heat pump integration in a cheese factory · pdf fileheat pump integration in a cheese factory...

Heat Pump Integration in a Cheese Factory

Helen Becker1, Aurélie Vuillermoz2, François Maréchal1

1 Industrial Energy Systems Laboratory (LENI)Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland

2 EDF R&D, Eco-efficiency and Industrial Process DepartmentCentre de Renardières, 77818 Moret sur Loing, France

PRES’11: 14th International Conference on Process Integration, Modeling and Optimization for Energy Saving and Pollution Reduction

H. Becker, A. Vuillermoz, F. Maréchal

Introduction Methodology Results Conclusion

Outline

• Introduction

• Process integration / heat pump integration

• Example of a cheese factory

• Methodology - Heat pump integration

• Option 1: without process modifications

• Option 2: with process modifications

• Results

• Conclusion

2



Process integration: Optimize the energy efficiency

3

Rawmaterials Products

By-Products

EnergyServices

EnergyWater Air Inert GasFuelElectricity

Support

Heat losses WaterSolids GaseousWaste

Representation of industrial processes

Reducing energy consumption and operating costs

Energy conversion and utility Units(e.g. heat pumps, steam boiler, cooling water, ...)

Process operation Units



Heat pump integration

• Heat pump integration potential

• Heat pump integration options

• No process modifications - heat exchange restrictions between process units and heat pumps --> integration of intermediate heat transfer units

• MILP problem with additional constraints (*)

• Process modifications - no heat exchange restrictions

• Conventional heat cascade model (MILP problem)

4

* Becker H., Girardin L. and Maréchal F., 2010, Energy integration of industrial sites withheat exchange restrictions, European Symposium on Computer Aided Process Engineering- ESCAPE 20, 1141–1146.



Example of a cheese factory

5

Rawmaterials(milk)

Products (cheese)By-Products (concentrated whey)

Energy Services

EnergyWater Air Inert GasFuelElectricity

Support

Heat losses WaterSolidsWaste

Energy conversion and utility Units(e.g. heat pumps, steam boiler, cooling water, ...)

Gaseous

Curdling

Evaporation

Prepasteu-

rization

Air-conditioningHot WaterCleaning

Pasteu-

rization

Forming Refining

Pasteurization

Packaging

Cream

Whey

Pasteurization



Process heat requirement definition

6

• Process operation units

• Definition of process streams for heat integration

Evaporation unit is modeled considering the existing thermal vapour

compression

tprod tons of product

Table 1: Process streams, !Tmin/2 values: 2.5 !C (liquids), 1 !C (gases)

Unit Name Tin Tout Heat load Unit Name Tin Tout Heat load[!C] [!C] [kWh/tprod] [!C] [!C] [kWh/tprod]

otherother_c1 100 190 367.8

pasto3pasto3_c1 74 80 84.1

other_h1 5 0.5 307 pasto3_c2 6 28 308.2other_h2 -0.3 -2.5 56.9

pasto4pasto4_c1 69 75 32.1

evapotech

evapo_c1 100 190 993.7 pasto4_c2 8.5 26 83.3evapo_h1 44 5 32.9 pasto5 pasto5_c1 66 76 54.2evapo_h2 44 25 198.1

proc6proc6_c1 105 105 131

evapo_h3 44 44 627.8 proc6_c2 78 78 49.6

pasto1pasto1_c1 6 48 568.2 proc6_c3 95 95 49.6pasto1_c2 48 75 344 proc7 proc7_c1 15 55 40.4pasto1_h1 75 4 904.6 proc8 proc8_c1 70 70 62.6

pasto2pasto2_c1 79 85 5 proc9 proc9_c1 35 35 33.8pasto2_h1 54 4 41.9 proc10 proc10_c1 32 25 175.5

heat heat_c1 35 35 153 CIP clean_c1 85 85 238

!1000 !500 0 500 1000 1500250

300

350

400

450

500

Heat Load [kWh/tprod]

Tem

pera

ture

[K

]

All streams

MER hot = 2146.3 kWh/tprod

MER cold = 892.4 kWh/tprod

(a) Grand composite curve

!1500 !1000 !500 0 500 1000 1500!0.2

!0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8


Carn

ot F

acto

r 1!

