/ MEDIA STATEMENT / This content is not written by Creamer Media, but is a supplied media statement.
The benefits of using industrial cement kilns as a waste solution for energy containing wastes are both obvious and double-sided, they completely destroy the waste and at the same time, replace precious fossil fuels.
The trend has been slow to catch on in South Africa, although it has been in use in other parts of the world for decades.
Cement kilns can use waste as a source of energy, replacing traditional fuels such as natural gas or coal. In South Africa, coal to fire the kilns has been the fuel of choice due to its ready availability and quality.
But this has been changing in recent years as South African cement manufacturers have begun to follow global trends and turned to waste to drive their kilning operations.
Natal Portland Cement (NPC) in Port Shepstone, part of the global InterCement group, is one manufacturer that has redesigned certain of its operations to accept various waste streams.
InterCement has operations in a number of countries, including three in Africa, namely South Africa, Mozambique and Egypt. In some of their operations, waste has replaced between 50-70% of their main traditional fuel source. InterCement Co-processing Manager Rafael Mauri described the use of waste for fuel as “the best way to reduce environmental impact in cement production and carbon footprint”.
“South Africa has good coal, but it is also a finite resource,” Mauri explained.
InterCement began with the conversion process of some of its cement kilns to accommodate new fuel types in South Africa in 2014 and in Mozambique the following year.
Waste management company EnviroServ supplies liquid waste to the KwaZulu-Natal manufacturing site to fire the rotary kilns which produce clinker that is then refined into cement.
“Any liquid hydrocarbon waste that is free of contaminants such as mercury, or halogenated hydrocarbons, and has low moisture content would be considered suitable as alternative fuel,” said Dr Johan Schoonraad, EnviroServ technical specialist.
Many of these hydrocarbons are residues of other recovery processes (such as solvent recovery and used motor oil recovery) or have been found not to be suitable for such a recovery process, and thermal destruction (incineration) or use as alternative fuel is then a better option.
“Some of these have historically been disposed to landfill sites and with proper stabilisation (treatment) prior to disposal are not mobile in the landfill environment. This would ‘lock’ them into the waste mass present in the landfill cell and prevent them escaping into the open environment. While this practice is not ideal from a resource re-use perspective (recovery of the energy), it has been found to be effective in managing some, but not all, hydrocarbon wastes,” Schoonraad said.
Dave Morrey, General Manager: Inland for EnviroServ, said that Europe, the United States and countries such as China and Japan, had been utilising cement kilns to dispose of waste for decades as environmental legislation has evolved.
“In South Africa though, landfill disposal is still cheap and converting cement kilns to be able to run off waste takes a large capex investment. Less so for liquid waste - as provided by EnviroServ - as cement kilns would basically just need a pump system set-up to facilitate the flow of the waste into the firing chamber of the kiln. Solid waste though, such as cardboard, poses a trickier and more expensive exercise as this waste would need to be broken down first before being injected into the process as waste fuel.”
In Europe and elsewhere globally, cement kilns are often located in or very near major cities or industrial sites, whereas in South Africa these facilities are often located hundreds of kilometres away, close to lime quarries. It is a long way to ferry waste in order to dispose of it.
Higher inset costs associated with kiln conversions and the fact that landfill sites still present the cheaper option, weigh against cement kilns being the preferred alternative for waste management.
Yet, as Morrey explains, this is the future of waste management and EnviroServ is embracing it. “The cement kilns want it (waste fuel), the legislation drives it,” Morrey said.
“We need to create more awareness of the possibilities and catch up, but we are heading in the right direction.”
The environmental benefits of using cement kilns as a waste solution are enormous and form part of a more rounded economy.
The benefits include energy being recovered from the waste that would otherwise have been lost as part of traditional disposal methods; hazardous materials are destroyed in the kilning process; a reduction in greenhouse emissions; less reliance on disappearing fossil fuels; and landfill sites only receiving wastes that don’t readily have a beneficial use.
Morrey added that the tightening of regulations now restricts the waste streams being sent to landfill, meaning there is more scope for waste to be diverted to cement kilns.
That said, there are still practical challenges to utilising waste as fuel for cement kilns. Only certain waste streams such as organic hydrocarbon-based waste is suitable as an alternative fuel. There is, however, a similar drive to recover value from suitable inorganic wastes containing mineral components suitable to cement manufacture. Various metal slags, among other inorganic wastes, have been used by the cement industry for many years, including those in South Africa.
For fuel use, much depends on the Calorific Value (CV) of the waste. The CV is the amount of energy, measured as heat, released by a unit of fuel upon complete combustion, and with the cement kiln process it is imperative that this be within a certain range.
“The energy content of fuels suitable for cement kilns can range from that of dry wood (~16MJ/kg) to that typical of crude oil (>45MJ/kg). Clearly less volume of the higher energy material is required than one with a low energy content to provide the same amount of heat required to get a kiln to the operating temperature required to make cement clinker (~2000°C in the primary flame/burner),” Schoonraad said. “The challenge often then becomes an issue of feeding sufficient volume of low energy material (~16MJ/kg wood) to replace a traditional fuel such as coal (~26-28MJ/kg) that has a high energy content. The feeder systems in many cases cannot feed the low energy material fast enough to maintain the required temperature and therefore 100% substitution is not possible, only partial substitution of some of the traditional fuel used.”
The waste also cannot contain halogens such as fluorides or chlorides that can negatively affect the lining and operation of the kilns.
Still, despite all these challenges, from the logistical aspect to the economic, it is clear that South Africa’s waste management industry has changed course for a greener, more sustainable future.
These building blocks are increasingly made from waste-fuelled cement.