Hot Carbonate Research Articles

CO2/CH4 separation by hot potassium carbonate absorption for biogas upgrading

In biogas upgrading to biomethane, the release of CO2 off-gas into the atmosphere is generally regarded as a carbon-neutral emission, but a significant loss of CH4 can occur in this step: considering the global warming potential of this latter compound, methane slip can worsen or even nullify the CO2 savings associated to biomethane. This study investigates a novel approach for biogas upgrading to biomethane, aimed at reducing the methane loss. A plant based on hot potassium carbonate was fed with 150–200 Nm3 h−1 of biogas from municipal waste. CO2 is removed in a K2CO3 absorption column, with negligible CH4 absorption. An assessment of biomethane quality was performed to check its compliance with recent National and European standard specifications. Results show that a methane slip below 0.1% can be achieved with this technology, thus significantly reducing the greenhouse gas emissions associated to biomethane industry. This leads to a lower capital expenditure because no off-gas post-treatment is required. Heat and electricity consumption were monitored, and operational expense resulted to be lower than membrane separation in the specific case study, by applying life cycle cost (LCC) methodology.

From biogas to biomethane: A process simulation-based techno-economic comparison of different upgrading technologies in the Italian context

Biogas production and its upgrading to obtain biomethane for use as a transportation fuel has been receiving increasing attention, particularly in Italy. In this work, three commercially developed technologies (Pressure Water Scrubbing, Hot Potassium Carbonate and Pressure Swing Adsorption) are critically compared. Accurate process simulations were carried out to evaluate and optimize the performances in terms of biomethane (and CO2) purity and recovery, as well as specific energy consumption and operating costs, considering a biogas throughput of 500 Nm3 h−1. Results from process simulation were used to develop a detailed Discounted Cash Flow analysis of the different technologies, taking into account the recent subsidies issued on March 19th, 2018 by the Italian legislation to promote biomethane development. All the three processes here considered are able to recover more than 90% of biomethane, with a purity higher than 98%. The economic analysis revealed that, according to the new incentive mechanism set by the Italian so-called Biomethane Government Decree (Government Decree 19/3/2018) the investment payback time would range between 3 and 6 years and the Net Present Value would be positive, whereas in the absence of any incentive the investment would not be profitable for any of these technologies.

Kinetic study and process model development of CO2 absorption using hollow fiber membrane contactor with promoted hot potassium carbonate

In this study, application of hollow fiber membrane contactor (HFMC) as an appropriate technology for absorption of CO2 from gas mixture is proposed. A mathematical model is developed based on a new kinetic for prediction of “non−wetted” mode of HFMC performance in the presence of hot potassium carbonate promoted by diethanolamine (DEA). The model validation results show an appropriate agreement with experimental data which is reported in literature. Study of some related parameters on CO2 removal efficiency indicates that increasing the liquid flow rate and number of fibers have positive effect on the CO2 absorption, whereas enhancing the gas flow rate decreases the rate of absorption. The results show that the counter−current operation mode has better performance with respect to co−current flow. Also when gas and liquid phases pass through the tube and shell sides respectively, due to increasing the contact surface in the liquid phase, the CO2 absorption will occur with higher efficiency than the case of gas flow in the shell side. Investigation of different absorption solvents indicates that the order of absorption rate of solvents is as follows: promoted hot potassium carbonate>2-amino-2-methyl-1-propanol (AMP)>DEA>methyldiethanolamine (MDEA)> blend of MDEA and DEA. Modeling analysis reveals that due to higher absorption rate of promoted hot potassium carbonate with respect to other solvents, the required operating temperature for chemical absorption is lower than other solvents and as a result, this advantage also improves physical absorption.

Mathematical modeling and optimization of carbon dioxide stripping tower in an industrial ammonia plant

In the present study, performance of an industrial regeneration tower has been examined and validated for stripping of carbon dioxide from diethanolamine (DEA)-promoted hot potassium carbonate solution. The applied model employs a comprehensive non-linear rate-based method to take into account the coupling between material and energy balances, thermodynamic vapor-liquid equilibrium (VLE) relations and chemical kinetics. VLE relations are used to model the flash section located on the top of tower. The penetration theory provides an appropriate desorption rate and enhancement factor for the chemical desorption which incorporates an extensive set of important reactions. The model predictions were compared with the operating data obtained from ammonia plant of a petrochemical complex. The impact of parameters such as steam temperature, potassium carbonate concentration, inlet temperature of rich solution, promoter concentration and column pressure on the tower performance have been examined and optimized. Acceptable agreements have been attained between the simulation and measured industrial data. The optimum conditions were found to be 2.5wt%, 1.6 barg, 401 and 378K for promoter concentration, column pressure, steam temperature, and inlet temperature of rich solution which demonstrate a good compatibility in comparison to optimum operational conditions.

