How to Save Energy Through Enhanced Automation

Transcription

1 How to Save Energy Through Enhanced Automation AIChE Spring Meeting 2008 Douglas White Emerson Process Management Standards Certification Education & Training Publishing Conferences & Exhibits

2 Speaker Doug White Principal Consultant and Vice President, APC Services Advanced Applied Technologies Process Systems and Solutions Emerson Process Management Many years experience designing, justifying, installing and commissioning advanced real time computer applications in the process industries. 2

3 Natural Gas Prices Natural Gas Prices (Henry Hub) $/ MMBTU Forecast 0 Jan-93 Jan-95 Jan-97 Jan-99 Jan-01 Jan-03 Jan-05 Jan-07 Jan-09 Date 3

4 Process Energy Usage Petroleum Refining Integrated Pulp/Paper Mill Cement Production Chemicals Ethylene Polyethylene EDC PVC EO EG Ethylbenzene Styrene Process Energy; MM BTU/ Ton Value; 10% Energy Reduction; $/ Ton ($7/ MMBTU) Largest Controllable Cost in Most Plants!

5 Session Objective Present some case studies of the many ways that automation, advanced automation and asset management can save energy in process plants 5

6 Outline How is energy used in process plants? How can automation help save energy? How do we implement an energy reduction program? 6

7 General Process Site Energy Flow Purchased Steam Purchased Fuel Raw Material As Fuel Purchased Power Central Steam Production Central Power Production Power Plant Process and Offsites Process Heating/ Cooling Process Fired Equipment Process Direct Fuel Usage Process Steam Drives Process Electric Drives Process Steam Generated Process Misc Electric Usage Export Steam Export Fuel Export Power 7

8 Average Chemical Site Energy Flow Purchased Steam Purchased Fuel 63% Raw Material As Fuel 37% Purchased Power Central Steam Production 32% Central Power Production 4% Power Plant Process and Offsites Process Heating/ Cooling Process Fired Equipment Process Direct Fuel Usage 22% Process Steam Drives Process Electric Drives Process Steam Generated 27% Process Misc Electric Usage 18% Export Steam Export Fuel Export Power 1% %-Equivalent BTU basis 2008 Emerson (Including Process Management losses) on total input 8

9 Integrated Pulping Paper Mill Energy Flow Purchased Steam Purchased Fuel 42% Raw Material As Fuel 50% Purchased Power 8% Central Steam Production 62% Central Power Production 25% Power Plant Process and Offsites Process Heating/ Cooling 5% Process Direct Fuel Usage 29% Process Steam Drives Process Fired Equipment 4% Process Electric Drives Process Steam Generated Process/ Fac Misc Electric Usage Export Steam Export Fuel Export Power %-Equivalent BTU 2008 basis Emerson (Including Process Management losses) on total input 9

10 Oil Refinery Energy Flow Purchased Steam 1% Purchased Fuel 25% Raw Material As Fuel 64% Purchased Power 10% Central Steam Production 34% Central Power Production 5% Power Plant Process and Offsites 6% Process Heating/ Cooling 44% Process Direct Fuel Usage 15% Process Steam Drives Process Fired Equipment Process Electric Drives Process Steam Generated Process Misc Electric Usage %-Equivalent BTU basis 2008 Emerson (Including Process Management losses) on total input Export Steam Export Fuel Export Power 10

11 Reducing Plant Energy Costs Reduce Usage Individual Equipment Improve Efficiencies Boilers, Heaters, kilns Maximize Useful Recovery - Preheat Minimize Losses Cooling water Minimize Motor Losses Unit Savings Optimize Process Unit Operations Distillation/ Fractionation Maximize Waste Heat Recovery Minimize waste/ off spec Site/ Multi Unit Savings Minimize Steam Losses and Downgrading Switch of steam drives for electric or vice versa Seasonal effects Reduce Cost of Production and Purchase Fuel Substitution Generation Maximization Boiler and Turbine Allocation Electric Purchase Optimization Automation and Advanced Automation are the keys to effective operation and minimum ongoing energy usage 11

