Bioenergy Observatory

Modeling of the combustion process June 2024

The feasibility of integrating mathematical modelling into the experimental study of the burning process of LQB fuel pellets samples has been investigated. Knowing the parameters that would need to be clarified during the study of the LQB fuel pellets combustion process (thermodynamics, gaseous emissions, PM emissions, bottom ash, and slag), the software applied to mathematical modelling of these parameters was clarified. A bibliometric analysis method was chosen to identify the software. The bibliometric analysis was carried out in the Scopus database. As a result, two software were identified: ANSYS Fluent software is suitable for modelling thermodynamic processes and gaseous emission streams. At the same time, XDEM software is ideal for modelling particle streams and ash/slag generation. It is planned to use these programmes for further work. Activities aimed at training in the use of these software have been launched (e.g. creation and setup of the correct model, theoretical basis, interpretation of results, etc.).

Participation in the international scientific conference CONECT 2024

Project team actively participated in the international scientific conference CONECT 2024, which took place from May 15 to 17 in Riga, Latvia. The conference organized a separate session on the sustainable use of bioresources and the energy potential of alternative biomass use. In total, there were two performances with presentations:

1. V. Kirsanovs “Biomass diversification for heat production: from theory to practice”
2. M. Dzikēvičs “Overview of low-quality biomass pellet combustion process mathematical modelling”

And two presentations with a poster:

1. O. Švedovs “Bibliometric Analysis of the Modelling of Low Quality Biomass Pellets Combustion”
2. V. Priedniece “Search for alternative raw materials for pellet production – a preliminary study”

Contacts were established with several foreign scientists and it was agreed to promote cooperation in the research of alternative biomass.

The problem of ash melting and slagging May 2024

In the process of burning biomass, ash is formed. Depending on the type of biomass, the amount of ash can vary from less than 1% to about 13%. Similarly, both the chemical composition and physical properties such as density change. These biomass properties affect both the combustion process and the behavior of the biomass ash left over from the combustion process. If the ash has a low melting point, then it is more likely to melt, stick together with other particles or stick to the internal surfaces of the boiler, and cause problems with the operation or durability of the boiler. Therefore, a high ash melting point is a desirable property of biomass. The melting point of ash is influenced by aspects such as the amount of silicates and phosphorus (the more, the lower the melting point) or the amount of calcium and magnesium (the more, the higher the melting point). Since the design of the boiler significantly affects the combustion process, the development of new fuel requires determining the possible melting temperatures and evaluating possible changes in the design or operation of the boiler in order to reduce the formation of fumes.

Development of a biomass resource assessment tool April 2024

Activities on the development of a complex biomass resource assessment tool was started. The development of the tool was based on the conducted research on the use of alternative biomass in the production of pellets and the characteristics of their burning process. Currently, the index includes technological and environmental dimensions and includes such indicators as the heat of pellet combustion, ash content, volume density, mechanical strength, ash melting temperature, emissions caused by the combustion process (CO, NOx, PM), boiler efficiency and others. The sustainability index of 8 different biomass pellets was calculated using the evaluation tool. The highest score was obtained for wood pellets, followed by beer wort, tree leaves and hemp pellets. Work on improving the biomass resource assessment tool will be continued, expanding the index with other indicators.

Life cycle assessment of fuel pellets April 2024

A life cycle analysis was performed for pellets with the highest potential: wood (as a reference), brewer’s spent grain (BSG), leaves, and hemp. The purpose of the life cycle analysis was to determine the environmental impact of the pellets, including three main stages – growing, production, and combustion. The growing stage was included for wood, leaf, and hemp pellets. The data used for the growing stage were based on the literature.  For BSG pellets, since they are a by-product of beer production, the growing stage was not included. For the production and combustion stages, the majority of data used were obtained during the experiment. The production stage accounted for electricity consumption during biomass processing and pellet pressing. The combustion stage included emissions released during combustion (CO, NOx, PM) and the electricity consumption of the boiler during combustion. 1 MWh as a functional unit was used. The base and alternative scenarios were analysed. The purpose of alternative scenarios is to identify processes or activities that could potentially reduce the overall environmental impact such as using electricity from renewable energy sources, transport that generates fewer emissions, flue gas treatment. Also, scenario excluding growing of biomass is analysed.

