GB2391607A

GB2391607A - Cryogenic gas storage with pre-evaporation buffer unit

Info

Publication number: GB2391607A
Application number: GB0301318A
Authority: GB
Inventors: Thomas Tsoi Hei Ma
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-08-02
Filing date: 2003-01-21
Publication date: 2004-02-11
Also published as: GB0301318D0

Abstract

A gas storage and delivery system periodically passes cryogenically stored gas 10 in discrete quantities via a buffer container 12, to a vapourisation tank 14. The buffering in the delivery systems permits the device to maintain a level of ready to use gas in the tank 14 between certain limits. The gas is tapped off for use in a gas usage device 16, which consumes gas for various purposes and may be such as a fuel cell, combustion engine, gas expander or the like. A heating system 40 - 50, may aide the vaporisation process in the vapourisation tank 14.

Description

( - 1 - 2391607

CRYOGENIC LIQUID UTILISATION MANAGEMENT SYSTEM

Field of the invention

5 The present invention relates to a management system for utilizing a cryogenic liquid as working fluid to produce a pressurized gas supply of the fluid.

Background of the invention

In stationary and mobile applications where there is a need to store a large quantity of gas under high pressure, such as compressed air or nitrogen, compressed hydrogen or compressed natural gas (CNG), the common practice is to provide a high pressure gas tank of sufficient volume to store a sufficient stock of the gas to meet demand for a time period or travelling range. This has the advantage that the gas could be drawn immediately from the tank in quick response to demand, but poses problems of size and 20 weight of the tank, and difficulty of refilling the tank at high pressure after it is empty.

As an alternative, the gas may be stored cryogenically in liquid form in a compact and low pressure thermally 25 insulated vessel and the gas produced when required by evaporating the liquid according to demand. This too poses problems in applications where the demand flow is highly fluctuating, including frequent stops and starts, making the supply of the gas difficult to control with undesirable 30 response lag.

Summary of the invention

With the aim of mitigating at least some of the above 35 problems, there is provided according to the present invention a cryogenic liquid utilization management system for utilizing a cryogenic liquid as working fluid to produce

- 2 a pressurized gas supply of the fluid, the system comprising a thermally insulated liquid storage vessel for storing the cryogenic liquid, a buffer chamber for temporarily holding a predetermined quantity of the cryogenic liquid, a gas s evaporation tank for evaporating and storing at high pressure the gas evaporated from the said quantity of cryogenic liquid, a gas utilization unit for receiving and using the pressurized gas stored in the gas evaporation tank, a venting chamber for receiving gas from the buffer lo chamber during venting of the buffer chamber, connecting pipes between the aforementioned system components with respective control valves in each pipe, and a controller for controlling the operation of the said respective valves according to a filling cycle for the buffer chamber 15 comprising steps in which the buffer chamber is sequentially isolated from the gas evaporation tank, vented and filled with a predetermined quantity of the cryogenic liquid from the liquid storage vessel, isolated from the vent and the liquid storage vessel, connected to the gas evaporation tank 20 in which the cryogenic liquid evaporates into gas at high pressure, and isolated from the gas evaporation tank again before the gas pressure in the gas evaporation tank is reduced below a predetermined lower value as gas is used by the gas utilization unit, whereupon the filling cycle for As the buffer chamber is repeated again.

The cryogenic liquid may be any liquefied gas such as liquid air, liquid nitrogen, liquid hydrogen or liquid natural gas (LNG). The gas utilization unit may include a 30 gas expander for generating mechanical power from the gas at high pressure. It may also include any device that consumes the gas for various scientific, industrial and combustion applications. In the case of hydrogen, the gas utilization unit may include a fuel cell for generating electricity 35 using the hydrogen gas as fuel. In the case of natural gas, the gas utilization unit may include an internal combustion engine for generating power using the natural gas as fuel.

- 3 - The invention is predicated upon the fact that when a predetermined quantity of cryogenic liquid at ambient pressure is confined in a strong chamber and evaporated, super-atmospheric pressures could be generated within the 5 chamber because the evaporated gas has no way of escape. If left with a sufficiently long time for the liquid to evaporate by absorbing heat from the ambient atmosphere through the walls of the strong chamber, the chamber would automatically become a high pressure gas tank filled with lo pressurized gas at ambient temperature without relying on a compressor to pump the gas into the tank.

