Influence of Ammonia Content in SNCR Fly Ash on Phase Composition and Morphology of Autoclaved Aerated Concrete (AAC)

2018 ◽  
Vol 276 ◽  
pp. 167-172 ◽  
Author(s):  
Lucie Galvánková ◽  
Matěj Lédl ◽  
Tomáš Opravil ◽  
Denisa Beranová ◽  
Jakub Tkacz
Keyword(s):  
Phase Composition ◽  
Fly Ash ◽  
Hydrothermal Reaction ◽  
Catalytic Reduction ◽  
Combustion Process ◽  
Ammonia Content ◽  
Autoclaved Aerated Concrete ◽  
Before And After ◽  
Dta Analysis ◽  
Aerated Concrete

In production of AAC the fly ash was used as a source of SiO2 for many years. Now, after introducing a selective non-catalytic reduction (SNCR) technology to coal combustion process, the fly ash contain ammonia in a form of soluble salts, such as NH4HSO4 and (NH4)2SO4, which causes problems during manufacturing the AAC. Among all the influence of ammonia ions to the phase composition of the final product was not fully described. The main aim of this contribution is to describe the influence of ammonia to phase composition and morphology of autoclaved aerated concrete (AAC). For preparing AAC in laboratory conditions, the fly ash with various content of ammonia was used. The amount of ammonia before and after the hydrothermal reaction was measured by VIS spectrofotometry. The phase composition of prepared samples was determined by means of X-ray diffractometry and confirmed by TG-DTA analysis. The influence of the ammonia to the morphology of final products was studied by scanning electron microscopy.

Effect of Ammonium Ion Content in Fly Ash after Selective Non-Catalytic Reduction (SNCR) on Physical and Mechanical Properties of Autoclaved Aerated Concrete (AAC)

2018 ◽  
Vol 276 ◽  
pp. 148-153
Author(s):  
Matěj Lédl ◽  
Lucie Galvánková ◽  
Rostislav Drochytka
Keyword(s):  
Mechanical Properties ◽  
Fly Ash ◽  
Power Plants ◽  
Catalytic Reduction ◽  
Combustion Process ◽  
Ammonium Ion ◽  
Mixing Process ◽  
Autoclaved Aerated Concrete ◽  
Aerated Concrete ◽  
The Impact

After introducing SNCR in coal combustion process in power plants, the valuable by-product such as fly ash remains contaminated with amount of ammonia in form of NH4HSO4, (NH4)2SO4 respectively, which became undesirable in AAC technology because the toxic ammonia is released in the air during the mixing process. This paper deals with the effect of varying ammonia content in fly ash after selective non-catalytic reduction (SNCR) on the physical-mechanical properties of the fly ash based autoclaved aerated concrete (AAC) with the main focus on determination of the impact of the various content of ammonium ion in fly ash on the initial consistency of fresh slurry, the residual content of ammonium ion in hardened aerated matrix and also the impact on the bulk density, compressive strength and tobermorite formation after hydrothermal treatment. Seven batches of AAC, made out of fly ash with rising content of ammonium ion from 0 ppm to 250 ppm, were tested and based on the results obtained it was found out that ammonia is released during the mixing process entirely and doesn‘t remain in AAC after autoclaving, moreover it doesn‘t affect the properties of both fresh slurry (no apparent foaming effect noticed) and thermally treated samples of AAC. Formation of tobermorite wasn’t negatively affected.

Carbonation of autoclaved aerated concrete containing fly ash

ce/papers ◽  
2018 ◽  
Vol 2 (4) ◽  
pp. 47-51 ◽  
Author(s):  
Bernd Winkels ◽  
Holger Nebel ◽  
Michael Raupach
Keyword(s):  
Fly Ash ◽  
Autoclaved Aerated Concrete ◽  
Aerated Concrete

Study on Production of Autoclaved Aerated Concrete by Coal Gangue Fly Ash

2013 ◽  
Vol 357-360 ◽  
pp. 949-954
Author(s):  
Ye Zhang ◽  
Peng Xuan Duan ◽  
Bao Sheng Jia ◽  
Lei Li
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Drying Shrinkage ◽  
Coal Gangue ◽  
National Standards ◽  
Raw Material ◽  
Autoclaved Aerated Concrete ◽  
Binder Ratio ◽  
Material Formulation ◽  
Aerated Concrete

In this paper, the low-silicon coal gangue fly ash is used to produce autoclaved aerated concrete. The influences of water binder ratio, coal gangue fly ash content, calcareous content and conditioning agents on the compressive strength of the autoclaved aerated concrete are investigated. Optimal raw material formulation and procedure are determined for the autoclaved aerated concrete. The compressive strength and frost resistance of autoclaved aerated concrete made by the optimal raw material formulation and procedure meet with the requirements of autoclaved aerated concretes of B05 grade, and its thermal conductivity, drying shrinkage reach the requirements of the relevant national standards of China.

