US20090116969A1

US20090116969A1 - Rail tank car evacuation and transfer system and method

Info

Publication number: US20090116969A1
Application number: US11/982,590
Authority: US
Inventors: R. Vance McVicker
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-11-02
Filing date: 2007-11-02
Publication date: 2009-05-07

Abstract

A rail tank car evacuation and transfer system and method. A method includes steps of providing an evacuation and transfer line having an inlet end and an outlet end, causing liquid contained inside the rail tank car to flow into the inlet end to at least a first location between the inlet and outlet ends of the evacuation and transfer line by pressurizing the interior of the rail tank car with a gas, sensing, at the first location, a change in the contents of the line from (a) consisting essentially of liquid to (b) including gas, and shutting off the flow through the line in response to the change.

Description

FIELD OF THE INVENTION

The present invention relates to rail tank car evacuation and transfer method and system. More particularly, the invention relates to evacuating the liquid contents of a tank car, and transferring the contents to an external, ground-based storage or holding tank, with the aid of pressurized air that is injected into the tank car.

BACKGROUND

Rail tanker cars are used to transport large quantities of liquid material. At the intended destination, the liquid is evacuated from the rail tanker car and transferred to an external, ground-based storage or holding tank. This is most straightforwardly done by opening a valve at the bottom of the tanker car and letting gravity feed the liquid to a pump, which pumps the liquid into the storage tank.
However, many of the liquids transported in rail cars are corrosive, and it is expensive to adapt a pump for pumping such liquids. As a more cost effective alternative, the art has developed a process of utilizing compressed air to pressurize the tanker car and drive the liquid out of the car through a transfer line that is built into the car and extends into the car's interior so that an inlet end of the line is immersed in the liquid. The line extends out from the tanker car through a port at the top of the car, and an outlet end of the line is provided at the storage tank, for depositing liquid traveling through the line under pressure into the tank. The storage tank is typically formed of plastic, so that it is not susceptible to corrosion.
The art has also recognized that, at the time the liquid becomes substantially emptied from the tanker car, the pressurized air will be introduced into the line and injected into the storage tank. This can cause fluctuations in the liquid level in the tank which render the float gauges that are typically used to measure the level ineffective. Moreover, if the storage tank is formed of a material with a relatively low tensile strength, such as plastic, hammering of the tank caused by the sudden introduction of a highly pressurized compressible fluid can result in catastrophic failure. To avoid this, the tank must be constructed more robustly than would otherwise be the case, increasing cost.
The prior art has attempted to solve this problem by preventing air from entering the line. Particularly, the level of the liquid is sensed and the flow is shut off as the level drops to within a predetermined range of the elevation of the hose inlet. To ensure that the flow is shut off before pressurized air enters the line, all of the liquid cannot be evacuated, i.e., the flow must be shut off prior to the time the liquid level drops to the elevation of the hose inlet.
It would be preferable to evacuate as much of the liquid as possible, so there is a need for a rail tank car evacuation and transfer system and method that provides for maximum evacuation while ensuring that the storage tank is protected from air pressure fluctuations.

SUMMARY

A rail tank car evacuation and transfer system and method is disclosed herein. A preferred system includes an evacuation and transfer line, a valve, and a sensor. The evacuation and transfer line has an inlet end and an outlet end. The inlet end provides for intake of liquid in the rail tank car and the outlet end provides for expelling the liquid from the line. The valve provides, in an open position, for flow of the liquid through the line and, in a closed position, for shutting-off the flow. The sensor senses, at a predetermined first location between the inlet and outlet ends, a change in the contents of the line from (a) consisting essentially of liquid to (b) including gas, and outputs a signal for switching the valve from the open position to the closed position in response to the change.
Preferably, the valve shuts off flow in the second configuration at a predetermined second location in the line, the first location being upstream of the second location.
A preferred method includes steps of (1) providing an evacuation and transfer line having an inlet end and an outlet end, (2) causing liquid contained inside the rail tank car to flow into the inlet end to at least a first location between the inlet and outlet ends of the evacuation and transfer line by pressurizing the interior of the rail tank car with a gas, (3) sensing, at the first location, a change in the contents of the line from (a) consisting essentially of liquid to (b) including gas, and (4) shutting off the flow through the line in response to the change.
It is to be understood that this summary is provided as a means of generally determining what follows in the drawings and detailed description and is not intended to limit the scope of the invention. Objects, features and advantages of the invention will be readily understood upon consideration of the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a rail tank car evacuation and transfer system according to the present invention.

