氧热法电石生产反应工艺及反应器设计研究
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摘要
煤是一种非常重要的化石能源，尤其我国“缺油、少气、富煤”，煤的消耗量很大，而所消耗的煤中高达70%的比例直接用于燃烧，造成极大浪费，如何最大程度的合理利用煤资源成为一个无法忽视的问题。对此，人们提出了将煤分级转化以制备多种化工产品，其中包含以煤焦为原料制备电石的氧热法电石生产工艺。相比传统方法，该方法无论在能耗还是在排放方面都有很大幅度改善，应用前景乐观，为此，有必要设计研究适用于氧热法电石生产的反应器。本论文依次从影响反应器性能的内因——反应化学和外因——反应器流动、传热和传质性能方面进行研究，以期为氧热法的工业应用提供参考。
首先，从热力学角度研究了电石合成吸热反应和富氧燃烧放热反应耦合化学反应体系的适宜的反应工艺条件以及热平衡和物料匹配。可知：
（1）焦炭和氧化钙可能路径是由CaO+3C→CaC_2+CO一步生成电石。
（2）不同比例进料对应不同的吸热和放热反应平衡。温度的升高或压强的降低，均有利于提高电石转化率；电石若进一步发生CaC_2+2CaO＝3Ca+2CO副反应，温度升高则该副反应的转化率将先升后降，在较低温度区间（低于2100℃）时，压力升高则转化率下降。为避免目的产物生成后又发生副反应消耗掉，同时避免CaC_2与CaO过度共熔而影响产品纯度，进料C宜大大过量，以2400℃为例，1molCaO宜匹配至少7.28molC。
（3）通过热匹配计算可知，对电石产品的纯度要求和物料处理量两方面因素共同决定碳燃烧反应匹配量条件及匹配量。从热力学角度考察，将电石合成与燃烧供热相耦合的氧热法是可行的。
然后，在外因方面，考虑反应体系特性，选择反应器构型——气流床反应器并进行初步设计，用FLUENT软件以CFD模拟方法研究了床中的传递和反应特性。结果表明：
（1）反应器内压力分布均匀，且压降低。
（2）气体沿反应器壁面向上运动，在中心轴线附近存在向下回流，产量加大将使反应段气流湍动加剧，扩大段和预热段的中心回流则明显减弱。
（3）炭粉燃烧供热可达到反应温度，保证反应正常进行。而随着产量增大，温度将升高且升高速率将逐渐放缓。
（4）固体进料颗粒粒度最小为100μm，两种粉料进入反应器后，不能均匀混合，应在进入反应器之前进行预混。两种粉料以特定的粒径匹配可实现同步沉降，提升反应和传递性能。由于颗粒粒度小且含载率低，气固相间在预热区段可达热平衡。
最后，本文为考察其它类型反应器在氧热法电石生产中的适用性，提出并初步设计了以淤浆鼓泡床反应器为原型的新型反应器并建立数学模型对其进行研究，采用MATLAB软件编程求解，研究表明：淤浆鼓泡床反应器的反应性能良好，且操作范围内物料恰好完全处于熔融态。产物浓度和反应转化率随着轴向床高增加而单调增加，其极限浓度约为50mol/L，此时不能通过增加反应器内留存电石留存液高度来提高转化率。
Coal is an important fossil energy. China, short of oil and gas while richin coal, enjoys a high consumption of coal, however,70%of that resort tocombustion, which is a tremendous waste. Therefore, how to make utmost useof coal becomes crucial. Hence an idea that converting coal into differentchemicals raised, including calcium carbide production from coke in theoxygen-fuel way. Compared with the traditional methods, the promisingproposal can significantly reduce the energy consumption and pollutantdischarge. To this end, it is necessary to design and research on reactors fit forit. In this paper, we study on reactors’ performance in terms of both internal(reaction system) and external factors (fluid flow, heat transfer and masstransfer) to provide reference to its industrial application.
