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Module 6: Flowsheet Environmental Impact

AssessmentChapter 11

David R. Shonnard

Hui Chen

Department of Chemical Engineering

Michigan Technological University

University of Texas at Austin Michigan Technological University2

Module 6: Outline

Educational goals and topics covered in the module

Potential uses of the module in chemical engineering courses

Review of environmental impact assessment methods

Application of Tier 3 environmental impact assessment to a detailed flowsheet - Chapter 11

After the flowsheet input output structure, unit operation designations, and mass/heat integration have been completed, the last step in the

process to improve the environmental performance of a chemical process design is to perform a detailed environmental impact assessment

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Module 6: Educational goals and topics covered in the module

Students will: learn to apply a systematic risk assessment methodology to the

evaluation of chemical process designs

integrate emission estimation, environmental fate and transport calculation, and relative risk assessment to rank process design alternatives

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Module 6: Potential uses of the module in chemical engineering courses

Process Design course:• develop and use environmental objective functions to rank process

design alternatives

• rank process designs quantitatively based on environmental criteria

Transport phenomena course:• Module on interphase mass transfer in the environment

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Module 6: Essential features of environmental impact assessment for

chemical process design

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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Module 6: Systematic risk assessment methodology

National Academy of Sciences, 1983

1. Hazard Identification (which chemicals are important?)

2. Exposure assessment (release estimation, fate and transport, dose assessment)

3. Toxicity assessment (chemical dose - response relationships)

4. Risk Characterization (magnitude and uncertainty of risk)

Result: Quantitative risk assessment (e.g. excess cancers)

Atmospheric dispersion Model, Ca

Thibodeaux, L.J. 1996, Environmental Chemodynamics, John Wiley & Sons

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Carcinogenic Risk Example (inhalation route)

Module 6: Quantitative risk calculation

Risk i = (Ca CR EF ED)

(BW AT )SF

i

Exposure Dose

Dose - Response Relationship,Slope Factor

Result: # excess cancers per 106 cases in the population; 10-4 to 10-6 acceptable

Disadvantage: Only a single compartment is modeled / Computationally inefficient Highly uncertain prediction of risk

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Carcinogenic Risk Example (inhalation route)

Module 6: Relative risk calculation

Relative Risk =

(Ca CR EF ED)

(BW AT )SF

i

(Ca CREF ED)(BW AT )

SF

Benchmark

= Ca SF i

Ca SF Benchmark

Result: Risk of a chemical relative to a well-studied benchmark compound

Advantage: If C is calculated for all compartments using a multimedia compartment model, computationally efficient

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Module 6: Tier 3 Relative risk index formulation

Exposure Potential Inherent Impact Parameter

Chemical “i”Benchmark Compound

Dimensionless Risk Index ( Ii*) =

[(EP)(IIP)]i

[(EP)(IIP)]B

Process Index (I) (Ii* )

i1

N

(mi)EmissionRate ofChemical, i

Chemical Specific

Process

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Module 6: Airborne emissions estimation

Unit Specific EPA Emission Factors Distillation/stripping column vents Reactor vents Fugitive sources

Correlation (AP- 42, EPA) Storage tanks, wastewater treatment Fugitive sources (pumps, valves, fittings)

Criteria Pollutants from Utility Consumption Factors for CO2, CO, SO2, NOx, AP- 42 (EPA) factors

Process Simulators (e.g. HYSYS)

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Waste stream summaries based on past experience

1. Hedley, W.H. et al. 1975, “Potential Pollutants from Petrochemical

Processes”, Technomics, Westport, CT

2. AP-42 Document, Chapters 5 and 6 on petroleum and chemical industries,

Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

3. Other sources

i. Kirk-Othmer Encyclopedia of Chemical Technology, 1991-

ii. Hydrocarbon Processing, “Petrochemical Processes ‘99”, March 1999.