Life cycle assessment of fuel pellets April 2024

A life cycle analysis was performed for pellets with the highest potential: wood (as a reference), brewer’s spent grain (BSG), leaves, and hemp. The purpose of the life cycle analysis was to determine the environmental impact of the pellets, including three main stages – growing, production, and combustion. The growing stage was included for wood, leaf, and hemp pellets. The data used for the growing stage were based on the literature.  For BSG pellets, since they are a by-product of beer production, the growing stage was not included. For the production and combustion stages, the majority of data used were obtained during the experiment. The production stage accounted for electricity consumption during biomass processing and pellet pressing. The combustion stage included emissions released during combustion (CO, NOx, PM) and the electricity consumption of the boiler during combustion. 1 MWh as a functional unit was used. The base and alternative scenarios were analysed. The purpose of alternative scenarios is to identify processes or activities that could potentially reduce the overall environmental impact such as using electricity from renewable energy sources, transport that generates fewer emissions, flue gas treatment. Also, scenario excluding growing of biomass is analysed.

Evaluation of risks from PM April 2024

A literature review has been done on particulate matter (PM) in biomass combustion. The formation of PM in natural and anthropogenic processes, as well as the division by size, is described. The impacts of PM on the environment, especially vegetation, and humans have been studied. The PM composition of different wood, biomass and fossil fuels types is studied to identify the most common chemical elements and potential problems that can come from the chemical composition of a material.

A study has been conducted on analysis methods and technologies used for PM and biomass chemical composition determination. Chemical elements that significantly influence ash melting temperature changes are identified.

Chemical composition analysis of Canadian goldenrod and hemp ash samples was done in cooperation with the RTU “Institute of Materials and Surface Engineering” using EDX and XRD methods. Results are included in a publication. Simultaneously, work to improve the testing methodology of alternative biomass ash using ICP-OES for the determination of chemical composition is ongoing.

Biomass diversification in large capacity biomass boilers March 2024

Based on the literature and statistical data analysis performed in activity 2.4. “Assessment of technologies for centralized heat supply” was concluded on potential solutions for biomass diversification in large capacity biomass boilers. Experimental study was carried out at activity 4.2. “Alternative use of biofuel in district heating”. Chip boiler with a nominal capacity of 2 MW was tested. Possibilities of replacing wood chips with a lower quality fuel – wood bark – were evaluated. In addition, the possibility of improving the combustion process by adding biomass with the highest quality – wood chips and sunflower pellets – was considered. The results of experimental research show that there are opportunities to diversify biofuels in existing energy sources, at the same time: 1) the use of lower quality biomass (bark) lowers the efficiency of the combustion process and increases gaseous emissions; 2) adding dry biomass (pellets and chips) to lower quality biomass improves energy efficiency and emissions. Experimental research will continue in search of better affordable solutions for biomass diversification.

Optimisation of the pellet combustion process February 2024

An experiment to optimise the combustion process was carried out on the mixture leaves and wood pellets, in which only the amount of oxygen concentration in the flue gases was changed. From the data obtained, it can be concluded that the frequency of air supply influences the burning process of the pellets, hence the emissions in the flue gas and the efficiency of the boiler. Too much air will increase emissions rates and reduce boiler efficiency, but too little air will also show the same trend, so optimisation tests are needed for each type of biomass to determine the most efficient air feed frequency when there are the least emissions and highest boiler efficiency. It is also possible to change the frequency of pellet feeding in a pellet pot, so it is important to find a balance between the frequency of air and pellet feeding so that pellets are sufficient during the combustion process and show low emission rates and high boiler efficiency when burned.

Energy recovery of cotton waste January 2024

On the road to climate neutral and the so-called “zero-waste” economy, the case study for replacing the part of wooden source in fuel pellets with cotton, recovered from sorted end-of-life clothing and other textile products was explored. During the case study, wooden fuel pellet samples were produced with a 10%, 20%, 30% and 40% share of recovered cotton. The values of the fuel characteristics of the samples formed were determined: calorific value, moisture content, ash content and chemical composition. The combustion process of the samples was examined in a low-capacity solid fuel pellet boiler and results were obtained for the heat produced, as well as for the consistency of the flue gases, including PM concentration. The results show that such a form of disposing of cotton, which essentially means the recovery of energy stored in cotton textile waste, is scientifically justified until the complete recycling of waste is achieved.

