US20070079892A1

US20070079892A1 - Gas filling system

Info

Publication number: US20070079892A1
Application number: US11/247,561
Authority: US
Inventors: Joseph Cohen; David Farese
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 2005-10-10
Filing date: 2005-10-10
Publication date: 2007-04-12
Also published as: CA2562003C; ATE431919T1; CA2562003A1; EP1772663A1; EP1772663B1; DE602006006887D1

Abstract

A system and method for supplying a gas from a supply of compressed gas to a receiving vessel by measuring the pressure of gas being directed into the receiving vessel in successive selected time intervals to determine the actual ramp rate of gas being directed into the receiving vessel and providing means for comparing the actual ramp rate with a desired ramp rate and controlling the gas flow rate in response to that comparison. In a preferred embodiment the pressure of the gas at an upstream end of the system is monitored and directed into a controller and this latter pressure is employed in determining the mass flow of gas into the receiving vessel.

Description

BACKGROUND OF THE INVENTION

This invention relates to a system and method for filling a receiving vessel or tank from a source of compressed gas, and more specifically to a system and method for filling a receiving tank or vessel, e.g., a receiving tank in a vehicle, in a manner that aids in preventing excess heating of the tank and also in eliminating excess fill time, particularly when filling large receiving tanks.
In a system for filling a receiving tank or vessel with compressed gas it is necessary to control the flow rate of the gas so that the receiving tank does not overheat. Overheating occurs as a result of both adiabatic compression of the gas, and, when the gas is hydrogen or helium, by the reverse Joule-Thompson effect. The heat of compression is partially offset by the isentropic expansion cooling within the storage vessel. Moreover, for gases other than hydrogen and helium, a conventional Joule-Thompson effect takes place, which can further mitigate against overheating resulting from the impact of adiabatic compression of gas in the receiving tank. However, even when charging a receiving tank or vessel with gases other than hydrogen and helium, the adiabatic compression of gas in the receiving tank does create an overheating concern.
For various fueling operations, such as in the delivery of gaseous hydrogen to a receiving tank in a vehicle, it is necessary to provide some form of flow control in order to avoid excess heating of the receiving tank and also to avoid excess fill time, particularly when filling a large receiving tank, e.g., a receiving tank in a large vehicle.
U.S. Pat. No. 6,786,245, assigned to Air Products & Chemicals, Inc., the assignee of the present application, discloses a programmable logic controller (PLC) that can receive information on pressure in the receiving tank, e.g., from the supply hose, which indirectly measures or reflects the pressure in the receiving tank, and on ambient temperature, and regulates the set point of the programmable pressure regulator using an I/P controller based upon these latter two parameters. The system can be seen best in FIG. 5 of the '245 patent. This latter system is believed to lack desired reliability, due to the potential for malfunctions associated with the control valve, the PLC, and/or the I/P controller.
Mickéet al., U.S. Pat. No. 5,826,632 discloses different options for controlling the flow of gas during a filling process, including the use of variable orifices, control valves and a fixed orifice in combination with a valve.
Kitayama et al., U.S. Pat. No. 6,210,482 discloses a system for feeding gases for use in a semiconductor system in which multiple orifices of the same or different size are employed to supply one or more of the gases.
Togasawa et al., U.S. Pat. No. 6,598,624 describes the effect of orifice diameter and upstream pressure on the fill rate to a hydrogen tank.
Petro, U.S. Pat. No. 4,487,187 discloses a system of parallel lines with solenoid valves and orifices supplying a compressible fluid such as methane or propane to an internal combustion engine; the orifice sizes being proportional to successive powers of 2.
Although the prior art does disclose various techniques for attempting to control flow rate of gases, none of the systems have recognized the benefit of controlling, or the desire to control the ramp rate of the gas to limit the temperature rise in a receiving tank, or vessel, and also, to avoid prolonged fill times, particularly when filling large tanks or vessels. It is to this latter-type of system that the present invention is directed.

