Paper No 12 MODELING AIR JET PENETRATION INTO GAS-PARTICLE SUSPENSION CROSS FLOW

ABSTRACT In the paper, numerical modeling of air jet mixing in gasparticle suspension is discussed. The theory on which the modeling is based on is presented and to get a reliable opinion of its capability as a boiler design tool, the results are compared with those obtained experimentally in a cold pilot boiler. Based on the research on the pilot unit, the modeling seems to give reliable results. The modeling has also been applied to a fullscale boiler. INTRODUCTION Two major applications for circulating fluidized bed (CFB) risers are fluid catalyt cracking and CFB combustion. As the size of CFB boilers has increased, problems with the penetration of air jets and mixing have been found. Because experimental work concerning mixing is extremely difficult, numerical modeling is an alternative possibility. However, in the modeling plenty of problems have been met although the first trials were made many years ago In order to improve mixing, jets are injected to the flowing suspension. Although jets in cross flows (JCFs) are found in many engineering applications as e.g. in aeronautical industry, the results concern mainly single-phase cases. Published results of jet penetration into gas-particle suspension found in CFB risers are very scarce As to the mixing, the first problem is to get the jet penetrated into suspension. After that, the mixing is controlled by the turbulence. The effect of particle-turbulence interaction is also difficult, when the particle concentration is large as in CFB risers. For the effect of particles on carrier gas turbulence experimenta

FBC2003-074 FIRESIDE DEPOSIT FORMATION IN BIOMASS FIRED FBC: A COMPARISON BETWEEN TESTS PERFORMED IN THREE SIGNIFICANTLY DIFFERENT SIZED COMBUSTORS

ABSTRACT This paper deals with the prediction of ash related problems in fluidized bed boilers during co-firing of various bio-fuels. A study was performed where the slagging and fouling behavior was monitored in three different sized bubbling fluidized bed combustors, a 20 kW semi-pilot reactor, a 2 MW pilot-scale device and a 105 MW full-scale boiler. The aim of the study was to learn about how well slagging and fouling in a small-scale device compares to a full-scale boiler and to see how well the slagging and fouling can be predicted with a small-scale device. Various types of Scandinavian bio-fuels as well as peat were used both separately and mixed. From all three devices ash and deposit samples were collected during as uniform and stable conditions as possible. The fuels used in the three devices during the test campaigns were carefully chosen so that they would be as similar as possible. Bed, furnace and flue gas temperatures were monitored as well as flue gas emissions. The fuels, ashes and deposits were analyzed on their main components and deposition rates were calculated based on the deposit measurements. These data were finally used for assessing the slagging and fouling propensity of the fired fuel. The paper compares and discusses the results from the three different size classes. INTRODUCTION Ash related problems such as slagging and fouling of heat exchanger surfaces and de-fluidization of the bed in fluidized bed firing systems continue to challenge the operators and designers. The problem has during the last 10 years received increased attention and substantial research efforts have been put into the area to both solve the problem as well as to predict it. Still, however, the problem remains, partly due to lack of basic knowledge about ash behavior in FBC systems, partly also due to the fact that new and more problematic fuels are introduced to the system. In many FBC applications also co-firing is used, and the traditional ash behavior prediction methods such as standard melting temperatures and ash composition based indexes were simply not designed to be able to predict co-firing cases. In this paper we present results from a study where we wanted to test how well ash behavior could be predicted in a small-scale rig compared to a full-scale FBC boiler /1/