Capacity issues on converting natural gas network to supply hydrogen

Abstract

It is expected that the existing natural gas network can be converted to carry hydrogen using the new polyethylene pipes installed through the UK’s ongoing Iron Mains Replacement Programme.

The energy density of hydrogen is considerably lower than natural gas. This means that in order to deliver the same energy to consumers as at present, the volume flow rate must be considerably greater.  As a corollary, the flow velocity will also be considerably higher. 

Here we explore the questions of whether existing networks can have sufficient capacity to deliver enough hydrogen to consumers, within existing flow and velocity constraints.  

We built a Python model of a hypothetical natural gas network, kept deliberately low in excess capacity.  The model was then tested with hydrogen.  This allowed the investigation of the effects on a range of pipe sizes, under differing pressure, flow and demand conditions.

We found that in most modelled situations sufficient hydrogen could be transported.  The lower density and viscosity of hydrogen mean that the pressure loss is less than might have been expected from the higher flow velocities, although there is still invariably a bigger pressure loss than for natural gas.  There are situations where the velocity and pressure tolerances are exceeded at peak times. 

In these cases, additional short term downstream storage, not exceeding 24 hours’ supply, and/or boosting the upstream pressure are required to restore service.

A means of predicting where constraints will be exceeded is also tentatively proposed.