Tail Gas Oxidizer Upgrade At Westcoast Energy Fort Nelson Gas Plant In Fort Nelson BC

PROJECT OVERVIEW

An Inproheat and Coen Co.  joint venture was contracted in 1982 to engineer, design and construct 600 MM BTU/hr Tail Gas Oxidizers to replace 3 existing obsolete oxidizers.

Original fuel trains were not part of the upgraded project. Federal and provincial environmental regulations require continuous availability of the oxidizer while the gas plant is in operation.

After an unscheduled plant shutdown in January 1997, it took considerable effort by plant maintenance and operation to re-start the oxidizer, causing a delay in the plant start-up that resulted in considerable financial consequences during a period of extremely high natural gas demand.

THE CHALLENGE

Westcoast Energy identified several sources of previous component failures in the fuel train system, all of which were outdoors. Equipment was difficult to service under artificial night light conditions with temperatures at -40ºC not including windchill factors. Typically, gas processing plants can operate continuously for 3 years without a scheduled shutdown, which usually does not exceed 7 to 10 days.

THE SOLUTION

To house the let down stations, fuel trains and pilot ignition system, Inproheat utilized a 40 ft. marine container. Windows, an access door, insulation, lighting, LEL detection and ventilation and heating systems were added to the container. An overhead trolley was also furnished to facilitate the removal and replacement of heavy items from the trains. High pressure (1000 PSIG) first and second cut gas-reducing stations were constructed inside the container. These let down stations incorporated parallel maintenance regulator branches allowing work on the main monitoring regulator set without shutting the plant down. Pressure transmitters were used to monitor and trend the regulator performance, in order to be able to schedule maintenance. They were connected to main fuel control, flow and safety shut-off manifolds, pilot pressure reducing station and waste gas pressure control train. Waste gas from a different process provides approximately 10% of the total fuel in the oxidizers and is mixed automatically into the main gas flow.

A steam flow control station was also mounted inside the container. The station is connected to an external natural gas/steam heat exchanger which compensates for the loss of gas temperature due to decompression.

The installation is rated Class 1 Div 1 explosion proof. All devices were shop wired and tested. Train assemblies were pressure tested and all regulators set up for correct regulation.

The objective of the design was to minimize the assembly fieldwork required during the 8 days plant shutdown.

THE RESULT

With the close cooperation of Westcoast Maintenance and Operation and Inproheat Engineering, the container was delivered on time (4 months after contract award). Start-up went according to the planned schedule and with very limited difficulties experienced during the adjusting period.

All critical components are now housed in a heated enclosure with the required operational redundancy and safety devices in place and servicing is now possible regardless of harsh outdoor weather conditions during the winter periods. The system will operate for three years without shutdowns.