Tank farm automation best practices
New Zealand system integrator implemented a dedicated tank farm control system based on remote input/output (I/O) couplers connected via EtherCAT.
The purpose of tank farms is to provide a safe environment for storing chemicals. Various raw materials such as gasoline, crude oil, liquefied natural gas, heavy oil, naphtha and other liquid chemicals are temporarily stored while they wait to be transported by ship, rail, tank truck or pipeline for further use or processing. Large tank farms are often located near oil production areas, petroleum refineries, chemical industry sites, large ports and major transshipment points.
The New Zealand system integrator, Automate-X, has used Beckhoff components to automate the tank farms of a leading global operator to create an interface between ship and shore while facilitating agile and competitive supply chains. The result is state-of-the-art terminals that provide the tank farm operator’s customers with high quality and safety without compromising on comprehensive environmental protection.
Chemicals pose a special challenge
The new tank farms for the global operator in New Zealand were designed to store flammable chemicals, so they are classified as plants with high hazard potential. This posed challenges for the tank farm operator and the system integrator, as there are stringent requirements regarding automation when storing potentially explosive and environmentally harmful chemicals.
The engineers at Automate-X had to consider numerous aspects, standards and features of explosion protection as well as functional safety when planning the automation concept. They also had to carry out a comprehensive analysis of the electrical and safety-related requirements. In the explosion protection zone, they needed to define the hazardous areas before selecting suitable explosion-proof components. Another factor to consider was all systems needed to guarantee maximum uptime to prevent a dangerous situation caused by a plant breakdown.
“We came up with the solution of implementing a dedicated control system based on remote I/O [input/output] couplers connected throughout the plant by EtherCAT. All safety-critical elements are monitored and controlled via a CX5130 embedded PC from Beckhoff running TwinSAFE. As a final safeguard against overfilling, the storage tanks are equipped with SIL3-certified vibrating fork probes,” said Marcel van Niekerk from Automate-X. “The gantry area for loading the tankers features infrared flame detectors that can trigger a spray foam system in the event of a fire to prevent a potentially catastrophic event. Additional safety components include emergency stop switches, NAMUR sensors to monitor valve statuses and a connection to fire alarm systems.”
In addition to the safety control system, Automate-X also installed a separate CX5130 that handles several tasks, including pump and valve control.
Benefits of PC control
It didn’t take long for Automate-X to decide in favor of Beckhoff — and PC-based control technology — because the open nature of the technology facilitates straightforward integration of third-party software and hardware (see Figure 1). This meant the Ignition supervisory control and data acquisition (SCADA) software platform could be incorporated into the tank farm project, and the tank farm operator’s existing drives were integrated into the automation system via EtherNet/IP.
Another key advantage for the project was the wide range of Beckhoff terminals, since the modular EtherCAT I/Os allow for the integration of safety, communication, redundancy and explosion protection components in a single system. “On a single I/O platform, we can accommodate digital I/O modules, TwinSAFE, analog Ex inputs, NAMUR inputs, HARTs and RS232/RS485 running on EtherCAT (see Figure 2). Not only does the EtherCAT redundancy ensure a high level of availability, but no other platform offers such flexible configuration options,” said Ben Haughey from Automate-X.
Intrinsically safe barriers are not required due to the use of ELX series EtherCAT terminals, which feature intrinsically safe interfaces (see Figure 3). This simplifies the electrical design and makes it possible to achieve signal acquisition in hazardous areas. The use of EtherCAT single-mode fiber-optic components enables communication between the tank farm operator’s extensive plant sections. In addition, the implementation of cable redundancy via a ring topology is possible via fiber optics to ensure a high level of plant uptime (see Figure 4).
Communication between the various controllers and the Ignition SCADA system is implemented using OPC UA. Operators can access the SCADA system using intrinsically safe tablets, allowing them to access plant data and control the plant from anywhere onsite. Communication between TwinCAT and SCADA is seamless via the TwinCAT OPC UA standard.
“We are delighted that we have been able to implement an innovative and consistent automation concept for the tank farms using Beckhoff components specifically for hazardous areas,” van Niekerk said. [see Figure 5] “Our customer can benefit from a reliable solution that will stand the test of time.”