Waste Generation and Release Estimation from Chemical Processes - Chapter 8.3. David R. Shonnard Department of Chemical Engineering

Transcription

1 Waste Generation and Release Estimation from Chemical Processes - Chapter 8.3 David R. Shonnard Department of Chemical Engineering 1

2 Outline After screening out a number of environmentally and economically inferior reaction pathways and raw materials, the design engineer can begin to identify unit operations in a relatively small number of flowsheets. An environmental evaluation should again be considered using emission estimation. l Educational goals and topics covered in the module l Identify and estimate emissions from process units - Chapter 8, section 3 2

3 Educational goals and topics covered in this lecture Students will: l estimate air emissions and other releases from process units after developing a preliminary process flowsheet, using software and hand calculations l have a better understanding of the mechanisms for pollutant generation and release from process units 3

4 Chapter 8.3 Identifying and estimating air emissions and other releases from process units 1. Identify waste release sources in process flowsheets and mechanisms for unit operations 2. Methods for estimating air emissions from chemical processes 3. Case study - Benzene to Maleic Anhydride process evaluation 4

5 Typical waste emission sources from chemical processes - Ch 8 1. Waste streams from process units 2. Major equipment - vents on reactors, column separators, storage tanks, vacuum systems,.. 3. Fugitive sources - large number of small releases from pumps, valves, fittings, flanges, open pipes,.. 4. Loading/unloading operations 5. Vessel clean out, residuals in drums and tanks 6. Secondary sources - emissions from wastewater treatment, other waste treatment operations, on-site land applications of waste,.. 7. Spent catalyst residues, column residues and tars, sludges from tanks, columns, and wastewater treatment, 8. Energy consumption - criteria air pollutants, traces of hazardous air pollutants, global warming gases, 5

6 Process waste release estimation methods 1. Actual measurements of process waste stream contents and flow rates or indirectly estimated based on mass balance and stoichiometry. (most preferred but not always available at the design stage) 2. Release data for a surrogate chemical or process or emission factors based on measured data 3. Mathematical models of emissions (emission correlations, mass transfer theory, process design software, etc.) 4. Estimates based on best engineering judgment or rules of thumb 6

7 Emission estimation methods: based on surrogate processes 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, 3. Other sources i. Kirk-Othmer Encyclopedia of Chemical Technology, ii. Hydrocarbon Processing, Petrochemical Processes 99, March

8 Distillation column emission and waste generation mechanisms Inert gas for safety Feed Tank N 2 Feed F, x F, x F,I Distillation Column Condenser Vent air emissions Distillate D, x D, x D,I High temperature degradation reactions Reboiler Still Bottoms Waste (sludges) Bottoms B, x B, x B,I =0 8

9 Distillation column emissions: Vent air emissions - N 2 mass balance F: Moles of feed. x F : Mole fraction of ethanol in the feed. x F,I : Mole fraction nitrogen in the feed. D: Moles of overhead product. x D : Mole fraction of ethanol in the overheads produc t. x D,I : Mole fraction of nitrogen in the overheads product. B: Moles of bottoms product. x B : Mole fraction of ethanol in the bottoms product. x B,I : Mole fraction of nitrogen in the bottoms product = 0 Moles N 2 = F x F, I Dx D, I B x B,I D = F ( x F x B x D x B ) x F, I =0.98{exp[x F ln(h EtOH ) +(1 x F )ln(h H2 O )]} 1 x D,I = 0.98{exp[x D ln(h EtOH ) +(1 x D )ln(h H2 O )]} 1 Vent emissions of EtOH = ( Moles N 2 )(VP EtOH /1 atm) Vapor pressure of EtOH at condenser Temp. 9

10 Liquid storage tank air emissions and waste generation mechanisms Vertical Fixed Roof Storage Tank Vent air emissions Tank Bottoms Waste (sludges) 10

11 Liquid storage tank emissions and waste generation mechanisms Vent air emissions Domed External Roof Storage Tank Tank Bottoms Waste (sludges) 11

12 Mechanisms of air emissions from storage tanks Emission Mechanisms; Fixed Roof Tank LTOTAL = LSTANDING + LWORKING Vent Vapor pressure of liquid drives emissions Roof Column T P Liquid Level - Weather, paint color/quality - Weather - liquid throughput, volume of tank 12

