UE 09: Gas and Hydrogen Grids and Storages

Question 1

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

Answer 1

True!

Question 2

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.

Answer 2

True!

Question 3

What is missing?

Wobbe index - basics

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

Answer 3

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

Question 4

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?

Answer 4

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

Question 5

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?

Answer 5

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.

Question 6

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

Answer 6

“Hydrogen embrittlement”

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

Question 7

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

Answer 7

“Protective internal coating”

“Pipe-in-pipe”

“Inhibitor gas”

“Increased maintenance”

Question 8

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

Answer 8

True!

Question 9

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

Answer 9

“20-30%”

Question 10

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

Answer 10

True!

Question 11

1) What types of underground gas storages are there?

2) Do they qualify for storing H2?

Answer 11

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

Question 12

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

Answer 12

True!