CLIAMS:WHAT IS CLAIMED IS:
1. A method of bleaching a textile fabric comprising:
bleaching the fabric with an aqueous solution of a caustic substance to remove oils, greases, waxes, fats, and motes that may be present within the fabric and peroxide to bleach the fabric;
bleaching the fabric with an ozone containing aqueous solution comprising ozone dissolved in water;
the bleaching of the fabric with the aqueous solution of the caustic substance and peroxide and the bleaching of the fabric with the ozone containing aqueous solution conducted in two separate steps such that the fabric is bleached to an intermediate whiteness index in one of the two separate steps and is thereafter, bleached to a final whiteness index in the other of the two separate steps; and
while bleaching the fabric with the ozone containing aqueous solution, maintaining the ozone containing aqueous solution at a sufficiently low temperature such that the ozone is maintained within the ozone containing aqueous solution in effective amounts to achieve one of an intermediate whiteness index and the final whiteness index at the conclusion of the bleaching of the fabric with the ozone containing aqueous solution.

2. The method of claim 1, wherein the one of the two separate steps is accomplished by the bleaching of the fabric to the intermediate whiteness index with the aqueous solution of the caustic substance and the peroxide and the other of the two separate steps is accomplished by the bleaching of the fabric to the final whiteness index with the ozone containing aqueous solution.

3. The method of claim 1, wherein the one of the two separate steps is accomplished by the bleaching of the fabric to the intermediate whiteness index with the ozone containing aqueous solution and the other of the two separate steps is accomplished by the bleaching of the fabric to the final whiteness index with the aqueous solution of the caustic substance and the peroxide.

4. The method of claim 3, wherein:
the fabric is wetted with a wetting agent, lubricant and demineralizing agent containing aqueous solution and the wetting agent, lubricant and demineralizing agent containing aqueous solution is stored as a first residual fluid prior to conducting the one of the two separate steps with the ozone containing aqueous solution;
a second residual fluid, formed from the ozone containing aqueous solution, is stored after conducting the one of the two separate steps with the ozone containing aqueous solution;
the aqueous solution of the caustic substance and the peroxide is formed with the use of the first residual fluid after having been stored; and
after the fabric has been bleached to the final whiteness index with the aqueous solution of the caustic substance and the peroxide, the fabric is rinsed with the second residual fluid liquid stored after the conducting of the one of the two separation steps with the ozone containing aqueous solution.

5. The method of claim 1 wherein the ozone containing aqueous solution is provided by contacting an ozone containing gas with water and indirectly cooling the ozone containing aqueous solution to a temperature in the range of between 20.0o C. and 40.0o C.

6. The method of claim 5 wherein the ozone containing aqueous solution has a pH between 6.5 and 7.0 and a dissolved ozone concentration of at least 6.0 milligrams per liter.

7. An apparatus for bleaching a textile fabric comprising:
a bleaching device to contact the textile fabric with chemical bleaching agents in liquid form comprising caustic substances to remove oils, greases, waxes, fats, and motes that may be present within the fabric and peroxide to bleach the fabric and an aqueous solution comprising ozone dissolved in water to also bleach the fabric;
the bleaching of the fabric with the aqueous solution of the caustic substance and peroxide and the bleaching of the fabric with the ozone conducted in two separate steps such that the fabric is bleached to an intermediate whiteness index in one of the two separate steps and is thereafter, bleached to a final whiteness index in the other of the two separate steps;
a first external flow circuit connected to the bleaching device and configured to circulate the liquid containing chemical bleaching agents in a first external flow path, external to the device and having a pump and a heat exchanger to heat the chemical bleaching agents during the chemical bleaching; and
a second external flow circuit in flow communication with the bleaching device to provide ozone containing aqueous stream to the device to bleach the fabric with the ozone containing aqueous stream, the second external flow circuit comprising:
a second flow path configured to circulate the ozone containing aqueous solution from the device and back to the device and having means for injecting an ozone containing stream into the second flow path and thereby forming the ozone containing aqueous solution and means for cooling the ozone containing aqueous solution and thereby maintaining the ozone in the ozone containing aqueous solution; and
an ozone generation system comprising an oxygen source and an ozone generator to convert the oxygen to ozone and thereby to form the ozone containing stream, the ozone generator connected to the ozone containing stream injecting means.

8. The apparatus of claim 7, wherein the device is a soft flow machine.

9. The apparatus of claim 8 wherein
the apparatus is configured to bleach the fabric to the intermediate whiteness index with the ozone and then to the final whiteness index with the aqueous solution of the caustic substance and peroxide; a recirculation circuit is connected to the device to recirculate residual fluids collected from the device back to the device, the residual fluids consisting of a first residual fluid composed of a wetting agent, lubricant and demineralizing agent containing aqueous solution and a second residual fluid formed from the ozone containing aqueous solution; and
said recirculation circuit having a third external flow path, external to the device including additional pumps to pump the residual fluids to first and second tanks and from the first and second tanks back to the device and control valves able to be selectively activated such that:
the first residual fluid is able to be directed into the first of the tanks prior to bleaching the fabric with the ozone;
the second of the residual fluids is able to be directed into the second of the tanks after the bleaching of the fabric with the ozone;
the first residual fluid is able to be directed from the first of the tanks back to the device so that the aqueous solution of the caustic substance and the peroxide is formed with the use of the first residual fluid; and
after the fabric has been bleached to the final whiteness index with the aqueous solution of the caustic substance and the peroxide, the second residual fluid is able to be directed from the second of the tanks back to the device so that the fabric is rinsed with the second residual fluid.

10. The apparatus of claim 7 or claim 9, wherein the ozone injecting means is an ejector.

11. The apparatus of claim 10, wherein the ozone containing aqueous solution cooling means is a vessel to collect the ozone containing aqueous solution, a cooling jacket surrounding the vessel and a chiller connected to the cooling jacket to circulate a coolant through the heat exchange jacket and thereby cool the ozone containing aqueous solution collected in the vessel.

