Petrokemija d.d., Croatia

Passing the Nitric Acid Test

Process News, Edition 04/11

A fertilizer producer in Croatia brings a 1960s manufacturing process up to modern safety standards with Simatic PCS 7.


The Petrokemija plant in Kutina, Croatia

Petrokemija, the largest fertilizer producer in Croatia, is all too familiar with dangerous processes. Fertilizer manufacturing starts with methane and water. At its plant in Kutina, Croatia, Petrokemija has two production lines manufacturing a total of 810 tons per day of 100 percent nitric acid. The safety systems in the plant were originally installed in the 1960s and consisted of electrical-relay protection systems and transistorized alarm modules. These had become unreliable over time, and as the first phase of updating the entire plant, Petrokemija decided to replace the safety and alarm systems to bring the plant up to present-day safety standards. Petrokemija set about the task of replacing the safety systems in three phases: the analysis phase, the implementation phase, and the operation and maintenance phase. In the analysis phase the existing and potential safety risks were identified. A specification was then drawn for the required Safety Integrity Level and for the measurable reduction in risk that the new safety system should deliver. From the specification, the logical safety system architecture was prepared, and this became the foundation for selecting the hardware architecture and related software to implement the safety functions.The main tasks of Petrokemija’s safety systems are monitoring all the important process parameters and promptly informing operators about potential dangers that could lead to disastrous unintended consequences and hazards. These functions have been provided by the old alarm, protection (trip, interlocks, and emergency shutdown), and process control systems. In order to increase the safety requirements the customer decided to revamp and upgrade the existing alarm safety protection system with a new microprocessor system. A time slot for the modernization was scheduled for the migration to the new alarm safety protection system Simatic PCS 7. It links the functionality of classical distributed control and logical systems in a common hardware and software platform with integrated engineering tools and operator interface to meet minimum safety standards with Safety Integrity Level 2 (SIL2) up to Level 3 (SIL3) according to IEC 61508 and IEC 61511.

A state-of-the-art solution

For the engineering of the safety functions, Petrokemija used the Simatic PCS 7 process control system and the Simatic Safety Matrix. The Safety Matrix follows the cause-and-effect method defined by the American Petroleum Institute, an extremely effective procedure for the description of safety functions and for the definition of marginal and emergency shut-down conditions. The controller level was retrofitted with Simatic PCS 7 AS 417-FH systems to replace the original electrical-relay safety protection systems and the transistorized alarm systems.Petrokemija’s own engineers, who were supported by Siemens in Croatia, took on the design, installation, and programming of the systems. The 20 operators at the plant had no previous experience with computer-controlled safety and alarm systems, so training presented something of a challenge. Both the user-friendly interface of Simatic PCS 7, especially the safety protection cause-and-effect matrix, and Siemens’ knowledge of the nitric acid production process contributed significantly to the successful outcome of the training program.The Simatic Safety Matrix was programmed for all possible causes and effects, and in the process of commissioning, a verification system for all safety conditions was developed and tested against random hardware faults. The system commissioning was further accelerated by the use of Simatic ET 200M terminal modules. These simplified the wiring to field sensors and actuators and saved Petrokemija both time and expense.


Petrokemija’s engineers took on the design, installation, and programming of the systems

Future extensions planned

The installation, testing, and training phases were completed in January 2011, and by the beginning of February both production lines were up and running with the new safety and alarm systems. The distributed I/O peripherals installed as part of the safety and alarm systems will be extended in the second phase of modernization. This will be the basis for eventually replacing all of the existing pneumatic control systems with computer-based control and information systems. The Simatic PCS 7 safety and alarm system is the foundation for the improvement and modernization of Petrokemija’s entire production process – and the quality, reliability, and efficiency in the process.

Fertilizer process control expertise in the United States

Simatic PCS 7 was the system of choice for the largest producer of nitrogen chemical and fertilizer products on the US East Coast. The company needed to continue to modernize its process safety strategies with a focus on ammonia suppression. Working with the solution partner aeSolutions from Greenville, South Carolina, Siemens adapted the fire and gas control system, which runs on a Simatic PCS 7 F system, to meet application needs. For this project, Siemens leveraged proven solutions utilized in the oil and gas industry and also drew on expertise gained through successful support for the installed systems. The solution for ammonia suppression consists of a fail-safe Simatic PCS 7 automation system. The Simatic Safety Matrix was utilized to engineer the safety functions. Using standard technology, the customer will benefit from reduced training and expenses and can better leverage the installed base. The uniform solution also provides improved information availability and system testing capabilities, and it helps to reduce response times.