Energy recovery of cotton waste January 2024

On the road to climate neutral and the so-called “zero-waste” economy, the case study for replacing the part of wooden source in fuel pellets with cotton, recovered from sorted end-of-life clothing and other textile products was explored. During the case study, wooden fuel pellet samples were produced with a 10%, 20%, 30% and 40% share of recovered cotton. The values of the fuel characteristics of the samples formed were determined: calorific value, moisture content, ash content and chemical composition. The combustion process of the samples was examined in a low-capacity solid fuel pellet boiler and results were obtained for the heat produced, as well as for the consistency of the flue gases, including PM concentration. The results show that such a form of disposing of cotton, which essentially means the recovery of energy stored in cotton textile waste, is scientifically justified until the complete recycling of waste is achieved.

Pellet burning process December 2023

The study of the combustion process of non-wood biomass took place in the “Environmental Monitoring Laboratory” of the Institute of Energy Systems and Environment at Riga Technical University, where an experimental stand has been established in accordance with LVS EN 303-5 standard. The study of the combustion process for each fuel took 3 hours. The chemical composition of the flue gases, the amount of particulate matter and the efficiency of the boiler were measured. Non-wood biomass types have been compared with each other and with the Ecodesign Directive, the Ecolabel and Class 3 of the LVS EN 303-5 standard. In the first round, 13 different types of biomass pellets were tested.

Testing of pellets November 2023

To evaluate the quality of the produced pellets, testing was conducted at the accredited “Environmental Monitoring Laboratory” of the Institute of Energy Systems and Environment at Riga Technical University. The accreditation scope of this laboratory is physical and mechanical testing of solid biofuels.  Pellets were tested according to the methodology based on ISO standards regarding the testing of solid biofuels. The performed tests were: moisture content (%), mechanical durability (%), bulk density (kg/m³), gross calorific and the net calorific value (MJ/kg), ash melting point (°C).

Pressing of pellets October 2023

The suitability of biomass for use as fuel is being tested in pellet boilers, which remain increasingly popular. The production of lab-level pellets takes place in small quantities (approximately 20 kg per portion) and with a relatively low-power machine. The machine is theoretically composed of two parts that are pressed against each other with little force. The bottom part is a circular disc with coned holes (matrix), where biomass is compressed. The lower part is connected to the electric motor, which rotates the matrix. The top part consists of rolls (push-rolls) that rotate because they are pressed onto the matrix. Biomass is extruded into the matrix in the place of contact and pellets are formed. There is significant friction in the process, so temperatures of up to 90 degrees ^oC are reached, which activates lignin in biomass and improves pellet strength. However, before production the biomass must be prepared – crushed (3-5 mm) and reached the appropriate moisture level (12-18%). If pellets from different biomasses are formed, they need to be mixed evenly.

Testing of biomass September 2023

Based on the inventory of biomass available in Latvia, various types of biomass were collected and brought to the laboratory. Immediately after bringing the biomass to the laboratory, a representative sample was taken for moisture determination. The biomass obtained from the moisture test was milled into powder form (particle size < 1 mm), which was used for the following tests: moisture content of the analysed sample (%), ash content (%), calorific value (MJ/kg), and ash fusibility (°C). Almost all biomass types tested showed an ash content greater than 2%, which means that most alternative biomass types will cause additional maintenance in the combustion boilers if used alone. The calorific value of most of the tested biomass types is greater than 16.5 MJ/kg, indicating their potential for use in pellet production and heat energy generation. Most of the tested samples showed an ash melting point below 1100 °C, indicating a potential risk of ash slag formation.

Collection of biomass August 2023

The project focuses on the production, testing and evaluation of non-wood biomass pellets. The experiments required harvesting about 50 kg of different biomass to be tested. In general, grass, leaves, reeds, Canada Goldenrod, brewing, straw, buckwheat, cotton and cannabis were harvested. In laboratory conditions, biomass was also dried for further use in pellet production.

Biomass inventory March 2023

Currently, the main biomass used for energy production is wood, which accounts for a total of 64 PJ in consumption in Latvia. In order to replace this amount of energy with lower quality or alternative biomass, an evaluation of material flows was carried out. A Sankey diagram approach is used to visualize material flows. These graphs show what amounts of resources are available and what amounts are being used. Inventory of biomass such as wood, straw, leaves, brewer’s spent grain and reeds and creation of flows has been carried out. For a large number of raw materials, data on their volumes are not available, so assumptions are essential. The relevant assumptions are based, where possible, on scientific literature, related statistical data and data from other countries.