Fieldbus improves petrochemical plant operation

Reduced design, installation and startup costs provided significant benefits

May 1999 Supplement
Feature Article

Fieldbus improves petrochemical plant operation

Reduced design, installation and startup costs provided significant benefits

O. Cruz, Deten Chemicals S. A., Camacari, Brazil, L. Castilho, Smar Equipamentos Industriais, Sao Paulo, Brazil; and D. Evans, Smar International Co., Houston, Texas

he Foundation fieldbus applications at Deten’s Brazilian petrochemical plants demonstrate the performance advantages and cost savings offered by this control architecture. Economic benefits to Deten, however, will continue long after the initial installation. Offline configuration, online diagnostics and the ease with which system additions are made contribute to the business results of its plants. Furthermore, the digital nature of Foundation fieldbus, coupled with emerging capabilities of the Internet, will provide ongoing manpower and diagnostics efficiencies.

Background. Deten Chemicals S.A., located in the petrochemical zone of Camacari, Bahia, Brazil, produces linear alkyl benzene, a basic raw material used in detergents. The plant’s 146,000 tpy production capacity is split between the Brazilian domestic market (85%) and exports (15%). It began production in 1981 and obtained ISO-9002 certification in 1993.

Like other chemical manufacturers, Deten is faced with a host of business challenges in today’s competitive marketplace. These include developing new products at a faster pace, responding quickly to special customer requests and remaining flexible enough to meet ever-changing market conditions. Chemical processors also must ensure they operate in compliance with government-imposed environmental and safety regulations, as well as conform to ISO 9000 quality guidelines, to do business internationally.

Control challenges. Chemical processing is a demanding industry requiring process control systems that provide reliability, flexibility and long / short-term economic benefits. Among the critical applications in this field are reactors and batch processes, as well as boiler and compressor controls. In these applications, achieving higher product consistency with reduced waste depends upon reliable, high-resolution data from the plant floor level. Increasing unit uptime depends upon quickly identifying plant conditions and predicting maintenance needs. Meeting regulatory requirements demands the ability to populate system databases with real-time process information.

After considering various plant automation alternatives, Deten made a strategic control technology decision with both immediate and long-term implications for its business. The company became one of the world’s first chemical producers to install a Foundation fieldbus-based control system on a commercial application.

Fieldbus solution. From Deten’s viewpoint, one of the primary reasons to install Foundation technology was to take full advantage of intelligent field instrumentation capabilities. Unlike older analog devices, fieldbus instruments can transmit multiple variables, including instrument diagnostics and identification information. Multiple variables from each fieldbus device can be brought into the plant control system for archival, trend analysis, process optimization studies and report generation. This allows processes to be fine tuned for better manufacturing throughput.

Foundation fieldbus’ device diagnostic capabilities also help plants reduce or avoid downtime. With fieldbus, plant personnel can perform predictive maintenance without waiting for a scheduled shutdown.

An initial Foundation fieldbus project was undertaken by Deten in December 1994 at its Quimica S/A plant. The project involved 63 instruments and 43 control loops. Success of this fieldbus application led to additional installations from 1995–1996, including more than 60 projects with 10–300 devices each.


	Fig. 1. The installation involved a variety of field devices.

In 1996, Deten decided to undertake a large-scale implementation of Foundation fieldbus at two of its Brazilian plants. A total of 980 field instruments, including pressure transmitters, temperature transmitters, flow meters, level gauges, positioners, fieldbus-to-current and current-to-fieldbus converters, and fieldbus programmable logic controllers (PLCs) were installed (Fig. 1). System management is carried out on a network of 12 operator workstations and integral supervisory software (Fig. 2).

A unique aspect of the Foundation fieldbus control system is its ability to provide supervisory management, redundancy (power, network, supervisory, instrument and data) and Internet integration. With fieldbus architecture, both redundant communications and redundant bus power systems are used for critical controls. This includes fieldbus communications between the PLCs and the motor control center, which has its own PLC. The system is configured so that safety and status information, as well as pulse trains with predetermined times, are sent between the PLCs as a watchdog timer. If the pulses are no longer received by the safety PLC, the system shuts down and its outputs are put in a safe state (Fig. 3).

Fig. 3. Safety and status information are sent between the PLCs as a watchdog timer.

In addition, triple-redundant instrumentation is installed on critical control loops. This includes three temperature transmitters that operate using a 2x3 voting scheme. Each transmitter is connected to a separate fieldbus process interface board. Redundant fieldbus instruments are used on all other control loops. Each loop has two temperature transmitters and one fieldbus-to-current (4-20 mA) converter. If the principle temperature transmitter stops working, the secondary temperature transmitter will send its data to the PID control block. If one of the fieldbus interface boards develops a problem, the data will be handled by another. If both transmitters and both interface boards stop working, a safety value is sent by the software block to the PID control block (Fig. 4).

Integrating Internet technology into the fieldbus control system improves the ability to oversee process operations. With this capability, plant personnel can verify process variables, perform online maintenance and monitor supervisory screens.

Results. Reduced design, installation and startup costs made possible by Foundation fieldbus have produced significant economic benefits for Deten. To date, the company has calculated a total project savings of 32–45%. For example, 457 fieldbus devices were installed using only 30 pairs of wire during the first phase of the 1996 project. This resulted in approximately 97% savings in cable costs. Other installation savings were achieved through reduced cable tray and panel costs.

The first phase of the Foundation fieldbus installation was carried out in just 23 days, including instrument configuration, installation and operation verification. Plant personnel also were able to integrate four human-machine interfaces and supervisory software during this period. Phase two was carried out in similar fashion. FB

The authors

Laercio Castilho, Jr., is application engineering department manager for Smar Equipamentos Industrialis in Sao Paulo, Brazil. He holds an electrical engineering degree from Barretos University in Brazil, and has 19 years of experience in systems projects and DCSs. Mr. Castilho has given numerous presentations worldwide.

Og Cruz is instrumentation manager for Deten Quimica in Brazil and has had numerous papers published in seminars in the Latin America marketplace.

Dave Evans is national sales manager for Smar International Co. - North America. Prior to joining Smar, he held positions as regional manager, product manager and direct sales manager at Peer Measurement — USA.

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