Loading system and method of use thereof

A system is provided for loading one or more transport tank, the system including one or more load lines for connecting between on-site storage tanks or vessels and the transport tanks; one or more vapour return lines for connecting between the transport tanks and an on-site flare or downstream units; an oxygen deficient medium source; one or more oxygen deficient medium blend supply lines connectable to each of the vapour return lines; a HMI/PLC for automation and control of the operations of the system; and a control panel in communication with the HMI/PLC for starting and stopping operation of the system. Gases displaced from the transport tanks during loading can be sent directly to flare or downstream units. A method is also provided for loading a fluid from one or more on-site storage tanks or vessels to one or more transportation tanks.

FIELD OF THE INVENTION

The present invention relates to an automated system for safe loading of transportation tanks for carrying hydrocarbons, hydrocarbon by-products and other volatile fluids, and for methods of using the same.

BACKGROUND OF THE INVENTION

During loading of hydrocarbons, hydrocarbon by-products or other volatile or hazardous fluids from onsite storage to a transport tank, there is always a displacement of the gaseous environment from inside the transport tank as it is getting filled. In the case of volatile fluids, there is also off-gassing, or the release of vapours off of the volatile fluid.

As fluids are loaded, these gaseous vapors, be they displaced vapours or off-gassing vapours, are typically released from the vent system on the transport tank. Typically, in industry practice, where such gas is “sweet” (for example, containing less than 5 ppm hydrogen sulfide) venting to atmosphere has been permitted by industry and regulatory agencies. In the case of systems with “sour” gas (for example, containing greater than 5 ppm hydrogen sulfide), vented gas vapors have been traditionally directed to sweetening or scrubbing units.

With the industry norms as described above there are inherent dangers and issues:

1. During loading, explosive, flammable and hazardous gases are released into the atmosphere from the transportation tank or scrubber vent;

2. The gases being released in loading can create a localized oxygen deficient atmosphere, which is a hazardous condition for workers onsite;

3. Odour complaints from adjacent land owners;

While tank gases could be flared to deal with the above issues, transportation tanks arriving on site with oxygen present cannot be safely connected to a flare or vapour recovery unit due to potential explosive conditions.

Furthermore, in the case of on-site sweetening units, there can be hazards related to the disposal of the rich sweetening chemicals once spent. There are further concerns with hazardous, hydrogen sulphide atmospheres being created and/or production outages when the sweetening chemicals are spent at inopportune times, or prematurely.

For the purposes of the present invention transport tanks are intended to include any mobile tank systems such as, for example, tank trucks, tank trailers or rail cars or pressurized floating containers.

CA Patent Appl. No. 2,349,349 is directed to a method and apparatus for evacuating a section of a natural gas pipeline, but does not address fluids loading or unloading and the need for dealing with gas emissions during such processes. U.S. Pat. No. 8,480,812 teaches a process for removing hydrocarbon contaminants and noxious gases from catalytic reactors in the vapour phase without using steam. US Patent Application No. 2010/0000252 is directed to a process for the loading, processing and conditioning of raw production gas, the production of compressed gas liquids and the storage, transport and delivery of pipeline quality gas and other products to market. However, it does not relate to a system for transport tank loading or unloading. U.S. Pat. No. 6,901,941 is directed to a vessel for the storage and transportation of bulk volumes of fluid and methods for using the same. U.S. Pat. No. 7,252,700 is directed to a method and mobile system for cleaning dirty gas from a newly stimulated gas well.

There is a need therefore to develop improved safe, loading systems and operational methods that can deal with vapour emissions from transport tanks.

SUMMARY

A method is further provided for loading a fluid from one or more on-site storage tanks or vessels to one or more transport tanks. The method involves the steps of providing a loading system comprising a source of oxygen deficient medium, one or more vapour return lines to flare or downstream units and a central HMI/PLC; purging the transport tank with oxygen deficient medium prior to loading; loading the transport tank with fluid; sending gases displaced from the transport tank during loading directly to flare or downstream units; and automatically monitoring and controlling of the operations of the system via the HMI/PLC.

A further system is provided for loading one or more transport tank. The system comprises one or more load lines for connecting between on-site storage tanks or vessels and the transport tanks; one or more vapour return lines for connecting between the transport tanks and an on-site flare or downstream units; an oxygen deficient medium source; one or more oxygen deficient medium blend supply lines connectable to each of the vapour return lines; a HMI/PLC for automation and control of the operations of the system; and a control panel in communication with the HMI/PLC for starting and stopping operation of the system. Gases displaced from the transport tanks during loading can be sent directly to flare or downstream units.

