Process for fueling of vehicle tanks with compressed hydrogen comprising heat exchange of the compressed hydrogen with chilled ammonia

Abstract

The invention relates to a process for fueling of vehicle tanks with compressed hydrogen comprising splitting ammonia into hydrogen and nitrogen in an ammonia cracking unit, compressing the hydrogen from the ammonia cracking unit, and dispensing the compressed hydrogen to the vehicle tanks in a hydrogen fueling unit comprising one or more dispensing units, wherein chilled ammonia is used to cool the compressed hydrogen before being dispensed to the vehicle tanks by heat exchange between the compressed hydrogen and the chilled ammonia so that the chilled ammonia is heated, and transferring the heated ammonia to the ammonia cracking unit.

Claims

1. A process for fueling of one or more vehicle tanks with compressed hydrogen comprising: passing ammonia through a first heat exchanger to cool a heat exchange fluid that is passed through the first heat exchanger to warm the ammonia; splitting the ammonia into hydrogen and nitrogen in an ammonia cracking unit after the ammonia is warmed via the first heat exchanger, compressing the hydrogen from the ammonia cracking unit, passing the heat exchange fluid that has been cooled via the first heat exchanger to a second heat exchanger positioned downstream of the ammonia cracking unit and downstream of at least one compressor performing the compressing of the hydrogen, passing the compressed hydrogen through the second heat exchanger to cool the hydrogen for dispensing the hydrogen at a hydrogen fueling unit comprising one or more dispensing units, the heat exchanger fluid passed to the second heat exchanger being warmed to cool the hydrogen passed through the second heat exchanger, and dispensing the cooled compressed hydrogen to the one or more vehicle tanks via the hydrogen fueling unit comprising one or more dispensing units.

2. The process according to claim 1, wherein the heat exchange fluid is passed within a closed heat exchange fluid loop defined between the first heat exchanger and the second heat exchanger so that heat exchange between the chilled ammonia and the compressed hydrogen is effected by a first heat exchange between the chilled ammonia and the heat exchange fluid in the first heat exchanger and a second heat exchange of the heat exchange fluid and the compressed hydrogen in the second heat exchanger.

3. The process according to claim 2, comprising: storing at least part of the heat exchange fluid in a heat exchange fluid storage tank positioned within the closed heat exchange fluid loop.

4. The process according to claim 3, wherein the heat exchange fluid is stored in the storage tank at a temperature close to the temperature it has after the second heat exchange, and/or is stored at a temperature close to the temperature it has after the first heat exchange.

5. The process according to claim 1, wherein at least one of: the ammonia is passed through the first heat exchanger in countercurrent flow with the heat exchange fluid passed through the first heat exchanger; and the hydrogen is passed through the second heat exchanger in countercurrent flow with the heat exchange fluid passed through the second heat exchanger.

6. The process according to claim 2, wherein a conventional refrigeration system is used for further cooling of the heat exchange fluid within the closed heat exchange fluid loop.

7. The process according to claim 2, wherein the chilled ammonia is in a liquid state and the first heat exchange involves vaporizing at least a portion of the ammonia in the liquid state.

8. The process according to claim 7, wherein the first heat exchange is utilized to provide an optimal phase change temperature of the ammonia in the liquid state and temperature needed for hydrogen cooling.

9. The process according to claim 7, wherein vaporization of ammonia is effected at sub-atmospheric pressure.

10. The process according to claim 1, wherein the heat exchange fluid is D-Limonene, FP40 or a water/glycol mixture.

11. The process according to claim 1, wherein the ammonia is liquid ammonia before the ammonia is passed to the first heat exchanger, the liquid ammonia having a temperature between −5° C. and −77° C., or having a temperature of between −25° C. and −77° C.

12. The process according to claim 1, wherein the temperature of compressed hydrogen output from the second heat exchanger is between −45° C. and +5° C. for filling of bus tanks and between −33° C. and −40° C. for filling of car tanks.

13. A system for performing the process according to claim 1, comprising the ammonia cracking unit for cracking ammonia, the at least one compressor for compressing the hydrogen output from the ammonia cracking unit and the one or more hydrogen dispensing units, wherein the system further comprises the first heat exchanger and the second heat exchanger cooperating for exchanging heat between the ammonia and the compressed hydrogen via the heat exchange fluid passed through a closed heat exchange fluid loop defined between the first heat exchanger positioned to warm the ammonia and the second heat exchanger positioned to cool the compressed hydrogen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will hereinafter be described in conjunction with the appended FIGURE wherein like numerals denote like elements.

(2) FIG. 1 shows an embodiment of the process and integrated system of the invention.

DETAILED DESCRIPTION

(3) In an embodiment, the system of the invention (hydrogen fueling station) for performing the process of the invention comprises an ammonia cracking unit in which ammonia is split into hydrogen and nitrogen and a hydrogen fueling unit for fueling of vehicle tanks with hydrogen from the ammonia cracking unit. The fueling unit also comprises one or more hydrogen compressing units wherein the hydrogen from the ammonia cracking unit is compressed, and one or more dispensing units for dispensing the compressed hydrogen to vehicle tanks which each comprise a nozzle through which the compressed hydrogen is passed to the vehicle tank.

(4) The system further comprises an ammonia storage tank in which chilled ammonia, which is delivered to the station form an outside source, is stored for further use. Still further, a first heat exchanger, which preferably is a counter flow heat exchanger, and a second heat exchanger, which also preferably is a counter flow heat exchanger, are present.