13 Module 4: Storage tank comparison - TANKS 4.0 Demonstration Toluene Storage Tank Calculation Toluene emissions only 516,600 gal/yr flowrate of toluene 15,228.5 gallon tank for each comparison Storage Tank Type Vertical Internal Domed External Fixed Roof Floating Roof Floating Roof Annual Emissions (lb) White Paint Grey (Medium) Paint Heated (White) Poor (Grey/Medium

14 Wastewater generation and RCRA sludges Petroleum refinery water processes 10 kg sludge/kg ppt RCRA waste 14

15 Wastewater generation and RCRA sludges Prevent Pollution Reverse Osmosis Device Petroleum refinery water processes 10 kg sludge/kg ppt RCRA waste 15

16 Emission Factors - major equipment Table Average Emission Factors for Chemical Process Units Calculated from the US EPA L&E Database Process Unit EF av ; (kg emitted/10 3 kg throughput) Reactor Vents 1.50 Distillation Columns Vents 0.70 Absorber Units 2.20 Strippers 0.20 Sumps/Decanters 0.02 Dryers 0.70 Cooling Towers 0.10 Estimates Only: Accuracy is only order-of-magnitude 16

17 Emission factors - fugitive sources; minor equipment E i (kg i /yr) = m i EF av N s

18 Example fugitive emissions from a chemical facility l 1,400 valves (168 in gas service), 3,048 flanges/connectors, 27 pumps in liquid service, 20 pressure relief valves, 20 sampling valves valves in gas service ( 168 valves) kg VOC lb 2.2 hr - valve 24 hr 365 days = 19,300 kg day yr lb VOC yr valves in liquid service ( valves) kg VOC lb 2.2 hr - valve 24 hr 365 days = 95,700 kg day yr lb VOC yr 18

19 Example Summary table fugitive emissions from a chemical facility Equipment type Emissions, lb/yr % of emissions by equipment type Valves 115, Flanges 108, Pumps 10, Pressure relief valves 40, Open-ended lines Sample connections 5,700 3 Total 276,

20 Emission factors - criteria pollutants from energy consumption E i (lb i /yr)= EF av (lb i /103 gal) ED(Btu / yr) HV(Btu / 10 3 gal) BE AP-42, Chapter 1, section 1.3, Air CHIEF CD, 20

21 Emission factors - CO 2 from energy consumption E i (lb i /yr)= EF av(lb i /10 3 gal) ED(Btu / yr) HV(Btu / 10 3 gal) BE AP-42, Chapter 1, section 1.3, Air CHIEF CD, 21

22 Emission correlations/models - storage tanks and waste treatment Software Tools Storage tanks TANKS program from EPA - Wastewater treatment WATER8 - on Air CHIEF CD - EPI Suite - Epiwin Treatment storage and disposal facility (TSDF) processes CHEMDAT8 - on Air CHIEF CD 22

23 Benzene to MA process V 2 O 5 2 C 6 H O > 2 C 4 H 2 O 3 + H 2 O + 4 CO 2 MoO 3 AP-42, Chapter 6, section 6.14, Air CHIEF CD, 23

24 Air emission and releases sources: Benzene to MA process Source Identification 1. Product recovery absorber vent 2. Vacuum system vent 3. Storage and handling emissions 4. Secondary emissions from water out, spent catalyst, fractionation column residues 5. Fugitive sources (pumps, valves, fittings,..) 6. Energy consumption 24

25 Emissions from energy consumption: Criteria pollutants (SO 2, SO 3, NOx, CO, PM) Process data for energy consumption 0.15 lb fuel oil equivalent per lb Maleic Anhydride product fuel oil #6 in a Normally Fired Utility Boiler 1% sulfur Boiler efficiency included in the energy usage data AirCHIEF Software 25