A further method is provided for loading a fluid from one or more on-site storage tanks or vessels to one or more transportation tanks. The method involves the steps of providing a loading system comprising one or more load lines connectable between the storage tanks or vessels and the transportation tanks, one or more vapour return lines connectable between the transportation tanks and a flare, a source oxygen deficient medium connectable to the one or more vapour return lines; and a central HMI/PLC; loading the transport tank with fluid; blending the vapour return lines with oxygen deficient medium; sending gases displaced from the transport tank during loading directly to flare or downstream units; and automatically monitoring and controlling of the operations of the system via the HMI/PLC.

The drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order more clearly to depict certain features.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The description that follows and the embodiments described therein are provided by way of illustration of an example, or examples, of particular embodiments of the principles of various aspects of the present invention. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the invention in its various aspects.

The present safe loading system relates to safe handling of gas emissions during the fluids loading or unloading of transport tank systems such as tank trailers.

The present system can be a fixed system located on-site or it can be a portable system that can be brought to and removed from the on-site location. In a preferred embodiment, the present system is portable and is more preferably skid or trailer mounted to provide portability for transportation to multiple fixed storage sites. The fluids for loading or unloading are typically sweet or sour hydrocarbons, sweet or sour hydrocarbon by-products such as produced water, although any number of further sweet or sour volatile fluids could be loaded or unloaded using the system of the present invention.

The safe loading system of the present invention allows for a number of tailored loading and unloading operations to be controlled depending on such factors as fluid type, transport tank type, working conditions etc.

The present system further eliminates the practice of having a transport tank vent to atmosphere, either directly or after a sweeting process during loading or unloading. Instead, displaced gasses and off-gas vapours can be sent directly to a flare or downstream units during loading or unloading, thereby reducing vapour emissions being released in vicinity of drivers of the transport tanks, operators and any other personnel present during loading and unloading. The above goal is achieved by uniquely using the present system to purge the vapour content of the transport tank with an oxygen deficient gas medium before loading. The oxygen deficient gas, together with any off-gassing vapours displaced from the transportation tank during loading are now well below the lower explosive limit (LEL) and can then be sent directly to flare or downstream units. This also reduces the need for sour gas sweetening units on-site, since the sour gas can be flared.

In purging the vapour content of the transport tank, the atmosphere within the transport tank is brought down to below LEL so that during the loading process the gas and vapours displaced from the transportation tank can be directed to a flare, combustion use, pressure vessel or vapour recovery unit.

When loading sour fluid or condensate, the present system allows for vapours to be sent directly to a flare stack, or to downstream units including a vapour recovery unit, a combustion unit for energy generation or back into a pressure vessel that may optionally be provided on-site. Therefore, it is to be understood that for the purposes of the present invention, the term “flare or downstream units” used throughout this description is intended to include flare stack, a vapour recovery unit, a combustion system or a pressure vessel.

The source of oxygen deficient gas can be any source well known to those skilled in the art, and such range of sources are included in the scope of the present invention. By way of example only and without intending to be limiting, such oxygen deficient medium can include any inert gas such as nitrogen, argon, xenon, helium, carbon dioxide, natural gas or other gases that fall below the LEL such as methane etc., which can be sourced by provision of gas cylinders on the system, or from other onsite operations. The oxygen deficient medium source can be sized to meet loading capacities and rates for the transport tank to be loaded or off-loaded, or can be oversized to meet a range of transport tank volumes. More preferably, the oxygen deficient medium source can displace a rate of 1-10 m3/min to match typical rates of off-loading or loading of fluid.

In a preferred embodiment, the present system includes a portable nitrogen generation system for nitrogen purging the transport tank prior to loading or during unloading. In this embodiment, the nitrogen system can incorporate any number of nitrogen sources including high a pressure nitrogen bottle mounted on the system, a nitrogen generation unit mounted to the system or a nitrogen membrane package mounted to the system.

More preferably, the present nitrogen system comprises an air compressor which feeds a compressed air storage vessel, which in turn feeds a nitrogen generation unit. The nitrogen generated can then be stored in a nitrogen storage vessel. In this embodiment, all of these units are mounted to the system of the present invention.

