Interconnector :: The System

The Interconnector system is more than just a pipeline. Since the UK and Belgian 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.

Interconnector Shippers are required to ensure that gas delivered to the system complies with all specified requirements. IUK does not offer any gas quality conversion service.

(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 IBT 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 is passed to the compressors.

(5) Compression: The compressors ‘pump’ the gas up to a pressure of around 135 bar.

(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 pipes containing the hot gas and where the pipes incorporate thin external fins to increase their surface area.

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

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

(9) Pressure Reduction: Gas arrives at IZT at a pressure higher than that in the Belgian transmission system and then flows through a pressure reduction valve to ensure it arrives at the system interface at the correct pressure.

(10) Heating: Reducing the pressure of gas has the opposite effect of compression, i.e. it is cooled. Water bath heaters 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 IZT and flows to IBT 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 IBT, lowers the temperature of the compressed gas.

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

(5) Filtering: At the IBT 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 temperature of gas arriving complies with the UK system specification.

(8) Metering: Gas leaving the IBT 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 IBT terminal are driven by four 27 MW gas turbine drivers, each with a power output equivalent to approximately 400 modern family cars.

At IZT 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. This provides a capability to generate a pressure of up to 140 bar and to flow up to 74 million cubic metres of gas per day in reverse flow mode.

Each compressor is essentially a set of blades arranged in a spiral which spins the gas outwards, causing it to accelerate and then to increase in pressure when the kinetic energy imparted to the gas is converted to pressure energy.

Operating at the maximum allowable pressure at IBT or IZT with normal connecting network pressures, calculations based on the Panhandle B equation give maximum physical flow rates in Forward Flow (IBT to IZT) of around 20 bcm/y and around 25.5 bcm/y in Reverse Flow.

On occasions when the relative pressures of the connecting UK and Belgian networks permit, an additional capacity of up to 3 bcm/y in either direction can be made available on an interruptible basis.

GAS QUALITY REQUIREMENTS