A well-known issue, yet difficult to solve
In Italy there are 2.2 million domestic pellet appliances, and 99 % of these fall below 35 kW (AIEL, 2024). It’s a huge and growing market (+75.6 % between 2014 and 2023) that is particularly sensitive to air quality and pollutant emission issues.
Yet, from a technological point of view, most stoves have carried the same limitation for years: a pellet feed that is only apparently constant, but in reality characterized by intermittent irregularities. In these phases, the air-fuel ratio is altered, combustion is penalized, and emissions at the flue increase significantly, even when evaluated over longer time intervals.
The paradox is that pellet technology was created precisely to be more controllable than wood combustion, but despite that the most common feed method, i.e. the volumetric screw, still introduces significant variability. Variability that becomes critical especially at partial loads, that is, in real-world operation that concerns most users.
We looked closely at the numbers. And the numbers confirmed that pellet feed, with traditional systems, is never truly constant.
K-INN Tech’s solution: a non-volumetric electromechanical device
Starting from this evidence, K-INN Tech undertook an R&D project with three clear objectives:
- Measure how irregular the traditional auger was, effectively defining a standard not yet existing among industry practitioners.
- Design an innovative electromechanical device, integrable into stove geometries, capable of obtaining a more stable feed rate.
- Experimentally verify the real impact on emissions, and not only: ease of cleaning, noise, and final footprint were taken into account.
The heart of the innovation lies in a simple but overlooked concept: if pellet is a non-uniform granular solid, a volumetric feeder can never guarantee a constant feed.
The new K-INN Tech device overcomes the structural limitation of the auger thanks to a non-volumetric movement principle, developed to:
● compensate for the physical variability of pellet (length, roughness, durability);
● guarantee a truly continuous, non-pulsed flow, even instantaneously;
● maintain a stable air-fuel ratio;
● operate both at nominal power and at reduced load.
The technology is now the subject of patent application no. 102024000006382 (22/03/2024).
Results from the experimentation
Feed rate consistency: dramatic improvement
Experimental data show that the new device markedly reduces feed variability:
● from 160 % to 46 % at nominal load
● from 230 % to 71 % at partial load
Those who work with plants and combustion know: such a reduction radically changes process stability.
Emissions: CO nearly halved, particulates more than halved
With the stove equipped with the new device, compared with the native auger:
● CO: –46 %
● NOx: unchanged (consistent with the fact that NOx depends on the nitrogen contained in the biomass)
● Particulate: –52 %
The reductions remain significant even at partial loads (CO: –38 %; PM: –44 %), where stove performance normally worsens.
Industrial compatibility
The device was designed from the beginning to be easily integrable into commercial appliances, with dimensional, construction, and cost constraints compatible with the domestic stove market.
Our experimental verification method: how we proved it works
Comparative tests were conducted on a 9 kW stove, suitably adapted to operate with two different configurations, without any modification to mechanical elements or sealing systems. Pellet was fed with:
- standard screwer, or
- K-INN Tech device
For both, the pellet and combustion air feed rates were measured over time, along with CO, NOx, and particulate concentrations (using a gravimetric method). The same air-pellet ratio was maintained throughout the experiment. The combination “more stable feeding → more stable combustion → lower emissions” proved evident, repeatable, and quantifiable. The experimental investigations and results were published in an international peer-reviewed scientific journal, and their are available at this link: https://doi.org/10.1016/j.renene.2024.122273.
A step forward for the entire domestic pellet heating supply chain
What could this technology change in the market?
This technology represents a concrete and proactive response to the direction taken by Italian and European legislators, which have introduced, and will continue to introduce, ever stricter limits on pollutant emissions from domestic biomass appliances. Clear examples are the five-star classification introduced by Italian DM 186/2017 and the ongoing revision of the Ecodesign Regulation 2022. Added to this is the role of regional authorities which, within their decision-making competencies on air quality, can adopt even more restrictive measures. One example is the Veneto Region, which with DGR 238/2021 prohibits the installation of heat generators with emission performance below four stars, clearly indicating a market direction toward ever cleaner technologies.
For the end user, our technology translates into a concrete benefit: a greater likelihood of being able to use the appliance over time, even under stricter regulatory contexts, reducing the risk of seasonal bans, usage limits, or premature obsolescence of the investment. In this scenario, emission reduction is not only an environmental requirement but a true competitive factor.
The peculiarity of the feeder also lies in its design oriented toward integration. It is not born to rewrite the design of stoves from scratch, but to adapt to existing models, allowing manufacturers to significantly improve emission performance without having to completely redesign an entire product line, and consequently limiting the economic impact related to regulatory adjustments
Conclusions
The shift from wood to pellet represented a first leap toward more controllable combustion. Indeed, regularizing the fuel feed is the natural evolution of a process that becomes increasingly governable thanks to technological developments. The result is a more regular combustion and significantly reduced emissions.
The device developed by K-INN Tech acts exactly at the root of this problem by regulating the pellet flow to the firebox and decreasing CO and fine particulate production by 50%.
For more information about the technology or to evaluate a collaboration, write to info@k-inntech.it
