MechChem Africa March 2017

March 2017

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MechChem Africa

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Petrochemical industries, oil and gas

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he existing 865 km Mozambique to

Secunda Pipeline (MSP) for natural gas

from Mozambique to South Africa is

currently the only sustainable source of

natural gas to South Africa and, in order to meet

the demand for natural gas in South Africa, the

transportcapacityofthislinehasbeensignificantly

increased. In order to facilitate this increase, a

combination of compressors and parallel lines – at

approximately128kmper section–had tobebuilt.

The Republic of Mozambique Pipeline

Investment Company (ROMPCO), owner of the

existing pipeline, represents a joint initiative

between Sasol, Companhia Mocambiçana de

Gasodutoand theSouthAfricanGasDevelopment

Company (iGas), and has played a pivotal role in

commercialisingMozambique’s natural gas supply.

With the backing of a successful first project,

Loop Line 1, Sasol Group Technology, which was

spearheading this project at ROMPCO’s behest,

appointed VGI Consulting Africa as the EPCM

contractor for the Loop Line 2 (LL2) undertaking.

The 26-inch LL2 adds further capacity to the

system through the installation of a 127 kmparal-

lel 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 commer-

cial and industrial hub that has earned the city of

Johannesburg the title of ‘Africa’s powerhouse’.

This feeder line supports residential, commer-

cial, 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 skids

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 tobepreheated toensure the temperaturedid

not dropbelowthepipelineminimumdesignmetal

temperature of zero – due to the Joule Thompson

cooling effect –while the flow ratewas controlled

andmonitored. A flow totaliser added the benefit

of measuring the normalised volume of gas con-

sumed 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 as-

sembly and testing of the heater skidwere done in

SouthAfricabeforedeliverytositeinMozambique.

Laetitia Botha, Energas Technologies product

engineer comments: “Energas specialises in the

Energas Technologies has completed a commission to design and supply a mobile heater

skid for the high-pressure natural gas line between Mozambique and South Africa.

The heater skid comprises a thyristor control panel, a

416 kW heater with isolation valves, flow meter, filter,

instrumentation and manually operated control valve

to measure, heat and control the filling of LL2 during

commissioning.

Mobile heater skid

for 127 km natural gas pipeline

design, manufacture 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 sig-

nificantly reduces schedule risk, siteestablishment

and workforce logistics.

“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 sec-

tions were being constructed. The heater skid is

only required once during the commissioning of

a new section and it is therefore not required as a

permanent installation. It’s a cost-effective solu-

tion to invest in amobile skid that canbe relocated

where needed.”

The heater skid comprises a thyristor control

panel, a 416 kWheater with isolation valves, flow

meter, filter, instrumentation and manually oper-

atedcontrol valve tomeasure, heat andcontrol 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 commis-

sioning the electrical heater was powered by a

diesel generator.

AMokveld equal percentage axial flowmanual

control valvewas chosen to control theflowof 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 andheating capacity allowed the

LL2 commissioning team to make effective use of

the gas volumes made available by the pipeline

operator, leading to the pipeline being commis-

sioned 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 through ongoing skid manufac-

turing projects in Ghana, the Western Cape and

Mozambique,” Botha concludes.