Siemens Industry, Inc. - Process Analytics

Use of process analytics for cracking processes in refineries – Case Study

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Crude oil processing Crude oil is a complex mixture of hydrocarbon compounds and relatively small quantities of other materials such as oxygen, nitrogen, sulphur, salt and water as well as inorganics and metals. It occurs naturally in the ground and was formed millions of years ago.

Crude oil varies from source to source in composition and colour. It is typically mixed with gases, which have to be separated from the crude oil befor it can be further processed. Crude oil itsel is of little use. To get the maximum value from crude, it needs to be refined and blended in a refinery into more valuable and useful petroleum products: fuels, lubricants, waxes, asphalt, plastics, fibres, detergents, fertilizers and many others.

An oil refinery is a well structured arrangement of manufacturing processes designed to perform physical and chemical changes in crude oil to convert it stepwise into intermediate and end products. Refinery processes have been and are continuously developed and optimized in response to changing market demands for certain products. Almost all refineries, regardless of their special product scope, use the same few basic processes like separation (distillation), conversion and treating. Cracking belongs to the most common conversion methods. Process analyzers, mainly process gas chromatographs but also continuous gas analyzers, are standard in a refineries process instrumentation. They deliver key data to process and product quality control and asset management. Siemens Sensors and Communication provides efficient analyzers, expertise and solutions to this tasks.

In the hydrocarbon processing industry (HPI), cracking is the process whereby complex organic molecules (e.g.heavy hydrocarbons) are broken down into simpler molecules by the breaking of carbon-carbon bonds in the base material. The rate of cracking and the nature of end products strongly depend on the temperature and presence of any catalysts. Process automation equipment including gas analysis instrumentation contributes essentially to control and optimize cracking processes.

Siemens Sensors and Communication, a leader in process analytics, has proven worldwide its competence to plan, engineer, manufacture, implement and service analyzer systems for use in cracking plants. This case study provides detailed information about that.

Refining process

The key objective of the refining process is to effect chemical reactions on the raw hydrocarbons. The refining process from crude oil to end-use products comprises several sub-processes (fig. 1).

Fractionation

Because crude oil is a mixture of hydrocarbons with different boiling temperatures, it can be separated by distillation (fractionation) into groups of hydrocarbons (called cuts or fractions) that boil between two specified boiling points (fig. 2).

Two types of distillation are performed: atmospheric and vacuum. Atmospheric distillation takes place in a distilling column at or near atmospheric pressure and at temperatures of 90 to 650 °C. To recover heavy distillates (residues) drawn off from the bottom of this column, the residue is fed to a second distillation column where the process is repeated under vacuum, called vacuum distillation. This allows heavy hydrocarbons with boiling points up to 800 °C to be separated.

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