Hydrogen
Contents
Basics
- The Element Hydrogen
- Main Uses Are:
- Fuel (mainly in space, or for fuel cells)
- Chemical Reactant ( Direct Reduced Iron etc)
- Lifting Gas
- Can be problematic to store due to it's ability to leak easily + Hydrogen Embrittlement Issues
Misc Info
- Enthalpy of combustion - 286kJ/mol - [1].
- Heat of combustion (per mass) - Compare to gasoline or diesel - enthalpy of combustion of hydrogen is about 3x as large - [2]
- Hydrogen has about 1/8 and 1/3 the volumetric density, resepctively, compared to propane and natural gas.
- Let's look at basic calculations.
- Compare to energy fuel efficiency of gasoline engine - 200 g/kWh, best marine diesel - 150 g/kWhr - [3]
Production
Biological
- Heard about this, seems to be mostly theoretical?
- Essentially interrupt photosynthesis
- Alss artificial photosyntesis
Electrolysis
- Mainly via pure water or an alkalai solution
- Brine Electrolysis etc can be used
Steam Reforming
- Hydrocarbons, mainly Methane can be turned in to hydrogen and carbon dioxide via Steam Reforming
Syngas
- Syngas -> Water-Gas Shift Reaction hydrogen and co2
Storage
Compressed
- Simplest, but least dense
Cryogenic
- Cools the hydrogen until it is liquid
- Very Dense (most dense short of slush/solid hydrogen?)
- Main issues are:
- Cooling Needed
- Insulated Containers Needed
- Boiloff
Mechanical/Chemical (need better name
- Metal Matracies
- Carbon (Activated carbon, carbon metamaterials etc)
Discussion on Feasibility of Compressed Hydrogen Storage Tanks
Pressurized storage of hydrogen: molar mass of hydrogen molecules is 2 g/mol. 1 mole is about 5 gallons. Pressurized to 100 atm (under 1500 PSI) - readily doable with high pressure electrolyzer - you get 200 grams per 5 gallon container. Max practical for volumetric reasons would be say up to 100 gallons of 20 cu ft volume in cylindrical tanks- say 2 meters by 1 meter wide (base of a single person car). Thus, 100 gallons volume at 100 atm gets you 4 kg of hydrogen. For combustion purposes - based on enthalpy of combustion - that is equivalent to about 12 kg of gasoline or diesel. That is about 3 gallons of fuel.
In practical terms - based on our Briggs and Stratton 27 hp gas engine - that is about 75 hp hours. Sufficient for a very small personal vehicle, and arguably more efficient than electric cars from the scalability and Decentralization Perspective.
For comparison to the volume of a propane container - a 20 lb tank of propane (5 gallons about) - is only 200 grams of hydrogen at 100 atmospheres. Not a lot.
Based on efficiency measures - heat engines being about 20% efficient - can we show that enthalpy of combustion gives a reliable measure of hp-hr? Gasoline is 50MJ/kg enthalpy of combustion. 50 MJ 50 MWs - or 14 kWh. This is 56 kWh of enthalpy for one gallon of fuel. Or 75 hp-h. A 27 hp engine running for 1 hour is about 30% efficiency - about right.
Another check - H2 is 150 MJ/kg. Thus, 4 kg in the 100 gallon / 100 atm storage have 600 MJ. Divide by 5 for 20% efficiency of internal combustion engines - or 120 MJ. That is 33kWhr of energy, or 44 hp-hr. Range might be about 200-400 miles. About 2 gallons of fuel equivalent.
Conclusions
- Feasible with efficient design; acceptable range
- Double the pressure of stored hydrogen - double the range or half the tank volume.
- Economics - doable with open source storage cylinders. Type I high pressure tank is the lowest rating for all pressure tanks, and has a max pressure of 200 atmospheres.
Some more background Research
- Sample results - [4] and [5], and [6] and [7]. 30 atm alkaline electrolyzer - [8].
- Electrolyzer costs - $1k/kW. For $3k we can have storage of H2 in PVC pipe - $1/watt for solar panels, $1k for an electrolyzer, and then we produce hydrogen at about 27hp-hr volume. This is enough for 4 hours of cooking on an industrial size burner. [9] - up to 30 ATM.
Sample Conclusion
30ATM alkaline electrolyzers are proven and available technology. [10]. Based on Hydrogen discussion, a maximum allowable tank size for a personal vehicle is 1 GGE - or about 27 hp hours. That is acceptable for a superefficient personal vehicle. The battery pack size for a Tesla is 80 hp-hr, at $15k so the hydrogen storage GGE/ESE is approximately 100x lower cost over an LCA time of 100 years than the Lithium Ion battery. The hydrogen storage is assumed to be 2400' of of 1" schedule 80 PVC pipe, based on 50-100 year PVC Lifetime.
Internal Links
External Links
- 3000 PSI storage - 100 gallon volume required for 7.5 gallon gasoline equivalent. [11]
- Online shop for hydrogen components and fuelcells http://fuelcellstore.com
- A Video on the Problems with Hydrogen ICE's
