METHOD FOR REDUCING FORCES (HOT FILL/RE-FILL)

Abstract

A method for controlling the magnitude of mechanical forces exerted by a solid ammonia storage material on walls of a container: determining a mechanical-strength limit of the container in terms of a hydraulic pressure P.sub.LIMIT or force F.sub.LIMIT under which the walls of container do not undergo plastic deformation, or deformation of more than 200% of deformation at the yield point; using a correlation between a temperature T.sub.SAT for the ammonia saturation/resaturation process, and the hydraulic pressure P.sub.MAT, or F.sub.MAT generated by the storage material during saturation/resaturation, to identify a minimum temperature T.sub.SATMIN where P.sub.MAT, or F.sub.MAT is kept below the limit for the mechanical strength by carrying out the saturation/resaturation process at the temperature T.sub.SAT fulfilling the condition of T.sub.SATT.sub.SATMIN.

Claims

1.-17. (canceled)

18. A method for controlling the magnitude of mechanical forces exerted by a solid ammonia storage material on walls of a container holding the storage material inside its interior volume when the storage material is undergoing saturation/resaturation with ammonia inside said storage container, said method comprising: a. determining a limit for the mechanical strength of the container in terms of a hydraulic pressure, hereinafter P.sub.LIMIT, or a hydraulic force, hereinafter F.sub.LIMIT, in its interior volume under which the walls of container do not undergo plastic deformation, or do not undergo deformation of more than 200% of a deformation at a yield point of the container walls; b. using a given correlation between i. a temperature for ammonia saturation/resaturation process of the storage material, hereinafter T.sub.SAT, and ii. the hydraulic pressure P.sub.MAT, or equivalent mechanical force F.sub.MAT generated by the storage material during saturation/resaturation at said temperature T.sub.SAT, to identify a minimum temperature, hereinafter T.sub.SATMIN, of the saturation/resaturation process where P.sub.MAT, or F.sub.MAT, exerted by the storage material is kept below the limit for the mechanical strength in terms of P.sub.LIMIT, or F.sub.LIMIT, of the container by carrying out the saturation/resaturation process at the temperature T.sub.SAT fulfilling the condition of T.sub.SATT.sub.SATMIN.

19. The method according to claim 18 wherein the storage material has a density, hereinafter D.sub.MAT, in wherein in the determination of T.sub.SATMIN, besides using the correlation between T.sub.SAT and P.sub.MAT; or F.sub.MAT, also a correlation with the density D.sub.MAT of the storage material is taken into account, as a higher density D.sub.MAT generally leads to higher mechanical forces exerted by the solid ammonia storage material on the walls of the container, where D.sub.MAT refers to the density of the ammonia storage material being fully saturated with ammonia.

20. The method according to claim 18 wherein the ammonia storage material is cooled during the saturation/resaturation process by a liquid cooling media having a boiling point, and wherein the saturation/resaturation process at the temperature T.sub.SAT fulfills the condition T.sub.CMBPT.sub.SATT.sub.SATMIN, where T.sub.CMBP is the boiling point of the cooling media.

21. The method according to claim 18 wherein the ammonia storage material is cooled during the saturation/resaturation process by a gaseous cooling media, and wherein the saturation/resaturation process at the temperature T.sub.SAT fulfills the condition T.sub.CMBPT.sub.SATT.sub.SATMIN, where T.sub.CMBP is an upper limit on the temperature at which the saturation/resaturation process is performed cooled by the gaseous cooling media.

22. The method according to claim 20 wherein T.sub.CMBP is 100 C.

23. The method according to claim 18 wherein the container has a mechanical strength which enables the container to withstand the pressure generated by desorbed ammonia at 85 C. with a volumetric expansion no greater than 0.1 volume-%.

24. The method according to claim 23, wherein the pressure generated by desorbed ammonia from the storage material at 85 C. is 12 bar.

25. The method according to claim 19 where P.sub.LIMIT, or F.sub.LIMIT, and subsequently T.sub.SATMIN are determined from: a. having an existing container design available, b. knowing from the existing design the value of P.sub.LIMIT, or F.sub.LIMIT, or using (i) standard mechanical engineering practice, (ii) hydraulic pressure measurements, or (iii) mechanical simulations to identity the value of P.sub.LIMIT, or F.sub.LIMIT, and c. using the known or identified P.sub.LIMIT, or F.sub.LIMIT, to determine the loading density D.sub.MAT and the saturation/resaturation condition T.sub.SATT.sub.SATMIN, or T.sub.CMBPT.sub.SATT.sub.SATMIN, to prevent P.sub.MAT, or F.sub.MAT, from exceeding P.sub.LIMIT, or F.sub.LIMIT.

