CNG to Hydrogen Conversion
I see CNG as a stepping stone to hydrogen, once that infrastructure is in place, and it's my understanding that you could actually run a CNG vehicle on hydrogen without any modification. Is there anyone out there who can elaborate on this and correct any inaccuracies in my understanding?
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Replies to This Discussion
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Permalink Reply by Daryl Oster on -
Presently the lowest cost source of hydrogen is steam cracking of natural gas. The process wastes about 30% of the energy in the NG, and produces as much CO2 as just burning the NG. AND burning H2 in an internal combustion engine produces oxides of nitrogen pollution.
Using electricity to produce H2 -- wastes about 30% of the electricity, then another 40% is lost in a fuel cell to turn it back into electrical energy to propel a car. The bottom line is hydrogen = hype (until a process is commercialized to produce H2 at lower cost than other energy sources -- OR nuke fusion of hydrogen is perfected -- both have been "10 years away" for the last 30 years.
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Permalink Reply by Kurt Stiffel on -
Hi Kathryn,
I understand that converting CNG gas stations - to hydrogen is a cheap and simple conversion and I believe the same is said of the cars too.
Regards,
Kurt
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Permalink Reply by Kenneth Koch on -
Kurt.
The assumption here is that you make the hydrogen from the natural gas. The problem here is that the hydrogen contains less energy and is MUCH more difficult to store.
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Permalink Reply by neil cox on -
Not withstanding "incorrect" in the next post: Hydrogen has less energy by volume than natural gas, and most other fuels and is more difficult to store and distribute. I'm unsure which assumption, but most hydrogen is made from natural gas as other sources cost two or more times as much, at present.
Made by electrolysis is less costly only is you need extreme purity or you ignore the cost of the electricity, put an unrealistic value on the oxygen produced as a byproduct and/or put an unreasonable cost on the polution released by making hydrogen from natural gas.
We could recover some hydrogen being vented by many processes, but the recovery cost typically, is not trivial, but the volume of hydrogen that could be recovered is trivial. Neil
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Permalink Reply by Bill Roach on -
Incorrect.
Regards,
W.E.Roach
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Permalink Reply by Warren Reynolds on -
Mr. Oster:
I see that you are discouraged about hydrogen. Let me assure you, it is alive and well ! You need to up date your information.
Yes, catalytic "cracking" of natural gas is a way of generating hydrogen with a by-product of powdered carbon for tires. The oil refineries use huge quantities of NG for producing hydrogen with a lot more used to heat the catalytic reactor to a high temperature. It is an energy intensive process.
Yes, the "big oil" companies are cracking natural gas at their hydrogen filing stations in California but will soon change when the solar-hydrogen units are installed.
Currently, electrolysis of water using a platinum electrodes requires about 50-60 Kwhr (varies with the amp/cm 2 ) to produce a kilogram of hydrogen at 65% efficiency. However, there is commercially available a new nano-tech non-platinum electrode electrolyzer that is about 90% efficient so the price of hydrogen will come down to below $2.20/kg which gets you about 22 miles in a fuel-cell car. A few auto comparisons:
Oil-well-wheels (ICE engine) car - 13% efficient
Oil-well-wheels (hydbrid) car - 21%
NG well-hydrogen (fuel cell) car - 42%
water-well-hydrogen (fuel cell) car - 45%
Which car do you want to drive ?
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Permalink Reply by Daryl Oster on
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Warren,
Thanks for the H2 update, i was aware of a nano-surface effect (as i recall it was a nano iron oxide) that helped decrease the internal resistance by stressing the bond angle of the water molecule -- was not aware that it was commercially available. So now only 65% waste of precious wind or solar electricity in the expensive E to H2 to E process.
IMO, far better to store electricity in a battery or ultracap at 10% to 20% loss. Best is to use the electricity directly and not waste any in a storage process.
For my money i'll wait and buy the Loremo ( www.loremo.com ). 124mpg 100mph. on BioDiesel, less money to buy the whole car than to just rebuild a fuelcell. Much lower cost to own and operate the Loremo, (or even a VW lupo at 80mpg). So in my book, H2 is not "alive and well" yet.
BTW, my Corolla will go 41 miles on $3.91 -- TODAY that is less per mile cost than the H2 "will come down to". And the gasoline price includes road tax -- does the H2 price? My Corolla cost less than $13,000 new in 2003, it has 135k miles with no non-maintenance repairs required, and several times we have traveled more than 500 miles on a tank of fuel.
The only thing that excites me about H2 FCs is the potential to run my notebook computer for a week or two on a small H2 cylinder (that promise has been 2 years off for the last 10 years).
My mind remains open, and i am hopeful that a breakthrough in ALL of the following areas will one day make H2-FC transport viable:
PV or small scale wind turbine cost per Watt (presently $6-$10, needs to be $1-$2);
Cost of hydrolyzer (and compressor or HP pump depending on storage system);
Cost of water purification (required to protect hydrolyzer electrodes) ;
Cost and size (or weight) of storage tanks (both in vehicle and at station);
Cost/Watt of FC (initial and lifecycle costs, precious metal price sensitivity, etc.);
Weight and size of FC
Reliability of FC (cat contamination, warm-up time, freeze damage, service life, etc.);
High explosion risk compared to BioDiesel.
