How to solve pollution due to crop burning in India

12 min readNov 11, 2020

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Crop residue is, in part, solar energy converted and stored in a physical form (and can be considered as renewable source of energy). Hence, not utilizing it for energy production is a wastage of energy. Traditionally, crop residue is also used for livestock feed and compost making, but these avenues consume only a portion of surplus residue leaving much of the residue as wastage.

Estimated 500–550 Mt (million ton) of crop residue is generated every year in India, of which ~56% is generated by rice (34%) and wheat (22%) alone, cereal crops (rice, wheat, pulses, etc.) all combined generate 70% of total crop residue. Out of total crop residue, surplus residue (residue remaining after being utilized for fodder and other such activities) is estimated to vary between 90 to 150 Mt of which roughly 44 Mt is from rice and 25 Mt from wheat (additional 24 Mt is generated from cotton, rest from other crops).

Punjab and Haryana contribute ~25 Mt and 12 Mt of surplus crop residue in a year respectively. In both the states, crop residue is generated across only in 1–3 months twice a year (one of which is concentrated around October-November giving rise to the problem of pollution in winter months).

Primarily, both wheat and paddy crops’ residue are burnt for clearing the fields because:

Majority of these crops are harvested through combine harvester which leaves longer size of stubble post harvesting
Gap time between the two crops, specially, between paddy — wheat crops is very low (15–25 days), due to which farmers want fields to be cleaned and prepared faster for the next crop
Management of residues post creation of bales, etc. is currently not financially viable as there are very few takers of such raw materials.
Financially, stubble removal will additionally cost farmer estimated Rs 1000/acre

Many corporate houses and societies (including CII, initiatives in three location in Ludhiana & Patiala) have tried various methods to control the burning of residue by compelling farmers to adopt alternative techniques for managing residue.

These alternative techniques can be classified broadly in three segments:

Composting of stubble in the field
Sowing techniques that doesn’t require removal of stubble
Removal of stubble from the field

Each technique requires separate set of implements and practices.

Apart from these techniques that can manage excess stubble generated, there are many other methods that can reduce or manage stubble. Few countries, including USA, regulate the burning of crop residue by either creating fix days for burning the crop residue (arrived based on weather conditions) or through a local body where farmers can apply for permission for burning the residue, which ensures that limited crop is burnt in a day.

Current choice of crop variety and cropping patterns adopted by farmers in Punjab and Haryana is also resulting in excess residue and requirement to clear farm in a short duration to prepare it for next crop. Choosing the right variety will significantly reduce the amount of residue that is generated. Currently, farmers are selecting crops that grow longer in height (to reduce crop infestation and damage) and hence generating higher quantities of residue. They also choose varieties which require longer duration to mature, this results in shorter fallow time interval between the crops (a longer interval of time would help in composting residue in-field).

Typically, it requires 90 to 120 days for decomposition to happen on field. However, this can be reduced to 15 to 25 days by using (bio-)chemicals that can accelerated the decomposition process.

In such techniques a (bio-)chemical is sprayed in the fields with stubble using simple spraying techniques like back-pack sprayers, the amount of spray required varies with brand and product. Post decomposition single pass of rotavator or reversible plough (based on soil type) is required to mix the composted material with the soil.

However, these chemicals can cost up to Rs 1,000 per acre. Additionally, higher (50+) horse power tractors are not readily available, which will be required to drive the implements for mixing composite. The hiring cost of such tractors is Rs 500–1000 per acre, bringing total cost of composting (to remove stubble) at Rs 2,000 per acre.

Composting will reduce the dependence of farmers on use of fertilizers, but due to low availability of experimental data on usage of composite, the impact on usage of fertilizer is unclear.

Farmers can also adopt techniques where they can sow next crop without the removal of stubble from field. In this, the stubble is cut in finer pieces and left on the field itself. Later, seed drills that can sow without the requirement of tillage is utilized for sowing seeds.

For utilizing this technique, few additional implements like mulcher and straw management system equipped harvester are required. Further, seeds needs to be sown using zero till seed drills for the next cropping season.

The cost for taking mulching services is around Rs 1000 per acre, harvesting will cost an additional Rs 500 per acre (due to SMS). Sowing using seed drill will cost upwards of Rs 1000 per acre, bringing the total cost to Rs 2500 per acre.

While government bodies are promoting this (mulching, straw management) by providing subsidies on the purchase of these equipment, these techniques are known to reduce the yield (for 2–3 years) and also increase the cost of production (as higher amount of pesticide is required in fields where previous crops’ straw is present). This makes it difficult for farmers to adopt this technique.

