EP4655505A1

EP4655505A1 - Hydrogen centrifugal compressor system with pressure ratio enhancement by water injection and operating method thereof

Info

Publication number: EP4655505A1
Application number: EP24708675.4A
Authority: EP
Inventors: Mukunda SHANKAR; Uday Karthik MEDURI; Vidyasagar RAMALINGAM RENGASAMY; Balachandran Kumaravelu; Simone CORBO
Original assignee: Nuovo Pignone Technologie SRL
Current assignee: Nuovo Pignone Technologie SRL
Priority date: 2023-02-23
Filing date: 2024-02-16
Publication date: 2025-12-03
Also published as: AU2024225945A1; IT202300003180A1; CN120712416A; WO2024175252A1; KR20250150640A; JP2026506729A

Abstract

A compressor system to compress a gas, like hydrogen. The compressor system comprises a multistage compressor, having a plurality of compressing stages for increasing the pressure of a gas flow path. The compressor system comprises an injection unit, with a plurality of nozzles for injecting a cooling fluid, such as water, into the gas flow path.

Description

Hydrogen Centrifugal Compressor System with Pressure Ratio Enhancement by Water Injection and Operating Method thereof

Description

TECHNICAL FIELD

[0001] The present disclosure concerns hydrogen compressor plant having a multistage hydrogen compressor, which is typically used for energy storage system and transportation. The present disclosure also concerns the operating method of such multistage hydrogen compressor.

BACKGROUND ART

[0002] Hydrogen compression is an energy-intensive process, and it is achieved through multiple trains of multi-stage compression, which operates at high speed. In the energy or process industry is the hydrogen typically obtained, for example, by electrolysis

[0003] In the energy or process industry, usually, a fluid is compressed by compressors. For instance, natural gas is a typical fluid that is compressed. The compressors can be axial or centrifugal, or a combination thereof, and can have a compression ration of the order of 2 or 3.

[0004] Currently, multistage hydrogen compressors are increasingly used for energy storage and, therefore, improvements aimed at increasing the pressure ratio would be welcomed in the technology.

[0005] Also, the polytropic head (or the energy per unit mass of gas) required to compress a gas up to a certain pressure ratio is inversely proportional to the molecular weight. Hence, for hydrogen compression, the energy required for compression is high when compared to any other gas such as the natural gas or the like. In fact, hydrogen at standard temperature and pressure has extremely low density, and hence large volume. Therefore, to process hydrogen for transport or storage, multiple compressor trains are generally needed. This requires large footprint and high capital expenditures, in view of the low molecular weight. SUMMARY

[0006] In one aspect, the subject matter disclosed herein is directed to a compressor system to compress a gas, such as hydrogen and the like. The system comprises a multistage compressor, which has one or more compressing stages capable of increasing the pressure of a gas flow path. The system comprises also an injection unit, having an injection conduit for injecting a fluid, and one or more nozzles, fluid dynamically connected to the injection conduit, for injecting the fluid into the gas flow path. The fluid has a temperature lower than the temperature of the gas flow, so that, when the fluid is injected into the gas flow, and comes into contact with the gas flow, the fluid vaporizes causing an increase in the molecular weight of the gas. The fluid has a temperature equal to or lower that the ambient temperature. The gas may be hydrogen, and the fluid may be water.

[0007] In another aspect, the subject matter disclosed herein concerns a compressing stage that may comprise an impeller, a diffuser connected to the impeller, a u-bend, connected to the diffuser, a return channel, connected to the u-bend. The compressing stage also has a fluid inlet obtained on the diffuser or on the u-bend. Each nozzle is arranged on a respective fluid inlet. In addition, the compressor may comprise a plurality of compressing stages, arranged in series, a gas inlet, through which the gas enters into the compressor, a gas outlet, through which the gas comes out after the compression, and a rotating shaft, to which the impellers are keyed, to compress the gas.

[0008] In another aspect, disclosed herein is a cooler that may have an inlet conduit connected to the gas outlet, an outlet conduit, through which the saturated vaporized fluid is conveyed, and a second outlet conduit, through which the condensate of the fluid is extracted.

[0009] In another aspect, disclosed herein is a multistage compressor, which may comprise an external casing, and an internal casing, which is shaped to contain the compressing stages. A distribution channel may be obtained in said internal casing, wherein the distribution channel is fluid dynamically connected to the injection conduit and with the nozzles. The distribution channel may be formed by a first part, and a second part. The first part may have a rectangular cross-section and the second part has a rectangular cross-section, smaller than the first part. A plurality of nozzles may be also installed on each distribution channel.

