ELECTROMAGNETIC HEATING REACTOR

Abstract

An electromagnetic heating reactor for heating a fluid stream contained within a supply conduit that is microwave and/or radio frequency, RF, transparent or substantially or partially transparent, in a microwave enclosure formed substantially of a conducting material. The cross-section area of the enclosure is not constant transverse to the fluid conduit and in which the fluid is continuously moved through the cavity to increase the temperature.

Claims

1. An electromagnetic heating reactor for heating a fluid stream flowing continuously through a conduit within a microwave cavity, characterised in that the microwave cavity has a first rectangular cross-section at one end where fluid enters the cavity and a larger second rectangular cross-section at the other end of the cavity where fluid leaves the cavity and a continuously increasing cross-sectional area along its length to the larger second rectangular cross section, and in that length of all of the sides of the larger second rectangular cross-section are equal to or greater than that of the longer of the sides of the first rectangular cross-section.

2. The electromagnetic heating reactor according to claim 1 in which the larger second rectangular cross section is square.

3. The electromagnetic heating reactor according to claim 1 characterised in that the microwave power supplied is between 100 W and 120 kW.

4. The electromagnetic heating reactor according to claim 1 characterised in that length of the microwave cavity is between 1 and 100 times inclusive the length of the longer of the sides of the first rectangular cross-section.

5. The electromagnetic heating reactor according to claim 4 characterised in that the length of the microwave cavity is between 5 and 15 times inclusive that of the longer of the sides of the first rectangular cross-section.

6. The electromagnetic heating reactor according to claim 4 characterised in that the cross-sectional area of the microwave cavity increases by at least 40% between the first rectangular cross-section and the second rectangular cross-section.

7. The electromagnetic heating reactor according to claim 6 characterised in that the cross-sectional area of the microwave cavity increases by at least 60% between the first rectangular cross-section and the second rectangular cross-section.

8. The electromagnetic heating reactor according to claim 1 characterised in that the microwave cavity has a first pair of opposed pair of congruent trapezoid sides.

9. The electromagnetic heating reactor according to claim 7 characterised in that the microwave cavity has an opposed pair of congruent rectangular sides.

10. The electromagnetic heating reactor according to claim 7 characterised in that the microwave cavity has a second opposed pair of congruent trapezoid sides, said second pair not being congruent with the first pair.

11. The electromagnetic heating reactor according to claim 1 characterised in that the longer of the sides of the first rectangular cross-section is between 30% and 80% inclusive of the free space wavelength of the applied electromagnetic energy supply.

12. The electromagnetic heating reactor according to claim 1 wherein a dielectric constant of the fluid to be heated is 2.1 or more.

13. The electromagnetic heating reactor according to claim 1 having an electromagnetic energy supply in a range of frequencies from 800 MHz to 4000 MHz inclusive.

Description

SUMMARY OF DRAWINGS

[0024] FIG. 1 shows one example heating reactor according to the invention;

[0025] FIG. 2 illustrates the geometric arrangement of the microwave cavity of FIG. 1; and

[0026] FIG. 3 shows a comparison of heating performance between two enclosures of similar length with the preferred geometry of the enclosure with increasing cross section and an enclosure with a consistent cross section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In FIG. 1, a microwave cavity 1 has a varying cross-section such that it is not resonant and is not mono modal. A conduit 2 contains the chemical product in the form of a fluid to be heated. The fluid flows through the conduit 2 from the bottom to the top of the microwave cavity 1 as shown in FIG. 1, in the same direction of travel as the microwave radiation in the cavity. The conduit 2 is microwave transparent for that part within the microwave cavity. The conduit 2 has joints and seals 3 and 4 to join the conduit 2 to external metallic pipes 5. Housing structures 6 and 7 are connected to an external frame and support the conduit 2. A waveguide 8 connects the cavity to a microwave generator source.

[0028] The microwave cavity has a rectangular cross-section at the end 9 where the conduit 2 and fluid enters the microwave cavity 1 and a square cross-section at the other end 10 where the conduit and fluid therein leave the microwave cavity. The microwave cavity has an increasing cross-section along its length between the end 9 and end 10. The length of the sides of the square cross-section at the end 10 of the microwave cavity is equal to or greater than that of the longer of the sides of the rectangular cross-section at the other end of the conductor. The cross section of the microwave cavity at the end 9 is the smallest and is a rectangle whose longest dimension is equal to the length of the sides of the square cross-section at end 10 of the microwave cavity. Thus, one pair of opposite faces 11 of the microwave cavity 1 comprises two congruent isosceles trapezoids and the other pair of opposite faces 12 of the microwave cavity 1 comprises congruent rectangles.

[0029] The inventors have found that good results are obtained if the cross-sectional area of the enclosure varies by a least 40% between the smallest and largest cross sections transverse to the fluid conduit path and best results if the cross-sectional area of the enclosure varies by a least 60% between the smallest and largest cross sections transverse to the fluid conduit path.

[0030] The conduit 2 is connected by the joints and seals 3 and 4 outside the microwave cavity to prevent the fluid chemical reactants from contaminating or attacking the interior of the electromagnetic microwave cavity.

[0031] Conduit 2 is at least partially transparent at microwave and/or radio frequency wavelengths. A suitable material can be selected from the group comprising glass, silica, polymer, PTFE, quartz, and sapphire.