12. The apparatus of claim 8, wherein;
the ozone injecting means is an ejector;
the ozone containing aqueous solution cooling means is a vessel to collect the ozone containing aqueous solution, a cooling jacket surrounding the vessel and a chiller connected to the cooling jacket to circulate a coolant through the heat exchange jacket and thereby cool the ozone containing aqueous solution collected in the vessel;
the second external flow path is connected to the first external flow path so that the ozone containing aqueous solution circulates from the device, through the heat exchanger and the second external flow path and then back to the device;
the second external flow path has a pair of control valves that can be selectively activated to circulate the ozone containing aqueous solution from the first external flow path to the second external flow path and then back to the device;
the pump of the first external flow path is a first pump; and
the second external flow path has a second pump positioned upstream of the ejector to pump the ozone containing aqueous solution as a motive fluid into the ejector.

13. The apparatus of claim 12 wherein
the apparatus is configured to bleach the fabric to the intermediate whiteness with the ozone and then to the final whiteness index with the aqueous solution of the caustic substance and peroxide;
a recirculation circuit is connected to the device to recirculate residual fluids collected from the device back to the device, the residual fluids consisting of a first residual fluid composed of a wetting agent, lubricant and demineralizing agent containing aqueous solution and a second residual fluid formed from the ozone containing aqueous solution; and
said recirculation circuit having a third external flow path, external to the device including third and fourth pumps to pump the residual fluids to first and second tanks and from the first and second tanks back to the device, respectively, and a set of control valves able to be selectively activated such that:
the first residual fluid is able to be directed into the first of the tanks prior to bleaching the fabric with the ozone;
the second of the residual fluids is able to be directed into the second of the tanks after the bleaching of the fabric with the ozone;
the first residual fluid is able to be directed from the first of the tanks back to the device so that the aqueous solution of the caustic substance and the peroxide is formed with the use of the first residual fluid; and
after the fabric has been bleached to the final whiteness index with the aqueous solution of the caustic substance and the peroxide, the second residual fluid is able to be directed from the second of the tanks back to the device so that the fabric is rinsed with the second residual fluid. ,TagSPECI:BLEACHING METHOD AND APPARATUS
Field of the Invention
[0001] The present invention relates to a method and apparatus for bleaching a textile material in which the textile material is treated with an aqueous solution containing caustic and peroxide and another aqueous solution containing dissolved ozone. More particularly, the present invention relates to such a method and apparatus for bleaching textile material in which the aqueous solution containing dissolved ozone is maintained at a low temperature during the bleaching of the textile material.
Background of the Invention
[0002] Bleaching of textile materials including textile filaments, strands, yarns or fabrics with the use of chemicals such as hydrogen peroxide is widely practiced. In a typical conventional hydrogen peroxide bleaching process used in the bleaching of a cotton fabric, the fabric is first treated with water containing auxiliary chemicals that serve as wetting agent, lubricant, and/or demineralizing agent to remove impurities such as oils, greases, waxes and fats, as well as to improve wettability. The fabric is then treated with a bleaching solution containing chemicals such as sodium hydroxide, hydrogen peroxide and a peroxide stabilizer agent for a period of at least 30 minutes at a temperature between 80.0o C. and 100.0o C. The peroxide stabilizer agent prevents the rapid decomposition of hydrogen peroxide at the elevated temperatures employed in such bleaching operations.
[0003] As well known in the art, the bleaching of cotton and cotton containing textiles such as knit fabric is carried out in what are known as soft flow machines of the type that are also used in dyeing fabrics. In such machines, the bleaching operation is carried out by first filling the machine with water and then adding auxiliary chemicals such as the wetting agent, lubricant and demineralizing agent. The fabric is then loaded into the machine and the fluid and fabric is heated to about 80.0o C. while the machine is operated. A caustic agent such as sodium hydroxide is then added with a quantity of hydrogen peroxide and a peroxide stabilizer to achieve necessary concentrations of sodium hydroxide, hydrogen peroxide and the stabilizer agent in the solution, for example 2.0 grams per liter, 2.5 grams per liter and 0.1 grams per liter, respectively. The temperature is raised to 95.0o C. to 100.0o C. and the bleaching process is continued for a specific time period, typically 30 minutes. The liquor in the machine is then drained. Any fragments of cotton seed husk, also known as motes, swell up by the alkali during the treatment and are removed. Thereafter, the system is filled with water and then heated to wash the fabric. After washing, resulting liquor is drained and the machine filled again with water to which acetic acid and a peroxide killer is added for neutralization. The fabric and liquor are circulated for sufficient time to neutralize the wetted fabric. The fabric is unloaded after draining the liquor in the machine. The whiteness index of the fabric will be in an upper range of 60 to 65 as measured by an internationally recognized index known in the art as the CIE Whiteness Index.
[0004] In both WO 89/05882 and US 5,244,466, the textile material is treated with both conventional chemical bleaching agents and an oxidizing gas such as oxygen or ozone gas at elevated temperature in separate steps. The oxidizing gas treatment step precedes or follows hydrogen peroxide or hypochlorite, and/or an alkaline bleaching step. The stepwise chemical bleaching and oxidizing gas bleaching of the fabric is carried out in a bleaching unit. Similar to the conventional chemical bleaching process described above, the bleaching unit is filled with water, chemical bleaching agents added in sufficient amount to achieve desired concentrations. Resulting alkaline liquor and wetted fabric is heated and chemical bleaching carried out at elevated temperature. For the oxidizing gas bleaching step, the ozone mixed with oxygen is introduced by an injection device into the alkaline liquor in the bleaching unit or into the circulating alkaline liquor in an expansion vessel in flow communication with the bleaching unit. The oxidizing gas collects in a head space above the liquid in the bleaching unit and some may dissolve in the alkaline liquor. Alternately, the oxidizing gas is introduced directly into a head space above the liquid in the bleaching unit. Necessary conditions indicated for effective oxidizing gas bleaching require both the oxidizing gas and the wetted fabric to be at elevated temperatures in the range of 70.0o C. to 100.0o C., and the wetted fabric to have pH in the alkaline range.
