GAS EXPORT ASSEMBLY

Abstract

A gas export assembly is provided including a gas production facility adapted to generate pressurized gas for export to a remote facility through a pipeline; a determining an upper humidity threshold for the export gas in the pipeline; a determining, on the basis of the upper humidity threshold, a pipeline inlet humidity for the export gas, which pipeline inlet humidity is lower than the upper humidity threshold; and a regulator stage adapted to adjust the humidity of the export gas to the pipeline inlet humidity.

Claims

1. A gas export assembly comprising: a gas production facility configured to generate pressurized gas for export to a remote facility through a pipeline; a means of determining an upper humidity threshold for an export gas exported in the pipeline; a means of determining, on a basis of the upper humidity threshold, a pipeline inlet humidity for the export gas, the pipeline inlet humidity being lower than the upper humidity threshold; and a regulator stage configured to adjust a humidity of the export gas to the pipeline inlet humidity.

2. The gas export assembly according to claim 1, wherein the regulator stage comprises a cooling module configured to extract water vapor from the pressurized gas.

3. The gas export assembly according to claim 1, wherein the regulator stage comprises a pressure reducer configured to reduce a pressure of the cooled and partially dried gas.

4. The gas export assembly according to claim 1, comprising a means of determining a lowest temperature in an interior of the pipeline and a means of determining a pressure in the interior of the pipeline at a region of lowest temperature.

5. The gas export assembly according to claim 4, wherein the upper humidity threshold is determined on a basis of the lowest temperature and the pressure.

6. An offshore facility comprising: a wind turbine; and a gas export assembly according to claim 1 powered by the wind turbine.

7. The offshore facility according to claim 6, wherein the gas production facility comprises a high-pressure PEM water electrolyzer assembly for a production of pressurized hydrogen gas.

8. A method of operating the gas export assembly according to claim 1, the method comprising: determining the upper humidity threshold for the export gas in the pipeline; determining, on the basis of the upper humidity threshold, the pipeline inlet humidity for the export gas, the pipeline inlet humidity being lower than the upper humidity threshold; adjusting the humidity of the export gas to the pipeline inlet humidity; and subsequently feeding the export gas into the pipeline.

9. The method according to claim 8, wherein the pipeline inlet pressure is determined on a basis of a desired outlet pressure.

10. The method according to claim 1, wherein the regulator arrangement comprises a pressure reducer, and wherein a pressure drop across the pressure reducer is determined on a basis of the pipeline inlet pressure.

11. The method according to claim 1, wherein a pipeline inlet temperature is deduced at least on a basis of the pipeline inlet humidity.

12. The method according to claim 1, comprising a step of determining a pressure profile over a length of the pipeline.

13. The method according to claim 1, comprising a step of determining a temperature profile in a pipeline interior over a length of the pipeline.

14. The method according to claim 1, comprising an initial calibration step in which temperature data is collected in an interior of the pipeline over a length of the pipeline.

15. The method according to claim 1, wherein the pipeline inlet humidity comprises a relative humidity of at most 85%.

Description

BRIEF DESCRIPTION

[0028] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0029] FIG. 1 shows a block diagram of an embodiment of the inventive gas export assembly;

[0030] FIG. 2 is a flowchart to illustrate the inventive method;

[0031] FIG. 3 shows temperature, pressure and relative humidity at different stages in the inventive method; and

[0032] FIG. 4 illustrates the concepts applied by the inventive method.

DETAILED DESCRIPTION

[0033] FIG. 1 is a simplified block diagram of an embodiment of the inventive gas export assembly 1. The diagram shows a high-pressure PEM electrolyzer 10, a heat exchanger 11, a pressure reducer 12 and an export pipeline 2. The gas export assembly 1 is implemented at an offshore location, and is powered by a wind turbine 41. The wind turbines of an offshore wind park can power many such high-pressure PEM electrolyzers 10 to generate large quantities of “green” hydrogen G.sub.10 at a favorably high purity. The coolant for the heat exchanger 11 may be cold seawater. The pipeline 2 between the wind turbine 41 and a destination facility 42 at a remote location may have a length of many kilometers.

