【作者】 李世光；

【导师】 胡浩权； 徐绍平；

【作者基本信息】 大连理工大学 ， 化学工艺， 2006， 博士

【摘要】 煤直接燃烧排放的SO₂能造成严重的环境污染,因此开发煤燃前脱硫生产低硫半焦的洁净煤技术迫在眉睫。本论文以生产低硫半焦为目标,在常压自由落下床反应器中研究了煤中硫在热解和共热解过程中的变迁规律。论文的主要研究内容和取得的主要结论如下: 1.煤中易分解的有机硫在500-800℃区间内被脱除,其中超过一半的有机硫以有机物的形式脱除到焦油中;煤中的黄铁矿在500-800℃区间内分解,煤的有机质起到促进黄铁矿硫脱除的作用;黄铁矿大量分解时伴随着无机硫向有机硫的转化反应,此转化反应在>800℃的高温区内能被有效抑制;煤中的碱性矿物质在800-900℃区间内能与H₂S发生固硫反应。对于含较多黄铁矿硫的高硫煤来说,较长的停留时间比较有利于煤热解生产低硫半焦;而对于低阶煤和含较多有机硫的煤来说,较短的停留时间比较合适。 2.充分利用煤颗粒在自由落下床反应器中停留时间短的特点,直接用空气做载气,对自由落下床反应器中煤在氧化性气氛下的快速热解行为和硫的变迁进行了研究。结果表明氧化性气氛可大大增加半焦的内比表面积,但对半焦产率的影响较小。煤中易分解的有机硫在550-700℃区间内被有效地脱除了;煤中黄铁矿在<600℃区间内大量分解;黄铁矿大量分解时伴随着无机硫向有机硫的转化反应,但在600℃附近此转化反应就已经得到有效地抑制。与惰性气氛相比较,氧化性气氛使煤中有机硫和黄铁矿硫的脱除温度降低了200℃左右。在较低的反应器温度条件下,氧化性气氛就能有效地降低无机硫的含量从而获得低硫半焦,如700℃时,兖州煤热解脱硫的各项指标（半焦收率:57.9%,全硫脱除率:65.1%,无机硫脱除率:90.8%,有机硫脱除率:47.2%,半焦全硫含量:1.9%,半焦无机硫含量:0.2%,半焦有机硫含量:1.7%）都优于惰性气氛下900℃时兖州煤热解相应的各项指标。并且煤中的黄铁矿硫能在较短的停留时间内被有效地脱除。继续升高反应器温度和增加停留时间并不能进一步有效地脱除硫,只能造成半焦大量烧失。在实验基础上,文中首次提出将氧化性气氛和还原性气氛下煤快速热解相结合的两步法脱硫工艺,可真正实现煤连续瞬间炭化脱硫生产低硫半焦。 3.根据煤和生物质以及自由落下床反应器的特点,指出自由落下床反应器中煤与生物质共热解可能存在协同效应。实验结果表明在反应器温度>800℃时,生物质快速热解富氢气体组分（H₂+CO）和不饱和烯烃（如乙烯）的产率迅速增加,远远高于煤的;并且煤和生物质由于黑度不同,引起二者在自由落下床中发生快速热解反应的更多还原

【Abstract】 Direct combustion of coal arouses serious pollution, especially "acid rains" by SO₂ emission. So it is necessary to remove sulfur from coal before combustion in order to protect the environment. Aiming to produce low-sulfur content char, desulfurization of coal during pyrolysis and copyrolysis with biomass in a free-fall reactor under atmospheric pressure was studied. The main research works and conclusions in this dissertation are as follows:1. Those unstable organic sulfurs in coal can be removed at temperature between 500 and 800℃, more than half of which can be released as organics in tar. The pyrite in coal decomposing at temperature between 500 and 800℃, and the organics in coal can promote removal of the pyritic sulfur. In this process there exists the reaction of transformation from inorganic sulfur into organic sulfur, which can be suppressed effectively at temperature higher than 800℃. At the same time the sulfur fixation reaction aroused by basic minerals in coal happens at temperature between 800 and 900℃. For the high-sulfur content coal containing much pyrite, a longer particle residence time is needed for a better sulfur removal. But for the lower rank coal and for the coal comprising more organic sulfur, a shorter particle residence time is appreciated.2. Considering the very short particle residence time in the free-fall reactor, air was directly used as carrier gas to study the fast pyrolysis and sulfur evolution of coal under oxidizing atmosphere. It shows that the surface area of the char is greatly increased, but the yield of the char only a little changed. Those unstable organic sulfurs in coal can be removed at temperature between 550 and 700℃. And the pyritic sulfur in coal can be removed at temperature lower than 600℃. Also it accompanies the transformation reaction in this process, but its effect can be eliminated at temperature as low as 600℃. It can be seen that the decomposition temperature of pyrite and the release temperature of those unstable organic sulfurs under oxidizing atmosphere are 200℃ lower than those under inert atmosphere. The pyritic sulfur can be effectively removed at a relatively low temperature under oxidizing atmosphere to produce low-sulfur content char. For example, the desulfurization of Yanzhou coal at 700℃ under oxidizing atmosphere can get better results, which are 57.9%, 65.1%, 90.8%, 47.2%, 1.9%, 0.2% and1.7% for the yield of char, the extent of total sulfur removal, the extent of inorganic sulfur removal, the extent of organic sulfur removal, the total sulfur content of char, the inorganic sulfur content of char and the organic sulfur content of char, respectively, than at 900℃ under inertatmosphere. In addition, the pyritic sulfur can be removed within a relatively short particle residence time. Further increasing the reactor temperature and the particle residence time can result in heavy loss of the char without more sulfur being effectively removed. Based on the experiment result, an original two-stage process combining oxidative pretreatment with hydrodesulfurization of the coal is proposed, through which can realize rapid desulfurization of coal to produce low-sulfur content char.3. The existence of the synergetic effect during copyrolysis of coal and biomass in the free-fall reactor is pointed out according to the characters of coal, biomass and the reactor. The experiment of fast pyrolysis shows that the yields of hydrogen-rich gas components （H2+CO） and olefin, such as C2H4, are rapidly increased at temperature higher than 800°C. As well as the difference of blackness between coal and biomass makes their pyrolysis reactions occur almost simultaneously under inert atmosphere in the free-fall reactor. The experiment of copyrolysis indicates that the synergetic effect exists, especially at a higher temperature, a higher blending ratio of biomass to coal and for coals with higher rank. At a low temperature, such as 650QC, biomass can fix sulfur into the char during coal copyrolysis with a large quantity of biomass. But at a high temperature, such as 800°C, biomass can enhance coal desulfurization to produce low-sulfur content char during coal copyrolysis with a little biomass: For bituminous coal, the copyrolysis is in favor ofi sulfur removed from coal to tar. Meanwhile, for lignite, it favors to remove sulfur from coal to gas.4. Nitric acid pretreatment can thoroughly remove the basic minerals and the pyrite from coal, but affects little on the organic sulfur in coal and the yield of organic in char. According to the experimental data from fast pyrolysis of both the raw coal and the HNC>3-pretreated coal, the rate of transformation from inorganic sulfur into organic sulfur can be quantitative calculated during fast pyrolysis of the raw coal.更多还原