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 (η) of a product paste to be delivered to a spray nozzle for spray-drying applications wherein the continuous determination of the shear viscosity (η) of the product paste is carried out in a bypass to the product paste stream to the spray nozzle.

Claims

1. Method of continuously determining the shear viscosity of a product paste in a processing line, wherein the continuous determination of the shear viscosity of the product paste is carried out in a bypass to the product paste stream, the bypass comprising a pump, a flow meter, a differential pressure tube and a pulsation damper and wherein 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.

2. Method according to claim 1, wherein the shear viscosity of the product paste is determined by the following steps: a) providing a constant feed-flow-rate of the product paste; b) determining the mass flow of the product paste; c) delivering the product paste to a pressure-drop-meter and determining the differential pressure; d) calculating the shear viscosity of the product paste on the basis of the laminar mass flow and the product density determined in step b), as well as the pressure drop determined in step c).

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

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

5. Method according to claim 1, wherein the product paste is to be delivered to a spray nozzle for spray-drying applications, wherein the continuous determination of the shear viscosity (TO) of the product paste is carried out in a bypass to the product paste stream to the spray nozzle.

Description

[0022] In the following the invention will be described in further detail by means of an embodiment thereof and the appended drawings.

[0023] 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;

[0024] FIG. 2 is a flow chart of a differential pressure drop method according to a specific embodiment of the invention;

[0025] FIG. 3 shows a principle of a measuring apparatus for the differential pressure drop method of the invention

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The differential pressure drop measuring apparatus 38 determines the shear rate and the shear viscosity η 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 η 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 ρ 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.

[0030] 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.

[0031] 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 η.

[0032] Accordingly the solving procedure is applied for a change in mass flow rate Qm and paste density ρ.

[0033] Universal Massflow-Characterization of Pressure Swirl Nozzle Flows:

[00001]$\begin{array}{cc}\frac{\mathrm{Qm}}{\eta .Math..Math.d_{\mathrm{sc}}}=2.1844.Math.{\left(\frac{d_{\mathrm{or}}}{d_{\mathrm{sc}}}\right)}^{1.2859}.Math.{\left(\frac{h_{\mathrm{sc}}}{d_{\mathrm{sc}}}\right)}^{0.4611}.Math.{\left(\frac{\sqrt{P.Math..Math.\rho }.Math.d_{\mathrm{sc}}}{\eta }\right)}^{0.9140}& \left(1\right)\end{array}$

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 η.sub.old to η.sub.new:

[00002]$\begin{array}{cc}\frac{{\eta }_{\mathrm{new}}}{{\eta }_{\mathrm{old}}}={\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{0.4611}.Math.{\left(\frac{{\eta }_{\mathrm{new}}}{{\eta }_{\mathrm{old}}}\right)}^{0.9140}.Math.{\left(\frac{P_{\mathrm{old}}}{P_{\mathrm{new}}}\right)}^{\frac{0.9140}{2}}& \left(2\right)\end{array}$

Solved for the spray pressure ratio:

[00003]$\begin{array}{cc}\frac{P_{\mathrm{old}}}{P_{\mathrm{new}}}={\left(\frac{{\eta }_{\mathrm{new}}}{{\eta }_{\mathrm{old}}}\right)}^{\frac{1-0.9140}{0.4570}}.Math.{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{\frac{-0.4611}{0.4570}}& \left(3\right)\end{array}$

In order to find a direct relation between plunger position h.sub.sc and shear viscosity η, the spray pressure ratio has to be found from another equation, see equations 4-6 below:

[0034] Universal Spray Droplet Size Characterization of Pressure Swirl Nozzle Sprays:

[00004]$\begin{array}{cc}\frac{D_{32,\mathrm{global}}}{d_{\mathrm{sc}}}=1.0798.Math..Math.{\mathrm{Re}}^{-0.2987}.Math.{{\mathrm{We}}^{-0.1709}\left(\frac{h_{\mathrm{sc}}}{d_{\mathrm{sc}}}\right)}^{-0.0772}.Math.{\left(\frac{d_{\mathrm{or}}}{d_{\mathrm{sc}}}\right)}^{0.9534}& \left(4\right)\end{array}$

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:

[00005]$\begin{array}{cc}\begin{array}{c}\frac{D_{32,\mathrm{global},\mathrm{old}}}{D_{32,\mathrm{global},\mathrm{new}}}=.Math.1\\ =.Math.{\left(\frac{{\mathrm{Re}}_{\mathrm{old}}}{{\mathrm{Re}}_{\mathrm{new}}}\right)}^{-0.2987}.Math.{\left(\frac{{\mathrm{We}}_{\mathrm{old}}}{{\mathrm{We}}_{\mathrm{new}}}\right)}^{-0.1709}.Math.{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{g}\right)}^{-0.0772}\\ =.Math.{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{-0.2987}.Math.{\left(\frac{{\eta }_{\mathrm{old}}}{{\eta }_{\mathrm{new}}}\right)}^{0.2987}.Math.{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{0.2987}\\ .Math.{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{0.1709.Math.2}.Math.{\left(\frac{h_{\mathrm{sc},\mathrm{old}}}{h_{\mathrm{sc},\mathrm{new}}}\right)}^{-0.0772}\end{array}\hspace{1em}& \left(5\right)\end{array}$

