Heat Exchanger Network Retrofit of Diesel Hydrotreating Unit Using Pinch Analysis

Diesel hydrotreating unit(DHT)is an integral part of the refinery,and its energy-saving optimization is of great significance to the enterprise.In this paper,process simulation software and energy management software are used to simulate the flowsheet and analyze the energy consumption,respectively.Stream data obtained from an existing DHT are applied in the pinch analysis for retrofitting the heat exchanger network(HEN)to achieve maximum energy utilization by using pinch analysis.Since DHT is constrained by pressure,the pressure factor is considered in the process of retrofitting.The results show that the amount of cross-pinch heat transfer is reduced,the inlet temperature of the furnace is increased by 55℃,and the amount of hot and cold utilities can be reduced by 70.25%and 50.16%,respectively.The economic evaluation indicates that the operating cost is saved by 4.39×10^(6)$/a,and the payback period is about 2 months.

Heat Exchanger Network Retrofit for Optimization of Crude Distillation Unit Using Pinch Analysis

Crude distillation unit(CDU)is regarded as the main energy consumer in the entire refinery process.In this paper,the process simulation software and the energy management software are used to simulate the flowsheet and analyze the energy consumption,respectively.Stream data obtained from an existing CDU are applicable in the pinch analysis.To reduce the amount of cross-pinch heat transfer,three approaches of resequencing,repiping,and adding heat exchangers are adopted.Compared with the existing CDU,the results demonstrate that the inlet temperature of the furnace can be increased by 25.4℃,the amount of hot and cold utilities can be reduced by 15.1%and 19.6%,respectively.The economic evaluation indicates that the operating cost is saved by 8×106$/a,and the payback period is about 9 months.

Gas Flare Design Debottlenecking Using Pinch Analysis

Gas flaring is concerned with the combustion of lighter ends of hydrocarbon mostly produced in association with crude oil. Flare networks are designed to handle the gas volume required to be flared. Most times, this flare networks are in close proximity but still have independent flare stacks, increasing risk to environment and cost on infrastructures. There is a need to integrate the flare networks in facilities within same area and through the application of Pinch Analysis concept, the resultant flare network can be optimized to give a system having optimal tail and header pipe sizes that will reduce cost and impact on environment. In the light of the foregoing, the concept of pinch analysis was used in debottlenecking integrated gas flare networks from a flow station and a refinery in close proximity. Both flare networks were integrated and the resultant gas flare network was optimized to obtain the optimum pipe header and tail pipe sizes with the capacity to withstand the inventory from both facilities and satisfy the set constraints such as Mach number, noise, RhoV2 and backpressure. Mach number was set at 0.7 for tail pipes and 0.5 for header pipes, noise limit was not to exceed 80 dB upstream and 115 dB downstream the sources, RhoV2 was limited to 6000 kg/m/s2 and the back pressure requirement was source dependent respectively. The fire case scenario was considered, as it is the worst-case scenario in the studies. When pinch analysis was applied in debottlenecking the combined gas flare network, it gave smaller tail and header pipe sizes which is more economical. A 20% decrease in pipe sizes was recorded at the end of the study.

Energy and Exergy Analysis for Low-Temperature Refrigeration System for Biogas Upgrading

Low-temperature refrigeration system for biogas upgrading has been developed by the Cryo Pur company based on cooling biogas in three steps： Removing most of the water content at -40 ℃, removing siloxanes and SVOCs at -85 ℃ and frosting CO2 at temperatures varying from -90 ℃ to -120 ℃. This process transforms biogas containing typically 60% methane, 35% CO2, 5% water vapor in methane containing 2.5% of CO2. This paper studies how a single low-temperature refrigeration system is able to cool biogas with an indirect system using low-temperature heat-transfer fluids. The exergy study defines the exergy losses and served as guidance for the energy/pinch analysis that is used for the design of the heat-exchanger series and the appropriate heat recovery. An optimal system could save up to 40% of the electric consumption of the refrigeration system.

Simultaneously Designing and Targeting for Networks with Multiple Resources of Different Qualities

This paper presents a new design procedure for the networks with multiple resources, such as hydrogen and water, of different qualities. The minimum consumption targets of the resources and pinch-causing sources can be identified as well during design. The objective of this work is to reduce the consumption of the resources with higher quality due to their higher cost. A few examples are investigated to show the proposed method. For a net-work of single resource with single contaminant, there is often only one pinch point for the resource. On the other hand, for a network of multiple resources with single contaminant, there might be a few different pinch points. Each resource might have its own pinch point, if its amount is sufficient. The contaminant concentration of the pinch-causing source for a resource with lower concentration will be below that of the higher-concentration resource(s).

Heat Integration for Different Separation Processes

The distribution of heat duties among individual separation subsystems and other aspects of heat integration in such systems are reviewed. Heat integration for different separation processes is investigated, using the pinch point method. Such a study will provide theoretical guide lines for the proper choice of a desirable separation process.

