Apparatus and method for the production of foam

Abstract

An apparatus for preparing foam for incorporation into cementitious slurry comprises a conduit having an inlet for receiving a gas feed and a surfactant feed, and an outlet for allowing the exit of foam. The conduit houses a porous plug that provides a partial barrier to fluid flow along the conduit, the plug comprising a plurality of particles that are packed in a regular array and that define a three-dimensional network of pores extending therebetween. The apparatus comprises a resilient component located between the plug and the conduit.

Claims

1. Apparatus for preparing foam for incorporation into cementitious slurry, comprising a conduit having an inlet for receiving a gas feed and a surfactant feed, and an outlet for allowing the exit of foam, the conduit housing a porous plug that provides a partial barrier to fluid flow along the conduit, the plug comprising a plurality of particles that are packed in a regular array, the particles defining a three-dimensional network of pores extending therebetween, wherein the apparatus comprises a resilient component located between the plug and the conduit.

2. Apparatus according to claim 1, wherein the resilient component comprises a sleeve disposed on a radially inward side of the conduit.

3. Apparatus according to claim 1, wherein the outlet comprises a sieve, the sieve comprising an array of projections that are directed towards the downstream end of the plug, the projections being arranged to provide a corresponding array of apertures therebetween, so as to allow foam to exit the plug.

4. Apparatus according to claim 3, wherein the projections are hemispherical.

5. Apparatus according to claim 4, wherein the diameter of the projections is between one and four times the diameter of the spherical particles.

6. Apparatus according to claim 1, wherein the outlet tapers in a downstream direction of the conduit, and/or the inlet flares outwardly in a downstream direction of the conduit.

7. A method of preparing foam for incorporation into gypsum slurry, comprising the steps of: providing an apparatus according to any one of the preceding claims; supplying a first feed and a second feed to the conduit via the conduit inlet, the first feed comprising a gas and the second feed comprising a surfactant; and driving the first and second feed through the plurality of particles to form a foam.

8. A method according to claim 7, further comprising the step of applying pressure to the sleeve in a radially inward direction of the sleeve, to urge the sleeve against the plug of beads.

9. A method according to claim 8, wherein the pressure is in the range 3-9 bar.

10. A method according to claim 7, wherein the gas pressure at the outlet of the conduit lies in the range 1-3 bar.

11. A method according to claim 7, further comprising the step of adding a stabilising additive to the foam.

12. A method according to claim 7, comprising the further step of incorporating the foam into a hydraulic binder slurry, such as a gypsum slurry.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will now be described by way of example with reference to the following Figures in which:

(2) FIG. 1 is a schematic section view of a conduit according to an embodiment of the second aspect of the invention.

(3) FIG. 2a is a schematic plan view of one of the sieves of the embodiment of FIG. 1.

(4) FIG. 2b is a schematic section view of the sieve of FIG. 2a.

(5) FIG. 3a is a schematic section view of the plug and sleeve of the embodiment of FIG. 1.

(6) FIG. 3b is a section view of a plug of particles held within a rigid sleeve, according to an illustrative example not forming part of the invention.

(7) FIGS. 4(a) and (b) are graphs showing the bubble size distributions for foams produced according to Comparative Example 1 and Example 1 in terms of cumulative area and cumulative number respectively.

(8) FIGS. 5(a) and (b) are graphs showing the pore size distributions for gypsum specimens produced according to Comparative Example 1 and Example 1 in terms of cumulative area and cumulative number respectively.

(9) Referring to FIG. 1, a pneumatic pinch valve 10 provides a channel for fluid flow. The pinch valve comprises a rigid outer shell 12 and a flexible inner sleeve 14. The rigid outer shell 12 and the flexible inner sleeve 14 are each generally cylindrical in shape, the flexible inner sleeve 14 being provided radially inwardly of the rigid outer shell 12.

(10) The outer shell 12 has flanges 13a,b bolted to each respective end. The inner sleeve 14 is secured at each respective end between the outer shell 12 and a respective flange 13a,b.

(11) The inner sleeve 14 may be formed from an elastomeric material, e.g. rubber.

(12) The outer shell 12 contacts the inner sleeve 14 at each end of the inner sleeve, while the mid-section of the outer shell 12 stands proud from the inner sleeve 14, thus providing a generally ring-shaped gap 16 between the outer shell 12 and the inner sleeve 14.

