MXPA97005681A - Recovery of helium for the fiber opt manufacture - Google Patents

Abstract

A method to recover helium from a fiber optic manufacturing process that allows the recovery of most stages in the manufacturing process, including the deposition and consolidation stages. The recovered helium can be refined to an intermediate level and then further refined to high purity and recycled to most stages in the manufacturing process. All helium can be purified only to an intermediate level for supply to the fiber extraction stage. Alternatively, the helium can be purified to an intermediate level and recycled to the fiber extraction stage while the rest is further refined to high purity and recycled to most stages in the manufacturing process.

Description

RECOVERY OF HELIUM FOR THE MANUFACTURE OF OPTICAL FIBER FIELD OF THE INVENTION This invention relates to helium recovery processes and more particularly to helium recovery processes associated with the manufacture of optical fiber.

BACKGROUND OF THE INVENTION Generally, processes to produce optical fibers use helium gas to improve fiber quality and manufacturing productivity. The manufacture of fiber optic is basically a two-phase process that involves the manufacture of a specially constructed glass bar called preform, and then, melting the preform and extracting it into a thin fiber. Preform fabrication typically involves two stages, deposition and consolidation, which can be combined as a continuous operation or divided into two separate ones. Commercial producers use various processes to manufacture the preforms, such as External Vapor Deposition (OVD), Modified Chemical Vapor Deposition (MCVD), Axial Vapor Deposition (VAD) and Plasma Chemical Vapor Deposition (PCVD). All are based on a thermal chemical vapor reaction that forms mixed oxides that are deposited as layers of glass deposited on a rotating high purity glass tube or bar that may or may not be retained as part of the preform. The resulting opaque soot mono-crystal is consolidated into a concreting process that removes impurities from the deposition process and impacts with the monocrystal to produce a clear preform ready for extraction and cutting. Currently helium has three primary uses in the manufacture of optical fiber, a transporting gas in the deposition of the preform, a sweeping gas in the consolidation of the preform and, in a heat transfer medium for fiber extraction. Helium is not required for the deposition stage although it can be used as a carrier gas, which means that Helium provides a medium or atmosphere in which the reactive vapors are dispersed and supplied to the deposition site. It is required that the consolidation stage clean impurities and, due to its inactivity and molecular size, there is practically no alternative when the goal is to produce preforms free of defects, pure. The preform manufacturing stages require high purity helium. However, a lower purity can be used to improve the cooling of the fiber in the fiber extraction step that is carried out in the extraction stations. Each of the three process steps introduces different impurities, contamination levels or heat levels inside the helium.

Fiber optic manufacturers generally use helium flows of "continuous passage" in all stages of the process, once used, the helium becomes a constituent of the waste stream. The traditional continuous flow helium flows used in fiber optic manufacturing processes are uneconomical and result in excessive consumption and unnecessary high cost. Helium is a non-renewable resource, limited with unique properties that allows certain processes to be executed. Many of these properties make it expensive to produce, transport and store. The costs of helium are an order of magnitude higher than those of nitrogen and several times higher than hydrogen or argon. These gases can be used as inferior substitutes for helium in some applications. Those industries that use helium in their production processes are among the fastest growing and their ever increasing demand will put increasing pressure on helium prices. In the past, the recovery and recycling of helium used in fiber optic manufacturing processes were not considered feasible due to purity requirements. However, U.S. Patent Nos. 5,452,583 and 5,377,491 describe a helium recovery process and the system for recycling helium. Although, both references are limited to the recovery of helium only from the fiber extraction stage of the optical manufacturing process. The recycled helium is fed back into the stage of extraction of the optical fiber that tolerates a helium of lower purity than in other stages of the process such as deposition or consolidation. The fiber extraction step in the fiber optic manufacturing process, based on current practice, can use helium with a lower purity ranging from about 90% to about 99%. The impurities normally contained in the helium recovered from the fiber extraction stage are particles, O2, N2, Ar and H2O. These impurities are relatively easy to remove compared to the impurities contained in the helium recovered from the other stages in the process.

