Page 12 - Gi_August2019

FLEXIBILITY IN GREAT

BRITAIN’S GAS NETWORKS

UKERC’s Dr Grant Wilson and Dr Paul Rowley present an gravity of the gas contained within
analysis of linepack and its flexibility using hourly data pipelines and pipeline internal volume.
This provides a calculated volume of
linepack under high-pressure operating
conditions, which is then expressed
as an equivalent volumetric measure
of gas in standard cubic metres at
standard conditions of atmospheric
pressure and ambient temperature.
With additional knowledge of the
calorific value of the gas, the volumetric
measure can be changed into an energy
equivalent measure such as GWh. The
FlexiNET project has used a constant of
11 kWh (39.6 MJ) per standard cubic
metre of gas for analysis.
Although linepack is defined as the
total gas/energy contained within the
high-pressure pipelines, it is important to
point out that gas pressure and therefore
the linepack has to remain above a
minimum safe operating pressure.
Linepack at this minimum pressure
he scale of the within-day this data has been presented, as hourly should therefore be considered as a
flexibility currently provided linepack data for the gas distribution permanent inventory of gas pipelines
by the natural gas transmission networks (GDNs or local gas networks) (even though there is a flow and constant
and distribution networks has not previously been available at an turnover of the actual gas molecules) and
T points to a formidable energy aggregated level. should not be considered as a measure
systems challenge; how to provide low- This analysis provides additional of useable energy.
carbon within-day flexibility to future evidence to help inform the debate For the purposes of the FlexiNET
energy systems at a reasonable cost. surrounding future energy systems by research, linepack is considered to be
The scale of energy that can be providing a better understanding of the the total amount of gas stored within the
stored and released by varying linepack level of within-day flexibility available pipelines, whilst linepack flexibility is
highlights its importance as a means to Britain’s existing energy systems. considered how much this can be varied,
of operational flexibility, helping in essence, a measure of the amount of
to balance the changes in national Great Britain’s demand for useable gas storage.
primary energy demand.
Great Britain’s demand for energy energy varies significantly over Britain’s gas transmission
varies significantly over a day and a day and between seasons, and distribution system
between seasons, caused by underlying caused by underlying patterns The majority of natural gas supplies
patterns of consumer behaviour and to Britain flow into the national
activity, many of which are repeated on of consumer behaviour and transmission system (NTS) at entry
a daily basis. Changing the pressure in activity, many of which are terminals connected to import pipelines
high-pressure gas pipelines varies the repeated on a daily basis or one of the three liquified natural gas
amount of linepack and allows Britain facilities.
significant flexibility to match its gas Major sites of natural gas demand
supply and demand over a day by What is linepack and how is it calculated? are connected directly to the NTS such
providing a method to store gas. Linepack is the amount of gas as combined cycle gas turbine (CCGT)
The UK Energy Research Centre’s contained within the higher-pressure power plants, gas storage, large industrial
FlexiNET project has analysed data pipelines (>7bar) of Britain’s users and pipelines that can be used for
from Britain’s transmission and transmission and distribution gas connection to other countries.
distribution gas networks to provide a infrastructure. Linepack is calculated by The largest annual demand for gas
more complete picture of the variation combining measurements of pressure, is from the GDNs, which are connected
of gas linepack. This is the first time temperature, compressibility, specific to the NTS at multiple offtake points.

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