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Swedish Technology to Reduce Stubble Burning

  • 04 Dec 2019
  • 2 min read

Why in News

The pollution from stubble burning in winter is a major factor for the sharp decline in air quality in Delhi. To overcome this issue, India is testing Swedish technology — torrefaction that can convert rice stubble into ‘bio-coal’.

  • The government has funded a pilot project at the National Agri-Food Biotechnology Institute in Mohali (Punjab) with a Swedish company to evaluate the feasibility of the technology.

Torrefaction Technology - Stubble to Bio-coal

  • Torrefaction is a thermal process to convert biomass into a coal-like material, which has better fuel characteristics than the original biomass.
  • The process involves heating up straw, grass, sawmill residue and wood biomass to 250 degrees celsius - 350 degrees celsius.
  • This changes the elements of the biomass into ‘coal-like’ pellets. These pellets can be used for combustion along with coal for industrial applications like steel and cement production.


  • The project has a capacity of converting 150-200 kilograms of paddy straw to bio-coal every hour and reduce CO2 emissions by 95%.
  • Torrefied biomass is more brittle, making grinding easier and less energy-intensive.
  • Compared to fresh biomass, storage of the torrefied material can be substantially simplified since biological degradation and water uptake is minimized.
  • The torrefied pellets are ideal for coal replacement because it has lower shipping and transport costs, lower sulfur and ash content (compared with coal), etc.


  • The volume of torrefied biomass is reduced only slightly, ~ 10-20% lower than the dried feedstock during the process.
  • Despite higher calorific values, energy density is not improved significantly.
  • Torrefaction does not reduce corrosion of machinery especially boiler tubes.


  • Bio-coal, also commonly referred to as synthetic coal, is created through the torrefaction of biomass.
  • The bio-coal has similar characteristics to traditional fossil-based coal, and thus viable option to reduce greenhouse gas emissions.


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