Gas: Corio City Gate Heater Installation Project

Zinfra Corio City Gate HD from Zinfra.

Client: Ausnet Services
Location: Corio, VIC

Gas Substation

Corio City Gate Heating System

Corio City Gate is AusNet Services’ most critical gas asset in terms of the number of customers it supplies and is the single supplier of natural gas to Geelong and the Bellarine Peninsula in Victoria.  The large region includes the townships of Port Arlington, Queenscliff, Torquay, Barwon Heads and Point Lonsdale.
Zinfra were contracted to procure, construct, install and commission a new heat exchanger and boiler to heat the natural gas prior to pressure reduction at the City Gate.

A Pressure Drop

The city gate’s job is to reduce gas pressure, as it arrives from the APA-owned 350mm Brooklyn to Corio transmission pipeline, from 7,200 kPA to 1700 kPA , then inject this gas into the Corio to Point Henry pipeline.
This pressure drop causes the gas temperature to fall.  Using technical terminology, the Joule-Thomson effect is said to occur.  With the temperature drop, the temperature of the outlet pipe of the city gate can reach below -10 degrees Celsius, causing a layer of ice to form on the exterior of the pipework.
Ice on the pipework, in turn, causes damage to downstream assets as well as rendering critical valves and regulators inoperable.  The low temperatures at the pressure reduction station also cause hydrocarbon condensates to drop out of the gas stream.

The Heater Solution

To overcome the problem of the Joules-Thomson effect on the city gate assets, AusNet Services determined it critically important to install an inline gas heater to prevent and mitigate the risks associated with the sub zero temperatures.
The heater is a shell in tube heat exchanger coupled to a boiler. Hot water is pumped between the boiler and heat exchangers as a means of transferring heat into the gas stream.
The existing gas filter location was chosen as the tie in point for the new heater.  This choice allowed the heater to be constructed and commissioned on site to avoid any disruptions downstream or to supply.  Given the existing filters needed to be removed from site and the age of the filters it was a good opportunity for AusNet Services to upgrade the filters with new models.

The new configuration means gas will now flow through a filter to the shell in tube heat exchanger.  A bypass has been constructed around the heat exchanger to allow for maintenance operations.  The gas piping is then tied into the existing filter outlet.

The boiler is provided with fuel gas from a branch at the outlet of the heat exchanger. The fuel gas is reduced in pressure to approximately 10kPa by a three stage pressure reduction process.  Each stage of the pressure reduction contains over pressure protection.  An electric heater manages the temperature drop associated with the extensive pressure drop across the fuel gas train.

The boiler unit control system maintains an outlet temperature at the city gate of two degrees Celsius, as controlled by a temperature transducer.  The control system has various safe guards to protect the system from break down and over-heating.
Successful Delivery

One of the biggest measures of success for the project was the importance of the city gate for AusNet Services and their biggest gas customer base; one hundred per cent supply had to be maintained throughout the project.  Zinfra was able to successfully deliver the project with no outages through careful planning, scheduling and sequencing.
Extensive civil works, including excavation of more than two metres as well as mechanical piping construction works, were conducted within metres of the existing city gate piping without incident or disruption.
A lengthy procurement phase added to the complexity of the project.  Long lead items included the heat exchanger, heater system, DN300 valves and DN300 filter, taking up to 30 weeks to procure.

The formal approval process with AusNet Services and the government gas regulator ESV (Energy Safe Victoria) meant Zinfra was required to produce a comprehensive construction safety management plan.  The final packaged plan included 35 health, safety, environment and quality documents for ratification by these stakeholders.
Construction, final installation, electrical and instrumentation works as well as commissioning have just been completed.  The project will be fully commissioned and operational by June 2014.


Zinfra is proud of their Safety record on this project – zero LTIs or MTIs.  The experienced technicians and workers followed rigorous safety standards to achieve this outstanding result.
In addition, Zinfra were able to exceed AusNet Services' KPIs and have completed the job with an excellent working relationship.