the influence of process design and controls on …€¦ · the influence of process design and...

PRO-TEM Special Session on Thermal Energy Management: Energy System & Efficiency Improvement

THE INFLUENCE OF PROCESS DESIGN AND CONTROLS ON ENERGY-SAVING OPPORTUNITIES OF

CONTINUOUS FRYING SYSTEMS

Hongwei WU

Savvas TASSOU and Tassos KARAYIANNIS

School of Engineering and Design, Brunel University, UK

Project Title

OPTIMISING THERMAL ENERGY RECOVERY, UTILISATION

AND MANAGEMENT IN THE PROCESS INDUSTRIES OPTITHERM

• Brunel University

• Newcastle University

• Northumbria University

• United Biscuits

• FloMech

• Chemistry Innovation KTN

• Beedes Ltd

• Sustainable Engine Systems Ltd

Project started: 1st Oct. 2009

Project duration: 36 months

Project Objectives

Investigate and develop methodologies for the

optimum thermal energy recovery from process

waste streams in the food and chemical process

industries to improve thermal performance and

minimise Greenhouse Gas Emissions.

Presentation Outline

■ Industrial crisp production line description

■ Frying system description

■ Development of 2-D fryer model

■ Control strategy

■ Preliminary results

■ Conclusions

Industrial Crisp Production Line

2-3 mm in thickness

30-40 mm in diameter

5-10% surface water

COMBUSTOR

FRYER

Fines Removal

Crisp Product

Fuel

Combustion Air

Re-circulated Exhaust Gas (30%)

Exhaust Gas

HEAT

EXCHANGER

Combustion Products

Foul Gas (Frying Vapour)

Air

Oil Inlet

Oil Outlet

Raw Potato

Surface Water

(raw potato)

1

2

3

4

5

7

8

6

9

10

11

13

14

12

Oil Return

～ 173 oC

～ 153 oC

～ 164 oC

Industrial Continuous Frying System

Plant Data for Combustor & HX

0

50

100

150

200

250

300

350

400

0

100

200

300

400

500

600

Fuel

flo

w r

ate

(m³/

hr)

Tem

per

atu

re (°C

) Combustion chamber temperature

Fuel flow rate

130

140

150

160

170

180

0 10 20 30 40 50 60 70 80 90 100

Tem

per

atu

re (°C

)

Processing time (min)

Oil temperature at HX outlet

Oil temperature at HX inlet

Stack temperature

520 ℃

164 ℃

154 ℃

173 ℃

280 m3/hr

Industrial Continuous Fryer

Foul Gas

Raw Potato Slices

Potato CrispsPaddle 1 Paddle 2 Hold Down

Takeout Conveyor

HfoOil Temperature Tfo

AirSurface Water

Oil

SupplyOil Return

Fines Removal

Free frying section

Oil Makeup

x

y

0 Lff

L

Plant Moisture and Oil Content

10

15

20

25

30

35

40

0

1

2

3

4

5

6

0 30 60 90 120 150 180

Oil

conte

nt

(%)

Mois

ture

conte

nt

(%)


37%

2.2%

1.2%

30%

2-D Frying (Fryer) Model

• Two-dimensional transient frying model solved with variable time-step

finite volume method (C++ environment);

• Considered the free frying section and surface water of raw potato slices;

• Key simulation parameters selected from plant data/literature. Foul Gas

Raw Potato Slices


Takeout Conveyor


AirSurface Water

Oil

SupplyOil Return

Fines Removal

Free frying section

Oil Makeup

x

y

0 Lff

L

Governing Equations

Frying oil

Potato slices

Oil uptake

2 2

1, 1,2 2

fo fo fo fo fo fo fo fo

fo eff x eff y fo fo cw

c T c T T Tv k k h A T T

t x x y

c c c c w w c w v v c v o o c oc T VF c T VF c T VF c T VF

t

c c c c w w c w v v c v o o c o

c

c T VF c T VF c T VF c T VFv

x

Vapour

source term

2 2

2, 2,2 2 w

c ceff x eff y VF w

T Tk k S H

x y

, , w

w w wc x c y VF

VF VF VFv v S

t x y

2 2

, , , ,2 2

o o o o oc x c y o x o y

VF VF VF VF VFv v D D

t x y x y

Key Simulation Parameters

Foul Gas

Raw Potato Slices


Takeout Conveyor


AirSurface Water

Oil

SupplyOil Return

Fines Removal

Free frying section

Oil Makeup

x

y

0

Parameters Value

Total Length of fryer 11 m Length of free frying section 2 m

Depth of frying oil 0.3 m

Mass flow rate of raw potato 1.2 kg/s

Thickness of potato slices 2.0 mm

Initial moisture content 0.75

Percentage of surface water 5%

Frying oil velocity 0.3 m/s Potato slice velocity 0.1 m/s

Heat transfer coefficient at free

frying section

Heat transfer coefficient after

free frying section

Frying oil inlet temperature 444 K

Parameters Value

650 W/ Km2250 W/ Km2

Length along fryer (m)

