城市生活垃圾直接气化熔融焚烧过程应用基础研究

【作者】 胡建杭；

【导师】 王华；

【作者基本信息】 昆明理工大学 ， 冶金能源工程， 2007， 博士

【摘要】 城市生活垃圾直接气化熔融焚烧处理技术能有效控制焚烧灰渣中的重金属和二恶英类有机物潜在的污染,避免与控制焚烧过程中二恶英类有机物的合成,具有理想的减容化、无害化和资源化效果。该技术是一种垃圾处理终端技术,在科学界,自从提出其概念并进行工业化应用以来,受到环保专家们的广泛关注,被认为是21世纪垃圾处理的新型可行技术和垃圾环保最具发展前景的新技术。因此,城市生活垃圾直接气化熔融焚烧处理已经成为废物处理领域新的研究热点。本文结合我国城市生活垃圾的组份特性,系统地开展了城市生活垃圾直接气化熔融焚烧过程的应用基础研究,为探索和创新城市生活垃圾新型焚烧处理技术提供一定的理论参考。研究分析了升温速率和气氛含氧量对生活垃圾气化焚烧过程动态产气特性的影响。在不同温度段,反应特征的变化较为明显,各个温度段的反应产物（CO、CO₂、H₂和CH₄）也都有很强的倾向性。温度和停留时间是决定气化燃烧过程气化率的主要因素。升温速率快慢影响瞬时产气量的多少,但是变化趋势基本相似;瞬时产气量因气化氧气浓度的增加而增加。干燥的混合垃圾在TG-DTG热分析过程主要可分为低温热分解气化阶段和高温热分解残留物燃烧阶段。升温速率不同,反应停留时间也不同,导致生活垃圾气化燃烧各阶段的温度范围有所变化,但是热失重最终趋势却不随升温速率的加快而改变。含氧量越高,燃烧反应就越剧烈,反应速率就越快。采用Doyle积分法依据TG-DTG数据建立了原生活垃圾气化燃烧动力学模型,拟合获得了生活垃圾气化燃烧第一阶段的反应机理方程均为f（a）=3/2（1-a）^4/3(（1-a）^1/3-1)^-1,第二阶段对应于10%、21%和56%含氧量气氛下的反应机理方程分别为f（a）:3（1-a）^2/3、f（a）=2（1-a）^3/2和f（a）=（1-a）²,并求得了不同升温速率和不同气氛下的动力学参数。在灰渣熔融过程中,分析了灰渣中主要成份CaO-SiO₂-Al₂O₃三元组份在熔融过程中可能发生玻璃体转化的各种复合反应,理论分析了各种反应的标准吉布斯自由能△G^θ和反应平衡常数K等热力学参数。研究分析了气氛、灰渣成分对灰渣熔融特性的影响。研究得出,为了降低灰渣的熔融温度,应控制灰渣中的CaO含量在33%和酸碱度在1左右,并实现在弱还原性的气氛下进行熔融处理。依据DSC曲线建立了焚烧灰渣熔融过程动力学模型,求出灰渣熔融过程的动力学参数。动力学模型为生活垃圾的直接气化熔融焚烧工艺设计提供了理论依据。实验研究了六种重金属（Hg、Pb、Cd、Zn、Cu、Cr）在直接气化熔融焚烧过程中的转化迁移特性。分析焚烧温度、熔融时间、气氛和含水率对重金属分布的影响。Hg、Pb和Cd是挥发性重金属,容易挥发转移到飞灰和烟气中;Cu和Cr是难熔性重金属,表现出很好的稳定性。Zn因氧化而不易挥发。灰渣的熔融对重金属的挥发有一定抑制作用,而HCl的存在却对重金属的挥发有促进作用。实验分析研究得出:焚烧炉内固硫剂固硫效果的好坏主要与反应温度、Ca/S、气体停留时间和固硫剂等有关。CaO的最佳固硫温度在800-900℃,最佳Ca/S是2.5～3左右。添加Fe₂O₃和草木灰有助于加强CaO的固硫效果。直接气化熔融焚烧处理可实现二恶英近零排放,熔渣中二恶英含量仅为0.001ng-TEQ/g,烟气中二恶英含量为0.072ng-TEQ/g。自行研发了半工业城市生活垃圾直接气化熔融炉焚烧系统（处理能力分别为1t/d和10t/d）并进行了批量试验。分析研究了处理能力对焚烧炉炉内温度和燃烧效率的影响,酸性气体（SO₂、NO_x和HCl）、二恶英类有机物和熔融渣的重金属浸出量等二次污染物的排放特性。试验表明,该焚烧炉系统在处理原生城市生活垃圾时,具有稳定高效的处理能力,可以实现二次污染物尤其是二恶英的低排放化和灰渣的回收利用资源化。研究表明,城市生活垃圾经过该直接气化熔融焚烧处理后,不仅可以实现垃圾燃烧热的利用,还可以降低二次污染物的排放和实现熔融渣的直接回收利用,具有理想的“三化”效果,应用前景广阔。更多还原

