甲烷氧化偶聯(lián)制乙烯反應器的數(shù)值模擬研究
發(fā)布時間：2018-07-16 11:13
【摘要】：甲烷氧化偶聯(lián)制乙烯工藝是最有希望工業(yè)化的甲烷直接轉化方法,但甲烷氧化偶聯(lián)反應是強放熱反應,催化劑床層容易形成熱點,工業(yè)裝置的溫度難以控制。僅采用實驗的方法實現(xiàn)反應器放大,會導致反應器開發(fā)成本高、周期長。計算流體力學是在流場計算的基礎上,同時考慮流動、傳熱、化學反應等多物理化學現(xiàn)象間的耦合作用,可以準確預測反應器的特性,為反應器的放大提供工藝數(shù)據(jù),降低開發(fā)成本、縮短開發(fā)周期。本文采用計算流體力學方法,利用修改參數(shù)后的Stansch反應動力學模型,首先建立了裝填Na2WO4-Mn/SiO_2顆粒催化劑的OCM固定床反應器實驗室裝置的計算模型,模擬了原料氣體流量為80ml/min常壓操作下顆粒固定床反應器的反應特性。通過對比顆粒催化劑固定床反應器出口處CH_4轉化率、CO_2等產(chǎn)物選擇性的計算值與實驗值,可以發(fā)現(xiàn),所有參數(shù)的計算值與實驗值誤差范圍為±2%,二者吻合較好,模型可靠；通過分析反應器的催化劑床層內(nèi)組分濃度、反應溫度、側壁面熱通量、壓力、流體密度和流速等參數(shù)分布表明：在催化劑床層的進口附近,OCM反應較快,該區(qū)域的溫度稍高于其它區(qū)域,包圍該區(qū)域的反應器壁面放熱較多,熱通量最大值為17500W/m~2；顆粒催化劑床層內(nèi)的OCM反應為變?nèi)莘e反應,并且生成物總摩爾數(shù)大于反應物總摩爾數(shù),導致流體速度沿流動方向逐漸增加,密度逐漸減小。然后,模擬了裝填Na_3PO_4-Mn/SiO_2/堇菁石整體式催化劑固定床反應器,采用與顆粒催化劑固定床反應器計算結果類似的處理辦法,分析計算結果。研究表明,反應器出口處主要參數(shù)計算值與實驗值的誤差范圍為±4%,模型可靠；由于邊界層、化學反應和整體式催化劑結構的影響,導致催化劑床層內(nèi)的流速沿內(nèi)壁面法向方向先升高再降低。裝填顆粒催化劑和整體式催化劑的兩段式固定床反應器可以將這兩種催化劑的優(yōu)點互補。在上述計算的基礎上,模擬研究了兩段式固定床反應器的反應特性,并考察了反應溫度和床層高度對反應器特性的影響。計算結果表明：顆粒催化劑床層內(nèi)OCM反應比整體式催化劑床層內(nèi)的劇烈；與顆粒催化劑床層相比,整體式催化劑床層在耗氧量較小的情況下,可以有效地提高C：產(chǎn)物選擇性和收率；反應溫度通過影響反應網(wǎng)絡內(nèi)各步反應的速率,進而影響各組分質量分數(shù)的分布,導致反應溫度為800℃時,C_2產(chǎn)物選擇性達到最優(yōu)值66.7%；當整體式催化劑床層高度為50mm、位于上游的顆粒催化劑床層高度變化時,由于顆粒催化劑床層出口處各組分的質量分數(shù)存在差異,改變了下游的整體式催化劑床層的進口條件,最終導致C_2收率在顆粒催化劑床層高度為1 Omm達到最優(yōu)值21.8%。由于兩段式固定床反應器內(nèi)整體式催化劑床層內(nèi)氧氣分壓較低,降低了整體式催化劑的活性,導致整體式催化劑無法發(fā)揮其高C：選擇性的優(yōu)勢。在兩段式固定床反應器的兩段床層之間補充氧氣,可以有效提高C_2產(chǎn)物收率。本文在兩段式固定床反應器模擬計算的基礎上,對中間補氧的兩段式固定床反應器進行模擬研究,并考察了補氧量和反應溫度對反應器特性的影響。計算結果表明：對于不同補氧量下的P_(10)M_(50)固定床反應器,補充的氧氣促進了整體式催化劑床層內(nèi)的OCM反應,導致反應器出口處的C_2選擇性和收率隨補氧量的增加而逐漸升高；對于不同溫度下補氧量為15%的P_(10)M_(50)固定床反應器,其整體式催化劑床層上的參數(shù)分布規(guī)律與無補氧的P_(10)M_(50)固定床反應器內(nèi)整體式催化劑床層上的參數(shù)分布規(guī)律類似。在上述模擬研究的基礎上,將兩段式固定床反應器進行放大,設計了乙烯產(chǎn)量為300ton/a的兩段式固定床反應器的中試裝置,并采用與實驗室小反應器模擬中相同的數(shù)學模型對其進行模擬,同時考察了冷卻劑流量和冷卻劑進口溫度對反應器特性的影響。通過分析列管式固定床中試反應器內(nèi)冷卻劑流速、溫度和反應氣體的組分質量分數(shù)以及壁面熱通量、對流換熱系數(shù)等反應器的特性參數(shù)的分布,得到如下結論：顆粒催化劑床層溫度是決定C_2H_6產(chǎn)量的主要因素,而整體式催化劑床層溫度是決定C_2H_4產(chǎn)量的主要因素；當冷卻劑流量為453ton/h,冷卻劑進口溫度為790℃,原料氣體流量為594Nm~3/h,原料氣體進口溫度為775℃,烷氧比為3時,所設計的反應器滿足設計要求。
[Abstract]:Based on the calculation of flow , heat transfer , chemical reaction and so on , it is possible to predict the characteristics of the reactor accurately and to reduce the development cost and shorten the development cycle .
