Compression or expansion device, with a piston lacking axial symmetry, with forced external circulation, intended for pseudo-isothermal transformations.

Abstract

A compression or expansion device with a piston lacking axial symmetry and forced external circulation, designed for pseudo-isothermal transformations. The invention relates to a device that reduces the temperature rises or falls of a fluid (3) during these thermodynamic transformations. It consists, at a minimum, of an elongated sealed cylinder (1), a movable solid or liquid piston (2) performing the compression or expansion, a fluid (3) undergoing this transformation, and two orifices providing the outlet (11) and inlet (10) of the fluid (3). External to the cylinder (1), the device includes a heat exchanger (4), pipes (6), and a blower (5). In the case of a liquid piston, a pump or hydraulic expander (8) ensures the movement of the hydraulic fluid (9) via a hydraulic orifice (14). The device may include movable physical separations, impermeable to the fluid (4), and external thermal reservoirs (7).The device is designed to improve the thermodynamic performance of compressors, turbines, heat pumps, ORCs, energy storage systems, and liquefaction units. Figure for the abstract: Fig. 2.

Description

Title of the invention: Compression or expansion device, with piston lacking axial symmetry, with forced external circulation, intended for pseudo-isothermal transformations.

[0001] The present invention relates to a device for compressing or expanding gaseous or supercritical fluids, intended to ensure pseudo-isothermal thermodynamic transformations.

[0002] In the field of compression or expansion of gaseous or supercritical fluids, the easiest equipment to build, seal, and operate almost always possesses axial symmetry in its main component that performs this compression or expansion. Thus, radial turbine, axial turbine, circular piston, helical screw, and vane compressors and expanders are extremely common. Even the various scroll compressors benefit from the uniformity of axial symmetry in their rotation.

[0003] Due to this characteristic, the compressions or expansions performed by these conventional devices follow an adiabatic thermodynamic transformation without any possible heat exchange, often called pseudo-isentropic. The term "pseudo" here reflects the fact that all devices also introduce a certain level of thermodynamic irreversibility compared to an ideal transformation. Any compression or expansion of the fluid will produce a rise or fall in its temperature, which can be interpreted according to the isentropic curve of the Enthalpy-Pressure diagram of the fluid in question, taking into account irreversibilities.

[0004] In a few rare applications, this raising or lowering of the temperature of the compressed or expanded fluid can represent an operational advantage. However, whenever the objective of this compression is purely to increase the fluid pressure, it can be calculated that, depending on the fluid composition, its initial states of pressure, temperature and specific volume, and depending on the desired compression ratio, the work required for this pseudo-isentropic compression is unfortunately 20% to 50% greater than that required for a pseudo-isothermal, i.e., non-adiabatic compression.

[0005] Similarly, whenever the objective of an expansion is purely to produce work, it can be calculated that, depending on the composition of the fluid, its initial states of pressure, temperature and specific volume, and depending on the desired rate of expansion, the work that could be produced by a pseudo-isothermal expansion would be 20% to 50% greater than that produced by a pseudo-isentropic adiabatic expansion.

[0006] For many years, numerous inventions have sought to approximate isothermal compression, naturally through the extraction or addition of heat during the transformation. These devices or processes are often complex, yet their results are modest. The most widespread method is staged compression or expansion, which employs a costly plurality of compressors or expanders, benefiting from heat extraction or addition between these stages. Another method is the injection of liquid droplets (of the fluid itself, or alternatively water or oil) during compression, such as the device described in patent EP2449259B1.Another method exploits the fact that the liquid in a "liquid piston" moistens, as it moves, a hollow mass with a large heat exchange surface (with walls, fins, or a highly porous packing), such as the device described in US patent 4446698A, which will reduce the temperature variation experienced by the fluid to be compressed or expanded.

[0007] In the invention that is the subject of this application, our simulation work has allowed us to explore a promising new path, but one which requires moving away from the ease of construction, sealing and operation of existing devices, which benefit from axial symmetry at the level of their main component ensuring this compression or this relaxation.

[0008] In addition to applications to pure compressions and pure expansions of industrial fluids or common natural fluids (O2, N2, CO2, CH4, NH3, H2O, H2, etc.) for densification, expansion or for uses of these fluids as refrigerants for thermodynamic cycles, this invention could also greatly facilitate the most complex liquefactions of fluids, by eliminating stages and / or reducing the number of multiple refrigerant cascades.Thanks to the progress of pseudo-isothermal compression, it would be possible, for example, to consider a significant simplification of methane liquefaction processes via the refrigeration of R744 (aka CO2), or the significant simplification of hydrogen liquefaction, which is very costly in capex and energy at currently 12-15 kWh / kg H2, via a simple cascade of refrigeration with R744 refrigerant liquefying R728 refrigerant (aka N2), and also ensuring the extraction of heat related to the conversion of ortho H2 into para H2.

[0009] In the device of the invention, the main physical component ensuring compression or expansion loses all axial symmetry and consists of one or more elongated pistons and cylinders, with a length-to-width ratio generally between 1.50 and 15 depending on the desired level of isothermal insulation, and equipped with at least two ports for the fluid's outlet and inlet at the ends of the elongated cylinder. The device also includes support for one or more external heat exchangers for the necessary heat extraction or input, as well as that of an external variable-speed blower. Forced external circulation is thus ensured in a closed loop between these components. It is estimated that the blower consumes significantly less energy than the energy saved through these pseudo-isothermal transformations.

[0010] In the pseudo-isothermal compression operation of a gaseous or supercritical fluid, the rapid circulation of the fluid along the longitudinal axis of the elongated cylinder allows it to undergo only a short compression at the molecular level before being immediately cooled to a set temperature in the external heat exchanger. The fluid is continuously imparted kinetic energy by the external blower. These fluid molecules then re-enter the cylinder-piston assembly to undergo further short compressions. This continues until the fluid reaches the desired pressure rise.

