Alternative Fuels: Trends and Prospects
Increasing population and industrialization have created dual problem of energy crisis and waste disposal.
B K Modi
L R Rajasekar
examine the trend towards using incinerable wastes as fuel in cement kilns in lieu of fossil fuels.
With rising population, rapid industrialization and improvement in living standards, the demand for energy is growing continuously. This has put a huge burden on our country's resources with increasing import bills of crude oil. India has the third largest coal reserves in the world and yet the country depends upon coal import to meet its internal requirement. At present, the country consumes almost 70 per cent of domestic coal for electricity generation and the rest for other usage. It is expected that at the current rate of coal consumption, the reserves in India will be exhausted in the next 70 years. To tackle the situation, we must look for alternative substances that can be used as fuel. The Government of India has recently announced new policies focusing on improving energy efficiency through the "Perform - Achieve - Trade" scheme and the compulsory usage of renewable energy through regulation on Renewable Purchase Obligation.
Using waste generated in our urban centres and by our industries, is one of the ways in which we can tackle the issue of fuel shortages in India. The quantum of waste generated varies across urban centres, depending upon several factors like lifestyle, population density, industrialization, etc. It is estimated that 11 Indian cities generate more than 1,000 tonnes of wastes daily and Mumbai alone generates more than 5,000 tonnes of solid waste daily. A significant portion of the waste contains organic matter, paper, cardboard, plastic, rubber, etc. These materials have good calorific value and therefore, present the option of using the waste as an alternative fuel. In addition, there are hazardous industrial wastes like paints, sludge, oil etc. that can be used as alternative fuel. The existing mechanism of disposal for municipal wastes is mostly through land-filling that is difficult, costly and associated with long-term health hazards. At the same time, most of the industrial wastes from different sectors are land-filled or find their way in alternate applications within the unorganized sectors posing significant health risk to the society.
Thus with increasing industrialization and population we have on one hand an ever increasing demand for energy and on the other, we are confronted with the problem of tackling wastes. A status report by IEA Coal Research shows that the worldwide trend is to find alternate ways of disposing wastes in useful manner, and burning them in cement kilns is one of the best and the safest ways.
Use of Municipal and Hazardous Wastes
Traditionally, the burning of wastes started in specifically designed incinerators, which were sometimes equipped with power generating units. Over the years, the cement kiln emerged as a better alternative to the incinerator because of some of its inherent characteristics. The concept found wide acceptability in developed countries. The following sections show the feasibility of burning wastes in Indian cement kilns.
The developed countries have been using wastes for over two decades to generate energy. Based on their experience, it has been found that the cement kilns are highly suitable for burning wastes. This is mainly due to the following reasons:
• High flame temperatures (2000oC) - ensures complete destruction of harmful pollutants.
• Residence time of combustion gases above 1000oC in excess of 3 - 4 seconds - ensures complete destruction of pollutants.
• Complete scrubbing of exhaust gases due to countercurrent flow of raw material - resulting in trapping of heavy metals, sulphur and other pollutants within the clinker.
• Inclusion of ashes and residual metals from the wastes within the clinker crystal structure.
• Kiln lines are equipped with ESPs/Bag Filters - ensuring negligible particulate emission.
• Intense contact between solid and gas phases - ensures condensation of volatiles, absorbs SO2 and neutralizes acid gases.
Cement kilns present an opportunity where burning waste is a recovery operation. This is because of the fact that the combustible parts of the waste replace fossil fuels and the non-combustible parts replace raw materials like silica, iron, etc. The environmental impact is negligible and the energy efficiency is the highest compared to incineration equipped with power generation. At the same time, the option offers benefits to the society in the following form:
• Conservation of non-renewable fossil fuels like coal/gas.
• Reduction in environmental impact related to coal mining
• No need for investment in incinerators.
• Overall lower CO2 and methane emissions by replacement of fossil fuel - Otherwise leading to burning of hazardous wastes in incinerators and fossil fuel in kilns.
• Conservation of raw materials for cement industry as hazardous wastes partially replaces some of the materials like silica, iron, etc.
The process problems associated with burning wastes in cement kilns can be tackled by adopting suitable technological changes and through process mastery.
Impact on Environment
The most important aspect is the likely impact of burning wastes in cement kiln. The results do not show any significant negative impact. The emission results measured in cement kiln burning wastes to the extent of 75 per cent of total fuel value have been reproduced in Table 1.
