# purging lines when converting from lp to natural?

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• 11-11-2012, 10:56 AM
thermofridge
Maybe I can help clear this up. First, we all know that propane has more heat potential than natural gas at the same pressure. The reason for this is that propane has a specific gravity of 1.562 at 70 degrees. Natural gas has a specific gravity of .667 at 70 degrees. When propane is introduced into natural gas lines, it is first mixed with air to bring its specific gravity down. So, when you open up the lines to reconnect to the natural gas meters, some air will enter the lines bringing the specific gravity of the remaining propane closer to that of natural gas. There will be no ill effects to the appliances.
• 11-11-2012, 01:23 PM
RoBoTeq
Quote:

Originally Posted by thermofridge
Maybe I can help clear this up. First, we all know that propane has more heat potential than natural gas at the same pressure. The reason for this is that propane has a specific gravity of 1.562 at 70 degrees. Natural gas has a specific gravity of .667 at 70 degrees. When propane is introduced into natural gas lines, it is first mixed with air to bring its specific gravity down. So, when you open up the lines to reconnect to the natural gas meters, some air will enter the lines bringing the specific gravity of the remaining propane closer to that of natural gas. There will be no ill effects to the appliances.

• 11-11-2012, 08:22 PM
snupytcb
could the lenght and size of the gas lines make a differance?
• 12-25-2012, 06:21 PM
MicahWes
Just start your furnaces. It won't hurt a thing.

I'm curious about this supposed adding of propane to natural gas for any reason? They wouldn't add it for increasing pressure...That is what the utilities compressor stations are for. I could see adding it to increase BTU/unit, but that seems like an impossible feat. NG feeders and mains run at at least 200psig and higher, so the propane would be a liquid in that instance and would be incompatible with the gas system. Even at the lower pressures of street-level mains (usually at least 60psig), propane would condense when the line temperature dropped below the mid 30's.
• 12-25-2012, 07:23 PM
Cooked
This is a very interesting thread that I just came across. I have a very special lady friend engineer, smart as a whip, (waaay smarter than me but that ain't sayin' much) that builds and installs NG compressor stations. I will ask her, she'll explain to me in gory detail.
• 12-25-2012, 07:47 PM
RoBoTeq
Maybe the addition of LP to natural gas during the colder days of winter is a Northern thing.
• 12-25-2012, 08:38 PM
Freezeking2000
I have heard in the past that many gases may be introduced to natural gas systems during peak demand to maintain supply.
• 12-25-2012, 09:28 PM
RoBoTeq
Quote:

Originally Posted by Freezeking2000
I have heard in the past that many gases may be introduced to natural gas systems during peak demand to maintain supply.

I don't doubt it. Any of the "anes" would boost natural gas. But LP is so abundant, being a byproduct of oil production. Also, BGE (Baltimore Gas & Electric) actually has large LP storage tanks and caves. Ironically, BGE has been the major promoter that LP gas is some sort of dangerous monster in its quests over the years to expand it's service areas.
• 12-25-2012, 10:11 PM
MicahWes
I seriously doubt LPG is ever stored in caves (unless it is in a steel vessel). Natural gas is very often stored in caves and other underground structures (and sometimes in pressurized vessels at low temperatures), but LPG is always stored as a liquid under pressure.
• 12-26-2012, 12:23 AM
RoBoTeq
Quote:

Originally Posted by MicahWes
I seriously doubt LPG is ever stored in caves (unless it is in a steel vessel). Natural gas is very often stored in caves and other underground structures (and sometimes in pressurized vessels at low temperatures), but LPG is always stored as a liquid under pressure.

Doubt it all you want, but it's true. LP is heavier than air, so caves are a perfect place to store it. In Cub Hill, MD, BGE has a cave storage facility that has been there for decades. I can't find it online, but I've been to the facility enough times in my youth, and the sign on the security fence clearly states that there are caves being used for LP storage for BGE.
• 12-26-2012, 12:43 AM
MicahWes
If LPG stored there, it must be in pressurized vessels in liquid form?
• 12-26-2012, 01:11 AM
RoBoTeq
Quote:

Originally Posted by MicahWes
If LPG stored there, it must be in pressurized vessels in liquid form?

From what I have been led to believe, the LP is simply pumped into the caves and pumped out when needed. As long as a cavern has all entrances and exits controlled, it makes a perfect, temperature stable storage area for the heavier than air LP gas. For safety, LP stored in caves would be pressurized and liquified after removing it from cavern storage facilities. At least that is what I have been told by BGE personnel who claim to have worked at the Cub Hill facility.
• 12-26-2012, 01:25 AM
RoBoTeq
Quote:

Liquefied Petroleum Gas (LPG), is a compressed by-product of petroleum
distillation. While Iowa is not a producer of petroleum or natural gas, it does
store large volumes of liquefied butane, propane, and ethane in excavated
"caverns" deep beneath the land surface. LPG products arrive in Iowa via
pipeline from Wyoming, Utah, and Canada and are injected into these underground
facilities, which provide safety, economy, and operating flexibility.

The storage caverns were excavated from shale or shaly limestone into rooms
about 20 ft wide and 20 ft high with 45 ft-wide pillars left for support. Two
LPG storage caverns are located in southeast Johnson County at depths of 490 ft
and 770 ft. They both began operation in the 1960's. In Polk County, three
storage caverns were excavated at depths of 375 ft, 595 ft, and 1,410 ft beneath
a single tract of land at the southeast edge of Des Moines. These became
operational between 1967 and 1970.
http://www.igsb.uiowa.edu/Browse/storegas/storegas.htm
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