12 Process Industry Energy Saving Primary Targets Fired Heaters Distillation/ Fractionation Central Power and Steam Production 12

13 How can Automation Reduce Energy Usage? 13

14 Variability Potential Energy Savings Example 12 Heater Stack O2 Variability O2, % Fuel Gas Flow Target :00 9:00 10:00 11:00 12:00 13:00 14:00 Time 0 14

15 Energy Savings Through Automation Target Areas Site- Wide Process Unit Draft Control O2 Equipment FI PI TC Mass Cont PI FC 3-5 Dens FF Fuel Gas FT 3-5 Bottoms Device, Loop 15

16 Saving Energy Automation Examples Improved Loop/ Multi-loop Control Performance FC 3-5 FT 3-5 Improved Measurements Better Control Valve Performance 16

17 Component Heating Values Fuel Gas Component Heating Value Component Heat of Combustion kcal/ NM3 (gross) Heat of Combustion kcal/ kg (gross) Hydrogen Methane Ethane Propane Butane Control Fuel Flows By Mass Instead of Volume 17

18 Energy Savings From Improved Measurements Hydrogen Plant Mass Measurement Objective: Control S/C ratio as close to 3.2 as possible but avoid going below Disturbance: Fuel gas C %; C ; N2, CO also fluctuate Test: Normal orifice plus GC max error 0.2; MMI max error 0.02 Benefits: Moving 0.2 ratio closer to limit worth 8 BTU/SCF of H2; 80 MMSCFD plant; $7 MM BTU gas $1.6 MM per year Ref: MMI WP_

19 Energy Losses Through Bypassing F 2 TC TC TC Fuel F 1 F 1 /(F 1 + F 2 ) Heat Loss Increase -% Reference: Shinskey; Energy Conservation Through Automation 19

20 Energy Savings Equipment Level FI Dens FF Mass Cont PI O2 Draft Control PI Fuel Gas TC Improved Multi-Loop Control Advanced Control Improved Performance Monitoring Improved Diagnostics 20

21 Steam System Control Issues 750 psig Vent PIC3 FIC2 PIC1 FIC1 TGA Objective: Maximum Flow to TGA Users Vent TGB 50 psig PIC4 PIC2 Condensate psig PRC Mean= Sig= Sec mlb/hr FRC Mean= Sig=6.987 Sec Problem: Pressure Instability in Header Limited Flow to TGA 21

22 Steam System Diagnosis Valves and Tuning %Out % 5% 220 sec PRC 1 OP Mean= Sig=9.381 Sec mlb/hr sec Flow controller to TGB has 5% deadband; Sec induces limit cycle in FRC2 pressure Mean= Sig=19.7 Sec psig PRC Mean= Sig=3.242 Sec Correction: Fix TGB turbine governor/ steam valve Tune controllers as system not individually Estimated value of increased flow to TGA - $3000/ day 22

23 Fired Heater Controls 23

24 Combustion Control 24

25 Heater/ Boiler Combustion Control Savings $/ Yr Savings 100 MM BTU/ Hr $7/ kscf Gas 400 F Stack Gas Rise $600,000 $500,000 $400,000 $/ Yr $300,000 $200,000 $100,000 $ % O2 25

26 Typical Heater APC Package HIC 353D PIC 359D TI 071 PIC 357D AIC 354D CO FIC 101 (Up to 4) FIC 102 Combustion Control FIC 103 FIC 104 H306 TI 072 TI 073 TI 043 TI 075 AIC 356D O2 TIC 362D FIC 361 TI 067 TI 069 TI 069 TI 070 TIC 361 Pass Balance MPC Block Fuel Demand Air Demand 26

27 Excuses For Not Improving Heater Controls Damper/ Air controls are not reliable Answer: Add positioners to dampers, with feedback to control system; Analyze and fix controller problems Don t have online analyzer/ can t maintain them Answer: Analyzers are cheaper and more reliable particularly mass flow meters. With higher fuel costs, they are well justified. 27

