Oil Gas (Refining)
Refineries are the main delivery point for crude oil. Complex, energy demanding processes abound here in the downstream sector, with the associated challenges of high temperatures, high pressures and sour as well as corrosive process fluids. Facility managers contend with significant power costs in addition to ensuring that their facilities meet the ever-growing environmental regulations imposed by their regional and federal governments. With these immense pressures and constraints, delivering an operating profit is becoming increasingly difficult. CIRCOR understands the tremendous challenges that are present here and can provide proven fluid-handling solutions which allow you to concentrate on running your operations.
Experience Supporting Critical Refining Processes
In all of the major oil Refining areas around the globe, CIRCOR provides proven fluid-handling solutions for applications such as:
- Process Charge Pumps
- Residuum & Vacuum Bottoms Pumps
- De-asphalting Pumps
- Tank Loading Pumps
- Waste & Slop Oil Pumps
The crude oil delivered to the holding tanks at the refinery is initially fed into the first stage process unit by the Process Charge system. The pumps operating at this location provide the necessary pressure boost to push the crude oil through the Desalter vessel, repeating the process carried out at the upstream facility, then through the super-heated steam furnace and finally into the base of the atmospheric distillation tower. Within this vessel the various components making up the heated process stream are separated due to their different boiling point temperatures and corresponding specific gravities, the denser fluids stratifying in the lower portion of the tower (i.e., heavy gas oil and residual) and the lighter distillates collecting in the upper portion of the vessel (i.e., gas, naphtha and gasoline). These isolated fluids are then individually piped away via a series of horizontal process connections situated at specific elevations on the side wall of the atmospheric distillation tower. Each of these distilled fluids then serves as the feedstock for a subsequent downstream Refining process in which a second Process Charge system is often needed to boost the medium into the unit.
When you survey a refinery process flow diagram, it is readily apparent that Process Charge equipment serves as the primary means of introducing kinetic energy into the process stream. High reliability is demanded from this rotating equipment. Continuous, uninterrupted operation must be maintained due to the complexity of the facility. Tight control of flow rates from unit to unit is critical to support the optimum throughput of the refinery. High process temperatures, as well as the handling of harmful, even toxic, process fluids dictates that proven API compliant equipment must be specified and used.
Suitable Pump Types:
From the base of the atmospheric distillation tower, the fractionated atmospheric residuum or heavier ends from the first stage refining process are conveyed to the vacuum tower. Due to the high viscosity of this residual fluid a charge pump is required to boost this byproduct to the vacuum tower. At this next refinery unit the medium is once again pre-heated prior to its introduction into the base of this vessel. The hot process stream is exposed to a hard vacuum. The sub-atmospheric pressure promotes vaporization of the heavier materials at temperatures below cracking conditions. Greater amounts of light ends are removed, including light and middle fractions of fuel oils, gas oils and a residuum called Vacuum Bottoms. The resulting vacuum residue, now even more viscous than the original residuum feedstock, again requires boosting to either the facility coking unit or asphalt plant, where the medium is cooked to produce coke for use in steel and aluminum production.
Nasty: a word which aptly describes these two fluid-handling services. Even at elevated process temperatures the extracted, residual fluids are highly viscous. Dispersed, solid contaminants that accompanied the crude oil feedstock are now concentrated by distillation in this byproduct, exposing the Residuum & Vacuum Bottoms pumps to an abrasive process fluid. In both applications NPSH / NPIP is at an absolute minimum due to the high vapor pressure of the process stream. Proper heat tracing and insulation of the pumps, and in particular their shaft seal(s), is essential to achieve good pump life. Operating the pumps at reduced speeds will also help to extend the design life of the pump rotating assembly and mechanical seals, while also affording the best suction lift capabilities.
Suitable Pump Types:
With the increasing use of heavy crude oil as a feedstock, refineries are modifying their facilities to include a De-asphalting system. The system, which is located downstream of the vacuum distillation tower, uses a pump to cycle the vacuum tower bottoms residuum through an additional treatment process to further harvest valuable distillates from the residue. A solvent like propane, pentane or butane is mixed with the charge stock prior to its entry into a vertical separation vessel to dissolve the molecular bonds of the inputted fluid, thereby increasing the yield of de-asphalted oil and asphaltenes. By means of a multistage separation and stripping process, the de-asphalted oil is further treated, to condition it for its ultimate use as feedstock for a fluid catalytic cracker or hydrocracker. The separated asphaltenes are reheated prior to injecting into a stripping vessel, with the final product being pumped to asphalt handling facilities for distribution to road asphalt plants or roof shingle manufacturers. De-asphalting services, similar to those residuum fluid-handling applications found on upstream distillation systems (atmospheric and vacuum types), need to manage highly viscous products due to the concentrated asphaltene content. This sticky process fluid, which is often laden with a high concentration of solid contaminants, demands a robust and efficient pumping technology. In these services proper heat tracing and insulation of the pumps, and in particular their shaft seal(s), is essential to achieve good pump life. Operating the pumps at reduced speeds will also help to extend the design life of the pump rotating assembly and mechanical seals, while also affording the best suction lift capabilities.
Suitable Pump Types:
The above-ground tanks at the refinery serve as the temporary, downstream staging point for the crude oil that has traveled to this location via pipeline, rail car, truck tanker or ocean vessel. Apart from crude oil 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. This crude oil inventory will support the smooth and around-the-clock operation of the refinery. Tank Loading systems handle this task.
As user experience bears out, seemingly simple services like Tank Loading systems can offer their challenges. Stripping 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. Depending on the regularity of the crude oil supply chain, these systems may be operated intermittently, demanding the repeated starting and stopping of drivers and pumps, increasing the potential for an unplanned discharge of process fluid.
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:
Waste & Slop Oil
A key part of the safe operation of a world-class refinery is the responsible managing of Waste & Slop Oil. Often these fluids contain a mixture of water, oils and other waste products from process stream spillage, overflow and controlled collections from on-site drainage systems. After consolidating in a drainage sump the fluids will likely separate, with inert solid wastes settling at the bottom of the sump along with the water and oil in the upper portion of the containment pit. In addition to these mediums, spent catalysts from Refining treatment processes may be present, which present their own environmental challenges. From a fluid-conveying standpoint the Waste & Slop Oil system must be capable of handling this non-homogeneous, stratified mixture, which due to aging can become highly viscous, as well as corrosive.
As experience bears out Waste & Slop Oil systems, although small in capacity and working pressure, can bring their own unique challenges. The systems are intended to be used only intermittently, which means that there are long idle periods between uses when the waste fluids can set up within close clearance areas of pumps and valves. On a related note, proper material selection for system components should not be underestimated due to the diverse makeup of the process fluid. The pump itself will be subjected to nearly continuous internal and external exposure to the process fluid. Internally it is fully wetted to permit immediate start-up without priming. Externally the pump is submerged beneath a top deck plate, ensuring that any waste oil leakage is captured within the sump.