Topic 11. Detailed Environmental Assessment of Chemical Process Flowsheets

Transcription

1 Topic 11. Detailed Environmental Assessment of Chemical Process Flowsheets University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 1

2 Outline The last step for improving the environmental performance of a chemical process design is a detailed environmental impact assessment of a process flowsheet Tier 3 assessment» How to formulate environmental impact indicators» How to draw the boundaries around the assessment - what to leave in - what to leave out» A methodology to integrate emissions estimation, environmental fate and transport, and relative risk assessment» Example application for VOC recovery/recycle University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 2

3 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 calculations, and relative risk assessment to rank process design alternatives University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 3

4 Boundaries for impact assessment Pre-Chemical Manufacturing Stages extraction from the environment transportation of materials refining of raw materials storage and transportation loading and unloading Chemical Manufacturing Process chemical reactions separation operations material storage loading and unloading material conveyance waste treatment processes Post-Chemical Manufacturing Stages final product manufacture product usage in commerce reuse/recycle treatment/destruction disposal environmental release airborne releases wastewater releases toxic chemical releases energy consumption solid/hazardous waste resource depletion Environmental Impacts global warming ozone layer depletion air quality smog acidification ecotoxicity human health effects, carcinogenic and non carcinogenic resource depletion Chapter 11: chemical manufacturing stage only - Chapter 13: all stages University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 4

5 Essential features of Tier 3 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 methodology Release estimates fate and transport exposure risk University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 5

6 Systematic risk assessment methodology National Academy of Sciences, 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, C a (mg/m 3 ) - a single compartment model Thibodeaux, L.J. 1996, Environmental Chemodynamics, John Wiley & Sons University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 6

7 Quantitative risk calculation Carcinogenic Risk Example (inhalation route) Exposure Dose Dose - Response Relationship, Slope Factor (mg/(kg d)) -1 Risk i = (C a CR EF ED) (BW AT) SF CR - contact rate (m 3 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 10 6 cases in the population; 10-4 to 10-6 acceptable Disadvantage: Only a single compartment is modeled / Computationally inefficient Highly uncertain prediction of risk i University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 7

8 Relative risk calculation (what is the relative toxic potency?) Carcinogenic Risk Example (inhalation route) Relative Risk = (C a CR EF ED) (BW AT) (C a CR EF ED) (BW AT) SF SF i Benchmark = [ C a SF] i C a 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 University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 8

9 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 CO 2, CO, SO 2, NOx, AP- 42 (EPA) factors Process Simulators (e.g. HYSYS ) University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 9

10 Multimedia compartment model formulation - chapter 11.2 Multimedia compartment model Processes modeled emission inputs, E advection in and out, D A intercompartment mass transfer, D i,j reaction loss, D R Model Domain Parameters surface area km 2 90% land area, 10% water height of atmosphere - 1 km soil depth - 10 cm depth of sediment layer - 1 cm multiphase compartments Mackay, D. 1991, Multimedia Environmental Models", 1 st edition,, Lewis Publishers, Chelsea, MI University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 10

11 Multimedia prediction for benzene, ethanol, and pentachlorophenol Mackay s level III model Emission scenario a) 1000 kg/hr Emission scenario b) 1000 kg/hr 1000 kg/hr Emission scenario c) University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 11

12 Multimedia compartment model input data Spreadsheet Environmental Property Unit Location Benzene Ethanol PCP Molecular Weight g/mole C Melting Point ûc C Dissociation Constant log pk a C Solubility in Water g/m 3 C E E+5 14 Vapor Pressure Pa C E E E-3 Octanol-Water Coefficient log K ow C Half-life in air hr C33 1.7E+1 5.5E E+2 Half-life in water hr C34 1.7E+2 5.5E E+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 E+3 University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 12

13 Multimedia compartment model: typical results Chemical Percentage (%) (emission scenario) Total mass Air Water Soil Sediment (kg) Benzene (a) 1.98x x10-3 Benzene (b) 1.41x x Benzene (c) 6.86x x10-3 Ethanol (a) 4.56x x10-3 Ethanol (b) 7.35x x Ethanol (c) 7.84x Pentachlorophenol (a) 2.07x Pentachlorophenol (b) 4.59x x Pentachlorophenol (c) 2.39x x (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 University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 13

14 Multimedia compartment model typical results - interpretations 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 K H results in high air concentrations and amounts b) high K OW results in high soil concentrations c) high reactions half lives results in highest pollutant amounts University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 14

15 Nine Environmental Impact / Health Indexes Relative Risk Index Global Warming Equation * I GW,i = GWP i Ozone Depletion * I GW,i * I OD,i = N C MW CO2 MW i = ODP i Smog Formation Acid Rain * I SF,i * I AR, i = MIR i MIR ROG = ARP i ARP SO2 GWP = global warming potential, N C = number of carbons atoms, ODP = ozone depletion potental, MIR = maximum incremental reactivity, ARP = acid rain potential. University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 15

