Kunio Yoshikawa

A comparison of co-combustion characteristics of coal with wood and hydrothermally treated municipal solid waste.

In this work, thermogravimetric analysis was used to investigate the co-combustion characteristics of wood and municipal solid waste (MSW) with Indian coal. Combustion characteristics like volatile release, ignition were studied. Wood presented an enhanced reaction rate reflecting its high volatile and low ash contents, while MSW enhanced ignition behavior of Indian coal. The results indicate that blending of both, wood and MSW improves devolatization properties of coal. Significant interaction was detected between wood and Indian coal, and reactivity of coal has improved upon blending with wood. On the other hand, MSW shows a good interaction with Indian coal leading to significant reduction in ignition temperature of coal and this effect was more pronounced with higher blending ratio of MSW. Hence MSW blending could more positively support the combustion of low quality Indian coal as compared to wood, due to its property of enhancement of ignition characteristics.

Absorptive removal of biomass tar using water and oily materials

Water is the most common choice of absorption medium selected in many gasification systems. Because of poor solubility of tar in water, hydrophobic absorbents (diesel fuel, biodiesel fuel, vegetable oil, and engine oil) were studied on their absorption efficiency of biomass tar and compared with water. The results showed that only 31.8% of gravimetric tar was removed by the water scrubber, whereas the highest removal of gravimetric tar was obtained by a vegetable oil scrubber with a removal efficiency of 60.4%. When focusing on light PAH tar removal, the absorption efficiency can be ranked in the following order; diesel fuel>vegetable oil>biodiesel fuel>engine oil>water. On the other hand, an increase in gravimetric tar was observed for diesel fuel and biodiesel fuel scrubbers because of their easy evaporation. Therefore, the vegetable oil is recommended as the best absorbent to be used in gasification systems.

Development of a high-temperature air-blown gasification system.

Current status of high-temperature air-blown gasification technology development is reviewed. This advanced gasification system utilizes preheated air to convert coal and waste-derived fuels into synthetic fuel gas and value-added byproducts. A series of demonstrated, independent technologies are combined to form the core of this gasification system. A high-temperature, rapid devolatilization process is used to enhance the volatile yields from the fuel and to improve the gasification efficiency. A high-temperature pebble bed filter is used to remove to the slag and particulates from the synthetic fuel gas. Finally, a novel regenerative heater is used to supply the high-temperature air for the gasifier. Component development tests have shown that higher gasification efficiencies can be obtained at more fuel-rich operating conditions when high-temperature air is used as the gasification agent. Test results also demonstrated the flex-fuel capabilities of the gasifier design. Potential uses of this technology range from large-scale integrated gasification power plants to small-scale waste-to-energy applications.

Metal nickel nanoparticles in situ generated in rice husk char for catalytic reformation of tar and syngas from biomass pyrolytic gasification

This paper aims to propose a novel catalytic pyrolytic gasification technology for the in situ conversion of tar and syngas, accompanied by the silica-based nickel nanoparticles generated in situ and the highly dispersed rice husk char (RHC), namely RHC Ni. Partially oxidized nickel oxides (i.e., NiO) in the carbon matrix of biochar can be carbothermally reduced to metallic nickel (Ni0) nanoparticles by reducing gases (e.g., CO) or carbon atoms during biomass pyrolysis. Moreover, due to its strong reducibility, the addition of sodium borohydride (NaBH4) can significantly promote the generation of Ni0 by the reduction of NiO, improving the biochars catalytic activity. An ultra-low tar yield can be achieved by pyrolysis of RH Ni and RH Ni–B at 750 °C, in terms of the high tar conversion efficiencies of 96.9% and 98.6%, respectively, compared with the pyrolysis of raw RH. It is noteworthy that the condensable tar could be catalytically reformed into the small molecules of non-condensable tar or gases, which contributes to improving the syngas fuel characteristics in the favor of power generation systems, corresponding to the lower heating value (LHV) of syngas increasing from 10.25 to 11.32 MJ m−3. In addition, the increase of the polymolecular Ni0 was most possibly caused by the disproportionation reaction and strong reducibility of NaBH4. In addition, the produced RHC Ni showed a good performance for the catalytic conversion of tar (conversion efficiency, 96.5%) through co-pyrolysis with biomass. After deactivation, the waste RHC Ni might be easily regenerated via thermal treatment or directly catalytically gasified into the applicable syngas, accompanied by the production of the silica-based nickel nanoparticles.

