Dewatering a hydrocarbon storage tank

A method of dewatering a hydrocarbon storage tank carrying a first fluid layer that includes a first hydrogen concentration and a second fluid layer that includes a second hydrogen concentration includes receiving, from a sensor and by a processor communicatively coupled to the sensor, a value representing an amount of backscattered neutrons sensed by the sensor. The sensor is attached to a surface of a wall of the tank adjacent a fluid outlet of the storage tank. The sensor is configured to sense neutrons backscattered from the first fluid layer and an interface layer. The method includes comparing, by the processor, the value to a threshold, and actuating, by the processor, a valve fluidically coupled to the outlet of the storage tank to drain the first fluid layer from the storage tank while preventing the interface layer from leaving the storage tank.

TECHNICAL FIELD

This disclosure relates to storing fluids in storage tanks and dewatering storage tanks.

BACKGROUND

A hydrocarbon storage tank can store fluids of different properties. Such fluids can form different layers of fluid inside the tank. In some cases, a water layer can accumulate at the bottom of the storage tank. If the water is not removed from the tank, the quality of hydrocarbons stored in the tank might deviate from desired specifications. Methods for dewatering hydrocarbon storage tanks are sought.

SUMMARY

Implementations of the present disclosure include a method of dewatering a hydrocarbon storage tank carrying a first fluid layer that includes a first hydrogen concentration and a second fluid layer that includes a second hydrogen concentration different than the first hydrogen concentration. The first fluid layer is separated from the second fluid layer by an interface layer. The first fluid layer is disposed between the interface layer and a base of the storage tank. The first fluid layer is configured to receive additional fluid from the tank that increases a width of the first fluid layer to increase an elevation of the interface layer with respect to the base of the tank. The method includes receiving, from a sensor and by a processor communicatively coupled to the sensor, a value representing an amount of backscattered neutrons sensed by the sensor. The sensor is attached to an external surface of a wall of the tank and between 1 to 3 inches above a fluid outlet of the storage tank. The sensor is configured to sense neutrons backscattered from at least one of the first fluid layer and the interface layer, the neutrons emitted by a neutron emitting device attached to the wall of the tank. The method also includes comparing, by the processor, the value to a threshold. The method also includes actuating, by the processor and based on a result of comparing the value to the threshold, a valve fluidically coupled to the outlet of the storage tank to drain the first fluid layer from the storage tank while preventing the interface layer from leaving the storage tank.

In some implementations, receiving the value includes receiving, from the sensor, the value sensed at a location between 1 to 3 inches above the fluid outlet of the storage tank.

In some implementations, actuating the valve includes opening the valve or closing the valve to drain the first fluid layer while preventing the interface layer from leaving the storage tank.

In some implementations, the first fluid layer includes a higher density than the second fluid layer such that the first fluid layer includes more hydrogen per unit volume than the second fluid layer.

In some implementations, comparing the value to the threshold includes comparing the value to a first threshold and to a second threshold lower than the first threshold, the first threshold representing a first amount of backscattered neutrons and the second threshold representing a second amount of backscattered neutrons lower than the first amount. Actuating the valve includes opening the valve when the value meets the first threshold and closing the valve when the valve meets the second threshold.

In some implementations, the method further includes, prior to actuating the valve, determining, by the processor and based on the comparison of the value to the threshold, that the interface layer is at the same elevation as the sensor or above the elevation of the sensor.

In some implementations, the neutron emitting device and the sensor are disposed in a neutron backscatter permanently coupled to the external surface of the wall of the tank. Receiving the information includes receiving the information from the neutron backscatter with the neutron emitting device continuously emitting neutrons into the storage tank.

In some implementations, the valve includes a motor-operated valve and where actuating the valve includes actuating a motor of the motor-operated valve.

In some implementations, the valve is coupled to a first pipe fluidically coupled to a second pipe fluidically coupled to the outlet of the tank, the second pipe including a second valve. Actuating the valve includes actuating the valve as the second valve remains closed.

In some implementations, the first fluid layer includes a water layer, the second fluid layer includes a hydrocarbon layer, and the interface layer includes an emulsion layer.

