Energy storage application of phase change material in refrigeration chemical production process

Abstract

Systems and methods for storing energy for refrigeration in a chemical separation process of a chemical plant are disclosed. Some such systems include: a phase change material (PCM); and a refrigerant circuit configured to circulate a refrigerant fluid in thermal communication with the PCM such that the PCM absorbs thermal energy from the refrigerant fluid at a point in a refrigeration cycle of the process. Some such methods include, during a release cycle, circulating a refrigerant fluid in thermal communication with a phase change material (PCM) such that the PCM absorbs thermal energy from the refrigerant fluid at a point in a refrigeration cycle of the process; wherein the PCM absorbs at least 10 MWh of energy from the refrigerant fluid during a period of 24 hours. The PCM is generally configured to transition from an initial state to a higher enthalpy state at the point in the refrigeration cycle at a transition temperature below a minimum operating temperature.

Description

Technical Field

[0001] The present disclosure relates generally to refrigeration circuits used in processes for producing chemicals, and more particularly, but not limited to, to using phase change materials (PCMs) to store refrigeration energy in chemical production processes. Background Art

[0002] As chemical plants shift from burning fossil fuels to meet daily energy needs to using electricity from the grid and / or from renewable energy, the availability and cost of electricity will change over time. For example, electricity from the grid is usually more expensive during peak hours. In addition, the generation of solar and wind energy varies with the time of day and weather conditions, for example, the night time and cloudy time period will reduce or interrupt the power generation of solar panels. Similarly, during periods of slow wind speed or no wind, the power generation of wind turbines will be reduced or interrupted. In addition, during peak hours when power production or grid capacity is tight, power companies may provide discounts to customers who can flexibly adjust consumption needs. Storing energy can avoid energy consumption from some external sources (such as the grid, solar energy, wind energy, etc.) during periods when energy is more expensive (such as peak hours) or periods when energy availability is limited (such as dark hours for solar energy or static hours for wind energy). Reducing external energy demand during peak hours of the grid also has the additional benefit of promoting grid stability. However, from a commercial perspective, it is usually very important for chemical plants to maintain consistent production, even during periods when external energy demand is reduced, that is, even when relatively less electricity is obtained from external sources. Summary of the invention

[0003] The systems and methods of the present invention utilize phase change materials (PCMs) to absorb thermal energy to operate or supplement a refrigeration cycle in a chemical separation process of a chemical plant, for example, a refrigeration cycle in which a compressor is driven by an electric drive (rather than burning fossil fuels). The PCM is "charged" by removing thermal energy from the PCM to transform the PCM from an initial state to a state of higher enthalpy, and then the PCM is "discharged" by absorbing thermal energy from the refrigeration cycle to reduce the external energy required for the refrigeration cycle (e.g., from electricity or the combustion of fossil fuels). For example, during periods when electricity from renewable energy sources is less or unavailable (e.g., during periods of reduced sunlight from a solar power source, or reduced wind from a wind power source) or when electricity from the grid is more expensive or unavailable (e.g., during peak hours, when the power company requires reduced electricity use to ensure grid stability, or during grid outages), the PCM can be used to reduce external energy requirements. It is believed that such uses of PCMs have never been used before for refrigeration in chemical separation processes in chemical plants, at least in part because such chemical separation processes require large amounts of energy. Traditionally, the scale of such energy requirements has been both cost-prohibitive and hampered by the technical challenges inherent in using PCMs to store such large amounts of energy. In addition, chemical processes that utilize refrigeration loops (e.g., steam crackers and ammonia plants) use steam derived from the combustion of fossil hydrocarbons as the primary energy source for refrigeration; although fossil hydrocarbons emit CO 2, but they are relatively unaffected by changes in electricity prices or energy supply needs. Additionally, some previous uses of PCM for "storing" energy generally recover the energy in the form of electricity, resulting in reduced efficiency, relative to the current use of PCM for absorbing heat energy from chemical separation processes (which does not require further conversion of heat energy into electricity). When used for refrigeration in chemical separation processes, PCM will generally have scalability advantages and other benefits over cryogenic liquefied storage systems. For example, PCM can be selected from materials that are not easy to burn, so it can be stored in large quantities and has lower safety risks. For liquefaction systems, for example, liquid nitrogen can be used instead of liquid ethylene to do this, but relative to hydrocarbon liquefaction, the cost is poor characteristics in terms of heat capacity and energy storage density. Another advantage includes avoiding the undesirable characteristics of gas phase materials, such as the need for large volumes and poor thermal conductivity. Liquefied gases generally have relatively high energy storage densities, but such gases generally require a large storage volume when in a gaseous state (unless air that can be discharged to the atmosphere is used, but doing so requires inhalation of replacement air at ambient temperature). Additionally, liquid thermal conductivity is typically 10 times or more that vapor thermal conductivity; for example, liquid ethylene and liquid nitrogen have thermal conductivities of 0.18 W / m / K and 0.155 W / m / K, respectively, while both ethylene vapor and nitrogen vapor have thermal conductivities of only 0.017 W / m / K. Higher thermal conductivity is very important for being able to access stored energy over a large energy storage volume in a reasonable amount of time. Even so, there is a tradeoff in that the enthalpy of fusion is typically much smaller than the enthalpy of vaporization for the same material. As an example, the enthalpy of fusion of ethylene is only 119 kJ / kg, while its enthalpy of vaporization is 482 kJ / kg. However, the other benefits of using a solid-liquid PCM, relative to cryogenic liquefaction, which instead relies on a gas-liquid transition, typically outweigh this tradeoff.

[0004] Solidifying the PCM requires the removal of thermal energy from the PCM; however, such removal of energy from the PCM is referred to herein as "charging" the PCM, because removing thermal energy to "charge" the PCM requires energy (from electricity or combustion of fossil fuels) to drive one or more compressors in the refrigeration cycle that cools the PCM. Once cooled and thus solidified, the PCM can absorb thermal energy from the chemical separation process that would otherwise require further operation of the compressors to continue to drive the refrigeration cycle of the chemical separation process. Thus, the initial removal of thermal energy from the PCM effectively "stores" energy that would otherwise be required to run the refrigeration cycle of the chemical separation process during the period in which the PCM is "discharged" by absorbing thermal energy from the chemical separation process.

[0005] For example, when a chemical plant draws energy from the grid, differences in electricity prices at different times of the day can be used to draw more energy from the grid during off-peak hours (when electricity is less expensive) to (a) run compressors in the refrigeration cycle of the chemical separation process and (b) to charge the PCM, and then to draw less energy from the grid during peak hours (when electricity is more expensive) by using the PCM to absorb thermal energy from the chemical separation process, replacing or combining with the compressor that may be used exclusively for the refrigeration cycle during off-peak hours. In some configurations, the compressor used in the refrigeration cycle of the chemical separation process may be larger than required for the chemical separation process, so that the compressor can be used for both the chemical separation refrigeration cycle and the PCM refrigeration cycle to charge the PCM. In other configurations, one or more separate compressors may be used for different PCM refrigeration cycles used when charging the PCM.

[0006] In some configurations of the system of the present invention for storing energy for refrigeration in a chemical separation process in a chemical plant, the system includes: a phase change material (PCM) (e.g., disposed in one or more insulated vessels); a refrigerant circuit configured to circulate a refrigerant fluid in thermal communication with the PCM so that the PCM absorbs thermal energy from the refrigerant fluid at a point in the refrigeration cycle of the process; wherein the PCM is configured to transition from a first state to a second state at this point in the refrigeration cycle at a transition temperature that is lower than a minimum operating temperature; wherein the PCM requires at least 10 MWh (e.g., 20 MWh, 30 MWh, 50 MWh, 100 MWh, 150 MWh, 200 MWh, 300 MWh, 500 MWh, 1000 MWh or more) to transition from the first state to the second state.

[0007] In some configurations of the systems of the present invention, the refrigerant circuit is part of a refrigeration system, the refrigeration system including a compressor configured to compress a refrigerant fluid so that the refrigerant fluid can be circulated to absorb thermal energy from the process, and the system is configured to: receive a cooled refrigerant fluid from the refrigeration system and circulate the cooled refrigerant fluid through the refrigerant circuit so that the refrigerant fluid absorbs thermal energy from the PCM; or receive a heated refrigerant fluid from the process and circulate the heated refrigerant fluid through the refrigerant circuit so that the PCM absorbs thermal energy from the heated refrigerant fluid. In some such systems, the refrigerant fluid is a first refrigerant fluid and the refrigerant circuit is a first refrigerant circuit, and the system further includes: a PCM refrigeration circuit including a compressor, and a second refrigerant circuit configured to circulate a second refrigerant fluid in thermal communication with the PCM so that the second refrigerant fluid absorbs thermal energy from the PCM.

[0008] In some configurations of the system of the present invention, the one or more insulated vessels are first insulated vessels, and the PCM is a first PCM, and the system further comprises: one or more second insulated vessels; a second phase change material (PCM) disposed in the second insulated vessel, the second PCM being configured to transition from an initial state to a state of higher enthalpy at a second transition temperature higher than the transition temperature of the first PCM; wherein the second PCM requires at least 10 MWh to transition from the initial state to the state of higher enthalpy. In some such configurations, the PCM, the second PCM, or both the first PCM and the second PCM together require at least 100 MWh (e.g., 150 MWh, 200 MWh, 300 MWh, 500 MWh, 1000 MWh, or more) to transition from the first state to the second state. In some implementations of the method of the present invention for storing energy for refrigeration in a chemical separation process of a chemical plant, the method includes: during a discharge cycle, circulating a refrigerant fluid in thermal communication with a phase change material (PCM) such that the PCM absorbs thermal energy from the refrigerant fluid at a point in the refrigeration cycle of the process; wherein the PCM is configured to transition from an initial state to a liquid state at a transition temperature below the lowest operating temperature of the refrigerant at the point in the refrigeration cycle; and wherein during a 24-hour period, the PCM absorbs at least 10 MWh of energy from the refrigerant fluid. In some such implementations, the method also includes: during a recharge cycle, circulating the refrigerant fluid in thermal communication with the PCM such that the refrigerant fluid absorbs thermal energy from the PCM until a majority (e.g., substantially all) of the PCM is in a solid state. In some such implementations, the 24-hour period includes one or more discharge cycles lasting a total of 2 to 22 hours, and one or more recharge cycles lasting a total of 2 to 22 hours. In some such implementations, the lengths of the recharging and discharging cycles are adjusted or selected based on a method selected from a group of methods consisting of: responding to a request from a grid operator to reduce electricity consumption; reducing the total electricity cost of continuously operating the process over a 24-hour period to take into account changes in electricity prices over a 24-hour period; and responding to a temporary interruption of at least one power source to the process.

[0009] In some embodiments of the method of the present invention, the temperature at which thermal energy is transferred between the PCM and the refrigerant fluid is selected so that the total energy required to perform the process in combination with the PCM during the energy release cycle is reduced, a baseline total energy is required to perform the process without the PCM for the same length of time, and the total charging energy required to charge the PCM during the charging cycle exceeds the total energy required to perform the process for the same length of time; and wherein the equation (baseline total energy - reduced total energy) ÷ total charging energy is equal to 60% or more.

[0010] Some implementations of the method of the present invention further include operating the compressor during the recharging cycle to simultaneously cool a refrigerant fluid circulating in thermal communication with the PCM and a refrigerant fluid used in a propylene or ethylene refrigeration system used in the process.

[0011] In some configurations of the inventive system and implementations of the inventive method, the compressor is electric, and optionally, a majority of the electricity to operate the compressor is obtained from a renewable source.

