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These City Gate Heaters are designed to pre-heat transmission pressure natural gas prior to de-pressurisation to normal reticulation pressures. This avoids liquid condensation and freezing in the pipeline affecting the operation of valves and regulation equipment at the de-pressurisation stations.
The GCD designed
heaters operate on an indirect heating basis which consists of a water bath with
two high pressure inspirating natural draft burners firing into immersion tubes.
A separate serpentine tube bundle immersed into the water bath is used to
transfer and absorb heat into the process natural gas.
The design duty is 500kW heat absorption into the process natural gas with a nominal water bath temperature of 70oC. Pipework connections by 250NB pipes and ANSI 900 flanges. The tube bundle is designed and manufactured to API 12K, AS 4041 Class 1 and ASME B31.3.
Tube bundle design conditions:-
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Natural Gas Pressure: |
3000 to 10,200kPa MAOP |
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Natural Gas Flowrate: |
0 to 400,000 Sm3/h |
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Natural Gas inlet Temperature: |
9oC (min) to 15oC (max) |
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Natural Gas Outlet Temperature: |
35oC |
Heater Shell
The water bath shells are horizontally orientated with two supporting saddles and are externally insulated and aluminium clad to minimise heat losses. The process gas tube bundle and fire tube assembly are flange mounted to the heater shell at opposite ends. This arrangement allows the equipment to be retractable for long-term maintenance. The water bath is 2.5 metres diameter by 7.5 metres long and holds 35,000 litres of water .
Control Principle
The principle of control of the system is regulation of the water bath temperature for the required outlet natural gas temperature. This is set from a remote analogue input signal. Burner start/stop, alarm conditions and operation status are communicated between the local control system and remote plant PLC system.
Combustion System
The water bath is heated by two high pressure natural draft burners mounted in a burner box and fire into the immersion tubes. The burner controls operate from an AGA approved flame management system and are designed to meet AS1375 and AGA codes. This requirement to meet type B gas appliance codes for water bath heaters is an area that pipeline operators are now requesting on new installations. Previous installations in operation have not had these requirements. Each immersion tube discharges to dedicated flue stack with spark arrestor.
Pipeline External Load Compensation
Sterling Asia has developed a system incorporating a stainless steel bellow to accommodate mechanical loads imposed onto the tube bundle by the expansion and contraction of the high pressure pipeline.
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© 2002 GCD International Pty Ltd. |