26. The method according to claim 18 where the procedure of determining T.sub.SATMIN includes an experimental mapping procedure in which experimental data points are obtained to establish an empirical relationship or correlation between the dependent variable P.sub.MAT, and the independent variable T.sub.SAT, said procedure comprising a. preparing at least one sample of ammonia storage material; b. carrying out ammonia desorption and resaturation experiments in a sample holder capable of measuring P.sub.MAT exerted by the material on the walls of the sample holder when the material is undergoing saturation/re-saturation, said procedure being carried out at different temperature levels T.sub.SAT; c. using the experimental data points to generate a function or interpolation formula P.sub.MAT=f(T.sub.SAT), or F.sub.MAT=f(T.sub.SAT).

27. The method according to claim 18 where the procedure of determining T.sub.SATMIN includes an experimental mapping procedure in which experimental data points are obtained to establish an empirical relationship or correlation between the dependent variable P.sub.MAT, or F.sub.MAT, and the independent variables T.sub.SAT and D.sub.MAT, said procedure comprising: a. preparing at least one sample of ammonia storage material with known density D.sub.MAT; b. carrying out ammonia desorption and resaturation experiments in a sample holder capable of measuring P.sub.MAT exerted by the material on the walls of the sample holder when it the material is undergoing saturation/re-saturation, said procedure being carried out at different temperature levels T.sub.SAT; c. using the experimental data points to generate a function or interpolation formula P.sub.MAT=f(T.sub.SAT, D.sub.MAT), or F.sub.MAT=f(T.sub.SAT, D.sub.MAT) in the case where samples with different densities D.sub.MAT are measured.

28. The method according to claim 19 where the procedure of determining T.sub.SATMIN is done by creating a relationship between P.sub.MAT, or F.sub.MAT, and T.sub.SAT via computer simulations using parameters describing the ammonia storage material, ammonia itself, and the storage material in saturated form.

29. The method according to claim 19 where the procedure of determining T.sub.SATMIN is done by creating a relationship between P.sub.MAT, or F.sub.MAT, and T.sub.SAT and D.sub.MAT via computer simulations using parameters describing the ammonia storage material, ammonia itself, and the storage material in saturated form.

30. The method according to claim 18 where the limit for the mechanical strength of the container in terms of the hydraulic pressure P.sub.LIMIT or the hydraulic force F.sub.LIMIT in its interior volume is the limit under which the walls of container do not undergo deformation of more than 110%, 120%, or 150% of the deformation at the yield point of the container walls.

31. A method of designing a container for accommodating solid ammonia storage material where a process temperature for ammonia saturation/resaturation T.sub.SAT and a target density of the storage material, D.sub.MAT, are fixed, and the outcome of the design method is a container design capable of withstanding a resulting exerted pressure from the material, P.sub.MAT, or force F.sub.MAT, upon ammonia saturation/resaturation, the method comprising using a known relation between T.sub.SAT, D.sub.MAT, and P.sub.MAT, or F.sub.MAT, to establish a value of P.sub.MAT, or F.sub.MAT, and use this value for the design of the container such that its mechanical strength measured in terms of a hydraulic-limit parameter P.sub.LIMIT, or F.sub.LIMIT, under which walls of the container do not undergo plastic deformation, or do not undergo deformation of more than 200% of a deformation at a yield point of the container walls, is equal to or exceeds the value of P.sub.MAT, or F.sub.MAT.