[0012] In some configurations of the systems of the invention and implementations of the methods of the invention, the PCM includes one or more components selected from the group consisting of paraffins (e.g., isopentane; n-hexane; 2-methylpentane; 2,3-dimethylbutane; n-octane; 2,3,3-trimethylpentane); alcohols (e.g., ethylene, ethylene glycol, 1-propanol, sec-butanol); polydimethylsiloxane; water; aqueous salt solutions; water-salt mixtures; organic chemicals; mixtures of two or more organic chemicals; eutectic mixtures of two or more organic chemicals; and mixtures of two or more inorganic chemicals. In some such systems and implementations, the PCM includes a water-salt mixture that includes one or more components selected from the group consisting of calcium chloride (CaCl 2 ); Calcium chloride (CaCl 2 ); lithium chloride (LiCl); magnesium chloride (MgCl 2 ); zinc chloride (ZnCl 2 ); Hydrogen chloride (HCl); Lithium sulfate (Li 2 SO 4 ); sodium chloride (NaCl); potassium chloride (KCl); aluminum nitrate (Al(NO 3 ) 3 ); any combination of two or more of the aforementioned components.

[0013] In some configurations of the inventive systems and implementations of the inventive methods, the PCM has a melting point of -170°C to 40°C (e.g., -150°C to 30°C, -120°C to 20°C, -100°C to 10°C, and / or -75°C to 5°C).

[0014] In some configurations of the systems of the invention and implementations of the methods of the invention, the refrigerant includes ethylene, propylene, ethane, propane, butane, ammonia, hydrofluorocarbons, hydrochlorofluorocarbons, or mixtures thereof.

[0015] In some configurations of the systems of the invention and implementations of the methods of the invention, the PCM is in a form selected from the group consisting of: a suspension, wherein the PCM is directly suspended in a liquid within an insulated vessel; an encapsulated suspension, wherein the PCM is encapsulated in a shell suspended in a liquid within an insulated vessel; and a plurality of containers, each container containing a portion of the suspension and including at least one heat transfer surface configured to permit thermal communication with the PCM. In some such configurations and implementations, the PCM is in the form of a suspension or an encapsulated suspension, and the system is configured to agitate the PCM within the insulated vessel.

[0016] In some such configurations and implementations, the process is selected from the group of processes consisting of a steam cracking process, an ammonia synthesis process, a hydrogen production process, a para-xylene production process, propane dehydrogenation, olefin metathesis, and natural gas processing.

[0017] The term "coupled" is defined as connected, although not necessarily directly, and not necessarily mechanically; two items that are "coupled" may be unified with each other. Unless otherwise expressly required by the present disclosure, the terms "one" and "an" are defined as one or more. The term "substantially" is defined as most but not necessarily all of the content referred to (and includes the content referred to; for example, substantially 90 degrees includes 90 degrees, and substantially parallel includes parallel), as understood by one of ordinary skill in the art. In any embodiment of the apparatus, kits and methods of the present invention, the term "substantially" can be replaced with "within [percentage]" of the specified content, where the percentage includes 0.1%, 1%, 5% and / or 10%.

[0018] The terms "comprise" (and any form of "including", "have" (and any form of "having"), "include" (and any form of "including"), and "contain" (and any form of "containing") are open-ended linking verbs. Thus, a device or kit that "comprises," "has," "includes," or "contains" one or more elements has the one or more elements, but is not limited to having only these elements. Similarly, a method that "comprises," "has," "includes," or "contains" one or more steps has the one or more steps, but is not limited to having only the one or more steps.

[0019] Furthermore, a device, apparatus, or system that is configured in a certain way is configured in at least that way, but it may also be configured in ways other than those specifically described.

[0020] Any embodiment of any of the apparatus and methods of the present invention may consist of or consist essentially of, rather than include / comprise / contain / have: any of the described steps, elements and / or features. Thus, in any of the claims, the term "consisting of" or "consisting essentially of" may replace any of the above open-ended linking verbs to alter the scope of a given claim if the open-ended linking verbs were used.

[0021] Details related to the above-described embodiments and other embodiments are given below.

[0022] Some details related to aspects of the present disclosure are described above, and other details are described below. Other embodiments, advantages, and features of the present disclosure will become apparent after reviewing the entire application, including the brief description of the figures, detailed description, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following figures are provided for illustration only and are not intended to limit the present disclosure. For the sake of brevity and clarity, each feature of a given structure is not always labeled in each figure in which the structure appears. The same label or reference number does not necessarily represent the same structure. On the contrary, the same reference number can be used to indicate similar features or features with similar functions, as can different reference numbers. The drawings of specific dimensions are drawn to scale (unless otherwise specified), which means that the dimensions of the elements shown are accurate relative to each other, at least for the embodiments shown in the figures.

[0024] Figure 1 A flow chart showing an embodiment of the method of the present invention is shown.

[0025] Figure 2A and Figure 2B Conceptual block diagrams of a first embodiment of the present invention's PCM energy storage system combined with a chemical separation process during charging and discharging cycles, respectively.

[0026] Figure 3A and Figure 3B A conceptual block diagram of a second embodiment of the present invention's PCM energy storage system combined with a chemical separation process during charging and discharging cycles, respectively.

[0027] Figure 4A and 4B An embodiment of a packaged PCM configuration is shown.

[0028] Figure 5 A schematic process diagram of an embodiment of an ethylene and propylene refrigeration system for a naphtha cracker is shown.

[0029] Figure 6The PCM energy storage system is shown for use during a charging cycle. Figure 5 Schematic process diagram of a first embodiment of one of the primary PCM energy storage systems of the present invention for a propylene refrigeration system.

[0030] Figure 7 shows the energy storage system during the discharge cycle of the PCM Figure 6 Schematic process diagram of a PCM energy storage system.

[0031] FIG. 8A to FIG. 8B The PCM energy storage system is shown for use during a charging cycle. Figure 5 Schematic process diagram of a first embodiment of one of the three-stage PCM energy storage systems of the present invention for an ethylene and propylene refrigeration system.

[0032] FIG. 9A to FIG. 9B shows the energy storage system during the discharge cycle of the PCM FIG. 8A to FIG. 8B Schematic process diagram of a PCM energy storage system.

[0033] FIG. 10A to FIG. 10B The PCM energy storage system is shown for use during a charging cycle. Figure 5 Schematic process diagram of a second high efficiency embodiment of one of the three-stage PCM energy storage systems of the present invention for an ethylene and propylene refrigeration system.

[0034] FIG. 11A to FIG. 11B shows the energy storage system during the discharge cycle of the PCM FIG. 10A to FIG. 10B Schematic process diagram of a PCM energy storage system.

[0035] Fig.12 Shows Shows Figures 6 to 11B Graph of the 24-hour-a-day energy demand of a PCM energy storage system.

[0036] Fig.13 A schematic process diagram of an embodiment of an ammonia refrigeration system is shown.

[0037] Fig.14 The PCM energy storage system is shown for use during a charging cycle. Fig.13 Schematic process diagram of yet another embodiment of one of the primary PCM energy storage systems of the present invention for an ammonia refrigeration system.

[0038] Fig.15 shows the energy storage system during the discharge cycle of the PCM Fig.14 Schematic process diagram of a PCM energy storage system.

[0039] Fig.16 The PCM energy storage system is shown for use during a charging cycle. Fig.13 Schematic process diagram of another embodiment of one of the primary PCM energy storage systems of the present invention for an ammonia refrigeration system, wherein the PCM energy storage system is configured for an asymmetric charging and discharging cycle. DETAILED DESCRIPTION

[0040] Referring now to the drawings, and in particular to Figure 1 and Figures 2A to 2B , Figure 1 A flow chart showing an embodiment 10 of the method of the present invention for using phase change materials in a refrigeration cycle in a chemical separation process of a chemical plant, and Figure 2A and Figure 2B It shows that in the charging cycle ( Figure 2A ) and energy release cycle ( Figure 2B ) during the PCM 104 in combination with a chemical separation process 108 in a chemical plant. In some embodiments, Figure 1 The method or process shown in is implemented by a digital controller such as a processor, which executes instructions from a memory to implement the following reference Figure 1 The steps described in Figure 2A and Figure 2B In an embodiment, a common refrigeration cycle 112 (eg, having one or more oversized compressors that are larger than the individual chemical separation processes) provides both refrigeration for the chemical separation process 108 and charges the PCM 104 .

[0041] In an initial step 14, the PCM 104 is "charged" by removing thermal energy from the PCM. In at least some implementations, a sufficient amount of thermal energy is removed to solidify at least some of the PCM, i.e., to transform the PCM from a liquid state to a solid state. Figure 2A During charging of the PCM, a common refrigeration cycle 112 is used to remove thermal energy from the PCM 104 and the chemical separation process 108, as indicated by the arrows in FIG.

[0042] At step 18, the method involves determining whether a release triggering event has occurred. Such a release triggering event can be or include, for example, reaching the time at which the PCM 104 is scheduled to "release" by absorbing thermal energy from the chemical separation process 108, receiving a request from a grid operator to reduce grid power consumption, observing a significant increase in the instantaneous cost of electrical energy supplied from the grid, predictive models indicating a significant increase in future electrical energy costs, or detecting a power outage from the grid or a local source (e.g., a renewable source or fossil fuel combustion). If the release triggering event does not occur, the process may include determining whether the PCM is fully charged, and if not, returning to step 14 to continue charging the PCM. In some implementations, the process includes adjusting the charging rate of the PCM (i.e., the rate at which thermal energy is removed from the PCM) based on the "charge" level of the PCM. For example, as the PCM approaches a fully charged state, the rate at which thermal energy is removed from the PCM may slow down. In some implementations, if the PCM is fully charged, the solidified or “charged” state of the PCM is maintained by continuing to remove thermal energy from the PCM at a rate that approximates the rate at which the PCM absorbs thermal energy from ambient sources (eg, due to inherent insulation limitations).

[0043] If, on the other hand, the discharge triggering event has occurred, the method continues to step 22 where the PCM is discharged via absorption of thermal energy from the chemical separation process (e.g., via a refrigerant circulating in thermal communication with the chemical separation process and the PCM). Figure 2B As indicated by the solid arrow in , the thermal energy from the PCM in 104 is used for process cooling in 108 . Figure 1 The dashed arrow in B is optional and indicates that additional process refrigeration for 108 can be provided by operating the refrigeration cycle 112 at a reduced load. In at least some cases or implementations, the refrigeration cycle 112 can be completely shut down so that all refrigeration for the chemical separation process is provided via the absorption of thermal energy from the chemical separation process by the PCM. In some implementations, such transfer of thermal energy from the chemical separation process to the PCM can be direct (e.g., transfer of a fluid of the chemical separation process that is in direct thermal communication with the PCM) or indirect (e.g., transfer of a fluid of the chemical separation process that is in thermal communication with a heat transfer fluid that is in direct thermal communication with the PCM). In this context, "direct thermal communication" means that there is no intermediate heat transfer fluid, and does not exclude thermal communication through an intermediate physical structure (such as, for example, a conduit for directing the flow of a process or heat transfer fluid) or through the wall of a container in which the PCM is disposed.

[0044] At step 26, the method involves determining whether a recharge trigger event has occurred. Such a recharge trigger event may be or include reaching a time scheduled by the PCM 104 to "recharge" by removing heat from the PCM, receiving an indication from a grid operator that a higher power consumption from the grid can be restored or that a period of time during which the operator requested a reduction in power consumption has expired, observing a significant reduction in the instantaneous cost of power supplied from the grid, predictive models indicating a significant reduction in future power costs, or detecting a restoration of energy availability from the grid or a local source (e.g., a renewable source or fossil fuel combustion). If the recharge trigger event has not occurred, the process may include determining whether the PCM is fully discharged, and if not, returning to step 22 to continue discharging the PCM. In some implementations, when sufficient energy is available (even if at a higher price), the process includes operating the compressor of the refrigeration cycle 112 at a reduced rate (relative to the full rate or desired rate when running the chemical separation process at the full rate or desired rate and charging the PCM) to provide energy from the chemical separation process 108, the PCM 104, or both the chemical separation process and the PCM (e.g., based on the “charge” level of the PCM and / or the amount or cost of energy available from the grid or other source). Figure 2B ) removes thermal energy. For example, as the PCM approaches a fully discharged state, the rate at which thermal energy is absorbed by the PCM may slow down. In some implementations, if the PCM is fully discharged and energy is available from other sources (even at a higher price), only the process refrigeration cycle is operated to run the chemical separation process without charging the PCM. If a charging trigger event has occurred and sufficient energy is available from the power grid or other source, the method returns to step 14, where the PCM is charged at a full charging rate or a desired charging rate; or, if the available energy is greater than the energy required to run the chemical separation process, but there is not enough energy to charge the PCM at the full charging rate or the desired charging rate, the PCM is charged at a reduced rate (relative to the full charging rate or the desired charging rate).

