Victor Aparicio, Carlos Balanza and Eduardo Zambrana, Empresa Petrolera CHACO, S.A., Santa Cruz de la Sierra, Bolivia

Due to the growth of its facilities, the Carrasco gas plant of Empresa Petrolera CHACO found that it needed to update its distributed control system (DCS) to enhance and maintain operational efficiency.

The control system of the Planta Carrasco had utilized older, centralized, proprietary technology, which did not allow for the use of modern instrumentation such as Hart and Fieldbus Foundation. A phased DCS conversion project allowed the company to gradually replace the old system components as the budget, time and production needs allowed.

The goal here is to describe how this conversion project was implemented to improve system efficiency, eliminate obsolescence, and reduce operations and maintenance costs.

Project overview

The growth of the Carrasco gas plant facilities over the past few years meant that a program for replacing and modernizing the existing DCS had to be developed. For both production and budgeting reasons, it was not possible to replace and update the whole control system all at once. Therefore, a decision was made to gradually replace the old system in three phases, outlined below.

First phase. The system migration began in 2005 with the installation of the new DCS. This phase entailed connecting the separators, measurement, gas re-injection system, LPG cargo station and the SCADA system to the new system, and interconnecting the old system through OPC.

Second phase. The new DCS was connected to the power generation, glycol dehydration, and separator control facilities, and the old DCS was replaced at the plant’s cryogenic facilities.

Third phase. The new DCS was deployed and implemented throughout the remaining plant areas to optimize all control links and increase plant efficiency.

The overall objective was to modernize the plant’s control system, which would provide the following advantages:

  • Fully automate the plant.
  • Improve system efficiency.
  • Reduce operational and maintenance costs.
  • Improve the quality of the final product.

The plant operations team also wanted to reap the benefits of the latest software and hardware; and, where possible, adopt industry standards so as to ensure greater system availability and operation. It was also hoped that the upgrade would extend the plant’s life cycle. An additional objective was for the system to be open for new additions of software with the external world (OPC, OLE, ODBC, etc.).

First steps

The first step involved a meeting of the entire plant operations and maintenance team, with a view toward defining the problem. Following a “what, where, when” analysis, the team agreed upon a overview of the plant’s problems and the proposed solutions. This “management of change” strategy was then submitted to management for approval. After management had approved the project, the operations team developed an implementation strategy.

Previous DCS problems

Prior to the upgrade, the Carrasco plant’s control system was a DCS that had been installed 10 years ago. It had the following characteristics:

  • Control signals and monitoring were collected in five cabinets and then sent to a central processor.
  • The system had gateways for SCADA communications with the Amine Plant’s PLC and the RTU of the wells in the Bulo Bulo field (five in all).
  • The instruments were connected to the field modules through 4-20 mA point-to-point connections.

There were a number of problems with the existing (old) DCS, including:

  • The system had old technology which entailed high maintenance costs, and it was often difficult to obtain spare parts.
  • The hardware and software were saturated, and no more instruments and I/O modules could be added to the system.
  • It was impossible to work with modern instrumentation such as Hart, Field-bus foundation, Profibus, and Ethernet.
  • The system was centralized. The whole control system was under a control processor, and when it broke down, the whole plant was shut down, with the consequent losses in production and time.
  • The software system was old, and could not be upgraded without totally changing to a more recent version, with the consequent cost of licenses.
  • It was impossible to obtain reports and historical data on Excel spread sheets.

Automation areas

Because this was a phased conversion, it was necessary to segment the plant into its various “areas of automation” so that we could move selected areas and functions to the new DCS system. In fact, this process led to a categorization of both automated and non- automated areas. Automated areas included cryogenic, dehydration and fractioning, the Bulo Bulo field, Amine plant, separation and compression facilities. Non-automated areas included generators, the Kanata field (eight wells), LGP loading, analytical instrumentation, re-injection, and glycol dehydration facilities. These areas have all the necessary instrumentation, and operate with local control loops and monitoring.