32. A container filled with a solid ammonia storage material with a storage density, D.sub.MAT, capable of desorbing and absorbing/reabsorbing ammonia, said container having a mechanical strength corresponding to a limit-pressure parameter, P.sub.LIMIT, or limit-force parameter F.sub.LIMIT, at which pressure, or force, inside the container the container does not undergo plastic deformation, or does not undergo deformation of more than 200% of a deformation at a yield point of the container walls, and said storage material in the container being filled with ammonia by a saturation/re-saturation process in which the saturation/resaturation of the storage material is performed with the storage material inside the container at a process temperature, T.sub.SAT, fulfilling the condition T.sub.SATT.sub.SATMIN, where T.sub.SATMIN is a minimum temperature of the saturation/resaturation process where P.sub.MAT, or F.sub.MAT, exerted by the storage material is kept below the limit for the mechanical strength in terms of P.sub.LIMIT, or F.sub.LIMIT, of the container.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Exemplary embodiments are now described, also with reference to the accompanying drawings, wherein

[0057] FIG. 1 shows the material expansion pressure, P.sub.MAT, during ammonia saturation plotted against the cooling medium temperature, T.sub.SAT;

[0058] FIG. 2 shows data points and a resulting model correlation between P.sub.MAT and different combinations of T.sub.SAT and D.sub.MAT;

[0059] FIG. 3 shows the normalized deformation of an ammonia storage container versus the number of resaturation cycles;

[0060] FIG. 4 shows an illustration of elastic and plastic deformation;

[0061] FIG. 5 shows an example of a process for resaturation storage material with ammonia inside containers with appropriate control of T.sub.SAT:

[0062] FIG. 6 shows an example of a computer-simulation method to establish a relationship between P.sub.MAT, or F.sub.MAT, and T.sub.SAT and, if applicable, D.sub.MAT, to determine T.sub.SATMIN.

DESCRIPTION OF EXAMPLES

[0063] The temperature level, T.sub.SAT, is determined by the temperature of the cooling media since the cartridges generate heat when ammonia is absorbing. Choosing different cooling media is possible while still fulfilling the T.sub.SATMIN.

[0064] FIG. 1 shows the material expansion pressure, P.sub.MAT, during ammonia saturation plotted against the cooling medium temperature, T.sub.SAT, during saturation of a material sample kept in a container capable of monitoring the expansion pressure. The mechanical pressure exerted by the material depends strongly on temperature, T.sub.SAT. The measurements are done for same sample but varying ammonia gas saturation pressures P.sub.SAT. This shows that the effect of P.sub.MAT is strongly an effect of temperature and not the ammonia gas pressure.

[0065] Hence, FIG. 1 shows data points and an empirical correlation (based on the data points) between the temperature T.sub.SAT for the ammonia saturation/resaturation process of the storage material, and the hydraulic pressure P.sub.MAT (the equivalent mechanical force F.sub.MAT could be used in an equivalent manner) generated by the storage material during saturation/resaturation at said temperature T.sub.SAT.

[0066] With a given limit for the mechanical strength of the given cartridge in terms of P.sub.LIMIT, or FLINT, under which the walls of cartridge do not undergo plastic deformation, or do not undergo deformation of more than 110%, 120%, 150%, or 200% of the deformation at the yield point of the container walls, a correlation of this type is used to identify a minimum temperature T.sub.SATMIN of the saturation/resaturation process where P.sub.MAT, or F.sub.MAT, exerted by the storage material is kept below the limit for the mechanical strength, of the cartridge. Having found T.sub.SATMIN the saturation/resaturation process is carried out at a temperature T.sub.SAT fulfilling the condition T.sub.SATT.sub.SATMIN.

[0067] Alternatively, the temperature T.sub.SAT at which the saturation/resaturation is performed may be predetermined and fixed. In this case the correlation of the type shown in FIG. 1 and described above is used for the design of a cartridge for the solid ammonia storage material capable of withstanding a resulting exerted pressure from the material, P.sub.MAT, or force F.sub.MAT. The relation between T.sub.SAT, and P.sub.MAT, or F.sub.MAT, is used to find the value of P.sub.MAT, or F.sub.MAT, that corresponds to the given value of T.sub.SAT. This found value of P.sub.MAT, or F.sub.MAT is then used for the design of the cartridge such that the cartridge's mechanical strength measured in terms of a hydraulic-limit parameter P.sub.LIMIT, or F.sub.LIMIT, under which walls of the cartridge do not undergo plastic deformation, or do not undergo deformation of more than 110%, 120%, 150%, or 200% of the deformation at the yield point of the container walls, is equal to or exceeds the value of P.sub.MAT, or F.sub.MAT.

