Method of continuously measuring the shear viscosity of a product paste

Abstract

The present invention relates to a method of continuously determining the shear viscosity () of a product paste to be delivered to a spray nozzle for spray-drying applications wherein the continuous determination of the shear viscosity () of the product paste is carried out in a bypass to the product paste stream to the spray nozzle.

Claims

1. A method of continuously determining a shear viscosity of a product paste in a processing line, the method comprising: continuously determining the shear viscosity of the product paste in a bypass to a stream of the product paste, the bypass comprising a pump, a flow meter, a differential pressure tube and a pulsation damper, and the shear viscosity is in a range of 20 to 1000 mPa.Math.s, the shear rate is greater than 1000 s.sup.1, and the Reynolds number is less than 2300; delivering the product paste to a spray nozzle for a spray-drying application; and adjusting a droplet size of the product paste, the adjusting comprises a control device calculating an output control parameter based on the shear rate and the shear viscosity of the product paste and also based on spray nozzle geometry parameters stored in a memory of the control device, the output control parameter is delivered to the spray nozzle which adjusts a swirl chamber piston to a calculated position to obtain a desired swirl chamber volume.

2. The method according to claim 1, wherein the determining the shear viscosity of the product paste comprising: a) providing a constant feed-flow-rate of the product paste; b) determining a mass flow of the product paste; c) delivering the product paste to a pressure-drop-meter and determining a pressure drop; d) calculating the shear viscosity of the product paste on the basis of the mass flow determined in step b), a known product density, as well as the pressure drop determined in step c).

3. The method according to claim 2, wherein the calculation in step d) considers also the constant bypass-mass-flow-rate.

4. The method according to claim 2, wherein the determination of the pressure drop in step c) is carried out according to a differential pressure drop method.

5. The method according to claim 2, wherein the pressure drop meter comprises a tube having a fluid inlet section and a fluid outlet section and a first, second, and third pressure drop measuring sections provided between the inlet section and the outlet section.

6. The method according to claim 5, wherein the second pressure drop measuring section is provided downstream of the first pressure drop measuring section, has a second internal diameter of the second pressure drop measuring section smaller than the first internal diameter of the first pressure drop measuring section, and has a second axial length shorter than the first axial length of the first pressure drop measuring section.

7. The method according to claim 6, wherein the second pressure drop measuring section comprises a second differential pressure meter measuring a second pressure drop, a second axial distance between second two static pressure measuring openings in a second wall of the second pressure drop measuring section is shorter than the first axial distance of the first differential pressure meter.

8. The method according to claim 5, wherein the third pressure drop measuring section is provided downstream of the second pressure drop measuring section opens into the outlet section, and the third pressure drop measuring section has a third internal diameter smaller than the second internal diameter of the second pressure drop measuring section and has a third axial length shorter than the second axial length of the second pressure drop measuring section.

9. The method according to claim 8, wherein the third pressure drop measuring section comprises a third differential pressure meter measuring a third pressure drop, and a third axial distance between third two static pressure measuring openings in a third wall of the third pressure drop measuring section is shorter than the second axial distance of the second differential pressure meter.

10. The method according to claim 5, wherein the first pressure drop measuring section is close to the inlet section, has a first internal diameter and a first axial length, and is connected to a first differential pressure meter measuring a first pressure drop.

11. The method according to claim 10, wherein a first axial distance between first two static pressure measuring openings in a first wall of the first pressure drop measuring section is substantially equal to the first axial length of the first pressure drop measuring section.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a flow chart of a process for controlling the spray droplet size of an spray nozzle apparatus and shows the role of the method of the invention;

(2) FIG. 2 is a flow chart of a differential pressure drop method according to a specific embodiment of the invention;

(3) FIG. 3 shows a principle of a measuring apparatus for the differential pressure drop method of the invention

(4) In a preferred embodiment, the method of the invention is carried out with a product to be delivered to a spray nozzle. Measuring product input parameters in line with the production process of the powder allows adjusting of the droplet size towards the minimum Sauter diameter possible inline and thus makes it possible to consider the complete range of spray viscosities during the production process of the powder to be produced.

(5) FIG. 1 is a flowchart of a process for controlling the spray droplet size of an agglomeration spray nozzle apparatus. The product paste in FIG. 1 indicated as concentrate is delivered to a dosing point 30, which leads a part of the product paste stream into a bypass line 32. The majority of the product paste stream is directed into a main product paste line 34. The bypass line 32 is redirected into the main product paste line 34 at a line junction 36 downstream of a differential pressure drop measuring apparatus 38 provided in the bypass line 32.

