Pinch analysis at Preem LYR II - Modifications

2014

Energy efficiency has become an important feature in the design of process plants due to the rising cost of energy and the more stringent environmental regulations being implemented worldwide. In South Africa as in other African countries, most of the chemical plants were built during the era of cheap energy with little emphasis placed on energy efficiency due to the abundance of cheap utility sources such as coal and crude oil. In most of these plants, there exists significant potential for substantial process heat recovery by conceptual integration of the plant's heat exchangers. Pinch Technology (PT) has been demonstrated to be a simple and very effective technique for heat integration and process optimization. This study applies the PT approach to retrofit the heat exchangers network of the Crude Distillation Unit (CDU), of a complex petroleum refinery with the aim to reduce utilities requirement and the associated gaseous pollutants emission. This objective is accomplished by firstly conducting an energy audit of the unit to scope for potential energy saving. The existing Heat Exchanger Network (HEN) was re-designed using the remaining problem analysis (RPA) to achieve improved process energy recovery while making maximum use of the existing exchangers. The aim is to maintain the existing plant topology as much as possible. This network was later relaxed trading heat recovery with number of heat transfer unit so as to optimize the capital cost. These were implemented in AspenPlus v7.2 environment. The cost implications of the retrofitted and evolved networks including the capital and operating costs were determined on a 5 years payback time basis. The Problem Table (PT) analysis revealed that the minimum utilities requirements are 75 MW and 55 MW for the hot and cold utilities respectively. Compared to the existing utilities requirements of 103 MW for hot utility and 83 MW for cold utility, this represent a potential savings of about 26 % and 33 % savings for the hot and cold utilities respectively. The target utilities usage in the re-designed network after applying Remaining Problem Analysis (RPA) was found to be 55 MW for the cold utility and 75 MW for hot utility. The relaxed HEN required a cold utility of 62.5 MW and hot utility of 81 MW. From the total cost estimation, it was found that, although an energy saving of 34% can be achieved by the redesigned network before relaxation, the capital cost, US$ 1670000 is significantly higher than for the existing network (about US$ 980000). The final relaxed network gave an energy saving of 34% and with total cost of US$ 1100000. It was recommended from the study after cost comparisons of the four different networks (the original network, the MER network, the relaxed network and a grass-root design) that the best network for the retrofit purpose was the relaxed HEN, because there is no major shift in iv deviation from the topology of the original network. From the analysis it was found that a 34% saving in energy cost could be achieved from this retrofit. The Total Annual Cost (TAC) for this network gives credence to the fact that this retrofit which applied the rules of pinch analysis can bring about real saving in energy usage. v research. He was paramount to the essence of the research. He assisted in obtaining the data used for the study from the Nigerian National Petroleum Company, whose help is also acknowledged. My sincere thanks also go to Dr. Adeniyi Isafiade, my co-supervisor for his invaluable advice, guidance and criticism throughout the research. vii TABLE OF CONTENTS DECLARATION .

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.

Increasing global competition and the petroleum crises have forced manufacturers of hydrocarbon products to improve the performance of their processes. In modern times, global warming is forcing a change in the way we consume fossil fuels and atmospheric carbon dioxide emissions are now recognized as a major cause of the greenhouse effect. The purpose of this work is to provide a methodology to apply energy integration to retrofit (EITR) a petrochemical plant using the Pinch Technology concept, building a heat exchanger network to reduce the overall consumption of hot and cold utilities. For this study, process data such as flow rates, temperature, pressure and composition for the process streams and utilities were obtained from a polyethylene production plant. Then the thermodynamic and transport properties for the process streams were calculated and data reconciliation was performed using the balances of mass and energy to provide data validation. With validated data, the energy integration algorithm was performed and the target of minimum utilities consumption was compared with the existing plant consumption. The polyethylene production plant used in the case study showed several options for energy integration improvements. Some of these options are presented in this work showing that it is possible to achieve significant economic benefits in the plant. Energy savings are realized via a modification in the existing heat exchanger network and by the use of a flue gas stream to produce steam and a process stream to produce chilled water. The results of this study indicated possible reduction in plant consumption of hot and cold utilities by 9% and 24% respectively, with a payback period estimated at 2.3 years.

