Selecting the right control and monitoring system for hazardous environments
12 April 2013
Control and monitoring is particularly critical for oil and gas refineries and petrochemical plants, where even the slightest uncontrolled increase in temperature could lead to an explosion. Any control and monitoring products used in these areas should be high quality and designed specifically for that purpose. In the European market, this means complying with stringent ATEX regulations.
Pentair Thermal Management partnered with Tobolsk Polymers LLC to provide frost protection and temperature maintenance systems to Russia’s largest petrochemical plant
A world of choice
Controlling a heat-tracing circuit can be as simple as a mechanical thermostat. However, in larger, more complex environments such as refineries or chemical plants, more sophisticated control and monitoring requirements are necessary. With a variety of options available, plant owners need to know that they are selecting the most appropriate system for their application. This is where complete heat management solutions providers can add real value – by partnering with a heat-tracing specialist at the beginning of the specification and design process, plant owners can be sure they are getting the best system and configuration for them.
Further to a simple thermostat, there are three advanced control options that plant owners can choose from. The first combines local control with local monitoring, with both of these elements located in the field. This is suitable for smaller applications where maintenance professionals are able to get to the site quickly and easily.
The second option combines central control with central monitoring which addresses the problem of sending maintenance operatives to the field since everything is controlled from a central location. Although this may be convenient for the operator, being in one location, they do not have precise, nuanced control over what is happening in the field. As a result, this system may not be appropriate for areas where exact, minute temperature changes need to be monitored.
The third approach combines local control with central monitoring. A 'best of both worlds' solution, this enables areas with small temperature changes to be controlled locally, with all of the source site data sent to a central location away from the field. This is also a highly cost-efficient option as it incorporates ‘daisy chain’ wiring, wherein all the control systems are connected to each other, with only one wire feeding back to a central location. Therefore fewer cables are required.
Once a plant owner has decided which type of control and monitoring system is most suitable for his site, he needs to ensure that it is approved for use in hazardous areas. In the European market, this means that all equipment and protective systems intended for use in potentially hazardous areas must comply with ATEX regulations. There are two ATEX directives – one for the manufacturer and one for the intended use of the equipment. The ATEX 95 equipment directive 94/9/EC covers equipment and protective systems intended for use in potentially explosive atmospheres, whereas the ATEX 137 workplace directive dictates the minimum requirements for improving the health and safety of workers potentially at risk from explosive atmospheres.
How can control and monitoring systems help plant owners comply with ATEX regulations? With a local control and central monitoring system, all maintenance can be carried out from the control room, so operatives do not have to go into the field as frequently. In terms of equipment, ATEX stipulates that any equipment used should not be flammable or at risk of sparking. To ensure this, control and monitoring systems can be fitted with a temperature limiter. Once a designated temperature limit is reached or a fault occurs within the permitted temperature range (probe break, short-circuit, component defect or power failure), the device switches off without delay. A system which combines local control with central monitoring and a temperature limiter (such as Pentair Thermal Management’s Digitrace NGC-20) is defined as a SIL 2 device under the Intermational Electrotechnical Commission's (IEC) standard.
It’s not just the components inside the device that make it safe for use. Many control boxes are double insulated and have been designed so that the live wire cannot touch the casing. As a result, the casing cannot generate an electric shock or cause a spark, even if the wires inside become loose.
When it comes to control and monitoring, today's plant owners have a lot to consider. What will be the most cost-effective option? Will maintenance personnel be able to get on-site quickly and easily if there's a problem? How will the plant continue to function and hazardous areas remain safe, while keeping costs down? The right control and monitoring system can provide the answer to all these questions, helping to reduce costs and the risk of accidents.
Case study – Temperature maintenance in action: Tobolsk Polymers LLC
Polypropylene (PP) is a versatile thermoplastic used in a wide variety of applications including packaging, stationery and laboratory equipment. As a great producer and consumer of PP, the Russian market has been growing steadily year on year, producing over 800 thousand tonnes of polypropylene in 2011 alone.To meet growing demand, PP producers such as Tobolsk Polymers LLC have been increasing production and investing in new facilities. Pentair Thermal Management partnered with Tobolsk Polymers LLC to provide frost protection and temperature maintenance systems to Russia’s largest petrochemical plant. The scope of this new project comprises a range of project management services, including design, engineering and installation support.
Providing solutions to this plant is not without challenges – the site is vast and many of the areas within the plant can be defined as hazardous. For example, part of the process to create PP involves the dehydrogenation of propane, a highly flammable substance. Pentair Thermal Management’s self-regulating heating cables and Digitrace NGC-20 control and monitoring systems were selected to keep the PP at the correct temperature and avoid any potential accidents. This challenging project called for innovative solutions.
Pentair Thermal Management’s Digitrace NGC-20 control system combines the benefits of a centralised control system with those of local control. Temperatures, ground fault currents and operating currents are all measured, displayed locally and communicated to a central location. In addition to supplying heat management solutions to these critical areas, Pentair Thermal Management also provided frost management systems for outside areas, including gutters, downpipes and roof inlets.
Commenting on the project, a representative from the construction company, Linde Dresden Engineering GmbH, said: “For a project of this scale and complexity, it was vital that we had a partner who could meet all of the technical challenges. Pentair Thermal Management’s broad range of technologies, combined with its experience on major projects provided a solution that met all our needs. The company’s support during the extensive engineering phase proved invaluable.”
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