Environmental Best Practices for MENA Cement Industry

Cement production in MENA region has almost tripled during the last 15 years, mainly on account of high population growth rate, rapid urbanization, increasing industrialization and large-scale infrastructural development. The growth of cement industry in MENA is marked by factors that are directly connected with sustainability, energy efficiency and raw material supply. Although the factors differ from country to country and cannot be generalized, there are major concerns regarding shortage of raw materials, GHG emissions, dependence on fossil fuels and lack of investment in technological innovations.

For the MENA cement sector, key points for an environment-friendly industry are use of alternative raw materials and alternative fuels, energy-efficient equipment and green technologies. As the use of alternative fuels and raw materials is still uncommon in the Middle East, guidelines and regulatory framework have to be defined which can set standards for the use of alternative or waste-derived fuels like municipal solid wastes, dried sewage sludge, agricultural wastes, drilling wastes etc.

Sewage Sludge

An attractive disposal method for sewage sludge is to use it as alternative fuel source in a cement kiln. Dried sewage sludge with high organic content possesses a high calorific value. Due to the high temperature in the kiln the organic content of the sewage sludge will be completely destroyed. The resultant ash is incorporated in the cement matrix. Infact, several European countries, like Germany and Switzerland, have already started adopting this practice for sewage sludge management.

The MENA region produces huge quantity of municipal wastewater which represents a serious problem due to its high treatment costs and risk to environment, human health and marine life. Sewage generation across the region is rising by an astonishing rate of 25 percent every year. Municipal wastewater treatment plants in MENA produce large amounts of sludge whose disposal is a cause of major concern.

For example, Kuwait has 6 wastewater treatment plants, with combined capacity of treating 12,000m³ of municipal wastewater per day, which produce around 250 tons of sludge daily. Similarly Tunisia has approximately 125 wastewater treatment plants which generate around 1 million tons of sewage sludge every year. Currently most of the sewage is sent to landfills. Sewage sludge generation is bound to increase at rapid rates in MENA due to increase in number and size of urban habitats and growing industrialization.

The use of sewage sludge as alternative fuel is a common practice in cement plants around the world, Europe in particular. It could be an attractive business proposition for wastewater treatment plant operators and cement industry in the Middle East to work together to tackle the problem of sewage sludge disposal, and high energy requirements and GHGs emissions from the cement industry.

Use of sludge in cement kilns will led to eco-friendly disposal of municipal sewage

Use of sludge in cement kilns will led to eco-friendly disposal of municipal sewage

Sewage sludge has relatively high net calorific value of 10-20 MJ/kg as well as lower carbon dioxide emissions factor compared to coal when treated in a cement kiln. Use of sludge in cement kilns can also tackle the problem of safe and eco-friendly disposal of sewage sludge. The cement industry accounts for almost 5 percent of anthropogenic CO2 emissions worldwide. Treating municipal wastes in cement kilns can reduce industry’s reliance on fossil fuels and decrease greenhouse gas emissions.

Municipal Solid Wastes and Biomass

Alternative fuels, such as refuse-derived fuels or RDF, have very good energy-saving potential. The substitution of fossil fuel by alternative sources of energy is common practice in the European cement industry. The German cement industry, for example, substitutes approximately 61% of their fossil fuel demand. Typical alternative fuels available in MENA countries are municipal solid wastes, agro-industrial wastes, industrial wastes and crop residues.

The gross urban waste generation quantity from Middle East countries has crossed 150 million tons per annum. Bahrain, Saudi Arabia, UAE, Qatar and Kuwait rank in the top-ten worldwide in terms of per capita solid waste generation. Solid waste disposal is a big challenge in almost all MENA countries so conversion of MSW to RDF will not ease the environmental situation but also provide an attractive fuel for the regional cement industry. Tens of millions of tyres are discarded across the MENA region each year. Scrap tyres are are an attractive source of energy and find widespread use in countries around the world.