(6) Downstream of the line junction 36 a mass flow meter 40, a density meter 42 and a spray pressure probe 44 are provided in the main product paste line. Downstream of the spray pressure probe 44 the main product paste line 34 enters a spray nozzle apparatus 1 through tube 25. The product paste delivered to the spray nozzle apparatus 1 is then sprayed into a spray drying chamber 46.

(7) The differential pressure drop measuring apparatus 38 determines the shear rate and the shear viscosity of the product paste delivered to the spray nozzle, according to one preferred embodiment of the invention. The data of the shear rate and shear viscosity are delivered from the differential pressure drop measuring apparatus 38 to a control device (SPS-control) 48. In the same manner, the product paste mass flow rate Q.sub.m determined in the mass flow meter 40, the product paste density determined in the density meter 42 and the spray pressure P of the product paste determined in the spray pressure probe 44 are also delivered to the control device 48. The shear rate has to be greater than 1000 s.sup.1.

(8) Control device 48 comprises a computer which calculates an output control parameter based on the above data delivered to the control device 48 and on the basis of known spray nozzle geometry parameters stored in a memory of the control device 48. The output control parameter is delivered to the spray nozzle apparatus 1 in order to adjust the swirl chamber piston 17 (plunger) to a calculated position in order to obtain a desired swirl chamber volume.

(9) The following equations 1-7 describe the solving procedure how to control the plunger position (given with h.sub.sc) based on a change in the paste shear viscosity .

(10) Accordingly the solving procedure is applied for a change in mass flow rate Qm and paste density .

(11) Universal Massflow-Characterization of Pressure Swirl Nozzle Flows:

(12) $\begin{array}{cc}\frac{\mathrm{Qm}}{d_{\mathrm{sc}}}=2.1844{\left(\frac{d_{\mathrm{or}}}{d_{\mathrm{sc}}}\right)}^{1.2859}{\left(\frac{h_{\mathrm{sc}}}{d_{\mathrm{sc}}}\right)}^{0.4611}{\left(\frac{\sqrt{P}{d}_{\mathrm{sc}}}{}\right)}^{0.9140}& \left(1\right)\end{array}$
The relation between spray pressure P and axial position of the plunger (given with h.sub.sc) is derived for the example of a shear viscosity change from .sub.old to .sub.new:

(13) $\begin{array}{cc}\frac{{}_{\mathrm{new}}}{{}_{\mathrm{old}}}={\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{0.4611}{\left(\frac{{}_{\mathrm{new}}}{{}_{\mathrm{old}}}\right)}^{0.9140}{\left(\frac{P_{\mathrm{old}}}{P_{\mathrm{new}}}\right)}^{\frac{0.9140}{2}}& \left(2\right)\end{array}$
Solved for the spray pressure ratio:

(14) $\begin{array}{cc}\frac{P_{\mathrm{old}}}{P_{\mathrm{new}}}={\left(\frac{{}_{\mathrm{new}}}{{}_{\mathrm{old}}}\right)}^{\frac{1-0.9140}{0.4570}}{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{\frac{-0.4611}{0.4570}}& \left(3\right)\end{array}$
In order to find a direct relation between plunger position h.sub.sc and shear viscosity , the spray pressure ratio has to be found from another equation, see equations 4-6 below:

(15) Universal Spray Droplet Size Characterization of Pressure Swirl Nozzle Sprays:

(16) $\begin{array}{cc}\frac{D_{32,\mathrm{global}}}{d_{\mathrm{sc}}}=1.0798{\mathrm{Re}}^{-0.2987}{{\mathrm{We}}^{-0.1709}\left(\frac{h_{\mathrm{sc}}}{d_{\mathrm{sc}}}\right)}^{-0.0772}{\left(\frac{d_{\mathrm{or}}}{d_{\mathrm{sc}}}\right)}^{0.9534}& \left(4\right)\end{array}$
Again, one can derive the Spray Pressure Ratio with the consistency conditions that D.sub.32-global-old and D.sub.32-global-new remain constant:

(17) $\begin{array}{cc}\begin{array}{c}\frac{D_{32,\mathrm{global},\mathrm{old}}}{D_{32,\mathrm{global},\mathrm{new}}}=1\\ ={\left(\frac{{\mathrm{Re}}_{\mathrm{old}}}{{\mathrm{Re}}_{\mathrm{new}}}\right)}^{-0.2987}{\left(\frac{{\mathrm{We}}_{\mathrm{old}}}{{\mathrm{We}}_{\mathrm{new}}}\right)}^{-0.1709}{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{g}\right)}^{-0.0772}\\ ={\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{-0.2987}{\left(\frac{{}_{\mathrm{old}}}{{}_{\mathrm{new}}}\right)}^{0.2987}{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{0.2987}\\ {\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{0.1709.Math.2}{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{-0.0772}\end{array}& \left(5\right)\end{array}$
And hence the solution, how to control the plunger height h.sub.sc,new based on a current position h.sub.sc,old:

(18) $\begin{array}{cc}\frac{h_{\mathrm{sc},\mathrm{new}}}{h_{\mathrm{sc},\mathrm{old}}}={\left(\frac{{}_{\mathrm{new}}}{{}_{\mathrm{old}}}\right)}^{-1.1289}& \left(6\right)\end{array}$
Combining equations 3 and 6 one receives the solution, how to control the spray pressure:

(19) $\begin{array}{cc}\frac{P_{\mathrm{new}}}{P_{\mathrm{old}}}={\left(\frac{{}_{\mathrm{new}}}{{}_{\mathrm{old}}}\right)}^{0.9508}& \left(7\right)\end{array}$

(20) FIG. 2 is a flowchart of the differential pressure drop method as applied in the differential pressure drop measuring apparatus 38 and according to a preferred embodiment of the invention. A feed pump 50 is provided in the bypass line 32 downstream of dosing point 30. The feed pump 50 ensures a constant feed-flow-rate in the differential pressure drop measuring apparatus 38 to enable shear rates which cover the second Newtonian viscosity plateau. Downstream of the feed pump 50 a mass flow meter 52 is provided through which the product paste in the bypass line 32 is directed into a pressure drop meter 54. The shear viscosity () of the product paste in the bypass line 32 is calculated from the mass flow measured in the mass flow meter 52, the known product density of the product paste and the pressure drop measured in the pressure drop meter 54. This calculation is either made in a computer (not shown) of the differential pressure drop measuring apparatus 38 or, the respective data are delivered to the control device 48 and the shear viscosity is calculated in the computer of the control device 48. In order to consider the fact that the pressure drop is measured in a bypass line 32 the bypass mass flowrate is adjusted by the feed pump 50 until the shear-rate is above 1000 s.sup.1, so that the second Newtonian plateau viscosity can be measured by the pressure drop-meter 54 within laminar flow conditions.

(21) A pulsation damper is also preferably provided in the bypass to reduce the noise in the pressure determination.

(22) In the present example the dosing point 30 regulates the bypass flow rate to keep the bypass flow pressure <20 bar at laminar flow conditions, with a Reynolds number below 2300.

(23) FIG. 3 shows the principle of a measuring apparatus (pressure drop meter) for the differential pressure drop method for determination of the second Newtonian plateau viscosity using three independent pressure drop recordings at three different shear-rates.

(24) The pressure drop meter 100 comprises a tube having a fluid inlet section 102 and a fluid outlet section 104 and three pressure drop measuring sections 106, 108, 110 provided between the inlet section 102 and the outlet section 104. The first pressure drop measuring section 106 which is close to the inlet section 102 has a first internal diameter d.sub.1 and a first axial length I.sub.1. A first differential pressure meter 112 measuring a first pressure drop p.sub.1 is connected to the first pressure drop measuring section 106 in a commonly known matter wherein the axial distance L.sub.1 between the two static pressure measuring openings in the wall of the first pressure drop measuring section 106 is substantially equal to the length I.sub.1 of the first pressure drop measuring section 106.

(25) The second pressure drop measuring section 108 is provided downstream of the first pressure drop measuring section 106. The internal diameter d.sub.2 of the second pressure drop measuring section 108 is smaller than the diameter d.sub.1 of the first pressure drop measuring section. The length I.sub.2 of the second pressure drop measuring section 108 is shorter than the length of the first pressure drop measuring section 106. The second pressure drop measuring section 108 comprises a second differential pressure meter 114 measuring a second pressure drop p.sub.2 wherein the distance L.sub.2 between the two static pressure measuring openings in the wall of the second pressure drop measuring section 108 is shorter than the distance L.sub.1 of the first differential pressure meter 112.

