AU2005321123A1

AU2005321123A1 - Method for controlled filling of pressurized gas tanks

Info

Publication number: AU2005321123A1
Application number: AU2005321123A
Authority: AU
Inventors: Jean-Yves Faudou; Jean-Yves Lehman; Jaya-Sitra Pregassame
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2004-12-22
Filing date: 2005-11-15
Publication date: 2006-07-06
Also published as: CA2592319A1; CN100572890C; CN101087975A; WO2006070141A1; FR2879719B1; JP2008525733A; EP1831598A1; EP1831598B2; ATE496256T1; KR20070114706A; DE602005026053D1; KR101192906B1; EP1831598B1; FR2879719A1; JP5019462B2; CA2592319C

Abstract

The method involves parametrizing the filling using a chosen derivative value of inlet pressure in a cylinder according to time. The value is chosen automatically or manually according to environmental temperature measured before the filling and the initial pressure of gas in the cylinder. The final pressure in the cylinder is calculated according to nominal filling capacity or calculated temperature.

Description

WO 2006/070141 PCT/FR2005/050947 METHOD FOR CONTROLLED FILLING OF PRESSURIZED GAS TANKS The invention relates to a method for controlling 5 the filling of gas cylinders. In the present invention, the terms "cylinders" and "tanks" which designate hermetically sealed containers for storing pressurized gas, are used as equivalents. 10 Since environmental conservation is becoming an increasingly pressing concern both for industrial companies and for private individuals, demand for "clean" fuels for motor vehicles is steadily growing. One possible alternative for replacing 15 conventional fuels is the use of gas. However, while filling a tank with gasoline or fuel oil, which are liquid fuels, is an easy and rapid operation, filling tanks with gas is a much more delicate operation. Owing to the compressibility of 20 gases, the filling can lead to considerable temperature rise and also raises the problem of "metering" the quantity of material transferred. In fact, the gas must be injected from a gas storage zone into pressurized gas tanks or cylinders 25 (200 bar or more depending on the gas and the application); the storage zone is itself under high pressure or under low pressure, in which case it is necessary to use a compressor. For safety reasons, the final pressure in the 30 tank, as well as the temperature of the gas in the tank and the mass of gas stored, must not exceed the tank strength limits as determined by the manufacturers of said tanks. Moreover, the faster the filling, the greater the temperature rise, and hence the more 35 difficult it is to optimize the quantity of gas inside the tank. Tanks are accordingly very often filled below their capacity, filling occurs more frequently, and WO 2006/070141 - 2 - PCT/FR2005/050947 consumption is difficult to assess, providing a source of discomfort for the user. Furthermore, it must be observed that the gas temperature inside the cylinder is very difficult to 5 obtain because it would require the installation of a temperature probe placed directly in the cylinder, with all the sealing problems that this implies, and a connection between the vehicle and the storage station for the exchange of data. 10 Obviously, the same difficulties arise for the supply of gas to all types of tanks or cylinders. Conventionally, the filling takes place at ambient temperature, using the principle whereby the measured parameters are controlled and/or the maximum values of 15 these parameters are estimated, that is, the pressure and/or temperature, using the onboard temperature measurement, that is, the measurement of the gas temperature in the cylinders, as in patent applications EP1205704 and EP1336795, or by using the measurement of 20 the mass injected, obtained by weighing (US 4 527 600, US 4 648 430, US 5 711 947, US 5 771 948, US 5 810 058, US 5 881 779) or by measuring the flow rate (US 4 993 462, US 5 238 030, US 5 752 552). Furthermore, another method for overcoming the 25 problem of insufficient filling consists in cooling the gas entering the cylinder to a temperature set at a value below the ambient temperature, as described in patent application EP1331289. However, the temperature selected is not optimized and does not represent a 30 comprehensive solution for the optimal and safe filling of the cylinders. Document EP 1 452 794 A2 describes a filling method at a rate depending on the ambient temperature, the filling being interrupted when the temperature 35 measured in the tank reaches a maximum limit.

