JP2006038068A - Pressure damping method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure damping method of obtaining the maximum pressure damping effect to restrict a damper container compact and capable of obtaining a high function with simple structure. <P>SOLUTION: In this pressure damping method to be used for a high-pressure flow passage, a pressure damping fluid is a single component or a mixture appropriately composed of appropriate combination of at least two kinds of components. In the supercritical pressure condition or more, temperature is adjusted so that dimensionless isothermal compressibility expressed with a formula 1: K<SB>T</SB>= P*<SB>KT</SB>exceeds 1.5, and operated. In the formula, P means pressure and<SB>KT</SB>means isothermal compressibility. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pressure buffering method used for a high-pressure channel of an incompressible fluid. In particular, the present invention relates to a method of thermally pressure buffering by controlling the fluid to an appropriate temperature and utilizing its compressibility.

  In general, in a high-pressure fluid supply apparatus, a pressure buffering method such as an accumulator is used in order to buffer the pressure of a piping system by storing or deriving a part of a fluid flowing through an incompressible high-pressure channel.

  As an accumulator, the structure as shown in FIG. 16 is generally used. Specifically, there is a container 1 connected to a high-pressure flow path 4 through which a high-pressure fluid (buffered fluid) 3 to be braked flows, and the buffer fluid 5 exists inside the container 1. At this time, for example, when the fluid flowing through the high-pressure channel 4 becomes excessive, the high-pressure fluid 3 in the high-pressure channel 4 flows into the container 1 and compresses the buffer fluid 5 enclosed in the container 1. Buffer pressure rise. On the contrary, when the fluid flowing through the high-pressure channel 4 is insufficient, the high-pressure fluid 3 in the container 1 flows into the high-pressure channel 4 and the buffer fluid 5 enclosed in the container 1 is expanded to buffer the pressure drop. To do. As a result, the accumulator pressure or buffering function functions.

  An example in which this configuration is used for buffering a fluid having a supercritical pressure is also known. This is based on the well-known property that when a fluid with a supercritical pressure is heated, compressibility is produced and behaves like a general gas (see Patent Document 1).

  In addition, as another configuration of the accumulator, a system such as a prada type, a piston type, a diaphragm type, or a metal bellows type is often used. These are different from the accumulator shown in FIG. 16 in that they have a partition wall that can be deformed or moved to partition between a high-pressure fluid (buffered fluid) to be braked and the buffer fluid. Due to the partition wall, mixing of the buffered fluid and the buffer fluid is suppressed, and an inert gas such as nitrogen is mainly used as the buffer fluid.

Specifically, a configuration as shown in FIG. 17 is conventionally known as a piston type accumulator. A piston 102 is slidably accommodated in a bottomed cylindrical outer case 101, an O-ring 103 or the like is fitted to the outer periphery of the piston 102, and a plug 104 is fixed to the opening 105 of the outer case 101, Further, nitrogen gas (buffer fluid) is sealed in the gas chamber S1 and sealed with a plug bolt 106, and the liquid chamber S2 is connected with a high-pressure fluid (buffered fluid). In this accumulator, the opening 105 of the outer case 101 is fixed by welding. (For example, refer to Patent Document 2).
JP-A-6-50492 JP-A-8-296601

  However, in the above method, in order to have a large pressure buffering function, it is necessary to enlarge the space for sealing the buffer fluid, and the pressure buffering means or device becomes large, which increases the cost burden. is there.

  Also, when the same kind of fluid is used as a buffer fluid, if the buffered fluid has a high operating pressure, the pressure buffer function with the same kind of fluid does not work sufficiently, and what kind of buffer fluid is suitable? May require detailed examination.

  Accordingly, an object of the present invention is to provide a pressure buffering method for drawing out the pressure buffering effect to the maximum and keeping the buffer container compact. It is another object of the present invention to provide a pressure buffering method having high functionality with a simple configuration.

  As a result of intensive studies to solve the above problems, the present inventor has found that the above object can be achieved by the pressure buffering method shown below, and has completed the present invention.

The present invention is a pressure buffering method for use in a high-pressure flow path, wherein the buffer fluid is a mixture of an appropriate composition of a single component or an appropriate combination of at least two types of components, the temperature was adjusted so as dimensionless isothermal compression ratio K _T represented by the following formula 1 is more than 1.5, characterized in that operation. Here, P is the pressure, and κ _T is the isothermal compression rate.

