WO2014121331A1

WO2014121331A1 - Industrial furnaces having oxidation control means and methods of operation thereof

Info

Publication number: WO2014121331A1
Application number: PCT/AU2014/000089
Authority: WO
Inventors: Brian Philip GOODEN
Original assignee: Furnace Engineering Pty Ltd
Priority date: 2013-02-08
Filing date: 2014-02-06
Publication date: 2014-08-14
Also published as: AU2014214536A1; AU2014214536B2

Abstract

The present invention provides a furnace system comprising: (a) a furnace having (i) a main treatment chamber, and (ii) entry and/or exit port(s), (b) a process gas source adapted to dispense the process gas into the main treatment chamber, (c) a marker gas source adapted to dispense a marker gas about the entry and/or exit port(s), (d) an exhaust system configured to extract an exhaust gas from the treatment chamber, (e) temperature measuring means disposed at location(s) allowing for detection of mixing of the marker gas with the process gas by reference to the temperature of the mixed marker and process gasses, wherein, in use the marker gas is warmer or colder than the process gas, and (i) when atmospheric oxygen is being drawn into the furnace via the entry or exit port the process gas is mixed with and warmed or cooled by the marker gas, and/or (ii) when exhaust gases are escaping via the entry or exit port the marker gas is mixed with and warmed or cooled by the process gas, situations (i) and (ii) being discernible by analysis of the temperature reading(s) of the temperature measurement means.

Description

INDUSTRIAL FURNACES HAVING OXIDATION CONTROL MEANS AND METHODS OF

OPERATION THEREOF

RELATED APPLICATIONS

The present application claims the benefit of United States provisional patent application 61 /762,649 having a filing date of 8 February 2013, the contents of the specification filed in respect of that application substantially incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to high temperature and low temperature furnaces of the type used in industry for treating process intermediates. The furnaces allow for a decreased exposure to oxygen of (i) intermediates processed by the furnace and (ii) oxidation sensitive parts of the furnace itself. BACKGROUND TO THE INVENTION

Furnaces have been used in industrial settings for many years. The intense heat produced by furnaces are typically used for melting, curing, sintering and the like.

A problem occurs in that heating of many materials renders them susceptible to oxidation, or susceptible to greater levels of oxidation than intended. Oxidation can lead to minor changes in the physical or chemical characteristics of the article being processed (commonly termed the "process intermediate"), or may result in complete destruction.

The prior art provides a number of approaches to the problem of temperature-induced oxidation. Many approaches are directed to the injection of a substantially inert gas (such as Nitrogen) into the main chamber of the furnace in an effort to displace atmospheric oxygen.

Whilst generally effective for furnaces adapted to heating process intermediates in a batch- wise manner, the simple purging of oxygen with an inert gas is of limited efficacy in furnaces used in continuous processing. In continuous processing methods, process intermediate is constantly fed into the entry port of the furnace, heated, and optionally cooled before being passed out at the exit port. The entry and exit ports are open to the atmosphere, and therefore liable to admit atmospheric oxygen into the furnace and oxidize the process intermediate under the elevated temperatures within the furnace.

One example of the problem of oxidation is in the manufacture of carbon fibre. Carbon fibre is produced by pyrolysis of a precursor fibre in an inert atmosphere at temperatures above 982°C/1800°F. Carbonization occurs in an ideally oxygen-free atmosphere inside a series of furnaces that progressively increase the processing temperatures. Typically, three types of continuous processing furnaces are required in the process: LT (low temperature, typically around 1000 degrees C), HT (high temperature, typically around 1600 degrees C) and UHT (ultra high temperature, temperatures in excess of 1800 degrees C).

The exclusion of oxygen prevents loss of the carbon produced at such high temperatures. In the absence of oxygen, only non-carbon molecules, including hydrogen cyanide elements and other volatiles generated during stabilization and particulates (such as local build up of fibre debris), are removed and exhausted from the oven for post-treatment in an environmentally controlled incinerator. In an effort to exclude oxygen from contacting the process intermediate, the entry and exit ports of a furnace are typically fitted with means for preventing oxygen intrusion. An inert gas such as nitrogen is typically injected about the entry and exit ports thereby limiting the ingress of atmospheric oxygen from the furnace surrounds. The inert gas is often injected in the form of a "gas curtain", as well understood in the art. A problem with this approach is that significant volumes of the inert gas can be consumed, leading to cost-inefficiencies. A further problem is that contaminated gases can be expelled via the furnace entry and exit ports. While the prior art provides for the use of various gas sensors to detect the escape of contaminants, not all species of gas can be detected. Furthermore, this approach fails to prevent the egress of gases.

A further problem in the art is that oxidation sensitive parts of a furnace can be degraded by the presence of even very low amounts of atmospheric oxygen. For example, graphite parts within a furnace can be rapidly oxidized where precautions to exclude atmospheric oxygen are insufficient. Parts such as liners, insulation jackets and electrodes are expensive to replace, and require shutting down of the furnace when failure occurs.

It is an aspect of the present invention to overcome or ameliorate a problem of the prior art by providing improved furnaces having means for limiting the ingress of atmospheric oxygen into a furnace. It is a further aspect to provide methods for operating furnaces to exclude atmospheric oxygen.

The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or 75 were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

BRIEF DESCRIPTION OF THE FIGURES

80

Fig. 1 is a diagram of a furnace system in lateral view according to the present invention.