Ecos 2005 18th International Conference on Efficiency Cost Optimization Simulation and Environmental Impact of Energy Systems, 2005

Exergy concept combined with pinch based approach are used for studying the optimal integration of energy conversion systems. The analysis first considers the representation of the hot and cold composite curves of the process and defines the energy and the exergy requirements. The basic assumption of the ∆T min required for the pinch analysis is represented as a distinct exergy loss that increases the exergy requirement of the process. The exergy composite curves put the focus on the opportunities for heat pumping in the process. The optimal integration of the utility system is then realised by extracting the energy conversion system configuration from a superstructure using a Mixed Integer Linear Programming formulation. In the latter, the heat cascade definition and the combined heat and power production balances are introduced as constraints and the exergy losses minimisation is used as an objective function. The resulting balanced exergy composite curves are used to visualise the exergy losses in the heat exchanges of both process and utilities. The analysis of the results is made using a definition of the exergy efficiency that accounts for the pinch point location, the process exergy and the exported energy services. 1 Nomenclature CHP Combined heat and power COP Coefficient of performance of the refrigeration cycles and the heat pumps ∆T min Minimum heat recovery approach temperature for the heat exchangers ∆T min /2 j Minimum heat recovery approach temperature contribution of the stream j ∆H Enthalpy difference [kW] ∆S Entropy difference [kW/K] e f uel specific exergy of the fuel [kJ/kg] M f uel fuel flowrate [kg/s] E Exergy [kJ] Eq Heat exergy [kJ] Eq cool Exergy available below the pinch point [kW] Eq f rg Exergy required for the refrigeration[kW] Eq heat Exergy required above the pinch point [kW] E + Exergy resource consumed by the process[kW] Eq hot a Heat exergy delivered by the hot streams above the ambience[kW] Eq hot r Heat exergy required to cool down the hot streams below the ambience[kW] Eq cold a Heat exergy required by the cold streams above the ambience[kW] Eq cold r Heat exergy delivered by the cold streams below the ambience[kW] GT Gas turbine HP Heat pump system LHV Lower Heating Value [kJ/kg] MER Minimum Energy Requirement MILP Mixed Integer Linear Programming P Pressure[bar] P low Evaporation pressure of a refrigeration cycle or a heat pump [bar] P high Condensing pressure of a refrigeration cycle or a heat pump[bar] Q Heat Load [kW] T Temperature [K] T in Inlet temperature of a stream [K] T out Target temperature of a stream [K] T low Evaporation temperature of a refrigeration cycle or a heat pump [K] T high Condensing temperature of refrigerationcycle or a heat pump [K] T 0 Ambient temperature [K] (298 K in this paper) Total 1 Equivalent energy computed with a fuel equivalence of 1.81 for the electricity (η el = 55%)[k

Journal of Power and Energy Engineering, 2013

Energy efficiency has become an important feature in the design of process plants with the rising cost of energy and the more stringent environmental regulations being implemented worldwide. In South Africa, as elsewhere, most process plants built during the era of cheap energy place little emphasis on the need for energy recovery due to the abundance of cheap utilities sources such as coal. In most of these plants, there exist significant potential for substantial process heat recovery by conceptual design of the heat recovery system. By maximizing heat recovery from the processes, there will be a reduction in the process utilities requirement and the associated environmental effects. Pinch analysis has been demonstrated to be a simple but very effective tool for heat integration and optimization of chemical plants. This study uses the pinch principle to retrofit the heat exchanger networks (HEN) of the crude distillation unit of an integrated petroleum refinery to evolve a HEN that features optimum energy recovery. The network was further relaxed by trading off energy cost with capital cost to obtain an optimal HEN topology not too different from the existing network. The simulation works were implemented in AspenPlus v8.0 environment. Analysis revealed that 34 per cent saving on energy usage per annum is realizable. This significant saving in energy also results in diminished gaseous pollutants associated with energy usage.