Cement kiln co-processing technology a highly sustainable and economically viable option for the management of different kinds of wastes from Municipal, Industrial and agricultural sources, says Ulhas Parlikar, Dy. Head, Geocycle India, ACC Limited
Large quantities of Municipal Solid Waste, Industrial Waste, Agricultural Wastes, Plastic wastes get produced in our country and very small quantity of it gets sustainably managed. Most of it tends to get into dump-yards or landfills and some of it gets burnt unscientifically or incinerated without harnessing the resource value present in these wastes. In the process the natural sources of materials and energy are getting exploited on very large scale and are also getting depleted very fast. If this huge and unsustainable exploitation of the natural materials is continued, we would be causing irreparable damage to our survival means.
Each waste has material and energy value present in it. If we are able to find ways and means of harnessing for our gainful utilizing to replace our natural resources, we will be able to avert the difficult situation that we are leading us inti. Cement kiln co-processing option provides this option of gainfully utilizing wastes as resources in the cement manufacture without impacting the emissions or product quality. The emissions from cement kiln get improved while undertaking coprocessing. Hence, it can be said that cement kiln co-processing of wastes provides an opportunity for “Mission Zero Waste”.
Cement kiln co-processing has been included in the new waste management rules notified by MoEFCC in 2016 as a preferred option for the management of all kinds of wastes that are derived from Municipal, Industrial and Agricultural sources. When waste is co-processed in cement kiln, they get utilized as Alternative Fuels and Raw materials (AFRs). In the process, they substitute the natural resources such as limestone, iron ore, bauxite, clay, coal, oil, gas etc that are used in cement manufacture. Therefore, these natural materials remain conserved for use in the future. The technical features of the cement kiln are provided in fig 1.
Cement kilns have very high temperature up to 2000 Deg C and large residence time. Hence the organic material present in waste gets fully combusted as fuel. The Destruction and Removal Efficiency (DRE) of cement kiln is substantially better than that of an incinerator. It has alkaline environment due to presence of large quantum of lime in the kiln and hence, all the acidic gases get fully neutralized. The ash containing inorganic materials gets utilized as raw material in the cement manufacturing process. These materials replace the natural raw materials and fuels used in the cement manufacturing process. In cement plant, therefore, the wastes substitute the natural raw materials such as limestone, iron ore, bauxite, clay etc. and fossil fuels such as coal, oil or gas and keep them conserved for future use.
Once the waste material is fed into the cement kiln, it gets completely disposed without any untoward impact on emissions or the product quality. There is no residue from the cement plant. Hence, the cement kiln co-processing delivers a “zero waste” solution.
- The advantages of cement kiln co-processing are following.
- Cement plants already exist near most of the towns and cities. Only the feeding arrangement needs to be implemented in the kiln. Hence the major infrastructure to provide solution is already existing.
- Cost involved in setting up facility to convert non-recyclable combustible waste into RDF and required feeding arrangement in the cement plant is very less.
- Cement plant does not need additional environmental control measures for pollution abatement. The existing ones are good enough even while treating simple plastics or complex hazardous wastes.
- Cement kiln co-processing does not leave any residue for landfilling. The residue gets utilized as Alternative Raw material in the manufacture of cement.
- Cement kiln co-processing has been amply demonstrated for its safe disposal capability for wastes through many trials in India.
- Co-processing is now being implemented successfully of different kinds of wastes including hazardous ones in >55 cement plants across the country and is gaining momentum. Considering the economic viability of the co-processing option, balance cement plants are also gearing up to undertake coprocessing of wastes.
- Cement kilns are well spread out throughout the country and most of them have created infrastructure for co-processing wastes in their kilns.
Cement kiln co-processing helps achieve Zero waste Mission for all kinds of wastes such as Municipal, Industrial and Agricultural ones.
1. Municipal Solid Waste
About 70 million tons per year of MSW is generated in our country and managing the same sustainably is a challenge that we are facing currently.
Fig 2 provides the typical constituents present in the MSW. As can be seen in this figure, each constituent has an application in which it can be gainfully utilized. However, for this utilization to become efficient and complete, it is important that the constituents are properly segregated so that each one is not contaminated with the other constituent.
The new SWM Rules mandate that primarily, this segregation must happen at the household level into Wet, Dry and Domestic Hazardous categories and these materials need to be transported to the respective management sites in the same segregated manner.