28 Distillation Controls 34

29 Typical Distillation Column PC FC LC FC Feed, F 20,000 BPD $50/ Bbl TC Reflux, R AR Distillate, D < 5%C5 ;$45/ Bbl > 5%C5; $38/ Bbl FC LC Bottoms, B < 5 %C4 ; $70/ Bbl > 5%C4; $50/ Bbl AC Reboiler, E $36/ Bbl FOE 35

30 Distillation Column Control Savings Cost Per Year Excess Reflux BPD Stabilizer Column $10/ MM BTU Steam $/ Yr $700,000 $600,000 $500,000 $400,000 $300,000 $200,000 $100,000 $ % Excess Reflux 41

31 Column Pressure Effect Relative Reboiler Cost Per Year Column Pressure Effect BPD Stabilizer 120% 100% 80% 60% 40% 20% 0% Pressure, PSIA Basis: Constant Separation Modeled With ChemSep Peng Robinson Equation of State 42

32 Energy Savings Site Wide Site Energy/ Utility Management Steam System Control Fuel System Control 43

33 Energy Management and Optimization System 44

34 Plant Utility Systems Many Opportunities for Savings BFW FB1 FB2 FB3 WHB1 WHB2 GT1 HRSG Many interacting decision variables Large number of constraints FG Vent Unit 1 Unit 2 PRV ST1 ST2 Vent HPS MPS Demin Plant PRV Unit 3 Unit 4 Unit 5 Make-Up Vent LPS Condensate 45

35 Optimizer Decisions Which boiler(s) should I run? What load? How much electricity should I produce? Buy? Sell? Is it economic to run the steam turbine? Which fuel should I buy? How much? Should I be using more steam drives or more electric drives? When will efficiency gain from maintenance balance the cost of shut down for this equipment? How does my actual compare with plan corrected to standard conditions? 46

36 Full Utility Optimization BFW FB1 FB2 FB3 WHB1 WHB2 GT1 HRSG Many interacting decision variables Large number of constraints FG Unit 1 Unit 2 PRV ST1 ST2 HPS MPS Demin Plant PRV Unit 3 Unit 4 Unit 5 Make-Up LPS Condensate 47

37 Overall Energy Optimization Strategy Continuously Calculate Production Costs Over Load Range with Current Fuel Mix Incorporate Constraints on All Equipment Decisions Made Through Rule Based Logic Boiler Load Allocation Distribute Steam Production Based on Cost and Constraints Turbine Load Allocation Distribute Steam for Minimum Cost with Constraints Tie-Line Control Control Electrical Purchase Based on Economic Decision and Constraints 48

38 Boiler Load Allocation 49

39 Load Allocation 90 Boiler Efficiency How to provide 200 kpph steam? No. 4 Load Most Efficient No Minimum Cost No Equal Loads No. 1 25,000 50,000 75,000 Boiler Load, lb/hr 50

40 Energy Savings via Site Energy Balance Flue Gas; 200 F Flue Gas; 200 F Fuel 24,393 kbtu/ hr 1600 psia; 940 F pph 200 psia Power 1000 KW 0 kbtu/hr Blow- Down 384 pph Blow- Down 271 pph Fuel kbtu/ hr 1600 psia; 940 F pph 200 psia 9600 pph Power 1000 KW 3754 kbtu/hr Make-Up 384 pph Condensate Steam; 125 psia 20,200 pph Make-Up 271 pph Condensate Steam; 125 psia 10,100 pph Naïve calculation, value 125 psia steam reduction = 1000 x (1031 Btu/ lb (ΔH v ) 0.7(eff))x $7/MMBtu (Fuel) = $10.31 per klb Actual site value 125 psia steam reduction = $4.08 per klb Reference: Kinney; Energy Conservation in Process Industries 51

41 Typical Energy Management System Benefits 1 3 % Overall site utility cost savings! 56

42 Example 57

43 Utilities Example Biomass Power Boiler Paper mill 160k PPH Fluidized-bed Boiler Fuels: Sludge Wood waste Tires Fuel gas Incentives: Maximize use of cheap fuels (Tires & Wood) Burn all the sludge to minimize land fill Maximize steam production 58