RHO:A Software Tool for Targeting and Design of Refinery Hydrogen Networks

Hydrogen management is important for refineries to improve their business efficiency.Various approaches such as pinch analysis and mathematical programming have been employed in the management of hydrogen system.However,it is not easy for site engineers to implement these techniques,due to the complicated procedures.At this point,it is necessary to develop a software that can implement the proposed methodologies automatically,which is really the goal of this work.The presented refinery hydrogen system optimization software(RHO)is a web based system.It is developed in the Java Web environment,where the subroutines of mathematical model developed in GAMS software can be easily called.RHO can generate graphics of both the hydrogen pinch diagram and the hydrogen distribution network.The purifiers as well as the physical distances between units are considered in the optimization model.In addition,there is a special module for the calculation of membrane separation,which is very important in the hydrogen network.The functions and the interfaces of the software are illustrated via practical cases.Case studies show the effectiveness of the RHO software.

Performance Assessment of Heat Exchangers for Process Heat Integration

Pinch Analysis is an attractive solution for reduction of thermal energy costs in thermo-chemical industries.In this approach,maximum internally recoverable heat is determined and a heat exchange network is designed to meet the recovery targets.The thermal performance of a heat exchanger over its lifetime is however a concern to industries.Thermal performance of a heat exchanger is affected by many factors which include the physical prop-erties of the shell and tube materials,and the chemical properties of the heat transferfluid.In this study,thermal performance of shell and tube heat exchangers designed to meet heat recovery targets in a Pinch Analysis study is simulated.The aim of this paper is to present predictions of thermal performances of shell and tube heat exchan-gers with different heat transferfluids and geometries as they undergo fouling degradation.Engineering approaches based on thermodynamic analysis,heat balance and Kern Design equations,as well as what-if simu-lation modeling are used in this work.Shell and tube heat exchangers were designed to meet internal heat recov-ery targets for three process plants,A,B and C.These targets were published in a separate paper.The effects of degradation of the tubes-due to incremental growth of fouling resistance-on thermal performance of the exchan-ger were simulated using Visual Basic Analysis(VBA).Overall,it was found that growth in fouling reduces ther-mal efficiency of shell and tube heat exchangers with an exponential relationship.An increase of 100%of fouling resistance leads to an average reduction of 0.37%heat transfer.Higher values of logarithmic mean temperature difference(LMTD)and higher ratios of external diameter to internal diameter of the exchanger tubes amplify the effect of fouling growth on thermal performance of the exchangers.The results of this work can be applied in pinch analysis,during design of heat exchangers to meet the internal heat recovery targets,especially in predicting how fouling growth can affect these targets.This can also be useful in helping operators of shell and tube heat exchangers to determine cleaning intervals of the exchangers to avoid heat transfer loss.

Heat Integration retrofit analysis --an oil refinery case study by Retrofit Tracing Grid Diagram

Heat Integration has been established over the last decades as a proven chemical engineering methodol- ogy. Two design implementations are often used in the industry： grassroots and retrofit. Although various methods have been developed for retrofit, it still needs more development to ensure simultaneously thermodynamic feasibility and economic viability. In this paper, a novel graphical approach has been developed to facilitate the understanding of the current situation and scope of improvement. The Retrofit Tracing Grid Diagram presents all streams and heat exchangers in temperature scale and the heat exchangers are clearly separated from each other, enabling clear visualisation of the current state. The tool incorporates the previously developed Cross-Pinch Analysis as well as path approach for retrofit. Additionally, the non-vertical heat transfer can be evaluated. The application of the developed tool has been validated on an oil refinery case study. The applicability of the tool is evident as it can reveal additional options for modification that none of the previous methods considered.

An area method for visualizing heat-transfer imperfection of a heat exchanger network in terms of temperature–heat-flow-rate diagrams

The identification of the imperfection originating from finite-temperature-difference heat transfer is an indispensable step for both the performance analysis and the better design of a heat exchanger network （HEN） with the aim of energy saving. This study develops a convenient area method for visualizing the heat-transfer imperfection of a HEN in terms of temperature-heat flow diagrams （ T-Q diagrams） by combining the composite curves that have already been used in pinch analysis and the re- cently developed entransy analysis. It is shown that the area between the hot and cold composite curves and the hot and cold utility lines on a T-Q diagram is just equal to the total entransy dissipation rate during the multi-stream heat transfer process occurred in a HEN, and this area can be used to graphically represent the total heat-transfer imperfection of the HEN. The increase in heat recovery or decrease in energy requirements with decreasing the minimum temperature difference, ATmin, of a HEN can then be attributed to a lower entransy dissipation rate, quantitatively represented by the decrease of the area between the composite curves and the utility lines. In addition, the differences between the T-Q diagram and the pre-existing energy level-enthalpy flow diagram （12-H diagram） in the roles of visualizing process imperfection and designing HENs are dis- cussed.