FIG. 2 is a schematic view of a carrying box for housing selected components associated with the operation of the system of FIG. 1 according to the invention.

FIG. 3 is a schematic view of a controller associated with the carrying box of FIG. 2 according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to specific preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.
Referring to FIG. 1, a rail tank car 10 is shown with liquid contents 12. Pressurized air is introduced into the car 10 through a pressurized air port 14 as is standard practice, although any pressurized gas could be used. The tank car preferably has an access port 16 disposed at the top of the car, above the level “L” of the liquid contents 12, though the access port 16 could be disposed at the bottom of the car, or at any other desired location without departing from the principles of the invention.
An evacuation line 18 is provided having two extreme ends 18 a and 18 b. The line 18 is of tubular configuration so that liquid contents 12 may enter the inlet end 18 a of the line, travel through the line, and exit the line at the outlet end 18 b.
The evacuation line 18 extends through the access port 16 into the interior of the car 10, so that the inlet end 18 a is submerged in the liquid contents 12 and, preferably, extends to a level “L₁” which is as near as is practical to the bottom of the car.
The outlet end 18 b of the evacuation line 18 is preferably disposed so that liquid contents 12 that are expelled from the line through the outlet end are collected in an external storage tank 20 that is preferably fixedly mounted to the ground. The storage tank 20 is preferably formed of plastic, for storing caustic or corrosive liquid contents 12; however, the storage tank 20 may be any prior art storage tank, and it is typically an existing structure located on site at the rail yard.
A shut-off valve 24 is disposed between the ends 18 a and 18 b of the evacuation line 18. The shut-off valve may have additional features or positions, but it is only required for purposes of the invention to provide for two positions, i.e. open and closed. In the open position, the valve 24 allows liquid contents 12 to flow through the line 18, and in the closed position, the valve shuts off this flow.
The valve position is responsive to a signal generated by a sensor 26. The sensor 26 senses a condition in the evacuation and transfer line 18 and signals the valve to change from the open position to the closed position in response. The particular condition sensed by the sensor 26 according to the invention is a change in the contents of the line 18, more particularly the introduction of any of the pressurized gas into the line, which occurs precisely when the liquid contents 12 drops to the level of the inlet end 18 a.
So long as the level of the liquid contents 12 in the car 10 are above the level of the inlet end 18 a of the line 18, only liquid will enter the inlet end 18 a, and the contents of the line 18 will be liquid and will not contain any pressurized gas. The sensor 26 is adapted to sense whether the contents of the line 18, at the location where the sensor is operative, are liquid and do not contain any pressurized gas, and so long as this condition is true, the valve 24 remains open. This allows the pressurized gas to force the liquid through the inlet end 18 a of the evacuation and transfer line, through the valve 24, and through the outlet end 18 b of the line, to dispense the liquid contents from the car 10.
However, when the level of the liquid contents 12 in the car 10 drops to the level of the inlet end 18 a, pressurized gas is able to enter the inlet end 18 a of the line 18. When any appreciable quantity of this gas reaches the sensor 26, the sensor senses this change in the contents of the line and signals the valve 24 to shut off the flow. This prevents the gas from reaching the end 18 b of the line 18, thereby isolating the end 18 b from pressure fluctuations that would otherwise result from a sudden change in the contents of the line from incompressible to compressible fluid.
Typically, the outlet end 18 b of the evacuation and transfer line 18 makes an air-tight seal with the storage tank 20 when the liquid contents 12 are being transferred from the car 10. Any pressure fluctuations occurring at the outlet end 18 b are therefore imparted to the tank. By avoiding such fluctuations, the present invention allows the use of a less robustly constructed tank, saving cost, and/or greater safety.
To ensure accurate and quick sensing, the sensor 26 preferably has at least a sensing portion 26 a that is disposed inside the evacuation and transfer line 18, so that it makes intimate physical contact with the flow through the line. However, it is possible to sense a change in state of the contents of the line 18 from outside the line and so providing for such intimate contact is not essential.
A preferred sensor 26 is an ultrasonic (i.e. acoustic) level switch such as that marketed under the mark SWITCH-TEK by Flowline Inc., 10500 Humbolt Street Los Alamitos, Calif. The preferred sensor outputs one or more electrical signals 28 (e.g., the step function shown in FIG. 3) when liquid contents 12 are mixed with any appreciable amounts of pressurized air (“the Condition”), it being understood that the sensor may provide any signal or indication, or combination of signals or indications, from which the Condition can be deduced. For example, the sensor may output a signal only when the Condition is not true, or it may output one signal when the Condition is true and another, different signal when the Condition is not true. The signal need not be electrical; it could be, e.g., mechanical, pneumatic or hydraulic.
