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Decarbonization of Heavy Industry

CENER is actively working on developing the technology needed to torrefy biomass and convert it into an effective substitute for coal and petroleum coke in pulverized combustion for generating high-temperature heat in industrial processes.

Among its various technological developments, CENER is currently intensely focused on developing the technology necessary to torrefy biomass and convert it into an effective substitute for coal and petroleum coke in pulverized combustion for generating high-temperature heat in industrial processes such as calcination kilns, sintering, cement manufacturing, or in blast furnaces in the steel industry.

One of the main energy objectives of the European Union is to decarbonize the energy sector. This requires the development of innovative technologies that enable more efficient processes for the use of renewable energies. The industrial sector in Spain consumes more than 1.4 million tons of these fuels, primarily petroleum coke[1], generating CO2 emissions exceeding 4 million tons.

To decarbonize these sectors, CENER is developing a process for torrefying residual biomasses. The torrefaction process transforms biomass into a solid biofuel with suitable properties to replace these fossil fuels in the mentioned applications. It improves its properties by increasing its energy content, reducing moisture content, and enhancing the particle size of the biofuel after grinding, along with other important properties for its use in these applications.

The net CO2 emitted during its combustion is zero, as it was absorbed from the atmosphere during biomass formation, accounting only for the emissions generated in the collection and transportation of biomass, and the production of the torrefied product, due to the use of fossil fuels and electricity of fossil origin in these parts. CENER has evaluated the reduction of emissions at around 90%, which will increase in the future with the decarbonization of the economy.

The mentioned sectors are subject to emission trading legislation, so the increase in CO2 prices and the gradual reduction of free allowances according to European legislation make this technology economically competitive.

CENER is developing this technology for the use of residual biomasses, such as agricultural and forestry residues, that do not impact the food market, land use for food cultivation, or the use of wood for manufacturing products like furniture, particle boards, paper, etc.

CENER is carrying out these demonstrations at its Biorefinery and Bioenergy Center, BIO2C, where the pilot torrefaction plant is located, with a capacity of 150-300 kg/h, an indirect heating rotary axis with thermal fluid (250-300ºC), and great flexibility regarding the raw materials to be processed. In this semi-industrial scale plant, the process is optimized for each raw material and the product for each application. Due to the pilot plant’s capacity, the results are directly applicable in the industrial sector in the short term.

The process involves chipping the received biomass, drying, torrefying, grinding, and, if necessary for logistical reasons, pelletizing. During the process, the chipping stage is crucial to reduce the size of the residues and ensure homogeneous drying and torrefaction both on the surface and inside. During the torrefaction process, the ground biomass is heated to 250-300º without oxygen, obtaining a completely homogeneous product.

During its developments, CENER has found that the main parameters affecting the thermal efficiency of the torrefaction process are biomass moisture and the degree of torrefaction (understood as the weight loss of biomass volatiles during the process on dry basis). It has also been observed that certain parameters affect it to a lesser extent, such as biomass reactivity, pile density, and the type of torrefaction technology used.

CENER has conducted multiple torrefaction tests in its pilot plant with a wide range of raw materials, including beech, pine, poplar, eucalyptus, paulownia, olive pruning, wheat straw, and biostabilized material. Additionally, it has optimized the torrefaction process, maximizing production capacity and thermal efficiency with values ranging from 91 to 96% depending on the moisture content of the raw material.

Furthermore, one of the most important milestones of the project has been the development of a high-quality torrefied straw pellet, with high calorific value, durability exceeding 97%, and pile density over 700 kg/m3. This development represents a significant milestone in the development of biomass torrefaction and pelletization of agricultural biomass.

CENER’s efforts over the years have focused on optimizing the process and verifying the industrial viability of using torrefied biomass as an ideal substitute for coal and petroleum coke in thermal uses in industry. The technology is now very close to market maturity and at the point of reaching an industrial plant.

[1] https://www.idae.es/informacion-y-publicaciones/estudios-informes-y-estadisticas/estadisticas-y-balance-energetico

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