It can be seen from the table that the stringent emission limits are met for all the harmful substances in spite of the wastes constituting up to 75 per cent of fuels in some of the kilns. These results are comparable with measurements with 100 per cent fossil fuels. Thus, the burning of wastes in kiln is environmentally compatible and technically sound, where organic matter is destroyed at high temperatures and inorganic matter is trapped in clinker. The added advantage comes from the overall lower emissions of green house gases due to replacement of fossil fuels.
Impact on Product Quality
The users of waste reported that there is no problem with regard to clinker or cement quality with waste as fuel. However, it is of utmost important to adjust raw mix, process conditions and fuel rate to stabilize clinkerisation. In addition, before burning the waste, it is necessary to study the compatibility of waste with existing raw mix and desired product quality.
A comparison between product quality with 100 per cent fossil fuels and with waste is reproduced in Table 2. There does not appear to be any significant difference in product quality, which can affect the end applications.
UltraTech took the initiative in the cement industry in India for burning waste in cement kilns in 2004. The company started taking trials at its facilities at Malkhed in Karnataka and Reddipalayam in Tamil Nadu as early as 2005, in collaboration with Central and state pollution control boards and waste generators. The trials were conducted at different facilities of the companies involving wastes like effluent treatment plant sludge, paint sludge, plastic, tyre chips, pharmaceutical waste, etc. The results showed no impact on environment and product quality. After getting the clearance from pollution control boards, the company has been using the approved wastes as fuel substitutes.
The plant located at Reddipalayam in Tamil Nadu uses agricultural wastes (rice husk, cashew nut shells, corn waste, groundnut husk, coconut coir etc), tyre chips, refuse derived fuels and industrial wastes. This facility has successfully used up to 10-14 per cent wastes as fuels over the last 5 years.
In a commendable example of public-private partnership, UltraTech Cement (at that time the legalities were completed by Grasim Industries) entered into an agreement with Jaipur Municipal Corporation to set up MSW processing plant at Langriyawas village, about 26 km from Jaipur in Rajasthan. Spread over 25 acres of land, the plant is based on German technology that converts MSW into refuse-derived fuels (RDF). Commissioned in January 2007, the plant is capable of extracting 150 tonnes of RDF per day from 500 tonnes of municipal waste, which is supplied by the Jaipur Municipal Corporation daily. The processed RDF is successfully disposed off at UltraTech's cement facility located at Khor, Madhya Pradesh. This unique initiative has helped in containing the ever-increasing problem of dealing with municipal waste by saving on landfill sites and creating a healthy pollution-free environment for future generations.
Apart from the above, several other cement facilities of UltraTech located in Andhra Pradesh, Rajasthan and Gujarat have been working with local pollution authorities and waste generators to dispose of wastes in cement kilns. For the last two years, the company has been disposing over 69,000 tonnes of waste successfully substituting around 1.15 per cent of its fossil fuel requirement and thus saving around 0.1 million tonnes of CO2 emission annually.
The cement industry has been closely working with the Central Pollution Control Board (CPCB) and other stake holders. The trials for burning several types of waste started in 2004-05 under the guidance of pollution control boards. After several trials across different plants, CPCB finally released the co-processing guidelines in Feb 2010, which provide a framework for burning of wastes in cement kilns.
The entire concept of waste disposal in developed countries is based on "Polluters' Pay" principle, where the waste generators either pay heavy land-fill taxes for land-dumping of wastes or dispose off incinerable wastes in cement kilns by paying a service charge to cement plant. The "Polluters' Pay" principle is yet to be institutionalized in India in its true spirit by way of discouraging the waste generators to opt for land-filling.
With increasing population and industrialization, India is facing the dual problem of energy crisis and waste disposal. UltraTech has been trying to turn this problem into an opportunity and win-win-win situation for waste generators, society and the company, as has been done globally. The incinerable wastes generated from various industrial segments and municipalities can be used as fuel in cement kilns by replacing fossil fuel. It is worthwhile to note that 1,000 tonnes of municipal waste can meet the energy requirement of a one million tonne cement plant.
UltraTech has been providing this service to waste generators over the last five years and some of its cement plants have successfully disposed off wastes to the tune of 15 per cent of fuel requirement. However, the long-term success lies in cohere policy on the subject to discourage land-filling along with creation of suitable infrastructure in accordance with the principles of "Polluters' Pay".