Sedimentology, petrography and early diagenesis of a travertine–colluvium succession from Chusang (southern Tibet)

The Chusang travertine is situated in southern Tibet at an altitude of ~4200m asl. in a cold-arid, periglacial environment and is characterized by interbedding of hydrothermal carbonate with colluvium. Here we present sedimentological and petrographical data to elucidate the depositional environment and sedimentary processes responsible for hydrothermal carbonate precipitation and early diagenetic alteration as well as clastic sediment accumulation and provide initial 230Th/U ages to constrain the time-depth of this travertine–colluvium succession.Three main travertine lithofacies have been identified: 1) a dense laminated lithofacies, 2) a porous layered lithofacies and 3) an intraclastic lithofacies that results from erosion of pre-existing hot spring carbonate. The colluvium is composed of cohesive debris flow layers that derived from mass-wasting events from the adjacent hillslopes. Micro-fabric analyses suggest that dense laminated travertine forms via rapid calcite precipitation from hot spring water seasonally subjected to severe winter cooling, while porous layered travertine results from seasonal dilution of hot spring water with rain water during the summer monsoon months, which in turn stimulates biological productivity and gives rise to a porous summer layer. Early diagenesis in the form of recrystallization and extensive formation of pore cements is common in the Chusang travertine, but never eradicates the original crystal fabrics completely.The sedimentary architecture of the deposit is conditioned by (i) the gently dipping (~10°) pre-existing terrain on which hot spring water is discharged from multiple travertine mounds causing laterally extensive travertine sheets to precipitate, and (ii) the adjacent much steeper (up to 30°) periglacial hillslopes that are the source area of repeated debris flows that accumulate on the travertine surface. The resulting travertine–colluvium succession has a total thickness of ~24m and 230Th/U dating suggests that the base of this succession has a minimum age of ~486ka, while the upper part (top-most ~8m) of the succession started accumulating in the earliest Holocene. We hypothesize that hot spring activity (and thus travertine precipitation) and the occurrence of debris flow events has a climatic nexus, i.e. are both triggered by phases of enhanced Indian summer monsoon.

Integrated control of postharvest decay on sweet orange fruits by hot water and Sodium Carbonate (Na2CO3) applications

Integrated control of postharvest decay on sweet orange fruits by hot water and sodium carbonate (Na2CO3) applications during subsequent storage at 28°C was investigated and the effect of such treatment on internal quality attributes of orange fruits determined. Mature sweet orange fruits without bruises were selected and washed in 2% sodium hypochlorite solution for 5 minutes before treatment. For ordinary sodium carbonate treatment (without hot water), selected fruits were separately immersed for 150 seconds in a water bath containing 2% (w/v) and 4% (w/v) sodium carbonate (Na2CO3) solutions. In another experiment, selected fruits were immersed for 150 seconds in a water bath containing hot water and sodium carbonate solution. Sodium carbonate concentrations at 2% (w/v) and 4% (w/v) in 45°C hot water temperature were tested. After treatment, the fruits were rinsed, allowed to air dry and then placed inside plastic buckets and stored at 25°C and 88% relative humidity and assessed weekly for mould infection. Result showed that fruits treated with 4% ordinary Na2CO3 concentration had no incidence of decay during the first week of storage. However, untreated fruits and fruits treated with ordinary 2% Na2CO3 concentration recorded 20.00% disease incidence in the first week of storage. The percentage decay of fruits later increased to 44.16±10.83 in all the fruits treated with 2% Na2Co3 concentration by week two and continued till third week when they were completely diseased, having 100% decay incidence. The causal organisms in the decaying fruits were Penicillium digitatum and Phytophthora palmivora. However, fruits treated with 2% Na2CO3 concentration in 45oC hot water recorded 0% decay incidence throughout storage duration which lasted for 6 weeks and as such implied that all the treated fruits were diseased free.

