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任務(wù)書(shū)
題目名稱(chēng)
200噸/天城市生活垃圾衛(wèi)生填埋場(chǎng)設(shè)計(jì)
學(xué)生學(xué)院
環(huán)境科學(xué)與工程學(xué)院
專(zhuān)業(yè)班級(jí)
姓 名
學(xué) 號(hào)
一、畢業(yè)設(shè)計(jì)（論文）的內(nèi)容
（1）文獻(xiàn)檢索、資料收集和翻譯；
（2）制定設(shè)計(jì)方案和設(shè)計(jì)計(jì)算內(nèi)容；
（3）編寫(xiě)設(shè)計(jì)說(shuō)明書(shū)和繪制工程圖紙；
（4）工程概算和經(jīng)濟(jì)分析。
二、畢業(yè)設(shè)計(jì)（論文）的要求與數(shù)據(jù)
（1）基本設(shè)計(jì)參數(shù)。垃圾衛(wèi)生填埋量200噸/天，核算相應(yīng)的垃圾滲濾液產(chǎn)生量、填埋氣的產(chǎn)生量及處理措施。
（2）技術(shù)要求。垃圾衛(wèi)生填埋場(chǎng)設(shè)計(jì)滿(mǎn)足相應(yīng)的國(guó)家標(biāo)準(zhǔn)，工業(yè)企業(yè)設(shè)計(jì)衛(wèi)生標(biāo)準(zhǔn)、大氣污染控制技術(shù)標(biāo)準(zhǔn)、國(guó)家相關(guān)技術(shù)政策、凈化效率和操作適應(yīng)負(fù)荷范圍等。
（3）可靠性要求。包括預(yù)定使用壽命，設(shè)計(jì)可靠性分析以及設(shè)計(jì)結(jié)果的敏感性分析等。
（4）經(jīng)濟(jì)性要求。包括工程概算、成本分析和技術(shù)經(jīng)濟(jì)分析。
（5）其它要求：包括制造工藝要求、節(jié)能要求、安全要求、質(zhì)量檢測(cè)要求以及應(yīng)遵循的國(guó)家法令、政策、規(guī)范和標(biāo)準(zhǔn)等。
三、畢業(yè)設(shè)計(jì)（論文）應(yīng)完成的工作
（1）紙質(zhì)設(shè)計(jì)說(shuō)明書(shū)及其電子版本；
（2）譯文及原文影印件。
（3）設(shè)計(jì)圖紙（平面布置圖、工藝流程圖、主要構(gòu)筑物圖、管道布置圖等）。
四、畢業(yè)設(shè)計(jì)（論文）進(jìn)程安排
序號(hào)
設(shè)計(jì)（論文）各階段名稱(chēng)
地點(diǎn)
起止日期
1
文獻(xiàn)檢索及資料收集
圖書(shū)館
2007.4.2-2007.4.12
2
外文資料熟悉及翻譯
圖書(shū)館
2007.4.13-2007.4.20
3
工藝設(shè)計(jì)及說(shuō)明書(shū)編寫(xiě)
設(shè)計(jì)室
2007.4.21-2007.5.25
4
工程繪圖
設(shè)計(jì)室
2007.5.26-2007.6.10
5
答辯階段
課 室
2007.6.11-2007.6.15
五、應(yīng)收集的資料及主要參考文獻(xiàn)
[1] 趙毅等.有害氣體控制工程.北京：化學(xué)工業(yè)出版社，2001
[2] 熊振湖.費(fèi)學(xué)寧.池勇等編.大氣污染防治技術(shù)及工程應(yīng)用.北京：機(jī)械工業(yè)出版社，2003
[3] 趙慶良.特種廢水處理技術(shù).哈爾濱：哈爾濱工業(yè)大學(xué)出版社，2004
[4] 中華人民共和國(guó)國(guó)家標(biāo)準(zhǔn).總圖制圖標(biāo)準(zhǔn)GB/T50103-2001
[5] 中華人民共和國(guó)國(guó)家標(biāo)準(zhǔn).建筑制圖標(biāo)準(zhǔn)GB/T50104-2001
[6] 中華人民共和國(guó)國(guó)家標(biāo)準(zhǔn).建筑結(jié)構(gòu)制圖標(biāo)準(zhǔn)GB/T50105-2001
[7] 李穎．城市生活垃圾衛(wèi)生填埋場(chǎng)設(shè)計(jì)指南．中國(guó)環(huán)境科學(xué)出版社．2005
[8] 馮向明 衛(wèi)生填埋場(chǎng)滲瀝液產(chǎn)生量控制研究? 城市垃圾處理技術(shù)，2003.03
[9] 方江華, 張筑志. 現(xiàn)代衛(wèi)生填埋工程研究與分析[J]. 中國(guó)安全科學(xué)學(xué)報(bào) , 2005,(10)
發(fā)出任務(wù)書(shū)日期：20xx年3月10日 指導(dǎo)教師簽名：
預(yù)計(jì)完成日期：20xx年6月12日 專(zhuān)業(yè)負(fù)責(zé)人簽章：
主管院長(zhǎng)簽章：
Study of the energy potential of the biogas produced by an urban waste landfill in Southern Spain
Montserrat Zamora Jorge Ignacio Pe′ rez Pe′ rezb,
Ignacio Aguilar Pave′ sc, A′ ngel Ramos Ridaoa
Section of Environmental Technology, Department of Civil Engineering, University of Granada, 18071 Granada, Spain
Section of Construction Engineering, Department of Civil Engineering, University of Granada, Granada, Spain
Received 8 April 2005; accepted 5 May 2005
Abstract
