Oil Gas (Transportation)
Transportation Overview
Efficiently and dependably transporting crude oil from upstream production facilities to storage operations is a challenging round-the-clock exercise. Downstream production commitments must be met‚ performance must be constantly monitored‚ and vessel and rail tank car schedules must be maintained‚ to satisfy the demand for crude oil. CIRCOR clearly understands these pressures and offers proven‚ reliable fluid-handling solutions that allow you to focus on running your operations.
Experience Throughout The Transportation Network
The applications below demonstrate the proven experience CIRCOR has for each facet of this complex system‚ supporting crude oil pipelines‚ rail car loading and unloading facilities‚ marine barges and FPSO vessels:
- Suction Booster Pumps
- Mainline Shipping Pumps
- Pipeline Re-injection Pumps
- Scraper Trap Pumps
- Chemical Injection Pumps
Suction Booster
At the initiating point of a main pipeline‚ crude oil is unloaded from temporary‚ above ground storage tanks. Prior to its delivery to the pumps installed at the initiating booster station‚ the crude oil often travels through a custody transfer meter‚ which accurately measures the volume of the crude oil provided by the end user. The accuracy of this meter is very much dependent on the velocity of the fluid delivered to it‚ so Suction Booster pumps play a very vital role at the start of the transportation process. Monitoring the contributed flow rate provided by an individual user is critical since the crude oil is often being uploaded into a common carrier pipeline further downstream of this location‚ where crude oil from several clients is batched or commingled. The elevated pressure contributed to the system by the Suction Booster pumps also provides the necessary NPSH / NPIP required by the pumps installed at the initiating booster station of the pipeline.
As field experience bears out‚ Suction Booster systems have their challenges. The crude oil‚ if allowed to sit in storage for too long‚ can see a significant increase in fluid viscosity. For the booster pumps this will result in increased input torque requirements being demanded by the pumps‚ due to additional viscous fluid drag on the rotating assemblies. Assuming the NPSH / NPIP requirements of the pumps can still be satisfied‚ the delivered flow rate will be impacted. In the case of centrifugal pumps it will be reduced. In the case of positive displacement pumps it will increase‚ which seems almost counterintuitive. The other main challenge Suction Booster pumps face is potential vortexing of air into the suction header feeding the pump when stripping out a storage tank. This is due to inadequate submergence of the takeoff connection fitted to the side of the tank below the tank liquid level.
Suitable Pump Types:
Mainline Shopping
After leaving the Suction Booster pumps‚ the crude oil is fed to the Mainline Shipping pumps‚ which are installed at the initiating booster station for the pipeline. The elevated supply pressure of the fluid satisfies the inlet energy requirements of these first stage pumps‚ allowing smaller‚ higher speed pumps to be used. The role of the Mainline Shipping pumps is to provide the necessary energy boost required to push the fluid through the downstream piping network to its intended delivery point. To achieve this objective it must overcome the pressure drop imposed by the downstream system‚ due to the declining pressure gradient as a result of friction losses and elevation changes. For long distance pipelines additional booster stations are often required. In these cases the Mainline Shipping pumps at the upstream station serve as the Suction Booster pumps for the next station downstream.
Mainline Shipping pumps‚ due to their near continuous operation‚ have very high reliability. Due to legislation imposed by pipeline regulators‚ as well as the crude oil quality specifications mandated by downstream refineries‚ the level of sediment and water that the pumps are exposed to is minimized‚ further extending the life of the equipment. In these applications‚ due to the flow rates managed and the pressure boost required‚ the key performance metric considered is efficiency. In many countries the main pipelines are operated by a separate company‚ or in the case of a state owned company by a separate division‚ whose primary operating expense is the energy demanded by the Mainline Shipping pumps. Saving energy here directly translates into increased profitability; and the potential savings‚ even with lower viscosity fluids‚ are tremendous.
Suitable Pump Types:
Pipeline Re-injection
To aid the end user’s operations and maintenance staffs‚ each pipeline booster station is equipped with a Pipeline Re-injection system. The functions served by this equipment are twofold: to provide a collection point for any process fluids that are drained from the Mainline Shipping pumps during normal operation‚ planned maintenance or an unplanned failure; and to provide a means for safely re-introducing these collected fluids into the main pipeline‚ thereby avoiding the need for mobilizing a vacuum truck to extract the drainage from the collection sump.