Implementations of the present disclosure also include an automatic dewatering system. The system includes a hydrocarbon storage tank including a fluid outlet, the tank carrying a first fluid layer including a first hydrogen concentration and a second fluid layer including a second hydrogen concentration different than the first hydrogen concentration. The first fluid layer is separated from the second fluid layer by an interface layer, the first fluid layer disposed between the interface layer and a base of the storage tank. The first fluid layer is configured to receive additional fluid from the tank that increases a width of the first fluid layer to increase an elevation of the interface layer with respect to the base of the tank. The system also includes a neutron emitting device disposed adjacent the fluid outlet of the storage tank, the neutron emitting device configured to emit neutrons into the tank to be backscattered from at least one of the first fluid layer and the interface layer. The system also includes a sensor attached to an external surface of a wall of the tank, the sensor disposed adjacent the fluid outlet of the storage tank, the sensor configured to sense neutrons backscattered from at least one of the first fluid layer and the interface layer. The system also includes a valve fluidically coupled to the fluid outlet of the storage tank. The system also includes a processor communicatively coupled to the sensor and to the valve. The processor is configured to compare a value received from the sensor to a threshold, the value representing an amount of backscattered neutrons sensed by the sensor. The processor is configured to actuate, based on a result of comparing the value to the threshold, a valve fluidically coupled to the outlet of the storage tank to drain the first fluid layer from the storage tank while preventing the interface layer from leaving the storage tank.

In some implementations, the sensor is configured to sense the value at a location between 1 to 3 inches above the fluid outlet of the storage tank.

In some implementations, the processor is configured to open the valve or close the valve to drain the first fluid layer while preventing the interface layer from leaving the storage tank.

In some implementations, the first fluid layer includes a higher density than the second fluid layer such that the first fluid layer comprises more hydrogen per unit volume than the second fluid layer.

In some implementations, the processor is configured to compare the value to a first threshold and to a second threshold higher than the first threshold, the first threshold representing a first amount of backscattered neutrons and the second threshold representing a second amount of backscattered neutrons higher than the first amount, and where the processor is configured to open the valve when the value meets the first threshold and close the valve when the valve meets the second threshold.

In some implementations, the sensor includes a sensing surface including a height parallel to a height of the tank, the sensor configured to sense a change of an amount of backscattered neutrons as the interface layer moves in elevation across the height of the sensor.

In some implementations, the neutron emitting device and the sensor are disposed in a neutron backscatter permanently coupled to the external surface of the wall of the tank, and the neutron emitting device is configured to continuously emit neutrons into the storage tank.

In some implementations, the valve is coupled to a first pipe fluidically coupled to a second pipe fluidically coupled to the outlet of the tank, the second pipe including a second valve, and the processor is configured to actuate the valve as the second valve remains closed.

In some implementations, the first fluid layer includes a water layer, the second fluid layer includes a hydrocarbon layer, and the interface layer includes an emulsion layer.

Implementations of the present disclosure also include a system including at least one processing device communicatively coupled to a sensor attached to a wall of a storage tank, the storage tank including a fluid outlet, the tank carrying a first fluid layer including a first hydrogen concentration and a second fluid layer including a second hydrogen concentration different than the first hydrogen concentration. The first fluid layer is separated from the second fluid layer by an interface layer, the first fluid layer disposed between the interface layer and a base of the storage tank. The first fluid layer is configured to receive additional fluid from the tank that increases a width of the first fluid layer to increase an elevation of the interface layer with respect to the base of the tank. The system also includes a memory communicatively coupled to the at least one processing device, the memory storing instructions which, when executed, cause the at least one processing device to perform operations that include receiving, from the sensor, a value representing an amount of backscattered neutrons sensed by the sensor, the sensor attached to an external surface of the wall of the tank and between 1 to 3 inches above the fluid outlet of the storage tank, the sensor configured to sense neutrons backscattered from at least one of the first fluid layer and the interface layer, the neutrons emitted by a neutron emitting device attached to the wall of the tank. The operations also include comparing the value to a threshold, and actuating, based on a result of comparing the value to the threshold, a valve fluidically coupled to the outlet of the storage tank to drain the first fluid layer from the storage tank while preventing the interface layer from leaving the storage tank.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring toFIG. 1, the present disclosure relates to using a neutron backscatter102to automatically dewater a hydrocarbon storage tank120. Hydrocarbon storage tanks carry hydrocarbons and other fluids. When the fluids inside the tank120settle, the fluid with the highest density is collected at the bottom of the tank120and the fluid with the lower density remains at the top of the tank120. Thus, a first fluid layer126(for example, a water layer) settles at the bottom of the tank120and a second fluid layer122(for example, a hydrocarbon layer) remains at the top the tank120. Between the hydrocarbon layer122and the water layer126, a transition layer or interface layer124(for example, a hydrocarbon emulsion layer) is formed. The water layer126increases in width as water particles from the emulsion layer124settle down into the water layer126. The elevation of the emulsion layer124changes as the water layer126increases in width. To maintain a high quality of the hydrocarbon per the required specifications, the percentage of water in the tank120must be minimized, hence the tank120is dewatered through a fluid outlet112(for example, a dewatering outlet at side of the tank or at the bottom of the tank, as shown inFIG. 7) connected to a pipe106to extract the water from the tank120. To manually dewater a storage tank, a gauge may be used to estimate the level of water in the tank120. Dewatering a tank120automatically saves time and resources, and allows the water to be extracted without exposing the emulsion layer124to the environment, preventing safety and environmental hazards. The neutron backscatter102detects the elevation of the emulsion layer124and sends such information to a processor (shown inFIG. 2) to actuate a valve104(for example, a motorized dewatering valve). The valve104is automatically opened and closed based on the readings of the neutron backscatter102to extract water from the tank120while preventing hydrocarbons from leaving the tank120.

