Energas Technologies, leading supplier of high-end and specialised equipment to the oil and gas industries in Southern Africa since 2001, has completed a commission by VGI Consulting Africa, on behalf of Sasol Group Technology, to design and supply a mobile heater skid to a budgeted $210 M pipeline expansion project. The additional 127 km 26” pipeline sees an increase in transport capacity of a high pressure natural gas line between Mozambique and South Africa.
The existing 865 km-long Mozambique Secunda Pipeline (MSP) natural gas pipeline from Mozambique to South Africa is currently the only sustainable source of natural gas supply to South Africa, and, in order to meet the demand for natural gas in South Africa, the transport capacity of this line was significantly increased. In order to facilitate this increase, a combination of compressors and parallel lines – at approximately 128 km per section – had to be built.
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, Sasol Group Technology, who were spearheading this project at ROMPCO’s behest, appointed VGI Consulting Africa as the EPCM contractor for Loop Line 2’s (LL2) undertaking.
The 26” LL2 adds further capacity to the system by the installation of a 127 km parallel pipeline to the existing MSP line that ties back into the MSP. The importance of this gas supply cannot be understated. Much of the supply is fed to the Gauteng region in South Africa, a commercial and industrial hub that has earned the city of Johannesburg the title of Africa’s powerhouse. This feeder line supports residential, commercial, power generation and industrial heating requirements in the Gauteng area. Further to this, the supply also supports the operations of Sasol’s liquids and chemical plants in Secunda and Sasolburg as well as other large, energy-intense industries nearby.
Commissioning of LL2 with Energas mobile heater skid
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 had to be preheated to ensure the temperature did not drop below the pipeline minimum design metal temperature of zero due to the Joule Thompson cooling effect while the flow rate was controlled and monitored. A flow totaliser added the benefit of measuring the normalised volume of gas consumed to achieve the required line pack.
The project specification called for the design, manufacturing 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 were done in South Africa before delivery to site in Mozambique.
Laetitia Botha, Energas Technologies Product Engineer comments, “Energas specialises in the design, manufacturing and supply of skid-mounted pressure reduction and metering stations to the natural gas industry. Most of these skids are for sites in remote areas and being able to complete the fabrication and assembly in South Africa reduces schedule risk, site establishment and workforce logistics significantly. Another benefit of the mobile heater skid 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. It’s a cost effective solution to invest in a mobile skid that can be relocated where needed.”
The heater skid comprises a thyristor control panel, 416k W 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 control 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.
A Mokveld equal percentage axial flow manual control valve was chosen to control the flow of gas from 116 Bar to initially atmospheric pressure. This required a special trim that allowed precise control while noise and vibrations were very low. The control valve and heating capacity allowed the LL2 commissioning team to make effective use of the gas volumes made available by the pipeline operator, leading to the pipeline to be commissioned much sooner than originally anticipated.
“The natural gas industry both in South Africa and Africa is a growing one and has a bright future ahead. We have directly felt the effects of this growth just in the line of skid manufacturing projects on the go in Ghana, the Western Cape and Mozambique,” Botha concludes.