AU7642187A

AU7642187A - Impregnation process and apparatus with a vacuum pump valve control system

Info

Publication number: AU7642187A
Application number: AU76421/87A
Authority: AU
Inventors: Derek Anthony Maude
Original assignee: Maude A E; Maude D A
Current assignee: Maude A E; Maude D A
Priority date: 1986-07-01
Filing date: 1987-07-01
Publication date: 1988-01-29

Description

IMPREGNATION PROCESS AND APPARATUS WITH A VACUUM PUMP - VALVE CONTROL SYSTEM

FIELD OF THE INVENTION

The present invention relates to a material impregnation system particularly useful in the treatment of cellulose, e.g. wood or wood composites. in this respect it is well known to impregnate wood with fire retardants and/or preservatives thereby improving the natural properties of the material. Typically copper chrome arsenic (CCA.) has been previously used as a treatment chemical however such is a toxic chemical and presents handling difficulties as well as potential environmental hazards due to post treatment leaching. CCA. is widely used as a preservative. Water soluble phosphates and microbiocides are also known to impart corrosion and mould resistance.

To improve the impregnation of the treatment agent and minimize the aforementioned problems it has been proposed to carry out the process under vacuum pressure conditions. Such- has been found to be very effective, however, the amount of treatment chemical and pressure conditions must be established empirically. These results only provide a rough guide as moisture content of the wood to be treated can vary widely and change the requirements for proper impregnation. Accordingly if vacuum-pressure impregnation is adopted it is usual to use an excess of treatment chemical and an extended treatment period.

It is an object of the present invention to provide a vacuum-pressure impregnation system which allows more effective impregnation and shorter treatment times.

It is also an object of the present invention to provide apparatus which more effectively carries out the impregnation process. DESCRIPTION OF THE INVENTION

Accordingly, in a first embodiment of the invention there is provided apparatus for vacuum-pressure impregnating material comprising:

(a) an autoclave having a main treatment chamber to receive material to be impregnated with treatment chemical and an upper chamber communicating with the main treatment chamber,

(b) pump means to urge treatment chemical into the main treatment chamber,

(c) sensing means located in an upper portion of the main treatment chamber to sense when treatment chemical has filled the main treatment chamber to a predetermined level and provide an output signal,

(d) evacuation means responsive to the output signal to evacuate air remaining in the main treatment chamber whereafter the pump means urges treatment chemical into the main treatment chamber until the main treatment chamber is full and the upper chamber is filled to a predetermined level,

(e) valve means in the upper chamber sealing the main treatment chamber and upper chamber against ingress of air,

(f) pressure means to apply pressure to the main treatment chamber thereby impregnating the material with treatment chemical,

(g) timer means regulating operation of the evacuation means and pressure means, and

(h) withdrawal means to remove treatment chemical from the main treatment chamber.

According to a second embodiment of the invention a method is provided of vacuum-pressure impregnating material comprising the steps of:

(a) locating the material in a main treatment chamber of an autoclave, the autoclave also including an upper chamber communicating with the main treatment chamber,

(b) partially filling the main chamber with treatment chemical to a first level at which the material is immersed, (c) applying a vacuum to the autoclave for a first predetermined period of time to remove air from the main treatment chamber, the upper chamber and the material, _c (d) filling the main treatment chamber totally and the upper chamber to a second level with treatment chemical,

(e) applying pressure to the main treatment chamber for a second predetermined period thereby impregnating

- _n the material with treatment chemical, and

(f) relieving the pressure from the main treatment chamber and emptying the main chamber of treatment chemical.

Typically the main treatment chamber is generally . -. spherical with hemispherical ends and the upper chamber is an open based cone or a frusto-cone. These chambers are sealingly connected about an opening in the main treatment chamber.

Characteristic of the invention is the speed which 0 the treatment chemical is introduced to and from the main treatment chamber. In one preferred form this is achieved by the withdrawal means including means to open an outlet in the main treatment chamber and air imput means to introduce air into the main treatment chamber to force treatment chemical through the outlet. 5

The most preferred form of air imput is a vacuum pump which may carry out the dual role of evacuation as well. The difficulty presented with vacuum pumps is how to control their operation in a reliable yet simple manner.