K _T = P * κ _T (Formula 1)
Usually, the larger the volume of the buffer means and the higher the compressibility of the buffer fluid, the higher the pressure buffer function. The present inventor further suggests that the effect of pressure buffering is effective to bring it closer to an isothermal process as much as possible, and in the case of a supercritical pressure fluid, it is optimal for increasing the isothermal compression rate and reducing the volume of the buffer container. It has been found that there is a temperature. In other words, as a condition of the buffer fluid, it is a mixture having an appropriate composition of a single component or an appropriate combination of at least two types of components, and the pressure is set to a supercritical pressure or higher, so that the compression rate is extremely high. The buffer function can be adjusted by controlling the temperature, and even if the conditions of the buffered fluid fluctuate, the buffer means can be easily adjusted to the optimum conditions. It becomes possible to do. In addition, it is possible to reduce the size of the buffer container and to reduce the size of the entire apparatus.

At this time, dimensionless isothermal compressibility K _T, if the condition of more than 1.0, the higher the value the pressure buffering function is preferred for high. However, it is difficult to have an effective buffer function by reducing the volume of the buffer fluid at a level slightly exceeding about 1.0, but in a region that performs an effective compression function by a relatively simple method. From the viewpoint of controlling the temperature of the fluid, _KT is preferably not less than a certain value exceeding 1.0. The present inventors, from the knowledge of the relevant art, including the analysis and experimental procedure of various fluids, dimensionless isothermal compressibility K _T as such optimum area is adjusted to greater than 1.5, it is preferred to operate Was devised.

  If the pressure of the high-pressure fluid is far from the critical pressure, buffering the same kind of fluid becomes ineffective, so it is preferable to buffer with a fluid having a critical pressure at a higher pressure. It can be realized by using a single component fluid different from the fluid in a state of supercritical pressure or higher.

  Furthermore, since these functions are limited in scope for single component buffer fluids, the inventor can also extend to mixtures of appropriate compositions of appropriate combinations of at least two components. In this way, a wide range of applications can be secured, and the pressure buffering effect can be maximized by selecting the material of the buffer fluid according to the fluid to be buffered (high pressure fluid) and setting its operating temperature. It becomes possible.

The present invention relates to a pressure buffering method for use in a high-pressure flow path, wherein the buffer fluid is a mixture having an appropriate composition of an appropriate combination of at least two components, and the pressure is higher than any of the critical pressures of the constituent fluids. high, gas-liquid two-phase zone state, the supercooled liquid state, in any of the superheated vapor state, dimensionless isothermal compression ratio K _T represented the temperature in equation 1 is adjusted to exceed 1.5 , Characterized by operation. Here, P is the pressure, and κ _T is the isothermal compression rate.

K _T = P * κ _T (Formula 1)
When a specific fluid is in a gas-liquid two-phase region and stored in a container having a certain volume, the function of absorbing the pressure change by adjusting the gas-liquid ratio if the temperature is set within a predetermined range (That is, corresponding to a pressure buffering function). The present inventor has devised that a pressure buffering method with a very high compressibility can be formed by using such a function and bringing the effect of pressure buffering as close to an isothermal process as possible. By the control, a pressure buffering method that can be easily adjusted and can be applied to various specifications can be formed. In addition to the gas-liquid two-phase region state, the same function is exhibited not only in the supercooled liquid state, the superheated steam state, and the state in which these fluids are transitioned transiently. By using it, it has become possible to form a pressure buffering method with a very high compressibility. In addition, as described above, in a supercritical pressure fluid, it is possible to increase the isothermal compression rate at an optimal temperature and to reduce the volume of the buffer container, thereby reducing the size of the buffer container and reducing the overall size of the apparatus. Can be achieved.

  The present invention is the pressure buffering method described above, characterized by including a pressure increasing means.

  The pressure buffering method in the present invention forms a pressure accumulating / buffering function under an optimum condition with a high compression rate by controlling the temperature of the buffer fluid. However, when the pressure of the high-pressure fluid is high, it may be desired to lower the operating pressure in the buffer container in order to obtain a high compressibility. At this time, it is possible to select a more optimal condition by adding a pressure increasing means between the high-pressure fluid side and the buffer container. Specifically, the pressure increasing means can be formed by using a piston or the like and making the pressure receiving area on the buffer container side larger than the pressure receiving area on the high pressure fluid side.

  The present invention is the pressure buffering method described above, characterized in that a means for promoting heat exchange with the temperature control means is added to a part of the container containing the buffer fluid to approximate the isothermal process.

  The pressure buffering method according to the present invention basically forms a pressure accumulating / buffering function under an optimum condition with a high compressibility by controlling the temperature of the buffer fluid. It has a function to follow. However, when a pressure change occurs, there is a risk that a time delay may occur in the stock pressure / pressure buffering. Therefore, by providing a gas-liquid thermal contact promoting means such as a cooling fin body in the buffer flow container, it is possible to quickly follow the change and maintain the temperature in the buffer container almost constant, and in an isothermal process. By bringing them closer, it is possible to maintain a high animal pressure / pressure buffering function.