[0005] The foregoing processes used in the bleaching of textiles have certain disadvantages that stem from the use of relatively high concentrations of chemical bleaching agents and lengthy treatment times at elevated temperature using such agents. The high concentrations of alkaline substances and hydrogen peroxide coupled with their use at elevated treatment temperatures can damage the textile. Typically silicates are used as peroxide stabilizer to control the rate of peroxide degradation, however these react with calcium and magnesium ions present in the solution to form undesirable products that deposit in the machinery and also affect softness of the bleached textile. Both liquid and gaseous effluents require expensive treatment prior to their disposal.
[0006] As will be discussed in detail hereinafter, among the many advantages of the present invention are the utilization of lower concentrations of caustic, hydrogen peroxide and peroxide stabilizer than the prior art and the use of ozone in a cost effective manner.
Summary of the Invention
[0007] The present invention is directed to a method and apparatus for bleaching a textile fabric. In accordance with such method, the fabric is bleached with an aqueous solution of a caustic substance to remove oils, greases, waxes, fats, and motes that may be present within the fabric and peroxide to bleach the fabric. The fabric is also bleached with an ozone containing aqueous solution comprising ozone dissolved in water. The bleaching of the fabric with the aqueous solution of the caustic substance and peroxide and the bleaching of the fabric with the ozone containing aqueous solution conducted in two separate steps such that the fabric is bleached to an intermediate whiteness index in one of the two separate steps and is thereafter, bleached to a final whiteness index in the other of the two separate steps. While bleaching the fabric with the ozone containing aqueous solution, the ozone containing aqueous solution is maintained at a sufficiently low temperature such that the ozone is maintained within the ozone containing aqueous solution in effective amounts to achieve one of an intermediate whiteness index and the final whiteness index at the conclusion of the bleaching of the fabric with the ozone containing aqueous solution.
[0008] The use of the ozone containing aqueous solution will reduce the amounts of chemicals required and the amounts of alkaline effluents produced. This in turn will improve bleaching economics and reduce environmental impact of the discharge of such chemicals because such chemicals are utilized in lower amounts than in the prior art. Also, damage to the fabric by alkaline solutions at elevated temperatures is minimized since the partial bleaching of fabric either from raw to an intermediate whiteness index, or from an intermediate whiteness index to a final desired whiteness index requires less chemicals and treatment times compared to complete bleaching from raw to the final desired whiteness index. For the ozone bleaching step, the present invention uses an aqueous solution at a low temperature containing effective amount of dissolved ozone to bleach raw fabric to an intermediate whiteness index or to bleach a partially bleached fabric having an intermediate whiteness index to a desired final whiteness index. Contrary to oxidizing gas bleaching solutions described above, the ozone bleaching step of present invention uses an aqueous solution to provide ozone for the bleaching action. As a result, the wetted fabric will not have an alkaline pH and the ozone will not be utilized at elevated temperature. In the present invention the aqueous solution containing dissolved ozone is cooled and introduced into the bleaching unit at a low temperature, leveraging higher solubility at the low temperature to provide necessary amount of dissolved ozone for effective bleaching of raw fabric or partially bleached fabric to the desired whiteness index.
[0009] In a method in accordance with the present invention, the one of the two separate steps can be accomplished by the bleaching of the fabric to the intermediate whiteness index with the aqueous solution of the caustic substance and the peroxide and the other of the two separate steps is accomplished by the bleaching of the fabric to the final whiteness index with the ozone containing aqueous solution. Alternatively, the one of the two separate steps is accomplished by the bleaching of the fabric to the intermediate whiteness index with the ozone containing aqueous solution and the other of the two separate steps is accomplished by the bleaching of the fabric to the final whiteness index with the aqueous solution of the caustic substance and the peroxide.
[0010] Where the ozone containing aqueous solution is used to achieve the intermediate whiteness index, the fabric is wetted with a wetting agent, lubricant and demineralizing agent containing aqueous solution and the wetting agent, lubricant and demineralizing agent containing aqueous solution is stored as a first residual fluid prior to conducting the one of the two separate steps with the ozone containing aqueous solution. A second residual fluid, formed from the ozone containing aqueous solution, is stored after conducting the one of the two separate steps with the ozone containing aqueous solution. The aqueous solution of the caustic substance and the peroxide is formed with the use of the first residual fluid after having been stored and after the fabric has been bleached to the final whiteness index with the aqueous solution of the caustic substance and the peroxide, the fabric is rinsed with the second residual fluid stored after the conducting of the one of the two separation steps with the ozone containing aqueous solution.
[0011] In any embodiment of the present invention, the ozone containing aqueous solution is provided by contacting an ozone containing gas with water and indirectly cooling the ozone containing aqueous solution to a temperature in the range of between 20.0o C. and 40.0o C. Preferably, the ozone containing aqueous solution has a pH between 6.5 and 7.0 and a dissolved ozone concentration of at least 6.0 milligrams per liter.
[0012] In another aspect, the present invention provides an apparatus for bleaching a textile fabric. Such apparatus has a bleaching device to contact the textile fabric with chemical bleaching agents in liquid form comprising caustic substance to remove oils, greases, waxes, fats, and motes that may be present within the fabric and peroxide to bleach the fabric and an aqueous solution comprising ozone dissolved in water to also bleach the fabric. The bleaching of the fabric with the aqueous solution of the caustic substance and peroxide and the bleaching of the fabric with the ozone conducted in two separate steps such that the fabric is bleached to an intermediate whiteness index in one of the two separate steps and is thereafter, bleached to a final whiteness index in the other of the two separate steps. A first external flow circuit is connected to the bleaching device and configured to circulate the liquid containing chemical bleaching agents in a first external flow path, external to the device. The first external flow path has a pump and a heat exchanger to heat the chemical bleaching agents during the chemical bleaching. A second external flow circuit is in flow communication with the bleaching device to provide ozone containing aqueous stream to the device to bleach the fabric with the ozone containing aqueous stream. The second external flow circuit comprises a second flow path configured to circulate the ozone containing aqueous solution from the device and back to the device. The second flow path has means for injecting an ozone containing stream into the second flow path and thereby forming the ozone containing aqueous solution and means for cooling the ozone containing aqueous solution and thereby maintaining the ozone in the ozone containing aqueous solution. An ozone generation system is provided that comprises an oxygen source and an ozone generator to convert the oxygen to ozone and thereby to form the ozone containing stream. The ozone generator is connected to the means for injecting the ozone containing stream into the second flow path.