WO 2006/070141 - 3 - PCT/FR2005/050947 Document US 5 628 349 describes a filling method and a filling rate which depends on the gas temperature measured in the tank. Document US 6 598 624 describes a filling method 5 in which the filling rate is adjusted according to the instantaneous pressure measured in the tank. All the methods described are either difficult to implement because the parameters to be measured are relatively inaccessible, particularly the internal 10 temperature of the gas, or are inappropriate for certain applications, such as weighing for the vehicle application, or use measurement means which lack accuracy in certain cases, particularly instruments for measuring the mass flow rate in the case of hydrogen, 15 so that the maximum temperature in the cylinder is not controlled, or which do not permit optimization of the filling. Thus a real need exists for a method for controlling gas cylinders or tanks which is at once 20 reliable regardless of the data available to the operator, and particularly when he cannot determine the temperature in the tanks, easy to implement, easy to use and suitable for any type of cylinder and any type of filling, particularly for rapid fillings. 25 The following terms are used in the present invention. The "nominal pressure" or "working pressure" is the maximum pressure that the gas feed can reach at a uniform temperature, for example at 15'C (288K), the 30 cylinder being full. The "nominal temperature" is the temperature at which the nominal pressure of the cylinder is defined (typically 15 0 C) . The "cylinder design temperature" is the maximum 35 temperature which can be reached in a cylinder in service, this value being given by the manufacturer.

WO 2006/070141 - 4 - PCT/FR2005/050947 The "nominal filling capacity" is the mass of gas which can be stored in a given cylinder. This value is also specified by the manufacturer and is generally given in the form of a nominal pressure at a nominal 5 temperature. The "maximum permissible temperature" of the cylinder is the maximum pressure which must not be exceeded in a cylinder in service. The present inventors, following lengthy and 10 thorough research, have found that the various requirements listed could be met by calculating a maximum filling pressure corresponding to the more severe of the following two conditions: nominal filling capacity and cylinder design temperature. If the final 15 filling pressure is lower than or equal to this maximum filling pressure, the filling operation remains within the operating limits of the cylinder. This method is called "safe" because it serves to satisfy the two safety limit values, that is, the 20 nominal capacity and the maximum permissible temperature of the cylinder. The maximum filling pressure is preferably calculated as a function of the ambient temperature and the initial pressure, which are previously measured, 25 and of the filling rate expressed for example in pressure units per unit time (in bar/seconds for example). In practice, the initial cylinder pressure is first measured by balancing the connector and the 30 filling line with the cylinders by injecting a small quantity of gas. The ambient temperature is also measured at the filling station. The ambient temperature measured at the station must be representative of the atmosphere around the cylinders. 35 In general, the temperature measured at the filling terminal is fairly representative of the temperature at the cylinders, but it may be useful to confirm this.

