Tuomas Valmari

The ash formation during co-combustion of wood and sludge in industrial fluidized bed boilers

Abstract Ashes from an industrial bubbling fluidized bed (BFB) and a circulating fluidized bed (CFB) boilers burning biomass and paper mill sludges are characterized. Bulk sampling was carried out with a simultaneous low pressure impactor sampling (BLPI) and with on-line monitoring of submicron ash gas phase size distribution. The principal ash forming mechanism was sintering of 1–10 μ m inorganic paper filler particles, into 5–200 μ m ash agglomerates. Despite few spherical particles no ash melting was detected. The fraction of vaporized and condensed ash was below 0.1 mass% in both units as determined with BLPI and with on-line monitoring. According to elemental mass size distributions no significant vaporization of any main element occurred including sodium and potassium. Wall deposit observed on refractory lining in BFB furnace was composed of sintered ash binding large ash and sand particles in the structure. No molten phases were detected to participate in the layer growth. Most quartz sand grains in the bed were covered by a thin layer of small ash particles, below 5 μ m in size.

In-stack particle size and composition transformations during circulating fluidized bed combustion of willow and forest residue

Abstract The in-stack transformations of the particle size and composition of the fly ash were studied experimentally during combustion of forest residue and willow in a 35 MW circulating fluidized bed co-generation plant. Samples of the in-stack fly ash were taken with 11-stage Berner low pressure impactors (BLPIs) at two locations in the flue gas stream, i.e., downstream of the circulating cyclone at a temperature of 810–850°C and downstream of the convective back pass at a temperature of 150–160°C. The mass size distribution of the fly ash was derived from weighing the BLPI substrate films. For obtaining the multielemental composition of the fly ash as a function of particle size, the BLPI films were analyzed by both particle-induced X-ray emission (PIXE) and instrumental neutron activation analysis (INAA).

Studies on Ash Species Release during the Pyrolysis of Solid Fuels with a Heated Grid Reactor

The release of alkalis (sodium and potassium) and five ash matrix elements (silicon, aluminium, iron, calcium and magnesium) during the pyrolysis of Polish coal, Pittsburgh #8 coal, peat and two wood chips was studied with a heated grid reactor using heating conditions relevant to fluidised bed combustion and gasification. Mineral particles or any other super micron fragments were found not to be released from any of the fuels during the pyrolysis. Less than 5 % of any of the elements studied were released from the fuels, with an exception of iron from wood chips. Some iron may have been released from the wood chips (less than 14 % from whole tree chips and less than 8 % from wood chips fuel fraction). Less than 1 % of iron was released from coals and peat.

Ash Transformations in the Real-Scale Pulverized Coal Combustion of South African and Colombian Coals

In this work, the formation of ash particles in the combustion of South African Klein Kopie coal and a Colombian coal was studied by measuring the ash particle characteristics upstream of the electrostatic precipitator (ESP) at a 510 MWe pulverized coal fired power plant. We measured the ash particle mass size distributions in the size range 0.01-50 µm using low-pressure impactors and pre-cutter cyclones. Also, samples were collected for computer controlled scanning electron microscopy (CCSEM) with a cyclone with an aerodynamic cut-diameter of about 1 µm. The cyclone-collected samples were analyzed with standard CCSEM procedure by depositing the particles on a filter, and by embedding the particles in epoxy hence acquiring the cross-section analysis of the sample. All major mineral classes in both coals were found to undergo extensive coalescence during combustion. Iron, calcium and magnesium rich particles resulting from the decomposition of pyrite, calcite and dolomite were found to coalesce with quartz and aluminosilicate particles. The size distributions of the fly ash determined with CCSEM and low-pressure impactor-cyclone sampler were found to be similar.