Oil

heig

ht

inth

efr

yer

(m)

0 1 2 3 4 5 6 7 8 9 10 110

0.1

0.2

0.3

0.4

0.5

370 376 383 389 396 402 409 415 422 428 435 441 448

T

Free frying section

T=446 K T=429 K

Lengthalongfryer(m)

Oil

height

inth

efry

er(m

)

0 0.5 1 1.5 2 2.50.2

0.25

0.3

Frying Oil Temperature Profile

428

432

436

440

444

448

0 1 2 3 4 5 6 7 8 9 10 11

Av

erag

e fr

yin

g o

il t

emp

erat

ure

(K

)


△T=Tin-Tout=17 K

Length alongfryer (m)

Potat

oslic

ehalf

thick

ness

(m)

0 1 2 3 4 5 6 7 8 9 10 110

0.0005

0.001

0.0015

0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75

Moisturecontent

Potato slice surface

Symmetric centre of potato slice

(100%)

Contour of Moisture and Oil Content

Final moisture

content=1.5%


Pota

tosl

ice

half

thic

knes

s(m

)

0 1 2 3 4 5 6 7 8 9 10 110

0.0005

0.001

0.0015

mfo: 0.0200.0250.0310.0360.0400.0470.0530.0580.0640.0690.0750.080

Oil content

(100%)

Potato slice surface

Symmetric centre of potato slice

Oil content at

fryer exit=8%

Surface Water, Moisture & Oil Content

0

0.05

0.1

0.15

0.2

0.25

0%

10%

20%

30%

40%

50%

60%

70%

80%

0 60 120 180 240 300 360 420 480

Su

rface

wate

r th

ick

nes

s (m

m)

Mois

ture

con

ten

t &

oil

con

ten

t (W

.B.)

Processing time (s)

Moisture content (wet basis)

Oil content (wet basis)

Surface water thickness

Post frying processes begin

Frying

processes

Model Validation

170

171

172

173

174

175 O

il T

emp (°C

)

Frying oil temperature

25

26

27

28

29

30

31

32

33

34

0 0.5

1 1.5

2 2.5

3 3.5

4 4.5

5

1 2 3 4 5 6 7 8 9 10

Oil

conte

nt

(%)

Mois

ture

conte

nt

(%)


Plant moisture content Simulated moisture content

Plant oil content Simulated oil content

Correlation of Moisture & Oil Content

6 1.83 5.38 2.52

82.58 10MC T m HD

5 1.34 1.04 0.69 1.755

82.068 10OC T m HD RPS

Frying System Model Implementation

Combustorm1

m4, T4Heat

Exchanger

T5 Fryer

Re-circulated exhaust gas

m10T8

m7

T8

m3m3T3

Foul gas

Mass flow rate

of potato slices

Moisture &

Oil Content

Measurement

parameters

Combustion products

Fuel

flow rate

Oil mass flow rate

at inlet of HX

Oil temperature at

outlet of HX

Rotating Paddle

SpeedHold Down

Speed

5 5 5

, ,

C p

C in C out

d V c TQ Q

dt

52.238.583.1

8

61058.2 HDmTMC

755.169.004.134.1

8

510068.2 RPSHDmTOC

5 5 5 6

8 7

7 7

p

p

m c T TT T

m c

Energy-saving Control Strategy

Fuel

Flow Rate

PID 1

Controller

Moisture content

COMBUSTOR

&

HEAT

EXCHANGER

PID 2

ControllerHold Down Speed

PID 3

Controller

Rotating

Paddle Speed

Oil content

Moisture content

setpoint

Oil content

setpoint

Oil temperature

setpointFrying oil

temperature

Foul gas (frying vapour)

FRYING

PROCESS

Frying System Model with PID Controller

dT5/dtComb.Cham.

