MechChem Africa

We profile SAIChE IChemE member Carl Sandrock, Gauteng chair, senior lecturer at the University of Pretoria and a process control specialist.

Carl Sandrock SAIChE IChemECarl Sandrock was born in Pretoria, but says he is from Johannesburg. His parents are Afrikaans but they brought him up to speak good English. He was raised mostly in South Africa, apart from a year of his childhood in Lytham St Annes in the UK, but instilled with a global perspective.

As a teenager, he describes himself as a computer geek, yet his mother refused to allow his father’s computer into the house, believing it would open the door to bringing work home. His father was in insurance, while also being a rally car owner, driver and enthusiast.

His parents should perhaps consult on how to raise well-balanced kids.

“I always knew I wanted to do something practical. I had the upbringing of an archetype-engineer, dismantling and fixing machines and embracing every new technology,” he tells MechChem Africa.

“During my school days, I was a bit of a ‘computer nerd’. My dad had one of the original green-screen Commodore computers, which had to be kept in the garage. I used to buy computer magazines and type in published program code to make things happen,” he says.

The young entrepreneur soon started programming for money. “I bought my first car from the proceeds of a program I wrote for my Dad’s insurance company. People making claims would phone the call centre from all over the country and I wrote a program to find local service providers based on the insured person’s postcode,” Sandrock recalls.

So why go into chemical engineering, we ask? “I had an ‘uncle’ who was a chemical engineer who worked on the mines. I was impressed and wanted to be like him,” he responds.

He became a student at the University of Pretoria back in 1997 and graduated with a chemical engineering degree in December 2001. Unsurprisingly, his final project was based on a computer program: to predict the plume shapes and emission distribution pat- terns from plant stacks. “There was already a strong focus on the environmental side of engineering at UP and we had an active environmental group. We also had to take a formal undergraduate environmental course.”

Immediately on graduating, Sandrock enrolled to do his MSc with a focus on process control. His MEng dissertation was based on work done for SAPPI SAICOR in KwaZulu- Natal, where he developed a model-based controller for the batch pulp digesters. “These are large reactors which are loaded with 140 t of wood and 150 m3 of cooking liquor. The wood is ‘cooked’ at 10 bar and 130 °C to remove the lignin and reduce the chain length of the cellulose. The final product is called ‘dissolving pulp’ and used in textiles and cigarette filters. The challenge is predicting how long the wood should be cooked for and is similar to trying to predict the cooking time of meat in a pressure cooker.

“Immediately on completion of my MSc in 2002, I was asked to fill in for the mass transfer lecturer who was emigrating. I was offered the post full time in 2003 and I have been at the university ever since. I always liked teaching, having made extra money as a student teaching people how to operate of fax machines and printers. My superpower is that I actually read the user manuals,” he tells MechChem Africa.

Carl Sandrock Sieve tray distillationAs a result of his lecturing duties, Sandrock quickly developed expertise in distillation columns, their design and optimisation, which quickly translated into consultancy work. “I work mostly in the food-ethanol industry on column designs for the distilling industry. These plants produce the neutral spirits used to make ready-to-drink beverages (RTDs) such as Smirnoff Ice or Brutal Fruit.

“Ethanol is azeotropic, which means that no matter how many times you distil it, it will never become 100% pure. So during the distillation process, there is a very well defined concentration limit.

“An ethanol sieve tray distillation column is like a big tube with multiple rows of perforated trays inside. As the vapour rises in the column, it passes from one tray to the next, bubbling though the condensed liquid in the tray above. The liquid, on the other hand, is channelled down the sides of the column, be- coming purer and purer in every tray as it falls. “The vapour concentrates the more volatile constituents while the less volatile or lower boiling point constituent becomes more concentrated in the liquid phase,” Sandrock explains.

“Separation by distillation is the workhorse of chemical engineering. It takes 40 to 60% of all the energy used by the chemical industry, and all of these columns work in the same way, whether separating ethanol and water; petrol and diesel; or producing oxygen, nitrogen and argon from liquefied air,” Sandrock explains.

“I participate on all levels of design for these systems, including first-principle design, design validation and I consult on the optimisation of built units,” he informs MechChem Africa, adding that his specific expertise involves small systems such as the Nuffield distillery in Springs. “On big multi-million rand plants, sophisticated centralised control systems and SCADAs are installed that enable the whole plant to be controlled and optimised while sitting in a control room. But on smaller systems, one often has to climb a column and take some measurements to find out what is going wrong.

“A key indicator is the pressure drop between the bottom and top of the column. If the operator tries to push too much product through, instead of the condensed liquid trickling gently down though the catchment trays, the column can end up full of foam. This is called flooding and when it happens the pressure goes sky high and the system trips.

“By characterising the column to determine its unique best operating point, the controls can be tuned to stabilise production for continuous operation,” he explains.

Another string to Sandrock’s bow is a different approach to modelling that arose due to his talent for programming …read more.

Click to download and read pdf

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