Process and Design Modifications to Retrofit a Conventional Wood Plant

Abstract

A transformation of an existing, conventional southern yellow pine (SYP) lumber pressure treatment plant that previously impregnated wood with non-sustainable chemicals, to using environmentally friendly sodium silicate formulations. The transformation may include adding heated storage tanks for solutions of siliceous solutions and adding a heater to an existing storage tank, installing delivery lines capable of handling high pH, viscous solutions between at least the pre-existing vacuum pressure impregnation tank and the added or existing heated storage tank, a CO.sub.2 storage tank with associated vaporizer and a CO.sub.2 recovery system, associated lines to and from the pre-existing vacuum pressure impregnation tank and the CO.sub.2 storage tank and the CO.sub.2 recovery system, pumps for circulating the solutions, and a thermal management system including: insulation and cladding on one or more of the tanks and lines, heat tracing on all level indicators; and insertion of heating coils in working tanks.

Claims

1. A method of upgrading a lumber vacuum-pressure impregnation process plant having a pre-existing vacuum pressure impregnation tank, feed lines, an original vacuum pump, and a lumber transport system, comprising: at least one of adding heated storage tanks for solutions of siliceous solutions and adding a heater to an existing storage tank; installing delivery lines capable of handling high pH, viscous solutions between at least the pre-existing vacuum pressure impregnation tank and the added or an existing heated storage tank; installing a CO.sub.2 storage tank with associated vaporizer and a CO.sub.2 recovery system; installing associated lines to and from the pre-existing vacuum pressure impregnation tank and the CO.sub.2 storage tank and the CO.sub.2 recovery system; installing pumps for circulating the solutions; and installing a thermal management system comprising: insulation and cladding on one or more of the tanks and lines; heat tracing on all level indicators; and insertion of heating coils in working tanks.

2. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing a second vacuum pressure impregnation tank and associated feed lines.

3. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 2, further comprising: upgrading or replacing, the pre-existing vacuum-pressure impregnation tank for the impregnation process for silicate impregnated wood.

4. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing an in-line kiln for drying silicate impregnated wood.

5. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing an in-line machine stress measurement system that quantifies silicate uptake.

6. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing a hyper-spectral analyzer, an x-ray analyzer, or acoustic analyzer system for wood morphology analysis.

7. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing a natural frequency measurement system configured to quantify silicate uptake.

8. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing a multi-input solution dispensing system prior to feed lines into the vacuum pressure impregnation tank wherein the multi-input solution dispensing system is configured for formulation control, quantification, and delivering two or more impregnation charges.

9. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing a delivery system configured to dispense aqueous solutions of high, neutral, and low pH solutions before and after impregnation steps.

10. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing an immersion delivery system configured to dispense aqueous solutions of high, neutral, and low pH solutions before and after impregnation steps.

11. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, wherein at least one of the solutions is a high pH viscous solution.

12. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 6, wherein the hyper-spectral analyzer system for wood morphology analysis is arranged for use before and after impregnation.

13. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing an autoclave configured to handle the siliceous solution pressurized to at least 190 psi.

14. The method of upgrading the lumber vacuum-pressure impregnation process plant in claim 1, further comprising: installing software for a controller configured to track, record, and analyze process variables for sodium silicate solutions, wherein the process variables include one or more of solution temperature, autoclave pressure, amounts of solution utilized, storage tanks temperatures, treatment autoclave temperatures, and duration of each stage of the process.

