biomass

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13
Q

What two broad groups can biomass be split into?

A 
Virgin biomass (wood, plants, leaves, crops and vegetables)
Waste biomass (solid and liquid wastes, sewage, animal, human wastes and agricultural wastes)
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14
Q

What organic materials make up biomass?

A

Carbohydrates, fats, proteins and small amounts of Na, P, Ca and Fe

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15
Q

What are the main components of biomass? Describe these.

A

Extractives (substances present in the vegetable or animal tissue that can be separated by successive treatment with solvents and recovered from the evaporation of the solution), fibre/cell wall components (provides structural strength to the plant, allowing it to stand tall without support. Typically made of carbohydrates (cellulose and hemicellulose fibres which impart strength) and lignin (hold the fibres together)) and ash.

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16
Q

What are the four different types of products of biomass conversion?

A 
Heat and power
Liquid fuels (ethanol, biodiesel, methanol)
Gaseous fuels (methane, syngas)
Solid fuels (charcoal, biochar)
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17
Q

Farm products corn, sugarcane and wheat make what fuel?

A

Ethanol

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18
Q

Farm products rapeseed, soybean and Jatropha make what fuel?

A

Biodiesel

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19
Q

Lignocellulosic materials wood, straw, husk, corn stover make what fuels?

A

Ethanol, diesel, gasoline

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20
Q

What are the challenges surrounding use of biomass?

A

Bulkiness, low energy density and inconvenient form make rapid transition difficult, cannot be stored or handles easily, therefore good to convert into liquid and gaseous fuels

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21
Q

What are the two major routes for conversion of solid biomass into liquid and gaseous fuels?

A

Biochemical and thermochemical conversion

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22
Q

How does biochemical conversion generally work?

A

Biomass molecules are broken down into smaller molecules by bacteria or enzymes.

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23
Q

Is biological or thermochemical conversion quicker?

A

Thermochemical is quicker but requires much more external energy input

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24
Q

What are the 3 types of biochemical conversion? Describe these.

A

Anaerobic digestion (only organic matter from biomass can be used, no oxygen, products are biogases methane and carbon dioxide and solid residues) , Aerobic digestion (composting) (with oxygen, produces heat, carbon dioxide and solid digestate), fermentation (commercial at the moment for starch and sugar based feedstock, sugar is converted into ethanol/other chemicals with the help of yeast, lignin is not converted and is left for combustion)

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25
Q

Why is pre-treatment and hydrolysis needed for fermentation?

A 
Cellulosic feedstock is difficult to break down the materials to fermentable sugars
Lignocellulose feedstock (wood, straw) requires pre-treatment (acid or enzyme) to break down the cellulose and hemicellulose into simple sugars needed by the yeast and bacteria for fermentation
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26
Q

How does pre-treatment before hydrolysis and fermentation work?

A

Pre-treatment with steam and acid occurs to break down the lignocellulose into its 3 constituents: cellulose, hemicellulose and lignin. This is done because the cellulose micro-fibrils are linked with hemicellulose embedded in lignin, so is inaccessible. Pre-treatment makes the biomass materials more accessible to either chemicals or enzymes for efficient product generation.

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27
Q

Draw how cellulose, hemicellulose and lignin make up the cell wall

A

Drawing 21

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28
Q

Define hydrolysis

A

Chemical decomposition in which a compound is split into other compounds by reacting with water

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29
Q

What is more advanced, acid or enzyme hydrolysis?

A

Acid hydrolysis is more technologically advanced and costs less than enzyme hydrolysis, however enzyme hydrolysis is more commonly used.

30
Q

Which thermochemical conversion of biomass is commercially mature?

A

Combustion

31
Q

What is the main driver for biomass thermochemical conversion?

A

Production of electricity and heat

32
Q

Draw a typical hydrolysis and fermentation process

A

Drawing 22

33
Q

Can biochemical or thermochemical conversion produce a larger diversity of products?

A

thermochemical

34
Q

Which part of the biomass is utilised in thermochemical conversion?

A

The whole thing

35
Q

How is syngas converted into liquid transport fuels?

A

The Fischer-Tropsch process

36
Q

Define liquefaction

A

Large molecules of wet feedstock (wet biomess) are decomposed into liquids (bio-oil) which has smaller molecules, which happens in the presence of a catalyst at low temperatures (300 degrees C) in the absence of oxygen.

37
Q

What 4 elements should be considered when deciding whether a biomass conversion plant is economically viable?

A

Availability of biomass over the project lifespan and market for the products,
Financial structure including loan gaurantees, investors, government subsidies
CAPEX and OPEX
Environmental impact, any applicable regulations and approval processes

38
Q

Name the 4 types of thermochemical conversion

A

Pyrolysis, gasification, liquefaction and combustion

39
Q

What is the RO (renewables obligation)?

A

Support mechanism for large-scale renewable electricity projects in the UK, which requires electricity suppliers to to derive electricity from a specific and continually increasing proportion of renewable sources or a penalty is applied. Green certificates are awarded to operators of accredited renewable plants for the eligible renewable energy they generate. These certificates can be traded.

40
Q

What is the RHI (renewable heat incentive)?

A

Provides financial assistance to generators of renewable heat and producers of renewable biogas and biomethane

41
Q

What is the CCL (climate change levy)?

