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Sustainable energy > Thermal electricity generation > Flashcards

Thermal electricity generation Flashcards

1
Q

What is the main parameter of combustion?

A

Amount of air

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2
Q

What are the main components of fuel?

A
  1. Carbon
  2. Hydrogen
  3. Oxygen
  4. Sulfur
  5. Nitrogen
  6. Minerals = ash
  7. moisture (H20)
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3
Q

What are consequences of low or high amounts of air in the combustion?

A
  1. Too much: emission rich of O2
  2. Too little: emission rich of CO
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4
Q

What’s approximately the power output of the gas and steam turbine in a CCGT?

A

2/3 gas turbine
1/3 steam turbine

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5
Q

What’s the efficiency of a GT and CCGT?

A

GT = 35-40%
CCGT = most modern CCGT’s are exceeding 60%

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6
Q

What is meant with the repowering of traditional plants?

A

Using the exhaust gases of a gas turbine to pre-heat the water-steam cycle before it enters the boiler. This increases the power output and the overall efficiency of the tradition unit where only a steam turbine is used and steam is only heated op by burning coal/oil/gas.

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7
Q

What is a PWR?

A

Pressurised Water Reactor => water stays liquid in primary circuit (315 degrees at 150 bar)
It consists of:
1. Primary loop (reactor and steam generator)
2. Secondary system (steam generator, condenser and turbine)
3.Tertiary condenser and cooling tower

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8
Q

What is a CHP system?

A

Combined heat and power: The total system efficiency of a CHP system is the sum of the net useful electric output (gas turbine) and net useful thermal output (steam generated from exhaust of GT) divided by the total fuel energy input. CHP systems typically achieve total system efficiencies of 60 to 80 %. Note that this measure does not differentiate between the value of the electric output and the thermal output; instead, it treats electric output and thermal output as having the same value which allows them to be added (kWh) In reality, electricity is considered a more valuable form of energy because of its unique properties.

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9
Q

What is an OCGT?

A

Open cycle gas tubrine: Low efficiency of 30% but fast for peaking in demand

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10
Q

What technologies can be used for cooling water?

A
  1. Semi-open cooling circuit with cooling tower
  2. Aerocondensor
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11
Q

What is the disadvantage of using cooling tower?

A

You need a high concentration factor to reduce the thermal discharge in the water that is pumped back into the river/sea. This can effect organisms. But this increases the water consumption.

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12
Q

What is an aerocondensor?

A

Air cooled condensor => no water is needed
Pros:
No thermal discharge in the river
No chemicals
No fresh water consumption
No health issues like Legionella

Cons:
Efficiency loss in hot summer
Max power is limited (High power = high temperatures = more difficult to cool with air)
High cost
Important land footprint => large space required

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13
Q

What are primary measures?

A

Control of the combustion parameters to reduce pollutant formation
e.g. Low-NOx burners, air staging in boiler, fuel pre-treatment,…

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14
Q

What are secondary measures?

A

Cleaning system at the outlet of the combustion unit to reduce pollutant emission
e.g. DeNOx, De-dusting, DeSOx,…

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15
Q

What is the impact of load variations in a power plant?

A

NOx emissions spike up

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16
Q

Why could the number of start ups of a CCGT be increased over the years?

A

The increasing share of renewable energy sources and their intermittent character.

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17
Q

What is the impact of more start ups of a CCGT?

A

More transient phases => CO2 and NOX emissions increase, but the relative emissions will decrease because of the use of renewable energyS

18
Q

What does SCR stands for?

A

Selective Catalyst Reduction: converts NOx using NH3 into N2 and H20. Catalysts that are used are: active elements Vanadium or Tungsten trioxide and titanium oxide as a base

Efficiency of 80-95%

19
Q

What are drawbacks of SCR?

A
  1. Ammonia slip: pollution, and fly ash quality
  2. SO3: higher SO2 to SO3 conversion (-> 5%), higher risk for sulphuric acid formation and condensation
  3. Ammonia BiSulfate (ABS): (NH4)HSO4 can condense in air-preheater, dew point 180 - 250°C
  4. Increased pressure drop: 5 to 15 mbar
  5. Ageing of catalyst decreases efficiency => regulary tests of activity needed
20
Q

What does SNCR stands for?

A

Selective non-catalytic reduction: same principle as SCR but without catalyst => higher NH3 injection is needed => higher ammonia (NH3) slip, lower efficiency

21
Q

What are drawbacks of SNCR?

