The R28-million Wadeville plant, capable of producing 3 MW of energy from three tons of calorific waste, was constructed in only seven months as opposed to the usual 12 to 18 months assigned to such a project. The accelerated building programme gave Prestige Thermal a competitive lead.

"There has been a global race to see who could produce the first fully operational commercially viable plant with the flexibility to operate with various waste streams, producing usable gas, within a certain timeframe," says Prestige Thermal sales and marketing director Mark Potgieter. "This is because of the newness of the technology and Prestige Thermal's desire to prove its place in the international market."

Potgieter says that, while other companies may also have expertise in pyrolysis, the highly specialised technology that allows the conversion of many different types of materials, is a competence specific to Prestige Thermal, and is a barrier to entry for would-be competitors in the market.

UK waste-to-energy specialist Hudol Thermal contracted Prestige Thermal to be the sole international equipment provider for the technology. As such, Prestige Thermal has been heavily involved in research and development in the area of waste-to-energy conversion equipment for six years, involving pyrolysis and autoclaving equipment specifically designed for black bag and other general waste.

The Prestige Thermal pyrolysis technology is an advanced conversion technology that has the ability to produce clean fuel gas of high calorific value from a wide variety of waste and biomass streams. The hydrocarbon content of the waste is converted into the gas, which is suitable for use in either gas engines associated with electricity generation or in boiler applications. In most applications there is no need for flue gas treatment.

This gas will typically have a calorific value of 19 MJ/m3 to 30 MJ/m3, depending on the nature of the waste material being processed. Biomass waste is associated with the lower calorific value, the higher calorific value being associated with other wastes such as sewage sludge. Gasses with higher calorific values can be produced when the waste contains reasonable quantities of synthetic materials like rubber or plastic.

The thermal decomposition process occurs at moderate temperatures, with a high rate of heat transfer to the biomass particles, and a short hot vapour residence time in the reaction zone. Several reactor configurations are used to assure this condition and, based on the weight of the original dry biomass, to achieve a yield of up to 85% gas product.

Each system can be arranged in batteries of pyrolysers and batteries of engines, or as suits the requirements of the project. Depending upon site conditions and the specific processing route, the biogas can be used to raise steam to use in electricity generating turbines, and also to supplement the steam feed for a front-end autoclave process.

Depending upon the environment, location, mass of material to be processed and specific site conditions, there are other methods of the converting cellulous fibre to electrical energy.

One can make use of full pyrolysis of the fibre and subsequently use the gas to raise steam and drive a turbine. It is also possible to use the gas directly, employed in gas engines to create electricity. In the case of the latter, low grade heat exiting the engine exhaust can be used to dry the fibre, with the remainder used to raise steam for use elsewhere or in other similar low grade heat applications.

Between 10% and 15% of the biomass that is processed ends up as inert waste product. But even this can be reused, either in a residue beneficiation process or else in low-value applications such as roadfill or non-hazardous landfill.

Autoclaving is a technology that has been practiced for many years and the process is proven for the treatment of medical waste and for the sterilisation of surgical equipment, but autoclaving of municipal solid waste (MSW) is a relatively new concept. In these cases the main purpose of autoclaving is to sterilise the waste material or equipment so as to destroy pathogens and other biological contaminants.

The application of autoclaving for MSW treatment is quite different, however. The sterilisation that occurs aids the process of separation, but the principal aim is to condition the material to aid downstream separation into constituent materials.

Prestige Thermal's autoclave design and downstream mass separation equipment contributes to high efficiency and rapid payback on investment.

For the past eight years, Prestige Thermal has enjoyed a consistent growth rate of 18% to 22% every year, in terms of staff and resources. Potgieter attributes the company's growth to its skills base. "We have acquired specialist skills from around the world," he says. "However, locally, the skills shortage has played a major role." He explains that artisans are extremely scarce at the moment and that companies are headhunting aggressively.

Following the crest of an industrial boom, Prestige Thermal's decision to involve itself in waste-to-energy conversion has been a strategic one in preparation for the eventual industrial slow down. When the industry slows, the traditional furnace side of Prestige Thermal's business may slow with it, but the company is expecting an opposite reaction in the waste-to-energy conversion equipment market. "We will have competitors in future, but ultimately, are distinguishing the company from the rest of the market," says Potgieter.

Prestige Thermal continues to develop integrated processes providing for recycling and the production of green power from waste input. In addition to the waste-to-energy plants, Prestige Thermal is currently involved in multiple large furnace projects including an autocatalyst plant, copper melting facility, a number of induction heating and brazing stations and multiple pyrolysis plants.