Study group report 2008: freeze protection in gasholders (National Grid)
This is the final report on the problem of freeze protection in gasholders, brought to ESGI64 by National Grid. Click on the link at the bottom to download the full report as a pdf document.

Report coordinator
Gail Duursma (University of Edinburgh)

Executive summary
In cold weather, the water seals of gasholders need protection from freezing to avoid compromising the seal. These holders have a large reservoirof "tank water" at the base which is below ground. At present freeze-protection is achieved by external heating of the seal water which is in a slotted channel called a cup. Electrical heating or circulation of heated tank water to the cup are examples of systems presently used. The tank water has a large thermal capacity and National Grid wishes to investigate whether circulation of the tank water without external heating could provide su±cient energy input to avoid freezing. Only tanks in which the tank water is below ground are investigated in the report. The soil temperature under the reservoir at depth of 10m and lower is almost constant.

Introduction

The problem scenario
In cold weather the water seals of gasholders need protection from freezing to avoid compromising the seal. These holders have a large reservoir of "tank water" at the base which is below ground. At present freeze-protection is achieved by external heating of the seal water which is in a slotted channel called a cup. Electrical heating or circulation of heated tank water to the cup are examples of systems presently used. The tank water has a large thermal capacity and National Grid wishes to investigate whether circluation of the tank water without external heating could provide su±cient energy input to avoid freezing.

The problem-solving approach
The thermal capacity of the tank water is the key to determining whether external heating is not needed. There are 3 major components of the system, viz. the tank water, the gas and the circulating water which would act as After initial brainstorming, it was clear that the problem could be treated as 4 major elements, namely the gas, the water delivery hose, the tank water and the water in the cup seal. A standard tank was specified, as shown in Fig 1 (tank full of gas) and Fig 2 (tank empty). The water delivery hose (not shown in Fig 1) lifts water from the tank to each seal. The four problems will be treated in turn.

Figure 1: Gasholder geometry.

Figure 2: Gasholder configuration when empty.

Download 'NationalGrid-FreezeProtectionInGasholders.pdf' (422 Kb).