By analyzing the concentration of components , the reaction temperature , the heat flux , pressure , fluid density and flow velocity in the catalyst bed of the reactor , it is shown that the OCM reaction is faster in the vicinity of the inlet of the catalyst bed , the temperature of the region is slightly higher than that of other regions , and the heat flux is more than 17500W / m ~ 2 .
The reaction of OCM in the bed of catalyst bed is variable volume reaction , and the total number of moles of product is greater than the total number of moles of reactants , resulting in a gradual increase in the velocity of the fluid along the flow direction and a gradual decrease in density . The results are analyzed by a similar approach to the calculation results of the fixed bed reactor of particulate catalyst . The results show that the error range of the main parameters at the outlet of the reactor and the experimental value is 鹵 4 % and the model is reliable ;
Due to the influence of boundary layer , chemical reaction and monolithic catalyst structure , the flow velocity in the catalyst bed is increased and then decreased in the direction of the inner wall surface method . The two - stage fixed bed reactor filled with granular catalyst and monolithic catalyst can complement the advantages of the two catalysts . On the basis of the above calculation , the reaction characteristics of the two - stage fixed bed reactor are simulated and the influence of reaction temperature and bed height on the characteristics of the reactor is studied .
Compared with the granular catalyst bed layer , the monolithic catalyst bed layer can effectively improve the selectivity and the yield of the product under the condition that the oxygen consumption is small ;
By influencing the rate of reaction in the reaction network , the reaction temperature affects the distribution of the mass fraction of each component , which results in the selectivity of the C _ 2 product reaching the optimum value 66.7 % when the reaction temperature is 800 鈩，
本文編號：2126207
[Abstract]:Based on the calculation of flow , heat transfer , chemical reaction and so on , it is possible to predict the characteristics of the reactor accurately and to reduce the development cost and shorten the development cycle .
By analyzing the concentration of components , the reaction temperature , the heat flux , pressure , fluid density and flow velocity in the catalyst bed of the reactor , it is shown that the OCM reaction is faster in the vicinity of the inlet of the catalyst bed , the temperature of the region is slightly higher than that of other regions , and the heat flux is more than 17500W / m ~ 2 .
The reaction of OCM in the bed of catalyst bed is variable volume reaction , and the total number of moles of product is greater than the total number of moles of reactants , resulting in a gradual increase in the velocity of the fluid along the flow direction and a gradual decrease in density . The results are analyzed by a similar approach to the calculation results of the fixed bed reactor of particulate catalyst . The results show that the error range of the main parameters at the outlet of the reactor and the experimental value is 鹵 4 % and the model is reliable ;
Due to the influence of boundary layer , chemical reaction and monolithic catalyst structure , the flow velocity in the catalyst bed is increased and then decreased in the direction of the inner wall surface method . The two - stage fixed bed reactor filled with granular catalyst and monolithic catalyst can complement the advantages of the two catalysts . On the basis of the above calculation , the reaction characteristics of the two - stage fixed bed reactor are simulated and the influence of reaction temperature and bed height on the characteristics of the reactor is studied .
Compared with the granular catalyst bed layer , the monolithic catalyst bed layer can effectively improve the selectivity and the yield of the product under the condition that the oxygen consumption is small ;
By influencing the rate of reaction in the reaction network , the reaction temperature affects the distribution of the mass fraction of each component , which results in the selectivity of the C _ 2 product reaching the optimum value 66.7 % when the reaction temperature is 800 鈩，
本文編號：2126207
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