Co-incineration of Municipal Solid Waste in Cement Industry

Transcription

1 Proceedings of the International Conference on Sustainable Solid Waste Management, 5-7 September 2007, Chennai, India. pp Co-incineration of Municipal Solid Waste in Cement Industry Axel Seemann Centre for Sustainable Development, Bangalore, India ABSTRACT The aim of the paper is to introduce the use of high calorific waste components as secondary fuel in cement plants. For this purpose the basic ideas and requirements of co-incineration will be explained. This includes physical properties of the secondary fuel to be produced from solid waste as well as technical requirements of the required pre treatment of the waste. The highly water containing organic part of municipal solid waste has to be separated from the high calorific fraction, which can be used as secondary fuel. The remaining organic components can be used for composting or for the generation of bio gas. Based on experiences in Europe as well as on studies on waste generation in the City of Bangalore and Karnataka, possibilities for the use of municipal solid waste as secondary fuel in India will be discussed in the paper. Keywords: Municipal Solid Waste, Mechanical Biological Waste Treatment, Recycling, Reuse, Anaerobic, Composting 1.0 INTRODUCTION The Indian gross domestic product (GDP) increased 2.5 times over past 2 decades. As a consequence of increasing industrial activity and a continuous rise of incomes, there has been as well a significant increase in waste generation in India. The present system of solid waste management in India, like any other fast growing countries has to be adapted to these changes. Illegal dumping is a major problem that raises significant concerns with regard to safety, property values, and quality of life in our communities. The Centre for Sustainable Development (CSD) in Bangalore has carried out studies on waste generation and the composition wastes. Based on information generated, approaches for the recycling of municipal solid waste have been developed and adapted to Indian conditions. Especially a combination of anaerobic composting of organic parts of waste combined with the use of high caloric waste as secondary fuel in cement plants is a very promising recycling option. 2.0 COMPOSITION OF MUNICIPAL SOLID WASTE IN INDIA The waste from residential, commercial and institutional activities in a municipality is commonly termed as Municipal Solid Waste (MSW). As defined in the Municipal Solid Waste Rules, 2000 municipal solid waste includes commercial and residential wastes generated in a municipal or notified area in either solid or semi solid form, excluding industrial hazardous wastes but including treated 348

2 Sustainable Solid Waste Management bio-medical waste. The quantity and the content of municipal solid waste (MSW) varies according to the socio-economic status and cultural habits, prevailing climate, location, urban structure, density of population and extent of non-residential activities. The Centre for Sustainable Development (CSD) in Bangalore has carried out studies on generation and composition municipal and industrial wastes. To assure representative results, the study covered main areas of urban waste generation. From focus areas waste samples were taken and analysed. The segregated wastes were weighed to ascertain the percentage composition of individual waste constituents. The waste composition is shown in Figure 1. Percentage wise constituents of Municipal Solid Waste in Residential Area 10,75% 6,00% 0,25% Metals 0,50% Organic matter 81,00% E - waste 0,25% Glass 1,25% Metals Glass E - waste Organic matter Percentage wise constituents of Municipal Solid Waste in Commercial Area Sample 1 Percentage wise constituents of Municipal Solid Waste in Slum area 12,00% 8,00% Coir 1,00% Coir 9,25% 12,25% 3,50% 5,00% Organic matter 69,00% Coconut shell 5,00% Coconut shell Organic matter Organic matter 75,00% Organic matter Figure 1 Composition of Municipal Solid Waste in India [Seemann 06] 3.0 MECHANICAL BIOLOGICAL TREATMENT (MBT) In waste management there is a worldwide push towards implementing a 3R strategy: Reduce, Reuse and Recycle. This policy puts an emphasis on energy recovery over the disposal of waste in landfills, encouraging technologies such as mechanical biological treatment (MBT) providing a high calorific fraction which can be used as secondary fuel. Mechanical-biological Waste Treatment (MBT) is a technique to pre treat solid waste prior to disposal. The facilities required can be operated with relatively simple equipment, i.e. with a low degree of automation and modest expenditures on process technology and structures. However, depending on the anticipated results of treatment and on financial and other conditions it is also possible to implement highly sophisticated and enclosed facilities with optimised process technology. The use of MBT in conjunction of using the high calorific fraction as secondary fuel could present a number of environmental advantages. In the field of recycling, there would be a reduction of odours and emissions arising from waste handling and treatment [Senkpiel/Ohgke 98], as well as an improved recycling of materials such as metals and finally the possibility of converting the organic fraction into soil conditioners (or compost). The energy recovery through production and use of secondary fuel in 349

