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Sugarcane biomass offers hope for embattled Nkomazi farmers

Sugarcane biomass offers hope for embattled Nkomazi farmers

South Africa is a land of incongruous extremes, a wonderful land of plenty mired in poverty. This is vividly illustrated in the sugar industry where the country has one of the largest reservoirs of short-cycle renewable biomass in the world, and yet many small-scale sugarcane farmers are in dire straits.

After struggling to make a liveable return from their land for many years, increasing numbers are giving up and leaving the industry. A project in Mpumalanga, led by Aurecon, to create value-added products from sugarcane biomass, has demonstrated promising potential to transform these farmers’ income generation capability.

At present, the sugar industry consumes only the millable stalk of the sugarcane, which accounts for 60% of the total biomass and includes the juice and the fibrous bagasse. The balance of the plant – one third of the available energy – made up of the green top and dry leaves is burnt away in the fields. The reasons for this wasteful practice have been the lack of suitable, simple technology to convert the energy in the cane residue into useful value-added products, as well as an industry structure that keeps the value in the sugar and molasses exclusively for the mill owners.

An extensive evaluation by Aurecon of the available conversion technologies and potential revenue earning products, including a pilot plant study, has made a clear case for using slow pyrolysis to convert sugarcane residues to ‘green’ charcoal briquettes. 

“The successful biomass to energy scheme hinges on two essential elements,” comments Jean Bouwer, Aurecon Project Manager.  “Advances in renewable energy technology have made more versatile and well-priced biomass-energy conversion available, and Aurecon has developed its Integrated Rural Energy Solution, a holistic business model drawing together work done by Stellenbosch University, Tshwane University of Technology and our own studies.”

The background

The project began with the Mpumalanga Cane Growers Association contracting Aurecon and the sugar producer TSB Sugar RSA, which markets under the well-known ‘Selati’ brand, to undertake a feasibility study to investigate ways of boosting economic development in the Nkomazi district of Mpumalanga through renewable energy projects. Focused on the need to assist the plight of previously disadvantaged small-scale sugarcane growers, the study received funding of €400 000 from the governments of Finland and Austria, hosted by the Development Bank of Southern Africa.

Sugarcane is an exciting source of renewable biomass because of its short-cycle renewability. The cane can be harvested between 8-10 times before it has to be replanted. The period between harvesting varies from 12 months in irrigated regions to 24 months in colder regions relying on rain. This compares with 8-10 years between harvests for timber. An attractive environmental benefit flowing from a sugarcane project is the potential for reducing deforestation with sugarcane producing significantly higher yields over an equivalent period and displacing three tons of wood for every ton of charcoal.

However, the primary immediate concern was how to create jobs in the desperately poor rural community of Nkomazi.

The pilot project indicated that a small 2 MW generation pyrolysis plant has the potential to generate more than 100 permanent jobs sustained by the sales of charcoal briquettes into the leisure charcoal market. 

Taking advantage of new technology

In its traditional form, the slow pyrolysis process has been used for thousands of years to produce charcoal for cooking fires. Charcoal was produced from wood by starving the combustion of oxygen resulting in a slow burn and achieved a high residual proportion of carbon. It was a process that took several days and generated heavy smoke pollution.

In the modern process, biomass feedstock is slowly heated to 400-500°C in an inert atmosphere with varying vapour residence time of 5-30 min. The resulting char can then be compressed into briquettes which are available for distribution. Emission control is done through scrubbers in the vent gas. But the most significant change has come from the scalability of fluidised bed technology providing a higher rate of heat transfer with the benefit of faster turnaround times and, consequently, allowing the use of smaller plant equipment.

“The factor that has been the Achilles heel of many attempted biomass renewable energy schemes was ensuring the availability of sufficient quantities of the biomass within a cost effective distance of the processing plant to ensure that energy production could sustain a community all year round. Aurecon has developed a proprietary business tool called ‘An integrated biomass transport and logistics model’, which evaluates and optimises a client’s business model to ensure sustainable profitability is achievable,” comments Bouwer.