[0032] Although in the description of FIG. 1 the external pipes 5 are of metal with connections 3 and 4 to conduit 2, conduit 2 may extend externally beyond the microwave cavity and the extension be coated with a metal or other conductive material, the pipes 5 coated with a polymer, such as PTFE or other for corrosion resistance. Optionally, the electromagnetic heating reactor may be arranged to provide electromagnetic energy at different frequencies separately or simultaneously.

[0033] The normal fluid to be heated would be liquid or substantially a liquid; preferably the fluid should have a dielectric constant of 2.1 or higher. Optionally, the electromagnetic heating reactor may be arranged to provide electromagnetic energy from about 100 W to 120 kW, but the inventors have found that the ideal range is between 100 W and 100 kW.

[0034] Optionally, the electromagnetic heating reactor may be further arranged to provide pulsed or continuous wave electromagnetic radiation.

[0035] The electromagnetic heating reactor should be arranged to provide electromagnetic energy at a frequency anywhere between 13 MHz and 300 GHz but ideally between 800 MHz and 4000 MHz.

[0036] Optionally, the conduit 2 within the electromagnetic enclosure may be coiled. This may increase the time the reactant is exposed to electromagnetic energy and/or allow a faster flow of fluid reactant through the conduit 2 and reduce the overall size of the reactor.

[0037] Optionally, the electromagnetic heating reactor may be further arranged to maintain reactant within the reactant supply conduit up to 300° C. and further up to 1000° C. by using high temperature materials such as quartz, ceramics, or other such high temperature materials, for instance. The lower range temperatures may be used for polymer reaction supply conduits and the high range temperatures may be used for quartz or ceramic based materials. Preferably, the reactant supply conduit may be pressurised between from 0.01 bar to 200 bar or higher. Elevated pressures may be used to prevent boiling of reactants. Alternatively, the reactant supply conduit may be operated at ambient or atmospheric pressure.

[0038] FIG. 2 illustrates the various dimensions associated with the microwave cavity 1 of FIG. 1.

[0039] The rectangular cross section at the end 9 where fluid enters the cavity 1 in conduit 2 is defined by sides with lengths the lengths “c” (the shorter side) and “d” (the longer side), and the square at the end 10 of the microwave cavity where fluid leaves a larger rectangle or square has sides of length “a” and “b”. The length of the cavity between the rectangle and the square is “t”, which is independent of the length “a” or “b” but is not usually less than the length “c”. In one embodiment “a” and “b” are both equal in length to “d”, but greater than “c”, resulting in the microwave cavity having a pair of opposed congruent trapezoid surfaces 11 and a pair of opposed congruent rectangular surfaces 12. In another embodiment, the lengths “a” and “b” are greater than “c” and “d” forming opposed pairs of surfaces 11 and 12 which are pairs of isosceles trapezoids, those of surface 11 being of a different geometry to those of 12 figure in FIG. 1.

[0040] The length of the reactor is governed by the flow conditions and the value of t between c to 100c is preferred with a preferable range of 5c and 15c.

ILLUSTRATIVE EXAMPLES

[0041] The following examples are of heating processes using the equipment of FIG. 1.

Example 1

[0042] The results of example 1 are illustrated in FIG. 3.

[0043] A 1% saline solution was passed through a silica conduit located centrally in a microwave cavity at a fixed rate and the temperature was measured at fixed points through the reactor to monitor the change in temperatures. A comparison was conducted between a conventional heating reactor with a constant cross section and a reactor, as shown in FIG. 1, with a rectangular cross-section at one end and a square cross-section at the other end, and a continuously changing cross-section along its length. In both cases the dimensions of microwave cavity where the saline solution entered the microwave cavity and overall length of the cavity were identical. The frequency of the applied electromagnetic field was 2.45 GHz. The standard deviation of the rate of temperature increase was determined. A cavity with increasing cross section showed a reduction of 49% in the standard deviation for heating rate through the reactor, which is a significant improvement and allows better prediction of temperature profiles.

Example 2

[0044] A 1% saline solution was passed through a silica conduit 2 located centrally in the microwave cavity at a fixed rate and the temperature was measured at fixed points through the reactor to monitor the change in temperatures. A comparison was conducted between a heating reactor with a constant cross section and a reactor with a rectangular cross-section at one end and a square cross-section and a continuously increasing changing cross-section along its length at the other end as shown in FIG. 1. In both cases the dimensions of the inlet and overall length were identical. The frequency of the applied electromagnetic field was 2.45 GHz. On average the reactor with constant cross section had an average energy transfer efficiency of 88.2%. The reactor with an increasing cross section achieved an average energy transfer efficiency of 96.3%

Example 3

[0045] A reactor with a rectangular cross-section at one end and a square cross-section at the other end, and a continuously changing cross-section along its length at the other end as shown in FIG. 1 was in a heating application containing a stub tuner but no sliding short to change the dimensions of the cavity and a reactant supply conduit at least partially or wholly enclosed within the enclosure. A solution of 1% saline was passed through the reactor at a constant rate and the system was operated with zero reflected power and over 96% energy transferred into the solution. The solution was changed to ethylene glycol and the stub tuner altered and the system was able to function with zero reflected power and high energy transfer efficiency. This example illustrates that the invention avoids the need to be tuned for each chemical system.