Modeling and Simulation of CO2 Absorption into Promoted Aqueous Potassium Carbonate Solution in Industrial Scale Packed Column

Carbon dioxide gas is a harmful impurity which is corrosive and it can damage the utilities and the piping system in industries. Chemical absorption is the most economical separation method which is widely applied in chemical industries for CO2 removal process. Hot potassium carbonate (K2CO3) is the most effective solvent that has been used extensively, especially for the CO2 separation process from gas synthesis and natural gas. This paper aims to develop mathematical model for investigating the CO2 absorption into promoted hot K2CO3 solution in industrial scale packed column in an ammonia plant. The CO2 was removed from the gas stream by counter-current absorption in two stages column. To represent the gas-liquid system, a rigorous mathematical model based on the two-film theory was considered. The model consists of differential mass and heat balance and considers the interactions between mass-transfer and chemical kinetics using enhancement factor concept. Gas solubility, mass and heat transfer coefficients, reaction kinetics and equilibrium were estimated using correlations from literatures. The model was validated using plant data and was used to compute temperature and concentration profiles in the absorber. The variation of CO2 recovery with respect to changes in some operating variables was evaluated. The effect of various kinds of promoters added into K2CO3 solution on the CO2 recovery was also investigated. The simulation results agree well with the plant data. The results of the simulation prediction, for the absorber pressure of 33 atm with a lean flow rate of 32,0867 kg/h, temperature of 343 K, and semi lean flow rate of 2,514,122 kg/h, temperature of 385 K, showed %CO2 removal of 95.55%, while that of plant data is 96.8%. © 2015 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Antisolvent Precipitation of Potassium Bicarbonate from KHCO3 + H2O + Ethanol/2-Propanol Systems in the CO2 Capture Process

For the energy-saving hot carbonate process, which contains a crystallization step, the antisolvent precipitation of potassium bicarbonate was investigated by adding ethanol and 2-propanol in a simulated effluent solution of CO2 absorption column. The feasibility of using the antisolvent was verified with the equilibrium data of ternary systems and a KHCO3 recovery. The ternary systems of KHCO3 + H2O + ethanol/2-propanol were equilibrated with varying amounts of alcohols at a preset temperature, and the equilibrium concentrations were determined using the cloud point method. In the ethanol system, a homogeneous and a solid–liquid phase were observed, whereas in the 2-propanol system, a liquid–liquid phase as well as the homogeneous and solid–liquid phases were observed. The equilibrium data were correlated with a local concentration parameter in the range of the antisolvent. From the correlation, the amount of antisolvent that has an effect equivalent to a cooling-only method and the optimum concentration...

Study of Di- and Polyamines as Activators in the Hot Potash Process for CO2 Capture

An alarming rise in the atmospheric level of CO2 beyond safe limits has posed an immediate threat to mankind. It has become necessary to look for new economic processes for its capture and for options that can lead to reduction in the cost of existing processes. Hot potassium carbonate is one of the most viable processes. Efforts are continuously being made to improve on the capacity and rate of absorption of this solvent primarily by the use of activators. The latest activators in this category belong mostly to amines like piperazine and other cyclic nitrogen compounds. However, their study so far has been very haphazard. The first systematic study on alkanol monoamine activators was initiated and reported earlier by the authors. This paper extends the study and discusses the effect of some acyclic and cyclic diamines and polyamines as activators on absorption and regeneration of CO2 in K2CO3 solution. The effect of the cyclic or acyclic nature of the molecule, number of substituents, their chemical nature and their spatial arrangement was investigated. The parameters studied for this effect are rich and lean amine loading of CO2, CO2 regenerated and pKa of activators. Interestingly, it was observed that the bulkiness and spatial arrangement of substituents is the most dominant factor. An unsubstituted cyclic diamine (piperazine) performs best in enhancing the absorption capacity of solvent whereas diethylenetriamine is the best in enhancing rate of absorption. The study reveals no specific correlation of pKa value of the amines with their effect as activator.

Energy and exergy analyses of an integrated gasification combined cycle power plant with CO2 capture using hot potassium carbonate solvent.