BRIEF SUMMARY OF THE INVENTION

In accordance with both the system and process of this invention the flow rate of compressed gas from a source to a receiving vessel or tank is controlled to achieve a desired ramp rate. “Ramp rate” is a change in pressure with time, e.g., either an increase or decrease in pressure with time.
In a gas filling system in accordance with this invention a receiving conduit communicates a source of compressed gas with a plurality of gas transmission lines that are in parallel with each other. A delivery conduit communicates with a vessel intended to receive compressed gas and also with the plurality of gas transmission lines. A control valve in each of a plurality of the gas transmission lines upstream of the delivery conduit communicates those gas transmission lines with the delivery conduit when in an opened condition. At least some, and preferably all of the gas transmission lines have differing orifice coefficients for transmitting gas at different flow rates therethrough.
A flow controller has a desired ramp rate communicating with it, and the flow controller operates to open and close selected control valves to thereby control the flow rate of gas to the receiving vessel. A pressure monitor downstream of the control valves measures the pressure of gas being directed into the receiving vessel in selected time intervals, to essentially monitor the actual ramp rate of the gas flowing into the receiving vessel. The pressure of gas measured by the pressure monitor is directed continuously to the flow controller, and the flow controller compares the desired ramp rate that communicates with it with the pressure of gas being monitored downstream of the control valves and controls the flow rate of gas through the transmission lines to the receiving vessel based upon that comparison.
In the preferred embodiments of this invention the flow controller increases the flow rate of gas when the actual ramp rate is lower than the desired ramp rate and decreases the flow rate of gas when the actual ramp rate is higher than the desired ramp rate.
Reference throughout this application to the desired ramp rate “communicating” with the flow controller includes programming the desired ramp rate directly into the flow controller (e.g., when the flow controller is a programmable logic controller or similar device), or feeding the desired ramp rate into the controller through another source, such as a remote computer system or other customer interface.
In the preferred embodiment of this invention the pressure monitor downstream of the control valves monitors the pressure of gas in the delivery conduit, which directly communicates with the receiving vessel or tank.
In the most preferred embodiments of this invention each gas transmission line has an orifice coefficient different from the orifice coefficient in every other transmission line. Most preferably each orifice coefficient differs from the next smallest orifice coefficient by a factor of substantially 2, to thereby permit a wide degree of control over the flow rate of gas through the gas filling system.
In a preferred system of this invention the mass flow of gas into the receiving vessel is determined to thereby determine the volume of gas employed to fill the vessel. This is particularly desirable when the receiving vessel is a gas tank in a vehicle, and actually is necessary in order to determine the volume of gas employed to fill the vessel, to thereby establish the selling price for the gas.
Specifically, in the preferred embodiment of this invention a second pressure monitor is employed upstream of the transmission lines for measuring the gas pressure upstream of the transmission lines and transmitting that gas pressure to the flow controller. The flow controller includes data regarding the size of orifices in the transmission lines that actually are communicating with the delivery conduit through opened control valves, and the flow controller functions to determine the mass flow of gas into the receiving vessel based upon the input from the second pressure monitor and the data representing the size of orifices in transmission lines is communicating with the delivery conduit through opened control valves.
In another embodiment of this invention for determining the mass flow of gas into the receiving vessel, the second pressure monitor upstream of the transmission lines is employed, in the same manner as in the above-described embodiment. However, in this embodiment the flow controller determines the ratio of the pressure measured downstream of the transmission lines, preferably by a pressure monitor in the delivery conduit, to the pressure measured upstream of the transmission lines by the second pressure monitor and then determines the mass flow of gas into the receiving vessel based upon that ratio.
In accordance with the broadest method of this invention a receiving vessel is filled from a source of compressed gas by the steps of measuring pressure of gas being directed into the receiving vessel in successive selected time intervals to determine the actual ramp rate of gas being directed into the receiving vessel, comparing the actual ramp rate with a desired ramp rate and controlling gas flow rate in response to that comparison.
Most preferably, the gas flow rate is increased when the actual ramp rate is determined to be lower than the desired ramp rate, and the gas flow rate is decreased when the actual ramp rate is determined to be higher than the desired ramp rate. Thus, in the preferred embodiment of this invention the gas flow rates are established and/or varied during the filling cycle to achieve, or approach, the desired ramp rate.
In a preferred method of filling a receiving vessel from a source of compressed gas in accordance with this invention, a gas filling system as described earlier herein is employed, and the method includes the steps of measuring the pressure of gas being directed into the receiving vessel in successive selected time intervals to determine the actual ramp rate of gas being directed into the receiving vessel; comparing the actual ramp rate with the desired ramp rate and controlling gas flow through the plurality of transmission lines in response to that comparison.