Since, if farmer avails any of above (and other such) techniques, it will be an additional cost to him/her without any value add in-terms of productivity increase or profit. Therefore, these have low adoption among farmers. However, the cost significantly reduces if residue is utilized by tying-up with upstream consumer of residue. There are multiple organizations (including cow stables, composter plants) that require crop residue as raw material for their routine activities.

For removing remaining stubble from the farm, farmers will have to avail implements like straw slasher. The cost of which turns out to be Rs 500 to Rs 1000 per acre

To make this financial viable, collaboration with up-stream players that consume residue is required. This will not only cover the cost of using/hiring implements that are required to remove subtle, but also can generate additional income for the farmers.

The best way to utilize crop residue is to use it in energy generation, but that in itself gives rise to two legged problem of logistics and storage.

Logistics: If we consider crop residue generated in state of Punjab alone, it will require moving 25 Mt of low bulk-density material from farms to storage units or consumption points. Density of straw generated from rice and wheat varies between 50–120 kg/m^3 (while density of coal varies 550–900 kg/m^3) i.e. a volume movement of 2–5 x 10^8 m^3 is required. This amount to a movement of roughly 50–125 lakh trucks. Further, ~1.6 Mt of residue provides same energy as 1 Mt of coal but, whereas coal would require only 30 thousand truck movement, crop residue will require 10-fold more trucks, 300 thousand trucks!
Storage: Again, considering only Punjab, if the generated residue is stored ensuring that the height of stored residue is 10 meters (~3 floors) then it will require 10–25 Km^2 of area (assuming they are equally generated twice a year and is consumed). Same energy if generated from coal will require only 2–3 Km^2 of area. Additionally, the straw needs to be stored at location with low humidity, such that the moisture content of straw doesn’t increases beyond 25%, otherwise it will give rise to fermentation.

To utilize crop residue for direct energy (electricity) production, it will require us to come up with very intricate logistics and storage plan. Also, we can’t have highly distributed power plants in a state as that will give rise to additional requirement of creation of as many power distribution-points (which is a challenge in itself). Therefore, crop residue will require considerable movement from the farms to energy production units.

A logistic chain which manages low density product in very low cost is already established in cities that manages household waste disposal. Similar setup can be created for crop residual collection and logistics, where marginal workers collect the crop residue locally, which is deposited in local collection points and then transferred to GP level then to Tehsil level to District level. Such a setup will also provide additional work opportunities to the work force. For storage, arid/barren locations can be identified where crop residues can be stored without requirement of any additional infrastructure.

An electricity production unit setup will require 18 months and Rs 5.5 crore (excluding land and financial arrangement) and minimum of 10 acres of land (excluding storage) for 7 MW power plant (anything below is not viable). Such a plant will roughly consume 0.5–0.7 Mt of crop residue in a year.

Since, directly using crop residue for energy production is logistics and storage intensive, converting residue into intermediate product will reduce both logistics and storage requirement. Intermediate products can be produced at local level, which can then be transferred to central storage for further processing. Conversion of crop residue into fuel or char is better than converting them to combustible gases as later is difficult to manage and transport. For both fuel and char, it will require setting up of kiln or furnace that can heat the crop residue to optimal temperature, atmosphere and pressure to extract higher calorific value substances. The remainder molasses can be used as fertilizers post treatment. 1 Mt of crop residue results in ~300–400 million L of oil or 0.1–0.3 Mt of char but of much higher bulk-density compared to crop residue reducing the volume that needs to be handled post-production by 50–200 times (based on production technique, output product, etc).

Such conversion plants can be maintained at GP level and run by either corporate societies or private players. The output (fuel or char) from such units will be easy to transport and store. The output of these plants can be further utilized in production of energy at a centrally located thermal plant or for other such processing units that utilizes higher polymeric compounds of carbon (like in ore reduction). This method also takes care of excess silica present in paddy residue.

For the traditional coal based thermal power plants the landed cost of coal is ~Rs 2,400 per ton (including ~Rs 600 per ton of transportation charges). This results in a fuel cost of Rs 1.7–2.0 per KWh. Total production cost of electricity from the thermal power plant comes out at Rs 3.5 per KWh.

The cost of production from biomass will depend on — raw material (straw or intermediate) and type of process utilized for energy production (direct combustion or gasification plus combustion). Typically, for direct combustion biomass plants the cost of fuel comes out to be Rs 3.5–4.0 per KWh (while the total production cost varies from Rs 6–8 per KWh based on production technique used), i.e. the landed cost required of crop residue should be ~Rs 2,400 per ton. However, as mentioned earlier, it requires 10-fold effort in moving crop residue compared with coal. Along with this, farmers should benefit from the sale of crop residue.