(13) The outer shell 12 has an air inlet 12a for allowing air into the ring-shaped gap 16.

(14) The inner sleeve 14 houses a plurality of spherical beads that are arranged in a close-packed three-dimensional array to form a plug 18. For example, the beads may be arranged in a three-dimensional hexagonal close packed array, a three-dimensional cubic close packed array, or a mixture of these two packing arrangements. Local packing irregularities may arise, e.g. where sub-arrays having different orientations meet, but overall, the packing of the beads is generally regular.

(15) The bead diameter is generally in the range 1-5 mm, preferably in the range 1-3 mm.

(16) The plurality of beads are supported within the pinch valve 10 by two support sieves 20a,b that are provided at an upstream end of the plug 18 and a downstream end of the plug 18 respectively.

(17) Referring to FIGS. 2a and 2b, each support sieve 20 has a base disc 21 that has hemispherical projections 23 arranged on one side. The hemispherical projections are arranged in a close-packed array such that in the central region of the sieve, each projection contacts six other projections (the projections close to the edge of the sieve each contact fewer other projections, due to edge effects). The gaps between projections define apertures that extend through the thickness of base disc.

(18) The hemispherical projections serve to hold the spherical beads away from the base disc 21, such that the beads are not able to block the apertures in the base disc. Typically, the hemispherical projections have a radius between one and four times the radius of the beads.

(19) An inlet conduit 22a is provided at an upstream end of the pinch valve. The inlet conduit 22a flares outwardly in a downstream direction of the pinch valve.

(20) An outlet conduit 22b is provided at a downstream end of the pinch valve. The outlet conduit tapers in a downstream direction of the pinch valve.

(21) In use, air is provided to the ring-shaped gap 16 to increase the air pressure within the gap to e.g. about 6 bar. The increased pressure causes the inner sleeve 14 to deform in a radially inward direction, such that it is urged against the surface of the plug 18. This helps to reduce the empty spaces between the plug and the inner sleeve, and helps to ensure that edge effects, such as a reduction in packing regularity of the beads, are reduced. Thus, the provision of the inner sleeve helps to promote regular packing of the beads across the entire body of the plug.

(22) The effects of providing a resilient sleeve around the plug 18 and using it to transmit a compressive force onto the plug are illustrated in FIG. 3. FIG. 3b shows a comparative example in which a plug of particles 18 is held in a rigid sleeve 14. Enlarged voids are present at the edge of the plug due to packing irregularities caused by the inability of the rigid sleeve to accommodate the particles. Furthermore, defects are present in the body of the plug, due to gaps in the array of particles. FIG. 3a shows how the resilient sleeve 14 may help to accommodate particles at the edge of the plug 18, while the application of a compressive force onto the plug assists in reducing defects within the plug.

(23) An air feed 28 and a surfactant solution feed 30 are provided to the inlet conduit 22a and are driven under pressure through the support sieve 20a, the plug 18, and the support sieve 20b to provide a foam feed 32 that exits the pinch valve 10 at the outlet 22b. Typically, the foam pressure at the outlet is about 2 bars.

(24) The pinch valve 10 is positioned such that the outer shell 12 and inner sleeve 14 are upright, and the inlet conduit 22a is above the outlet conduit 22b.

(25) The following worked Examples are presented by way of illustration only.

COMPARATIVE EXAMPLE 1

(26) Foam was generated by passing constant flows of air and foaming agent solution into a foam generator equipped with rotor/stator parts, that is, a dynamic foam generator. The foam generation conditions were set as follow: Foam generator speed: about 2900 rpm Rotor/Stator gap: about 0.5 mm Foaming agent: Hyonic PFM10 foaming agent from GEO Speciality Chemicals (this is an unstable foaming agent) Foaming agent concentration: about 0.5 wt % Foam density: about 91 g/l