[0045] Figure 3A and Figure 3B 1 and 10 show a conceptual block diagram of an alternative configuration 100a of the PCM energy storage system of the present invention combined with a chemical separation process during charging and discharging cycles, respectively. The operation of configuration 100a is similar to that of configuration 100( FIG. 2A to FIG. 2B ) is substantially similar, the main difference being that configuration 100a includes an additional PCM refrigeration cycle 116 with its own compressor. Figure 1 At step 14 of the method shown in FIG. 1 , the process refrigeration cycle 112 removes thermal energy from the chemical separation process 108, and the PCM refrigeration cycle 116 removes thermal energy from the PCM 104 to charge the PCM. Figure 1At step 22 of the method shown in FIG. 1 , the PCM releases energy by absorbing heat energy from the chemical separation process 108, such as Figure 3B Additional process refrigeration may optionally be provided by a process refrigeration cycle 112, such as Figure 3B In at least some cases or implementations, the process refrigeration cycle 112 and the PCM refrigeration cycle 116 can be completely shut down so that all refrigeration for the chemical separation process is provided by the PCM absorbing heat energy from the chemical separation process, and heat energy is not removed from the PCM at the same time. FIG. 2A to FIG. 2B As described in configuration 100, in some implementations, such thermal energy transfer from the chemical separation process to the PCM can be direct (e.g., transferring a fluid of the chemical separation process that is in direct thermal communication with the PCM) or indirect (e.g., transferring a fluid of the chemical separation process that is in direct thermal communication with a heat transfer fluid that is in turn in direct thermal communication with the PCM).

[0046] As mentioned above FIG. 2A to FIG. 2B As described above with respect to configuration 100 of FIG. 1 , for configuration 100a, in some implementations, when sufficient energy is available (even if at a higher price), the method includes operating the compressor of the process refrigeration cycle 112 at a reduced rate (relative to the full rate or desired rate when the chemical separation process is operated with only the process refrigeration cycle) to remove thermal energy from the chemical separation process 108, operating the compressor of the PCM refrigeration cycle 116 at a reduced rate (relative to the full rate or desired rate when the PCM is charged at the full rate or desired rate) to remove thermal energy from the PCM 104, and / or simultaneously operating the compressor of the process refrigeration cycle at a reduced rate and operating the compressor of the PCM refrigeration cycle at a reduced rate (e.g., Figure 3B In some implementations, if the PCM is fully discharged and energy is available from other sources (even at a higher price), only the compressor of the process refrigeration cycle 112 is operated to run the chemical separation process and the compressor of the PCM refrigeration cycle 116 is not operated to charge the PCM.

[0047] Although Figure 1 Process Examples and FIG. 2A to FIG. 2B and FIG. 3A to FIG. 3B The system embodiments in utilize a single PCM, but the methods and systems of the present invention may include multiple PCMs (e.g., at different temperatures) and multiple refrigeration cycles, such as two PCMs with different freezing temperatures, or three PCMs with three different freezing temperatures, such as to provide staged cooling for a process refrigeration cycle.

[0048] Phase Change Materials (PCM)

[0049] Phase change materials are generally capable of absorbing or releasing (preferably large amounts) of heat at a specific target temperature, and, at least for some embodiments of the systems and methods of the present invention, preferably with minimal volume change. Typically, physical phase changes of condensed phase materials exhibit this type of behavior. The transition from a solid phase to a liquid phase is a typical transition that meets this criterion. However, other transitions may also be utilized in certain embodiments of the systems and methods of the present invention. For example, under the operating conditions (e.g., temperature) of certain embodiments, some PCMs may change from a solid state to a liquid state. By further example, some PCMs may exhibit other types of phase transitions in which enthalpy changes nonlinearly at a specific temperature (or within a specific temperature range), such as from one solid state to another solid state (e.g., changes in crystal structure due to molecular reorganization), from an amorphous state to a solid state, from a gel state to a solid state, from a liquid state to a gel state, or from an amorphous state to a different amorphous state. In a multi-component mixture, there may or may not be some component transfer between one state and another, such as a liquid solution of a solvent and a solute forming a 2:1 solvent and solute compound in a solid phase. To describe this generally without listing all of the specific phases of the many possible systems, a PCM can be described as transitioning between a first state and a second state when heat is added to the PCM, and transitioning from the second state to a lower enthalpy first state when heat is removed from the PCM.

[0050] Various materials and mixtures can be used for PCM, for example, such as paraffins (e.g., pentane; n-hexane; 2-methylpentane; 2,3 dimethylbutane; n-octane; 2,3,3 trimethylpentane), alcohols (e.g., ethylene glycol; 1-propanol; sec-butyl alcohol; ethanol, isopropanol), polydimethylsiloxane, water, aqueous salt solutions, eutectic salt solutions, eutectic mixtures of two or more organic or inorganic chemicals, and / or combinations thereof (e.g., a combination of two paraffins, a combination of two alcohols, a combination of an alcohol and an aqueous salt). Various salts can be used in the salt solution, for example, such as calcium chloride (CaCl 2 ); lithium chloride (LiCl); magnesium chloride (MgCl 2 ); zinc chloride (ZnCl 2 ); Hydrogen chloride (HCl); Lithium sulfate (Li 2 SO 4 ); sodium chloride (NaCl); potassium chloride (KCl); aluminum nitrate (Al(NO 3 ) 3); various commercially available eutectic salt solutions (e.g., E-65 available from PCM Products Ltd., Cambridgeshire, UK), and combinations thereof. In addition, different PCM components can be mixed in proportion to achieve a desired freezing point in a given refrigeration cycle. For example, the refrigeration systems of the C2 splitter and deethanizer in a naphtha cracker typically operate in a temperature range of about -42°C to about 0°C, where the PCM can be a eutectic salt mixture with a transition temperature of -65°C. By further example, the demethanizer in a naphtha cracker typically operates in a lower temperature range with a lower limit of about -100°C, and therefore requires a PCM with a lower phase transition, for example, pure ethanol (-114°C) or a eutectic mixture of ethanol and water (-118°C) or ethanol and another alcohol (such as methanol).

[0051] There are several options for including the PCM in the systems and methods of the present invention. First, the PCM can be disposed in one or more insulated vessels through which heat exchange conduits define a flow path for the refrigerant. Conduits (e.g., tubes, shells, fins, or connectors) disposed within the vessel permit heat transfer between the refrigerant within the conduit or heat exchanger and the PCM within a given vessel (outside the conduit). In at least some configurations, the PCM is stirred or agitated within the container to prevent temperature gradients and improve heat transfer. In this first option, the volume of the PCM will typically include more than the minimum volume required for the desired heat capacity, because a constant liquid phase is typically required to promote stirring or agitation during the "charging" of the PCM to promote the constant transfer of thermal energy from the PCM. For example, the PCM can be suspended in a liquid (i.e., a suspension in which the PCM is in solid form). The relative proportions of liquid and solid can be designed according to system needs. For example, a relatively large passive storage system may have a continuous and somewhat separated solid and liquid phase. The stirring or agitation system can be configured to control the PCM in a suspension of smaller particles that are easily pumped and transferred to a heat transfer device, or simply suspended by a fluid circulation to homogenize a system with heat storage capabilities. In some implementations, the PCM can be in the form of smaller encapsulated beads that contain the PCM in its liquid and solid states, such that the beads can be suspended in a liquid that has a freezing point lower than the PCM. When the PCM is not encapsulated, the PCM is suspended as a suspension in a solution or as an emulsion (e.g., n-decane (CH 2 (OH)—CH 2When a (OH) solution is suspended, a nucleating agent may be included in the liquid to promote nucleation during freezing in the solution rather than on the heat transfer surfaces, where nucleation may interfere with or inhibit the transfer of thermal energy through these surfaces. Some such systems and methods may include supercooling or undercooling before nucleation / crystallization occurs. For example, a liquid solution may sometimes be cooled below its freezing point without a nucleation reaction but does not solidify and forms crystals. In this case, a nucleating agent may be introduced and / or the liquid may be stirred to initiate the nucleation process and thereby cause the liquid to solidify.

[0052] A second option is to contain the PCM in a large number of relatively small insulated containers (e.g., formed of HDPE). These containers can be formed alone or in combination with other such containers to conform to and contact the contours of the refrigerant conduits, thereby improving heat transfer between the refrigerant and the PCM. For example, for a conduit having a circular cross-section like a typical pipe, the container can include a circular channel or a semi-circular indentation to contact the conduit. By further example, the conduit can be shaped to have a relatively flat rectangular cross-section that is sized to fit within the planar wall of the container.

[0053] In a third option, the PCM may be contained in a plurality of plastic or metal housings, the geometry of which is selected so that these may be stacked or suspended (e.g., in parallel) inside an insulated vessel so that a refrigerant or heat transfer fluid (when a secondary loop system is employed) may pass between (and / or through) and contact each container to transfer thermal energy between the PCM and the refrigerant or heat transfer fluid through the walls of the container. This approach provides a large surface area for the transfer of thermal energy. Figure 4A An example of such a container is shown, which is formed from a polymer and is substantially rigid to allow multiple containers to be stacked. Figure 4A The container defines a plurality of grooves to maximize the surface area available for transfer of thermal energy between the PCM inside the container and the refrigerant or heat transfer fluid outside the container. Figure 4B Another example of such a container is shown, which is formed of a polymer and is flexible (such as a plastic kitchen bag). As shown in the figure, Figure 4B The container also defines a plurality of grooves along which two sides of the bag structure are joined to define an elongated zigzag channel to maximize the surface area for heat transfer, facilitate bag filling, and promote uniform distribution of the PCM within the bag structure when the bag structure is suspended in a container through which a refrigerant or heat transfer fluid circulates.

[0054] The first of the three PCM inclusion options has the advantages of smaller overall container size, simpler construction, and higher heat transfer rates. The second of the three PCM inclusion options reduces the corrosion rate by completely containing the refrigerant in the conduit and completely containing the PCM in each container. The third of the three PCM inclusion options provides the advantage of a large heat exchange area with a convenient form factor. In some implementations with a single PCM, the PCM can be configured to require at least 10MWh (e.g., 20MWh, 30MWh, 50MWh, 100MWh, 150MWh, 200MWh, 300MWh, 500MWh, 1000MWh or more) to transition from an initial state to a higher enthalpy state. In other implementations with multiple PCMs, the PCMs can be configured to collectively require at least 100MWh (e.g., 150MWh, 200MWh, 300MWh, 500MWh, 1000MWh or more) to transition from an initial state to a higher enthalpy state.

[0055] refrigerant

[0056] Various refrigerants can be used for chemical separation process refrigeration and / or PCM charging. Examples of refrigerants suitable for certain implementations of the methods and systems of the present invention include ethylene, propylene, ethane, propane, butane, ammonia, hydrofluorocarbons, hydrochlorofluorocarbons, and mixtures thereof. As will be appreciated by one of ordinary skill in the art, the refrigerant for a given refrigeration cycle can include one or more selected components such that the refrigerant is in a gaseous state at higher temperatures of the refrigeration cycle and in a liquid state at lower temperatures of the refrigeration cycle.

[0057] Heat transfer fluid

[0058] For configurations where a heat transfer fluid indirectly transfers thermal energy between the PCM and the refrigerant of a given chemical separation refrigeration cycle, the heat transfer fluid may include one or more of any of the components known for use in such heat transfer fluids. Suitable heat transfer fluids remain in the liquid phase under the conditions of the relevant portion of the refrigeration cycle and under the conditions under which heat transfer occurs between the heat transfer fluid and the PCM. For example, diethyl ether (which freezes at 154+ / -7K and boils at 307.7+ / -0.2K at atmospheric pressure) is a heat transfer fluid suitable for use in a typical de-methanizer refrigeration system.

