Influence of Fine Fuel Particles on Ash Deposition in Industrial-Scale Biomass Combustion: Experiments and Computational Fluid Dynamics Modeling

Abstract

This work focuses on the contribution of fuel particles with diameters smaller than 1 mm on the ash deposition behavior of different kinds of biomass feedstock. Special emphasis lies on their impact on industrial-scale boilers. For this purpose, we conduct lab-scale experiments and numerical simulations of biomass boilers in the megawatt range. First of all, we present experimental results from combustion and deposition experiments derived from a 100 kWth lab-scale fluidized bed furnace featuring a vertical deposition probe in the flue gas duct. To assess the slagging propensity of fine particles, different amounts of ground fuels were introduced into the combustion chamber. The experiments show a significantly higher amount of deposits (by a factor of 3.9–5.7) in the presence of fine particles in comparison to pelletized feedstock. Scanning electron microscopy with energy-dispersive X-ray spectroscopy and laser diffraction measurements were carried out, identifying the prevailing deposition mechanisms with respect to the respective feedstock. Subsequently, we draft a fast and scalable computational-fluid-dynamics-based model for the combustion of these fuel particles and ash deposition in megawatt-range biomass boilers. The main focus lies on collision-induced deposition of molten ash particles carried away from the fuel bed, thus burning in the flue gas channel. This modeling approach is capable of identifying the principal sections suffering from ash deposits in the combustion chamber and can be used to evaluate potential mitigation and avoidance strategies.

Study on Erosion Behavior and Separation Efficiency of a Shale Gas Vertical Separator

“…In 1996, McLaury proposed an erosion model suitable for water-carrying sand, , which is mainly used to simulate the erosion caused by solid–liquid flow. The mathematical expression is as follows: where F is an empirical constant; Bh is the Brinell hardness value of the wall target, N/mm 2 ; and k is 0.59 when the target material is steel.…”

“…where E is the mass loss of the target material worn by erosion, kg/m 3 ; K is a constant; V is the impact velocity of particles, m/ s; n is an empirical value, ranging from 2.3 to 2.5 for metals; and f(α) is a function of impact angle. In 1996, McLaury proposed an erosion model suitable for water-carrying sand, 9,28 which is mainly used to simulate the erosion caused by solid−liquid flow. The mathematical expression is as follows:…”

Early Detection of Agglomeration in Fluidized Beds by Means of Frequency Analysis of Pressure Fluctuations

“…Especially, quasi-isothermal conditions allow for efficient combustion as temperature peaks and emissions are reduced. − However, studies on the combustion of biogenic solid fuels in fluidized bed furnaces show that high-temperature chlorine corrosion and slag deposition can occur. Furthermore, agglomerations in the bed material and the subsequent defluidization of the fluidized bed are other major problems. ,− …”

A Methodology for Measuring the Heat Release Efficiency in Bubbling Fluidised Bed Combustors

“…With the rise of renewable energy sources, fluidised bed combustion was found to be highly interesting also for the thermal conversion of biomass. The key challenges for the combustion of biomass are ash-related aspects resulting from their higher inorganic content and especially their lower ash-melting temperatures, which cause severe slagging phenomena in grate furnaces [1,[4][5][6][7][8]. Fluidised bed combustion, in contrast, offers an isothermal temperature distribution within the bed to face these problems, but also with a beneficial emission behaviour concerning nitrogen-oxides and the possibility of an in-situ desulphurisation [3,6].…”