  As described above, by controlling the temperature of the buffer fluid, the pressure buffer effect can be maximized and the buffer fluid container can be pressed compactly. In particular, the buffer fluid is selected as a single component or a mixture having an appropriate composition of an appropriate combination of at least two components, pressure control above the supercritical pressure, gas-liquid two-phase region state, supercooled liquid state, By adopting any superheated steam state, a pressure buffering method with a very high compressibility can be formed. Further, by providing a pressure increasing means between the buffer fluid and the buffered fluid, it is possible to select a more optimal condition and to secure a stable pressure accumulation / buffer function. As described above, according to the present invention, it is possible to provide a pressure buffering method that is compact and highly functional with a low cost by a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The accumulator pressure and buffering action can obtain higher efficiency as the compression rate of the buffer fluid is higher. In general, it is well known that a liquid has a small compressibility and a gas has a large compressibility. Therefore, when the substance transitions from a liquid to a gas, the compressibility tends to increase as the temperature increases. However, based on the analysis of the inventor described later, when the temperature change of the compressibility under the condition of the critical pressure or higher is actually examined using carbon dioxide (CO ₂ ) as an example, it is as shown in FIG. That is, the compressibility becomes a curve having a peak at a temperature higher than the critical temperature under a predetermined pressure condition. Therefore, it is possible to form a stable and very high compressibility state by controlling the temperature of the buffer fluid near the critical temperature. Such characteristics are not limited to the above CO ₂ , and the same applies to other fluids such as parahydrogen (H ₂ ) as shown in the examples.

Specifically, in FIG. 1, Pr and Tr are the critical pressure and the critical temperature obtained by dividing the pressure P and the temperature T by the critical pressure Pc = 73.77 bar and the critical temperature Tc = 304.13K, respectively. When Pr = 1.1, there is a sharp peak (K _T = 11.9) at a temperature slightly higher than the critical temperature, Tr = 1.015. As the pressure increases, the value of the peak decreases and the width increases. It turns out that the temperature corresponding to the peak moves to the high temperature side.

In the present invention, the non-dimensional isothermal compression ratio K _T represented by the following formula 1 can hold a high compression ratio state when exceeding 1.5. Here, P is the pressure, and κ _T is the isothermal compression rate.

K _T = P * κ _T (Formula 1)
When the dimensionless isothermal compression ratio _KT is 1.5 or more, preferably 2 or more, an accumulator having a highly efficient pressure buffering function can be obtained.

That is, for example, when CO ₂ is used, it is difficult to improve the compression ratio in a region where the compression ratio slightly exceeds 1.0 near Pr under a condition where Pr exceeds 2, as shown in FIG. The volume of the fluid cannot be reduced. In actual operation, the pressure of the buffer fluid changes within a certain range, so it is necessary to allow for a further margin. It may be necessary to change the compression rate of the buffer fluid depending on the condition of the buffered fluid, and it is preferable that the compression rate has a predetermined variable width depending on the temperature of the buffer fluid. That is, it is preferable that the buffer fluid has a maximum compressibility within a predetermined temperature range as in the case where Pr in FIG. 1 is 1.5 or less. Such request, the compressibility analysis or considering the empirical result characteristics, dimensionless isothermal compressibility K _T of buffer fluid which is suitable for practical application of which will be described later various buffer fluid (mixture including a fluid) 1.5 As mentioned above, the conclusion of more preferably 2 or more was obtained.

Next, a pressure buffering method using a buffer fluid different from the high pressure fluid will be described.
That is, when the buffer fluid as described above is limited to the same type of fluid as the high-pressure fluid, the pressure buffer function has a limit, and it may be difficult to obtain a sufficient buffer effect. Specifically, as shown in FIG. 1, when CO ₂ is used, the peak value of _KT is 1 when Pr is between 3 and 4, and at higher pressures, _KT is 1 in all temperature ranges. It turns out that it becomes the following. That is, when P> Pc and the distance from Pc is large, the buffering of the same kind of fluid becomes ineffective. The use of CO ₂ as a buffer gas at such a high pressure is limited to the case where there is little concern about contamination. Accordingly, as a result of a detailed examination of what is suitable as a buffer fluid when the operating pressure of the buffered fluid is high, it has been found that it is useful to use the following configuration.

  (A) By a method of filling a supercritical buffer fluid in an accumulator container having a partition wall, a buffering effect can be expected because Pc is high. Here, the buffer fluid can generate a high Pc state by selecting an appropriate material pair including the case where the buffer fluid is a mixture of at least two components by mixing the appropriate materials, and the temperature range can be adjusted. It becomes possible.

  (B) A buffer fluid in a two-phase region is stored in an air chamber of an accumulator having a partition wall or connected to a gas phase portion of a gas-liquid container for the buffer fluid. Here, the buffer fluid can generate a high Pc state by selecting an appropriate material pair including the case where the buffer fluid is a mixture of at least two components by mixing the appropriate materials, and the temperature range can be adjusted. It becomes possible.

