Since the invention of MDF people have been looking for ways to improve the gluing of wood fibre in this process. The main goal was always to reduce resin consumption for defined panel properties.

Many different approaches have been taken for the typical blowline blending as well as some alternative steps with so-called dry blending after the fibre drying process.

Markus Jonsson, of Sunds Fibertech, addressed the subject during his presentation paper at the well-attended European Wood Based Panels Symposium in Hamburg in October.

Mr Jonsson told WBPI that some progress has been made over the years with resination systems, but most of the systems have got more complex and thus more expensive and costly to run.

“What was considered state of the art in blowline blending until now typically requires additional steam injection to improve resin spreading in the blowline,” he explained.

“Some systems also require intensive maintenance of high-pressure pumps with high electric energy consumption. Dryresination systems require additional space, high investment, and significant operating cost due to additional fans and still bear the risk of fibre and glue lumps.”

Of course, improving a system and lowering resin consumption has generally meant an additional investment cost, as well as potentially increased other operating and maintenance costs.

Sunds also points out that the conventional blowline blending with external nozzles always bears the risk of build-ups along the blowline due to poor mixing or instability regarding variations in throughput.

The Internal Resin Injection System featuring the concentric flow principle where a central nozzle is placed in the blowline

The ideal situation for the resin distribution, says Mr Jonsson, is when fibre and resin flow as well as pressure conditions in the blowline and from the resin injection are in a perfect balance and the resin spreads out into most of the centre part of the blowline.

However, if this ideal situation gets out of balance due to some flow or pressure fluctuations, the resin is either crawling along the blowline wall or hits the opposite wall. This, Mr Jonsson says, leads to poor mixing and even higher resin demand as well as build-ups and cleaning demand.

“Most of the time the ideal situation only exists in theory. Everybody knowing real plant life probably has experience with pulsation of the refiner and or fluctuation of steam pressure for resin atomization.”

NEW APPROACH FOR MDF BLOWLINE BLENDING

Given this background, Sunds Fibertech decided to rethink blowline blending from scratch.

Instead of trying to fine-tune existing technology and adding another piece of kit that may increase complexity, Sunds Fibertech took another approach – the concentric flow principle.

This is based on a simple principle: a central nozzle is placed in the blowline. The fibre-steam flow from the refiner is guided around the nozzle.

At the tip of the nozzle the fibre-steam flow is guided towards the centre of the blowline. At the same time resin is injected and tends to expand into the fibre-steam flow. This creates extremely high turbulence in the following section of the blowline.

“There is a strong mixing effect that reduces the required resin amount,” explained Mr Jonsson.

The Internal Resin Injection System by Sunds Fibertech

“At the same time build-ups are minimized because the fibre-steam flow around the central nozzle is acting like a protection sleeve along the critical section behind the resin injection point.”

The concentric flow principle, he says, is designed to provide a high stability with regards to changes in throughput and shortterm variations. Such variations do not lead to direct spray of resin onto the blowline wall.

There is already real industrial experience using this principle, known as Sunds’ Internal Resin Injection System. From start-up in mid 2023, a European producer of MDI bonded boards and UF bonded boards has been using the system.

For MDI, says Sunds, it is possible to apply the complete resin volume via the Internal Resin Injection System. For UF it is possible to cut off more than 50% of the conventional nozzles.

Since the installation, the manufacturer has reported that the blowline stays clean and does not have to be cleaned any more after an MDI production campaign. An additional benefit reported is that MDI resin consumption could be reduced.

When using the system with UF resin, an increase in the internal bond of the panels was immediately recognized by the manufacturer. UF resin dosage could also be reduced.

In summary, the reported benefits of the Internal Resin Injection System are that it can inject the full amount of MDI resin, more than half of UF resin, and can be operated without steam for atomizing, with a medium pressure pump (20 to 30 bars) and an easy change between resins (MUF/UF & MDI) with automatic shut-down and start-up sequence.

As of now, Sunds Fibertech reports to have sold five internal resin units. It will have further updates soon of the performance of the system from start-up panel production facilities in Asia Pacific and South America.

The new Internal Resin Injection System by Sunds Fibertech was clearly one of the hot focus topics at the Hamburg Symposium, with delegates showing interest in the quoted benefits of resin consumption reduction and the simplification of plant operation and production costs.

The system was presented at Ligna 2023

With energy costs being such a big issue in recent years, panel producers are clearly keen to find ways to lower energy usage, including lowering steam consumption which reduces thermal energy demand and dryer load.

The prospect of reducing electricity costs and a whole new simplified approach to the maintenance of complex dosing and nozzle systems are also attractive propositions.

Sunds reports that the return on investment for installing the Internal Resin Injection System typically take between 12 to 18 months.

Such technology definitely falls in the class of a disruptive technology in the panel industry resin application process, and it will be interesting to watch its progress in the years to come.