India: Govt pushes for plastic waste in steelmaking to curb emissions, coal imports

• Partial coke substitution in BFs will boost energy efficiency
  
  
• Aim is to curb waste, promote recycling and reuse
  
  
• UNDP, NITI Aayog working to ramp up recycling infra
  
  

The Ministry of Steel (MoS) has drawn up a sustainable roadmap for utilisation of plastic waste in steel production with the objective of reducing waste through recycling and reuse, minimising carbon emissions and lessening the country's dependence on metallurgical coal imports.

The Steel Research and Technology Mission of India (SRTMI) under the aegis of the MoS has prepared the roadmap in alignment with the global best practices adopted by steelmakers in Japan, Europe and Australia where plastic is used as a fuel as well as reductant in blast furnace (BF), coke oven and electric arc furnace (EAF).

Circular economy

"In a coke oven around 1% of coal can be replaced by plastic waste and around 30-40 kg can be additionally utilised in BF. The iron and steel industry has the potential to use more than 2-3 million tonnes (mnt) of plastic waste at present, which can be increased to more than 8 mnt by 2030,"a senior ministry official told SteelMint on condition of anonymity as the report is yet to be ratified and published.

India is the fifth largest generator of plastic waste in the world and generation is increasing at a very fast rate as per capita plastic waste generation has almost doubled over the last five years. The United Nations Development Programme (UNDP) and NITI Aayog have started a programme for effective plastic waste management and most of the states have set up Material Recovery Facility (MRF) centres for sorting, storage and processing of plastic waste.

The long-term goal is to adopt a circular economy, increase recyclability and reuse, minimise plastic waste going into landfills and cut steelmaking emissions. The Ministry of Environment, Forest and Climate Change has issued a gazette notification on 18 January 2022 proposing changes in the existing Plastic Waste Management Rules 2016 and replacing it PWM Rules-2022.

Cutting emissions, boosting efficiency

During incineration of plastic, carcinogenic gases like dioxins and furans are produced and such generation can be avoided if waste plastic is utilised in pyrolysis processes like coke oven or high temperature applications like BF or EAF. In such processes, plastic wastes are depolymerised into chemicals having smaller molecular weights, for example carbon monoxide and hydrogen.

"In the BF feedstock recycling of plastic wastes, combustion generates heat and gasification produces reducing gases such as carbon monoxide and hydrogen to reduce the iron ore into iron and can be used in place of coke or pulverised coal. Thus, it can help in reducing coke as well as PCI injection coal, both of which are imported in India," the official pointed out.

Plastics have higher hydrogen content than coal. Hydrogen evolved from the plastics acts as the reductant alongside the carbon monoxide. The advantages of using plastic wastes are:

• Reduction in the amount of plastic wastes being landfilled or incinerated.
  
  
• Lower consumption of both coke and PCI.
  
  
• Decrease in CO2 emissions since the combustion energy of waste plastics is generally at least as high as PCI normally injected and the higher ratio of hydrogen to carbon means less CO2 is produced within the BF. Pyrolysis of plastic in the BF and coke oven leads to a net reduction of emissions by around 160 kg CO2/ t of waste plastic.
  
  
• Lower energy consumption as hydrogen is a more favourable reducing agent than carbon.
  
  
• High energy efficiency of 80% or more as about 60% of the injected plastics are consumed in the reduction of the iron ore, and around 20% of the energy in the remaining 40% of the gases.
  
  
• Lower sulphur improves the quality of the hot metal and lower alkalis improves operations as alkali content can contribute to coke degradation, sinter disintegration and deterioration of the refractory furnace lining.
  
  
• Low emissions of dioxins and furans. .
  
  
• Use of waste plastics in EAF helps to improve slag property and thus increase refractory life.
  
  

Technical parameters

Some steel producers using waste plastic in BF have observed that injecting 1 kg of waste plastic replaced about 1.3 kg of pulverised coal in the BFs of Japan's JFE Steel. Substitution of coke by waste plastic is limited to around 30%, although values up to 40% have been observed. However, de-chlorination of certain types of plastic is necessary before injection into BF.

SRTMI has cited a study in which the plastic injection rate was maintained at 50 kg/thm (per tonne of hot metal) and the PCI rate was kept constant at 139 kg/thm. The coke rate was reduced from 385 kg/thm without plastic to around 320-350 kg/thm to compensate for the plastic addition.

The results of the study show that the amount of BF gas and its calorific value (CV) increased with the addition of waste plastic. The increase in CV can be attributed to a higher CV of plastics as compared to coke. The hydrogen content in the BF off gas also increased from 4.6 % (without plastic) to 5.4-7.3% for the different plastic resins. Higher hydrogen content in the BF gas promotes higher rates of iron oxide reduction and BF productivity.

Use of waste plastic in coke ovens leads to the production of coke, coke oven gas (COG) and hydrocarbon oil. Waste plastics are collected, agglomerated and charged in the coke oven with coal. Nippon Steel and Sumitomo Metal Corporation has developed a commercial scale waste plastic recycling process which is operational and successfully converting plastic into coke, COG and hydrocarbon oil. In order to maintain coke strength, most plants are restricting usage up to 1% mass of plastic addition.

Trials in India

At JSW Steel's Vijayanagar Works in Karnataka, innovative new techniques were developed as part of the 'Recycling of plastics in electric arc furnace' project in which plastic waste is used as a replacement for coke fines as a foaming agent in the electric arc furnace. The environmental, social and economic benefits are:

• Recycling approximately 340 t of plastic waste every year.
  
  
• Reducing the use of coke fines by approximately 340 t per year (10% of total coke fines used in the furnace).
  
  
• Minimising Vijayanagar Works' climate change impact by reducing CO2 emissions from the use of coke fines by over 1,000 t.
  
  
• Reducing the percentage of iron oxide in slag by 0.7%.
  
  

Tata Steel has also made laboratory as well as field trials for using waste plastic in coke ovens. Based on the plant trials it was concluded that for top charge ovens, plastic addition up to 0.5% can safely be done without any deterioration in coke strength. For stamp charge ovens, Tata Steel was able to take trials for plastic addition in coke making only up to 0.1%. This was due to unavailability of waste plastics.

Outlook

Thus, given bulk supply security, the iron and steel Industry can help in recycling large stocks of waste plastic in a productive manner provided some mechanism for collection, sorting, segregating and shredding is established in the country.

The Indian steel industry consumes about 70 mnt of coking coal annually at present. The National Steel Policy (NSP) envisages consumption of 161 mnt by 2030-31. Assuming 1% of plastic waste in coal blend, there is a potential for replacement of 1.61 mnt of coke by 2030-31.

NSP envisages about 160 mnt of BF production by 2030-31. Assuming consumption of 40 kg of plastic waste/t of hot metal (about 10% replacement of coke +PCI), the potential of plastic waste usage in BF is 6.4 mnt by 2030-31.

Similarly, EAF steel production is likely to go up to 50 mnt by 2030-31. "Utilisation of waste plastic in EAF can be specifically considered in the EAF units in north India, where there is no BF or coke ovens," a Steel Ministry source said.