(5) The two heat exchangers are in fluid connection through a pipe system of insulated pipes which forms a closed heat exchange fluid loop. In the loop further present is at least one storage tank for the heat exchange fluid and at least one pump for cicrculating the heat exchange fluid in the loop.

(6) The first heat exchanger is arranged so that it receives chilled ammonia from the ammonia storage tank which is heat exchanged in counter flow with heat exchange fluid present in the heat exchange fluid loop.

(7) Usually, the chilled ammonia will be in a saturated liquid state at a temperature of between −5 and −77° C., and the temperature of the heat exchange fluid before the first heat exchange will be between −35 and −43° C. for car fueling, and −10 to −30° C. for bus fueling.

(8) Hydrogen from the ammonia cracking unit is compressed upstream of the ammonia cracking unit, which preferably is done up to a pressure of 30 MPa or more. Hydrogen is pressured up to 40 MPa or more for H35 fueling, or 90 MPa or more for H70 fueling.

(9) The fueling unit further comprises one or more hydrogen storage tanks in which the compressed hydrogen is stored after the hydrogen has been obtained from the ammonia cracking unit.

(10) The temperature of the compressed hydrogen before the second heat exchange is usually close to ambient temperature, usually between −20° C. and 40° C. in the US, and the temperature of the heat exchange fluid will be between between −35 and −43° C. for car fueling, and −10 to −30° C. for bus fueling.

(11) The second heat exchange is effected so that the desired temperature of the compressed hydrogen for dispension to vehicle tanks is obtained, which is usually between −45 and +5° C. For example, a temperature of 0° C. for filling of bus tanks and −40° C. for filling of car tanks may be selected.

EXAMPLE

(12) FIG. 1 shows an embodiment of the process and system of the present invention. Chilled ammonia, usually in liquid state, is delivered to the system from an outside source and is stored in ammonia storage tank 2 until it is fed to the ammonia cracking unit 1. The ammonia cracking unit 1 splits the NH.sub.3 into N.sub.2 and H.sub.2, and may operate in the 5-40 barg pressure range, most commonly in the 7-20 barg range.

(13) The H.sub.2 from the ammonia cracking unit 1 is submitted to one or more compression stages in one or more compressors, such as the reciprocating H.sub.2 compressor 7 shown in FIG. 1, to pressure it up to 40 MPa or more for H35 fueling, or 80 MPa or more for H70 fueling.

(14) The compressed hydrogen is then directed to one of the hydrogen storage banks, such as H.sub.2 storage tank 8, controlled by valve 9. When a vehicle is ready to be filled, valve 10, or in case of several hydrogen storage tanks the appropriate cascade valve, will open, allowing H.sub.2 from the storage tank 8 to flow to the H.sub.2 dispenser 11, and ultimately to the vehicle tank (not shown). Cascading is well known to the skilled person and is described, for example, in U.S. Pat. No. 8,899,278, starting in col. 1, line 17.

(15) The system further comprises a first heat exchanger 3 which is arranged to received chilled ammonia from the ammonia storage tank 2 for example by means of a pump (not shown). After heat exchange, the heated ammonia is further led to the ammonia cracking unit 1. In heat exchanger 3, in counter current flow to the ammonia is a heat exchange fluid, such as FP 40 or a water/glycol mixture, which is cooled by the heat exchange with the ammonia.

(16) The cooled heat exchange fluid may be stored in heat exchange fluid storage tank 5 and is, when needed, pumped further by pump 6 to heat exchanger 4, in which in counter current flow compressed hydrogen is led through which, accordingly, is cooled down to the desired temperature for vehicle tank filling through dispenser 11.

(17) Heat exchanger 3 and, independently, 4 may be any common heat exchanger, such as a shell-and-tube heat exchanger. The pipe system in which the heat exchange fluid is pumped around is thermally isolated to avoid heating of the heat exchange fluid by the environment.

(18) In one embodiment, the chilled ammonia is in a liquid state, so that heat exchanger 3 may further comprise an expansion unit (not shown) wherein the liquid ammonia is partially, or fully, evaporated during heat exchange with the heat exchange fluid to make use of the vaporization enthalpy of the liquid ammonia for cooling the heat exchange fluid.

(19) For example, if the hydrogen flow rate to be provided by the ammonia cracking unit 1 is 7.5 tons/day, assuming a 100% conversion 42.2 tons/day of ammonia is to be delivered to the ammonia cracking unit 1. Given that the heat capacity of liquid ammonia is 4.744 kJ/kg NH.sub.3/K, by heating liquid ammonia during heat exchange by 20 K, a cooling energy of about 4 million kJ is available for cooling of compressed hydrogen.

(20) Furthermore, in embodiments where vaporization of liquid ammonia is used, given that ammonia vaporization enthalpy at 34.15° C. is 23.5 kJ/mol NH.sub.3 and assuming again 42.2 tons/day of ammonia flow, a cooling energy available from complete vaporization of ammonia is about 58.3 million kJ/day.

(21) The cooling energy may be used to cool the heat exchange fluid, which, in turn, is used for cooling compressed hydrogen. Again assuming a hydrogen flow rate of 7.5 tons/day which are to be cooled and given the heat capacity of hydrogen being 14 kJ/kg H.sub.2/K, for example, a cooling energy of about 6.825 million kJ would be necessary to cool said hydrogen from 25° C. to −40° C. which in part or in full can be provided by the ammonia cooling energy to the heat exchange fluid in heat exchanger 3.