Module 6: Release estimates based on surrogate processes

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Model Domain Parameters• surface area - 104 -105 km2

• 90% land area, 10% water• height of atmosphere - 1 km• soil depth - 10 cm• depth of sediment layer - 1 cm• multiphase compartments

Multimedia compartment model Processes modeled• emission inputs, E• advection in and out, DA

• intercompartment mass transfer, Di,j

• reaction loss, DR

Module 6: Multimedia compartment model formulation

Mackay, D. 1991, ”Multimedia Environmental Models", 1st edition,, Lewis Publishers, Chelsea, MI

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Module 6: Multimedia compartment model input data

Environmental Property UnitSpreadsheet

Location Benzene Ethanol PCPMolecular Weight g/mole C6 78.11 46.07 266.34

Melting Point ° C C7 5.53 115 174

Dissociation Constant log pKa C8 4.74

Solubility in Water g/m3 C11 1.78E+2 6.78E+5 14

Vapor Pressure Pa C12 1.27E+4 7.80E+3 4.15E-3

Octanol-Water Coefficient log Kow C13 2.13 -0.31 5.05

Half-life in air hr C33 1.7E+1 5.5E+1 5.50E+2

Half-life in water hr C34 1.7E+2 5.5E+1 5.50E+2

Half-life in soil hr C35 5.5E+2 5.5E+1 1.7E+3

Half-life in sediment hr C36 1.7E+3 1.7E+2 5.50E+3

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Module 6: Multimedia compartment model typical results

Chemical Percentage (%)

(emission scenario) Total mass(kg)

Air Water Soil Sediment

Benzene (a) 1.98x104 99.59 0.29 0.12 1.0x10-3

Benzene (b) 1.41x105 4.48 95.17 5.5x10-3 0.35

Benzene (c) 6.86x104 20.61 1.61 77.78 5.8x10-3

Ethanol (a) 4.56x104 92.87 3.85 3.28 2.9x10-3

Ethanol (b) 7.35x104 0.22 99.7 7.8x10-3 0.08

Ethanol (c) 7.84x104 0.92 5.64 93.42 0.02

Pentachlorophenol (a) 2.07x106 0.26 2.56 97.07 0.11

Pentachlorophenol (b) 4.59x105 7.2x10-5 96.19 0.03 3.78

Pentachlorophenol (c) 2.39x106 2.9x10-4 0.54 99.44 0.02

(a) 1000 kg/hr emitted into the air compartment(b) 1000 kg/hr emitted into the water compartment(c) 1000 kg/hr emitted into the soil compartment

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1. The percentages in each environmental compartment depend upon the emission scenario

a) the highest air concentrations result from emission into the air

b) the highest water concentrations are from emission into water

c) the highest soil concentrations are from emission into soil

d) highest sediment concentrations are from emission into water

2. Chemical properties dictate percentages and amounts

a) high KH results in high air concentrations

b) high KOW results in high soil concentrations

c) high reactions half lives results in highest pollutant amounts

Module 6: Multimedia compartment model typical results - interpretations

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Module 6: Nine Environmental Impact /Health Indexes

R ela t iv e R isk In d e x E q u a tio n

IG W , i* GWP i

G lo b a l W a r m in g

IG W , i* N C

MW C O2

MW i

O zo n e D ep le t io nIO D, i

* ODP i

S m o g F o rm a tio nI S F, i

* MIR i

MIR R O G

A cid R a inIA R, i

* ARP i

ARP S O2

GW P = g lo b a l w a rm in g p o ten tia l, N C = n u m b er o f c a rb o n s a to m s, O D P = o zo n ed e p le tio n p o te n ta l, M IR = m a x im u m in c re m e n ta l rea c tiv ity , A R P = a c id ra in p o ten tia l .

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R e l a t i v e R i s k I n d e x E q u a t i o n

H u m a n T o x i c i t yI n g e s t i o n R o u t e I *

IN G C W , i LD 5 0, To lu en e

C W , To lu en e LD 5 0, i

H u m a n T o x i c i t yI n h a l a t i o n R o u t e I *

IN H C A , i LC 5 0 , To lu en e

C A , To lu en e LC 5 0, i

H u m a nC a r c i n o g e n i c i t yI n g e s t i o n R o u t e

I *C IN G

C W , i HV i

C W , B en zen e HV B en zen e

H u m a nC a r c i n o g e n i c i t yI n h a l a t i o n R o u t e

I *C IN H

C A , i HV i

C A , B en zen e HV B en zen e

F i s h T o x i c i t yI *

F T C W , i LC 5 0 f , P C P

C W , P C P LC 5 0 f , i

L D 5 0 = l e t h a l d o s e 5 0 % m o r t a l i t y , L C 5 0 = l e t h a l c o n c e n t r a t i o n 5 0 % m o r t a l i t y ,a n d H V = h a z a r d v a l u e f o r c a r c i n o g e n i c h e a l t h e f f e c t s .

