Oil Gas (Storage)
Storage Overview
Vital: one word that encapsulates the critical function that Storage facilities provide to the global oil and gas market. In these operations the incoming crude is temporarily stored. Heavy off-spec grades of crude are mixed with more premium grades of crude to improve their marketability. The varied inventory needs to be turned over quickly, and many of the fluids present handling challenges due to their high viscosity. When a shipment request is received the downstream demand must be satisfied immediately. CIRCOR understands the hourly pressures that are present here and can provide proven fluid-handling solutions which allow you to focus on running your operations.
Tank Farms And Terminals Expertise
Daily conveying fluids into, around and out of storage terminals is another critical area where CIRCOR has proven experience. Our technologies are used extensively for applications such as:
- Tank Loading & Unloading Pumps
- Tank Blending Pumps
- Tank Heater Circulation Pumps
- Bitumen & Asphalt Emulsion Transfer Pumps
- Shipping Pumps
Tank Loading & Unloading
The above-ground tanks at the Storage terminal serve as the midstream receiving and distribution point for the crude oil that has traveled to this location via pipeline‚ rail car‚ truck tanker or ocean vessel. In addition to crude oil and heavy fuel oil‚ a wide range of premium‚ light end hydrocarbons (e.g.‚ sales oil‚ naphtha‚ distillates and gasoline) are also cycled through these temporary holding points. Apart from those products arriving via pressurized pipeline‚ all of the other aforementioned transportation methods will require process pumps to unload their cargo and to transfer it to the Storage tanks. At the required time‚ the tanks will then need to be unloaded to support blending activities at the terminal‚ or for exporting by means of vessels berthed at the terminal jetty or via a supply pipeline interconnected to a nearby downstream process facility.
As user experience bears out‚ seemingly simple services like Tank Loading & Unloading systems can offer their challenges. Stripping tanks‚ rail cars and tanker vessels demands that the pumps regularly operate under very difficult inlet conditions with tight NPSH / NPIP margins‚ often managing vortexed air that has entered into the supply manifold due to low submergence of the takeoff connection fitted to the side of the tank below the tank liquid level. The terminals themselves‚ due to the range of fluids managed and their volumes‚ are comprised of various tank sizes. Their differing working heights and effective volumes require the same Loading & Unloading systems to reliably support an extremely wide range of flow requirements‚ forcing kinetic pumps to operate well outside of their reliable‚ design working limits. This is further complicated by the fact that system operation at terminals is intermittent‚ demanding the repeated starting and stopping of drivers and pumps each day‚ increasing the potential for an unplanned discharge of process fluid. At these locations‚ more than in the Transportation network‚ leaks are extremely dangerous. Volatile hydrocarbons are inventoried on the premises‚ and explosive‚ airborne hydrocarbon vapors are potentially present in and around the rotating equipment.
Suitable Pump Types:
Tank Blending
Prior to exporting, some of the fluids temporarily stored at the tank farm will be made use of for blending operations. Lower-quality, off-spec crude oils may be upgraded to improve their marketability by mixing them with premium oils of greater value, or several fluids may be combined together to suit the design specification of a regional, downstream client. To perform these tasks Tank Blending pump systems are required to accurately meter in the prescribed volume(s). Working alongside this equipment are circulating systems, either mixers or pumps, to ensure that the blended fluids are consistently commingled. At a predetermined time, based on the fluid volumes involved, a terminal operator will take a sample of the blended mixture for analysis by the on-site quality assurance lab to ensure that the desired product has been achieved.
Effective blending is nearly a petroleum science, where process control is vital to operational profitability. System pressures and their corresponding system head resistance will vary during these tasks, challenging operators to maintain control of the blending rates handled by the fluid-conveying systems. Pumping equipment not able to tolerate low flow rate excursions will struggle with poor Mean Time Between Failures (MTBFs).
Suitable Pump Types:
Tank Heater Circulation
While viscous fluids like heavy fuel oils, low API grades of crude oil, or bitumen are inventoried at Storage terminals, maintaining the optimum process fluid temperature is critical to achieving trouble-free operation of the facility. If the fluids are allowed to cool, the viscosity of these mediums will increase, restricting the volume of product that can be exported from the tank due to the increased system resistance imposed by the downstream process piping. In turn, additional driver brake horsepower and extra inlet energy will be demanded by the Loading & Unloading pumps, due to additional viscous drag on the pumping rotor(s) and increased inlet losses within the suction area of the pump casing. To help mitigate temperature losses to the surrounding environment, the tanks, piping and loading/unloading equipment are well insulated. The process fluid is in turn continuously cycled from the storage tank by the Tank Heater Circulation system through an external heating package, typically a fired hot mineral oil design, with the heated oil being returned back to the tank. This arrangement is well suited to Storage tanks, as it eliminates the safety and maintenance hazards associated with immersion heaters and promotes the heat transfer to the process fluid without the need for a mixer, which would be impractical on larger tanks.