  (C) The pressure is converted to a low pressure by the pressure increasing means or the pressure shifting means and buffered with a fluid in the two-phase region or near Pc.

Here, the pressure buffering method in a supercritical multi-component fluid will be described in more detail.
When the buffer fluid is a mixture composed of an appropriate composition of an appropriate combination of at least two components, the critical pressure of the buffer fluid can be increased, and a highly compressible state can be created. The buffer function can be adjusted by controlling the temperature. Specifically, as will be described in the examples described later, by using a mixture of argon (Ar) and ammonia (NH ₃ ), a mixture of helium (He) and CO ₂ , etc. as a buffer fluid, It is possible to adjust the temperature at which the critical pressure state is formed, and operation and control can be performed under conditions with a high compression rate.

  In addition, by selecting a mixture that can form a gas-liquid two-phase region inside the container as the buffer fluid at the operating pressure on the high-pressure fluid side, the temperature range can be adjusted and a state with a high compressibility can be created. be able to. That is, the excess of the high-pressure fluid is buffered by liquefying the buffer fluid, and the shortage of the high-pressure fluid is buffered by vaporization of the buffer fluid. Thus, even if surplus / shortage of the high-pressure fluid occurs, it has a function of changing the gas-liquid ratio of the buffer fluid and following the change.

Further, FIG. 2-1 to 2-3 shows the temperature change in _{K T} in a single component (CO _2), in the region of the liquid slightly supercooled than the saturation temperature, substantially Pc>P> 0.9 * Pc In this range, there is a region of K _T > 1, and when the temperature is raised, it increases toward the saturation temperature. In the region of steam slightly superheated from the saturation temperature, there is a region of K _T > 1 up to the low pressure region. Such characteristics can be used as a buffer function as in the case of the gas-liquid two-phase region, and an optimal buffer function can be formed by controlling the temperature to a predetermined temperature. Furthermore, since the same function is exhibited even in a state where these are transitioned transiently, such a function can be used.

Based on the above knowledge, a basic embodiment in the case of configuring an actual accumulator will be described with reference to FIG. Specifically, the buffer fluid 5 is present in the container 1 connected to the high-pressure channel 4 through which the high-pressure fluid (buffered fluid) 3 to be braked flows, and the high-pressure fluid 3 is in a supercritical state (operation). for pressure> critical pressure Pc), which adjusts the temperature so that the dimensionless isothermal compressibility K _T exceeds 1.5. As described above, _KT is preferably 1.5 or more, more preferably 2 or more. In order to ensure such conditions, temperature control is performed by arranging a constant temperature means 6 including a heating means, a temperature detection means, and a heat insulation means around the container 1. Therefore, the volume of the accumulator can be reduced, and the apparatus can be made compact.

  The buffer function in the container 1 at this time is, for example, when the fluid flowing through the high-pressure channel 4 becomes excessive, the high-pressure fluid 3 in the high-pressure channel 4 flows into the container 1 and compresses the buffer fluid 5. Buffer pressure rise. On the contrary, when the fluid flowing through the high-pressure channel 4 is insufficient, the high-pressure fluid 3 in the container 1 flows into the high-pressure channel 4 and expands the buffer fluid 5 to buffer the pressure drop. As a result, the accumulator pressure or buffering function functions. The container 1 is provided with a connecting portion 7 and is used for filling the buffer fluid 5 or for additional connection of another container when the volume of the container 1 is small. In addition, the space part corresponding to the container 1 is not limited to one each, but by utilizing the buffer effect of arranging a plurality of space parts in series or the dispersion effect of arranging in parallel, It is possible to further enhance the function of the accumulator. It is needless to say that such an accumulator can have various configurations depending on the purpose, and is not limited to the configuration of FIG.

  In addition, when P> Pc and the distance from Pc is large, the buffering of the same kind of fluid becomes ineffective, so it is converted to a low pressure by the pressure increasing means or the pressure shifting means, and It is possible to buffer with a fluid in the two-phase region or near Pc. Specifically, as illustrated in FIG. 4, a container 12 is added as a pressure increasing means between the container 1 and the container 2, and a slidable piston 8 b is disposed inside the container 12. The piston 8a arranged is interlocked by the connecting portion 13, the pressure receiving surface 8d on the container 2 side of the piston 8b is formed to have a larger area than the pressure receiving surface 8c on the high pressure flow path 3 side of the piston 8a, and the piston 8b The container 1 side space 12b of the divided container 12 is provided inside the thermostatic means 6 of the container 1. Here, not only the above-described configuration example in which the container 12 is separated from the container 1, but also a configuration in which the container 12 is built in and integrated in the container 1, or a piston mechanism can be provided instead of the container 1.

