Vacuum dewatering of paper SPCI Convention September 2013 Karlstad University
Content of presentation - Energy consumption of vacuum systems - Influence of vacuum dwell time and vacuum level - at Karlstad University Air flow measurements Steady flow modelling (one phase) Unsteady flow modelling (two phases) - -
Paper grade No of PM Energy consumption Lowest Highest Fine paper 27 37 kwh/ton 132 kwh/ton Liner board 18 32 kwh/ton 115 kwh/ton Data from Lahtinen & Karvinen (2010)
Considerable spread among industrial data: Vacuum pumps and flow control systems differing in efficiency? Vacuum needed for other things than dewatering the paper material alone? Paper producers aiming at different dry content after vacuum dewatering?
Räisänen et al., Paperi ja Puu 78: 461-467 Data from 1996 Increased vacuum level leads to an increased achievable dry content
Neun, Tappi Journal 77(9): 133-138 Data from 1994 Shorter sampling times
Granevald et al., NPPRJ 19(4): 428-433 Data from 2004 Forming fabric will influence dewatering
Pujara et al., Drying Technology 26(3): 341-348 Data from 2008 Dry content will reach an almost constant value
Åslund et al., NPPRJ 23(4): 403-408 Data from 2008 Investigated dewatering of different kinds of pulp
Nilsson, Drying Technology (accepted) Data from 2013
- summary The dry content increases with the vacuum dwell time. The dewatering rate is high initially and decreases until it is close to zero. The dry content will reach an almost constant level which increases with the vacuum level. Choice and preparation of pulp will influence the achievable dry content. Choice of forming fabric will influence the dewatering rate and the achievable dry content.
at Karlstad University: Air flow measurements
at Karlstad University: Steady flow modelling (one phase)
at Karlstad University - Steady flow modelling (one phase) Air flow rate is the model result - Unsteady flow modelling (two phases) Dry content and flow rates rates of water and air as a function of time are model results - Time & air flow rate needed for design purposes
at Karlstad University: Unsteady flow modelling (two phases) How? Fiber diameter is measured Amount of free water is estimated Structure is built up in CFD software Movement of the boundary between water and air is traced by the program
at Karlstad University: Unsteady flow modelling (two phases) t = 0.2 ms t = 0.4 ms Model predictions A rapid initial dewatering of large pores is followed by a reduced dewatering rate as water from smaller pores is removed. Air flow increases and a steady flow rate will be reached. Rezk et al., Chemical Engineering Science 101: 543-553 Data from 2013
Industrial data Lahtinen & Karvinen (2010) Nilsson, Drying Technology (accepted)
Improvement of current CFD model - 3D fiber network, network compression and forming fabric influence
A better description of the amount of water that can be removed by application of vacuum Rewetting in laboratory equipment and in paper machines
Thank you!