CHE441 Chemical Processes Synthesis and Design I Lecture 1: Syllabus, Introduction, and Heuristic rules

Course Information Instructor: Mingheng Li Office: Phone: Course Schedule:MWF 1:00-2:05 P.M. (section 3) 2:15-3:20 P.M. (section 1) Office Hours:MWF 8:40-noon Prerequisites:CHE304 and CHE313 Corequisite:ChE451L Course Webpage:

Texts and References  Texts(Required):  Turton et al, Analysis, Synthesis, and Design of Chemical Processes (4th Edition), Prentice Hall. (This book will be used in the next three quarters)  Lecture notes by Dr. Nguyen  References:  Peters, Timmerhaus and West, Plant Design and Economics for Chemical Engineers, 5th Edition, McGraw Hill,  Towler and Sinnott, Chemical Engineering Design, Butterworth-Heinemann, 2nd Edition,  Seider, Seader, Lewin, Product and Process Design Principles: Synthesis, Analysis, and Evaluation, 2nd Edition, Wiley,  Coulson and Richardson, Chemical Engineering Design.  Yu, Process Design for Chemical Engineers (available from Amazon.com)  Perry, Chemical Engineers Handbook. 3

Course Objective  This course is the first of the design series. The objective is to give the students a working knowledge of design principles as applied in chemical engineering processes and operations. In this course, the students will learn how to design major equipment common to most chemical processes. The students will also learn how unit operations fit together and interact in these processes and the basic procedure in process engineering design. Finally, the students will learn the impact of engineering solution on the environment. 4

Course Outcomes The students will have  Ability to design pumps and compressors  Ability to design steam and refrigeration cycles  Ability to design knockout drums and surge vessels  Ability to design an optimum heat exchanger network  Ability to size reactors  Ability to design separation units 5

Grading Homework5% (will be checked after you take the exam) Midterms40% Final45% Pop quiz (bonus)5% Total105% A : % A- : 90-93% B+ : 87-90% B : 83-87% B- : 80-83% C+ : 77-80% C : 73-77% C- : 70-73% D+ : % D : 60-67% F : 0-60% The student's course grade is determined by the total number of points he/she earns during the quarter. Make-up exams will not be given; a missed exam may be made-up only if absence is due to a legitimate reason approved by the instructor and substantiated by written verification. No late homework. No make-up exams. 6

Tentative schedule WeekTopicsHomeworkAdditional Material 1Introduction to Process Designhw1heuristic rules 2Material transfer and storagehw2 3Material transfer and storage, midterm 1hw3 4Reactor designhw4 5Heat integration using pinch technologyhw5 6Heat exchanger designhw6 7Mass transfer equipmenthw7 8Mass transfer equipment, midterm 2hw8 9Basic concepts in environmental engineering- 10Course overview, project presentation- Tentative schedule: Final Schedule 7

Advices  It is your responsibility to participate in your learning. Learning is not a spectator sport. It will take time (minimum of 9 hours per week for this course), effort, work, and involvement. You should study on a regular basis and not cram for tests, participate in class by being actively involved in dialogue with your classmates and instructor, think about what you are learning, and apply what you have learned to solve other related problems. Arriving late, leaving early, chatting with your neighbors, doing your other homework, or having beepers and cellular phones turned on during class time are behaviors unacceptable in this class.  I do fail students if they do not earn enough points. 8

What is Process Design?  In Chemical engineering, process design is the design of processes for desired physical and/or chemical transformation of materials. Process design is central to chemical engineering, and it can be considered to be the summit of that field, bringing together all of the field's components. Ref: InputOutput ? InputOutput ? DesignSynthesis 9

Layers in the Process Design A corporate decision into what business area to FOCUS R&D + Economic decision into which chemical route R&D on the chemistry for optimum: conditions, topologies, type, etc. R&D on separation & purification for product quality, recovery, cost, etc. Heat exchanger networking to minimize energy consumption Design for overall utility systems including the plant site 10

Documentations in Process Design  Block Flow Diagram (BFD) – conceptualizes a clear overflow of processes  Process Flow Diagram (PFD) - contains all the necessary information to complete material and energy balances on the process.  Piping and Instrumentation Diagram (P&ID) – contains all the process information necessary for the construction of the plant.  Specifications - Written design requirements of all major equipment items.  Others - Operation manual, control description, FAT procedure, etc. 11

Process Design Courses  CHE design major equipment (pumps, compressors, heat exchanger, reactor, column, etc.) for unit operations.  CHE design two typical chemical processes (ammonia manufacturing process and the oil refining process).  CHE Team project to perform process design and cost estimating of a complete plant with attention to environmental constraints. 12

Heuristic Rules in Chemical Engineering Design  Heuristic rules bring engineering experience into process design (especially for major equipment design) to initiate a practical design.  Experience is typically what turns a good engineer into a great engineer.  Some engineers may estimate the size of an equipment without doing detailed calculations.  At many stages of chemical process analysis and design, heuristic rules (or rules of thumb) can save much time.  Good references:  Stanley M. Walas, Chemical Process Equipment: Selection and Design, Butterworth-Heinemann  Carl R. Branan, Rules of Thumb for Chemical Engineers (5 th edition), Stephen Hall  Three small files can be downloaded here (heurist.pdf and ExpRules.xls and chp3.pdf)heurist.pdfExpRules.xlschp3.pdf 13

