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Why are On-Site Gas Systems the cost effective way to go?
The Truth About On-Site Gas Systems.
On-Site Gas Systems allows you to receive what you pay for. No one gets all of the gas or evaporated liquid out of a dewer or tank.
Since dewers are always venting boiled off N2, their release valves degrade
over time. For this reason, dewers, which ordinarily hold 4,500 SCF of N2,
could hold less when they arrive at a customer’s plant and can vent off
their gas at different rates. A dewer which is brand new and perfectly
efficient, if not used, will vent off all of its gas in about five days.
What you really pay for with bulk
Let’s follow the process of filling a liquid N2 tank.
There are no flow meters for liquid N2. There are no tank gauges like you
have on your car for bulk liquid gases.
A bulk liquid tanker truck is filled at the cryogenic air separation plant
and weighed. The weight of the truck determines the number of gallons of
liquid in the truck. You are charged based on this figure.
Since the DOT has strict guidelines about the pressure allowed in the truck,
it starts releasing N2 into the air as soon as it’s filled. Estimates vary
between 3 and 5% of the truck’s volume is released during the road trip to
your plant.
If the truck stops at another customer’s location before yours, a best-guess
estimate based on tank inches is made as to how much goes to one customer
and how much goes to the next and the next, etc. In fact, the best-case
scenario is that you gets about 90-95% of what you are charged for into
their bulk tank. Then the tank evaporation begins.
The Truth about bulk liquid tanks
Since Nitrogen boils at 320 degrees Fahrenheit below zero, the N2 in a bulk
liquid tank is always boiling. The standard bulk tank has a relief valve
like a pressure cooker, which releases evaporated (boiled off) liquid N2
when the pressure builds to a certain point.
This means that eventually, all of the liquid N2 will boil, vaporize and
release into the atmosphere. The pressure builds up from the surface of the
liquid N2. The speed with which the customer uses N2 has very little effect
on the amount of boil-off. Picture a pressure cooker in which we draw off
water from the bottom.
Evaporation and pressure build up comes from the surface and fills the space
above the liquid. Since pressurization is fairly rapid and vaporous, if the
cooker is nearly full or nearly empty, it has little effect on the speed of
build up of vapor above the surface of the liquid.
Further, since the N2 is boiling at such a low temperature, it has very
little effect on the process if the tank is located in Alaska or in Florida,
i.e. ambient temperature. The reality, and this figure comes directly from a
bulk gas specialist at AirGas, is that a bulk cryogenic tank boils off at a
rate of 2% of the volume of the tank (not the volume of liquid in the tank)
per day.
This means that if a tank is a 1, 500 gallon tank, 30 gallons per day or
3,000 SCF will vent into the atmosphere every 24 hours. This figure will be
the same if the tank is full or nearly empty. We do not take this figure
into account when we size a system to add a fudge factor for ourselves but
it is important for you to make a customer understand what he is paying to
nitrogenate the air every day.
A great deal for the gas company
Bulk tanks can cost the gas company $50,000 or higher. The company receiving
the tank has to put in a pad 7-9 feet thick of concrete depending on the
state to support the heavy weight of the tank and the liquid N2.
Very few customers own their own bulk tanks. With a new application or
factory about to be built, the cost of the generator can be made more
competitive by the fact that the customer will have to spend $25,000 to
$50,000 to put in the pad for the bulk system.
To that end, the gas company charges the customer a rental charge for the
tank as well as a delivery charge for the liquid. In some states there are
environmental charges as well for traveling over the road with liquid N2.
When you compute your potential savings with liquid, always be sure to
figure in demurrage, tank rental, fuel surcharges and environmental charges
Gas company contracts
The contract that you or one of your predecessors signed with the Gas
Company is a document that makes most attorneys shutter. It reads like the
Trump prenuptial agreement and you’re the bride.
If it’s like most gas company contracts, it goes for 7 years before it
automatically renews unless you notify them at least on year in advance of
the end of the contract. It probably says that if you change your gas needs
in a way that requires a hardware change on their part, the contract
automatically starts again for another 7 years. It says that, if the gas
company decides to raise your cost per gallon of liquid or your CCF (hundred
cubic feet ) of gas, you have the right to go out for bid.
However, If you get a better price, the gas company has the option to meet
that price. Did I mention that the contract then automatically begins again
for another 7 years? You are driven to sign such a contract because every
gas company forces it in one form or another. If you do not sign, you pay an
outrageous cost per CCF. It appears that it gives you control of your cost
but it only indentures you to the gas company. This contract walks a fine
line of legality and, at best, forces you to deal with one gas company
almost for life.
Owning or leasing your own system can free you from the contract.
Just by starting the process you will absolutely save money
No matter what happens, this process will save you money. After all the
pricing quoting and battling has been done, the gas company contract has
ended and the numbers have been examined, the Bulk Gas company, which may
end up just venting the N2 at their cryo plant if they lose your business,
may drop their prices to an irresistible level.
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