Implementations of the present disclosure may provide one or more of the following advantages. Efficient dewatering system resulting in better quality hydrocarbons. The system can save on cost of labor as the system is automatic. Additionally, water can be extracted from a hydrocarbon storage tank without exposing hydrocarbons to the environment.

FIG. 1shows an automatic dewatering system100used in a flat-bottomed hydrocarbon storage tank120. The automatic dewatering system100includes a neutron backscatter102attached to an external surface136of a wall138of the tank120to detect an elevation of fluids inside the tank120. As described earlier, the hydrocarbon storage tank120carries the first fluid layer126and the second fluid layer122separated by the interface layer124. The first fluid layer126can be a water layer and the second fluid layer122can be a hydrocarbon layer such as crude or refined oil. The water layer126reflects neutrons more efficiently or effectively than the hydrocarbon layer122or the emulsion layer124. More specifically, because water has higher physical density than crude oil (for example, 1 g/cc versus 0.85 g/cc), there is more hydrogen present in the water layer126than in the hydrocarbon layer122or the emulsion layer124. Because more hydrogen is present in a volume unit of water than in oil, the neutron beam of the neutron backscatter102illuminates or reaches more hydrogen in the water layer126. Additionally, carbon atoms in hydrocarbons compete for the available neutrons and capture the neutrons at a rate around 18 time higher than the oxygen atoms in water (for example, neutron capture cross section of carbon is 3.5 millibarn versus neutron capture cross section of oxygen is 0.19 millibarn). The first fluid layer or the water layer126is disposed between the interface layer124and a base128(for example, a flat base such as a bottom plate) of the storage tank120. The hydrocarbon emulsion layer124can be an oil-in-water layer or a water-in-oil layer, consisting of small globules of water surrounded by oil. With the help of gravity, small water droplets coalesce to form bigger droplets. The bigger water droplets settle down to increase the width of water layer126. Such increase in width of the water layer is detected by the neutron backscatter102to automatically open and close the valve104.

Referring toFIG. 2, the neutron backscatter102includes a neutron emitting device105and one or more neutron detection sensors103. As explained earlier, neutrons are backscattered more effectively from water than from hydrocarbons. A neutron detector like proportional counters (for example, BF3 or3He) or a semiconductor neutron counter can be used to recognize, based on the number of backscattered neutrons from the fluids in the tank, if the fluid at the level of the neutron backscatter102is the water layer126or another fluid (for example, the interface layer124). For example, the neutrons emitting device105and the sensor103can be disposed inside a housing of the neutron backscatter102. The neutron backscatter102can be permanently attached to the external surface of the wall of the tank120. As shown inFIGS. 1 and 2, when the fluid outlet112is disposed on a side wall of the tank120, the neutron backscatter102can be disposed adjacent the fluid outlet112of the storage tank129at a predetermined elevation with respect to the base of the tank. For example, the neutron emitting device105(or the neutron backscatter containing the neutron emitting device) is attached to the external surface136of the wall138of the tank120and is disposed directly above the fluid outlet112. The neutron emitting device105continuously emits neutrons into the tank120. As further described in detail later with respect toFIG. 7, when the fluid outlet is at the base128of the tank120, the neutron backscatter102is disposed on the sidewall138of the tank120, near the base128of the tank120.