  Further, when a pressure change occurs in the high-pressure fluid 3, there is a possibility that a time delay may occur in the livestock pressure / pressure buffer in the container 1. By providing the heat exchange accelerating means 14 with the constant temperature means 6 inside the container 1, the temperature inside the container 1 is maintained almost constant, and a high animal pressure / pressure buffering function is maintained by approaching an isothermal process. It becomes possible. Specific examples of the heat exchange accelerating means 14 include a shell-and-tube heat exchanger as shown in FIG. 5 and a tubular body having a fin body. A means with a high heat exchange rate that can promote gas-liquid heat contact is suitable. By connecting to the constant temperature means 6 and maintaining the heat exchange promoting means 14 at a temperature that is not different from the control temperature of the constant temperature means 6, the temperature in the container 2 can be kept constant.

  Hereinafter, the result of analyzing the conditions for enhancing the pressure buffering effect will be described in detail mainly in the case of supercritical pressure.

(1) To keep the accumulator size compact, it is effective to appropriately control the temperature of the buffer fluid. In other words, for the analysis of the accumulator size in the isothermal process, the isothermal compression rate κ _T shown in the following equation _,
κ _T = − (dv / dP) t / v = (dρ / dP) t / ρ
Is available.
When a change in kappa _T is negligible in the range of [Delta] P, the volume Vo of the buffer fluid required to absorb the change of ΔV alteration of pressure [Delta] P,
V ₀ = (ΔV / ΔP) / κ _T. . . . . (1)
It can be expressed as.
Especially when using an ideal gas,
κ _T = 1 / P. . . . . (2)
It becomes.

(2) Now, for the compression ratio,
κ _S = − (dv / dP) s / v = (dρ / dP) s / ρ. . . . . (3)
There is also an adiabatic compression ratio κ _S represented by:
The sound speed Vs is
Vs = sqrt ((dρ / dP) s)
And
κ _S = v / Vs ² = 1 / Vs ² / ρ. . . . . (4)
A relationship exists.
In particular, κ _S is important when the pressure change in the accumulator is fast. Conversely, with respect to gradual changes, to suppress the V ₀ is advantageous to choose a large fluid kappa _T.

(3) to characterize the properties of the buffer fluid, it is effective introduction of dimensionless isothermal compressibility K _T = P * κ _T is where the ratio of the case of an ideal gas.
Similarly, the expression of dimensionless adiabatic compression rate K _S = P * κ _S is also used for the adiabatic compression rate.
Between κ _T and κ _S ,
κ _T = κ _S * Cp / Cv. . . . . (5)
The relationship exists.
Since thermodynamically always Cp> Cv, the relationship of κ _T > κ _S holds.

(4) As a general recognition, it is well known that liquid has a low compressibility and gas has a high compressibility.
When transitioning from a liquid to a gas, the compressibility tends to increase as the temperature increases.
Unless otherwise specified, the following analysis was based on NIST data, which is highly reliable worldwide.

(5) Taking CO ₂ as an example, the temperature change of _KT is examined with P> Pc using the equations (4) and (5), as shown in FIGS.
In FIG. 1, Pr and Tr are the critical pressure and the critical temperature obtained by dividing the pressure P and the temperature T by the critical pressure Pc = 73.77 bar critical temperature Tc = 304.13K, respectively. When Pr = 1.1, there is a sharp peak (K _T = 11.9) at a temperature slightly higher than the critical temperature, Tr = 1.015. As the pressure increases, the value of the peak decreases and the width increases. It turns out that the temperature corresponding to the peak moves to the high temperature side. Further, the peak value of Pr is K _t between the 3 and 4 is 1, at higher pressures, K _T is seen to be a 1 or less in all temperature range.

Further, in FIG. 6, P = 1.5Pc (about 100.7bar) _K T in, _{K S} and _K T for _{N 2} at the same pressure and temperature, _K value of _S is also _{K T _N 2, K S _N} 2 As shown. The K _T value for CO _{2 has} a peak value (approximately 2.5) near 54 ° C., whereas the K _T value for N ₂ is 1 or less (0.95 to 0.96) in the indicated temperature range. It is. At this pressure, the size of the pressure accumulator can be made compact by using CO ₂ heated to near 54 ° C. as a buffer gas compared to N ₂ that is generally used. On the other hand, it is a result of the advantageous slight CO ₂ at 67 ° C. or higher in comparison with _{N 2} for _{K S.}
It can be understood from the CO ₂ isovolume curve (v = vc) shown in FIG. 7 that the _KT peak shifts to the high temperature side as the pressure increases. In the range shown, it is almost a straight line, and a tendency similar to that shown in FIGS. 1 and 6 is observed. As P> Pc, the fluid density abruptly changes from a liquid to a gas around the isovolume curve (v = vc). The transition point is shifted to a higher temperature side as the pressure P is separated from Pc. Since the compressibility is a differential property with respect to P, it has a peak near this transition point. This is determined to be the main factor that increases _KT .