It should be understood that the sensor 26 could sense the introduction of pressurized gas into the line 18 by recognizing changes in the properties or characteristics of the flow other than acoustics. For example, the sensor could employ a heated element and sense a change in the temperature of the element as a result of a change in heat transfer, or the sensor could recognize a change in the transmission of a light beam.
Persons of ordinary skill will readily appreciate that, if multiple signals are provided by the sensor, logic may be provided to decode the signals for operation of the valve 24 in accord with the aforedescribed method. In the simplest case, where a single signal representative of a change in the contents of the evacuation and transfer line 18 from (a) consisting of liquid to (b) including gas, no additional logic is required.
In the preferred embodiment of the invention, the shut-off valve 24 is a pneumatically operated 2-way direct acting valve such as that marketed as the 8290 Series Angle Body Multi-Purpose Valve by ASCO Valve, Inc., 50-60 Hanover Road, Florham Park, N.J. 07932. The valve is preferably operated by components that are housed in a suit-case sized carrying box 30, and that can be easily carried to the car 10 and quickly connected to and disconnected from the valve 24.
FIG. 2 shows selected components of the carrying box 30 in schematic form. Included in the box 30 is a 70 in³pressurized gas storage tank 32 containing nitrogen gas at 2800 psi. The output of the storage tank 32 is pressure reduced to 100 psi by a regulator 34 and made available as an output to the valve 24 through a gas output line 36. An end 36 a of the gas output line 36 is fitted with a connect/disconnect fitting 35 for quick connection to and disconnection from the valve 24.
The gas output line 36 is switched by a 2-way solenoid valve 37. The valve 37 is controlled by a controller 38 via line “A.” The sensor 26 outputs a signal “S” carried on a sensor output line 39 to the controller 38. An end 39 a of the sensor output line 39 is fitted with a connect/disconnect fitting 33 for quick connection to and disconnection from the sensor 26. FIG. 3 shows the controller 38 in more detail.
The basic operation is as follows: When the sensor senses fluid in the evacuation transfer line 18, the signal S signals the controller 38 to maintain the solenoid valve 37 in its open position, so that air flows from the storage tank 32 through the gas output line 36 and fitting 35 into the valve 24, the pressurized air in turn maintaining the valve 24 in an open position. Assume, arbitrarily for descriptive purposes, that the solenoid valve 37 and the valve 24 are normally closed, and the signal S is low when liquid is sensed and toggles high when gas is first sensed. The controller 38 may simply amplify and invert (41 in FIG. 3) the signal S to control the solenoid valve 37.
When air is first sensed at the sensor 26, the signal S changes to signal the controller to control the valve 37 to shut off the flow of air from the tank 32, to close the valve 24.
On start-up, there will typically be no liquid at the sensor 26, so the controller 38 is preferably adapted to over-ride or ignore the signal S and so control the valve 37 so as to maintain the valve 24 in the open position for a predetermined time sufficient to allow liquid to reach the sensor. Preferably, the controller 38 includes a timer 40 for this purpose. Assuming again that the solenoid valve 37 is opened by applying power, the timer 40 applies power to the valve 37 for the pre-set time, typically about 5-7 seconds, regardless of the value of S.
After the valve 24 is closed as a result of emptying the tanker car, there is typically some liquid remaining in the evacuation and transfer line 18, and it is desirable to remove this remaining liquid. For this purpose, a manual valve 42 may be provided in the line 18, preferably upstream of the valve 24, allowing for variable flow. The valve 42 is preferably fully open during operation of the system, i.e., during the time that liquid is flowing through the line 18.
After the tanker car is emptied and the valve 24 closes, the valve 42 is manually closed. Next the valve 24 is re-opened by toggling a switch 44 of the controller 38 (to position “1”) which over-rides the control provided by the signal S (which is high). Then the valve 42 is manually opened a relatively small amount, to restrict the flow rate and allow a manually controlled bleed of the line 18. When this bleed is complete, the switch 44 is toggled again (to position “2”), returning control of the valve 37 to the signal S, to again close the valve 24, at which time the manual valve 42 may be re-opened.
Power for the aforementioned operation is preferably provided by a 12V/14 A battery 40 (line “C”). The pressurized air port 14 may be used to expel pressurized air from the tank car after evacuation operations are complete.
It is to be understood that, while a specific rail tank car evacuation and transfer system and method has been shown and described as preferred, other configurations and methods could be utilized, in addition to those already mentioned, without departing from the principles of the invention.
The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions to exclude equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