In accordance with a preferred method of this invention the mass flow of gas into the receiving vessel is determined by monitoring the pressure of gas upstream of the control valves employed in the transmission lines, determining the size of orifices in the transmission lines communicating with the receiving conduit through opened control valves and calculating the mass flow of gas into the receiving vessel based upon these latter two parameters.
In an alternate method for determining the mass flow of gas into the receiving vessel the pressure of gas upstream of the control valves is monitored, the ratio of the pressure of gas being directed into the receiving vessel to the pressure of gas upstream of the control valves it is determined, and based upon that ratio the mass flow of gas into the receiving vessel is calculated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by way of example with reference to the accompanying FIGURE which is a schematic view showing a representative gas filling system in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the FIGURE, a gas filling system for supplying a gas from a supply of compressed gas 12 to a receiving tank or vessel 14 is schematically illustrated at 10. The gas filling system 10 can be employed to fill a receiving vessel or tank 14 with a variety of different gases, e.g., hydrogen, helium, or natural gas. A particularly desirable use of the filling system 10 is for filling a receiving tank or vessel 14 with hydrogen, and in particular, to a system for filling a receiving tank or vessel of a vehicle with hydrogen.
Still referring to the FIGURE, the gas filling system 10 includes a supply of gas, e.g., hydrogen, from a pressurized source 12. A variety of pressurized sources can be employed, such as a single storage tank, a number of storage tanks, a pipe line supply, or a supply from a compressor. The gas is directed from the pressurized source 12 to a receiving tank 14 through a plurality of gas transmission lines in parallel with each other. In the illustrated system five transmission lines are shown at 16, 18,20,22 and 24. However, in accordance with the broadest aspects of this invention the number of transmission lines can be varied within wide limits, and the number of such transmission lines does not constitute a limitation on the broadest aspects of this invention.
The source 12 of compressed gas communicates with the plurality of transmission lines l6, 18, 20, 22 and 24 through a receiving conduit 26. The downstream ends of each of the transmission lines communicate with the receiving tank or vessel 14 through a delivery conduit 28.
Control valves, which preferably are solenoid valves 16 a, 18 a, 20 a, 22 a and 24 a, are located in the transmission lines 16, 18, 20, 22 and 24, respectively.
Still referring to the FIGURE, orifice plates, schematically illustrated at 16 b, 18 b, 20 b, 22 b and 24 b are provided in each of the transmission lines 16, 18, 20, 22 and 24, respectively, and these orifice plates include passages of different dimensions, whereby the orifice coefficient (Cv) of each of the transmission lines is different from the orifice coefficient in every other line.
In a preferred embodiment of this invention the orifice coefficients Cv of the passages in the orifice plates successively increase by a factor of 2. In particular, assuming that orifice plate 16 a has a relative orifice coefficient of 1, then orifice plate 18 b has an orifice coefficient of substantially 2; orifice plate 20 b has an orifice coefficient of substantially 4; orifice plate 22 b has an orifice coefficient of substantially 8 and orifice plate 24 b has an orifice coefficient of substantially 16.
As illustrated, the system 10 includes a pressure monitor 30, preferably monitoring pressure in the delivery conduit 28 at predetermined, selected time intervals, and continuously feeds the pressure measurements (which increase over time) to controller 32, which preferably is a programmable logic controller (PLC). The programmable logic controller 32 preferably includes a desired ramp rate programmed into it. However, it is within the scope of this invention to actually feed or direct a signal into the programmable logic controller 32 from a separate source or interface, such as a suitable customer computer interface schematically illustrated at 34. Based upon the required or desired ramp rate, either as programmed into the PLC 32 or inputted into the PLC from a separate source or interface 34, the PLC functions to open one or more of the control valves 16 a, 18 a, 20 a, 22 a and 24 a to establish the desired flow of gas.
For example, the PLC may open valve 20 a to establish a flow rate through orifice plate 20 b for a predetermined period of time, e.g., 5 seconds, while measuring the pressure rise during that period of time. That specific rise in pressure provides an estimate of the size of the receiving tank, which, in turn, provides a baseline for selecting the valves to be opened initially to establish the desired, proper ramp rate.
As the gas is flowing through the delivery conduit 28 into the receiving tank 14, the pressure within the tank will continuously increase. The pressure increase over preselected periods of time is monitored by pressure monitor 30, which feeds a signal indicative of the pressure increase to the PLC 32. The pressure increase that continuously is directed to the PLC during the preselected period of time represents the actual ramp rate of the gas flow into the receiving tank 14. This ramp rate is compared to the desired ramp rate that either is programmed into the PLC 32 or directed to the PLC through a separate interface 34, to determine whether the actual ramp rate is either lower or higher than the desired ramp rate.
If the actual ramp rate is lower than the desired ramp rate the PLC will operate selected control valves 16 a through 24 a to increase the flow rate through the transmission lines 16, 18, 20, 22 and 24, and thereby increase the actual ramp rate.
If the actual ramp rate is determined to be higher than the desired ramp rate then the PLC 32 will function to control the valves 16 a through 24 a in a manner to reduce the flow rate of gas through the transmission lines 16 through 24, and thereby lower the actual ramp rate of gas into the receiving tank 14.