OBJECTS OF THE INVENTION It is therefore an object of this invention to provide a helium recovery method that will reduce the unit cost to produce optical fibers by economically recovering a substantial portion of the helium that would otherwise be output. It is a further object of the invention to provide recovery and recycling methods that dramatically reduce the consumption per unit of helium in the manufacture of optical fibers. It is a further object of the invention to provide a method that can allow the recovery of helium from most points of use in the manufacturing process of the optical fiber and the recycling of recovered helium to most points of use. Another object is to provide a cost incentive for fiber optic manufacturers to use higher helium flow scales to take advantage of the unique heat transfer properties of helium to improve the fiber optic processing scales, which at it reduces the cost of manufacturing.

BRIEF DESCRIPTION OF THE INVENTION This invention comprises a method for recovering helium from two or more stages in a fiber optic manufacturing process. Recovered helium can also be recycled to most stages of the manufacturing process. This can be done by recovering the helium from at least one stage in addition to the fiber extraction step, purifying the recovered helium to an intermediate level and then purifying and providing the recovered helium to the helium supply line for use in the most of the processing stages. In one embodiment, helium is recovered from most of the processing steps, purified to an intermediate level and recycled only to the fiber extraction stage. In a preferred embodiment helium is recovered from most of the process steps, purified to an intermediate level and a portion is supplied to satisfy the needs of the fiber extraction stage, while the remainder is further purified and supplied to the other stages of the manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages will come to mind of those skilled in the art from the following description of the preferred embodiments and the accompanying drawings in which: Fig. 1 is a schematic diagram of an embodiment of the invention in where helium is recovered from all stages in the fiber optic manufacturing process, it is purified and made available to all stages in the process; Fig. 2 is a schematic diagram of an embodiment of the invention wherein helium is recovered from all stages in the optical fiber manufacturing process, purified although it is available only for the fiber extraction step of the manufacturing process; and Fig. 3 is a schematic diagram of a preferred embodiment representing a combination of the embodiments of the invention in Figs. 1 and 2 wherein the helium is recovered from all stages in the optical fiber manufacturing process and purified to the level necessary for supply to the fiber extraction stage and then the rest of the recycled helium is further purified for the supply to the stages of consolidation and / or deposition.

DETAILED DESCRIPTION OF THE INVENTION The recovery method of the invention accommodates the recovery of contaminated helium streams not only from the optical fiber extraction step of the manufacturing process, but also from the preform consolidation and / or preform deposition stages. The recovered helium could be purified to a lower degree of purity to supply the extraction and / or purified stations to a higher level of purity and be available at all stages of the process. manufacture. The preferred embodiment of the invention is a combination of those two options where a sufficient quantity of the recovered helium is purified to a lower purity for supply to the fiber extraction stage in the extraction stations and the rest is purified to high purity and recycled towards the other stages of the process. The level of purification of the recovered helium depends on which stage of the process the helium is being recycled. The manufacture of the preform and consolidation processes, whether executed in two separate stages or a combined operation, normally requires high purity helium in the range of approximately 99.99% to approximately 99.9995%. The fiber extraction process, based on current practice, can utilize a purity lower on the scale of about 90% to about 99%. The helium that could be recovered from each of these stages has a purity of approximately 75%. In Fig. 1, the optical fiber materials 23 are introduced to a fiber optic manufacturing process. The optical fiber materials 23 enter the preform deposition stage 20 of the manufacturing process, then the consolidation stage 30 and finally the optical fiber extraction stage 40. In each stage, the optical fiber materials 23, 33 , 43 are contacted and processed with helium 21, 19, 17, respectively. The fiber optic materials include various combinations of O2, H2, CH, Ar, SiCl4, GeCI4, PoCI3, Bcl3, N2 and others. Impurities in fiber optic materials typically include HCl, H2O, O2, H2 and Si and Ge compounds. The helium 21, which is provided through the inlet 29, can be used to improve the deposition step of the preform 20 of the manufacturing process by taking advantage of its inactivity and its unique heat transfer properties. Helium 21 can serve as a carrier gas usually in combination with argon and nitrogen. The discharge gas 5 which is recovered from the outlet 28 of the deposition stage 20 is at an elevated temperature and initially consists of a normal stream of inert gas containing N2 and Ar with a low concentration of helium and contaminated with the combustion products of hydrogen and oxygen or methane and oxygen, silicon, germanium, phosphorus, boron, other similar compounds, particles and water. It is less likely to recover and process through the recycling system if the helium content is not substantial. The helium 19 is introduced through the inlet 39 to be used as a scavenging gas in the consolidation step of the preform 30. The helium 19 together with chlorine and possibly other gases (not shown) are fed into the consolidation furnace and they flow into a hot preform with which they are included in consolidation stage 30. At kiln temperatures, chlorine and helium infiltrate through the glass in the preform. Chlorine reacts with any included moisture to form hydrogen chloride and oxygen gas. Helium scavenges unreacted chlorine, oxygen chloride and oxygen from the preform. The discharge gas 4 which is recovered from the outlet 38 of this consolidation stage 30 is at an elevated temperature and contains helium contaminated mainly with chlorine, hydrogen chloride gas, oxygen and other gases that may have been introduced which are related to the practices of the individual producer. The discharge gas 4 can also include contaminants that result from air infiltration, such as particles, O2, N2, Ar and H2O. The helium 17 introduced through the inlet 49 is used as a means of heat exchange in the extraction of the fiber. The purpose of helium is to improve the cooling of the optical fiber so that the discharge gas 3, which is recovered from the outlet 48, can be at an elevated temperature and includes contaminants introduced as a result of the air entering the system, that is, particles, O2, N2, Ar and H2O. The fiber optic product flows through stream 45. Typically, all discharge gas streams 3, 4, 5 can be combined to provide a single feed stream 6 to the recovery unit which includes, in this embodiment, a intermediate gas purification system 50 and a final gas purification system 60. However, separate or even multiple feed streams and purification systems may be desired for geographic or process reasons. The intermediate gas purification stage 50, in its simplest form provides the functions necessary to remove moisture at very low levels. The specific components of the intermediate gas purification step 50 will be described with reference to Fig. 3. From this purification step 50, a dry and clean gas stream 9 is obtained, with a purity in the scale of about 90% up to about 99%, suitable for feeding to the final purification units 60 where up to 99.99% helium is further purified. The purified helium 11, from the final purification system 60, has the properties and characteristics necessary to be combined with the helium of integration 1 from the external helium supply system 14. Alternatively, this stream of purified helium recovered 11 can be supplied to a storage container or provided for use in another process. The helium-fed stream 2 which is a combination of the purified helium 11 and the helium of integration 1 provides helium at all process stages by means of streams 17, 19 and 21.

Alternative final purification processes include membranes, pressure oscillation adsorption (PSA), thermal oscillation adsorption (TSA), chemisorbent systems (vacuum tuner), gas phase catalytic conversion systems, and cryogenic enhancers. The membrane or purification systems PSAs generally provide the technically and economically most viable alternatives for helium recovery applications. Those systems can include power compressors.

In another embodiment of the invention as shown in Fig. 2, the complete intermediate product stream 12, which leaves the intermediate gas purification step 50, can be supplied to the fiber extraction stage 40. A step of additional conditioning 55 which may include filtration or cooling of intermediate 12 before it is introduced to the fiber extraction stage 40. The lower purity helium stream 13 leaving the further conditioning step 55 has a purity of about 90 % up to about 99% required for the extraction step of the fiber 40 and enters the extraction station with any helium of integration 17 as a combined stream 15.

