Shigekatsu Mori

Studying the mechanisms of ignition of coal particles by TG-DTA

The mechanisms of ignition of coal of different quality, such as anthracite, bituminous coal and lignite, were studied by thermogravimetry (TG) and differential thermal analysis (DTA). Experiments on coal ignition were carried out at a low heating rate (10 K min−1) with particle sizes ranging from 37 to 4000 μm. It is concluded from this experimental work that 1. (1) ignition measurement by TG-DTA is an excellent method for accurate determination of the ignition temperature of coal particles; 2. (2) with increasing coal quality from lignite through bituminous coal to anthracite, the type of ignition changes from homogeneous ignition through hetero-homogeneous ignition to heterogeneous ignition, and the ignition temperatures also increase; 3. (3) with increasing coal particle size, the type of ignition of Kaipin bituminous coal changes from hetero-homogeneous to homogeneous ignition, and ignition of the char separates from that of the volatile matter and shifts to a higher temperature, whereas both types of ignition of Loy Yang lignite coal and Hongay anthracite coal are not effected by particle size.

Combustion test of refuse derived fuel in a fluidized bed

Abstract Power generation from refuse derived fuel (RDF) is one of the promising technologies for the utilization of municipal solid waste. To understand the combustion behavior of two kinds of RDF burnt in a fluidized bed incinerator, commercial sized RDF was fed continuously into a 0.3×0.3 m 2 and 2.73 m high bubbling type fluidized bed combustor. Gases such as CO, NO x , SO x and HCl concentrations in the flue gas from the combustor were detected by a continuous measurement system. It was found that, for RDF-A which is lower in density and strength than RDF-B, the concentrations of CO in flue gas are high and are strongly affected by the air ratio. When secondary air was injected, the CO concentrations for both RDF-A and RDF-B were decreased. The increase in the air ratio led to an increase of NO x concentration when only primary air was injected at a bed temperature of 1073 K. The addition of secondary air effectively reduced the NO x level for both RDF-A and RDF-B. The temperature where the HCl concentration was the lowest was about 1073 K. Nonetheless the concentrations of HCl were always less than 60 ppm in all experiments. The HCl removal ratio by the calcium compound was higher than 70% even though the bed temperature was higher than 1173K. This indicates that the added calcium compound in the RDFs effectively controlled the HCl emissions.

Fundamental study of the behavior of chlorine during the combustion of single RDF.

A fundamental study of the combustion characteristics and the de-HCl behavior of a single refuse-derived fuel (RDF) pellet was carried out to explain the de-HCl phenomena of RDF during fluidized bed combustion and to provide data for the development of high efficiency power generation technology using RDF. In this research, combustion and pyrolysis experiments were carried out in an electrical furnace using a series of model and actual RDF samples. The de-HCl capability of Ca(OH)2 in RDF was evaluated by measuring the emission fraction of HCl in the flue gas and the capture fraction of Cl in the residue. It was found that the capture fraction of Cl components in the residue increased from 0 to nearly 70% when the molar ratio of Ca/Cl was changed from 0 to around 13. Apparently, the capture fraction also decreased with increasing oxygen concentration in the feed gas. The devolatilization process of RDF was confirmed to be a very important part of de-HCl process. The effect of temperature profile of the RDF pellet on the de-HCl process, as it varies with the heating rate of RDF and the oxygen concentration in the vicinity of the sample, is discussed.

DRYING OF CLAY AND NONCLAY MEDIA : HEAT AND MASS TRANSFER AND QUALITY ASPECTS

Abstract The researches on drying of clay and nonclay media are briefly reviewed and the role of drying in the manufacturing process is summarized. The drying process must be carefully controlled to maintain the desired product configuration. Inefficient completion of drying and poor operation of the dryer influence directly the product quality. The importance of R&D on the heat and moisture transfer phenomena, shrinkage mechanisms, deformation behavior, strain-stress relations and the internal pressure in the media during drying is stressed. Suggestions are given for further improvement of the drying process and improved design of the molding and casting processes for higher product quality

Combustion of refuse derived fuel in a fluidized bed

Power generation from Refuse Derived Fuel (RDF) is an attractive utilization technology of municipal solid waste. To explain the behavior of RDF-fired fluidized bed incinerator, the commercial size RDF was continuously burnt in a 30×30 cm bubbling type fluidized-bed combustor. It was found that 12 kg/h of RDF feed rate was too high feed for this test unit and the CO level was higher than 500 ppm. However, 10 kg/h of RDF was a proper feed rate and the CO level was kept under 150 ppm. Secondary air injection and changing air ratio from the pipe grid were effective for the complete combustion of RDE. It was also found that HCl concentration in flue gas was controlled by the calcium component contained in RDF and its level was decreased with decreasing the combustor temperature.

