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Biomass Flashcards

1
Q

Share of biomass in 20 years compared to coal?

A

Equal

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2
Q

Define the term biomass

A

Includes all matter of organic origin. Biomass comprises of plants, animals and biogenic residues

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3
Q

Describe an example of a biomass conversion pathway and a possible way of usage

A

Ver slides 1 Biomassa

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4
Q

Which natural process makes the use of biomass theoretically CO2
free? What has to be regarded in the balance?

A

Photosynthesis. With use of light energy, CO2 can be asorved and converted into organic compounds/plant biomass.

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5
Q

Which factors determine the production of biomass (name 3) ?

A

Temperature, water, and humus

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6
Q

Name 4 different types of biomass, their options of utilization (1
each) and their advantages/difficulties (1 each)

A
  • Ligneous biomass, direct thermal use for the production of heat/electricity, favourable combustion characteristics, low emissions; accumulation of tar during gasification
  • Herbaceous biomass, production of biogas, cultivable without pesticides; Unfavourable properties for thermal use
  • Vegetable oil plants, use of vegetable oil, the direct use in an engine is possible; Just some parts of the plant are used
  • Sugary biomass, production of bioethanol, applicable in low-temperature conversion processes such as the production of biogas or bioethanol; Just a part of the heating value is converted
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7
Q

What is meant by the “exploitable potential” of biomass?

A

Describes the expected share of energy supply. Due to different obstacles (lack of acceptance or information), economic potential does not get exploited instantaneously.

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8
Q

What is the approximate (technical) potential of bioenergy (share of primary energy demand) in Germany? Which type of biomass would have the biggest share?

A

17.4%, energy crops and straw.

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9
Q

Assume you want to substitute a coal power plant with a power
plant that uses straw as fuel. What would be a problem and why?

A

We would need 19 times the same wagons filled with straw, comparing it to wagons filled with coal.

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10
Q

Why is a biomass power plant limited in its power capacity? Which
use case does therefore make sense?

A

Because biomass demands much more space to make the same energy.
Biomass is particularly applicable for decentralized utilization

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11
Q 
Which parameter influences the heating value significantly? Sketch
the relation (no exact values)
A

Humidity (see biomass slides 1)

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12
Q

What is the difference between fuel humidity and water content?

A

Fuel humidity is the ratio between m_water and m_fuel. While water content is the ratio between m_water and the sum of m_water and m_fuel

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13
Q

Straw and hay contain significantly more … than coal.

A

water content/humidity

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14
Q

Explain and sketch the 4 points during ash melting!

A

Sintering point: ash particles agglutinate on their boundary surface
Softening point: first signs of ash softening (surface changes, shrinking, the edges get round shaped)
Hemispheric point: the sample becomes hemispherical
Flowing point: the sample is molten to one third of it’s original height

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15
Q

How can you enhance/alter biomass properties? Name different

kinds of processes and one process + enhanced property each.

A

By pretreatment of biomass.
Physical, chemical, thermophysical, thermocheical, biological. Physical processes generally include biomass washing, comminution. Chemical processes include processes such as washing with organic solvents, dilute acid treatment.

  • Biomass Torrefaction
  • HydroThermal Carbonization
  • Steam Explosion

Improve of LHV/HHV

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16
Q

What is the goal of torrefaction and what happens during the

process?

A

During torrefaction, moisture and some volatile organic compounds volatilize from the biomass. Torrefaction improves the physical properties, chemical composition, and energy and storage properties of biomass.

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17
Q

What is HTC? Compared to torrefaction?

A

HTC is suitable for treatment of waste biomass such as sewage sludge, empty fruit bunches, olive mill wastewater. The process is generally more severe than torrefaction for similar conditions

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18
Q

What happens in the steam explosion process?

A

Mixing biomass with saturated steam. Quick depressurization. Biomass impacting on walls and particles causes fiber disruption

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19
Q

Utilization paths?

A

Energy crops, harvest residues, organic by-products, organic waste. (see slides biomass 1)

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20
Q

Express the fuel utilization efficiency of heat generation in terms of
the lower heating value!

A

n=.Q_use/.m*LHV

ration between useful heat output and thermal input

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21
Q

Sketch the relation between temperature/CO content and air ratio for combusting 2 solid fuels with different humidity. Why is the
minimum of CO not at λ = 1?

A

The fuel needs to be well mixed with the oxidant, which only happens if lambda is a little bit over 1 (see slides biomass 2)

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22
Q

Which two problems arise when trying to optimize the efficiency of
a heat generator? Explain by using the fomula η = 1 - Tend/Tad where
Tend is the flue gas temperature at the boiler outlet and Tad the flue
gas temperature at the boiler inlet

A

The flue gas temperature (Tend) is limited downwards.