Sanitary landfills have been and continue to be one of the most common ways to dispose of urban waste although such landfills inevitably generate waste management problems. Landfills are an important source of anthropogenic CH4 emissions. In this sense the European Union has passed regulations regarding the effective management of biogas within the framework of an EU policy for renewable energies. The sealed landfill analyzed in this study is an example of energy recovery, but in this case the biogas generated by the landfill is being re-used to produce electrical energy. This article presents the results of the economic viability study, which was carried out previous to the construction of the installation. The results based on the use of empirical and theoretical models show the biogas to have a 45% proportion of methane and an overall flowrate ranging from 250 to 550 N m3/h. It is presently being used to produce electricity amounting to approximately 4,500, 000 kW h/year. The economic viability of the installation was estimated by means of the Internal Recovery Rate (IRR) for an exploitation period of 7 years.
Keywords: Landfill gas; Energy recovery; Renewable energy; Economic analysis
Contents
1. Introduction 1
1.1. Environmental impacts of landfill gas 1
1.2. Landfill gas as a renewable energy source 2
1.3. Legal questions 2
1.3.1. Directive 96/61/CE regarding the integrated prevention and control of pollution 3
1.3.2. Directive 99/31/CE on landfilling of waste 3
1.3.3. Resolution 97/C76/01 on an EU waste management strategy 3
1.3.4. Communication regarding a strategy for the reduction of methane emissions 4
2. An urban waste landfill in Granada (Spain) 5
2.1. Profile of the landfill 5
2.2. Production and characterization of wastes 6
2.3. Quantification of the theoretical production/yield of biogas 6
2.3.1. Empirical estimate of biogas 7
2.3.2. Theoretical and actual production of biogas 8
3. Installation design 10
3.1. Collection and extraction system 10
3.2. Energy recovery system 11
4. Economic viability 11
5. Conclusions 12
6. References 12
1. Introduction
1.1. Environmental impacts of landfill gas
Waste disposal in landfills can generate environmental problems such as water pollution, unpleasant odors, explosion and combustion, asphyxiation, vegetation damage, and greenhouse gas emissions [1–3]. Different methods are presently being used to evaluate these problems in order to find solutions for them [4–7].
Landfill gas (LFG) is a naturally occurring by-product of the decomposition of organic waste in sanitary landfills, and is produced during the microbially mediated degradation of the organic portion of waste. An example of the conversion of a biomass into usable energy can be seen in sanitary landfills that produce an amount of biogas of about 0.350 N m3/kg of solid urban waste [8,9].
Landfill gas is generated under both aerobic and anaerobic conditions. Aerobic conditions occur immediately after waste disposal due to entrapped atmospheric air. The initial aerobic phase is short-lived and produces a gas mostly composed of carbon dioxide.
Since oxygen is rapidly depleted, a long-term degradation continues under anaerobic conditions, thus producing a gas with a significant energy value that is typically 55% methane and 45% carbon dioxide with traces of a number of volatile organic compounds (VOC) [10–12]. Most of the CH4 and CO2 is generated within 20 years of landfill completion, whereas emissions may continue for 50 years or more.