16 Nine Environmental Impact / Health Indexes Relative Risk Index Human Toxicity Ingestion Route Human Toxicity Inhalation Route Human Carcinogenicity Ingestion Route Human Carcinogenicity Inhalation Route Equation I * ING = C W,i LD 50,Toluene C W,Toluene LD 50,i I * INH = C LC A,i 50,Toluene C A,Toluene LC 50,i C I * W,i HV i CING = C W,Benzene HV Benzene C I * CINH = A,i HV i C A,Benzene HV Benzene Fish Toxicity I * FT = C W,i LC 50 f, PCP C W, PCP LC 50 f,i LD 50 = lethal dose 50% mortality, LC 50 = lethal concentration 50% mortality, and HV = hazard value for carcinogenic health effects. University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 16

17 Process Simulator Output or Conceptual Design EFRAT Physical Properties, Toxicology, Weather, Geographical, and Emission Factors Databases List of Chemicals, Equipment specifications, Utility consumption, Annual throughput Chemicals, Equipment specifications, annual throughput Chemicals, K H, K OW Chemicals, τ, LC 50, HV, MIR Air Emission Calculator Chemical Partition Calculator Relative Risk Index Calculator Chemical I1 I2 In Emission Rate Report A B..... MS Excel C..... n..... MS Excel Multi-Criteria Decision Analysis University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 17

18 Software tools for environmental impact assessment of process designs 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 University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 18

19 Absorption - distillation process: analysis of VOC recovery/recycle Gaseous Waste Stream Toluene & Ethyl Acetate kg/h each; 12,000 scfm, balance N 2 Vent ; % recovery of Toluene and Ethyl Acetate Vent Absorption Column Distillation Column 50/50 Mass Mixed Product HYSYS Flowsheet Make-up oil Absorption oil (C-14) 10 to 800 kgmole/h University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 19

20 Absorption - distillation process: (boundaries on analysis?) Yes, data is easy to obtain given fuel type No, eqpt. Is same for all options Equipment Suppliers Energy Suppliers Equipment Energy Equipment Emissions Equipment Suppliers No, data is difficult to obtain Material Suppliers Toluene Ethyl Acetate Uses of Toluene & Ethyl Acetate No, data is difficult to obtain No, they are recycled University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 20

21 Unit-specific emission summary UNIT OPERATION Mass Emission rate (kg/hr) Flow Toluene Ethyl C-14 SOx NOx CO 2 CO TOC "METHOD" (kg/hr) Acetate Absorption Column "HYSIS" 19, Distillation "emission Column factor" Fugitive "emission Sources factor" Storage Tank "correlation" Reboiler Energy (10 6 Btu/hr) Total Emissions (kg/hr) Where are the centers for energy consumption and emissions? 100 kgmole/hr Oil Flow Rate; Oil Temperature = 82 F; T=180 F University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 21

22 Risk index summary Relative Risk Index (I*) Compound I* GW I* OD I* SF I* AR I* ING I* INGC I* INH I* INHC I* FT Toluene Ethyl Acetate SOx NOx CO CO C TOC Which chemicals have the highest impact indexes? University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 22

23 Process environmental summary 100 kgmole/hr Oil Flow Rate; Oil Temperature = 82 F; T=180 F Process Index (I) = (I i *) (m i ) N i = 1 All units in kg/yr Emission from I FT I ING I INH I GW I SF I AR utility 0.00E E E E E E+04 absorber 4.67E E E E E E+00 tank 3.36E E E E E E+00 distillation column 5.06E E E E E E+00 fugitive 3.12E E E E E E+00 Emission of I FT I ING I INH I GW I SF I AR Ethyl Acetate 4.68E E E E E E+00 Toluene 1.92E E E E E E+00 Tetradecane 0.00E E E E E E+00 Carbon dioxide 0.00E E E E E E+00 Carbon monoxide 0.00E E E E E E+00 Nitrogen dioxide 0.00E E E E E E+03 Sulfur dioxide 0.00E E E E E E+03 TOC 0.00E E E E E E+00 - going beyond the release of mass to the release of impact - University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 23

24 VOC recovery by absorption into tetradecane (C14) Toluene Ethyl Acetate Absorber Oil Flow Rate (kgmole/hr) C14 is more selective for toluene - substitute a more EA-selective absorber solvent University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 24

25 Environmental Index Profiles 3000 A I GW I AR I SF Absorber Oil Flow Rate (kgmoles/hr) A complex response over the parameter space for I GW, I AR, and I SF University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 25

26 Environmental Index Profiles 3000 B I FT I ING I INH Absorber Oil Flow Rate (kgmoles/hr).. A similar response over the parameter space for I FT, I ING, and I INH University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 26

27 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 University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 27

28 Normalization and Valuation of Indices (create a single index for decision-making) Normalized Index I N k = I k ˆ I k Process Index National Index Weighting of Index Categories Process Composite Index I PC = (I k N W k ) k Weighting Factors global warming 2.5 ozone depletion 100 smog formation 2.5 acid rain 10 carcinogenic 5 noncarcinogenic 5 ecotoxicity 10 Source: Eco-Indicator 95 framework for life cycle assessment, Pre Consultants, University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 28

29 Process Composite Index I SF and I ING dominate the I PC index I PC Absorber Oil Flow Rate (kgmoles/hr). A single index makes decision-making easier, but information is lost University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 29

30 Recap Tier 3 assessment» How to formulate environmental impact indicators» How to draw the boundaries around the assessment - what to leave in - what to leave out» A methodology to integrate emission estimation, environmental fate and transport, and relative risk assessment» Example application for VOC recovery/recycle University of Texas at Austin - Michigan Technological University - Rowan University - US EPA 30