Specialist in process efficiency & energy conservation TAPPSA, 19-20 Oct 2010.

Specialist in process efficiency & energy conservation

TAPPSA , 19-20 Oct 2010

Maximising Drying Rate through Automation

TAPPSA , 19-20 Oct 2010

- Datta Kuvalekar

Overview of session

TAPPSA , 19-20 Oct 2010

-Importance of Drying rate

-Factors affecting Drying rate

-How to enhance Drying rate

-Focus on Automation

TAPPSA , 19-20 Oct 2010

The Drying rate

• The ability of the driers to evaporate moisture in the web

• Measured as the quantity of moisture evaporated per unit drier area per unit time

• Typically measured as kg/h-m2

• Different grades operate with different drying rates.

• TAPPI has published Drying rate curves as a function of Steam temperature

• Dictated by the Moisture profiles, Drier surface area

TAPPSA , 19-20 Oct 2010

Whats a Good Drying rate?

• Obviously Higher Drying rates are better !

• On Indian Machines specially Kraft 10- 15 kg/h-m2 have been measured

• On MG Cylinders 40-100 kg/h-m2 have been measured

• on Writing printing machines , 16-20 kg/h-m2 are normal.

• But can we target 25 kg/h-m2 on driers and +200 kg/h-m2 on Yankees?

TAPPSA , 19-20 Oct 2010

Importance of Drying rate

• Its an indicator of efficient drier operation and Heat Transfer

•Helps assess Drying capacity

supply steamair and dirt

paper

felt

cylinder shell

condensate hard sediment

evaporating water

HEAT

supply steamair and dirt

paper

felt

cylinder shell

condensate hard sediment

evaporating water

HEAT

TAPPSA , 19-20 Oct 2010

Water evaporates from paper Paperboard

Steam in

Blow-through steam & condensate out

Condensate out Syphon Dryer shell

Various Aspects of the drier

TAPPSA , 19-20 Oct 2010

The heat transfer from the steam to the paper can be expressed by means of

the formula:

Q = U· S· (Ts - Tp)

Q: Flow of heat U: Coefficient of heat transfer S: Drying surface Ts: Temperature of the steam Tp: Temperature of the paper

The Heat Transfer Equation

TAPPSA , 19-20 Oct 2010

The most important factor affecting heat transfer :

• the thickness of the layer of condensate• Cylinder wall thickness• The layer of air between the dryer and the paper • Properties of the paper • Dirt • Incondensable gases • Superheated steam

TAPPSA , 19-20 Oct 2010

The thickness of the condensate inside the dryer depends on:

·       The quantity of condensate

·        The rotation speed

·        The condensate drainage device.

·        Amount of blowthrough steam

·        Dissolved Air circulation

Condensate – The Main Bottleneck in Drying rate

Condensate is a barrier to heat transfer and hence should be minimised

TAPPSA , 19-20 Oct 2010

1. Stationary 2. Puddling 3. cascading 4. Rimming

Fig. 1Steam in dryer,

but norotation.

Condensate shown in blue colour at the

bottom of dryer.

Fig. 21st, Stage: Puddle. As

dryer begins to move up dryer shell.

Some rimming-thin film-occurs

Fig. 32nd Stage: Violent cascading action occurs as speed

increases and more condensate moves farther up the dryer

shell. Film of rimming

condensate increases in thickness.

Fig. 43rd. Stage: Complete

Rimming. When sufficient speed is

reached cascading action

stops and complete rimming

occurs.

Condensate behaviour depends on the velocity of the cylinders and the paper thickness.

TAPPSA , 19-20 Oct 2010

Condensate –The most critical element of the smooth drier operation

• Removing Condensate effectively and continuosly is key to machine runnability

• Condensate removal depends on :

• Machine speed

• Type of Siphon and clearance

• Differential Pressure between steam and condensate side.

• Good Condensate removal generally leads to high drying rates.

TAPPSA , 19-20 Oct 2010

Other Factors that affect Drying rate

• Drier surface temperature

• contact of sheet with drier surface

• Felt tensions

• Thickness of Paper and internal microstucture

• Pocket Humidity

• Inside hood temperature ( pocket)

TAPPSA , 19-20 Oct 2010

POCKET VENTILATION

DUCT

FELT

The pocket Humidity Effect

TAPPSA , 19-20 Oct 2010

So where does Automation contribute to maximise Drying rate ?

TAPPSA , 19-20 Oct 2010

Role of Automation

• Automation on the drier section helps maintain steam pressures , Differential pressures and Level

• Condensate removal becomes more constant as differential pressures stabilise across driers leading to

production rates.

• Control of the drying environment through exhaust humidity control. PV supply control and zero level

control.

• Control of moisture setpoints through QCS leads to control on drying rate demand in case of drier limited

machines.

Steam and Condensate system

Dryers: wet end Dryers Dryers

Condenser

Separating vessel

Motive steam

Pressure control for first separating vessel

Pressure control

Flow control valve

Meter

Level control

MFP14

ZOOM IN FOR DETAIL

TAPPSA , 19-20 Oct 2010

Differential pressure control– Key to condensate removal

TAPPSA , 19-20 Oct 2010

Drying Environment control – The Automated Hood and PV system

TAPPSA , 19-20 Oct 2010

Conclusion

• Drying rates can be maximised through various Interventions

• Condensate removal is the key element.

• Automation supports maintenance and maxmisation of Drying rates on

all machines

• Start with measuring the drying rate on your machine and cross check

dependent parameters.

Thank you

Specialist in process efficiency & energy conservation