Hydrothermal Treatment of Date Palm Lignocellulose Residue for Organic Fertilizer Conversion: Effect on Cell Wall and Aerobic Degradation Rate

Date palm (Phoenix roebelenii) woodchips, a residue of palm tree plantations, was subjected to hydrothermal treatment (HTT) at mild reaction conditions (160°C < T < 220°C, 0.6 MPa < P < 2.4 MPa) for 30 min, and the effect of treatments on the cell wall (CW) solubilization and subsequent aerobic degradation rate (as CO production) was tested under controlled composting conditions during 63 days of incubation (38°C). The HTT at 160 and 180°C reaction temperatures notably solubilized hemicellulose, decreasing the fraction of this CW polymer from 34.1% in the untreated material, to 9.5 and 4.6% in the respective residues. However, treatment at 200 and 220°C reaction temperatures rapidly liquefied the lignin, which apparently went into solution with hemicellulose and appeared to stabilize a portion of this polysaccharides against hydrolysis. Consequently, the fraction of hemicellulose in 200 and 220°C – treated residues gradually increased; the respective values were 5.8 and 9.4%. The treatment temperature of 180°C was the most effective HTT temperature for subsequent aerobic degradation by solubilizing the largest portion of hemicellulose within the CW, which had two consequences: 1) it supplied additional readily bioavailable form of carbon, which in turn promoted rapid microbial activities in the early stage of decomposition; and 2) it created pores and cavities within the CW, which permitted rapid bacterial penetration and CW degradation. As a consequence, biodegradation of the residue treated under this reaction temperature proceeded rapidly and stability was reached within 21 days, compared to 63 days of continued degradation for the untreated CW. The enhanced biodegradability was also partially linked to the effect of 180°C treatment temperature on solubilization of amorphous cellulose and partial hydrolysis of lignin. Based on the results, the HTT system can successfully be used as a pretreatment step to accelerate the aerobic digestion rate of date palm residues for the production of organic fertilizers.

High temperature air combustion boiler for low BTU gas

A new concept boiler where fuel can be efficiently combusted by high temperature preheated air is proposed and experimental demonstration is done. This boiler is suitable for low BTU gas derived from gasification process of coal and wastes with no dioxin emission. This boiler is characterized by the following features; uniform heat flux field, augmentation of heat transfer, reduction of combustion noise level, suppression of NOx emission and compactness. Preliminary experiments using natural gas as a fuel demonstrate above distinct performance as well as good agreement with three-dimensional numerical simulation.

Characteristics of Pulverized Coal Combustion in High-Temperature Preheated Air

The use of high-temperature, low oxygen-content air for pulverized coal combustion is presented. Laboratoryscale tests were conducted in a drop-tube furnace to cone rm the performance of such a combustion system. The furnace wall was maintained at 1300 ± C by a ceramic heater, and the high-temperature preheated air (around 1000 ± C) was supplied by a regenerative burner. NOx formation and combustion efe ciency of the furnace were measuredforvariousairpreheat temperature, excess-airratio, and oxygen concentrationintheair. Measurements indicatedthatincreasingairpreheatresultsinincreasedcombustionefe ciency andreduced NOxemission,whereas decreasing theoxygen contentofthecombustion airleads to largereduction in combustionefe ciency, accompanied witha slightdecreaseorincreasein NOx. Itcan beconcluded from thetestresults thattheuseof high-temperature, diluted air is not suited for pulverized coal combustion.

