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Permalink Reply by Catfish on August 21, 2009 at 3:47

Logically it would take more than 20 unless it only involved dedicated routes for pick up and delivery. A better idea would be the states install these filling sites at their weigh stations. Then there would be enough and the state would recoup their investment through profit. Bring the governors of the lower 48 and the heads of some national carriers together and get ur done. Simple solution.

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Permalink Reply by Mac Davis on August 21, 2009 at 7:22

There are quite a few trucks that run the same route over and over taking stuff from one fixed terminal to another. The concept has some merit. Railroads do this all the time, but railroads will almost always be much more energy efficient than trucks.

However, who's going to commit to buying natgas capable trucks when you can't count on the cross-country natgas stations being there for a fixed number of years into the future? I remember the last time there was a big push for natgas fueled vehicles, publicly accessible natgas refueling stations popped up, people and business bought natgas fueled vehicles, and then the stations disappeared.

I think there'd need to be some guaranteed time period for which the stations would continue to operate, some sort of price guarantee, or some sort of guaranteed rebates to replace or convert the trucks if the stations shut down.

Would you invest the money to create a natgas fleet if the stations might or might not stay open on the whims of a government program?

What happens if one of the 20 or so natgas fueling stations shuts down due to technical problems? Do you have to park your trucks and wait for it to be repaired because you don't have enough fuel to reach the next station? What if it's open, but there's so many trucks and so few pumps that it takes 4 hours to get fueled? What if there are traffic, road construction, or weather problems and it's hard to get to the particular refueling station?

I wonder why we don't hear much about natgas powered locomotive diesels? It seems like a great match. Locomotives fuel at fixed, company owned fueling locations. They could probably use LNG instead of CNG. One would think that the cost savings would be so attractive that the railroads would "get on board."

Maybe someone should put a bug in Boone's ear about railroad locomotives.

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Permalink Reply by Mike Hughes on August 22, 2009 at 4:21

Even more cost efficient, in the short term and interium, would be to install a LNG tanker outfitted with a metered dispensing device at every truck stop as demand grew. Instead of pulling up to the pump, you would pull up next to the stationed tanker and fule up. Simple as that, therefore deliverability should not be the issue.

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Permalink Reply by Mac Davis on August 22, 2009 at 8:08

I wonder if anyone is considering LNG powered trucks or only CNG powered trucks?

Trucks would seem like a great application for LNG power. It seems to me that the biggest drawback to LNG for transportation is that if you let the vehicle sit, the LNG boils off. You have to do something with the methane produced. If you vent it, you have an explosion hazard if you're indoors. Methane is a more powerful greenhouse gas than CO2. You also have fuel being wasted.

A truck will probably spend less time sitting without the engine running than cars. You can more easily restrict an LNG powered truck to not be parked in an unvented garage with fuel in the tank. A truck owned by a commercial company is more likely to get proper maintenance to whatever vent gas handling system it has. This might be as simple as having an automatic "pilot light" gas burning system to burn any methane to CO2 to reduce the greenhouse gas footprint. You shouldn't be boiling off enough gas to cause an explosion hazard if the truck is parked outside.

A proper, safe, and non-greenhouse LNG or LNG/CNG truck refueling station is going to be more complicated than simply parking a tanker truck, due to the evaporation/venting problem.

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Permalink Reply by Les Bamburg on August 22, 2009 at 10:31

Mac, the methane does not boil off - it stays in the fuel tank.

Yes - for heavy duty trucks is more viable than CNG. Due to the energy density, the trucks have an energy efficiency and cruising range similar to diesel. By the way, many refuelling stations supply both LNG and CNG.

Refuelling stations are not much different than current truck stops. The issue is developing a supply distribution network.

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Permalink Reply by Mac Davis on August 22, 2009 at 20:28

Mac, the methane does not boil off - it stays in the fuel tank.

No, that's wrong.

Be sure you're not confusing LNG,(Liquid Natural Gas) with LP (Liquefied Petroleum) gas. LNG is methane kept at around -161 degrees C at normal atmospheric pressure. LP gas is chemicals other than methane, mostly propane and/or butane.

LP gas tanks keep the fuel in a liquid state through high pressure. LNG tanks keep the methane in a liquid state at normal atmospheric pressure by keeping it cold.

Most LNG storage tanks use "auto refrigeration" to keep the liquid methane cold enough to stay liquid as heat leaks into the tank from the surrounding environment. The heat causes some of the liquid methane to boil, which cools the remaining liquid methane enough to keep it from rising above the boiling point of methane. This cooling through boiling is called "auto refrigeration."

It's exactly like a teapot of boiling water. As some of the water turns to steam and escapes, it cools the remaining liquid water, keeping it at 212 degrees until you boil away all the water. Seal up the teapot so no steam escapes, and you get a big boom.

Goodness knows, I won't claim Wikipedia as an authoritative source, but the following articles do correctly explain the physics involved.

http://en.wikipedia.org/wiki/Liquefied_natural_gas
http://en.wikipedia.org/wiki/LNG_storage_tank
http://www.energy.ca.gov/lng/faq.html

There are numerous other sources that explain the process.

The trick is what do you do with the gaseous methane that is inevitably produced in an LNG storage tank.

Best of all is to use the methane as fuel in some useful application. For instance, in a moving truck, you burn it to fuel the engine. In a LNG tanker, you run the ship's engines in part off the gaseous methane. In a fixed storage tank, you may be able pump the gaseous methane into the local natural gas pipeline system.