[0034] FIG. 2 is a flowchart 20 to illustrate the inventive method. In a preparatory step 21, the lowest temperature T.sub.c in the pipeline is determined or estimated. This can be done using temperature sensing means as explained above. In another preparatory step 22A, the minimum inlet pressure P.sub.in is determined in order to achieve a satisfactory flow rate through that pipeline. This can be done using information regarding the dimensions of the pipeline, a required or desired flow rate, and a desired outlet pressure P.sub.out. From the minimum inlet pressure P.sub.in, the pressure P.sub.c at the coldest or “critical” pipeline region is estimated in step 22B.

[0035] From the lowest temperature T.sub.c and the corresponding pressure P.sub.c, an upper threshold ϕ.sub.C for the relative humidity of the export gas is determined in a subsequent step 23 as explained above regarding equation (1). From this, and with knowledge of the changes in temperature and pressure between pipeline inlet and the coldest pipeline region, a suitable level of relative humidity ϕ.sub.in at the pipeline inlet 2.sub.in is determined in step 24 such that equation (1) is satisfied over the entire pipeline.

[0036] The temperature and pressure of the gas to be fed into the pipeline 2 can be manipulated in two ways in order to achieve this: the hot pressurized gas can be cooled, since cooling will result in condensation of water vapor; and the gas can be decompressed or expanded, since a decrease in pressure is associated with a decrease in relative humidity.

[0037] The required minimum pressure P.sub.in at the pipeline inlet 2.sub.in can be determined from a desired gas flow rate and the known pressure drop ΔP.sub.2 across the pipeline, i.e.,

ΔP.sub.12=P.sub.10−P.sub.in   (3)

where P.sub.out is the desired pressure at the pipeline output 2.sub.out. Since the pressure drop across the cooling unit 11 may be assumed to be negligible, the required pressure drop ΔP.sub.12 across the pressure reducer 12 can be determined from

ΔP.sub.12=P.sub.10−P.sub.in   (3)

[0038] In the inventive method, the pressurized wet gas G.sub.10 originating from the gas production facility 10 is cooled in step 26. This step of cooling will result in condensation of water vapor, so that the gas G.sub.11 output by the cooling unit 11 is partially dried and has been cooled to a suitable lower temperature T.sub.11. The pressure drop across the cooling unit 11 may be assumed to be minimal.

[0039] Subsequently, the cooled (and partially dried) gas G.sub.11 is decompressed in step 27 to reduce its pressure. The decompressor output pressure P.sub.12 is essentially the pipeline inlet pressure P.sub.in. Within the constraints of equation (3), the decompression stage 12 achieves a large pressure drop to obtain a favorably low relative humidity ϕ.sub.in of the gas G.sub.12 at the decompressor output, i.e., at the pipeline inlet 2.sub.in such that

ϕ.sub.in{T.sub.in, P.sub.in}«π.sub.C   (4)

[0040] i.e., the relative humidity at the pipeline inlet is significantly lower than the critical relative humidity ϕ.sub.C by a favorably large margin, bearing in mind that the temperature of the gas G.sub.2 (in the pipeline as shown in FIG. 1) will drop as it travels through the pipeline 2, reaching its lowest temperature at the critical region 2.sub.C. However, since the relative humidity of the gas at the pipeline inlet 2.sub.in was deliberately reduced by the treatment stages 11, 12, the increase in relative humidity at the lower temperature T.sub.C and pressure P.sub.C at the pipeline critical region 2.sub.C is such that the upper limit ϕ.sub.C for relative humidity is not exceeded.

[0041] The temperature at the pipeline inlet 2.sub.in can be at any level as long as equation (1) will apply over the length of the pipeline 2. The temperature of the inlet gas G.sub.12 may be raised if desired, without affecting its relative humidity, since water vapor is not removed in a heating process.

[0042] Depending on various factors such as pipeline length, electrolyzer output temperature, etc., the temperature of the inlet gas G12 may affect the pipeline temperature profile. In such conditions, the cooling unit 11 may be regulated to cool its output gas G11 to suitable temperature T.sub.11.