When the fluid outlet112is at the sidewall of the tank120, the sensor103is disposed directly or substantially directly above the fluid outlet112of the storage tank120. For example, a bottom end140of the sensor103can be vertically separated from the fluid outlet112by a distance of 2 inches. The sensor103(or the neutron backscatter102containing the sensor) is attached to the external surface136of the wall138of the tank. The sensor103has a sensing surface that has a height ‘h’ parallel to a height of the tank120. The sensor103senses a change of the amount of backscattered neutrons as the interface layer124moves in elevation across the height of the sensor103. A processor108or processing device disposed above or near the neutron backscatter102can be communicatively coupled (for example, electrically coupled) to the sensor103. The processor can include a memory160communicatively coupled to the processor. The memory can store instructions that cause the processor to perform the functions described in the present disclosure. As further described in detail later with respect toFIGS. 3-6, the processor uses the information received from the sensor103to control a valve configured to dewater the tank120.

The neutron emitting device105can be a radioactive source of high energy neutrons that emits neutrons into the tank120through the wall138of the tank120. The hydrogen atoms of the fluids inside the tank120moderate these to low energy or thermal neutrons which can be readily measured with the sensor103. For example, as neutrons emitted by the neutron emitting device105react with the hydrogen atoms of the fluids, neutrons are backscattered or reflected back to the sensor103. Thus, the higher the hydrogen concentration of a liquid, the higher the amount of neutrons that are backscattered to the sensor103. The neutron emitting device105emits neutrons into the tank120to be backscattered from at least one of the first fluid layer126and the interface layer124. As the elevation of the interface layer124increases or decreases, the amount of backscattered neutrons sensed by the sensor103changes.

FIGS. 3-6illustrate a process of dewatering the storage tank120using the automatic dewatering system100. Referring toFIG. 3, the automatic dewatering system100includes the neutron backscatter102, and the processor108communicatively coupled to the sensor (seeFIG. 2) of the neutron backscatter102or coupled directly to the neutron backscatter10. The system100also includes a motor-operated valve104communicatively coupled (for example, through a cable110or wirelessly) to the processor108. The valve104is fluidically coupled, through the pipe106, to the outlet112of the storage tank120. The valve104is actuated by the processor108to drain the first fluid layer126from the storage tank120while preventing fluid from the interface layer124from leaving the storage tank120. For example, the processor108receives a value from the neutron backscatter102and compares the value to one or more thresholds. The value represents an amount of backscattered neutrons sensed by the sensor at a location directly above or near the fluid outlet112of the tank120. The processor108actuates, based on a result of comparing the value to the one or more thresholds, the valve104to close or open the valve104. More specifically, a first amount of neutrons are backscattered from the water layer126and a second amount of neutrons, lower than the first amount, are backscattered from the emulsion layer124. The processor108can compare the value to a first threshold and a second threshold. The first threshold represents a first amount of backscattered neutrons and the second threshold representing a second amount of backscattered neutrons lower than the first amount. For example, the first threshold is a value that represents most or all neutrons being backscattered from water (for example, that the water layer is at the elevation of the sensor), and the second threshold is a value that represents most or all neutrons being backscattered from the emulsion layer (for example, that the emulsion layer is at the elevation of the sensor). When the value (for example, the amount of backscattered neutrons) meets the first threshold, the valve104is opened and when the value meets the second threshold, the valve104is closed.