And hence the solution, how to control the plunger height h.sub.sc,new based on a current position h.sub.sc,old:

[00006]$\begin{array}{cc}\frac{h_{\mathrm{sc},\mathrm{new}}}{h_{\mathrm{sc},\mathrm{old}}}={\left(\frac{{\eta }_{\mathrm{new}}}{{\eta }_{\mathrm{old}}}\right)}^{-1.1289}& \left(6\right)\end{array}$

Combining equations 3 and 6 one receives the solution, how to control the spray pressure:

[00007]$\begin{array}{cc}\frac{P_{\mathrm{new}}}{P_{\mathrm{old}}}={\left(\frac{{\eta }_{\mathrm{new}}}{{\eta }_{\mathrm{old}}}\right)}^{0.9508}& \left(7\right)\end{array}$

[0035] 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 (η) 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 η 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.

[0036] A pulsation damper is also preferably provided in the bypass to reduce the noise in the pressure determination.

[0037] 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.

[0038] 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.

[0039] 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 Δp.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.

[0040] 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 Δp.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.

[0041] 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 Δp.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.

[0042] 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.

[0043] The following equation 8 is used to calculate the shear viscosity η for laminar tube flows (Re<2300), applied to all 3 differential pressures Δp.sub.1, Δp.sub.2 and Δp.sub.3 (respectively measured at 112, 114 and 116, FIG. 8), by replacing Δp.sub.i and the corresponding tube dimensions (R.sub.i and L.sub.i) in equation 8:

[0044] Only, if the shear viscosity η.sub.i is equal (η.sub.1=η.sub.2=η.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.

[00008]$\begin{array}{cc}{\eta }_i=\frac{\pi .Math.R_i^4.Math.\Delta .Math..Math.p_i.Math.\rho }{8.Math.\mathrm{Qm}.Math.L_i}& \left(8\right)\end{array}$

with following definitions of symbols: [0045] R.sub.i: tube radius (R.sub.1, R.sub.2 and R.sub.3) in [m] [0046] Δp.sub.i: tube pressure drop (Δp.sub.1, Δp.sub.2 and Δp.sub.3) in [Pa] [0047] ρ: product density in [kg/m3] [0048] Qm: mass flow rate in [kg/s] [0049] L.sub.i: tube length (distance L.sub.1, L.sub.2 and L.sub.3) in [m]

TABLE-US-00001 TABLE 1 Abbreviations and formula Symbol, Abbreviation Description Units D3.sub.2,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 [00009]$\hspace{1em}\begin{array}{c}\mathrm{Weber}.Math..Math.\mathrm{number}\\ \mathrm{We}=\frac{{\rho }_{\mathrm{liquid}}.Math.u_{\mathrm{bulk}}^2.Math.d_{\mathrm{orifice}}}{{\sigma }_{\mathrm{liquid}}}\end{array}$ — Eu [00010]$\hspace{1em}\begin{array}{c}\mathrm{Euler}.Math..Math.\mathrm{number}\\ \mathrm{Eu}=\frac{P}{{\rho }_{\mathrm{liquid}}.Math.u_{\mathrm{bulk}}^2}\end{array}$ — Re [00011]$\hspace{1em}\begin{array}{c}\mathrm{Reynolds}.Math..Math.\mathrm{number}\\ \mathrm{Re}=\frac{{\rho }_{\mathrm{liquid}}.Math.u_{\mathrm{bulk}}.Math.h_{\mathrm{sc}}}{\mu }\end{array}$ — u.sub.bulk [00012]$\hspace{1em}\begin{array}{c}\mathrm{Bulk}.Math..Math.\mathrm{velocity}.Math..Math.\mathrm{at}.Math..Math.\mathrm{swirl}.Math..Math.\mathrm{chamber}.Math..Math.\mathrm{inlet}\\ u_{\mathrm{bulk}}=\frac{\mathrm{Qm}}{{\rho }_{\mathrm{liquid}}.Math.h_{\mathrm{sc}}.Math.b_{\mathrm{ch}}}\end{array}$ [m/s] Qm Mass flow rate [kg/s] P Spray pressure [Pa] ρ.sub.liquid Liquid density [kg/m.sup.3] η.sub.liquid Liquid shear viscosity [Pa .Math. s] σ.sub.liquid Surface tension [N/m] PDA Phase-Doppler Anemometry —

[0050] 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.