Fuel Pellets from Solid Wastes

MSW is a poor-quality fuel and its pre-processing is necessary to prepare fuel pellets to improve its consistency, storage and handling characteristics, combustion behaviour and calorific value. Technological improvements are taking place in the realms of advanced source separation, resource recovery and production/utilisation of recovered fuel in both existing and new plants for this purpose. There has been an increase in global interest in the preparation of Refuse Derived Fuel (or RDF) containing a blend of pre-processed MSW with coal suitable for combustion in pulverised coal and fluidised bed boilers.

Pelletization of Urban Wastes

Pelletization of municipal solid waste involves the processes of segregating, crushing, mixing high and low heat value organic waste material and solidifying it to produce fuel pellets or briquettes, also referred to as Refuse Derived Fuel (RDF) or Process Engineered Fuel (PEF) or Solid Recovered Fuel (SRF). The process is essentially a method that condenses the waste or changes its physical form and enriches its organic content through removal of inorganic materials and moisture. The calorific value of RDF pellets can be around 4000 kcal/ kg depending upon the percentage of organic matter in the waste, additives and binder materials used in the process.

The calorific value of raw MSW is around 1000 kcal/kg while that of fuel pellets is 4000 kcal/kg. On an average, about 15–20 tons of fuel pellets can be produced after treatment of 100 tons of raw garbage. Since pelletization enriches the organic content of the waste through removal of inorganic materials and moisture, it can be very effective method for preparing an enriched fuel feed for other thermo-chemical processes like pyrolysis/ gasification, apart from incineration.

Pellets can be used for heating plant boilers and for the generation of electricity. They can also act as a good substitute for coal and wood for domestic and industrial purposes. The important applications of RDF in the Middle East are found in the following spheres:

  • Cement kilns
  • RDF power plants
  • Coal-fired power plants
  • Industrial steam/heat boilers
  • Pellet stoves

The conversion of solid waste into briquettes provides an alternative means for environmentally safe disposal of garbage which is currently disposed off in non-sanitary landfills. In addition, the pelletization technology provides yet another source of renewable energy, similar to that of biomass, wind, solar and geothermal energy. The emission characteristics of RDF are superior compared to that of coal with fewer emissions of pollutants like NOx, SOx, CO and CO2.

RDF production line consists of several unit operations in series in order to separate unwanted components and condition the combustible matter to obtain the required characteristics. The main unit operations are screening, shredding, size reduction, classification, separation either metal, glass or wet organic materials, drying and densification. These unit operations can be arranged in different sequences depending on raw MSW composition and the required RDF quality.

Various qualities of fuel pellets can be produced, depending on the needs of the user or market. A high quality of RDF would possess a higher value for the heating value, and lower values for moisture and ash contents. The quality of RDF is sufficient to warrant its consideration as a preferred type of fuel when solid waste is being considered for co-firing with coal or for firing alone in a boiler designed originally for firing coal.

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Sustainability in MENA Cement Industry

The population in the MENA countries has doubled during the last 30 years (from ca. 110m in 1980 to almost 220m in 2010). As per conservative estimates, the rate of urbanisation in the MENA countries will exceed 70% five years from today (average for all developing countries: 54%). The proceeding urbanisation and the population increase involve several problems and challenges for the national governments and also for the cement industry. The cement production of countries in the MENA region has almost tripled during the last 15 years up to approximately 500m tons  Since the start of national revolts and demonstrations in MENA countries in 2011 the problems of especially young Arabs have attracted the attention worldwide.

Environmental problems that accompany a fast growing population and increasing urbanisation are, among others, increasing consumption of energy and raw materials, increasing land use in order to satisfy the increasing food demand, infrastructure development, disposal of increasing amounts of waste and development of sewage systems. Solving these generation spanning problems is a challenging task for the national governments.

Naturally, such high growth rates also affect the cement industry. In the MENA countries it consists of various companies, part of them listed on the stock exchange. A number of cement companies has, partly for cost aspects, responded to the negative consequences of the rapid population growth. The following paragraphs describe the cement industry’s approaches to push a sustainable development in certain sectors. They are partly driven by own responsibility and partly by regulations of the national governments. In this context it should be mentioned that the growth of the cement industry is already partly limited by factors that are directly connected with sustainability and raw material supply.

