Drying training Equipment Operation and control

Drying

•Introduction

•Background

•Why is it Important?

•Drying Theory

•Equipment Operation and Control

RELATIVE COST OF WATER REMOVAL

FORMER PRESS DRYER

0

5

10

15

20

(Drainage) (Evaporation) (Compression)

WATER REMOVED (kg water/kg fiber)

CONSISTENCY

1.3

95%

825

10-13%

5.3

40%

Rela

tive C

ost

Exhaust Air

Recirculated Air

Supply Fan

Combustion Air

Condensate

Hood

Exhaust Fan

Fresh Air Steam

Burner

Yankee

Fuel

Evaporated Water

Air

Tissue Machine Drying System

YANKEE & HOOD SYSTEMS

Air Impingement

Dryer Shell

Steam

Drying: Simultaneous Heat & Mass Transfer

Sheet

Mass T

r. (

Evap

.)

Heat

Tr.

Heat

Tr.

YANKEE

HOOD

Drying

•Introduction

•Yankee Dryer

•Steam In

•Condensate Out

•Drying Theory


•Hot Air In

•Evaporated Moisture Out

•Yankee Hood

Backside (Drive Side)

Frontside (Tending Side)

Steam In

KC Stayed Head Yankee Dryer

Stay Bar

Blowthrough Steam & Condensate Out

Blowthrough Steam & Condensate Out

Shell

Journal

Head Head

Condensate Removal Pipe

Yankee Dryer Heat Transfer Coefficients

Sheet

R Coat = 1/h Coat

R Shell = 1/h Shell =t/k Shell

R Cond = 1/h Cond

R Sheet =1/h Sheet

1/U D

Condensate

Dryer Shell

Coating

Steam

Heat

Tra

nsfe

r Sheet/Coating

Adhesion

Dryer/Coating

Adhesion

Motive Steam

Warm Up Steam

Atmosphere

Condensate

Dryer

Hood

Flash Tank

Yankee Dryer Steam & Condensate System

Sight Glass

Model of Condensate Behavior

Ponding Cascading Rimming

0 0.1 0.2 0.3 0.4 0.5 0

500

1000

1500

Condensate Rimming Thickness (in)

Hong & Appel

White & Higgins

Condensate Rimming Velocity D

rye

r S

pe

ed

(fp

m)

0

0.020

0.015

0.010

0.005

0.025

Dryer Speed (fpm)

Heat Transfer Resistance of Condensate

Rimming Speed

1000 2000 3000 4000 5000

Co

nd

en

sa

te R

es

ista

nc

e

(Hr

Ft

F

/BT

U

2

Ways to Avoid the Rimming Effect

Minimize the condensate layer

Bypass the condensate layer

Create Turbulence

Condensate Out

Ribbed Dryer With Soda Straw Condensate System

Shell Ribs

Grooves

Soda Straws

Dryer Rotation

Movement in

Relation to Dryer

Shell

Condensate

Movement in

Relation to Dryer

Shell

Minimum Condensate Thickness

Maximum Condensate Thickness

GRAVITY

Top

12

3 9

6

Spilling Over Behind Bars

Wave Advances Ahead of Bars

Spilling Over Ahead of Bars

Wave Advances Behind Bars

Spoiler Bars

Rotation

Basic Hood Design

100,000 cfm

100,000 cfm

Typical HTHV Hood

100,000 cfm

100,000

cfm

25,000 cfm

?

25,000 cfm

?

Infiltration / Exfiltration

Suck / Spill

100,000 cfm

100,000

cfm

25,000 cfm

?

0 cfm

?


Suck / Spill

100,000 cfm

100,000

cfm

0 cfm

?

25,000 cfm

?


Suck / Spill

Typical Counter-flow Hood

Identified Problems on B1

• Make-up air dampers closed

• This condition results in the hood not being

balanced (infiltration/exfiltration)

• This condition make the system less energy

efficient.