26 Emissions from energy consumption: continued SO lb SO2 1 gal #6 ( 1%S) %S 10 3 gal # lb #6 SO lb SO3 1 gal #6 ( 1%S) %S 10 3 gal # lb # lb #6 lb MA 0.15 lb #6 lb MA = lb SO x10-3 lb MA = 3.53 lb SO lb MA = lb SO x10-4 lb MA = 0.13 lb SO lb MA NOx 67 lb NOx 1 gal # lb # gal # lb #6 lb MA = 1.50x10-3 lb NOx lb MA = 1.50 lb NOx 10 3 lb MA CO 5 lb CO 1 gal # lb # gal # lb #6 lb MA = 1.12x10-4 lb CO lb MA = 0.11 lb CO 10 3 lb MA PM 9.19 lb PM %S 10 3 ( 1%S) 1 gal #6 gal # lb # lb #6 lb MA = 2.06x10-4 lb PM lb MA = 0.21 lb PM 10 3 lb MA 26

27 Uncontrolled Air emission / releases Benzene to MA Process (lb/10 3 lb MA) Release Source Maleic Anhydride Benzene Xylene Criteria Pollutants CO 2 Tars and oxygenates i Methods used (MA) Venting from 1 storage tanks Absorber column 2 vent (CO) Vacuum system 2 vent Fugitive 3 Emissions Loading/unloading 4 operations Wastes from vacuum columns Energy use 6 emissions Total , Vertical fixed-roof tank; surrogate for MA is perchloroethylene; Tanks 4.0 program from EPA 2 Hedley et al Potential Pollutants from Petrochemical Processes. Technomic, West Port, CT AP-42 chapter 6 section 6.14, Air CHIEF CD, 3 Typical chemical industry emission factor from Berglund and Hansen, Equation 8.3-4, chapter 8, Green Engineering textbook. 5 Hedley et al Potential Pollutants from Petrochemical Processes. Technomic, West Port, CT 6 AP-42, Chapter 1, section 1.3, Table , Air CHIEF CD, 27

28 Flowsheet evaluation - n-butane to maleic anhydride Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 15, pp

29 Module 4: Uncontrolled Air emission / releases n-butane to MA Process (lb/10 3 lb MA) Release Source Methods used Maleic Anhydride (MA) n-butane Venting from storage tanks Absorber column vent Vacuum system vent Fugitive 4 Emissions Loading/unloading operations Wastes from vacuum columns Criteria Pollutants CO (CO) 1033 Energy use 7 emissions Tars and oxygenates Total ,633 1 Vertical fixed-roof tank; Tanks 4.0 program within the Environmental Fate and Risk Ass essment Tool (EFRAT) (see module 6) 2 from stream information using a commercial process simulator, HYSYS 3 from emission estimation program in EFRAT using the emission factor for a vacuum distillation column. 4 Typical chemical industry emission factor from Berglund and Hansen, Equation 8.3-4, chapter 8, Green Engineering textbook. 6 Hedley et al Potential Pollutants from Petrochemical Processes. Technomic, West Port, CT 7 from emission estimation program in EFRAT using emission factors for energy consumption, AP-42, Chapter 1, Air CHIEF CD, bituminous coal for electricity demand only 29

30 Tier 2 environmental assessment indexes 1. Energy: [total energy (Btu/yr)] / [production rate (MM lb/yr)] 2. Materials: [raw materials (MM lb/yr)] / [production rate (MM lb/yr)] 3. Water: [process water (MM lb/yr)] / [production rate (MM lb/yr)] 4. Emissions: [total emissions and wastes (MM lb/yr)] / [production rate (MM lb/yr)] 5. Targeted emissions: [total targeted emissions and wastes (MM lb/yr)] / [production rate (MM lb/yr)] 30

31 Benzene to MA Process Conclusions from emissions summary 1. Chemical profile: CO 2 > CO > benzene > tars-oxygenates > MA 2. Toxicity profile: Benzene > MA > CO > tars-oxygenates > CO 2 3. Unit operations profile: Absorber vent > energy consumption > vacuum system vent - Pollution prevention and control opportunities are centered on benzene, the absorber unit, and energy consumption - 31

32 Summary/Conclusions 1. Methodologies/software tools - process synthesis: emission factors surrogate process information from historical sources emission estimation software: TANKS 4.0, AirCHIEF 7.0, process simulator packages, Tier 2 environmental assessment 32