Does not compute: density = 180*volume ?

Is it that 118g of methane would take 180 times the tanks volume at standard temperature and pressure?

Yosef,
A bit less. The wording is a bit unwieldly.
1,000 liter/meter3
0.717kg methane/meter3 @ STP
118g/liter
~164.5 times STP density

One GGE (Gallon of gasoline equiv.) of cng at 88 % methane is about 5.6 pounds or about 2,500 grams. can one of you engineer types convert 20 gge to a volume using the data in the article with the carbon filler at 500 psi? Also, it sounds like the fueling must be done in a liquid form. I am a 5 year driver of natural gas vehicles , not an engineer, so data from engineer / science types are welcome.

Lakewood,

Given the numbers you supplied, the long division comes out this way:

2,500 grams of CNG = 1 GGE
20 GGE = 2,500 x 20 = 50,000 grams of CNG per tankful.

This adsorbtion material can store 118 grams of CNG per liter of volume, given standard compression.

50,000 grams divided by 118 grams/liter = ~424 liters of volume for a storage tank.

Since there are about 3.8 liters per gallon, a tank large enough to carry 424 liters would be about 112 gallons large, in American terms.

I rather doubt that fueling must be done while the NG is liquified. LNG is not stored at pressure, while tanks using this material are specifically designed to operate under 500 lb/sq.in. of pressure. Rather, it seems that the point of this material is to allow fuel tanks to store large amounts of gaseous NG at pipeline pressures -- no need for a high-pressure compressor or an ultrastrong tank, as is currently used in CNG automotive applications.

Since a tank that employs this material would have to be five times the size of a gasoline tank supplying the same range, you'd either have to sacrifice range, payload capacity, or engine performance (to increase efficiency to allow equal miles on less fuel). A large pickup truck might be able to handle one of these with little problem. If these tanks could be integrated into the structure of the vehicle, you might be able to squeeze in more volume without taking up prime trunk or underbody space. Since this is gas under pressure, and unusually shaped tank should not affect the ability of fuel to drain into the outflow. Finally, even with reduced range between fillups, you'd still probably find plenty of customers for such a vehicle, if the other incentives were right.

The real innovation that this system allows is reducing the expense and complexity of the fueling infrastructure. CNG need not be reduced to fleet operators with access to special compressors. Gas stations who want to sell CNG to private customers no longer need very expensive and specialized compressors and high-pressure transfer hoses to fill up a car. Instead, you can tap directly into a standard 500 lb/sq.in. gas pipeline and hose it right into the car.

I wonder if this would allow a type of V2G operation of the natural gas grid. You could probably run your stove or water heater right off you car's gas tank without having to worry about stepping down the pressure. At the same time, my understanding is that the NG grid has a little more "give" to it than does the electric grid, so flattening out demand spikes with V2G is probably a lot less useful here.

Thank's NBK , My 2001 Honda civic GX has a kevlar cylinder( made by Lincoln composites) , of 100 litre volume and it uses most of the trunk. The cng capacity @ 3600 psi 70deg.f. is 8 gge, but real world it is about 5.5 gge useable. So for long trips I usually rent a gasoline car. The fuel tank also is the most costly component of the vehicle , acording to honda. I have not purchased the available home fueling compressor , not cost effective.
I wonder if the carbon adsorbsion material requires pure methane ? Pipeline natural gas has a lot of other stuff in it. (nitroren,propane,water, etc).

Perhaps you have to heat it slightly.

112 gallons of NG for 20 gge? No sweat. If a car capable of 30mpg, it would need only 10 gallons to go 300 miles. If it is capable of 60mpg like the Prius, then it would need only 5 gallons of gasoline. So, divide 112 by 4 will get you 28 gallons. 14 gallons can be in one tank under the seat, and the other 14 gallons can be under the trunk. Run-flat tire can eliminate spare tire. To retain the same trunk space, the car will have the back raised like a station wagon. Lithium battery with improved volumetric density over NiMh will take less space, for HEV.

"How to get the methane back out?"
As the pressure decreases from 500psi, the methane will come out to maintain equilibrium, until the tank is drained to zero pressure. No need for heating.

I think that pure methane is desirable, but other materials will come in and will come out according to the equibrium constant of each chemical, just like in a chemical equilibrium reaction. Believe it or not, even carbon monoxide will get out of your hemoglobin, even though the rate of dissociation of CO out of Hgb will be much lower than the rate of association of CO to Hgb. It's all about equilibrium state. Higher molecular-weight hydrocarbons or hydrophobic materials will probably adsorb much more tightly to the carbon and eventually will decrease the capacity of your NG tank.

Perhaps Biogas could be used in place of NG? I'd be curious to know what percentage of NA's oil usage could be displaced through the use of biogas.

Rafael,

I suppose a government could impose a large yearly revenue tax on the registration of a grid-compatible NG car, or a similar tax on a home compressor unit (if grid-pressure storage doesn't work out), to make up for some of the lost revenue. At the same time, that would not tax usage incrementally, so it would hardly be ideal. Increased user fees for high-value pieces of infrastructure like bridges, tunnels and superhighways appeals to the most to me on policy grounds.

