Compressed natural gas for home heating?

Sal Santamaura

Conventional wisdom seems to be that compressed natural gas (CNG) is not used as a heating fuel because it's more expensive than propane.  Given the trends in crude oil and natural gas prices of late, I wonder whether that situation is changing.



What insight can you informed Wallies shed on the possibility of CNG becoming available for home heating in areas of the country where natural gas utilities don't exist?  It would appear to be win-win on multiple fronts, using some of the surplus, domestically produced natural gas as well as cutting oil imports for No. 2 and propane.



Thanks in advance for your comments.

Henry

LNG

You mean Liquified Natural Gas

bill_105

you mean this stuff?

  Natural Gas being delivered to Fairbanks





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bob eck

Liquid nat gas companies

are there any Liquid Nat gas companies in Eastern Pennsylvania area? if so how does that price compare to oil and LP gas?

Rod

LNG vs Propane

Keep in mind there is a huge difference between propane and natural gas BTU wise.

NG is about around 1000 btus per cubic foot and propane is up around 2500 btu per cubic foot so make sure your comparing "apples to apples and oranges to oranges" when you compare pricing etc.

- Rod

icesailor

CNG Vs. LNG:

I think you may be confusing two very different products. CNG or Compressed Natural Gas is like what you would have in a tank of compressed air. SCUBA tanks use Compressed Air that is compressed up to 2500#. There is no such thing as Liquefied Air though you can compress the parts to a liquid.

If you take a cubic foot of natural gas and compress it, it will take up a smaller amount of space. If you take an unlimited amount of natural gas and continue  to compress it, you can compress it down to a liquid. Then called, Liquefied Natural Gas (LNG) that becomes highly unstable and difficult to handle. It is not easy to vaporize it back to a gas without special handling that you don't need with Liquefied Petroleum Gas, which vaporizes easily and is easy to use.

It is highly unsafe to try to use LNG in a vehicle. But, you can compress the gas like a SCUBA tank and use it. The new issue is how high can you safely compress the gas.

I believe that what you see in the ads is LNG being used for "Peak Shaving" where they vaporize LNG and add it to a gas system during times of high demand. I don't know the expansion ratios of LNG to a gaseous, usable product but it is substantial. And another problem with the vaporization is that you must heat the liquid gas as you vaporize it because it is stored at more than 350 degrees F below zero.

Or something like that.

Sal Santamaura

No, I meant CNG,...

...certainly not LNG.  The extremely low temperature storage requirements of LNG make no sense for individual home heating applications.

Sal Santamaura

I didn't confuse the two products.

While LNG has 2.4 times the energy density of CNG, LNG isn't practical for individual home heating applications.  My question is whether there's any sign of a CNG market developing to supply individual residences.  The economics might be getting to where it can compete with LPG.

Robert O'Brien

Sal

I thought the same thing,but the energy density of CNG is very low,would need a huge tank to store a reasonable number of BTU's

icesailor

Compressed pressures:

A very large tank under tremendous pressure.

I would like to be very far away and watching with binoculars if and when it split open.

Henry

LNG

LNG is NOT compressed, it is cooled down. It is extremely safe in that state. In the 90s Iran hit a LNG ship with an exocet missile. The ship did not burn nor did it explode! The LNG actualy put the fire out! We have done demonstrations using a pot of LNG and applying a lighter and even torch to the open pot. The vaporising natural gas put the flame out.

The problem with compressed NG is that you can only get somuch into a tank. For example, Two 30 gallon tanks in a van will only provide sufficient NG for about 120 miles! To heat a house one would need a very large tank much larger than a 500Lb propane tank.

Sal Santamaura

How large...

...is a "very large tank?"  There are many residential installations that bury 1 or 2 1,000-gallon LPG tanks.  As long as one is digging holes anyway, if the fuel cost per BTU makes sense, it might not be out of the question to install even larger tanks for CNG.  That's what I'm driving at.

SWEI

economics

Of carrying full tanks of CNG around making exchanges for empties?

Of making gaseous transfers at 3500 PSI and waiting to fill up a tank?

Of buying and managing specialized tanks which are at least 12 TIMES the size of an equivalent commodity steel LPG tank?

Sal Santamaura

OK, on the third point...

...I'm willing to yell "uncle."  :-)



I don't think exchanging tanks is a viable approach.  If cars can be made to function  on CNG, your second concern seems surmountable.  However, if the tanks need to be 12 times the size of comparable LNG tanks (is that volume or linear dimensions?), it's probably impractical.

icesailor

Expansion Rates:

You need to find out the expansion rate of a gallon of liquid petroleum gas (LPG) and a gallon of Liquefied Natural Gas. And compare the two. LNG is much higher but I don't know off the top of my head.

The danger of LNG is that it is stored to stay liquid at 392 degrees below zero. It's like steam in a boiler. If the steam is at 15#, and you drop the pressure to zero, the entire contents want to vaporize into steam. When the liquid gas rises in temperature, it wants to convert back to a vaporous gas. The vaporization of the liquid, keeps the liquid cold. If the opening in the tank is small enough to contain the flow of liquid/gas coming out of the whole, you may be OK. If not, it has the potential of being a real problem.

Last I knew, they still close the port of Boston when LNG tankers go through to the terminal in Everett, MA. The ship has the Right Of Way. LNG tankers on the highway, usually travel at night. They don't want those fools in little fast sporty cars cutting off LNG tanker trucks and causing accidents. LPG trucks have a bad enough problem.

SWEI

tank size

I found a discussion where someone did the math and got 14x volume of CNG at 2,250 PSI versus LPG.  LPG tanks get filled to 80% of their nameplate volume (I've seen 90% with stationary tanks) but CNG tanks have much thicker walls, so I figured 12x was probably safe.  They'll hold more at 3,600 PSI, but that would probably increase the difficulty of filling the tank from a truck.



