Hydrogen refuelling based on bladder accumulator-based compression

Hydrogen refueling stations play a crucial role in enabling the widespread adoption of hydrogen-fuelled vehicles as a clean and sustainable transportation option. The refueling process at these stations involves a series of carefully orchestrated steps to ensure the safe and efficient transfer of hydrogen from the station to the vehicle. Understanding the processes involved in hydrogen refueling is essential for optimizing the refuelling.

One of the major important processes in hydrogen refueling is its compression. The energy density of hydrogen in terms of volume is very less compared to the commonly used fuels today. At ambient conditions, hydrogen has a density of 0.089 kg/ m³. This property of hydrogen makes it challenging to store and transport hydrogen to obtain useful work from it. Hence, hydrogen is compressed and stored in high-pressure tanks. This can be achieved using conventional mechanical compressors.

Mechanical compression consumes a certain amount of energy and hence contradictory to mechanical compression the H2REF project funded by the EU tries to achieve similar high compression rates and higher efficiency using hydraulics and bladder accumulators. The H2REF project comprises of a consortium of 6 partner companies from the EU countries. This article gives you a brief explanation of hydrogen compression using hydraulics and bladder accumulators.

Conventional Hydrogen refueling

When refueling hydrogen at a hydrogen refueling station (HRS), several processes occur between the station and the vehicle being refueled. First, hydrogen is delivered and stored in the primary hydrogen storage. Then, the stored hydrogen is compressed to the required filling pressure to increase its energy density. The compressed hydrogen is either directly filled into the vehicle tank or stored in buffer storage before being dispensed into the vehicle. This compression process is energy-intensive, utilizing 7 to 13% of the lower calorific value of hydrogen. To prevent thermal degradation of the vehicle's fuel tank, the hydrogen is pre-cooled before refueling. During the refueling process, a leak test is conducted, and communication between the vehicle and the station occurs via an infrared interface. The fueling process is controlled based on data transmitted and received, including tank size, fill level, pressure, and temperature. The flow and level of fuel are calculated using a hydrogen flow measuring meter, enabling the process to be aborted if necessary. In case of communication failure, the filling process is based on predefined table data specified in the filling protocol.

Bladder accumulator-based hydrogen compression

A Bladder accumulator is a welded or forged pressure vessel consisting of a bladder and ports for gas and fluid inlet. The bladder acts as a gas proof screen separating the fluid section and gas section. The bladder holds the hydrogen gas inside and is surrounded by fluid which is connected to an external hydraulic circuit. When the hydraulic circuit pumps the fluid inside the bladder accumulator the bladder pressure increases thereby compressing the hydrogen gas inside to the required pressure.

Since the delivering pressure for hydrogen refuelling is high, carbon composite pressure vessels are used. The main advantage of bladder accumulator-based compression is the robustness, reliability, and scalability of the hydraulics technology and carbon composite pressure vessels. These components are already matured and standardized thereby minimising the cost of hydrogen compression.

Hydrogen refuelling based on bladder accumulators.

A hydrogen refuelling station based on bladder accumulators consists of a Gas Storage, Compression, and buffer module, Process chiller, Hydraulic power unit, and a Dispenser.

• The hydraulic power unit houses the hydraulic tank, air compressor, electrical cabinet with PLC control, air compressor, motor, pump and hydraulic intensifier.
• The bladder accumulators along with heat exchangers are housed inside the compression and buffer module.
• The hydrogen from the storage system is sent to the compression accumulator. The hydraulic system then compresses the gas to a pressure of 350 bar.
• This high-pressure hydrogen is then cooled using a heat exchanger and sent to the transfer accumulator where it gets further compressed to 900 bar.
• This high-pressure hydrogen is then precooled and filled into the vehicle tank through the dispenser.

In conclusion, bladder accumulator-based compression offers a promising solution for hydrogen refueling, addressing the challenges associated with storing and transporting hydrogen. This technology, as demonstrated by the H2REF project, utilizes hydraulics and bladder accumulators to achieve high compression rates and efficiency. The use of mature and standardized components, such as carbon composite pressure vessels, ensures the robustness and reliability of the system while minimizing the cost of hydrogen compression. By understanding and implementing this bladder accumulator-based compression systems, hydrogen refueling stations can optimize their infrastructure and contribute to the wider adoption of hydrogen fuel cell vehicles as a clean and sustainable transportation solution.

References:

1. About H2Ref | H2Ref. (2020, January 6). H2Ref. http://www.h2ref.eu/about-h2ref/
2. HOW IT’S MADE - A hydrogen refueling station using bladder accumulator-based compression - JEC. (n.d.). JEC. https://www.jeccomposites.com/news/how-its-made-a-hydrogen-refueling-station-using-bladder-accumulator-based-compression/
3. REASONTEK CORPORATION. (2023, February 16). Bladder Accumulators - Reasontek Corp. Reasontek Corp. https://www.reasontek.com/bladder-accumulators/