Refractory Materials for Biofuel Boilers

The energy equipment usable for solid biofuel incineration usually operates upon aggressive conditions. The internal structures (lining) of the equipment are made of refractory materials that are affected by combined loads: thermal, mechanical and chemical (i.e. high temperature–up to 1200°C, chemical impact of alkaline compounds and slag, repeating thermal shocks, abrasive effect caused by solid particles and so on). A majority of traditional refractories usable for lining in such equipment are not durable. Upon certain conditions of use (such as high local temperatures, influence of alkaline biofuel combustion products and so on), durability of the traditional materials is 1–2 years only. The opportunities of new refractory materials application should be set upon taking into account the conditions of operation for biofuel boilers of specific types. In this section - the data on the peculiarities of using refractory materials in biofuel boilers are reviewed, and the impact of aggressive operating conditions of such thermal equipment on the properties of refractory materials is discussed. In addition, the investigations results of refractory castables alkali resistance and its explosive spalling are discussed. The recommendations for use of refractory materials in biofuel boilers are also presented

The effect of liquid glass on the deformation of refractory binder/Skystojo stiklo įtaka kaitrai atsparaus rišiklio deformacijoms

The structure formation of a refractory binder of liquid glass, ferrochrome slag and dispersed chamotte has been studied. It has been found that there is a close relationship between the density of liquid glass used and sharp expansion of binder at the temperature of 500–600 °C: the lower the density, the lower the expansion of the material. To find the reason for this deformation of a binder, the specimens of dried out liquid glass (sodium hydro silicates) heating tests (Fig 1) and the specimens of dried out mixtures of liquid glass and some inert refractory materials (Table 2) dilatometric tests (Fig 2) have also been made. This investigation showed that sodium hydro silicates films bloated during heating. In order to determine structural changes under high temperature, X-rays investigation of refractory binder was made (Fig 5). This investigation showed that the reaction at the solid phase starts at the temperature over 600 °C and had no effect on the deformation of binder at 500–600 °C. It has been shown that the deformations occurring at 500–600 °C are caused by bloating of sodium hydro silicates (non-reacted liquid glass during hardening) films of the binder. First Published Online: 30 Jul 201

Hydration Processes of Four-Component Binders Containing a Low Amount of Cement

Results of research on hydration of four-component binders containing very high amounts of supplementary cementitious materials were presented. The samples were composed of blended pozzolana (a mix of conventional fly ash and spent aluminosilicate catalyst), cement (about 20 wt.% in the binder) and Ca(OH)2. Spent aluminosilicate catalyst was proposed as activating component which can improve properties of low-cement blends, while the role of Ca(OH)2 was to enhance pozzolanic reaction. Early and later hydration periods of such blends were investigated by calorimetry, TG/DTG, FTIR and X-ray diffraction. Initial setting time as well as compressive strength were also determined. It was concluded that enhancement of reactivity and improvement of properties of fly ash–cement binders are possible by replacing a part of fly ash with more active fine-grained pozzolana and introducing additional amounts of Ca(OH)2. The spent catalyst is mainly responsible for accelerating action during the first hours of hydration and for progress of early pozzolanic reaction. Fly ash develops its activity over time, thus synergic effect influences the later properties of composites. Samples containing blended pozzolana exhibit shorter initial setting times and higher compressive strength, as well as faster consumption of Ca(OH)2 compared to the reference. Investigated mixtures seem to be promising as “green” binders, alternatives to cement, after optimizing their compositions or additional activating procedure

The effect of sodium silicate and its solution on the properties of refractory complex binder/Natrio silikato kiekio ir jo tirpalo tankio įtaka kompleksinio kaitrai atsparaus rišiklio savybėms

