FBC Ashes Research Articles

Impact of Fly Ashes from Combustion in Fluidized Bed Boilers and Siliceous Fly Ashes on Durability of Mortars Exposed to Seawater and Carbonation Process.

This article presents test results of aggressive environment impact, i.e., seawater, acid solutions and carbonation, on the durability of cement–ash mortars. Tests were conducted on CEM I 42.5R-based mortars containing 35 to 70% by mass of FBC fly ash from brown and black coal combustion in a homogeneous form and mixtures of 35% by mass of siliceous fly ashes (CFA) and 35% by mass of FBC fly ash. It was demonstrated that in normal conditions (20 °C), FBC ashes showed higher pozzolanic activity than CFA, except when their curing temperature was increased to 50 °C. FBC ashes increased mortars’ water demands, which led to an accelerated carbonation process. In an environment of Cl- ions, cement–ash mortars showed more Ca2+ ions leached and no expansive linear and mass changes, which, with their increased strength, might be an argument in favour for their future use in construction of coastal structures resistant to seawater. FBC ash content may be increased to 35% by mass, maintaining mortars’ resistance to seawater, acid rain and carbonation. A favourable solution turned out to be a FBC and CFA mixed addition to cement of 35% by mass each, in contrast to mortars containing 70% of FBC fly ash in homogeneous form.

Lightweight Aggregate Produced with Cold-Bonding of Fly Ash and Binder

Main object of this paper are results of ash usage in order to create artificial aggregates. Ashes are mineral residue of coal burning in thermal power stations. Fly ashes (high temperature ashes) are highly used in practice as supplement of cement and silicate components of silica materials. FBC ashes are not used such great scale. They can be used for restoration, mounds or for example also for production of ash autoclaved aerated concrete. [1] Production of artificial aggregate from sintered ash is possible mainly because of the fly ashes. [2] Focus of this paper is to compare various types of ashes for lightweight aggregate produced with cold-bonding. Apart from the fly ashes and FBC ashes are also tested bottom ashes from FBC technology. From the results could be assumed, that bottom ashes compared to their granularity could be used only very hardly. Fly ashes splendidly react with cement and reach higher strengths. But they need more than 10 % of binder in order to reach quality results. FBC ashes better cooperate with quicklime, but in order to reach suitable parameters they need smaller portion of binder.

A comparative study of geopolymers synthesized from OXY-combustion and chemical looping combustion bottom ashes

The generation of geopolymers from OXY-FBC and CLC bottom ashes has not yet been reported. In this study, geopolymers from OXY-FBC and CLC bottom ash were synthesized and compared with geopolymers from FBC bottom ash. The bottom ashes used in this study were generated from the combustion of high ash South African coal. FBC and OXY-FBC bottom ashes were divided into two, viz: the first half was coarse, while the second half was grinded into fine particles. The bottom ashes were mixed with sodium silicate (Na2SiO2) and sodium hydroxide solutions (5M, 10M and 15M) and the pastes were cured at 60°C for 10days. The properties of the geopolymers were characterized using: TGA, FTIR and SEM-EDX techniques. TGA analysis showed that FBC geopolymer with 5M NaOH had the least amount of % weight loss, which indicates that it had a better thermal stability than synthesizing geopolymers with higher NaOH concentrations. Coarse FBC geopolymer (C-A1) had a higher thermal stability than fine FBC geopolymer (F-B1), therefore indicating that there is no need to grind the ash. OXY-FBC showed the opposite, therefore indicating the need to grind the ash in order to attain a better thermal stability of the geopolymer. The EDS analysis showed that the geopolymers produced an N-A-S-H gel and an incomplete N-A-S-H gel, instead of the C-(A)-S-H gel. Geopolymers synthesized from 5M NaOH (C-A1, F-B1 and C-C1), 10M NaOH (F-D2) and 15M NaOH (F-E3) had the most degree of geopolymerisation as seen on the FTIR spectrum. Geopolymers (F-D2) synthesized from 10M NaOH and fine OXY-FBC bottom ash had greater degree of geopolymerisation.