Agriculture plays an important role in the economies of most of the countries in the Middle East and North Africa region.  Despite the fact that MENA is the most water-scarce and dry region in the world, many countries in the region, especially those around the Mediterranean Sea, are highly dependent on agriculture. Egypt is the 14th biggest rice producer in the world and the 8th biggest cotton producer in the world. Similarly Tunisia is one of the biggest producers and exporters of olive oil in the world. Such high biomass production rates should be welcomed by the cement industry since these materials comprise cotton stalks, rice husks and rice straw which serve ideally as alternative fuels. However it is ironical that olive kernels – the waste from Tunisian olive production – is exported to European power plants in order to save fossil fuel-derived CO2 emissions there, while Tunisia imports approximately 90% of its energy demand, consisting of fossil fuels.

Drilling Wastes as Alternative Raw Material

The reduction of clinker portion in cement affords another route to reduce energy consumption. In particular, granulated blast furnace slags or even limestone have proven themselves as substitutes in cement production, thus reducing the overall energy consumption. The Middle East oil and gas industry has made a lot of effort in order to reduce the environmental impact of their activities. The use of drilling wastes and muds is preferable in cement kilns, as a cement kiln can be an attractive, less expensive alternative to a rotary kiln. In cement kilns, drilling wastes with oily components can be used in a fuel-blending program to substitute for fuel that would otherwise be needed to fire the kiln.

Conclusions

The cement industry can play a significant role in the sustainable development in the Arab countries, e.g. by reducing fossil fuel emissions with the use of refused derived fuels (RDF) made from municipal solid waste or biomass pellets. The cement companies in the Middle East can contribute to sustainability also by improving their own internal practices such as improving energy efficiency and implementing recycling programs. Businesses can show commitments to sustainability through voluntary adopting the concepts of social and environmental responsibilities, implementing cleaner production practices, and accepting extended responsibilities for their products.  

The major points of consideration are types of wastes and alternative fuels that may be used, standards for production of waste-derived fuels, emission standards and control mechanisms, permitting procedures etc. Appropriate standards also need to be established for alternative raw materials that are to be used for clinker and cement production.

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Deleterious Impact of Tire-Burning Kilns

Decorative arts such as woodworking, weaving as well as ceramics and other pottery have a long and honored tradition.  In fact, some of the earliest examples of pottery originate from the Middle East from the time of 6500 BC. In order to meet the ceramic industry’s high energy demand, much of the developing world, MENA in particular, is resorting to cheaper alternatives such as fueling kilns by burning tires and other harmful materials. Though modern technology has led to clean and efficient kiln usage in the developed world, these options come with a high price tag when referring to industrial demands for ceramics and other fired products.

Burning of tires and other rubber materials as a primary source of energy for kilns is particularly concerning.  In other areas of the world, like India, where the concerns lie in the harmful effects of coal-fired kilns, areas like Morocco and other North African countries are dealing with harmful impacts of tire burning. While burning tires does provide an efficient source of energy, the harmful effects of such burning far exceed the benefits. 

Scrap tires are used as a supplement to traditional fuels such as coal or wood fuel because of their high heating value. Typically, for each pound of scrap tire rubber burned it equates to 15,000 BTUs of energy and a single tire can burn for up to 50 minutes.  This equates to 25 percent more energy being produced than coal. Regardless of the efficiency, the fumes that are being released from tire burning have been shown to be extremely toxic to human health and harmful to the environment. 

Dangers to Public Health

Open tire fire emissions include "criteria"pollutants, such as particulates, carbon monoxide (CO), sulfur oxides (SOx), oxides of nitrogen (NOx), and volatile organic compounds (VOCs). They also include "non-criteria" hazardous air pollutants (HAPs), such as polynuclear aromatic hydrocarbons (PAHs),dioxins, furans, hydrogen chloride, benzene, polychlorinated biphenyls (PCBs); and metals such as cadmium, nickel, zinc, mercury, chromium, and vanadium.

