Detailed Environmental Assessment of Chemical Process ...

Michigan Technological University1

David R. ShonnardDepartment of Chemical Engineering

Michigan Technological University

Detailed Environmental Assessment of Chemical Process Flowsheets - Chapter 11


Outline

! Educational goals and topics covered in the module

! Review of risk assessment concepts

! Introduction to environmental multimedia models

! Tier III environmental impact assessment for chemical process flowsheets

After the completing flowsheet input output structure, unit operation designations, and mass/heat integration, the last step for improving the environmental performance of a chemical process design is a detailed

environmental impact assessment of a process flowsheet


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 designalternatives


Design Stage P2 Tools Environmental Evaluation

Book Chapter

1. Earliest Design Stage

• Green Chemistry • atom efficiency

Tier 1 (persistence, bioaccumulation, toxicity)

7, 8

2. Preliminary Design Stage

Release estimation, optimum choice of • mass separating agents • process units • processing conditions

Tier 2 (material usage, energy consumption, emission of targeted pollutants)

8, 9

3. Detailed Design Stage

• Process integration methods • multimedia environmental fate modeling • relative risk assessment

Tier 3 (environmental fate and transport, relative risk assessment)

10, 11

Review of the hierarchical design process for pollution prevention


Boundaries for impact assessment

Chemical Manufacturing Process

• chemical reactions• separation operations• material storage• loading and unloading• material conveyance• waste treatment processes

Pre-Chemical Manufacturing Stages

• extraction from theenvironment

• transportation of materials• refining of raw materials• storage and transportation• loading and unloading

Post-Chemical Manufacturing Stages

• final product manufacture• product usage in commerce• reuse/recycle• treatment/destruction• disposal• environmental release

airborne releases wastewater releases solid/hazardous waste

toxic chemical releases energy consumption resource depletion

Environmental Impactsglobal warming ozone layer depletion air quality – smog acidification ecotoxicityhuman health effects, carcinogenic and non carcinogenic resource depletion

Chapter 11: chemical manufacturing stage only - Chapter 13: all stages


Essential features of environmental impact assessment for chemical process design

Computationally efficient→ Environmental performance indices to be quickly calculated

using output from commercial process simulators

→ Multiple environmental impacts considered

Link waste generation and release to environmental impacts→ Environmental indices linked to process parameters

Impacts based on a systematic risk assessment methodologyRelease estimates → fate and transport → exposure → risk


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)

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

Atmospheric dispersion Model, Ca (mg/m3)


Carcinogenic Risk Example (inhalation route)

Quantitative risk calculation

Riski = (Ca × CR × EF × ED)

(BW × AT)× SF

i

Exposure DoseDose - Response Relationship,Slope Factor (mg/(kg•d))-1

CR - contact rate (m3 air inhaled / day)EF - exposure frequency (days exposed / yr)ED - exposure duration (yr)BW - body weight (kg)AT - averaging time (number of days in a lifetime)

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

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


Carcinogenic Risk Example (inhalation route)

Relative risk calculation(what is the relative toxic potency?)

Relative Risk =

(Ca × CR × EF × ED)

(BW × AT)× SF

i

(Ca × CR × EF × 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


Airborne emissions estimation - chapter 8

"" 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)


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

Multimedia compartment model formulation -Chapter 11.2

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


Fugacity - a thermodynamic property of a chemical and represents the “escaping tendency” of the chemical from an environmental phase (air, water, or solid) and has units of pressure (Pa).

At equilibrium, the fugacity of a chemical in one phase is equalto the fugacity of the chemical (i) in the adjoining phasefor example:

fi (air) = fi (water)

Also, the fugacity is related to the molar concentration using the fugacity capacity, Z

Ci (air) = fi Z(air)

Multimedia compartment model - fugacity


Fugacity of a chemical in air

f = y φ PT ≈ P

y = mole fraction of the chemical in air

φ = fugacity coefficient - accounts for non-ideal behavior (≈ 1)

PT = total pressure in the air (Pa)

P = partial pressure of the chemical in air (Pa)

Ideal Gas Law

C1 = n/V = P/(RT) = f/(RT) = f Z1

Z1 = 1/(RT)

Fugacity capacity of the air


Table 11.2-1 Fugacity Capacities (Z) Values for the Various Phases and Compartments Environmental Phases Phase Densities (kg/m3) Air Phase Z1 = 1/(R T) 1.2 Water Phase Z2 = 1/H 1,000 Soil Phase Z3 = [1/H] Koc φ3 ρi /1000 2,400 Sediment Phase Z4 = [1/H] Koc φ4 ρ4 /1000 2,400 Suspended Sediment Phase Z5 = [1/H] Koc φ5 ρ5 /1000 2,400 Fish Phase Z6 = [1/H] 0.048 ρ6 Kow 1,000 Aerosol Phase Z7 = [1/(R T)] 6x106/PS

