Thermal Decomposition Of Limestone Research Articles

Evaluation of environmental sustainability of one-part geopolymer binder concrete

Production of ordinary Portland cement (OPC) is a carbon-intensive process that generates significant amounts of carbon dioxide (CO2) gas from the combustion of fossil fuels and thermal decomposition of limestone. Overall, cement industries are responsible for around 7 % of global CO2 emissions which poses a considerable threat to global climate change because of its greenhouse effects. The recent advent of geopolymer shows great potential to reduce carbon footprints by utilizing the industrial by-products, such as fly ash and ground granulated blast furnace slag (GGBS) and convert into a binding material. Generally, geopolymer binders are made using aluminosilicate compounds (fly ash and or GGBS) and an alkali activator (combination of sodium silicate and sodium hydroxide solution) called “two-part geopolymer”. Despite having superior engineering properties to conventional OPC concrete, geopolymer concrete has not been widely adopted in concrete industry so far. The safety hazards in mixing and handling geopolymer concrete posed by sodium hydroxide is one of the barriers to the adaptation of geopolymer concrete. Replacing liquid sodium hydroxide with less hazardous alkali materials, such as sodium carbonate powder not only makes the geopolymer binder less hazardous and easier for mixing and handling process but also makes it more environmentally sustainable because of its lower embodied energy compared to sodium hydroxide. This study investigates the environmental sustainability of structural grades one-part geopolymer concrete and compares the results with OPC concrete of same strength grades. This investigation also includes a comparison between various types of geopolymer concrete of 40 MPa and 50 MPa grades produced in previous studies. This study found that one-part geopolymer binder concrete emits around 65 % less CO2 than OPC concrete of same strength grades, which is also 23 % less than geopolymer concrete of same strength grades produced in previous studies.

Lime Based Construction Materials as a Carbon Sink

Lime is used in a variety of industrial sectors (e.g. construction materials, iron and steel industry, flue gas cleaning, etc.) By the thermal decomposition of limestone (CaCO3), known as calcination, two products are obtained: CO2 and quicklime, i.e. calcium oxide (CaO). There is a growing interest in quantifying and improving the potential of CO2 absorption of lime containing products during their operational life. The carbonation occurs during the lifetime of the lime application and it consists in the absorption of atmospheric CO2 that closes the loop by forming calcium carbonate back. Thus, a portion of the CO2 emitted during calcination is reabsorbed and stored in a permanent stable form. A literature review was carried out on the Carbonation Rate (CR) of lime used in three different construction materials: air-lime mortars, mixed air-lime mortars and hemplime. Out of 205 scientific publications reviewed, only 57 provide information about CR, specifically 21 for air-lime mortars, 27 for mixed air-lime mortars and 9 for hemplime. CR is 80-92% for pure air-lime mortars, 20-23% for mixed ones and 55% for hemplime. For all the materials, the CR trend over time was also assessed, according to the Fick’s law.

A multi-stage, multi-reaction shrinking core model for self-inhibiting gas–solid reactions

Some thermal decomposition reactions display self-inhibiting behaviour, where the produced gas negatively influences the reaction progress. Further, a build-up of internal pressure caused by the product gas may alter the reaction pathway in a way that favours one pathway over others. Two well-known cases of this kind of reaction are the thermal decomposition of limestone and gibbsite, in which carbon dioxide and water vapour are the produced gases, respectively. A multi-stage, multi-reaction, shrinking core model is proposed for the simulation of this type of process. The model emphasises the role of the produced gas, not only in mass transfer, but also in the reaction kinetics. It includes parallel and series reactions, allowing for the formation of an intermediate species. The model has been applied to the conversion of gibbsite to alumina, including the formation of intermediate boehmite. Modelling results for gibbsite conversion, boehmite formation and its subsequent consumption, as well as alumina formation, agree well with literature data; the corresponding kinetic parameters are estimated for all reactions. Significantly, the experimentally-observed plateaux in the particle’s temperature history are predicted by the model. The role of heating rate and particle size on boehmite formation is also evaluated using the model, and is in agreement with observation.

Sulfur Dioxide Production from Phosphogypsum: Thermodynamic Analysis and Experimental Results

Phosphogypsum or chemical gypsum is a by-product generated in the manufacture of phosphoric acid, generated in the proportion of 4 to 6 tons for every ton of acid produced by the fertilizer industry. Its reuse is important from the economic, social and environmental point of view. The purpose of this paper is to investigate the thermodynamic condition of sulfur dioxide recovering from thermal decomposition of phosphogypsum. The main advantage of this process is to return the sulfur dioxide to sulfuric acid manufacturing. In this case, sulfur demand by fertilizer industry and phosphogypsum generation could be greatly reduced. Experimental results were obtained from a lab scale rotary kiln. Theoretical approach and experimental setup were validated by using the actual data from thermal decomposition of limestone. Theoretical and experimental results showed the thermal decomposition of phosphogypsum is thermodynamically feasible only at high temperatures.

Thermal decomposition of limestone in a large scale thermogravimetric analyzer

The decomposition of calcium carbonate spheres has been investigated using limestone particles of sizes 7, 5 and 2 mm in a large scale thermogravimetric analyzer under near isothermal conditions. Experiments were conducted in atmospheres of pure N 2, and 7%, 14% and 21% CO 2-N mixtures. Data are interpreted in terms of apparent activation energy E and frequency factor A assuming a first-order reaction and Arrhenius temperature dependence of the rate constant. Microscopic analysis has shown that the decomposition reaction takes place at the boundary between the undecomposed carbonate and the layer of porous lime formed outside. This boundary moves towards the center of the particle but remains spherical in shape.

Thermal decomposition of limestone and gypsum by solar energy

The thermal decomposition of limestone and gypsum by concentrated solar radiation was studied. A 1.5-kW solar furnace was used to obtain the required reaction temperature. Maximum conversions of 65% and 38% were obtained for CaCO 3 and CaSO 4·H 2O decomposition, respectively.

Discussion of “thermal decomposition of limestone in a fluidized bed”

Discussion of “thermal decomposition of limestone in a fluidized bed”

Thermal decomposition of limestone in a fluidized bed

Particles of limestone of 16 to 28 and 60 to 100 mesh sizes were decomposed in a fluidized bed. A mathematical model for the thermal decomposition was proposed comprising the thermal decomposition at the interface within particles and the related heat and mass transfer steps. It was assumed in this model that the particles are completely mixed within the fluidized bed and that gas is in upward plug flow. Fractional decomposition of limestone particles and the bed temperature during thermal decomposition calculated from this model coincide very well with the experimental results. It was further revealed that the overall reaction rate of 60 to 100 mesh size particles is virtually determined by the rate of heat transfer from the reactor wall to the fluidized bed, and that both rates of interfacial reaction and heat transfer from the wall to the bed contribute to the overall decomposition rate of 16 to 28 mesh size particles.

石灰石の熱分解速度について

石灰石の熱分解速度について

石灰石の熱分解速度の解析法

石灰石の熱分解速度の解析法

A stathmographic and kinetic investigation of the thermal decomposition of lime-stone

A stathmographic and kinetic investigation of the thermal decomposition of lime-stone