Although the factors differ from country to country and cannot be generalised, there are a few major concerns, for example:

  • Fuel shortage
  • Dependence on oil
  • Lack of investment in innovations

Let’s have a closer look on the limiting factors and innovation potential based on practical examples.

Saudi Arabia

In many industrialised countries the continuous and tailored supply of the industry with fossil fuels is only a question of price.  But the fact that of all countries, it was cement plants in the own country that repeatedly reported shortages of fossil fuel supply (heavy fuel oil), was certainly an important reason for the government to get closely involved in this matter.

Cement producers in the Kingdom of Saudi Arabia obtain state-subsidised natural gas at a price of US$ 0.75/mmbtu from the state-owned oil company “Saudi Aramco”. Formerly, the cement production costs resulting thereof were on average US$ 28.8/ton of cement (costs in neighbouring countries: Kuwait US$ 59.2/ton, UAE US$ 47.8/ton, Oman US$ 37.0/ton) which made it redundant to deal with the topic of energy. In India, a country with one of the highest energy costs in the world, the production of one ton of cement costs US$ 70.0/ton in 2010.

Due to such low energy prices and a steadily growing demand the production capacities grew constantly. Currently, the industry accounts for approximately 40% of the overall energy demand of the country. Analysts estimate that this demand will even double within the next 15 years. However, it is planned to reduce this disproportionate energy demand of the industry.

Under the patronage of HRH Prince Abdulaziz bin Salman, the state-owned oil company “Saudi Aramco” is developing a so-called “Mandatory Energy Efficiancy Program” (MEEP) for the entire Saudi-Arabian industry. The plan of MEEP is to “establish mandatory policies and regulations with the objective of reducing existing and future energy consumption levels in the industrial sector”.

For the national cement industry this approach implies investments in energy-saving measures. Key points for an energy-efficient industry are identified as

  • Use of alternative raw materials
  • Use of alternative fuels
  • Training and education in energy efficiency

As the use of alternative fuels and raw materials is not yet common in the Kingdom of Saudi Arabia, guidelines and a regulatory framework have to be defined which set standards for the use of alternative or waste-derived fuels like municipal solid wastes, dried sewage sludge, drilling wastes and others. It has to include:

  • Types of wastes and alternative fuels that may be used by the cement industry
  • Standards for the production of waste-derived fuels
  • Emission standards and control mechanisms while using alternative fuels
  • Standards for permitting procedures

Appropriate standards also need to be established for alternative raw materials that are to be used for clinker and cement production. In order to achieve an energy-efficient production special education, further training and workshops for the involved staff have to be carried out.

Egypt

The current political developments in Egypt influence the local cement industry significantly. The government expects additional sources of revenue on the one hand from selling licences for the construction of new cement plants and on the other hand from a reduction of subsidies for fossil fuels. Since these news are not a surprise for the local cement plants, they started to invest in the implementation of alternative – mostly biomass-derived fuels. One of them is CemexAssiut that not only started using different kinds of biomass, but also, most notably and exemplary, established plantations for the production of biomass (here: “Casuarina”) that are irrigated with pretreated sewage water from the city Assiut.

Egypt is the 14th biggest rice producer in the world and the 8th biggest cotton producer in the world. Egypt produced about 5.67 million tons of rice and 635,000 tons of cotton in 2011. The area of cotton crop cultivation accounts for about 5% of the cultivated area in Egypt. The total amount of crop residues is about 16 million tons of dry matter per year. Cotton residues represent about 9% of the total amount of residues. Such high 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.

The use of waste-derived alternative fuels is, however, more complicated. Although for example Cairo produces some 15,000 tons of waste each day, it is not easy for the cement plants to obtain this waste since they are in direct competition with the informal sector that controls approx. 60% of the local waste total. So-called Zabbaleen or scavengers – mostly young people who do not have other options – make their living by collecting and selling waste-derived recyclables.

