Shiro Kajitani

Study on char deposition characteristics on the heat exchanger tube in a coal gasifier: relationship between char formation and deposition characteristics

Abstract In a coal gasifier and heat exchanger, adhered and deposited ash and char inhibit heat transfer making the stable operation of the gasifier difficult. Since heat transfer performance of the heat exchanger directly affects the output of Integrated Coal Gasification Combined Cycle plants, it is important to understand the effect of char on the characteristics of adhesion and deposition on the heat exchanger tube beforehand. However, very few studies have been conducted concerning the relationship between chars property and its adherability, which varies depending on the coal type and the operating conditions. In this study, we first conducted an analysis of the characteristics of heat transfer in the heat exchanger of the pilot plant gasifier to understand the effects of the properties of the char on the heat transfer in the heat exchanger. Using a bench-scale gasifier at CRIEPI, a transformation of the char morphology took place as the gasification reaction progressed. In the experiment, char from three distinct coal types was made to adhere on a plate and then allowed to re-entrain, so that the inter-particle adhesion strength of the char could be measured. Using the char from the same coals, deposition experiments on a horizontal tube placed in a drop tube furnace were also conducted to examine the mechanism of char adhesion on the heat exchanger tube.

Development of Oxy-Fuel IGCC System With CO2 Recirculation for CO2 Capture: Experimental Examination on Effect of Gasification Reaction Promotion by CO2 Enriched Using Bench Scale Gasifier Facility

To cope with global warming problem, utility companies are required to reduce CO2 emission from pulverized coal fired power plants. Japanese utility companies are advancing various measures to improve plant thermal efficiency and to promote utilization of biomass as a fuel. In Europe and America, CO2 capture and storage (CCS) technology is regarded as one effective approach, and various demonstration projects are planned all over the world. However, the introduction of conventional CO2 capture system to power station causes a decrease in the plant thermal efficiency and an increase in the power generating cost. In this reason, it is necessary to develop a new power generating system with high thermal efficiency. Therefore, Central Research Institute of Electric Power Industry (CRIEPI) proposed an innovative integrated coal gasification combined cycle power generating system (IGCC) with CO2 capture whose plant thermal efficiency is very high, and is working on the research and development of the new system. This is a system to combine a new oxygen-CO2 blown coal gasifier in that captured CO2 is used with the closed gas turbine in which coal gas from the gasifier is burned with the gas mixed oxygen and recycled exhaust CO2 . The system has the following features. The gasification performances improve greatly. The processes of concentrating and separating CO2 are unnecessary. It is estimated that the carbon conversion efficiency (CCE) and the cold gas efficiency (CGE) in oxygen-CO2 blown gasifier improve more than conventional oxygen blown gasifiers by the effect of the gasification reaction promotion of CO2 by gasifying coal with oxygen and CO2 . As a result, the gasifier and the char recycling system can make to compact, and the equipment cost can be reduced. This paper reports on examination of CO2 promotion effect on the gasification performances by gasification test using a bench scale gasifier facility.Copyright

Upgrading of Wet Biomass by Oil Slurry Dewatering Process: Calcium Addition and Catalytic Activity for Gasification

A food processing waste with ca. 65wt％ moisture content has been subjected to dewatering treatment in kerosene with simultaneous calcium addition for gasification. Special attention was paid to the dispersion state of calcium and its catalytic activity for subsequent char gasification. Gasification reactivities of the chars were determined under isothermal conditions by thermogravimetry (TG) analysis. It was found that reactivities increased with Ca content up to a saturation level (SL) of about 2.7 wt％, above which the reactivities were approximate constant. The different catalytic activities of calcium were interpreted as being due to its dispersion state. For loading content lower than SL, Ca(OH)2 highly dispersed into matrix without crystallization, whereas the excess addition led to the formation of the crystallized structure, and therefore had no additional catalytic activity. The results of the present study indicated that oil slurry dehydrating process could provide an effective and practical catalyst loading procedure for biomass fuels with high water content.