Energy and exergy analyses were studied for an integrated gasification combined cycle (IGCC) power plant with CO2 capture using hot potassium carbonate solvent. The study focused on the combined impact of the CO conversion ratio in the water gas shift (WGS) unit and CO2 recovery rate on component exergy destruction, plant efficiency, and energy penalty for CO2 capture. A theoretical limit for the minimal efficiency penalty for CO2 capture was also provided. It was found that total plant exergy destruction increased almost linearly with CO2 recovery rate and CO conversion ratio at low CO conversion ratios, but the exergy destruction from the WGS unit and the whole plant increased sharply when the CO conversion ratio was higher than 98.5% at the design WGS conditions, leading to a significant decrease in plant efficiency and increase in efficiency penalty for CO2 capture. When carbon capture rate was over around 70%, via a combination of around 100% CO2 recovery rate and lower CO conversion ratios, the efficiency penalty for CO2 capture was reduced. The minimal efficiency penalty for CO2 capture was estimated to be around 5.0 percentage points at design conditions in an IGCC plant with 90% carbon capture. Unlike the traditional aim of 100% CO conversion, it was recommended that extremely high CO conversion ratios should not be considered in order to decrease the energy penalty for CO2 capture and increase plant efficiency.

A multiscale modeling of carbon dioxide absorber and stripper using the Karhunen–Loève Galerkin method

A multiscale packed bed model is proposed to simulate industrial carbon dioxide absorber and stripper employing the hot potassium carbonate process promoted by piperazine. At a macro scale, a material and energy balance for the packed bed is built with the consideration of basic reaction chemistry, phase equilibria and solution thermodynamics, where the facilitated mass transfer of CO2 caused by chemical reactions is taken care of by an enhancement factor. At a micro scale, the enhancement factor is calculated from the concentration profiles of chemical species in the liquid film around packing materials. The computational burden for the numerical solution of a set of diffusion–reaction equations at each macro scale location is circumvented by means of the Karhunen–Loève Galerkin (KLG) method. The present multiscale model, where the KLG method treats the micro scale process of diffusion and reaction in the liquid film, is found to yield accurate predictions at a reasonably small computational cost. This method of solving multiscale problems can be applied not only to the present CO2 absorption/desorption processes but also to various systems in science and engineering, where the necessity of multiscale resolution is important.

Mathematical modeling of carbon dioxide removal using amine-promoted hot potassium carbonate in a hollow fiber membrane contactor

In this study, a mathematical model has been developed for absorption of carbon dioxide into promoted hot potassium carbonate in hollow fiber membrane contactors (HFMC). The model, which is based on a conventional split flow absorber (CSFA) unit data of Shiraz Petrochemical Complex, has been validated with the experimental data obtained from literature for CO2 absorption in MEA promoted NaOH solution as a solvent. The model prediction of carbon dioxide absorption in HFMC has been compared with CSFA. The results indicated that HFMC can be used as an industrial alternative for CO2 absorption. Absorption of CO2 in promoted hot potassium carbonate is simulated and compared with N–methyldiethanolamine (MDEA), diethanolamine (DEA), 2–amino–2–methyl–1–propanol (AMP) and aqueous blend of DEA and MDEA. The results represented that the performance of various absorbent solutions for CO2 removal is as follows: Promoted hot potassium carbonate > AMP > DEA > MDEA > blend of MDEA and DEA. Also investigation of related parameters in carbon dioxide absorption indicated that the removal efficiency enhances with increasing liquid velocity, number of fibers, temperature and also decreasing gas velocity in the membrane contactor.

Study of corrosion behaviour of A106 carbon steel absorber for CO2 removal in amine promoted hot potassium carbonate solution (Benfield solution)