Tunisia

Some years ago, Tunisia already invested in the establishment of an organised waste management system in form of a state-owned agency named “ANGED”. Funded by the national German KfW development bank, numerous waste collection points as well as organised landfills have been built. Additionally, a special collection centre for hazardous waste was erected in Jradou. This centre was operated by MVW Lechtenberg’s Partner Nehlsen AG, the German Waste Management Group, collecting and processing wastes like used oils and solvents. Such wastes are ideal alternative fuels. A fact that is also known to the local cement companies that planned to use them in their plants. Unfortunately, due to public opposition the centre was closed and the projects for the processing of alternative fuels have been suspended since then.

Tunisia is one of the biggest producers and exporters of olive oil in the world. It also exports dates and citrus fruits that are grown mostly in the northern parts of the country. It seems paradox that for example 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 fuel.

Morocco

The Moroccan cement industry has already achieved a greater success regarding the use of alternative fuels. Cement plants, mostly owned by the international companies Lafarge, Cimpor, Holcim and Italcimenti, already invested years ago in the environmentally friendly use of alternative fuels and alternative raw materials due to the development of world market prices. Also the only local competitor, CIMAT, has started preparing for the implementation of alternative fuels immediately after completion of its new plant (a 5-stage double string calciner from Polysius) in Ben Ahmed, near Casablanca.

In the year 2003 an agreement on the use and import of alternative fuels (used tyres at the time) was made between the Association Professionelle de Ciment and Moroccan government. Since last year attempts are being made to agree on an industry regulation that sets standards for the use of all appropriate special waste available in Morocco.

United Arab Emirates

The United Arab Emirates, represented by Dr. Rashid Ahmad Bin Fahd, Minister of Environment and Water, recently issued a decision streamlining the activities of cement plants all over the country. The resolution will affect all existing and new cement factories across the country. Its provisions obligate the industry to prepare a report assessing the impact of cement plants on the environment.

According to the decision, this report has to be prepared by a consulting firm having expert knowledge regarding environmental protection in the cement industry. This is certainly the first step to evaluate the current situation which will be followed by an investigation of alternatives towards a sustainable development. Interest in the implementation of alternative fuels already exists among the national cement industry which is proven not least by the numerous planned investment projects.

Conclusions

The cement industry in the MENA region will change significantly within the next years. This change will focus on the improvement of energy efficiency and on the increased use of alternative raw materials and alternative fuels. This will include high investments in technology and in the human resources sector where the creation of new jobs, especially in the field of environmentally friendly and sustainable development, provides a perspective for the growing, young population of the MENA countries.

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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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Energy Efficiency in Saudi Cement Industry

Saudi Arabia is the largest construction market in the Middle East, with large development projects under way and many more in the planning stage. The cement industry in the country is evolving rapidly and is expected to reach annual clinker production of 70 million tonnes in 2013 from current figure of 60 million tonnes per year. The cement industry is one of the highest energy-intensive industries in the world, with fuel and energy costs typically representing 30-40% of total production costs. On an average, the specific electrical energy consumption typically ranges between 90 and 130 kWh per tonne of cement. Keeping in view the huge energy demand of the cement industry, the Saudi Arabian government has been making efforts to reduce the energy consumption in the country towards a more sustainable.

Energy Demand in Cement Production

The theoretical fuel energy demand for cement clinker production is determined by the energy required for the chemical/mineralogical reactions (1,700 to 1,800 MJ/tonne clinker) and the thermal energy needed for raw material drying and pre-heating. Modern cement plants which were built within the last decade have low energy consumption compared to older plants.  The actual fuel energy use for different kiln systems is in the following ranges (MJ/tonne clinker):

  • 3,000 – 3,800 for dry process, multi-stage (3 – 6 stages) cyclone preheater and precalcining kilns,
  • 3,100 – 4,200 for dry process rotary kilns equipped with cyclone preheaters,
  • 3,300 – 4,500 for semi-dry/semi-wet processes (e.g. Lepol-kilns),
  • Up to 5,000 for dry process long kilns,
  • 5,000 – 6,000 for wet process long kilns and
  • 3,100–6,500 for shaft kilns.

Energy Efficiency in Cement Industry

With new built, state-of-the-art cement plants, usually all technical measures seem to be implemented towards low energy consumption. So, how to reduce it further?

