It is essential that crude oil and other fossil raw materials are stored and treated safely, not least because of the considerable explosion hazard. The Dutch company Saval BV has therefore designed a special fire extinguishing system for floating-roof tanks.
Controllers and I/O modules, together with WLAN access points from Phoenix Contact, enable web-based status monitoring of the system.
As the explosion hazard is very high in specific areas of crude oil tanks, these tanks are classified as Zone 0 areas according to the ATEX directive.
In the fixed-roof tanks that are used in most cases, an explosive atmosphere is formed between the material to be stored and the fixed roof when they are being filled.
Floating-roof tanks, the roof of which floats on the stored liquid, are an alternative solution. Since these roofs move freely, a flexible seal is required in the tank wall area.
However, between the tank wall and the seal, there is a space where small amounts of gas given off by the stored material will accumulate. If the gas mixes with the ambient air, this produces a flammable mixture. Static electricity, which can be produced by a lightning strike or sparks, can trigger a fire that is still manageable immediately after it starts. If the fire remains undiscovered, however, it can quickly develop into an uncontrollable fire source.
With these issues in mind, Saval has designed a fire extinguishing system that consists of an extinguishing container that can protect tanks with a circumference of 40 meters in conjunction with a sprinkler system. Floating-roof tanks, which have a diameter of 120 meters, sometimes require several extinguishing systems.
In the automated fire extinguishing system, two digital signals, which provide information on the status of the fire protection system, need to be monitored. Each fire extinguishing system has a level switch, which monitors the fill level in the fire extinguishing container, and a pressure switch that provides information on system pressure.
The area next to the floating-roof seal is a designated Zone 0. The two digital signals are collected in distributor boxes installed in Zone 1. If a fire starts, the level and pressure switches are activated at the same time. If, on the other hand, there is a leak in the sprinkler system, only the pressure switch is activated. The same applies to the level switch, which is switched on if there is a leak in a fire extinguishing container.
Intrinsically safe I/O modules can be added seamlessly to the local bus
According to the concept for the central solution, the digital signals are transmitted via cables to a monitoring panel installed in the non-hazardous area. The monitoring panel consists of a modular ILC 171 ETH controller and the intrinsically safe Ex i I/O modules from the Inline product range specifically developed for potentially explosive areas by Phoenix Contact.
The intrinsically safe terminal blocks are supplied with power by a special Inline module. They can be added seamlessly to the local Inline bus of the controller and record the digital signals from the level and pressure switches.
Forwarding of signals via PROFINET and WLAN
If the oil tanks do not have a communication structure that can be used, it can be extremely difficult to lay new cable routes. With this in mind, Saval has designed a distributed solution - the SK 3100 protective container. This protective container contains a modular PROFINET controller with intrinsically safe modules.
The decentral SK 3100 station monitors up to four fire extinguishing systems and transmits the signals via WLAN to a centrally installed SK 3000 monitoring panel that contains a modular ILC 330 PN high-performance controller. WLAN access points are used to transmit the data between SK 3100 and SK 3000.
The devices satisfy the IEEE 802.11e standard and support the PROFINET assistance mode, which means that the two Inline controllers can communicate with one another via the PROFINET protocol. Individual PROFINET packets can also be prioritized. The packets with the highest priority are then exchanged via the WLAN interface before all other Ethernet packets.
Web-based visualization of device status and malfunctions
The web-based WEBVISIT visualization software from Phoenix Contact is used to monitor the solution. As such, the controller must have an integrated web server, as is the case with the Inline controllers used.
In order to access the visualization on the web server of the PLC, all that is needed is its IP address. The data is then displayed on the operation and monitoring device. The visualization developed by Saval indicates the status of the pressure and level switches as well as the power supply to the control system.
It also generates a corresponding alarm in the event of malfunctions. Saval uses WP10 touchscreens to display the data.