Making Centrifugal Pumps More Reliable

Introduction Compressors are used whenever it is necessary to flow gas from a low-pressure system to a higher-pressure system. Flash gas from low-pressure vessels used for multi-stage stabilization of liquids, oil treating, water treating, etc.; often exists at too low a pressure to flow into the gas sales pipeline. Sometimes this gas is used as fuel, and them the remainder is flared or vented. In many instances, it is economically attractive to compress this gas to a high enough pressure so it can be sold. Compression may also be required for environmental reasons. Flash gas that might otherwise be flared may be compressed for sales or gas produced with oil (associated gas) may be compressed for re-injection to avoid, flaring or to help maintain reservoir pressure. In some marginal gas fields, and in many larger gas fields that experience a decline in flowing pressure with time, it may be economical to allow the wells to flow at surface pressures below that required for gas sales. In such cases, a booster compressor (one where the ratio of discharge to suction pressure is low) may be installed. Booster compressors are also used on long pipelines to restore pressure drop lost to friction. The use of large compressors is probably more prevalent in oil field facilities than in gas field facilities. Oil wells often require low flowing surface pressures and the gas that flashes off the oil in the separator must be compressed. Often, natural gas is, injected into the tubing of the well to lighten the column of liquid and reduce downhole pressure. This "gas lift" gas is produced back with good fluids at low pressure. Compressors are used so the lift gas can be recirculated and

Introduction Centrifugal pumps are used to increase pressure in a liquid for the purpose of transporting the liquid through piping and other devices for use in an industrial  process. With the higher pressure, the liquid can be transported in short or long pipelines for delivery to an ultimate destination. Examples include water pipelines, refined petroleum and crude oil pipelines. The pressure generated by the pump is gradually depleted as the liquid flows through the pipeline, due to friction in the pipe, as well as any elevation increase from the point of origin to the destination point. The liquid as it enters the pump has a certain amount of energy, due to its initial pressure (pressure energy), position (potential energy) and its velocity (kinetic energy). The potential energy depends on the location of the liquid from some datum, such as sea level. The kinetic energy is due to the motion of the liquid. The sum of three components is the total energy of the liquid. As the liquid comes out of the pump, energy is imparted by the rotating element (impeller) in the pump and the liquid pressure increases. The velocity of the liquid also changes from that at the pump inlet. In a centrifugal pump, the liquid is accelerated by centrifugal force during its passage through the rotating pump impeller and, finally at the exit, the kinetic energy is converted to pressure energy as it exits the pump volute into the discharge piping.