【作者】 王雅平；

【导师】 谢克昌；

【作者基本信息】 太原理工大学 ， 物理化学， 2010， 硕士

【摘要】 氮氧化物和硫氧化物是燃煤过程中产生的主要有害物之一,也是我国“煤烟型”大气污染的主要污染物之一。为了减少氮氧化物和硫氧化物的形成与排放,需对其形成机理及影响其生成的因素有深刻的认识,在此基础上,设计合理的工艺过程,最终达到减少污染物排放的目的。本文在前人工作的基础上,针对原煤及脱硫煤在不同气氛下热解/气化过程中NH3、HCN和H2S形成与释放的行为进行了研究,以期对煤热转化过程中煤中硫和氮的释放规律和相互影响有进一步的认识。实验选用兖州原煤(YZ),以及研磨后经酸(HCl和HN03)、微波处理,逐级脱硫后的煤样作为实验用煤样,采用固定床反应器进行快速升温和程序升温热解/气化实验,并用离子色谱定量分析氮氧化物和硫氧化物的前驱体-NH3、HCN和H2S的生成量。反应气氛为Ar、C02、5%O2/CO2和10%O2/CO2,实验温度为773K、873K.973K、1073K、1173K,得到的主要研究结果如下：(1)煤热解／气化过程中H2S的形成三种煤样H2S的生成率随温度的变化呈现出一致的趋势,程序升温过程中,873K时达到最大值,随后随温度升高而降低；快速升温过程中,973K时达到最大,随后酸洗脱硫煤与其它两种煤出现不同的趋势。H2S的生成与煤中硫的存在形态有关,温度较低时,H2S主要来源于黄铁矿和不稳定含硫有机物的分解,此时H2S的生成量较大；温度较高时,H2S的生成主要来源于较稳定的含硫化合物分解,此时H2S的生成量较低。脱硫后的煤样在热解和气化过程中生成的H2S产率减小,这说明酸洗或酸洗微波脱除的含硫化合物是煤中的无机硫和热稳定性相对较弱的有机硫。H2S的生成率随温度的变化受气氛的影响,在Ar和CO2气氛下,H2S的生成率随温度的升高而增大,在973K时出现峰值；5% O2/CO2和10%O2/CO2气氛下,H2S的生成率随温度的升高而降低,且氧含量越高H2S的生成率越低。程序升温热解过程中,H2S的生成主要集中在程序升温阶段；快速热解过程中,H2S的生成主要集中在进样阶段。煤中硫的脱除对程序升温和恒温阶段以及进样和非进样阶段释放的H2S的比例有影响,煤中硫含量越低,恒温阶段及非进样阶段H2S生成的比例越高,说明H2S的生成主要源于挥发分的释放,新生焦产生的H2S与煤中硫的形态有关。(2)煤热解/气化过程中NH3和HCN的形成原煤和脱硫煤快速升温热解生成的NH3均表现为随温度的升高而增大,在1073K出现最大值后降低,HCN的生成率均随温度的升高而线性增大；程序升温热解中,随温度升高NH3和HCN的生成率增大,973K时出现一最大值后降低。快速热解过程中,煤中硫的脱除促进NH3的生成但抑制HCN的生成；程序升温热解过程中,硫的脱除表现为促进NH3和HCN的生成。程序升温CO2气化过程中,硫含量越低的煤生成NH3产率越大,而HCN生成率在原煤热解中最大；快速升温CO2气化过程中,原煤和酸洗煤的NH3和HCN的生成率基本相当,而硫含量低的酸洗微波共脱硫煤NH3和HCN的释放率均明显降低。模型化合物吡啶和噻吩混合气体热解生成的NH3和HCN小于吡啶热解,特别是NH3生成量明显降低,说明煤中硫的释放和NH3生成存在竞争。进样方式不同主要影响挥发分的析出和半焦与挥发分的相互作用,进而影响HCN和NH3生成所必需的含氢基团的形成及其向表面迁移的难易程度,快速升温热解/气化过程中,NH3和HCN的生成率均明显大于程序升温热解过程。三种煤样的NH3和HCN在快速升温热解进样阶段的释放均远大于非进样阶段；程序升温热解的升温阶段远大于恒温阶段,硫的脱除明显改变了在进样阶段或程序升温阶段的释放比例。更多还原