The Suitability of Fly Ash for Use in Concrete According to EN 450 Based on their Particle Size

2018 ◽  
Vol 276 ◽  
pp. 110-115
Author(s):  
Martin Ťažký ◽  
Martin Labaj ◽  
Rudolf Hela
Keyword(s):  
Fly Ash ◽  
Power Plants ◽  
Catalytic Reduction ◽  
Raw Materials ◽  
Thermal Power ◽  
Combustion Process ◽  
Thermal Power Plants ◽  
Mechanical Parameters ◽  
Fly Ashes ◽  
The Impact

The by-products of energy industry are nowadays often affected by new limits governing the production of harmful gases discharged into the air. These stricter and stricter criteria are often met by electricity producers by changing the combustion process in thermal power plants itself. Nowadays, the SNCR (selective non-catalytic reduction) application is quite common in the combustion process in order to help reduce the nitrogen oxide emission. This article deals with the primary measures of thermal power plants, which in particular consist of a modified treatment of raw materials (coal) entering the combustion process. These primary measures then often cause the formation of fly ash with unsuitable fineness for the use in concrete according to EN 450. The paper presents the comparison of the physico-mechanical parameters of several fly ashes with a different fineness values. The primary task is to assess the impact of non-suitable granulometry in terms of EN 450 on the other physico-mechanical parameters of fly ashes sampled within the same thermal power plant. Several fly ashes produced in the Czech Republic and surrounding countries were evaluated in this way.

scholarly journals Ammonia in Fly Ashes from Flue Gas Denitrification Process and its Impact on the Properties of Cement Composites

Buildings ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 225 ◽  
Author(s):  
Agnieszka Michalik ◽  
Joanna Babińska ◽  
Filip Chyliński ◽  
Artur Piekarczuk
Keyword(s):  
Fly Ash ◽  
Flue Gas ◽  
Coal Combustion ◽  
Catalytic Reduction ◽  
Structural Features ◽  
Cement Composites ◽  
Fly Ashes ◽  
Ammonia Content ◽  
Denitrification Process ◽  
Flue Gas Denitrification

The paper presents the results of research on the properties of fly ashes from the process of flue gas denitrification by selective non-catalytic reduction (SNCR), consisting of dosing urea into the coal combustion chamber. The research was carried out on two types of fly ash: Silica fly ash from flue gas denitrification and ash from a traditional boiler without the flue gas denitrification process. The scope of comparative studies included physicochemical and structural features of ashes, as well as slurries and mortars with the addition of ashes. Fly ash from denitrification, whose ammonia content at the time of sampling was 75 mg/kg at the maximum, was examined. Our own research has shown that fly ash from flue gas denitrification is characterized by a higher value of losses on ignition and ammonia content in comparison to ashes without denitrification. It was shown that the ammonia content in the analyzed range does not limit the use of fly ash as an additive to cement and concrete.

Preparation of new cementitious system using fly ash and dehydrated autoclaved aerated concrete

2014 ◽  
Vol 29 (4) ◽  
pp. 726-732 ◽  
Author(s):  
Zhonghe Shui ◽  
Jianxin Lu ◽  
Sufang Tian ◽  
Peiliang Shen ◽  
Sha Ding
Keyword(s):  
Fly Ash ◽  
Autoclaved Aerated Concrete ◽  
Aerated Concrete ◽  
Cementitious System

Influence of Gypsum Additive on the Formation of Tobermorite in Autoclaved Aerated Concrete

2016 ◽  
Vol 714 ◽  
pp. 116-121 ◽  
Author(s):  
Ester Helanova ◽  
Rostislav Drochytka ◽  
Vit Cerný
Keyword(s):  
Chemical Composition ◽  
Hydrothermal Reaction ◽  
Raw Materials ◽  
Fly Ashes ◽  
Sem Images ◽  
X Ray ◽  
Autoclaved Aerated Concrete ◽  
Variable Chemical ◽  
Aerated Concrete

The quality of the aerated concrete strongly depends on the chemical composition of the raw materials, as well as the process of the hydrothermal reaction during autoclaving. Due to the variable chemical composition of fly ashes, it is necessary to identify the effect of each ion on the formation of the microstructure of aerated concrete. This paper examines the process of formation of tobermorite with the addition of sulphates in various percentage representation. The microstructure of aerated concrete is assessed using SEM images and the mineralogical by means of X-ray analysis.

Influence of Fluidized Fly Ash on the Selected Physical-Mechanical Properties of the Autoclaved Aerated Concrete

2014 ◽  
Vol 899 ◽  
pp. 409-414 ◽  
Author(s):  
Alena Struhárová ◽  
Stanislav Unčík ◽  
Svetozár Balkovic ◽  
Mária Hlavinková
Keyword(s):  
Mechanical Properties ◽  
Fly Ash ◽  
Chemical Properties ◽  
Physical And Chemical Properties ◽  
Amorphous Phases ◽  
Autoclaved Aerated Concrete ◽  
Aerated Concrete ◽  
Free Cao ◽  
Physical And Chemical ◽  
And Chemical Properties

Fluidized fly ash has different physical and chemical properties compared to fly ash emerging from classic combustion. It contains amorphous phases resulting from a dehydration of clay minerals as well as unreacted sorbent of CaCO3, free CaO and anhydrite (CaSO4). Work targets the possibilities of production of an autoclaved aerated concrete (AAC) from fluidized fly ash, and its influence on particular physical-mechanical properties of autoclaved aerated concrete.

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