Proposed solution

The proposed solution included the following steps:

  • Update the old DCS to a new technology.
  • Increase the speed in the field modules.
  • Increase in software’s capacity and security.
  • Manage the modern instrumentation.
  • Maintain connection with old instruments.
  • Update obsolete equipment.

Executing the project

The new DCS system is distributed in different areas, in DCS cabinets that are connected to the control room by means of Ethernet optic fiber. Two PCs have been added to the control room for graphic information, and the corresponding software for configuring the applications of the new DCS system has been updated as well. Special care was taken to follow the appropriate norms and standards during implementation. Communications between the two systems is performed with OPC. The new system has the capacity to monitor the old system and present graph screens of the whole plant on its HMI.

When building the new system, design standards were used from the old DCS. This was done so that the operators would be familiar with the graphics. The OPC system enables plant personnel to obtain reports and historic variables on Excel spread sheets.

The operators were trained in the handling of the system, alarms, screens, and set point changes. Maintenance personnel were trained in the configuration of the system, control loops, and equipment calibration.

The supplier provided technical support in the planning and implementation of the project, and has remained available for advice and help in all of the project’s various stages. This helps plant personnel maintain the system with new versions of software and firmware that are available on the market.

Phase one

For the implementation of the first phase, the project team worked directly with the operations personnel and the supplier. All the instruments and database were tested in the supplier’s offices. The installation of the cabinets was carried out one day before the migration. The maintenance team prepared a report of signals and power supply (100VAC and 24VDC) before the migration. The day of the migration, operations planned the work in such a way that they only passed to local control (in field) the affected areas of the old DCS. This allowed the plant to continue operations without shutting down, and complete the migration in six hours, the shortest time frame possible. All of the connections followed the appropriate standards for Zone 2, Div. 1. While developing this phase, there were no unforeseen plant shutdowns, and the whole implementation process was carried out without any great inconvenience.

Phase two

The objective of this phase was to completely replace the old DCS system, including the following control processors:

  • Room II – Control processor in charge of the generating and compression areas.
  • Plant II – Control processor in charge of the fractioning and turbo-expansion areas.
  • Plant III – Control processor in charge of the dehydration and hot environment areas.

For this phase, in which the entire old system was replaced, a plant shutdown was scheduled that allowed the work to be performed safely.

Phase three

The objective of this phase was to optimize the control loops and the production parameters to fulfill the proposed objectives. The new DCS system has now been fully implemented, and the Carrasco gas plant has been fully automated. New start up and shut down sequences have been written, and new instrumentation has been added as well.

Project update

Plant personnel are now converting these instruments to the Hart protocol, with the goal of having the whole plant instrumentation (transmitters and control valves) under the same protocol. Crews are also carrying out an instrumentation?management program which entails a range of inspection, calibration, qualification and?preventive maintenance procedures. This program is expected to be complete in the first half of 2008. A planned fourth phase calls for a safety instrumented system (SIS) to be deployed through the entire plant.

Conclusions

The hardware and software substitution of control systems should be carefully planned, following the ISA-CAP model for an automation project. It is a good idea to limit the project’s scope to any needed operational improvements, since these are inevitably linked to both budget and time. The selection of the supplier must be responsibly carried out, bearing in mind the need for local technical support such as maintenance and supply infrastructure. Joint work between maintenance and operational personnel is vitally important to insure that the project has a high life cycle.

It is important to develop an operator training course before or during the project’s implementation, thus getting the operator to participate in the project. Special care must be taken when selecting the hardware and software, since this must permit its easy integration with future phases and technologies.

On this project, the OPC’s structure allowed plant personnel to open the control system to other systems. This enables the plant to interconnect with the different control systems of other fields that Empresa Petrolera CHACO owns or operates.

Acknowledgment

Based on a paper presented at the ISA EXPO, held in Houston, Texas.