【作者】 王杰；

【导师】 石明岩；

【作者基本信息】 广州大学 ， 建筑与土木工程（市政）（专业学位）， 2021， 硕士

【摘要】 焚烧是城市污泥常用处置手段之一,但污泥热值低、焚烧不稳定。生物质具有高热值、硫/氮含量低的特点,可以与污泥制成混合燃料实现能源化利用。为此,本文利用污泥和典型生物质（红木、玉米芯、花生壳）制成混合燃料,并对燃料的燃烧特性、重金属的迁移转化规律进行了研究。研究内容和结果如下:首先,利用正交试验研究了生物质占比、燃料粒径和生物质种类对混合燃料热值的影响。发现生物质占比对燃料热值影响相对最为显著,燃料粒径影响最弱。其次,采用热重试验分别对污泥和生物质的燃烧特性进行了分析,并探讨了生物质占比和升温速率对污泥和生物质混烧过程的影响。得到:（1）污泥和生物质的热重（TG）和微商热重（DTG）曲线可分为四个阶段:水分蒸发阶段、挥发分析出及燃烧阶段、固定碳燃烧阶段和燃尽阶段。与生物质相比,污泥具有较低的失重率（36.5%）、着火温度（234℃）和较高的燃尽温度（840℃）。（2）在生物质占比为20%～50%的范围内,混合燃料的着火温度、可燃性指数和综合燃烧特性指数均随生物质占比增加而增加,燃尽温度则随之减小。生物质占比为50%时获得试验条件下最佳燃烧性能:最大燃烧速率为4.34～7.64%/min、可燃性指数为6.13×10^-5～8.43×10^-5、综合燃烧特性指数为0.99×10^-7～1.77×10^-7。其中,污泥与红木混烧表现最为突出,花生壳与玉米芯则较为接近。（3）在升温速率为5%/min～30%/min的范围内,混合燃料着火温度、可燃性指数、燃尽判别指数、综合燃烧特性指数均随升温速率的增加而增加,燃尽温度则呈现先增加后减小的规律。升温速率为30%/min时燃烧性能最佳:最大燃烧速率为8.65%/min～12.10%/min、可燃性指数为11.71×10^-5～13.27×10^-5、燃尽判别指数为2.15×10^-4～4.96×10^-4、综合燃烧特性指数为3.04×10^-7～5.82×10^-7。其中,污泥与红木混烧表现最为突出,花生壳与玉米芯则较为接近。最后,研究了生物质占比和焚烧温度对混合燃料焚烧灰渣中重金属（Zn、Cu、Cr、Pb、Ni）迁移转化规律的影响。得到:（1）混合燃料焚烧时,随生物质占比的增加,大部分重金属挥发率呈逐渐降低趋势。当红木比例由20%增加至80%时,Zn、Cu、Cr、Pb的挥发率分别由42.5%、23.1%、36.6%和67.6%降至32.6%、13.1%、17.2%和48.3%,Ni挥发率甚至已降低至0;当玉米芯比例由20%增加至80%时,Zn、Cu、Cr、Pb挥发率分别由44.7%、21.6%、26.8%、50.2%降至3.0%、6.0%、2.1%、30.3%,而Ni却全部残留在灰渣中;当花生壳比例由20%升至80%时,Zn、Cu、Cr、Ni的挥发率呈降低趋势。其中,Zn、Cr、Ni挥发率在比例超过60%时就已趋近0。表明生物质占比在一定范围内增加利于降低Zn、Cu、Cr、Ni的污染风险,但对焚烧灰渣中重金属形态则基本没有影响。（2）在450℃～900℃范围内,随焚烧温度的增加,重金属挥发率呈不同程度地增加,增幅为11.8%～85.3%,焚烧温度的升高增加了重金属的挥发性污染。与污泥焚烧相比,挥发率降低了9.8%～28.4%,生物质的掺入降低了污泥焚烧时的重金属挥发性污染。随焚烧温度的升高,灰渣中重金属生物有效态（酸溶态+可还原态）逐渐减少,残渣态逐渐增加,焚烧温度的升高利于降低灰渣的重金属生物有效性和毒性。与焚烧前相比,重金属生物有效态减小了7.7%～32.9%,残渣态增加了10.7%～48.9%,表明焚烧利于增强污泥稳定性。（3）在450℃～900℃范围内,随焚烧温度升高,污泥、玉米芯、花生壳共混烧（玉米芯、花生壳比例分别为30%）时重金属的迁移转化规律与污泥+玉米芯、污泥+花生壳混烧时相似,重金属挥发率和残渣态比例则介于二者之间,从降低重金属污染角度,污泥宜与玉米芯制成燃料焚烧。（4）根据重金属的潜在生态风险评价结果,污泥混烧生物质灰渣中重金属的生物可利用度和生态毒性、地累积指数、内梅罗指数、潜在生态风险指数均明显低于污泥,重金属污染程度有所减轻。污泥中Zn、Cr、Pb、Ni的风险级别均为低风险,Cu为很高风险级别,污泥和灰渣的高生态风险主要是由Cu造成的。综合燃烧性能、防控重金属风险和处理成本等因素,污泥宜与玉米芯制成燃料焚烧。更多还原

