In Spring 2016 everyone will be racing to Pullman to check out the innovative modular hydrogen fueling station designed by WSU Engineering students! The purification team is tasked with the goal of allowing our design to output a gas that is 99.999% pure hydrogen gas. To put our goal into perspective let’s relate it to our famous WSU Martin Stadium. The capacity of Martin Stadium is approximately 35,000 people, if each one of those people represented a molecule of our output gas only 3 of those people could not be hydrogen molecules for us to succeed. Our challenge is to output pure hydrogen with less than one hundred parts per million of impurities as required by SAE J2719.
During the design process the Hydrogen Source and Purification teams have worked closely together. We finalized and submitted a design to the H2-Refuel Competition that utilizes electrolysis to separate hydrogen from water or methane.
What makes our design so innovative is the modularity. Electrolysis was determined to be the best option for the competition design due to the input of the system. We have also researched ideal design alternatives if Syn-Gas is inputted instead.
|Input: Methane, Water, Electricity||Input: Syn-Gas (Hydrogen, Carbon Monoxide & Carbon Dioxide)|
|Output: Gaseous Hydrogen and Waste Gases|
|Musts: Reach a purity of 99.995% or greater|
|Should: Generate Power, Output at high pressure, Easily Accessible|
There are many different commercially available ways to purify a gas. Our challenge is to find the right method that meets all of the system needs and links well with the other subsystems. The following processes are the most commercially available and proven hydrogen purification technologies today:
Palladium Membrane Diffusion: As the name suggests, this method uses the chemical element palladium (Pd) and typically a silver alloy. Together they posses the ability to only allow hydrogen to pass through when subjected to temperatures of approximately 300 °C.
Palladium Membrane advantages include exceeding hydrogen purity standards, unlimited lifetime (no vessel replacement), low power consumption, customizable by flow rate. The purifier does not require replacement since the inlet impurities are trapped on the inlet side of the palladium and vented continuously.
Cryogenic Separation: Is the process of selectively purifying gases by boiling them in liquified states at various boiling temperatures. The process would possibly require small heat exchangers to turn any liquid input into a gas before it went through separation.
The Cryogenic Separation system separates impurities by cryogenic adsorption. A pressurized hydrogen gas is inputed into the system and enters a series of heat exchangers and adsorbent beds to produce a 99.99% pure hydrogen gas. Silica gel is the main adsorbent material used, which is submerged in liquid nitrogen during the process. Some of the key benefits of utilizing this technology are ease of on-site maintenance, small footprint, low operational cost, output meets hydrogen fuel purification standards.
Pressure Swing Adsorption (PSA): Pressure swing adsorption is when components of a gas mixture are adsorbed on a solid material matrix using high pressure, such as active carbon and zeolite. These different components are then desorbed at a low pressure and can then be siphoned off.
Chemical Adsorption: A method of separating gas components through specific adsorption zones. The most prominent method in use is carbon nanotubes, carbon is well known for being porous and being able to absorb gases. Difficult to find commercially available units, typically this method is found in large scale industrial operations.
Physical Absorption: Is a puriificaiton method where either liquid absorbs a gas or solid absorbs a liquid. Unwanted molecules attach themselves to a substance of volume and the desired molecules, will still be in the same state. For our application, this method would consume to much space.
A House of Quality ranks the relationship between system requirements and different design options. As we research and develop our purification system these relationships will help us optimize our design.
Ranking System: Each purification process was given a rank of 1-4 for each quality characteristic.
1-Bad 2-Good 3-Great 4-Ideal
Manufacturing cost, Safety & Modularity were all multiplied by 3 because they are most relevant and important requirements to our sub system. Reliability is also multiplied by 2 due to its relevance of meeting hydrogen fuel purification standards.
