Device for providing gases at increased pressure

Abstract

The invention relates to a device for providing gases at increased pressure, said device consisting of: at least one hollow housing (1), the cavity of which is filled with an open-pore metal structure and a phase-change medium and to which a connection line (3.1) is connected that is connected to at least one compressor (3); and at least one supply (4) and at least one discharge (4) for the alternating supply of temperature-control fluid at different temperatures in order to melt and solidify the phase-change medium. According to the invention, an incompressible liquid is present at least in the connection line (3.1) and on one side of the compressor (3).

Description

[0001] Device for providing gases at increased pressure

[0002] The invention relates to a device for providing gases at elevated pressure. In particular, compressed air can be provided.

[0003] The technical and economic potential for waste heat utilization (temperature level < 100 °C) amounts to approximately 18% of the final energy consumption of German industry (Pehnt , M.; Bödeker, J.; Arens, M.; Jochem, E.; Idrissova , F., 2010), but only a few processes allow the sensible use of waste heat with a

[0004] Temperature level of well below 100°C. Around 7% of industrial electricity consumption in Germany is used to generate compressed air. Compressed air is also a very expensive form of energy, as only approximately 7% of an air compressor's electrical power consumption is converted into mechanical compression work. Despite the associated technical complexity, an investment in systems for generating compressed air using waste heat could pay for itself within a reasonable period of time (Nuremberg Chamber of Industry and Commerce for Middle Franconia, 2012). The invention also solves the problem of converting low-level waste heat into mechanical energy in a more economical way, thus significantly reducing the electricity consumption for generating compressed air in industrial plants with small to medium compressed air requirements.

[0005] In principle, the aim of compressor systems is to create a modular arrangement of several small compressors that respond more efficiently to different consumption requirements and thus save energy compared to a single large compressor. However, these small systems are generally not equipped with waste heat recovery, resulting in very poor overall efficiency. The use of mechanical energy by directly coupling compressors to motors, for example, in combined heat and power (CHP), is another option for using the required energy for secondary processes in parallel. However, in this case, the electrical power, not the resulting waste heat, is used for compression.

[0006] By using the waste heat from large compressor systems > 100 kW (approximately 75% of the power consumption due to heat loss) for other ancillary processes in production, such as heating, air conditioning, process water, etc., the expensive compressed air generation is indirectly partially offset. However, this is uneconomical for smaller applications.

[0007] Very large compressor systems also use their own waste heat to improve compression efficiency, but this is uneconomical for low compressed air requirements.

[0008] The use of low-level waste heat generated in other operational processes has so far been limited to the immediate needs of the plant for domestic water heating or preheating processes in production. Often, the waste heat generated significantly exceeds these needs, so the excess waste heat must be dissipated unused into the environment.

[0009] It is known to utilize the volume change of a phase-change material (PGM) during a phase change from solid to liquid to generate mechanical energy using pistons or rotary pistons. However, concepts for minimizing cycle times during phase changes to such an extent that economical operation and sufficiently small sizes can be achieved are lacking. Power density data are not provided.

[0010] It is therefore an object of the invention to provide possibilities with which the cycle time and the efficiency in the compression of a gas can be shortened or increased by utilizing the volume change of a phase change medium during its phase change.

[0011] According to the invention, this object is achieved with a device having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in the dependent claims.

[0012] A device according to the invention for providing gases at elevated pressure consists of at least one internally hollow housing, the cavity of which is filled with an open-pore metal structure and a phase change medium, and to which a connecting line is connected to at least one compressor. Furthermore, at least one inlet and at least one outlet are provided for an alternating supply of temperature control fluid at different temperatures for melting and solidifying the phase change medium. An incompressible liquid is also contained at least in the connecting line and on one side of the compressor. Multiple inlets and outlets, each arranged at a distance from one another, are advantageous in order to achieve a faster heating or cooling rate and / or a more uniform temperature transfer during the phase changes.

[0013] Phase-change media are preferably those whose melting point lies within a temperature range in which the waste heat from an industrial process is also to be utilized and whose maximum usable temperature is below 100 °C, especially below 60 °C. In principle, gases or liquids can be used as temperature control fluids. For example, air or water are just as suitable as any other fluid. However, it should ideally not undergo a phase change from gaseous to liquid or even solid within the temperature range used for the operation of the device.

