Emi OHNO’s research while affiliated with IHI Corporation and other places

Biomass fuel is promoted toward a target of net GHG zero emissions in 2050 that Japanese government announced last October 2020. Using biomass pellets in pulverized coal fired power plants are recently increasing. IHI has supplied the co-firing power plants of 30cal% or more biomass pellets with coal. The biomass particles after pulverization by biomass mills are transported to the burners through the fuel pipes by air. Deposition of the biomass particles in a fuel pipe on the way to a burner make a serious impact on the stable combustion and boiler operation. It is important to understand conditions of occurring deposition in order to prevent the deposition of the biomass particles in the fuel pipe. However, various types of pellets are used, and conditions of occurring deposition is depending on the size and shape of the biomass particles. In this test, the transportation of two types of biomass particles is observed by using a transparent horizontal pipe with 30m length. This result suggests that conditions of occurring deposition is different depending on the shape of biomass particles.

Coal-fired power generation is expected to continue to be used in the future. In this process, coal must first be pulverized, and vertical roller mills are used. However, during the pulverization process, abnormal vibration called self-excited vibration rarely occurs. In previous study, a small element testing machine was used to investigate this problem. The relationship between the slip ratio and the coefficient of friction between the roller and the powder showed a characteristic change when abnormal vibration occurred, but it is not clear whether this is the cause of the self-excited vibration. To investigate whether the characteristic relationship between the slip ratio and friction coefficient observed during abnormal vibration is a cause of self-excited vibration, a simulation model was created by applying the relationship between the slip ratio and friction coefficient in the experiment to a mechanical model for a small element testing machine and comparing the results with those of the experiment. As a result, the model was able to represent the vibration frequency that was confirmed in the experiment when abnormal vibration occurred. However, the dependence of the roller horizontal acceleration on the running speed could not be confirmed. The relationship between the slip ratio and the coefficient of friction could not be reproduced, but the change in the coefficient of friction could be reproduced. The vibration modes that are observed when abnormal vibration occurs were confirmed, but it is not clear whether they can be regarded as self-excited vibration or not.

The influence of oxygen concentration on the char burnout characteristics of the coniferous tree (beefwood) and broadleaf tree (beech), ưhich are abundantly available in Vietnam under-reacting temperature of 800 o C, and 1000 °C was investigated using Macro TG. The obtained results showed that in rich O2 concentration, the particle size has little effect on char oxidation. However, the carbon conversion rate and the whole time of conversion decreases with an increase in particle size. There were some excepted cases contracting to this trend, mainly due to the difference in char samples' morphological structure at different sizes and operating temperatures in lean O2 concentration. The characteristics of biomass strongly affect the char oxidation rate. In all experiments, the conversion rate of char oxidation of the inside part of beefwood is higher than the bark's conversion rate. The oxidation rate of beech bark is higher than the one of the inside parts of the beech. There is no significant difference in char oxidation rate between the inside part of the beefwood and beech wood bark. However, all kinds of biomass in this study have a faster rate of oxidation than coal.

Biomass fuel is promoted toward a target of net Greenhouse Gas zero emissions in 2050 that Japanese government announced last October 2020. IHI have supplied the co-firing power plants of 30cal% or more biomass pellets with coal. The biomass particles after pulverization by biomass mills are transported to the burners through the fuel pipes by air. Deposition of the biomass particles in fuel pipes on the way to a burner make a serious impact on the stable combustion and boiler operation. It is important to understand the conditions under which deposition occurs. However, the velocity of starting deposition is depended on the size and shape of the biomass particles. In this test, the transportation of two types of biomass particles is observed. This result suggests that the air velocity not to deposit is different depending on the shape of biomass particles.

The reduction of CO2 emissions is required worldwide to prevent global warming. In the field of power generation, the reduction of CO2 emissions from coal-fired boilers is an urgent issue. In order to this problem, the use of hydrogen as a fuel, which does not emit CO2 when burned, is attracting attention. However, the cost of transporting and storing hydrogen has become an issue for its widespread use. The use of ammonia (NH3) as an energy carrier is attracting attention as a solution to this problem, since it has a high hydrogen content and is easier to liquefy, transport and store than hydrogen. In a previous study, we succeeded in co-firing pulverized coal/NH3 at a co-firing ratio of 20 % (on a lower heating value basis) with reduced NOx generation using a combustion test facility with a heat input of 10 MW. The objective of this study is to develop a burner that can achieve a higher co-firing ratio to simplify the system and to apply it to an actual boiler.

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.

This work focused on investigating the influence of the characteristics and size of the particle on combustion characteristics of char of the coniferous tree (beefwood) and broadleaf tree (beech) that are abundantly available in Vietnam during a low-oxygen combustion condition under different reacting temperatures (800 °C and 1000 °C). Results showed that reaction temperature plays a significant role in the rate of char oxidation. In the case of higher temperature, the rate of char oxidation is significantly shorter than that of lower temperature. The effect of particle sizes on oxidation is not as large as that of temperatures. In general, the rate of oxidation and the complete time of that decrease with increase in particle size. The characteristics of biomass strongly effect on the rate of char oxidation. In all experiments, the conversion rate of char oxidation of the inside part of the beefwood is higher than that of beefwood bark. Char oxidation rate of beech bark is higher than or nearly equal to that of the inside part of the beech. There is no significant difference in the rate of char oxidation between the inside part of the beefwood and beech wood bark. However, all kinds of biomass in this study have a faster rate of oxidation than that of coal. Therefore, these works can support the design of combustion reactors in a commercial plant.

In Japan, a feed-in tariff was introduced to promote and expand the renewable energy ratio to 22-24% by FY 2030. Biomass is one of important renewable energy. Recently, several biomass projects for not only fluidized bed boilers, but also pulverized coal fired boilers, are being planned around the world to reduce CO2 emissions as the main reason. The required particle size of woody biomass for combustion in a pulverized coal fired boiler is around 1mm, while that of coal is several tens of m. Woody biomass particles grinded by a mill are sent to burners via a fuel pipe by air. It is important to measure the particle size distribution in order to understand combustibility and grindability. However, it was unknown whether the particle size distribution could be measured by the same sampling method for pulverized coal. We conducted sampling tests of woody biomass particles in a fuel pipe using the isokinetic sampling method. As a result, we observed that the flow of woody biomass particles in the pipe was significantly non-uniform to the influence of the upstream elbow. It is necessary for woody biomass to measure at a pitch of at least 45 in order to obtain the particle size distribution in a fuel pipe.

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.