Ta/T

[!]

othersutility

(b) Integrated composite curves (Case1)

Figure 2: Grand composite curve of the process and integrated composite curve of the utilitysystem using Carnot scale.

3.1 Heat pump integration option 1: No process modifications allowedHeat pumps are used to valorize waste heat from the process below the pinch point bydriving it above the pinch point with the help of mechanical power, reducing thereforehot and cold utility requirements. In the first approach, the process can not be modified.Thus, the direct heat exchange between a potential heat pump and the process is not al-lowed. The approach from Becker et al. (2010) is applied: two sub-systems (in this casethe process and the heat pump) cannot exchange heat directly. A closed cycle heat pumpusing the refrigerant R245fa is considered. By analyzing the shape of the grand compositecurve, appropriate operating conditions for the heat pump and the intermediate networkcan be estimated. Then, simultaneously the interdependent flow rates of the utility units,heat pumps and the heat distribution fluids are defined, in order to minimize the operatingcosts. The potential of a closed cycle heat pump without direct heat exchange is illustrated



Energy Integration

0 500 1000 1500 2000 2500 3000 3500 4000 45000.2

0.1

0

0.1

0.2

0.3

0.4

0.5


Ca

rno

t F

acto

r 1

- T

a/T

[-]

Cold streamsHot streams



7

!1000 !500 0 500 1000 1500250

300

350

400

450

500


Tem

pera

ture

[K

]

All streams



Hot and cold composite curves Grand composite curve

Waste heat at 44°CHeat pump integration ?

Current hot utility 2345 kWh/tprod



Methodology - indirect and direct heat pump integration

• Indirect heat pump integration

• Heat pump cannot exchange directly with the process

• Closed cycle heat pump

• Process modifications are not allowed

• Transfering heat via intermediate heat transfer units

• Direct heat pump integration

• Heat pump can exchange directly with process

• Open cycle heat pump / mechanical vapour compression

• Process modifications are allowed

• Modifying layout of evaporation unit

8



Indirect heat pump integration

9

Sub-system

1

Sub-system

2

Sub-system

3

Heat transfer system (HTS)

No direct heat exchange possible

Direct heat exchange possible

General

units (GU)

Heat transfer

units (HTU)

Energy Support

Electricity Fuel Water Air Inert Gas

Heat losses Solids Water GasWaste

Raw

materials

Energy

servicesProductsByproducts

• Introduction of subsystems with restricted matches *

• Introduction of intermediate heat transfer units (two water loops)

* Becker H., Girardin L. and Maréchal F., 2010, Energy integration of industrial sites withheat exchange restrictions, European Symposium on Computer Aided Process Engineering- ESCAPE 20, 1141–1146.

r245fa heat pump

Cheese process

Intermediate water loop high temperature

Waste heatheats water

HP coldsource

HP hotsource

Satisfieshot process

demand

Intermediate water looplow temperature



Indirect heat pump integration

• Advantages

• No process modifications --> no supplementary investment costs

• Safety and product quality

• Disadvantages

• High temperature lift --> small COP

• Considering storage problem --> supplementary costs

10

!1000 !500 0 500 1000 1500!0.2

!0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8


Carn

ot F

acto

r 1!

Ta/T

[!]

othersutility

Natural gas consumption: 2157 kWh/tprodCurrent natural gas consumption: 2895 kWh/tprod

Saving potential 25 %



Direct heat pump integration - Analyzing evaporation unit

11

Waste heat producer for heat pump

Optimizing evaporation unit ?

Replacing thermal vapour compression with a MVR unit ?

Milk inlet

Effect 1

T1

P1

Effect 3

T3

P3

Effect 2

T2

P2

steam

product

steam

condensates

To thermal vapour compression

....

To effect 4 and 5 ...

