Kazuyoshi Ichikawa

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.

Numerical Simulation of Coal Ash Particle Behavior in Entrained Flow Coal Gasifier

The objective of this study is to develop an evaluation tool for a design and performance of a coal gasifier by a numerical simulation technique. In the present paper, a gas-particle two phase reacting flow calculation is carried out for a prediction of phenomena in an entrained flow coal gasifier due to coal and ash particles behavior, such as ash deposition on the wall. A transportation of the coal particles is modeled via a Lagrangian manner. The ash particle adhesion on the wall of the gasifier is discriminated by an empirical ash adhesion model based on a liquid phase fraction concept in the ash particle. The gas phase properties are calculated by three dimensional time-mean Eulerian conservation equations. The turbulent flow field is determined by the k-e two equations model. Radiative heat transfer is calculated by the discrete transfer radiation method. Coal gasification reaction model is composed of three chemical processes in the current model: a pyrolysis, a char gasification and gas phase reactions. 2 tons/day (t/d) air-blown pressurized entrained flow coal gasifier, which has been constructed and operated by Central Research Institute of Electric Power Industry (CRIEPI) was targetted. As a result, a relationship between an operating condition (air ratio) of the gasifier and the gasifier performance is presented. The trend of the ash deposition on the gasifier inner wall is also presented. Comparison between the computational and the experimental results shows that the most feature of the gasifier performance and the profile of the ash deposition have been captured by the present model. It was confirmed that the numerical simulation approach is very useful for the assessment of gasifier performance and operation support.Copyright

Examination of Gasification Characteristics of Pressurized Two-Stage Entrained Flow Coal Gasifier. Comparison of Basic Performance with 2T/D and 200T/D Coal Gasifier.

The program for a 200T/D entrained flow coal gasification pilot plant was initiated in fiscal year 1986 and successfully finished fiscal year 1996. In this program, a two stage pressurized air-blown entrained flow coal gasifier was adopted, which CRIEPI and Mitsubishi Heavy Industry, Ltd, have developed jointly using a 2T/D bench scale P.D.U.. In the 200T/D pilot plant, domestic Taiheiyo coal, and Australian Moura, Warkworth coal were used for test runs. On the other hand, the commissioned tests of these 3 types of coals by NEDO/IGC Association have been carried out in CRIEPIs 2T/D coal gasifier, prior to the pilot plant operation. The research results obtained by the 2T/D gasifier were reflected in the operation of the pilot plant. From gasification test results with 2T/D and 200 T/D gasifiers, the gasification characteristics such as carbon conversion efficiency, cold gas efficiency and heat absorption rate to gasifier wall were evaluated.