Both criteria and non-criteria pollutants can cause significant short and long term health effects.  Depending on the length and degree of exposure, these health effects could include irritation of the skin, eyes, and mucous membranes, respiratory effects, central nervous system depression, and cancer.  The EPA suggests that any unprotected exposure to these emissions be avoided.  Furthermore, uncontrolled tire burning has been proven to be 16 times more mutagenic, meaning capable of inducing genetic mutation, than traditional residential wood combustion in a fireplace, and 13,000 times more mutagenic than coal-fired utility emissions with good combustion efficiency and add-on controls.

Especially troubling is the exposure that children living within these communities are inadvertently being subjected to. Children, foetuses, nursing babies, elderly, asthmatics, and immune suppressed individuals are all much more vulnerable to the pollutants released burning tires. Even a nursing woman can transfer the pollutions she inhales to a baby through the fat in her breast milk.  During breast-feeding, infants are exposed to higher concentrations of organic pollutants than at any subsequent time in their lives. Burning tires only adds to that toxic burden. Saving money on fuel by burning tires should not take precedence over public health. Unfortunately, in small villages and other underdeveloped areas where tire burning kilns sustain much of the local economy, exposure to these toxins is inevitable with the current practices being employed.  

Huge Environmental Costs

In addition to the negative effects tire burning has on the health of humans, it also has environmental costs that have not yet been discussed. The three main effects tire burning has on the environment is air, water, and soil pollution.   The airborne pollution caused from the tire burning kilns is significant.  The black fumes contain heavy metals and other harmful pollutants that linger in the air and can lead to acute to chronic health hazards. 

In terms of water and soil pollution, according to the EPA, “for every million tires consumed by fire, about 55,000 gallons of runoff oil can pollute the environment unless contained and collected”.  If uncontained, this runoff can then be carried away by rainwater to local water sources contaminating them.  Additionally, the remaining residue can cause two types of pollution; these are immediate pollution by liquid decomposition products penetrating soil, and gradual pollution from leaching of ash and unburned residues following rainfall or other water entry.

While the burning of tires is not considered recycling, there is an argument regarding whether it is worse to landfill tires or reuse them to recover energy.  While even in the United States the Environmental Protection Agency (EPA) recognizes that the use of tire-derived fuels is a viable alternative to the use of fossil fuels, there are other factors that need to be considered.  For instance, in more developed areas of the world, regulations are in place such as the Clean Air Act which minimizes the amount of emissions being released by businesses as well as the fact that technology exists that can help clean and filter the emissions before they are released into the air. On the other hand, in less developed areas of the world, environmental regulations and technology of this magnitude may not exist thus,exposing those citizens to more of the environmental and health related effects of uncontrolled tire burning.  While many factors contribute to either argument, all in all this particularly issue is under examined and results in the impairment of health and the safety of entire communities in the developing world. 

References

Air Emissions from Scrap Tire Combustion. (1997) (pp. 1-117). Washington, DC.: United States Environmental Protection Agency.

Frequent Questions. (2013). 2014, from http://www.epa.gov/epawaste/conserve/materials/tires/faq.htm#ques14

Gratkowski, M. T. (2012). Burning Characteristics of Automotive Tires. Fire Technology, 50(2), 379-391. http://link.springer.com.www.libproxy.wvu.edu/article/10.1007/s10694-012-0274-9/fulltext.html#Sec11

Mayer, J. (2005). Tire burn could cause children severe harm. 2014, from http://www.lesspollution.org/my_turn.html

Potential Environmental Impact of Uncontrolled Tyre Fires. (from 2008, ongoing.). 2014, from http://www.mfe.govt.nz/publications/waste/end-of-life-tyre-management-jul04/html/page6.html

Tire Fires. (2013). 2014, from http://www.epa.gov/osw/conserve/materials/tires/fires.htm

Tire-Derived Fuel. (2012). 2014, from http://www.epa.gov/osw/conserve/materials/tires/tdf.htm

 

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Production and Applications of Crumb Rubber

Tens of millions of tires are discarded across the Middle East every year. Disposal of  waste tires is a challenging task because tires have a long life and are non-biodegradable. The traditional method of waste tires management have been stockpiling or illegally dumping or landfilling, all of which are short-term solution. 