A

CCL is charges on all energy supplied to industry and commerce, agriculture and public administration services, and as of 2015 renewable electricity is not exempt

42
Q

What is ECA (enhanced capital allowance)?

A

Enables businesses to claim 100% first-year capital allowances on their spending on qualifying machinery

43
Q

What is EEFS (energy entrepreneurs fund scheme)?

A

Funded by the department of energy and climate change, support is awarded to the development of innovative, new technologies, products and processes in the areas of energy efficiency and building technologies and power generation and storage. This is competitive.

44
Q

What is CTEEF (carbon trust energy efficiency finance)?

A

Flexible loans for SMEs to allow investment in energy saving equipment

45
Q

What are the main two types of drying biomass?

A

Passive drying (out in the sun) and active drying

46
Q

What is the typical moisture value of biomass, what does it depend on and what does it impact?

A

30-60%, depends on the type of biomass and the location/environment

47
Q

What are the 3 main impacts of a high moisture content of biomass?

A
  • Moisture content reduces CV, overall efficiency and combustion T
  • Reduced combustion T = incomplete combustion, which may produce tars that might condense in downstream equipment resulting in clogging, frequent shut-down and system failure
  • Water may re-condense in the flue gas and cause corrosion
48
Q

How do you design a combustion system to handle high moisture?

A

Make use of some of the heat of combustion to dry the fuel as it approaches the combustion zone

49
Q

What moisture contents can gasifiers and pyrolysers handle?

A

10-20 wt%

50
Q

Is biochemical or thermochemical conversion more suited to handling high moisture contents?

A

Biochemical

51
Q

What is the impact of high moisture on biomass transport?

A

Lower energy density by mass compared to dry biomass, therefore transport is less efficient and more costly.

52
Q

What is the impact of high moisture on biomass storage?

A

Greater risk of decay, mould formation, fire risk from elevated temperature due to heat from composting in storage, good ventilation and air flow is needed

53
Q

Why is active drying more expensive than passive drying?

A

It requires input of energy from an external source (can be from excess process heat so less expensive, or a dedicated heating unit

54
Q

What does drying time depend on in passive drying?

A 
Material characteristics (size, density, shape, moisture content)
Storage conditions (temperature, method of stacking, air flow, humidity)
55
Q

What drying medium is used in active drying?

A

Hot air (rotary dryers) or steam (superheated steam dryers)

56
Q

What kind of dryers are most commonly used?

A

Air rotary driers as they are less sensitive to particle size and have a larger capacity, however the fire risk is higher

57
Q

Why are superheated steam dryers safer than rotary driers?

A

They do not use oxygen

58
Q

What percentage of total processing costs can drying be?

A

30%

59
Q

What is the difference in cost between pellets including and excluding the drying costs?

A

52.2-81.7 euro/t compared to 73.5-94.6 euro/t

60
Q

Why is pelletisation carried out?

A

To increase the bulk density therefore reducing volume which improves transport and feeding abilities (less dust formation and lower transportation cost)

61
Q

What will be included for standards for pellets?

A

Thermal value, mercury and chlorine content

62
Q

What are the current disadvantages of pellets?

A

There is no technical specification to quantify pellet characteristics (density, size, moisture etc), and there is no quantification made to characterise a standard test for pellet strength or durability

63
Q

How is pellet strength measured?

A

Radially using a Tensometer

64
Q

Define biomass combustion

A

The exothermic reaction between oxygen and hydrocarbons in biomass

65
Q

What are the two types of small biomass boilers?

A

Manually fired boilers (burn through boilers, under-burn boilers, reverse combustion boilers), automatically fired burners (compact units, stoker-fired units, boilers with pre-furnace)

66
Q

What are the main disadvantages of using biomass as fuel?

A
  • It is bulky and costly to transport
  • Low energy density
  • Readily absorbs moisture
  • Agricultural wastes have highly variable compositions and may arrive in very wet conditions, especially in winter
  • Highly heterogeneous (could produce very dusty and corrosive hot gases during pyrolysis/gasification)
  • Supply is seasonally dependent
  • Generally putrescible (short storage life) and can become infested with vermin
67
Q

What are the 3 main challenges in energy from biomass?

A

Fuel composition, transportation/handling, boiler reliability

68
Q

What causes fouling in wheat straw?

A

Ash deposit during combustion

69
Q

What causes corrosion and fouling in general?

A

High content of highly alkaline metals

70
Q

What is the capacity of the EON biomass power plant in Sheffield?

A

30MW (20-25MW electricity plus 5-10MW of heat), 180,000 t/yr of clean recycled wood waste, reduces 80,000 t/yr of CO2

71
Q

What is the capacity of the Elean biomass power plant in Cambridgeshire?

A

World’s 2nd larggest straw burning power station, 40 MW electricity, 200,000 tonnes burning capacity (up to 25% moisture content), produces steam at 540 degrees C, 92 bar, 18m high straw barns, 25 m high central boiler
Furnace operating parameters: air T 174 degrees C, theoretican air - 3.63 Nm3/kg straw, straw feed rate = 20 tonnes/hr, air/fuel ratio = 1.73

CPE406 Energy from Biomass and Waste (8 decks)

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