There are much more viable alternatives to using fossil or water derived H2 for transportation -- and they do not rely on breakthroughs.
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Permalink Reply by Warren Reynolds on
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Oster:
A lot of older cars today still get 20-25 mpg so gas at $4/gal gets them 20-25 miles. Hydrogen is less expensive and will remain so for decades since solar energy is free. Gasoline will go back up to over $6/gal. in a 6 months. Europe gasoline is already $9/gal. Two years ago it was $7.
The carbon fiber tanks developed in 1999 can hold 10,000 psi of hydrogen. It has been thoroughly tested in auto crashes that flatten cars and shred gasoline tanks and the carbon tanks survived. It is safer than gasoline that flows to the ground and catches fire in a car crash. Hydrogen, on the other hand, just leaks upward since it is lighter than air. Both the European and American Safety Agencies have accepted the tank.
The fuel cell efficiency is 90% when operated correctly. (Nernst Eqn. theor. limit is 96%; it does not fall under the Carnot thermodynamic category). The nano-tech metals and new cheaper ion-transfer polymers will bring the price of the fuel down shortly. When properly installed, it will operate at temperatures as low as -10 deg. C. For lower temperatures, a small trickle of hydrogen would keep it warm at less than
-10. Several small carbon tanks at 10,000 psi will get you about 250-300 miles.
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Permalink Reply by Kathryn Bryant on -
So what would need to be done to convert from CNG to hydrogen? Would the tank need to be replaced with a carbon fiber tank or would the CNG tank work?
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Permalink Reply by Daryl Oster on
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Warren,
I do not argue the theoretical efficiency of FC is higher than ICE efficency, yet my limited reading indicates the theorietical maximum is 83% -- not 96% as you assert. (perhaps the difference in reacting to vapor or liquid water?)
Like i said i am willing to keep an open mind and accept that the theory may eventually get reduced to practice at a competitive price. Currently, there are many cost issues preventing H2 viability.
http://www.renewableenergyworld.com/rea/news/ate/story?id=52182
Comparing a $100k+ H2 setup and/or $600/mo lease H2 car capable of 10c/mile fuel cost; to a 10 year old car that gets 25mpg is not a viable comparison -- for someone with such an old car, the wiser investment is still the Corolla costing $15k offering the same fuel cost AND much lower operating cost. Perhaps that is why there are more Corollas than any other car in the world. As i said, H2 - FC still has many value hurtles to clear -- it all boils down to benefit to cost ratio.
I have never heard of a FC that achieved 90% efficiency. Was that on air or pure oxygen? At what temperature? What was the cell voltage?
More efficient FC are heavy and bulky and costly. What is the specific mass (kg/kW), the specific cost ($/W), and the specific size (l/W)? What is the operating life? What in the TBO? What is the cost of an overhaul?
Also FCs have poor efficiency at low output -- as in a car during cruise -- or most of the time.
What is the cost of the several small 10ksi carbon fiber tanks to get 300mile range?
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Permalink Reply by Cobraphx (Matt) on -
Well, I don't know where your water-well-hydrogen (fuel cell) car - 45% efficiency comes from. But let's compare your numbers to a battery electric vehicle.
We know the HHV of Hydrogen is 39.4 kWh/kg
"50-60 Kwhr (varies with the amp/cm 2 ) to produce a kilogram of hydrogen at 65% efficiency", we'll call it 60kWh/kg of H2.
So your theoretical 90% efficient electrolyzer consumes 44kWh/kg. But this exclusive of compressing the H2 to a pressure suitable for on board storage. This requires a minimum of 5000psi and is most commonly 15,000psi or liquefied go get a decent range (the Honda Clarity uses Liquefied H2). To compress 1 kg of H2 to 15,00psi requires another 7-10kWh, liquefying H2 can take 17-60kWh of energy depending on the size of the facility. So the 39.4kWh (1 kg) of hydrogen requires 67kWh - 120kWh to get into the tank.
You can always take that electricity and use it directly in a battery electric vehicle. The 100kWh it takes to put each kg of H2 in the Honda Clarity will power a pure EV for quite a few miles...
We also know that on the EPA combined cycle the Tesla Roadster ( a high performance pure electric vehicle) gets 3.25 miles per kWh plug to wheels.
So with the 60kWh of electricity to generate each kg (ignoring compression losses) to drive the "water-well-hydrogen (fuel cell) car - 45%" which goes 22mi on that 1 kg of hydrogen, the Tesla roadster would drive 195 miles (60kWh x 3.25mi/kWh). Not sure what that makes the efficiency of the Tesla? It goes 8.8 times as far as the 45% efficient fuel cell car on he same amount of electricity input.
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