Claims

1. A rail tank car evacuation and transfer system, comprising:

an evacuation and transfer line having an inlet end and an outlet end, the inlet end for intake of liquid in the rail tank car and the outlet end for expelling the liquid from said line;

a valve providing, in an open position, for flow of the liquid through said line and, in a closed position, for shutting-off said flow;

a sensor for sensing, at a predetermined first location between said inlet and said outlet ends of said evacuation and transfer line, a change in the contents of said evacuation and transfer line from (a) consisting essentially of liquid to (b) including gas, and outputting a signal for switching said valve from the open position to the closed position in response to said change.

2. The system of claim 1, wherein said valve shuts off flow in said second configuration at a predetermined second location in said line, said first location being upstream of said second location.

3. The system of claim 1, further comprising a storage tank for storing liquid expelled from said line.

4. The system of claim 3, wherein said storage tank is formed substantially of plastic, for storing a corrosive liquid.

5. The system of claim 4, wherein said valve shuts off flow in said second configuration at a predetermined second location in said line, said first location being upstream of said second location.

6. The system of claim 3, wherein said valve shuts off flow in said second configuration at a predetermined second location in said line, said first location being upstream of said second location.

7. The system of claim 6, wherein at least a sensing portion of said sensor is disposed inside said line, so as to be in intimate contact with said contents.

8. The system of claim 7, wherein said sensor includes an ultrasonic level switch.

9. The system of claim 6, wherein said sensor includes an ultrasonic level switch.

10. The system of claim 5, wherein said sensor includes an ultrasonic level switch.

11. The system of claim 4, wherein said sensor includes an ultrasonic level switch.

12. The system of claim 3, wherein said sensor includes an ultrasonic level switch.

13. The system of claim 2, wherein said sensor includes an ultrasonic level switch.

14. The system of claim 1, wherein said sensor includes an ultrasonic level switch.

15. A method for evacuating and transferring liquid contents from a rail tank car, comprising the steps of:

providing an evacuation and transfer line having an inlet end and an outlet end;

causing liquid contained inside the rail tank car to flow into the inlet end to at least a first location between the inlet and outlet ends of the evacuation and transfer line by pressurizing the interior of the rail tank car with a gas;

sensing, at said first location, a change in the contents of said evacuation and transfer line from (a) consisting essentially of liquid to (b) including gas; and

shutting-off the flow through said line in response to said change.

16. The method of claim 15, wherein said step of shutting off the flow is performed at a predetermined second location in said line, said first location being upstream of said second location.

17. The method of claim 16, wherein said step of sensing includes making intimate contact with said contents for sensing said change.

18. The method of claim 15, wherein said step of sensing includes making intimate contact with said contents for sensing said change.