Practical Application of Joule Heating to the Sterilization of Plantation Grown Pinus radiata Logs

Pinus radiata (D. Don) log exports are one of New Zealand’s major foreign revenue earners, with 12.8 million cubic metres, valued at nearly NZ$1.7 billion, shipped in 2011. Most trading partners require logs to be treated before shipment from NZ, to prevent the inadvertent import of unwanted pests. This is carried out by the use of the fumigants methyl bromide (MeBr) or phosphine. MeBr is an ozone depleting substance and has been phased out for all but quarantine and phytosanitary purposes. The New Zealand Environmental Protection Agency requires that, by 2020, MeBr used in New Zealand is recaptured after use. Alternative phytosanitary treatment methods are required, with heat being one option. Trials using electrical Joule heating were begun at the EPECentre in 2007. Early results indicated that the technique was worthy of deeper investigation. Further EPECentre funded work, with later support from the Stakeholders in Methyl Bromide Reduction and the Ministry for Primary Industries Primary Growth Partnership, has shown that the technique could be used to successfully treat logs in accord with importing country requirements. The work is now funded as part of a six year STIMBR-Ministry of Business, Innovation and Employment co-funded research programme, led by Scion. A test rig, incorporating novel segmented electrodes and an automated data acquisition and energy control system, has been built and commissioned in the HV laboratory at UC. This rig is powered by a single phase Foster Regulator (FR) which provides 0 to 400V at 0 to 500A, within a 100kVA envelope. The FR output is stepped up by a 200kVA, 240V:11kV transformer, to provide up to 11kV across the log, at up to 11A. The automated energy control system drives the FR to provide maximum power to the log, within the equipment constraints, while integrating the active power supplied until a preset quantity of energy has been injected into the log, to raise its temperature by the desired amount. The rig has successfully been used to treat 3.3m long, 0.5m diameter logs. About 30 to 40kWh of energy per m3 are required. Thus, on a 16 hour per day, all year round operation, around 400 to 500GWh, from about 80MW of generation, would be required on a nationwide basis (2012 data). The paper presents and discusses electrical and log temperature data from the rig, along with planned future developments and a sneak preview of how a wharf-located production machine might operate

Proof of Concept Studies for the Practical Application of Joule Heating as a Phytosanitary Treatment for Export Pinus radiata (D. Don) Logs

Following initial feasibility work in 2007 [1] and a MAFBNZ funded project in 2009 [2], the Joule heating concept for log sterilization was incorporated into the STIMBR PGP project as section 1.5.2. This report details the construction, commissioning and testing of the log sterilizing apparatus which had largely been conceived and designed by the EPECentre before the start of this project. The procedure for sterilizing test logs is described and the results obtained with two such logs are presented and discussed against the objectives of section 1.5.2. Finally suggestions for further work, refinements to the system and tests to fill gaps in current knowledge are proposed, including the author’s current impression as to how a wharf-side machine might operate. Tests on the first log show that after treatment all measured locations in the timber exceed 56C for over 5 hours. Tests on the second log show that after treatment all measured locations in the timber exceed 56C for over 8 hours and 70C for about 3.5 hours. In both cases this includes the geometric centre of the log. These tests, therefore, show that Joule heat sterilization undoubtedly can work

Preliminary results from an electromagnetic groundwater flow measurement system

Groundwater makes up the majority of the world’s fresh water. Modelling these flows requires verification against measured data. Currently this data is obtained from monitoring wells, a complex and expensive task. A proposed electromagnetic measurement system would simplify the collection of ground truth values and allowed improved model tuning. This technique requires measurement of sub-microvolt scale signals in the presence of large interference. A test system has been developed to validate the technique, and this paper presents some preliminary results from initial testing. Experiments show that significant harmonic distortion is present and that the signal levels fluctuate. Both these effects appear to be due to the electrode-electrolyte interfaces

Practical Joule Heating for Phytosanitary Log Treatment

A team at the University of Canterbury’s Electric Power Engineering Centre (EPECentre) has developed a laboratory machine and process that can rapidly and reliably Joule heat the sapwood of softwood timber. This treatment, initially intended for phytosanitary purposes, has been demonstrated on multiple full-sized, New Zealand (NZ) grown, Pinus radiata logs. The team has been working with Scion (NZ’s Forest Research Institute) and Canterbury University’s Departments of Forestry, Chemical & Process Engineering and Electrical & Computer Engineering, with funding from NZ’s Ministry of Business, Innovation and Employment (MBIE) and industry organization Stakeholders in Methyl-bromide Reduction (STIMBR). A publications search shows that the Joule heating idea was trialled as a veneer log pre-treatment by the US Department of Agriculture Forest Service, Madison, Wisconsin in 1953. More recently some computer modelling work has been done in France for the same purpose, but the idea has not been commercialized, seemingly due to insufficient understanding of the process to overcome the problems of uneven heating profile. The EPECentre team has studied the electrical and thermal behaviour of freshly harvested P. radiata in sufficient depth to create both a full Computational Fluid Dynamics (CFD) model and a simplified computer model. The simplified model is sufficiently robust to generate control parameters enabling the machine to successfully heat all sapwood parts of every log tested to above 60o C, for ISPM-15 type compliance over a half hour period

Impact of inverter energy systems on fuse protection of low voltage networks

With the introduction of inverter energy systems (IESs) to electricity distribution networks, it is important for electricity distributors to know the nature of new challenges to basic protection systems in the low-voltage (LV) network as the penetration of IESs in distribution networks increases. For any feeder on a low voltage network hosting IESs, fault currents will have a contribution from both the upstream source and from the IESs connected on that same feeder. The clearing times of upstream fuses can be affected by the additional current contribution from IESs. It is shown how fuse coordination can be preserved in LV networks with high penetrations of IES, so that cables are still protected. An IES will shut off under fault conditions either because the voltage dips below a threshold, or the upstream fuse clears the fault. Guidelines are presented to help combat sympathetic tripping and blinding of fuse protection systems