Progress 09/01/14 to 02/28/18
Outputs
Target Audience:Target audiences include the International Plant Protection Convention's Technical Panels on Phytosanitary Treatment and Forestry Quarantine, and all participating National Plant Protection Organizations, the wood products industry, international shipping companies, USDA-APHIS-PPQ, and the wood science community. Additional audiences include scientists and the public concerned with preventing or mitigating the spread of exotic species around the world through shipping materials. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?During this project, postdoctoral research Dr. Manoj Dubey attended the International Forestry Quarantine Research Group meeting and was exposed to the working of the International Plant Protection Convention. During the past year our new postdoc Dr. Karolina Szymona received extensive training in radio frequency technology, the use of temperature data acquisition software, and assisted with writing a grant proposal. How have the results been disseminated to communities of interest?We launched our RF treatment of WPM website http://abe.psu.edu/research/bio-based-products/wood-packaging in 2014. The website design has been devoted to key documents (e.g. ISPM-15, ISPM-3, FAO Guidance document on DH) and relevant news, multi-media-gallery, publications and reports of research findings. To keep our shareholders and other interested parties informed we have utilized our website to post experiments results via Powerpoint presentations. In addition we have met with and exchanged information with our Stakeholder Advisory Committee to assist in removal of the needed revisions to the adopted ISPM-15 DH treatment restrictions in Annex 1. The data supporting these revisions were published in Dubey et al. (2016). We have also been directly communicating with key trade associations and pallet manufacturers who have recently partned with us on continued research on RF with pressure and have become members of our Stakeholder Advisory Committee. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The most important goal of this project was to provide empirical evidence for the IPPC technical panels to recommend removal of restrictive language in ISPM-15 Annex 1 that limits the size of materials that can be treated with dielectric heating to < 20 cm in size and within a 30 minute treatment duration. We conducted experiments with radio-frequency (RF) and microwave (MW) heating for phytosanitary treatment of green wood in compliance with ISPM-15 and compared treatment time, depth of electromagnetic wave (EMW) penetration and heating uniformity between these two forms of dielectric heating. White oak wood cants (48 cm long with cross-section dimensions ranging from 10x10 cm2 to 25x25 cm2) were heated in a 19 MHz RF or 2.45 GHz MW laboratory oven using an equivalent heating power (3.4 kW). For each specimen, temperature was measured at different depths (distance from the upper face). Specimens were held in the treatment chamber for 2 minutes after the target temperature of 60 ?C was achieved through the profile of the specimen to ensure compliance with the ISPM-15 treatment schedule. Thermal image analyses of treated specimens as well as theoretical depth of penetration for dielectric energy were explored. Wood specimens were also heated using RF at high power (9-11 kW) and results were compared with RF heating at 3.4 kW. For wood with cross-section dimensions of 10x10 cm2 to 15x15 cm2, heating rates for RF and MW were relatively similar. However, above 15x15 cm2, RF heating was more than 40% faster with greater heating uniformity than MW. The theoretical values derived for depth of penetration and thermal image analyses indicate that RF (19 MHz) penetrates wood more uniformly and is better suited than MW (2.45 GHz) for bulk volume treatments of wood. A peer reviewed publication showing that the 20 cm limit on wood size that can be treated with RF was unnecessary and that treatment times of > 30 minutes do not reduce efficacy of the treatment schedule. These results were provided to the appropriate technical panels of the IPPC to allow removal of these restrictions in the ISPM-15 treatment schedule for dielectric heating. We also completed multiple commercial scale experiments, first using a manual, limited power density