[0011] In the pseudo-isothermal operation of expansions of a gaseous or supercritical fluid, the rapid circulation of the fluid along the longitudinal axis of the elongated cylinder allows it to undergo, at the molecular level, only a short expansion before being immediately reheated to a set temperature in the external heat exchanger, the fluid being continuously imparted kinetic energy by the external blower. These fluid molecules then re-enter the cylinder-piston assembly to undergo further short expansions. This continues until the fluid reaches the desired pressure reduction.

[0012] Of course, it is necessary to tolerate a small variation in the temperature of the fluid in the elongated cylinder-piston assembly, for example of 5, 10 or 15 Kelvin, so that the heat exchange, generally by sensible heat, can be carried out in the external exchanger.

[0013] In a preferred embodiment of the invention, a liquid-piston, using the movements of a hydraulic fluid by one or more hydraulic pumps or expanders, achieves the volume change necessary for compression or expansion, always within an elongated cylinder. The sealing problems expected with non-cylindrical solid pistons are thus avoided in this embodiment, although a regular ovalization at its ends should allow an elongated solid piston to operate without excessive leakage, as demonstrated by a Japanese Honda NR750 racing motorcycle in 1979-80.

[0014] An improvement can be made to the piston-liquid device in that, to limit the risks of dissolution of the fluid in the hydraulic fluid—a dissolution detrimental to maintaining its mass in the device and detrimental to the operation of the hydraulic pump or expander due to the onset of cavitation—a movable physical separation between the hydraulic fluid and the fluid to be compressed or expanded can also be provided. This separation can This can be achieved, for example, by confining the hydraulic fluid and / or the fluid to be compressed or expanded using flexible cover(s), such as a membrane or bladder, or by incorporating a specific separating fluid or a floating solid membrane at the interface between the propellant fluid and the hydraulic fluid. A specific adjustment of the hydraulic fluid's pH can sometimes also address this dissolution issue.

[0015] The attached drawings illustrate the invention:

[0016] [Fig. 1] shows, in the particular case of the Enthalpy-Pressure diagram of the fluid CO2, the difference in enthalpy variations between a conventional isentropic compression, of segment AB, followed by the cooling of segment BC, and an isothermal compression of segment AC, of ​​the same starting and ending points, carried out by 11 circulations tolerating a temperature increase of 15 Kelvin, or carried out by 32 circulations tolerating a temperature increase of 5 Kelvin.

[0017] [Fig.2] describes the entire device in the preferred liquid piston mode. The An elongated cylinder (1) receives the liquid piston (2). The fluid (3) circulates in the external heat exchanger (4) via the external blower (5), through the pipes (6), from the outlet port (11) to the inlet port (10). The movement of the liquid piston is ensured by a pump or hydraulic expander (8) allowing the hydraulic fluid (9) to enter and exit through the hydraulic port (14). External thermal reservoirs (7), which can simply be the environment, allow for the extraction or supply of heat.

[0018] [Fig. 3] shows a detailed cross-sectional view of the elongated cylinder (1). The latter receives the piston liquid (2). The fluid outlet ports (11) and the fluid inlet ports (10) are clearly visible, as is the hydraulic port (14). The elongated cylinder (1) must be able to withstand high pressures; therefore, it is fitted here with flanges (12) allowing the attachment of its ends (13), which are movable here for ease of assembly.

[0019] [Fig. 4] shows a 3D view of the elongated cylinder (1). The fluid outlet ports (11) are obscured, while the fluid inlet ports (10) and the hydraulic port (14) are clearly visible. The elongated cylinder (1) must be able to withstand high pressures; therefore, it is fitted here with flanges (12) for securing its ends (13), which are movable for ease of assembly.

[0020] [Fig. 5] illustrates the mesh of a finite element simulation of the circulation of the fluid (3) and its states of pressure, temperature and specific volume at different points internal to the cylinder-piston assembly.

Claims

Demands

1. The device consists of at least one cylinder (1), at least one movable physical component ensuring compression or expansion, materialized by one or more pistons, including the choice of a liquid piston (2) in a preferred embodiment of the invention, at least one fluid (3) undergoing this compression or expansion in gaseous or supercritical phase, at least two orifices dedicated to the outlet (11) and the inlet (10) of the fluid (3) at the ends of the length of the cylinder (1) as well as at least one heat exchanger (4) connected by pipes (6) incorporating an external variable speed blower (5), a forced external circulation thus being ensured in a closed loop between these pieces of equipment, characterized by the fact that the cylinder (1) has an elongated shape, with a length-to-width ratio generally between 1.50 and 15 along its longitudinal axis.

2. Device according to claim 1 characterized in that a liquid piston (2), using the movements of a hydraulic fluid (9) by one or more hydraulic pumps or expanders (8) is assigned the function of carrying out, via a hydraulic orifice (14), the variation in volume necessary for the compression or expansion of the fluid (3) in the elongated cylinder (1).

3. Device according to claim 2 characterized in that, to prevent dissolution of the fluid (3) in the hydraulic fluid (9), a movable physical separation is provided, such as one or more flexible tarpaulins in the form of a membrane or bladder, or a floating solid membrane, or a specific separation fluid, or a specific adjustment of the pH of the hydraulic fluid (9).

4. Use of a device according to any one of claims 1 to 3 for carrying out pseudoisothermal compressions or expansions of a fluid (3) for the purpose of producing heat or cold, or absorbing or producing work, or simplifying certain gas liquefaction cycles.

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