[0043] FIG. 3 shows temperature, pressure and relative humidity at different stages in the inventive method as explained in FIG. 1 and FIG. 2. The uppermost part of the diagram shows the temperature profile 31 of hydrogen gas between its output from the gas production facility 10 through all stages of the inventive gas export assembly 1 and through the pipeline 2. To illustrate the effect of the inventive method, the X-axis represents distance. The pipeline 2 can have a length L2 of many kilometers.

[0044] In a first step 21, the lowest or “critical” temperature T.sub.c along the pipeline 2 is established. From the relationship between temperature, pressure and relative humidity, it can be established that the relative humidity of the export gas will be highest at this point 2.sub.C along the pipeline. Embodiments of the invention are based on the insight that, by keeping the relative humidity below a certain threshold at this point 2.sub.C along the pipeline, condensation of water vapor can be avoided. A suitable upper threshold ϕ.sub.C of relative humidity for that pipeline region 2.sub.C is then chosen, for example 90%.

[0045] A pressure profile 32 can be established from a known desired rate of gas transfer along the pipeline, i.e., a pressure differential can be identified to achieve a desired flow rate. Knowing the pressure P.sub.out of the export gas at the pipeline outlet, and knowing the pipeline length L2, the pressure P.sub.in at the pipeline inlet can be determined, for example by extrapolation. This allows the pressure P.sub.c at the critical region of the pipeline 2 to be determined in step 22B of the flowchart.

[0046] Using the known information about temperature and pressure profiles 31, 32 along the pipeline 2, and the established maximum relative humidity ϕ.sub.C at that critical region 2.sub.C, a suitable relative humidity ϕ.sub.in at the pipeline inlet 2.sub.in is then determined as explained above in step 24. With this lower relative humidity ϕ.sub.in as “target”, a suitable temperature drop ΔT.sub.11 across the cooling unit 11 and a suitable pressure drop ΔP.sub.12 across the pressure reducer 12 are determined. These parameters are chosen to result in a reduced relative humidity ϕ.sub.in at the pipeline inlet 2.sub.in, so that, by the time the export gas reaches the critical region 2.sub.C of the pipeline, its relative humidity will not be able to increase above the identified threshold ϕ.sub.C.

[0047] With these criteria, the cooling and decompression steps 26, 27 can be performed to achieve the desired relative humidity ϕ.sub.in. For example, if the wind energy plant is located in the North Sea and the coolant is seawater at a temperature in the order of 10° C.-12° C., the temperature of the hydrogen gas G.sub.10 can be reduced relatively quickly from an initial temperature T.sub.10 in the order of 70° C. to a lower temperature T.sub.11 in the order of 10° C., thereby extracting a significant fraction of the water content from the gas G.sub.10. The pressure of the gas G.sub.11 at the output of the cooling unit 11 remains essentially unchanged. The pressure of the partially dried and cooled gas G.sub.11 can be reduced from its initial pressure P.sub.10 in the order of 6000000 Pa (60 bar) to a desired pipeline infeed pressure P.sub.in in the order of 3000000 Pa (30 bar). The temperature of the gas G.sub.12 at the output of the decompression unit 12 remains essentially unchanged.

[0048] The combination of infeed temperature T.sub.11 and infeed pressure P.sub.in ensure that the relative humidity of the export gas in the pipeline 2 will not rise above the upper threshold ϕ.sub.C of relative humidity in the pipeline, so that even at the critical low-temperature in the pipeline 2, condensation of the residual water vapor will not occur.

[0049] FIG. 4 illustrates the concepts applied by the inventive method. Initially, as indicated on the left, the high-pressure PEM electrolyzer outputs hydrogen G.sub.10 at a high temperature T.sub.10 and a high pressure P.sub.10. During the temperature-reduction stage 11 of the regulator, the gas undergoes isobaric cooling during which the pressure P.sub.10 remains essentially the same, but the temperature is reduced from the initial temperature T.sub.10 to the inlet temperature T.sub.11. During the pressure-reduction stage 12 of the regulator, the gas undergoes isothermal decompression during which the temperature T.sub.11 remains essentially the same, but the pressure is decreased from the initial pressure P.sub.10 to the inlet pressure P.sub.in.

[0050] Although the present invention has been disclosed in the form of embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0051] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. The mention of a “unit” or a “module” does not preclude the use of more than one unit or module.