African Fusion June 2015

AFRICAN FUSION

June 2015

Cover story: Afrox

na1100ha sitenear Pofadder in

the Northern Cape, The 100MW

KaXu Solar One concentrated

solar power (CSP) plant has now been

commissioned. It is the first CSP plant

in South Africa to use parabolic trough

technology. Following close on its heels

are Khi Solar One, a 50 MW power tower

CSP plant outside Uppington, and the

50 MW Bokpoort solar parabolic trough

CSP plant, which is nearing completion.

In addition, the 100MWEskomplant

in Uppington has been approved for

construction and three CSP plants were

announced as preferred bidders by the

Department of Energy in the third round

of the government’s Renewable Energy

Independent Power Producer Procure-

ment Programme (REIPPPP): Kathu So-

lar Park, Redstone Solar Thermal Power,

and Xina Solar One, all of whichwill have

100 MW capacities and significant night

time storage capability – Redstone is

promising a full 12-hours of energy stor-

age, a first in Africa.

TheNorthern Cape is clearly becom-

ing South Africa’s solar energy hub.

Afrox has developed customised

solutions in response to the specific and

unique requirements of theCSP industry

and, in particular, the challenges associ-

ated with having operations in remote

areas of the Northern Cape. “A simple

visit to a CSP site takes a week, particu-

larly if equipment has to be delivered,”

Pieterse points out.

Welding and cutting

solutions

At the starting point of Afrox’s CSP offer-

ing are its welding and cutting products

for the construction phase of projects

and, later, for scheduled maintenance

during shutdowns. “Our fabrication spe-

cialists work closely with construction

contractors to ensure a full understand-

ing of the on site needs. Once these have

been established, welding consumables

and gases, aswell aswelding equipment

is sourced from the nearest Afrox sales

outlet,” Pieterse tells

African Fusion

“Parabolic trough plants such as

Bokpoort require 20 000 km of pressure

piping to bewelded, alongwith the sup-

port structures for a solar field consist-

ing of 588 600 m² of mirrors. The site is

3.0×1.5 km in area and consists or rows

of piping running above the parabolic

troughs, whicharepolished steelmirrors

that track the suns moment across the

sky to focus sunlight onto the pipes,”

he explains.

Inside thepipes anoil-based transfer

fluid is steadily heated as it is pumped

through the field towards the generation

plant at its centre. “The fluid reaches

temperatures of about 400 °C, which is

just belowthe critical creep temperature

for piping, so you don’t need to use

chrome-moly materials for the piping.

This is a pressurised circuit, though, so

high quality welding is essential for reli-

able operation,” he continues.

Onsite pipe welding is done using

the TIG process for root runs followed

by fill and capping passes using low

hydrogen MMA electrodes. “We were

awarded the contract for the supply of

TIG welding wires and the Argon gas for

the Bokpoort CSP contract, along with

the LH welding consumables,” he adds.

Molten salt storage solutions

A key feature of the Bokpoort CSP plant

is themolten salt storage system, which

will endeavour to provide more than

nine hours of electrical generation ca-

pacity (1 300 000 kWh

thermal

) after sunset

or during cloudy weather.

The molten salt is contained in two

In response to the specific requirements and needs of

establishing and operating concentrated solar power (CSP)

plants, Afrox has developed a comprehensive product and

energy solutions offering to specifically suit the industry.

AfricanFusion

talks toJohanPieterse, Afrox’s businessmanager

for the manufacturing industries.

Gas and welding solutions

for the CSP industry

huge storage vessels. These have also

been constructed onsitewith Afrox-sup-

plied consumables, using a combination

of MIG/MAG, flux-cored arc welding and

submerged arc welding processes.

Pieterse explains: “During the day,

the transfer fluid heated by the para-

bolic troughs is passed through heat

exchangers, which heat the molten salt

being stored in the tanks. At night, the

hot salt is thenpumped throughanother

heat exchanger where it is used to create

steam for the turbine after hours.”

Because of the high temperatures

and corrosive nature of the molten salt,

stainless steel piping is used for these

circuits, which is welded using Afrox’s

TIG range of wires and its Argon gas for

the root passes and cappedusing Afrox’s

stainless steel range of electrodes.

A large part of Afrox’s contribution to

the Bokpoort CSP plant arose because

of its industrial gas expertise. “The salt

only melts at 200 °C, and it needs to be

melted before it can be used as a heat-

exchange fluid. We have developed an

LPG storage and supply system to melt

the salt on start up of the plant and fol-

lowing shut-downs,” Pieterse reveals.

Afrox’s modular and portable skid-

based container system consists of a

series of containerised bulk LPG storage

tanks along with all of the evaporators

necessary to supply the fuel for the

initial salt melt. The whole system is

transported to site and offloaded in a

designated area. Once the salt ismolten,

the system is no longer needed on site,

so to save space and investment costs it

can be transported to and deployed at

another site or returned toour stores un-

til requiredagain,” he tells

AfricanFusion

In addition, themolten salt requires

and inert atmosphere in order to ‘blan-

ket’ the thermal storagemedium, that is,