Ash Deposition: A Systems Approach

Abstract

In recent years there has been extensive research and modeling efforts to establish or predict the deposition characteristics of an ash in a coal-fired system. The advances have been developed concurrently with improvements of analytical techniques to characterize coal minerals, ashes, and deposits. The results of these research and development efforts are at the stage of application to the many industrial problems associated with ash deposition. This paper introduces and discusses how the information derived form the characterization and modeling of ashes can be used as an integral part of engineering solutions to ash-related behavior in boilers. The major ash-related problem in boilers is of course the formation of deposits on the heat transfer surfaces. The various models developed to predict coal mineral transformation tend to be limited in scope when attempting to apply the results to full-scale units. In order to solve or mitigate the difficult problem of ash deposition detailed knowledge of the scope of the problem and doe operating and design details must be considered. The approach taken at Riley Stoker Corporation as an original equipment manufacturer (OEM) has need to understand how the deign and operation of a boiler us influenced by ash deposition, and how, given a new coal or different load constraints, the design or operation can be modified to minimize the effect on efficiency, availability, and maintenance. 680Design of coal-fired systems are based, to a large extent, on how ash behaves in a boiler. Therefore, an accurate and reliable assessment of the deposition characteristics of an ash is required. This assessment can no generally be obtained by utilizing standard methods for determining fouling/slagging propensities. Detailed analysis and characterization of the coal, ashes, and if available deposits, is necessary to obtain knowledge of ash behavior. Furthermore, actual operating and performance data of the unit is required in order to determine not only the impact of the ash on boiler operation and performance but also the effects of changing operation or design on ash behavior and total unit performance. This paper illustrates a method under development which will be used to relate the unit-specific data with a detailed a determination of the ash related behavior. The ash behavior is determined through the use of extensive characterization of ash samples and deposits obtained through on-site evaluation. By combining the data from the ash characterization with performance and operation modeling efforts an accurate assessment of the impact of ash behavior on the system can be obtained. This assessment can then be used to determine the potential benefits of modifications in operation, design, fuel to the system under study. The purpose of this paper is to describe methods to obtain key aspects of ash behavior with respect to deposition which can be utilized by the boiler designers and operators. These methods are in addition to the standard techniques to assess and predict ash characteristics and incorporate the recent developments in analytical techniques.