[0059] Example

[0060] Examples 1 to 3: Naphtha Cracker Refrigeration System

[0061] Several embodiments were modeled for operating a refrigeration cycle to produce ethylene via a naphtha cracker, particularly a naphtha cracker in a front-end demethanizer configuration, using the PCM energy storage system and method of the present invention. Figure 5 An embodiment 200 of a refrigeration system for a naphtha cracker is shown, and more specifically, a schematic process diagram of an embodiment including an ethylene refrigeration system 204 and a propylene refrigeration system 208 of a naphtha cracker is shown. The refrigeration system in the embodiment provides several different temperature levels for process cooling duties in various parts of the naphtha cracker.

[0062] A typical or "existing" ethylene refrigeration system 204 includes a first compression stage having a first evaporator 212 and a first compressor 216, a second compression stage having a second evaporator 220 and a second compressor 224, and a single condensation stage having a first condenser 228 and a second condenser 232. The pressure of the condensed ethylene is reduced by valves 240 and 236, which reduces the boiling point of ethylene so that cooling can be obtained. Valve 240 reduces the pressure to about 4.5 bara, which causes a mixture of vapor and liquid to boil at about -73°C. Valve 236 reduces the pressure to about 1.1 bara, which causes a mixture of vapor and liquid to boil at about -102°C. In operation, a portion of the ethylene from valve 240 is sent to the second evaporator 220, and the ethylene from valve 236 is sent to the first evaporator 212. In the first evaporator 212, the liquid phase ethylene absorbs heat energy and boils to a gaseous state at a temperature of -102°C and a pressure of 1.1 bara. The gaseous ethylene from the first evaporator 212 is then delivered to the first compressor 216, in which the gaseous ethylene is compressed to a first pressure of 4.5 bara (absolute pressure). In the second evaporator 220, the liquid phase ethylene absorbs heat energy and boils to a gaseous state at a temperature of -73°C and a pressure of 4.5 bara. The gaseous ethylene from the second evaporator 220 is then mixed with the compressed ethylene from the first compressor 216, and the combined gaseous ethylene is then delivered to the second compressor 224, in which the combined gaseous ethylene is further compressed to a second pressure of 15.6 bara. The compressed gaseous ethylene from the second compressor 224 is then delivered to a condenser, wherein the compressed gaseous ethylene is partially condensed in the first condenser 228 and then further condensed in the second condenser 232. In the illustrated configuration, the heat transfer fluid circulates through the first condenser 228 to absorb heat energy from the condensing ethylene for the propylene refrigeration system, and the heat transfer fluid circulates through the second condenser 232 to absorb additional heat energy from the condensing ethylene also for the propylene refrigeration system.

[0063] Typical or "existing" propylene refrigeration system 208 includes three compressor stages and one condenser stage. The first compression stage includes the first evaporator 244, the second evaporator 248 in parallel, and the first compressor 252. The second compression stage includes the third evaporator 256, the fourth evaporator 260 in parallel, and the second compressor 264. The third compression stage includes the fifth evaporator 268 and the third compressor 272. The condenser stage includes a single condenser 276. In operation, the pressure of the condensed propylene from the condenser 276 is reduced to three different pressure levels via valves 288, 284 and 280, which reduces the boiling point of propylene and is therefore able to provide cooling for the process. After the pressure is reduced, a mixture of vapor and liquid is obtained at a temperature determined by the boiling point under the reduced pressure. These mixtures are transported to the evaporators 244, 248, 256, 260, 268 of the first compression stage, the second compression stage, and the third compression stage. In the first evaporator 244 and the second evaporator 248, liquid propylene absorbs heat energy and boils into a gaseous state at a temperature of -46°C and a pressure of 1.1 bara. As indicated by the dotted line of the first condenser 228 from the ethylene refrigeration system 204, the heat energy from the first condenser 228 is used as a heat energy source in the evaporator 256 to boil propylene. The gaseous propylene is then transported to the first compressor 252, in which the gaseous propylene is compressed to a first pressure of 4.5 bara and a temperature of -46°C. In the third evaporator 256 and the fourth evaporator 260, liquid propylene absorbs heat energy and boils into a gaseous state at a temperature of -23°C and a pressure of 2.8 bara. As indicated by the dotted line of the second condenser 232 from the ethylene refrigeration system 204, the heat energy from the second condenser 232 is used as a heat energy source in the evaporator 244 to boil propylene. The gaseous propylene from the evaporator 256, 260 is then mixed with the compressed propylene from the first compressor 252, and the combined gaseous propylene is then delivered to the second compressor 264, in which the combined gaseous propylene is further compressed to a second pressure of 7.8 bara and a temperature of 41°C. In the fifth evaporator 268, the liquid phase propylene absorbs heat energy and boils to a gaseous state at a temperature of 10°C and a pressure of 7.8 bara. The gaseous propylene from the evaporator 268 is then mixed with the compressed propylene from the second compressor 264, and the combined gaseous propylene is then delivered to the third compressor 272, in which the combined gaseous propylene is further compressed to a third pressure of 18.3 bara. The compressed gaseous propylene from the third compressor 272 is then delivered to the condenser 276, where it is condensed. In normal operation, valves 280, 284 and 288 are used to reduce the pressure of the flowing propylene. During the operation of using PCM to release energy, these valves can also be used to cut off the flow or propylene.The first valve 280 can be closed to prevent propylene from flowing to the first evaporator 244 and the second evaporator 248; the second valve 284 can be closed to prevent propylene from flowing to the third evaporator 256 and the fourth evaporator 260 or any one of the first evaporator 244 and the second evaporator 248; and the third valve 288 can be closed to prevent propylene from flowing to the fifth evaporator 268, the third evaporator 256 and the fourth evaporator 260 or any one of the first evaporator 244 and the second evaporator 248.

[0064] As described above, the three modeled systems are "charged" by transferring heat energy from the PCM to the refrigerant to freeze the PCM and boil the refrigerant to freeze the PCM, and the systems are "released" by transferring heat energy from the refrigerant in a gaseous state to condense the refrigerant and melt the PCM into a liquid state. For example, the PCM for these modeled examples is assumed to be an aqueous eutectic salt mixture that undergoes a liquid-solid phase transition at a single temperature.

[0065] In each of these three embodiments, the process is modeled using a "symmetrical" cycle, where the "charging" cycle is equal in length to the cycle that "discharges" the PCM. For example, during each 24-hour period, the PCM may be "charged" for 12 hours, and "discharged" for 12 hours, as shown in FIG. Fig.12 As shown. The thermal energy absorption from external (e.g. ambient) sources is not considered (assumed to be zero). In the design of real-world systems, such external thermal energy can be accommodated by enlarging the PCM volume and the thermal capacity of the compressor taking into account specific insulation values. These models assume that the PCM is directly dispersed in the suspension or encapsulated in small spheres in the suspension. The process simulation was performed in CHEMCAD using the SRK method.

[0066] In Examples 1 and 2, the corresponding systems are modeled using a compressor in a propylene refrigeration system that provides additional compression within the refrigeration system to charge the PCM. Such compressors can be expanded, for example, when an existing system is converted to operate using the PCM energy storage system of the present invention, or can simply be increased in size to be sufficient to provide such additional compression when a new system is developed. In Example 3, the system is modeled using an additional refrigeration unit or loop (relative to a system without an added PCM system), in which an independent compressor is used to "charge" each PCM reservoir. The PCM refrigeration loop or unit is only used to "charge" the system when surplus energy is available. In all three examples, an existing refrigeration unit that interacts with the PCM system is modified with a new exchanger to transfer thermal energy to the PCM to condense propylene vapor. It is also assumed that the existing refrigeration unit will be or will be modified to be driven by an electric drive (rather than burning fossil fuels) and that the added PCM refrigeration unit will also be driven by an electric drive to model the three systems.

[0067] The single-level or single-stage system in Example 1 uses a single PCM reservoir to store "cold" during periods of surplus or low-cost energy, and then utilizes the stored "cold" when energy is in short supply or costly. This single-stage system is the simplest and therefore the cheapest to build (relative to the multi-stage systems in Examples 2-3).

[0068] As will be appreciated by one of ordinary skill in the art, the choice of charging temperature (pressure) can affect the efficiency of energy storage; however, for simplicity, Examples 1 and 2 assume that the charger will operate at the same temperature and pressure levels as an existing charger without a PCM. In Example 3, efficiency is significantly improved by selecting the charger operating pressure to reduce the temperature difference, as discussed in more detail below.

[0069] Modeling indicated that maximum energy recycling requires a three-stage PCM system with three PCM reservoirs and the ability to shut down the propylene compressor during discharge, as discussed in more detail below with reference to Examples 2 and 3.

[0070] Example 1: Primary PCM system for naphtha cracking ethylene and propylene refrigeration system

[0071] Figure 6 shows the PCM energy storage system during the charging cycle, for Figure 5 A schematic process diagram of a modeled embodiment of a primary PCM energy storage system 300 for a propylene refrigeration system 208, and Figure 7 The PCM energy storage system 300 during energy discharge is shown. As shown, adding the PCM system includes adding a PCM system evaporator 304 to the first compression stage of the propylene refrigeration system 208, wherein the first PCM system evaporator 304 is connected in parallel with the first evaporator 244 and the second evaporator 248; and adding a PCM system condenser 308 to the second compression stage of the propylene refrigeration system 208, wherein the PCM system condenser 308 is connected in parallel with the third evaporator 256 and the fourth evaporator 260. The adding PCM system also includes a pump 312 and a PCM reservoir 316 as well as conduits and valves to deliver heat transfer fluid from the PCM to the PCM system evaporator and condenser.

[0072] like Figure 6As shown, during charging of the PCM reservoir 316, a PCM suspension or heat transfer fluid is circulated from the PCM reservoir 316 by pump 312 to the evaporator 304, where heat energy is transferred from the PCM suspension or heat transfer fluid to propylene at a temperature of -46°C to boil the propylene. In the case where a heat transfer fluid is utilized, the heat transfer fluid is then returned to the PCM 316, where it absorbs additional heat energy from the PCM reservoir at the PCM's freezing point of -34°C, and so on, until the PCM is fully "charged" or solidifies, or charging is otherwise suspended. In the case where the PCM is contained in a suspension, the PCM "charges" or solidifies upon cooling and is returned to the PCM reservoir, ultimately resulting in a fully charged suspension of PCM in the reservoir. At the modeled charging rate, the evaporator 304 removes thermal energy from the PCM suspension or heat transfer fluid at a rate of 109.1 MW, so that during the 12 hour charging period, 1309 MWh of energy is removed from the PCM 316 reservoir. In other words, 1309 MWh of cold or hot capacity is "stored" so that when the PCM reservoir is "discharged", the PCM reservoir can later absorb up to 1309 MWh of thermal energy from the propylene refrigeration system (minus any inefficiencies introduced by, for example, absorbing thermal energy from an external source). Figure 5 and Figure 6 As indicated by the difference between , the compressor needs to input additional energy to provide the compression required to "charge" the PCM reservoir. Specifically, the first compressor 252 is powered from 7.6 MW ( Figure 5 ) increased to 22.6MW( Figure 6 ), the second compressor 264 increases from 20.7 MW to 44.4 MW, and the third compressor 272 increases from 28.0 MW to 55.9 MW. Overall, the energy requirements of the compressors increase from 66.8 MW ( Figure 5 ) to 133.4 MW (of the propylene refrigeration system 208 combined with the PCM energy storage system 300 Figure 6 ).

