logging in or signing up Heat integration and HEN Design tabish288 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: Embed: Flash iPad Copy Does not support media & animations WordPress Embed Customize Embed URL: Copy Thumbnail: Copy The presentation is successfully added In Your Favorites. Views: 1336 Category: Education License: All Rights Reserved Like it (2) Dislike it (0) Added: August 25, 2010 This Presentation is Public Favorites: 0 Presentation Description A presentation for those who are interested to study the basics of "heat Integration and heat exchanger network design (Pinch Technology). Comments Posting comment... By: yudistywn (20 month(s) ago) thx bro :D Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Slide 1: HEAT INTEGRATION HEAT INTEGRATION: Department of Chemical Engineering University of Engineering And Technology, Lahore A.N.Tabish 2009-MS-Chem-25 HEAT EXCHANGER NETWORK DESIGN Slide 2: INTRODUCTION: A cold process stream can be heated by using steam or any hot utility, available at a temperature higher than the target temperature of process stream and a hot process stream can be cold by using cooling water or any cold utility, available at a temperature lower than the target temperature of process stream. Situation refers the maximum use of utility that is merely an operating cost, and maximum annualized cost that demands a larger rate of return to make the process profitable. A cold process stream can be used to lower the temperature of hot process stream, which heats up the cold stream as well. Hence minimizing the use of utility and ultimately operating cost and total annualized cost. HEAT INTEGRATION email@example.com Slide 3: “Heat Integration”, enables the maximum heat exchange between process streams using “Pinch Technology”, that revealed various methods to maximize process-to-process heat exchange and minimized the use of utilities through an integrated network of heat exchangers. Application of Pinch analysis minimizes the energy consumption of chemical processes by calculating thermodynamically feasible energy targets and achieving them by optimizing heat recovery systems, energy supply methods and process operating conditions. It is also known as process integration, heat integration, energy integration or pinch technology. firstname.lastname@example.org Slide 4: Improvement in the energy consumption obtained after successive designs of given product. Slide 5: PROFITABILITY OPTIMIZATION: Design for “Minimum Capital Cost” Design for “Minimum Energy Cost” Optimum Design for “Minimum Energy Cost” Slide 6: Simple process flow sheet Heat integrated flow sheet email@example.com Slide 7: PINCH TECHNOLOGY: Data Extraction: To formulate the process flow sheet and perform heat and mass balance. Minimum Approach Temperature: To select the minimum temperature difference that can be allowed across any heat exchanger in the network. Composite Curves: To draw the enthalpy vs. temperature graph for cold streams as well as for hot streams Minimum utility targets: To calculate the minimum heating and cooling requirements that must be supplied by utility system. Heat Exchanger Network (HEN) Design: To design a network of heat exchangers to exchange the energy between process and utility streams. Network Relaxation and Optimization: To modify the network to eliminate the small exchangers which are not cost effective. Process Change: To alter the process conditions of unit operations and other streams to maximize heat integration. firstname.lastname@example.org Slide 8: DATA EXTRACTION: Process Flowsheet Operating Conditions for process streams & unit operations Heat and mass balance Hot and cold stream allocation email@example.com Slide 9: MINIMUM APPROACH TEMPERATURE (ΔTmin): Slide 11: Area and cost variation with ΔTLM Slide 12: COMPOSITE CURVES: firstname.lastname@example.org Slide 13: The hot streams plotted separately The composite hot stream Slide 14: The cold streams plotted separately The composite cold stream Slide 15: MINIMUM UTILITY TARGET: For an efficient network synthesis it is required to evaluate MAXIMUM ENERGY RECOVERY (MER) so that MINIMUM UTILITY TARGET can be selected and network may be designed so as to satisfy the energy requirements for each process stream that is the determination of minimum hot and cold utility requirements in the process. Three methods are widely used for the estimation of minimum utility requirement. Graphical method Algebraic method Computer based methods email@example.com Slide 16: MINIMUM UTILITY TARGET: (Graphical Method) Production of Maleic Anhydride from Benzene Slide 17: HEAT EXCHANGE STREAM DATA firstname.lastname@example.org Slide 18: INITIAL TEMPERATURE INTERVAL TABLE Slide 19: Initial composite diagram with ΔTmin = 28 oC Hot stream pinch Temperature = 358 oC Cold stream pinch Temperature = 330 oC. So, ΔTmin at pinch point is 28 oC. While allowable ΔTmin for chemical processes is 3 - 10 oC. Slide 20: Revision of temperature interval table Slop of the curve at pinch point = 0.0475 Intercept of the curve = - 440 For y = mx + c Modified enthalpy change rate at 358 oC is 16800 kJ/sec. This value of 16800 must be increased to 17000 to make the temperature approach at the pinch point to 10oC. Therefore 200 kJ/hr must be added to every enthalpy change rate value associated with the streams to be heated. Hence, Difference of baseline enthalpy change rates = 200 kJ/sec So, Revised baseline enthalpy change rate for streams to be cooled = 17200 kJ/sec. email@example.com Slide 21: Revised temperature interval table Slide 22: Revised composite diagram with ΔTmin = 10 oC Minimum heating utility required = 17232 – 17200 = 32 kJ/sec Minimum cooling utility required = 11000 – 1200 = 9800 kJ/sec Revised composite diagram with ΔTmin = 10 oC firstname.lastname@example.org Slide 23: MINIMUM UTILITY TARGET: (Algebraic