It is therefore a separate aspect of the present 0 invention to provide a control system for a vacuum pump. Clearly, whilst this control system has been principally developed for use with the impregnation system described above it is not so limited to that application.

More particularly, the control system comprises a 5 control system for a vacuum pump comprising: (a) a first chamber to be positively pressurized comprising an inlet and a first and second outlet; (b) a second chamber to be negatively pressurized comprising a first and second inlet and an outlet;

(c) regulation means including

(i) a first valve means associated with the first _cb outlet of the first chamber and the first inlet of the second chamber, to close either the first outlet or first inlet and open the other; (ii) a second valve means to open or close the

10 second outlet of the first chamber; and (iii)a third valve means to open or close the second inlet of the second chamber; and

(d) control means to operate the valve means to (i) (a) open the first outlet of the first chamber;

15

(b) close the second outlet of the first chamber;

(c) close the first inlet of the second chamber;

(d) open the second inlet of the second

2.0 chamber; and

(ii) (a) open the first inlet of the second chamber;

(b) close the second inlet of the second chamber;

25

(c) close the first outlet of the first chamber;

(d) open the second outlet of the first chambe .

Characteristic of this control system is the maintenance of

30 each chamber in either its positively or negatively pressurized condition notwithstanding that it is only being actuated to either evacuate or pressurize a remote chamber. Further, this means that the vacuum pump may be easily and readily change from either condition.

35

For ease of fabrication, it is preferred to have one of the chambers on top of the other and the valve arrangement located internally of the chambers.

The valve means may be butterfly valves or other means capable of opening or closing the inlet or outlet. Typically these valves may be controlled by the use of levers which may be interconnected by appropriate linkage. The linkage and valves will be actuated remotely in response to the desired state of the autoclave. Pistons connected to the levers has been found to be a particularly simple and effective method of actuating the valve means.

It has also been found preferable to locate a silencer chamber adjacent the negative and positively pressurized chambers and to run all conduits through this chamber. This allows significant noise reduction and facilitates achieving noise regulation levels.

This arrangement also lends itself to compact manufacture thereby avoiding the bulky nature of conventional control systems.

As previously indicated in the impregnation method the material to be impregnated is immersed in treatment chemical and it is desirable for most if not all of it to be covered. This enables the bulk of the treatment chemical to occupy most of the main treatment chamber and minimizes the time taken to achieve the subsequent evacuation and filling steps.

The autoclave is usually pressurized by use of a pump applied to the treatment chemical. Typically pressure impregnation is carried out at between 1200 and 1500 kpa, more preferably about 1380 kpa, for periods of two to three hours.

The removal of treatment chemical after impregnation can be accelerated by maintaining the pressure upon the autoclave and opening an outlet in the main treatment chamber. Preferable the main treatment chamber is then again evacuated of air which withdraws excess treatment chemical from the material. Further the main treatment chamber can be pressurized before and/or after this subsequent evacuation to remove remaining amounts of treatment chemical from the chamber.

As mentioned the control system is particularly suited to use in this method as it can be easily changed from the evacuation mode to the pressurized mode to remove _t- the remainder of the treatment chemical from the main treatment chamber.

The various aspects of the invention is now illustrated with reference to the accompanying drawings in which: _ιn Figure 1 is a control system for a vacuum pump in an evacuation position.

Figure 2 is a control system for a vacuum pump in a pressurized position.

Figure 3 is a chemical dosing chart. ₁₅ Figure 4 is a partial flow diagram of the impregnation system according to one aspect of the invention.

Figure 5 is a further partial flow diagram of the impregnation system used in Figure 4. __n Figure 6 is a partial flow diagram of the chemical supply used in Figure 4.

Figure 7 is a sequential illustration of the method according to the invention.

As shown in Figures 1 and 2, the control system __ comprises a housing 10, including three chambers being silencer chamber 11, positive chamber 12 and negative chamber 13. The positive chamber is provided with an inspection hatch which allows easy checking and maintenance of the valve system discussed below.

