Patent Application
20230405866
This present disclosure relates to transforming an existing, conventional southern pine (SYP) wood pressure treatment plant that previously impregnated wood with non-sustainable chemicals, such as CA (copper azole), CCA (chromated copper arsenate), and ACQ (alkaline copper quaternary) into a plant to treat wood with environmentally friendly sodium silicate formulations or other sustainable formulations. Wood means dimensional lumber, plywood, engineered wood such as LVL (laminated veneer lumber), OSB (oriented strand board) and mass timber, including CLT (cross laminated timber), and related products.
Wood is one of the oldest building materials used in human civilization due to its strength, availability, and performance characteristics. Despite these characteristics, wood suffers if exposed to prolonged wet conditions and due to its poor resistance to insect, fungal, and other biological attacks. As a result of this susceptibility, treatments are applied to wood to improve its durability to insects, fire retardancy, and environment conditions. These treatments have traditionally been in the form of metal or other environmentally unfriendly chemicals, such as CA (copper azole), CCA (chromated copper arsenate), and ACQ (alkaline copper quaternary), and in the case of fire retardancy enhancements, OPFR (organophosphorus flame retardants), and chemicals such as ammonium phosphate and ammonium borate.
Plywood is processed in a similar manner in which plywood panels in bundles would flow on conveyors or moved by fork lifts to an autoclave. After processing in the autoclave, the plywood is transferred to a drying kiln, and then to labeling, packaging, and shipping.
The process of impregnating non-sustainable chemicals such as chromated copper arsenate is a standard practice in the wood industry. The chemical formulations are fluids that are low in viscosity and readily absorbed into the wood and, as such, the manufacturing process used for them requires a less demanding application process than the process applications describe below for sodium silicate (Na2O)x·SiO2 and related metal silicate based solutions. Thus, to adjust an existing wood processing plant reactor to the demands of sodium silicate solutions requires processing equipment that can handle a polar, caustic, aqueous solution that may possess some non-Newtonian characteristics to impregnate the wood. A further distinction in the sustainable process using sodium silicate is that the sodium silicate must be cured to form a cohesive solid and this is accomplished by CO2 delivery to lower the pH of the impregnated solution, or another suitable method, to below about 9.
There is a need to transform an existing lumber pressure treatment plant to a cost-efficient, environmentally-friendly, i.e. all-green plant for treating wood that can eliminate toxic chemicals and provide enhancing strength properties, increased fire resistance ratings that meet or exceed current international and domestic recognized building and building materials standards, while maintaining other desirable properties such as resistance to rot, bacteria, and insects while also providing other desired properties without using toxic chemicals. The transformed lumber treatment plant is capable of treating wood according to the methods disclosed in U.S. Patent Publication 2021/0170623 entitled Green Process for Modifying Wood, the content of which is incorporated by reference.
The method for processing timber begins with the insertion of kiln strips into lumber packets. Alternatively, the method is performed without inserting kiln strips in the lumber packets. Next, the lumber packets are strapped and, then the impregnation process can begin in the autoclave. Once the lumber is inserted into the autoclave, the autoclave is placed under vacuum. According to one aspect of the invention, the vacuum is −28 to −30 psi for about 30 minutes. Other vacuums can be drawn between −15 psi and −50 psi. The process chemicals disclosed in the aforementioned patent publication are next inserted into the autoclave for a requisite time at an elevated pressure and elevated temperature. Next a vacuum is again drawn on the wood in the autoclave, which is then filled with carbon dioxide and allowed to remain under pressure for periods of time ranging from 20 minutes to 24 hours. The reactor is unheated. However, the silicate solution is preheated to 60-70° C., although a broader temperature range between 50-80° C. can be used. The solution once introduced is then pressurized at 190 psi for 90 min, followed by vacuum at −28 psi for about 5 minutes, completing with pressurization to 50 psi for 20-30 min. While these ranges are exemplary, a broader range is conceivable. The carbon dioxide is then removed by, again, placing the autoclave under vacuum. Once the vacuum is released, the lumber is removed from the autoclave and allowed to dry for 24 to 48 hours. The lumber is then reinserted into the autoclave. A vacuum is drawn and the process chemicals are injected into the autoclave for a second time at elevated pressure and elevated temperature. The chemicals are then removed by drawing a vacuum on the autoclave, and may be followed by a second treatment with CO2 or alternatively removed from the autoclave and kiln dried at about 50° C. for a period of five to seven days. It should be noted that the temperature and cycle times may vary depending on environment conditions, load sizes, wood sizes, at the time of drying. After drying, the kiln strips are removed and the lumber is brushed and stamped. The brushed and stamped lumber is then ready for sale to market.