100,000

50,000

10,000

40,000

Exhaust Tubes

Supply Plenum

Exhaust Plenum

Exhaust Duct

Supply Ducts

Burners or Heat Exchangers

Supply Fans

Exhaust Air

Exhaust Fans

Fresh Air

Fresh Air

Tissue Machine Dryer Hood

FEATURES SUITABLE FOR:

- New machines

- Rebuilds / replacements

- No limit for paper width

VALUES

- lower energy consumption

at same (competitors’)

performance

= Less cost per ton

TECHNICAL DATA

- Impingement speed up to 37400 fpm

- Impingement temp. up to 950 °F

- Specific evaporation up to 41 lb/hft2

Metso Paper Basic SC- Yankee Hood

Drying

•Introduction

•Condensate Removal System

•Steam and Blowthrough Control

•Hood Air System

•Drying Theory


29 Gravities

Condensate Removal

7000 kg/hr Steam Input

7000 kg/hr Condensate Output

How do you get Condensate out of a

Yankee Dryer ?

• Differential Pressure

• Blow Through Steam

– Velocity Control

0

Pressure Drop vs. Blowthrough Flow

Blowthrough Flow (kg/hr)

0

600

500 1000 1500 2000 2500 3000

150

300

450

Density

System

Blowthrough Curve

Density + Friction

(1)

(2) (3)

Pre

ssure

Dro

p (

kP

a)

Friction

0

PRESSURE DROP VS. BLOWTHROUGH

EFFECT OF SPEED INCREASE


0

600

500 1000 1500 2000 2500 3000

150

300

450 1600 m/min

1500 m/min

Friction

Density

Dro

p P

ressure

(kP

a)

Two Phase Flow Regimes Bubbly Flow

Slug Flow

Churn Flow

Annular Flow

Pressure Drop vs. Blowthrough Flow Effect Of Condensing Rate Increase


0 500 1500 2500 3000

0

150

300

450

600

700 kPa

800 kPa

Pre

ssu

re D

rop (

kP

a)

1000 2000

Controlling Blowthrough Flow

•Stable condensate removal -

Annular flow velocity > 21 m/sec.

Reduces the density with more steam.

Makes condensate removal easier

•Pressure drop is not a reliable indicator of

blowthrough flow.

Blowthrough should be controlled by

controlling flow.

(Or in the case of B3 – Velocity)

Effect of Yankee Pressure

On Density and Blow-Through

•Steam density changes significantly with pressure

100 psig steam (7 bar) -- 0.24 m^3/kg

50 psig steam (3.5 bar) – 0.42 m^3/kg

•The higher the density the more blow-through

steam is required for good evacuation.

For consistent condensate removal if we

operate at various Yankee steam pressures

we need to have various blow through

(Velocity) set points.

Ribbed Yankee With Soda Straws

Kimberly-Clark Condensate Scoop

Steam & Condensate In

Condensate & Steam Out

Dryer Shell

Scoop

Condensate Layer

Yankee Dryer Steam & Condensate System

LIC

DPI

PIC

TT

PI

Motive Steam

Warm Up Steam

PIC

Vent Valve Blowthrough Valve

Thermocompressor

Warm-up Valve Steam Make-up Valve

LIC

Steam/Condensate Separation

Blowthrough & Vent Valves

Steam Supply Control

F.T.

Condensate

Dryer

Sight Glass

FIC

Function: Allows blow through steam and condensate to separate.

Condensate Separation System

LIC

Sight Glass

TT

PI

LIC F.T.

Condensate

Dryer

DPI

Blowthrough and Vent Valves

Vent Valve Blowthrough Valve

F.T.

Functions:

> Control Blowthrough Flow

> Vent Non-Condensible gases to Atmosphere Dryer

FIC

Yankee Dryer Steam Supply System

Motive Steam

Warm Up Steam

Warm-up Valve Steam Make-up Valve

Functions:

> Control dryer steam pressure

> Recover blow through steam

Thermo Compressor

Blowthrough Steam

Dryer

PIC

Thermocompressor

Discharge

Nozzle

Diffuser

Body (Mixing Area)

Suction Inlet

Motive Steam Inlet

Actuator

Spindle

Inlet

Diffuser

Nozzle

Thermocompressor Zones

Discharge

Suction

Expansion Mixing Compression

-100

55

60

65

75

70

80

85

90

95

100

50 -60 -80 -40 -20 0 20 40 60 80 100

Effect of Thermocompressor Nozzle Opening

on Suction Flow

% Suction Flow

Discharge

Nozzle

Diffuser

Suction Inlet

Motive Steam Inlet

Actuator

Spindle

% M

otive N

ozzle

Open

Thermocompressor Sizing

The thermocompressor spindle can regulate

dryer steam pressure.