30 Pipe 14 extends externally of the housing 10 to a source of negative pressure - and extends through the silencer chamber 11 and positive chamber 12 into negative chamber 13. Pipe 15 extends from outside housing 10 into the silencer chamber 11. Pipe 16 is connected externally of

35 the housing 10 to a source of positive pressure + and extends through the silencer chamber 11 into the positive chamber 12. Pipe 17 is externally connected to a chamber (not shown) which is to be evacuated or alternately positively pressurized. It extends through the silencer chamber 11 into the positive chamber 12 and is sealingly connected to a valve 20. Pipe 18 extends from the silencer chamber 11 into the positive chamber 12 and is sealingly connected to a valve 22 which valve 22 is also sealingly connected to valve 20. Pipe 28 extends from negative chamber 13 into the positive chamber 12 and also connects with valve 20. Pipe 19 extends between silencer chamber 11 and negative chamber 13. Interposed in pipe 19 is valve 21. Valve 20, 21 and 22 are each provided with arms 24, 26 and 25 respectively. Linkage 27 connects arms 24, 26 and 25. Arm 25 extends either side of valve 22 and is connected at one end to an accuation piston 23, that end being distant and on the opposite side of the valve 22 to the connection between linkage 27 and arm 25.

Positive chamber 12 has a drain pipe 31 which extends from the positive chamber 12 through negative chamber 13 and vents externally of housing 10.

The control system operates as follows:- As indicated. Figure 1 depicts the flow of air from a evacuation chamber (not shown). In particular, as pipe 14 is connected externally of housing 10 to a source of negative pressure, it draws air from negative chamber 13. The drop in pressure in negative chamber 13 causes suction upon pipes 28 and 27. Valve 21 is closed preventing air to be drawn from the silencer chamber 11. Valve 20 is open allowing air to be drawn from pipe 17 through valve 20 into pipe 28. Valve 22 is in the closed position preventing air to be drawn through valve 22 either from the positive chamber 12 or pipe 18. Accordingly, air is drawn from the evacuation chamber (not shown) through pipe 17 via valve 20 into pipe 28. Pipe 28 channels the air into negative chamber 13 and the air is subsequently removed from negative chamber 13 via pipe 14 to the source of negative pressure

The source of positive pressure + is not discontinued during the evacuation operation. Air is forced under pressure through pipe 16 and expelled into the positive chamber 12. Whilst valve 22 is closed to prevent air being sucked from the positive chamber 12 into valve 20, it nevertheless permits air from the positive chamber 12 to

_ enter valve 22 and pass into pipe 18. The air in pipe 18 is b expelled into the silencer chamber 11 and vented to the atmosphere via pipe 15. As mentioned valve 22 in pipe 19 is closed thus preventing air passing therethrough into the negative chamber 13.

Figure 2 depicts the control system effecting 0 pressurization to the evacuation chamber (not shown). Pressurized air + enters pipe 16 and is discharged into positive chamber 12. Valve 22 is open permitting air to flow into valve 20 which is also open to divert the air into pipe 17. Valve 22 prevents air entering pipe 18. Valve 20 5 prevents air entering pipe 28. The pressurized air in pipe 17 expels into the evacuation chamber (not shown) .

During this operation, the source of negative pressure is still maintained usable by opening valve 21. Atmospheric air is-drawn down pipe 15 into silencer chamber 0 11 and withdrawn through pipe 19 via valve 21 into the negative chamber 13. This air is, in turn, drawn up pipe 14 towards the source of negative pressure.

The positioning of the valves 20, 21 and 22 are achieved by actuating piston 23 which moves the valves via 5 arms 24, 25 and 26 and linkage 27.

It has been found that in the pressurization mode, air has a high moisture content which is substantially deposited in the positive chamber 12 prior to its entry in valve 22. Should excess liquid accumulate in the positive 0 chamber 12, float 29 will lift removing plug 30 from one end of drain pipe 31. This liquid flows down drain pipe 31 until the level of float 29 relocates plug 30 in drain pipe 31.

In this control system, all air necessarily passes 5 through or into the silencer chamber 11. This chamber reduces the noise normally associated with such operation thus meeting regulatory noise restraints.

The control system described herein enables the vacuum pump to be alternatively operated in a simple manner.

The system is very compact whilst still maintaining ease of _c service and low capital outlay compared with conventional systems.