As shown inFIG. 3, the emulsion layer124is at a higher elevation than the sensor or the neutron backscatter102. The water layer126has increased in width to at an elevation that covers all or most of a height of the neutron backscatter102. At such elevation, the sensor of the neutron backscatter102senses an amount of backscattered neutrons that meet the first threshold. Such amount is the value sent from the sensor to the processor108. When the processor108determines that the value meets the first threshold, the processor108opens the valve104to dewater the tank120. Referring toFIG. 4, the neutron backscatter102continues to emit neutrons into the tank120as the water leaves the tank and the elevation of the emulsion layer124decreases. As the elevation of the emulsion layer124decreases to the elevation of the neutron backscatter102, the amounts of neutrons detected by the sensor of the neutron backscatter decreases. The processor108receives the value sensed by the sensor and compares the value to the thresholds. The second threshold is a value low enough to allow the elevation of the emulsion layer to decrease such that most or all of the emulsion layer falls to the elevation of the sensor. As shown inFIG. 5, when the processor108determines that the value meets the second threshold (for example, when the value of backscattered neutrons is low enough to indicate that the emulsion layer is about to reach the fluid outlet), the processor108closes the valve104. As shown inFIG. 6, the valve104is kept closed as the water level increases again to move the emulsion layer124to an elevation higher than the sensor of the neutron backscatter102. When such elevation is higher, the valve is opened again as described earlier with respect toFIG. 3. Thus, when the amount of backscattered neutrons is decreasing (e.g., the width of the water layer126is increasing to move the emulsion layer124above the elevation of the sensor), the valve remains closed until the first (high) threshold is met and the valve is opened. When the amount of backscattered neutrons decreases (e.g., the width of the water layer126is decreasing to move the emulsion layer124to the same elevation of the sensor), the valve remains open until the second (low) threshold is met and the valve is closed.

FIG. 7illustrates an example of an automatic dewatering system200according to a different implementation. The dewatering system200is implemented in a storage tank120that has its fluid outlet112at the base128of the tank120. The neutron backscatter102is disposed between 1 to 3 inches (for example, 2 inches) above the fluid outlet112of the storage tank (or above the level of the base128). Additionally,FIG. 7shows an example in which the automatic dewatering system200is retrofitted into an existing dewatering system. In some examples, the automatic dewatering system200is implemented to provide an automatic option of dewatering the storage tank120and a manual option of dewatering the storage tank120. A motor-operated valve134is coupled to a first pipe136fluidically coupled to a second pipe146fluidically coupled to the outlet of the tank112. The second pipe146has a second valve144that is configured to be opened and closed manually. The second pipe146can be, for example, an existing pipe that is part of a manual dewatering system. Similar to the automatic dewatering system ofFIG. 1, the automatic dewatering system200has a neutron backscatter102disposed above the fluid outlet112and a processor108that actuates the motor-operated valve134based on readings of the neutron backscatter102. The processor108actuates the valve134as the second valve144remains closed. For example, the second valve144can be used to dewater the tank120when the automatic dewatering system200is being maintained or replaced, and remain closed as the automatic dewatering system200operates to dewater the tank120.

FIG. 8shows a flowchart of an example method800of dewatering a hydrocarbon storage tank. The method includes receiving, from a sensor and by a processor communicatively coupled to the sensor, a value representing an amount of backscattered neutrons sensed by the sensor, the sensor attached to an external surface of a wall of the tank and directly above a fluid outlet of the storage tank, the sensor configured to sense neutrons backscattered from at least one of the first fluid layer and the interface layer, the neutrons emitted by a neutron emitting device attached to the wall of the tank (805). The method also includes comparing, by the processor, the value to a threshold (810). The method also includes actuating, by the processor and based on a result of comparing the value to the threshold, a valve fluidically coupled to the outlet of the storage tank to drain the first fluid layer from the storage tank while preventing the interface layer from leaving the storage tank (815).

Although the present implementations have been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereupon without departing from the principle and scope of the disclosure. Accordingly, the scope of the present disclosure should be determined by the following claims and their appropriate legal equivalents.

Ranges may be expressed in the present disclosure as from about one particular value, or to about another particular value or a combination of them. When such a range is expressed, it is to be understood that another implementation is from the one particular value or to the other particular value, along with all combinations within said range or a combination of them.

Although the following detailed description contains many specific details for purposes of illustration, it is understood that one of ordinary skill in the art will appreciate that many examples, variations, and alterations to the following details are within the scope and spirit of the disclosure. Accordingly, the example implementations described in the present disclosure and provided in the appended figures are set forth without any loss of generality, and without imposing limitations on the claimed implementations. For example, the implementations are described with reference to a tee pipe fitting. However, the disclosure can be implemented with any appropriate pipe fitting that connects two or more pipes flowing fluids of different pressures.