In order to prevent a rapid change in flow rate, thereby creating an undesired pressure pulse of gas to the receiving tank 14, the various solenoid valves 16 a through 24 a can be sequenced in a manner to minimize the change in total orifice coefficient. For example, if solenoid valve 20 a is opened and the flow rate needs to be increased to maintain the proper ramp rate, valve 16 a would be opened to increase the total orifice coefficient from 4 to 5, i.e., a change of only one unit. If additional flow is required, valve 16 a would be closed and valve 18 a would be opened so that the total orifice coefficient is increased to 6, i.e., an additional increase of only one unit. Thus, by providing different orifice coefficients in the various transmission lines, such that each orifice coefficient differs from the next smallest orifice coefficient by a factor of substantially two, the system can be controlled in a manner to gradually increase (or decrease) the total orifice coefficient communicating with the receiving tank 14 in single units.
From the above explanation it should be apparent that the gas filling system 10 in accordance with this invention functions to selectively control flow rates through one or more of the transmission lines 16 through 24 during the filling cycle to achieve, or approach, a desired ramp rate. As stated earlier, this desired ramp rate either is programmed into the PLC 32 or is directed to the PLC from a separate interface 34.
Still referring to the FIGURE, the gas filling system 10 also is designed to determine the mass flow of gas into the receiving tank 14. In this manner, the quantity of gas directed into the receiving tank can be monitored, e.g., in order to determine the proper amount to be charged for the gas.
In order to measure the mass flow of gas into the receiving tank the gas filling system 10 is provided with a second pressure monitor 36 located upstream of the transmission lines 16 through 24. More preferably, the second pressure monitor 36 is connected to the receiving conduit 26 to monitor the pressure within that line. The absolute pressure level in line 26 is dependent upon the number of valves 16 a through 24 a that are opened, to thereby communicate the compressed gas with orifices having varying orifice coefficients.
By including a second pressure monitor 36 in the receiving conduit 26 the mass flow of gas into the receiving vessel can be determined, preferably by one of two methods. In both methods the pressure measured by the monitor 36 is directed into the PLC 32 and is employed in the determination of the mass flow of the gas.
In one of the two methods for determine the mass flow of gas into the receiving vessel, the PLC 32 includes data representative of the size of the orifices in the transmission lines that are in communication with the delivery conduit 28 through opened control valves, and the PLC 32 processes both data representing the gas pressure measured by the monitor 36 and data representative of the size of orifices in the transmission lines 16-24 communicating with the delivery conduit 28 through opened control valves for determine, or calculating, the mass flow of gas into the receiving vessel 14. This gas flow can be displayed visually on a read out screen or panel, or in other ways known to individuals skilled in the art.
It should be noted that people skilled in the art fully understand how the PLC 32 is capable of processing pressure data determined by pressure monitor 36 and data representative of the size of the orifices in the transmission lines communicating with the delivery conduit through the open control valves to thereby calculate the mass flow of gas into the receiving vessel. Therefore, no further explanation is believed to be necessary.
In accordance with a second method for determining the mass flow of gas into the receiving vessel the flow controller 32 determines the ratio of the pressure measured downstream of the transmission lines by the pressure monitor 30 to the pressure measured upstream of the transmission lines by the pressure monitor 36, and based upon that ratio, employs the appropriate formula for determining the mass flow of gas into the receiving vessel.
In particular, when the ratio of the downstream pressure measured by the monitor 30 to the upstream measured by monitor 36 is less than 0.5, choked flow exists. That is, the gas flowing through the system is flowing at the speed of sound through the various orifices, and based upon this condition; the mass of material flowing through the system can be calculated using the appropriate equation employed for choked flow. It should be understood that measuring the choked flow has no effect on the flow rates of the gas, but rather is used to measure the mass of material flowing through the system. It also should be understood that people skilled in the art clearly know and can select the appropriate equation to use when choked flow exists.
If the ratio of the pressure measured by the pressure monitor 30 to the pressure measured by the pressure monitor 36 is greater than 0.5 then choked flow does not exist, and a different equation is utilized by the PLC 32 to determine the mass flow of gas through the system 10. As in the previous systems, the determined gas flow can be displayed on a visually observable monitor, or can be displayed in other ways known in the art. It also should be understood that people skilled in the art clearly know and can select the appropriate equation to use when choked flow does not exist.
The gas filling system 10 of this invention is extremely effective in avoiding excess heating of a receiving tank receiving a charge of compressed gas, in particular, either hydrogen or helium. Both of these latter gases tend to heat up as a result of adiabatic compression of the gas and the reverse Joule-Thompson effect. This problem of overheating exists even though the heat of compression is partially offset by isentropic expansion cooling within the storage vessel 12.
An additional benefit achieved by the present invention is that the filling time for both small and large receiving tanks can be maintained the same, by simply employing the same ramp rate in both filling operations. This is not the case when other methods are employed to control the fill rate, such as controlling the flow rate of gas based on the absolute pressure increase in the receiving vessel, as is disclosed in the Togasawa et al '624 patent, which was identified earlier in this application.
Although illustrated and described herein with reference to certain specific embodiments, the present invention is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention.