15. A plant to perform a lumber vacuum-pressure impregnation process, comprising: timber handling equipment configured to transport timber from a receiving area to a plurality of stations, wherein the stations comprise: a first vacuum pressure impregnation tank that is coupled to a first heated storage tank, a first blend tank, a first vacuum source, and delivery lines configured to handle high pH, viscous solutions between at least the first vacuum pressure impregnation tank and the heated storage tank; at least one storage area; a second vacuum pressure impregnation vessel that is coupled to a second heated storage tank, a second blend tank, a second vacuum source, and delivery lines configured to handle high pH, viscous solutions between at least the first vacuum pressure impregnation tank and the heated storage tank; at least one CO.sub.2 storage tank with an associated vaporizer and a CO.sub.2 recovery system coupled to at least the first and second vacuum impregnation vessels; at least one kiln; at least labelling station; at least one packing station; and at least on shipping station; a thermal management system comprising: insulation and cladding on one or more of the vessels, tanks, and lines; and heat tracing sensors; and pumps configured to circulate solutions.

16. The plant to perform a lumber vacuum-pressure impregnation process of claim 15, further comprising: an autoclave configured to handle a siliceous solution pressurized to at least 190 psi.

17. The plant to perform a lumber vacuum-pressure impregnation process of claim 15, further comprising: a controller configured to track, record, and analyze process variables for sodium silicate solutions, wherein the process variables include one or more of solution temperature, autoclave pressure, amounts of solution utilized, storage tanks temperatures, treatment autoclave temperatures, and duration of each stage of the process.

18. The plant to perform a lumber vacuum-pressure impregnation process of claim 17, wherein the controller is a programmable logic controller.

Description

BRIEF DESCRIPTION OF FIGURES

[0031] The invention will be described in more detail on the basis of an exemplary embodiment. In the figures:

[0032] FIG. 1 is a flow chart showing an exemplary implementation of a wood treatment process;

[0033] FIG. 2 is a schematic layout for a transformed lumber processing plant for the wood modification process of FIG. 1;

[0034] FIG. 3 is a schematic layout for an existing lumber processing plant;

[0035] FIG. 4 is an exemplary agitator;

[0036] FIGS. 5A and 5B show a tank with an agitator; and

[0037] FIG. 6 is a flowchart for transforming a treatment plant.

DETAILED DESCRIPTION OF THE FIGURES

[0038] A transformed southern pine wood pressure treatment plant uses a non-toxic and environmentally sustainable process for modifying wood using sodium silicate formulations or other environmentally friendly formulations. An exemplary implementation of the treatment process is shown in FIG. 1. The impregnation liquid is prepared by mixing a silicate mix with water in a feed tank. Optionally, boric acid, sodium borate, sodium hydroxide or other impregnation efficiency inducing compounds including surface acting agents may be added to this feed tank. The last solution preparation can include multiple additives for treatment. The mixture can be pumped to a working tank for heating and agitation. Once a size of lumber is selected, the untreated lumber is placed in an impregnation vessel/autoclave. The autoclave is placed under vacuum and then the liquid mixture from the working tank is added to the impregnation vessel/autoclave. Once the liquid mixture is added, pressure is applied to the autoclave. Next, pressure is reduced and the impregnation vessel/autoclave is placed under vacuum. Optionally, a second impregnation step is included that involves addition of a second, typically higher concentration of impregnating solution to the autoclave. After the impregnation vessel/autoclave is placed under vacuum, gaseous carbon dioxide from carbon dioxide processing apparatus is introduced into the impregnation vessel/autoclave. Next, the treated lumber is removed from the impregnation vessel/autoclave.

[0039] According to one aspect on the invention, certain quality control testing is performed to evaluate the treatment process. These processes are developed and customized to know if the impregnation has been successful. The treated lumber is then heated and dried using a conventional sawmill kiln.

[0040] According to one aspect of the invention, a second impregnation process is performed. This second impregnation can be performed in the same equipment or using additional processing equipment. The once-treated lumber is loaded into the pressure vessel where it undergoes vacuum, pressure, and vacuum cycles. The lumber is then dried a second time.

[0041] A surface cleaning is performed on the treated lumber. Next, the treated lumber can undergo a quality control analysis. The treated lumber is then stamped, bundled, and packaged for shipping.