An acre of field generates 1.0–2.5 ton of crop residue depending on type of crop variety. If farmers are paid a meagre sum of Rs 500–1000 per ton of crop residue. Then it leaves with only Rs 1,500–2,000 per ton for transportation. For regular dense material the average trucking cost comes out to be Rs 1.3 per ton per km, hence, for crop residue the average truck cost will range Rs 10–13 per ton per km. Therefore, it will not be economically viable to move crop residue beyond 100–150 Km from the point of origin. This will encompass 50–75 lakhs acre of agriculture land producing 1.75–2.50 Mt of crop residue annually, enough to run a 12 MW power plant (higher MW power plants are more economically viable compared to lower MW plants).

Cost per kilowatt of electricity generated from various sources

However, to compare the energy generated with other sources of energy, electricity generated from biomass combustion is of higher cost, due to higher pre-processing and residual management. Therefore, the rate of electricity needs to be subsidised to provide biomass-based power plant equal grounds with others.

Alternatively,

Intermediate treatment of crop residue can be done at local level to convert them into directly combustible material for thermal power plants and then transported to already established thermal plants.

To create intermediate product, crop residue needs to undergo pyrolysis. The intermediate product type depends on the type of technique used for pyrolysis. Fast pyrolysis generates bio-oil as the product, whereas, slow pyrolysis generates bio-char as the product. It is easier to store, handle and transport solids over liquids therefore, slow pyrolysis is preferred over fast pyrolysis (slow and fast are nomenclature, the time required for fast pyrolysis is under 5 seconds and slow pyrolysis is under 30 minutes). Bio-char can be directly used in thermal power plants as a substitute to coal without any major modification.

Small size pyrolysis system for generating bio-char

A typical setup for slow pyrolysis with 200-ton daily intake capacity will cost ~ Rs 45–50 Lakhs to setup (life: 10 years) (excluding land cost). The whole process can be broken in following steps (based on the stakeholders involved)

Collection of crop residue in field and loading it in trolley → Transport from field to the pyrolysis unit → Storage and processing of crop residue in pyrolysis unit → Bio-char storage and/or local sale → Transport to Mega power plants

Collection of crop residue in field and loading it in trolley: It requires 1 labour per acre to collect the straws on the field and load them into the trolley. Typical labour hiring cost is at Rs 400 per day, bringing the cost of collection at Rs 400 per acre (pessimistic assumption of labour taking a whole day for collection).

Transport from field to the pyrolysis unit: An acre of field generates 1.0–2.5 ton of crop residue, which can be accommodated in a single tractor pulled trolley. Typical hiring charges of tractor trolley is Rs 500 per trip. This brings the landed cost of crop residue at pyrolysis unit at Rs 350–900 per ton. Assuming that the crop residue collection and transportation cost matches the amount that is to be paid to farmer for crop residue.

Storage and processing of crop residue in pyrolysis unit: Storage required for 20 days of raw material will be around 3 x 3 meter. The total plant would require ~100 m^2 of area including the plant setup, cooling area and storage. For processing, 9 FTE manpower would be required (including security and maintenance) costing ~ Rs 80,000 per month. Additionally, ~ Rs 40,000 per month would be required for power cost. Hence, the running cost of the unit per month is Rs 1,20,000 per month or Rs 4,000 per day (Rs 5,000 per day to include any other overhead).

Bio-char storage and/or local sale: Bulk density of bio-char is 3 to 5 times higher than crop residue, hence, storage area required for storing bio-char would be considerably less than crop residue. Assuming a truck load of bio-char is stored at the plant before shipping, it will require a space of 1–2 m^2. Bio-char can also be sold in local market to farmers as it is a very good source of carbon required for good plant growth. Currently, bio-char is being sold at Rs 5–13 per Kg.

Transport to Mega power plant: Bio-char transportation cost is similar to the transportation cost of coal. To make bio-char at par with the coal, the landed cost of bio-char at the plant should be Rs 2,400 per ton. Since, bio-char would not require longer line haulage the transportation cost on an average would be Rs 400 per ton from pyrolysis plant to power plant. Rs 2,000 per ton price for bio-char, however, the project will be viable at Rs 3,750 per ton. Bio-char, however, would be a tiny fraction of the raw material required by the power plant, therefore, they will be able to bear the higher cost of bio-char.

Additionally, government can incentivize power plant on the purchase of bio-char

Further resources:

How to solve pollution due to crop burning in India

Written by Shadow Strike