دانلود رایگان ترجمه مقاله عملیات تقطیر یکپارچه حرارتی (نشریه الزویر 2010)

عملیات تقطیر یکپارچه حرارتی

Heat integrated distillation operation

Abstract

Increasing energy demand, consequently high crude oil prices and growing concern for pollution motivated the researchers to explore more energy-efficient and environment-friendly process technologies. Although the heat integrated distillation has been researched for a number of decades, unfortunately it has not yet been commercialized mainly due to high investment cost, complex equipment design, control problem in consequence of severe interaction and nonlinearity, and lack of experimental data at sufficiently large scale to verify the theoretical predictions. It is true that some progress has been made in theory but for practical applications many questions still remain. Among the broader research needs the following areas are identified for heat integrated distillation column: rigorous dynamic modeling, optimal design, multiple steady state analysis, system identification, synthesis and implementation of high-quality nonlinear control, and importantly experimental evaluation. It is also suggested to investigate the feasibility of heat integration in the reactive distillation schemes and in the two distillation columns having no direct connections.

1 Introduction

Distillation, which is the workhorse of chemical process industries, is quite energy intensive and accounts for an estimated 3% of the world energy consumption [1,2]. It is a fact that energy consumption in distillation and CO2 gases produced in the atmosphere are strongly related. The higher the energy demands are, the larger the CO2 emissions to the atmosphere are. This is because the energy is mostly generated through the combustion of fossil fuel.

To improve the energy efficiency, the heat integration concept was first introduced almost 70 years ago. The basic idea of heat integration approach is that the hot process streams are heat exchanged with cold process streams. In this manner, resources are used more economically. So far, various heat integrated distillation schemes have been proposed. An excellent review [3] has discussed recently these schemes. In the present review, many other heat integration schemes developed so far are discussed in depth. Although several heat integration techniques are covered in this paper, the main focus is placed on the so-called heat integrated distillation column (HIDiC) technique (Fig. 1).

At the end of 1930s, Brugma [4] first proposed a thermally coupled distillation column. This energy-efficient separation operation was re-introduced by Wright [5] and latter analyzed by Petlyuk [6]. Freshwater [7,8] is the first researcher who explored a novel distillation technique that describes the heat transfer from rectifying section to stripping section in a single unit. In the subsequent stage, Flower and Jackson [9] analyzed this approach performing different numerical experiments based on the second law of thermodynamics. Among the various energy-efficient distillation systems, the heat pump-assisted distillation column was first proposed in the mid-1970s [10–12]. The use of mechanical compression as heat pump is economical mainly in separating the low relative volatility mixtures. In recent years, the advanced forms of heat pump-assisted distillation technology are reported in literature [13,14].

The HIDiC concept was first introduced for gas separation processes by Haselden [15]. Since 1977, Mah and his team members [16,17] evaluated the heat integrated distillation column operation under the name of secondary reflux and vaporization (SRV), where only part of the rectifying and stripping sections was integrated for heat transfer. It is notable that they formulated a steady-state equi librium stage SRV model for the first time based on the Wang–Henke tridiagonal matrix method [18] incorporating the trim-reboiler, trim-condenser and compressor in the column structure. In the next, the authors [19,20] extended the internal heat integration to the whole rectifying and stripping sections.

Takamatsu, Nakaiwa and coworkers [21–24] are devoted from the mid 1980s for improving the heat integrated distillation technology. They thoroughly analyzed to evaluate the benefits offered by the heat integrated distillation column over a conventional distillation system. In the next, they [25–27] proposed a unique HIDiC structure that has neither a trim-reboiler nor a trim-condenser and this structure is usually referred to as the ideal heat integrated distillation column (i-HIDiC).

Recently, it is shown [28] that the i-HIDiC is more energy saving operation than the general HIDiC that includes both the reboiler and condenser along with the internal heat integration arrangement. However, when the feed rate has increased above the designated value, the ideal HIDiC is not economical. And in such a case, the HIDiC configuration is preferably used [3].

To achieve an appropriate heat balance, that is, to run the column without a reboiler and a condenser, the feed mixture needs to be preheated before introducing into the ideal heat integrated distillation column. This feed preheating arrangement can also be applied for the HIDiC, if required. When hot overhead vapor outlet of rectifying column of the i-HIDiC is reused as a potential hot utility for the feed preheating, the distillation configuration is referred to as the intensified i-HIDiC (int-i-HIDiC) [3,28]. It is worth noticing that the intensified i-HIDiC is more energy efficient compared to the i-HIDiC [28].

In the recent years, several groups are actively involved in research on energy-efficient distillation column design (e.g., [29– 31]), analysis (e.g., [32,33]) and operations (e.g., [31,34]). Since 1990, several heat integrated distillation structures have also been patented [35–41]. However, a little progress has been noted on steady state multiplicity, optimal process design, system identification, nonlinear controller synthesis and implementation, and experimental testing. The main intention of this review is to focus the present status and future scope of research on heat integrated distillation columns.

In the present review, the work is organized as follows. At the beginning (Section 2), the importance of heat integration in distillation operation has been presented followed by the discussion on several energy-efficient separation techniques in Section 3. The next part (Sections 4 and 5) includes the recent applications of heat integration concept and then the different HIDiC structures. The scope of future research on HIDiC is highlighted in Section 6. Finally, in Section 7, the conclusions are presented.