First, as the internal factor, the characteristics of reaction system,including thermal equilibrium and coupling, were studied. The results suggestthat:
(1) The formation of calcium carbide from coke and calcium oxide ismost likely to follow the pathCaO+3C→CaC_2COdirectly.
(2) Different feed ratios lead to different equilibrium systems. The equilibrium conversion rate of calcium carbide increases with an increase intemperature or a decrease in pressure. The conversion rate of the side reactionthat proceeds with calcium carbide initially increases, and then decreases withincreasing temperature.
(3) According to the calculations, the heat matching feeds and conditionsdepend on the throughput and the purity of calcium carbide. Thus underappropriate conditions, coupling calcium carbide synthesis with cokecombustion in a reactor is feasible.
Next, in terms of the external factor, the entrained-flow reactor, a specificreactor type, was picked and then preliminarily designed. The CFDsimulations of the designed reactor indicate that:
(1) The pressure in the reactor is well-distributed and close to theatmosphere, it increases regularly with the increase in yield.
(2) The gas flows upwards in the wall region and backwards in the centerregion. The turbulence of airflow in the reacting section is intensified and thereflux in the expanding section and the preheating section is weakened withthe increase in yield.
(3) Fine coke combustion could reach the required temperature to ensurethe smooth synthesis. The temperature rise slows down with the increase inyield.
(4) The minimum size of solid particles is100μm. The twoparticle-shaped reactants cannot mix uniformly and automatically, hence premix is preferential. They can settle simultaneously via size match, whichcould enhance the transfer and reaction efficiency. There is no difference intemperature between the gas and the particles because of the small particlesize and low solid content.
At last, a reactor based on the slurry bubble column reactor is put forward,then preliminarily designed and mathematically modeled to research theapplicability of other reactor types. The solutions via programming inMATLAB demonstrate that: the reactor behaves well, and the feeds becomeliquid-state eutectic mixtures at the whole operation range. Along the reactorheight, the concentration and the conversion rate of the product increases, andthe maximum concentration is50mol/L approximately, where the conversionrate can no longer enhance by the height growth in retained liquid calciumcarbide.
首先，从热力学角度研究了电石合成吸热反应和富氧燃烧放热反应耦合化学反应体系的适宜的反应工艺条件以及热平衡和物料匹配。可知：
（1）焦炭和氧化钙可能路径是由CaO+3C→CaC_2+CO一步生成电石。
（2）不同比例进料对应不同的吸热和放热反应平衡。温度的升高或压强的降低，均有利于提高电石转化率；电石若进一步发生CaC_2+2CaO＝3Ca+2CO副反应，温度升高则该副反应的转化率将先升后降，在较低温度区间（低于2100℃）时，压力升高则转化率下降。为避免目的产物生成后又发生副反应消耗掉，同时避免CaC_2与CaO过度共熔而影响产品纯度，进料C宜大大过量，以2400℃为例，1molCaO宜匹配至少7.28molC。
（3）通过热匹配计算可知，对电石产品的纯度要求和物料处理量两方面因素共同决定碳燃烧反应匹配量条件及匹配量。从热力学角度考察，将电石合成与燃烧供热相耦合的氧热法是可行的。
然后，在外因方面，考虑反应体系特性，选择反应器构型——气流床反应器并进行初步设计，用FLUENT软件以CFD模拟方法研究了床中的传递和反应特性。结果表明：
（1）反应器内压力分布均匀，且压降低。
（2）气体沿反应器壁面向上运动，在中心轴线附近存在向下回流，产量加大将使反应段气流湍动加剧，扩大段和预热段的中心回流则明显减弱。
（3）炭粉燃烧供热可达到反应温度，保证反应正常进行。而随着产量增大，温度将升高且升高速率将逐渐放缓。
（4）固体进料颗粒粒度最小为100μm，两种粉料进入反应器后，不能均匀混合，应在进入反应器之前进行预混。两种粉料以特定的粒径匹配可实现同步沉降，提升反应和传递性能。由于颗粒粒度小且含载率低，气固相间在预热区段可达热平衡。
最后，本文为考察其它类型反应器在氧热法电石生产中的适用性，提出并初步设计了以淤浆鼓泡床反应器为原型的新型反应器并建立数学模型对其进行研究，采用MATLAB软件编程求解，研究表明：淤浆鼓泡床反应器的反应性能良好，且操作范围内物料恰好完全处于熔融态。产物浓度和反应转化率随着轴向床高增加而单调增加，其极限浓度约为50mol/L，此时不能通过增加反应器内留存电石留存液高度来提高转化率。