WO 2006/070141 - 5 - PCT/FR2005/0509 47 The system then calculates the maximum pressure corresponding to the nominal mass or to the design temperature, using the measured parameters, that is the ambient temperature and the initial pressure in the 5 cylinder, and using the value of the rate determined in pressure units per unit time. During the filling, the gas pressure is measured at the connector or the filling line, downstream of the sonic element. The pressure measured at this level is equal to the 10 pressure in the cylinders during filling. A robot then calculates the derivative of this pressure with respect to time and this parameter is representative of the tank filling rate. The filling is then interrupted when the pressure in the cylinders reaches the maximum 15 value thus calculated. Thus the filling has been controlled exclusively using the measured input pressure. According to the invention, it is therefore necessary to measure the tank temperature in real time. 20 According another particular embodiment, the value of the derivative of the gas input pressure as a function of filling time or rate in pressure units per unit time can be determined by two criteria: " Either the filling rate will serve to obtain a 25 minimum filling ratio of the cylinder commensurate with its nominal filling capacity, and regardless of the filling time. This minimum filling ratio is an intrinsic datum of the system and corresponds to a value compatible 30 with the client's requirement. In the field of hydrogen vehicle filling, for example, the client may typically demand a minimum filling ratio of 90%, for example. " Or the filling rate must serve to complete the 35 filling within a given maximum period of time and regardless of the filling ratio at the end of filling. This maximum filling time is an WO 2006/070141 - 6 - PCT/FR2005/050947 intrinsic datum of the system and corresponds to a value compatible with the client's requirements. In the field of hydrogen vehicle filling, for example, the client may typically 5 demand a maximum filling time of 3 minutes, for example. Once the criterion is selected, the filling rate may then depend on the ambient temperature and the previously measured initial pressure. 10 These choices (which criterion and which limit value) can be left to the initiative of the client or the operator of the filling station, and can be made before each new filling or fixed for all fillings. This rate is typically between 0.05 bar/s and 15 20 bar/s preferably between 0.10 and 15 bar/s and even more preferably between 0.5 bar/s and 12 bar/s. According to an advantageous alternative, the filling can be carried out "cold" that is, the filling is carried out with gas cooled to a given temperature. 20 According to this particular embodiment, the gas input temperature in the cylinder is calculated according to the following parameters: the initial pressure, ambient temperature, final filling pressure and filling rate, to obtain the nominal storage 25 capacity of the cylinder, in a given filling time, while complying with the operating limits of the cylinder. The final pressure can be set arbitrarily or according to the process conditions, for example. 30 However, it must be lower than the maximum permissible pressure for the cylinder. For example, in the case in which the pressurized cylinder is filled by balancing pressurized storage vessels, the final pressure is limited by the storage pressure of the vessels, or even 35 to a lower value because of the pressure balancing. The input gas temperature thus determined serves to meet the following two conditions: the nominal WO 2006/070141 - 7 - PCT/FR2005/050947 capacity is reached and the operating limits of the cylinder are respected. This method is both "safe" and "optimal", because it helps to optimize the mass of gas finally stored in 5 the cylinder, while complying with the operating limits of the cylinder. In practice, the initial pressure of the cylinders is first measured by balancing the connector and the filling line with the cylinders by injecting a small 10 quantity of gas. The ambient temperature is also measured at the filling station. The ambient temperature measured at this station must be representative of the atmosphere surrounding the cylinders. In general, the temperature measured at the 15 filling terminal is fairly representative of the temperature at the cylinders, but it may be useful to confirm this. A filling rate in pressure units per unit time is determined. A final filling pressure is also set by the operator. 