[0068] FIG. 2 shows data points and a resulting empirical model correlation between P.sub.MAT and T.sub.SAT similar to FIG. 1, however for different ammonia-storage-material densities D.sub.MAT, with D.sub.MAT being a parameter in the representation of P.sub.MAT as a function of T.sub.SAT of FIG. 2 for four different levels of D.sub.MAT, labeled as A to D g/cm.sup.3, B1.13 g/cm.sup.3, C1.25 g/cm.sup.3 and g/cm.sup.3). The ammonia storage material in degassed form is SrCl.sub.2, and Sr(NH.sub.3).sub.8Cl.sub.2 in fully saturated form. As a reference point, the density is calculated when the material is in its saturated form. For each density level there is a strong correlation with T.sub.SAT. The model equation best describing the experimental model data done on small material samples is of the form P.sub.MAT=A*exp(B*T.sub.SAT+C*D.sub.MAT), but any kind of mathematical representation giving a good data representation is envisaged. Three illustrations, labelled as P.sub.LIMIT-1, P.sub.LIMIT-2, and P.sub.LIMIT-3, are made, where a certain P.sub.LIMIT-3 is linked to another density D.sub.MAT than that of P.sub.LIMIT-1 and P.sub.LIMIT-2, and as a result the required saturation temperature, T.sub.SATMIN, is located on the X-axis. To ensure that P.sub.MAT is not exceeding P.sub.LIMIT it can be seen that T.sub.SAT has to be equal toor largerthan T.sub.SATMIN, i.e. T.sub.SATT.sub.SATMIN.

[0069] With a given limit for the mechanical strength of the given cartridge in terms of P.sub.LIMIT, or F.sub.LIMIT, under which the walls of cartridge do not undergo plastic deformation, or do not undergo deformation of more than 110%, 120%, 150%, or 200% of the deformation at the yield point of the container walls, and a given target density D.sub.MAT of ammonia-storage material in the cartridge, a correlation of this type is used to identify a minimum temperature T.sub.SATMIN of the saturation/resaturation process where P.sub.MAT, or F.sub.MAT, exerted by the storage material is kept below the limit for the mechanical strength, of the cartridge. Having found T.sub.SATMIN for the given P.sub.LIMIT and D.sub.MAT the saturation/resaturation process is carried out at a temperature T.sub.SAT fulfilling the condition T.sub.SATT.sub.SATMIN.

[0070] Alternatively, the temperature T.sub.SAT at which method is performed may be predetermined and fixed. If one of various available target densities D.sub.MAT of ammonia-storage material in the cartridge is also given, the correlation of the type shown in FIG. 2 and described above is used for the design of a cartridge for the solid ammonia storage material capable of withstanding a resulting exerted pressure from the material, P.sub.MAT, or force F.sub.MAT. The relation between T.sub.SAT, D.sub.MAT, and P.sub.MAT, or F.sub.MAT, is used to find the value of P.sub.MAT, or F.sub.MAT, that corresponds to the given values of T.sub.SAT and D.sub.MAT. The determined value of P.sub.MAT, or F.sub.MAT, is then used for the design of the cartridge such that the cartridge's mechanical strength measured in terms of a hydraulic-limit parameter P.sub.LIMIT, or F.sub.LIMIT, under which walls of the cartridge do not undergo plastic deformation, or do not undergo deformation of more than 110%, 120%, 150%, or 200% of the deformation at the yield point of the container walls, is equal to or exceeds the value of P.sub.MAT, or F.sub.MAT.

[0071] FIG. 3 shows proof of the features of the present invention. Data are shown for cartridges undergoing consecutive cycles of NH.sub.3-degassing and NH.sub.3-resaturation. In this example, the tested cartridges are cylindrical and made of aluminum. In the specific design used in these cartridges, the end-caps represent the weakest point and are made to be able to withstand at least 1.7 MPa gas pressure without plastic deformation (i.e. P.sub.LIMIT=1.7 MPa), corresponding to P.sub.LIMIT-2 of FIG. 2. The ammonia-storage-material density is approx. 1.13 g/cm.sup.3 in this example, which is supposed to correspond to D.sub.MAT-A in FIG. 2. Then it can be seen from FIG. 2 that the analysis gives T.sub.SATMIN at approx. 38 C. In the conventional resaturation process the ammonia gas pressure was approx. 7-8 bar, and a cooling media of water was kept at about 20 C (T.sub.SAT 20 C.) to have fast cooling by removal of ammonia absorption heat from the cartridge, i.e. below T.sub.SATMIN 38 C.). It is observed from the testing that even when these units are consistently operated at much lower pressure than P.sub.LIMIT=1.7 MPa (desorption pressure for degassing: 2-4 bar; corresponding to 0.2-0.4 MPa; saturation pressure=7-8 bar, corresponding to 0.7-0.8 MPa), the cartridge deforms inelastically even after only a few saturation cycles, and the cartridges can no longer be used even before reaching, e.g., ten refills since they do no longer fit in the installation volume. This is shown for two different units of same type.