Figures 4, 5 and 6 are partial flow diagrams which together illustrate the apparatus according to one aspect of the invention. 0 When utilizing this apparatus it is necessary to carry out an initial moisture content test upon the wood to be treated. In Figure 3 a dosing chart is reproduced from which the concentration of chemical may be selected. The chart plots percentage moisture against concentration of treatment chemical (litres per cubic meter of material) and type of wood. In this respect:

Type of Wood A,B,C, - High Density

D,E,F,G,H . - Moderate Density

I,J,K,L,M,N - Medium Density^'

0,P,Q,R - Low Density

As shown in Figures 4, 5 and 6, autoclave 32 comprises a treatment chamber 33 and an upper chamber 34. Treatment chemical 35 is fed to treatment 33 from supply tanks A, B and C Supply tank A is a work tank into which recycled used chemical 36 is passed after engaging a treatment filter 43. Tank B is a bulk concentrated chemical supply whilst tank C is a bulk water supply.

Once the concentration of treatment chemical 35 has initially been selected from the chart illustrated in Figure 3, the outlet of tanks A, B and C are set to ensure correct formulation. The amount of concentrated chemical released into conduit 37 is closely controlled by sensor 55 located in conduit 37 which regulates control valve 38 in dependence up monitoring of treatment chemical formulation by sensor 55. Swing check valves 40 and 41 are associated with tanks A and C respectively to prevent back flow of chemical.

Interposed in conduit 37 is a pneumatic valve 42 which can selectively close the conduit. Similarly check valves 44 and 45 are located in conduits 46 and 37 to allow recycling of used chemical 36. Sensor 47 senses the presence of treatment chemical.

As indicated upper chamber 34 is sealingly attached to treatment chamber 33. A level sensor 50 is situated in treatment chamber 33 at a level above the upper level of the material to be treated (not shown) . Connected to upper chamber 34 are conduits 48 and 47. Conduit 48 can selectively pressurize upper chamber 34 and treatment chamber 33. This pressurization is achieved by the use of vacuum pump apparatus 51. Conduit 49 can selectively evacuate upper chamber 34 and treatment chamber 33 again using vacuum pump apparatus 51. As noise is generated in generating the vacuum or pressure silencers and filters 52 are utilized.

A pressure relief valve 53 is incorporated between conduit 48 and the vacuum pump 51 for safety reasons.

Pressure pump 54 is located in conduit 37 and is operable to pressurize the treatment chemical 35 flowing into treatment chamber 33 and pressurize the autoclave 32.

The method of operation of the apparatus is as follows and is also explained in conjunction with Figure 7.

The autoclave 32 is initially in the empty condition AA. Wood 55 is tested for moisture and an appropriate amount of concentrated chemical is selected. Wood 55 is then placed into the treatment chamber 33 and sealed therein (condition BB). Sensor 55 regulates control valve 38 to allow and maintain the predetermined amount of concentrated chemical to enter conduit 37 in combination with amounts from tanks A and C Treatment chemical 35 is pumped into treatment chamber 33 and prevented from flowing into conduit 46 by check valve 44.

The treatment chemical 35 fills treatment chamber 33 until level sensor 50 senses it at which time valve 42 is closed (condition CC). Conduit 48 is closed and conduit 49 evacuates the air from the autoclave (condition DD). Valve 42 is reopened which floods the autoclave up^' to the level of conduit 48 (condition EE). _c Pressure pump 54 is operated to pressurize the autoclave 32 for a predetermined period (condition FF.) Pump 54 ceases operation, valve 45 closes conduit 37 and used treatment chemical 36 is blown from the treatment chamber (condition GG) into conduit 46 for treatment in 0 filter 43 and recirculation to tank A.

Conduit 48 is closed and conduit 49 opened to apply a vacuum and withdraw excess treatment chemical from the face of the material which accumulates in the lower portion of the main treatment chamber 33 (condition HH). Conduit 49 is closed and conduit 48 opened to apply air into and pressurize upper chamber 34 and treatment chamber 33 (condition HH) . Valve 42 is open to permit residual used treatment chemical 36 to be blown from the treatment chamber 33 (condition II) .

Thereafter the autoclave 32 is opened and the treated wood removed.

The system and apparatus of the invention permit operation of the impregnation plant at close to ideal conditions. The modified autoclave gives an effective evacuation of the main chamber allowing an improved impregnation of the material. Accordingly the invention achieves greater impregnation with short treatment times than previously known. Treatment costs are therefore reduced.