[0010] In another aspect, the subject matter disclosed herein concerns nozzles that may have an increasing flow rate if they are more distanced from the nozzle closer to the connection point of the injection conduit to the distribution channel; in other words, nozzle flow rate increases as the distance increases between the nozzle and the point where the injection conduit fluidly connects to the distribution channel. The distribution channel may have a variable cavity/cross-section.

[0011] In another aspect, disclosed herein is an injection unit that may comprise a plurality of controlled electric valves, each one connected to a respective nozzle through a respective pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 illustrates a schematic of water injection in a hydrogen compressor according to a first embodiment of a compressor system;

Fig. 2 illustrates a cross-sectional view of a compressing stage according to the first embodiment;

Fig. 3 illustrates a longitudinal section of the compressing stage of Fig. 2;

Fig. 4 illustrates a perspective view of a longitudinal section of the compressing stage of Fig. 2;

Fig. 5 illustrates a graph showing the effect of water injection on the performance curves of a hydrogen compressor;

Fig. 6 illustrates a graph showing the power consumption of the compressor system as a function of the flow;

Fig. 7 illustrates a graph showing the pressure ratio of the compressor system as a function of the flow;

Fig. 8 illustrates a second embodiment of the multistage hydrogen centrifugal compressor system with a variable area cavity to ensure uniform pressure of water injection; Fig. 9 illustrates a third embodiment of the multistage hydrogen centrifugal compressor system with ports with increasing areas to ensure the delivery at uniform pressure;

Fig. 10 illustrates a fourth embodiment of the multistage hydrogen centrifugal compressor system with equivalent pipe losses to inject at uniform pressures; and

Fig. 11 illustrates a fifth embodiment of the multistage hydrogen centrifugal compressor system.

DETAILED DESCRIPTION OF EMBODIMENTS

[0013] Compressors are well-known machines used to compress gases. In particular, compressors can be used to compress hydrogen gas. In fact, compressed gas is usually used for energy storage and energy transportation. To this end, multiple compressor trains are required, which have large footprints, as well as high maintenance and operating costs. According to one aspect, the present subject matter is directed to improve the compression process and the costs thereof, by reducing the number of stages of the compressor itself. This is achieved by spraying and injecting water continuously at every stage, until saturation is reached. In this way, the molecular weight of hydrogen is increased through the vaporized water introduced into the flow path, causing a reduction of the power consumption.

[0014] Referring now to the drawings, Figures 1, 2, 3, and 4 show a schematic view of a first embodiment of the multistage hydrogen centrifugal compressor system 1.

[0015] Specifically, the multistage hydrogen centrifugal compressor system 1 comprises a compressor 2, an injection unit 3, and a cooler 4.

[0016] The compressor 2 comprises a plurality of compressing stages 21, arranged in series, or in cascade, a gas inlet 22, through which the gas enters along the arrow A, a gas outlet 23, through which the gas comes out along the arrow B, a rotating shaft 24 and a stator or diaphragm 25. The compressing stages 21 are contained in a casing 26, which comprises an external casing 261, to protect the entire compressor 2, and an internal casing 262, which is internally shaped to contain the stages 21 and the respective parts.

[0017] Each compressing stage 21 comprises an impeller 211, keyed to the rotating shaft 24, a diffuser 212, provided on the downstream side of the impeller 211, a u-bend 213, provided on the downstream side of the diffuser 212, and a return channel 214, downstream of the u-bend 213. The compressing stages 21 have the function of increasing the velocity and then the pressure of the injected gas, thanks to the impeller 211, and the specific shapes of the diffuser 212 and the u-bend 213. Each stage 21 increases the pressure of the injected gas introduced through the gas inlet 22, where in the present embodiment the gas is hydrogen.

[0018] In addition, for each compressing stage 21 there is one or more fluid or water inlets 27 connected to a respective water injection conduit 31 of the injection unit 3, as better described below. In association with each one of the water inlets 27 there is installed a respective nozzle 33, which is then arranged in correspondence of the u- band 213 or the diffuser 212. Specifically, each nozzle 33 is arranged to nebulize the water into the gas flow path while passing through the u-band 213 or the diffuser 212. The water inlets 27 are connected to the u-bend 213 of each compressing stage 21.

[0019] The discharge fluid coming out of the compressor 23 passes through a cooler 4, which helps condense the water to liquid. This gets separated at the separator, which is a filtering centrifuge capable of separating liquids from gases in a gas-liquid mixture.

