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H2-Refuel The Compressor Team from ME 316

From left to right: Cameron Stone, Greg Wallace, Nathaniel Jones, Riley Howard, Will Wilber

Compressors have been the Achilles heel of hydrogen refueling stations worldwide. Our team intends to change that. Instead of the normal 10,000 psig output we are going after a reasonable 200 psig. This is attainable thanks to our patent pending vortex tube system.

 

 

Background

 

In March of 2013, it was stated by Mr. Bill Elrick of the California Fuel Cell Partnership that one of the hindrances to deployment of fuel cell electric vehicles (FCEVs) is the lack of standardization and codes.1 The U.S. Department of Energy states, “It is projected that the current state of hydrogen compressor technology will not be able to meet future infrastructure demands in a cost-effective manner.”2 Research is being done to solve problems related to hydrogen compressors.2, 3, 4 So hydrogen compressor design is still in its early stages. Our challenge is to find a compressor that is both reliable and functional for our needs.

Related codes and standards

 

Compression Methods

Most hydrogen compressors (especially for refueling stations) operate via piston, scroll, or diaphragm. The various types of compressors and their advantages are as followed:

Piston Compressor [More Info]– Uses a piston to compress fluid. A design that has been tried again and again, and that can be made as simple or complex as needed.  They are efficient and can be made in large sizes, but tend to be costly and have many moving parts.

scroll compressor
Scroll Compressor Cycle of Operation

Diaphragm Compressor [More Info] – Instead of a piston, this uses a flexing diaphragm to manipulate pressure.  Metal-based diaphragms are low volume but high pressure.  Rubber/Silicone diaphragms are high volume, low pressure and need replacement often.  Working fluid will not touch moving parts, contamination concerns are low.

Scroll Compressor  [More Info] – Uses one fixed and one moving spiral.  The moving spiral orbits but does not rotate to pushes fluid against the non-moving one to create suction and compression.  These are quiet, smooth, and reliable, especially at lower volumes.  They have fewer moving parts but are highly susceptible to debris (which should not be present in our system).

Electrochemical Hydrogen Compressor

Ionic Liquid Piston Compressor [More Info] – Acts similarly to  piston compressor, but uses an ionic liquid rather than a metal piston.  These have very few parts and are long lasting.  Produces very little waste heat.

Electrochemical hydrogen compressor [More Info] –  Uses electricity to separate hydrogen into protons and electrons and force them across a membrane.  Can maintain high pressure, is compact, uses no moving parts, and has good efficiency.

Hydride Compressor [More Info] – Absorbs hydrogen ions at low temperature and pressure and expels them at high pressure when heated.  High volume flow rate with no moving parts, but expensive and heavy and produce waste heat.

 

Some compressor systems have been studied and tested to great lengths.  Others are barely in research and development.  Since we will not have the time or funding to create a compressor from scratch, we are limited to more established methods of compression: piston, scroll, or diaphragm.  The most efficient method for us is to chose a pre-developed compressor from a company that specializes in their construction.

 

Design Specifications

The compressor takes in hydrogen from 2 components: the “hot” gas expelled from the vortex tube and excess hydrogen from the storage tank.  This injects the hydrogen back into the pre-cooling cycle and the vortex tube where it will be liquefied and then stored.  To maximize system efficiency, the following are our requirements:

  • 200psi Output Pressure: The vortex tube requires a certain amount of pressure to operate at its highest efficiency. When the gas enters, it is forced into a spiral at high speeds.  This high speed cannot be achieved without high pressure forcing it through the device.  By calculating the ideal pressure for the vortex tube, we arrive at needing compression of approximately 200psi.
  • 1.5-5g/s Mass Flow Rate: Our system must produce 50 kg of liquid hydrogen each day. With the current mass flow rate, this only requires the compressor to run for 3 hours each day. This allows plenty of room for expansion if the design changes to a higher output.
  • Oil-Free: To ensure that no lubricants or oils leach into the hydrogen, we will use a compressor that uses no oil in the working space.
  • Inexpensive: Funds are limited. The source and purification teams alone are expected to take up to half the budget.
  • Dependable: Any time spent out of commission is money lost. The H2 Refuel Prize desires a system able to operate for 98% of the time.
  • Compact: The entire space of the container is only about 600 cubic feet. The storage and the source groups are expected to take up about 400 cubic feet combined!

HOQ (v2)

Design Alternatives

  1. RIX 4VX (3 g/s) [RIX Industries]
  • Piston type
  • 200 psig discharge
  • 3 g/s (259.2 kg/day) flowrate
  • 30 Hp
  • 5-6 months lead time
  • Oil-Free
  • Designed for Hydrogen
  • Air-Cooled
  • Size: 54″W x 27″L by 33″H
  • Weight: 750 lb

2.  RIX 4VX (5 g/s)

  • Piston type
  • 200psig discharge
  • 5 g/s (432 kg/day) flowrate
  • 35 Hp
  • 5-6 months lead time
  • Oil-Free
  • Designed for Hydrogen
  • Air-Cooled
  • Size: 54″W x 27″L by 33″H
  • Weight: 750 lb

 

 

 

 

4vx compressor4vx3 compressor

We intend to use the 3 g/s (259.2 kg/day) system because when combined with the output of the electrolyzer it produces optimal hydrogen flow into the vortex tube, about 3.6 g/s. We also will choose a model that expels hydrogen at a pressure of 200 psig. This pressure is equivalent to the hydrogen exiting the electrolyzer and is the lower limit of usable pressure across the vortex tube.

 

Economics

1.    Estimated cost: $130,000
2.    Estimated maintenance cost for first ten years (life of station): $188,000 (at $18,800/year)
3.    Cost to set aside for maintenance: $138,500 (Assumes 6% interest on set aside money, 10 years as shelf life, and constant yearly cost as $18,800 for maintenance.  These give a P/A of 7.3601 )
4.    Depreciates to $46,600 after 10 years (based off $130,000 base and an iterative depreciation at a 10 year recovery period).

 

 

 

What’s next?

In essence, we need to acquire a high quality compressor to move the hydrogen along it’s path efficiently.  In doing this, we can achieve the goals of the H2 design competition and create a working hydrogen refueling station.

With the hydrogen sufficiently compressed and the gas flowing as needed, it can finally move on to the next stages.  All the output of the compressor will next go through a heat exchanger system to remove excess heat and then move on to the pre-cooling system.

 

 

Washington State University