The Potential Use of the FBC Ash for the Preparation of Blended Cements

Ashes from fluidized bed combustion, i.e. FBC ashes, are not being practically used for the production of hydraulic binders. The problem is their chemical and mineralogical composition. FBC ashes are characterized by a higher content of SO3, highly active free CaO and sometimes higher loss on ignition. The higher proportion of these substances has resulted in volume and temperature instability. However, FBC ashes could be used within a certain limit concentration in binders with relatively similar chemical-mineralogical composition such as Portland cement. The potential use of FBC ash for the preparation of blended Portland cements was studied in this paper. For this purpose, two types of FBC ashes and one type of traditional fly ash were selected. The first representative was a filter FBC ash, the second one was a bed FBC ash. Fly ash from pulverized coal combustion was used for comparison. The samples were prepared by co-grinding of the selected ash, Portland clinker and gypsum in a laboratory ball mill to a given value of specific surface area. Ash content was 15% and 30% of the total sample weight. The samples were subjected to the determination of basic technological properties – the water/cement ratio, setting times, strength, and soundness. The course of the hydration process was monitored by the qualitative method of X-ray diffraction analysis (XRD). The hydration product quantification was performed by the thermogravimetric analysis (TGA/DTA). The amount of CaO attributable to Ca(OH)2 and CaCO3 was quantified. Based on the results, a conclusion was made that the utilization of FBC ash in blended Portland cement production is possible. The values of the physical-mechanical properties of the blended cements based on FBC ashes are similar to the reference. In the case of lower FBC ash content, they are even comparable with ordinary Portland cement.

The FBC Ash as a Hydraulic Ingredient of Hydraulic Lime

This work is focused on the possibilities of utilization of ashes from fluidized bed combustion, i.e. FBC ashes, for the manufacturing of hydraulic lime. Alternative hydraulic binders are becoming very popular in the present due to requirements on reducing CO2 emissions. FBC ash is an easily available, though not easily usable raw material. Because it has several hydraulic characteristics, it can create a hydraulic binder together with lime. Mixtures of hydrated lime and FBC ash from filters and from a bed were prepared in this work. The main criterion was the hydraulic modulus. The physico-mechanical properties were observed and were compared with the reference sample, which was hydraulic lime from industrial production. The prepared hydraulic limes achieved similar parameters as commercially manufactured hydraulic limes or lower strength class cements.

Influence of the Fly Ash Character on Quality of Artificial Aggregate

In a world is of ever-increasing pressure on the use of fly ash in building materials. Despite these efforts the majority of produced energy by-products end up as reclamation material and only small part as high-quality materials. Technology of sintered artificial aggregate is fully based on the fly ashes and allows processing a high percentage of this raw material. The work is devoted to assessing the impact of fly ash character on the quality artificial aggregate. There were selected three fly ashes from high-temperature combustion technology and two from the FBC combustion. The results clearly show that the FBC ashes are not too useful for sintered aggregate technology. For fly ashes is determined primarily by their fineness and the amount of amorphous silica phase.

Utilization of Bottom Ash for Sintered Artificial Aggregate

At present high temperature fly ashes are already quite widely used as a secondary raw material in building materials. Fly ashes are usually able to fully replace classical materials. FBC ashes also gradually finding their place for example in production of autoclaved aerated concrete, in binders or solidification of hazardous waste. However, the coarser types of energy by-products are relatively difficult to use. Therefore, this part of the work focused on the study of usability of bottom ashes for artificial sintered aggregates. The article will focus on results of laboratory firing in muffle furnace, dedicated to testing of maximum bottom ash content in the mixture with the fly ash and special type of clay.

Utilization of FBC ashes

Ash collected from the low-sulfur subbituminous coal-fired Foster Wheeler Energia Oy pilot-scale circulating PFBC tests in Karhula, Finland, and from AEP's high-sulfur bituminous coal-fired bubbling PFBC in Brilliant, Ohio, were evaluated in laboratory and pilot-scale ash use tests. Options evaluated for these ashes were construction-related applications, such as cement production, fills and embankment, soil stabilization and synthetic aggregate production, as well as an amendment for acidic and sodic soil and mine spoil as described in Part 2 of this paper. The tests related to construction applications, described herein, led to the following conclusions. (1) PFBC ash does not meet the ASTM chemical requirements as a pozzolan for cement replacement (ASTM C618). However, there is potential for its use as a pozzolan and as a set-retardant (gypsum replacement) in type-IP Portland cement production. (2) PFBC ash shows relatively high strength development (> 2.75 MPa), low expansion (< 0.01%) and low permeability (k < 10−5 cm s−1), making it a viable fill and embankment material. (3) Lime-enhanced (e.g. 3.6 wt% CaO added) PFBC ash develops high strength (> 27.5 MPa), manageable early expansion, and wet-dry and freeze-thaw cycle durability (< 1 wt% loss after 12 cycles), making it a suitable agent for soil stabilization. (4) Synthetic aggregate produced with lime-enhanced PFBC ash develops high crushing strength (> 135 kg), resistance to Los Angeles (LA) abrasion resistance (10–30 wt% loss) and soundness resistance (< 5%), making the ash an excellent material for synthetic aggregate production for construction applications. In summary, PFBC ash appears to be a viable material for use in a number of construction-related applications.

