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Tuesday, September 2, 2014

Non-Contact Digital Valve Controllers Yield MRO Savings at Chinese Chemical Plant

After Emerson Process Management, in Marshalltown, Iowa, replaced the existing digital valve positioners in the Shanghai Ethylene Cracker Complex (SECCO) with new digital valve controllers, the SECCO plant gained better control, production efficiency and uptime – and $40,000 in annual maintenance savings.

SECCO is the largest integrated chemical facility in China. The complex includes a naphtha-fed ethylene cracker and 10 downstream derivative plants with thousands of control valves of different brands, types and sizes.

Temperature fluctuations in chemicals production processes caused high variability in the end product, which, combined with vibration of the pipeline, often led to damage and replacement of the positioners on these valves — and thus downtime. SECCO was averaging three months before malfunction but as frequently as every two weeks. After SECCO engineers and Fisher valve specialists from Emerson discussed ways to address this problem, SECCO decided to replace the facility’s positioners with new digital valve positioners from Fisher.

The Fisher Fieldvue DVC6200f digital valve controller is a Foundation fieldbus-communicating instrument that converts a digital control signal into a pneumatic output to an actuator. It can be retrofitted in place of existing analog positioners on most Fisher and non‐Fisher pneumatic actuators. Foundation fieldbus is an all-digital, serial, two-way communications system that serves as the base-level network in a factory or plant automation environment. It is an open architecture platform developed by the Fieldbus Foundation.

The Fieldvue DVC6200f offers linkage-less, non-contact position feedback to reduce vibration-induced problems, as well as diagnostics and Foundation fieldbus communication to alert operators of potential valve problems. Conventional positioners rely on a physical connection between the position-sensing element and the valve, and severe vibration tends to cause wear and tear and damage to the linkage that provides feedback on the valve position.

Non-contact technology gives digital valve controller extended service life in the demanding chemicals field. Credit: Emerson Process Management

The DVC6200f uses a hall effect sensor located on the housing between two “pole pieces.” The magnet array is made of a series of magnets of different strengths. The magnet array is mounted on the valve stem. As the valve stem moves, the magnet array also moves (relative to the sensor), causing a changing magnetic field at the sensor. The sensor measures the change in the magnetic field.

This travel feedback technology thus has no linkages or touching parts, eliminating physical contact between the valve stem and the DVC6200f. There are no wearing parts, so cycle life is maximized.

The DVC6200f instrument is mountable onto any valve, which was especially important in SECCO’s case. Also important to SECCO was high process reliability from the DVC6200f’s Foundation fieldbus diagnostic capability to predict problems before they occur, which allows operators to take pre-emptive action to minimize process variability or avoid a plant shutdown.

After installation, operations at the facility were enhanced by better stability and control. Production efficiency improved, while waste and rework were reduced. Valve performance has been more reliable, and uptime has increased because of less frequent valve failure and fewer scheduled maintenance.

SECCO has saved an estimated $40,000 annually by eliminating the frequent replacements of positioners as well as maintenance, labor and potential production loss.



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