An Environmental Assessment Framework for Chemical Process Designs

1

• An Environmental Assessment Framework for
  Chemical Process Designs
• David R. Shonnard, Speaker
• Hui Chen
• Chemical Engineering
• Michigan Technological University
• Dennis S. Hiew
• Essential Technologies, Inc
• Houston, TX
• United Engineering Foundation Conference, Clean
  Products and Processes II
• November 14-19, 1999, Lake Arrowhead, CA
• Session Applications of Life Cycle Assessment

2
Seminar Outline

• Introduction to Process Design for Pollution
  Prevention
• Framework for Assessing Environmental Impacts of
  Designs
• Application of Framework for Single Parameter
  Optimization
• Generalized Economic/Environmental Optimization
  Strategy
• Progress in Implementing Optimization Strategy
• Conclusions

3
Life Cycle Concepts
Energy
Energy
Energy
Energy
Raw Materials Extraction
Chemical Manufacturing
Product Manufacturing
Use and Disposal
Wastes
Wastes
Wastes
Wastes
Up to 80 of Hazardous Waste Generation
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Process Design for Pollution Prevention

• Limitations of pollution control for
  environmental management
• ? expensive to treat wastes
• ? future liability for hazardous waste
  management
• ? hidden costs for compliance, monitoring,
  and reporting
• Benefits of pollution prevention
• ? reduced waste treatment costs
• ? increased production efficiency
• ? less liable for expensive clean -ups in the
  future
• Computational tools are needed to integrate
  environmental considerations into process designs

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Computational Tool for Environmental Impacts of
Chemical Process Designs

• Computationally efficient
• ? Environmental performance metrics quickly
  calculated using output from commercial process
  simulators
• Link waste generation and release to
  environmental impacts
• ? Environmental metrics linked to process
  parameters
• Impacts based on a systematic risk assessment
  methodology
• ? Release estimates - fate and transport -
  exposure - risk

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Systematic Risk Assessment Methodology

• National Academy of Sciences, 1983
• 1. Hazard Identification (which chemicals are
  important?)
• 2. Exposure assessment (fate and transport,
  exposure assessment)
• 3. Toxicity assessment (chemical dose - response
  relationships)
• 4. Risk Characterization (magnitude and
  uncertainty of risk)
• Result Quantitative risk assessment (e.g. excess
  cancers)
• Relative risks needed for chemical process
  evaluation
• ? Compare designs and retain low impact options.

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Relative Risk Calculation

• Carcinogenic Risk Example (inhalation route)

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Relative Risk Index Formulation
Exposure Potential
Inherent Impact Parameter
Benchmark Compound
Chemical i
Process Emission Rate
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Emissions Estimation

• Unit Specific EPA Emission Factors
• Distillation/stripping column vents
• Reactor vents
• Correlation (AP- 42, EPA)
• Storage tanks
• Fugitive sources (pumps, valves, fittings)
• Chemical Industry Emission Factors
• Average fugitive sources
• Criteria Pollutants from Utilities
• DOE-derived and stoichiometry CO2 factors
• AP- 42 (EPA) factors

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Level I Fate / Transport Model

• Partition Coefficients
• KH Henrys Constant
• Kow Octanol/water Coefficient
• Landscape Properties
• ? Volume Fractions
• ? Mass Densities

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Nine Environmental Impact / Health Indexes
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Nine Environmental Impact / Health Indexes
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Process Simulator Output or Conceptual Design
List of Chemicals, Equipment specifications,
Utility consumption, Annual throughput
EFRAT
Physical Properties, Toxicology, Weather,
Geographical, and Emission Factors Databases
Chemicals, Equipment specifications, annual
throughput
Chemicals, KH, KOW
Chemicals, t, LC50, HV, MIR
Air Emission Calculator
Chemical Partition Calculator
Relative Risk Index Calculator
Emission Rate
Chemical
I1
In
I2
Report
. . . . .
A B C n
. . . . .
MS Excel
. . . . .
. . . . .
Multi-Criteria Decision Analysis
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Single Parameter Environmental Optimization
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Flowsheet Environmental Assessment
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Flowsheet Environmental Assessment (cont.)
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Interpretation of Results