20 The system then calculates a gas temperature at the cylinder inlet using the following measured parameters: ambient temperature, initial pressure in the cylinder (measured at the connector), and using the final pressure set by the operator or by the process 25 conditions, and the value of the derivative of the pressure with respect to time. If the temperature thus calculated is higher than the ambient temperature, the operator implements the method according to the embodiment previously described 30 (filling is interrupted when the input pressure reaches the maximum filling pressure corresponding to the more severe of the following two conditions: nominal filling capacity and cylinder design temperature). If the temperature thus calculated is lower than 35 the ambient temperature, the gas entering the cylinder must be cooled to this temperature. The input temperature thus calculated allows filling up to the WO 2006/070141 - 8 - PCT/FR2005/05094 7 nominal load while remaining within the operating limits of the cylinder, the filling is terminated when the pressure in the cylinders reaches the predefined pressure. 5 According to another "cold" filling mode, the filling temperature is a fixed condition. In this case, the final filling pressure may be the pressure calculated to permit effective filling. According to this particular embodiment, the final 10 filling pressure is determined and calculated according to the following parameters: the initial pressure, ambient temperature, gas temperature entering the cylinder and filling rate, in order to reach the nominal storage capacity of the cylinder, in a given 15 filling time, while complying with the operating limits of the cylinder. The inventive method is particularly useful for rapid fillings, especially fillings of motor vehicles. In the present invention, a rapid filling is a 20 filling which must be completed in a period of between 1 minute and 10 minutes. This time depends on the cylinders to be filled and/or the type of vehicle (scooter, car or bus, for example). The present invention is usable regardless of the 25 type of gas. It may, for example, concern methane, hydrogen, oxygen, nitrogen, helium, etc. The vehicle application is particularly aimed at natural gas or methane and hydrogen. The cylinders or tanks have a variable capacity 30 according to their purpose. For example, for private cars, the total capacity is about 100 to 150L. The vehicle may be equipped with a single tank of this capacity or a plurality of smaller tanks placed in parallel. 35 Advantageously, the shape of the cylinder must be such that at the end of filling, it provides for obtaining a uniform gas temperature. This feature WO 2006/070141 - 9 - PCT/FR2005/050947 depends on the geometry of the cylinder, which is advantageously generally cylindrical in shape, with a ratio of length L to diameter D, L/D, lower than 6, preferably between 1 and 5, and even more preferably 5 between 1 and 4. Furthermore, advantageously, the tanks to be filled are arranged horizontally or vertically, and in this case, the filling is carried out from the top downward. 10 The invention is described in greater detail in the following examples, which are provided exclusively to illustrate the invention and are nonlimiting. 15 EXAMPLES Examples 1 and 2: Safe filling by estimation of the final pressure In examples 1 and 2 below, the cylinder used is a 20 Dynetek 150L cylinder. The filling gas is hydrogen. The following notations are used: 25 - Pf = final pressure in bar, Pf = Min (Pf 85 c; Pfioomass) where Pfloomass is the limit pressure above which the nominal mass stored in the cylinder is exceeded and Pfs5oc is the limit pressure above which the temperature limit of 30 the cylinder is exceeded. - Tamb = ambient temperature in K - PO = initial pressure in bar - (PO, 15'C) = initial pressure normed to 15*C in bar 35 - V= rate in bar/s - Tr = filling gas temperature (K) - Tf = final temperature in K.