High temperature air-blown woody biomass gasification model for the estimation of an entrained down-flow gasifier

A high temperature air-blown gasification model for woody biomass is developed based on an air-blown gasification experiment. A high temperature air-blown gasification experiment on woody biomass in an entrained down-flow gasifier is carried out, and then the simple gasification model is developed based on the experimental results. In the experiment, air-blown gasification is conducted to demonstrate the behavior of this process. Pulverized wood is used as the gasification fuel, which is injected directly into the entrained down-flow gasifier by the pulverized wood banner. The pulverized wood is sieved through 60 mesh and supplied at rates of 19 and 27kg/h. The oxygen-carbon molar ratio (O/C) is employed as the operational condition instead of the air ratio. The maximum temperature achievable is over 1400K when the O/C is from 1.26 to 1.84. The results show that the gas composition is followed by the CO-shift reaction equilibrium. Therefore, the air-blown gasification model is developed based on the CO-shift reaction equilibrium. The simple gasification model agrees well with the experimental results. From calculations in large-scale units, the cold gas is able to achieve 80% efficiency in the air-blown gasification, when the woody biomass feedrate is over 1000kg/h and input air temperature is 700K.

Drying Enhancement of Clay Slab by Microwave Heating

ABSTRACT The effect of internal heating by microwave on the drying behavior of a slab was studied. A wet sample of kaolin pressed into a slab was subjected in microwave irradiation of 2.45 GHz. The absorption of microwave energy into a wet slab can be expressed by a function of the moisture content and the pathway length, which is a similar form to Lambert-Beers law. The drying behavior was compared among three modes: microwave irradiation, hot air heating and radiation heating in an oven. Microwave heating with a constant power resulted in breaking the sample when the internal temperature achieves at 373 K. However, if the power was controlled to maintain the temperature less than the boiling point of water, the drying succeeded without any crack generation until the completion with a significantly faster drying rate than in convective heating or in the oven. It is also noted that the transient behavior of the temperature is quite different from the conventional drying.

Adsorption removal of pollutants by active cokes produced from sludge in the energy recycle process of wastes.

This study proposes a recycling system of sludge into active cokes and the fundamental examinations for the application were carried out. In the system, active cokes were produced by carbonizing pellets of sludge in a steam stream. Pyrolysis gas yielded by carbonization can be available to a fuel for a steam generation boiler. The exhaust heat from the boiler is used sequentially for drying of sludge. The active cokes are applied to the adsorbent for dioxin removal in exhaust gas from incinerators of wastes, or for purification of gas obtained in a gasification process of wastes, particularly removal of H2S. The used adsorbent is not recycled, but incinerated in the furnace without a desorption process to decompose adsorbed dioxin or to oxidize H2S for a sequential desulfurization process of SO2. Dry pellets of sludge were carbonized in a quartz tube reactor under various atmospheres. The micro pore structure and the adsorption performance of the cokes produced without activation process were examined. The micro pore structure was influenced by the temperature, the sort of flow gas (N2, CO2 and steam) and carbonization time, and the active cokes produced under the condition of the temperature 823 K for 60 min in the steam atmosphere had a largest specific surface area in the diameter less than 5 nm. The amount of benzene adsorption as an alternative substance of dioxin into the active cokes had a similar quality to a commercial active char produced from coal if it was evaluated by adsorption per a unit specific surface area. This fundamental knowledge must be reflected to an optimum design for development of a simple continuous process to produce the active cokes by a fluidized bed type of the carbonization furnace.

EFFECT OF INTERMITTENT HEATING ON DRYING-INDUCED STRAIN-STRESS OF MOLDED CLAY

ABSTRACT Parametric analyses of the strain-stress in the drying process are performed to study the influence of the intermittent drying on the behaviors of drying-induced strain-stress and deformation as well as the drying characteristic. The transient three-dimensional problem of strain-stress and heat and moisture transfer in a slab is solved simultaneously by the finite element method. The dimensionless parameters are introduced to generalize the problem in the conservation equations of heat and moisture transfer. The intermittent drying is modeled by applying periodically smaller and larger Biot numbers to the boundary conditions. The maximum tensile and compressive stresses fluctuate, and fall remarkably during the smaller Biot number period when a slab is heated intermittently. The peak stress of the fluctuation exceeds beyond the case in the continuous healing where the overall drying rate is almost equivalent to that in the intermittent beating, but the reduction of the stresses takes place rapidl...

EFFECT OF HEATING MODES ON INTERNAL STRAIN–STRESS FORMATION DURING DRYING OF MOLDED CERAMICS

Parametric analyses in drying processes of molded ceramics are performed to investigate the influence of heating modes on the formation of drying-induced strain–stress as well as the drying characteristic. The transient three-dimensional problem of strain–stress and heat and moisture transfer in a slab is solved simultaneously by the finite element method. Three modes of hot air, intermittent and internal heating are compared by modeling in the normalized parameters. The tensile and compressive stresses fluctuate, and fall remarkably during the low Biot number period when the slab is heated intermittently. In the internal heating mode, the drying rate is the fastest but stress formation is maintained at the lowest level among the three modes. This effectiveness of the internal heating is investigated experimentally by employing the microwave heating as well.