The CO2 absorber is one of the largest pressure vessels in ammonia plants, which are suffering from severe corrosion problems worldwide. The aim of the present study is to examine the corrosion behaviour of A106 carbon steel absorber for CO2 removal in amine promoted hot potassium carbonate solution (Benfield solution). This study simulates CO2 removal unit in ammonia production process at Abu Qir Fertilizers and Chemical Industries Company (Alexandria, Egypt) and many other plants all over the world. A typical Benfield solution contains hot potassium carbonate K2CO3, potassium bicarbonate KHCO3, diethanol amine (DEA) as a promoter and potassium metavanadate KVO3 as corrosion inhibitor. The rate of galvanic corrosion of carbon steel absorber/stainless steel pall packings couple in Benfield solution was measured without adding the corrosion inhibitor KVO3 in order to measure the influence of corrosive solution. The corrosion rate was measured by weight loss technique in relation to different operating parameters such as solution velocity, solution temperature, %K2CO3, CO2 loading, %DEA and the effect of the presence of solution contaminants. In general, increasing solution velocity, solution temperature, %K2CO3, CO2 loading and the presence of solution contaminations increase the corrosion rate. However, the increase in %DEA in solution decreases the corrosion rate. The strong dependence of corrosion rate on both solution and gas velocities indicates the diffusion controlled nature of the corrosion process. In addition, estimation of activation energy revealed a value of 4·8 kcal mol−1. Surface morphology study depicted the presence of a porous solid film of corrosion products on carbon steel surface. It has been found that the liquid phase diffusion of bicarbonate to the steel solution interface is the rate determining step.

An assessment of different solvent-based capture technologies within an IGCC–CCS power plant

This study evaluates three different solvent absorption processes for the pre-combustion capture of CO2 for a black coal IGCC (Integrated Gasification Combined Cycle) power-plant, with the aim of determining the best solvent process for pre-combustion capture. The three solvent processes are MDEA (mono diethanolamine), hot potassium carbonate and Selexol™. The study involves detailed thermodynamic models of the entrained flow gasifier, synthesis gas processes, CO2 capture process and the gas turbine and steam turbine combined cycle plant.IGCC without capture yielded an efficiency of 45.02%. For the CO2 capture processes at 90% CO2 capture, the power generation efficiencies are almost identical for MDEA and Selexol™ with 36.39% and 36.42%, respectively. The IGCC with the hot potassium carbonate process yielded the highest efficiency with 37.33%. This improvement is attributed to the higher operating temperature of the absorber which allows water vapor in the synthesis gas to be sent to the gas turbine resulting in a greater power production from the gas turbine.A multi-objective optimization is performed by varying different decision variables in the IGCC with the hot potassium carbonate capture process. By optimizing these variables, an efficiency of 39.31% is obtained – a 2% point improvement for 90% capture.

Solubility of Carbon Dioxide in Activated Potash Solutions in the Low and High Gas Loading Regions

In the Hot Potassium Carbonate Process, carbon dioxide (CO2) is removed from gaseous streams by chemical absorption in an aqueous solution of potassium carbonate (K2CO3). It is common to activate the solvent by adding borates and vanadates as promoters. In the present investigation, we investigate the influence of borates and vanadates on the equilibrium solubility of CO2 in aqueous solutions of K2CO3. The solubility of CO2 in four activated aqueous solutions of K2CO3 was determined experimentally at two temperatures that are typical for CO2 absorption (343 K) and solvent regeneration (383 K) in the Hot Potassium Carbonate Process. The mass fraction of K2CO3 in the solvent was 0.26 g/g, and the mass fractions of boron (vanadium) was varied between 0.006 g/g and 0.013 g/g (0.01 g/g and 0.02 g/g). Two experimental setups were used: A headspace gas chromatography technique was applied to determine the solubility of CO2 at partial pressures of CO2 between 1 kPa and 140 kPa, and the synthetic gas solubility te...

Aqueous Potassium Bicarbonate/Carbonate Ionic Equilibria at Elevated Pressures and Temperatures

Aqueous bicarbonate/carbonate ionic equilibria play an important role in determining the practicality of various aqueous-alkaline fuel cells and the hot carbonate process for removing carbon dioxide from synthesis gas streams. These equilibria are also of interest to scientists concerned with climate change. In this article, we report measurements of aqueous bicarbonate/carbonate ionic equilibria between 150 and 320 °C at the solutions’ respective saturation pressures. The aqueous bicarbonate ions are not stable at temperatures above 150 °C: the bicarbonate decomposes into carbonate and aqueous CO2. The dissolved CO2 is released from the solution when the reaction vessel is quickly cooled and depressurized, leaving behind stable carbonate ions in a solution with increased pH. A thermodynamic analysis of these findings indicates that the spontaneous and endothermic bicarbonate decomposition reaction proceeds with a positive change in entropy.

