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.
 
 


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.
 
 


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 a lot of money just 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
 
 


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.
 
 

Why reward them when they've been overcharging you for years? I'm sure you agree. It is time to break the shackles and become your own supplier.

It’s up to you.