There are two possible solutions for the problem of LFG emissions. One solution is the extraction and flaring of the LFG, a method often used in the past to reduce the pressure of the LFG as well as its odor. The other solution is to reuse LFG for other purposes. Since its total chemical energy is sufficient to sustain the operation of a gas turbine, it is evidently a valuable energy resource. In fact, it can be used as a supplementary or primary fuel to increase the production of electric power, as a pipeline quality gas and vehicle fuel, or even as a supply of heat and carbon dioxide for greenhouses and various industrial processes [1,13].
The use of biogas as a fuel source is environmentally sound because it contributes to a reduction of fossil fuel use and mitigates the greenhouse effect. In particular, the emissions of CH4, one of the two greenhouse gases emitted, are almost 21 times more dangerous than carbon dioxide for the greenhouse effect [8,14]. Landfills comprise the principal source of anthropogenic CH4 emissions, and are estimated to account for 3–19% of anthropogenic CH4 emissions globally [15]. The recovery of landfill gas for use as an energy resource is now an area of vital interest since it is a creative solution for both environmental pollution and energy shortage [16,17].
This article presents the results of a study of the energy potential of a sanitary landfill located in southern Spain (Granada) previous to the installation of internal combustion engines in the autumn of 2003.
1.2. Landfill gas as a renewable energy source
When the Kyoto Protocol and the Marrakech Agreement of 2001 go into effect, developing countries may have to significantly reduce greenhouse gas emissions in the coming decade. In a parallel way, they will also have to seek a way to minimize the socioeconomic impact of such a policy. The increased use and promotion of renewable energy technologies seem to be a viable solution [8,13,18].
In Spain the deployment of such energy technologies is regulated by strategic plans and laws such as the Plan de Fomento de Energ?′as Renovables1 (PLAFER) [19] and the Real Decreto 2818/98 [20] regarding electricity production by installations using renewable energy sources, waste products, and co-generation.
The Andalusian regional government, as part of its environmental policy, has developed a series of strategic plans regarding the planning, organization, and coordination of action in this area. In 2000 the second Plan Energe′tico de Andaluc?′a2 (2003–2006) [21] was implemented. This plan seeks to bring together all of the directives regarding energy initiatives that will be carried out in Andalusia during the stated time period. This plan is committed to environmental protection and targets the diversification of energy sources with a view to making use of the abundant renewable energy resources available in the region.
In 2000 energy consumption in Andalusia amounted to 11,569 ktep and within this same time period renewable energies accounted for 649 ktep. The contribution of biomass to the structure of energy consumption was 90% followed by hydraulic energy with 5.3% [21].
In Spain there have been various initiatives aimed at the recovery of biogas from urban waste landfills as shown in the following examples [22]: (i) Ser?′ n (Asturias) with waste deposits of 408,234 Tm/year and a nominal power of six engines at 750 kW, one engine at 300 kW, and two engines at 250 kW; (ii) Artigas (Bilbao) with waste deposits of 243,361 Tm/year and a nominal power of two engines at 450 kW; (iii) San Marcos (San Sebastian) with waste deposits of 146,172 Tm/year and a nominal power of two engines at 650 kW; (iv) Gungora (Pamplona) with waste deposits of 118,016 Tm/year of waste and a nominal power of one engine at 750 kW. This information is eloquent proof that biomass is a significant source of renewable energy. An example of the conversion of a biomass into usable energy can be seen in sanitary landfills.
1.3. Legal questions
Although in Spain there is no legislation that specifically regulates the efficient management of biogas in controlled deposits of urban waste, the European Union has published recommendations and enacted directives that have already begun to significantly affect Spain.
1.3.1. Directive 96/61/CE regarding the integrated prevention and control of pollution
Incorporated into Spanish legislation as Ley 16/2002, Directive 96/61/CE was passed to prevent and reduce the contamination of the atmosphere, water, and soil produced by industrial activity, and includes the treatment and elimination of urban waste. Salient aspects of this directive are the following [23]: (i) Member States of the European Union must take the necessary measures to provide that the competent authorities ensure that installations are operated in such a way that all the appropriate preventive measures are taken against pollution, in particular through application of the best available techniques; (ii) Energy must be used efficiently, and necessary measures taken to prevent serious accidents and limit possible negative impacts; (iii) When an industrial installation is closed down and ceases operation, necessary measures must be taken upon definitive cessation of activities to avoid any pollution risk and return the site of operation to a satisfactory state (post-closure responsibility).