Coal is an important fossil energy. China, short of oil and gas while richin coal, enjoys a high consumption of coal, however,70%of that resort tocombustion, which is a tremendous waste. Therefore, how to make utmost useof coal becomes crucial. Hence an idea that converting coal into differentchemicals raised, including calcium carbide production from coke in theoxygen-fuel way. Compared with the traditional methods, the promisingproposal can significantly reduce the energy consumption and pollutantdischarge. To this end, it is necessary to design and research on reactors fit forit. In this paper, we study on reactors’ performance in terms of both internal(reaction system) and external factors (fluid flow, heat transfer and masstransfer) to provide reference to its industrial application.
First, as the internal factor, the characteristics of reaction system,including thermal equilibrium and coupling, were studied. The results suggestthat:
(1) The formation of calcium carbide from coke and calcium oxide ismost likely to follow the pathCaO+3C→CaC_2COdirectly.
(2) Different feed ratios lead to different equilibrium systems. The equilibrium conversion rate of calcium carbide increases with an increase intemperature or a decrease in pressure. The conversion rate of the side reactionthat proceeds with calcium carbide initially increases, and then decreases withincreasing temperature.
(3) According to the calculations, the heat matching feeds and conditionsdepend on the throughput and the purity of calcium carbide. Thus underappropriate conditions, coupling calcium carbide synthesis with cokecombustion in a reactor is feasible.
Next, in terms of the external factor, the entrained-flow reactor, a specificreactor type, was picked and then preliminarily designed. The CFDsimulations of the designed reactor indicate that:
(1) The pressure in the reactor is well-distributed and close to theatmosphere, it increases regularly with the increase in yield.
(2) The gas flows upwards in the wall region and backwards in the centerregion. The turbulence of airflow in the reacting section is intensified and thereflux in the expanding section and the preheating section is weakened withthe increase in yield.
(3) Fine coke combustion could reach the required temperature to ensurethe smooth synthesis. The temperature rise slows down with the increase inyield.
(4) The minimum size of solid particles is100μm. The twoparticle-shaped reactants cannot mix uniformly and automatically, hence premix is preferential. They can settle simultaneously via size match, whichcould enhance the transfer and reaction efficiency. There is no difference intemperature between the gas and the particles because of the small particlesize and low solid content.
At last, a reactor based on the slurry bubble column reactor is put forward,then preliminarily designed and mathematically modeled to research theapplicability of other reactor types. The solutions via programming inMATLAB demonstrate that: the reactor behaves well, and the feeds becomeliquid-state eutectic mixtures at the whole operation range. Along the reactorheight, the concentration and the conversion rate of the product increases, andthe maximum concentration is50mol/L approximately, where the conversionrate can no longer enhance by the height growth in retained liquid calciumcarbide.