L

where R = gas constant (8.314 Pa• m3/[mole•K]) T = absolute temperature (K) H = Henry's constant (Pa•m3/mole) Koc = organic-carbon partition coefficient Kow = octanol-water partition coefficient ρi = phase density for phase i (kg/m3) φi = fraction of organic carbon in phase i (g/g) Environmental Compartments Air Compartment (1) ZC1 = Z1 + 2x10-11 Z7 Water Compartment (2) ZC2 = Z2 + 5x10-6 Z5 + 10-6 Z6 Soil Compartment (3) ZC3 = 0.2 Z1 + 0.3 Z2 + 0.5 Z3 Sediment Compartment (4) ZC4 = 0.8 Z2 + 0.2 Z4


Intermedia transport

DiffusionNij = Dij (fi) (moles/h)

Dij = diffusion transport parameter from compartment i to j (moles/(Pa•hr))

fi = fugacity of a chemical in environmental compartment i (Pa)

Convection

N = GZf (moles/h)

G = volumetric flow rate of material (rainwater, suspended sediment, )

f = fugacity of a chemical in the transported phase i (Pa)


Table 11.2-3. D Values in the Mackay Level III model (Adapted from Mackay andPaterson, 1991)

Compartment Process Individual D

air (1) - water (2) diffusion DVW = 1/(1/( u1AWZ1) + 1/(u2AWZ2))rain wash out DRW = u3AWZ2

wet/dry deposition DQW = u4AWZ7

air (1) - soil (3) diffusion DVS = 1/(1/(u5ASZ1) + 1/(( u6ASZ2) +(u7ASZ1)))

rain wash out DRS = u3ASZ2

wet/dry deposition DQW = u4ASZ7

water (2) - sediment (4) diffusion u8AWZ2

deposition u9AWZ5

sediment (4) - water (2) diffusion u8AWZ2

resuspension u10AWZ4

soil (3) - water (2) water runoff u11ASZ2

soil runoff u12ASZ3

advection (bulk flow) emissions andbulk flow in Ii = Ei + GAiCBi

bulk flow out DAi = GAiZCi

reaction DRi = kRi Vi ZCi


Table 11.2-4. Mole Balance Equations for the Mackay Level III Fugacity Model

Air I1 + f2D21 + f3D31 = f1DT1

Water I2 + f1D12 + f3D32 + f4D42 = f2DT2

Soil I3 + f1D13 = f3DT3

Sediment I4 + f2D24 = f4DT4

where the left hand side is the sum of all gains and the right hand side is the sum of alllosses, Ii = Ei + GaiCCi, I4 usually being zero. The D values on the right hand side are;

DT1 = DR1 + DA1 + D12 + D13

DT2 = DR2 + DA2 + D21 + D24

DT3 = DR3 + DA3 + D31 + D32

DT4 = DR4 + DA4 + D42

The solution for the unknown fugacities in each compartment is;

f2 = (I2 + J1J4/J3 + I3D32/DT3 + I4D42/DT4) / (DT2 - J2J4/J3 - D24 D42/ DT4)f1 = (J1 + f2J2)/J3

f3 = (I3 + f1D13)/DT3

f4 = (I4 + f2D42)/DT4

where J1 = I1/ DT1 + I3 D31/(DT3DT1)J2 = D21/DT1

J3 = 1 - D31D13/(DT1 DT3)J4 = D12 + D32D13/DT3


Multimedia prediction for benzene, ethanol, and pentachlorophenol

Mackay’s “level III” modelEmission scenario a)

Emission scenario b)

Emission scenario c)

1000 kg/hr

1000 kg/hr

1000 kg/hr


Multimedia compartment model input data

Environmental Property

Unit

Spreadsheet Location

Benzene

Ethanol

PCP

Molecular 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


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


1. The percentages in each environmental compartment depend upon the emission scenarioa) 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 soild) 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 concentrationsc) high reactions half lives results in highest pollutant amounts

Multimedia compartment model typical results - interpretations


Tier 3 Relative risk index formulation for one environmental impact category - Ch 11.3

Exposure Potential Inherent Impact Parameter

Chemical “i”Benchmark Compound

Dimensionless Risk Index (Ii*) =

[(EP)(IIP)]i

[(EP)(IIP)]B

Process Index (I) = (Ii* ) ×

i = 1

N

∑ (mi)EmissionRate ofChemical, i

Chemical Specific

Process


Indicators for the Ambient Environment

��

�� Relative Risk Index Equation

IGW ,i* = GWPi

Global Warming

IGW ,i* = NC

MWCO2

MWi

Ozone Depletion

IOD,i* = ODPi

Smog Formation

ISF,i* =

MIRi

MIRROG

Acid Rain

IAR ,i* =

ARPi

ARPSO2

GWP = global warming potential, NC = number of carbons atoms, ODP = ozone depletion potental, MIR = maximum incremental reactivity, ARP = acid rain potential.