【Abstract】 Incineration is one of the common disposal means of municipal sludge,but sludge has low calorific value and incineration is unstable.Biomass has high calorific value and low sulfur/nitrogen content,and can be made into a fuel mixture with sludge for energy utilization.To this end,this paper makes a fuel mixture using sludge and typical biomass（mahogany,corn cob,peanut shell）,and investigates the combustion characteristics of the fuel and the migration and transformation patterns of heavy metals.The research contents and results are as follows.Firstly,the industrial analysis,element analysis and calorific value determination of sludge and biomass were carried out.Proportion of biomass（20%～50%）of single biomass and sludge,fuel particle size and biomass type on fuel calorific value were studied by orthogonal test.The results show that the proportion of biomass has the most significant effect on the calorific value of fuel,and the fuel particle size is the weakest.Next,the combustion characteristics of single sludge and biomass were analyzed separately using thermogravimetric tests,and the effects of biomass percentage and heating rate（5-30%/min）on the mixing process were investigated.It was obtained that.（1）The thermogravimetric（TG）and micro-commercial thermogravimetric（DTG）curves of sludge and biomass can be divided into four stages:water evaporation stage,volatile analysis out and its combustion stage,fixed carbon combustion stage and combustion exhaustion stage.Compared with biomass,sludge has a lower weight loss（36.5%）,ignition temperature（234°C）and higher burnout temperature（840°C）.（2）In the range of 20%to 50%of biomass,the fuel ignition temperature,flammability index and overall combustion characteristics index increased with the increase of the ratio,while the combustion temperature decreased.The best combustion performance under the test conditions was obtained when the biomass proportion was 50%:the maximum combustion rate was 4.34～7.64%/min,the flammability index was 6.13×10^-5～8.43×10^-5,and the overall combustion characteristics index was 0.99×10^-7～1.77×10^-7.（3）In the range of heating rate from 5 to 30%/min,the fuel ignition temperature,flammability index,burnout discrimination index and comprehensive combustion characteristics index increased with the increase of heating rate,while the burnout temperature increased and then decreased.The best combustion performance was achieved at a heating rate of 30%/min:the maximum burning rate was 8.65～12.10%/min,the flammability index was11.71×10^-5～13.27×10^-5,the burnout discrimination index was2.15×10^-4～4.96×10^-4,comprehensive combustion characteristics index is 3.04×10^-7～5.82×10^-7.Among them,sludge and mahogany mixed firing performance is the most prominent,followed by peanut shells.Finally,the migration and transformation laws of heavy metals（Zn,Cu,Cr,Pb,Ni）in incineration ash were investigated by the biomass percentage and incineration temperature.It was obtained that.（1）When mixed fuels were burned,the volatilization rate of most heavy metals showed a gradual decrease with the increase of the biomass percentage.When the proportion of mahogany increased from 20%to 80%,the volatilization rates of Zn,Cu,Cr,and Pb decreased from 42.5%,23.1%,36.6%,and 67.6%to 32.6%,13.1%,17.2%,and 48.3%,respectively,and the volatilization rate of Ni had even decreased to 0;when the proportion of corn cob increased from 20%to 80%,the volatilization rates of Zn,Cu,Cr,and Pb decreased from 44.7%,21.6%,26.8%,and 50.2%to 3.0%,6.0%,2.1%,and 30.3%,respectively,while Ni was all left in the ash residue;when the proportion of peanut shells increased from 20%to 80%,the volatilization rates of Zn,Cu,Cr,and Ni showed a decreasing trend.Among them,the volatilization rates of Zn,Cr,and Ni converged to 0 when the ratio exceeded 60%,indicating that the increase of biomass proportion in a certain range is beneficial to reduce the risk of pollution of Zn,Cu,Cr,and Pb.In addition,the percentage of biomass has almost no effect on the heavy metal form in the incineration ash.（2）In the range of 450°C to 900°C,the volatility rate of heavy metals increased to different degrees with the increase of incineration temperature,and the increase was 11.8%to85.3%,and the increase of incineration temperature increased the volatile pollution of heavy metals.Compared with sludge incineration,the volatilization rate decreased by 9.8%～28.4%,and the incorporation of biomass reduced the volatile pollution of heavy metals during sludge incineration.The bio-available state（acid soluble state+reducible state）of heavy metals in ash gradually decreased and the residue state gradually increased with the increase of incineration temperature,and the increase of incineration temperature was beneficial to reduce the bioeffectiveness and toxicity of heavy metals in ash.Compared with the pre-incineration period,the bioeffective state of heavy metals decreased by 7.7%～32.9%,and the residue state increased by 10.7%～48.9%,indicating that incineration is beneficial to enhance sludge stability.（3）In the range of 450℃～900℃,with the increase of incineration temperature,the migration and transformation pattern of heavy metals in the co-burning of sludge,corn cob and peanut shell（30%of corn cob and peanut shell respectively）is similar to that in the co-burning of sludge/corn cob and sludge/peanut shell,and the volatilization rate of heavy metals and the proportion of residue state are between them,so from the perspective of reducing heavy metal pollution,it is desirable to incinerate sludge with corn cob as fuel.From the perspective of reducing heavy metal pollution,sludge should be burned as fuel with corn cob.（4）According to the results of potential ecological risk evaluation of heavy metals,the bioavailability and ecotoxicity,ground accumulation index,Nemero index,and potential ecological risk index of heavy metals in sludge mixed with biomass ash were significantly lower than those in sludge,and the degree of heavy metal pollution was reduced.The risk levels of Zn,Cr,Pb,and Ni in sludge are low risk,and Cu is very high risk level,and the high ecological risk of sludge and ash residue is mainly caused by CuTaking into account factors such as combustion performance,prevention and control of heavy metal risks and treatment costs,sludge is preferable to be incinerated with corn cobs as fuel.更多还原