Interconnector :: The System

The Interconnector system is more than just a pipeline. Since the UK and Belgium gas transmission systems operate at similar pressures, compressors are required to ‘pump’ the gas from one system to the other. In addition, gas heaters are required to ensure that the temperature of gas flowing into Belgium or the UK does not fall below a specified limit.

(1) Filtering: Gas flowing from the UK system passes through filters which remove any dust particles which could damage the compressors.

(2) Metering: A metering system then records how much gas has flowed.

(3) Direct Access Connection: Gas from the UK transmission system is mixed with flow from the SILK direct access connection (which is filtered and metered at the Shell Bacton Terminal).

(4) Liquid Separation: The gas stream passes through a large vessel known as a ‘knock out drum’ which will separate out any liquid droplets to ensure no liquid droplets are passed to the compressor.

(5) Compression: The compressors ‘pump’ the gas up to pressure of around 135 bar, about 60 times the pressure of a car tyre.

(6) Cooling: Compressing the gas causes it to heat up, so the hot gas leaving the compressors is cooled by a bank of ‘fin-fan’ coolers to avoid high temperatures in the sub-sea pipeline. These work by blowing cool air over hot gas pipes with thin fins to increase their surface area.

(7) Sub-sea Pipeline: The gas enters the sub-sea pipeline and flows the 235km to Zeebrugge, driven by the pressure difference along the pipeline.

(8) Filtering: At the Zeebrugge terminal, the gas is filtered once again, to remove any particles picked up in the line.

(9) Pressure Reduction: If the pressure is higher than that in the Belgian transmission system, then the pressure must be reduced across a valve.

(10) Heating: Reducing the pressure of gas has the opposite effect of compression, i.e. it is cooled. Water bath heaters are used to ensure the temperature of gas flowing into the Fluxys system remains above the 2ºC limit.

(11) Metering: Gas leaving the IUK system is metered by Fluxys on their terminal.

REVERSE FLOW

In UK Import mode, the system effectively works in reverse. Gas from the Fluxys pipeline network is compressed at Zeebrugge and flowed to Bacton from where it enters the National Grid system.

(1) Filtering: Gas flowing from the Belgian system passes through strainers which remove any particles which could damage the compressors.

(2) Compression: The compressors increase the gas pressure to around 140 bar.

(3) Cooling: A bank of ‘fin-fan’ coolers, similar to those at Bacton, lowers the temperature of the compressed gas.

(4) Sub-sea Pipeline: The gas enters the sub-sea pipeline and flows the 235km to Bacton, driven by the pressure difference along the pipeline.

(5) Filtering: At the Bacton terminal, the gas is filtered to remove any particles picked up in the line.

(6) Pressure Reduction: The pressure is reduced across a valve to match the UK system pressure.

(7) Heating: Boilers and heat exchangers are used to ensure the gas temperature matches the UK system specification.

(8) Metering: Gas leaving the Bacton terminal is metered before entering the UK system.

COMPRESSOR TECHNOLOGY

Compressing 58 million cubic metres of gas per day up to 135 bar requires a significant amount of power. The four compressors at the Bacton terminal are driven by four 27 MW gas turbine drivers, each with the equivalent power of approximately 400 modern family cars.

At Zeebrugge each compressor is connected to a variable speed drive. This comprises a converter transformer, which controls the voltage and frequency of power supplied to a 35 MW synchronous electric motor.

The compressor is essentially a set of blades arranged in a spiral which spin the gas outwards, causing it to accelerate and increase pressure.