A
  1. Ammonia slip: pollution, and fly ash quality
  2. Ammonia BiSulfate (ABS): (NH4)HSO4 can condense in air-preheater, dew point 180 - 250°C
  3. Lower efficiency in comparison to SCR
  4. Used at higher temperatures: high t° => risk of undesired oxidation of ammonia:
    4 NH3 + 5 O2 = 4 NO + 6 H2O
22
Q

What are de-dusting systems?

A

Mechanical:
Cyclone (centrifugal)
Settling chamber
Filters
Scrubbers
Electrical:
Electrostatic Precipitator (ESP)
Wet ESP (WESP)

23
Q

What is EPS and how does it work?

A

Electrostatic precipitators catch dust by applying a strong electric field between discharge electrodes (vertical wires) and collecting electrodes (vertical plates). The particles are attracted to the collecting electrodes.
3 steps:
1. Charging of suspended particles
2. Collection of charged particles on the collecting electrodes
3. Removal of precipitated matters from collecting electrode

24
Q

What is WESP?

A

Wet Electrostatic precipitators using water to remove the particles of the collecting electrodes.

25
Q

What are differences between fabric filters and ESP?

A

Compared to ESP’s:
- Higher pressure drop: 100-200 vs. 25 mmWC
- Variable pressure drop
- Sensitive to abrasion and chemical attacks
- High energy consumption
- Complex operation
- High maintenance (OPEX)
- Same CAPEX
- Constant emission removal (even improved for small particles)
- Insensitive to ash resistivity => fuel flexibility

26
Q

What does FGD stands for?

A

Flue Gas Desulphurization = DeSOx system = secondary measure

27
Q

What is a wet scrubber?

A

Injection of limestone (CaCO3) sorbent that reacts with the harmfull SO2. Efficiency of 92-99% for SO2 and 50% SO3

28
Q

What are key environmental issues?

A
  1. Energy efficiency
  2. Emissions to air
  3. Emissions to water
  4. Residues (combustion residues or waste)
  5. Noise and vibrations
29
Q

What does NEE stands for?

A

Net Energy Efficiency

30
Q

What factors impact the NEE?

A
  1. Auxiliary power
  2. Fuel preparation
  3. By-product treatment
  4. Flue gas treatment (FGT)
  5. Waste water treatment
  6. Cooling system
  7. Transformers, fans, pumps (auxiliary power)
  8. Ambient temperatures of air (GT, CCGT) and water (steam cycles and CCGT)
  9. Load factor: lower efficiency at lower loads, frequent start-ups and shutdowns
31
Q

What’s the advantage of CHP?

A

Combined heat and power uses the waste heat from the outlet of a gas turbine to heat water.

32
Q

What emissions are there?

A
  1. NOx
  2. SOx
  3. Dust
  4. CO
  5. Metals
  6. GHG
    ….
33
Q

On what is NOx emissions strongly dependent?

A

It is strongly temperature dependent, if temperature stays < 1000 => much lower NOx is formed

34
Q

What is the effect of NOx?

A

Role in acid rain formation
Role in smog formation
Role in particulate matter formation

35
Q

What industry sector delivers the biggest part of NOx/SOx/dust emissions?

A

Thermal power stations and other combustion stations (NOx = 55%; SOx = 67%; dust = 48%)

36
Q

How are SOx formed?

A

The sulphur in the fuel is oxidised during the combustion. Mostly S02 is formed and around 1% SO3 is formed. When SCR is applied for DeNOx SO2 is oxidated to SO3 => 1% => 5%.

37
Q

What is the effect of SOx?

A
  1. Acidification
  2. Toxic gases
  3. Role in particulate matter formation
38
Q

What is dust?

A

Particulate matter that comes for the majority of mineral fractions of fuel. Also unburned carbon and condensed volatile compounds form dust. Dust isn’t only formed by combustion but also during storage, handling and preparation of fuel.

39
Q

What is the effect of dust?

A
  1. Harmful for the lungs; the smaller the particles, the deeper it goes
  2. PM2.5 (= < 2.5micrometer) => stick around and travel further away due to the wind
  3. > 10micrometer => local impact
  4. Efficiency of removal systems in function of the size of the particles
40
Q

What is the effect of dust?

A
  1. Harmful for the lungs; the smaller the particles, the deeper it goes
  2. PM2.5 (= < 2.5micrometer) => stick around and travel further away due to the wind
  3. > 10micrometer => local impact
  4. Efficiency of removal systems in function of the size of the particles
41
Q

What does FGD stands for?

A

flue gas desulphurization (FGD)

Sustainable energy (17 decks)

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