EXAMPLE 1

(27) Foam was generated by passing air and a foaming agent solution through a static foam generating apparatus of the type shown in FIG. 1. In this case, the foam generation conditions were set as follows: Filling particles: spherical particles of about 1 mm diameter. Foam generator counter-pressure: about 2 bar Pinch valve inner pressure: about 6 bar Foaming agent: STEOL DES32i from Stepan Company (this is an alkyl ether sulphate-based foaming agent having an average carbon chain length in the range C8-C12) Foaming agent concentration: about 1 wt % Foam density: about 91 g/l.
Foamed Slurry Preparation

(28) The pre-generated foams were then gently blended with pre-mixed gypsum stucco slurry in varying proportions to produce multiple gypsum specimens having different levels of density (from 0.5 up to 0.8 g/cm.sup.3). Typical slurry compositions are shown in Table 1:

(29) TABLE-US-00001 TABLE 1 Target dry density (g/cm.sup.3) 0.8 0.7 0.6 0.5 Stucco 1 1 1 1 Water (weight ratio to stucco) 0.77 0.75 0.72 0.69 Foam (weight ratio to stucco) 0.03 0.05 0.08 0.11
Results: Quantitative Analysis of Foam Morphology and Microstructure of Gypsum Specimens

(30) The morphology of the foam and the core structure of gypsum specimens were analysed in using optical microscopy equipment and ImageJ? software.

(31) Curves 1 and 2 on FIG. 3(a) show the cumulative volume distributions of the foam bubbles generated in Comparative Example 1 and Example 1 respectively. Curves 1 and 2 show the respective first derivatives of the cumulative volume distributions. The volume average bubble size ({umlaut over (X)}.sub.w) for Comparative Example 1 and Example 1 is defined by the position of the peak of Curve 1 and Curve 2 respectively.

(32) Similarly, Curves 3 and 4 on FIG. 3(b) show the cumulative number distributions of the foam bubbles generated in Comparative Example 1 and Example 1 respectively. Curves 3 and 4 show the respective first derivatives of the cumulative number distributions. The number average bubble size ({umlaut over (X)}.sub.n) for Comparative Example 1 and Example 1 is defined by the position of the peaks of Curve 3 and Curve 4 respectively.

(33) The bubble size dispersity .sub.X(foam) is calculated as the ratio of volume average bubble size to the number average bubble size.

(34) Curves 5 and 6 on FIG. 4(a) show the cumulative volume distributions of the pores present in the cores of the gypsum specimens prepared in Comparative Example 1 and Example 1 respectively. Curves 5 and 6 show the respective first derivatives of the cumulative volume distributions. The volume average pore size ({umlaut over (X)}.sub.w) for the gypsum specimens of Comparative Example 1 and Example 1 is defined by the position of the peak of Curve 5 and Curve 6 respectively.

(35) Similarly, Curves 7 and 8 on FIG. 4(b) show the cumulative number distributions of the pores present in the cores of the gypsum specimens prepared in Comparative Example 1 and Example 1 respectively. Curves 7 and 8 show the respective first derivatives of the cumulative number distributions. The number average pore size ({umlaut over (X)}.sub.n) for the gypsum specimens of Comparative Example 1 and Example 1 is defined by the position of the peaks of Curve 7 and Curve 8 respectively.

(36) The pore size dispersity (.sub.X(core)) is calculated as the ratio of volume average pore size to the number average pore size.

(37) TABLE-US-00002 TABLE 2 Comparative Example 1 Example 1 Foam {umlaut over (X)}.sub.w (foam) 81 ?m 298 ?m {umlaut over (X)}.sub.n (foam) 49 ?m 267 ?m .sub.x (foam) 1.65 1.12 Core structure {umlaut over (X)}.sub.w (core) ~335 ?m ~340 ?m {umlaut over (X)}.sub.n (core) ~174 ?m ~292 ?m .sub.x (core) 1.92 1.16
Results: Mechanical Testing

(38) The indentation strength results for Comparative Example 1 and Example 1 are set out in Table 3. The test consists of measuring the indentation strength using a spherical head indenting tool of about 8 mm diameter. The indentation strength (called also rigidity) corresponds to the slope of the curve relating the strain (N) versus the deformation (mm).

(39) TABLE-US-00003 TABLE 3 Normalised indentation rigidity (N/mm) Core density (g/cm.sup.3) ? 0.02 Comparative Example 1 Example 1 0.8 100% 120% 0.7 100% 140% 0.6 100% 160% 0.5 100% 200%