Mobile heater skid for natural gas pipeline

Energas Technologies has completed a commission by VGI Consulting Africa on behalf of Sasol Group Technology to design and supply a mobile heater skid to abudgetedUS$210m pipeline expansion project.

The additional 127km 26” pipeline sees an increase in transport capacity of a high-pressure natural gas line between Mozambique and South Africa.

The existing 865km-long Mozambique Secunda Pipeline (MSP) natural gas pipeline, which runs from Mozambique to South Africa, is currently the only sustainable source of natural gas supply to South Africa.

In order to meet the demand for natural gas in South Africa, the transport capacity of this line was significantly increased with a combination of compressors and parallel lines (approximately 128 km per section) built.

The Republic of Mozambique Pipeline Investment Company (ROMPCO), owner of the existing pipeline, represents a joint initiative between Sasol, Companhia Mocambiçana de Gasoduto and South African Gas Development Company (iGas), and has played a pivotal role in commercialising Mozambique’s natural gas supply.

With the backing of a successful first project, Loop Line 1 (LL1), Sasol Group Technology appointed VGI Consulting Africa as the engineering, procurement, construction management(EPCM) contractor for Loop Line 2’s (LL2) undertaking.

The 26” LL2 adds further capacity to the system by the installation of a 127km parallel pipeline to the existing MSP line which ties back into the MSP. The feeder line supports residential, commercial, power generation and industrial heating requirements in Gauteng.

For the commissioning of LL2, the new line was filled and pressurised from atmospheric pressure to a line pack pressure of 116 bar. The filling gas was preheated to ensure the temperature did not drop below the pipeline minimum design metal temperature.

The project specification called for the design, manufacture and supply of a transportable skid-mounted electrical gas heater with flow control in accordance with ASME 31.8, ASME VIII and SANS 10108. Design, fabrication, complete assembly and testing of the heater skid was done in South Africa before delivery.

“Most of these skids are for sites in remote areas and being able to complete the fabrication and assembly in South Africa significantly reduces schedule risk, site establishment and workforce logistics,” says Laetitia Botha, Technologies Product Engineer, Energas.

“Another benefit is that it could be relocated and used at different site points or locations as the new pipeline sections were being constructed. The heater skid is only required once during the commissioning of a new section and therefore not required as a permanent installation.”

The heater skid comprises a thyristor control panel, 416kW heater with isolation valves, flow meter, filter, instrumentation and manually operated control valve to measure, heat and control the filling of LL2 during commissioning.

The thyristor controller monitors the gas temperature at the outlet of the control valve and controls the power to the heater’s elements in order to maintain an outlet gas temperature of 10˚C. During commissioning the electrical heater was powered by a diesel generator.