The natural gas in the commercial sized line coming into my place of employment is only 15PSI not 500 We drop it down to 3PSI before it enters the Bldg, and less than 1 PSI before the burner head. Where are these 500PSI gas lines some are speaking of?

How about government to pick up full bill for roads, bridges, public transportation, and other communication and infrastructure systems, making backbone of our society?

Economics tells us that a requisite for the optimal allocation of resources is that the price of products and services reflect their true cost (including external costs). If the state builds infrastructure X and then lets everyone use it for free, then it will be used more than is socially optimal thus necessitating further investments by the state (say additional capacity, more maintenance, dealing with more pollution etc.). Also, those who use X more than the average will then get an effective subsidy which is paid by the rest of society.

Which ultimately is why we have things like vehicle taxes, fuel taxes, road tolls and whatnot instead of paying everything via say income taxes.

Andrey,

The classic argument for free provision of certain basic public goods incorporates two strands that you get at in your posts:

1. Excessive transaction costs associated with restricting service to payers: You get at this point with your example of the public bus, which inefficiently loads from only one door (instead of all doors) in order to make sure that everyone pays the fare. Another example would be to try to imagine a system that forces every motorist to pay a cash toll each time he pulls out of his driveway and onto a city street. Where would you put all the tollbooths?

However, technology and technique can get around some of these problems. In Europe, buses often load from all doors, and riders are obliged to validate a ticket at a stamping or punching box, several of which are located on board the bus. Failure to do so risks a large fine if an inspector should find you without a properly validated ticket, incentivizing compliance. This can be done using simple low-tech paper tickets and uniquely-patterned or date-stamped punches, to prevent the re-use of validated tickets on subsequent rides (as I've seen done in Romania), or the use of higher-tech electronic fare media. Gas taxes, in the second example, are a rough proxy for the use of (and payment for) ungated city streets.

2. Small marginal cost with differing marginal benefit argument: In our city streets example, if the marginal cost of allowing one additional car are minimal, and the utility derived by the motorist is somewhat more than minimal, it makes sense, from a welfare-economics point of view, to allow that motorist to use the facility. If the proposed toll is higher than the marginal utility of the prospective motorist (set that high in an effort to recoup the fixed costs of opening the road), though, it will discourage this welfare-maximizing use. This is not a good result.

To use some arbitrary numbers to illustrate the point, let us assume that the fixed cost of opening and maintaining a road is $2000 per year, the marginal cost for each journey on that road is $0.50, the expected traffic on the road is about 2000 vehicles per year, and the utility derived by motorist A from his journey on the road is $4 while the utility derived by motorist B from his journey is $1. As the road operator, you would want to set your toll at $1.50 per journey -- $0.50 to offset the marginal cost of each journey, and $1 to help defray the fixed cost -- which, when spread over the expected 2000 motorists, will just cover that cost.

Under these circumstances, motorist A will make the journey ($4 utility - $1.50 toll = $2.50 surplus), while motorist B will not make the journey ($1 utlity - $1.50 toll = -$0.50 surplus). This will be so even if motorist B is the 2001th motorist -- the fixed costs are already accounted for, his journey will only impose an additional $0.50 costs, and those could be covered by charging him only $0.75 in tolls, leaving a profit of $0.25 to the road operator, and a surplus of $0.25 to motorist B. Under these circumstances, paying for the road out of general taxes and making access to it free is the most sensible thing to do, which is the argument you are getting at. "Backbone of our society," as I choose to understand your words, is just a way of labeling important services which have -- when examined on some relevant scale -- relatively high fixed costs, low marginal costs, wide appeal, and a range of possible valuations (some of which may be quite high) across the mass of consumers, and which are most efficiently delivered when transaction costs associated with fee-charging are minimized. That's why a per-email fee is generally stupid -- while the capital investments made in the internet infrastructure may be large, the marginal cost of each additional email is fairly small. Only in spam-like quantities is it an issue -- and that may in fact justify a miniscule per-message tax (think in terms of tenths or hundredths of a cent) which would not affect a private user at all, which would only minimally influence a large corporate user with legitimate (and therefore somewhat valuable) messages, but which would make spam unprofitable. Implementing the tax, however, so that it actually falls on the original sender might prove impossible, and if it is imposed on the middleman or recipient it would probably have perverse incentive effects.

However... when the marginal cost is not so low, this whole scheme breaks down. Marginal costs are non-low in certain predicatable circumstances. The most important one is scarcity, which is a condition that can often plague extremely high-value pieces of infrastructure. The marginal costs of sending in a bunch of extra cars into the Lincoln Tunnel or the Lion's Gate Bridge during rush hour is not small at all, in terms of the congestion they contribute. More broadly, automobile usage is now considered less low-marginal-cost then we previously thought, due to environmental concerns, urban land-use concerns, foreign-oil concern, etc.

At any rate, congestion and other non-low marginal cost situations justify, in my mind, considerable reliance on user fees.

Tanks of any pressure can be used as multiple small tanks or one large tank without any theoretical weight penalty. This applies to cylindrical as well as sperical tanks. ..HG..