Co-processing plastic waste
Process

Co-processing plastic waste

Vikas Damle

With emerging prices of raw materials for cement production, there arises a need for an alternative resource. RK Shrivastava, Madhya Pradesh Pollution Control Board, Dr BN Mohapatra, Dr Anand Rai, Sunil Kumar Vyas and Chander Shekhar co-process plastic waste in the cement kiln without affecting the quality.

Never would have one imagined waste to be an integral part of the construction industry. However, it has been more than 20 years now, and cement companies world over continue to utilise waste as an alternative fuel in cement kiln. Though, the alternative fuel movement in India is at a nascent stage, a few cement companies have started utilising waste from cement manufacturing process as alternate fuel and raw material to reinforce its competitiveness and contributing to solutions of waste and benefitting the environment. Waste generation has increased considerably particularly in the developing economies. Interest in co-processing municipal solid waste and sewage sludge is rising.The energy intensiveness of cement production processes and increasing fuel prices, combined with fuel deficit, forced the cement industries to search for technologies based on waste derived alternate fuels. Coal and pet coke are the primary fuels for the cement industries. Alternative fuels contribute towards lowering the emission of green house gases by replacing the use of fossil fuels with materials that would otherwise have to be incinerated with corresponding emissions and final residue. Incineration of any waste in dedicated incinerator results in non-utilisation of energy from this valuable waste rather it requires additional energy for incineration and increments the green house gas emissions. Thus, the cement industry can use part of this waste as alternative fuel and raw material, which reduces usage of fossil fuels.

Established in the year 1985, Vikram Cement Works (VCW), a unit of UltraTech, is flagship unit of cement business of Aditya Birla Group Company. Located at Khor, a village in Neemuch, Madhya Pradesh, the unit started with a single manufacturing line of 1500 TPD capacity in the year of its inception. The journey of excellence with technological up gradation such as retrofitting of coolers, continual improvements anf optimisation projects resulted in three units (Line-I, II and III) with ultimate capacity of 4.0 MTPA cement production. The unit is producing Gray Cement and Clinker.

Plastic waste generated from different cities and towns is a part of Municipal Solid Waste. The disposal of polythene bags and other non-recyclable plastic wastes generates serious problems for the municipalities and corporations. Being non-biodegradable, gives an ugly appearance as well as impacts by leaving the land infertile, and chokes the drain. Indiscriminate burning of the same causes environmental hazards.

To overcome the above problem, VCW had taken an initiative to dispose plastic and polythene waste for energy recovery in cement kiln thereby replacing fossil fuel to conserve the natural resources under the mega drive of Madhya Pradesh Pollution Control Board, Bhopal.

Co-processing of plastic and polythene waste has following environmental benefits

  • High flame temperature of 2000 0C, material temperatures up to 14500C and residence time of four to five seconds in oxygen rich atmosphere ensures complete destruction of waste and harmful pollutants.
  • Complete scrubbing of exhaust gas due to countercurrent flow of raw material - resulting in trapping of heavy metals, sulphur and other pollutants within clinker.
  • The waste generated does not require subsequent processing. Cement kiln operates under negative pressure or draft, thus preventing the generation of
  • fugitive emission.
  • With the large mass of clinker processed inside the cement kiln, there is a presence of a huge thermal inertia thereby eliminating the possibility of rapid swings in temperature.
  • Inclusion of ashes and residual metals from the wastes within the clinker crystal structure.
  • Kiln lines equipped with ESP/ bag filters- ensures negligible particulate emission.
  • Destruction and removal efficiency of greater than 99.9 per cent..

Co-processing plastic waste

The need for alternate fuel arises due to the paucity of natural resources. This co-incineration of plastic waste in cement kiln helps in recovery of energy and eco-friendly disposal. Vikram Cement Works uses alternative fuel in its cement kiln since 2007 and conducted several trails to find out the impact of gases on environment and product quality. After successful trial runs, VCW started usage of plastic and polythene in the cement kiln from September 2008 under the guidance of M.P. Pollution Control Board and has obtained regular permission for usage of waste polythene bags, pouches, waste polythene and plastic waste as a co-fuel in cement kiln. the waste is collected by the network of the company and is gathered from the cities like Indore, Ujjain, Nagda and Pithampur.

System for shredding of plastic waste

Shredding machines have been installed to reduce the size of of the plastic. The polythene waste is reduced to 20 mm and is fed in the precalciner. In this automated machine the trucks loaded with plastic waste can be directly unloaded in the hoppers. From the hoppers plastic waste is transported through a small covered belt conveyor to the shredder, which shreds the plastic waste into very small pieces. Then, the shredded plastic waste is pneumatically conveyed to closed storage bunkers. From the storage bunkers, the plastic waste is transported through covered conveyor belt of alternate fuel feeding system.

Characteristics of plastic and polythene-Proximate and ultimate analysis of plastic and polythene was done by our laboratory and the results are given in table-1.

Plastic and Polythene consumption - The efforts have been made to maximise the plastic waste disposal in cement kiln. The year wise plastic and polythene consumptions are as follows:

Source emission monitoring during use of plastic and polythene (2011-12)- During FY 2011-12, we have monitored the PM, SO2, NOx and CO in raw mill+ kiln stack during plastic co-incineration and results are given in table-2.

Impact study on clinker quality

A comparative study of clinker quality with and without using plastic and polythene in our cement kiln reveals that there is no negative impact on clinker, quality. Results of the same are given in table-3.

Physical properties of cement

The clinker samples collected before and during co-processing of plastic and polythene were ground in the laboratory ball mill with same amount of gypsum at identical fineness. The complete physical testing was carried out in quality control laboratory and the result reveals that there is no negative impact observed in cement quality. Results are given in table-4.

Conclusion

The co-processing result shows that there is no adverse impact on the environment,clinker and cement properties. Hence co-processing of plastic waste is one of the best alternatives for its disposal, saving of energy resource, in ecological sustainable and environmental friendly manner.

(The paper was presented by R.K. Shrivastava, Madhya Pradesh Pollution Control Board, Dr. B. N. Mohapatra, Dr. Anand Rai, Sunil Kumar Vyas, Chander Shekhar and Vikram Cement Works a unit of UltraTech.)

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