【Abstract】 The NOX and SOX are the main gas pollutants during coal combustion. In order to reduce the emission of NOX and SOX, it is necessary to understand the formation of NOX, SOX and their precursors during coal pyrolysis and gasification. The formation and destruction of NOX, SOX precursors during coal pyrolysis and gasification are affected by many factors. Based on the previous work on the formation of NOX precursors during coal pyrolysis and gasification, the main purpose of this study was to experimentally investigate the release rules and mechanism of NH3. HCN and H2S during pyrolysis and gasification of raw coal and desulfurized coal.In this paper, Yanzhou raw coal, which contains high sulfur, was chosen as experimental sample (noted as Y-YZ). After Y-YZ coal was washed with nitric acid, pyrite was removed, and this desulfurised coal sample was noted as S-YZ. Treating S-YZ with NaOH and microwave, a part of organic sulfur was also removed, this coal was noted as S+W-YZ. The formation of NH3, HCN and H2S during fast heating and programmed-heating pyrolysis/gasification by using a quartz fixed-bed reactor coupled with IC analyzer. The release of H2S during coal pyrolysis/gasification was researched. The effect of several factors, such as temperature, feeding method, atmosphere and sulfur in coal, on the formation of HCN and NH3 were also studied systematically.Main results are as follows:(1) Formation of H2S during coal pyrolysis/gasificationThe yields of H2S from three coals pyrolysis with temperature have the same change trend. It increases in the lower temperature range and reaches a maximum value, which is 973K for fast heating process and 873K for programmed-heating process. The fromation of H2S has relationship with sulfur form in coal. Pyrite and unstable organic sulfur compound can decompose into H2S when temperature is lower than 973K. For stable organic sulfur compound in coal, it is hard to form H2S even at higher temperature. The yields of H2S from desulfrised coal pyrolysis were lower than that from raw coal. This shows that inorganic sulfur and unstable organic sulfur were removed after coal was treated with acid and microwave.The yield of H2S from coal pyrolysis in Ar is higher than that from coal gasification in oxidative atmosphere. The higher oxygen content in gas is, the lower yields of H2S is.H2S mainly come from the pyrolysis of coal during temperature heated for programmed-heating process and feeding period for fast heating process. The sulfur in coal have obvious effect on the ratio of H2S formed in the periods of constant temperature and not feeding. This shows that H2S is mainly released from volatiles and the H2S from fresh char is related with the forms of sulfur in coal.(2) Formation of NH3 and HCN during coal pyrolysis/gasificationThe yields of HCN increases with the increase of pyrolysis temperature in fast heating process. The yields of NH3 also increases with the increase of temperature to the maxmum value at 1073K and then deceases. For programmed heating process, The yields of NH3 and HCN increase with temperature increasing and reache the maxmum value at 973K. The feeding ways influence the release of volatile and the interaction of volatile and char. This can affect the availability of H radical, which is necessary for HCN and NH3 formation. As a result, the yields of HCN and NH3 changed.Effect of atmosphere on the release of NH3 and HCN was investigated in CO2,5%O2/CO2 and 10%O2/CO2. The exist of CO2 has two effects on NH3 formation. One is inhibiting NH3 formation. This is mainly due to depletion H radical by CO2 adsorption on coal surface. The other one is favoring NH3 formation. The reason for this is that gasification of coal in CO2 can generate more radicals. These two effects compete when reaction proceeds, and will leads to different results. In 5%O2/CO2 and 10%O2/CO2, NOx will be formed from oxidative reaction of HCN and NH3 with O2.The yield of NH3 from desulfurised coal pyrolysis and gasification was higher than that from raw coal. The result from the model compounds pyrolysis also shows that formation of HCN and NH3 decreases when thiophene exists in reaction system. This indicated that the existence of sulfur has influence on the formation of NH3 and HCN. In other word, formation of H2S competes with formation of HCN and NH3.The yields of HCN and NH3 from the pyrolysis of coal in the period of temperature heated for programmed-heating process and feeding period for fast heating process are dominant. The sulfur in coal have obvious effect on the ratio of HCN and NH3 formed in the periods of constant temperature and not feeding.更多还原