[0020] The injection unit 3 comprises a control system 32 for controlling the amount of injected water for the required pressure ratio. The control system 32 can be, for example, a computer or programmable logic controller that can function autonomously or it can be controlled by a remote computer or central logic unit (not shown in the figure), to control the multistage hydrogen centrifugal compressor system 1.

[0021] Also the injection unit 3 comprises a plurality or a manifold of injection conduits 31, each one connected, to a respective water inlets 27 of the compressor 2, through a nozzle 33.

[0022] The injection unit 3 has the function of controlling the of water into each compressing stage 21 of the compressor 2. The water supply can be uniform, namely the quantity of water passing through each injection conduits 31 can be the same, or it can be differentiated, depending on the needs. In this case, the water passing through each injection conduits 31 can be adjusted by the control system 32 by suitable flow control devices, such as pumps and the like. [0023] Referring now in particular to Figure 4, in the inner casing 262, in correspondence with each compressing stage 21, a distribution channel 29 is obtained and machined. Specifically, for each compressing stages 21, there is a respective distribution channel 29, which is circumferential and has a toroidal shape. In the embodiment illustrated, the distribution channel 29 is arranged side-by-side the u-bend 213 of each compressing stage 21.

[0024] Each a distribution channel 29 is fluid dynamically connected to at least one respective water injection conduit 31. Specifically, the In the embodiment shown, each distribution channel 29 is fluid dynamically connected to one u-bend 213. and to one respective water injection conduit 31, such as through the injections unit 3 it is possible to inject or spray water into a distribution channel 29 by the nozzles 33 connected to it.

[0025] Also, in the embodiment shown, each distribution channel 29 has a cross-section ideally formed by two connected parts, a first part 291, and a second part 292. The first part 291 is rectangular as well as the second part 292. Also, in the present embodiment the first part 291 is larger than the second part 292, to better adapt to the available space close to the u-bend 28.

[0026] In other embodiments, the distribution channel 29 can have different cross- sectional shapes, for example, a circular or squared cross-sectional shape.

[0027] The cooler 4 comprises an inlet conduit 41, connected to the gas outlet 23 of the compressor 2 from which gas saturated comes, a second outlet conduit 43, for extracting the condensate of the colling operation, and an outlet conduit 42, which conveys the saturated water vapor, as better explained below. The cooler 4 cools the compressed gas to below its dew point, to allow the removal of the moisture and the water vapor. The cooler 4 can be in general of the type normally used in the Oil and Gas industry, for instance.

[0028] The operation of the multistage hydrogen centrifugal compressor system 1 is as follows.

[0029] When the multistage hydrogen centrifugal compressor system 1 operates, com- pressing the hydrogen gas through each stage by the impellers 211, water is continuously injected into each compressing stage 21 through the water injection conduits 31 and through the water inlets 27. The water is then nebulized into the u-bend 213 by the nozzles 33, at every compressing stage 21, until saturation is reached. The water absorbs heat from the process gas (hydrogen), thereby getting vaporized and simultaneously cooling the process gas. The water then vaporizes, because of the temperature shock caused by meeting the hot gas flow path. At the same time, the water increases the molecular weight of the gas, improving the gas (which is hydrogen in the present embodiment) compression process.

[0030] This lowers the head required by of each stage and improves the compression power requirement with respect to compressing pure hydrogen. The power absorbed by a centrifugal compressor is a product of head and efficiency (refer general compressor literature). The head inversely varies with molecular weight. Hence, increasing the molecular weight has the impact of lowering the head and thereby the power. The amount of water injected into each compressing stage 21 is controlled by the control system 32 of the injection unit 3. After compression operation of the gas by the compressor 2, the excess water is removed by the cooler 4.

[0031] Specifically, the fluid is injected in the gas path to increase molecular weight, as it is immediately vaporized at injection since the fluid temperature is typically at an ambient or lower temperature, thus lower than gas temperature. This causes the fluid vaporization. The vapor has its own density and so does the gas, namely the hydrogen, such that the density of the mixture is higher than that of the gas (hydrogen) only.

[0032] Normally, the gas relative humidity is less than 100%. In addition, the temperature of the gas flow will typically be high enough to vaporize the fluid immediately as they come into contact.

[0033] The erosion, possibly caused by the fluid, which is usually water, is avoided by a coating. Instead, the possible corrosion, still possibly caused by the fluid, is avoided by a proper selection of materials, such as erosion resistant stainless steel or by adapting the shape of the impeller at the inlet to minimize erosion.