[0073] like Figure 7As shown, during discharge of the PCM reservoir 316, the PCM suspension or heat transfer fluid is circulated from the PCM reservoir 316 by pump 312 to the condenser 308, where heat energy is transferred from the propylene vapor to the PCM suspension or heat transfer fluid at a temperature of -23°C to condense the propylene at a pressure of 2.8 bar. The condensation of the propylene vapor in the condenser 308 occurs simultaneously with the evaporation of the propylene liquid in the evaporator 256. These flows may be achieved at substantially the same pressure due to the thermosiphon effect, where the boiling liquid in the evaporator 256 reduces the density of the fluid, thereby providing a driving force for the condensed liquid in the condenser 308 to take its place. Alternatively, the propylene may be pumped through a conduit in thermal communication with the PCM suspension (e.g., through a pipe of a container in which the PCM suspension is placed). The PCM suspension or heat transfer fluid returns to the PCM 316 where the PCM reservoir absorbs thermal energy from the PCM suspension or heat transfer fluid at the PCM's freezing point of -34°C, and so on until the PCM is completely "de-energized" or liquefied, or energy de-energization is otherwise suspended. Figure 5 and Figure 7 As indicated by the difference between , the compressor requires less energy input to provide the compression required to operate the propylene refrigeration system 208. Specifically, the first compressor 252 remains unchanged at 7.6 MW ( Figure 5 , Figure 7 ), the second compressor 264 is reduced from 20.7 MW to 0 MW, and the third compressor 272 is reduced from 28.0 MW to 3.3 MW. Figure 7 In the embodiment of FIG. 1 , two "Xs" are shown to indicate that the propylene refrigeration cycle can be operated essentially as two independent cycles: a low pressure cycle in which 2.8 bar propylene is condensed using the PCM stored in 308; and a high pressure cycle in which 18.3 bar propylene is condensed using ambient cooling in 276. Overall, the energy requirements of these compressors are reduced from the 66.8 MW ( Figure 5 ) is reduced to 21.4 MW ( Figure 7 ). In other implementations, it may be beneficial to maintain at least a nominal load on the second compressor (264). Table 1 summarizes the condenser energy input of the ethylene and propylene refrigeration system during standalone operation and combined operation with the PCM energy storage system in its charging and discharging cycles:

[0074] Table 1: Energy input and output of a primary PCM system

[0075]

[0076] In terms of the battery, an additional 66.6 MW of energy is used to charge the thermal "battery" during the 12 hour charging period (799 MWh), and then during the discharge period, the amount of energy required to operate the refrigeration system 200 is reduced by 45.4 MW over the 12 hour discharge period (545 MWh), resulting in an efficiency of 68.2%. The efficiency is reduced at least in part by a modeled temperature difference of 23°C between the charging temperature of -46°C at the evaporator 304 and the discharge temperature of -23°C at the condenser 308. In other implementations, the efficiency can be improved by reducing the magnitude of this temperature difference.

[0077] In order for heat to flow from the PCM to the refrigeration system during charging or from the refrigeration system to the PCM during discharge, a temperature difference must exist. The temperature difference can be characterized in different ways, such as the temperature difference between two points at different physical locations, or the average temperature difference between multiple groups of points within the PCM volume and multiple groups of points within the refrigeration system. Similarly, there must be a temperature difference between the manufacturing product process and the refrigeration system. In heat transfer applications, the logarithmic mean temperature difference is well known and used in many analyses. Sufficient temperature difference or gradient is required even within the PCM volume in order to transfer the required heat out (and subsequently into) during the operating cycle. Additional temperature gradients may be required to take into account the size of the PCM volume, the heat transfer area in contact with the PCM, or heat transfer through the container wall in the case of encapsulated PCM. For example, while conventional refrigeration systems only require a few degrees of temperature difference between the refrigerant and the process, a logarithmic mean temperature difference of 3°C, 5°C, 9°C or more will take into account the heat flux into the internal area of ​​the PCM range. Other considerations for temperature driving force include providing sufficient crystallization kinetic rate when solidifying the PCM, or providing sufficient crystal nucleation rate to operate the charging cycle near saturation when few crystals are present. Temperature differences can be managed by designing the amount of heat transfer area close to the PCM surface.

[0078] Example 2: Three-stage PCM system for naphtha cracking ethylene and propylene refrigeration system

[0079] FIG. 8A to FIG. 8B The PCM energy storage system is shown for use during a charging cycle. Figure 5 A schematic process diagram of a modeling embodiment 400 of a three-stage PCM energy storage system for an ethylene refrigeration system 204 and a propylene refrigeration system 208; and FIG. 9A to FIG. 9BA schematic process diagram of a PCM energy storage system 400 during its energy release cycle is shown. As shown, adding the PCM system includes adding three separate PCM stages, each with its own PCM reservoir, pump, evaporator, and compressor. Specifically, the first PCM stage includes a first PCM system evaporator 404 added to the second compression stage of the ethylene refrigeration system 204 and connected in parallel with the evaporator 220, a first PCM system condenser 408 added to the first compression stage of the propylene refrigeration system 208, a pump 412, and a first PCM reservoir 416. As modeled, the PCM used in the first stage (PCM reservoir 416) has a freezing point of -50°C and has sufficient volume to store 672MWh of energy. The second PCM stage includes a second PCM system evaporator 420 added to the first compression stage of the propylene refrigeration system 208 and connected in parallel with the evaporators 244, 248; a second PCM system condenser 424 added to the propylene refrigeration system to receive at least a portion of the compressed gaseous propylene output from the compressor 252; a pump 428; and a second PCM reservoir 432. As modeled, the PCM used in the second stage (PCM reservoir 432) has a freezing point of -34°C and has sufficient volume to store 547MWh of energy. The third PCM stage includes a third PCM system evaporator 436 added to the second compression stage of the propylene refrigeration system 208 and connected in parallel with the evaporators 256, 260; a third PCM system condenser 440 added to the propylene refrigeration system to receive at least a portion of the compressed gaseous propylene output from the compressor 264; a pump 444; and a second PCM reservoir 448. As modeled, the PCM used in the second stage (PCM reservoir 448) has a freezing point of -6°C and has sufficient volume to store 209 MWh of energy.

[0080] like FIG. 8A to FIG. 8B As shown, during charging of the PCM system 400, the PCM suspension or heat transfer fluid circulates between the ethylene refrigeration system 204 or the propylene refrigeration system 208 and the corresponding PCM reservoir. Fig. 8A), a PCM suspension or heat transfer fluid is circulated from a first PCM reservoir 416 by a pump 412 to an evaporator 404 where heat energy is transferred from the PCM suspension or heat transfer fluid to ethylene at a temperature of -73°C to boil the ethylene. The PCM suspension or heat transfer fluid then returns to the PCM reservoir 416 where it absorbs additional heat energy from the PCM reservoir at the PCM's freezing point of -50°C, and so on until the PCM in the PCM reservoir 416 is fully "charged" or solidified, or charging is otherwise suspended. At the modeled charging rate, the evaporator 404 removes heat energy from the heat transfer fluid at a rate of 56.0 MW, so that 672 MWh of energy is removed from the PCM 416 reservoir during the 12 hour charging period. In other words, 672 MWh of cold or hot capacity is "stored" so that when the PCM reservoir is "discharged", the PCM reservoir 416 can later absorb up to 672 MWh of thermal energy from the propylene refrigeration system (minus any inefficiencies introduced, for example, by absorbing thermal energy from an external source). In the second PCM stage, the PCM suspension or heat transfer fluid is circulated from the second PCM reservoir 432 by pump 428 to the evaporator 420, where thermal energy is transferred from the PCM suspension or heat transfer fluid to propylene at a temperature of -46°C to boil the propylene. The PCM suspension or heat transfer fluid then returns to the PCM reservoir 432, where it absorbs additional thermal energy from the PCM reservoir at the PCM's freezing point of -34°C, and so on, until the PCM in the PCM reservoir 432 is fully "charged" or solidified, or charging is otherwise suspended. At the modeled charging rate, the evaporator 420 removes thermal energy from the heat transfer fluid at a rate of 45.6 MW, so that during the 12 hour charging period, 547 MWh of energy is removed from the PCM reservoir 432. In other words, 547 MWh of cold or hot capacity is "stored" so that when the PCM reservoir is "discharged", the PCM reservoir 432 can later absorb up to 547 MWh of thermal energy from the propylene refrigeration system (minus any inefficiencies introduced, for example, by absorbing thermal energy from an external source).

[0081] In the third PCM level ( Figure 8B), the PCM suspension or heat transfer fluid is circulated from the third PCM reservoir 448 by pump 444 to the evaporator 436, where heat energy is transferred from the PCM suspension or heat transfer fluid to propylene at a temperature of -23°C to boil the propylene. The PCM suspension or heat transfer fluid then returns to the PCM reservoir 448, where it absorbs additional heat energy from the PCM reservoir at the PCM's freezing point of -6°C, and so on, until the PCM in the PCM reservoir 448 is fully "charged" or solidified, or charging is otherwise suspended. At the modeled charging rate, the evaporator 436 removes heat energy from the heat transfer fluid at a rate of 17.4 MW, so that during the 12 hour charging period, 209 MWh of energy is removed from the PCM reservoir 448. In other words, 209 MWh of cold or hot capacity is "stored" so that when the PCM reservoir is "discharged", the PCM reservoir 448 can later absorb up to 209 MWh of thermal energy from the propylene refrigeration system (minus any inefficiencies introduced, for example, by absorbing thermal energy from an external source).

[0082] like Figure 5 and FIG. 8A to FIG. 8B As indicated by the difference between , the compressor needs to input additional energy to provide the compression required to "charge" the PCM storage. Specifically, the ethylene second compressor 224 is from 6.8 MW ( Figure 5 ) increased to 22.5MW( Fig. 8A ), the first propylene compressor 252 increased from 7.6MW to 22.4MW, and the second propylene compressor 264 increased from 20.7MW to 49.4MW ( Figure 8B ), and the propylene third compressor 272 is increased from 28.0 MW to 55.9 MW. Overall, the compressor energy demand is increased from 66.8 MW ( Figure 5 ) to 159.8 MW ( FIG. 8A to FIG. 8B ).

[0083] like FIG. 9A to FIG. 9B As shown, during the discharge of the PCM system 400, the PCM suspension or heat transfer fluid circulates between the propylene refrigeration system 208 and the corresponding PCM reservoir. Fig. 9A), the PCM suspension or heat transfer fluid is circulated from the first PCM reservoir 416 to the condenser 408 by pump 412, where heat energy is transferred from the propylene to the PCM suspension or heat transfer fluid at a temperature of -46°C to condense the propylene. The PCM suspension or heat transfer fluid returns to the PCM reservoir 416, where it absorbs heat energy from the PCM suspension or heat transfer fluid at the PCM's freezing point of -50°C, and so on, until the PCM in the PCM reservoir 416 is completely "discharged" or liquefied, or charging is suspended for other reasons.

[0084] In the second PCM stage, the PCM suspension or heat transfer fluid is circulated from the second PCM reservoir 432 by pump 428 to the condenser 424, where heat energy is transferred from the propylene to the PCM suspension or heat transfer fluid at a temperature of -23°C to condense the propylene. The PCM suspension or heat transfer fluid returns to the PCM reservoir 432, where it absorbs heat energy from the PCM suspension or heat transfer fluid at the PCM's freezing point of -34°C, and so on, until the PCM in the PCM reservoir 432 is completely "de-energized" or liquefied, or charging is otherwise suspended.

[0085] In the third PCM level ( Fig. 9B ), the PCM suspension or heat transfer fluid is circulated from the third PCM reservoir 448 to the condenser 440 by pump 444, where heat energy is transferred from the propylene to the PCM suspension or heat transfer fluid at a temperature of 10°C to condense the propylene. The PCM suspension or heat transfer fluid returns to the PCM reservoir 448, where it absorbs heat energy from the PCM suspension or heat transfer fluid at the freezing point of the PCM at -6°C, and so on, until the PCM in the PCM reservoir 448 is completely "discharged" or liquefied, or charging is suspended for other reasons.

[0086] like Figure 5 and FIG. 8A to FIG. 8B As indicated by the difference between , the compressor inputs less energy to provide the compression required to operate the refrigeration systems 204 and 208. Specifically, the propylene first compressor 252 is reduced from 7.6 MW to 0 MW ( Fig. 9A ), the propylene second compressor 264 is reduced from 20.7MW to 0MW ( Fig. 9B ), and the propylene third compressor 272 is reduced from 28.0 MW to 0 MW. Overall, the energy demand of the compressor is reduced from 66.8 MW ( Figure 5 ) is reduced to 10.5 MW ( Figures 9A-9B ).

