Laboratory study and modeling of calcium carbonate production from calcium chloride solution by absorbing carbon dioxide from industrial gases

Master thesis in the field of chemical engineering

Abstract

Laboratory study and modeling of calcium carbonate production from calcium chloride solution by absorbing carbon dioxide from industrial exhaust gases

Dearly

Amin Alamdari

The effect of carbon dioxide concentration on the precipitation of calcium carbonate species and the kinetics of calcium carbonate precipitation at different concentrations of carbon dioxide in exhaust gases from factories with calcium chloride bypass flow of Soda Ash industrial unit, which is a rich source of calcium, were investigated. In this research, experiments were performed at ambient temperature and pressure in a 2-liter crystallizer. In order to investigate the effect of impurities in the real sample on the deposition process, a number of comparative tests were conducted between the real sample and the synthetic sample without impurities, and the effect of different concentrations of carbon dioxide on the deposition process of calcium carbonate produced from pure calcium chloride solution and the bypass flow of its soda unit was studied. Carbon dioxide concentration affects the shape of sediment species. The size of the particles as well as the amount of produced sediment is also affected by the concentration of carbon dioxide. Changing the concentration of carbon dioxide in the solution changed the kinetic parameters of growth, nucleation and adhesion. The determination of the kinetic parameters of the process was done by matching the laboratory results with the results of the mathematical model, and the optimization of the kinetic parameters was done using the genetic algorithm optimization method. Keywords: calcium carbonate, distillation unit circumference, carbon dioxide, morphology, mathematical modeling, kinetic parameters.

1-1- The importance of research

Climate changes have increased due to greenhouse gases released into the atmosphere. Carbon dioxide is the most famous greenhouse gas, which has increased the emission of this gas into the atmosphere due to the dependence of the world economy on fossil fuels as an energy source. CCS technology [1] is a technology that stabilizes the concentration of carbon dioxide in the atmosphere and includes three stages of trapping carbon dioxide at the production point, pressurizing it in the form of SCF [2] and storage (Pires et al., 2011). The soda production process includes units such as light soda, heavy soda, baking soda, calcination, compressors, filtration, lime kilns, lime milk, carbonation, ammonia recovery, salt purification, and ammonia absorption. In the ammonia recovery unit, there is a tower in the form of a shell and tube, in which reaction (1-1) is performed at high temperature to separate ammonia gas from dissolved ammonium chloride in the presence of lime milk:

(1-1) NH4CL+CA (OH) 2 ? Cacl2+NH3+H2O

The output of this tower is the steam with water ammonia and calcium chloride is transferred to the power plant. Ammonia gas goes to the top of the tower, and calcium chloride free from ammonia gas leaves the tower and is transferred to a tank by a pump, and finally it is transferred to the wastewater outside the factory. In this study, an attempt is made to produce calcium carbonate from two waste streams (carbon dioxide from factories and the waste stream of sodaash production unit). The valuable product of calcium carbonate is used in papermaking, pharmaceutical, medical, etc. industries. In this research, laboratory studies of the effect of the concentration of carbon dioxide emitted from factories on calcium carbonate deposition and kinetic studies of calcium carbonate deposition and the rate of nucleation, growth and adhesion of calcium carbonate particles produced at different concentrations of carbon dioxide in the gases exiting the unit[3] are investigated. 1-2- CCS technology CCS technology concentration It stabilizes carbon dioxide in the atmosphere and consists of three steps of trapping carbon dioxide at the point of production, pressurizing it as SCF and storage. CCS also includes biotechnological processes such as the use of trees or microalgae [4] to trap carbon dioxide.

Carbon dioxide is separated in the production source (such as power plant, cement factory, etc.) by gas absorption, surface absorption, membrane separation and cryogenic distillation methods, then the trapped gas mixture is compressed into a liquid and the supercritical fluid is transported by pipelines or ships to the place where it must be stored, and is stored on land, stored in the ocean and converted into mineral matter. (Pires et al., 2011)

1-2-1- Carbon dioxide trapping systems

Carbon dioxide trapping is done on three different systems:

Pre-combustion systems[5]

Post-combustion systems[6]

Oxygen fuel systems[7]

Figure 1 of this It shows the three systems schematically.

Figure 1- Carbon dioxide trapping in three systems (Gibbins et al., 2008)

The pre-combustion system is used for exhaust gases with a low concentration of carbon dioxide. The most widely used separation process for trapping carbon dioxide is absorption process with amine solution. Carbon dioxide absorption with low concentration requires a chemical solvent with high solubility. Carbon dioxide with low concentration is used to increase extraction from oil reservoirs, urea production, food and beverage industries.

In the post-combustion system, fuel is reformed by oxygen or steam to form a mixture of hydrogen and carbon dioxide, then carbon dioxide is separated from hydrogen and pure hydrogen is burned by air in the power plant. Separation of carbon dioxide and hydrogen is done by membrane, surface absorption and gas absorption. Biomass[8] and natural gas can also be used as fuel for this system. The purpose of this system is to convert carbon fuels into non-carbon fuels, where the chemical energy of carbon is transferred to hydrogen. One of the advantages of the post-combustion system compared to the pre-combustion system is the higher concentration and pressure of carbon dioxide in the output stream, and one of its main disadvantages is the high investment cost. The products of combustion are carbon dioxide and water. In combustion with air, nitrogen gas acts as a source of heat, so combustion with pure oxygen causes an increase in temperature compared to combustion with air. The return flow of carbon dioxide causes the temperature to decrease to normal temperatures. In the outlet stream, the concentration of carbon dioxide is 80 percent by volume, one of the important advantages of this system is the absence of NOx formation (Gibbins et al., 2008). Separation by membrane and cryogenic distillation.

1-2-2-1- Gas absorption

Gas absorption is a physical or chemical process in which atoms, molecules or ions of the gas phase are absorbed in the liquid phase. Gas absorption is a common process in the chemical industry and is mostly used to investigate the behavior of gas streams containing acid gases such as CO2-H2S-NOX on an industrial scale. Alkanolamines are mostly used in gas absorption. The disadvantages of the gas absorption process are summarized as follows:

Limitation of absorption

Corrosion of equipment

High cost of solvent recovery

Solvent loss due to evaporation

In the existing technologies for capturing carbon dioxide from exhaust gases, the absorption process with monoethanolamine [9] has received more attention in recent years.

1-2-2-2-Surface absorption

Surface absorption is a practical process for trapping carbon dioxide on an industrial scale. Surface adsorption is a selective process in which liquid molecules or gas mixtures adhere to surfaces. These molecules are absorbed by the surfaces even in low concentrations in the gas flow. The properties of absorbed particles (molecular size, molecular mass and polarity) and properties of the absorption surface (polarity, cavity size and space) determine the quality of absorption.

Since surface absorption is an exothermic process, regeneration of the adsorbent is done through desorption at high temperature. Surface absorption is mostly used in the pre-combustion system.