[0034] Referring now to Figure 5, a diagram pressure/flow rate is plotted, for showing the performance of the multistage hydrogen centrifugal compressor system 1 with and without water injection. In particular, it can be appreciated that with water injection also with high flow rates, of around 1.8X 10⁵ m³h the overall gas pressure is around 4 bars.

[0035] Also, Figures 6 and 7 show two diagrams, illustrating that for a same mass flow and pressure ratio, the power consumption is lower when water (H2O) is injected in the into the gas path flow (which is water, H2).

[0036] Specifically, the graph in Fig. 6 has on the abscissa the flow, in a non-dimensional parametrization is reported, while on the ordinate the power consumption is reported (again in a non-dimensional parametrization). Instead, referring to the graph of Fig. 7, on the abscissa the flow (in a non-dimensional parametrization) is reported, while on the ordinate the pressure ratio is reported (in a non-dimensional parametrization). As it can be seen, at an increase of the flow, when water is injected into the gas flow, the power consumption is reduced as well as the pressure ratio, which at a certain threshold is lower than in the case of no water is injected.

[0037] The molecular weight of the process gas (hydrogen, or H2) is temporarily increased by mixing it with water vapor. Fine atomized spray of water is introduced into the gas compression path, which is vaporized upon introduction, thereby cooling the gas and increasing the molecular weight of the gas mixture. This effect reduces the polytropic head required for the compression and hence requires fewer stages and less power to compress the same amount of hydrogen gas.

[0038] The molecular weight of the gas is “temporarily” increased, because the water can be removed till the saturation is reached downstream the cooler 4, which is arranged downstream the compressor 2. As explained earlier, downstream the compressor, the cooler and separator are present, which help achieve the desired effect mentioned above.

[0039] After that the cooler 4 cools down the gas, hydrogen with saturated water vapor is conveyed through the first outlet conduit 42, while the condensate is extracted through a second outlet conduit 43.

[0040] Referring to Figures 8, 9, 10, and 11, additional embodiments of the distribu- tion channel 5 are shown. In general, cooling injection is done only at one or two locations or ports along the 360 degree of the compressor 2. The efficiency of droplet conversion to vapor can be improved by injecting at multiple locations (6-8) at 360 deg of the diaphragm.

[0041] Specifically, referring to a second embodiment illustrated in Figure 8, the toroidal distribution channel 29 has a variable cavity/cross-section to ensure uniform pressure of water injection This is due to the varying resistance offered by the toroidal cavity to the fluid flow at various circumferential positions in the cavity.

[0042] Referring to Figure 9, a third embodiment of the multistage hydrogen centrifugal compressor system 1 is shown, where, to ensure uniform delivery of water into the distribution channel 29, the nozzles 33 have a different flow rate. Specifically, the water to be introduced into the distribution channel 29 is supplied through the water injection conduit 31, and the respective water inlet 27. Therefore, the water pressure to the nozzles 33 closer to the water inlet 27 is higher than that to the farther ones. This difference would cause a non-uniform distribution of the water in different parts of the distribution channel 29, and therefore a non-uniform saturation of the gas. The flow rate of each nozzle 33 is then higher if they are more distanced from the water inlet 27. In this way, it is compensated the lower water pressure to the nozzles 33 that are farther from the water injection conduit 31.

[0043] Therefore, still referring to Figure 9, the flow rate of nozzle 33 placed diametrically opposed to that closer to the water inlet 27, which, as mentioned is connected to the water injection conduit 31 through which the injection unit 3 supplies water.

[0044] Referring to Figure 10, a fourth embodiment of the multistage hydrogen centrifugal compressor system 1 is shown, where it is included equivalent pipe losses to inject at uniform pressure. The individual pipes are aligned such that they provide a varied resistance to the flow. The alignment of the pipes varies with respect to the direction of the fluid flow. The closer to the upper region, the more angled the pipe is with respect to the direction of the flow. The minimum angle is 90 degrees, which is at the bottom, and in the circumferential progression upward, the angles of the respective pipes increases. In this case, there is not a distribution channel 29, instead, an injection pipe connects the water injection conduit 31 to a respective nozzle 33. [0045] Figure 10 depicts an external passage functioning the same as the distribution channel 29, which is designed to deliver fluid (water in this case) at uniform pressure across 360 degrees. At the nearest location to the water injection conduit 31, the resistance from the piping would be maximum and at the farthest location, the resistance would be minimum, thus ultimately ensuring uniform pressure throughout the injection nozzles.

