Vacuum dewatering of paper SPCI Convention September 2013

Transcription

1 Vacuum dewatering of paper SPCI Convention September 2013 Karlstad University

2 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) - -

3 Paper grade No of PM Energy consumption Lowest Highest Fine paper kwh/ton 132 kwh/ton Liner board kwh/ton 115 kwh/ton Data from Lahtinen & Karvinen (2010)

4 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?

5 Räisänen et al., Paperi ja Puu 78: Data from 1996 Increased vacuum level leads to an increased achievable dry content

6 Neun, Tappi Journal 77(9): Data from 1994 Shorter sampling times

7 Granevald et al., NPPRJ 19(4): Data from 2004 Forming fabric will influence dewatering

8 Pujara et al., Drying Technology 26(3): Data from 2008 Dry content will reach an almost constant value

9 Åslund et al., NPPRJ 23(4): Data from 2008 Investigated dewatering of different kinds of pulp

10 Nilsson, Drying Technology (accepted) Data from 2013

11 - 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.

12 at Karlstad University: Air flow measurements

13 at Karlstad University: Steady flow modelling (one phase)

14 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

15 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

16 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: Data from 2013

17 Industrial data Lahtinen & Karvinen (2010) Nilsson, Drying Technology (accepted)

18 Improvement of current CFD model - 3D fiber network, network compression and forming fabric influence

19 A better description of the amount of water that can be removed by application of vacuum Rewetting in laboratory equipment and in paper machines

20 Thank you!