In the invention, when the buffer chamber and the gas evaporation tank are at substantially ambient air 15 temperature, the stored heat from their thick walls (thermal capacity of the wall material) could be sufficient to evaporate the filled quantity of cryogenic liquid and raise the temperature of the gas in the gas evaporation tank to substantially ambient temperature.

In a co-pending British patent application GB 0300239.1 by the same applicant, a cryogenic liquid evaporation system is proposed in which a heat transfer liquid (such as glycol) circulated between a gas evaporation tank and an external heat exchanger is provided for accelerating the evaporation of the filled quantity of cryogenic liquid and raising the temperature of the gas in the gas evaporation tank rapidly to the nominal working temperature of the heat exchanger.

The heat transfer liquid also maintains the walls of the gas lo evaporation tank at substantially ambient temperature which is the working temperature of the heat exchanger, thus preventing ice from forming outside the gas evaporation tank. To enhance the heat transfer directly to the gas and to the walls, the heat transfer liquid is sprayed directly 35 inside the gas evaporation tank.

- 4 In use, the predetermined filled quantity of cryogenic liquid during each filling cycle of the buffer chamber should be such that the resulting increase in gas pressure in the gas evaporation tank does not exceed a predetermined s safe upper value.

Thus, as the pressurised gas in the gas evaporation tank is progressively being depleted through usage by the gas utilization unit, the control system of the present I lo invention would automatically maintain within the gas evaporation tank cyclically filled quantities of the gas between a lower pressure limit and an upper pressure limit at substantially ambient temperature. This is a batch process which avoids continuous evaporation of the liquid to 15 gas in real time in response to changing flow demand, but produces and stores sufficient quantity of the gas in advance time to meet the expected flow demand between the filling cycles. Each batch is small enough to be stored in a relatively small and light- weight high pressure gas tank 20 ( the gas evaporation tank) thus eliminating the problem of having to store a large stock of the gas at high pressure in large and heavy stock gas cylinders.

The invention has the advantage that the evaporation of! 25 the cryogenic liquid to gas does not take place in real time when the gas is being used, but takes place over a period of time between the filling cycles. In this case, the sustainable delivery rate of the gas from the tank would depend on the quickest time taken for each fill of the 30 cryogenic liquid to evaporate which sets the frequency of the filling cycles. This in turn is determined by the stored heat energy in the walls of the buffer chamber and the gas evaporation tank, the source of external heat for warming the cryogenic liquid and the walls, and the rate of 35 heat transfer from the source. Preferably, the source of external heat is air at ambient temperature and the cryogenic liquid and the walls are warmed by a heat transfer

- 5 - liquid circulated around an external ambient air heat exchanger. The high pressure gas produced from the cryogenic 5 liquid may be used to generate mechanical power in a gas expander before the gas is used in other ways at lower pressure. Since ambient air is generally heated to the surroundings temperature by solar energy, the preferred heat source of the present invention at least contributes to lo converting some solar energy to mechanical power by using the cryogenic liquid to produce the high pressure expansion gas. Of course, the cryogenic liquid itself requires a 5 substantial amount of energy to produce, but when considered in the scale of a large industrial plant producing the liquid, the cost per unit volume of the cryogenic liquid could be sufficiently low in comparison with the extracted mechanical energy from the gas, so that the cryogenic liquid 20 utilization system of the present invention could still be economically viable as a convenient and environmentally clean mechanical energy source even without considering the chemical energy that may also be extracted from the gas as a fuel in the case it is hydrogen or natural gas.

In the case of air or nitrogen, a controlled flow of the evaporated gas at high pressure could be discharged through a gas expander for power generation in a manner analogous to a steam engine or an air motor or air turbine 30 driven by compressed air. This could find application in an automobile as a motive unit without combustion, in which the stored energy medium in the vehicle tank is liquid air or liquid nitrogen and the exhaust discharged from the gas expander is gaseous air or gaseous nitrogen. Compared with 35 a conventional compressed air driven vehicle carrying on-

board a large and heavy compressed air storage tank at high pressure, the gas expander driven vehicle of the present

- 6 invention will have a significantly smaller and lighter high pressure gas tank (the gas evaporation tank), while the i travelling range will be much bigger because of the cryogenic liquid storage.

