Black Wattle to Electricity – The Gondwana Biomass Plant

May 8, 2018


Homeowner Steve Nightingale from Red Rocks 27 shares with us on the Gondwana Biomass Plant

I remember some years ago talking to Mark Rutherfoord and Rein van der Horst about setting up a biomass plant on Gondwana using the black wattle as the free fuel/feedstock to generate electricity. This set me thinking that the feasibility of such a plant would be a suitable multi-disciplinary project for my university students who are in the final year of an MSc. I typically have two teams of six students each per year with backgrounds in civil, mechanical, electrical/electronic, chemical, aeronautical and medical engineering. Two teams were selected and the project ran from the beginning of October 2015 until the end of February 2016. Technical and financial information was provided by Mark on behalf of Gondwana. Various representatives from Eskom, the South African government and various independent organisations also provided information, which helped tremendously.

We had the benefit of experience from a similar biomass project in Penrith in the UK, where the owner of a large chicken farm had built a biomass plant to provide electricity and heating for his farm. He ran into difficulties after eighteen months, largely because he had insufficient assistance in running and maintaining it properly. Eventually, he abandoned it. Some years later, the project plant was bought and re-commissioned by a small experienced biomass company, which managed it successfully for five years before our Gondwana biomass project started. It is still being run successfully today. A technically knowledgeable accountant from the biomass company came and gave a presentation to my students to give them a sound background on the issues with building and running such a plant and the project began in earnest. The company pointed out that although it made a profit of 9 – 11% per annum, this would not be possible without the UK government subsidy for electricity generation projects based on biomass plants. This sounded a warning bell, that such a project on Gondwana might not be financially viable as there were no subsidies for such projects in South Africa at that time.

The feasibility studies from both teams, operating independently, concluded that such a project was not financially viable, which was disappointing. However, as with any project of this type, one has to make assumptions on issues such as the cost of collecting the black wattle, the cost of drying it to the correct humidity level, the cost of preparing the feedstock to the correct size, capital and operating costs of the plant etc. These assumptions have a wide variance associated with them, but at the time such a project looked to be too high a risk to be profitable in the long term.

An interesting thing then happened. In 2017, Mark was able to obtain a small 60 kW biomass plant at zero cost. He only had to cover the expense for it to be transported to Gondwana and fund the erection, commissioning and operation. Therefore, the capital equipment costs were removed from the concept. Joe Erasmus and Marcel du Preez took took the project on with Marcel organizing and commissioning the plant, which began operating in November 2017. This was reported in the minutes of the Gondwana homeowners’ meeting last year. I came to Gondwana in November, 2017 together with an engineering colleague from the UK and we spent some time with Joe who showed us round the plant. We all agreed there was nothing like ‘learning by doing’ to find out the real values of some of the unknown parameters identified in the university studies mentioned above.

The biomass plant is situated behind the workshop in the staff village. It generates 60kW and is shown in the picture below. It is not possible to see it from the road; you have to drive up to the workshop. You will probably hear it humming away before you see it if you decide to make a visit.

The basic principles are as follows:

  1. The unit has a downdraught gasifier. Pieces of wood, black wattle in this case, are dried and cut up into small pieces. These need to have a humidity level of around 18%, which is easily achieved by drying them in a covered area for about a week.
  2. The wood or feedstock is then fed via a hopper into the top of the biomass plant and into a reservoir. It is then fed into a closed combustion chamber at regular intervals. The wood burns and air is pumped down through the burning wood and the gasses produced are extracted underneath the fire. Under the correct conditions, the extracted gas contains hydrogen, carbon dioxide, carbon monoxide and methane together with charcoal, tar and water.
  3. The gas is then filtered and cooled to remove charcoal, tar and water and fed into a modified 6-cylinder petrol engine driving a 3-phase generator. The generator can then be switched in to the electrical network to provide electricity for the staff village instead of taking it from the grid.

What is proving to be invaluable is the experience gained by actually operating such a plant. It can be operated by one person and, although it has a number of automatic control systems, it relies on the operator keeping an eye on the process and making small adjustments while it is operating.

The plant is currently being run from 8:30am till 5pm to allow downtime for daily maintenance. Future plans being considered are given below:

  1. Build a cover or roof over the whole plant with solar cells. These would provide electricity during the day with the plant operating at night after sundown.
  2. Build a laundry on the premises to make use of the excess electricity.
  3. Sell the charcoal and tar byproducts.

So, go and have a look.

In conclusion, we have black wattle, an invasive alien tree species, turned into desirable ‘green’ electricity for the benefit of all on Gondwana. So, for those of you who like a little engineering with your wildlife, have a word with Joe and I’m sure he would be delighted to show you around. If everything proves successful, Gondwana will probably be purchasing a much larger one in the not-too-distant future to provide electricity for the staff village, villas, Kwena and Lehele and is in keeping with the sustainable ethos of Gondwana game reserve.

Text: Steve Nightingale
Photography: Raquel de Castro Maia