Temp in KComb.Cham.T

emp in oC

Combustion Air Inlet (kg/s)

Combustion Products Outlet (kg/s)

Comb.Prod. Density with Temp

Comb.Prod. Cp with Temp

Comb.Prod. Cp with Temp

Comb.Prod. Cp

with Temp

Comb.Cham.

Temp in K

T5

T5 t5

T5

Combustion Products Outlet mass flow rate (kg/s)

T6

Cp5

T7

m7

cp_o

T7

T5

Stack temperature (K)

mfuel+mair+mfoulgas

Stack temperature in oC

Cp-Recirculated gasT_Recir

mRecir

Foul Gas Mass Flow Rate (kg/s)

cp3*Foul Gas Temp (K)

Comb. Cham.Temp. in oC

Stack temp. in oC

Oil content

Fryer outlet oil temp (oC)

Moisture content

HEX oil outlet temp oC

1

2

3

4

5

6

Oil Temp at HEX outlet

Hold Down Speed

Rotating Paddle Speed

Fuel flow rate (kg/s)

HEX oil outlet Temp.

Right side of combustor equation

f(u)

Unit vonversion

f(u)

Stack temperature in oC

Simout3

Rotating paddle speed

SIMOUT

RESULTSProduct6

Product2

Prod5

Prod4

Prod1

Prod0

PID

PID Controller3

PID

PID Controller2

PID

PID Controller1

f(u)

Oil Content

f(u)

Moisture Content

Memory1

Memory

Simout2

Hold down speed

f(u)

HEXT8

f(u)

HEXT1

Simout1

Fuel vol flow rate

f(u)

Fryer Outlet Oil Temp (oC)

f(u)

Fryer Outlet Oil Temp (K)

Simout4

Foul gas flow rate

f(u)

Foul Gas Temp (K)

f(u)

Foul Gas Temp

f(u)

Foul Gas Mass Flow Rate

f(u)

Fcn4

f(u)

Fcn3

f(u)

Fcn2

f(u)

Fcn1

1

s

Eq.A

Dot Prod3

Dot Prod2

Dot Prod1

Dot Prod

Divide

fai

Const9

CVfuel

Const8

theata

Const7

cp_o

Const6

31.19

Const5

0.099

Const4

Effectiveness

Const3

VC

Const2

roufuel

Const11

T_Air

Const10

Q_Cw

Const1

Cp_Air

Const

f(u)

Combustor

Add

A8A7

A6A5

A4

A3

A2

A1

[ttime uinit]

.m fi le

5

setpoint3

4

setpoint2

3

setpoint1

2

Potato Slice Mass Flow Rate

1

m7

Fryer

Heat Exchanger

Combustor

Potential Energy Saving Opportunity

150

200

250

300

350

400

450

150

155

160

165

170

175

180

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

Fuel

flo

w r

ate

(m³/

hr)

Fry

ing o

il t

emper

ature

(°C

)

Processig time (min)

Controlled frying oil temperature Plant frying oil temperature

Controlled fuel flow rate Plant fuel flow rate

174 ℃

170.5 ℃

284 m3/hr

258 m3/hr

Moisture and Oil Content with Control

20

22

24

26

28

30

32

34

36

38

40

0.5

1

1.5

2

2.5

3

3.5

4

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

Oil

conte

nt

(%)

Mois

ture

conte

nt

(%)


Controlled moisture content Plant moisture content

Controlled oil content Plant oil content

1.7% (setpoint）

35% (setpoint)

200

250

300

350

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85

Fuel

flo

w r

ate

(m³/

hr)


Plant fuel flow rate Controlled fuel flow rate

Preheating Combustion Air

284 m3/h

246 m3/h

Increasing the combustion air temperature from 25 oC to 120 oC

while maintain the frying oil temperature to the setpoint (170.5 oC)

Main Conclusions

■ A conjugate 2-D transient frying model has been

developed and validated against plant data;

■ Percentage of surface water could be an important

factor that influences the energy consumption;

■ Model refinement and sensitivity analysis is

implemented to establish correlation equations;

Main Conclusions (cont’d)

■ Design a model based controller for overall system

simulation and control;

■ Better control of combustion fuel flow rate can

produce up to 10% energy savings whilst

maintaining product quality;

■ Preheating the combustion air temperature could

contribute a further up to 5% energy saving;

■ Effective control can also reduce fluctuations in

product quality.

Acknowledgements

UK Engineering and Physical Sciences Research Council

(EPSRC).

Industrial partners and academic collaborators from the

Universities of Newcastle and Northumbria.

-THE END-

THANK YOU!

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