[0013] In any embodiment of the present invention, the device can be a soft flow machine.
[0014] Where the apparatus is configured to bleach the fabric to the intermediate whiteness with the ozone and then to the final whiteness index with the aqueous solution of the caustic substance and peroxide, a recirculation circuit is connected to the device to recirculate residual fluids collected from the device back to the device. These residual fluids consist of a first residual fluid composed of a wetting agent, lubricant and demineralizing agent containing aqueous solution and a second residual fluid formed from the ozone containing aqueous solution. The recirculation circuit has a third external flow path, external to the device and including additional pumps to pump the residual fluids to first and second tanks and from the first and second tanks back to the device and control valves. The control valves are able to be selectively activated such that the first residual fluid is able to be directed into the first of the tanks prior to bleaching the fabric with the ozone and the second of the residual fluids is able to be directed into the second of the tanks after the bleaching of the fabric with the ozone. The selective activation of the control valves also allows the first residual fluid is able to be directed from the first of the tanks back to the device so that the aqueous solution of the caustic substance and the peroxide is formed with the use of the first residual fluid and the second residual fluid is able to be directed from the second of the tanks back to the device so that the fabric is rinsed with the second residual fluid, after the fabric has been bleached to the final whiteness index with the aqueous solution of the caustic substance and the peroxide.
[0015] Preferably, the ozone injecting means is an ejector and the ozone containing aqueous solution cooling means is a vessel to collect the ozone containing aqueous solution, a cooling jacket surrounding the vessel and a chiller connected to the cooling jacket to circulate a coolant through the cooling jacket and thereby cool the ozone containing aqueous solution collected in the vessel. The second external flow path can be connected to the first external flow path so that the ozone containing aqueous solution circulates from the device, through the jacketed vessel and the second external flow path and then back to the device. The second external flow path has a pair of control valves that can be selectively activated to circulate the ozone containing aqueous solution from the first external flow path to the second external flow path and then back to the device. Preferably, the pump of the first external flow path is a first pump and the second external flow path has a second pump positioned upstream of the ejector to pump the ozone containing aqueous solution as a motive fluid into the ejector. Where the apparatus is configured to bleach the fabric to the intermediate whiteness index with the ozone and then to the final whiteness index with the aqueous solution of the caustic substance and peroxide, the recirculation circuit has a third pump to pump the residual fluids from the device to the first and second tanks and a fourth pump to pump the residual fluids from the first and second tanks back to the device, and the control valves within the third external flow path are a set of control valves able to be selectively activated as described above.
Brief Description of the Drawings
[0016] Although the present invention concludes with claims distinctly pointing out the subject matter that Applicants regard as their invention, it is believed that the invention will be better understood when taken in connection with the accompanying drawings in which:
[0017] Fig. 1 is a process flow diagram of an apparatus for carrying out a method in accordance with the present invention; and
[0018] Fig. 2 is a process flow diagram of an alternate embodiment of an apparatus for carrying out a method in accordance with the present invention.
Detailed Description of the Invention
[0019] In the present invention bleaching to a final whiteness index is achieved by treating the textile with low concentrations of hydrogen peroxide and caustic in a chemical bleaching step either before or after a treatment step with an ozone containing aqueous solution. Since the bleaching is divided between a chemical bleaching step and an ozone treatment step, lower concentrations of chemicals such as hydrogen peroxide and caustic are able to be utilized as compared with the prior art. Further, since the ozone containing aqueous solution is maintained at a low temperature, such solution is able to contain sufficient amounts of dissolved ozone to accomplish its part of the required bleaching while also reducing the amount of ozone and therefore, the oxygen consumed in producing the ozone that would otherwise be required.
[0020] With reference to Figure 1, a bleaching apparatus 1 is illustrated that uses a bleaching device 10 such as a soft flow machine having a treatment vessel 12 to house and bleach a load of fabric 14. An alternative to a soft flow machine would be a jigger or winch machine or a device to continuously spray the aqueous bleaching solutions or to pass the fabric through a trough containing aqueous bleaching solutions or combinations, thereof. The transfer of liquid to the fabric may also be done in known devices that circulate the aqueous bleaching solutions in a chamber where the fabric is rotated along or against the flow of liquid. The bleaching of the fabric 14 is initiated by opening a valve 16 in the water line 18 to introduce a water stream 20 into the treatment vessel 12. The water used at this stage of the bleaching process is fresh water at ambient temperature. The valve 16 is closed after adding sufficient quantity of water into the treatment vessel 12 that typically will have a weight of between 10.0 and 15.0 times the weight of the fabric load to be bleached. A wetting agent is added into the treatment vessel 12 by opening a valve 22 provided in an inlet conduit 24. The fabric 14 is then loaded into the bleaching device 10 and the end sides of the fabric are stitched so as to form a loop. The bleaching device 10 is provided with a winch 26 that is rotated by an electric motor, not illustrated. The fabric 14, as illustrated, is looped over the winch 26, and the rotation of the winch causes the fabric 14 to be circulated in the treatment vessel and thus, contact the aqueous solutions used in the bleaching of the fabric 14.