The wet material needs to be converted into compost or biogas and the technologies for this conversion are mature and proven. The lesser the contamination of other constituents in this wet material, better is the yield and quality of the product produced from it. Avoiding exposure of the batteries and e-waste to it ensures that the compost product produced from its processing is not contaminated with the heavy metals which is normally a concern. Use of properly produced compost helps reduce the use of chemical fertilizers which are produced by processing the natural materials containing, Carbon, Nitrogen, Phosphorous and Sulfur. Hence the natural materials that provide these ingredients remain conserved due to use of wet waste derived compost.
The dry material needs to be segregated into recyclables, nonrecyclables and inert for managing them appropriately. The inert material that is not contaminated with any heavy metals can be used for filling the low-lying areas. This act facilitates avoidance of indiscriminate digging of lands.
The recyclables are plastics, metals, papers & clothes. These need to be properly segregated into individual streams and sent for recycling. Better is the segregation of the individual streams and substreams, better is their recyclability. The larger the amount of recycling, lesser is the requirement of the virgin feed stocks for producing these materials and hence these materials remain conserved in the nature for use in future.
The non-recyclables contain combustible materials such as thermocol, rexin, rubber, old & torn clothes, contaminated paper, plastics & clothes, tube pieces, tire pieces, multi layer packaging, thin plastics, etc. These are the ones that are generally found discarded into road side locations, dump yards, etc. In cement plants these materials get utilized as alternative fuels and raw materials (AFRs) wherein the entire material and energy value present in it is gainfully utilized in the cement manufacturing process.
The domestic hazardous waste, that contains bio-medical, e-waste and hazardous wastes, needs to be transported to the waste management facility where it can be separated into respective waste streams. The bio-medical waste is then sent to the bio-medical treatment facility, the e-waste to e-waste treatment facility and Hazardous waste to the hazardous waste treatment facility.
2. Industrial Hazardous and nonhazardous wastes
Industry generates many kinds of hazardous and non-hazardous wastes. Hazardous wastes include different kinds of ETP sludges, process residues, waste solvents and oils, waste hazardous chemicals, expired medicines and hazardous products, exhausted process catalysts, etc. The quantum of Industrial hazardous waste that is non-recyclable is about 4 million tons per year. The non-hazardous wastes consist of expired food items, expired FMCG materials, plastic wastes, rubber wastes, residues from non-hazardous products, etc. There is no specific evaluation available on the amount of non-hazardous wastes generated in the country but obviously this is also very large. Earlier these materials were disposed off by way of landfill or incineration where in there was no recovery of the resource value present in the wastes. The new Hazardous & Other Waste Management Rules 2016 have mandated that these wastes are managed as per the waste management hierarchy which is provided in the Fig 2.
As per the waste management hierarchy depicted in Fig 3, it is required that the waste generation is minimized and if it is still getting generated, then is explored for its reuse or recycle. If it is not feasible to reuse or recycle, then it should be evaluated for co-processing first and only after that for waste to energy. In case both options are not feasible, then only the waste needs to be sent for disposal by landfill or incineration options. The responsibility of ensuring compliance to waste management hierarchy has been put on the waste generator.
Generally, waste generators evaluate the options of Reduce / Reuse / Recycle very critically and adopt them. However, when the same is not feasible, they are required to be disposed. It is mandated in the Hazardous & Other Waste Management Rules 2016 that the option of cement kiln co-processing for recovering the resource value present in the waste is evaluated by them. Cement kiln manages these wastes in a manner that there is no residue left of the waste thereby providing an opportunity to achieve the “Mission Zero Waste”
3. Non-cattle feed Agro-wastes
From rough estimates, it is evaluated that the amount of noncattle feed Agro wastes generated in our country is >300 Million Tons per year. Most of these agro wastes are burnt in the fields after harvest causing huge damage to the environment due to untoward emissions released from this act.
This phenomenon is observed every year when the left-over materials are set on fire in the fields in north which cause the pollution to travel long distances up to Delhi. If these agro-wastes are properly collected and utilized in the cement kilns as alternative fuels, the entire energy value present in them can be properly harnessed. There is no residual ash and hence this provides a very desirable solution for managing these agrowastes. In case the cement plants are not available in the viable proximity, then the same can be evaluated for utilization in the nearby Thermal Power plants also. Although, not so efficient as cement kilns, Thermal Power plants also harness the energy value and facilitate the reduction in the overall utilization of the waste generated in the country.