Figs. 2 to 4 are diagrammatical representations of gas flows within a furnace system according to the present invention

85

Fig. 5 is the result of a gas velocity analysis within a dual zone curtain chamber.

SUMMARY OF THE INVENTION

90 In a first aspect the present invention provides a furnace system comprising: (a) a furnace having (i) a main treatment chamber, and (ii) entry and/or exit port(s) (b) a process gas source adapted to dispense the process gas into the main treatment chamber, (c) a marker gas source adapted to dispense a marker gas about the entry and/or exit port(s), (d) an exhaust system configured to extract an exhaust gas from the treatment chamber, (e)

95 temperature measuring means disposed at location(s) allowing for detection of mixing of the marker gas with the process gas by reference to the temperature of the mixed marker and process gasses, wherein, in use the marker gas is warmer or colder than the process gas, and (i) when atmospheric oxygen is being drawn into the furnace via the entry or exit port the process gas is mixed with and warmed or cooled by the marker gas, and/or (ii) when00 exhaust gases are escaping via the entry or exit port the marker gas is mixed with and warmed or cooled by the process gas, situations (i) and (ii) being discernible by analysis of the temperature reading(s).

In a further aspect, the present invention provides a method of replacing a first undesired05 gas with a second desired gas in a furnace, the method comprising the steps of: (i) applying a vacuum or partial vacuum to the furnace or portion thereof to substantially remove the first gas and (ii) admitting the second gas into the vacuum or partial vacuum.

Yet a further aspect of the present invention provides a method for decreasing damage to a o process intermediate within a furnace, or damage to a furnace part, the method comprising the step of introducing an oxygen scavenger into a process gas Further provided by another aspect of the present invention is a gas curtain for a furnace, the gas curtain having gas flow characteristics adapted to disrupt atmospheric oxygen bound to a process intermediate passing through the gas curtain.

In another aspect, the present invention provides an apparatus configured to produce a gas curtain as described herein. A further aspect of the present invention provides an entry and/or exit port(s) for a furnace, the port(s) comprising adjustable choke(s) and/or baffle(s).

In another aspect the present invention provides a method for operating a furnace, such that in use (i) an environmental gas is substantially excluded from the furnace and/or (ii) a pollutant gas is substantially prevented from entering the environment, the method comprising providing a furnace system as described herein, and utilizing the temperatures detected at the temperature measuring means to balance the entry flow rate of process gas and exit flow rate of gas extracted through the exhaust system. In one embodiment, the furnace system comprises a gas curtain, and wherein the furnace system is balanced such that the curtain gas flow rate is sufficiently high so as to provide a buffer for any expected decrease in the flow rate of gases passing through the extraction system.

DETAILED DESCRIPTION OF THE INVENTION

After considering this description it will be apparent to one skilled in the art how the invention is implemented in various alternative embodiments and alternative applications. However, although various embodiments of the present invention will be described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention. Furthermore, statements of advantages or other aspects may apply only to specific exemplary embodiments, and not necessarily to all embodiments covered by the claims. Throughout the description and the claims of this specification the word "comprise" and variations of the word, such as "comprising" and "comprises" is not intended to exclude other additives, components, integers or steps.

150

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this 155 specification are not necessarily all referring to the same embodiment, but may.

Use of the terms "first" and "second" herein is not intended to infer any aspect of chronology, proximity, position, importance, relevance or the like. The terms are used interchangeably, and are intended only to refer to the separate nature of the so-described features.

160

The present invention is predicated at least in part on Applicant's finding that balancing the flows or input gases and output gasses is important in containing exhaust gases within a furnace system while still limiting the ingress of potentially damaging oxygen. Accordingly, in a first aspect the present invention provides a furnace system comprising:

165

(a) a furnace having (i) a main treatment chamber, and (ii) entry and/or exit port(s)

(b) a process gas source adapted to dispense the process gas into the main treatment chamber,

170 (c) a marker gas source adapted to dispense a marker gas about the entry and/or exit port(s),

(d) an exhaust system configured to extract an exhaust gas from the

treatment chamber,

(e) temperature measuring means disposed at location(s) allowing for 175 detection of mixing of the marker gas with the process gas by

reference to the temperature of the mixed marker and process gasses, wherein, in use the marker gas is warmer or colder than the process gas, and (i) when 180 atmospheric oxygen is being drawn into the furnace via the entry or exit port the process gas is mixed with and warmed or cooled by the marker gas, and/or (ii) when exhaust gases are escaping via the entry or exit port the marker gas is mixed with and warmed or cooled by the process gas, situations (i) and (ii) being discernible by analysis of the temperature reading(s).

185

Applicant has found that the presence of a marker gas about the entry or exit ports provides means for balancing the flow of gases through the furnace. The present system allows an operator to finely balance the flow of gases through the furnace such that the ingress of atmospheric oxygen into the furnace is lessened, while also lessening the egress of toxic 190 exhaust gases from the furnace into the operating environment.

Without an ability to finely balance the flow of gases, furnace are typically set up in an unbalanced manner leading to either (i) exclude atmospheric oxygen by the maintenance of a net flow of gas from the furnace to the atmosphere (this allowing the escape of significant

195 amounts of exhaust gases), or (ii) prevent the escape of exhaust gases (this allowing the ingress of damaging atmospheric oxygen into the furnace). The ability to analyse gas flows within a furnace by the use of a marker gas allows for the manipulation of variables (such as exhaust extraction rate, air curtain flow rate, process gas flow rate, and the like) to establish process conditions such that little or no ingress of atmospheric oxygen into the furnace

200 occurs, and additionally with little or no egress of exhaust gases.