Changes in spindle opening also change suction

flow (blowthrough).

This can result in blowthrough flow instability

and problems with condensate removal.

Thermocompressors should be sized so that

they remain 100% open 100% of the time.

Hood

Yankee

Remove Evaporated Water

Supply Hot Air

Control Creping Moisture

Functions of a Dryer Hood

Three Main Control Parameters

• Air Temperature – Temperature of the impingement air reaching the sheet

• Impingement Velocity – Nozzle Velocity of the air reaching the sheet

• Return Humidity – Humidity of the air at the entrance to the burner

Effect of these Parameters on Heat

Transfer Rate

Hood Drying Rate Impact

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 2 4 6 8 10 12 14 16 18 20

Hood Rw (# / hr-sq ft)

No

rma

lize

d v

alu

e o

f

Ide

pe

nd

en

t V

ari

ab

les

Effect of Humidity Effect of Temperature Effect of Nozzle Velocity

Effect of These Parameters on

Fuel Cost

Natural Gas Consumption Rate

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Normalized Gas Consumption

No

rma

lize

d v

alu

e o

f

Ind

ep

en

de

nt

Va

ria

ble

s

Effect of Humidity Effect of Temperature Effect of Nozzle Velocity

Exhaust Tubes

Supply Plenum

Exhaust Plenum

Exhaust Duct

Supply Ducts

Burners or Heat Exchangers

Supply Fans

Exhaust Air

Exhaust Fans

Fresh Air

Fresh Air

Tissue Machine Dryer Hood

Main Gas

Combustion Air

Main Gas

Combustion Air

TT TT

TC TC TV TV

Tissue Machine Hood System

Temperature Control

PT PT

TC TC TV TV

Tissue Machine Hood System

SC SC

Air Velocity (h ) Control

Dampers

a

Hood - Yankee Clearance

The hood must supply air in a way to:

•Penetrate the air boundary layer.

•Promote effective mass transfer.

Initial jet diameter depends on nozzle diameters

and the shapes of their edges.

As the jets travel farther from the nozzle exits,

they begin to break up.

Optimum heat transfer occurs when the nozzle

to sheet spacing is 4-7 nozzle diameters.

Hood

Yankee

Exhaust Air Out

Energy In

Cold Air In

Effect of Exhaust Air on Hood Energy

Air Humidity 0.2 0.4

Drying Rate 4%

Drying Cost 25%

Drying

•Introduction

•Yankee Dryer

•Yankee Hood

•Drying Theory


•Operating Centerlines

Drying

•Introduction

•Drying Theory

•Equipment and Control

•Best Practice Development

• The Best Practices

Current Best Practices

Hood System Performance

KPI-01 Hood

Performance Fuel consumption is less than 3.0 MMBTU/MT

KPI-02 Hood

Performance

Pressure distribution difference between crescent headers in the same hood half,

with profiling dampers open, is maintained at less than plus or minus 5%.

Safety

HD-01 Safety Lockout and confined space entry procedures are in place and practiced.

HD-02 Safety No water streams or sprays are used to contact high temperature or insulated surfaces of

the hood.

HD-03 Safety Mechanical stops are checked annually to make sure the hood cannot contact the

Yankee.

HD-04 Safety Personal protective equipment is provided and used when working around hoods.

HD-05 Safety Air Nozzle Best Practices are in use when cleaning around hoods

HD-06 Safety Burner management interlocks are checked annually. (Fuel High/Low Pressure Switch)

(Proof of Combustion Air Flow) (High Burner Temperature Shutdown)

Rate of Rise 1.) Put LIC in Manual 2.) Lower level in FV 3.) Close isolation

valves (manually)

4.) Measure time for

condensate to

rise a given height

Measurement Locations

LIC

Sight Glass

TT

PI

LIC F.T.

Condensate

Dryer

DPI

5.) Restore system to

normal


Wet End

Exhaust

Humidity

Operating

Temperature Operating

Temperature

Dry End

Exhaust

Humidity


Hood Pressure

Measurements

Combustion Fuel

And Air Pressure

Measurements

Supply Fan Speed

Engineering

Drying training Equipment Operation and control