[0042] To perform the impregnation process above, an existing, conventional southern pine (SYP) lumber pressure treatment plant has to be modified. A conventional lumber pressure treatment plant typically includes a lumber infeed chain, a chemical storage system, a water storage system, a treatment chemical blending tank, a feed product tank, an autoclave where the lumber impregnation takes place, and a drip tray for product draining.

[0043] Preferably, the conventional equipment for the conventional treatment process is used for the upgrades and modifications. Alternatively, the conventional equipment can be replaced.

[0044] A large product delivery tanker offloading station, with associated piping is added. The new or existing chemical storage tank(s) are insulated with insulating material and cladded with a protective material. Insulation and cladding is also added to the feed line(s) between the storage tank and the blending tank, to the blending tank, and to the product feed line(s) to and from the working tank and to and from the autoclave.

[0045] According to one aspect of the invention, to heat the product a heating coil is installed in each of the working tanks. The heating coils are preferably horizontal coils inserted in the vessels. Heat tracing of the level indicators are added or upgraded for each of the working tanks, the blending tank, the autoclave, and the chemical feed tank. The change or addition of the heat tracing components is a precaution because typical level indicators are magnetic float indicators, which would be impacted by the higher viscosity chemical solution.

[0046] According to one aspect of the invention, an updated tote system for adding specialty chemicals to the main blending tank is installed. Totes are large plastic containers that hold liquids. In operation, a feedline is inserted into a tote and the liquid pumped out of the tote. Furthermore, a digitally controlled chemical feeder system can be installed and used to accomplish the specialty chemicals blending more precisely and efficiently.

[0047] The pumps and filters in the conventional plant are also upgraded. The pumps circulate treatment solution between storage tanks and treatment vessels as well as circulate treatment solution within the tanks and vessels. The enhanced pump is configured to pump the higher viscosity chemical solution to the working tanks. The pumps preferably use a filter sock type filter. According to one aspect of the invention, the filter medium is a 200 micron sock.

[0048] A carbon dioxide storage tank and associated vaporizer are installed, with a feed and return line to the autoclave. In addition, one or more double plug block valves with actuators are installed in these two lines.

[0049] According to one aspect of the invention, the piping in the conventional factory is rerouted to allow unimpeded flow of the higher viscosity silicate solutions. This re-routing may vary depending on the specific design of the existing plant, but should have as a priority removing flow constrictions, introducing unnecessary turbulence, and be as direct as possible.

[0050] The existing plant piping preferably remains intact, but changes are made to the working tank filter and pump system as noted above. In addition, all piping is insulated and clad to keep heat losses to a minimum to accommodate the operating temperatures of 50 C. to 100 C.

[0051] Agitation equipment is installed in the product working tanks. An exemplary agitator is shown in FIG. 4. The agitator comprises a motor 1, gearbox 2, seal assembly 3,4, drive shaft 5, and impeller 6. The impeller is driven clockwise as shown. FIGS. 5A and 5B show a tank with the agitator installed. Preferably, the agitators are large, paddle type agitators that provide a homogenous chemical product mix. The agitation and pump recirculation system provides a well-mixed formulation for the impregnation step.

[0052] To maintain the operating temperatures, heating coils are added as well as insulation and cladding, as discussed above. The heating coils maintain the chemical mixture, referred to as the product, at a temperature of approx. 50-95 C. While some steps in the impregnation systems may use chemicals at room temperature, the steps that require heated chemicals are more energy efficient when thermal insulation is provided, thus providing more consistent process results, and reduce product material losses.

[0053] Carbon dioxide gas is used in the process for the precipitation of the chemical added to the wood, through the lowering of the pH. Therefore, a CO.sub.2 gas storage delivery and recovery system is installed. A liquid carbon dioxide storage vessel is installed, along with the requisite vaporizer. A two inch piping system is installed and fed into a rear top area of the autoclave as well as a return vent line.