Module 6: Nine Environmental Impact /Health Indexes

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Multi-Criteria Decision Analysis Multi-Criteria Decision Analysis

. . . . . . . . . . Chemical I1 InI2

EmissionRate

AABBCC

nn . . . . . . . . . .

ReportReport

Process Simulator OutputProcess Simulator Outputor Conceptual Designor Conceptual Design

EFRATEFRAT

. . . . . . . . . .

. . . . . . . . . . MS ExcelMS Excel®®

List of Chemicals, Equipment specifications, Utility consumption, Annual throughput

Chemicals,Equipment specifications, annual throughput

Chemicals, KH, KOW

Chemicals,, LC50, HV, MIR…

Physical Properties, Toxicology, Physical Properties, Toxicology, Weather, Geographical,Weather, Geographical,

and Emission Factors Databasesand Emission Factors Databases

Air Emission Air Emission CalculatorCalculator

Chemical Partition Chemical Partition CalculatorCalculator

Relative Risk IndexRelative Risk IndexCalculatorCalculator

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Environmental Fate and Risk Assessment Tool (EFRAT)• links with HYSYS for automated assessments

WAste Reduction Algorithm (WAR)• reported to be linked with ChemCAD

• US EPA National Risk Management Research Laboratory

Cincinnati, OH

Dr. Heriberto Cabezas and Dr. Douglas Young

US Environmental Protection Agency

National Risk Management Research Laboratory

26 W. Martin Luther King Dr.

Cincinnati, OH 45268

Module 6: Software tools for environmental impact assessment of

process designs

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Gaseous Waste StreamToluene & Ethyl Acetate193.5 kg/h each; 12,000scfm, balance N2

Vent

Vent ; 21 - 99.8 % recoveryof Toluene and Ethyl Acetate

Make-up oilAbsorption oil (C-14)10 – 800 kgmole/h

50/50 MassMixed Product

AbsorptionColumn

DistillationColumn

Module 6: Absorption - distillation process:analysis of an existing separation

sequence

HYSYS Flowsheet

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Module 6: Unit-specific emission summary

100 kgmole/hr Oil Flow Rate;

Oil Temperature = 82˚F; T=180˚FWhere are the centers for energy consumption and emissions?

UNIT OPERATION Mass

Flow Toluene Ethyl C-14 SOx NOx CO2 CO TOC

"METHOD" (kg/hr) Acetate

Absorption

Column "HYSIS" 19,840 0.002 128 4.23

Distillation "emission

Column factor" 259.1 0.019 0.007

Fugitive "emission

Sources factor" 259.1 0.062 0.062

Storage

Tank "correlation" 259.1 0.0014 0.0014

Reboiler

Energy (10 6 Btu/hr) 6.16 3.93 0.52 499 0.129 0.007

Total Emissions (kg/hr) 0.088 128.07 4.23 3.93 0.52 499 0.129 0.007

Emission rate (kg/hr)

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Module 6: Risk index summary

Which chemicals have the highest impact indexes?

Compound I* GW I* OD I* SF I* AR I* ING I* INGC I* INH I* INHC I* FT

Toluene 3.34 0 0.9 0.0 1 0 1.0 0 0.02

Ethyl Acetate 2 0 0.3 0.0 9.7 0 3.3 0 0.04

SOx 0 0 0.0 1.0 0 0 0.0 0 0.00

NOx 40 0 0.0 0.7 0 0 0.0 0 0.00

CO2 1 0 0.0 0.0 0 0 0.0 0 0.00

CO 0 0 0.0 0.0 0 0 141.2 0 0.00

C-14 3.1 0 0.0 0.0 0 0 0.0 0 0.00

TOC 3.1 0 1.0 0.0 0 0 0.0 0 0.00

Relative Risk Index (I*)

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Module 6: Process environmental summary