Compilation impact parameters in: Appendix D. Allen, D.T. and Shonnard, D.R., Green Engineering : Environmentally-Conscious Design of Chemical Processes, Prentice Hall, pg. 552, 2002


Indicators of Toxicity��

��

Relative Risk Index Equation

Human Toxicity Ingestion Route I*

ING =CW ,i LD50, Toluene

CW ,Toluene LD50,i

Human Toxicity Inhalation Route

I*INH =

CA, i LC50,Toluene

CA, Toluene LC50,i

Human Carcinogenicity Ingestion Route

I*CING =

CW ,i HVi

CW , Benzene HVBenzene

Human Carcinogenicity Inhalation Route

I*CINH =

CA, i HVi

CA,BenzeneHVBenzene

Fish Toxicity

I*FT =

CW,i LC50 f , PCP

CW, PCP LC50 f ,i

LD50 = lethal dose 50% mortality, LC50 = lethal concentration 50% mortality, and HV = hazard value for carcinogenic health effects.


Nine Environmental Impact /Health Indexes


IGW ,i* = GWPi

Global Warming

IGW ,i* = NC

MWCO2

MWi

Ozone Depletion

IOD,i* = ODPi

Smog Formation

ISF,i* =

MIRi

MIRROG

Acid Rain

IAR ,i* =

ARPi

ARPSO2

GWP = global warming potential, NC = number of carbons atoms, ODP = ozone depletion potental, MIR = maximum incremental reactivity, ARP = acid rain potential.



Human ToxicityIngestion Route I*

ING =CW ,i LD50,Toluene

CW,Toluene LD50,i

Human ToxicityInhalation Route I*

INH =CA, i LC50,Toluene

CA, Toluene LC50,i

HumanCarcinogenicityIngestion Route

I*CING =

CW, i HVi

CW,Benzene HVBenzene

HumanCarcinogenicityInhalation Route

I*CINH =

CA,i HVi

CA,BenzeneHVBenzene

Fish ToxicityI*

FT =CW,i LC50 f , PCP

CW,PCP LC50 f ,i

LD50 = lethal dose 50% mortality, LC50 = lethal concentration 50% mortality,and HV = hazard value for carcinogenic health effects.

Nine Environmental Impact /Health Indexes


MultiMulti--Criteria Decision Analysis 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,ττττ, 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


SCENE: A Software to integrateenvironmental and economiccriteria with decision analysis

Chen, H. and Shonnard, D.R. Industrial and Engineering Chemistry Research, 43, 535-552, 2004


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, OHDr. Heriberto Cabezas and Dr. Douglas YoungUS Environmental Protection Agency

National Risk Management Research Laboratory26 W. Martin Luther King Dr.Cincinnati, OH 45268

Software tools for environmental impact assessment of process designs


Gaseous Waste Stream Toluene & Ethyl Acetate 193.5 kg/h each; 12,000 scfm, balance N2

Vent

Vent ; 21 - 99.8 % recovery of Toluene and Ethyl Acetate

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

50/50 Mass Mixed Product

Absorption Column

Distillation Column

Absorption - distillation process:analysis of an existing separation sequence

HYSYS Flowsheet


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 (106 Btu/hr) 6.16 3.93 0.52 499 0.13 0.01

Total Emissions (kg/hr) 0.088 128.07 4.23 3.93 0.52 499 0.13 0.01

Emission rate (kg/hr)


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*)


Process environmental summary

All units in kg/yr

Emission from I FT I ING I INH I GW I SF I AR

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 I FT I ING I INH I GW I SF I AR

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*) ×i = 1

N

∑ (mi )100 kgmole/hr Oil Flow Rate;

Oil Temperature = 82˚F; ∆∆∆∆T=180˚F


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)

Toluene Ethyl Acetate


Environmental Index Profiles

0

500

1000

1500

2000

2500

3000

0 100 200 300 400 500

Absorber Oil Flow Rate (kgmoles/hr)

IGW

100 IAR

4 ISF

A


Environmental Index Profiles

0

500

1000

1500

2000

2500

3000

0 100 200 300 400 500

Absorber Oil Flow Rate (kgmoles/hr)..

400 IFT

10 IINH

0.1 IING

B


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 highervalue

Multiple indexes complicate the decision


! Normalized Index

! Weighting of Index Categories

Normalization and Valuation of Indices

INk =

Ik

ˆ I k

Process Index

National Index

IPC = (INk × Wk )

k∑Process Composite Index

Weighting Factors

global warming 2.5ozone depletion 100smog formation 2.5acid rain 10carcinogenic 5noncarcinogenic 5ecotoxicity 10

Source: Eco-Indicator 95 framework for life cycle assessment, Pre Consultants, http://www.pre.nl


Process Composite Index

0.000

0.001

0.002

0 100 200 300 400 500

Absorber Oil Flow Rate (kgmoles/hr) .

I PC

ISF and IING dominatethe IPC index


! 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

Maleic anhydride from n-butane process flowsheet evaluation


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


Maleic anhydride flowsheet with heat integration


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


IGWISF IAR IING

IINH IFT

Dibutyl Phthalate

Dibenzyl EtherDGBEA1.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)

Maleic anhydride from n-butane: effects of absorber oil choice

16.3%reduction

85.1%reduction

81.7%reduction

42.1%reduction


Recap

! 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

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