Claims

1. A gas filling system for supplying a gas from a supply of compressed gas to a receiving vessel, said filling system including:

a. a source of compressed gas;

b. a receiving conduit communicating the source with a plurality of gas transmission lines in parallel with each other;

c. a delivery conduit communicating with a receiving vessel and with said plurality of gas transmission lines;

d. a control valve in each of a plurality of said gas transmission lines upstream of said delivery conduit for communicating said each of said plurality of gas transmission lines with said delivery conduit when in an opened condition; at least some of said gas transmission lines having differing orifice coefficients for transmitting gas at different flow rates therethrough;

e. a flow controller for opening and closing selected control valves to control the flow rate of gas to said receiving vessel and having a desired ramp rate communicating therewith;

f. a pressure monitor downstream of the control valves for measuring the pressure of gas being directed into the receiving vessel in selected time intervals and continuously transmitting said pressure of gas to said flow controller, said flow controller comparing the desired ramp rate communicating therewith with said pressure of gas and controlling the flow rate of gas through the transmission lines to said receiving vessel based upon the comparison of the desired ramp rate with said pressure of gas.

2. The gas filling system of claim 1, wherein said flow controller is a programmable logic controller having the desire ramp rate programmed therein.

3. The gas filling system of claim 1, wherein the desire ramp rate is transmitted to the flow controller from another source.

4. The gas filling system of claim 1, wherein said pressure monitor measures pressure of gas in said delivery conduit in selected time intervals.

5. The gas filling system of claim 1, wherein each gas transmission line has an orifice coefficient different from the orifice coefficient in every other gas transmission line.

6. The gas filling system of claim 5, wherein each orifice coefficient differs from the next smallest orifice coefficient by a factor of substantially 2.

7. The gas filling system of claim 1, wherein said pressure monitor measures an increase in pressure in successive selected time intervals, which constitutes an actual ramp rate of gas being directed into said receiving vessel, said flow controller comparing the actual ramp rate with the desired ramp rate and controlling the flow rate of gas through the transmission lines to said receiving vessel based upon the difference between the actual ramp rate and the desired ramp rate.