In order to improve thermal and mechanical characteristics of a traditional binder with liquid glass a complex binder consisting of liquid glass, its hardener and alumina cement (“Gorkal 70” containing not less than 70 per cent of AI2O3) was tested. Sodium silicate and its solution effect on physical and mechanical properties of a new refractory complex binder (Table 1, Fig 2) were investigated. The results obtained show that compressive strength of binding compound with high quantity of sodium silicate (N3) is the lowest after it had been cured, dried and fired at 300–600°C (Fig 3). It was also found that the strength of a complex binder with small quantity of sodium silicate (N1) in the temperature range of 20–600°C is 2–3 times as high as that of a traditional binder with dispersed fire-clay. The study in the formation of the structure of a complex binders dilatometric tests have also been made. After initial heating at 80–500°C the compositions contracted (Fig 4) due to dehidratation. At the temperature range of 580–750°C the contraction of compositions continue due to reactions at the solid phase. The hypothesis of the hardening mechanism in the complex binder was proposed. Liquid glass tends to restrain the hydration of the alumina cement though hardeners and sodium silicate interaction result in the intense formation of sodium calcium hydrosilicates. Therefore, a complex binder contains less sodium silicate than a traditional one while being used at higher temperature. First Published Online: 26 Jul 201

Portlandcemenčių su aktyviais atliekiniais priedais kietėjimo proceso ypatumų tyrimai

<p>Darbe tiriamas naftos krekingo katalizatoriaus atliekų (FCC) ir žemakrosnės dulkių (CD) poveikis skirtingų CEM portlandcemenčių kietėjimo procesui ir fizikinėms mechaninėms savybėms. Tyrimams naudoti šie portlandcemenčiai pagal EN 197-1: CEM I 42,5 R (PCR), CEM I 42,5 N (PCN), CEM II/A-S 42,5 N (PCSN). Taikant ultragarso impulso sklidimo greičio (UIG) matavimo metodą, buvo tiriamas grynų portlandcemenčių (PC) tešlų ir tešlų, kuriose 10 % cemento buvo pakeista atliekiniais priedais, tarp jų ir gerai žinomu pucolaniniu priedu - silicio dioksido mikrodulkėmis (MS) - struktūros kitimas, taip pat mineralinės sudėties bei fizinių mechaninių savybių pokyčiai. Nustatyta, kad priedų poveikis priklauso tiek nuo paties priedo savybių (smulkumo, cheminės sudėties), tiek nuo cemento smulkumo bei mineralinės sudėties. CD iš tirtų priedų labiausiai mažina cemento tešlų išsiliejimo rodiklį. FCC poveikis kietėjančių cemento tešlų struktūros kitimui yra panašus kaip MS, tik ne toks ryškus. FCC pastebimai spartina tik smulkesnio cemento (PCR) pradinės struktūros susidarymą, kitiems cementams įtaka nedidelė. Toliau (po 24 h) visų cemento tešlų su FCC struktūra kurį laiką kinta lėčiau, tačiau po 28 parų jų struktūra jau tankesnė nei grynų cemento tešlų. Atitinkamai kinta ir stiprumo savybės: tešlų su FFC ankstyvasis stipris (po 2 parų) yra mažesnis, po 28 ir 90 parų - didesnis nei grynų cemento tešlų. CD poveikis tiek struktūros kitimui, tiek stiprio savybėms yra kitoks: pradžioje (iki 24 h) PCR ir ypač PCSN struktūra keičiasi sparčiau, PCN - beveik nekinta. Tolesnį kietėjančių tešlų struktūros tankėjimą CD priedas lėtina. Cementų ankstyvajam stipriui CD įtaka nedidelė, o po 28 ir 90 parų PCR ir PCN tešlų su CD priedu stipris mažesnis, PCSN - didesnis nei kontrolinių tešlų. Tokį poveikį tikriausiai nulėmė CD esančios šarminių elementų priemaišos (K⁺ ir Na⁺ katijonai). Šios priemaišos portlandcemenčių ankstyvąjį stiprį paprastai didina, o tolesnį jo augimą lėtina. PCSN struktūros stiprumas padidėja tikriausiai dėl šarminių priemaišų aktyvinamojo poveikio šlakams. OH^- jonų koncentracijos cemento suspensijose tyrimai parodė, kad pradžioje (iki 3 h) CD, panašiai kaip MS ir FCC, sumažina OH^- koncentraciją, tačiau toliau 28 paras ji didėja ir tampa gerokai didesnė nei kontrolinėse suspensijose.</p><p><a href="http://dx.doi.org/10.5755/j01.ms.17.1.254">http://dx.doi.org/10.5755/j01.ms.17.1.254</a></p