(6) The temperature change of _KT was similarly investigated also about the single phase area of P <Pc.
The values shown in FIGS. 2-1 to 2-3 are the values of K _T and K _{S when} P is 0.95 * Pc, 0.9 * Pc, and 0.7 * Pc.
First, in the liquid region slightly supercooled from the saturation temperature, there is a region of K _T > 1 in the range of approximately Pc>P> 0.9 * Pc. Increasing the temperature increases towards the saturation temperature. In the region of steam slightly superheated from the saturation temperature, there is a region of K _T > 1 up to the low pressure region. As the temperature is lowered, it increases towards the saturation temperature. In any case, the peak value increases as it approaches Pc, and diverges at T = Tc in the limit of P → Pc. These _KT abnormalities in the P <Pc region are connected to the P> Pc region.

The above calculation is for CO ₂ , but according to the principle of the corresponding state, it is determined that the same tendency is shown if the other molecules are converted with Pc and Tc.

(7) Further, look at this trend from another angle.
The Boyle curve is defined by (d (Pv) / dp) t = 0. This is equivalent to the condition of K _T = 1.
The Boyle curve for Ar is shown in FIG. An example of a Boyle curve for the van der Waals equation of state is shown in FIG. The Boyle curve starts from the state of the saturated liquid, passes through the vicinity of the supercritical point (bypassing the low temperature / high pressure side), reaches a maximum pressure of about 3.5 Pc (27/8 * Pc in the van der Waals equation of state), and the low pressure Head to the gas phase on the high temperature side.
In fact, K _T > 1 is satisfied with respect to the non-dimensional isothermal compression ratio within this curve.

(8) The above analysis is based on the case where a single component is used as the buffer fluid. However, in the system to be used, the temperature and pressure of the high-pressure channel are specified, and the selection of the buffer fluid substance and its operating temperature and pressure The issue is how to set the. With regard to the selection of the buffer fluid material, note that it creates a state with a high compressibility. In reality, many other factors need to be considered, such as the adequacy of the operating temperature of the buffer fluid, the safety, ease of handling, and availability of the fluid. The critical pressure and critical temperature of typical substances are shown in Table 1 (quoted from the National Astronomical Observatory edition “Science Chronology” published by Maruzen Co., Ltd.) The critical temperature is widely distributed from low temperature to high temperature. It can be seen that CO ₂ has a relatively large critical pressure near room temperature. Familiar substances with higher critical pressure are NH ₃ and water. However, it may be difficult to handle because the critical temperature becomes high.

緩衝流体の物質の選定での第一の方法は、これら比較的大きな臨界圧力を持つ物質を選ぶことである。但し、先述のように、圧縮率の大きな状態に対する温度が受け入れ難い場合や余りにも高圧で充分な圧縮率が稼げない場合には別の方法を見出す必要がある。

The first method in selecting the buffer fluid material is to select materials with these relatively large critical pressures. However, as described above, another method needs to be found when it is difficult to accept a temperature for a state where the compression ratio is large or when a sufficient compression ratio cannot be achieved at a high pressure.

(9) Specifically, there is a method using a multi-component buffer fluid instead of a single component, and an overview of the vapor-liquid equilibrium of a two-component system at high pressure is given for the ethylene-n-heptane system.
FIG. 10 shows a PT diagram of a mixture having a constant composition when the ethylene (C ₂ H ₄ ) concentration is 89.31 mol%, 60.52 mol%, and 28.57 mol%. AA ′ and BB ′ are vapor pressure curves of a single component of C ₂ H ₄ and n-heptane, respectively, and points A and B are critical points. Since the boiling point and dew point of the mixture are different, for example, in the case of C ₂ H ₄ 60.5%, the gas-liquid two-phase region is a region sandwiched between the boiling point curve of D′ DC and the dew point curve of E′EC. The point is the critical point in this composition. When the C ₂ H ₄ concentration is changed, a critical locus indicated by a broken line of AC′CB from the point A of 100 mol% to the point B of 0 mol% is drawn. In a mixture of combinations in which the critical temperatures of the two components are moderately separated, as in this example, the intermediate composition has a higher critical pressure than any single component constituting the mixture.
This fact has important implications for the selection of buffer fluids at high pressure.
Even if it is difficult to select a state where the dimensionless isothermal compression ratio _KT is large for a single component due to high pressure, a critical pressure can be obtained by properly mixing the composition with a mixture of at least two components selected appropriately. By increasing the value, it is possible to generate a state where _KT is large in an appropriate temperature range.
For example, a mixture of a substance having a critical point at an extremely low temperature such as He, hydrogen (H ₂ ), nitrogen (N ₂ ) and a substance having a critical point at a high temperature (such as He—CO ₂ ) has a high critical pressure in a wide temperature range. The gas-liquid two-phase region extends to a relatively high pressure.
In a multi-component system, even if pressure is specified, the equilibrium temperature depends on the composition, so it is necessary to select the composition in consideration of the operating temperature of the accumulator.