operational control system (~1200 bd ft capacity) RF unit, followed by a more modern RF installation with high precision power control and larger capacity system (~5000 bd ft). We learned that water movement or vapor release can cause non-steady state volumetric heating with significant thermal energy losses as the wood approaches or exceeds a critical temperature of » 50 °C. To correct for energy loss and better maintain constant heating we found that a 20% or higher power density became necessary to reach the temperature of 60 °C for 1 min (per the ISPM-15 dielectric schedule). Various techniques were investigated to contain heating losses, including use of a thermal insulation barrier, resulting in some heating improvements, but it was not practical for large-scale (bulk) volume treatment processes. In early 2016, we found that we could minimize the surface energy loss problem from the workload during RF treatment by adding pressure of 5-15 psi during treatment. With this innovation, we saw vastly improved heating uniformity during the commercial scale trial conducted on ~3,300 bd ft of cant material. This preliminary experiment using added pressure was conducted on a workload of freshly sawn (above fiber saturation) mixed ash (Fraxinus spp.) cants and showed moisture losses of only 1-3%, avoiding drying-related wood surface checking defects. There was clear evidence of reduced evaporative cooling that significantly increases the time required to reach and maintain lethal temperatures for all pests in the wood. However, this testing was done using an improvised pressurization system that was not an original component of the RF unit. It was highly inefficient because applied pressure could not be closely regulated due to leaks. So, we subsequently designed a fully integrated pressure/vacuum and RF oven system that was built by a Canadian company and installed in our research lab at PSU in October 2017. The ~3.0 cubic meter prototype of this RFP equipment (6.86 MHz, 50-kW heating output capacity) can bulk treat up to 1200 bd ft. at one time, representing a real-world commercial operation. Each treating cycle represents the rough equivalent of ISPM-15 sanitized raw material sufficient to build 82 standard 42"x48" Grocery Manufacturers Association (GMA) pallets that are widely used for international shipping of commerce goods. Penn State issued a patent on this new technology. With this new unit, we conducted a series of commercial scale trials to determine how much we could reduce treatment duration to improve cost effectiveness. As an example, we tested a 55 piece workload of 4"x 6" by 8.5 ft length yellow poplar cants, which is equivalent to ~800 bd ft of green pallet material using the 6 kV RF generator setting. We compared applied pressure of 15 psi during treatment to RF with no pressure. Using pressure reduced the treatment time by 42% and reduced nonlinear dielectric heating behavior. We also found that we can treat pallet components rather than raw cants, which eliminates treatment of wood that will be discarded following pallet construction, saving the company money on energy consumption. For this experiment, we selected 155 ash cants at random and 100 were resawn to 1.375" thickness stringers with an 800-piece recovery (sufficient to build 267 pallet frames); the remaining 55 cants (4" x 6") were used for comparison, producing equal volume workloads. A slightly different pressurization protocol was used between the two treatments due to issues with malfunctioning fiber optic probes (15 psi pressure applied 95 min into the treatment cycle of the stringers vs. the same pressure applied 65 min after starting treatment of the cant workload). Thermal-images taken 12-15 min post treatment showed that using equivalent power and equivalent load volumes, greater and more uniform volumetric heating was observed with the pallet component (stringer) load compared to treatment of the raw cants. Also the stringers took 21% less time to comply with the treatment schedule than the cants (and thus a 21% gross reduction in total energy consumption).
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Dubey, M.K., J. Janowiak, R. Mack, P. Alder, and K. Hoover. 2016. Comparative study of radiofrequency and microwave heating for phytosanitary treatment of wood. European J Wood Sci. 74: 491500.