Hydrothermal Upgrading of Korean MSW for Solid Fuel Production: Effect of MSW Composition

In Korea, municipal solid waste (MSW) treatment is conducted by converting wastes into energy resources using the mechanical-biological treatment (MBT). The small size MSW to be separated from raw MSW by mechanical treatment (MT) is generally treated by biological treatment that consists of high composition of food residue and paper and so forth. In this research, the hydrothermal treatment was applied to treat the surrogate MT residue composed of paper and/or kimchi. It was shown that the hydrothermal treatment increased the calorific value of the surrogate MT residue due to increasing fixed carbon content and decreasing oxygen content and enhanced the dehydration and drying performances of kimchi. Comparing the results of paper and kimchi samples, the calorific value of the treated product from paper was increased more effectively due to its high content of cellulose. Furthermore, the change of the calorific value before and after the hydrothermal treatment of the mixture of paper and kimchi can be well predicted by this change of paper and kimchi only. The hydrothermal treatment can be expected to effectively convert high moisture MT residue into a uniform solid fuel.

Determination of chemical kinetic parameters of surrogate solid wastes

Results on the thermal decomposition behavior of several important components in solid wastes are presented under controlled chemical and thermal environments. Thermogravimetry (TGA) tests were conducted on the decomposition of cellulose, polyethylene, polypropylene, polystyrene and polyvinyl chloride in inert (nitrogen), and oxidative (air) atmospheres. Inert condition tests were performed at heating rates of 5, 10, 30, and 50°C/min while the oxidative condition tests were performed at one heating rate of 5°C/ min. Differential scanning calorimetry (DSC) was also used to measure the heat flow into and out of the sample during thermal decomposition of the material. The TGA results on the mass evolution of the materials studied as a,function of temperature showed that the cellulose contained a small amount of moisture whereas no moisture was found in the other materials examined. The DSC curve showed the heat flow into and out of the sample during the process of pyrolysis and oxidative pyrolysis. The temperature dependence and mass loss characteristics of materials were used to evaluate the Arrhenius kinetic parameters. The surrounding chemical environment, heating rate, and material composition and properties affect the overall decomposition rates under defined conditions. The composition of these materials was found to have a significant effect on the thermal decomposition behavior. Experimental results show that decomposition process shifts to higher temperatures at higher heating rates as a result of the competing effects of heat and mass transfer to the material. The results on the Arrhenius chemical kinetic parameters and heat of pyrolysis obtained from the thermal decomposition of the sample materials showed that different components in the waste have considerably different features. The thermal decomposition temperature, heat evolved and the kinetics parameters are significantly different various waste components examined. The amount of thermal energy required to destruct a waste material is only a small faction of the energy evolved from the material. These results assist in the design and development of advanced thermal destruction systems.

Thermal decomposition characteristics of critical components in solid wastes

The thermal and chemical behavior of the various compounds present in solid wastes is significantly different during all phases of thermal destruction. To develop advanced design for waste thermal destruction it is imperative that one must examine the thermal destruction behavior of different components in the wastes under controlled conditions. Results are presented on the thermal decomposition characteristics during the decomposition of polyethylene, polypropylene, polystyrene, polyvinyl chloride, and cellulose under controlled thermal and chemical environment. These compounds represent important composition of the wastes. Thermogravimetry (TGA) tests and Differential Scanning Calorimetry (DSC) tests have been conducted on the thermal decomposition of above materials (polyethylene, polypropylene, polystyrene, polyvinyl chloride, and cellulose) in inert (nitrogen) atmospheres. The tests were performed at a sample heating rate of 5, 10, 30, and 50°C/min. The DSC curves showed the heat flow into and out of the sample during the process of pyrolysis. The material composition and properties, heating rate, and surrounding gas chemical environment affect the material decomposition rates under defined conditions. The composition of waste materials significantly affects the thermal decomposition behavior. Experimental results show that decomposition process shifts to higher temperatures at higher heating rates as a result of the competing effects of heat and mass transfer to the material. The results on the maximum decomposition temperature and heat of pyrolysis obtained from the thermal decomposition of surrogate wastes showed significant different features between these materials. Energy evolved at the early stages from certain easy to decompose materials can be used to destruct the other materials that decompose at higher temperatures or require more energy to decompose. The energy required to decompose the material is only a small fraction of the chemical energy evolved from material. The results presented here assist in the design and development of advanced thermal destruction systems.