[0046] Also, referring to Figure 11, a fifth embodiment of the multistage hydrogen centrifugal compressor system 1 is illustrated, where the injection unit 3 comprises a plurality of controlled electric valves 34, each one connected to a respective nozzle 33 through a pipe 311. In this way, it is possible to adjust the pressure on each nozzle 33. Specifically, each electric valve 34 can be individually controlled by the control system 32 of the injection unit 3.

[0047] The nozzles 33 can be fixed or retractable. Fixed nozzles are easier to design. However, there is a possibility of the wash nozzles getting clogged when not being used.

[0048] Retractable nozzles 33 can be inserted/retracted when necessary. An advantage of the retractable nozzles 33 is that they can be replaced without stopping the compressor 2. The actuation of the retractable nozzles 33 can be manual or automated.

[0049] While aspects of the invention have been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirt and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

[0050] Reference has been made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to "one embodiment" or "an embodiment" or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase "in one embodiment" or "in an embodiment" or "in some embodiments" in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0051] When elements of various embodiments are introduced, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Claims

Hydrogen Centrifugal Compressor System with Pressure Ratio Enhancement by Water Injection and Operating Method thereof CLAIMS

1. A compressor system (1) to perform the compression of a gas, such as hydrogen and the like, comprising: a multistage compressor (2), having one or more compressing stages (21) capable of increasing the pressure of a gas flow path, characterized in that the compressor system (1) further comprises an injection unit (3), having at least one injection conduit (31) for injecting a fluid, and one or more nozzles (33), each nozzle fluid dynamically connected to a respective injection conduit (31), for injecting the fluid into the gas flow path.

2. The compressor system (1) of claim 1, wherein the fluid has a temperature lower than the temperature of the gas flow, so that when the fluid is injected into the gas flow, the fluid vaporizes upon contact with the gas flow causing the increase of the molecular weight of the gas.

3. The compressor system (1) of claim 2, wherein the fluid has a temperature equal or lower than ambient temperature.

4. The compressor system (1) of any one of the preceding claims, wherein each compressing stage (21) comprises: an impeller (211); a diffuser (212) connected to the impeller (211); a u-bend (213), connected to the diffuser (212); and a return channel (214), connected to the u-bend (213); wherein at least one fluid inlet (27) is obtained on the diffuser (212) or on the u-bend (213), and wherein each nozzle (33) is arranged on a respective fluid inlet (27).

5. The compressor system (1) of claim 4, wherein the multistage compressor (2) comprises a plurality of compressing stages (21), arranged in series, a gas inlet (22), through which the gas enters into the multistage compressor (2), a gas outlet (23), through which the gas comes out after the compression, and a rotating shaft (24), to which the impellers (211) are keyed, to compress the gas.

6. The compressor system (1) of claim 5, comprising cooler (4), having an inlet conduit (41) connected to the gas outlet (23) of the multistage compressor (2), an outlet conduit (42), through which the saturated vaporized fluid is conveyed, and a second outlet conduit (43), through which the condensate of the fluid is extracted.

7. The compressor system (1) of any one of claims 5 - 6, wherein the multistage compressor (2) comprises an external casing (261), and an internal casing (262), which is shaped to contain the compressing stages (21); wherein a distribution channel (29) is obtained in said internal casing (262), wherein the distribution channel (29) is fluid dynamically connected to the injection conduit (31), at a connection point, and to the one or more nozzles (33).

8. The compressor system (1) of claim 7, wherein the distribution channel (29) is formed by a first part (291), and a second part (292).

9. The compressor system (1) of claim 8, wherein the first part (291) has a rectangular cross-section and the second part (292) has a rectangular cross-section, smaller than the first part (291).

10. The compressor system (1) of any one of claims 7-9, wherein the one or more nozzles (33) is installed in the distribution channel (29).

11. The compressor system (1) of claim 10, wherein the flow rate of the one or more nozzles (33) increases as the distance increases between the one or more nozzles and the connection point where the distribution channel (29) is fluid dynamically connected to the injection conduit (31).

12. The compressor system (1) of any one of claims 5-9, wherein the distribution channel (29) has a variable cavity/cross-section.

13. The compressor system (1) of any one of claims 1-6, wherein the injection unit (3) comprises a plurality of controlled electric valves (34), each one connected to a respective nozzle (33) through a respective pipe (311).

14. The compressor system (1) of any one of the preceding claims, wherein the gas is hydrogen, and wherein the fluid is water.