In the case of hydrogen, a hydrogen fuel cell may be used to drive a vehicle supplied with a controlled flow of gaseous hydrogen fuel from a small and light-weight high pressure gas tank, while the bulk of the fuel is stored as I lo liquid hydrogen in the main tank. The evaporated hydrogen gas at high pressure may first be passed through a gas expander for generating some mechanical power before being passed at lower pressure to the fuel cell.

15 Similarly, in the case of natural gas, a CNG fuelled internal combustion engine may be used to drive a vehicle supplied with a controlled flow of natural gas from a small and light-weight high pressure gas tank, while the bulk of the fuel is stored as liquid natural gas (LNG) in the main 20 tank. The evaporated natural gas at high pressure may first be passed through a gas expander for generating some mechanical power before being passed at lower pressure to the engine.

25 In the above automobile applications, the present invention is particularly effective in hot climate offering a high rate of gas evaporation because of the high ambient temperature hence a high rate of power generation, plus the benefit of free air conditioning inside the vehicle by 30 taking advantage of the cooling effect of the cryogenic liquid. In cold climate or in high demand driving conditions, the evaporation of the filled quantity of cryogenic liquid 35 may be too slow to match demand but could be speeded up by introducing a heater to heat the heat exchanger. In this case, the additional heat energy required to supplement the

( - 7 - heat energy in ambient air could conveniently be heat from a solar heating panel, or heat produced using the evaporated gas as fuel if it is hydrogen or natural gas. A burner may be used to burn the gas directly for producing heat.

Alternatively electricity generated by using the gas in a fuel cell or in an internal combustion engine may be used to heat the heat exchanger electrically. In the case of an internal combustion engine, the exhaust gas heat from the engine may be used to the heat the heat exchanger.

Another heat source to the heat exchanger available in automobile applications is the frictional heat generated during braking and retardation of the vehicle. A friction heat generator may be included in the drive-train of the 5 vehicle for energy recovery during frequent stops/starts of the vehicle and this heat energy may be transferred to the heat exchanger, thus improving the efficiency of the vehicle in city driving conditions.

to Heating of the heat exchanger with the additional heat sources well above ambient temperature could also increase the thermal efficiency of the gas expander and extend the operating range of the vehicle.

25 Changing the application to a completely different context, the invention could be used in a gymnasium for producing hypoxia air used by athletes for fitness training under simulated high altitude conditions.

30 In this case, a liquid nitrogen utilization management system of the present invention could be used to supply nitrogen gas at low pressure to a nitrogen gas dispensing system in the gymnasium for diluting the breathing air to the desired low-oxygen level. The nitrogen gas dispensing 35 system may comprise a network of nitrogen gas outlet plug- in points from which many users can each plug in their own personal breathing apparatus designed to dispense the

- 8 - nitrogen gas in small pulses in the vicinity near the nose to be inhaled in parallel with ambient air to produced the desired hypaxic air for each user. Alternatively, the nitrogen gas dispensing system may comprise a large s enclosure or room in which the nitrogen gas is mixed in proportion with the room ambient air and circulated to produce an artificial low-oxygen environment shared by several users. In either case, the supply of nitrogen gas from cryogenic liquid nitrogen for producing hypoxia air lo represents a cost-effective commercial concept requiring the lowest capital investment and the lowest operating cost compared with other known systems such as on-site air separation units based on permeable membrane or pressure swing absorption methods to produce the nitrogen gas.

A gas expander may also be included in the gymnasium to extract some of the high pressure gas energy to power the ancillary equipment of the hypoxia training facility before dispensing the gas at low pressure. It could also save some 20 operating cost of running the air conditioning system of the gymnasium by making use of the cooling effect of the liquid nitrogen during evaporation.

Brief description of the drawing

The invention will now be described further, by way of example, with reference to the accompany drawings in which Figure 1 shows a schematic view of a cryogenic liquid utilization management system operating at 30 substantially ambient temperature, and Figure 2 shows a similar schematic view of a cryogenic liquid utilization management system operating above ambient temperature.