Energy efficiency is based on the following three pillars

  • Technical optimization
  • Alternative raw materials for cement and clinker production
  • Alternative fuels

In Europe, the new energy efficiency directive from 2011 intends to reduce the energy consumption of the overall industry by 20%, achieving savings of 200billion Euros at the energy bill and with the goal to create 2 million new jobs within Europe. This approach will have a significant influence also on the cement industry. Saving 20% of the energy consumption is a challenging goal, especially for plants with state-of-the-art technology.

In older plants modernizations in the fields of grinding, process control and process prediction can, if properly planned and installed, reduce the electricity consumption – sometimes in a two digit number.

Alternative Fuels

Alternative fuels, such as waste-derived fuels or RDF, bear further 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. The European cement industry reaches an overall substitution rate of at least ca. 20%.

Typical “alternative fuels” available in Saudi Arabia are municipal solid wastes, agro-industrial wastes, industrial wastes and some amount of crop residues. To use alternative or waste-derived fuels, such as municipal solid wastes, dried sewage sludges, drilling wastes etc., a regulatory base has to be developed which sets

  • Types of wastes/alternative fuels,
  • Standards for the production of waste-derived fuels,
  • Emission standards and control mechanism while using alternative fuels and
  • Standards for permitting procedures.

Alternative Raw Materials

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.

To force the use of alternative raw materials within the cement industry, also – and again –standards have to be set, where

  • Types of wastes, by-products and other secondary raw materials are defined,
  • Standards for the substitution are set,
  • Guidelines for processing are developed,
  • Control mechanisms are defined.

Conclusions

To reduce the energy consumption, an energy efficiency program, focusing on “production-related energy efficiency” has to be developed. Substantial potential for energy efficiency improvement exists in the cement industry and in individual plants. A portion of this potential will be achieved as part of (natural) modernization and expansion of existing facilities, as well as construction of new plants in particular regions. Still, a relatively large potential for improved energy management practices exists and can be exhausted by determined approaches.

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Waste-to-Energy Pathways

Waste-to-energy is the use of modern combustion and biological technologies to recover energy from urban wastes. The conversion of waste material to energy can proceed along three major pathways – thermochemical, biochemical and physicochemical. Thermochemical conversion, characterized by higher temperature and conversion rates, is best suited for lower moisture feedstock and is generally less selective for products. On the other hand, biochemical technologies are more suitable for wet wastes which are rich in organic matter.

Thermochemical Conversion

The three principal methods of thermochemical conversion are combustion (in excess air), gasification (in reduced air), and pyrolysis (in absence of air). The most common technique for producing both heat and electrical energy from wastes is direct combustion. Combined heat and power (CHP) or cogeneration systems, ranging from small-scale technology to large grid-connected facilities, provide significantly higher efficiencies than systems that only generate electricity.

Combustion technology is the controlled combustion of waste with the recovery of heat to produce steam which in turn produces power through steam turbines. Pyrolysis and gasification represent refined thermal treatment methods as alternatives to incineration and are characterized by the transformation of the waste into product gas as energy carrier for later combustion in, for example, a boiler or a gas engine. Plasma gasification, which takes place at extremely high temperature, is also hogging limelight nowadays.

Biochemical Conversion

Biochemical processes, like anaerobic digestion, can also produce clean energy in the form of biogas which can be converted to power and heat using a gas engine. Anaerobic digestion is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biofertilizer and biogas. Anaerobic digestion is a reliable technology for the treatment of wet, organic waste.  Organic waste from various sources is biochemically degraded in highly controlled, oxygen-free conditions circumstances resulting in the production of biogas which can be used to produce both electricity and heat.

In addition, a variety of fuels can be produced from waste resources including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The resource base for biofuel production is composed of a wide variety of forestry and agricultural resources, industrial processing residues, and municipal solid and urban wood residues. Globally, biofuels are most commonly used to power vehicles, heat homes, and for cooking.

Physico-chemical Conversion

The physico-chemical technology involves various processes to improve physical and chemical properties of solid waste. The combustible fraction of the waste is converted into high-energy fuel pellets which may be used in steam generation. The waste is first dried to bring down the high moisture levels. Sand, grit, and other incombustible matter are then mechanically separated before the waste is compacted and converted into pellets or RDF. Fuel pellets have several distinct advantages over coal and wood because it is cleaner, free from incombustibles, has lower ash and moisture contents, is of uniform size, cost-effective, and eco-friendly.