[0072] Applying the method of the present invention to this example (viz. to a cartridge of the same type filled with the same storage material with the same density, i.e. the same T.sub.SATMIN) the following has been found: The same test has been carried out, however with the cooling media kept at about 55 C (T.sub.SAT 55 C.), i.e. above T.sub.SATMIN 38 C.). The lower part of the graph on FIG. 3 shows degassing/refill cycles when the process and design constraint according to the method of the present invention is fulfilled. It is seen that fulfilling the saturation process condition (triangles) eliminates the massive plastic deformation observed after few cycles with the conventional method (the hollow and filled square points).

[0073] FIG. 4 shows an exemplary illustration of the relationship between strain (deformation) and stress on a metal member, e.g. a container. Plastic deformation (also referred to as inelastic deformation) of a container occurs when the stress created by the material gives a strain on the container wall that exceeds the level at the so-called yield point: The material deforms (strains) because of the stress (created by F.sub.MAT, or P.sub.MAT). When T.sub.SAT>T.sub.SATMIN, the stress created by the material is reduced and the container remains in the area of elastic deformation.

[0074] As schematically shown in FIG. 4, in the elastic-deformation regime the relation between stress and strain is nearly linear while in the plastic-deformation regime the strain-stress relation becomes nearly flat (meaning that the material continues to deform even if the stress is not increased). The transition between the linear and the flat relation typically has a continuously changing slope; i.e. the change is slope is not abrupt but extends over a finite strain range. The yield point is defined to be the stress at which a material begins to deform plastically; more specifically, the yield point is typically just before the transition from the linear to the flat part of the relation (when looking into the direction of increasing strain).

[0075] In some embodiments described herein the limit for the mechanical strength of the container in terms of the pressure, PUNT, or the force, F.sub.LIMIT, is defined to be the pressure, or the force, in the container's interior volume under which the walls of container do not undergo plastic deformation; i.e. there is no deformation beyond the yield point.

[0076] In other embodiments, however, a small degree of plastic deformation is acceptable; i.e. a strain beyond the yield point in the transition to the flat plastic-deformation regime before it becomes completely flat. In these embodiments the mechanical strength of the container in terms of the pressure, P.sub.LIMIT, or the force, F.sub.LIMIT, is defined to be the pressure, or force, that causes no deformation beyond a point in the transition region of the stress-strain diagram which is referred to as maximum acceptable plastic deformation, or MPD. The point MPD is defined as the maximum degree of plastic deformation that is acceptable for a certain container after which is does no longer fit into the physical application for which it is intended. Ideally, there is no plastic deformation (as indicated in the pervious paragraph) but in some special circumstances a minor degree of plastic deformation can be accepted; in such cases the parameter MPD can be 110, 120, 150, or 200% of the strain (=deformation) at the yield point. For example, if a sample container of diameter 100 mm can elastically deform by 0.5 mm just below the yield point (which means that it would there still return to normal shape), then MPD in this case at a strain of 200% of the strain at the yield point would be at maximum 1 mm, and the resulting maximum diameter would be 101 mm.

[0077] FIG. 5 shows an example of resaturation of a plurality of containers filled inside with storage ammonia material of the sort described above. The storage containers are immersed in a trough filled with cooling media (e.g. cold water), and are thus cooled by the cooling media. The temperature of the cooling media is controlled with a suitable device for control of the temperature of the media to reach a targeted saturation temperature T.sub.SAT, e.g. a sensor for measuring the cooling-media temperature and a feed-back controller comparing the measured temperature with a target temperature and adjusting the temperature, or the flow, of the cooling media to counteract any difference between the measured and the target temperature. Common methods for creating movement of the cooling media to increase heat transfer from the container undergoing saturation can be applied, such as actively creating circulation of the cooling media in the trough by means of a pump or propeller. Ammonia is supplied as pressurized gas to the inside of the storage containers.

