1 Modelling the bulk cooler in NPK 4

1 Modelling the bulk cooler in NPK 4 as a series of CSTR’s Presented by Bjørn Tore Mathisen Department of Chemical Engineering December 2013 Modelling the bulk cooler in NPK 4 as a series of CSTR’s, by Bjørn Tore Mathisen

2 Program • • Background: The hot norwegian summers Introducing the Solex thermal. TM bulk cooler An unexpected phase change The single CSTR mass and energy balances Expanding to a CSTR in serie model Model scaling to fit design data Parameter discussion and justification

3 An unconventional bottleneck; the midsummer heat • The 2012 plant wide expansion. • From 1. 9 million tonnes/year to 2. 1 milion • Plant wide bottleneck rundown. Figure 1 | Typical hot norwegian midsummer night

4 Introducing the Solex thermal. TM bulk cooler. • Solid – liquid heat exchange • NPK 4 version includes counter current and cocurrent flow

5 An unexpected phase change • AN phase change in the bulk cooler T range • Chosen modelling technique – the ∆Tphase = 1 o. C solution

6 Modelling as a Single CSTR

7 Modelling as a series of CSTR’s

8 Simulink S-function as PDE solver

9 Initial BC temperature profile • Does not hit outlet target values. • Lacking phase change modelling.

10 Adjusted model • Introducing p. alfa and p. beta • Modifying the heat transfer coefficient and the NPK heat capacity. • Implemented the phase change model

11 Parameter justification • p. alfa decreases effective cp. NPK • p. beta decreases effective heat transfer area.

12 The 250 tonn/h scenario • PI control by using the SIMC rules • Cooling water flow rate skyrockets • p. beta unreliable in temperature range outside of design values