As you can see purification is critical to the system because it is highly related to many important requirements such as, cost, power usage, reliability, ease of maintenance, hydrogen output, contamination & modularity
Palladium Diffusion Membrane –
- ~ 98.00% Pure Hydrogen
- Max inlet pressure 300 psi (SAES Purifier)
- 390 – 410 °C Inlet Temperature
Cryogenic Absorption Separation –
- ~90-98% Pure hydrogen
- Inlet pressure 300-700 psi
- 360 °C inlet temperature maximum
Pressure Swing Adsorption –
- ~ 60% Pure Hydrogen
- Input pressure ~160 psi
- 30°C Input Temperature
The station we are designing has two possible input hydrogen streams. We need two different recommendations since each input stream has very different physical attributes.
For the H2 Refuel competition input: (water, methane, electricity)
The Source team is working with the Purification team to use an electrolyzer system to separate the hydrogen molecules into a pure hydrogen gas stream. For more information on this system recommendation see the Source Technical Information page.
For the Syn-Gas input stream: (N2, H2, methane, CO2, and CO)
Our recommendation for the syn-gas stream is a system consisting of two separate purification technologies placed in series. We are considering a pressure swing adsorption initially, followed by a cryogenic separation system. Since we are proposing combining these systems for maximum purification possibility we will most likely utilize custom systems on both accounts to have the greatest opportunity to meet our needs.
Assuming the interest rate is 6%, cost of the system is $100,000 and the maintenance annually is $4,000 (estimated cost of start up, repair, replacement parts, annual service, etc..). The following data is obtained.
Initial cost of system: $100,000
Estimated Cost = C (F/P, 6%, 10) = $100,000 x 1.7908 = $179,080
Estimated Maintenance Cost for first 10 years:
Maintenance Cost = $4,000 x 10 = $40,000
Total Estimate = $179,080 + $40,000 = $219,080
About $219,080 should be set aside now to cover the cost of the subsystem for the next 10 years.
If we purchase this for $100,000 with a 10 year recovery period the system will decline as follows.
1. d=0.100(100,000) = $10,000 lost BV=100,000-10,000 = $90,000
2. d=0.180(90,000) = $16,200 lost BV=90,000-16,200 = $73,800
3. d=0.144(73,800) = $10,627.20 lost BV=73,800-10,627.20 = $63,172.80
4. d=0.115(63,172.80) = $7,264.87 lost BV=63,172.80-7,264.87= $55,907.93
5. d=0.092(55,907.93) = $5143.53 lost BV=55,907.93-5143.53 = $50,764.40
6. d=0.074(50,764.40) = $3,756.57 lost BV=50,764.40-3,756.57 = $47,007.83
7. d=0.066(47,007.83) = $3,102.52 lost BV=47,007.83-3,102.52 = $43,905.31
8. d=0.066(43,905.31) = $2,897.75 lost BV=43,905.31-2,897.75 = $41,007.56
9. d=0.065(41,007.56) = $2,665.49 lost BV=41,007.56-2,665.49 = $38,342.07
10. d=0.065(38,342.07) = $2,492.23 lost BV=38,342.07-2,492.32 = $35,849.84
Therefor the estimated depreciation value of our sub component after 10 years is $35,849.84
The modular hydrogen fueling station designed by WSU Engineering students is a daunting task that requires complex subsystems to work together in harmony if this goal is to be reached. Our challenge as the purification team was to output pure hydrogen gas at 99.999% purity with less than one hundred parts per million of impurities as required by SAE J2719.
Our recommended designs are modeled around two separate hydrogen streams, one for the hydrogen competition, another for syn-gas. In collaboration with the source team an electrolyzer system that separates the molecules will used for the hydrogen competition while a custom system that utilizes both pressure swing adsorption and cryogenic separation will be used for syn-gas.
As the design process concludes for the hydrogen refueling station it is time to turn the focus towards the build. The first step for the purification team is to source an affordable electrolyzer for the hydrogen refueling competition as well begin researching the purification unit for the syn-gas. As of November 2015 the purification team was awarded a $ 30,000 dollar grant to start this research into this new custom system for syn-gas. This is the first step in ensuring that the WSU H2 Refuel team will make a significant mark on the competition but also in future hydrogen refueling across the country!