If your truck or tanker is stopped and can't use up the gaseous methane in the engine, you have to do something with the gaseous methane.

Sometimes, you re-refrigerate it and put the liquid methane back into the storage tank, but that requires an external power source, or using part of the methane to run an engine to provide power to run the refrigeration system.

You could burn the gas as a flare. Simply venting it to the atmosphere unburned might be acceptable in some cases if the amount of gas produced is low enough not to be an explosion hazard, but methane is supposed to be a powerful greenhouse gas, so that would be unpopular. I would expect almost all LNG storage systems to have some sort of "vent to the atmosphere" system as the last resort, on the theory that venting it slowly beats blowing up the LNG tank.

Interestingly enough, you cannot turn methane into a liquid at room temperature no matter what pressure you apply to it.

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Permalink Reply by Les Bamburg on August 23, 2009 at 5:04

Mac, sorry LNG can be stored in various systems. Write-ups in wikipedia would only address some of the systems.

Large storage tanks at LNG plants & regas terminals are extensively insulated and operate at near atmospheric pressure. At LNG plants the boil-off gas is either used as fuel or re-condensed. At regas terminals the boil-off gas is used as fuel with the excess compressed and delivered to the pipeline.

Until last year, the boil-off gas for all LNG transport ships was utilized as fuel to power the ship either in steam boilers or duel fuel engines. Last year, Qatar began placing their Q-Flex and Q-Max ships in service. These ships include equipment to "re-liquify" the boil-off gas and are powered by diesel engines.

Smaller LNG storage tanks, including the fuel tanks on LNG powered trucks, are designed to handle up to some pressure level (ie 125 psi). As the tanks experience some heat leak, the boil-off gas causes the LNG pressure to gradually increase. Because these storage systems have full containment there is no venting or flaring required. Typically, the trucks consume the fuel in 1-3 days. This would be similar to storing other fuels such as LPG or hydrogen.

By the way, I have a lot of experience with greenhouse gas lifecycle analysis associated with various transport fuels such as CNG, LNG, LPG, etc. I would caution against the validity of some things you may read in so called "expert" studies regarding these fuels. It is sad how some consultants, academia and government agencies can publish such mis-information in areas they do not fully understand.

Attachments:

• NGL Guide [Compatibility Mode].pdf, 35 KB

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Permalink Reply by Mac Davis on August 23, 2009 at 12:38

If you'll go back and read again, I said almost all of that.

Glad to hear that some LNG tankers are re-liquefying, but I assume they burn some of the methane to power the refrigeration systems. If they're burning diesel oil to power the refrigeration systems, that sort of only shifts the fuel/greenhouse burden.

The pressurized tank only works for a short period time, and only "buffers" the problem. After a while, you still have a "boiloff budget" of methane that you have to consume. You still have to consume x amount of methane per day long term. Some systems also pump the boiled off methane into a separate, pressurized storage tank, but that's only a buffer as well. If you park the truck for a long period of time, the LNG will be consumed somehow.

How long will one of these pressurized tanks hold the LNG before they have to vent?

Liquid methane in LNG tanks boils. The only question is how do you handle the gaseous methane produced. Sometimes you can use it or recycle it, but sometimes you have to waste it.

It's not necessarily that big of a problem. There are probably lots of fleet trucks that run the engine almost 24/7/365 anyway. Some of them use electric generators to provide cab power/air conditioning when parked and these could probably use up the boiloff gas anyway.

Stored LNG "decays" over time in that a certain average amount of liquid methane has to be consumed or disposed of every day, unless you have an external power source to power a refrigeration system.

Just for fun, I did the calculation. If you take a full container of liquid methane, seal it, and let it warm up to room temperature, the pressure will theoretically be around 9000 PSI. The calculation may be a little bit off, because the pressure is high enough that the ideal gas law may be somewhat inaccurate, but it's still a darn high pressure.

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Permalink Reply by Les Bamburg on August 23, 2009 at 13:04

Mac, my descriptions are not theory but reality regarding how LNG is currently distributed and consumed as a transportation fuel.

Bottom line is the LNG does not boil off when used as a transportation fuel so that is not a drawback. No need for pilot lights or vents.

Also keep in mind LNG is only utilized for large heavy duty trucks and buses.

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Permalink Reply by Les Bamburg on August 22, 2009 at 10:36

Mike, LNG transport trucks are not equipped for fuelling vehicles and you loose distribution efficiency if your truck is sitting. An alternative is the use of portable LNG storage tanks that can be dropped off and picked up for refill.

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Permalink Reply by Mac Davis on August 23, 2009 at 12:53

It may not be that bad of an idea. You couldn't use a current standard LNG transport truck, but maybe you could either design a "refueling" LNG truck design, or have a separate towable refueling station unit that could be parked somewhere and you bring LNG trucks to it.

The towable refueling station unit would need some sort of refrigeration system, either electrically or generator powered, or some sort of venting/burnoff/emergency relief system in case you don't use the LNG fast enough to keep it cold. You'd need various safety appliances and fueling systems.

You'd need an appropriate site to use such a system.

I wonder if a "portable" LNG fueling system is a viable idea?

Les, what do current design over the road LNG transport trucks do about boiloff?

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Permalink Reply by Les Bamburg on August 23, 2009 at 13:09

Mac, as discussed above there is no issue with boil-off and no current need for a refrigeration system. Current refuelling systems have storage capacity sized with sufficient margin to avoid any venting issues.

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