As field experience demonstrates, Tank Heater Circulation systems can be challenging as well. At start-up, the process fluid within the external piping circuit (feed and return) can become highly viscous. In contrast to the Storage tank, this portion of process piping holds a relatively small volume of fluid compared to the total surface area of the manifold, where heat loss can occur. At start-up the full Tamk Heater Circulation system will be taxed. The pumps may be starved from an NPSH / NPIP standpoint and may cavitate. More driver shaft power will be required to push this viscous slug back to the tank, due to the increased accumulated pressure drops across the valves and the heat exchangers. Heat tracing the pumps and controlling their operation with adjustable speed drives are effective means of managing this temporary condition to help maintain equipment reliability, and will avoid unnecessarily over-sizing the pumps to deal with this short term requirement.
Suitable Pump Types:
Bitumen & Asphalt Emulsion Transfer
To support regional road construction projects, Storage terminals located in nearby locations are often designed to inventory liquid bitumen and asphalt (used for traditional hot-slab paving) and their associated emulsions (which are used for cold-mix paving). In all cases these fluids serve as “binders” which cement the loose aggregate rock into a pseudo-solid mass that can be applied to road surfaces. The liquid bitumen and asphalt must be handled quickly, being transferred into insulated tanker truckers for immediate shipping to batch heater, semi-continuous or continuous drum mix plants. The emulsion forms of these binding agents, although less viscous and only requiring heating to approximately 40°C (105°F), are shear-sensitive fluids that can become readily damaged when conveyed by pump types that aggressively handle the product.
As operator experience bears out, the transfer of these fluids can be challenging. Hot liquid bitumen and asphalt must be handled at temperatures approaching 190°C (375°F) to keep the paving cement at a workable viscosity that can be directly used as feedstock by the downstream production plant. Even at these elevated temperatures, both fluids possess a certain “stickiness” that can contribute to premature mechanical seal failures if the proper API flush plans (e.g., Plan 11 and Plan 62) are not employed. Although asphalt and bitumen both contain small percentages of sulfur and some small solid particulate, product-lubricated pump designs, as well as external bearing pump types can be reliably used, dry-running being the operational requirement that would favor the use of the later technology for stripping applications.
Suitable Pump Types:
Shipping
The export Shipping pumps that operate at the storage terminal provide the necessary pressure boost to convey the required feedstock cross-country to the facilities of their respective downstream clients via an onshore distribution pipeline. Depending on the process fluid viscosity, the Tank Unloading pumps may effectively serve as the Suction Booster pumps for the Shipping units to satisfy their NPSH / NPIP requirements. For long distance fluid transfer, additional intermediate booster stations may be needed to support the delivery of the product to its intended end destination.
Like all intermittent services, Storage terminal Shipping pumps can face operational challenges. As both the Shipping pump and its corresponding driver are being regularly started and stopped, the potential exists for moisture to be drawn into the bearing housings of each machine. During the intervening idle periods the conveyed process fluids can also set up within the internals of the pump, in particular in the seal housing areas, where vulnerable components like mechanical seals are located. Care must be taken in designing a suitable equipment lubrication scheme and pump shaft sealing arrangement, including the necessary API flush plans, to achieve the required availability of the Shipping pumps.
Suitable Pump Types:
Waste & Slop Oil
The export Shipping pumps that operate at the storage terminal provide the necessary pressure boost to convey the required feedstock cross-country to the facilities of their respective downstream clients via an onshore distribution pipeline. Depending on the process fluid viscosity, the Tank Unloading pumps may effectively serve as the Suction Booster pumps for the Shipping units to satisfy their NPSH / NPIP requirements. For long distance fluid transfer, additional intermediate booster stations may be needed to support the delivery of the product to its intended end destination.
Like all intermittent services, Storage terminal Shipping pumps can face operational challenges. As both the Shipping pump and its corresponding driver are being regularly started and stopped, the potential exists for moisture to be drawn into the bearing housings of each machine. During the intervening idle periods the conveyed process fluids can also set up within the internals of the pump, in particular in the seal housing areas, where vulnerable components like mechanical seals are located. Care must be taken in designing a suitable equipment lubrication scheme and pump shaft sealing arrangement, including the necessary API flush plans, to achieve the required availability of the Shipping pumps.