Characterisation of FBC ashes from co-combustion of coal with oily residues

Characterisation of FBC ashes from co-combustion of coal with oily residues

Characterisation of FBC ashes from co-combustion of coal with oily residues

In order to evaluate the environmental impact resulting from co-combustion of oily sludges, a detailed characterisation of the ashes produced was carried out. The main bulk composition and the trace elements were determined, thus allowing a comparison of the ashes produced from coal to those from co-combustion of the residue with and without limestone. The leachability was evaluated with two different standards, a European Norm and the US TCLP. The results differed according to the leaching pH dependence. Of the trace metals analysed, only Cr failed to meet the limits of natural groundwater by the EN procedures. The utilisation of limestone, thus capturing sulphates and part of Cl, had an adverse effect over the leachability. Cr was especially sensible, as the toxic hexavalent form was favoured in this case. The LOI of the ashes was found to be very high. As several mechanisms are believed to contribute to the overall result, low ashing temperatures are required for ashes from residues containing Cl, alkaline salts and carbonates. TGA was found to be a highly valuable technique to evaluate the unburned material.

Pacification of FBC ash in a pressurized TGA

The high CaO content of FBC ashes causes difficulties with their management. The use of CO2 to recarbonate or pacify the ashes was suggested in order to increase the concentration of CaCO3 in the ashes and decrease the amount of free lime. Work was performed using a Cahn 1100 pressurized TGA on coal and petroleum coke FBC residues at 0.1 and 1.1MPa. Both hydrated and nonhydrated ashes were tested. Conversion of the CaO to CaCO3 in nonhydrated ashes ranged from 9 to 27.4% while hydrated ashes showed conversion levels of 51.7–60%.

99/00608 Study of ashes from municipal wastes incinerated in classical grate boilers and FBC units—solidification of MWIR with FBC coal ashes for disposal

FBC is now widely used to burn low quality coals because of its ability to meet environmental regulations, especially where SO{sub 2} emissions are of concern. The technology is also promising for a number of other fuels, especially those having high chloride contents. The characteristics of any fuel depend strongly on the combustion technique and temperature. Thus, FBC ashes would be expected to be substantially different from grate incinerator ashes. This study looks at the characteristics of ashes (MWIR) from municipal wastes, originated from various cities in Europe, and incinerated in FBC and classical grate furnace facilities. Information is also provided on the heavy metal contents and leaching characteristics of the various MWI residues. All the results are examined in light of possible utilization strategies and landfill regulations regarding the potential for co-disposal of incinerator ashes with coal derived residues from FBC boilers to render the monoliths inert and resistant against hazardous events that may occur during ultimated and definitive storage.

Structural and thermal behavior of coal combustion and gasification byproducts: SEM, FTIR, DSC, and DTA measurements

Structural and thermal behavior of coal combustion and gasification byproducts: SEM, FTIR, DSC, and DTA measurements

Sintering mechanisms of FBC ashes

The agglomeration of solid particles is discussed on the basis of various sintering mechanisms. Three major mechanisms are identified and considered to be important in CFB combustion: sintering caused by 1. (1) partial melting, 2. (2) viscous flow and 3. (3) gas-solid chemical reactions. Recent results achieved with a laboratory sintering test are related to these sintering mechanisms. The test, based on compression strength measurements on heat-treated cylindrical ash pellets, showed clear differences in sintering tendency among five coal ashes. The temperature at which sintering began varied between 500 and 900 °C. For two brown coal ashes, partial melting was found to cause sintering, whereas viscous flow was probably the dominant sintering mechanism for ashes from a bituminous coal and an anthracite. SO 2 in the atmosphere increased the sintering tendency for two of the brown coal ashes. One brown coal also showed a slight increase in sintering at 600 °C when CO 2 was present in the atmosphere. This increase could not be detected at higher temperatures. For the bituminous coal ash no change in sintering tendency could be detected when SO 2, CO or both were present in the gas phase.