More preferably the flow rate and pressure of the oxygen deficient medium are monitored and regulated, more preferably to maintain oxygen deficient medium pressure within the transport tank to never exceed 175 kPa (25 psi), but to also purge the transport tank within a desired amount of time, which may be in some instances around 10 minutes.

The vapour return lines4of the present system have an oxygen sensor AIT1001to monitor the composition of gas being vented from the transport tank. In a case where oxygen levels of the vent gas reach an explosive limit, the present system comprises controls to automatically shut down loading of the tank with fluid.

Most preferably, all valves for purging or displacing the volume of the tank are automated and controlled by the HMI/PLC. The valves may be air actuated valves. The vapour return lines4can be used for displacing transport tank volume with oxygen deficient medium during unloading. The load lines2A/2B each comprise a pressure gauge PI1003/PI1004, a purge connection520A/520B to the oxygen deficient source500, and valves XV7201/XV7001mounted at the connection end from the onsite storage tanks or vessels and valves50A/50B at the connection end before the loading pump on the transport tank. It should be noted that any number of load lines2may be provided on the system, each possibly dedicated to a particular fluid to be loaded or unloaded. But it is also possible to have one or multiple non-dedicated load lines2on the system, such that more than one transport tank can be unloaded or loaded at the same time with either the same or different fluids. Oxygen deficient medium can be passed through the load lines for purging the transport tank, during which process displaced gases from the transport tank are vented to atmosphere either directly, or in the case of sour displaced gases, via the scrubber.

The system preferably comprises the control panel501by which the driver of the transport tank can indicate the type of fluid being loaded or unloaded and to start or stop the process. The central HMI/PLC can be located on the system, and can be accessed locally or from a remote location from which loading and unloading can be controlled, readings taken and progress displayed.

The present system is fully automated, needing the driver to merely hook up the load lines2A/2B and vapour return lines4, indicate on the control panel501the type of fluid being loaded and start the process, at which point the central HMI/PLC, taking input from the pressure and flow monitors, oxygen level sensors AIT1001and controlling the valving, automatically manages the purging, loading and/or unloading process, until the driver's transport tank level indicator indicates a full load or unload level, or the storage tank is full or empty or from a signal from the fluid metering on the present system, at which point the driver can stop the operation via the control panel. Optionally, the HMI/PLC may also have a manual override such that an operator at the HMI/PLC may remotely control the opening and closing of valves by reading the oxygen level data from the oxygen level monitors.

In a preferred method for loading fluid into a transport tank using the system of the present invention, the transport tank is first located near the system, preferably with the load pump of the truck carrying the transport tank facing the system. Next, the vent of the transport tank is connected to the vapour return lines4of the system. In a situation in which the system is being used for the first time at a particular site, the vapour return line4of the system that goes to flare or downstream units will also be connected to the on-site flare or downstream units, in other cases, this connection to flare or downstream units is already made. Again, if the system is being used for a first time, then the load lines2are connected to the on-site storage tank or vessel that fluid is being loaded to or from. As previously stated, the load line2to be connected can be a dedicated load line2for a particular fluid from a particular on-site storage tank or vessel, or it can be a universally usable load line. This storage tank or vessel is located on site and could include separation vessels, storage vessels etc. The other end of the load lines2is then connected to a load pump located on the transport tank, which in turn pumps into the transport tank. The valve ZSO-7301on the vapour return line4connected to the transport tank is opened as is the valve of the predetermined load line2A/2B at its connection to the transport tank. Next, the valves XV-7201/XV-7001on the load line2A/2B to the on-site storage tanks or vessels are opened. During first site commissioning, the type of fluid being loaded is selected, typically from the options of sweet hydrocarbon, sour hydrocarbon, sweet by-product or sour by-product, which are also programmed into the HMI/PLC. The load pump is started on the transport tank and the system is started from the control panel. At this point of the present method the central HMI/PLC controls and fully automates the loading process.

The vapour return line4is opened and the oxygen deficient medium source lines520A/520B/510into the load line2A/2B and to vapor return line4are also opened and the load lines are purged by running the oxygen deficient medium through them.

As the displaced gases from the transport tank are purged they are directed to flare or downstream units.

During loading, vent gas oxygen content is continually monitored. The vapour return line4is open to vent gases either to the flare or downstream units.