The combustion temperature (Tad) is limited upwards.

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23
Q

What is the main factor for efficient heat generation within biomass
combustion? Which 3 parameters influence the firing efficiency?

A

Flue gas losses determine the efficiency of a heat generator.
Return temperatures, air excess and fuel humidity.

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24
Q

Propose 3 ways to optimize (plus one realization possibility

therefor (each)) biomass combustion plants?

A

Reduction of the excess air: by staged combustion.
Reduction of the flue gas temperature: by low return temperatures
Reduction of other losses: burnout (ash losses)

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25
Q

Advantages of a staged/non-adiabatic (cooled) combustion? better air ratio at nominal temperature 900 °C?

A

lower lambda required, which means less losses in flue gas heat content

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26
Q

Name a problem with stoker-fired furnaces and a possible solution
therefor

A

Incomplete burnout, low ash melting temperatures require a high excess air ratio, local temperature maxima lead to NOx emissions.
The solution might be the recirculation reduces the oxygen share in the combustion chamber and leads to lower combustion velocities and therefore lower temperature maxima.

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27
Q

Why can you achieve an efficiency higher than 100% using flue gas condensation?

A

Thanks to flue gas condensation, which releases heat (latent heat), because the definition of efficiency only considers the LHV

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28
Q

Due to which behavior of biomass is the combustion temperature
limited?

A

ash melting behavior of biomass

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29
Q

Is the combustion temperature of biomass furnaces higher or

lower than that of natural gas or coal.

A

the combustion temperature and he efficiency of biomass furnaces are lower than those of natural gas or coal

30
Q

Name two firing concepts of biomass combustion and sketch one concept.

A

Underfeed stoker and grate firing (see slides biomass 2)

31
Q

Name a burnout control mechanism.

A

spreader feeding

32
Q

How does fluidized bed combustion work? What is an advantage?

A

The heat gets discharged mainly over the freeboard. High-turbulence fluidized bed provides ideal mixing. Fuel is mixed into a fluid bed. (watch video in class biomass 2)

33
Q

Is biomass firing more complex than coal firing?

A

Yes, they are mainly derived from coal firing concepts

34
Q

State two advantages of pellets and briquettes

A

High energy density. Low residual moisture, good storage ability.

35
Q

Can heating with biomass be more cost-effective than heating with fossil fuels?

A

yes

36
Q

What is the cheapest way of heat generation (in domestic

systems)?

A

split log boiler

37
Q

Give one state of the art power engine/one innovative concept for power engines used with biomass combustion and biomass
gasification

A

With biomass combustion: Steam turbine.

With biomass gasification: Gas turbine, Combined cycle, Gas engine

38
Q

Explain and sketch the Clausius Rankine Cycle

A

Biomass slides 3

39
Q

Show the differences between electrical efficiency, CHP

(combined heat and power) efficiency and exergetic efficiency by giving their formulas!

A

Electrical efficiency: n_el=P_el/(.m_fuelLHV)
CHP efficiency: n_b=(P_el+.Q_heat)/(.m_fuelLHV)
Exergetic efficiency: n_ex=1-.E_v/.E_q

40
Q

What does the CHP coefficient σ express? What is the mean CHP
coefficient?

A

The CHP coefficient is the ratio between generated electrical power and available heat flow rejection (on the condenser).
The mean CHP coefficient is calculated accordingly, using the electrical work and the available heat from the cool generation

41
Q

Types of turbines: name 3 different steam turbines for CHP plants.
What are there differences (especially in terms of σ. Sketch their characteristic map (electric output vs. useful heat output)
qualitatively?

A

Backpressure turbine, Sigma=0.25
Extraction condensing turbine, Sigma=2-oo
Extraction-condensing turbine with detachable low pressure part, Sigma=0.25-oo
(see slides biomass 3)

42
Q

When do we use an Organic Rankine Cycle? What are the
differences between the Organic Rankine Cycle and the (Clausius)
Rankine Cycle ? Sketch (Ts diagram)!

A

it uses an organic medium instead of water steam.

it is basically the same cycle, but since the medium is different the shape of the curve

43
Q

What working fluid can we use in an organic working cycle? What are the necessary characteristics of the working fluid?

A

For high temperature applications: silicone oil
For low temperature applications: hydrocarbons, aromatics.
They must induce low enthalpy differences, low number of stages, adjusted pressure conditions, low operating and maintenance expenses.

44
Q

Assume you want to utilize biomass in a CHP powerplant < 1MW.
Which thermodynamic cycle would you suggest to be able to produce
power?

A

Organic Rankine cycle

45
Q

Give 2 advantages and 2 problems of a stirling engine.