Method) Algebraic method is also termed as “Problem Table Method”. Although composite curves can be used to set energy targets, yet they are inconvenient because they are based on a graphical construction. The problem table is the name given by Linnhoff and Flower to a numerical method for determining the pinch temperatures and the minimum utility requirements; Linnhoff and Flower (1978) also termed as “Temperature Interval Method”. Once understood, it is the preferred method, avoiding the need to draw the composite curves. email@example.com Slide 24: Hot stream Temperature: Cold stream Temperature: Shifted temperatures for data: firstname.lastname@example.org Slide 25: Shifted temperatures for data: The temperature interval heat balance: Slide 27: HEAT EXCHANGER NETWORK DESIGN HEAT EXCHANGER NETWORK DESIGN: email@example.com Slide 28: PROBLEM STATEMENT: Given a number NH of process hot streams (to be cooled) and a number NC of process cold streams (to be heated), it is desired to synthesize a cost-effective network of heat exchangers that can transfer heat from the hot streams to the cold streams. Given also are the heat capacity of each process hot streams, FCP,u; its supply (inlet) temperature, Ts,u; and its target (outlet) temperature, Tt,u, where u = 1, 2 ,………., NH. Given also are the heat capacity of each process cold streams, FCP,v; its supply (inlet) temperature, Ts,v; and its target (outlet) temperature, Tt,v, where v = 1, 2 ,………., Nc. Available for service are NHU heating utilities and NCU cooling utilities whose supply and target temperatures (but not flowrates) are known. Slide 29: CAPITAL AND ENERGY COSTS: Heat exchanger network that would seem appropriate to most when energy is cheap and capital expensive. Heat exchanger network that would seem appropriate to most when energy is expensive and capital cheap. Slide 30: CAPITAL AND ENERGY COSTS Cont’d…..: Capital Cost = f(Thermodynamic effects) = f(Driving forces, Heat loads) Evidently, as we go to tighter designs (i.e. to reduce driving forces) we need less utility and the overall heat load decreases. Capital cost then increases with reduced driving forces (we all know that) but decreases with reduced heat load (we rarely consider this point). Slide 31: CAPITAL AND ENERGY COSTS Cont’d…..: Slide 32: HEAT EXCHANGER NETWORK DESIGN: The process streams are drawn as horizontal lines, with the stream numbers shown in square boxes. The Hot streams are drawn at the top of the grid, and flow from left to right. The cold streams are drawn at the bottom, and flow from right to left. The stream heat capacities CP are shown in a column at the end of the stream lines. Heat exchangers are drawn as two circles connected by a vertical line. The circles connect the two streams between which heat is being exchanged; that is, the streams that would flow through the actual exchanger. Heater and coolers are drawn as a single circle, connected to the appropriate utility. Slide 33: THE PINCH DESIGN METHOD: If the energy target set by the composite curves is to be achieved, the design must not transfer heat across the pinch by: Process-to-process heat transfer Inappropriate use of utilities QHmin QCmin firstname.lastname@example.org Slide 34: THE PINCH DESIGN METHOD Cont’d…..: Stream matching is started at the pinch point to avoid the violation of the assumption of ∆Tmin. If the design is started away from the pinch at the hot end or cold end of the problem, then initial matches are likely to need follow-up matches that violate the pinch or the ∆Tmin criterion as the pinch is approached. If the design is started at the pinch, then initial decisions are made in the most constrained part of the problem. This is much less likely to lead to difficulties later. If such matches are not made, the result will be either use of temperature differences smaller than ∆Tmin or excessive use of utilities resulting from heat transfer across the pinch. email@example.com Slide 35: THE PINCH DESIGN METHOD Cont’d…..: firstname.lastname@example.org Slide 36: THE PINCH DESIGN METHOD Cont’d…..: Slide 37: THE PINCH DESIGN METHOD Cont’d…..: Slide 38: THE PINCH DESIGN METHOD Cont’d…..: email@example.com Slide 39: THE PINCH DESIGN METHOD Cont’d…..: At the pinch, the match starts with a temperature difference equal to ∆Tmin. The relative slopes of the temperature–enthalpy profiles of the two streams mean that the temperature differences become smaller moving away from the pinch, which is infeasible. On the other hand, in second Figure match involving the same hot stream but with a cold stream that has a larger CP. The relative slopes of the temperature–enthalpy profiles now cause the temperature differences to become larger moving away from the pinch, which is feasible. Thus, starting with ∆Tmin at the pinch, for temperature differences to increase moving away from the pinch. firstname.lastname@example.org Slide 40: THE PINCH DESIGN METHOD Cont’d…..: email@example.com Slide 41: THE PINCH DESIGN METHOD Cont’d…..: If a cold stream is matched with a hot stream with smaller CP, (i.e. a steeper slope), then the temperature differences become smaller (which is infeasible). If the same cold stream is matched with a hot stream with a larger CP (i.e. a less steep slope), then temperature differences become larger, which is feasible. Thus, starting with ∆Tmin at the pinch, for temperature differences to increase moving away from the pinch. firstname.lastname@example.org Slide 42: THE PINCH DESIGN METHOD Cont’d…..: email@example.com Slide 43: THE PINCH DESIGN METHOD Cont’d…..: Slide 44: THE PINCH DESIGN METHOD Cont’d…..: firstname.lastname@example.org Slide 45: THE PINCH DESIGN METHOD Cont’d…..: email@example.com Slide 46: THE PINCH DESIGN METHOD Cont’d…..: firstname.lastname@example.org Slide 47: HEAT EXCHANGER NETWORK DESIGN: You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.