3 Co-Incineration of Municipal Solid Waste in Cement Industry cement kilns is a major advantage saving natural resources and reducing green house gas emissions. MBT consist of the two main technical elements the den mechanical treatment ant the biological treatment. The configuration of MBT plants as well as the chosen equipment can differ extremely. MBT plants can incorporate a number of different processes in a variety of combinations. The "mechanical" element is usually an automated mechanical sorting stage. This either removes recyclable elements from a mixed waste stream, such as metals, plastics and glass or processes them. It typically involves factory style conveyors, industrial magnets, eddy current separators, drum sieves, shredders and other tailor made systems. The "biological" element refers to either: Anaerobic digestion, Aerobic composting or to a combination of both techniques In general it can be said that processing biodegradable waste either by anaerobic digestion or by composting, MBT technologies help to reduce the contribution of greenhouse gases to global warming. But in anaerobic digestion being the more efficient option. Figure 2 shows flow sheeting diagrams for main MBT configurations. The simplified dry stabilisation technique on the right hand side can be an option to introduce the MBT technique in emerging Conventional MBA Technique Municipal Solid Waste Dry Stabilisation Technique Municipal Solid Waste Simplified Dry Stabilisation Technique Municipal Solid Waste Mecanical Treatment Mecanical Treatment Low High Biological Treatment Biological Treatment Mecanical PostTreatment Mecanical PostTreatment Biological Treatment Secondary Fuel Mecanical Post- Treatment Co- Incineration Low High Low High Landfill Landfill (Ash) Recycling/ Landfill Secondary Fuel Recycling/ Landfill Secondary Fuel Figure 2 Flow Sheeting Diagrams for Main MBT Configurations [Nelles Et Al 07], [SWMPP 06] 350

4 Sustainable Solid Waste Management countries, having a high amount of organics in their municipal solid waste. This technique is currently in a trial stage in Thailand by the Thai-German Solid Waste Management Project (TWMP), Bangkok a cooperation of the Ministry of Natural Resources and Environment (MoNRE) in Thailand and the German Technical Cooperation (GTZ) 4.0 APPLICATION OF MBT UNDER INDIAN CONDITIONS The waste composition as well as the climatic conditions in India differ very much from European countries were MBT-Techniques are commonly applied. First experiences with the introduction of MBA-techniques under Asian conditions have been made in Thailand by the Thai-German Solid Waste Management Project (TWMP) in Bangkok a cooperation of the Ministry of Natural Resources and Environment (MoNRE) in Thailand and the German Technical Cooperation (GTZ). To use the municipal solid waste maintained in the MBT for other applications the material was segregated into three fractions by sieving drums: diameter less than 10 mm, between 10 and 40 mm and diameter more than 40 mm. The sieved products have been investigated for composition, physicalchemical characteristics as well as for its heating value. The results of the analysis of the physical and chemical composition of the municipal solid waste after MBT are shown in the figures below. Figure 3 compares the composition of the high calorific fraction after MBT of 5 and 9 months. In respect of the main components the composition is very similar after 5 month and 9 month treatment. The content of plastic, which has a high calorific value is 72 % after 5 months and 80 % after 9 months treatment. Figure 3 Composition of the High after 5 Months (Left) and 9 Months (Right) MBT [ERC/GTZ 07] The physical and chemical characteristics of the solid waste treated by a 5 and 9 months MBT process is shown in Table 2. It is obvious that the characteristics of 5 months MBT are about the same as that for a 9 months treatment. The fine fraction below 10 mm is mainly compost, while the fraction bigger than 40mm contains the high calorific materials, which is indicated by the parameters density and volatile solids. While the density is approx 132 to 143 kg/m3 compared to 590 to 816 kg/m3 for the fraction less than 10mm, the content of volatile solids is much higher in the high calorific fraction (790 to 842 mg/g) to 215/175 mg/g in the fraction less than 10mm. 351

5 Co-Incineration of Municipal Solid Waste in Cement Industry For most of the parameters the concentration of heavy metals in the treated solid waste is lower than the limiting values for secondary fuels in Europe (see Table 3). Arsenic is the only exception exceeding the limits. The high concentration of aluminium and iron in the materials is even useful for cement production, which needs these metals as additives for the clinker. The most critical heavy metal, mercury, is within the limits for secondary fuels. Therefore, the use of the high calorific fraction as fuel in cement production seems to be feasible. The is fortified by the high calorific value of the material with a diameter greater than 40 mm which is much higher than for the other fractions and approximately at the same level as the heating value of diesel fuel. Table 2. Physical and Chemical Characteristics After 5 and 9 Months MBT Process [ERC/GTZ 07] Parameter < 10 mm 5 months MBT 9 months MBT 10 mm - 40 mm > 120 mm < 10 mm 10 mm - 40 mm > 120 mm Phisical & chemical Density (kg/m3) Moisture content (%) Total solids (mg/g) Volatile Solids (mg/g) Ash Content (mg/g) Organic Carbon (mg/g) Hydrogen (mg/g) Nitrogen (mg/g) ph Chloride (mg/g) Sulfate (mg/g) Heavy metals As (mg/kg) Cr (mg/kg) Fe (mg/kg) Al (mg/kg) Hg (mg/kg) ND Cu (mg/kg) Mn (mg/kg) Ni (mg/kg) ND ND ND ND ND ND Cd (mg/kg) ND ND ND ND Pb (mg/kg) value As collected (J/g) Moisture free (J/g)

6 Sustainable Solid Waste Management Table 3. Maximal Content of Heavy Metals in Secondary Fuels in Europe [MUNLV 05] Parameter Content of Heavy Metals in mg/kg TS Average Maximal Cadmium Cd 4 9 Thallium Tl 1 2 Mercury Hg 0,6 1,2 Antimony Sb Arsenic As 5 13 Lead Pb Chromium Cr Cobalt Co 6 12 Copper Cu ** ** Manganese Mn Nickel Ni Vanadium V Tin Sn CO-PROCESSING OF MUNICIPAL SOLID WASTE IN CEMENT KILNS Cement production has very high energy requirements, which typically account for 30-40% of the production costs (excluding capital costs) [Coprocem 06]. Traditionally, the primary fuel has been coal, but a wide range of other fuels is also used, including petroleum coke, natural gas and oil. In addition to these fuels, various types of waste can be used as fuel. Co-processing refers to the use of waste materials in industrial processes, such as cement production. The co-processing of selected waste materials in the cement industry is a proved alternative and possible solution for treatment of high caloric wastes. Co-processing has the following characteristics during the production process: The alkaline conditions and the intensive mixing favour the absorption of volatile components from the gas phase. This internal gas cleaning results in low emissions of components such as SO 2, HCl and, with the exception of mercury and thallium, this is also true for most of the heavy metals. The clinker reactions at 1450 C allow incorporation of ashes and in particular the chemical binding of metals to the clinker. Figure 4 shows the feeding points and the temperature profile of a rotary kiln for clinker production. The Primary firing system can be used by macerated materials as lignite, treated fractions of waste, scrap wood as well liquid waste as used oil, solvents and heavy fuel oil. The secondary firing can be used for tyres, paper and sewage sludge. Beside the physical requirements on the fuel the temperatures in the kiln limit the used of secondary fuels. While some plastics, tyres and some kind of sludges can be fired at the secondary firing, Fuels containing hazardous substances have to be fired at the main burner. Only the use in the main burner ensures that hazardous substances are destroyed due to the high temperatures above 1450 C combined with a residence time of over 2 seconds. A major restriction for the use of secondary fuels is the content of chlorine. High chlorine contents lead to corrosion problems in the cement plant but also to problems at the connection of the pre-heater 353

