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Ch E 452: Process Design, Analysis, and Simulation Process Synthesis and Design Methodology

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Title: Ch E 452: Process Design, Analysis, and Simulation Process Synthesis and Design Methodology


1
Ch E 452 Process Design,Analysis, and
SimulationProcess Synthesis andDesign
Methodology
  • David A. Rockstraw, Ph.D., P.E.
  • New Mexico State University
  • Chemical Engineering

2
Process DesignCourse Objectives
  • By the end of this course, you will be able to
  • Design and size unit operations to accomplish a
    specific process step
  • Integrate and arrange process units according to
    industrially accepted standards, hazards review
    procedures, and federal regulations to achieve an
    overall processing objective
  • Build simulate a process in ASPEN Plus
  • Estimate capital costs of unit ops, construction
    costs, product processing costs (raw materials,
    labor, and utilities), and process profitability
    and
  • Optimize a process based on profit.

3
Engineering
  • Purpose - To create new material wealth by
    chemical or biological transformation and/or
    separation of materials.
  • Design The creative activity whereby we
    generate ideas and translate them into equipment
    and processes for producing new materials or for
    significantly upgrading the value of existing
    materials.

4
Synthesis Analysis
  • 1 design problem ? highly under-specified
  • assumptions are absolutely necessary during the
    synthesis stage
  • Process units to use must be selected
  • Interconnection of process units must be selected
  • Operating conditions must be specified
  • Synthesis is difficult because there are 104 -
    109 unique ways of accomplishing the same goal.
    Hence, design tasks are very open-ended.

5
Synthesis Analysis
  • Design engineer desires to find the lowest
    alternative of the 104-109 possibilities, while
    still considering such intangibles as
  • safety environmental contraints
  • simplicity of start-up/operation/shut-down
  • Use rules-of-thumb or heuristics to eliminate
    some alternatives from consideration, and to
    design a number of alternatives for comparison.
  • More rigorous design calculations applied when a
    potentially profitable alternative is found.

6
Engineering Methodology
  • Engineering Method a solution strategy
    following successive refinements in the design,
    maintaining focus on the overall problem.
  • The Engineering Method vs. the art of painting

7
Painting
  • Starts with a pencil sketch, including only the
    most significant details of the painting.

8
Engineering Design
  • Start with a pencil sketch, including only most
    significant details of processing plant.
  • Seek most expensive parts of the process and
    significant economic trade-offs.

9
Painting
  • Evaluate the preliminary drawing, and make
    modifications, using only gross outlines for
    subjects of the picture.

10
Engineering Design
  • Evaluate initial guess of process, and generate
    potential alternatives that may lead to
    improvements.
  • In such, generate a reasonable process design
    before adding significant detail.

11
Painting
  • Adds color, shading and the details of the
    various gross outlines of objects.
  • Major modifications made if warranted.

12
Engineering Design
  • Use rigourous design costing procedures for the
    most expensive equipment items.
  • Improve material energy balances via rigor.
  • Add small, less expensive items necessary for
    operation but having little impact on plant cost.

13
Engineering Method
  • A piece of artwork is finished when additional
    effort reaches a point of diminishing returns.
  • i.e., little value is added from much additional
    effort.

14
Engineering Method
  • There is never a single way to paint a great
    Madonna and Child or a landscape.
  • Different process routes can be used to produce
    the same chemical or material at similar costs.

15
Engineering Method
  • It is an art of judgment to know what level of
    detail to include in the various stages of
    developing a painting or a process.

16
Levels of Engineering Design
  • Based on cost accuracy
  • Order-of-Magnitude or Ratio Estimate
  • Based on similar previous cost data ?40
  • Study or Factored Estimate
  • Based on knowledge of major equipment items ?25
  • Preliminary, Budget Authorization, or Scope
    Estimate
  • Based on sufficient data to permit budgeting
    ?12
  • Definitive or Project Control Estimate
  • Based on almost complete data, but prior to
    completion of drawings and specifications ?6
  • Detailed or Contractors Estimate
  • Based on complete engineering drawings,
    specifications, site surveys ?3

17
Definitions
  • expensed engineering
  • engineering work performed in the development
    stage of a project prior to capital funds being
    committed (through Scope Estimate).
  • capitalized engineering
  • engineering work performed on a project after
    capital funds are committed to implement the
    project (Definitive and Detailed Estimates).