[0021] The liquid in the treatment vessel 12 is circulated through a first external flow path 28. The liquor is drawn out of the treatment vessel 12 through line 34, pumped by a first pump 30 to a sufficient elevated pressure. The resulting pressurized liquor flows from pump 30 through line 36 into a heat exchanger 32 where the liquor is heated. Heat exchanger 32 can be a known device using steam for purposes of such heating. After the heating of the liquor, the resulting heated liquor is returned to the treatment vessel 12 through line 38. Once liquor circulation begins within the first external flow path 28, a lubricant and a demineralizing agent is introduced into the treatment vessel 12 through inlet conduit 24 by opening valve 22. At this point, the temperature of the circulating liquor is raised to 80.0o C. by introducing a steam stream 40 through another inlet conduit 42. The fabric and the liquor while in a heated state are circulated for 3 minutes and then, valve 22 is again opened and a caustic consisting of sodium hydroxide, hydrogen peroxide and a peroxide stabilizer are then introduced into the treatment vessel 12 through inlet conduit 24. The temperature of the circulating liquor within first external flow path 28 is then raised to 95.0o C. by controlling the flow rate of steam stream 40 into the heat exchanger 32 through the use of a flow control valve 44. A temperature sensor 46 is located to sense liquor temperature inside treatment vessel 12 and to provide a signal referable to the temperature to a controller 48. Controller 48, that can be, for instance, a known controller using proportional, integral and differential control methodology. Controller 48 produces a feedback signal that is transmitted to flow control valve 44 by means of electrical conductor 50 and thereby control its opening to maintain a temperature setpoint. Although not illustrated, but as would be known by those skilled in the art, controller 48 would be provided with a temperature input that could be varied at will for purposes of setting a temperature setpoint and the feedback signal would be generated to maintain the temperature in the treatment vessel 12 within +/- 3.0o C. of such a setpoint.
[0022] The treatment with caustic at about 95.0o C. is continued for 30 minutes. At the end of this treatment, the flow of steam stream 40 to the heat exchanger 32 is terminated by closing control valve 44. A cooling water stream 52 at temperature of 35.0o C. is then introduced into heat exchanger 32 by opening a control valve 54 in an inlet line 56 to cool the circulating liquor to 80.0o C. The control valve 54 regulates the cooling water flow to control the temperature of liquor inside the treatment vessel 12 based on a signal from temperature sensor 46 fed into controller 48 that controls control valve 54 to maintain the new temperature setpoint of 80.0o C. by means of a feedback signal transmitted through electrical connection 58 to such valve. Upon reaching the desired setpoint temperature, the pump 30 and winch 26 are switched off, and cooled liquor inside the treatment vessel 12 is drained by opening a drain valve 60. Upon completion of the draining, the drain valve 60 is closed.
[0023] The fabric 14 is then subjected to a neutralization treatment step wherein the treatment vessel 12 is filled with fresh water by water stream 20 introduced into the treatment vessel 12 by opening valve 16. The quantity of water used for such purposes is again roughly between 10.0 and 15.0 times the weight of the fabric 14. The winch 26 and pump 30 are then switched on to circulate the fabric and liquor. Neutralization chemical agents such as acetic acid and peroxide killer are dosed into the water in the treatment vessel 12 through inlet conduit 24. The neutralization process is carried out for 9 minutes. During this period, liquor passes through the heat exchanger 32 in the first external flow path 28 without the liquor flow being heated. Upon completion of the neutralization step, the winch 26 and pump 30 are switched off and the liquor in the treatment vessel is drained by opening drain valve 60. The resulting wetted fabric 14 in the treatment vessel 12 at this stage is mote-free, and has an intermediate whiteness index which should be between 45 and 55 on the CIE Whiteness Scale.
[0024] The partially bleached fabric is now subjected to an ozone bleaching stage in which, again, the treatment vessel 12 is filled with fresh water introduced as a water stream 20 through water line 18. The resulting liquor in contact with the fabric inside the treatment vessel has a pH in the range of between 6.5 and 7.0 and preferably neutral. An isolation valve 62 in the first external flow path 28 is closed and valves 64 and 66 are opened to enable circulation of liquor through a second external flow path 68 that serves as an ozone circulation circuit. This second external flow path 68 is configured to draw liquor from the treatment vessel 12, flow through a portion of first external flow path 28 into the second external flow path 68 and return the liquor back to the treatment vessel 12 through line 38 in the first external flow path 28. The liquid having a neutral pH is drawn out of the treatment vessel 12 by starting first pump 30 and passing liquid through heat exchanger 32 into the second external flow path 68 wherein ozone is dissolved in circulating liquid to provide an aqueous solution containing sufficient amount of dissolved ozone for bleaching action, thereby raising the whiteness of the fabric 14 to a final whiteness of between 60 and 70. During this portion of the bleaching process, steam is not added to the heat exchanger 32 and it serves merely as a passage for the flow and not as a heater. As could be appreciated, embodiments of the present invention are possible in which the second external flow path 68 is entirely separate from the first flow path 28 and separately connected to treatment vessel 12 of device 10.
[0025] In the illustrated embodiment, more specifically, when control valves 64 and 66 are set in open positions, the liquid is routed from valve 64 through a line 70 to an optional pump 72 that pumps the liquid to provide necessary head for serving as a motive fluid to an ejector 76 to entrain and dissolve ozone and thereby form the ozone containing aqueous solution. As is known in the art, ejector has a venturi to produce a low pressure field to draw the ozone into the pumped motive liquid. It is understood that an in-line sparger could be used as an alternative to an ejector. The pumped liquid from pump 72 flows through a conduit 74 to the ejector 76 and from ejector 76 through conduit 78 to a vessel 80 where the ozone containing aqueous solution accumulates and is cooled. The accumulated ozone containing aqueous solution is then fed back to the treatment vessel 12 through conduit 82, valve 66 and line 38. The vessel 80 has a heat exchange jacket 84 coupled to a chiller 86 by inlet and outlet lines 88 and 90. Ozone for dissolution is provided to the ejector 76 from an ozone generation system 92 through line 94. The solution containing dissolved ozone in vessel 80 is indirectly cooled by the chiller 86 through circulation of cooling fluid from chiller to the heat exchange jacket 84 through the inlet and outlet lines 88 and 90. Although not illustrated, chiller 86 has a circulation pump for such purposes. In such manner, the ozone dissolved aqueous solution is cooled to a low temperature in the range of between 20.0o C. and 40.0o C. The ozone dissolved aqueous solution at a low temperature can also be formed by sufficiently cooling the pumped liquid or ozone containing gas or both, fed to the ejector 76 by locating and sizing appropriate equipment before ejector 76 to deliver the ozone dissolved aqueous solution at a low temperature in the range of between 20.0o C. and 40.0o C to the treatment vessel 12 with or without additional cooling means after ejector 76. Even though indirect heat exchange means are shown in Fig. 1, the second external flow path 68 can be configured to have direct contact cooling means employing liquid nitrogen, cold nitrogen vapor, cold nitrogen gas or cold air as a coolant. The aqueous solution at a low temperature, which contains a sufficient amount of dissolved ozone, between 6.0 and 12.0 milligrams dissolved ozone per liter of water, is provided to the treatment vessel 12 to further bleach the mote-free, partially bleached fabric 14 to a final whiteness index in the range of between 60.0 and 70.0 as measured on the CIE Whiteness scale. This ozone bleaching operation is conducted for a time period of between 30 and 40 minutes.