44 Solid Fuel Composition Control Sludge Presses Tire Derived Fuel (TDF) TDF Target M VSM FC M Sludge Recovery Hopper Sludge Bin Sludge Target FC FC HC RSP Bark Yard Silo 1 HC RSP Silo 2 FC Bark Target WS Solid Fuel Bin HC RSP VSM VSM WS WS RSP HC Solid Fuel To Boiler 59

45 Boiler Control To ID Fan FC Solid Fuel Solid Fuel FC Boiler Overfire Air Ports (18) PC FC FC To ID Fan Speed Control Combustion Control Secondary Air Blower Primary Air Blower Fuel Gas FC RSP NC Load Burners (4) Lance Burners (16) TC Avg TI A-F FC To Ash Handing Ash Screws (2) HS M M HS TI Air Preheater 60

46 Boiler Process Control Issues Varying water in sludge Long delay & lag times (20 60 minutes) to change fuel composition Fuel composition time constants are a function of fuel bin level Solid fuel composition in fuel bin is unknown Bed temperature constraints (max & min) Multiple operators controlling same unit Different operating philosophy used by each shift 61

47 Solid Fuel Composition Control Sludge Presses M Tire Derived Fuel (TDF) TDF Target VSM MPC Block M Sludge Recovery Hopper Sludge Bin Sludge Target FC FC HC RSP Bark Yard Silo 1 HC RSP Silo 2 Bark Target FC WS Predicted BTU Content Solid Fuel Bin HC RSP VSM VSM WS WS RSP HC Solid Fuel To Boiler 62

48 Boiler Control To ID Fan FC MPC Outputs Solid Fuel Solid Fuel FC Boiler Overfire Air Ports (18) PC FC FC To ID Fan Speed Control Combustion Control Secondary Air Blower Primary Air Blower Fuel Gas FC RSP NC Load Burners (4) Lance Burners (16) TC Avg TI A-F FC To Ash Handing Ash Screws (2) HS M M HS TI Air Preheater 63

49 Power Boiler Sludge TPH Key Current Average SLDG New Average Max Sustainable 12/20/00 1/9/01 1/29/01 2/18/01 3/10/01 3/30/01 4/19/01 64

50 Power Boiler Bark Fuels TPH Key Current Average BARK New Average Max Sustainable 12/20/00 1/9/01 1/29/01 2/18/01 3/10/01 3/30/01 4/19/01 65

51 Power Boiler APC Benefits Power Boiler Difference in Hourly Costs & (Savings) Natural Gas $2.22 Sludge Disposal ($23.04) Sludge Ash Disposal $9.18 TDF $0.46 TDF Ash Disposal $0.00 Waste Wood $26.91 W Wood Ash Disposal $0.77 Total $16.50 Package Boilers Displaced Natural Gas ($98.42) Total Savings $56k / mo $672k / yr Project Justified: Replacement of required pneumatic instruments DCS Hardware / Software APC Tools Turnkey Engineering Services Net Savings, $/Hr ($81.92) 66

52 Issues in Evaluating Plant Energy Usage Unit energy usage depends on production rate Unit energy usage variance dependent on production rate Need to correct to standard unit conditions 67

53 Unit Energy Usage Energy Usage Btu Specific Energy Usage Btu /Bbl Throughput - % Max Capacity 68

54 Energy Usage - Example MMBTU/Hr Emerson Process Production Management T/Hr 69

55 Unit Energy Usage x x x x x Variance Increases at Lower Rates x x x x x x Specific Energy Usage Btu /Bbl x x x x x x x x x x x x x Confidence Limits x x x x x Throughput - % Max Capacity 70

56 Unit Energy Usage - Example MMBTU/Ton Production 72

57 Excuses for Doing Nothing Not enough manpower - Too busy doing other things Our plant is special analysis based on other sites doesn t apply We run our plant well already, there won t be any big savings found Ostrich - (If we find something obvious, management will ask why we didn t find it before) 76

58 Summary Energy is the largest controllable cost in process operation it s efficient production and use are keys to plant profitability Automation and Advanced Automation are keys to effective use and management of energy in the plant Implementation of a program to save energy requires a disciplined approach to evaluation and analysis 77

59 Questions? Comments? More material on subject: 78