Once the fluid is loaded onto the tank, as indicated by a transport tank level indicator (not shown) on the tank, the load line2A/2B is shut in at its connection XV7201/XV7001to the on-site storage tank or vessel and an air bleed connection (not shown) is opened to allow flushing of the load line2A/2B to vacate it of fluids. The driver stops the process via the control panel, at which point the connections to the transport tank truck are shut in.

At this point all lines are disconnected from the transport tank, and can be disconnected and open ends capped. The transport tank is now ready for transport.

While the present system has been discussed for use in the safe loading and unloading of transport tanks, there are a number of further applications for which one or more elements of the present system can be utilized and taken advantage of. The present system, providing a portable source of purge gas (that is, oxygen deficient medium) can also be transported and used at sites where purging for safe work practice is required. It can also be used in the safe primary loading of stationary vessels.

In an embodiment of the present system, as depicted inFIG. 1, the source of oxygen deficient gas500; is added to both the fluid load lines2A/2B for purging the transport tanks; and is also connected to the one or more vapour return lines4. The one or more vapour return lines4connect directly from the transport tanks to an on-site flare stack, there is no scrubber unit and there is no venting to atmosphere. In the embodiment ofFIG. 1, purged and displaced gasses and off-gas vapours can be sent directly to a flare or downstream units, thereby reducing vapour emissions being released in vicinity of operators and any other personnel present during loading and unloading.

Oxygen deficient gas500is used as a purge gas to purge the vapour content of the transport tank before loading. The oxygen deficient gas is also added as a blend gas directly to the vapour return lines4during purging, thereby lowering the oxygen content of the purged gas sufficiently so that it can all be flared, without sending any gas to atmosphere. In such cases the combination of oxygen deficient gas medium into the load lines2A/2B to purge the vapour content of the transport tank, together with the blending of the displaced gasses with an oxygen deficient medium into vapour return line4ensures that the displaced gas is always below the LEL and can always be flared, without the need for an initial period of venting to atmosphere.

Since there is no need to initially vent to atmosphere, there is also no need to scrub vapour content of the transport tank that could be sour or contain hydrogen sulphide. Even sour or hydrogen sulfide containing vapour can be flared. Since the vapour content of the transport tank is brought down below LEL right at the start of purging, gas and vapours displaced from the transport tank during the loading process the can also continue to be directed to a flare, combustion use, pressure vessel or vapour recovery unit. In the present embodiment when purging or loading in sour conditions, the present system allows for vapours to be sent directly to a flare stack, or to downstream units including a vapour recovery unit, a combustion unit for energy generation or back into a pressure vessel that may optionally be provided on-site. Therefore, it is to be understood that for the purposes of the present invention, the term “flare or downstream units” used throughout this description is intended to include flare stack, a vapour recovery unit, a combustion system or a pressure vessel.

With reference toFIG. 1, the oxygen deficient gas source500is directed via purge supply line520to the load lines. A meter M1may optionally be included to monitor flow rates and control valve7101can control flow rates on oxygen deficient gas to the load lines. In the case of more than one storage tank being on site and more than one load line being provided on the present unit, purge supply line520may optionally branch to supply each load lines, as shown inFIG. 3, for example only as lines520A and520B. Valving on each branch of purge supply lines520A and520B, for example valves7201and7202onFIG. 3, can be used to direct oxygen deficient gas to the desired load line.

Oxygen deficient gas may be directed via a blend supply line510to the vapour return lines4. A flow meter M2and flow control valve7102may be included on blend supply line510to monitor and control flow of oxygen deficient gas into the vapour return line4.

Flow of oxygen deficient gas into the vapour return line4is monitored and controlled to keep oxygen levels in the vapour return below the LEL. As before, an oxygen sensor AIT1001may be included on the vapour return line4to monitor LEL levels.

The system embodied inFIGS. 1 and 2, preferably comprises the control panel501by which the driver can indicate the type of fluid being loaded or unloaded and to start or stop the process. A separate central HMI/PLC can be located on the system, and can be accessed locally or from a remote location from which loading and unloading can be controlled, readings taken and progress displayed.

The present system is fully automated, needing the driver to merely hook up the load and vapour return lines4, indicate on the control panel the type of fluid being loaded and start the process, at which point the central HMI/PLC, taking input from the pressure and flow monitors, oxygen level monitors and controlling the valving, automatically manages the purging, loading and/or unloading process, until the driver's transport tank level indicator indicates a full load or unload level, or the storage tank is full or empty or from a signal from the fluid metering on the present system, at which point the driver can stop the operation via the control panel.