( - 9 Detailed description of the preferred embodiment

In Figure 1, the system comprises a thermally insulated liquid storage vessel 10 for storing the cryogenic liquid, a 5 buffer chamber 12 for temporarily holding a predetermined quantity of the cryogenic liquid, a gas evaporation tank 14 for evaporating and storing at high pressure the gas evaporated from the said quantity of cryogenic liquid, a gas utilization unit 16 for receiving and using the pressurized lo gas stored in the gas evaporation tank 14, a venting chamber 18 for receiving gas from the buffer chamber 12 during venting of the buffer chamber 12, connecting pipes 20, 22, 24, 26 between the aforementioned system components with respective control valves 30, 32, 34, 36 in each pipe, and a 15 controller (not shown) for controlling the operation of the said respective valves according to a filling cycle for the buffer chamber 12. During the filling cycle, the buffer chamber 12 is sequentially isolated from the gas evaporation tank 14, vented to substantially ambient pressure through So the venting chamber 18, filled with a predetermined quantity of the cryogenic liquid at substantially ambient pressure from the liquid storage vessel 10, isolated from the venting chamber 18 and the liquid storage vessel 10 before connected to the gas evaporation tank 14 in which the cryogenic liquid 25 evaporates into gas at high pressure, and isolated from the gas evaporation tank 14 again before the gas pressure in the gas evaporation tank 14 is reduced below a predetermined lower value through gas usage by the gas utilization unit 16, whereupon the filling cycle for the buffer chamber 12 is 30 repeated again.

The cryogenic liquid stored in the liquid storage vessel 10 may be any liquefied gas such as liquid air, liquid nitrogen, liquid hydrogen or liquid natural gas as (LNG). The gas utilization unit 16 may include a gas expander for generating mechanical power from the gas at high pressure. It may also include any device that consumes

- 10 -

the gas for various scientific, industrial and combustion applications. In the case of hydrogen, the gas utilization unit 16 may include a fuel cell for generating electricity using the hydrogen gas as fuel. In the case of natural gas, 5 the gas utilization unit 16 may include an internal combustion engine for generating power using the natural gas as fuel.

In Figure 1, when the buffer chamber 12 and the gas lo evaporation tank 14 are at substantially ambient air temperature, the stored heat from their thick walls (thermal capacity of the wall material) could be sufficient to evaporate the filled quantity of cryogenic liquid and raise the temperature of the gas in the gas evaporation tank 14.

A heat transfer liquid 40 (such as glycol) circulated by means of a pump 42 between the gas evaporation tank 14 and an external ambient air heat exchanger 44 with fins 46 and fan 50 is also shown in Figure 1 for accelerating the to evaporation of the filled quantity of cryogenic liquid and raising the temperature of the gas in the gas evaporation tank 14 rapidly to substantially ambient temperature. The heat transfer liquid 40 also maintains the walls of the gas evaporation tank 14 at substantially ambient temperature As during repeated filling cycles, thus preventing ice from forming outside the gas evaporation tank 14. To enhance the heat transfer directly to the gas and to the walls, the heat transfer liquid 40 is sprayed directly inside the gas evaporation tank 14 by means of a spray nozzle 48.

In use, the predetermined filled quantity of cryogenic liquid during each filling cycle of the buffer chamber 12 is such that the resulting increase in gas pressure in the gas evaporation tank 14 does not exceed a predetermined safe 35 upper value.

Thus, as the pressurised gas in the gas evaporation tank 14 is progressively being depleted through usage by the gas utilization unit 16, the control system of the present invention would automatically maintain within the gas evaporation tank 14 cyclically filled quantities of the gas between a lower pressure limit and an upper pressure limit at substantially ambient temperature. This is a batch process which avoids continuous evaporation of the liquid to gas in real time in response to changing flow demand, but lo produces and stores sufficient quantity of the gas in advance time to meet the expected flow demand between the filling cycles. Each batch is small enough to be stored in a relatively small and light-weight high pressure gas tank (the gas evaporation tank 14) thus eliminating the problem 5 of having to store a large stock of the gas at high pressure in large and heavy stock gas cylinders.