• Significant reductions at 50 kgmole/hr flow rate
• ? Global Warming Index - 41 reduction
• ? Smog Formation Index - 86 reduction
• ? Acid Rain Index - small increase
• ? Inhalation Route Toxicity Index - 38
  reduction
• ? Ingestion Route Toxicity Index - 38 reduction
  
• Absorber oil choice is not an optimum
• ? Oil selectively absorbs toluene, but ethyl
  acetate has a higher economic value
• Multiple indexes complicate the decision

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Generalized Economic/Environmental Optimization

• Traditional Process Improvement Paradigm
• 1. Establish source reduction or emission
  reduction targets.
• 2. Optimize process using economic-based
  objective functions.
• Deficiency - Traditional approach may preclude
  more optimum design configurations that can only
  be realized through simultaneous economic and
  environmental optimization.

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Process Improvement Methodology
Define Primitive Problem Simulate Base Case
Process
Process Diagnostic Summaries (PDS)
Identify parameters from important process units
Integrated Design Tools - SCENE Economic
- DORT Environmental - EFRAT AHP
- DEAR Process Simulator
Scaled Gradient Analysis (SGA)
Identify a reduced parameter set
Perform optimization using reduced parameter set
Multi-Variable Optimization (MVO)
Optimum Design Configuration
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Case Study Application
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Unit-Specific Emission Summary
100 kgmole/hr Oil Flow Rate Oil Temperature
82F DT180F
Where are the centers for energy consumption and
emissions?
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Risk Index Summary
Which chemicals have the highest impact indexes?
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Process Diagnostic Summary Environmental
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Scaled Gradient Analysis(Douglas, 1988)
Design Parameter Selection
Design Parameters
Scale Factors 1. Absorber oil flow rate
300kgmol/hr 2. Absorber oil feed
temperature 30F 3. DT across heat
integration exchanger 180F
Scale Factor Selection
HYSYS Simulation
SCENE Simulation
Scaled Gradient Analysis Based on Environmental
and Economic Indexes
Ranked Parameters
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Scaled Gradient Analysis Results
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Scaled Gradient Analysis Results
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SGA Parameter Ranking
X1 absorber oil flow rate (AOFR) X2 absorber
oil temperature (AOT) X3 DT heat integration
exchanger
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Interpretation of SGA Results

• Absorber oil flow rate is the dominant parameter
  to consider in subsequent optimization.
• Economic and Environmental-Based SGAs yielded
  similar assessments
• ? Ranking orders were nearly the same
• ? Economic and environmental optimum are at
  higher AOFR
• ? Economic and environmental optimum are at
  lower AOT
• ? Economic and environmental optimum are at
  greater DT

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AHP Hierarchy Structure
Final Ranking Qualitative Weightings Qualit
ative Weightings Qualitative
Weightings Quantitative Weightings
Process Option
Economic Indices
Pollution Indices
Biotic
Human
Abiotic
Payback Period
Net Present Value
Fixed Capital Investment
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Current Projects and Future Directions

• Simultaneous economic and environmental
  optimization
• ? Scaled gradient analysis to reduce parameter
  set
• Integration with a commercial process simulator
• ? Economic assessment - NPV, FCI, PP
• ? Environmental assessment
• ? Hierarchy decision analysis
• Uncertainty analysis for index calculations
• ? Fate and transport properties - KH, Kow, t
• ? Impact properties - MIR, LD50, LC50
• Pinch analysis and integration of environmental
  assessment
• ? Optimum heat integration for
  condensation-based VOC separations

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Acknowledgements

• Funding
• 1. U.S. Environmental Protection Agency and
  the National Center for Clean Industrial and
  Treatment Technologies (CenCITT) at MTU
• 2. NSF - Lucent Technologies Research
  Fellowships in Industrial Ecology

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Acknowledgements

• Participants
• Faculty
• Bruce A. Barna, Tony N. Rogers, and David R.
  Shonnard
• Staff
• Andrew A. Kline (Sr. Research Engineer/Scientists
  )
• Students
• Graduate Students Hui Chen, Brendan ODonnell
• Undergraduate Students W. Blanchard, M.
  Quarles, R. Essiambre