[0014] The device can then be operated by first adding a temperature control fluid at a temperature lower than the melting point of the phase change medium, which is then cooled to a temperature below the melting point. The phase change medium then solidifies and its volume decreases, resulting in a pressure drop in the cavity, the connecting line, and on one side of the compressor cylinder. This pressure drop causes a compressor piston to move towards the connecting line, or a diaphragm in a diaphragm compressor to deform accordingly. This allows a gas to be sucked in on the opposite side of the compressor with the intake valve open. This gas will later be compressed when the phase change from solid to liquid occurs, thereby increasing the volume of the phase change medium.This increases the pressure on the side facing the connecting line in the compressor cylinder, which in turn is used to move the piston or deform the diaphragm in the opposite direction, thereby compressing the gas previously drawn into the cylinder. The compressed gas can be discharged from the cylinder via a valve and then used.

[0015] The valves can be designed as check valves that open or close depending on the applied pressure.

[0016] However, at least one pressure and / or temperature sensor can also be installed inside the housing. The measured values ​​can then be used to influence the opening and closing of the valves for the intake and compression of the respective gas in the compressor cylinder.

[0017] The incompressible fluid transmits the forces that lead to the movement or deformation of the moving parts of the compressor as a result of the volume change of the phase change medium.

[0018] The open-pore metal structure should have a porosity of at least 80%, preferably at least 90%. In principle, any metal can be used, but those with good thermal conductivity, such as Cu or Al, are preferred, with Al being preferred for cost reasons. Alloys can also be used.

[0019] The open-pore metal structure is preferably a fiber structure, in which the metal fibers are preferably aligned largely parallel to the main heat flow direction in the phase change medium. Metal fibers can particularly advantageously be aligned perpendicular to the flow direction of the temperature control fluids, so that the thermal conduction from the respective temperature control fluid to the phase change medium can be further improved.

[0020] By combining a phase-change medium with an open-pore metal structure, the thermal conductivity of the metal can be utilized to shorten the time required for each phase change, which in turn can be used to shorten the cycle time during device operation. A phase change, regardless of direction, can be achieved in approximately 30 seconds or less, resulting in a cycle time of approximately 60 seconds or less.

[0021] The at least one compressor can be a piston compressor or a diaphragm compressor.

[0022] Advantageously, the cavity of the housing should be filled with the phase change medium in its solidified state such that the cavity is filled to a maximum of 90%, preferably a maximum of 80%, with phase change medium and the open-pore metal structure, and the free remaining cavity in the housing is filled with the incompressible liquid. It is particularly advantageous if the volume of the cavity not filled with solid phase change medium and metal at least approximately corresponds to the change in volume that occurs during a phase change from solid to liquid. This ensures that at least the largest part of the phase change medium is in direct contact with the metal of the open-pore metal structure throughout the entire operating time of a device according to the invention. This contributes to shortening cycle times during phase changes and can therefore increase efficiency.If this condition is not met, liquid phase change medium outside the area of ​​the open-pore metal structure will solidify considerably more slowly than material inside the structure and would thus lead to a considerable extension of the cycle time during solidification.

[0023] The phase change medium should have a melting temperature in the range of 20 °C to 120 °C. A temperature control fluid should be supplied alternately, once at a temperature that is at least 5 °C lower than the respective melting temperature of the phase change medium, and then a temperature control fluid with a temperature that is at least 5 °C higher than the respective melting temperature of the phase change medium.

[0024] The supplied volume flow of cold tempering fluid should be selected so that during the entire time required for the phase change medium to solidify, the temperature of the cold tempering fluid does not exceed the melting temperature of the phase change medium. During the time required for the phase change medium to melt, the temperature of the warm tempering fluid should not fall below the melting temperature of the phase change medium by maintaining an appropriately large volume flow.

[0025] In principle, gases can be used as a temperature control fluid by simply flowing along or against the outside of the housing to either cool or heat it according to the respective phase change. The surface area of ​​the housing should be enlarged using contour elements such as ribs, which can be particularly advantageous for gaseous temperature control fluids.

[0026] However, it is possible to pass the temperature control fluid through at least one temperature control chamber that is in contact with the housing.

[0027] However, since liquids generally have a higher heat capacity, the use of temperature control chambers through which liquid temperature control fluid flows is more advantageous. This also means that the ambient environment is not as affected as with freely flowing gases.

[0028] For this purpose, the housing can be arranged between two temperature control chambers through which the temperature control fluid flows. Thermal insulation and / or a pressure plate can be arranged on two oppositely arranged, outward-facing surfaces. The thermal insulation and / or the pressure plates with the temperature control chambers can be clamped to one another with the housing by means of clamping elements. Pressure plates can lead to a uniform force effect of the clamping elements on the other elements of the device, thus preventing damage. Such arrangements can also be formed from several such structures, which can be arranged in series and / or parallel.