【Abstract】 The direct gasification & melting incineration of municipal solid waste（MSW） can decrease the pollutions of heavy metals and dioxins in incineration residue and avoid the synthesize reaction of dioxins in MSW incineration.The technology has ecologically and satisfying purpose of reducing the volume and the weight,harmless and resource.The technology is considered as terminal way of MSW management by environmentalists after it had been studied and experimented.This technology was deemed to be an ideal realized technology in 21century.Therefore,the direct gasification & melting incineration of MSW becomes one of the most significant research communities.The emphasis of this study is on the fundamentals of the direct gasification & melting incineration of MSW in according to the characteristic of MSW in China. It is useful in innovate the thermal treatment technology of MSW.Firstly,it was studied that the heat rate and atmosphere effect on the characteristic of MSW gasification and combustion.The results show:the transformation of MSW gasification and combustion is distinct in different temperature region.The reaction products of MSW gasification and combustion have strong orientation,such as CO、CO₂、H₂ and CH₄.The gasification rate of MSW is mainly determined by temperature and detention time.The volume of MSW instantaneous gasification is influenced by the varieties of heat rate. When the concentration of oxygen increase,the volume of MSW instantaneous gasification increase,too.Whereas the variety trend is similar.The TG-DTG thermal analysis showed that the dry MSW include the stage of pyrolysis and gasification in low temperature and the stage of char combustion in high temperature course.The temperature range of thermal process is diverse due to the difference of heat rate and detention time.The finally trend of thermogravimetric analysis are invariability with the speeding up of heat rate. Increase in oxygen concentration,enhance the combustion reaction.The kinetic model of raw MSW gasification and combustion is built according to TG-DTG data with the method of Doyle integral.The mechanism equation of first stage is f（a）=3/2（1-a）^4/3(（1-a）^1/3-1)^-1,the mechanism equation of second stage is f（a）=3（1-a）^2/3in 10%oxygen,f（a）=2（1-a）^3/2in 21%oxygen and f（a） =（1-a）² in 56%oxygen.The Kinetics parameters of raw MSW gasification and incineration were obtained in different heat rate and atmosphere.Secondly,the melting mechanisms of MSW incineration were investigated. Incinerator residue normally has CaO,SiO₂ and Al₂O₃ as major constituents. The thermodynamics of incineration residue,such as composite reaction,Gibbs and balance constant of CaO-SiO₂-Al₂O₃ system were characterized during melting process.The characteristics of incineration residue melting were experimented,we also analyze how the content of CaO,SiO₂,Al₂O₃ and the condition of the experimentation impact the characteristics of fusion on solid residues.The experimental results show:it should be controlied that the content of CaO is 33%by weight,ache-alkalinity is 1 and the melting atmosphere is tiny deoxidize atmosphere in order to reduce the melting temperature of incineration residue.In addition,the kinetics model of incineration residue melting transition was regressed from the experimental data of DSC.The kinetics parameters of incineration residue melting transition were obtained.The aforementioned results and model of incineration residue melting form the basic fundamentals for the practical engineering and optimal design of the direct gasification & melting incineration process.Subsequently,migration characteristics of heavy metals（cadmium,chromium, nickel,lead,copper and zinc）in the gasification and melting incineration system of MSW were investigated by experiments.Effect of several factors such as temperature,melting time and atmosphere on the volatilization of heavy metals were discussed in details.The results show that cadmium and lead are volatile metals,while chromium,nickel and cooper are refractory volatility heavy metals.Vitrification of the residues inhibited slightly heavy metals vaporization from MSW gasification and melting incineration,however,the volatility of heavy metals was variational for different compound species.The volatilization rate of heavy metals was fluctuating with the increasing of temperature.The limited zinc was vaporized since a substantial amount of the zinc was converted into ZnO in high temperature oxidation atmosphere.The vaporization percentage of heavy metals vaporization was stable over 30 minutes of melting time.The influence degree of the added HCl and SO₂ on each heavy metal was different.HCl will enhance the vaporization of heavy metals, but the effect of SO₂ on vaporization percentage of heavy metals was not obvious.The mechanisms of desulphurization was studied during the direct gasification & melting incineration of MSW.The influences of operational conditions on the desulphurization efficiency such as reaction temperature,ratio of Ca/S,resident time and absorbents were investigated.The results shown that the CaO has been good at desulphurization,when the reaction temperature is 800～900℃and the ratio of Ca/S is 2.5～3.The desulphurization sorbent of CaO added Fe₂O₃ or plant ash can enhance the desulphurization efficiency of sorbents.Finally,the Semi-pilot scale test was studied in two self-developed direct gasification & melting incineration system,one capacity is 1 t/d,and another capacity is 10t/d.The process of direct gasification & melting MSW incineration was analyzed,and combustion efficiency,chamber temperature distributing and the factors that influence the emissions of NO_x,HCI and SO₂ were studied.The results of experiment demonstrate:when the ability of incinerator is ideal and the run is steady-going,combustion efficiency is more than 95%.The content of heavy metals were less than the rule of environment law in the flue gas,the leaching content of heavy metals were also meet with environmental criterion in melted slag,flue gas is 0.072 ng-TEQ/Nm³,melted slag is 0.001ng-TEQ/g.The emission content of NO_x is added up rapidity with temperature increasing in chamber.Increasing second air or excess air coefficient significantly increased the sulfur-retention efficiency of CaO,and decreased the emission content of SO₂ in flue gas.However,the effect of excess air coefficient on HCl concentration is inconspicuous in flue gas in MSWI. Therefore,this technology can simultaneously realize low emissions dioxin, high efficiency of electric power generation,obtaining stable and useful vitrified slag and reducing in the amount of exhaust gas.Therefore,the process of direct gasification & melting incineration is a feasible method to realize harmless disposal of municipal solid waste（MSW）. The technology has advantages of simple structure and harmless treatment thoroughly.Direct Gasification & Melting technology is tacking with the development of environment-friendly technology and its products are harmonious with the external environment.更多还原