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Progress 09/01/14 to 08/31/15
Outputs
Target Audience:Target audiences include the International Plant Protection Convention and all participating National Plant Protection Organizations, the wood products industry, international shipping companies, USDA/APHIS, and the wood science community. Additional audiences include scientists and the public concerned with preventing or mitigating the spread of exotic species around the world through shipping materials. Changes/Problems:Due to inconsistent heating and longer treatment times using the RF vacuum drying kiln at Forestville NY, a new RF vacuum drying kiln with improved facilities has been identified at the company mentioned above located in Ste. Saint Marie, MI to conduct further trials. These developments may alter our experimental design. What opportunities for training and professional development has the project provided?A post-doctoral researcher attained greater proficiency and further career advancement including: new knowledge about technical and policy aspects of phytosanitary treatment of wood and wood packaging materials; professional skills required for working in an industrial environment, skills for operating DH ovens, preparation of wood specimens for DH and subsequent analysis of data output; expertise in taking optical-temperature measurements and IR image analysis, in addition to investigating dielectric properties of wood at different frequencies; experience in writing grants, reports and manuscripts; networking skills through project partners (USDA APHIS, FPI Canada, PSC Inc.), IFQRG members and other post-doctoral fellows through the Penn State Post-Doctoral Society. The post-doc learned how to develop a website and took primary responsibility for populating a website on our research. He participated in a series of professional development seminars and training programs for post-doctoral researchers organized by the Office of Postdoctoral Affairs, PSU and he also took workshops sponsored by the IT department and Schreyer's Institute for Teaching Excellence. Furthermore, the post-doc also served as a judge for poster competitions for graduates and post-doctoral scientists at PSU. Based on the recent cooperative agreement with an industrial RF oven manufacturer and continued work to test commercial scale ash pallet materials, PSU investigators have been asked by the American Softwood Lumber Committee (ASLC) for their representatives to observe our data collection activities. ASLC is the primary oversight authority for phytosanitary certification of US certified pallet treaters on quality assurance issues, e.g. ISPM-15 compliance. The goal is to train key personnel to better understand the systematic application of RF heating since the recent adoption of dielectric heating under ISPM-15. How have the results been disseminated to communities of interest?Recently, a website on the general aspects of DH, phyto-sanitary treatment of WPM and objectives of this project was launched and can be viewed at the following web-link: http://abe.psu.edu/research/bio-based-products/wood-packaging. The website includes key documents (e.g. ISPM-15, ISPM-3, FAO Guidance document on DH), relevant news, a multi-media photo and video gallery, and links to our publications and reports. Research findings have been shared with industry leaders in North America via a poster presentation and a technical note was circulated in the meeting of science & technology advisory council of NWPCA (National Wooden Pallet and Container Association) during their Annual Leadership Conference held in Tucson, AZ, in March 2015. Two presentations covering (i) comparison of laboratory scale RF and MW heating of WPM and (ii) preliminary cost analyses were given at the 12th International Forestry Quarantine Research Group (IFQRG) meeting held at the Food & Agricultural Organization of the UN in Rome, Italy in 2014.The first meeting of the Extension Advisory Committee (EAC) was also held in Rome in concert with the IFQRG meeting in which all the committee members expressed their full support and willingness to advocate the use of DH technology. The US National Plant Protection Organization officer of USDA agreed to pursue modifications in the language of ISPM-15 regarding DH restrictions as discussed in our proposal. The team also provided technical expertise to the Capacity Development Committee of the International Plant Protection Convention to assist with development of training materials on the newly adopted Annex 1 of ISPM-15 on dielectric heating and in the development of a guidance document. The guidance document was designed to help dielectric equipment developers and National Plant Protection Organizations to produce/certify that equipment for this purpose can meet the schedule as indicated in ISPM-15 Annex. A manuscript that presents our research on MW and RF comparing heating uniformity and heating depth has been accepted with minor revision by the European Journal of Wood and Wood Products. Another manuscript comparing the potential environmental impacts of microwave phytosanitary treatment of wooden pallets to conventional heat and methyl bromide treatments was submitted to the Journal of Forest Policy and Economics. As a result of the research and extension activities of our research team as described for Objectives 1 and 2 of this study, the Technical Panel for Phytosanitary Treatments (TPPT) drafted revisions to the DH treatment requirements in Annex 1 of ISPM-15. The TPPT recommended deletion of the following language: (1) material to be treated cannot exceed 20 cm in any dimension; (2) treatment must be completed in 30 minutes, and (3) only MW has been shown to meet the prescribed treatment schedule. This revised language is currently out for country consultation and should be adopted by 2017 according to the current chair of the TPPT. What do you plan to do during the next reporting period to accomplish the goals?Research is planned to collect depth of RF wave penetration data, heating uniformity and treatment time on commercial stacks of mixed ash wood cants in a new 25' long RF vacuum drying kiln (6.8 MHz), which is to be installed in Aug 2015 at Ste Saint Marie, MI. The purpose of this study is to obtain faster treatment times and better heating uniformity. This will further generate evidence that the 20 cm dimension limit for WPM using dielectric heating is unnecessary and should be removed. New dielectric properties using equipment running at 6.8 MHz will be tested using green ash wood to explore the development of standard RF volumetric treatment schedules for other WPM. The preliminary cost model developed will be refined by addition of these new data sets. More data will be collected for verification and validation of the cost curves that have been generated thus far. This verified cost information will be used in an economic study using GTAP Economic software to determine the potential changes in GDP and economic trade balances due to adaptation of dielectric heat treatment of wooden packaging at various levels of implementation around the world. Research findings will be presented at the 13th IFQRG meeting in York, U.K. in October 2015 and at the Methyl Bromide Alternative Outreach conference in San Diego and other relevant forums. The second meeting of the extension advisory committee will be held in Oct 2015 during the 13th IFQRG meeting in York. The extension website will be continuously improved with new information. The website will be promoted among stakeholders such as pallet manufacturers, DH oven developers, researchers and regulators through conferences, meetings and web networking.