[0029] To achieve an output of 1 kW, a maximum of 5 kg, preferably a maximum of 4 kg, of phase change medium should be contained in the cavity.

[0030] The compressor concept proposed here, which can be operated with waste heat, enables the in-house use of low-temperature waste heat (< 125 °C, preferably below 80 °C) from production processes for the compression of gases, especially compressed air or industrial gases, thus opening up additional waste heat utilization potential for most companies. This minimizes conventional pressure generation with electrically operated compressors and also increases energy efficiency by utilizing existing and previously unused waste heat.

[0031] For this purpose, the volume change of phase change media (PCM), particularly those based on paraffins, is utilized during melting / solidification. The basic structure of a so-called PCM compressor module consists of a thermal linear drive, the compressor, and, if required, a power transmission, which can be either hydraulic or directly mechanical.

[0032] The thermal linear actuator can be equipped with temperature-controlled housings in which open-pore metal structures (50% to 90% open porosity) infiltrated with PCM are installed. The PCM in the housing is temperature-controlled via fluid-controlled heating / cooling chambers (temperature control chambers), through which hot and cold temperature control fluids flow cyclically. Depending on the temperature level of the low-temperature waste heat, a PGM can be selected that melts when exposed to hot temperature control fluid and then solidifies again when exposed to cold temperature control fluid. The use of porous metal structures in the PCM enables rapid melting and solidification (1 cycle = melting + solidification) in < 60 s. This is what makes economical operation possible, as the thermal conductivity of the metal in contact with the PCM allows sufficiently short cycle times to be achieved and the size of the device to be minimized.During the phase change of the PCM, for example, volume changes of approximately 12% are possible with paraffins. The resulting linear movement of a drive can be transmitted either by a hydraulic fluid or directly mechanically to a piston or diaphragm compressor. Since the energy input should only be applied to the PCM and the temperature control components, the compact pressure chamber in the hollow housing should be thermally insulated to absorb the actual force to the PCM module. The expansion of the PCM generates very high forces, which, according to measurements on the paraffin RT42, correspond to a pressure of 800 bar. If lower ultimate pressures are to be provided, correspondingly larger gas volumes can be compressed to the ultimate pressure in just one cycle by selecting an appropriate volume ratio.The waste heat released during compression can be reused to operate the device by using the waste heat to heat the tempering fluid used for melting.

[0033] The use of thermally conductive structures formed with the open-pore metal structure in the PCM leads to faster energy transport throughout the entire PCM volume compared to the state of the art, resulting in increased dynamics during device operation. This, along with the serial connection of several housings with corresponding accessories used for temperature control, enables a faster operating frequency. In contrast to known technical solutions, the high power density and dynamics enable a very compact system volume of approximately 40 l to be realized for a device whose compression power can correspond to an electrically driven compressor in the 5 kW class. The short cycle time (melting + solidification) enables the realization of a large number of compression cycles per unit time. As the number of cycles increases, the amount of compressed gas obtained also increases.Thus, as the number of cycles increases, the costs for a given amount of compressed gas produced also decrease. Only by utilizing this concept with a correspondingly rapid phase change of the PGM can specific costs per amount of compressed air produced be achieved, specifically for compressed air, which are economically competitive with conventional (electric) compressors.

[0034] The integration of the thermally driven compressor module into a central compressed air supply, which can be supplied by the low-temperature waste heat from internal production processes that is normally dissipated unused, leads to the following advantages:

[0035] • Reduction in electrical energy consumption and thus operating costs for in-house compressed air generation. Theoretically, it would also be possible to initially generate electricity using low-level waste heat with an ORC process and then use this electricity for compressed air generation using electrically operated compressors. However, since the ORC process is also a heat-power process, which, for thermodynamic reasons, is associated with similarly low exergetic efficiencies as the direct compressed air generation using a device according to the invention, the compressed air yield per unit of waste heat would be considerably lower via this detour.

[0036] • Possibility of downscaling the compressors used in the event of a replacement investment or modernization of existing compressor stations.

[0037] • Replacement of high-quality electrical energy with generally unused low-temperature waste heat.

[0038] • Scalable design concept enables easy adaptation to different performance requirements and the available waste heat quantities.

[0039] • The new construction concept enables the costs of compressed air generated using low-temperature waste heat instead of electrical energy to be reduced to such an extent that the investment costs are amortised in a short time.

[0040] The invention can be used as a replacement or extension of existing systems for industrial compressed air generation. Compressed air applications, e.g., for cleaning, cooling, and pneumatics.

