Ljubica Matijašević

Energy recovery by pinch technology

This paper shows how the application of pinch technology can lead towards great energy savings. The heat exchanger network of a nitric acid plant has been studied and it was found that it is possible to reduce requirements for cooling water and medium pressure steam. In order to enable these savings, three heat exchangers should be replaced with new ones. Energy consumption in steam power system increases slightly. However, the final result is a reduction of energy costs and a payback time of 14.5 months.

Multi-Product Dividing Wall Columns: A Simple and Effective Assessment and Conceptual Design Procedure

The objective of this paper is to further exploit and demonstrate the potential benefits of a V-min diagram based analysis, using a fifteen component feed mixture as base case. Detailed explanations are given on how to interpret properly a V-min diagram and use it for DWC assessment. Emphasis is on how to set the component or fraction splits to maximize potential gains as well as how to handle some variations in the feed with the same purpose. Interestingly, it appeared that depending on the choice and specification of interesting products (components or fractions), a simplified four-product DWC and even five-product DWC could be an interesting option for aromatics processing plants.

Analysis of Cooling Water Systems in a Petroleum Refinery

An important area in process integration is the development of methodologies to minimize water and energy use in industry. More than 20 % of the energy consumption in industry is associated with cooling and heating water. This paper presents analysis and optimization of a re-circulating cooling water system, with the aim to satisfy any supply conditions for the cooling tower. The part of the atmospheric crude oil distillation unit was chosen for analysis and synthesis of cooling water systems by the Kim and Smith design (KSD) method. The load of the cooling tower and the cost related to the cooling water system could be reduced by modifying the configuration of the heat exchanger network. In this paper, the KSD methodology for a developed heat exchanger network is expanded with the principle based on the heuristic algorithmic water sources diagram procedure (WSD) to synthesize the mass exchange network. These procedures are advantageous compared with other methodologies since hand calculation is used, a very useful feature for process engineers. The cooling water network was synthesized, leading to a 40 % reduction in cooling tower load, and consequently, lower operating costs and water consumption.

Integration of hydrogen systems in petroleum refinery

Considering the importance of hydrogen in crude oil refining, it is necessary to ensure its most efficient use to satisfy refinery hydrogen requirements. Effective hydrogen management provides maximum utilization of hydrogen. The mass balance of streams containing hydrogen plays a key role in addressing the hydrogen-network optimization problem. The purpose of this work was to analyze the refinery hydrogen network, composed of hydrogen sources and sinks. Mass integration principles and techniques have been applied in the optimization of the refinery hydrogen network. The methodology of hydrogen network integration is presented in a case study of a local petroleum refinery. The main objectives are to provide different solutions for reducing the amount of hydrogen not properly used in the local refinery and which is mostly sent to the fuel system, as well as the operating costs. Hydrogen pinch analysis is applied for targeting the minimum hydrogen consumption of the hydrogen system. A superstructure- based mathematical model of the hydrogen network is developed to minimize the total operating costs. The non-linear programming optimization problem is solved by using optimization software GAMS. An additional hydrogen purification unit is introduced in the existing hydrogen network and the effect on the overall network is investigated. Network design with two hydrogen purification units has proved to be an optimal solution, with respect to the chosen objective function. These analyses and their results can assist the refinery to reduce and improve the efficiency of hydrogen management. The analyses covered only the existing equipment without additional investment.