WO1990004910A1

WO1990004910A1 - Microwave pipe warmer

Info

Publication number: WO1990004910A1
Application number: PCT/AU1989/000464
Authority: WO
Inventors: Allan Reginald Fry; Ralph William Davies; Paul White
Original assignee: Industrial Microwave Applications Pty. Limited
Priority date: 1988-10-25
Filing date: 1989-10-25
Publication date: 1990-05-03
Also published as: AU4487789A; CA2001520A1

Abstract

A fluid pumping apparatus comprising a pipe section (1) to contain a viscous fluid to be pumped. The pipe section (1) includes a substantially transparent window (4) impermeable by the fluid, in use, allowing microwave energy from a source to be directed into the pipe section (1) to elevate the temperature of the fluid within the pipe section (1). The apparatus preferably includes a waveguide (5) inclined with respect to a longitudinal axis of the pipe section (1) to direct microwave energy through the window (4).

Description

Title: MICROWAVE PIPE WARMER Field of the Invention

The present invention relates to a fluid pumping apparatus which utilises microwave energy to raise the temperature of fluids within a section of pipe.

The invention has been developed primarily to facilitate the pumping of viscous fluids and the processing of chemical reactants and will be described hereinafter with reference to these applications. However, it will be appreciated that the invention is not limited to these particular fields of use. Background Art

In the past, it has generally not been feasible to pump many high viscosity. fluids, particularly over long distances or where the fluid to be pumped is at a relatively low temperature.

However, the viscosity of most fluids drops rapidly with increase in temperature and so by first heating the fluid, it does become feasible to pump higher viscosity materials over longer distances due to the resultant reduction in viscosity.

According to previously employed techniques, a temperature rise in a viscous fluid has been achieved by the application of heat to the outer surface of a pipe carrying the fluid to be pumped. This heat has hitherto been applied either directly from a conventional electric heater or alternatively by use of a heated water or steam jacket.

However, such existing techniques for warming pipes are relatively inefficient to the extent that it is necessary to heat the pipe before the material within the pipe can be heated. This is particularly wasteful of energy in colder climates or in applications where larger diameter or thicker pipes are used.

This problem is exacerbated if the material to be pumped is a poor thermal conductor, since energy input must be relatively high in order to achieve the requisite temperature increase. Worse still, if the thermal energy is not transmitted uniformly through the material due to insufficient or non-uniform thermal conduction, the material can move i a "slug" down the pipe.

These problems cannot always be overcome by the application of additional heat because materials having poor thermal conduction characteristics give rise to such steep temperature gradients that the layers nearest the pipe wall can be burnt, vaporised or otherwise undesirably affected by excessive heat before sufficient heat has been transferred to the material near the centre of the pipe to achieve the desired reduction in viscosity.

Furthermore, if the material to be pumped contains solids and liquids, or a mixture of liquids of varying boiling points, it may not be feasible to heat the material to a temperature above the boiling point of the most volatile component.

It is an object of the present invention to provide a fluid pumping apparatus which overcomes or substantially ameliorates one or more of the abovementioned disadvantages of the prior art or at least to provide industry with an alternative system. Disclosure of the Invention

Accordingly, in a first aspect, the invention consists in a fluid pumping apparatus comprising a pipe section to contain a viscous fluid to be pumped and including a substantially microwave transparent window impermeable by the fluid, said window in use allowing microwave energy from a source to be directed into said pipe section to elevate the temperature of said fluid within said pipe section.

Preferably, the pipe section comprises an inner sleeve of substantially microwave transparent material, and an outer casing having an opening therein to define said microwave transparent window.

The apparatus preferably further comprises a waveguide inclined with respect to a longitudinal axis of the pipe section to direct the microwave energy through the window.

The apparatus preferably also includes a choke flange section configured to permit propagation of microwave energy when the flange section contains the fluid to be pumped and to substantially impede propagation of microwave energy beyond the flange section when the flange section is devoid of the fluid.

