Behavior of Inorganic Matters during Coal Gasification

  • Author / Creator
    Hosseini, Seyyedali
  • Inorganic particle deposition and unsteady slag flow is one of the main issues in entrained-flow gasifiers causing several problems, especially, tap hole blockage and emergency shutdown. For the first part of the experiments in this study, slag collector probe was used to take depositions and analyze blockage in terms of operating conditions and particle trajectories. Increasing the temperature resulted in higher total deposition. Although, by increasing the temperature the weight of slag droplets increased, but, it did not guarantee the safe operation by preventing blockage. The reason was understood to be related to different effects of temperature on ash deposition and slag flow rate. Increasing the temperature, increased stickiness of the particles and amount of the deposition, but, decreased the viscosity and caused higher slag flow rate which could remove more deposition from the plate. Using two coal types proved that ash composition has essential effect on the amount and thickness of the deposition. For fuel with higher ash viscosity, increasing the temperature resulted in higher blockage probability. Back-Scattered Electron (BSE) of this fuel showed that iron-bearing particles on the surface of slag made the surface sticky for other particles to stick. For this fuel, the effect of increase in the particle stickiness was higher than the decrease in slag viscosity. Computer Controlled Scanning Electron Microscopy (CCSEM) analysis of this fuel showed that the percentage of excluded minerals was higher than included ones and most of iron-bearing particles were in excluded condition. The coal with higher calcium content had lower ash viscosity and increasing the temperature resulted in higher slag flow and lower blockage probability. CCSEM analysis of this fuel showed that most of calcium was in included nature which resulted in more particle coalescence making big agglomerations. The most important understanding of comparing the results of these two fuels was that inorganic matter loading (especially loading rate of iron and calcium) can be more effective than the viscosity in inorganic deposition. Increasing particle velocity mostly resulted in lower deposition. The reason is most probably related to the residence time, carbon conversion and kinetic energy. Large particles at low temperature and high gas flow had lowest deposition tendency. Two different types of feeder configurations were used to evaluate the effect of particle trajectory. The results showed that the particle injection pattern has significant effect on the deposition growth at different locations. The feeder leading the particles to collide with the wall in a narrow area resulted in severe deposition near the feeding spot. Other feeder with wider sticky surface resulted in more uniform deposition with lower thickness. Finally, it was understood that the traditional deposition models must be enhanced by considering new parameters such as iron loading, mineral association types and the deposit surface formed by aerodynamic of the feeder. The difference of the iron concentration on the surface and bulk of depositions made a motivation to investigate the possibility of the surface reactions. Analyzing slag surface under reducing and inert atmosphere showed that iron can react with gaseous species and leave the surface which can lead to a decrease in the surface stickiness. The second set of the experiments is performed based on controlled injection of the inorganic particles. The results showed higher deposition by increasing the temperature. Increasing the particle velocity slightly decreased the deposition at lower temperature and slightly increased the deposition at higher temperature. It was understood the effect of velocity is related to the liquid fraction of particles. Increasing the impact angle of the particles slightly led to higher deposition. Effects of the impact angle and velocity were much lower than the effect of temperature. A 2D-axisymetric model was developed to simulate inorganic deposition. Particle interaction with the wall was introduced to the model as User Defined Function (UDF). The operating condition parameters and the properties of the inorganic matters were considered in the sub-model and the results were saved in User Defined Memory (UDM). Comparison of the modeling and experimental results showed a reliable accuracy of location of deposition, but, the error of the amount of deposition was high which thought to be reasonable considering the simplifying assumptions. It was understood ignoring the mineral association with coal could be the main source of errors.  

  • Subjects / Keywords
  • Graduation date
    Fall 2015
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.