引文
[1] http://www.sinopecnews.com.cn/info/2006-06/15/content_389127.htm
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[4]牙金艳.乙炔中磷化氢测定方法的改进[J].维纶通讯,2009,29(1):40-41
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[8]吴樟生.我国电石行业现状分析与未来展望[J].化工管理,2007,34(9):67-71
[9]陈伟雄.我国电石市场分析[J].化工科技市场,2005,28(4):50-51
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[19]Müller M B. Structure, properties and reactions of CaO in burnt lime. Part3. Compositereaction of CaO and C in solid and liquid state[J]. Scandinavian Journal of Metallurgy,1990,35(19):210-217
[20]Guodong Li, Qingya Liu, Zhenyu Liu. Production of calcium carbide from fine biochars[J].Angewandte Chemie.2010,49(45):8480-8483
[21]Mu J J, Hard R A. A rotary kiln process for making calcium carbide[J]. Industrial&Engineering Chemistry Research,1987,26:2063-2069
[22]李国栋.粉状焦炭和粉状氧化钙制备碳化钙新工艺的基础研究[D].北京化工大学,2011
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[2]中国煤炭资源预测与评价[R].北京:中国煤田地质总局,1999
[3]钱伯章,朱建芳.煤化工发展中的前景与问题[J].西部煤化工,2008,23(2):7-16
[4]牙金艳.乙炔中磷化氢测定方法的改进[J].维纶通讯,2009,29(1):40-41
[5]辛彩芬,钱新荣.电石乙炔制化工产品路线评述[J].化学进展,1994,6(1):62-84
[6]陈英军.我国电石工业坝状、消费市场及发展方向[J].中国非金属矿工业导刊,2004,43(5):89-90
[7]王炳盛,刘亚奎.电石生产的发展方向[J].中国氯碱,2007,45(5):43-44
[8]吴樟生.我国电石行业现状分析与未来展望[J].化工管理,2007,34(9):67-71
[9]陈伟雄.我国电石市场分析[J].化工科技市场,2005,28(4):50-51
[10]蔡杰.我国电石行业现状及发展建议[J].化工技术经济,2006,24(9):6-9
[11]梁锡伟,刘立成,邵冰然.电石法PVC生产原料现状及前景预测[J].聚氯乙烯,2005,12(3):1-6
[12]熊谟远,岳宏亮.电石生产加工与产品开发利用及污染防治整改新技术新工艺实用手册[M].北京:化学工业出版社,2005,992-993
[13]李承志.2006年中国PVC产业动态与分析[J].聚氯乙烯.2007,38(8):47-52
[14]李闽豫.半密闭式电石炉烟气治理设备选择与实践[J].现代化工,1999,19(1):8-10
[15]郑国汉.电石生产技术进展[J].现代化工,1985,105(3):22-25
[16]Rai H J, Gregory N W. The time dependence of effusion cell steady-state pressures of carbonmonoxide and calcium vapors generated by the interaction of calcium oxide and graphite[J].The Journal of Physical Chemistry,1970,74:529-534
[17]Hiroaki Tagawa, Sugawara. The kinetics of the formation of calcium carbide in a solid-solidreaction[J]. Bulletin of the Chemical Society of Japan,1962,35(8):1276-1279
[18]Wang Jie, Morishita, Takarada Takayuki. High-temperature interactions between coal charand mixture of calcium oxide, quartz, and kaolinite[J]. Energy&Fuels,2001,76(15):1145-1152
[19]Müller M B. Structure, properties and reactions of CaO in burnt lime. Part3. Compositereaction of CaO and C in solid and liquid state[J]. Scandinavian Journal of Metallurgy,1990,35(19):210-217
[20]Guodong Li, Qingya Liu, Zhenyu Liu. Production of calcium carbide from fine biochars[J].Angewandte Chemie.2010,49(45):8480-8483
[21]Mu J J, Hard R A. A rotary kiln process for making calcium carbide[J]. Industrial&Engineering Chemistry Research,1987,26:2063-2069
[22]李国栋.粉状焦炭和粉状氧化钙制备碳化钙新工艺的基础研究[D].北京化工大学,2011
[23]Kameyama N. Electrochemistry: Theory and applications[M]. Tokyo: Maruzen,1956:134-141
[24]Müller M B. Structure, properties and reactions of CaO in burnt lime. Part2. Diffusion ofcarbon into solid lime[J]. Scandinavian Journal of Metallurgy,1990,67(19):191-200
[25]黄俊虎.电石产品[M].北京:化学工业出版社,1990:15-19
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