According to a second aspect, the invention consists in a method of pumping a viscous fluid through a pipe section, comprising the steps of transmitting microwave energy into the pipe section through a microwave transparent window impermeable to the fluid to elevate the temperature and thereby decrease the viscosity of the fluid, and applying a differential pressure across the pipe section to cause the fluid to flow through the pipe section.

Preferably, the microwave energy is directed into the pipe section at an acute angle with respect to a longitudinal axis of the pipe section by means of a waveguide.

Preferably also, the method comprises the further step of substantially impeding the propagation of microwave energy beyond the pipe section when the pipe section is empty by means of a choke flange section forming part of the pipe section and disposed at one end thereof.

In a preferred form of the invention, the fluid within the pipe section is maintained at a pressure above atmospheric pressure.

According to a third aspect, the invention consists in a method of processing a plurality of chemical reactants, comprising the steps of passing the reactants through a pipe section, transmitting microwave energy into the pipe section through a microwave transparent window impermeable to the reactants, and applying a differential pressure across the pipe section to cause the reactants to flow through the pipe section.

In a preferred form of the invention, the reactants within the pipe section are maintained at a pressure above atmospheric pressure. Brief Description of the Drawings

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a plan view showing part of a fluid pumping apparatus incorporating a microwave pipe warmer in accordance with the present invention;

Figure 2 is a cross-sectional side elevation of the microwave pipe warmer depicted in figure 1;

Figure 3 is an end elevation of the microwave pipe warmer depicted in figures 1 and 2;

Figure 4 is an enlarged sectional detail of area A depicted in figure 2. Preferred embodiments of the Invention

Referring to the drawings, there is provided an apparatus for introducing microwaves into a pipe carrying a viscous fluid to be pumped or a plurality of chemical reactants to be processed. The apparatus comprises a main body 1 in the form of a pipe section including spaced apart end flange sections 2 and 3, a microwave transparent window 4 and a waveguide 5 inclined at an acute angle with respect to the pipe section. The remote end 6 of the waveguide 5, terminates in a flange 7 adapted to be connected to a conventional microwave generating source (not shown) to direct microwave energy from the source, through the window 4 and into the pipe section to elevate the temperature of the fluid within the pipe, and thereby lower its viscosity to enable it to be pumped more efficiently. The flange sections 2 and 3 enable the apparatus to be incorporated into a conventional piping system (not shown) .

It may be observed from figure 2 that the main body 1 of the apparatus, which is preferably fabricated from non-magnetic electrically conductive material such as stainless steel, incorporates an inner sleeve 8 of substantially microwave transparent, microwave inert material such as polytetrafluoroethene sold under the trade name TEFLON, which serves a triple function.

Firstly, the sleeve is dimensioned so that the internal wall of the main body 1 as presented to the viscous material flowing through the pipe is smooth and continuous, and not of a stepped configuration due to the main body 1 of the apparatus being of a larger diameter than the inner diameter of the end flange sections 2 and 3. Secondly, the sleeve must not inhibit the passage of microwaves from the waveguide 5 into the main body 1 so the sleeve acts as a window through which microwave radiation may pass. Thirdly, the sleeve must be impermeable to prevent the egress of fluid from region 9 into the waveguide and microwave generating area.

The main body 1 together with flange sections 2 and 3 are proportioned and dimensioned such that the microwaves are substantially uniformly absorbed into the fluid passing through the apparatus. The parameters which will determine the dimensions of the main body and flange formations are the specification of the microwave source itself (which will necessarily be in accordance with one of the ISM bands within the electromagnetic spectrum), the dielectric constant or relative permittivity of the viscous fluid being pumped through the apparatus, and the dielectric constant of the sleeve 8 and the outer casing. In this embodiment, the internal diameter and length of flanges 2 and 3 are related to the wavelength of the microwave radiation such that these flange formations act as chokes in order to impede the propagation of microwaves past the flanges and into the associated piping (not shown) of the system when the pipe section is empty of fluid.

