Waste Co-processing as Alternative fuel (AF) and Alternative raw material (ARM)

MOHAMMAD MOHIUDDIN

Email: mohin27@yahoo.com

Received 28 April 2012; received in revised form 30 September 2012; online published 1 October 2012

 

Abstract: Hazardous and other waste materials are no longer considered as mere waste, but are treated as valuable resources. Other than generating electricity or preparing manure by processing waste materials, these wastes can be co-processed as alternative fuel or alternative raw material, or in both forms in the resource intensive industries, like cement, steel etc. Only thing that counts is maintaining a number of prescribed process requirements.

 

Introduction

Resource-intensive industries, nowadays, involve the use of waste in manufacturing processes for the purpose of resource recovery and reduction in the use of conventional fuels and/or raw materials through substitution. This phenomenon, the use of wastes as raw material or as a source of energy or both, is familiar as Co-processing. Mainly employed in energy intensive industries (EII) such as cement, lime, steel, glass, paper and power generation (wikipedia1), co-processing is treated as material recycling and energy recovery efforts by replacing the use of natural mineral resources and fossil fuels respectively in industrial processes. Under ideal conditions, good combustion destroys most of the non-metallic, toxic organic compounds in hazardous waste and leaves ash residues which are easier to dispose of than raw, untreated wastes. Co-processing is a popular term of industrial ecology (IE) – a new dimension of the modern business sustainability.In particular, the co-processing of waste in kilns, the subject of appropriate guidelines, allows the recovery of the energy and/or mineral value from waste, while the intended products are being manufactured.

The Basel Convention [2] places obligations on countries that are Parties to ensure the environmentally sound management (ESM) of hazardous  and other wastes. In this regard, the guiding principle, broadly accepted for securing a more sustainable waste management system, is the waste hierarchy of management practices (with due consideration given to the protection of the environment and human health). The hierarchy places waste prevention (avoidance) and operations that may lead to resource recovery, recycling reclamation, direct re-use or alternative uses, in a pre-eminent position relative to operations which do not lead to such possibility. Thus, where waste avoidance is not possible, reuse, recycling and recovery becomes a preferable alternative to non-recovery operations. To this end, co-processing in kilns provides an environmentally sound resource recovery option for the management of hazardous and other wastes, preferable to land-filling and incineration.

 

Alternative Fuel (AF) and Alternative Raw Material (ARM)

Waste materials used for co-processing are referred to as alternative fuels (AF) and alternative raw materials (ARM). Alternative fuels and raw materials are predominantly wastes or by-products from agricultural, domestic, forestry or industrial processes comprising biomass (e.g., rice husk), animal meal, sewage sludge, municipal solid wastes, used tyres, spent solvents, waste oils, etc.

A wide range of hazardous waste materials can be co-processed, such as ETP sludge, paint thinners, paint sludge, refinery sludge, used oil, solvents or end-of-line products from the transport sector, etc. Solids and liquids from the cleanup of past uncontrolled hazardous waste dump sites can also be blended as AF and ARM into hazardous waste streams.

fields (as is the case with agricultural organic waste), methane gas is produced (Kabir and Halim, 2011, ChE Thoughts 2(1), pp 16). Methane, a powerful Greenhouse Gas, is 21 times more potential (Global Warming Potential) than CO2.Replacing traditional fossil fuels with AF will reduce overall greenhouse gas (GHG). Three global problems: a) unsustainable waste management practices, b) the increasing scarcity of fossil fuels, and c) climate change, are the main drivers behind the growing substitution of so-called alternative fuels (AF) for conventional fuels. Replacing traditional fossil fuels with AF reduces overall CO2 emissions because, in their traditional disposal methods, many of the AF used will otherwise generate CO2emissions with no energy recovery. Therefore, emissions generated by the combustion of AF with biomass contents are considered “carbon neutral”. In fact, during the natural decomposition process that occurs when waste is landfilled or left in the fields (as is the case with agricultural organic waste), methane gas is produced (Kabir and Halim, 2011, ChE Thoughts 2(1), pp 16). Methane, a powerful Greenhouse Gas, is 21 times more potential (Global Warming Potential) than CO2.

 

Hazardous wastes not recommended for co-process

Not every kind of waste can be used for co-processing, keeping in view the environment, health, safety and operational concerns. The wastes listed below are normally not recommended for co-processing till otherwise proved/evidenced for.

  • Biomedical waste
  • Asbestos containing waste.
  • Electronic scrap.
  • Entire batteries.
  • Explosives.
  • Corrosives.
  • Mineral acid wastes.
  • Radioactive Wastes.
  • Unsorted municipal garbage.

 

Benefits of Alternative Fuels (AF)

The benefits of substituting alternative fuels (AF) for conventional fuels include:

• Resource saving: By recovering energy from wastes, AF save conventional non-renewable fossil fuels, contributing to the sustainability of our world.

• Waste management: AF offer local communities and governments a neat, final, and environmentally friendly solution to dispose of wastes, effectively avoiding the use and hygienic challenges of landfills. Rapid urbanization with significant increase in municipal solid waste coupled with stringent environmental regulations to reduce landfill disposals are generating worldwide interest in the recovery of energy from Municipal Solid Wastes (MSW).

