Oil and gas industry process analytics in ethylene production plants – Case Study


Courtesy of Siemens Industry, Inc. - Process Analytics

Ethylene is the largest volume industrially produced organic material and its majority is used in the production of polymers and derivatives. Between a variety of processes the thermal cracking of hydrocarbons in the presence of steam (steam cracker) is mostly used. Regardless of the process type, all plants require process analytical equipment to collect reliable and accurate process data for process control, product quality, and plant safety.

Siemens, a leader in process analytical instrumentation, has proven over decades its capability to plan, engineer, manufacture, implement and service analyzer systems for use in ethylene plants worldwide. This case study provides an overview of the steam cracking process and describes how Siemens, with its outstanding analyzer technology, application know-how and system integration expertise can provide remarkable user benefits.

Current worldwide production is about 95 MM tons/year and is projected to increase for the foreseeable future. A typical modern plant produces in excess of 800,000 tons/year. Feedstock to ethylene plants ranges from light Ethane/Propane mix to heavy naphta and vacuum gas oils. Most plants are designed with raw material flexibility in mind. Majority of ethylene produced is used in the production of polymers and ethylene derivatives such as ethylene oxide and glycol. A typical ethylene plant also makes a number of other important chemicals such as propylene, butadiene and pyrolysis gasoline.

In the past years, Ethylene plants have evolved into highly integrated, highly flexible processing systems that can profitably adjust to changing raw material availability and market demands for Olefins products. Advanced process control technologies are used in Olefins plants and have greatly improved products quality, plant efficiency and resulted in quick payback of the investment.

Typical process features of an ethylene process are short residence time in the furnace, high selectivity, feedstock flexibility, operational reliability and safety, easy start-up, and energy efficiency.

Process analytics is a key issue for process control by online monitoring the various process streams in ethylene and propylene production. Process analytics maximizes yields and ensures product quality specifications.


Ethylene, H2C=CH2, is the lightest olefin. It is a colorless, flammable gas, which is produced mainly from petroleum-based feedstocks by thermal cracking in the presence of steam. Ethylene has almost no direct end uses but acts almost exclusively as an intermediate in the manufacture of other chemicals, especially plastics.

Ethylene may be polymerized directly to produce polyethylene, the world’s most widely used plastic. Ethylene can also be chlorinated to produce1,2-dichloroethane, a precursor to the plastic polyvinyl chloride, or combined with benzene to produce ethylbenzene, which is used in the manufacture of polystyrene, another important plastic. Smaller amounts of ethylene are oxidized to produce chemicals including ethylene oxide, ethanol, and polyvinyl acetate.

Ethylene quality depends on users requirements in downstream processes. No single chemical grade ethylene exists, but ethylene content normally exceeds 99,7%. Sulfur, oxygen, acetylene, hydrogen, carbon monoxide and carbon dioxide are the most troublesome impurities that must be controlled carefully.

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