The flanges need not necessarily be of similar cross section to the piping utilised in the plant. For example, if the diameter of the flanges was considerably less than that of the piping used in the plant then manifolding could be utilised such that a number of pipe warmers may be placed in parallel configuration.

Not only must the diameter of the main body 1 and flange sections 2 and 3 be chosen such that microwaves may adequately propagate in the main body and warm the viscous material but the dimensions of the end flange are preferably such that microwaves will not propagate outside the apparatus in the absence of material to be pumped. This is possible due to the fact that the dielectric constant of air is considerably different to that of most materials which are likely to be passed through the apparatus and consequently the flanges and associated joining pipes may be tuned so as to choke the passage of microwaves and ensure that they are attenuated to an acceptable level before leaving the system if the pipe is empty. This is important in order to prevent the piping of the plant acting as a waveguide network permitting microwaves to pass down empty pipes and into areas where they could present significant dangers.

In the past, sealing of liners has been a problem in construction of systems having multiple pipe sections joined in line. PTFE (polytetrafluoroethene) sold under the trade name TEFLON is a good microwave transparent material. However, it is subject to creep over long time periods, particularly when exposed to high temperatures and this makes it difficult to maintain a good seal in a long multi-section pipe. To overcome this difficulty, a ceramic tube may be used to provide a dimensionally stable, non-compressible structural support for a microwave transparent teflon liner whereby a good seal can be maintained in a multiple section piping network.

It will be noted from figure 4 that flange 3 is designed to be connected to opposing flange 10 on the main body 1 of the apparatus. The flange 3 also includes a step 11 whereby the interengagement between flange 3 and flange 10 results in compression of the teflon sleeve 8 thereby effecting a good internal fluid seal at the interface 12 between flange 3 and sleeve 8.

In many pumping and processing applications it is desirable to maintain the pressure and/or temperature within the pipe section at above ambient conditions. This may be achieved by a pump such as a peristaltic pump at one or both ends of the apparatus. Alternatively, the positive pressure head from a fluid reservoir or simply the backpressure from the system or a pressure control valve can be used.

By the application of microwave energy directly to the fluid material to be pumped, uniform heating results and slugging or overheating of the surface layers adjacent the pipe is effectively avoided. Since the pipe itself is not heated except by thermal conduction from the material, significant energy can be saved.

It should be noted that the axis of the waveguide forms an acute angle with respect to the axis of the pipe such that a slowly increasing amount of the fluid is presented to the microwave wave-front as it travels along the waveguide. In this way, the wave-front of the microwave radiation sees a gradual change in impedance as it travels towards, and is absorbed by the substance to be heated. This configuration avoids an abrupt change in impedance which would cause undesirable reflections back along the waveguide to the microwave source.

Conventional "tuned-T-sections" are often used to achieve good coupling by impedance matching. However, such tuning is highly dependent upon the material to be heated and a particular tuned waveguide-T-junction is therefore limited to a relatively small selection of substances having a narrow range of dielectric constants. The inclined configuration of the waveguide of the present invention also permits the waveguide to function relatively independently of the dielectric constant of the material to be heated and so in the apparatus described, minimal tuning is necessary and materials having a far greater range of dielectric constants may be conveniently used without modifications to the system.

According to a further aspect of the invention, there is provided a method of processing a plurality of chemical reactants in the apparatus described. This form of the invention is particularly suitable for processing liquids or multi-phase solid/liquid mixtures where it is desired to raise the temperature and/or pressure of the materials to be processed.

In particular, many chemical reactions and processes can be initiated, sustained or otherwise controlled by the application of microwave energy to the reactants to be processed. Thus, it will be appreciated that in such applications, the present invention provides a safe environment wherein pressure, temperature and microwave energy levels can be accurately controlled to produce the desired reaction rates and conditions in either a continuous or batch process. It will also be apparent that reactants may be introduced at different points along the pipe section.

By maintaining the reactants at a pressure above atmosphereic pressure, higher temperatures can be reached in the pipe section without vaporisation of the more volatile components and the consequential thermal inefficiencies. This positive pressure can be achieved by designing the system to ensure that a positive backpressure is maintained. Alternatively, fluid pumps such as peristaltic pumps placed at one or both ends of the apparatus, or a positive pressure head from a fluid reservoir can be used.