• Local economic development: In many cases, the economic activity related to the development of the AF supply chain fosters local value creation and employment.

• Climate change mitigation: AF, particularly biomass fuels and the biomass fraction of household wastes, help reduce the CO2 footprint and eliminate emission of this most significant greenhouse gas.

• Potential local environmental benefits: Many AF have also been shown to reduce other kiln emissions—particularly nitrogen oxide (NOx)—thereby enhancing local air quality.

 

Global Practice especially in Cement Kiln– Utilization and Volume of AF

Fossil fuels and raw materials have been successfully substituted by different types of wastes in cement kilns in Europe, Japan, United States, Canada and Australia since the beginning of the 1970s (GTZ/Holcim, 2006).The countries with the largest quantities co-incinerated in cement industry alone were France and Germany (>800,000 tpa) followed by Belgium and Austria (> 100,000 tpa). [3]

 

Technical requirements and Operating conditions for co-processing in Cement Manufacturing:

Although the practice varies among individual plants, cement manufacture can consume significant quantities of wastes as fuel and non-fuel raw materials. This consumption reflects the process characteristics in clinker kilns, which ensure the complete breakdown of the raw materials into their component oxides and the recombination of the oxides into the clinker minerals. The essential process characteristics for the use of hazardous and other wastes, fed to the kiln via appropriate feed points, may be summarised as follows (European IPPC Bureau, 2009) [2]:

–        Maximum temperatures of approximately 2000°C (main firing system, flame temperature) in rotary kilns;

–        Gas retention times of about 8 seconds at temperatures above 1200°C in rotary kilns;

–        Material temperatures of about 1450°C in the sintering zone of rotary kilns;

–        Oxidising gas atmosphere in rotary kilns;

–        Gas retention time in the secondary firing system of more than 2 seconds at temperatures above 850°C; in the precalciner, the                           retention times are correspondingly longer and temperatures are higher;

–        Solids temperatures of 850°C in the secondary firing system and/or the calciner;

–       Uniform burnout conditions for load fluctuations due to the high temperatures at sufficiently long retention times;

–        Destruction of organic pollutants due to the high temperatures at sufficiently long retention times;

–        Sorption of gaseous components like HF, HCl, and SO2 on alkaline reactants;

–        High retention capacity for particle-bound heavy metals;

–        Short retention times of exhaust gases in the temperature range known to lead to formation of polychlorinated dibenzo-p-dioxins               and polychlorinated dibenzofurans (PCDDs/PCDFs);

–        Complete utilisation of fuel ashes as clinker components and hence, simultaneous material recycling and energy recovery;

–        Product specific wastes are not generated due to a complete material utilisation into the clinker matrix (although some cement plants dispose of CKD or bypass dust);

–        Chemical-mineralogical incorporation of non-volatile heavy metals into the clinker matrix.

 

Limiting Factors

Although using alternative fuels is desirable, occasionally they cannot be used due to processing issues, lack of permits or poor availability. While traditional fuels have the disadvantage of high cost, they are generally more uniform and more capable of providing a consistent heat profile. The cost benefits and environmental advantages associated with alternative fuels make them highly desirable for many companies. However, because of factors like limited availability, high entry costs, potential process issues and quality concerns, AF may not be a suitable choice for every plant. Though the cost savings associated with alternative fuels may be significant, there are usually a number of drawbacks that can adversely affect output and product quality to varying degrees. For example, most alternative fuels are usually associated with excess air and high moisture. Co-processing plants should be designed, equipped, built and operated to prevent air pollution, especially at ground level, due to emission. Ambient air quality should be maintained while discharging exhaust gases, so as to safeguard human health and the environment. Above all, the management of the co- processing plant should be in the hands of a skilled person, competent enough to manage the hazardous wastes in an environmentally sound manner.

 

Conclusion

The co-processing of hazardous waste materials in an environment friendly manner is definitely a praiseworthy method of waste disposal; but it can turn into a risky job for the environment as well as for health, if it is handled in non-prescribed way. If the required temperature is not maintained, hazardous gas like dioxin and furan (D&F) may generate, posing great risk to health. Hence, as long as proper provision is not established in the kiln facilities, co-processing of hazardous waste should not be allowed. Moreover, during handling, transportation and co-processing of the waste materials, appropriate safety measures need to be incorporated.

 

Useful References:

  1. Wikipedia – The Free Encyclopedia; http://en.wikipedia.org/wiki/Co-processing; Cited: 12 July, 2012]
  2. Draft technical guidelines on co-processing of hazardous waste in cement kilns (UNEP/CHW/OEWG/7/INF/14, 23 March 2010)
  3. EC- Refuse Derived Fuel, Current Practice and Perspectives, 2003
  4. EIPPCB 2009. Integrated Pollution Prevention and Control Bureau, Draft Reference Document on Best Available Techniques in the Cement, Lime and Magnesium Oxide Manufacturing Industries (May 2009).
  5. Guidelines on Co?processing in Cement/Power/Steel Industry, February 2010, Central Pollution Control Board, India.

 

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