These days, natural gas is extracted in remote regions and then shipped around the world. To make optimal use of the cargo capacity, compressors are used aboard production platforms and tankers to compress the energy carrier into liquefied gas. For a leading manufacturer of these systems, R. Stahl regularly supplies Ex protected IS1 Remote I/O control stations for use in Zone 1 with intrinsically safe internal wiring, which, amongst other things, have to be adapted to overcome the limited installation space on the compressors.
Ex protected control stations with remote I/O
The customer, a machine builder specialising in the oil and gas industry, fits compressors to dozens of large tankers every year. These compressors are installed below deck wherein, outside of the gas tanks, space is limited. For this reason, the machines and their control stations with remote I/O modules and various digital display and signalling elements must be compact. And because this equipment is installed in the immediate vicinity of the gas, it is essential that it has Zone 1 explosion protection.
As part of a series of commissions in which systems were to be fitted to new LNG tankers for end customers from Russia and Norway, the machine builder worked with R. Stahl and the primary manufacturer of the main automation solution in these projects to design a system suitable for these applications. The collaboration began with comprehensive testing, which included weighing up the different networking alternatives. In this phase, a very compact system design was also specified for the control and distribution boxes in order to overcome problems of limited space.
The signals from sensors and actuators around the compressors that are linked via the IS1 remote I/O system are transmitted to the distributed control system via Profibus DP. The number of modules used for a broad spectrum of signal types can be tailored to the customer’s exact requirements.
One of the key advantages is that the installation is incredibly easy to expand: further modules can be added at any time, the operator simply has to plug them in and they are ready for operation. All modules can also be hot-swapped in situ as required. The intrinsically safe bus system can be operated with copper conductors or fibre optics and, if required, can be designed with system or media redundancy.
The seawater-resistant enclosure materials and vibration-resistant design of IS1 systems, coupled with their resistance to the effects electromagnetic energy, which satisfies the strict EMC requirements that apply on board due to the ship radio, make them perfect for maritime applications. In addition to DNV and ABS certification, IS1 can also be designed to comply with the requirements of numerous other certificates, giving the customer the flexibility they need to use it in locations all across the world. The Zone 1 system passed the rigorous ship tests with flying colours – not only can it be used below deck, but it can also be used universally above deck if required.
Fit for purpose station design
R. Stahl has been installing systems on ships and offshore platforms for around 30 years. Besides the IS1 system, the range of items produced for installation on ships includes a vast array of other explosion-protected electrical equipment. The IS1 solution for a redundant system, comprises a total of seven enclosures of varying dimensions. The control and distribution boxes for the compressors are protected against explosions by a combination of Ex d and Ex e types of protection and are equipped with indicator lamps, rotary switches and pushbuttons, as well as emergency stop buttons produced by R. Stahl in-house. Warning and indicator devices or vibration sensors produced by other manufacturers can optionally also be integrated.
In the first instance, the design of the stations makes them easy to install. Stainless steel enclosures were used for the compressor control stations. These offer IP65 protection, with the option to upgrade to a higher level if required. They are very easy to connect in series and the compact cabinets feature multiple small doors to allow easy access, despite the limited space at the mounting location.
For more information contact Preshan Moodliar, Stahl Esaco, +27 (0)11 608 3120, [email protected], www.esaco.co.za
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