The system also monitors the strength of the treating solution to an accuracy of + or - 0.1%. This far exceeds current specific gravity meters, thus enabling more accurate retention of treatment chemical at a large saving in cost, as the chemical solution is sampled condtinuously and automatically. As it enters the autoclave, flow control valves vary the solution strength to maintain this accuracy, thus eliminating hand mixing and adjusting AFTER the chemical has entered the autoclave.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: ϊ„. Apparatus for vacuum-pressure impregnating material comprising:

(a) an autoclave having a main treatment chamber to receive material to be impregnated with treatment chemical and an upper chamber communicating with the main treatment chamber,

(b) pump means to urge treatment chemical into the main treatment chamber,

(c) sensing means located in an upper portion of the main treatment chamber to sense when treatment chemical has filled the main treatment chamber to a predetermined level and provide an output signal,

(d) evacuation means responsive to the output signal to evacuate air remaining in the main treatment chamber, the pump means urging treatment chemical into the main treatment chamber until the main treatment chamber is full and the upper chamber is filled to a predetermined level,

(e) valve means in the upper chamber sealing the main treatment chamber and upper chamber against ingress of air,

(f) pressure means to apply pressure to the main treatment chamber thereby impregnating the material with treatment chemical,

(g) timer means regulating operation of the evacuation means and pressure means, and

(h) withdrawal means to remove treatment chemical from the main treatment chamber.
2. Apparatus according to claim 1 wherein the main treatment chamber is generally cylindrical with hemispherical ends.
3. Apparatus according to any one of claims 1 or 2 wherein the upper chamber is an open based cone or a frusto-cone.
4. Apparatus according to any one of claims 1 to 3 wherein the upper chamber is in sealed connection about an opening- in' the main, treatment chamber.
5. Apparatus according to any one of claims 1 to 4 wherein the pump means is inoperable when the evacuation means is operable.
6. Apparatus according to any one Of claims 1 to 5 wherein the withdrawal means includes means to open an outlet in the main treatment chamber to allow escape of treatment chemical.
7. Apparatus according to claim 6 wherein the withdrawal means also includes evacuation means to evacuate the treatment chamber of air and withdraw excess treatment chemical from the material.
8. . Apparatus according to either claims 6 or 7 wherein the withdrawal ^'means also includes air imput means to introduce air into the main treatment chamber to force treatment chemical through the outlet.
•9. Apparatus according to claim 8 wherein the air imput means and evacuation means are a vacuum pump.
10. Apparatus according to claim 9 wherein the vacuum pump is controlled by a control system comprising:

(a) a first chamber to be positively pressurized comprising an inlet and a first and second outlet;

(b) a second chamber to be negatively pressurized comprising a first and second inlet and an outlet;

(c) regulation means including

(i) a first valve means associated with the first outlet of the first chamber and the first inlet of the second chamber, to close either the first outlet or first inlet and open the other; (ii) a second valve means to open or close the second outlet of the first chamber; and (iii)a third valve means to open or close the second inlet of the second chamber; and (d) (i) (a)- open the first outlet of the first chambe ;

(b) close the second outlet of the first chamber;

(c) close the first inlet of the second chamber

(d) open the second inlet of the second chamber; and

(ii) (a) open the first inlet of the second chamber;

(b) close the second inlet of the second chamber;

(c) close the first outlet of the first chamber .

(d) open the second outlet of the first chamber.
11. Apparatus according to claim 10 wherein the first chamber is located atop of the second chamber.
12. Apparatus according to claim 10 wherein the second chamber is located atop the first chamber.
13. Apparatus according to any one of claims 10 to 12 additional comprising a silencer chamber.
14. Apparatus according to any one of claims 10 to 13 wherein the regulation means is located in either or both the first chamber or second chamber.
15. Apparatus according to any one of claims 10 to 14 wherein the first valve means comprises a first butterfly valve actuated by a first lever.
16. Apparatus according to any one of claims 10 to 15 wherein the second valve means comprises a second butterfly valve actuated by^' a second lever.
17. Apparatus according to any one of claims 10 to 16 wherein the third valve means comprises a third butterfly valve actuated by a third lever.
18. Apparatus according to any one of claims 15 to 17 wherein the control means comprises the first, second and third levers interconnected by a linkage.
19. Apparatus according to claim 18 wherein the control system additional comprises a remotely actuated piston connected to one of the first, second or third lever.
20. Apparatus according to any one of claims 10 to 19 wherein the first chamber includes means to remove any

