Cryogenic fluid dispensing system and method

1 . A system for dispensing a cryogenic fluid comprising:

a. a bulk tank configured to contain a supply of a cryogenic liquid;

b. a first sump;

c. a first liquid feed valve configured to direct the cryogenic liquid from the bulk tank to the first sump when in an open condition and to prevent transfer of the cryogenic liquid from the bulk tank to the first sump when in a closed condition;

d. a first positive displacement pump positioned within the first sump and configured to pump and be submerged in cryogenic liquid when the first sump contains cryogenic liquid above a predetermined liquid level within the first sump;

e. a motor positioned outside of the first sump;

f. a drive rod operatively connected between the motor and the first positive displacement pump so that the motor drives the first positive displacement pump via the drive rod;

g. said drive rod passing through and exposed to vapor above cryogenic liquid in the first sump so that heat from the motor is transmitted by the drive rod into the first sump so as to cause an increase in pressure within the first sump above cryogenic liquid within the first sump above a saturation pressure corresponding to a temperature of the cryogenic liquid in the first sump so that cryogenic liquid within the first sump is subcooled;

h. a delivery line in fluid communication with an outlet of the first positive displacement pump, said delivery line configured to direct cryogenic fluid from the first positive displacement pump to a use device when the first positive displacement pump is activated, the delivery line including a vaporizer;

i. a gas buffer tank inlet line branching off of the delivery line downstream of the vaporizer, the gas buffer tank inlet line including a gas buffer tank inlet valve;

j. a gas buffer tank outlet line including a gas buffer tank outlet valve; and

k. a gas buffer tank configured to selectively receive, via the gas buffer tank inlet line, and store vapor from the vaporizer when the gas buffer tank inlet valve is open and to selectively deliver pressurized vapor to a headspace of the first sump via the gas buffer tank outlet line when the gas buffer tank outlet valve is open.

2 . The system of claim 1 further comprising a first vapor return valve configured to direct vapor from the first sump to the bulk tank when in an open condition and to prevent transfer of vapor from the first sump to the bulk tank when in a closed condition.

3 . The system of claim 1 further comprising:

f. a second sump;

g. a second liquid feed valve configured to direct liquid from the bulk tank to the second sump when in an open condition and to prevent transfer of liquid from the bulk tank to the second sump when in a closed condition;

h. a second positive displacement pump positioned within the second sump and configured to pump and be submerged in cryogenic liquid when the second sump contains cryogenic liquid above a predetermined liquid level within the second sump;

and wherein the delivery line is in fluid communication with an outlet of the second positive displacement pump, said delivery line configured to direct cryogenic fluid from the second positive displacement pump to a use device when the second positive displacement pump is activated.

4 . The system of claim 3 further comprising a second vapor return valve configured to direct vapor from the second sump to the bulk tank when in an open condition and to prevent transfer of vapor from the second sump to the bulk tank when in a closed condition.

5 . The system of claim 3 wherein the first and second positive displacement pumps are two-stage positive displacement pumps configured to deliver vapor.

6 . The system of claim 3 wherein the first and second positive displacement pumps are single stage positive displacement pumps and wherein the delivery line includes a vaporizer.

7 . The system of claim 1 wherein the first positive displacement pump is a single stage positive displacement pump.

8 . The system of claim 1 wherein the bulk tank includes an inner vessel and an outer jacket with vacuum insulation therebetween.

9 . The system of claim 1 further comprising a liquid level sensor configured to determine a liquid level within the first sump.

10 . The system of claim 1 further comprising a pressure sensor configured to determine a pressure within a top portion of the first sump.

11 . The system of claim 10 further comprising a temperature sensor configured to determine a temperature of cryogenic liquid within the first sump.

12 . The system of claim 1 further comprising a sump pressure building circuitry including a pressure building heat exchanger configured to selectively receive and vaporize liquid from the first sump and deliver vapor to a headspace of the first sump.

13 . A system for dispensing a cryogenic fluid comprising:

a. a bulk tank containing a supply of a cryogenic liquid;

b. a first sump containing cryogenic liquid received from the bulk tank;

c. a first liquid feed valve configured to direct the cryogenic liquid from the bulk tank to the first sump when in an open condition and to prevent transfer of the cryogenic liquid from the bulk tank to the first sump when in a closed condition;

d. a first positive displacement pump positioned within the first sump and submerged in the cryogenic liquid contained in the first sump, said first positive displacement pump pumping the cryogenic liquid contained in the first sump;

e. a motor positioned outside of the first sump;

f. a drive rod operatively connected between the motor and the first positive displacement pump so that the motor drives the first positive displacement pump via the drive rod;

g. said drive rod passing through and exposed to vapor above cryogenic liquid in the first sump whereby heat from the motor is transmitted by the drive rod into the first sump so that pressure within the first sump above the cryogenic liquid within the first sump is above a saturation pressure corresponding to a temperature of the cryogenic liquid in the first sump so that the cryogenic liquid within the first sump is subcooled;

h. a delivery line in fluid communication with an outlet of the first positive displacement pump, said delivery line directing cryogenic fluid from the first positive displacement pump to a use device, the delivery line including a vaporizer;

i. a gas buffer tank inlet line branching off of the delivery line downstream of the vaporizer, the gas buffer tank inlet line including a gas buffer tank inlet valve;

j. a gas buffer tank outlet line including a gas buffer tank outlet valve; and

k. a gas buffer tank configurated to selectively receive, via the gas buffer tank inlet line, and store vapor from the vaporizer when the gas buffer tank inlet valve is open and to selectively deliver pressurized vapor to a headspace of the first sump via the gas buffer tank outlet line when the gas buffer tank outlet valve is open.

14 . The system of claim 13 , further comprising:

a first vapor return valve configured to direct vapor from the first sump to the bulk tank when in an open condition and to prevent transfer of vapor from the first sump to the bulk tank when in a closed condition.

15 . The system of claim 13 , wherein the first positive displacement pump is a single stage positive displacement pump.

16 . The system of claim 13 , wherein the bulk tank includes an inner vessel and an outer jacket with vacuum insulation therebetween.

17 . The system of claim 13 , further comprising:

a liquid level sensor configured to determine a liquid level within the first sump.

18 . The system of claim 13 , further comprising:

a pressure sensor configured to determine a pressure within a top portion of the first sump.

19 . The system of claim 18 , further comprising:

a temperature sensor configured to determine a temperature of cryogenic liquid within the first sump.

20 . The system of claim 13 , further comprising:

a sump pressure building circuitry including a pressure building heat exchanger configured to selectively receive and vaporize liquid from the first sump and deliver vapor to a headspace of the first sump.