[0026] Although not illustrated, the ozone generation system 92 can include a chiller to manage the heat generated in the ozone production step. In this regard, ozone generation system 92 will conventionally consist of an oxygen source, ozone generation reactor for e.g. using corona discharge, and a chiller to manage the heat produced in the ozone generation reactor. It will be typically sized to convert an oxygen gas stream 96 into ozone product containing between 8.0 and 10.0 percent ozone in oxygen by weight. The ozone product is metered within line 94 by a valve 98. Any ozone product gas entrained in the circulating liquid returning from the second external flow path 68 into treatment vessel 12 is vented through a vent 100 connected to a blower 102.
[0027] At the end of ozone bleaching step the supply of oxygen to the ozone generation system and the flow of ozone product gas to the ejector 76 is terminated. Pumps 30 and 72, winch 26 and air blower 102 are all shut down and the liquor in treatment vessel 12 is drained by opening valve 60. The bleached fabric is then unloaded from the device 10.
[0028] In another embodiment of the present invention the fabric is first subjected to ozone bleaching followed by hydrogen peroxide and caustic treatment. These treatments can be carried out in the bleaching apparatus 1 shown in Fig. 1. A more preferred apparatus 2 for this sequential treatment is shown in Fig. 2 because apparatus 2 is designed to conserve the use of chemicals such as wetting agents, lubricants and demineralizing agents as well as having the ability to re-use potentially environmental toxic liquids that otherwise would be discharged. It is to be noted, however, that where ozone bleaching precedes the chemical bleaching step, while such conservation is desirable, embodiments of the present invention are possible that do not employ such conservation. In order to avoid repetition of explanation, the same reference numbers will be used in Figures 1 and 2 to refer to like equipment in structure having the same function in both of such illustrations. In this regard, the bleaching apparatus 2 contains a bleaching device 10, a first external flow circuit 28, a second external flow circuit 68 and an ozone generation system 92. Additionally, the bleaching apparatus 2 contains a recirculation circuit 104.
[0029] Bleaching apparatus 2 is used by first filling the treatment vessel 12 with water 20. A wetting agent is added through inlet conduit 24, fabric 14 is loaded, winch 26 and pump 30 are started and lubricant and demineralizing agent are added through inlet conduit 24. The temperature of fabric 14 and the circulating liquor is raised to 80.0o C. by heating the liquid in heat exchanger 32 by introducing steam 40 through line 42. Typically, the fabric 14 and liquor are circulated for 3 minutes and then winch 26 and pump 30 are switched off. The liquor containing wetting agent, lubricant and demineralizing agent is drained from the treatment vessel 12 into a first tank 116 in the recirculation circuit 104 by opening control valves 106 and 112 and starting third pump 108. The pumped liquor flows through conduit 110, valve 112 and conduit 114 into first tank 116 for storage and use in a later step in the treatment vessel 12. Upon completion of draining, third pump 108 is shutdown, control valves 106 and 112 closed and the recirculation circuit 104 isolated from the bleaching device 10.
[0030] The wetted fabric 14 is then first subjected to ozone bleaching. The treatment vessel 12 is filled with required quantity of fresh water (10.0 to 15.0 times the weight of fabric) through water line 18. The resulting liquid in contact with the fabric 14 inside the treatment vessel 12 has a pH in the range of 6.5 to 7.0 and preferably neutral. The ozone bleaching step in apparatus 2 is carried out in the same manner as that described above for apparatus 1. The liquid in the treatment vessel is circulated through flow pathways and equipment in the first external flow circuit 28 and second external flow circuit 68 to provide liquid containing dissolved ozone in sufficient amounts and at a low temperature to the treatment vessel 12 through line 38. Ozone for dissolution is provided from the ozone generation system 92 through valve 98 and line 94 to the ejector 76 in the second external flow circuit 68. Cooling of the liquid containing dissolved ozone in vessel 80 is accomplished by circulating a coolant stream from chiller 86 through jacket 84 of vessel 80. The cooled aqueous solution returned to the treatment vessel 12 contains sufficient amount of dissolved ozone, between 6.0 and 12.0 milligrams dissolved ozone per liter of water, and is at a temperature in a range of between 20.0o C. to 40.0o C., preferably in the range of 25.0o C. and 30.0o C. The ozone bleaching step is continued for a longer period of time of about 90 to 120 minutes. The resulting fabric has an intermediate whiteness index in the range of between 45.0 and 60.0 as measured on the CIE Whiteness Scale.
[0031] At the end of ozone bleaching step the supply of oxygen to the ozone generation system and the flow of ozone product gas to the ejector 76 is terminated. The liquid in the treatment vessel 12 is withdrawn and stored for re-use as a rinsing fluid in a later step. For this purpose the winch 26 is switched off, pumps 30 and 72 shutdown, and flow communication between the bleaching device 10 and a second tank 122 in the recirculation circuit 104 is established by opening control valves 106 and 118 and starting third pump 108. The pumped liquid flows into tank 122 through line 110, control valve 118 and line 120 for storage and use in a later step. Upon completion of draining, pump 108 is shutdown, control valves 106 and 118 closed, and the second tank 122 isolated.