18
Stages of the Design Process
  • Ratio Estimate (feasibility survey)
  • Factored Estimate (conceptual design)
  • Preliminary/Definitive/Detailed Designs
  • Construction
  • Start-up operations

Cost consequences for design changes increase as
the process moves from phases 1 thru 4.
19
Step 1 - Feasibility Survey
  • Gathering of data for quick-estimate, including
  • availability of suppliers, specifications and
    cost of raw materials
  • thermodynamic/kinetic data for reactions
    (including by-product reactions)
  • existing facilities equipment available
  • facilities equipment needed
  • corrosion data
  • safety requirements
  • chemical and physical properties of all
    reactants, products intermediates
  • shipping (DOT regulations)
  • patent licensing restrictions

20
Step 2 - Conceptual Design
  • process development
  • flowsheet definition
  • cost estimate
  • technology package
  • simulation
  • PFD
  • spec sheets
  • line lists
  • equipment lists
  • environmental safety review

21
Process Development
  • The collection of additional reaction and
    physical property data (after preliminary design)
    to increase the accuracy of the quick-estimate
    generated from the feasibility survey.
  • May include lab research and/or pilot operations
    as necessary to obtain missing information.
  • Semi-works data is collected to obtain design
    data, including accurate material and energy
    balances, an understanding of the effects of
    various process conditions and corrosion data.

22
Step 3 Process Design
  • equipment design
  • piping layout
  • plot plan
  • instrument loop diagrams
  • safety review
  • environmental permitting
  • Stages
  • preliminary, detailed, firm

23
Preliminary Design
  • Rough design, calculations kept at a minimum
  • Costs likely based on factored estimates and
    design is based on approximate methods.
  • Used as a tool to determine whether continued
    development is justified.
  • Preliminary design is a workable process for the
    production of desired product.
  • Includes simplified flow diagram, rough material
    balance from which direct raw materials costs are
    calculated, specs for each process unit, utility
    estimates labor requirements.

24
Preliminary Design
  • From this design, capital investment product
    cost can be determined.
  • These documents are continually modified as
    piloting reveals new information about the
    process, often suggesting changes to the design.

25
Preliminary Design
  • Once development is complete, preliminary designs
    used to prepare technology package, from which
    detailed-estimates designs are prepared.
    Package includes
  • manufacturing process
  • material energy balances
  • temperature pressure ranges
  • materials of construction
  • raw material and product specs
  • utilities requirements
  • rates, yields, cycle times
  • plant site and plot plan

26
Definitive/Detailed Designs
  • Definitive Design
  • Includes more details than the quick-estimate,
    though not detailed equipment designs specs
    are, nor detailed PIDs.
  • Transition from Preliminary to Detailed Designs
    tied to a financial commitment to proceed.
  • Detailed Design
  • Includes detailed PIDs, plot plans, pipe layouts
    wire diagrams, design specifications for each
    component, costs for equipment and raw materials
    based on quoted prices from vendors.

27
Step 4 - Construction
  • site prep
  • vessel fabrication
  • facilities erection
  • piping conduit/wiring
  • control loop checkout
  • safety review
  • operator training

28
Step 5 Start-up Operations
  • pressure testing
  • flow testing / instrument calibration
  • closed loop operation
  • startup safety review
  • startup
  • operation
  • environmental monitoring

29
Use of Computer Simulation in the Process Design
Process
budget capital cost
block diagram
finalize PFD
specify equipment
initial PFD
finalize engineering flow
mass balancing
equipment design
finalize instrument types
heat balancing
equipment costs
detailed construction, mechanical, instruments,
piping, civil, layout
operating costs
capital costs
control capital cost
optimize process route
optimize budget design
construction
Process Design Simulation
production
profit loss accounting
Plant Simulation
30
Optimized Designs
Optimum Economic Design
  • The Optimum Economic Design is represented by
    the design resulting the least total cost when
    selecting between two or more alternate designs
    for which each design option provides equivalent
    processing results.

optimum economic design spec
f2(d)
f1(d) f2(d)
cost (/time, /unit of production)
f1(d)
design variable (d)
31
Optimized Designs
Optimum Operating Design
  • For an operation in which all degrees of freedom
    are fixed, the optimum operating design is the
    one for which a value for the independent
    variable optimizes the unit operation (i.e.,
    maximizes reactor yield, product separation, heat
    recovery,...).

optimum value for design variable
overall yield
A B ? C
e.g., product yield
yield based on reation rate
yield based on equilibrium condition
design variable (d)
32
Decision Hierarchy
  • Input data and Batch vs. continuous process
  • Input-output structure of flowsheet
  • Raw materials typically account for 33-85 of
    product cost thus, overall material balances are
    a dominant design factor.
  • Recycle structure of the flowsheet
  • Allows evaluation of separation needs
  • Separation System structure
  • Vapor recovery, liquid recovery
  • Heat integration
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