The balancing of gas flows is typically effected by altering the rate of extraction of exhaust gases, and/or altering the flow rate of input gases. In one embodiment therefore, the exhaust system draw is adjustable, for example by adjusting an exhaust fan revolution rate.

205 In another embodiment, the flow rate(s) of input gas(es) is adjustable. It is a further advantage of that adjustment of input gas flow rates allows for minimization of the amount of inert gas to be used. Adjustment of flow rates can be achievable by any means known to the skilled artisan including the use of a valve, constrictor, choke, diverter, altering pressure of the gas source, and the like.

210 Balancing the flow of gases further provides an ability to minimise cooling of the process gas by mixing with (i) a curtain gas or (ii) a dedicated cooling gas present in the system. For example, when pre-heated process gas is introduced into the discharge end of the furnace an incorrect balance of gas flows and exhaust will typically result in either cooling the preheated process gas from the cooling gas (or indeed heating the cooling gas) thereby

215 reducing overall effectiveness or thermal efficiency of the system. The most difficult area is at the discharge end of the furnace where pre-heated process gas is introduced into the muffle right adjacent to the cooler where cooling gas is introduced. As used herein, the term "marker gas" is intended to mean a gas that is introduced for the 220 purpose of potentially mixing and cooling the process gas. The marker gas may be dedicated to aforementioned purpose, or may serve another purpose in the system. For example, the marker gas may also be a cooling gas (for the cooling of treated process intermediate before exiting the furnace), or a curtain gas (for establishing a gas curtain at an exit or entry port of the furnace). Given the possibility of the marker gas contacting the 225 process intermediate or oxidation sensitive parts of the furnace, the marker gas is typically an inert gas which does not substantially alter or degrade a process intermediate under treatment by the furnace, or a component of the furnace per se. Typically, the marker gas is Nitrogen but may be another gas such as Argon.

230 The ability to balance gas flows is improved whereby the inert gas is injected at a temperature which is significantly lower than that of the process gas. Thus, a relatively small amount of cold inert gas mixed with the process gas stream will lead to a measurable alteration of the exhaust gas temperature, thereby indicating the net flow of atmospheric oxygen into the furnace.

235

In one embodiment, the system comprises a cooling means configured to cool the inert gas to a temperature less than about 30, 25, 20, 15, 14, 13, 12, 1 1 , 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 , or 0 degrees Celsius. Preferably, the cooling means is adapted to cool the inert gas to a temperature less than about 15 degrees Celsius.

240

The primary function of the process gas is typically the bulk displacement of undesired gases from the main chamber (such as oxygen) in which case it is also typically an inert gas. Alternatively the process gas may be a gas that facilitates a desirable reaction within the furnace, such as the use of hydrogen to chemically reduce a process intermediate.

245

The marker gas may the same species as the process gas. To that end it will be understood that a marker gas may be a gas that facilitates a desirable reaction within the furnace, or inhibits an undesirable reaction.

250 In one embodiment, the marker gas is a mixture of gases. For example, the marker gas may be a combination of cooling gas and curtain gas. Alternatively, a combination of cooling gas and curtain gas may have no function as a marker gas.

It will be appreciated that the temperature measuring means is/are located in position(s) of

255 the furnace where the process gas and marker gas will mix when (i) atmospheric oxygen is being drawn into the furnace via the entry or exit port the process gas is mixed with and cooled by the marker gas, and/or (ii) when exhaust gases are escaping via the entry or exit port. In one embodiment the temperature measuring means is/are placed in one or more of the following locations:

260

Typically, the temperature measuring means are remotely readable and preferably electric or electronic in nature. Thermocouple devices are particularly suitable in the context of the present invention.

265 To more fully illustrate the components and operation of the system a simple example follows, with reference now made to Fig 1 . This example is relevant to the balance of gas flow about an exit port. If the preheated nitrogen process gas is set to 500°C and the cooler nitrogen gas (which is also the marker gas) is supplied at 10°C, measuring 500°C at thermocouple 12d and exhaust thermocouple 12b would indicate insufficient rate of draw

270 from the process exhaust (not shown). Measuring 10°C at thermocouple 12d with stationary (or cold) process intermediate would indicate an excessive exhaust draw for that cooling gas flow rate and/or curtain gas flow rate.

With reference to the set up of gas flows about an entry port, the process exhaust and any 275 excess from the inlet curtain will exit via the exhaust port. Excessive exhaust draw will be indicated by a low temperature at thermocouple 12b, and exhaust thermocouple 12a will be lower than process exhaust thermocouple 12b as it is drawing in cold air from the gas curtain. Insufficient exhaust draw rate will be indicated by a raised temperature at thermocouple 12a.

280

It will be appreciated that an optimal balance point need not necessarily be achievable with the present system: the balance only need be sufficient so as to avoid atmospheric oxygen from entering the furnace (where there is excessive exhaust draw) or to avoid unnecessary chilling of the pre-heated nitrogen as seen at thermocouple 3 being much less than the pre- 285 heat of thermocouple 6. Advantageously, the system is adjustable such that a slight drop from the hot nitrogen set point to thermocouple 6 indicating that the direction of flow is from the cooler to the process, but the amount is preferably small and only decreasing the temperature of the preheated nitrogen by a small amount.

290 The ability to analyse gas flows within a furnace as provided by the present systems allows for the automation of furnace set up and operating conditions. For example the system, in some embodiments, may be partially or completely controlled by a processor-based device such as a computer. Temperature readings may be detected by thermocouples operably connected to the computer. Software-based algorithms may be used to analyse the 295 readings, with the software directing control of input gas flow rates and exhaust draw rates in order to optimise running of the system. Rates may be altered by way of electrically or electronically controllable valves of the type well known to the skilled artisan. Such automated systems may run continuously during the processing of process intermediate thereby ensuring that optimal conditions are maintained.

300

In one embodiment, the system comprises a gas curtain having gas flow characteristics adapted to disrupt atmospheric oxygen bound to a process intermediate passing through the gas curtain.

305 In a further aspect, the present invention provides a gas curtain for a furnace, the gas curtain having gas flow characteristics adapted to disrupt atmospheric oxygen bound to a process intermediate passing through the gas curtain.

Applicant has found that traces of atmospheric oxygen bind to the surface of process 31 0 intermediates (such as carbon fibre intermediate), and that the use of a gas curtain having the aforementioned gas flow characteristics can be effective in removing the bound oxygen.

In one embodiment of the gas curtain, or a system comprising the gas curtain, the gas curtain comprising two regions: the first region having gas flow characteristics adapted to 315 avoid the ingress of atmospheric oxygen into the furnace, the second region having gas flow characteristics adapted to disrupt and displace atmospheric oxygen on a process intermediate passing through the gas curtain.

The zone which is disposed closest the entry or exit port of the furnace (i.e. immediately 320 adjacent to the atmosphere) is substantially incapable of disrupting the bound oxygen, being configured to avoid turbulence and introduction of atmospheric oxygen.

Thus, processing intermediate initially enters the first zone of the gas curtain. The flow in this region is, in one embodiment, substantially laminar. As used herein the term 325 "substantially laminar" is intended to include the circumstance whereby the direction of flow is substantially coplanar with the walls of the chamber and/or the process intermediate. This arrangement leads to the substantial inhibition of turbulence about the interface between the first zone and the atmosphere which could lead to the ingress of oxygen into the furnace. At this point, molecular oxygen is still bound to the surface of the process intermediate. 330 However, once moved into the second zone the bound oxygen is substantially disrupted by the flow characteristics of gas in the second region, which is substantially turbulent. In one embodiment, the gas flow in the second region is directed substantially perpendicularly to the plane of the process intermediate.

335 In one embodiment, the system comprises an apparatus configured to produce a gas curtain as described herein.

In a further aspect the present invention provides an apparatus configured to produce a gas curtain as described herein.

340

The apparatus will typically be in the form of a purge chamber or similar construct, configured to be mountable in operable communication with the main chamber of the furnace and/or an entry or exit port.

345 In one embodiment, the apparatus comprises one, several or a plurality of jets configured to direct gas at high velocity onto a surface of the process intermediate. Preferably, the jets are configured to direct gas onto all surfaces of the process intermediate. Where the process intermediate is substantially ribbon-like (as for the manufacture of carbon fibre) the apparatus comprises jets adapted to direct gas onto the upper and lower surface of the

350 ribbon.

Suitably, the jets may be formed by aperture(s) disposed within a metal plate. The plate is typically fabricated from stainless steel, of thickness about 10 mm. Aperture diameter in some embodiments is typically about 1 , 2, 3, 4, or 5 mm, and preferably about 3 mm. A 355 positive gas pressure is provided behind the plate. The pressure is typically less than about 1 kPa, with the gas being ejected at velocity through the apertures. Impingement velocity will vary, at least in part according to the fragility of the process intermediate, and is typically less than about 0.5 m/sec.

360 The apparatus may comprise two horizontally opposed, substantially parallel plenum plates, each plate being devoid of apertures in a first region (to form the first, non-turbulent, region of the gas curtain) and having a plurality of apertures in the second region (to form the second, turbulent, region of the gas curtain). Typically, the second region is of greater length than the first. The ratio of length of first region to second region may be about 3:1 .

365 The absolute dimensions of the first and second may be varied by the skilled person according to the general dimensions of the furnace and/or the process intermediate. The number of apertures, length of curtain, and the flow rate of curtain gas determines the impingement velocity on the product. Control of impingement velocity may be required in 370 order to customize for a particular process intermediate. For example, impingement velocity may be decreased to flutter or movement of the intermediate so as to avoid damage. Advantageously, In one embodiment the aforementioned parameters are adjustable. In one embodiment the plates are configured to be replaceable to facilitate customization.

375 Another parameter that may be varied is the distance between the plenum plates.

Accordingly, in one embodiment of the apparatus the plates are adjustable so as to allow variation in the distance between the plates. Adjustability of the gap between the plenum plates allows for optimization of this distance. A typical aim of the adjustment will be to provide the smallest workable gap allowing for the catenary formed by the process

380 intermediate, together with the lowest oxygen ingress at the lowest inert gas consumption.

The plates may be adjusted in a perpendicular direction with reference to the process intermediate, with external gauges indicating the position of the internal plenum plates.

In a preferred embodiment of the invention the curtain gas is also the cooling gas, with the 385 gas curtain comprising or consisting of or consisting essentially of a substantially turbulent region. The substantially turbulent region of the gas curtain may be formed by a plate having one, several or a plurality of jets configured to direct gas at high velocity onto a surface of the process intermediate. In this embodiment, the curtain acts also as a cooling means, lowering the temperature of the process intermediate before exposure to 390 atmospheric oxygen. Cooling process intermediate by the application of a turbulent cooling gas provides for rapid and effective decrease in temperature of the process intermediate. By contrast, prior art methods relying on the conduction and/or radiation of heat away from the process intermediate are significantly slower in cooling the intermediate. Inclusion of a convective means to dissipate heat (such as by the impingement of a gas stream on or 395 about the process intermediate) provides more rapid and complete cooling of the process intermediate.

Preferably, the cooling gas curtain consists of, or consists essentially of, a substantially turbulent region. Cooling gas curtains as described (and also apparatus for producing 400 same) are particularly advantageous when used at the exit port of the furnace, at which location there is no requirement for a region having substantially laminar gas flows. An economic advantage is further provided by this embodiment given that the cooling gas also functions to exclude atmospheric oxygen from the furnace chamber.

405

In one embodiment of the system, the entry and or/exit port(s) comprise adjustable choke(s) and/or baffle(s).

In a further aspect, the present invention provides entry and/or exit port(s) for a furnace, the 410 port(s) comprising adjustable choke(s) and/or baffle(s).

An adjustable choke may be placed at the entry and/or exit portal(s) either ends of the heating and cooling chambers. It has been found that having the smallest possible workable gap for the process intermediate to pass through further decreases the ingress of 415 atmospheric oxygen into the furnace.

The choke mechanism may comprise 1 or 2 sliding plates covering the entry or exit port. Preferably, the choke comprises 2 sliding plates with each plate sliding independently of the other such that the position of the slot formed between the two plates (for receipt of process 420 intermediate) may be altered (between an upper position and a lower position). An advantage of this embodiment is the ability to feed the process intermediate in a higher position to take account of catenary of the intermediate. Where the furnace comprises plenum plates (as discussed supra) the ability to raise the process intermediate above the lower plate may be necessary.

425

In some circumstances, the narrow opening created by the choke creates a high velocity of escaping process gas. Without wishing to be limited by theory it is proposed that this area of high velocity reduces ingress of atmospheric oxygen into the chamber.

430 The ability to adjust the build-up of free fibres over continuous use is inevitable. It is therefore necessary to include access into the furnace interior for maintenance. The ability to open the chokes facilitates removal of such debris.

The baffle(s) have a choke-like function acting to inhibit the entry of environmental gases 435 into the furnace, while still allowing for the passage of materials into and out of the furnace.

The baffle(s) is/are typically plate-type baffle(s), and may be adjustable independently to any choke(s) present. , In other embodiments, a choke and baffle are adjustable in a dependent manner. In one embodiment, the system comprises (i) a vacuum pump configured to apply a vacuum 440 or partial vacuum to the furnace or portion thereof to substantially remove a first undesired gas and (ii) means for admitting a second desired gas into the vacuum or partial vacuum.

In another aspect the present invention provides a method of replacing a first undesired gas with a second desired gas in a furnace, the method comprising the steps of: (i) applying a 445 vacuum or partial vacuum to the furnace or portion thereof to substantially remove the first gas and (ii) admitting the second gas into the vacuum or partial vacuum. In some embodiments, the level of vacuum is greater than about 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24 or 25 kPa.. Advantageously, the method may be repeated 2, 3, 4, 5, 6, 7, 8, 9 or 10 times.

450

It is proposed that prior art methods of conditioning furnaces before use by simple purging with an inert gas before the furnace is taken above the temperature that graphite oxidizes, (around 400 degrees Celsius) are not sufficient. It is further proposed that such methods are insufficient where the process intermediate is highly sensitive to oxidation such as 455 intermediates in carbon fibre manufacturing processes.

While larger and more easily accessible voids may be purged with sufficient volume changes of nitrogen, relatively large volumes of atmospheric oxygen may remain trapped in insulation behind the furnace muffle in pockets and voids. In some approaches of the prior there is an 460 attempt to reach these smaller pockets and air trapped in the insulation by means of injecting the inert gas behind the insulation at multiple positions and over a period of hours or even days. In practice, furnaces conditioned in this way still show evidence of some oxidation of the graphite board and insulation.

465 The use of a vacuum in the present methods provides a further advantage by allowing for leak detection before use. In one embodiment, the method comprises the step of sampling the gases during and/or after admission of the desired gas, wherein the presence of the undesired gas (typically oxygen) is indicative of a leak in the furnace.

470 In accordance with this method, the present invention provides in another aspect a furnace configured to furnace to maintain a partial vacuum. The vacuum may be maintained during a start up conditioning phase and prior to a steady state continuous production phase. The furnace is designed to sustain the forces acting on it from the atmosphere when holding the desired vacuum. For example, all joints are particularly designed to be form an air tight seal. 475 The two normally opened entry and exit ports may be temporarily made air tight by the fitting of end caps.

The furnace can then be conditioned by drawing a partial vacuum then purging back with inert gas, typically nitrogen. This may be done several times, thus rapidly replacing the 480 residual oxygen with nitrogen. This will achieve penetration of nitrogen into the voids and cavities more quickly and using less nitrogen than a flushing process.

Advantageously, the vacuum is achieved by the use of a venturi vacuum pump, typically of a metallic construction. A venturi pump has been found to be particularly suitable given a lack

485 of moving parts, making it possible to continue to establish a vacuum at elevated temperatures even where the furnace is heated. Under conditions of elevated temperature, trapped pockets of air within the furnace (and particularly air trapped within insulation) insulation will expand enabling a greater proportion be removed by vacuum. When purging back, it is then possible to purge back with preheated nitrogen. Purging back with cold

490 nitrogen would re-cool the insulation. Maintaining the heat of the insulation is important so as to drive off any moisture from in the chamber which also would otherwise be a potential oxidiser.

In one embodiment, the furnace system of the present system comprises sealing means 495 (such as a door, a flap, a plate, or a plug) disposed about the entry and/or exit ports, the sealing means configured to seal the main chamber against the ingress or egress of a gas. The provision of sealing means is typically for the purpose of maintaining a partial vacuum or partial pressure within the furnace, or otherwise isolating an internal area of the furnace from the atmosphere.

500

In one embodiment, the sealing means is/are preferably temporary doors capable of sealingly engaging with a surface surrounding the entry or exit port of the furnace. The door may be bolted to the surrounding surface, with an optional compressible material disposed between a face of the door and the surrounding surface. The door may be fabricated from 505 any material deemed suitable by the skilled person, and may be fabricated from a metal such as steel or aluminium.

The sealing means may be configured to be installable for testing and/or atmosphere conditioning of the furnace and optionally easily removable for commencing processing of product intermediate once testing and/or conditioning is complete.

510 The sealing means may facilitate leakage testing of the furnace, and in which case is configured to contain gas at a pressure of between about 1 .5 kPa and about 20 kPa. Leakage testing using a vacuum at the equivalent negative pressures is also contemplated. Where applications require pressurization of the furnace, pressure or vacuum relief means 515 (such as a valve, tap, or rupture disk) is included. Conveniently, the pressure or vacuum relief means may be incorporated into the sealing means.

The sealing means may facilitate conditioning of the furnace atmosphere by allowing establishment of a partial vacuum (optionally between about -0.5 kPa and about -10 kPa) 520 within the furnace, and then introducing a desired gas (such as inert gas) or a gas mixture into the furnace. Optionally, the gas mixture or gas mixture is introduced at a positive pressure (i.e. greater than atmospheric, and optionally between about 0.5 kPa and about 10 kPa).

In another embodiment, there is no vacuum established, however the desired gas or gas 525 mixture us introduced at a positive pressure as described immediately supra.

The sealing means may also function in maintaining the integrity of the furnace atmosphere during a cool down period, or when the furnace is not in use by introducing an inert gas at a slight positive pressure into the furnace chamber. This maintains the integrity of the furnace 530 atmosphere for periods of inactivity.

The use of sealing means as described supra configured to allow the establishment of a partial vacuum and partial positive pressure, may be utilized in the dry out process (typically implemented when a furnace is first put in use) for removing moisture from the refractory 535 insulation. In this situation the flow of dry and optionally heated gas (typically an inert gas) may be selectively directed through the insulation by (i) valving the vacuum on the inner muffle and pressure on the outside of the insulation, or (ii) vacuum on the outside and pressure on the inside thereby facilitating the dry out process.

540 Applicant has further found that current methods for purging atmospheric oxygen from furnaces before use in not completely effective. At the filing date of this application, the accepted approach was to simply flush volumes of Nitrogen through the furnace before use. However, Applicant has discovered that many types of insulation used in furnaces (such as graphite felts) include spaces within which oxygen may be trapped. The oxygen may slowly

545 leach from the insulation and bind to the process intermediate leading to damage. To overcome this problem, Applicant proposes that that a vacuum be first applied to the furnace to remove as much atmospheric oxygen as possible before flushing with inert gas. The evacuated spaces expand to accept the inert gas. The process of applying a vacuum and flushing with inert gas may be repeated a number of times.

550

Applicant has further discovered that (particularly in the processing of highly oxidation- sensitive material such as carbon fibre) even where exhaustive attempts are made to exclude atmospheric oxygen from a furnace, very small amounts may still be present on process intermediate.

555

Apart from the negative effects of trace amounts of oxygen on process intermediate, trace amounts of oxygen can cause the destruction of sensitive parts of furnaces that are operable for extended periods of time (such as weeks or months). Sensitive parts are exposed to high temperatures in the presence of oxygen, albeit in very low amounts. It is proposed that 560 the introduction of an oxygen scavenger (such as a reductant) into the process gas will limit the need to replace oxygen sensitive furnace parts.

In one embodiment, the system comprises an oxygen scavenger gas source adapted to dispense the scavenger gas into the main treatment chamber

565

Accordingly, another aspect of the present invention provides a method for decreasing damage to a process intermediate within a furnace, or damage to a furnace part, the method comprising the step of introducing an oxygen scavenger into a process gas. In one embodiment, the process intermediate is a carbon fibre process intermediate.

570

In one embodiment, the scavenger gas is a hydrogen gas (such as molecular hydrogen). The scavenger gas is typically administered as a set proportion to the inert process gas. Proportions of 0.5, 1 .0, 1 .5 or 2.0% (vol/vol) are found to be generally effective.

575 The present invention will be now more fully described by reference to the following non- limiting preferred embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

580 Reference is made to Fig. 1 which represents a low temperature furnace, and in which the components are numbered as follows:

1 . Furnace casing

2. Curtain chamber 585 3. Upper plenum plate

4. Process gas preheat and furnace tube cooling

5. Process Intermediate

6. High capture fume hood

7. Lower plenum plate

590 8. Insulated furnace chamber

9. Curtain gas inlet

10. Process gas inlet

1 1 . Adjustable curtain choke

12a. Process gas thermocouple

595 12b. Process gas pre-heat thermocouple

12c. Curtain exhaust thermocouple

12d. Intermediate vestibule gas thermocouple

Thermocouples (12a, 12b, 12c, 12d) are disposed at 4 locations about the furnace system 600 of Fig 1 . The locations were chosen to provide information on gas flows sufficient to allow manipulation of the system to prevent the egress of exhaust gases into the atmosphere while preventing the ingress of atmospheric oxygen.

The temperatures at the various thermocouples assist in setting up the balance of flows in 605 the curtain, process and exhaust. The method provides parameters of a steady state condition at the temperatures need to stabilise in time. With this curtain design, a measure may be employed in order to set up that balance prior to knowing what the steady state temperatures are for given operating condition.

610 This measure makes use of the well known smoke pencil to provide a visual indication of direction of gas flow. The curtain flow and exhaust is typically rendered temporarily inoperable for this test so that the smoke is not influenced by the curtain flow or exhaust flow. A furnace process flow for the required dilution of atmospheres is selected from prior experience. Starting from a fully closed state, the extraction exhaust valves are opened very

615 slowly until the extraction is seen to exactly balance the process flow. At that time the smoke from the pencil is neither being blown outwardly for drawn inwardly into the furnace. Accordingly, (when re-applied) all the curtain flow will exit the respective port of the furnace. This amount of curtain flow provides a buffer to reduce the risk of atmospheric air intake air as may occur with even a slight variation in extraction suction. The greater the curtain flow,

620 the greater the buffer against deleterious air intake. It is common that the exhaust port blocks up with debris over time thereby leading to a decrease in the gas extraction rate. If this continues unattended, there would reach a point when the egress of gases from the furnace becomes greater than the exhaust can 625 accommodate and polluted process gas will be forced out past the curtain(s). Consequently a pollutant sensor (such as an HCN sensor) positioned at the internal side of the curtain.? Upon detection of an escaped pollutant an alarm may be triggered. This alarm is provides a warning that extraction is insufficient and possibly that the extraction port is at least partially occluded.

630

It may therefore be seen that the curtain arrangement provided for by the present furnace system design allows for the use of a known flow rate of inert atmosphere as a buffer to reduce the risk of air entering the furnace. It also provides for the incorporation for a detection system (with an optional alarm) capable of detecting inadequate or blocked 635 exhaust. In addition there is provided a measurable temperature record of the stable balanced condition so that it can be compared with other unsatisfactory conditions, or reproduced in subsequent production runs.

Reference is made to Figs. 2, 3, and 4 which represent the curtain chamber about an inlet 640 port of a low temperature furnace, and in which the components are numbered as follows:

2. Upper plenum plate

4. Lower plenum plate

6. Aperture in plenum plate

8. Space intervening between upper and lower plenum plates

10. Process intermediate

12. Curtain chamber casing

14. Laminar flow region

16. Turbulent gas flow region

650

In Figs 2, 3, and 4, process intermediate 10 is fed into the inlet port in a right to left direction. It will be noted that the intermediate 10 passes into a space 8 defined by the upper 2 and lower 4 plenum plate. The intermediate 10 first passes is a laminar flow region 14, the direction of gas flow being represented by arrowed lines. In the region 14, the plenum plates 655 are devoid of apertures 6. From the region 14, the process intermediate 10 passes into the turbulent gas flow region 14 where pressurised gas is passed through apertures 6 such that the gas stream (direction indicated by arrowed lines) impinges directly on the surfaces of the process intermediate 10, thereby dislodging atmospheric oxygen. 660 Fig 2 demonstrates the flow of curtain gas where the furnace system is set up with substantially optimal exhaust draw. It will be seen that only very low amounts of cool curtain air (shown by dashed arrowed lines) are drawn to toward the furnace chamber (disposed to the left side of the drawing). The very low amount of cooled curtain gas mixes with the process gas to only marginally cool the process air.

665

Fig 3 demonstrates the flow of curtain gas where the furnace system is set up with excessive exhaust draw. The heavy arrowed lines show that greater volumes of curtain gas are drawn toward the furnace chamber, thereby mixing with the process gas. The higher levels of the cooled curtain gas act to cause more significant

670

Fig 4 demonstrates the flow of curtain gas where the furnace system is set up with insufficient exhaust draw. In this circumstance, it will be noted that process gas (shown by the dashed arrowed lines) enters the curtain chamber, and that no cooled curtain gas mixes with the process gas in the area toward the furnace chamber (disposed to the left of the 675 drawing). Accordingly, the temperature of the process gas remains substantially unchanged.

Reference is now made to Fig 5, which shows the velocity of gas (by reference to the color key) within a dual zone gas curtain. The impingement of higher velocity gas as jets (in lighter blue) can be clearly seen directed toward the carbon fibre (shown as the central white 680 line). The area of laminar air flow is seen toward the right of the drawing, as the continuous light blue areas above and below the process intermediate.

The invention has been described predominantly by reference to the manufacture of carbon fibre. It is anticipated that the skilled artisan, when apprised of the present disclosure, may 685 by no more than routine experimentation trial the invention on other manufacturing processes. Accordingly, embodiments using materials other than carbon fibre are included with the scope of this application.

Finally, it is to be understood that the inventive concept in any of its aspects can be 690 incorporated in many different constructions so that the generality of the preceding description is not to be superseded by the particularity of the attached drawings. Various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit or ambit of the invention.

695

Claims

CLAIMS:

1 . A furnace system comprising:

(c) a marker gas source adapted to dispense a marker gas about the entry and/or exit port(s),

(d) an exhaust system configured to extract an exhaust gas from the treatment chamber,

(e) temperature measuring means disposed at location(s) allowing for

detection of mixing of the marker gas with the process gas by reference to the temperature of the mixed marker and process gasses,

wherein, in use the marker gas is warmer or colder than the process gas, and (i) when atmospheric oxygen is being drawn into the furnace via the entry or exit port the process gas is mixed with and warmed or cooled by the marker gas, and/or (ii) when exhaust gases are escaping via the entry or exit port the marker gas is mixed with and warmed or cooled by the process gas, situations (i) and (ii) being discernible by analysis of the temperature reading(s) of the temperature measurement means.

2. The system of claim 1 wherein the exhaust system flow rate is adjustable.

3. The system of claim 1 or claim 2 wherein the flow rate of the process gas and/or marker gas is adjustable

4. The system of any one of claims 1 to 3 comprising cooling means configured to cool the process gas.

5. The system of any one of claims 1 to 4 wherein the temperature measuring means is/are placed in locations allowing for the detection of a change in temperature of the process gas, and/or a cooling gas, and/or a curtain gas.

6. The system of any one of claims 1 to 5 comprising a gas curtain having gas flow characteristics adapted to disrupt atmospheric oxygen bound to a process intermediate passing through the gas curtain.

7. The system of claim 6 wherein the gas curtain comprises two regions: the first region 735 having gas flow characteristics adapted to avoid the ingress of atmospheric oxygen into the furnace, the second region having gas flow characteristics adapted to disrupt and displace atmospheric oxygen on a process intermediate passing through the gas curtain.

8. The system of claim 7 wherein the gas flow in the first region is substantially laminar, 740 and/or the gas flow in the second region is substantially turbulent.

9. The system of any one of claims 1 to 8 comprising an apparatus configured to produce a gas curtain described in any one of claims 6 to 8.

745 10. The system of claim 9 wherein the apparatus is substantially in the form of a purge chamber, configured to be mountable in operable communication with the main chamber of the furnace and/or an entry or exit port.

1 1 . The system of claim 9 or claim 10 wherein the apparatus comprises 1 , several or a 750 plurality of jets of configured to direct gas at high velocity onto a surface of a process

intermediate

12. The system of claim 1 1 wherein the jets are formed by aperture(s) disposed within a metal plate.

755

13. The system of any one of claims 9 to 12 wherein the apparatus comprises two horizontally opposed, substantially parallel plenum plates, each plate being devoid of apertures in a first region and having a plurality of apertures in a second region.

760 14. The system of claim 13 wherein the distance between the plenum plates is variable.

15. The system of any of claims 1 to 14 wherein the entry and or/exit ports comprise adjustable choke(s) and/or baffle(s).

765 16. The system of claim 15 wherein the choke comprises 2 sliding plates with each plate sliding independently of the other such that the position of the slot formed between the two plates may be altered.

17. A system according to any one of claims 1 to 16 comprising (i) a vacuum pump 770 configured to apply a vacuum or partial vacuum to the furnace or portion thereof to substantially remove a first undesired gas and (ii) means for admitting a second desired gas into the vacuum or partial vacuum.

18. A system according to any one of claims 1 to 17 comprising an oxygen scavenger 775 gas source adapted to dispense the scavenger gas into the main treatment chamber.

19. A method of replacing a first undesired gas with a second desired gas in a furnace, the method comprising use of a system according to any one of claims 1 to 18.

780 20. A method according to claim 19 comprising the steps of: (i) applying a vacuum or partial vacuum to the furnace or portion thereof to substantially remove the first gas and (ii) admitting the second gas into the vacuum or partial vacuum.

21 . A method according to claim 20 wherein the vacuum or partial vacuum is applied by 785 a venturi vacuum pump.

22. A method for decreasing damage to a process intermediate within a furnace, or damage to a furnace part, the method comprising use of a system according to any one of claims 1 to 18.

790

23. A method according to claim 22 comprising the step of introducing an oxygen scavenger into the process gas

24. A method for disrupting atmospheric oxygen bound to a process intermediate 795 comprising use of a system according to any one of claims 1 to 18.

25.. A method according to claim 23 comprising passing the process intermediate through the gas curtain, the gas curtain having gas flow characteristics adapted to disrupt atmospheric oxygen bound to a process intermediate passing through the gas curtain.

800

26. A method for operating a furnace, such that in use (i) an environmental gas is substantially excluded from the furnace and/or (ii) a pollutant gas is substantially prevented from entering the environment, the method comprising providing a furnace system according to any one of claims 1 to 18, and utilizing the temperatures detected at the temperature 805 measuring means to balance the entry flow rate of process gas and exit flow rate of gas extracted through the exhaust system.

27. A method according to claim 26 wherein the furnace system comprises a gas curtain, and wherein the furnace system is balanced such that the curtain gas flow rate is sufficiently 81 0 high so as to provide a buffer for any expected decrease in the flow rate of gases passing through the extraction system.