As experience bears out‚ Pipeline Re-injection systems‚ although small in makeup‚ can have their challenges as well. Due to the high reliability of Mainline Shipping pumps‚ re-injection pump systems will generally be employed intermittently. The fluids collected over time in the drain sumps often age. Water‚ oil and solids‚ due to their differing densities‚ separate with the crude oil‚ becoming more viscous due to lower ambient temperatures. This phenomenon occurs within the pump internals as well. The pump system therefore must be designed to handle the necessary breakaway torque to overcome the additional viscous drag on the rotor(s). The shaft sealing arrangement of the pump must also be simple‚ while being robust enough to avoid damage during start-up. When the system is initiated by the user‚ the pumps will need to self-prime in a high suction lift condition‚ since no vacuum priming system will be available at the booster station. Ideally these re-injected fluids‚ due to their potential makeup‚ should be re-introduced downstream of the mainline shipping pumps to avoid damaging critical wear surfaces with a fluid stream laden with abrasive solids. To achieve this end‚ the re-injection pumps must be capable of pushing the collected fluids into the transportation line at pressures greater than full pipeline pressure.
Suitable Pump Types:
Scraper Trap
A key part of the reliable operation of large, long distance crude oil transportation pipelines is the cleaning of the internal wall of the pipe itself, as well as the removal of settled solids. These substances, if not properly dealt with, can lead to the subsequent fractures of the pipe wall in the affected areas and costly environmental leakage. If fractures do not readily occur, the accumulated solids will inevitably create flow assurance problems within the pipeline by reducing the working volume of the pipeline, or even blocking the line altogether. These obstructions typically occur where the internal line velocities are reduced due to pressure drops across elbows and valves, or where due to topographical changes the solids are able to separate because of their differing density as compared to the crude oil. To prevent or remedy these conditions, a close-fitting, mechanical device equipped with scrapers and/or brushes called a “pig” is inserted into the pipeline and travels through the line by the energy provided by the mainline booster pumps, removing the undesirable contaminants. At a predetermined delivery point, the pig is isolated in a Scraper Trap vessel. The contaminated fluids collected are pumped from this vessel to a tanker truck for removal to a treatment facility.
As experience bears out, Scraper Trap systems have their challenges. By the nature of the service, the fluids being managed are contaminated with settled solids which are suspended in a viscous oil mixture. To further complicate this service, the Scraper Trap vessel when isolated is at full line pressure, meaning that the suction of the pump tasked to drain this vessel is immediately exposed to an extremely high suction pressure. Once a sufficient volume of fluid has been extracted from the vessel to reduce the internal pressure, a valve is opened to vent the tank, to facilitate the safe draining of the trap. To perform in this duty the pump used must have good suction lift capabilities, due to the high viscosity of the fluid being managed and the minimal vertical height between the underside the Scraper Trap and suction centerline of the pump. To complicate matters further, these services are intermittent, so the fluid-handling technology selected must be robust enough to reliably restart after a long, idle period.
Suitable Pump Types:
Chemical Injection
Fluid conditioning: a fundamental role of flow management to ensure optimal production rates and sustainable pipeline integrity. By means of the controlled injection of chemicals like corrosion inhibitors and Drag Reducing Agents (DRAs), uninterrupted, peak throughput can be achieved from a pipeline. Many of these chemicals or agents are comprised of very expensive, long-chain polymers that are extremely sensitive to fluid shearing when conveyed by mechanical equipment. Precise metering of the prescribed volume into the flow network will increase both the operational profitability, by allowing additional volume to be transported through the same pipeline with the same pressure drop, and the longevity of the transportation circuit, by means of guarding against the attack of corrosive salts and microorganisms into the internal surface of the pipe wall. Ensuring that the Chemical Injection equipment is capable of passively handling these fluids without damaging the stability of the polymers is a critical requirement that needs to be respected when evaluating technical solutions.
As experience bears out, these small Chemical Injection systems need to be well engineered. In many cases, due to the overall length of a pipeline, the injection skid, supply tank and controls are installed in remote, unmanned areas. Reliability is critical, since the equipment will typically only be revisited to refill the chemical supply tank. As these systems are directly connected to the main pipeline, the pumps must be capable of withstanding exposure to full line pressure in the event of an unplanned shutdown. For this reason, sealless, magnetically driven pumps are favorably viewed, as they eliminate the possibility of any process fluid being discharged into the environment.