Specialist in process efficiency & energy conservation TAPPSA, Oct 2010

Maximising Drying Rate through Automation TAPPSA, Oct Datta Kuvalekar

Overview of session TAPPSA, Oct Importance of Drying rate -Factors affecting Drying rate -How to enhance Drying rate -Focus on Automation

TAPPSA, 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, Oct 2010 Whats a Good Drying rate? Obviously Higher Drying rates are better ! On Indian Machines specially Kraft kg/h-m2 have been measured On MG Cylinders kg/h-m2 have been measured on Writing printing machines, kg/h-m2 are normal. But can we target 25 kg/h-m2 on driers and +200 kg/h-m2 on Yankees?

TAPPSA, Oct 2010 Importance of Drying rate Its an indicator of efficient drier operation and Heat Transfer Helps assess Drying capacity

TAPPSA, Oct 2010 Water evaporates from paper Paperboard Steam in Blow-through steam & condensate out Condensate out SyphonDryer shell Various Aspects of the drier

TAPPSA, 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, 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, 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, Oct Stationary 2. Puddling 3. cascading4. Rimming Fig. 1 Steam in dryer, but no rotation. Condensate shown in blue colour at the bottom of dryer. Fig. 2 1st, Stage: Puddle. As dryer begins to move up dryer shell. Some rimming-thin film-occurs Fig. 3 2nd 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. 4 3rd. 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, 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, 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, Oct 2010 POCKET VENTILATION DUCT FELT The pocket Humidity Effect

TAPPSA, Oct 2010 So where does Automation contribute to maximise Drying rate ?

TAPPSA, 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 endDryers 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, Oct 2010 Differential pressure control– Key to condensate removal

TAPPSA, Oct 2010 Drying Environment control – The Automated Hood and PV system

TAPPSA, 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