Solution for stubble burning

In North India, Diwali initiates an extended period of foul air. Diwali is a harvest festival, and fields are then replanted. Across Punjab, Haryana, Rajasthan, Madhya Pradesh, the National Capital Region (NCR), western Uttar Pradesh, farmers clear stubble from the previous crop by setting it on fire. The Indian Space Research Organisation doesn’t release data on this, but in 2021 National Aeronautics and Space Administration (Nasa) detected over 57,000 stubble-fires in North Indian fields between November 1 and November 14.

This is literally a quick, dirty, cheap method. It releases harmful gases and suspended particulate matter (SPM) and causes smog that drives air quality index (AQI) off the scale. While there are many other contributors to poor AQI, stubble burning contributes between 35-45 per cent of atmospheric pollution in this season.

For several years, burning was banned. But the ban was never enforced due to the political clout of farmers. After the government lost its face-off over the three farm laws, it also lifted the ban on stubble burning.

The NCR is now spraying chemicals to inhibit burning. The Ministry of Agriculture also deploys equipment to harvest stubble. But this costs more than matchboxes, so there’s low uptake. Kerala and the North East use ducks as an organic recycling solution; the ducks eat stubble and are then processed into duck ghee roast. Unfortunately, duck hasn’t caught on in North Indian cuisine.

Another solution from the Ministry of Power (MoP) is to harvest stubble, compact it into pellets and to burn those pellets in thermal power plants as a coal substitute. The MoP has mandated thermal plants must substitute 5 per cent of their coal with biomass pellets for the next 25 years (or the life of the plant, if that is less). Ideally this biomass component should be raised to 10 per cent.

These pellets could be made in-house or sourced via long-tenure contracts tendered with pellet suppliers. That would create a supply chain, where farmers sell stubble to pellet-makers, who sell pellets to power plants. It would also count towards renewables obligations for power generators and distributors. Extra costs could be pass-through.

Burning pellets releases COs, SPM, etc. But it is categorised as “green” since plants absorb Carbon dioxide (Co2). So unlike coal or natural gas, pollutants are removed by the same agents that produce biomass. There’s been lots of controversy about a blanket green categorisation. If trees are cut for biomass and replanted, the replacements take a while to become meaningful CO2 removers. The European Union has narrowed its Renewable Energy Directives to exclude biomass derived from cutting trees. The Joe Biden administration is under pressure from the scientific community to similarly de-categorise biomass from

tree-felling.

The Indian assumption is, only waste or surplus biomass (stubble, straw) will be used. This is fast renewal and more “green”, since the next crop is immediately planted and rice/ wheat is fast-growth. India’s agro-surplus biomass is about 250 million tonnes per annum by some estimates.

The technology is simple. Sugar mills have been doing co-generation for a century, using bagasse – the waste product after cane is crushed. Europe did it through World War II. Pellets are easily manufactured, stored and transported. Power plants can even source biomass and do it onsite. By torrefaction (heating in an inert atmosphere) biomass can be dried and turned water-resistant for even easier storage.

But biomass cost per energy unit generated may be higher than thermal coal. Pellets yield lower calories per kg compared to coal. Some studies claim end-to-end carbon impact from biomass harvesting, to pellet creation, to burn, is higher than the impact from coal mining to burn. But in North India, a few plant chimneys spewing smoke may cause less smog and less AQI deterioration, than lakhs of fields set on fire.

The MoP says 39 power plants consumed over 80,000 tonnes of biomass and generated 55 GW between April-July 2022. That’s much less than 5 per cent, but it’s also 500 per cent growth in biomass usage year-on-year. The acid test for biomass use will be this winter. If this scheme does reduce stubble burning and leads to better AQI, the increased power costs would be more than balanced off by the reduced healthcare needs.