Heat Exchanger Network Design

In synthesizing optimal heat recovery networks, Composite Curve (CC) plots and Problem Table Algorithms (PTAs) have been the most popular tools for determining the minimum energy targets, whereas Grid Diagrams (GDs) have been widely utilized for heat exchanger network (HEN) design. However, CCs are cumbersome to construct. Additionally, PTAs offer numerical advantages but little insight into the impact of process streams on pinch points and heat recovery bottlenecks. Meanwhile, GDs are separately needed to diagnose HEN pinch rule violations. This paper introduces the Grid Diagram GDT) as an alternative tool for determining pinch points and utility targets as well as for the retrofitting of HEN. The GDT combines numerical and visualization advantages into a single diagram. The GDT, which is represented according to a stream interval temperature scale and is developed based on fundamental Composite Curve geometry, can provide vital information during the identification of the pinch points and energy targets of a process as well as enhance the intuitive visualization of pinch rule violations that are especially useful for the rapid and effective debottlenecking of an existing heat recovery system to maximize its thermal energy efficiency. This paper also demonstrates the application of the GDT in addressing a single-pinch problem, multiple-pinch problem and an industrial case study involving a palm oil refinery.

The synthesis of heat exchanger networks (HENs) has mainly been done through the use of approximate models for each of the individual heat exchangers that comprises the network. These approximate models do not adequately take into account key parameters such as the overall heat transfer coefficient , TEMA standards, pressure drops, FT correction factors, and multiple shells. These factors can significantly alter the cost of the network. This paper presents a new methodology for the synthesis of heat exchanger networks using detailed heat exchanger design models that takes into account the aforementioned design parameters. The newly developed method involves the following steps. First, a SYNHEAT (Yee and Grossmann, 1990) MINLP model is solved. The individual exchangers for the resulting network are then designed using heuristics, TEMA standards and the Bell-Delaware method. From the designs obtained for these individual exchangers, correction factors are inserted into the SYNHEAT model that account for changes in overall heat transfer coefficient, TEMA choices, pressure drops, Ft correction factors and the effect of multiple shell passes. The SYNEAT model is then rerun and individual exchangers redesigned and the procedure repeated until convergence is achieved. For each iteration the change in each correction factor is limited to avoid the omission of certain solutions. While the methodology cannot guarantee global optimality it can ensure that the synthesised processes are physically achievable and has also been shown to converge on physically meaningful parameters without the explicit formulation of complicated non-linear equations in the MINLP formulation.

The present paper proposes a technique to enlarge the capabilities of pinch analysis. Conventional pinch analysis is limited to heat exchange between streams of unchanging composition, whereas in reality, much heat exchange occurs in components such as chemical reactors, mixers etc. This can be overcome by introducing virtual heat exchangers that convert the considered components into equivalent heaters and coolers where the stream compositions remain unchanged. In this way, they are automatically taken into consideration in the current pinch analysis packages, which may lead to different and better optimisation. A client-server interface program has been written to introduce virtual heat exchangers after completion of the process analysis through Aspen Plus and before entering the pinch analyser Super Target. The application of virtual heat exchangers is next illustrated through a simple example for methanol synthesis.

Objective of this review paper reviews the literatures related to the parallel and counter flow of different types of heat exchangers and modifications made to improve the performance. Various papers were reviewed from those papers what are the developments in parallel and counter flow heat exchanger are summarized. The development of any system is need because it helps to optimize, improve performance or reduce the cost of system. The heat exchanger development did by many researchers using software's, design methods, changing the designs, changing shape of tubes, applying second law of thermodynamics etc. The fluid velocity, Reynolds number, overall heat transfer coefficient, baffle spacing, number of baffles, pressure drop, LMTD, helix angle of tubes plays very important role in heat exchanger performance.

Nowadays, decreasing the amount of natural resources and increasing the price of it, motivates to consider energy conservation as a main concern of many process industries, especially oil, refinery and petrochemical plants.
Pinch Analysis (PA) is a powerful method for identifying and selecting technical solution to improve efficiencies and provide an optimum procedure for energy saving.
This paper analyses, the effectiveness of applying PA to optimize energy consumption for a given set of process streams in a Petrochemical Company in Iran. In this study, firstly, the interested process streams have been selected, maximum heating and cooling load are computed, and then composite curves have been drawn - by Matlab code - which provides a visual profile of the availability of heating or cooling from the process streams. Secondly, the cost of recovered heat is computed in terms of fuel saving, which confirms applying PA could save significant amount of fuel expenses for the company. Finally, the corresponded Heat Exchanger Network (HEN) has been designed, and the investment costs for heat exchangers have been computed in order to find out payback time of the investment costs which is approximately 17 months for this case study.