This disclosure presents a cost-effective solution to transform or repurpose existing lumber processing plants by making novel technical changes to pre-existing plants. Not only is this cost effective, but once the reactors have been thoroughly cleaned and modified, a potentially hazardous waste condition at existing plants can be eliminated.
The wood pressure treatment plant is configured to perform a wood vacuum-pressure impregnation process. The plant to be modified has a pre-existing vacuum pressure impregnation tank, feed lines, vacuum pump(s), and a wood transport system. At least the following additions and modifications are made to the existing plant for non-toxic and environmentally sustainable processing:
According to one aspect of the invention, a process control information system is installed that is configured to manage, monitor, and record the wood vacuum pressure impregnation process and other related processes. The process control information system is further configured to optimize key performance indicators including, silicate solution temperatures, autoclave pressures, and vacuum, pressurization and carbon dioxide cycles durations.
According to one aspect of the invention, software is added to an existing or upgraded Programmable Logic Controller (PLC) system to function in conjunction with digital and mechanical recording devices to track, record, and analyze the process variables in real time for sodium silicate solutions. 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 software provides the collected data that can be used to further optimize the process.
The sodium silicate solutions require processing equipment that can handle a polar, caustic, aqueous solution that may possess some non-Newtonian characteristics to impregnate the wood.
According to one aspect of the invention, the pH of the silicate solution is typically between 10-12.
According to one aspect of the invention, the insulation, which is the material that prevents heat loss and serves as the actual thermal insulator, is typically fiberglass, and the cladding is a protective coating over the insulator, typically a corrugated metal.
According to one aspect of the invention, the components are added so that a two-step impregnation process can be performed.
According to one aspect of the invention, one or more kilns are installed that are in-line kilns for drying the silicate impregnated wood.
According to one aspect of the invention, an in-line machine stress measurement system is added for the lumber following the impregnation step for silicate uptake quantification. There are several alternatives to implement the stress measurement system. A first alternative is a device configured to measure density of wood by removing a small sample and plotting density. An example would include a drill and related components typically used to test poles and related structures. A second alternative is an industrial scale lumber strength measuring device that uses X-ray and other imaging technology to assess lumber. This device can determine density of both finished product and to grade incoming lumber to preferentially shift lower density wood for impregnation. This device can also perform natural frequency analysis. Another alternative would be a system that uses sound transmission, which is generally used to assess tree health. Such a system can be adapted to analyze the filled silicate composites because the silicate filler will change the density of the wood and could be measured by this technique non-destructively. Additionally, or alternatively, bending stress measurements can be used.
According to one aspect of the invention, a hyper-spectral analyzer system, an x-ray analyzer, or acoustic analyzer system is added so that the lumber can be analyzed for wood morphology analysis both before and after impregnation. Hyperspectral analysis measures spectroscopic data across a variety of wavelengths, typically in the near infrared for wood, to determine a surface composition of the product.
According to one aspect of the invention, a natural frequency measurement system is added for silicate uptake quantification. Natural frequency is a characteristic vibration mode of a material. It is obtained in much the same manner that one would use to get a tuning fork to resonate. The wood beam is struck and the resulting frequency is measured.
According to one aspect of the invention, a multi-input solution dispensing system is added upstream of the feed lines into the impregnation tank(s) for formulation control and quantification, which are capable of delivering two or more impregnation charges.
According to one aspect of the invention a spray and/or an immersion delivery system is included that is configured to dispense aqueous solutions including solutions that are high, neutral, and low pH, both before and after impregnation steps. The continuous spray setup would include a conveyor or the like and the wood would pass under a plurality of spray heads to treat the wood. An immersion delivery system would include a tank into which the wood would be immersed.
According to one aspect of the invention software is used in the facility to work with digital and mechanical recording devices programmed to track, record, and analyze the key process variables in real time including 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 invention will be described in more detail on the basis of an exemplary embodiment. In the figures:
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
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.
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.
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.
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.
Preferably, the conventional equipment for the conventional treatment process is used for the upgrades and modifications. Alternatively, the conventional equipment can be replaced.
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.
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.
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.
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.
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.
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.
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.
Agitation equipment is installed in the product working tanks. An exemplary agitator is shown in
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.
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 CO2 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.
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.
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.
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).
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.
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.
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.
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.
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.
This is a U.S. nonprovisional Application claiming priority on Application No. 63/352,899 filed Jun. 16, 2022, the content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63352899 | Jun 2022 | US |