1.3.2. Directive 99/31/CE on landfilling of waste
After various proposals, drafts, and discussions to find common ground on environmental protection, Directive 99/31/CE (Real Decreto 1481/2001 in the Spanish legal code) was enacted and passed. It contains the following regulations regarding the management of gases [24]: (i) Appropriate measures will be taken to control the accumulation and emission of landfill gas; (ii) At all landfills where biodegradable wastes are deposited, gas will be recovered, treated and recycled. If the gas obtained cannot be used to produce energy, it should be burnt; (iii) The storage, treatment, and reuse of landfill gas will be carried out in such a way as to avoid, insofar as possible, negative impacts on the environment and public health; (iv) Gas should be monitored at each section of the landfill. In those landfills in which gas cannot be reused to create energy, it will be monitored at the site where such gas is emitted or burnt.
1.3.3. Resolution 97/C76/01 on an EU waste management strategy
Resolution 97/C76/01 was passed on February 24, 1997. In Article 35 it specifically affirms that members of the European Union should take the necessary cleanup measures to guarantee the restoration of former landfill sites and other contaminated locations to a satisfactory state [25].
1.3.4. Communication regarding a strategy for the reduction of methane emissions
In order to take into account the potential effect of methane emissions on the climate, this communication points out the need to analyze the problems derived from such emissions as well as the need to identify sources and drainage sites. It also underlines the necessity of establishing a common strategy. This would basically consist of methods of reducing emissions as well as a set of guidelines in this regard that would be incorporated into the legislation of Member States.
Among the measures to be implemented would be the establishment of an objective for the reduction of emissions to be achieved in a given time period. The political measures established would be evaluated according to their cost–benefit in terms of potential economic and social consequences.
According to a previous study, the main focus should be on those sectors that make the largest contributions to methane emissions, notably agriculture, waste and energy which in 1990 accounted for 45, 32 and 23% of EU methane emissions, respectively.
The main source of the methane emissions derived from waste management is the anaerobic fermentation of the organic material deposited in landfills. Communication COM(96)557 includes the following recommendations [26]: (i) A distinction should be made between existing landfills and new landfills; (ii) In the case of existing landfills, authorities should improve their technological capacity and environmental level by incorporating the infrastructure necessary for the management of methane emissions; (iii) In the case of new landfills, the permits granted to controlled anaerobic deposits should be strictly monitored. In any case, it is always necessary to verify whether there are other ways of limiting methane emission, and at the same time incorporate highly efficient systems for its reception and energy evaluation; (iv) When such evaluation is not feasible, the infrastructure necessary for its total combustion should be available and operative; (v) Finally, Member States should develop economic incentives to favor the recovery of methane gas, the use of technologies, and the reduction of the amount of organic matter deposited in landfills.
Decision 99/296/CE published on April 26, 1999, modified Decision 93/389/CEE regarding the monitoring of CO2 and other greenhouse gases such as methane. This decision affirms that Member States should make an inventory of the sources of gas emissions and their elimination by drainage sites, as well as describe the policies and national regulations adopted to reduce such emissions, and thus facilitate their total elimination.
As can be observed, these regulations are somewhat ambiguous in reference to the measures to be taken for the efficient management of biogas. Nevertheless, what is clear is the message regarding the need to reduce and minimize the negative impact that uncontrolled biogas emission has on the environment.
2. An urban waste landfill in Granada (Spain)
2.1. Profile of the landfill
The landfill studied in this article is located 2 km northeast of Granada, a city in southern Spain with a population of 300,000 inhabitants. The landfill, with a surface area of 46.54 Has, was in active operation from 1984 to 1999. During this period, the waste was deposited on a hillside running along the river Beiro with an average altitude of 870 and 500 m (see Fig. 1).
The landfill is of medium density, and over the years was progressively covered with layers of soil from the same area and similar to that found in the bed of the landfill. The waste compacting process was carried out by means of compacting equipment, with a waste compacting degree of 0.7–0.9 Tm/m3. The leachate was collected in pools where it was pumped out again to be recirculated in the landfill. The extraction of the gas was carried out by a series of gas extraction wells separated by distances of 30–35 m.