LPG's conveniently located triple point makes it both a decent transportation fuel and refrigerant. The magic of phase change always impresses me -- one of the cooler examples of applied physics IMO.

icesailor

CNG Tanks

Check the codes (if any allow it) on a 3500 gallon ASME tank rated at 3500#, the weight and cost.

Then, think about a truck with a tank, filled with compressed gas at 3500# PSI, driving around making deliveries. It's not like a LPG gas truck that can pump product until it is empty. If you fill to 2,000# PSI, once the pressure in the tank reaches 2,000 PSIG, you can't make deliveries.

There is a CNG fueling station near where I live. I think that there is a maximum size of tank you can use in a car. Gas tanks are a big enough bomb, Without adding CNG to the mix.

SWEI

gas pressure

Precisely!

Tim McElwain

CNG

is compressed natural gas operating out of cylinders designed to hold the gas at around 2,000 lbs pressure. Unless things have changed it is used mostly for automobiles and trucks and other vehicles for fuel on engines designed to operate with natural gas. I drove a van and then later a car that ran on CNG. It can either be slow filled (overnight) or fast fill at a dedicated pump for that purpose. There was some limited use by a company called Corp Brothers for use on boats as a replacement for LP for cooking and gas refrigerators. I know of no code which would allow it for use in place of pipeline Natural Gas or LP at a residential or commercial application..



LNG is Liquefied Natural Gas (it is not compressed) which is stored in large tanks that can keep the gas at around -270° F it is typically used to subsidize the local natural gas supply when extreme weather conditions dictate the need for more gas than the utility may have purchased under normal purchasing agreements. The concept is by taking 600 cubic feet of gas and reducing its temperature to -270 degrees (boiling point) or so the gas will change into a liquid. LP gas (Propane boiling point is -44° F)  This allows for storage of the 600 cubic feet into a 1 (one) cubic foot area. LNG is not feasible for local natural gas supply unless for a very large customer base as the cost of these storage facilities is very high.



There is also SNG which is Synthetic Natural Gas produced from landfill and other decaying materials and is also very expensive.



Your choices today on the price scale is #2 oil most expensive, LP is next and then natural gas.

Tim McElwain

Most municipalities over

react concerning the delivery of LNG. The shut down highways and shipping lanes. The same highways and shipping lanes that allow gasoline and propane delivery with no restrictions other than DOT placarding on the vehicles or ships. LNG is actually safer than natural gas in its normal gas state.

icesailor

LNG:

Isn't LPG a byproduct of crude oil refining and capturing the gas byproduct, and then compressing it to a liquid? Where the boiling point is around atmospheric pressure and a temperature to boil around 23 degrees or somewhere? I don't know. But temperature regulates the vaporization or boiling.

Everyone always talks of LNG being stored at 392 degrees below zero (-392 degrees). . They take Natural Gas and compress it to massive pressures. The gas vapor pressure in the Macondo Well in the Gulf blowout was over 5,000 # pressure. But a vapor. But when you compress the NG, the act of compression causes heat which must be taken away. The more you compress, the more you need to remove the heat. Sooner or later, with enough compression, the vapor will be converted to a liquid. The pressure  needed to keep in that state isn't much but it must be kept cold and insulated. The vapor has to be held at that cold pressure because as the pressure drops, the liquid vaporizes, giving up the stored heat/cold and keeping the liquid cold in the tank. To effectively use the liquid, you need to heat the liquid because as it expands, it is too cold for use?

I'm asking because I seriously don't know. I've never seen an explanation of the process. Other than that they cool it to -392 degrees. That must be one big refrigeration unit.

Where I live on Cape Cod, there is a LNG site in Yarmouth where they inject LNG into the system to keep the pressure up. Whatever that gas company is, they have redundant pumps. If one goes down, they have a back up. But if that one goes down, the pooch is screwed because if the pressure drops in the winter, they must turn off every house affected by the shut down and physically be present when they turn the gas back on. A very expensive proposition.

Down the street from where I live, there is a place where they have a "Tap" in the system so that should this double failure occur, they have a way of putting gas into the system. One time, I was riding my mountain bike by and there was a big hole dug with two huge flatbed trailers parked. One had two 2.5 million BTU hot water boilers on it with quick disconnect hoses, connected to the other trailer that had a HUGE stainless steel heat exchanger(s) on it with quick disconnect hoses on the ground. No third tanker truck. I finally found someone there after a few days and the guy explained that the set up was to be able to pump vaporized gas into the system if the other pump in Yarmouth was failing. That there were these insertion points all over New England. That there were a few more on Cape Cod. That when they left this site in a few days, after the repair in Yarmouth, they were going to Vermont to "Stand-By" for another repair. That they had two or three of these set-ups to use when needed. All they needed was the LNG tanker truck to make it work. You need the heat BTU's to help with the vaporization from -392 to room temperature.

Can you explain it? I really don't know officially.

The Apollo 13 Fuel Cell LOX tank exploded in space because a thermostat failed that controlled the vaporization heater in a LOX tank. The Teflon wire insulation caught fire in the pure O2 atmosphere. The transition is tricky.

I understand what you say about the tankers on the road. Where I work and used to live, someone started bringing LPG in tankers as bulk storage. The local fire personnel lost their minds. The only way it could be driven through downtown to the facility was with a fire engine escort. It was years before it got old. They have never had an issue with the LPG tankers. 

robertclan

CNG Tanks

Before natural gas can be used  as a fuel and higher molecular weight of hydrocarbans .Natural gas is often informally referred to simply use for home.

____________

CNG Tanks