Takehiko Furusawa

Nitric oxide reduction by char and carbon monoxide: Fundamental kinetics of nitric oxide reduction in fluidizedbed combustion of coal

Abstract The reduction of nitric oxide during combustion of coal char in a fluidized-bed combustor was examined with respect to two reactions : a char-catalysed reaction; and a char-consuming reaction, which control nitric oxide emissions. The relative importance of the two reactions was investigated by measuring detailed material balances for the reactions. The product distribution was explained in terms of three fundamental parallel reaction paths. Reaction rates were investigated with a fixed-bed flow reactor over the temperature range 883–1194 K, the same as the fluidized bed combustor.

Relation between CO2-reactivity of coal char and BET surface area

Abstract Gasification rates of different carbonaceous materials were measured at temperatures from 1073 K to 1273 K and carbon dioxide partial pressure of 50 kPa. The surface areas of the chars were also measured at various levels of conversion. The conversion rates per unit BET surface area remained mostly constant over the range of higher conversion ( X > 0.4) and rates thus evaluated were expressed by a common straight line in an Arrhenius plot. Thus under the experimental conditions used differences in the gasification rates of various carbonaceous materials were interpreted by use of surface area only.

Flow of dense fluidized particles through an opening in a circulation system

Abstract Circulation of dense fluidized particles was studied in a two-dimensional bed which was divided by a partition plate with an opening to form two portions of fluidized beds with different gas velocities. The circulation rate of dense fluidized particles between the two beds was studied, by controlling the size of the opening and the gas velocity of an upflowing bed. The tested dimensions were 0.4 m × 0.1 m cross-section and 1.6 m height. The impulse response method using tracer particles treated by fluorescent dyes was employed to measure the circulation rate of solids, and signals from the tracer particles were detected by two optical fiber probes installed in a downcomer. The pressure drop across an opening through which fluidized particles were transported from a downflowing incipiently fluidized bed to an upflowing bubbling fluidized bed was measured directly, using a differential pressure transducer. The results show that the circulation rate of solids was controlled by the superficial velocity of an upflowing fluidized bed and the ratio of the opening area to the cross-sectional area of the downcomer. An equation taking account of the voidage of an upflowing bubbling bed was developed in order to correlate the circulation rate of solids with the pressure drop across an opening and with the opening ratio. The circulation rate observed for a single-vessel circulation system developed previously by the authors could also be well explained by the present analysis.

Conversion of char-bound nitrogen to nitric oxide during combustion

Conversion of char-bound nitrogen to NOx during combustion was measured for chars formed from nine coals. The effects of pyrolysis condition and coal rank of the parent coal on conversion of char-bound nitrogen to NOx are discussed. A model of NOx formation through combustion and NOx reduction on the internal surface of a single char particle was developed. The experimental results were fairly well explained by the model.

Prediction of CO2 gasification rate of char in fluidized bed gasifier

Abstract Chars from 14 different parent coals were produced in fluidized bed and the initial porosity and surface area were correlated with carbon content in the parent coals. Combination of previous results with the present experimental results led to the description of change in carbon dioxide gasification rate with increased conversion. The values calculated by the proposed equation were compared not only with the present data but also with the gasification rates reported by previous investigators. Carbon dioxide gasification rates of chars can be estimated by this equation.

CHEMICAL VAPOR DEPOSITION AND HOMOGENEOUS NUCLEATION IN MONOSILANE PYROLYSIS WITHIN INTERPARTICLE SPACES -APPLICATION OF FINES FORMATION ANALYSIS TO FLUIDIZED BED CVD-

The rate of silane pyrolysis was measured over the temperature ranging from 823K to 973K and over a relatively wide range of monosilane and hydrogen concentrations in quartz tube reactors with and without seed silicon particles. The homogeneous nucleation rate and heterogeneous CVD rate were separately evaluated and formulated as functions of temperature, and silane and hydrogen concentrations. The previously reported experimental observation of fines formation within fluidized bed CVD reactor was quantitatively explained using the present kinetics.

Development of a new system for circulating fluidized particles within a single vessel

Abstract A new system for circulating fluidized particles within a single vessel has been developed which has the same advantages as the dual-bed systems widely used for the FCC process and the Fluid Coker process. The interior of the vessel was divided into four sections by intersecting two flat vertical plates at right angles. Two sections were used for the upflowing bubbling fluidized beds and the other two sections were used for the downflowing bubble-free fluidized beds. Fluidized particles were circulated between the two upflowing beds, which were to be used as reactors, through the two downflowing beds, which were to be used as downcomers. Solid particles were fluidized by several streams of gas injected at several stages of the bed. The effects of these gas injection rates on the circulation rate of solids were investigated. The circulation rate of solids was measured using both a measuring box, which collected the overflowing particles, and the downward motion of a gauze net induced by the descending particles. The static pressure distribution within the vessel and the residence time distribution for coarse foreign solids in the system were measured. The present research demonstrated that the proposed system potentially had the same advantages as the conventional dual-bed system, and that the system can be applied to the simple gasification of biomass and solid wastes.

22 Nox emission control from a fluidized bed combustor of coal: Effects of in situ form char on “NO” reduction

Abstract A reaction of nitric oxide with char is known to play a significant role in the destruction of “NO” in a fluidized bed combustion system of coal. The kinetic behavior of the reaction in the presence of oxygen was investigated by means of a fixed bed reactor at a temperature of 500–680°C as well as a fluidized bed at a temperature of 600–800°C. The results indicated that the rate of “NO” reduction was significantly increased by the presence of oxygen up to 750°C and the rate was not significantly reduced at 800°C.

Gasification of biomass in a fluidized bed

Abstract The possibility of a gasification process for biomass material by use of a high-temperature fluidized bed was investigated. Lauan chips were chosen as an example of wood material from a tropical area and peanut shells as an example of agricultural waste. Gasification of these materials was carried out in a fluidized bed in the temperature range 400 – 1000 °C. The amounts of gas, char, tar and organic compounds produced were then measured. Finally, the feasibility of a process to gasify these materials was discussed based on the experimental results. The following results were obtained: (1) The yield of the product gas from the high-temperature carbonization of biomass material reached 87%, even when steam was not used for the reaction. (2) The maximum calorific value of the gas produced by means of the heat carrier method was 3870 kcal/N-m 3 when the gasification temperature was about 900°C.

Nitric oxide reduction by carbon monoxide over calcined limestone enhanced by simultaneous sulphur retention

Abstract Nitric oxide reduction by carbon monoxide over calcined limestones is enhanced by the coexistence of sulphur dioxide over a temperature range pertinent to f luidized-bed combustion. This demonstrates that the reduction of nitric oxide formed in fluidized-bed combustion of coal is promoted by simultaneous sulphur retention under a staged air firing. Thermogravimetric analysis indicated that the enhanced reduction of nitric oxide was attributed to the increase in catalytic activity of the calcined limestones used partially for sulphur retention.