生質柴油製程之整廠程序設計與控制

Plantwide Design and Control of Biodiesel Production

10.6342/NTU.2008.01503

沈胤亨

生質柴油製程 ； 反應器設計 ； 程序設計 ； 整廠控制 ； biodiesel production ； reactor design ； process design ； plantwide control

國立臺灣大學化學工程學系學位論文

2008年

碩士

余政靖

繁體中文

本研究探討生質柴油製程設計與控制，針對鹼性觸媒氫氧化鈉催化之大豆油與甲醇轉酯化反應系統，選擇三油酸甘油酯（triolein）代表精煉之大豆油，並以基團貢獻法UNIFAC估算相平衡，採用Noureddini and Zhu（1997）所回歸的二階基本反應速率式參數。根據反應產物間相互溶解度差異極大，及單酸甘油酯轉化為甘油之反應平衡常數較大此兩種特性，以分相槽將反應器出口物流液液分離，並利用富含甲醇的甘油相產物回流至反應器再使用，藉以提高反應器內過量反應物之莫耳數比。利用反應系統內部之甘油相回流，達到限量反應物三酸甘油酯99 mol％轉化率，可將反應系統所須進料莫耳數比降低至原先的60％以下。 為了確認此內部回流反應系統能改善製程，分別針對兩種不同反應系統進行整廠程序設計，計算年總成本（TAC）並找出各自最適化設計架構。其中，使用內部回流反應系統將整廠程序最小年總成本降低至傳統反應系統的79％，整廠程序所須之能耗約可減少31％。在系統動態方面提出利用溫度控制之控制架構，雖然造成產品組成稍有偏差，但最終產品仍能達到生質柴油的燃料規範，藉由動態模擬得知，此控制架構能夠排除整廠程序±20%之煉量擾動，驗證了此整廠程序操作之可行性。

This work explores the design and control of biodiesel production processes. Triglyceride reacts with methanol to form methyl esters and glycerol. The transesterification reaction is catalyzed by homogeneous alkaline, NaOH in this example. Triolein is used to represents refined soybean oil and the vapor-liquid-liquid equilibria are estimated using UNIFAC. The reaction kinetics is taken from Noureddini and Zhu (1997). Because the reactor effluent exhibits phase separation (two-liquid phase), a reaction/separation system is devised to improve the conversion. This is a combined reactor and decanter module with internally recycled glycerol phase which is rich in one of the reactant, methanol. The result shows that, to achieve the same conversion level (99%), the proposed simultaneous reaction/separation system reduces the molar feed ratio (methanol/triglyceride) by a factor of 40%. Next, the design is extended to of the entire biodiesel production plants, including recycle and purification systems. Comparison is made between the conventional and the proposed reaction systems. Design objective is to minimize the total annual cost (TAC) by varying dominant design variables. The results show that a 20% reduction in the TAC can be achieved using the simultaneous reaction/separation system. This also corresponds to a 31% reduction in the energy cost. Finally, plantwide operability of the entire biodiesel production plant is evaluated. The entire plant consists of 35 control loops and simulation results indicate that the proposed process can handle 20% production rate changes with reasonable dynamic performance.

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