WO 2006/070141 - 10 - PCT/FR2005/050947 Calculation equations PfiOOmass, which is the limit final pressure above which the nominal mass stored in the cylinder is exceeded, is 5 determined by the following equation (1): Pf 1 0%mass (a x LN(V)+b) x (PO, 15 0 C) + c x LN(V) + d (1) Tamb 10 Where a, b, c, and d are coefficients obtained by regression (by tests or simulations) . These coefficients may optionally be specific to a type of cylinder. 15 Pf5oc, which is the final limit pressure above which the cylinder design temperature is exceeded, is determined by the following equation (2): Pf85c = AA x P0 3 + BB x P0 2 + CC x PO + DD 20 Where AA = aaa x Tamb 2 + aab x Tamb + aac BB = bba x Tamb 2 + bbb x Tamb + bbc CC = cca x Tamb2 + ccb x Tamb + ccc 25 DD = dda x Tamb2 + ddb x Tamb + ddc And where the coefficients aaa, aab, aac, bba, bbb, bbc, cca, ccb, ccc, dda, ddb and ddc are third order polynomials of the filling rate V. 30 The various coefficients determined are specific to a type of cylinder and are determined by regression (by tests or simulations). 35 For cold filling, PfiOoormass which is the final limit pressure above which the nominal mass stored in the cylinder is exceeded, is determined by the following equation: WO 2006/070141 - 11 - PCT/FR2005/050947 Pfioomass = Tambx [ (axLN (V) +b) x (PO, 15C)+ (cxLN (V) +d) ]+ (e+fxPO+gxV) x (Tr-Tamb) 5 Where a, b, c, d, e, f and g are coefficients obtained by regression (by tests or simulations) . These coefficients may be specific to a type of cylinder. a, b, c, and d may be the same coefficients as those used for filling with gas at ambient temperature. 10 Example 1: The operator wishes to fill a Dynetek 150L cylinder whereof the maximum service temperature is 85 0 C (358K) with hydrogen. 15 He measures the ambient temperature (32 0 C) and the initial pressure at the cylinder inlet (50 bar). He decides to fill this cylinder at a rate of 2 bar per second. The computer then advises him using the equation 20 (1) that Pfioomass = 447 bar and that Pf 85 % = 304 bar. The final filling pressure is then equal to the lower of these two values or 304 bar. The operator adjusts the filling rate to 2 bar per second and starts filling while measuring the pressure 25 at the connector, as indicated previously. A robot calculates the derivative of this pressure with respect to time for controlling the rate of rise in pressure with respect to the setpoint of 2 bar/s. When this pressure reaches 304 bar, the filling is 30 stopped. The filling protocol thus followed is summarized in the table below. Parameter Value Determination Method Ambient temperature 32 0 C Fixed measurement Initial pressure 50 bar Fixed measurement Filling rate 2 bar/s Operator's choice WO 2006/070141 - 12 - PCT/FR2005/050947 Maximum permissible 304 bar Calculation pressure Filling ratio 70% Calculation Final temperature 1 ' 85 0 C Calculation Total filling time 2.1 min Calculation ("parameter limiting the filling Example 2: The operator wishes to fill a Dynetek 150L 5 cylinder whereof the maximum temperature is 85 0 C (358K). He measures the ambient temperature (200C) and the initial pressure at the cylinder inlet (60 bar). He then decides to fill this cylinder at the rate of 2 bar 10 per second. The computer advises him with the help of the following equation that for a 100% filling, the final pressure is 427 bar. The final pressure corresponds to a final 15 temperature of 85 0 C and is higher than 438 bar. The lower of the two values clearly corresponds to 427 bar. The operator then adjusts the filling rate to 2 bar per second and starts filling while measuring the pressure at the connector, as indicated previously. A 20 robot calculates the derivative of this pressure with respect to time for controlling the rate of rise in pressure with respect to the setpoint of 2 bar/s. The filling is interrupted when the pressure reaches 427 bar. 25 The filling protocol thus followed is summarized in the table below. Parameter Value Determination Method Ambient temperature 20 0 C Fixed measurement Initial pressure 60 bar Fixed measurement Filling rate 2 bar/s Operator's choice Maximum permissible 427 bar Calculation WO 2006/070141 - 13 - PCT/FR2005/050947 pressure Filling ratio~ 1 100% Calculation Final temperature 77 0 C Calculation Total filling time 3.1 min Calculation parameterr limiting the filling Example 3: Safe filling optimized by estimation of the input temperature 5 The operator wishes to fill with hydrogen a Dynetek 150L type cylinder whereof the service pressure is 350 bar and which can withstand a maximum pressure of 438 bar. The operator wishes to terminate the filling at a pressure of 400 bar. 10 The operator measures the ambient temperature (35 0 C) and the pressure at the cylinder inlet (30 bar). He decides to fill this cylinder at the rate of 1.25 bar per second. The computer advises him that the filling must be 15 carried out at a gas input temperature of -33 0 C. The operator then adjusts the gas input temperature to -33'C and the filling rate to 1.25 bar per second, and starts filling while measuring the pressure in the cylinder. The pressure is measured 20 dynamically at the connector. A robot calculates the derivative of this pressure with respect to time for controlling the rate of rise in pressure with respect to the setpoint of 1.25 bar/s. When the pressure in the cylinder reaches 400 bar, 25 the filling is stopped. The filling protocol thus followed is summarized in the table below. Parameter Value Determination Method Ambient temperature 35 0 C Instantaneous measurement Initial pressure 30 bar Fixed measurement Filling rate 1.25 bar/s Operator's choice WO 2006/070141 - 14 - PCT/FR2005/050947 Final pressure 400 bar Operator's choice Filling temperature -33 0 C Calculation Example 4: The operator then wishes to fill the same cylinder with a gas available at 0 0 C. The filling conditions 5 are: ambient temperature = 30 0 C and cylinder input pressure = 15 bar. The operator wishes to fill the cylinder at the rate of 2 bar per second. The computer advises him that the filling must be interrupted at a pressure of 425 bar. 10 The operator then adjusts the gas input temperature to 0*C and the filling rate to 2 bar per second and starts filling while measuring the pressure in the cylinder. When the pressure in the cylinder reaches 425 bar, the filling is stopped. 15 The filling protocol thus followed is summarized in the table below. Parameter Value Determination Method Ambient temperature 30 0 C Instantaneous measurement Initial pressure 15 bar Fixed measurement Filling rate 2 bar/s Operator's choice Filling temperature 0 0 C Operator's choice Final pressure 425 bar Calculation