Fig. 3 shows a preferred embodiment of the invention which is a combination of the two previous embodiments described with reference to Figs. 1 and 2. This preferred embodiment distributes the intermediate product stream 9 in the two streams 10 and 12. The stream 12 is supplied to the fiber extraction stage 40, which may require the additional conditioning step resulting in a filtered stream. and cooled 13. The stream 13 could be combined with the integration helium from the stream 17 and fed to the extraction station 40 as the stream 15. The remaining portion stream 10, from the stream of intermediate product 9, is processed to high purity in a final purification step 60 to produce the helium stream 11 with the characteristics necessary to replace the new helium 1 in those stages of the process selected to receive helium feed 2. In each embodiment of the invention, the Gas collection ballast 25, 16 can be used to mitigate variations in flow conditions and improves control. Also, the recovered helium feed stream 6 can be processed in a pre-treatment step 35 and compressed before being delivered to the intermediate gas purification step 50. The pre-treatment step 35 could include cooling, filtration and / or further conditioning to provide an optimum compressor feed 7. The nature and extent of the supplemental conditioning depends on the constituents of the feed stream 6, and on the type of compressor 45 selected to process that feed stream. Although various types of compressor 45 can be used, a "water ring" compressor is preferred since it can substantially contribute to the purification of the gas as long as it is promoting the pressure of the recovered gas. If the compressor feed 7 contains chlorine and / or hydrogen chloride from the consolidation process and / or other acid gases that are formed if the moisture is present, a process of the extraction type is typically used to remove those impurities. If a "conventional" compressor such as the screw, diaphragm or reciprocating compressor is used, it would be necessary to remove these impurities, most likely by extraction before compression. If a "water ring" compressor is used, the water seal on the compressor can be adapted to execute, at least partially, the extraction function. If further cleaning of the gas is necessary, it would be included in the subsequent compression gas treatment, such as the final purification step 60. The compressor 45 raises the pressure of the compressor feed 7 to the level required for the through-processing. of purification systems and, subsequently, to the level required for supply to the selected fiber optic manufacturing stages. Any compressor suitable for the helium service, which can reach the required pressure, can be used with this system. However, the currently selected type establishes or influences the purification requirements of the compressed gas stream 8 which is processed in an intermediate gas purification step 50. The specific intermediate purification processes and / or the equipment may vary in some way depending on the moisture content in the compressed gas stream 8 and the allowable content of the intermediate product stream 9. However, a typical installation could include for example a filter to remove any remaining particles, a water separator, conglutination filters to remove all liquid water and a pressure swing adsorber dryer (PSA) to remove the water vapor to the required level, (those individual components are not shown in Fig. 3). If a conventional compressor is used in the compression step 45, the systems of the state of the art will be required in the intermediate purification stage 50 to protect against all the oil remnant. If a water ring compressor is used, a caustic extractor may be required in the intermediate purification stage 50 to completely neutralize the remaining acid components in the stream before drying. The inlet pipe to the compressor also typically includes a temperature gauge (not shown) and a pressure transmitter (not shown) that provides a control signal for the compressor recirculation cycle.

Process control and product quality are preferably maintained by a system of analyzers 52, 62, controllers 59, 69 and automatic valves 54, 64. The process stream is continuously monitored for chlorine, oxygen, hydrogen chloride analyzers and humidity to ensure that the level of those contaminants in the recovered helium product is within the specified limits. If excessive amounts of these contaminants are present at the monitoring points there is an alarm and a signal to the controller 59, 69 to close the product supply valve 54, 64 in the product supply line and ventilate the helium as streams of scrap 56, 66 until the purity returns to acceptable levels. The integration helium from the on-site supply system continues to flow to sustain operations. The manufacture of optical fiber, with its vast potential for a very high and rapid scale of growth, is an important helium consumer. The immediate impact of this recovery-recycling technology will be the reduction of unit costs to produce optical fibers by 1) the economic recovery of a substantial portion of the helium that would otherwise be discharged; and 2) provide a cost incentive for manufacturers to use higher helium flows to increase production scales. The unique heat transfer properties of helium can enable higher production speeds which, in turn, reduce the manufacturing cost.