Thermal stability and viscosity behaviors of hot molten carbonate mixtures

Direct coal fuel cell (DCFC) systems have been receiving renewed interest to achieve higher efficiency than hydrogen-based fuel cell systems. However, their success strongly depends on a reliable transport system in which molten carbonate (MC) mixtures are continuously circulated as an electrolyte together with coal particles into the porous anode. The objective of this study is to investigate the thermal properties of a binary mixture of lithium carbonate and potassium carbonate, such as its fusion temperature, dynamic viscosity, and thermal stability, under coal-free conditions. The results for the mixture are given over a limited range of composition and temperature.The viscosity of carbonate mixtures was measured in a falling sphere viscometer operated in the Stokes’ flow region. Their thermal stability experiencing a decomposition reaction was evaluated in two separate apparatus, thermogravimetric analyzer and calcinations furnace, at various temperatures. Specifically, the rate of weight loss of carbonate mixture was measured and compared with theoretical values predicted by the minimization method of Gibbs free energy.The results show significant weight loss of the mixture from decomposition over this temperature range which can be solely attributed to the decomposition of lithium carbonate content—a phenomenon that may present operational difficulties in an actual DCFC system.

Analysis of CO2 Separation with Aqueous Potassium Carbonate Solution in a Hollow Fiber Membrane Contactor

Hot potassium carbonate solution is a promising absorbent for economical sequestration of CO2 from flue gas. In the present study, a 2D mathematical model was developed to analyze the absorption of carbon dioxide from a gas mixture into an aqueous solution of potassium carbonate using a microporous hollow fiber membrane contactor operated under nonwetted or partially wetted conditions. The set of partial differential equations for the liquid, membrane and gas phases were solved by applying a numerical procedure, and the model results were validated with available experimental data in the literature. A parametric study was done using the validated model in order to achieve an optimized CO2 capture. It was found that the rate of absorption increases significantly with increasing the liquid temperature, and there is an optimum carbonate concentration which gives maximum absorption flux at each solution temperature. A comparison between potassium carbonate and diethanolamine solutions was done under nonwetted...

The unusual behavior of a Milos bentonite in cement suspensions

Bentonites from different deposits worldwide often show unexplainable differences with respect to their performance in different applications. Examples are the water uptake capacity and bleaching ability ( Kaufhold, 2001; Kaufhold et al., 2010). The present study focused on the rheological parameters of bentonite-cement slurries used in civil and underground engineering. By measuring the viscosity and yield point of several different Na +-activated calcium bentonites mixed with blast furnace cement, behavior of a Milos bentonite was detected characterized by an unusual increase of the viscosity after addition of the cement. A detailed mineralogical characterization was conducted to identify the reason. The most striking difference of the samples was the content of soluble silica making up 27 mass% of the bentonite (soluble in hot sodium carbonate solution). However, the addition of silica gel to bentonites free of soluble silica proved the effect on the rheological parameters viscosity and yield point.

Comparison of several packings for CO 2 chemical absorption in a packed column

CO 2 capture and storage has gained widespread attention as an option for reducing greenhouse gas emissions. Chemical absorption and stripping of CO 2 with hot potassium carbonate (K 2CO 3) solutions has been used in the past, however potassium carbonate solutions have a low CO 2 absorption efficiency. Various techniques can be used to improve the absorption efficiency of this system with one option being the addition of promoters to the solvent and another option being an improvement in the mass transfer efficiency of the equipment. This study has focused on improving the efficiency of the packed column by replacing traditional packings with newer types of packing which have been shown to have enhanced mass transfer performance. Three different packings (Super Mini Rings (SMRs), Pall Rings and Mellapak) have been studied under atmospheric conditions in a laboratory scale column for CO 2 absorption using a 30 wt% K 2CO 3 solution. It was found that SMR packing resulted in a mass transfer coefficient approximately 20% and 30% higher than that of Mellapak and Pall Rings, respectively. Therefore, the height of packed column with SMR packing would be substantially lower than with Pall Rings or Mellapak. Meanwhile, the pressure drop using SMR was comparable to other packings while the gas flooding velocity was higher when the liquid load was above 25 kg m −2 s −1. Correlations for predicting flooding gas velocities and pressure drop were fitted to the experimental data, allowing the relevant parameters to be estimated for use in later design.