^'liquid accumulating therein.
21. A control system for a vacuum pump comprising:

(a) a first chamber to be positively pressurized comprising an inlet and a first and second outlet;

(b) a second chamber to be negatively pressurized comprising a first and second inlet and an outlet;

(c) regulation means including

(i) a first valve means associated with the first outlet of the first chamber and the first inlet of the. second chamber, to close either the first outlet or first inlet and open the other;

(ii) a second valve means to open or close the second outlet of the first chamber; and

(iii)a third valve means to open or close the second inlet of the second chamber; and (d) (i) (a) open the first outlet of the first chamber;

(b) close the second outlet of the first chamber;

(c) close the first inlet of the second chamber;

(d) open the second inlet of the second chamber; and

(ii) (a) open the first inlet of the second chamber;

(b) close the second inlet of the second chamber;

(c) close the first outlet of the first chambe ;

(d) open the second outlet of the first chamber.
22. A control system according to claim 21 wherein the first chamber is located atop of the second chamber.
23. A control system according to claim 21 wherein the second chamber is located atop the first chamber.
24. A control system according to any one of claims 21 to 23 additional comprising a silencer chamber.
25. A control system according to any one of claims 21 to 24 wherein the regulation means is located in either or both the first chamber or second chamber.
26. A control system according to any one of claims 21 to 25 wherein the first valve means comprises a first butterfly valve actuated by a first lever.
27. A control system according to any one of claims 21 to 26 wherein the second valve means^' comprises a second butterfly valve actuated by a second lever.
28. A control system according to any one of claims 21 to 27 wherein the third valve means comprises a third butterfly valve actuated by a third lever.
29. A control system according to any one of claims 26 to 28 wherein the control means comprises the first, second and third levers interconnected by a linkage.
30. A control system according to claim 29 wherein the control system additional comprises a remotely actuated piston connected to one of the first, second or third lever.
31. A control system according to any one of claims 21 to 30 wherein the first chamber includes means to remove any liquid accumulating therein.
32. A method of vacuum-pressure impregnating material comprising the steps of:

(a) locating the material in a main treatment chamber of an autoclave, the autoclave also including an upper chamber communicating with the main treatment chamber,

(b) partially filling the main chamber with treatment chemical to a first level at which the material is immersed,

(c) applying a vacuum to the autoclave for a first predetermined period of time to remove air from the main treatment chamber and upper chamber,

(d) filling the main treatment chamber totally and the upper chamber to a second level with treatment chemical,

(e) applying pressure to the main treatment chamber for a second predetermined period thereby impregnating the material with treatment chemical, and

(f) relieving the pressure from the main treatment chamber and emptying the main chamber of treatment chemical.
33. A method according to claim 32 including the additional step (g) applying a vacuum to the autoclave for a third period of time to remove excess treatment chemical from the material.
34. The method of either claims 32 or 33 wherein the material is cellulose.
35. The method of either claims 32 or 33 wherein the material is wood or wood composites including chip board and paper waste.
36. The method according to any one of claims 32 to 35 wherein the material is substantially immersed in the treatment chemical prior to the application of the vacuum.
37. The method according to any one of claims 32 to 35 wherein the material is totally immersed in the treatment chemical prior to the application of the vacuum.
38. The method according to any one of claims 32 to 37 wherein the pressure applied is from 1200 to 1500 kpa.
39. The method according to claim 38, wherein the pressure applied is about 1380 kpa.
40. The method according to any one of claims 38 and 39 wherein the pressure is applied for between two to three hours.
41. The method according to any one of claims 32 to 40 wherein the pressure is relieved from the main treatment chamber by withdrawal of treatment chemical.
42. The method according to any one of claims 32 to 40 wherein the main treatment chamber is emptied by introducing air under pressure to the main treatment chamber thereby forcing treatment chemical through an outlet in the main treatment chamber.
43. The method according to either claims 41 or 42 wherein the treatment chemical is treated and recycled for use in the autoclave.
44. The apparatus according to any one of claims 1 to 31 when used to carry out the method according to any one of claims 32 to 43.