The specific features of the invention are shown in one or more of the drawings for convenience only, since each feature can be combined with other features according to the invention. Those skilled in the art will recognize alternative embodiments and are intended to be included within the scope of the claims. For example, controllers 59, 69 may be combined within a single microprocessor that triggers an alarm and generates shut-off and vent signals for one or both valves 54, 64 when sensors 52 or 62 detect excessive contaminants.

Claims (13)

1. A method for recovering helium from an optical fiber manufacturing process, comprising: (a) providing helium to an optical fiber manufacturing process that includes the stages of deposition, consolidation and fiber extraction, each stage using an apparatus that has an entrance and an exit; (b) provide the process material at each stage of the optical fiber manufacturing process where it is brought into contact with the helium; (c) recovering at least a portion of said helium, such as recovered helium, from the exit of the fiber extraction stage and at least one other step, selected from the deposition and consolidation steps and, providing the recovered helium to a intermediate gas purification system; (d) providing the helium recovered from the intermediate gas purification system to a final purification step; and (e) introducing said at least a portion of the helium gas recovered from the final purification stage into the entry of at least one of the steps of the optical fiber manufacturing process. The method of claim 1, wherein the plurality of the helium stream recovered from the intermediate gas purification system is on the scale from about 90% to about 99%. The method of claim 1, wherein the purity of the helium stream recovered from the final purification step is on the scale from about 99% to 99.9995%. The method of claim 1, wherein a portion of the helium recovered from the intermediate purification system in step (c) is provided at the entrance to the fiber extraction stage and the rest of the recovered helium is further purified. in the final purification stage and provided to at least one stage selected from the deposition and consolidation stages of the optical fiber manufacturing process. The method of claim 4, wherein the helium recovered from the intermediate gas purification system in step (c) that is provided at the entrance to the fiber extraction stage has a purity of about 90% to about 99% and the rest of the recovered helium that is further purified in the final purification step and is provided to at least one step selected from the deposition and consolidation steps of the fiber optic manufacturing process has a purity from about 99% up to approximately 99.9995%. The method of claim 1, wherein the helium recovered from the final purification step in step (d) is combined with the integration feed of an external helium delivery system to jointly supply at least one of the stages of the fiber optic manufacturing process. The method of claim 1, wherein the recovered helium is compressed before being provided to the intermediate gas purification system. The method of claim 7, wherein the compression is achieved by a water ring compressor. The method of claim 1, wherein the recovered helium is pretreated and compressed before being provided to the intermediate gas purification system. The method of claim 1, wherein the helium recovered in step (e) is provided to the fiber extraction stage and to at least one other stage selected from the deposition and consolidation stages of the fiber manufacturing process optics. 11. A helium recovery method from an optical fiber manufacturing process, comprising: (a) providing helium to a fiber optic manufacturing process that includes the stages of deposition, consolidation and extraction of fiber, each stage having an entrance and an exit; (b) provide the process material at each stage of the fiber optic manufacturing process where it is contacted with helium; (c) recovering at least a portion of said helium, such as recovered helium, from the exit of the fiber extraction stage and at least one other stage, selected from the deposition and consolidation stages and, the supply to a purification of intermediate gas; (d) providing the helium recovered from the intermediate gas purification system to the inlet of the fiber extraction stage. The method of claim 10, wherein the helium recovered from the intermediate gas purification system has a helium purity of from about 90% to about 99%. The method of claim 10, wherein the helium recovered from the intermediate gas purification system is processed in an air conditioning stage before being provided to the fiber extraction stage.