[0087] Table 2 summarizes the condenser energy input for the ethylene and propylene refrigeration systems during standalone operation and combined operation with the three-stage PCM energy storage system in its charging and discharging cycles:

[0088] Table 2: Energy input and output of the three-stage PCM system

[0089]

[0090]

[0091] In terms of the battery, an additional 93 MW of energy is used to charge the thermal "battery" during the 12 hour charging period (1116 MWh), and then during the discharge period, the amount of energy required to operate the refrigeration system 200 is reduced by 56.3 MW over the 12 hour discharge period (676 MWh), resulting in an efficiency of 60.5%. The efficiency is reduced at least in part by the following modeled temperature gaps: (1) 27°C between the charging temperature of -73°C at the evaporator 404 and the discharge temperature of -46°C at the condenser 408 for the first PCM stage; (2) 23°C between the charging temperature of -46°C at the evaporator 420 and the discharge temperature of -23°C at the condenser 424 for the second PCM stage; and (3) 33°C between the charging temperature of -23°C at the evaporator 436 and the discharge temperature of 10°C at the condenser 440 for the third PCM stage. In other implementations, the efficiency can be improved by reducing the magnitude of the temperature gap. Overall, the three-stage system increases the thermal capacity of the PCM system by 24%, but with that increased capacity comes increased complexity and the corresponding cost of building a more complex system.

[0092] Example 3: High efficiency three-stage PCM system for naphtha cracking ethylene and propylene refrigeration system

[0093] FIG. 10A to FIG. 10B shows the PCM energy storage system during the charging cycle, for Figure 5 A schematic process diagram of a modeling embodiment 400a of a high efficiency three-stage PCM energy storage system for an ethylene refrigeration system and a propylene refrigeration system; and FIG. 11A to FIG. 11B A schematic process diagram of a PCM energy storage system 400a during its discharge cycle is shown. System 400a is substantially similar to system 400, with the primary difference being that system 400a includes a separate refrigeration unit 500 for charging the PCM reservoir of system 400a, and thus the PCM system condensers 408, 424, and 440 are located in a second refrigeration unit 500 along with the ethylene refrigeration system 204a and the propylene refrigeration system 208a, as described in more detail below.

[0094] Ethylene refrigeration system 204a is similar to ethylene refrigeration system 204, the main difference being that system 204a omits the first compression stage (condenser 212, compressor 216, and valve 236) and uses condenser 220a to remove heat energy from the PCM suspension or heat transfer fluid of the first PCM stage. Specifically, system 204a includes a compression stage with evaporator 220a and compressor 224a, and a single condensation stage with first condenser 228a and second condenser 232a. In operation, condensed ethylene from condensers 228a, 232a is transported to evaporator 220a. In evaporator 220a, condensed ethylene absorbs heat energy and boils to gaseous state at a temperature of -60°C and a pressure of 7.5 bara. Gaseous ethylene from evaporator 220a is then transported to compressor 224a, in which gaseous ethylene is compressed to a pressure of 19.0 bara (absolute pressure) and a temperature of 4°C. The compressed gaseous ethylene from compressor 224a is then delivered to the condenser, where it is partially condensed in the first condenser 228a and then further condensed in the second condenser 232a. In the illustrated configuration, the heat transfer fluid circulates through the first condenser 228a to absorb heat energy from the condensing ethylene for the propylene refrigeration system, and the heat transfer fluid also circulates through the second condenser 232a to absorb additional heat energy from the condensing ethylene also for the propylene refrigeration system. The ethylene refrigeration system also includes a valve 240a that can be closed to prevent ethylene from flowing to the evaporator 220a.

[0095] The propylene refrigeration system 208a includes three compressor stages and one condenser stage. The first compression stage includes the first evaporator 244a, the second evaporator 248a in parallel and the first compressor 252a. The second compression stage includes the third evaporator 256a, the fourth evaporator 260a in parallel and the second compressor 264a. The third compression stage includes the third compressor 272a. The condenser stage includes a single condenser 276a. In operation, the condensed propylene from the condenser 276a is delivered to the evaporators 244a, 248a, 256a, 260a of the first and second compression stages, and is directly delivered to the compressor 272a of the third compression stage. In the first evaporator 244a and the second evaporator 248a, the condensed propylene absorbs heat energy and boils into a gaseous state at a temperature of -37°C and a pressure of 1.6 bara. As indicated by the dotted line of the first condenser 228a from the ethylene refrigeration system 204a, the heat energy from the first condenser 228a is used as a heat energy source in the evaporator 244a to boil propylene. The gaseous propylene is then delivered to the first compressor 252a, in which the gaseous propylene is compressed to a first pressure of 4.3 bara and a temperature of 8.9°C. In the third evaporator 256a and the fourth evaporator 260a, the condensed propylene absorbs heat energy and boils to a gaseous state at a temperature of -10°C and a pressure of 4.3 bara. As indicated by the dotted line of the second condenser 232a from the ethylene refrigeration system 204a, the heat energy from the second condenser 232a is used as a heat energy source in the evaporator 256a to boil propylene. The gaseous propylene from the evaporators 256a, 260a is then mixed with the compressed propylene from the first compressor 252a, and the combined gaseous propylene is then sent to the second compressor 264a, where the combined gaseous propylene is further compressed to a second pressure of 8.6 bara and a temperature of 38° C. In the third compression stage, the condensed propylene from the evaporator 276a is mixed with the compressed propylene from the second compressor 264a, and the combined gaseous propylene is then sent to the third compressor 272a, where the combined gaseous propylene is further compressed to a third pressure of 18.3 bara and a temperature of 78° C. The compressed gaseous propylene from the third compressor 272a is then sent to the condenser 276a, where it is condensed. The propylene refrigeration system also includes: a first valve 280a, which can be closed to prevent propylene from flowing to the first evaporator 244a and the second evaporator 248a; a second valve 284a, which can be closed to prevent propylene from flowing to the third evaporator 256a and the fourth evaporator 260a or any one of the first evaporator 244a and the second evaporator 248a; and a third valve 288a, which can be closed to prevent propylene from flowing to the compressor 272a, the third evaporator 256a and the fourth evaporator 260a or any one of the first evaporator 244a and the second evaporator 248a.

[0096] As described above, PCM system 400a is substantially similar to system 400, with two major differences. First, for charging the PCM: In the first PCM stage, evaporator 220a of system 204a is used instead of evaporator 404 ( Fig. 8A ); In the second PCM stage, evaporator 248a is used instead of evaporator 420 ( Fig. 8A ); and in the third PCM stage, evaporator 260a is used instead of evaporator 436. Second, the first PCM stage includes a first pump 412a for circulating the PCM suspension or heat transfer fluid for "charging" and a second pump 412b for circulating the PCM suspension or heat transfer fluid for "discharging"; the second PCM stage includes a first pump 428a for circulating the PCM suspension or heat transfer fluid for "charging" and a second pump 428b for circulating the PCM suspension or heat transfer fluid for "discharging"; and the third PCM stage includes a first pump 444a for circulating the PCM suspension or heat transfer fluid for "charging" and a second pump 444b for circulating the PCM suspension or heat transfer fluid for "discharging". According to the modeling, the PCM used in the first stage (PCM reservoir 416a) has a freezing point of -50°C and has sufficient volume to store 672MWh of energy, the PCM used in the second stage (PCM reservoir 432) has a freezing point of -29°C and has sufficient volume to store 547MWh of energy, and the PCM used in the third stage (PCM reservoir 448) has a freezing point of 0°C and has sufficient volume to store 209MWh of energy.

[0097] like FIG. 10A to FIG. 10B As shown, during charging of the PCM system 400a, the PCM suspension or heat transfer fluid circulates between the ethylene refrigeration system 204a or the propylene refrigeration system 208, 208a and the corresponding PCM reservoir. Fig. 10A), a PCM suspension or heat transfer fluid is circulated from a first PCM reservoir 416 by a pump 412a to an evaporator 220a where heat energy is transferred from the PCM suspension or heat transfer fluid to ethylene at a temperature of -60°C to boil the ethylene. The PCM suspension or heat transfer fluid then returns to the PCM reservoir 416 where it absorbs additional heat energy from the PCM reservoir at the PCM's freezing point of -50°C, and so on until the PCM in the PCM reservoir 416 is fully "charged" or solidified, or charging is otherwise suspended. At the simulated charging rate, the evaporator 220a removes heat energy from the heat transfer fluid at a rate of 56.0 MW, so that 672 MWh of energy is removed from the PCM 416 reservoir during the 12 hour charging period. In other words, 672 MWh of cold or hot capacity is "stored" so that when the PCM reservoir is "discharged", the PCM reservoir 416 can later absorb up to 672 MWh of thermal energy from the propylene refrigeration system (minus any inefficiencies introduced, for example, by absorbing thermal energy from an external source).

[0098] In the second PCM stage, the PCM suspension or heat transfer fluid is circulated from the second PCM reservoir 432 by pump 428a to the evaporator 248a, where heat energy is transferred from the PCM suspension or heat transfer fluid to propylene at a temperature of -37°C to boil the propylene. The PCM suspension or heat transfer fluid then returns to the PCM reservoir 432, where it absorbs additional heat energy from the PCM reservoir at the PCM's freezing point of -29°C, and so on, until the PCM in the PCM reservoir 432 is fully "charged" or solidified, or charging is otherwise suspended. At the simulated charging rate, the evaporator 248a removes heat energy from the heat transfer fluid at a rate of 45.6 MW, so that 547 MWh of energy is removed from the PCM reservoir 432 during the 12 hour charging period. In other words, 547 MWh of cold or hot capacity is "stored" so that when the PCM reservoir is "discharged", the PCM reservoir 432 can later absorb up to 547 MWh of thermal energy from the propylene refrigeration system (minus any inefficiencies introduced, for example, by absorbing thermal energy from an external source). Fig. 10B), the PCM suspension or heat transfer fluid is circulated from the third PCM reservoir 448 by pump 444a to the evaporator 260a, where heat energy is transferred from the PCM suspension or heat transfer fluid to propylene at a temperature of -10°C to boil the propylene. The PCM suspension or heat transfer fluid then returns to the PCM reservoir 448, where it absorbs additional heat energy from the PCM reservoir at the PCM's freezing point of 0°C, and so on, until the PCM in the PCM reservoir 448 is fully "charged" or solidified, or charging is otherwise suspended. At the simulated charging rate, the evaporator 436 removes heat energy from the heat transfer fluid at a rate of 17.4 MW, so that 209 MWh of energy is removed from the PCM reservoir 448 during the 12 hour charging period. In other words, 209 MWh of cold or hot capacity is "stored" so that when the PCM reservoir is "discharged", the PCM reservoir 448 can later absorb up to 209 MWh of thermal energy from the propylene refrigeration system (minus any inefficiencies introduced, for example, by absorbing thermal energy from an external source).

[0099] like Figure 5 and FIG. 10A to FIG. 10B As indicated by the difference between , the compressor needs to input additional energy to provide the compression required to "charge" the PCM storage. Specifically, the ethylene compressor 224a of system 500 requires 11.1 MW ( Fig. 10A ), the first propylene compressor 252s requires 16.0MW, and the second propylene compressor 264a requires 17.8MW ( Fig. 10B ), and the propylene third compressor 272a requires 26.5 MW. Overall, the energy requirements of the compressors are increased from 66.8 MW ( Figure 5 ) to 138.2 MW ( FIG. 10A to FIG. 10B ).

