Possibilities and effects of using waste materials as energy in cement industry

Author: Prof. Dr Aleksandar Jovović, University of Belgrade, Faculty of Mechanical Engineering

Waste is first of all a community and health hazard, and secondarily a resource – the problem needs to be resolved, and the resource used. On the other hand, many analyses have concluded that this century will be a century of cities, which means a century of waste.

However, waste collection through separation at the source is not organized well enough in Serbia, with 19% of waste, or 420,000 tons annually, being disposed without any significant treatment at seven landfills built in line with EU standards, and the rest at unsanitary landfills.

On the other hand, the EU’s Thematic Strategy on the Prevention and Recycling of Waste is aimed at using waste as a resource, primarily for obtaining secondary raw materials and energy, which is one of the goals of the circular economy.

At that, there is no pre-defined best way to treat any waste stream. The best available technologies (BAT) are defined under many regulations and compulsory recommendations. Thermal treatment alone is allowed for certain types of hazardous waste, as only high temperatures and other appropriate technical terms at relevant facilities secure conditions to break down harmful components.

Waste-to-energy in the cement industry

The cement industry worldwide is seeking to increase the use of alternative fuels for production, both to decrease energy dependence on conventional fossil fuels and to mitigate the adverse environmental impact.

The use of waste as alternative fuel in the cement industry began in the 1970s, and the number of cement factories using alternative fuels and materials has since grown worldwide. The waste treatment process development has particularly accelerated in Germany, as well as in many other EU member states, since the adoption of the Landfill Directive in 1999, as well as tight biodegradable waste disposal criteria after 2005.

In order to attain the goals of processing biodegradable waste, it was necessary to speed up the development of pre-treatment and treatment with the aim of reducing the share of organic components, and this is where the use of waste in the cement industry has become very efficient. As a result, the three main factors that led to an exceptional increase in the use of fuel from waste are new obligations concerning municipal waste disposal, their implementation and the implementation of the Kyoto Protocol, and the liberalization of the energy market, which intensified economic pressure on energy producers/consumers.

Today, almost all large cement and building materials producers use waste as fuel, substituting more than 70% of their heat needs (Table 1 and Figure 1).

The main users of fuel from waste are factories of cement manufacturers Cemex, Portlandzementwerk, and Heidelberg Cement in Germany, and Holderbank in Switzerland, while Ciments d’Obourg in Belgium cut out fuel expenses, replacing 80%-90% of fuel with waste.

There have been similar experiences with facilities in Italy (Ambiente, which fully adapted the cement factory in Ravenna to use waste as fuel, and Cementerie Merone), Norway (Dalen, Brevik, Kjopsvik, Slemmenstad), the UK (Blue Circle Westbury Works has been using fuel from municipal waste since 1977 and scrap tires at BC Hope Works and BC Plymstock Works since 1985), and the US, where thermal processing grew especially significant after the Environment Protection Agency (EPA) passed a regulation on the protection and renewal of resources in 1976, even though 25 cement factories had already used one million tons of municipal waste annually as alternative fuel.

The cement industry worldwide is seeking to increase the use of alternative fuels for production, both to decrease energy dependence on conventional fossil fuels and to mitigate the adverse environmental impact.

The environmental advantages of using fuel obtained from waste at rotary kilns for the production of clinker are:

• high kiln temperatures (1800-2000°C) guaranteeing complete waste combustion and breakdown of all components potentially harmful for the environment;
• a material’s long treatment in kilns at temperatures above 1100°C due to a rotary kiln’s length and slow rotation, a technological feature of the cement production process;
• there is no combustion process residue; i.e. all unburned fuel components are embedded into clinker;
• the alkaline conditions during clinker calcination limit the emission of acid gases due to alkaline reactions within a kiln;
• rational investment – an investment in a rotary kiln so that it can use waste as fuel is minimal compared to the construction of a waste incineration facility;
• there are no significant changes of air emissions compared to the use of fossil fuels.

The technological basis of the clinker production process is the rotary kiln with accompanying equipment. Compared to the technological process and construction of a rotary kiln, the primary part of the rotary kiln for the production of clinker, i.e. the kiln burner (where the temperature is the highest) can use not only classic fuel, but also pulverized lignite, solid-recovered fuel (SRF), wood chips, as well as used oils, solvents, and oil fuel. On the other side of the kiln, i.e. its feed, waste tires (car and other tires), waste sludge, etc. can be dosed (Figure 2).