[0054] According to one aspect of the invention, upgrades to the plant programmable logic controller (PLC) system are also installed. The existing PLC control system can be used but must be upgraded with logic changes and the addition of the new control loops, as well as appropriate software upgrades. The upgrades are provided at least in part in the temperature indication and control system. This upgrade is important for steady state operation where multiple impregnation cycles are taking place. The addition of fresh chemicals to the process on an ongoing basis requires a fast heater response and this logic is provided by the upgraded PLC.

[0055] According to one aspect of the invention software is added to the Programmable Logic Controller (PLC) system to function in conjunction with digital and mechanical recording devices programmed to track, record, and analyze the key process variables in real time. The process variables include solution temperature, autoclave pressure, amounts of solution utilized, storage tanks and treatment autoclave temperatures, duration of each stage of the process and correlations between these variables. The collected data can be used to further optimize the process.

[0056] In a conventional treatment process, the lumber is stacked in packets with one layer on top another. For the modified plant and process kiln strips are inserted prior to the treatment process. The kiln strips achieve two objectives. First, the kiln strips ensure that the lumber is well impregnated by providing space between layers. Second, the kiln strips allow the product to be kiln dried to reach the KD19 standard (Kiln-Dried to 19% moisture content).

[0057] This modified process using kiln strips comprises receiving wood, inserting kiln strips, strapping lumber packets, performing a one or two step impregnation operation, kiln drying the material, breaking down the packets and removing the kiln strips, and preparing final lumber packets for dispatch.

[0058] FIG. 2 is a schematic process layout for a transformed wood processing plant for the wood treatment process of FIG. 1. The wood processing plant has a timber receiving section 210, which may be the same or different than the storage and shipping area 290. The transformed wood processing plant includes one, two, or more vacuum pressure impregnation vessels 220, 240. If space permits, two or more vacuum pressure impregnation vessels 220, 240 are installed.

[0059] The first pressure impregnation vessel 220 is coupled to a silicate storage vessel 222 via a blend tank 224. There is also a vacuum source 226 and carbon dioxide storage 228 coupled to the first pressure impregnation vessel 220. A storage and acclimation area 230 is provided for the lumber that is processed in the first pressure impregnation vessel 220.

[0060] The second pressure impregnation vessel 240 is coupled to a silicate storage vessel 242 via a blend tank 244. There is also a vacuum source 246 and carbon dioxide storage 248 coupled to the first pressure impregnation vessel 240. It should be noted that the vacuum source 226 can be the same as the vacuum source 246. Further, the carbon dioxide storage 228 can be the same as the carbon dioxide storage 248. Piping can be provided so that only a single vacuum source and/or carbon dioxide storage is required.

[0061] A storage for kiln drying 250 is provided for the kiln 260 in which the processed lumber is dried. Tilt hoist 270 is used to lift and tilt the lumber. A label and packaging station 280 is provided as well as a storage area 290 for shipping. As previously mentioned, the storage area 290 can be the same or different than the timber receiving area 210.

[0062] FIG. 6 is an overview of the steps to transform and/or update a treatment plant. The steps can be performed in any order but are presented in accordance with one aspect of the invention. At step 110, heated storage tanks for solutions of siliceous solutions are added and/or a heater is added to an existing storage tank. Delivery lines capable of handling high ph, viscous solutions are installed between at least the pre-existing vacuum pressure impregnation tank and the added or existing heated storage tanks at step 120. At step 130, a CO.sub.2 storage tank with associated vaporizer and a CO.sub.2 recovery system is added. At step 140, associated lines to and from the pre-existing vacuum pressure impregnation tank and the CO.sub.2 storage tank and the CO.sub.2 recovery system are installed. Pumps are then installed for circulating the solutions at step 150. Finally, at step 160, a thermal management system is installed that includes one or more of: insulation and cladding on one or more of the tanks and lines, heat tracing on all level indicators; and insertion of heating coils in working tanks.

[0063] Thus, while there have been shown, described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps that perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.