WHAT DATA IS SHARED?
The data originates from a single compressor on Aker BP’s Valhall oil platform in the North Sea. Aker BP selected the first stage compressor on the Valhall because it is a subsystem with clearly defined boundaries, rich in time series and maintenance data.
The data set available in the Cognite Data Platform includes time series data, maintenance history, and Process & Instrumentation Diagrams (P&IDs) for Valhall’s first stage compressor and associated process equipment: first stage suction cooler, first stage suction scrubber, first stage compressor and first stage discharge coolers.In addition, data from the compressor’s lubrication system, dry gas seal system and condition monitoring system (temperature and vibration) will be available.
The data set represents the first of four stages for compression of natural gas on the Valhall PH platform. The purpose of the gas train is to compress and treat the gas to meet the required export pressure and specification, with a total capacity of 4,06 MSm3/d (143 MMscf/d).
((illustration of the system))
The first stage compressor (23-KA-9101) is an electrically-driven, fixed-speed centrifugal compressor which receives gas from the separators at approximately 3 barg pressure. Before reaching the compressor, the gas is cooled in the first stage suction cooler (23-HA-9103), which is a shell-and-tube heat exchanger. The cooled gas flows into the first stage suction scrubber (23-VG-9101), which removes liquid droplets before the gas enters the compressor. The gas is compressed to approximately 12 barg and flows through a pair of discharge coolers (23-HA-9114/9115) before entering the second stage of compression.
The following utility systems are also included in the data set:
- The lubrication system for the first stage compressor. The system is comprised of pumps, coolers, filters, heating elements, and associated monitoring equipment, the purpose of which is to reduce friction and mechanical wear and to prevent overheating and corrosion in the compressor internals.
- The dry gas seal system (DGS), the purpose of which is to prevent the process gas inside the compressor from escaping to the atmosphere.
- The condition monitoring system (CMS), which monitors temperatures and vibrations in the motor, gearbox and compressor.
Automatic control of the first stage compressor and associated process equipment is achieved by the following control loops:
- The temperature at the suction cooler outlet is controlled by regulating the amount of cooling medium flowing through the shell side of the suction cooler.
- The level in the first stage suction scrubber is controlled by regulating the amount of liquid flowing out of the scrubber. Excess liquids are sent back to the 2nd stage separator.
- The pressure in the first stage separator is controlled by regulating the suction throttle valve (STV) upstream of the first stage suction scrubber, which controls the amount of gas sent to the compressor.
- Anti-surge protection is achieved by recycling gas from downstream the discharge coolers back to the inlet. The amount of gas to be recycled is controlled by regulating the anti-surge valve (ASV). Since the recycle line is connected just upstream of the STV, the pressure control and anti-surge control loops have strong interactions.
- The temperature at the discharge cooler outlet is controlled by regulating the amount of cooling medium flowing through the shell side of the discharge cooler(s).