# Effect of Paper Sludge and Dendromass on Properties of Phytomass Pellets
## 1 Introduction  
The European Union is working to move to clean energy, which means a decrease in the consumption of fossil fuels and an increase the proportion of renewable fuel energy sources. The issue of plant biomass, which is beginning to be used in larger quantities, is currently being addressed. Plant biomass can be processed into pellets or other forms for combustion purposes. Combustion of agricultural pellets brings with it various problems, and one of the most common is the low melting point of ash. The most important issue is the deformation temperature of the ash, i.e., when the ash starts to stick to the walls and parts of the boiler. After reaching the deformation temperature, the ash turns into slag, sinter, and other agglomerates. This means that combustion is influenced, and may even be stopped. The disadvantages of straw and other residues are also higher amounts of ash, and forming aggressive compounds during combustion. After reaching the deformation temperature, the ash turns into slag, sinter, and other agglomerates. These agglomerates inhibit the air supply to the base burning layer, such that the combustion process can be limited. This means that combustion is disrupted, and may even be stopped. Some of the ash particles are transferred by the flue gases and form deposits on the boiler walls. Higher emissions from the combustion of plant biomass containing undesirable compounds, compared to wood pellets, also cannot be ignored [1; 2; 3; 4]. There are several ways to eliminate or reduce these disadvantages. One of the possibilities is to optimize the combustion device, or co-combustion of plant biomass, with another fuel. Co-firing of wheat straw, pine stem wood, and softwood bark in a 150 kW boiler shows less signs of slaging and fouling propensities than combustion of pure straw. The proportion of plant biomass is given on the basis of the effect on the individual properties of the combustion process [5]. The co-firing of straw and natural gas has proved ineffective since the ash caused exposure to superheaters. The high flue gas temperature in the boiler was the reason forstraw ash sticking on the walls. These problems are reduced by co-firing coal and straw because the coal contains sulfur, and ash adds Al and Si. The ash and sulfur binds the alkali from the straw, inhibiting deposit formation and corrosion. It was determined that the concentration of sulfur resulted in a decrease of chlorine-induced corrosion in waste combustors. Based on calculations, the content of sulfur changes the melting point of the potassium compound to higher temperatures (from approximately 800 to 1100 \({}^{\circ}\)C). The co-firing of straw and coal can be an effective method to utilize straw for power production [6; 7; 8]. The results of co-firing these fuels in a full-scale power plant indicated a decrease of NO and SO\({}_{2}\) concentrations, and this was achieved by the addition of straw up to 20%. The decrease in NO concentration was due to lower overall fuel-N conversion. The sulfur reduction was recorded with increasing straw proportion, and could be associated with the high potassium concentration of straw [9]. Improving the properties of plant biomass can be also achieved by adding various additives that increase the melting temperature of ash. Additives have various chemical compositions, and in the work of [PERSON] et al. the ash related issues of briquettes were mitigated with phosphorus-based additives. Maize straw briquettes with the addition of ammonium dihydrogen phosphate and calcium phosphate monobasic significantly inhibited ash slagging and melting problems [10]. The influence of kaolin and dolomite as additives to the different straws was also investigated. These additives were added to rape, wheat, and barley straw ashes at 550 \({}^{\circ}\)C, and the results showed that the low melting points of the straws could be enhanced by kaolin and dolomite [11]. The tests of ashes from mixtures of rye straw and three additives were done at the same conditions.