Though hydrogen has proven its value as a sustainable fuel, it remains cost-prohibitive due to the lagging infrastructure necessary for widespread adoption. Common culprits are not the fuel cells or vehicles, but the transportation and operational equipment — especially the critical technologies for hydrogen compression and decompression.
“Operational expenses are really bad, and that changes what options are available,” said Dave Hull, regional VP at Bosch Rexroth. “There are two ways to look at this currently: a gaseous compressor or a liquid hydrogen compressor. Liquid is the future for high volume and scaling because liquid makes the density of hydrogen much smaller, so you can get more hydrogen in less space, transport it, and store energy like a battery.”
The CryoPump Station includes new electro-hydraulic technology that dispenses hydrogen fuel at a rate of
600 kg/h in 10 min. Image: Bosch Rexroth
Bosch Rexroth partnered with FirstElement Fuel, the largest distributor of hydrogen at scale. The company operates approximately 40 hydrogen refueling stations in California and dispenses more than two million kilograms of hydrogen per year. FirstElement Fuel informed Hull and his team that 90% of the problems at filling stations lie in compressing hydrogen.
“Almost 40% of the fuel that shows up at your station never actually makes it into the vehicle,” said Hull. “Imagine if 40% of the gasoline just spilled on the ground and evaporated and never got in the car. That’s a huge cost that needs to be addressed and fixed.”
The problem Hull described is called boil-off, when liquid hydrogen evaporates into a gas as unwanted heat inevitably enters the cryogenic storage tank. Traditional hydrogen filling stations use a small pump to compress hydrogen into storage cylinders for dispensing, where pump inefficiencies and hydrogen losses have been accepted due to technology limitations. Additional losses occur during transfill, when transported hydrogen is transferred to the filling station storage tanks before compression.
Hull and his team, in collaboration with FirstElement Fuel, started from scratch and designed a new cryogenic pump and CryoPump Station that eliminates the storage cylinder system and related valving and equipment. This simplifies the filling station and improves installation, operation, and maintenance costs. It also eliminates losses during transfill.
“Liquid hydrogen is at 23 Kelvin. There’s some really weird stuff that happens at those temperatures. It’s almost absolute zero. It’s very cold to make it a liquid. To pump that efficiently, if you put any energy into it, it wants to become a gas,” said Hull. “Simply put, compressing a gas is five times more energy-intensive than compressing a liquid. So if you can put liquid hydrogen into your compressor and then compress it in one shot, we can do that with the power of this hydraulic system extremely efficiently.”
The CryoPump Station consists of two hydraulic stages. In stage 1, liquid hydrogen is kept extremely cold at 16 bar, ready for dispensing or to feed stage 2. In stage 2, cold liquid hydrogen from stage 1 enters, and another set of hydraulic cylinders compresses it from 16 to 900 bar in one stroke. The cylinders are powered by electric motors, and the station’s power electronics and digital controls drive the system.
Stage 1 keeps liquid hydrogen at 16 bar and includes two servo-hydraulic pumps. Liquid hydrogen can be dispensed to a vehicle or fed into stage 2. Image: Bosch Rexroth
“A Rexroth servo is a variable-speed motor, and we can vary the speed of the input to the hydraulic pump,” said Hull. “The hydraulic pump is variable stroke, so we rotate the motor always in the same direction so that it keeps the same speed, and then we’re able to change the direction of the hydraulic fluid by adjusting the pump. And there’s no valve in between, no valve at all. So the system perfectly matches the required load to the power input.”
Stage 2 includes two servo-hydraulic speed pumps that compress liquid hydrogen to
900 bar in one stroke. Image: Bosch Rexroth
Hull noted that most hydraulic systems are designed to modulate power with valves. He compared it to driving a car with one foot on the gas to ensure there is enough power, and one foot continuously modulating the brake to control the system. This method is inefficient and wastes energy as heat.
“We’ve eliminated all of that by simply only driving with the gas pedal. And we modulate the gas pedal so that it exactly matches how much load is required from our system,” he said.
When a vehicle arrives at the filling station, no matter the pressure in its tank, whether it is 300 bar, 400 bar, or otherwise, when the cryogenic pump plugs into the vehicle, the pump will match the vehicle’s tank pressure. This load-matching provides tremendous energy efficiency gains and can fill vehicles in record time.
“It has a high enough flow rate that it can fill a Class 8 truck in less than 10 minutes,” said Hull. “It’s exactly the same as if you were filling it up with diesel.”
The CryoPump Station can supply one liquid and two gaseous hydrogen dispensers, providing a flow rate of 600 kg/h. With a footprint of less than 11 m² and a noise level of less than 65 dB(a), they can even be used in residential areas.
To view an interactive demonstration of the CryoPump Station and its major components, visit: virtual-world.boschrexroth.com/cryopump-station.
Bosch Rexroth
boschrexroth.com/en/us/industries/hydrogen
Filed Under: Featured, Pumps & Motors
