Experimental investigation of Zhundong high‐calcium coal ash adhesion characteristics on metal surfaces at high temperatures

Abstract A single-factor field experiment was carried out at the Cultivar Evaluation Station in Szczecin-Dabie in 2008-2010. The soil on which this experiment was set up is formed from light loamy sand (lls). In respect of granulometric composition, it is classified to the category of light soils, of soil quality class IV b and good rye complex. In the experiment, compost produced with municipal sewage sludge by the GWDA method was used. This compost contained clearly more nitrogen and phosphorus in relation to potassium. The content of heavy metals (Cd, Cu, Mn, Ni, Pb and Zn) in composts did not exceed standards of the Regulation of the Minister of Agriculture and Rural Development (Official Journal of Laws No. 165, item 765 of 2008) referring to organic fertilisers. In the study design, the following fertilisation treatments were applied: I - carbonate lime (CaCO3) at a dose of 1.5 Mg CaO · ha-1, II - high-calcium brown coal ash at a dose of 1.5 Mg CaO · ha-1, III - municipal sewage sludge compost at a dose of 250 kg N·ha-1, IV - municipal sewage sludge compost at a dose of 250 kg N · ha-1 + high-calcium brown coal ash at a dose of 1.5 Mg CaO · ha-1 (1st year of study), V - high-calcium brown coal ash at a dose of 1.5 Mg CaO · ha-1 (1st year of study), and 0.75 Mg CaO · ha-1 in following study years each, VI - municipal sewage sludge compost at a dose of 250 kg N · ha-1 + high-calcium brown coal ash at a dose of 1.5 Mg CaO · ha-1 (1st year of study), and 0.75 Mg CaO · ha-1 in following study years each. In addition, mineral fertilisation was applied annually in the form of multi-component fertiliser Polifoska 20, complex fertiliser Polimag S and ammonium nitrate. A test plant was perennial grass - Amur silver grass (Miscanthus sachariflorus). The obtained results show that Amur silver grass biomass contained on average the most nitrogen, ie 6.87 g·kg-1 d.m., in 2008, while the most phosphorus (0.39 g P·kg-1 d.m.), potassium (7.82 g K·kg-1 d.m.), magnesium (0.98 g Mg·kg-1 d.m.) and sulphur (1.19 g S·kg-1 d.m.) in 2010, whereas the most calcium ie 4.13 g Ca kg-1 d.m., in 2009. Significantly more nitrogen, calcium and sulphur was contained by Amur silver grass biomass from the objects where municipal sewage sludge compost had been applied without and with addition of high-calcium brown coal ash when compared to calcium carbonate or high-calcium brown coal ash being applied at a dose of 1.5 Mg CaO · ha-1. Differences in average phosphorus, potassium and magnesium contents in test plant biomass from particular fertilisation objects were not significant. The biomass of Amur silver grass contained significantly more cadmium, nickel, lead and zinc as affected by organic fertilisation without and with addition of high-calcium brown coal ash when compared with the objects where solely calcium carbonate or high-calcium brown coal ash had been introduced into soil. Differences in the average content of cadmium, nickel and zinc in test plant biomass from the objects fertilised with municipal sewage sludge compost without and with addition of high-calcium brown coal ash were not significant. The uptake of heavy metals by Amur silver grass biomass, ie its mean value of three harvest during three years of its cultivation, can be arranged in the following descending order of values: Zn > Mn > Pb > Cu > Ni > Cd. The degree of cadmium, copper, manganese, nickel, lead and zinc bioaccumulation in test plant biomass differed, depending on the fertilisation applied. The average degree of cadmium, nickel, lead and zinc accumulation after three study years was intense for all fertilisation objects, whereas average for copper and manganese.

