In order to reduce CO2 emission from coal-fired boiler, it is expected that ammonia is used as a fuel which has no carbon content. In that case, it is concerned that NOx concentration in flue gas increases because ammonia has more nitrogen content than coal. In this study, with 10 MWth test furnace, ammonia and pulverized coal co-firing test was conducted with ammonia velocity as a parameter at 20 % co-firing rate. The result shows that NOx concentration in flue gas of co-firing is as same as that of single coal combustion. In addition, co-firing test for evaluating effect of two-stage combustion ratio, heat input and fuel ratio on NOx was conducted. The results show that condition for reducing NOx concentration in ammonia co-firing is clarified.

Removal of ash deposits formed on boiler tubes or furnace walls is required to inhibit the slagging and fouling problems. The effect of coal type on the growth and gravity shedding of ash deposits was evaluated by ash deposition experiments and scanning electron microscope (SEM) analysis of the cross-sectional structures of the ash deposits. Three types of pulverized coalbituminous, subbituminous, and lignite coalswere tested in the experiments. The behavior of ash deposition on a water-cooled tube inserted at an inner furnace temperature of 1673 K was evaluated by video camera observation, temporal variation of the tube surface temperature, and chemical equilibrium calculations. For the subbituminous and lignite coals, the cycle periods of ash shedding were longer than that of the bituminous coal because of the formation of a wider ash deposit. The distributions of particle packing fraction (PPF), the particle sizes, and the chemical compositions of the ash particles within the deposits were analyzed by an SEM and a computer-controlled SEM. A powder layer was formed near the tube, and the PPF in the deposit gradually increased with the growth of the deposit because of ash coalescence. The effects of the PPF on the ash shedding were larger than that of the chemical compositions. Therefore, the deposit detachment occurred within the powder layer that became low strength due to the low PPF. Additionally, the thickness of the residual deposit that remained on the tube after ash shedding depended on the thickness of the powder layer in the deposit. The subbituminous and lignite coals have formed a deposit with a thin powder layer because ash coalescence progressed near the tube surface. Therefore, their residual deposits have been thin compared with the bituminous coal. The findings of this study can be put to practical use in the design of pulverized coal-fired boilers.

In coal-fired power generation, it is necessary to pulverize coal, and a vertical roller mill with excellent crushing efficiency has become the mainstream. However, In the process of pulverization by compression and shear, abnormal vibrations, which are considered to be self-excited vibration, occurs rarely. As a method of reducing self-excited vibration, adding water has been empirically performed in the field. Since the powder state changes due to water addition, it is necessary to investigate how the vibration characteristics and slip characteristics change. In this paper, we examined the effects of adding water to Artificial coal, Sub-bituminous coal A, and Sub-bituminous coal B with different powder characteristics on the dynamic friction characteristics and dynamic response generated between the roller and the powder. Investigating the relation between the RMS value of the horizontal acceleration response and the slip ratio indicates the degree of slippage of the roller. Next, we investigated the relation between the dynamic frictional characteristics generated during rolling and the slip ratio and found that the Slip-Stick phenomenon remarkably appeared at the test machine speed at which the vibration acceleration was maximum even when water was added. Also, a frequency analysis showed that when the vibration acceleration increased, the resonance frequency decreased, and the phenomenon of uniting was confirmed for all types of coal, suggesting that the abnormal vibration that occurred was self-excited vibration.

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