Crumb rubber is a term usually applied to recycled rubber from automotive and truck scrap tires. There are two major technologies for producing crumb rubber – ambient mechanical grinding and cryogenic grinding. Of the two processes, cryogenic process is more expensive but it produces smoother and smaller crumbs.

Ambient Mechanical Grinding

In ambient mechanical grinding process, the breaking up of a scrap tire happens at or above normal room temperature. Ambient grinding is a multi-step technology and uses whole or pre-treated car or truck tires in the form of shred or chips, or sidewalls or treads. The rubbers, metals and textiles are sequentially separated out. Tires are passed through a shredder, which breaks the tires into chips.

The chips are fed into a granulator that breaks them into small pieces while removing steel and fiber in the process. Any remaining steel is removed magnetically and fiber through a combination of shaking screens and wind sifters. Finer rubber particles can be obtained through further grinding in secondary granulators and high-speed rotary mills.  

Ambient grinding is the production process used by the majority of crumb producers. The machines most commonly used for fine grinding in ambient plants are:

  • Secondary granulators
  • High speed rotary mills
  • Extruders or screw presses
  • Cracker mills

Cryogenic Grinding

Cryogenic grinding refers to the grinding of scrap tires at temperatures near minus 80oC using liquid nitrogen or commercial refrigerants. Cryogenic processing generally uses pre-treated car or truck tires as feedstock, most often in the form of chips or ambiently produced granulate.

Processing takes place at very low temperature using liquid nitrogen or commercial refrigerants to embrittle the rubber. It can be a four-phase system which includes initial size reduction, cooling, separation, and milling. The material enters a freezing chamber where liquid nitrogen is used to cool it from –80 to –120 °C, below the point where rubber ceases to behave as a flexible material and can be easily crushed and broken.

Because of its brittle state, fibres and metal are easily separated out in a hammer mill. The granulate then passes through a series of magnetic screens and sifting stations to remove the last vestiges of impurities. This process requires less energy than others and produces rubber crumb of much finer quality.  

Applications of Crumb Rubber

Both ambient and cryogenic processing can be repeated to produce finer particles. Increasingly, the two with their attendant technologies, are combined into one continuous system in order to benefit from the advantages and characteristics of each and to reduce overall costs.

The ambient system is generally used for the initial size reduction phases. The cryogenic system is used to further reduce the material in size and then to remove the metals and textiles. The outputs from either or both systems can be used directly or as feedstock for further processing.

Rubber crumb is sold as feedstock for chemical devulcanization or pyrolysis processes, added to asphalt for highway paving and pavement sealers, or used for the production of a large number of recycled rubber-containing products. Some of the major applications of crumb rubber are as follows:

Sport Surfaces

  • Kindergarten Playgrounds and Recreation Areas
  • School Sports Areas
  • Athletic Tracks
  • Tennis and Basketball Courts

Automotive Industry

  • Bumpers
  • Splash Guards and Fenders
  • Floor Mats for Cars and Trucks
  • Floor Liners for Trucks and Vans

Construction

  • Hospital, Industrial, and Bathroom Flooring
  • Floor Tile
  • Foundation Waterproofing
  • Dam, Silo, and Roof Liners

Geotechnical/Asphalt Applications

  • Rubberized Asphalt for Roads and Driveways
  • Drainage Pipes
  • Soil Conditioner
  • Porous Irrigation Pipes
  • Road Building and Repair

Adhesives and Sealants:

  • Adhesives and Sealing Compounds
  • Textured and Non-Slip Paints
  • Roof Coating and Waterproofing

Shock Absorption and Safety Products

  • Shock Absorbing Pads for Rails and Machinery
  • Sound Barriers for Highways
  • Abrasion Lining in Mining Equipment

Rubber and Plastic Products

  • Pipe Insulation and Lining
  • Garbage Cans
  • Shoe Soles and Heels
  • Wire and Cable Insulation