Peanut Shells to Power

Prodeman’s 10-MW renewable power plant is solely burning agricultural waste from peanut production.
By Holger Streetz | April 26, 2021

Argentina produces 1 million tons of peanuts on 1.2 million hectares (ha) (4,633 square miles), rotating use of the fields for peanut production every fourth year. The harvest of Argentina’s peanut fields largely depends on the amount of rainfall. On average, the yield is three tons per ha. Producing nearly 90%, Cordoba is the hotspot of Argentinian peanut production. In the heart of peanut plain, Prodeman, a vertically integrated peanut producer, built an electric power plant that generates 70 gigawatt-hours of electric power annually. I was able to interview Jorge Rubén Ciravegna, the engineer behind Prodeman’s 10-MW renewable power plant, which is solely burning agricultural waste from peanut production.    
Energy Dense
The fuel for Prodeman’s power plant is abundant. Each hectare of peanuts leads to 1.1 tons of peanut shells. One cubic meter of peanut shells weighs 300 kilograms (kg), or 18.7 pounds per square foot. Peanut shells have a high calorific value of 17,570 kg. One ton of peanut shells produces 1.25 megawatt-hours (MWh) of electricity.

 Farmers used to be glad to get the hardly putrescible agricultural waste off their fields. Now, prices for peanut shells range around $35 per ton. Prodeman’s power plant operates 24/7 with raw material stock from leased land that is farmed with its own equipment. Since the company’s approach is to add as few additional energies as necessary, baling the peanut shells is the only treatment. This improves transportability and storing, as harvesting and power generation are delayed. Baling densifies the material by a factor of 3.5 and enables Prodeman to source from a larger radius, storing the material more efficiently.

The plant burns peanut shells in a water tube boiler to produce high-pressure steam. The steam turbine operates with 480 degrees Celsius at 67 bar pressure (900 degrees Fahrenheit at 972 psi) and a constant throughput of 40 tons/hour. The peanut shell consumption is 0.8 tons/MW, equating to up to 200 tons for daily consumption. The steam turbine is capable of producing 80,000 MWh of electric energy annually, which is supplied to the national electric grid.

To further increase its utilization ratio, Prodeman uses the ash resulting from peanut shell combustion to produce bricks. The project complies with the provisions of the 2015 Paris Agreement and allows greater sustainability in environmental, economic and social aspects. From an environmental point of view, it responds to several problems at the same time: Unlike fossil fuels, when combusted, biomass does not create an increase in the net amount of greenhouse gases. Fossil fuels are concealed in the earth and affect the atmosphere when extracted and burned. Without the project, certain CO2 emissions from the clinker kiln would be unavoidable. The project represents an eco-efficient and cost-effective way to solve the problem of final disposal of peanut shells that would otherwise be waste.
Argentina Funding for Renewable Energy Projects
Argentina has a variety of funding for renewable energies. Prodeman won the tender mainly because the fuel is an abundant waste product. The low additional process energy, short distances to consumers and low logistic costs added to the decision. The equipment mainly comes from national manufacturers. The steam turbine, however, is from Brazil. The typical investment range for waste-to-energy and renewable energy projects in Argentina ranges between $1.8 million and $2.5 million/MW. Biogas projects reach $4 million/MW. Prodeman’s power plant cost $1.9 million USD/MW, thus ranging along the bottom. Prodeman’s electricity contract is publicly accessible—the company is selling electricity from renewable energies to the grid for $150/MWh.

Prodeman’s business model has proven to be successful. The company sells the renewable energy to the Interconnected Energy System, administered by Cammesa S.A, under the national tender offer program for renewable energies (Renovar Ronda 2). The program stipulates the annual volumes fed into the national energy grid, as well as payment. The contract has a duration of 20 years.

A Jack-of-All-Trades
The man who won the tender for financing a renewable energies concept using peanut shells is Jorge Rubén Ciravegna. He is a mechanical and electrical engineer with 30 years of experience. He began his career in the early 90s, commissioning peanut processing plants. He later became CEO of the public utility company of the city of Deheza, followed by a decade of work in project development and as technical director for several Argentinian blue chip companies. Ciravegna planned and commissioned the power plant for Prodeman S.A.

Densification: Not at all Costs
Prodeman attempted to pelletize the peanut shells, but the issues were numerous. The shells lack lignin or other binders that could stabilize the pellet. Therefore, their transportability is very constrained. Additionally, there is excessive sand and other residue mixed with the shells, causing extreme wear on roller shells, leading to shell life below 200 hours. Other than baling, Prodeman has no process of which the energy needed to refine and prepare the peanut shells is worth the benefits. The utilization concept is ongoing, however, and many resources have been allocated to finding new utilizations for peanut shells.

Author: Holger Streetz
Chief Operating Officer, Bathan AG
[email protected]

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