[0032] The stored liquid in tank 116 containing wetting agent, lubricant and demineralizing agent is thereafter returned to the treatment vessel 12 through conduits 128, 140 and line 18 by opening valves 124 and 142 and starting a fourth pump 130. Upon completion of transfer, fourth pump 130 is shutdown, and first tank 116 and recirculation circuit 104 isolated from the treatment vessel 12 by closing control valves 124 and 142. The winch 26 and first pump 30 are switched on to circulate fabric within the treatment vessel and liquor through the first external flow path 28. Sodium hydroxide, hydrogen peroxide, and peroxide stabilizer are added through inlet conduit 24 to the liquor in the treatment vessel 12 and thus, liquor containing the wetting agent, lubricant and demineralizing agent is reused as makeup for the chemical bleaching solution rather than being discarded into the environment. The entire mass of fabric and liquor in the vessel is heated to 95.0o C. to 100.0o C. by heating the circulating liquor in heat exchanger 32 by regulating flow of steam 40 to heat exchanger 32. This chemical bleaching step at elevated temperature is continued for 30 to 40 minutes, then flow of steam stream 40 to heat exchanger 32 is stopped and cooling water stream 52 at a temperature of 35.0o C. is introduced into heat exchanger 32 by opening control valve 54 in line 56 to cool the circulating liquor to 80.0o C. Upon completion of chemical bleaching step, winch 26 and pump 30 are stopped and the cooled liquor drained from the treatment vessel 12 by opening valve 60. Once draining is complete valve 60 is closed.
[0033] The fabric in the treatment vessel 12 is now subjected to a rinsing step. For this purpose liquid stored in second tank 122 following completion of ozone bleaching step is utilized. Flow communication between treatment vessel 12 and tank 122 in recirculation circuit 104 is re-established by opening valves 126 and 142, and starting fourth pump 130. The stored liquid is transferred from tank 122 to treatment vessel 12 through conduits 128, 140 and 18. Upon completion of transfer, fourth pump is shutdown, and valves 126 and 142 closed to isolate tank 122 and recirculation circuit 104 from treatment vessel 12. The winch 26 and pump 30 are started again and the entire mass of fabric and liquor in the treatment vessel is heated to 80.0o C. by circulating liquor through first external flow path 28 and heating the liquor in heat exchanger 32 by regulating steam flow 40. The washing of fabric is continued for about 9 minutes, then winch 26 and pump 30 are stopped and liquor drained by opening valve 60. Upon completion of draining, valve 60 is closed. Here again, rather than discarding the liquor produced during the ozone bleaching step, the present invention allows its reuse in washing the fabric.
[0034] The washed fabric is next subjected to neutralization treatment step in a manner similar to that described above for apparatus 1. The treatment vessel is filled with fresh water at 25.0o C. to 30.0o C. to which neutralization agents such as acetic acid and peroxide killer are added through inlet conduit 24 and the fabric and water circulated for about 9 minutes by starting winch 26 and pump 30. During this period, liquor passes through the heat exchanger 32 in the first external flow path 28 without the liquor flow being heated. Upon completion of the neutralization step, winch 26 and pump 30 are stopped and liquor in the treatment vessel is drained by opening valve 60. Upon completion of draining, valve 60 is closed and fabric unloaded. The resulting fabric is mote-free, and has a final whiteness which should be between 65 and 70 on the CIE whiteness scale.
[0035] A pilot scale setup of the apparatus shown in both Figures 1 and 2 was built using a soft flow machine rated to handle a fabric load of 5.0 to 25.0 kg as the bleaching device 10 and experiments conducted using commercially available chemicals to supply the wetting agent, the lubricant, the demineralizing agent, the peroxide stabilizer, and the peroxide killer.
[0036] The pilot scale setup of apparatus 1 shown in Fig. 1 was used for an exemplary base case of a bleaching operation conducted in accordance with prior art techniques using caustic and hydrogen peroxide. The treatment vessel 12 in the bleaching device 10 was first filled with 150 liters of water for treating 15 kg of fabric. Sufficient amount of wetting agent was added through inlet conduit 24 to achieve a concentration of 0.7 gram per liter, followed by loading of fabric. Then lubricant and demineralizing agent were added through inlet conduit 24 to achieve concentrations of 0.75 grams per liter and 0.5 grams per liter, respectively. The entire mass was heated to about 80.0o C. by starting winch 26 to circulate fabric and pump 30 to circulate liquor through first external flow path 28 and treatment continued for nearly 9 minutes. Sodium hydroxide, hydrogen peroxide and peroxide stabilizer were then added in sufficient amounts to achieve concentrations of 2.0 grams per liter, 2.5 grams per liter and 0.1 grams per liter, respectively. The temperature of the fabric and the liquor in the treatment vessel was raised to between 95.0o C. and 100.0o C. by circulating the peroxide containing liquor having a pH in the range of between 12.0 and 13.0 through the heat exchanger 32 and regulating flow of steam 40. The chemical treatment was continued for 30 to 40 minutes and then entire solution was cooled to 80.0o C. and drained.
[0037] The treatment vessel 12 was again filled with water and entire mass of fabric and liquid in the treatment vessel heated to 80.0o C. by starting winch 26 and pump 30 and regulating flow of steam 40 to heat exchanger 32. Washing of fabric was continued for about 9 minutes. Upon completion of wash cycle, winch 26 and pump 30 were stopped, and liquor was drained through valve 60. Next, the treatment vessel 12 was filled with water having a temperature of between 25.0o C and 30.0o C. Sufficient amount of acetic acid added to achieve acetic acid concentration of 0.8 grams per liter, and sufficient amount of peroxide killer added to achieve peroxide killer concentration of 0.2 grams per liter for neutralization, both chemicals added through inlet conduit 24. The neutralization step was carried out for about 9 minutes while circulating the fabric inside the treatment vessel using winch 26, and circulating liquor through first external flow path 28. Then the liquor was drained, and fabric unloaded. The whiteness index achieved was in the range of 60.0 to 65.0 on the CIE Whiteness Scale.