7 Co-Incineration of Municipal Solid Waste in Cement Industry to the cement kiln. Chlorine containing plastics as PVC are melting at low temperatures. The melted plastic can hamper or even block the material flow form the pre heater into the cement kiln. Due to this problem cement industry in Europe is limiting the content of chlorine in secondary fuel to 0.3 to 0.5 mass-%, depending on the company and cement kiln. These limits are even stricter than the limiting values set by the authorities, which are allowing a chlorine content of 1 mass-%. Figure 4 High after BMT evaporation cooler Secondary firing system - old Exhaust tyres gas to electro- - paper static sludge precipitator - sewage sludge VDK C Mehlaufgabe 150 C 850 C raw meal dosage Monitoring firing temperatur C Primary firing system o Macerated material -lignite - treated fractions of industrial waste - scrap wood o Liquids - waste oil, used solvents - heavy fuel oil Main Burner 2000 C 2 1 Figure 5 Feeding Points and Temperature Profile of a Rotary Kiln with Cyclone Preheater [Ebertsch 07] 6.0 CONCLUSIONS The high calorific fraction of municipal solid waste can be used as secondary fuel in cement industry according to its physical composition. Concerning the chemical properties of the material there are still some open points. The major concern is the content of chlorine arising from PVC in the waste. As 354

8 Sustainable Solid Waste Management a next step towards the use of high calorific fraction of municipal solid waste in cement industry, the PVC content has to be analysed. This analysis is carried out by CSD but till now the results are not available. PVC is a limiting material in secondary fuels due to its low melting point and especially because chlorine can react to dioxin and furan, which are extremely poisonous substances. In order to obtain the high calorific fraction of municipal solid waste a pre treatment of the waste is absolutely required. Biological mechanical treatment BMT is a very good option combining aerobic or anaerobic composting with mechanical cutting and segregation. BMT generates a high calorific fraction that can be used as secondary fuel. The application of BMT with Asian waste composition and climatic conditions in Thailand showed promising results. On the one hand BMT converts the organic fraction into a stable and non reactive material, which can be land filed without risk. In some cases the organic can even have the quality to be used as manure. The use as mature requires a very strict monitoring and management of the waste input stream into the BMT process. A broad application of BMT combined with the use of the high calorific fraction as fuel in cement kilns could solve more than one problem of infrastructure in India. There is the general problem of proper management of municipal solid waste including avoidance of wild dumping and other negative effects for the environment like ground water contamination by leaking pump sides and landfills. But the concept is also a solution for another problem. Secondary fuel can be used by the high energy demanding Indian cement industry saving the natural coal resources in India. REFERENCE Centre for Sustainable Development, CSD 04, Study on the Composition of Industrial Waste in Bangalore City, Bangalore, (2005). Centre for Sustainable Development, CSD 05, Study on the Composition of Municipal Solid Waste in Bangalore City, Bangalore, (2005). Seemann, A, Seemann 06, Solid and Industrial Waste Management in India Cases of Karnataka -, in: proceedings of Sixth International Ecocity Conference (Ecocity6), 3 rd to 6 th December 2006, Bangalore, India, (2006). Seemann, A., Seemann 07, Co-Processing of high calorific Wastes - techno-economical evaluation of Paint Sludge Recycling Techniques - in: South Indian Stakeholder Meeting, Bangalore, May (2007). The GTZ-Holcim Public Private Partnership: Summary, Coprocem 06, Guidelines on Co-processing Waste Materials in Cement Production, (2006). Senkpiel, K., Senkpiel/Ohgke 98, Ohgke H.: Abbau von Biomuell durch anaerobe Fermentation, in: Gesundheits-Ingenieur-Hausphysik-Bauphysik-Umwelttechnik, 119 (1998), Heft 6 Ebertsch, G., Ebertsch 07, Co-Processing of Hazardous Waste in Cement Kilns European Experience Legislation and Requirements, South Indian Stakeholder Meeting, Bangalore, (May 2007). Environmental Research Centre (ERC) Naresuan University, Gesellschaft fuer Technische Zusammenarbeit, ERC/GTZ 07, Solid Waste Management Programme for Phitsanulok, Summary Report - Characteristics of Solid Waste after Mechanical Biological Treatment (MBT), Phitsanulok, (April 2007). Nelle, M., Nelles et al 07, Morscheck, G.; Degener, P.: MBA-gute Technik mit Verbesserungsbedarf, in UmweltMagazin, Maerz (2007). Environmental Research Centre (ERC) Naresuan University, SWMPP 06, Solid Waste Management Programme for Phitsanulok, Phitsanulok, Thailand, (2006). 355