A

Pros: Ideal for gaseous and liquid fuels, exhaust gases from solid fuels, low emissions and acoustic emissions due to the controlled external combustion.
Cons: Sealing, heat-transfer, efficiency

46
Q

For which use case do steam engine make sense? What are the

main issues?

A

It’s the alternative to steam turbines for low power output.

Sealing-lubrification, and it must be an oil free operation

47
Q

What is the purpose of co-firing power plants? Name 2

advantages.

A

Co-firing allows electricity generation from biomass with efficiencies similar to large coal power plants, 10-20% of coal can be substituted.
Considerably low costs, improvement of the economic efficiency of coal-fired power plants, highest short-term CO2 reduction potential.

48
Q

What is commonly used for electricity generation from biomass?

A

Steam power plants are commonly used.

49
Q

What is a problem when using syngas? Give two possible solutions
to avoid this problem!

A

Syngas has to be cooled down to 70ºC for use in engines.

Tar free gasifier, elimination of tars, concepts with hot gas cleaning and tar elimination/conversion

50
Q

What is another (technical) problem of gasification?

A

Heat input

51
Q

Give 2 types of gasification. What is their difference? Which has the higher calorific value?

A

Autothermal gasification has 100% of useful gas.
Allothermal gasification has 70% useful gas.
Auto-thermal = 2 – 5MJ/kg, Allo-thermal > 10MJ/kg

52
Q

Give 2 important gas characteristics of a biogas

A

Ignitability and burning rate.

Knock resistance.

53
Q

Name 2 types of fixed bed gasifiers!

A

Counter-flow gasifier and co-current gasifier.

54
Q

Which other types of gasifiers exist?

A

Entrained flow gasifier.

55
Q

Sum up the potential of thermal gasification of biomass

A

Biomass gasification is a next generation technology
– For the development of biomass-based decentralized, standardized plants for
electricity generation.
• Biomass is mainly used locally.
• Decentralized small-scale plants for electricity generation are more
efficient with gaseous fuels.
– For generation of hydrogen and synthetic fuels.
• Biomass gasification plants for synthesis and power generation have
been successfully demonstrated over the last decades.
• Biomass gasification needs further research and development for
successful commercialization (combustion is more mature)

56
Q

Name one advantage of a heatpipe reformer.

A

High heating values allow efficient heat and electricity generation.

57
Q

Sketch the general process flow scheme for biogas production.

A

See slides biomass 4

58
Q

What are the environmental conditions for anaerobic fermentation in the fermenter? Give 2 essential parameters.

A

Oxygen: Must have a low-oxygen atmosphere for anaerobic conditions in the fermenter.
Temperature: Must have for Psychrophilic temperatures of 25ºC; for Mesophilic 32-42ºC; for Thermophilic 50-57ºC.

59
Q

Give the general reaction equation for biogas production. How do
we call the two (chemical) steps of the process.

A

C6H12O6+2H2O–3CO2+3CH4+2H2O.

Fermentation to acetate and biological methanation.

60
Q

Name two different substrate types (raw materials) of biomass.
Which types are commonly used as main feed materials, which as
additives?

A

Manure and silage are used as main feed materials.

Green waste, lawn cuttings, roadside greenery, frying oil, kitchen waste, leftovers, brewer grains are used as additives

61
Q

What are the 2 general different types of fermenters?

A

Horizontal and vertical

62
Q

In which power plants can biogas be used? What type of engine
(more than one possible) or turbine would therefor be necessary?

A

CHP plants. It would be needed gas-otto engines, gas-diesel engines, pilot injection engine, micro gas turbines and fuel cells

63
Q

CHP plants that use biogas have produce around 37 % waste heat
and heat losses. What can you do to improve the efficiency?

A

Waste heat utilization with ORC, transportable heat storage tank, feeding in the natural gas network.

64
Q

What could be alternative use cases of biogas to CHP-use of

biogas in biogas plants?

A
  • Micro gas turbines

* Fuel cells

65
Q

Arrange in increasing energy content

A

Straw, wood, seed oil

66
Q

why decentralized

A

Power capacity of biomass PP is low due to low energy density hence high amount of storage and transportation required

67
Q

Is biomass CO2 free?

A

It can be CO2 Free if it is decentralized.

68
Q

Technical problems with ash melting and chlorine content

A

Combustion temperature is limited by the ash melting behavior - control the furnace temperature to avoid ash melting.
Corrosion

69
Q

Composition of biogas

A

CO2 25 to 55% and CH4 45 to 70%

70
Q

Types or configuration of combined heat and electricity plant with biomass combustion

A

Extraction condensing steam turbine with (without) detachable low pressure part

71
Q

Why temperature in fermenter is necessary to maintain?

A

organism die above and below temp

72
Q

which parameter has more impact in the efficiency of power plant with respect to temp?

A

Air ratio (labda)

RET (4 decks)

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