All units in kg/yrEmission from IFT IING IINH IGW ISF IAR

utility 0.00E+00 0.00E+00 1.44E+05 5.21E+06 1.70E+02 1.27E+04

absorber 4.67E+04 1.08E+07 3.73E+06 2.36E+06 3.74E+05 0.00E+00

tank 3.36E+00 6.43E+02 2.55E+02 2.95E+02 1.09E+02 0.00E+00

distillation column 5.06E+00 6.43E+02 3.60E+02 6.82E+02 3.12E+02 0.00E+00

fugitive 3.12E+01 5.30E+03 2.35E+03 2.90E+03 1.12E+03 0.00E+00

Emission of IFT IING IINH IGW ISF IAR

Ethyl Acetate 4.68E+04 1.09E+07 3.73E+06 2.24E+06 3.72E+05 0.00E+00

Toluene 1.92E+01 1.22E+03 1.22E+03 4.07E+03 2.11E+03 0.00E+00

Tetradecane 0.00E+00 0.00E+00 0.00E+00 1.15E+05 1.14E+03 0.00E+00

Carbon dioxide 0.00E+00 0.00E+00 0.00E+00 4.87E+06 0.00E+00 0.00E+00

Carbon monoxide 0.00E+00 0.00E+00 1.44E+05 0.00E+00 0.00E+00 0.00E+00

Nitrogen dioxide 0.00E+00 0.00E+00 0.00E+00 3.40E+05 0.00E+00 6.39E+03

Sulfur dioxide 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 6.36E+03

TOC 0.00E+00 0.00E+00 0.00E+00 6.51E+02 1.35E+02 0.00E+00

Process Index (I) (Ii*) i1

N

(mi )100 kgmole/hr Oil Flow Rate;

Oil Temperature = 82˚F; T=180˚F

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Module 6: VOC recovery by absorption into tetradecane (C14)

0

20

40

60

80

100

120

0 100 200 300 400 500 600

Absorber Oil Flow Rate (kgmole/hr)

% R

eco

very

of

VO

Cs

Toluene Ethyl Acetate

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Module 6: Environmental index profiles

0 10 2050

100200

300400

500

IGW

100 IAR

10 IINH0

500

1000

1500

2000

2500

3000

Absorber Oil Flow Rate (kgmoles/hr)

Indexes(kg/hr)

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Module 6: Interpretation of environmental assessment results

Risk 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 - 78 % reduction Ingestion Route Toxicity Index - 18 % reduction Ecotoxicity (Fish) Index - 19 % reduction

Absorber oil choice is not an optimum Oil selectively absorbs toluene, but ethyl acetate has a higher value

Multiple indexes complicate the decision

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Use of EFRAT : evaluate the MA process

Basecase (Dibutyl phthalate absorber oil) with and without heat integration

Simulate 3 case studies using heat integrated flowsheet» Dibutyl phthalate absorber oil» Dibenzyl ether absorber oil» Diethylene glycol butyl ether acetate absorber oil

Module 6: Maleic anhydride from n-butane process flowsheet evaluation

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Follow the tutorial instructions given in the notebook!

The SCENE file has been linked to a HYSYS case file

Add three additional emission sources

Complete the relative risk assessment calculations

Module 6: Maleic anhydride from n-butane:

Use of EFRAT on basecase flowsheet

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Module 5: Heat integration of the MA flowsheet

Without Heat Integration

9.70x107 Btu/hr-9.23x107 Btu/hr

2.40x107 Btu/hr

-4.08x107 Btu/hr

Reactor streams generate steam

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Module 5: Maleic anhydride flowsheet with heat integration

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Module 6: Maleic anhydride from n-butane:

effect of heat integration on risk indexes

IGW ISF IAR IINGIINH

IFT

No Heat Integration

Heat Integration1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E+10

Relative Risk Indexes

(kg/yr)

30.4%reduction

72.2%reduction

RemainingIndexes areunchanged

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IGWISF IAR

IINGIINH

IFT

Dibutyl Phthalate

Dibenzyl Ether

DGBEA1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E+10

Relative Risk Index

(kg/yr)

Module 6: Maleic anhydride from n-butane:

effects of absorber oil choice

16.3%reduction

85.1%reduction

81.7%reduction

42.1%reduction

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Module 6: Summary / Conclusions

Educational goals and topics covered in the module

Potential uses of the module in chemical engineering courses

Review of environmental impact assessment methods

Application of Tier 3 environmental impact assessment to a detailed flowsheet - Chapter 11 » Heat integration of the Maleic Anhydride flowsheet

» Effects of absorber oil choice for the MA flowsheet