[0038] The pilot scale setup of apparatus 1 was then used, again for exemplary purposes, to conduct a bleaching operation in accordance with the present invention in which chemical bleaching with the use of a caustic and hydrogen peroxide was followed by bleaching with an aqueous ozone containing solution. The treatment vessel 12 was filled with 150 liters of water for treating 15 kg of fabric. Sufficient amount of a wetting agent was added to achieve a concentration of 0.7 gram per liter, followed by loading of fabric (15 kg). Then sufficient amounts of lubricant and demineralizing agent were added through inlet conduit 24 to achieve concentrations of 0.75 grams per liter and 0.5 grams per liter, respectively. The entire mass was heated to about 80.0o C. and treatment carried out for only 3 minutes. Sodium hydroxide, hydrogen peroxide and peroxide stabilizer were then added through inlet conduit 24 in lower amounts to achieve concentrations of 1.0 gram per liter, 1.0 gram per liter and 0.04 grams per liter, respectively. The temperature of entire mass of fabric and liquor in the treatment vessel 12 was raised to a temperature of between 95.0o C. and 100.0o C. by heating circulating peroxide containing liquor having a lower pH in the range of 11.0 to 12.0 in heat exchanger 32 by regulating flow of steam 40. The chemical treatment was continued for 30 to 40 minutes and the entire solution was cooled to 80.0o C. and drained.
[0039] Following the chemical treatment, the treatment vessel was filled again with fresh water having a temperature of between 25.0o C. and 30o C. The fabric was then washed with the water for 9 minutes followed by addition of sufficient amount of acetic acid to achieve acetic acid concentration of 0.4 grams per liter and sufficient amount of peroxide killer to achieve a concentration of 0.1 grams per liter. The neutralization step was carried out for about 9 minutes, and liquor drained. Intermediate whiteness index of the fabric was measured which was in the range of between 45.0 and 55.0 units on the CIE Whiteness scale, and the fabric was mote-free. The treatment vessel was then filled with fresh water and ozone bleaching of partially bleached fabric was carried out for 30 minutes using an aqueous solution containing between 6.0 and 12.0 milligrams per liter of dissolved ozone at a temperature of between 25.0o C. and 30.0o C. and having a pH of about 7.0. The ozone bleaching step resulted in a mote-free fabric having a final whiteness index in the range of between 60.0 and 65.0 on the CIE Whiteness Scale.
[0040] A pilot scale setup of apparatus 2, shown in Fig. 2, was used to conduct an exemplary bleaching operation in accordance with the present invention in which the ozone bleaching preceded the chemical bleaching.. The treatment vessel 12 was first filled with 150 liters of water for treating 15 kg of fabric. Sufficient amount of wetting agent introduced through inlet conduit 24 to achieve a concentration of 0.7 gram per liter, followed by loading of fabric (15 kg). Then sufficient amounts of lubricant and demineralizing agent were added to achieve concentrations of 0.75 grams per liter and 0.5 grams per liter, respectively. The entire mass was heated to about 80.0o C. and the treatment continued for 3 minutes. The entire liquor after treatment was then transferred to tank 116 in recirculation circuit 104.
[0041] The treatment vessel 12 was filled with fresh water. The fabric was then subjected to ozone bleaching using aqueous solution having a pH of about 7.0, containing between 6.0 and 12.0 milligrams per liter of dissolved ozone and at a temperature of between 25.0o C. and 30.0o C. The ozone bleaching was carried out for a time period between 90 and 120 minutes yielding a whiteness index in the range of between 50.0 and 60.0 as measured on the CIE Whiteness scale. The liquid in the treatment vessel 12 was then transferred to tank 122 in recirculation circuit 104 for storage and later use.
[0042] The stored liquor from tank 116 containing wetting agent, lubricant and demineralizing agent was transferred back into treatment vessel 12. Hydrogen peroxide, sodium hydroxide, and peroxide stabilizer in lower amounts were added through conduit 24 to achieve lower concentrations of 1.0 gram per liter, 1.0 gram per liter and 0.04 grams per liter, respectively. The entire mass of fabric and liquor was heated to between 95.0o C. and 100.0o C. For this purpose the circulating liquor at a pH in the range of between 11.0 and 12.0 was heated in the external heat exchanger 32 by regulating flow of steam 40. The bleaching step continued for 30 to 40 minutes. At the conclusion of this stage of the bleaching process the liquor cooled to 80.0o C. and then drained.
[0043] The treatment vessel 12 was then filled with previously stored liquid in tank 122 to rinse the fabric. Entire mass of fabric and liquid in the treatment vessel 12 was heated to 80.0o C. by circulating liquid through the first external flow circuit and heating the liquid in heat exchanger 32 by regulating flow of steam 40. Washing of fabric was continued for about 9 minutes and then the liquid drained.
[0044] The treatment vessel was again filled with required quantity of fresh water, 150 liters, then sufficient amount of acetic acid added to achieve a concentration of 0.4 grams per liter and sufficient amount of peroxide killer added to achieve a concentration of 0.1 grams per liter to carry out neutralization. The fabric and liquor at a temperature of 25.0o C. to 30.0o C. was circulated for 9 minutes. At the conclusion of the neutralization step, the liquor drained and fabric unloaded. This process resulted in a mote-free fabric having a final whiteness index in the range of between 65.0 and 70.0 as measured on the CIE Whiteness Scale.
[0045] As is apparent from the examples set forth above, the amount of sodium hydroxide, hydrogen peroxide and peroxide stabilizer used in a process carried out in the present invention is roughly half of that required in a prior art bleaching process. As a result, the neutralization requires acetic acid concentrations and peroxide killer use that is also roughly one half of that required in the prior art.
[0046] While the present invention has been described with reference to a preferred embodiment, as will occur to those skilled in the art, numerous changes, additions and omissions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims.