UE 09: Gas and Hydrogen Grids and Storages Flashcards

1
Q

True or false?

1960s and 1970s: Switching from Town gas to Natural gas

  • Before natural gas was commonly used, so-called “Town gas” or “Coal gas” was produced locally at many cities from coal
  • Towngas was a mixture of several gases which differed from city to city (roughly 50% H2, 20% CH4, 15% N2, 10% CO)
  • Most German cities switched from town gas to natural gas in the 1960s and 1970s
  • West-Berlin kept using towngas until the 1990s for independency reasons
A

True!

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2
Q

True or false?

2020s: Switching from L-Gas to H-Gas

  • L-Gas has a different composition than H-Gas and a lower heating value
  • The Netherlands, which are the main supplier for L-Gas, announced to reduce their natural gas production and will therefore stop supplying Germany from 2029.
A

True!

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3
Q

What is missing?

Wobbe index - basics

  • Fuel gas moves through pipes due “…”.
  • At the same pressure lighter gases (“…”) flows “…”.
    –> Density and calorific value “…”
    –> But decreasing the density “…”
A

Wobbe index - basics

  • Fuel gas moves through pipes due to pressure differences.
  • At the same pressure lighter gases (lower density) flows faster.
    –> Density and calorific value per mass correlate negatively
    –> But decreasing the density does not increase the calorific value per mass at the same rate
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4
Q

Wobbe index

1) What is the Wobbe index?

2) What has to be given in order to exchange two gases which have different calorific values with minimal adjustment-effort?

A

1) Wobbe index

  • Is a characteristic value for the interchangeability of gases with regard to heat load
  • A distinction is made between upper (Ws) and lower (Wi) Wobbe indices
  • Formula

W_s = H_s / root (d) ; W_i = H_i / root (d)
d = p_fuel_gas / p_air

(H_s: HHV, H_i: LHV, d: relative density)

2) What has to be given in order to exchange two gases which have different calorific values with minimal adjustment-effort?

  • If both gases have the identical Wobbe index, they provide the same heat output/load at a burner, even if their calorific values differ
  • In this case e.g. the burner nozzle does not need to be replaced
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5
Q

Using the natural gas grid for blends of hydrogen and natural gas is often suggested as a transitional solution.

What do you think advantages and disadvantages of blending hydrogen with natural gas might be?

A

What do you think advantages and disadvantages of blending hydrogen with natural gas might be?

Advantages

  • Uses existing infrastructure
    –> The natural gas grid is already built, so blending avoids the need for immediate, large-scale investment in new hydrogen pipelines.
  • Kick-starts the hydrogen market
    –> Encourages production and demand, even if small at first. It helps hydrogen producers find a market while large-scale hydrogen users are still developing.
  • Reduces emissions gradually
    –> Even a 10–20% hydrogen blend can lower CO₂ emissions from heating and industrial gas use.
  • Supports energy security
    –> Domestic hydrogen blending can reduce reliance on fossil gas imports (a hot topic in Europe).

Disadvantages

  • Limited blending potential
    –> Most existing gas infrastructure and appliances can only handle up to 10–20% hydrogen without safety or performance issues.
  • Energy inefficiency
    –> Hydrogen has a lower energy content per volume, so blending reduces the overall calorific value of the gas mix.
  • Economic inefficiency
    –> Using expensive green hydrogen in low-efficiency systems (like residential heating) is not the best use of this valuable energy carrier.
  • Delays full decarbonization
    –> Blending might slow investment in dedicated hydrogen infrastructure, which is ultimately needed for climate targets.
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6
Q

What is missing?

“…”

  • “…”
  • Depending on the material (some steel types are more at risk than others, plastic pipes are not affected)
  • Risk factors: High pressure and frequent pressure changes
  • Needs to be considered when constructing new or repurposing existing pipelines for hydrogen
A

“Hydrogen embrittlement”

“Due to its small size H2 diffuses through the metal and creates cracks which lead to material failure over time”

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7
Q

What is missing?

Solution options for hydrogen embrittlement

“…”

  • Protective coating on the inside of the pipeline
  • No experience with existing pipelines, only done during construction until now

“…”

  • Installation of a thin plastic pipeline within the existing pipeline
  • The outer pipeline provides stability, the inner pipeline protection

“…”

  • Adding small percentages of another gas (e.g. 2% CO or 0.015% O2) which reduces hydrogen embrittlement

“…”

  • Frequent maintenance to detect failures
  • Lifetime of pipeline about 25% lower
A

“Protective internal coating”

“Pipe-in-pipe”

“Inhibitor gas”

“Increased maintenance”

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8
Q

True or false?

Compressor and metering stations

  • Hydrogen has different compressibility than natural gas
    –> Compressor needs to be replaced
  • Hydrogen is a smaller molecule than natural gas
    –> Seals and gaskets need to be replaced
  • Motor will be fuelled by electricity instead of natural gas
    –> Motor needs to be replaced
A

True!

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9
Q

What is missing?

Repurposing natural gas pipelines for hydrogen only costs “…” of the construction of new pipelines.

–> Repurposing is preferable whenever possible!

But

  • Sometimes new connections are needed for which no natural gas pipelines exist
  • Only possible when a pipeline is not needed for natural gas anymore

–> Construction of new pipelines in parallel to existing ones saves some cost as well, as no new corridors are needed

A

“20-30%”

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10
Q

True or false?

Repurposing gas distribution networks

  • Shrinking number of natural gas customers and demand
    –> Maintaining the same network length with fewer customers leads to rising network tariffs
    –> Rising network tariffs lead to even fewer customers
  • We will need part of the distribution networks for supplying hydrogen to industry
  • Large parts of the distribution networks might become obsolete, as connections to households will not be needed for hydrogen (or would be very expensive)
  • A possible shutdown of infrastructure needs to be communicated well in advance to prevent problems for industrial and household customers
A

True!

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11
Q

1) What types of underground gas storages are there?

2) Do they qualify for storing H2?

A

1) What types of underground gas storages are there?

  • Storages in depleted gas fields and aquifers
  • Salt cavern storages

2) Do they qualify for storing H2?

Storages in depleted gas fields and aquifers

  • Risk of ground instabilities, as hydrogen attacks some types of rock
  • Risk of bacterial methanation (loss of hydrogen)
  • Contamination of stored hydrogen
    –> Probably not suitable for hydrogen

Salt cavern storages

  • Hydrogen does not react with salt rock
  • Already tested for several years
  • Only little contamination of stored hydrogen
    –> Well suitable for hydrogen
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12
Q

True or false?

Repurposing and construction of salt caverns for hydrogen

  • Similar to natural gas now, Germany might have the largest hydrogen storage capacities in the EU in the future
  • Within Germany, hydrogen will probably be stored in Northern Germany, even for consumers in the South
A

True!

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