Claims

1. A method for filling a pressurized gas cylinder, the filling being parameterized using a 5 predefined value of the filling rate such as a derivative of the input pressure in the cylinder as a function of time, the filling being controlled using the input pressure in the cylinder, characterized in that the filling is interrupted when the input pressure 10 reaches a maximum filling pressure, calculated according to the filling rate, the maximum filling pressure in the cylinder being calculated to match the more severe of the following two conditions: the nominal filling capacity, that is, the mass of gas that 15 can be stored in the given cylinder in the form of a nominal pressure at a nominal temperature, or the cylinder design temperature, that is, the maximum temperature that can be reached in the cylinder in service. 20

2. The method as claimed in claim 1, characterized in that the maximum filling pressure is calculated according to the ambient temperature and the initial pressure in the cylinder. 25

3. The method as claimed in claim 2, characterized in that the ambient temperature and the initial pressure in the cylinder are measured before filling. 30 4. The method as claimed in any one of claims 1 to 3, characterized in that the filling rate is selected according to a desired filling rate and/or according to a desired filling time. 35 5. The method as claimed in claim 4, characterized in that the filling rate is selected according to the WO 2006/070141 - 16 - PCT/FR2005/050947 ambient temperature and the initial pressure of the gas in the cylinder measured before filling.

6. The method as claimed in any one of the 5 preceding claims, characterized in that the filling rate is expressed as a derivative of the input pressure in the cylinder as a function of time and is between 0.05 bar/s and 20 bars, preferably between 0.10 and 15 bars, and even more preferably between 0.5 bar/s 10 and 12 bar/s.

7. The method as claimed in one of the preceding claims, characterized in that the filling rate is selected either by the operator at the time of filling 15 or automatically.

8. The method as claimed in any one of the preceding claims, characterized in that the filling is controlled only using the input pressure in the 20 cylinder.

9. The method as claimed in any one of the preceding claims, characterized in that the cylinder is filled at a temperature calculated according to the 25 initial pressure, the ambient temperature and the maximum filling pressure.

10. The method as claimed in claim 9, characterized in that the filling temperature is calculated according 30 to the filling rate.

11. The method as claimed in claim 10, characterized in that the maximum filling pressure is calculated according to the initial pressure, the 35 ambient temperature, the cylinder input gas temperature and the filling rate. WO 2006/070141 - 17 - PCT/FR2005/050947

12. The method as claimed in any one of claims 9 to 11, characterized in that the calculated filling temperature is lower than the ambient temperature. 5 14. The method as claimed in any one of the preceding claims, characterized in that the cylinder is generally cylindrical in shape with a ratio of length L to diameter D, L/D, lower than 6, preferably between 1 and 5, and even more preferably between 1 and 4. 10

15. The method as claimed in any one of the preceding claims, characterized in that the maximum filling pressure (Pfioo% mass) corresponding to the precondition of the nominal filling capacity of the 15 cylinder is calculated by the equation: Pf 1 0%mass (a x LN(V)+b) x (PO,15 0 C) + c x LN(V) + d (1) Tamb 20 where: - Tamb is the ambient temperature in K, - V is the cylinder filling rate in bar/second, - PO is the initial pressure in bar, and (PO, 150C) is 25 the initial pressure normed to 15'C in bar, - a, b, c, and d are coefficients determined by regression.

16. The method as claimed in any one of the 30 preceding claims, characterized in that the maximum filling pressure (Pfioo% mass) corresponding to the precondition of the nominal filling capacity of the cylinder is calculated by the equation: 35 mass = Tambx[(axLN(V)+b)x(PO,15"C)+(cxL(V)+d)]+ (e+fxPO+gxV)x(Tr-Tamb) (2) where WO 2006/070141 - 18 - PCT/FR2005/050947 - Tamb is the ambient temperature in K, - Tr is the filling gas temperature in K - V is the cylinder filling rate in bar/second, - PO is the initial pressure in bar, and (PO, 15 0 C) 5 the initial pressure normed to 15'C in bar, - a, b, c, d, e, f and g are coefficients determined by regression.

17. The method as claimed in any one of the 10 preceding claims, characterized in that the maximum filling pressure (Pf85 0 C) corresponding to the precondition of the cylinder design temperature is calculated by a polynomial equation of the type: 15 Pfse5c = AAPO" + BBPO"- + CCPOn- 2 + DDPO"~3 + ... + ZZ where: - PO is the initial pressure in bar, - n is an integer and is at least equal to 3, 20 - and the coefficients AA, BB, CC, ... , ZZ are polynomial functions of the filling rate specific to the filled cylinder and obtained by regression.