  The present invention verifies and optimizes the optimum conditions for operating the buffer fluid based on the above analysis.

As an example, propane (C ₃ H ₈ ) and H ₂ are used as a buffered fluid and C ₃ H ₈ , N ₂ , CO ₂ , H ₂ , He, Ar, NH ₃ or The case where these combinations were used as a buffer fluid was verified.

Although the high-pressure fluid is used in many fields, U.S. Pat. No. 4,531,529 was referred to in selecting the pressure-temperature conditions of the high-pressure fluid in Examples 1 and 2 below. In the above patent, methane, ethane, C ₂ H ₄ , C ₃ H ₈ , isobutane, n-butane, R-12, and R-22 are listed as fluids. Among them, utilization of C ₃ H ₈ is mentioned. It has been detailed. The supercritical condition temperature is 32 to 120 ° C., and the pressure is a maximum of 142 Kg / cm ² g (= 140 bar). A typical value is 106 Kg / cm ² g (= 105 bar).

<Example 1>
An accumulator using CO ₂ as a buffer fluid is used for pressure buffering in a high-pressure channel of C ₃ H ₈ (temperature: 32 to 120 ° C., pressure: 105 bar). The critical pressure Pc for C ₃ H ₈ is about 42.5 bar, whereas the critical pressure Pc for CO ₂ is about 73.8 bar.
FIG. 11 shows the temperature change of the dimensionless isothermal compression rate at 105 bar. The case where N ₂ or C ₃ H ₈ is used as the buffer fluid is also shown.
The dimensionless isothermal compression ratio is about 0.96 in the display range in the case of commonly used N ₂ , and becomes 1 or more at about 160 ° C. or higher when C ₃ H ₈ itself is used, but the maximum value is about Stayed at 1.24. On the other hand, when CO ₂ was used, the maximum value was about 2.88 at about 50 ° C., and was 2 or more in the range of about 46 to 64 ° C., indicating that the buffering effect of CO ₂ was excellent. As for the dimensionless adiabatic compressibility, it was shown that nitrogen is about 60 ° C. or less, CO ₂ is about 60 to 180 ° C., and C ₃ H ₈ is about 180 ° C. or more.

<Example 2>
An accumulator using NH ₃ as a buffer fluid is used for pressure buffering in a high-pressure channel of C ₃ H ₈ (temperature of 32 to 120 ° C., pressure of 140 bar). The critical pressure Pc of C ₃ H ₈ is about 42.5 bar, while the critical pressure Pc of NH ₃ is about 112.8 bar.
FIG. 12 shows the temperature change of the dimensionless isothermal compression rate at 140 bar. The case where N ₂ and CO ₂ are used as the buffer fluid is also shown.
The dimensionless isothermal compression ratio is about 0.93 in the display range in the case of N ₂ , takes about 1.64 maximum value at about 75 ° C. when CO ₂ is used, and 1.5 in the range of about 66 to 92 ° C. That's it. On the other hand, when NH ₃ was used, a maximum value of about 5.37 was obtained at about 146 ° C., indicating that the buffering effect of NH ₃ was excellent.

<Example 3>
In a cold neutron source apparatus using an accelerator, a high-pressure parahydrogen (H ₂ ) circulation loop having a supercritical pressure of about 15 bar and a temperature of about 20 K is used for neutron deceleration. In this loop, the temperature dependence of the dimensionless isothermal compression rate at 15 bar when an accumulator using H ₂ itself as a buffer fluid was used was examined. For comparison, the same supercritical gas He was used as a buffer fluid.
When the temperature change of the non-dimensional isothermal compression rate is obtained, as shown in FIG. 13, in the case of He, the display range is constant at about 0.96, while H ₂ itself is about 34.1K and has a maximum value of about 6.08. In the range of about 33.7 to 36.3 K, the value was 2 or more, indicating that the buffering effect of H ₂ itself is excellent.