For the process of combustion and clinker sintering, i.e. cement production, to be reliable and in line with quality standards, only separated and sorted waste with a known composition is suitable for the process of co-incineration at cement plants. Accordingly, the following are considered to be alternative fuels (Figure 3):

• Used car tires;
• Meat and bone meal, animal fat;
• Plastics;
• Packaging waste;
• Waste wood, impregnated sawdust;
• Paper and cardboard;
• Sewage sludge, paper sludge;
• Agricultural and organic waste;
• Oil shale;
• Distillation residue;
• Coke of chemical origin;
• Waste oils, oily water;
• Used solvents.

The following types of waste are not used in the process of co-incineration:

• Radioactive waste;
• Electric and electronic waste (EE waste);
• Batteries and vehicle batteries (in their entirety);
• Reactive waste, including explosive waste, waste that contains cyanide and waste that reacts in contact with water;
• Waste containing mercury;
• Waste of unknown or undetermined composition.

Every element of the generation of (obtaining) fuel from waste, its further treatment, examination, determining characteristics important for health safety and health safety and human health, and determining characteristics important for thermal treatment is regulated by technical standards adopted, inter alia, by the Institute for Standardization of Serbia.

Impact of using waste as fuel on air quality

The experience of cement plants used solid fuels from waste as alternative fuels shows that there are no gas and solid particle emissions above the emission limit values (ELV) and no danger that transporting and/or combustion waste materials will lead to a deterioration of air quality in the immediate environment and the greater area where the plant is located. Figure 4 shows that dioxin and furan emissions from a number of different types of facilities using waste as fuel and thermal waste treatment facilities are higher by a multiple factor than the same emissions from cement kilns.

Experiences of cement plants in Serbia are also very positive. Even when fuels of significantly poorer quality than solid recovered fuels (SRF) are co-incinerated, emissions below ELV were measured. (Source: Jovović, A., Radić, D., Stanojević, M., Obradović, M., Todorović, D., Radovanović-Jovin, H., Georgijev, Z., Vujić, B., Šandin, Z., Đurić, T., Popin, D. (2011): Elements of the Environment, Air. Pp. 40-93, in Puzović, S. and Radovanović-Jovin, H. (eds.) The Environment in the Autonomous Province of Vojvodina: Situation-Challenges-Perspectives. The Provincial Secretariat for Zoning, Construction and Environmental Protection, Novi Sad)

Also, modeling air pollution is often use to project extreme emission and meteorological conditions and their environmental impact. As an example, Figure 5 shows the results of modeling carbon monoxide diffusion from the fuel mill and rotary kiln stack, when using SRF at the cement plant. Given the maximum allowed values, it is evident that the facility’s potential impact, in view of certain pollutant components, would be negligible.

Instead of a conclusion

Given that a hazardous waste treatment facility or a hazardous and non-hazardous waste incineration facility cannot be built in Serbia, waste is still exported to countries where facilities are located even in city centers, as part of district heating systems, whereas these countries are the epitome of the quality of life, environmental protection, etc.

The EU’s Thematic Strategy on the Prevention and Recycling of Waste is aimed at using waste as a resource, primarily for obtaining secondary raw materials and energy, which is one of the goals of the circular economy.

However, if there is political will at all levels to resolve this problem, then there will be a way. Not all countries in the world that are environmental leaders today have always acted in such an orderly fashion, nor did Serbia’s population and businesses, up until some 30 years ago, differ significantly from these countries in terms of environmental protection, having even been more progressive in many segments.

The expressions such as “not in my back yard” and “not in my term of office” were coined in the cradle of the waste management system, the United Kingdom. But in time, the population’s confidence was built as awareness of responsibility grew. While Serbia regressed, these countries progressed faster and faster, which is why traveling in EU countries today may seem strange to Serbian citizens. The people are the same, yet there are no plastic bags littering the streets and hanging from the trees, no bones dragged by stray dogs and cats, no gauze and bandages strewn all over parks surrounding clinical centers. Therefore, the question arises as to why the alternative would not be possible in Serbia, if we consider, even for a moment, that this would mean a better quality of life. It would be a historic project for this country to implement an EU-like system of managing waste for all Serbian citizens, which would show that waste can be managed in a proper way.

Experiences gained through the operation of complex chemical-technological systems that existed in the 1970s and the 1980s, restoring certain school courses, and more seriously controlling the facilities’ operations could almost certainly ensure reliable work. At the same time, a ban on hazardous waste exports that will soon take effect in the EU will force Serbia to solve the problem on its own. On the other hand, all these problems also provide an opportunity to profit by investing in the construction and management of such a facility. Using a suitable, possibly energy facility, by allocating a portion of it, could potentially serve as the solution. Until then, and even then, the cement industry and the rest of the construction sector remain a model of responsibility concerning waste management.