[0100] like FIG. 11A to FIG. 11B As shown, during the discharge of the PCM system 400a, the PCM suspension or heat transfer fluid circulates between the propylene refrigeration system 208 and the corresponding PCM reservoir. Fig.11A), the PCM suspension or heat transfer fluid is circulated from the first PCM reservoir 416 by pump 412b to the condenser 408a, where heat energy is transferred from propylene to the PCM suspension or heat transfer fluid at a temperature of -46°C to condense the propylene. The PCM suspension or heat transfer fluid returns to the PCM reservoir 416, where the PCM reservoir absorbs heat energy from the PCM suspension or heat transfer fluid at the PCM's freezing point of -50°C, and so on, until the PCM in the PCM reservoir 416 is completely "de-energized" or liquefied, or charging is suspended for other reasons. In the second PCM stage, the PCM suspension or heat transfer fluid is circulated from the second PCM reservoir 432 by pump 428b to the condenser 424a, where heat energy is transferred from propylene to the PCM suspension or heat transfer fluid at a temperature of -23°C to condense the propylene. The PCM suspension or heat transfer fluid returns to the PCM reservoir 432 where it absorbs thermal energy from the PCM suspension or heat transfer fluid at the PCM's freezing point of -29°C, and so on, until the PCM in the PCM reservoir 432 is completely "discharged" or liquefied, or charging is otherwise suspended.

[0101] In the third PCM level ( Fig. 11B ), the PCM suspension or heat transfer fluid is circulated from the third PCM reservoir 448 to the condenser 440a by pump 444b, where heat energy is transferred from the propylene to the PCM suspension or heat transfer fluid at a temperature of 10°C to condense the propylene. The PCM suspension or heat transfer fluid returns to the PCM reservoir 448, where it absorbs heat energy from the PCM suspension or heat transfer fluid at the freezing point of the PCM at 0°C, and so on, until the PCM in the PCM reservoir 448 is completely "discharged" or liquefied, or charging is suspended for other reasons.

[0102] like Figure 5 and FIG. 11A to FIG. 11B As indicated by the difference between , the compressor of the propylene refrigeration system 208 requires less energy input to provide the compression required to operate the refrigeration systems 204, 208. Specifically, the propylene first compressor 252 is reduced from 7.6 MW to 0 MW ( Fig.11A ), the propylene second compressor 264 is reduced from 20.7MW to 0MW ( Fig. 11B ), and the propylene third compressor 272 is reduced from 28.0 MW to 0 MW. Overall, the energy demand of the compressor is reduced from 66.8 MW ( Figure 5 ) is reduced to 10.5 MW ( ) of the ethylene refrigeration system 204 and the propylene refrigeration system 208 combined with the three-stage PCM energy storage system 400a during the PCM discharge period. FIG. 11A to FIG. 11B ).

[0103] Adding a separate refrigeration unit 500 for charging allows the temperature difference to be reduced to improve the efficiency of the PCM system. Table 4 shows FIG. 8A to FIG. 8B , FIG. 9A to FIG. 9B The three-stage PCM system FIG. 10A to FIG. 10B , FIG. 11A to FIG. 11B The weighted average temperature difference between the charging / discharging temperature of the high-efficiency three-stage PCM system is reduced from 26°C to 15°C at the temperature of the high-efficiency three-stage system.

[0104] Table 4: Heat transfer temperature

[0105]

[0106]

[0107] Table 5 summarizes the condenser energy input of the ethylene and propylene refrigeration system of Example 3 during standalone operation and combined operation with the three-stage PCM energy storage system in its charging and discharging cycles:

[0108] Table 5: Energy input and output of HE three-stage PCM system

[0109]

[0110]

[0111] In the case of the battery, an additional 71.4 MW of energy is used to charge the thermal "battery" during the 12 hour charging period (857 MWh), and then during the discharge period, the amount of energy required to operate the refrigeration system 200 is reduced by 56.3 MW of energy over the 12 hour discharge period (676 MWh), resulting in an efficiency of 78.9%. The efficiency is thus improved by the reduction of the following modeled temperature gaps: (1) 14°C between the charging temperature of -60°C at the evaporator 220a and the discharge temperature of -46°C at the condenser 408a for the first PCM stage; (2) 14°C between the charging temperature of -37°C at the evaporator 248a and the discharge temperature of -23°C at the condenser 424a for the second PCM stage; and (3) 20°C between the charging temperature of -10°C at the evaporator 260a and the discharge temperature of 10°C at the condenser 440a for the third PCM stage. Thus, the efficiency of HE three-level system 400a is improved from 60.5% to 78.9% relative to three-level system 400, but at the expense of increased complexity and expense.

[0112] Examples 4 to 5: Ammonia Refrigeration System

[0113] Several embodiments were modeled for using the PCM energy storage system and method of the present invention to operate a refrigeration cycle of an ammonia refrigeration system representative of refrigeration systems used in various chemical separation processes such as, for example, ammonia synthesis. Fig.13 A schematic process diagram of an embodiment 600 of such an ammonia refrigeration system is shown.For these purposes, the ammonia refrigeration system 600 was modelled at a cooling load of 50 MW at -32°C (1.05 bar evaporator pressure).

[0114] A typical or "existing" ammonia refrigeration system 600 includes three compressor stages. The first compression stage includes a first evaporator 604, a first compressor 608, and a first condenser 612. The second compression stage includes a first flasher 616, a second compressor 620, and a second condenser 624. The third compression stage includes a second flasher 628, a third compressor 632, and a third condenser 636. The ammonia refrigeration system also includes a first valve 640 for reducing the pressure from the first flasher 616 to the first condenser 604, a second valve 644 for reducing the pressure from the second flasher 628 to the first evaporator 616, and a third valve 648 for reducing the pressure from the third condenser 636 to the flasher 628.

[0115] In operation, the condensed ammonia from the first flasher 616 is delivered to the first evaporator of the first compression stage 604. In the first evaporator 604, the condensed ammonia absorbs heat energy and boils into a gaseous state at a temperature of -32°C and a pressure of 1.05 bara. The gaseous ammonia is then delivered to the first compressor 608, in which the gaseous ammonia is compressed to a first pressure of 2.7 bara and a temperature of 44.2°C. In the first condenser 612, the compressed ammonia is cooled to a temperature of 35°C at a pressure of 2.5 bara. In the second compression stage, the condensed ammonia from the second flasher 628 is delivered to the first evaporator 616, and the gaseous ammonia from the first evaporator 616 is delivered to mix with the ammonia leaving the first condenser 612 to form a combined gaseous ammonia at a temperature of 31.2°C and a pressure of 2.5 bara. The combined gaseous ammonia is then delivered to the second compressor 620, in which the gaseous ammonia is compressed to a second pressure of 6.4 bara and a temperature of 121°C. In the second condenser 624, the compressed ammonia is cooled to a temperature of 35°C at a pressure of 6.2 bara. In the third compression stage, the cooled ammonia from the third condenser 636 is sent to the second evaporator 628 of the compression stage, and the gaseous ammonia from the second flasher 628 is sent to mix with the ammonia leaving the second condenser 624 to form a combined gaseous ammonia at a temperature of 35°C and a pressure of 6.2 bara. The combined gaseous ammonia is then sent to the third compressor 632, in which the gaseous ammonia is compressed to a third pressure of 6.2 bara and a temperature of 121°C. In the third condenser 636, the compressed ammonia is condensed at a temperature of 35°C and a pressure of 6.2 bara and then sent to the second flasher 628, as described above.

[0116] In Example 4, the process was modeled using a "symmetric" cycle, where during each 24-hour period, the PCM was "charged" for 12 hours and "discharged" for 12 hours, as shown in Fig.12 As shown. In Example 5, the process was modeled using an "asymmetric" cycle, where the PCM was "charged" for 18 hours and "released" for 6 hours during each 24-hour period. The heat energy absorbed from external sources (e.g., the environment) was not taken into account (assumed to be zero). In the design of real-world systems, such external heat energy can be accommodated by enlarging the PCM volume and the heat capacity of the compressor by taking into account specific insulation values. These models assume that the PCM is directly dispersed in the suspension or encapsulated in small spheres in the suspension. The process simulation was performed in CHEMCAD using the SRK method.

[0117] In Examples 4 and 5, the respective systems are modeled by charging the PCM with a separate refrigeration unit. Both systems are modeled by assuming that the existing refrigeration units will be or will be modified to be driven by an electric drive (rather than burning fossil fuels) and that the added PCM refrigeration units will also be driven by an electric drive.

[0118] Example 5: Primary PCM system for 50MW ammonia refrigeration system (symmetric charging and discharging)

[0119] Fig.14 The PCM energy storage system is shown for use during a charging cycle. Fig.13 A schematic process diagram of a modeled embodiment of a primary PCM energy storage system 300a of an ammonia refrigeration system 600, and Fig.15 The PCM energy storage system 300a is shown during discharge. The system 300a is similar to the system 300, with the main difference that the system 300a includes a separate refrigeration unit 600a for charging the PCM reservoir of the system 300a, and therefore the PCM system condenser 604a is disposed in the second refrigeration unit 600a, as described in more detail below. As shown, adding the PCM system includes adding the PCM system condenser 308a to the first compression stage of the ammonia refrigeration system 600a (where the first PCM system condenser 308a is in parallel with the first evaporator 604a), a pump 312a and a PCM reservoir 316a, and conduits and valves to deliver heat transfer fluid from the PCM to the PCM system evaporator and condenser.

[0120] PCM refrigeration system 600a is similar to system 600 in that system 600a includes three compressor stages, but uses propane as a refrigerant instead of ammonia. The first compression stage includes a first evaporator 604a and a first compressor 608a. The second compression stage includes a first flash evaporator 616a and a second compressor 620a. The third compression stage includes a second flash evaporator 628a, a third compressor 632a, and a condenser 636a. The refrigeration system also includes: a first valve 640a, which can be closed to prevent ammonia from flowing from the first flash evaporator 616a to the first condenser 604a; a second valve 644a, which can be closed to prevent ammonia from flowing from the second flash evaporator 628a to the first flash evaporator 616a; and a third valve 648a, which can be closed to prevent ammonia from flowing from the condenser 636a to the flash evaporator 628a.

[0121] In operation, the condensed propane from the first flasher 616a is delivered to the first evaporator 604a of the first compression stage. In the first evaporator 604a, the condensed propane absorbs heat energy and boils into a gaseous state at a temperature of -41°C and a pressure of 1.05 bara. The gaseous propane is then delivered to the first compressor 608a, in which the gaseous propane is compressed to a first pressure of 2.7 bara and a temperature of -2°C. In the second compression stage, the condensed propane from the second flasher 628a is delivered to the first flasher 616a, and the gaseous propane from the first flasher 616a is delivered to mix with the propane leaving the first compressor 6081 to form a combined gaseous propane at a temperature of -5°C and a pressure of 2.7 bara. The combined gaseous propane is then delivered to the second compressor 620a, in which the gaseous propane is compressed to a second pressure of 6.2 bara and a temperature of 33°C. In the third compression stage, the cooled propane from the condenser 636a is sent to the second flasher 628a of the compression stage, and the gaseous propane from the second flasher 628a is sent to mix with the propane leaving the second compressor 620a to form a combined gaseous propane at a temperature of 27° C. and a pressure of 6.2 bara. The combined gaseous propane is then sent to the third compressor 632a, where the gaseous propane is compressed to a third pressure of 14.1 bara and a temperature of 66° C. In the condenser 636a, the compressed propane is condensed at a temperature of 39° C. and a pressure of 13.9 bara and then sent to the second flasher 628a, as described above.

[0122] like Fig.14 As shown, during charging of the PCM reservoir 316a, the PCM suspension or heat transfer fluid is circulated from the PCM reservoir 316a by pump 312a to the evaporator 604a, where thermal energy is transferred from the PCM suspension or heat transfer fluid to propane at a temperature of -41°C to boil the propane. The PCM suspension or heat transfer fluid then returns to the PCM 316a, where it absorbs additional thermal energy from the PCM reservoir at the PCM's freezing point of -37°C, and so on, until the PCM is fully "charged" or solidified, or charging is otherwise suspended. At the modeled charging rate, the evaporator 604a removes thermal energy from the PCM suspension or heat transfer fluid at a rate of 50MW, so that during the 12 hour charging period, 600MWh of energy is removed from the PCM 316a reservoir. In other words, 600MWh of cold or hot capacity is "stored" so that when the PCM reservoir is "discharged", the PCM reservoir can later absorb up to 600MWh of thermal energy from the ammonia refrigeration system 600 (minus any inefficiencies introduced, for example, by absorbing thermal energy from an external source). Fig.13 and Fig.14As indicated by the difference between , the compressor needs to input additional energy to provide the compression required to "charge" the PCM reservoir. Specifically, the first compressor 608a of system 600a requires 7.0 MW ( Fig.14 ), the second compressor 620a requires 8.5 MW, and the third compressor 632a requires 11.1 MW. Overall, the energy requirements of the compressors are reduced from 22.5 MW ( Fig.13 ) increases to 49.1 MW for the ammonia refrigeration system 600 combined with the refrigeration unit 600a and the PCM energy storage system 300a.