<Example 4>
The case where the pressure in Example 2 was increased to 180 bar and a mixture of Ar and NH ₃ was used as a buffer fluid was also examined. The critical pressure Pc of Ar is about 48.7 bar, while the critical pressure Pc of NH ₃ is about 112.8 bar.
FIG. 14 shows a calculation result of the non-dimensionalized isothermal compressibility at a pressure of 180 bar for a mixture of Ar 21 mol% and NH ₃ 79 mol% by a modified Redrich-Kwon state equation. For comparison, NH ₃ alone is also shown.
When NH ₃ is used alone, a maximum value of about 2.51 is obtained at about 168 ° C., and becomes 2 or more in the range of about 160 to 184 ° C. On the other hand, a mixture of Ar 21 mol% and NH ₃ 79 mol% takes a maximum value of about 2.03 at about 124 ° C., becomes 1.5 or more in the range of about 113 to 153 ° C., and takes a maximum value of 124 ° C. or less. Was a gas-liquid two-phase region state, and a temperature of 124 ° C. or higher was a superheated steam state.
From the viewpoint of non-dimensional isothermal compression ratio, it is advantageous to use NH ₃ alone at a temperature close to 168 ° C. However, it is an explosive gas in that the operating temperature can be lowered by using a mixture with Ar. There is an effect of diluting NH ₃ with an inert gas.

<Example 5>
The case where the pressure in Example 2 was increased to 200 bar and a mixture of He and CO ₂ was used as a buffer fluid was also examined. The critical pressure Pc for He is about 2.27 bar, whereas the critical pressure Pc for CO ₂ is about 73.8 bar.
FIG. 15 shows the calculation result of the dimensionless isothermal compressibility at a pressure of 200 bar for a mixture of He 55 mol% and CO ₂ 45 mol% using a modified Redrich-Kwon equation of state. It has been found that the dimensionless isothermal compression ratio is in the range of about 64.2 to 70.2 ° C. and has very large values of about 648 to 18.8, respectively. Within this range, the mixture was in a gas-liquid two-phase region.

  As described above, since various fluids can be applied as buffered fluids in the present invention, the use of high-pressure fluid can be extended to multiple branches. Further, in the present application, the description is limited to the basic usage method, but a more useful system configuration can be formed by arbitrarily combining the above configuration examples. Moreover, it is clear that it can be applied to more cases by combining with various technologies, and has high versatility.

Explanatory diagram illustrating change in compressibility of fluid versus critical temperature Explanatory diagram illustrating temperature change of CO ₂ compression rate Explanatory diagram illustrating temperature change of CO ₂ compression rate Explanatory diagram illustrating temperature change of CO ₂ compression rate Explanatory drawing which shows the structural example of the accumulator which concerns on this invention Explanatory drawing illustrating the configuration of the pressure increasing means according to the present invention Explanatory drawing illustrating the configuration of the heat exchange promoting means according to the present invention Explanatory diagram illustrating temperature change of fluid compressibility Explanatory diagram illustrating the isovolumetric curve of CO ₂ Explanatory diagram illustrating the Boyle curve for Ar Explanatory diagram illustrating the Boyle curve for the van der Waals equation of state Explanatory drawing which shows the vapor pressure curve of ethylene-n-heptane system Explanatory drawing which shows the temperature change of the compression rate in Example 1. FIG. Explanatory drawing which shows the temperature change of the compression rate in Example 2. FIG. Explanatory drawing which shows the temperature change of the compressibility in Example 3. Explanatory drawing which shows the temperature change of the compressibility in Example 4. Explanatory drawing which shows the temperature change of the compression rate in Example 5. FIG. Explanatory drawing which shows the example of 1 structure of the accumulator which concerns on a prior art Explanatory drawing which shows the other structural example of the accumulator which concerns on a prior art.

Explanation of symbols

1, 2, 12 Container 3 High-pressure fluid (buffered fluid)
4 High-pressure channel 5 Buffer fluid 6 Constant temperature means 7 Connection part 8 Piston 9 Sealing means 13 Connection part 20 Heat exchange promoting means

Claims (4)

A pressure buffering method for use in a high-pressure channel, wherein the buffer fluid is a mixture of a single component or an appropriate composition of an appropriate combination of at least two components, and the temperature is expressed as pressure buffer method dimensionless isothermal compression ratio K _T represented by 1 is adjusted to exceed 1.5, characterized in that operation. Here, P is the pressure, and κ _T is the isothermal compression rate.
K _T = P * κ _T (Formula 1) A pressure buffering method for use in a high-pressure flow path, wherein the buffer fluid is a mixture composed of an appropriate composition of an appropriate combination of at least two components, and the pressure is made higher than any of the critical pressures of the constituent fluids. liquid two-phase region state, the supercooled liquid state, in any of the superheated vapor state, the dimensionless isothermal compression ratio K _T represented the temperature in equation 1 is adjusted to exceed 1.5, operated A pressure buffering method. Here, P is the pressure, and κ _T is the isothermal compression rate.
K _T = P * κ _T (Formula 1)   3. The pressure buffering method according to claim 1, further comprising a pressure increasing means. The pressure buffering method according to any one of claims 1 to 3, wherein a means for promoting heat exchange with the temperature control means is added to a part of the container containing the buffer fluid to approximate an isothermal process.

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