Masanobu Hasatani

Effects of coal properties on recycled-NOx reduction in coal combustion with O2/recycled flue gas

The emission of NOx and the reduction of recycled-NOx in coal combustion with O2/recycled flue gas were experimentally studied in an electrically heated up flow combustor under low recycling ratio with three kinds of coal: a high volatile bituminous, a medium volatile bituminous and a semi-anthracite. The recycled flue gas was simulated with the mixture of CO2 and NOx. NOx emissions from the combustion of the three coals were firstly investigated under the recycling ratio ranging from 0 to 0.4 but without recycled-NOx. The results show that the relative release rate of fuel-nitrogen to volatile matter and the partitioning of volatile-N and char-N are more critical than volatile matter content and nitrogen content in coal for NOx emissions, especially in the fuel lean combustion. The experimental data on recycled-NO reduction indicate that the reduction efficiency increased with fuel equivalence ratio and recycling ratio. In the fuel rich region, the reduction efficiency reached as high as 80% at a fuel equivalence ratio of 1.4. The experiments on the replacement of NO recycle by NO2 recycle indicated that the same reduction efficiencies of recycled-NO2 as those of recycled-NO were reached for the high volatile bituminous, while the reduction efficiencies of recycled-NO2 were always lower than those of recycled-NO for the semi-anthracite coal.

Development of a “volume heat-trap” type solar collector using a fine-particle semitransparent liquid suspension (FPSS) as a heat vehicle and heat storage medium Unsteady, one-dimensional heat transfer in a horizontal FPSS layer heated by thermal radiation

Abstract The objective of this work is to develop a “volume heat-trap” solar collector in which a fine-particle semitransparent liquid suspension (FPSS) is used as a heat vehicle and heat storage fluid. In the first step of our fundamental research, a multiband model, taking into consideration the effect of fine particle suspension in a continuous fluid on radiation and absorption characteristics, was formulated to analyze the unsteady one-dimensional heat transfer in a horizontal FPSS layer heated by thermal radiation. The experiments were conducted for three kinds of suspensions: diethylphthalate-graphite, -carborundum and -silicon dioxide. The time-changes of temperature distributions within the suspension layer were measured under step- and intermittent-radiative heating conditions, using an infrared lamp bundle as a simulated model of solar radiation. The experimental data obtained for the rate and efficiency of heat collection, as well as for the unsteady temperature distribution within the FPSS layer, show satisfactory agreement with calculations based on the proposed theoretical analysis. It is the feelings of the authors that the FPSS used as a heat collection fluid in this work has a good heat transfer characteristics to enable the development of high efficient solar collector.

A Numerical Study of Transient Deformation and Stress Behavior of a Clay Slab During Drying

ABSTRACT A transient three-dimensional analysis was carried out on internal strain-stress as well as heat and the moisture transfer in a ceramic slab during drying. A model was developed to analyze viscoelastic behavior, heat conduction and moisture diffusion. The basic equations were solved by the finite element method. The effects of several dimensionless parameters are discussed to find an optimum drying process and a precise design of molds in ceramic production. The stress and the gradient of moisture content were influenced significantly by the Biot or Lewis number. When the moisture diffusion is enhanced or the drying is controlled well so as to form only gentle gradients of moisture content in the slab, the maximum tensile stress can be reduced. Nonuniform drying results in the develoment of warp and increase in the maximum tensile stress. The drying characteristics were not appreciably influenced by shrinkage.

- VISCOELASTIC STRAIN-STRESS AND HEAT/MOISTURE TRANSFER -

ABSTRACT The theoretical analysis was developed to predict the deformation characteristic of formed clay during a drying process in a ceramic production. The three dimensional strain-stress distribution as well as heat and moisture transfer in a slab shape of clay were simultaneously analyzed by a finite element method. Linear viscoelasticity was assumed for the strain-stress analysis to account the effect of creep. The calculated result agreed well with an experimental result performed for a slab clay heated by hot air flow during the preheating and constant drying rate periods. A large tensional stress, which may generate a crack, was observed initially around the surface area. It was also found that the time behavior of the volume change of the formed clay is significantly influenced on the drying conditions and/or the drying rate.

