Argentina produces 1 million tons of peanuts on 1.2 million hectares (4633 square miles) and rotates peanut fields for production every four years. The harvest of peanut fields in Argentina depends largely on rainfall. The average yield is three tons per hectare. Cordoba accounts for nearly 90% of the national peanut production and is the main area for peanut production in Argentina. In the heart of this peanut plain, vertically integrated peanut producer Prodeman has built a power plant. We interviewed Jorge Rubén Ciravegna, the chief engineer of Prodeman’s 10MW renewable energy power plant, which only burns agricultural waste from the production of peanuts.

Energy Density

The Prodeman power plant has sufficient fuel. Peanuts per hectare can produce 1.1 tons of peanut shells. Peanut shells weigh 300 kilograms per cubic meter, or 18.7 pounds per square foot. Peanut shells have a high calorific value, about 3700 kcal/kg. One ton of peanut shells can generate 1.25MWh of electricity.

In the past, farmers were happy to take agricultural waste that was hard to rot directly from their fields. Now, the price of peanut shells is around US$35 per ton. Proudman’s power plant operates 24 hours a day, and the raw materials come from leased land and are cultivated with its own equipment. Since the company’s method is to add as little extra energy as possible, packing peanut shells is the only way to deal with it. Since the time between harvesting and power generation is extended, transportability and storage are improved. Packing increases the density of materials by a factor of 3.5 and allows Proudman to obtain source materials with a larger radius, thereby storing them more efficiently.

The plant burns peanut shells in a water-tube boiler to produce high-pressure steam. The steam turbine operates at 480 degrees Celsius and 67 bar pressure (900 degrees Fahrenheit, 972 psi pressure), with a constant delivery capacity of 40 tons/hour. The consumption of peanut shells is 0.8 tons/MW, which is equivalent to 200 tons per day. The steam turbine can generate 80,000 MWh of electricity per year, which is supplied to the grid.

In order to further improve its utilization rate, Proudman uses the ash from the burning of peanut shells to produce bricks. The project complies with the provisions of the 2015 Paris Agreement and has greater environmental, economic and social sustainability. From an environmental point of view, it can deal with several problems at the same time: Unlike fossil fuels, biomass combustion does not increase the net emissions of greenhouse gases. Fossil fuels are hidden in the earth’s crust and affect the atmosphere when they are extracted and burned. Without this project, some carbon dioxide emissions from the clinker kiln will be inevitable. The project provides an ecological and cost-effective method to solve the problem of final disposal of peanut shells, which would otherwise become waste.