Making the most of biomass

In Cuba, the use of biomass by state entities continues to be a viable path towards changing the energy matrix.

The national energy matrix in Cuba is currently composed 95% of fossil fuels, which confirms the urgent need to implement projects linked to the use of renewable energy sources as the main alternative to renovate the generation of electricity.

In this regard, authorities of the Ministry of Agriculture point out that in the country there are some 54 industrial facilities for rice production, whose consumption generates more than 70,000 tons of husk, equivalent to 20,588 tons of diesel.

Data collected in the Bioenergy Atlas of Cuba in 2022 reveal that there is a volume of 38,173.94 tons of agroindustrial waste per year that can be used for gasification, both for electricity generation and for the use of gases in processes.

Granma newspaper takes a look at the experience of two entities located in the provinces of Matanzas and Granma to verify the impact that the use of one of these renewable sources, biomass, has on energy efficiency and fuel savings for the country. It also takes a look into the symbiosis between the Ciro Redondo power plant and its adjacent bioelectric plant in Ciego de Avila, whose synchronization is expected to contribute some 60 megawatts (MW) to the nation.

FROM RICE HUSK TO FUEL

The installation of a bio-mass gasifier several years ago in the unit known as Secadero de Arroz de Amarillas, in the municipality of Calimete, in the province of Matanzas, is a fact of notable importance for a sector that faces the immense challenge of generating part of its own energy.

It is one of the first plants of its kind installed in a rice processing plant in the island, which has managed to produce fuel gas from rice husks (waste derived from the grain milling process), through the Biomás-Cuba Project, managed by the Indio Hatuey Experimental Station of Pastures and Forages, and financed by the Swiss Agency for Development.

The main advantage of the new program is that it contributes to replace the volume of diesel required daily by the rice drying system, as long as the flow of raw material is continuous, says Alexis Blanco Suárez, deputy director of the Empresa Agroindustrial de Granos in Matanzas.

Thus, the start-up of the plant makes it possible to replace, in part, the 700 liters of diesel fuel needed to dry rice at the Amarillas basic business unit (UEB in Spanish), while the gases released from the combustion process do not harm the environment.

According to Dr. Giraldo Martín Martín, a researcher at the Indio Hatuey Pasture and Forage Experimental Station, another benefit of the gasifier installed in the Amarillas dryer is that, at the same time, the system produces a material called charcoal, which has proven to be efficient in soils.

But, unfortunately, it is not possible to supply electricity to the grid with the residual rice straw because the material and technical conditions to do so have not been available so far.

In Giraldo Martín's opinion, the instability in the rice drying process, due to intermittency with the raw material, even reduces the momentum of the attempt to make the most out of the biomass with the gasifier installed in the Secadero de Arroz de Amarillas.

However, taking into account that biomass is a renewable source of energy, and its use reduces dependence on fossil fuels, the province is also undertaking the assembly of a similar plant in the Antonio Maceo Agroindustrial UEB, located in Hoyo Colorado, in the municipality of Martí.

There it is planned that biomass will contribute with about 14 % of the total electricity generation in the country, a goal that is still very distant, but which should not be given up.

DRYING TONS OF CORN WITHOUT A LITER OF DIESEL FUEL

More than two years after its start-up, the grain drying, processing, storage and packing plant -belonging to José Manuel Capote Sosa Empresa Agroindustrial de Granos - in the eastern province of Granma, has not yet used a single liter of diesel to dry the more than 9,000 tons of corn that have arrived to that facility up to 2022,.

Ángel Tamaño Yero, director of the Grain UEB, located within the plant, states with pride. He explains that the corn drying process is based on the use of biomass.

"For this process, not only do we use rice husks and firewood, but we also adapted the oven to take advantage of corn residues, such as the leaves and the particles of the tusa," he adds.

Likewise, the executive explains that other tests have been made with the jute and cotton residues wasted by the Texoro factory, which does not have a way to recycle these by-products. "This is an alliance that benefits both parties, because the factory does not have a destination for the reuse of its waste".

According to Tamaño Yero, the real impact of the use of biomass in the plant can be seen in terms of numbers. "Here, for example, to dry a ton of corn or beans, an average of 15 liters of diesel would be needed, and the capacity of our drying tower is 30 tons, so we are talking about saving around 450 liters of fuel each time the tower is used, which in a day represents about 1,350 liters".

On the other hand, to dry 30 tons of corn with biomass, an average of 300 to 400 kilograms of rice husks (which come from the Jucarito mill of the Capote Sosa company) and one cubic meter of firewood, whose price does not exceed 25 pesos in local currency, are used.

If we do the math, the savings are also remarkable, emphasizes the director of the Grain UEB. He specifies that the expense, for diesel fuel, would amount to more than 9,000 pesos per day with the drying of the 90 tons of corn; which is "money that today the plant saves in its entirety. Without a doubt, these are truly amazing numbers and results," he concludes.

OBSTACLES BETWEEN THE POWER PLANT AND THE BIOELECTRIC PLANT

Many setbacks have prevented the synchronization between the Ciro Redondo power plant and its adjacent bioelectric plant, a unique symbiosis in the generation of electricity in the country with the use of sugarcane biomass and sickle bush. At the end of October, both plants will carry out tests to start the harvest on the schedule date, December 22.

Therefore, expectations are high in the crossing between the plant and the power plant, in order to materialize the project that marks the beginning in Cuba of the use of renewable energy, based on sugarcane biomass and sickle bush

Ariel Díaz Román, plant manager at the Ciro Redondo bioelectric plant, states that, for example, in the months of July and August, a great effort was made to help the country's energy situation and they generatedin this period 22,621.5 megawatt hours (MWh) and delivered 19,701.5 MWh d to the National Electric System.

Although these figures are still small in relation to the potential, they do constitute a starting point to know exactly the weak points and where the work should be directed before the real start-up.

"We solved some problems that arose during the generation time with a boiler, with the use of forest biomass, and other activities that had to be corrected, modified and adjusted for the burning of bagasse, the fuel produced by the plant," he says.

Regarding the biomass guarantee for the coming harvest, the manager answers that the plant aims to use 100% of the bagasse, "for which the plant is designed, although we will always burn part of forest mass that we are accumulating. We would use the forest biomass during start-up and to make up for unforeseen or planned stoppages, such as maintenance of the power plant".

In short, the purpose of the project is that the plant generates with stability around 60 MW of power because the country needs this contribution without further delay.

Translated by ESTI