In 1999 with a view to mitigating the negative environmental impact, the landfill was sealed. Subsequently, plans were drawn up to construct installations to extract biogas and reuse it to create electrical energy. The project was carried out that same year by INAGRA (company belonging to CESPA3).
The average annual precipitation in this region fluctuates from 66 to 400 mm during the seasons of autumn and winter. The average annual temperature in Granada largely depends on the weather station where the measurements are obtained. The average temperature is 15.3 1C as measured at the Cartuja weather station in the city, whereas it is 14.81 at the airport weather station, 10 km outside the city.
The temperature in Granada is influenced by the proximity of the Sierra Nevada mountain range. The highest temperatures occur during the summer months, while the lowest ones occur in December and January. The thermal variation in the average annual temperatures is significant, and amounts to almost 20 1C. This is the same variation that exists between daytime and nighttime temperatures.
The potential evapotranspiration of the area, as calculated by the Thornthwaite Method, reaches values ranging from 700 to 900 mm. There is generally a period of draught in the summer months.
The landfill is located on the Alhambra formation, made up of conglomerates and sands, immersed in a large clayey basin, reducing the capacity of water transmission in the subsoil. There are no aquifers or signs of surface or groundwater at the landfill site.
After the landfill was sealed, urban waste from Granada, as well as that from other neighboring cities and towns, was treated at the Planta de Recuperacio′n y Compostaje, a waste recovery and composting installation that had recently opened in the town of Alhendin, 20 km outside of Granada. The main products treated at this plant are: metals, paper and cardboard, plastics and containers of mixed composition, organic material for the elaboration of compost, other wastes.
2.2. Production and characterization of wastes
During its period of maximum activity, a total of 1,420,000 Tm of waste were deposited at the landfill. A clear increase of waste production can be observed in Fig. 2, which shows the amount of waste deposited at the landfill from 1984 to 1999. This is typical of tendencies in recent decades and in consonance with the average rate of waste generation [18,27].
The waste was analyzed in order to obtain its macroscopic composition. The results of the field study is appear in Table 1.
2.3. Quantification of the theoretical production/yield of biogas
A number of methods have been used to estimate CH4 emissions at waste disposal sites. These methods vary greatly, not only in their assumptions, but also in their complexity and in the amount of data required. Some are based on the theoretical gas yield, whereas others use a first-order kinetics equation [28–32].
2.3.1. Empirical estimate of biogas
Table 1
Macroscopic composition of the landfill waste
The estimate of biogas production has been carried out by means of empirical calculation, in other words, a calculation using both experimental and theoretical data. Based on the macroscopic characteristics of the waste and the degradability data given in the previous section, as well as the analysis of the sample of gas spontaneously emitted from the landfill, it was possible to postulate the chemical formula of the waste (see Table 2).
Macroscopic
composition of
waste
Weight (%)
Humidity
(%)
Weight of
dry waste
(%)
Degradability of dry waste (%)
Fast
Slow
Total
Organic waste
30.50
75.00
7.63
75.00
7.00
82.00
Wet Paper/
24.00
20.00
19.20
30.00
20.00
50.00
Cardboard
1.50
35.00
0.98
10.00
20.00
30.00
trimmings
Textiles
1.00
20.00
0.80
0.00
10.00
10.00
Plastic
21.00
1.00
20.79
0.00
0.00
0.00
Metals
5.00
1.00
4.95
0.00
0.00
0.00
Glass
12.00
1.00
11.88
0.00
0.00
0.00
Others and inert
5.00
1.00
4.95
5.00
16.00
21.00
matter
Total
100.00
28.83
71.17
11.82
5.44
17.26
Table 2
Estimated chemical formula of waste
Dry fraction Degradables Chemical formula
71.17% 17.26% C44 H70O29N
Table 3
Estimated biogas production and methane concentration
Methane production (m3/Tm) Biogas production (m3/Tm) Methane concentration (% v/v)
82.43 160.21 51.39
The amount of biogas produced per ton of waste has been defined by the decomposition equation. The results obtained for a 40-year decomposition period are summarized in Table 3.
2.3.2. Theoretical and actual production of biogas
The previous section presents the possible generation of biogas per ton of waste, the composition of which was calculated hypothetically. It is a stoichiometric calculation on the basis of hypothetical data, but reality inside an actual landfill is much more complex. Another element of great importance in the evaluation of potential landfill gas production is the kinetics of decomposition. Some researchers use models or algorithms based on equations that presuppose the exact knowled