[0123] like Fig.14 As shown, during discharge of the PCM reservoir 316a, the PCM suspension or heat transfer fluid is circulated from the PCM reservoir 316a by pump 312a to the condenser 308a in the ammonia refrigeration system 600, where heat energy is transferred from the ammonia to the PCM suspension or heat transfer fluid at a temperature of -32°C to condense the ammonia. The PCM suspension or heat transfer fluid returns to the PCM 316a, where the PCM reservoir absorbs heat energy from the PCM suspension or heat transfer fluid at the PCM's freezing point of -37°C, and so on, until the PCM is completely "discharged" or liquefied, or discharge is otherwise suspended. Fig.13 and Fig.14 As indicated by the difference between , the compressors of the ammonia refrigeration system 600 require less energy input to provide the compression required to operate the ammonia refrigeration system 600. Specifically, the first compressor 608 is reduced from 5.8 MW to 0 MW, the second compressor 620 is reduced from 7.9 MW to 0 MW, and the third compressor 632 is reduced from 8.8 MW to 0 MW. Overall, the energy requirements of the compressors are reduced from 66.8 MW ( Fig.13 ) is reduced to 0 MW ( Fig.14 ).

[0124] Table 6 summarizes the condenser energy input of the ammonia refrigeration system during standalone operation and combined operation with the PCM energy storage system and the additional PCM refrigeration system in each of the charging cycle and the discharging cycle of the PCM energy storage system:

[0125] Table 6: Energy input and output of a primary PCM system with a dedicated refrigeration unit for charging

[0126]

[0127]

[0128] In terms of the battery, an additional 26.6 MW of energy is used to charge the thermal "battery" during the 12 hour charging period (319 MWh), and then during the discharge period, the amount of energy required to operate the ammonia refrigeration system 600 is reduced by 22.5 MW over the 12 hour discharge period (270 MWh), resulting in an efficiency of 84.6%. This efficiency is higher than the previous embodiment, at least in part because the temperature difference between the PCM charging temperature and the PCM discharge temperature is smaller, specifically, the temperature difference between the charging temperature of -41°C at the evaporator 604a and the discharge temperature of -32°C at the condenser 308a is 9°C.

[0129] Example 6: Primary PCM system for 50MW ammonia refrigeration system (asymmetric charging and discharging) Fig.16 The PCM energy storage system is shown for use during a charging cycle. Fig.13 A schematic process diagram of another modeling embodiment 300b of one of the primary PCM energy storage systems of the present invention for an ammonia refrigeration system. The PCM system 300b and the PCM refrigeration unit 600b are respectively Figure 14 to Figure 15The PCM system 300a and PCM refrigeration unit 600a are substantially similar, with three major differences. First, the PCM energy storage system 300b is configured for an asymmetric charging and discharging cycle, specifically, charging for 18 hours and discharging for 6 hours in each 24-hour period. Second, because the PCM system 300b only needs to run half the time (6 hours) of the ammonia refrigeration system 600, the thermal capacity of the PCM reservoir 316b is 300MWh (half of the PCM reservoir 316a). Third, because the PCM refrigeration unit 600a only needs to "charge" 300MWh in 18 hours (rather than 12 hours), the propane compressors 608a, 620a, and 632a do not need to compress propane at as high a rate as the corresponding compressors when used with the PCM refrigeration system 300a. Specifically, compressor 608a only needs to operate at a rate of 2.3 MW (compared to 7.0 MW when used with system 300a for a symmetrical charge / discharge cycle), compressor 620a only needs to operate at a rate of 2.8 MW (compared to 8.1 MW when used with system 300a for a symmetrical charge / discharge cycle), and compressor 632a only needs to operate at a rate of 3.7 MW (compared to 8.8 MW when used with system 300a for a symmetrical charge / discharge cycle). Therefore, for compressors 608a, 620a, 632a, a smaller capacity compressor can be used, thereby potentially reducing costs, or the same size compressor can be used and just operated at a lower compression ratio. The relatively large size of the system in Example 5 allows for greater flexibility, if budget permits, because the larger system can also be operated on an asymmetrical schedule, such as 18 hours of charge and 6 hours of discharge, or 14 hours of charge and 10 hours of discharge, in which case the discharge cycle will only deplete a portion of the thermal capacity of the PCM reservoir.

[0130] Table 7 summarizes the condenser energy input of the ammonia refrigeration system of Example 6 during standalone operation and combined operation with the PCM energy storage system and the additional PCM refrigeration system in each of the charging cycle and the discharging cycle of the PCM energy storage system:

[0131]

[0132]

[0133] In terms of the battery, an additional 8.8 MW of energy is used to charge the thermal "battery" during the 18-hour charging period (159 MWh), and then during the discharge period, the amount of energy required to operate the ammonia refrigeration system 600 is reduced by 22.5 MW over a 6-hour discharge period (135 MWh), resulting in an efficiency of 85.2%. This efficiency is roughly the same as the system of Example 6, but the longer charging period and reduced PCM capacity reduce the size of the PCM refrigeration system 600a by approximately two-thirds.

[0134] The above description and examples provide a complete description of the structure and use of exemplary embodiments. Although certain embodiments have been described above with some degree of particularity or with reference to one or more separate embodiments, those skilled in the art may make many changes to the disclosed embodiments without departing from the scope of the invention. Therefore, the various illustrative embodiments of the present invention are not intended to be limited to the specific forms disclosed. On the contrary, they include all modifications and substitutions that fall within the scope of the claims, and embodiments other than the illustrated embodiments may include some or all of the features of the illustrated embodiments. For example, components may be combined into a single structure, and / or connections may be replaced. In addition, where appropriate, aspects of any of the above embodiments may be combined with aspects of any other described embodiments to form other embodiments having comparable or different properties and solving the same or different problems. Similarly, it should be understood that the above benefits and advantages may relate to one embodiment or to several embodiments.

[0135] The claims are not intended to include, nor should they be interpreted as including, method-plus-function or step-plus-function limitations, unless such limitations are explicitly recited in a given claim using the phrases "a method for" or "a step for," respectively.

Claims

1. A system for storing refrigeration energy in a chemical separation process of a chemical plant, characterized in that: The system comprises: one or more insulated containers; a phase change material (PCM), the phase change material being disposed in the thermally insulating vessel; a refrigerant circuit that circulates a refrigerant fluid configured to be in thermal communication with the PCM such that the PCM absorbs thermal energy from the refrigerant fluid at a point in a refrigeration cycle of the process; wherein the PCM is configured to transition from an initial state to a higher enthalpy state at a transition temperature below a minimum operating temperature at the point in the refrigeration cycle; and Wherein the PCM requires at least 10 MWh to transition from the initial state to the higher enthalpy state.

2. The system of claim 1, wherein the refrigerant circuit is part of a refrigeration system, characterized in that The refrigeration system includes a compressor configured to compress the refrigerant fluid so that the refrigerant fluid can circulate to receive heat energy from the process, and the system is configured to: receiving a cooled refrigerant fluid from the refrigeration system and circulating the cooled refrigerant fluid through the refrigerant circuit such that the refrigerant fluid absorbs thermal energy from the PCM; or A heated refrigerant fluid is received from the process and circulated through the refrigerant circuit such that the PCM absorbs thermal energy from the heated refrigerant fluid.

3. The system of claim 2, wherein the refrigerant fluid is a first refrigerant fluid, characterized in that and the refrigerant circuit is a first refrigerant circuit, and the system further comprises: A PCM refrigeration circuit includes a compressor, and a second refrigerant circuit configured to circulate a second refrigerant fluid in thermal communication with the PCM such that the second refrigerant fluid absorbs thermal energy from the PCM.

4. The system according to any one of claims 2 to 3, characterized in that Wherein the compressor is electric.

5. The system according to any one of claims 1 to 4, characterized in that The PCM has a phase transition below the temperature range of -170°C to 40°C.

6. The system according to any one of claims 1 to 5, characterized in that wherein the one or more insulated vessels are first insulated vessels, and the PCM is a first PCM, and the system further comprises: one or more second insulated vessels; a second phase change material (PCM) disposed in the second thermally insulated vessel, the second PCM being configured to transition from an initial state to a higher enthalpy state at a second transition temperature higher than the transition temperature of the first PCM; Wherein the second PCM requires at least 10 MWh to transition from the initial state to the higher enthalpy state.

7. The system according to any one of claims 1 to 6, characterized in that wherein the PCM comprises one or more components selected from the group consisting of: paraffins; alcohol; Polydimethylsiloxane; water; Aqueous saline solutions; water-salt mixture; Organic chemicals; mixtures of two or more organic chemicals; Eutectic mixtures of two or more organic chemicals; and A mixture of two or more inorganic chemicals.

8. The system according to claim 7, characterized in that wherein the PCM comprises a water-salt mixture comprising one or more components selected from the group consisting of: Calcium chloride (CaCl2); Calcium chloride (CaCl2); Lithium chloride (LiCl); Magnesium chloride (MgCl2); Zinc chloride (ZnCl2); Hydrogen chloride (HCl); Lithium sulfate (Li2SO4); Sodium chloride (NaCl); Potassium chloride (KCl); Aluminum nitrate (Al(NO3)3); A combination of any two or more of the foregoing components.

9. The system according to any one of claims 1 to 8, characterized in that wherein the PCM is in a form selected from the group consisting of: a suspension, wherein the PCM is suspended directly in a liquid within the insulated vessel; encapsulating a suspension, wherein the PCM is encapsulated in a shell suspended in a liquid within the insulated vessel; as well as A plurality of containers, each container containing a portion of the suspension and including at least one heat transfer surface configured to permit thermal communication with the PCM.

10. The system according to claim 9, characterized in that The PCM is in the form of a suspension or an encapsulated suspension, and the system is configured to agitate the PCM within the insulated vessel.

11. The system according to any one of claims 1 to 10, characterized in that The process is selected from the group consisting of a steam cracking process, an ammonia synthesis process, a hydrogen production process, a paraxylene production process, propane dehydrogenation, olefin metathesis and natural gas processing.

12. A method for storing energy for refrigeration in a chemical separation process in a chemical plant, characterized in that: The method comprises: During an energy release cycle, circulating a refrigerant fluid in thermal communication with a phase change material (PCM) such that the PCM absorbs thermal energy from the refrigerant fluid at a point in a refrigeration cycle of the process; wherein the PCM is configured to transition from an initial state to a higher enthalpy state at the point in the refrigeration cycle at a transition temperature below a minimum operating temperature of the refrigerant; and Wherein during a 24-hour period, the PCM absorbs at least 10 MWh of energy from the refrigerant fluid.

13. The method according to claim 12, characterized in that The 24-hour period includes one or more energy release cycles lasting a total of 2-22 hours, and one or more energy recharge cycles lasting a total of 2-22 hours.

14. The method according to claim 13, characterized in that The lengths of the recharging cycle and the discharging cycle are adjusted or selected based on a method selected from the group consisting of: responding to requests from grid operators to reduce electricity consumption; reducing the total electricity cost of continuously operating the process over the 24 hour period to take into account changes in electricity prices over the 24 hour period; and Responsive to a temporary interruption of at least one power source of the process.

15. The method according to any one of claims 12 to 14, characterized in that The method further includes operating the compressor during the recharging cycle to simultaneously cool a refrigerant fluid circulating in thermal communication with the PCM and a refrigerant fluid used in a propylene or ethylene refrigeration system for the process.

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