Ashwani Pahuja, Director General, NCB
The National Council for Cement and Building Materials (NCB) has been pushing for the use of alternate fuels and raw materials in cement manufacture. Ashwani Pahuja, Director General, NCB, speaks on the role that the entity plays.
How have things changed over the last decade on the subject of alternate raw materials and fuels?
The cement sector has a vital role to play as India has a lot of potential for development in the infrastructure and construction segments. The Indian government is taking many steps to boost infrastructure activities such as development of Smart Cities, Housing for All, Make in India, Swachh Bharat Mission, etc.
India´s cement demand is expected to reach 550-600 million tonnes per annum (MTPA) by 2025. Under the 12th Plan period, coal requirement for the cement industry is assessed to be in the range of 63-96 million tonnes (46-70 million tonnes for cement production and 18-27 million tonnes for captive power). In view of the shrinkage in linked coal supply to cement plants, the gap in fuel supply has aggravated the shortage of coal to cement industry, necessitating the search of alternative fuels as well as raw materials.
Various potential Alternative Fuels & Raw Materials (AFR) that are being utilised in the cement industry include pre-processed industrial wastes, sorted municipal solid waste (MSW), discarded tyres and tyre chips, expired medicines and fast-moving consumer goods, waste oils and solvents, non-recyclable plastics, textiles and paper residues, biomass (such as rice husk, coconut shells, groundnut shells, etc.). Efforts are ongoing towards utilisation of Refuse-Derived Fuel (RDF) from MSW and effluent treatment sludge from waste water treatment plants. The use of AFR in the Indian cement industry has been increasing since 2010.
Lime sludge from paper and allied industries is being utilised as a source of raw material for manufacture of cement. The current clinker-to-cement ratio in India is estimated at 0.74, compared to a global average of 0.80.
NCB has investigated a number of waste materials for use as either raw mix component or as a mineral additive in cement manufacture. Some of the investigated materials include different types of slags such as lead-zinc slag, copper slag, steel slag, marble industry waste, barium sludge, spent pot lining waste, ETP sludge, jarosite, spent fluidised catalytic cracking equilibrium catalyst, etc. Some of these waste materials like copper and lead zinc slag, spent pot lining (SPL) waste and barium sludge were also found effective as mineralizers for improving the burning of cement raw mix. Jarosite, a waste from metallic zinc extraction through hydrometallurgical process, was found effective as partial substitute for gypsum for set control of cement. Up to 5 per cent addition of lead-zinc slag, coper slag, steel slag and spent fluidised catalytic cracking equilibrium catalyst is now allowed as performance improver in OPC.
The Indian cement industry is taking constructive steps towards effective and significant utilisation of alternate fuel and alternate raw materials over the last decade. There is a keen requirement to look into solutions towards policy guidelines, lack of waste pretreatment facilities, and commercialisation of futuristic technologies that would further increase the utilisation level of alternate fuel and raw materials.
Is there any visible change in the role played by various pollution control boards?
CPCB initiated the concept of co-processing of waste in cement kilns in 2005 and developed guidelines, including monitoring protocol for co-processing of waste as an energy resource or as an alternate raw material in the cement industry. The waste materials approved for using as an alternate fuel are used tires, meat and bone meal, animal fat, plastics, packaging waste, waste wood, paper, sludge (paper, fibre & sewage), waste oil, coal slurries, spent solvents, etc.
Detailed procedures and guidelines including emission monitoring were published to give permission to industry for quick approval for incineration of wastes in cement kilns and for trial runs. CPCB granted approval for trial runs of various categories of wastes for more than 30 cement plants for co-processing. A bilateral programme on co-processing of wastes from SINTEF, Government of Norway, was initiated to give international exposure to officers of Central and state pollution boards and the environment ministry.
Some of the initiatives taken by CPCB & SPCBs are given below:
Not much is seen to have been done on the use of low grade limestone....
As per Indian Bureau of Mines (IBM), low grade limestone reserves in India are about 32,632 million tonne, 33.5 per cent of the total limestone reserves of 97430 million tonne. In addition, due to the poor and variable quality of coal with high ash content, even a part of the cement grade limestone is turning to be low grade for cement manufacture. Utilisation of low grade limestone must be given immediate attention and priority through development of new type of cement. Low grade limestone can be utilised for cement manufacture through any of the following techniques:
Plants like Ramco Cements and India Cement have limestone beneficiation units at their plants to upgrade the cement raw material and extend the life of mines. NCB is currently investigating the use of low grade limestone as a performance improver in blended cements. Studies are also being taken up to investigate the feasibility of using low grade limestone as a blending component in manufacture of Portland limestone cement and also in newer types of composite cement.
What has been the progress on the use of industrial waste as fuel? Can you also give us more details on co-processing?
The cement industry across the globe is focused on reducing its carbon footprint through utilisation of waste as a social commitment, and also to reduce cost of production. Cement kiln is considered to be the best incinerator for a wide range of wastes with the additional benefit of zero ash generation.
