Congrès s Annuel ATIP Annecy 27-29 29 avril 2005 DUAL REPRESENTATION OF MINIMUM ENERGY REQUIREMENTS APPLICATIONS TO P&P PROCESSES David Brown Zoé Périn-Levasseur François Maréchal Jean Paris EP Montréal EP Montréal EFP Lausanne EP Montréal EFP Lausanne EFP Lausanne ATIP 2005 1
Highlights Minimum energy requirement (MER) Integrated process-energy system Pinch analysis & MER Dual representation Application to P&P operations Heating of a process stream Dilution and heating Paper machine drying section Illustration : Integrated TMP-Newsprint Mill Concluding remarks ATIP 2005 2
Integrated Process-Energy System ATIP 2005 3
Minimum Energy Requirement : Process Side 200 Heat Production, Q Hot 150 Heat Consumption, Q Cold T(oC) 100 Hot Composite Curve Cold Composite Curve MER = Q Hmin Pinch (ΔT min=10 o C) 50 0 Q Cmin =60 Internal Heat Recovery, Q exch Q Hmin =20 0 100 200 300 400 500 600 Q (kw) Q Cmin= Q Hot +Q Hmin + Q Cold ATIP 2005 4
Process MER and Grand Composite Curve Shifted Temperatures 200 Hot streams : T f = T i - T min/2 Cold streams : T f = T i + T min/2 T(oC) 150 100 50 0 0 100 200 300 400 500 600 Q (kw) Table of temperatures Actual ( o C) IN/OUT Shifted ( o C) IN/OUT Cp (kw/ o C) 170/60 165/55 3 150/30 145/25 1.5 20/135 25/140 2 80/140 85/145 4 ATIP 2005 5
Process MER and Grand Composite Curve Diagram Construction Q (kw) Q Hmin = 20 (kw) 60 T Shifted ( o C) 180 160 Q Hmin -82.5 75-15 2.5 140 120 100 80 60 40 Pincement, ΔTmin = 10 o C Q Cmin = 60 (kw) 20 0 Q Cmin 0 20 40 60 80 100 Q (kw) ATIP 2005 6
Dual Representation: Energy Requirement and its Technical Implementations Cold Stream Definition for One Demand Heat Exchanger P 60 o C S 179 o C 110 o C T( o C) 110 60 Reservoir Heater (CST model) S 179 o C P 60 o C 110 110 o C T( o C) 110 Q exch Q P: process stream, D: dilution, S: steam Q exch Q MER = Q exch, determined from demand on utility ATIP 2005 7
P&P Application 1 : Dilution and heating Heat Exchanger P D 60 o C 110 o C S 179 o C 5 o C 110 o C T( o C) 110 60 S 179 o C 5 Q Reservoir Heater (CST model) P 60 o C D 5 o C S 179 o C T( o C) 110 110 110 o C Q Steam Injection P D S 60 o C 5 o C 179 o C 110 o C 5 ATIP 2005 8 Q P: process stream, D: dilution, S: steam T( o C) 179
Heating by steam injection : The pinch point pitfall Steam should not be used below the pinch point This does not result in any net energy savings The effect is: the more in, the more out ATIP 2005 9
P&P Application 2 : PM Drying section HP steam MP steam LP steam Stream Stream Table P (kpa) T ( C) m (t/h) HP 1650 267 69 Wet sheet Uncondensed vapor Dried sheet HP cond. 1510 199 69 MP 445 148 12 MP cond. 305 134 12 LP 340 143 14 LP cond. 200 121 14 HP cond. MP cond. LP cond. ATIP 2005 10
PM Drying Section : Process and Utility Representations Process GCC (Thermodynamic demand) Utility GCC (Technological demand) 3 1 2 Water evaporation 8 7 6 5 4 Paper & water heating 9 1 HPS superheating 2 Production of HPS 3 HPS post condensation 4 Exchange between HP water preheating and HP condensate 5 Production of MPS 6 Exchange between HP & MP water preheating and HP condensate 7 Production of LPS 8 MHS and LPS post condensation 9 Condensate reheating ATIP 2005 11
Illustration : Integrated TMP-Newsprint Mill ATIP 2005 12
Thermodynamic MER chip washing & preheating + TMP, DIP & PM whitewater heating Miscellaneous: Soot blowing Saw mill Heating (misc.) Primary Effluent treatment refiners Deaerator Sheet drying Secondary refiners T min = 10 K Pinch point (threshold) at 283 K Process MER = 79 MW Diagram implies maximum heat recovery; HX network to be defined ATIP 2005 13
Technological MER LP steam to drying section HP steam to drying section MP steam to drying section soot blowing Primary refiners T min = 10 K Pinch point at 373 K Process MER = 79 MW Deaerator Chip preheat Chip washing Secondary refiners TMP, DIP & PM whitewater heating Effluent treatment Sawmill Heating (misc.) System integration represented by the two GCCs are different, corresponding heat recovery network will be different ATIP 2005 14
Integrated Process-Energy System Production MER by energy conversion Thermodynamic or technological MER ATIP 2005 15
MER Production by Energy Conversion A Steam flowrates optimized H E G F D F B F G C Multiple pinch points Combined heat and power Minimum fuel consumption A Combustion (fossil/biomass) B Combustion gases recovery C Water preheating D HP steam production E HP steam superheating F Steam utilisation in process G Process GCC H Expansion turbines ATIP 2005 16
Proposed modifications Recuperation of heat from secondary refiner exhaust steam (21% reduction of utility steam) Heat exchangers for whitewater and wood chip heating & use of a condensing extraction turbine, recycle condensate to boilers (10 % reduction of utility steam) Higher outlet pressure of boilers to improve cogeneration of electricity ATIP 2005 17
An overview of process energy enhancement Data extraction Reconciliation Pretreatment Pinch analysis Targeting Violations detection Dual representation Condensates recovery System closure Engineering Optimisation Quantum gains : New technologies ATIP 2005 18