[0041] The pumping of gases or liquids in systems (e.g. thermally operated piston pump in a heating or cooling circuit) is also a possible area of ​​application.

[0042] The invention will be explained in more detail below by way of example.

[0043] It shows:

[0044] Figure 1 shows in schematic form an example of a device according to the invention.

[0045] In the example shown in Figure 1, a housing 1 is present, the cavity of which contains approximately 25 kg to 30 kg of RT42 as a suitable paraffin (melting point approx. 42 °C, latent heat 135 kJ / kg, specific heat capacity 2 kJ / (kg*K)) as a phase change medium, as well as aluminum metal fibers as an open-pore metal structure with a porosity of 90%. The cavity inside the housing 1 is thus 90% filled. The remainder of the cavity and a connecting line 3.1 leading to a compressor 3 contain a synthetic hydraulic oil as an incompressible fluid. By means of the hydraulic fluid, changing pressures, which vary depending on the instantaneous volume filled by the phase change medium in the cavity of the housing 1, can be used to move a piston or deform a diaphragm inside the compressor 3 in order to influence the pressure inside the cylinder on the other side.The compression and suction of the gas to be compressed by the device can be achieved as explained in the general part of the description.

[0046] In this example, the housing 1 is arranged between two temperature control chambers 2, with the outer walls of the housing 1 and the temperature control chambers 2 preferably being in direct, flat contact with each other. This can be achieved by means of the clamping elements 6, which in this example are formed by U-profiles with screw connections. For better insulation and a more even distribution of pressure force, thermally insulating pressure plates 7 are arranged on the outward-facing surfaces of the temperature control chambers 2 and are also clamped with the clamping elements 6.

[0047] At least one supply line 4 and at least one outlet line 5 for a temperature control fluid are connected to each of the temperature control chambers 2. The supply line 4 and the outlet line 5 are arranged in the region of opposite end faces of the temperature control chambers 2, so that the respective temperature control fluid flows through at least almost the entire length of the respective temperature control chamber 2, and a corresponding heat exchange between the temperature control fluid and the contents of the cavity inside the housing 1 can be achieved, with which the entire volume can be cooled to solidify the phase change medium or heated to melt the phase change medium.

[0048] The compressor 3 can be a piston compressor or a diaphragm compressor.

[0049] With the device a compression power of up to 5 kW can be achieved.

Claims

Patent claims 1. Device for providing gases at increased pressure, comprising at least one internally hollow housing (1), the cavity of which is filled with an open-pore metal structure and a phase change medium, and to which a connecting line (3.1) is connected, which is connected to at least one compressor (3), as well as at least one feed (4) and at least one discharge (4) for an alternating feed of tempering fluid at different temperatures for melting and solidifying the phase change medium, an incompressible liquid being contained at least in the connecting line (3.1) and on one side of the compressor (3).

2. Device according to claim 1, characterized in that the open-pore metal structure has a porosity of at least 70%, preferably at least 80%.

3. Device according to one of the preceding claims, characterized in that the compressor(s) (3) is / are a piston compressor or a diaphragm compressor.

4. Device according to one of the preceding claims, characterized in that the open-pored metal structure is a fiber structure in which the fibers in the plane of the main heat conduction direction are aligned largely parallel to this plane, or an open-pored metal foam.

5. Device according to one of the preceding claims, characterized in that the cavity of the housing (1) is filled with the phase change medium in its solidified state in such a way that the cavity is filled to a maximum of 90% with phase change medium and open-po- rous metal structure and the free remaining cavity in the housing (1) is filled with the incompressible liquid.

6. Device according to one of the preceding claims, characterized in that the phase change medium has a melting temperature in the range 20 °C to 120 °C and tempering fluid can be supplied alternately once with a temperature which is at least 5 °C lower than the respective melting temperature of the phase change medium and then with a temperature which is at least 5 °C higher than the respective melting temperature of the phase change medium.

7. Device according to one of the preceding claims, characterized in that the housing (1) is arranged between two temperature control chambers (2) through which the temperature control fluid flows.

8. Device according to one of the preceding claims, characterized in that a thermal insulation and / or a pressure plate (7) is arranged on two oppositely arranged surfaces on which the pressure plates point outwards, and the pressure plates (7) are clamped against one another with the temperature control chambers (2) and the housing (1) by means of clamping elements (6).

9. Device according to one of the preceding claims, characterized in that in order to achieve an output of 1 kW, a maximum of 5 kg, preferably a maximum of 4 kg, of phase change medium is contained in the cavity.

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