[0078] FIG. 6 shows a diagram of a simulation method to estimate or predict the relationship between T.sub.SAT, D.sub.MAT and the resulting pressure P.sub.MAT (or F.sub.MAT). Relevant parameters describing ammonia and the ammonia storage material (with/without ammonia absorbed), referred to as Thermodynamic input, and independent variables as well as the density, D.sub.MAT of the ammonia storage material are fed to a computer model such as a Finite Element Method (FEM) simulation. For example, the computer model outputs P.sub.MAT (or F.sub.MAT) as a function of T.sub.SAT and given D.sub.MAT. This enables a minimum temperature T.sub.SATMIN to be identified of the saturation/resaturation process where P.sub.MAT (or F.sub.MAT) exerted by the storage material is kept below the limit for the mechanical strength in terms of P.sub.LIMIT, or F.sub.LIMIT, of the container.

FURTHER EXAMPLES

Example 1: Procedure for Determining Forces from Saturation at Various Temperatures, and Finding a Minimum Saturation Temperature T.SUB.SATMIN .for a Given Cartridge

[0079] In order to determine the relation between temperature, material density and saturation forces from ammonia storage material several experiments were conducted following a general procedure:

[0080] A predetermined mass of dry SrCl.sub.2 powder was loaded in a reactor volume, which to was then closed. The mass of SrCl.sub.2 was determined to yield a certain density, D.sub.MAT, after saturation of SrCl.sub.2 with ammonia. It was determined by multiplying the density by the volume of the reactor and dividing by the molar mass of fully saturated Sr(NH.sub.3).sub.8Cl.sub.2 and multiplying by the molar mass of SrCl.sub.2.

[0081] The closed-off reactor was evacuated to remove ambient air and then subjected to a pressure of ammonia gas. The uptake of ammonia was followed by weighing the reactor and it was in this way ensured that the SrCl.sub.2 was completely saturated by ammonia. During the uptake the force of the saturating SrCl.sub.2 acting one end of the reactor was measured using a load cell. The temperature of the reactor walls were actively controlled using Peltier-elements.

[0082] After complete saturation the reactor was heated and the pressure at the outlet fixed to just above ambient pressure to degas ammonia from the reactor. The material was degassed for a fixed time before a pressure of ammonia was applied again to resaturate the material. In this way a sample could be recycled several times and the force measurement could be conducted for several temperature points.

[0083] To create the full map of the force for various temperatures and densities the reactor was loaded several times with various mass of SrCl.sub.2 each cycled at various temperature points.

[0084] This procedure could be made for any relevant material capable of absorbing ammonia reversibly. Other examples of suitable ammonia storage materials are CaCl.sub.2, BaCl.sub.2 or any other metal ammine complex in pure form or as a mixture of salts. The typical formula for metal ammine complexes is: M(NH.sub.3).sub.XH.sub.Y where M is a metal ion, X is the coordination number for ammonia (from 0 up to 8 or even 12 in some salts), H is a halide (e.g. chloride ion) and Y is the number of halide ions in the complex. In saturated form the SrCl.sub.2 and CaCl.sub.2 salts absorb 8 ammonia molecules (Sr(NH.sub.3).sub.8Cl.sub.2 or Ca(NH.sub.3).sub.8Cl.sub.2.

[0085] With a given limit for the mechanical strength of the given cartridge in terms of P.sub.LIMIT, or F.sub.LIMIT, under which the walls of cartridge do not undergo plastic deformation, or do not undergo deformation of more than 110%, 120%, 150%, or 200% of the deformation at the yield point of the container walls, and a given target density D.sub.MAT of ammonia-storage material in the cartridge, a relation of this type is used to identify a minimum temperature T.sub.SATMIN of the saturation/resaturation process where P.sub.MAT, or F.sub.MAT, exerted by the storage material is kept below the limit for the mechanical strength, of the cartridge. Having found T.sub.SATMIN for the given P.sub.LIMIT and D.sub.MAT the saturation/resaturation process is carried out at a temperature T.sub.SAT fulfilling the condition T.sub.SATT.sub.SATMIN.

