Alfa Laval Pump Handbook

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 : 1.1 Why water treatment? Pure water [H2O] is a colourless, odourless and tasteless liquid. It plays a huge part in everyday life: 70% of the earth’s surface is covered by water in the form of oceans, and the rest of the planet has large quantities of water in the form of lakes, rivers and watercourses, ice and snow, and humidity, as well as the principal element of animal life (>50%) and plants (approx. 80%). When we talk about water in general, we usually mean water for some specific purpose, e.g. drinking water or process water for industry. This is where the term water treatment comes into the picture, as the available water resources or that provided by nature is not always of a suitable quality for immediate use for the specific purpose. Drinking water must be pure, and should preferably taste good too, and it must not contain substances that could cause problemswith daily use. Process water, which is water that forms a direct and important part of a process or product in industry, must have a chemical composition and temperature that is precisely suited to the specific requirements.

Summary Centrifugal pumps perform many important functions to control the built environment. The physics and basic mechanics of pumps have not changed substantially in the last century. However, the state of the art in the application of pumps has improved dramatically in recent years. Even so, pumps are still often not well applied, and become common targets in retrocommissioning projects where field assessment and testing can reveal significant energy savings potential from optimizing pump performance. Typically, retrocommissioning finds that pump flow rates do not match their design intent and that reducing flow rates to match load requirements or eliminating unnecessary pressure drops can save energy. As the example below illustrates, decisions made during the design phase have implications throughout the operating life of the building. Although fully optimizing any design will require some effort after installation, the prevalence and magnitude of the savings that are commonly found in retrocommissioning and ongoing commissioning begs the larger question: How much greater would the savings be if pumps were selected and applied optimally during the design phase?

Main Types of Compressors  The compressor is the heart of a mechanical refrigeration system.  There is the need for many types of compressors because of the variety of refrigerants and the capacity, location and application of the systems.  Generally, the compressor can be classified into two basic types: positive displacement and roto-dynamic.