Utilizing Class I Div. 2 Circuit Breakers in Liquid Natural Gas Applications

The chemical make-up of natural gas includes complex contaminate such as CO2, H2S, CO and other acidic gases which can hinder the liquefaction process.  For example, CO2 can freeze on the exchanger surfaces, plugging lines and reducing plant efficiency.  Therefore there is a need to extract the CO2 before the liquefaction process begins. This is needed not only to overcome the process bottle necks, but also to meet LNG product specifications, prevent corrosion of process equipment and the plant environment.  

There are many gas treating processes available for the removal of CO2 from natural gas.  These processes include: chemical solvents, physical solvent, adsorption processes, hybrid solvents, and physical separation.  These chemical and physical solvents or a combination of these have been used extensively in existing LNG facilities.  There is one common factor to all of these gas treating processes. They all require a sophisticated Automation/Process Control system.  Most of these systems are configured with a high level, redundant DCS or PLC controller, utilizing industrial networks to connect the 100’s of inputs and outputs, both analog and digitally based for the instrumentation and valves used to control and monitor the entire process.  These applications are also considered to be in Hazardous locations for electrical control equipment and instrumentation, mainly because of the possibility of explosion during liquefaction and re-gasification processes and electrical arcing components incorporated into the control cabinet.  This environment is known as a Class I, Division 2, Hazardous location.

In recent months E-T-A, along with Salof Companies, a leading Liquid CO2 and LNG system supplier, successfully deployed its new solid state electronic product on an LNG Pre-Treatment application.  

Several factors lead the Salof Control Engineering team to implement this new technology into its design including, the need to meet specifications to protect all field devices with overload and short circuit protection, as well as provide a means for individual disconnection of each field load in a Class I, Division 2, hazardous location.  Alan Dingeldein, EPM/Control Engineer on the project, discovered this new solid state technology through an electronic newsletter sent by Weidmuller.   By integrating E-T-A’s solid state device, Salof benefitted from better protection for field devices than any other technology available for 24VDC switch mode power supplies.  The E-T-A product is designed to detect both an overload and short circuit condition within 200 ms of the over-current event.  Because this component has a current-limit function it will supply no more than 1.3 times rated current of the circuit breaker at any time during the fault condition, then after 3 seconds completely disconnects the current from the switch mode power supply to the load.  In the event of an overload or short circuit, the device allows for individual disconnection between the power source and the load via a power switch on the face of the product.  Other models have a Remote Reset option allowing a PLC/DCS control output to disable or disconnect the current flow to the field load preventing the power supply from being compromised by a single point of failure.