Fast track automation of LPG terminal in Mexico

The facility for receipt, storage and delivery of LPG at Atotonilco is one of the most modern in Mexico. It has a design capacity of 20,000 bpd and caters to 160 tankers a day.

The terminal feeds the PEMEX Cactus pipeline, passing within 18 km of the terminal, and this location ensures the delivery of LPG for the central-eastern section of Mexico. The terminal facility must pass strict controls and administrative standards for quality, safety and environmental protection.

The terminal’s main function is the receipt, storage, safety and filling of tankers with LPG. The product is received at a pressure of 20 kg/cm² and is stored in two areas at ambient room temperature and a pressure of 7 kg/cm², each with a capacity of approximately 4000 m³.

The objectives for the automation project encompassed the following key requirements:

1. The control system should provide safety and flexibility in operation as well as correct and reliable integration with the existing systems of Pemex Gas and Basic Petrochemicals.
2. The safety system must monitor 100% of operations and comply with all environmental and safety requirements to international standards.
3. The implementation must be done in a period not exceeding one week.

Best practices for operation and control of the terminal for receipt, storage and delivery added to the list of objectives:

• Ensure a filling capacity of 12,500 to 50,000 bpd in the first stage.
• Cover the LPG demand in quantity and quality in the central-western area of the country.
• Achieve operating cycles and life of the facilities to operate for 30 years.

The construction of the terminal facility represented a major challenge for the company’s EPC (engineering, procurement and construction) contractor. The project required a comprehensive solution to include the process control system of the terminal (supervision of inventories and filling of tank trucks), as well as the safety instrumented systems of the terminal (emergency stop system and fire and gas system).

The project also required an access control system to ensure proper communication with the Pemex administrative system (SAP), and the control and safety systems of the terminal.

A team of experts from Emerson Process Management collaborated with the terminal operator from the FEED stage (front end engineering and design) and throughout the project. Emerson proposed the use of a DCS for automation of the terminal, although initially the project included the use of PLCs. The decision to use DCS was in turn supported by the company that operated as an auditor (AEC Independent Engineering Services), whose goal was to have the assurance that the terminal assets not lose value in the short term.

In the end, Emerson’s DeltaV digital automation system, and two DeltaV SIS safety systems, one for the fire and gas system and another for emergency shutdown, were implemented.

Emerson installed measurement skids in the custody transfer points and in the terminal itself. Emerson also installed all the instrumentation of the plant, with the exception of the radar level gauges in the spherical storage tanks.

The implementation and commissioning of the terminal was performed in 24 hours, after which the plant reached its design capacity of 20,000 bpd, which met the deadlines and expectations of planned production. Smooth collaboration between EPC, contractors and Emerson occurred during the execution of the work: the stages of installation, commissioning and even after.

The results of the implementation were considered successful. In just eight days after the launch, the capacity was increased by 220%, to load more than 40,000 bpd. The main enabler for achieving this result, according to the experts themselves, was the design flexibility of the plant and the robustness of the operational control system which accommodated significant changes in the production capacity.

Another example of the flexibility of the system was the remarkable improvement in the tanker filling time. In plants with the same characteristics, this process may take typically an hour and a half, with an error of up to 50 kg. The Atotonilco terminal conducted this process in half the time, and with error of less than 1 kg, which enabled a filling capacity of up to 160 trucks per day in its 10 filling islands. This represented 40 trucks more per day than similar plants.

The control system installed has been able to increase the reliability of the operation to more than 99%, and the integration of the Pemex system (SCADA and SAP) was realised without any inconvenience.

For the safety system, Emerson’s DeltaV SIS was used, meeting 100% of the international normative and functional safety standards IEC 61508-3 and IEC 61511-1.

The fire and gas system of the terminal also uses Emerson’s DeltaV SIS system, which protects the plant in a distributed manner. It allows users to detect the conflict area and act directly on it. The system is connected with fire and gas detectors, and regulates the pressure of water against fire, and controls the start/stop sequence of the main electric pump motor, fire pump and relief pump. Visual and audible alarms, as well as deluge system valves, are integrated to this system. Conversely, the emergency stop system regulates the operation of emergency block valves, which are responsible for isolating the involved area, or, if a contingency warrants, users can isolate the terminal facility as a whole.

An important aspect of the terminal automation system is its ability to interact with the hydraulic system that operates the fast cutting valves that work in conjunction with sprinkler systems. These valves (known as ‘vickers’) are installed in the areas and operate when the stored fluid temperature exceeds 40°C, or when the reservoir level rises above the permitted, or there is a leak in an area close to the tanks.

The system accurately coordinates between the fire and gas system, the emergency stop system and the process control system, along with the safety measures taken in the plant. The plant has since achieved a milestone of 730 days without an accident (May 2012).

“The system is so flexible and reliable that it can operate optimally at all times and also meet seasonal increases in demand,” said the manager of the Atotonilco terminal, Moses Decto. “The plant is 100% controlled by means of a single system that allows us to monitor and control all the variables.”

Following the successful results of the Atotonilco automation project, the same group is analysing the incorporation of new terminals. The next stage of the process will be the Tuxpan terminal, which will be interconnected via a new Tuxpan pipeline. For communication across the network, the Tuxpan pipeline SCADA system will communicate with the terminal, including the safety of the pumping stations and control systems.

*Marcelo Carugoes is Director of Refining, and Fernando Mirafuentes is Manager of Solutions and Engineering for Mexico, from Emerson Process Management Latin America.

The original version of this article was published in Spanish in Petrotecnia magazine in December 2013.