# Real-time measurement of particle size and concentration in flue gases during biochar production – Dekati® ELPI®+ - Savonia AMK > Particle size and concentration measurements expand the operations of the Varkaus campus. ## The Vesihiili Project The “Vesihiili” project investigates and demonstrates the production and use of biochar, including applications in water filtration and as a growing medium. Through these demonstrations, the project accumulates expertise in the use of biochar for filtration via field trials, while also supporting the launch of circular economy businesses based on biochar production. These actions help create conditions for new biochar-related economic activities, particularly in sparsely populated areas. ## Advanced Measurement Technology As part of the energy technology implementation, investments are being made alongside the development project, including the purchase of a Dekati® High Resolution ELPI®+ (Electrical Low Pressure Impactor, HR-ELPI®+), with the additional High-Temperature (HT) upgrade. With the ELPI®+ instrument, we are able to perform real-time measurement of particle size distribution and total concentration. The system covers a wide particle size range from 6 nm to 10 μm using a single measurement technique. Thanks to the HT-upgrade, we can measure gases between 10–180 °C without the need for dilution or sample conditioning. This allows us to provide accurate measurements even at low sample particle concentrations and without the risk of sample transformations in a dilution system. ## Measurement Principles The measurement process begins by charging particles to a known level using a corona charger. These charged particles are then classified according to their aerodynamic particle size, which describes how a particle behaves in air and corresponds to the diameter of a sphere of unit density that has the same aerodynamic properties as the real particle. Size classification takes place in a 14-stage low-pressure cascade impactor. The first stage of the impactor acts as a pre-separator stage, removing particles larger than 10 μm from the sample. The last stage, covering 6 nm to 16 nm, is a back-up filter stage that collects particles too small to be deposited by impaction on the preceding stages. Each stage is electrically insulated and equipped with sensitive electrometers that measure the charge carried by the collected particles. The resulting current signal is directly proportional to particle number concentration and size. The system classifies particles into 14 size fractions, but it can be expanded to up to 500 fractions using the HR-ELPI®+ software, enabling highly detailed analysis. Our current applications do not require post-chemical or gravimetric analysis, which allows us to use sintered metal collection plates, enabling long-term maintenance free operation. ## Applications in Biochar Production In the Vesihiili project, the ELPI®+ will be used to determine the particle size and concentration of aerosol-phase particles generated during biochar production. Biochar is produced through pyrolysis of biomass at high temperatures in an oxygen-free or low-oxygen environment. The ELPI®+ allows us to track how different process parameters such as reactor temperature, residence time, and feedstock type influence aerosol emissions throughout the pyrolysis process. This information is important for both improving reactor performance and ensuring that biochar production systems meet environmental standards. ## Comparison with Gravimetric Methods Our services already include accredited dust particle emission measurement using the gravimetric method (SFS-EN 13284-1:2017). Comparing ELPI®+ with this gravimetric method highlights how number-based and mass-based approaches differ, especially for fine and ultrafine particles where mass is very small but number concentration is high. In addition, ELPI®+ results can be compared with the results of the plant’s continuous emissions monitoring systems and the gravimetric method as a quality assurance tool. ## Training and Implementation A two-day training session on the ELPI®+ instrument was conducted by Dekati experts at Riikinvoima Power Plant. During the training, the Vesihiili-project’s research team from Varkaus Campus gained insights into aerosol fundamentals, the construction and operating principles of ELPI®+ and HT-ELPI®+, and essential user maintenance procedures. Hands-on exercises included assembling the HT-ELPI®+ system and performing real-time measurements. ## Project Funding The Waterchar project is a project co-financed by the EU, financed from the Just Transition Fund (JTF), and the funding authority is the Regional Council of North Savo. ## Authors * Research Engineer Raquel Mier González, Savonia-amk * RDI specialist Maarit Janhunen, Savonia-amk * Research Engineer Janne Ylönen, Savonia-amk * Technical sales specialist Markus Nikka, Dekati Oy * Technical support engineer Paxton Juuti, Dekati Oy ## References * Dekati 2024. ELPI®+ User Manual Ver 1.7. * Afshar, M. & Mofatteh, S. 2024. Biochar for a sustainable future: Environmentally friendly production and diverse applications. https://doi.org/10.1016/j.rineng.2024.102433 * Riikinvoima s.a. Briefly in English. https://riikinvoima.fi/briefly-in-english/. Accessed 12.11.2025.