8. The gas filling system of claim 7, wherein said flow controller increases the flow rate of gas when the actual ramp rate is lower than the desired ramp rate and decreases the flow rate of gas when the actual ramp rate is higher than the desired ramp rate.

9. The gas filling system of claim 1, including a second pressure monitor upstream of said transmission lines for measuring gas pressure upstream of said transmission lines and transmitting data representative of said gas pressure upstream of said transmission lines to said flow controller; said flow controller including data representative of the size of orifices in transmission lines communicating with said delivery conduit through opened control valves, said flow controller including means for processing data representing said gas pressure upstream of said transmission lines and data representative of the size of orifices in transmission lines communicating with said delivery conduit through opened control valves for determining the mass flow of gas into said receiving vessel.

10. The gas filling system of claim 1, including a second pressure monitor upstream of said transmission lines for measuring gas pressure upstream of said transmission lines and transmitting data representative of said gas pressure upstream of said transmission lines to said flow controller; said flow controller determining the ratio of the pressure measured downstream of said transmission lines to the pressure measured upstream of said transmission lines and determining the mass flow of gas into said receiving vessel based upon said ratio.

11. A method of filling a receiving vessel from a source of compressed gas employing a system including a receiving conduit communicating with said source of compressed gas and with a plurality of transmission lines in parallel with each other; a deliver conduit downstream of said plurality of transmission lines communicating with said receiving vessel, a control valve in each of a plurality of said gas transmission lines upstream of said delivery conduit for communicating said each of said plurality of gas transmission lines with said delivery conduit when in an opened condition; at least some of said gas transmission lines having differing orifice coefficients for transmitting gas at different flow rates therethrough and a flow controller for opening and closing selected control valves to control the flow rate of gas to said receiving vessel, said flow controller having a desired ramp rate communicating therewith, said method including the steps of measuring the pressure of gas being directed into the receiving vessel in successive selected time intervals to determine actual ramp rate of gas being directed into the receiving vessel; comparing the actual ramp rate with the desired ramp rate and controlling gas flow through said plurality of transmission lines in response to said comparison.

12. The method of claim 11, including the step of monitoring the pressure of gas upstream of said control valves, determining the size of orifices in transmission lines communicating with said receiving conduit through opened control valves and calculating the mass flow of gas into said receiving vessel based upon said pressure of gas upstream of said control valves and the size of orifices in transmission lines communicating with said receiving conduit through opened control valves.

13. The method of claim 11, including the step of monitoring the pressure of gas upstream of said control valves, determining the ratio of the pressure of gas being directed into the receiving vessel to the pressure of gas upstream of said control valves and based upon said ratio calculating the mass flow of gas into said receiving vessel.

14. A method of filling a receiving vessel from a source of compressed gas including the steps of measuring pressure of gas being directed into the receiving vessel in successive selected time intervals to determine actual ramp rate of gas being directed into the receiving vessel; comparing the actual ramp rate with a desired ramp rate and controlling gas flow rate into said receiving vessel in response to said comparison.

15. The method of claim 14, wherein the step of controlling gas flow rate is carried out by increasing the gas flow rate when the actual ramp rate is lower than the desired ramp rate and be decreasing the gas flow rate when the actual ramp rate is higher than the desired ramp rate.

16. The method of claim 14, including the steps of measuring gas pressure between said source and a plurality of transmission lines in parallel with each other and including control valves therein, said control valves being operable between opened and closed conditions, transmission lines with opened valves therein communicating said source with a delivery conduit communicating with said receiving vessel downstream of said transmission lines, determining the size of orifices in transmission lines communicating with said delivery conduit through opened control valves and calculating the mass flow of gas into said receiving vessel based upon said pressure of gas upstream of said control valves and the size of orifices in transmission lines communicating with said delivery conduit through opened control valves.

17. The method of claim 14, including the steps of measuring gas pressure between said source and a plurality of transmission lines in parallel with each other and including control valves therein, said control valves being operable between opened and closed conditions, transmission lines with opened valves therein communicating said source with a delivery conduit communicating with said receiving vessel downstream of said transmission lines, determining the ratio of the pressure of gas being directed into the receiving vessel to the pressure of gas between said source and said plurality of transmission lines and based upon said ratio calculating the mass flow of gas into said receiving vessel.