It will also be apparent that the present invention will also have application in hydrometalurgical processes, and other processes where it is necessary or desirable to raise the temperature of materials to be processed or pumped.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

1. A fluid pumping apparatus comprising a pipe section to contain a viscous fluid to be pumped and including a substantially microwave transparent window impermeable by the fluid, said window in use allowing microwave energy from a source to be directed into said pipe section to elevate the temperature of said fluid within said pipe section.

2. An apparatus according to claim 1 wherein said pipe section comprises an inner sleeve of substantially microwave transparent material, and an outer casing having an opening therein to define said microwave transparent window.

3. An apparatus according to claim 1 or 2 further comprising a waveguide inclined with respect to a longitudinal axis of said pipe section to direct said microwave energy through said window.

4. An apparatus according to claim 2 wherein said inner sleeve is composed of polytetrafluoroethene (PTFE) .

5. An apparatus according to claim 2 wherein said inner sleeve is composed of a ceramic material.

6. An apparatus according to claim 2 wherein said inner sleeve is composed of a ceramic material lined with PTFE.

7. An apparatus according to any one of the preceding claims wherein said pipe section includes a choke flange section configured to substantially impede the propagation of microwave energy beyond said flange section when said flange section is devoid of the fluid.

8. An apparatus according to any one of the preceding claims and further including pump means to maintain a pressure differential across said pipe section to cause said fluid to flow through the pipe section.

9. An apparatus according to claim 8 wherein said pump means comprises a peristaltic pump.

10. An apparatus according to any one of the preceding claims wherein said fluid within said pipe section is maintained at a pressure above atmospheric pressure.

11. An apparatus according to claim 10 wherein said fluid within said pipe section is maintained at a pressure above atmospheric pressure by means of a pressure head from a fluid reservoir.

12. An apparatus according to claim 10 wherein a pair of pumps are disposed at either end of said pipe section to maintain the fluid within said pipe section at a pressure above atmospheric pressure.

13. An apparatus according to claim 12 wherein said pair of pumps are driven by a common drive system.

14. A method of pumping a viscous fluid through a pipe section, comprising the steps of transmitting microwave energy into the pipe section through a microwave transparent window impermeable to the fluid to elevate the temperature and thereby decrease the viscosity of the fluid, and applying a differential pressure across the pipe section to cause the fluid to flow through the pipe section.

15. A method according to claim 14 comprising the further step of directing said microwave energy into the pipe section at an acute angle with respect to a longitudinal axis of the pipe section by means of a waveguide.

16. A method according to claim 14 or claim 15 comprising the further step of substantially impeding the propagation of microwave energy beyond said pipe section when said pipe section is empty by means of a choke flange section forming part of said pipe section and disposed at one end thereof.

17. A method according to any one of claims 14 to 16 comprising the further step of maintaining the fluid within said pipe section at a pressure above atmospheric pressure.

18. A method according to claim 17 wherein said fluid is maintained at a pressure above atmospheric pressure by means of a pressure head from a fluid reservoir.

19. A method of processing a plurality of chemical reactants, comprising the steps of passing the reactants through a pipe section, transmitting microwave energy into the pipe section through a substantially microwave transparent window impermeable to the reactants, and applying a differential pressure across the pipe section to cause the reactants to flow through the pipe section.

20. A method according to claim 19 comprising the further step of directing said microwave energy into the pipe section at an acute angle with respect to a longitudinal axis of the pipe section by means of a waveguide.

21. A method according to claim 19 or claim 20 comprising the further step of substantially impeding the propagation of microwave energy beyond said pipe section when said pipe section is empty by means of a choke flange section forming part of said pipe section and disposed at one end thereof.

22. A method according to any one of claim 19 to 21 comprising the further step of maintaining the reactants within said pipe section at a pressure above atmospheric pressure.