In the system ofFIG. 1, there may be a number of ways to control oxygen levels in the vapour return line. As a first example, at the start of purging the transport tank, valve7102on the blend supply line510can be set to a predetermined position to ensure a maximum oxygen deficient medium flow into the gas coming off of the purged transport tank. For example pressure in transport tank may determine the position of valve7102. The supply of oxygen deficient medium is dependent on the content of oxygen in the transport tank vapours being purged. As such, the likely highest levels of oxygen in the transport tank vapours would occur if the transport tank vapours were mainly air, leading to an oxygen content of about 21% in the transport tank vapours. In such cases, a flow rate of oxygen deficient medium in the blend supply line510should be set relative to the oxygen deficient medium flow in the purge supply lines to achieve a blend that is below 8% oxygen. It would of course be understood by a person of skill in the art that the flow ratio needed to stay below LEL levels will vary based on composition of vapours being purged, flow rates, temperatures, pressures and other conditions in the vapour return lines4.

At the beginning of purging the transportation tank, oxygen deficient medium may also be added to the load lines2A/2B via purge supply lines520A and520B. The flow rate of oxygen deficient medium into the load lines2A/2B will depend on such factors as the pressure or volume of gases in the transportation tank and the desired rate of purging the transportation tank. Valves XV7202and XV7002can then slowly be closed as loading begins.

WhileFIG. 1shows a single source500of oxygen deficient medium, it would be understood by a person of skill in the art that more than one source of oxygen deficient gas may be provided on the present system. Such sources500might contain the same or different types of oxygen deficient gas. For example, the load lines2A/2B may be connected to a source of nitrogen and the vapour return line4may be connected to a source of natural gas. As such, the system serves to purge with one type of oxygen deficient medium and blends with another.

Programming in the central HMI/PLC can preferably ensure that the desired flow ratio is maintained and can control valve7102to maintain the desired blend supply flow rate. The central HMI/PLC controls valve openings on the purge supply and blend supply lines520,510via valves7101and7102. Flowmeters M1and M2and oxygen sensor1001are used to verify the operation. The flowmeters M1and M2can be used to verify position of control valves7101and7102, and the central HMI/PLC can make minor adjustments to each control valve opening.

Once the oxygen level in the vapour return line4is measured at a predetermined low, for example 3% oxygen in the vapour return line4, it is possible to stop flow from the blend supply line510by closing valve7102. At this point, oxygen deficient medium is only being supplied from the purge supply line520.

Should for any reason there be no reading from oxygen sensor1001, it is also possible to maintain necessary flow ratios by reading flow meters M1and M2and maintaining a predetermined flowrate of oxygen deficient medium to the load and vapour return lines4.

Most preferably, all valves for purging or displacing the volume of the tank are automated. The valves may be air actuated valves. As before, the vapour return lines4connected with the blending supply line can be used for displacing transport tank volume with oxygen deficient medium during unloading.

More preferably, the oxygen deficient gas is natural gas as both the purge gas and the blending gas.

With no scrubber in the system ofFIG. 1, there is no need to monitor chemical supply to a scrubber to avoid depletion.

Typically, once the transportation tank is purged with oxygen deficient medium via purge supply lines520A and520B, the tank can be loaded from inside storage tanks or vessels and the displaced vapours, having satisfactorily low oxygen levels, are directed to flare. However, the HMI/PLC may also operate to open valve7102during the loading process, after purging, if needed, to ensure the oxygen levels stays below 8% even during a loading. In such cases, oxygen level readings are taken at oxygen sensor AIT1001and should oxygen levels climb to a predetermined rage, valve7102can be opened. For example, should oxygen levels reach 6% the HMI/PLC may start up the blend supply line510again.

In the embodiment ofFIG. 4, oxygen deficient medium from source500is supplied only as a blend gas into the vapour return lines4and there is no oxygen deficient medium added to the load lines. In this embodiment, the transportation tank is not purged ahead of loading, instead the load lines2A/2B load the transportation tank directly upon start of the process. Flow of oxygen deficient medium in the blend line510is maximized to lower oxygen content in the displaced gas to below 8% oxygen. Flow rate is monitored through flow meter M3and oxygen content of the vapour return line is monitored by oxygen sensor1001as before.