(26) A third pressure drop measuring section 110 is provided downstream of the second pressure drop measuring section 108 and the third pressure drop measuring section 110 opens into the outlet section 104. The internal diameter d.sub.3 of the third pressure drop measuring section 110 is smaller than the diameter d.sub.2 of the second pressure drop measuring section 108 and the length I.sub.3 of the third pressure drop measuring section is shorter than the length I.sub.2 of the second pressure drop measuring section. The third pressure drop measuring section 110 comprises in a commonly known manner a third differential pressure meter 116 measuring a third pressure drop p.sub.3. The distance L.sub.3 between the two static pressure measuring openings in the wall of the third pressure drop measuring section 110 is shorter than the distance L.sub.2 of the second differential pressure meter 114.

(27) The differential pressure drop meter 100 allows the measurement of three independent pressure drop recordings of the first, the second and the third differential pressure drop meters. Utilizing these three differential pressure drop probes in series, a single mass flow rate causes three increasing wall shear rates with the decreasing tube diameter.

(28) The following equation 8 is used to calculate the shear viscosity for laminar tube flows (Re<2300), applied to all 3 differential pressures p.sub.1, p.sub.2 and p.sub.3 (respectively measured at 112, 114 and 116, FIG. 8), by replacing p.sub.i and the corresponding tube dimensions (R.sub.i and L.sub.i) in equation 8:

(29) Only, if the shear viscosity .sub.i is equal (.sub.1=.sub.2=.sub.3) between the 3 differential pressures, the 2.sup.nd Newtonian shear viscosity is found and used e.g. in equation 1 and 7, etc.

(30) $\begin{array}{cc}{}_i=\frac{.Math.R_i^4.Math.p_i.Math.}{8.Math.\mathrm{Qm}.Math.L_i}& \left(8\right)\end{array}$
with following definitions of symbols: R.sub.i: tube radius (R.sub.1, R.sub.2 and R.sub.3) in [m] p.sub.i: tube pressure drop (p.sub.1, p.sub.2 and p.sub.3) in [Pa] : product density in [kg/m3] Qm: mass flow rate in [kg/s] L.sub.i: tube length (distance L.sub.1, L.sub.2 and L.sub.3) in [m]

(31) TABLE-US-00001 TABLE 1 Abbreviations and formula Symbol, Abbreviation Description Units D.sub.32,global Global Sauter diameter as found [m] from PDA measurements of spray d.sub.sc Swirl chamber diameter [m] (smallest diameter of swirl chamber spiral) h.sub.sc Swirl chamber height [m] (axial height of swirl chamber) d.sub.or Orifice diameter [m] (diameter of opening made in orifice plate) b.sub.ch Width of swirl chamber inlet [m] channel (smallest width of inlet channel which leads into the swirl chamber) We $\begin{array}{c}\mathrm{Weber}\mathrm{number}\\ \mathrm{We}=\frac{{}_{\mathrm{liquid}}{u}_{\mathrm{bulk}}^2{d}_{\mathrm{orifice}}}{{}_{\mathrm{liquid}}}\end{array}$ Eu 0$\begin{array}{c}\mathrm{Euler}\mathrm{number}\\ \mathrm{Eu}=\frac{P}{{}_{\mathrm{liquid}}{u}_{\mathrm{bulk}}^2}\end{array}$ Re $\begin{array}{c}\mathrm{Reynolds}\mathrm{number}\\ \mathrm{Re}=\frac{{}_{\mathrm{liquid}}{u}_{\mathrm{bulk}}{h}_{\mathrm{sc}}}{}\end{array}$ u.sub.bulk $\begin{array}{c}\mathrm{Bulk}\mathrm{velocity}\mathrm{at}\mathrm{swirl}\mathrm{chamber}\mathrm{inlet}\\ u_{\mathrm{bulk}}=\frac{\mathrm{Qm}}{{}_{\mathrm{liquid}}{h}_{\mathrm{sc}}{b}_{\mathrm{ch}}}\end{array}$ [m/s] Qm Mass flow rate [kg/s] P Spray pressure [Pa] .sub.liquid Liquid density [kg/m.sup.3] .sub.liquid Liquid shear viscosity [Pa .Math. s] .sub.liquid Surface tension [N/m] PDA Phase-Doppler Anemometry

(32) The invention should not be regarded as being limited to the embodiment shown and described in the above but various modifications and combinations of features may be carried out without departing from the scope of the following claims.