An Example: Heat Exchangers  For conservative estimate set F = 0.9 for shell and tube exchangers with no phase changes, q = UAFΔT lm. When ΔT at exchanger ends differ greatly then check F, reconfigure if F is les than New Design: 14

An Example: heuristic rules for heat exchangers  Standard tubes are 3/4 in. OD, 1 in. triangular spacing, 16 ft long; a shell 1 ft dia accommodates 100 sqft; 2 ft dia, 400 sqft, 3 ft dia, 1100 sqft.  Note that heat exchanger design shall comply with TEMA standard (we will discuss about TEMA in detail later). The diameter of shell size determines how many tubes can be put in a heat exchanger. This rule allows you to quickly estimate the heat exchange area. 15

Cont’d  Tube side is for corrosive, fouling, scaling, and high pressure fluids. Shell side is for viscous and condensing fluids.  Mechanical cleaning is easier on tube side than shell side. The critical Reynolds number for the shell side is about 200. For a highly viscous medium or a low flowrate turbulent flow can be obtained easier at the shell side. Condensing fluids drain better on the shell side. 16

Cont’d  Pressure drops are 0.1 bar (1.5 psi) for boiling and bar (3-9 psi) for other services.  Note that there is pressure drop (not increase) in boilers. If pressure drop is too high in a shell-and-tube heat exchanger, you should change the design, e.g., using more tubes or increasing baffle spacing. 17

Cont’d  Minimum temperature approach is 10ºC (20ºF) for fluids and 5ºC (10ºF) for refrigerants.  Approach temperature determines the heat transfer area, hence the cost of the heat exchanger. If approach is too small, the heat transfer area will be large. 18

Cont’d  Cooling water inlet is 30ºC (90ºF), maximum outlet is 45ºC (115ºF).  For cooling water, the outlet temperature can never be close to its boiling point. This is because a high temperature will cause severe fouling issue in heat exchangers. 19

Cont’d  Heat transfer coefficients for estimating purposes, W/m2ºC (Btu/hr ft2ºF): water to liquid, 850 (150); condensers, 850 (150); liquid to liquid, 280 (50); liquid to gas, 60 (10); gas to gas, 30 (5); reboiler, 1140 (200). Maximum flux in reboiler 31.5 kW/m2 (10,000 Btu/hr ft2). When phase changes occur, use a zoned analysis with appropriate coefficient for each zone.  You would notice that liquid would have a higher heat transfer coefficient than gas. This is mainly because of the physical property such as density. Note that Nu increases when Re increases. In detailed design, U is solved by empirical correlations, but this rule would give you a good starting point. 20

Cont’d  Double-pipe exchanger is competitive at duties requiring m 2 ( ft 2 ).  When the heat transfer area is small, you will not use a shell and tube heat exchanger. 21

Cont’d  Compact (plate and fin) exchangers have 1150 m2/m3 (350 ft2/ft3), and about four times the heat transfer per cut of shell-and-tube units. 22

Cont’d  Plate and frame exchangers are suited to high sanitation services, and are % cheaper in stainless steel construction than shell-and-tube units. 23

Cont’d  Air coolers: Tubes are in. OD., total fined surface m2/m2 (ft2/ft2 bare surface), U = W/m2ºC ( Btu/hr ft2 (bare surface) ºF). Minimum approach temperature = 22ºC (40ºF) Fan input power = kW/(MJ/h) [2-5 hp / (1000 Btu/hr)]. 24

Cont’d  Fired heaters: radiant rate, 37.6 kW/m2 (12,000 (Btu/hr ft2); convection rate, 12.5 kW/m2 (4,000 Btu / hr ft2); cold oil tube velocity = 1.8 m/s (6 ft/s); approximately equal transfer in the two sections; thermal efficiency see Table 3.7b; flue gas temperature ºC ( ºF) above feed inlet; stack gas temperature ºC ( ºF).  If you know the duty, this rule can be used to estimate the areas required in the radiant section and the convective section. Type of Heater/FurnaceTypical Range of Thermal Efficiencies (based on % of Lower Heating Value of fuel transmitted to process stream) Industrial Boiler (Water-Tube) Thermal Fluid Heater (1) Hot Water (2) Diphenyls (Dowtherm TM ) (3) Molten Salt (4) Mineral or Silicon Oil Reactive Process Heaters Non-Reactive Process Heaters % % % % Table 3.7b Typical Thermal Efficiencies of Fired Heaters and Furnaces 25

Example (homework 1-1)  For the acetone process shown in Figure 1a (Turton et al, Analysis, Synthesis, and Design of Chemical Processes), check the design specifications for the heat exchanger E-401 (A = 70.3 m 2 ) against the heuristics in Table 3.7 (Lecture Notes). E-401 is a feed vaporizer with the following data for zoned analysis. The temperature of stream 2 entering the heat exchanger is 32 o C and the temperature of high-pressure steam (hps) is constant at 254 o C. ZoneQ (MJ/hr) U(W/m 2  o K) T( o C) at the end of zone I II2,2801, III

Solution Note that F = 1 in all three zones because there is phase change. Because of the 10,000 Btu/hr/ft2 maximum flux in reboiler rule, the minimum area in zone 2 should be m2 instead of 3.73m2. 27

Assignments  Read the heuristic rules in the three files provided in the slides. Do the homework problems