Impacts
What was accomplished under these goals?
Under an equipment lease agreement with Ben Aaron Lumber, Inc. (Forestville, NY), commercial-scale RF heating trials for bulk treatment of WPM were performed in an industrial capacity (1200 bd ft volume) RF (4.6 MHz oven frequency, max 150 kW heating power) vacuum drying kiln. A total of 13 trials were performed to investigate volumetric heat development and heating behavior in commercial size stacks (2', 3' and 4' height) of hardwood sawlog cants commonly used as the primary raw material source for domestic and international shipping pallet construction, i.e., mixed white oak, mixed red oak and mixed ash. These trials demonstrated that RF effectively heats large bulk packs (up to 121 cm treatment load), which far exceeds the 20 cm restriction on treatment loads included in the current ISPM-15 for DH. However, heating in wood stacks, especially 4' stacks, were non-uniform and treatment time exceeded 3.5 hours due to limited power output (only 32-57 kW) of the RF drying kiln we used and uneven distribution of RF waves across the electrode plates. No significant improvements in terms of increasing power output and even distribution of RF waves were noticed with the installation of a heat exchanger, increasing the capacity of the water cooling tank, modifying the electrode through installation of an aluminum sheet around the top electrode (paddled/winged/tapered electrode) or covering the wood stacks with woolen blankets. To perform further trials with better heating uniformity and faster treatment time a new RF vacuum drying kiln (6.8MHz, 50KW with modern controls and software) was found and separate memorandum of understanding has been signed with Superior Marine & Environmental Services LLC (SMES, Sault Ste. Marie, MI). Complex dielectric properties that describe relative permittivity and loss factors for green (>25% moisture content) of white oak, red oak and ash wood at 4.6 MHz frequency were measured at the Centre of Dielectric Studies at PSU. Good correlation was observed between the dielectric constant and moisture content of the wood. These data combined with the commercial-scale experimental trials will facilitate development of standard RF volumetric treatment schedules for other WPM. The first step of an economic analysis was initiated. The cost of energy input in the dielectric (RF) treatment process was calculated based on laboratory-observed treatment times and fundamental energy engineering equations. These trials and calculations provided the team with an energy-cost estimate of 25 cents per pallet for phytosanitary treatment using RF. Cost data were collected from actual heat-treating operations to establish a statistical sample from which a more general population of heat-treating costs could be developed through computer simulation. This simulation was performed and distributions were developed for individual cost components of electricity, chamber fuel, and maintenance. From these data, we obtained a total cost curve for conventional heat treatment of wooden pallets in North America. A graph was developed to aid in the comparison and evaluation of RF treatment chamber investment versus conventional heat treatment at variable electricity cost rates. The results of the Forestville, NY trials provided marginal improvement in data quality from an economic perspective, and were therefore not added to the existing cost model simulation. Data from the upcoming Michigan trials is expected to increase the robustness of the dataset and will be incorporated into the cost model. General economic trade modeling with GTAP software was begun this year, and will be completed after the inclusion of the Michigan data to the cost model. This ongoing work will produce an estimate of the potential global economic impact of dielectric treatment of WPM at expected rates of implementation around the world, and compare these estimates with alternative scenarios of methyl bromide treatment and conventional heat treatment in various countries.
Publications
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