The biomass operation

Small-scale sugarcane growers (SSGs) in Mpumalanga typically produce 450 000 ton per year of sugarcane. Currently in the study area, there are still more than 1 200 SSGs with an average plantation size of 7 ha producing and delivering sugarcane to the TSB mills at Malelane and Komati.

Sugarcane as biomassTraditionally, after the sugarcane has been harvested the tops and green leaves, containing some 30% of the energy available in the plant, remain in the field as a ‘trash blanket’. The trash has a moisture level of around 60% and the longer it is left to dry the higher the yields that can be collected. 

The trash blanket serves to preserve ground moisture and protect the ratoons – the stump of the cut sugarcane that will sprout to produce a new crop. At this stage, farmers are allowing approximately a quarter of the trash to be gathered as biomass feedstock.  It is baled and transported a maximum of 25 km on tractor drawn flatbed trailers to the pyrolysis plant.

The feasibility study estimated an average annual biomass yield of 18 000 ton of ‘wet’ feedstock that is equivalent to 7 233 ton of oven-dry feedstock after passing through a rotary drier. Processing in the slow pyrolysis plant produces 2 228 ton of product charcoal briquettes.  Recognising that a sustainable business in briquettes requires a proven market and distribution network, the study investigated these aspects and took the costs into consideration in the financial modelling.

Competing in established market

The competition for the new biomass briquettes is the well-established wood charcoal.

In 2004, South Africa produced an estimated 205 000 ton of charcoal for the consumer and industrial markets.

Of the 120 000 ton per year used by the consumer market, 70 000 ton was sold domestically and the rest exported. (Since 3 kg of wood produces 1 kg of charcoal, it can be deduced that it requires the destruction of 210 000 ton of trees every year to satisfy South Africa’s consumer charcoal market!)

To learn the characteristics of the charcoal market, a consumer survey was conducted predominantly within a 100 km radius of the proposed site for a full commercial pyrolysis plant.  Briquettes were selling at a ratio of 2,5:1 against charcoal, with the long burning characteristics and ease of lighting briquettes positive values, although price was still the dominant factor.  The majority (64%) of consumers preferred charcoal to wood for braais. A briquette market in the area of 120 ton per month was estimated. 

Commercial concept

The study indicated that a viable opportunity existed to build a R20 million commercial charcoal briquette production plant based on slow pyrolysis of sugarcane residual biomass, which would show better returns and more reliable returns than other product options such as bio-oil, or electricity even though electricity would realise renewable energy preferential rate when sold into the grid. 

The success of the scalable fluidised bed pyrolysis technology means that it can grow as SSG production increases and may even accommodate large-scale growers wishing to make their biomass available, which could more than double the supply of biomass to 38 000 ton within five years.   

Experienced as an enabler of sustainable practices, Aurecon is now equipped to evaluate any similar potential biomass business prospects and manage the concept through to establishment of an optimised operation with a virtually assured return. The business model is ready to be offered to other partners for application in sugar growing areas.

Socio-economic impact 

The scheme to produce briquettes creates a specialised sector in the Nkomazi community’s sugar industry that adds value along the entire production chain. In addition, the operation of the pilot plant alone created 16 formal employment opportunities. Ultimately, it is hoped that the business will be a community owned organisation with labour sourced from the local area. The necessary skills are not available at present and attention will be given to training, establishing apprenticeships and appropriate mentoring.

The achievement

“Aurecon has successfully developed a business model programme and incorporated the latest processing pyrolysis technology to bring to reality the processing of sugarcane residues as a viable and entirely new sugar industry opportunity,” says TSB’s Justin Murray, Grower Affairs Manager for the Mpumalanga Cane Growers Association. “The small sugarcane growers in the Nkomazi region at last have real hope of improving their revenue and having a sustainable future in sugar.”    

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