Applicability of zeolite for CO2 storage in a CaO-CO2 high temperature energy storage system

Many reversible thermal dissociation reactions have been reviewed for storing thermal energy at very high temperatures, such as high temperature heat from power plants. Among them, dissociation of CaCO3 seems very promising as the material can dissociate at 1098 K under atmospheric condition and the reactants involved are free from toxicity. One of the dissociation products, CO2 gas, requires a storage system. Three CO2 storage systems are being considered and the thermal operating efficiencies, COP, of the respective CaO-CO2 energy storage systems are evaluated. It is found that the system with a zeolite adsorbent for CO2 storage becomes quite comparable to other systems when the adsorptivity of the adsorbent increases to higher values. The CO2 adsorption characteristics of zeolite 13X and super activated carbon under a temperature range 303–573 K are studied. Based on the adsorption data, it is found that zeolite 13X adsorbent can be used as a CO2 storage medium in a CaO-CO2 high temperature thermal energy storage system.

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

Performance of flammability of kerosene and NOx emission in the porous burner

The present study aims to develop the porous ceramic burner applicable to the Stirling engine, boilers and gas turbines using liquid fuels with the flammability in a large input load. As a liquid fuel, kerosene is supplied dropwise on the top surface of the porous ceramic plate and ignited on the bottom surface. The combustion behavior of the burner is examined by measuring the profiles of temperature and composition of combustion gas along the centerline in the chamber. The promotion effect of combustion is examined experimentally by installing a wire net at the chamber outlet. The boundary condition of the combustion changes substantially in the presence of the wire net. The behavior of NOx formation can be correlated by a function of the equilibrium NO concentration at a maximum temperature in the burner.

Combustion characteristics in oil-vaporizing sustained by radiant heat reflux enhanced with higher porous ceramics

Liquid vaporizing combustion in porous ceramic burner has fine flame stability and characteristic of low emission. On the other hand, vaporization control has been seldom mentioned. In this work, kerosene vaporizing type combustor equipped with a porous ceramic plate, which has the porosity of 85%, is developed in order to enhance a rate of vaporization of the liquid fuel. The stability of combustion and NOx emission characteristics were investigated in fuel vaporizing ceramic combustion. The plate burner is made of Al2O3 ceramic which has an optical-thickness of 0.54. The optically thin ceramics improved flame stability and enhances more fuel vaporization rate than optically thick ceramics. The thermal radiation energy from flame and the furnace walls can penetrate easily through the large pore of the ceramic plate. It is found possible to dispense the electric power for the fuel vaporization and the stable combustion is self-sustained by enhancement of vaporization, where the reflux rate of radiant heat was no less than 2% of the heating value.

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...

Deformation Behavior of Ceramic Slabs by Nonuniform Drying

ABSTRACT The presenr paper is to study the transient deformation characteristics of molded ceramics undergoing nonunifom drying. The linear viscoelasticity was assumed for the strain-stress analysis. Three dimensional equations of the strain-stress as well as heat and moisture transfer werc solved numerically by the Galerkln finlle element melhod using isoparametric parameters of twenty-nodes so to allow easily the application to any feature of ceramics. Both the analysis and experiments were carried out to be compared on the behavior of drying and deformation for a slab clay in preheating and constant drying rare periods. When the bottom surface of the slab uras shielded to model the nonuniform drying. a warp phenomrnon to the opposite side of the shielded surface was observed experimentally as drying by hot air heating proceeds. The behavior could be successively simulaled by the present theoretical model. The degree of warp became rcmarkabel with a rise in air temperature or nonuniformity of drying. Th...