Stakeholders in Methyl Bromide Reduction Inc (STIMBR)

This story was showcased in our 2019/20 Annual Report

The Stakeholders in Methyl Bromide Reduction Inc (STIMBR) has undertaken extensive research seeking alternative chemical and non-chemical treatments for methyl bromide.  The use of methyl bromide, an ozone destroying fumigant, is permitted for treating imports and exports under international agreements.

However, New Zealand forest and horticultural industries assisted by government and other co-funding including from AGMARDT have invested over $45 million over the last decade seeking sustainable alternatives.  A new chemical fumigant has been identified for treating exported logs to rid them of unwanted insects and is waiting for Environmental Protection Authority approval.

AGMARDT has co-funded work with STIMBR on the use of a non-chemical treatment using electricity applied directly to logs is showing exciting promise. Previously this work focused on advancing the development of the Joule heating technology. The present project, co-funded by STIMBR and AGMARDT has been concentrating on the key areas to de-risk the design, construction, and commissioning of a pilot production plant.

  1. Development of a Smart Electrode for the automatic determination of heartwood and sapwood portions within logs. This is essential for calculating the required electrical energy to reach the treatment temperature profile needed to achieve the required temperature within a given log.
  2. Development of a Static Frequency Converter (SFC) control system for automation of the optimal electrical energy injection into each log, according to the profile for each log determined by the Smart Electrode image and computational modelling.
  3. Detailed computational modelling of a wide range of representative export pine logs, to optimize the excitation-relaxation regime so that we are able to achieve fast, efficient treatment without the risk of damaging the wood in a log from localized overheating.

Progress to date include a reduced scale electrode system is being built and laboratory testing will take place in early October 2020 to confirm the mechanical design, the computational modelling, and the heartwood-sapwood discrimination software already developed. This will inform construction of the full-sized pilot system capable of handling logs up to 500mm diameter.

Control software and hardware has been successfully developed and tested (with variable resistance loads) on the UC laboratory Ametek SFC. Testing on full-sized logs is due to take place before the end of September 2020.

Computational modelling of multiple cases of logs with variable heartwood-sapwood proportions, internode length, node branch number and branch sizes is underway. COMSOL software has allowed the use of curvilinear co-ordinates (not readily available in ANSYS) which leads to more realistic hotspot modelling around knots. This is because this coordinate system correlates better with the timber grain and allows realistic rendition of actual anisotropy.

While the commercial use of this technology requires further development, the positive results are proving exciting and will assist in de-risking the production of a working small-scale pilot plant. If that proves successful a full-scale prototype will be built.

“AGMARDT has co-funded projects with STIMBR on the use of a non-chemical treatment using electricity applied directly to logs is showing exciting promise. The current project will assist in the development of a pilot production plant of the technology.”