One-pass biomass harvesting on show

August 30, 2012

Vryheid-based EnviroMulch and AHWI SA have brought biomass harvesting a step closer with the introduction into the South African market of a Biomass Harvester. The AHWI RT400, fitted with an AHWI 600 Biomass Harvester head, is capable of accumulating and shredding post-harvest residue and dumping it into a trailer in one pass.

Biomass harvester on show in Vryheid One-pass biomass harvesting on show
The biomass harvester on show, Vryheid. Just a few sticks remain after one pass.
Post-harvest trash from biomass harvester Harvested biomass
The biomass harvester gobbles up post-harvest slash. The end product ... harvested biomass.


This versatile machine is equally adept in a forestry application or in a bush/alien vegetation clearing operation, where it is currently being used very successfully in Namibia by Schwenk Cement (see accompanying article).

The AHWI biomass harvester was demonstrated at a recent field day held in Vryheid, organised by EnviroMulch and AHWI. Foresters representing most of the big forestry companies, as well as private farmers, came from far and wide to watch the AHWI gobble up a few rows of trash left behind by a harvesting operation. The shredded biomass was loaded directly into a tractor-drawn trailer travelling alongside the harvester.

The harvester head travels just above ground level so it accumulates all the standing residue, leaving behind just a thin layer of small sticks and trash.

The million dollar question is, what do you do with the biomass that has been accumulated? Basically, you need to find a market close by, within a 75 km radius or so, in order to recover the cost of the operation.

The total cost of the harvester (based on the Namibia bush-clearing operation) is estimated by the manufacturers to be Euro 180 to 220 per hour. This is total machine cost including the operator, fuel, maintenance and depreciation. Productivity is between seven to 20 tons biomass per hour, depending on the material. The Namibia operation is currently yielding 10 tons biomass per hour.

The total cost of biomass delivered to the plant is Euro 27,60 per ton. The cost of biomass per Kw/h is Euro 6,90. This is cheaper than the cost of B-grade coal at Euro 65,00 per ton, or Euro 10,83 per Kw/h.

Horst Hellberg of EnviroMulch, who makes extensive use of the AHWI mulchers on his Vryheid farm, has been testing the Biomass Harvester on a wattle compartment which was felled after 10 years. He removed 122 tons/ha pulpwood, 24 tons/ha bark, 12 tons/ha charcoal timber and 21 tons/ha biomass, and says he still left some material behind.

Fuel consumption on the RT 400 Biomass Harvester was around 52.6 litres/hour. The operation yielded approximately 16 tons biomass per hour.

Horst is currently using the smaller AHWI RT200 as an inter-row mulcher, and the RT400 on compartments after they have been clearfelled. The RT 400 can be used with either a mulching head or the biomass harvester head. He is convinced that there are many benefits to mulching. These include reduction of fire risk, retaining a protective layer over the soil which retains moisture and nutrients, and facilitating early and easy re-planting. The cherry on the top, according to Horst, is that mulching will ensure long-term productivity of the soil.

He says it’s important to use the right machine for the job to keep costs down, and in the mulching game, smaller is not necessarily cheaper.

In addition, Horst uses a de-stumping head to remove stumps on the extraction routes, and has developed a tractor-powered pitting head, known as a Pitmeister, to take his mechanised system a step further.

“In a few years time it may be illegal to use a match to reduce post-harvest slash, so what are the alternatives?” he said.

Steve Glutz, director of AHWI SA and a partner in EnviroMulch, said that in forestry applications, it is important to match the harvesting operation with the mulching/biomass harvesting operation that follows.

“When the trash is too high, the mulching or biomass harvesting operations battle. So we changed from a five-row system to a two-row system and the machines coped well with the smaller brushlines.”

Steve used a mulcher effectively to clear up a compartment on his farm that was damaged by a tornado. He also uses a mulcher to clear every 20th row in his compartments to provide easy vehicle access.

However, he believes that biomass harvesting is the way to go because you only handle the material once.

These machines also have applications outside of forestry, for example, clearing alien invasive bush. EnviroMulch has been using a mulcher to do bush clearing on a game farm that was severely affected by alien bush encroachment, improving the animal carrying capacity five-fold in the process.

After the presentations, there was much discussion among participants about the viability of biomass harvesting in South Africa, with everyone in agreement that a market needs to be found for biomass within a 75 kms radius of the harvest site.

In the Zululand area, biomass could be used as feedstock for the boilers at the mills, but the Vryheid area would be more problematic due to the long distances to the mills.

However, one of the participants, Christo Snyman, said that wherever there is industry present, there could be a market for biomass. He said boilers are used in many industries and if you can get the biomass material to work as feedstock for the boilers, you have a huge potential market. Most boilers in industry are currently using oil or coal.

His company sources wood waste from sawmills and supplies 12 000 to 15 000 tons a month to mills in Swaziland to be used as boiler feedstock.

He said all the sugar mills are also trying to utilize their biomass in their boilers. “There is a change of mindset taking place out there. With time the markets will come.”

Dirk Längin of Mondi said many forestry companies were interested in the opportunities for biomass harvesting, and suggested that Forest Engineering South Africa should provide a platform for gathering information that the whole industry could benefit from. He said it would be important to keep the cost of delivering biomass to the market down as it would be competing against coal, and the coal price is fairly low.

Christo explained that in Swaziland, the price of coal dropped from R1 400/ton to R890/ton after his company started supplying the mills with biomass.

According to Horst, the AHWI biomass harvester is in South Africa on loan from AHWI Germany for a period of six months, and urged forestry businesses to use the opportunity to test it in their plantations. He said the cost for hiring the RT400 biomass harvester (including the tractor-trailer) would be around R1 400 per hour – excluding the cost of fuel.

Namibia biomass project is a win-win
Namibia-based Schwenk Cement has launched an ambitious project to utilise biomass to replace coal to power their cement plant. The biomass is obtained by clearing alien invasive bush in a 75 km radius around the plant, using nine AHWI biomass mulchers similar to the one demo'd by EnviroMulch in Vryheid.

Apart from the fact that the biomass is cheaper than the low-grade coal it replaces, the bush clearing has brought major benefits to the surrounding farmers. Research done in the area shows that in 1958, the carrying capacity of the veld in the area around the plant was eight ha/one head of cattle. By 2000, this ratio was down to 26 ha/one head due to encroaching bush.

Thus, the bush clearing is doing an invaluable job in opening up the grasslands again so that it makes cattle farming more viable. It is also benefiting the global climate by reducing the plant's reliance on fossil fuels, and reducing Schwenk's fuel costs.

The project was started in 2009, and is currently achieving around 10 tons biomass per ha. The aim is to harvest 85 000 tons biomass in this manner every year.

Published in June 2012

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