The present thermal substitution rate in the cement industry in Europe is around 40 per cent, as compared to around 1 per cent in India. However, the bigger players, like UltraTech and Holcim, have much higher substitution rates of up to 10 - 15 per cent in some of their plants, due to better planning in capturing the waste market, along with adequate investment for the installation of state-of-the-art technology for sustainable co-processing of industrial waste. The smaller cement manufactures are also working their way ahead to capture a share of the waste market to become more cost competitive.
With the utilisation of latest technologies like gasification and pre-processing of Municipal Solid Waste, oxygen enrichment along with more unified policies from Central Pollution Control Board such as ´polluter to pay´ and taxation for using waste for land filling, similar regulation across the states for waste identification & transport permits and better pre-processing facilities to improve the quality and consistency of industrial waste will increase the overall waste utilisation in the cement industry.
Co-processing is the use of waste as raw material or as a source of energy (or both), to replace natural mineral resources (material recycling) and fossil fuels such as coal, petroleum and gas in industrial processes, in energy intensive industries, such as cement, lime, steel, glass, and power generation. Waste materials used for co-processing are referred to as AFR. To be useable for co-processing they need to be qualified by analysis, selection, pre-processing etc.
Give us some idea on the use of Municipal Solid Waste (MSW) as fuel. Which municipal corporations have been moving towards use of MSW?
MSW is the residential and commercial solid, or semi-solid wastes, generated in a municipal area, including treated bio-medical wastes but excluding industrial hazardous wastes. The composition of municipal waste varies greatly from country to country and region to region and changes significantly with time. In India the biodegradable portion, which mainly includes food and yard waste, dominates the bulk of MSW by making up approximately 50 per cent of the total MSW. Some facts about Indian MSW:
This large amount of MSW can be used to generate energy. Several technologies have been developed that make the processing of MSW for energy generation cleaner and more economical than ever before.
The various technologies for conversion of MSW to fuel are as follows:
Status of MSW as fuel/energy in India
The objective of treating MSW is to reduce its volume and generate energy and electricity during this process. In India, various installations have been established in the recent past for generation of power as well as pre-processing of MSW to RDF. In India, 32 plants have been proposed, four are under construction and 11 are in operation.
What has been the effect on refractory lining where industrial waste is used as fuel? To what extent are the gases coming out of the kiln affected? Does it call for additional precautions?
The different types of industrial wastes used as fuel in cement plants are biomass, RDF from MSW, used tyres and rubber residues, hazardous waste and industrial plastic waste, etc. Besides containing calorific value, these industrial wastes contain various volatile matters like alkalis, sulphur and chlorides.
Plants using AF have an increased risk of refractory failure due to higher input of chloride and sulphur. Fluctuating feed rate of AF due to its inhomogeneity and inconsistent calorific value causes temperature and CO peaks in kilns. These reduce refractory life due to thermal shocks and erosion due to reactions in reducing condition. To compensate variable burnout behaviour and different reaction kinetics, frequency of lengthening and shortening of the flame length increases. This reduces coating stability, resulting in more high temperature exposure to refractory bricks. Increased frequency in ring formation causes refractory spalling. To compensate for fluctuations in heat input by AF and to maintain low sulphur volatility, kiln draft is increased, which increases higher kiln backend temperature and high temperature exposure to refractory bricks. Delayed ignition and longer flame shifts the burning zone towards kiln inlet and reduces coating formation on refractory, causing premature spalling and shorter refractory life.
Contamination of kiln gas with dioxin and furans is very limited as they get destroyed above 1,000 0C and the temperature in the burning zone is at 1,400 to 1,500 0C. Hence dioxin and furans are not an issue in case they are fired in the main burner. Again with lower flame temperature, generation of thermal NOx gets reduced. Hence, the effect on kiln gas due to waste utilisation remains within the environmental limits. However, presence of higher moisture percentage and requirement of more air results in increased exit gas volume, thereby limiting the production.
Additional precautions for reducing the effect of sulphur and chloride volatility are considered in raw mix preparation to maintain the desired alkali to sulphur ratio. High momentum multichannel burners and modern pre-calciners with hot meal staging facility and sufficient residence time are installed along with modifications carried out in clinker cooler for higher secondary air temperature, for increased percentage utilisation of alternate fuel. Enhanced process control as well as monitoring and controlling of key process parameters have reduced the chances of uncontrolled emission at increased percentage of industrial combustible waste utilisation.
The use of specially designed spalling resistant and coating repellent refractory bricks and modifying the mix design of the raw materials are recommended as precautionary measures while using industrial wastes as fuels in cement plants.
What is the target set for industry in terms of Thermal Substitution Rate (TSR)? Will the industry reach the target?
The Indian cement industry is failing to realise the potential for alternative fuels and raw material utilisation, but has resolved to raise TSR to 25 per cent by 2030, from the current level of less than 1 per cent. This was the conclusion of a two-day conference on co-processing in cement plants, convened by the Washington-based Institute for Industrial Productivity (IIP) and the Cement Manufacturers´ Association of India.
At present the TSR is 0.5-1 per cent in the Indian cement industry. The target of 25 per cent TSR appears to be critical for the cement industry due to some policy barriers like absence of ´polluter pays´ policy besides no landfill tax, measures which are significant for enhancing availability of waste to be utilised as alternative fuel.