Example 2: Finding a Metal Wall Thickness Based on a Fixed Saturation, Temperature, and Storage-Material Density

[0086] A refill process has been established to refill cartridges at a temperature of 20 C. The ammonia storage material density given is 1175 g/cm.sup.3, which gives a material pressure P.sub.MAT=3.2 MPa. The cartridge is cylindrical, with an outer diameter of 178 mm due to requirements of available space on certain vehicles on the market. It is decided to make the cartridge from a deep-drawn aluminum-alloy casing. After deep-drawing, the aluminum alloy has a yield strength of 170 MPa; the yield strength, or yield point is defined to be the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible.

[0087] The minimum shell thickness of the cylinder can now be determined by the thin-walled assumption:

[00001]$t=\frac{\sqrt{\frac{{\mathrm{Pd}}^2}{}+d^2}-d}{2}=\frac{\sqrt{\frac{3.2.Math..Math.\mathrm{MPa}.Math.{\left(178.Math..Math.\mathrm{mm}\right)}^2}{170.Math..Math.\mathrm{MPa}}+{\left(178.Math..Math.\mathrm{mm}\right)}^2}-178.Math..Math.\mathrm{mm}}{2}=0.83.Math..Math.\mathrm{mm}$

Example 3

[0088] Given a certain design pressure and design temperature, the allowable stress (from vessel material) and required vessel radius (from volume), a common approach is the design by a rule method, following design rules such as the ASME Boiler and Pressure Vessel Code; ASME Section VIII Division 1.

[0089] The ASME design code gives for a thin walled design R/t>=10 (R=vessel radius, t=wall thickness) the following design formulas for cylindrical shell minimum wall thickness requirement.

[0090] Considering circumferential stress:

[00002]$t=\frac{P*\mathrm{Ro}}{S*E+0.4*P}$

[0091] Considering longitudinal stress:

[00003]$t=\frac{P*\mathrm{Ro}}{2*S*E+1.4*P}$

t=Wall thickness (in.)
P=Design pressure (psi)
Ro=Outside radius (in.)
S=Allowable stress (psi)
E=Weld joint efficiency factor

[0092] Similarly the allowable pressure can be calculated using the ASME code and design by rule method. Given a design temperature, allowable stress (from vessel material), vessel radius (from volume) and wall thickness, the following formulas provide the maximum allowable pressure.

[0093] Considering circumferential stress:

[00004]$P=\frac{S*E*t}{\mathrm{Ro}-0.4*t}$

[0094] Considering longitudinal stress:

[00005]$P=\frac{2*S*E*t}{\mathrm{Ro}-1.4*t}$

[0095] By way of example, the allowable pressure based on given vessel material and geometry is calculated for a thin walled deep drawn cylindrical aluminum shell.

t=3 mm=0.118 in
Ro=98 mm=3.504 in
S=133.3 MPa=16437.6 psi (based on yield strength of Aluminum alloy at 170 MPa, and a safety factor of normally 1.5 according to ASME code)

E=1

[0096] Allowable pressure based on circumferential stress:

[00006]$P=\frac{16437.6.Math..Math.\mathrm{psi}*1*0.188.Math..Math.\mathrm{in}}{3.504.Math..Math.\mathrm{in}-0.4*0.118.Math..Math.\mathrm{in}}=561.6.Math..Math.\mathrm{psi}=3.9.Math..Math.\mathrm{Mpa}$

[0097] Allowable pressure based on longitudinal stress:

[00007]$P=\frac{2*16437.6.Math..Math.\mathrm{psi}*1*0.188.Math..Math.\mathrm{in}}{3.504.Math..Math.\mathrm{in}-0.4*0.118.Math..Math.\mathrm{in}}=1163.0.Math..Math.\mathrm{psi}=8.0.Math..Math.\mathrm{Mpa}$

[0098] Taking the lowest value from the calculations above gives allowable pressure 3.9 MPa.

[0099] Furthermore, there is, as mentioned above, a design safety factor of 1.5 in the calculation. This leads to an allowable pressure PUNT of 3.9 MPa/1.5=2.6 MPa.

[0100] Using the correlation of FIG. 2 for a density of D.sub.MAT-C a value of the minimum temperature T.sub.SATMIN at which the saturation/resaturation process is to be carried of approx. 40 C. for this specific value of D.sub.MAT is obtained.

[0101] All publications and existing systems mentioned in this specification are herein incorporated by reference.

[0102] Although certain methods and products constructed in accordance with the teachings of the invention have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all embodiments of the teachings of the invention fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.