Utilization of biomass fuel is attracting more attention due to its advantage to the global warming problem. Biocoke (BIC), highly densified biomass briquette, has unique features such as economical advantages for its versatility of biomass resources, high volumetric calorific value because of its high density and high mechanical strength. The BIC made of Reynoutria japonica (Japanese knotweed), cylindrical blocks with 48 mm in diameter and 85 mm in length, are selected in the study. To investigate the fundamental thermal and combustion properties of the BIC, ignition and combustion behaviors are observed in the hot air flow. The results show that the ignition mode and the mass loss rate during the flaming combustion are influenced by the supplied air temperature with an interesting manner. This may be ascribed to the thickness of the heated layer inside the BIC depending on the preheating condition. This is because the heated thickness strongly controls the evolution characteristics of pyrolysis gas and the temperature distribution inside the BIC depends on the distinctive property of the BIC, high density. Finally, a new concept of BIC combustion method is proposed considering the BIC unique physical features as well as its fundamental combustion characteristics.
Characteristics of flame propagation over combustible hydrates, methane hydrate and natural gas hydrate, in a laminar flat plate boundary layer has been investigated experimentally. The fine powder hydrate is packed in an insulated container and set flush with the bottom wall of the wind tunnel. The free stream velocity (U∞) is varied from 0.4m/s to 1.1m/s. The hydrate is ignited at the downstream end of the container when the surface temperature at the center of the hydrate surface reaches that at the igniton (Ts,ig). Ts,ig is varied from -80℃ to -20℃. The motion of the flame propagation is recorded by a digital video camera. The location of the leading flame edge is measured by using the image of the video camera. Two types of flame propagation are observed. When Ts,ig is low, the flame propagates almost linearly with time with the velocity around 3-4mm/s. In this case, the flame propagation velocity is determined by the dissociation rate of the hydrate. When Ts,ig is relatively high, the periodic flame propagation is observed. The maximum flame propagation velocity reaches around 800mm/s. In this case, the premixed mixture is formed over the hydrate surface because the hydrate can dissociate in the atmospheric condition and the flame propagates in the premixed mixture.
Scale-modeling is a powerful tool to understand the detail of a large-scale fire. A scale-model experiment must be so designed that it reproduces the prototype phenomenon. In doing so, several hypotheses must be established based on dimensional considerations and their validity must be tested. This article discusses techniques to conduct a reliable scale-modeling study and presents some examples.
Global demand for formation of sustainable society has been becoming stronger. In this situation a role of waste incineration facilities have diversified from reduction of the environmental pollution to gain in the efficiency of power generation. In this document we mentioned a high efficiency waste to energy plant. The strongest point of the plant is high temperature air combustion technology that can realize the stable combustion with low excess air, which is originally developed by JFE Engineering Corporation to meet the social requirements.
In Japan, the sewage sludge quantity has been increasing gradually as the spread of sewage increases. It is indispensable to reduce the amount of sludge because it is difficult to increase the final disposal dump newly. Especially, combustion process is selected in the big city and its outskirts. Recently, the reduction of the nitrous oxide exhausted by incinerating the sewage sludge is requested for the global warming prevention. Moreover, there is a trend that tries to use the sewage sludge that is the “carbon-neutral biomass” as the energy resource. In this report, it shows the outline of sewage treatment process, typical sludge properties and a general sewage sludge combustion method, and it introduces a recent sewage sludge treatment trend.
Heating actions using industrial furnaces enables the material to change its mechanical and/or scientific/chemical properties to desired conditions. Various kinds of industrial furnaces in different sizes are often used in each industry. In Japan, the estimated number of industrial furnaces is about 39000. Energy saving development of industrial furnaces started with the first oil crisis on 1973. Since then various kinds of development and improvement have been performed. Examples of blast furnace plants and reheating furnaces for rolling mill are given on this paper. The development of the high temperature air combustion system of high performance furnaces is succeeded and getting spread in the market. JIFMA's activities for International standards for industrial furnaces ISO/TC244, new work item of method of measuring energy balance and calculating efficiency will contribute to the low carbon society.
Among many methods for reducing NOx emission, a self-recirculating type burner has received considerable attention in small boilers because the NOx emission level can be well reduced without great cost and space. In this study, further reduction in the NOx emission has been attempted by cooling the recirculating gas, because the mass flow rate of the recirculating burned gas under cold flow condition is larger than that under burning condition, and hence, it can be expected that the combustion air will be diluted to greater extent with the recirculating burned gas if the recirculating gas is cooled down. Results show that the NOx emission is decreased by the cooling. For example, the NOx level of 22 ppm for a 65 kW burner at air excess ratio 1.4 is decreased to 13 ppm if the recirculating gas of 775℃ is cooled down to 575℃. Measurements in the combustion field show that the highest temperature in the reaction zone is decreased to 1122℃ and the NOx level is reduced around 10 ppm just downstream the main reaction zone, suggesting that NOx formation is almost ceased and saturated. Additional measurements for various heat output burners of 140, 620, and 1620 kW also show that the NOx emission levels can be successfully decreased by the cooling. Therefore, it is confirmed that cooling of the recirculating gas is very useful to further reduce the NOx emission in the self-recirculation type burner.