Manuel Eduardo Ferreira

Ash Sintering in a Biomass Pellet Boiler

The market for residential pellet burning equipments is well developed in some European countries like Germany, Austria and Italy and rapidly expanding in others. As a consequence the pellet production has also grown, although a large fraction is destined for industrial applications such as coal co-combustion. Due to the existence of chemical elements such as Na, K and Si, the pellet combustion can lead to agglomerated ashes on the grate of the burner causing problems for its proper operation.The present work aimed to study the influence of temperature and air flows in the ash agglomeration at the grate. For this purpose, it was assembled an experimental setup that, in a brief, description consists of: i) boiler, whose burner allows the regulation of the primary and secondary air flow, ii) variable flow exhaust gases extraction system, iii) controllable feeding system, iv) heat dissipation system, v) data acquisition and control system, vi) exhaust gases analysis system.The results indicate an increased formation of agglomerated ash with increasing of temperature. In addition, they also suggest the influence of excess air and primary air fraction in that formation, and the existence of an optimum working condition for high excess air and a primary air fraction of around 30%. The application of swirl in the secondary air improves both the flame stability and enables an efficient combustion into regions where the ash agglomeration is reduced. Moreover, they also show that there are other factors that influence the ash agglomeration, mostly related to the changing of the chemical elements ratio due to vaporization of the more volatile species.Copyright

Development and Optimization of a Small Scale Pellet Burner

Environmental concerns and the drive to reduce the dependence on petroleum brought the use of renewable energies to the forefront. Biomass appears as a very interesting alternative for direct conversion into heat. In this context, densified forms of biomass such as pellets are of great relevance because of their easy of use, high efficiency and low emissions.The practical interest in pellet combustion has been driven by the domestic heating sector, which favors the characteristics that are intrinsic of this fuel, despite its relatively higher price. However, the growing costs of fossil fuels have extended the interest of pellet fuels into industrial applications, including co-firing in power stations.A fast growing market includes the retrofitting of existing fuel boilers and furnaces with alternative burners that can be fitted into existing combustion systems. Such an approach has proved very attractive due to the low installation cost and the growing existence of fuels produced in the vicinity of the end user. This involves in most cases a custom built application which requires a high level of flexibility to variable operating conditions.This work reports on the development of a 120 kW pellet burner. A prototype of the burner was built that enables the independent control of the air supply into various regions of the combustion chamber and an accurate supply of fuel. The burner was fitted into a testing furnace of cylindrical shape oriented horizontally. Its diameter is 0.5 m and is constructed in a modular fashion with a total length of 2.2 m. All the facility is fully instrumented and includes: temperature data in various locations inside the chamber, flue gases emissions (CO, CO2, NOx) measurements and flow rates.The objective of the test and development is to optimize the combustion over the thermal load range of the facility. The excess air, fuel supply (primary and secondary) and the shape of the furnace grate enable the optimization of the burner with CO emissions of approximately 50 ppm, well below the acceptable limits.Copyright

Optimization of an Effervescent Atomizer to the Combustion of Residue Oils

This paper reports the geometrical optimization of an effervescent atomizer used in the combustion of used recycled oils. The objective was to obtain stable flames while minimizing the emission levels. A test facility was designed and constructed, which included: a furnace rated at a thermal input of 300 kW and a swirl generator as a part of the burner setup for the application of the effervescent atomizer. Other auxiliary facilities were also included, such as: cooling system, air supplies and pre-heating gas burner. Combustion tests were carried out with used recycled oil having a viscosity of 46 mm2 /s (50°C) and a higher heating value of 44.6 MJ/kg. Results included qualitative observations of the ignition and flame stabilization, emission concentrations and LDA velocity measurements of the flow field produced by the swirl generator with and without flame. The results show a good performance of the swirl generator in the process of fuel/air mixing inside the furnace, which results in very low emission levels. The various tests carried out with different geometric configurations of the burning facility clearly suggest that the high velocity and penetration of the spray require an adequate design of the swirl generator and the nozzle orifice, in order to obtain a good air/fuel mixture inside the furnace.Copyright

Drying Kinetics of Solid Biomass

The growing costs of conventional energy resources has significantly changed the economies and led to an increased demand for biomass. Biomass in its natural state has a high moisture content, which reduces the combustion efficiency and may cause problems in its processing. One of the most widely used forms of solid biomass concerns pellets that are often manufactured from saw dust. The manufacturing process requires that the raw material should be supplied in controllable conditions of humidity (in the order of 10%, dry basis); otherwise the final product will have poor mechanical properties. So it is essential to do the drying process to reduce the moisture content to acceptable values and to improve the efficiency of using of this product. In this way becomes necessary to study the various parameters that influence the drying process of biomass. For this purpose a drying wind tunnel was built. The facility consists of a ventilator, an electrical heating system and settling chamber and a testing chamber. This facility allows the study of the influence of moisture content and initial grain size of samples and the temperature and air velocity in the drying process of biomass. Air is supplied into a sample of biomass and its temperature and humidity are monitored along time. The humidity is measured by weighting the sample at regular intervals. Measurements were carried out on pine sawdust that was sieved into samples of various particle size. The temperature and air velocity was varied for each sample and the drying kinetics were used to derive working correlations from the experimental data. The results have shown that the gas temperature is the most important parameter in the drying of sawdust. The data was also correlated with dimensionless parameters.Copyright

Optimization of a Small Scale Pellet Boiler

Environmental concerns and the drive to reduce the dependence on petroleum based fuels brought the use of renewable energies to the forefront. Biomass appears as a very interesting option for direct conversion into heat. In this context, densified forms of biomass such as pellets are of great relevance because of their easy of use, high efficiency and low emissions. Expected trends in the biomass market suggest that equipments should operate over a wide range of thermal loads and with fuels derived from lower quality raw materials; simultaneously, a high efficiency and low emissions are taken for granted. Currently, biomass domestic boilers prove to be very sensitive to fuel characteristics and load conditions. This work reports on the development of a 15 kW net pellet boiler. A prototype was built that enables the independent control of the air supply into various regions of the combustion chamber and an accurate supply of fuel. The test rig also includes: boiler and flue gases extraction system; feeding system; heat dissipation system; flue gas analyzer; data acquisition system and all sensors. In order to optimize the combustion conditions, pollutant emissions and their relation with feeding conditions, primary and secondary air flow rate and excess of air was analyzed. The results suggest that this burner is a promising for implementation in domestic boilers. The advantages are: CO emissions well below those observed in similar equipments and the capacity to maintain the emissions level constant under different loading conditions.Copyright