Properties of suspension and pastes of different types of microsilica with various deflocculants

Microsilica is currently being used in a wide range of refractory castables and its quality influences performance, particularly flow and set of castables. In the present work, two different types of microsilica “Elkem ASA Materials” (grade 983U) and polish “Silimic” have been investigated. It was established that the differences between the characteristics of paste and suspensions of microsilica (pH, electric conductivity, viscosity) depend on the quality of microsilica. The influence of type and amount of microsilica on the pH, electric conductivity and viscosity behavior of alumina cement Gorkal-40 and microsilica pastes has been investigated in details. Deflocculants Castament FS-20 and sodium tripolyphosphatum were used to control the characteristics of the investigated materials. The influence of their amount on the characteristics of various suspensions and pastes was estimated. It is shown that rheological characteristic of middle cement castable, which contains in its composition with microsilica of low quality, may be increased considerably if the right amount of the right deflocculant is added

Effect of Hollow Corundum Microspheres Additive on Physical and Mechanical Properties and Thermal Shock Resistance Behavior of Bauxite Based Refractory Castable

This paper analyses the effect of hollow corundum microspheres (HCM) on both physical-mechanical properties (density, ultrasonic pulse velocity, modulus of elasticity, and compressive strength) and thermal shock resistance behavior of refractory medium cement castable with bauxite aggregate. Moreover, the scanning electron microscopy (SEM) results of HCM and refractory castable samples are presented in the paper. It was found that the replacement of bauxite of 0–0.1 mm fraction by HCM (2.5%, 5%, and 10% by weight of dry mix) had no significant effect on the density and compressive strength of castable, while the modulus of elasticity decreased by 15%. Ultrasonic pulse velocity (Vup) values and the visual analysis of the samples after thermal cycling showed that a small amount of HCM in composition of refractory castable could reduce the formation and propagation of cracks and thus increase its thermal shock resistance

Investigation of structure formation in complex binder mater

This study deals with the particularities of structure formation and hydration of the complex binder, which consists of liquid glass, metallurgical slag and high aluminate cement (Al2O3 > 70 %). According to the ultrasonic and exothermal temperature results, it was determined that due to the reaction between liquid glass and dicalcium silicate the highest hardening intensity was found in the first 20 minutes; however, the hydration of cement takes place much later, i.e. in the hardened structure. SEM investigations of the complex binder showed that its structure is dominated by areas where cement particles are joined by nanostructures (<50 nm) of the products formed during the reaction between liquid glass and hardener, and that the surface of most cement particles is coated by layers of nanoparticles sized from 30 nm up to 100 nm, i. e. the products of cement hydration

Kompozicinės rišamosios medžiagos struktūros formavimosi tyrimai

This study deals with the particularities of structure formation and hydration of the complex binder, which consists of liquid glass, metallurgical slag and high aluminate cement (Al2O3 > 70 %). According to the ultrasonic and exothermal temperature results, it was determined that due to the reaction between liquid glass and dicalcium silicate the highest hardening intensity was found in the first 20 minutes; however, the hydration of cement takes place much later, i.e. in the hardened structure. SEM investigations of the complex binder showed that its structure is dominated by areas where cement particles are joined by nanostructures (70%), struktūros formavimosi ir hidratacijos ypatumai kietėjimo metu. Ultragarso ir egzotermijos temperatūros tyrimais nustatyta, kad kompozicinis rišiklis dėl skystojo stiklo ir dikalcio silikato reakcijos sukietėja jau per pirmąsias 20 minučių, tačiau aliuminatinio cemento hidratacija vyksta daug vėliau, t.y. jau sukietėjusioje struktūroje. Tiriant kompozicinį rišiklį skenuojamuoju elektroniniu mikroskopu (SEM), nustatyta, kad struktūroje vyrauja plotai, kur cemento daleles sujungia skystojo stiklo ir kietiklio reakcijos produktų nanostruktūros (<50 nm), daugumos cemento dalelių paviršius padengtas 30 nm–100nm dydžio nanodalelių sluoksniais – cemento hidratacijos produktais