Download Full-text

Experimental Investigation of Adhesive Bonding for Post‐installed Rebars into Concrete at High Temperatures

IABSE Congress, New York, New York 2019: The Evolving Metropolis ◽

10.2749/newyork.2019.1169 ◽

2019 ◽

Author(s):

Thanyawat Pothisiri ◽

Pitcha Jongvivatsakul ◽

Vanichapoom Nantavong

Keyword(s):

Experimental Investigation ◽

High Temperatures ◽

Mechanical Behaviour ◽

Epoxy Resins ◽

Adhesive Bonding ◽

Elevated Temperatures ◽

Adhesive Bond ◽

Steel Rebar ◽

Pull Out ◽

Embedment Length

<p>The use of post‐installed rebars into existing reinforced concrete structures bonded with epoxy resins was constantly increasing due to the advantage of equivalent or even higher bearing capacities at service temperature, compared with conventional cast‐in‐place rebars. Previous studies have examined the effects of different parameters on the mechanical properties of bonded post‐installed rebars at normal temperature. These studies showed that, for rebar diameter equal to 10 mm, the load bearing capacity increases linearly with the embedment length up to 75 mm. However, upon exposure to high temperatures, the glass transition of epoxy resins may occur and affect the mechanical behaviour of the adhesive bond. Studying the mechanical behaviour of an adhesive anchor at high temperatures is therefore necessary. An experimental investigation is conducted herein to examine the characteristics of the adhesive bonding stress between steel rebar and concrete interface at elevated temperatures using a series of pull‐out tests with varying rebar diameters and embedment lengths.</p>

Download Full-text

Calcium‐Bearing Minerals Transformation during Underground Coal Gasification

Minerals ◽

10.3390/min9110708 ◽

2019 ◽

Vol 9 (11) ◽

pp. 708 ◽

Cited By ~ 1

Author(s):

Liu ◽

Ma

Keyword(s):

Coal Gasification ◽

Ternary Phase Diagram ◽

Energy Dispersive Spectrometer ◽

Coal Ash ◽

Scientific Basis ◽

Experimental Results ◽

Underground Coal Gasification ◽

Morphological Transformation ◽

Reaction Conditions ◽

High Calcium

Calcium‐bearing minerals are one of the main typical minerals in coal and coal ash. In the process of coal thermal conversion, calcium‐bearing minerals undergo different morphological transformation in which the reaction temperature, pressure, and atmosphere are important factors affecting their transformation. The reaction process of underground coal gasification (UCG) could be clearly divided into pyrolysis, reduction, and oxidation and the typical calcium‐bearing minerals are expected to indicate the actual reaction conditions of UCG. A high‐calcium coal, Zhundong coal, was used in this research. The products of UCG were prepared and the minerals were identified by X‐ray diffraction (XRD) and a scanning electron microscope coupled with an energy‐dispersive spectrometer (SEM‐EDS). The thermodynamic calculation was used to assist in understanding the transformation behaviors of calcium‐bearing minerals. The experimental results show that the calcium‐bearing mineral is gradually converted from gypsum (CaSO4·2H2O) in the raw coal into anhydrite (CaSO4) during the pyrolysis process. In the reduction stage, anhydrite reacts with the reducing gas (CO) to produce oldhamite (CaS), and the oldhamite is stably present in the reduction ash. During the oxidation process, oldhamite is first transformed into CaSO4, and then CaSO4 is converted into CaO. Finally, CaO reacts with Al2O3 and SiO2 to produce gehlenite (Ca2Al2SiO7) at 1100 °C. As the oxidation temperature rises to 1400 °C, gehlenite is transformed into the thermodynamically stable anorthite (CaAl2Si2O8). With the further progress of the reaction, anorthite will co‐melt with iron‐bearing minerals above 1500 °C. The ternary phase diagram of SiO2–Al2O3–CaO system proves that anorthite and gehlenite are the typical high‐temperature calcium‐bearing minerals when the mole fraction of SiO2 is higher than 0.6. Moreover, the gehlenite is converted to anorthite with the temperature rise, which is consistent with experimental results. This study provides a scientific basis for understanding the UCG reaction conditions.

Download Full-text