By Dr S S V Ramakumar, Chief Technology Officer & Member, Management Committee, AM Green
India, as per estimates, generates every year approximately 20 MMT of surplus agricultural residues of different crop varieties. Discounting some quantity of the same for animal/cattle fodder, a large amount of the same is available for value addition. In the absence of proper value addition avenues, often these residues will pose disposal issues and end up as environmental menace, when resorting to burning. Recent technological advances make these residues a precious bio-energy resource. Many green energy options can be derived from these residues like second generation ethanol (E2G), compressed biogas and a host of platform green chemicals. The recent value-added green product that is being thought of from these residues is sustainable aviation fluids (SAF). Let’s explore the possibilities.
The aviation industry accounts for 2-3 per cent of global CO2 emissions. The International Civil Aviation Organization (ICAO) as a part of larger climate goals has put forward the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA). As per CORSIA standards, the compliance phase starts from 2027 from which time, each country needs to reduce its aviation emission footprint by 50 per cent by 2050 from a base line of 2005 levels.
Aircrafts are normally propelled by petroleum derived jet fuel and global annual consumption at pre-COVID levels is 360 billion litres. Emission reduction measures in an aircraft generally by efficiency improvement, electrification and resort to clean fuel propulsion by hydrogen. Any engine modification is extremely cost & time intensive, and rest of the measures stated are farfetched. Hence, the easiest of CORSIA emission compliance measures is to blend a certain permissible amount of clean burning bio-/sustainable aviation fuel in the normal jet fuel. This way one can easily meet the emission reduction target by virtue of lesser CO2 emissions emitted by SAF. The blending percentage of SAF depends on its nature and production pathway and the target quantum of emission reduction being aimed. The blending percentage, to start with, varies from as low as 2 per cent to as high as 50 per cent.
Production Pathways
Presently, there are nine pathways approved by ASTM International, formerly known as American Society for Testing and Materials, to produce SAF from various feedstocks. These are coal, Hydroprocessed Esters and Fatty Acids (HEFA), fermented sugars and alcohols. As far as India is concerned, Alcohol-to-Jet (ATJ) and HEFA based technologies are more suitable. More than HEFA which suffers feedstock availability concerns, ATJ is a more plausible technology. Alcohols (mostly ethyl alcohol) can be produced from a variety of bio-feedstocks including agri residues. That’s how agri residues caught the flight of imagination of one and all for value addition into SAF. The degree of value addition can be inferred from the fact that SAF is currently priced three times higher than conventional fossil-based ATF (jet fuel).
The ICAO proposes SAF blending as 2 per cent by 2025, 5 per cent by 2030,17.5 per cent by 2035, 40 per cent by 2040, 45 per cent by 2045 and 65 per cent by 2050. A recent announcement by the Ministry of Petroleum and Natural Gas (MoPNG), the Centre stipulates the indicative target of 1, 2 and 5 per cent of SAF blending in ATF in India by 2027, 2028 and 2030 respectively initially for international flights. One per cent blending of SAF by 2027 as per current Indian ATF consumption levels is equivalent to around 100 TPD, if we restrict to only international flights. Many leading countries like Brazil, Norway, the USA, the UK and Indonesia have announced blending targets ranging from as low as 0.5 per cent immediately to up to 30 per cent by 2030 and various fiscal incentives and reward schemes for blending in place.
Ethanol can be produced from essentially two or three pathways using agri/bio feedstocks. Most common way of producing ethanol is by fermentation of sugar/sugar syrup or sugar cane molasses, maize which is known as 1G pathway. Lignocellulosic agri residues like rice, wheat, paddy straw, various specialised grasses (energy crops like Napier, Switchgrass etc.) can also yield ethanol through a 3-step bio-chemical process of pre-treatment, hydrolysis (saccharification) and fermentation which is also known as E2G. There is a third pathway where CO2/CO emissions in the off-gases of steel mills and refineries can be fermented to yield ethanol (which we can call third generation ethanol (E3G). All these types of ethanol can be further upgraded through chemical processes to form SAF. Of these, the carbon intensity of 1G ethanol is estimated to be high and hence SAF produced from the 1G feedstock is not EU RED-II/III compliant thereby making them barred presently for European markets. Indian and the US regulatory systems accept SAF produced from any type of ethanol.
Indian ethanol production projections by 2030 from all routes explained above would reach the 2000 crore litre mark. Of this quantity, even if gasoline blending by 2030 at 20 per cent requires 1000 crore litres, India would be surplus in ethanol. Hence, ATJ pathway is one of the potential pathways to produce SAF in India. IndianOil has announced the construction of 86 KTPA of SAF plant at their Panipat Refinery using LanzaJet (USA) ATJ technology. Several private players are also in the process of setting up commercial scale SAF facilities in India.
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