PH PH PH PH



Direct heat pump integration - Process modifications

• Keep evaporation layout

• CASE A : Thermal vapour compression is replaced with mechanical vapour compression (MVR)

• Modify pressure of effects

• CASE B: Realizing all effects in parallel & integration of a MVR unit

• CASE C: Optimizing layout of evaporation & integration of 3 MVR units

• Constant area of each evaporator

12

Qi = Ui · Ai · (Tvap ! Tprod)



Direct heat pump integration

• Advantages

• Better energy efficiency

• No storage problem

• Disadvantages

• Process modifications may give higher investment costs

• MVR is in direct contact with the product

13



Comparison of scenarios

14

Heat recovery

r245faHP

AMVR

BMVR

CMVR

• Current consumption: 2895 kWh/tprod of natural gas, 194 kWh/tprod of electricity

• Results with heat pump integration

Unit Case1 Case2 Case3 Case4 Case5Operating Cost [Euro/tprod] 107 96 97 93 75Fuel consumption [kWh/tprod] 2582 2157 2245 1935 1513Electricity consumption [kWh/tprod] 97 189 150 281 249Cooling water [kWh/tprod] 934 682 996 449 495CO2 emissions [kg/tprod] 530 453 467 417 328



Saving potentials - Results

15

‐60

‐40

‐20

0

20

40

60

Heat recovery r245fa HP A MVR B MVR C MVR

Saving potentials [%]

Operating Cost

Fuel consumption

Electricity consumption

CO2 emissions



Investment cost estimation

16

facilities and installations of the company.

Table 2: Comparison of utility integration

Unit Case1 Case2 Case3 Case4 Case5Operating Cost [Euro/tprod] 107 96 97 93 75Saving potential [%] -14.9 -23.6 -22.8 -26 -40.7Fuel consumption [kWh/tprod] 2582 2157 2245 1935 1513Saving potential [%] -10.8 -25.5 -22.5 -33.1 -47.8Electricity consumption [kWh/tprod] 97 189 150 281 249Saving potential [%] -50 -2.6 -22.6 44.8 28.4Cooling water [kWh/tprod] 934 682 996 449 495CO2 emissions [kg/tprod] 530 453 467 417 328Saving potential [%] -12 -24.8 -22.5 -30.8 -45.5

Table 3: Technologies

Case2 Case3 Case4 Case5Ehp [kW] 372 (max) 239 (mean) 241 698 297 + 136 + 152InvC [kEuro] 771.6 (max) 516.2 (mean) 519.9 1354.8 1285.1Payback [Years] 3.6 (max) 2.4 (mean) 2.7 5.0 2.6

5 AcknowledgementsThe authors wish to thank ECLEER for supporting this research and collaborating in itsrealization.

ReferencesBecker H., Girardin L. and Maréchal F., 2010, Energy integration of industrial sites with

heat exchange restrictions, European Symposium on Computer Aided Process Engi-neering - ESCAPE 20, 1141–1146.

Becker H., Maréchal F. and Vuillermoz A., 2011, Process integration and opportunity forheat pumps in industrial processes, International Journal of Thermodynamics, ECOS2009 special issue, accepted.

Kapustenko P. O., Ulyev L. M., Boldyryev S. A. and Garev A. O., 2008, Integration of aheat pump into the heat supply system of a cheese production plant, Energy 33, 882–889.

Linnhoff B. and Townsend D., 1983, Heat and power networks in process design. part1: Criteria for placement of heat engines and heat pumps in process networks, AIChEJournal 29 (5), 742–748.

Pavlas M., Stehlík P., Oral J., Kleme! J., Kim J. and Firth B., 2010, Heat integrated heatpumping for biomass gasification processing, Applied Thermal Engineering 30, 30–35.

Wallin E. and Berntsson T., 1994, Integration of heat pumps in industrial processes, HeatRecovery Systems & CHP 14 (3), 287–296.

r245faHP

AMVR

BMVR

CMVR

• Used equation

• Heat pump size for r245fa heat pump

• max: peak power of the heat source

• mean: heat source is stored and progressively upgraded

InvC = f · 1500 · 1600.1 · E0.9hp [Euro]



Conclusions

• Operating cost saving potentials

• Heat recovery & Optimized refrigeration cycle 15%

• Closed cycle indirect heat pump integration 25%

• Optimized evaporation unit & MVR 20% - 40%

• Heat pump potential & Improvement of process efficiency

• Possibility of two different approaches

• Investment cost relation & Rentability

• Closed cycle indirect heat pump integration (2.4-3.6 years)

• Evaporation & MVR (2.6-5 years)

17



18

Thank you for your attention !

heat pump integration in a cheese factory · pdf fileheat pump integration in a cheese factory...

Documents