The invention has the advantage that the evaporation of the cryogenic liquid to gas does not take place in real time So when the gas is being used, but takes place over a period of time between the filling cycles. In this case, the sustainable delivery rate of the gas from the tank 14 would depend on the quickest time taken for each fill of the cryogenic liquid to evaporate which sets the frequency of Is the filling cycles. This in turn is determined by the stored heat energy in the walls of the buffer chamber 12 and the gas evaporation tank 14, the source of external heat for warming the cryogenic liquid and the walls, and the rate of heat transfer from the source. Preferably, the source of 30 external heat is air at ambient temperature and the cryogenic liquid and the walls are warmed by a heat transfer liquid 40 circulated around an external ambient air heat exchanger 44 as shown in Figure 1. Apart from taking heat from ambient air, the heat exchanger 44 may also be heated 35 directly by the sun.

- 12 -

Alternatively, as shown in Figure 2, the source of external heat for heating the heat exchanger may include a fuel burner 52, an electric heater 54, or a friction heat; generator 56. The friction heat generators 56 may be -

5 incorporated in a vehicle drive-train as a supplementary braking means for slowing down the vehicle, thus converting some of the vehicle's kinetic energy to heat energy for heating the heat exchanger 44. A thermal enclosure 58 may be provided if desired to maintain the heat exchanger 44 lo above ambient temperature.

Claims

- 13 CAIMS 1. A cryogenic liquid utilization management system for

utilising a cryogenic liquid as working fluid to produce 5 a pressurised gas supply of the fluid, the system comprising a thermally insulated liquid storage vessel for storing the cryogenic liquid, a buffer chamber for temporarily holding a predetermined quantity of the cryogenic liquid, a gas evaporation tank for evaporating and storing at high lo pressure the gas evaporated from the said quantity of cryogenic liquid, a gas utilisation unit for receiving and using the pressurised gas stored in the gas evaporation tank, a venting chamber for receiving gas from the buffer chamber during venting of the buffer chamber, connecting 15 pipes between the aforementioned system components with respective control valves in each pipe, and a controller for controlling the operation of the said respective valves according to a filling cycle for the buffer chamber comprising steps in which the buffer chamber is sequentially 20 isolated from the gas evaporation tank, vented and filled with a predetermined quantity of the cryogenic liquid from the liquid storage vessel, isolated from the vent and the liquid storage vessel, connected to the gas evaporation tank in which the cryogenic liquid evaporates into gas at high pressure, and isolated from the gas evaporation tank again before the gas pressure in the gas evaporation tank is reduced below a predetermined lower value as gas is used by the gas utilization unit, whereupon the filling cycle for the buffer chamber is repeated again.
2. A cryogenic liquid utilization management system as claimed in claim 1, wherein the predetermined quantity of cryogenic liquid filled during each filling cycle of the buffer chamber is such that the resulting increase in gas 35 pressure in the gas evaporation tank after the liquid has evaporated does not exceed a predetermined safe upper value.

- 14 -
3. A cryogenic liquid utilisation management system as claimed in claim 1 or 2, wherein a heat exchanger is provided for maintaining the walls of the gas evaporation tank at substantially ambient temperature.

s
4. A cryogenic liquid utilisation management system as claimed in claim 3, wherein the heat exchanger is an ambient air heat exchanger.

lo
5. A cryogenic liquid utilisation management system as claimed in claim 3, wherein the heat exchanger is heated by the sun.
6. A cryogenic liquid utilisation management system 5 as claimed in claim 3, wherein the heat exchanger is heated by a fuel burner.
7. A cryogenic liquid utilisation management system as claimed in claim 3, wherein the heat exchanger is heated 20 by an electric heater.
8. A cryogenic liquid utilisation management system as claimed in claim 3, wherein the heat exchanger is heated by a friction heat generator.
9. A cryogenic liquid utilisation management system as claimed in any preceding claim, wherein the gas utilisation unit includes a gas expander for generating mechanical power from the gas at high pressure.
10. A cryogenic liquid utilisation management system as claimed in any one of claims 1 to 9, wherein the cryogenic liquid is hydrogen and the gas utilisation unit includes a fuel cell for generating electricity using the 35 hydrogen gas as fuel.

- 15
11. A cryogenic liquid utilization management system as claimed in any one of claims 1 to 9, wherein the cryogenic liquid is natural gas and the gas utilization unit includes an internal combustion engine for generating power 5 using the natural gas as fuel.
12. A cryogenic liquid utilization management system as claimed in any one of claims 1 to 9, wherein the cryogenic liquid is nitrogen and the gas utilization unit lo includes a nitrogen gas dispenser for preparing a mixture of hypoxia air for athletic training.