Chemical Absorption System Research Articles

Removal of Carbon Dioxide from Biogas with Pilot Chemical Absorption System at Different Operating Conditions

Removal of Carbon Dioxide from Biogas with Pilot Chemical Absorption System at Different Operating Conditions

Design, optimization and controllability of an alternative process based on extractive distillation for an ethane–carbon dioxide mixture

Alternative configurations based on cryogenic extractive distillation were proposed and simulated by using Aspen Plus 7.0® coupled to a multi-objective stochastic optimization procedure (differential evolution, DE). The evaluation of the performances of the proposed configurations was focused on the ethane–carbon dioxide azeotrope separation considering different liquefied hydrocarbon fractions as entrainers. The design alternatives were compared to the conventional chemical absorption system.The proposed sequences were simultaneously Pareto optimized by minimizing the total annual cost (TAC) and maximizing the acid gas removal. Complementary studies regarding the theoretical control properties, the thermodynamic efficiency and the greenhouse gases generation were conducted for several representative operating conditions obtained from the Pareto optimized fronts. The proposed cryogenic extractive distillation sequences realized the higher carbon dioxide removal together with the lower TAC compared to the conventional chemical absorption system.

Gas-filled membrane absorption: a review of three different applications to describe the mass transfer by means of a unified approach

This work involves the presentation of a general approach to describe the gas-filled membrane absorption process by analyzing three different applications. Ammonia removal from wastewater was described in a previous work using a resistance-in-series model. In this contribution, this model has been applied to describe the HCN removal from wastewater as well as to characterize the transfer of SO2 from wines to a receiving solution to develop a new method for enhanced quantification of sulfite content. The experimental results of this novel technique for SO2 quantification and its theoretical validation are presented in this study. The analyzed operations are based on hydrophobic hollow fiber contactors, which are used to physically separate two aqueous phases: a feed solution containing a volatile compound and a reactive receiving solution. Mainly removal of three volatile compounds under this configuration was analyzed: NH3, HCN, and SO2. By this way, a unified description based on a resistance-in-series model was developed for the three chemical absorption systems, obtaining good agreement between experimental data and the predicted values. Furthermore, the extraction percentages were significantly high (up to 99.9%) for the three systems. The mass transfer model shows a significant influence of the hydrodynamic conditions of the feed solution, gas solubility, and the rate of reaction on the performance of the process.

Reaction modelling of a microstructured falling film reactor incorporating staggered herringbone structures using eddy diffusivity concepts

Falling film microreactors are ideally suited for fast exothermic reactions due to their large surface to volume ratio (up to 20,000m2/m3) which greatly intensifies mass transfer. Despite the enhanced mass transfer characteristics of these reactors, mass transfer between the phases can still be the rate limiting step. To improve mass transfer, staggered herringbone structures were incorporated on the microchannel floor of falling film microreactors [1]. It was shown experimentally that reactors with herringbone structures increased CO2 absorption in 1M NaOH solution by up to 42%. Modelling of this system can be computationally prohibitive. This is due to its three-dimensional nature and the complexity of incorporating gas/liquid absorption and reaction with chaotic flow. For the CO2 chemical absorption system, a pseudo 3D approach has been implemented to account for such a modelling complexity [2]. In this work, the complexity of modelling the effect of herringbone structures was simplified using an effective diffusion coefficient calculated via an eddy diffusivity approach. Good agreement between the experimental data from Ziegenbalg et al. [1] and the simulations was obtained. The simplification suggested opens the possibility to model complicated systems with minimum computational expenditure.

Reduction of CO2capture plant energy requirement by selecting a suitable solvent and analyzing the operating parameters

Among various developed methods for CO2 capturing from industrial flue gases, chemical absorption system is still considered as the most efficient technique, because of its lower energy requirement and also its applicability for low concentration of CO2 in the inlet gas stream. Also, it can be used to retrofit the existed power plants, which are the major industrial CO2 emission sources, without changing their design condition. Selection of a suitable solvent is the first parameter that should be considered in the design of capture plants that use absorption technology. The most important challenge for using chemical solvents is finding the optimum operating conditions to minimize the energy requirement. Study of technical parameters can be helpful to improve the overall capture plant efficiency. In this paper, CO2 capture plant has been simulated for different solvents to compare their performance and energy requirement. To improve the plant overall efficiency, effect of the main operating factors such as amine flow rate, temperature, inlet gas temperature, and pressure has been studied in this paper. This analysis indicates the best chemical solvent for various cases of inlet flue gas. This parametric study reduces the overall energy requirement and helps design a cost-effective plant. Copyright © 2012 John Wiley & Sons, Ltd.

Pre-combustion CO 2 capture from natural gas power plants, with ATR and MDEA processes

Among the various configurations of fossil fuel power plants with carbon capture, this paper focuses on pre-combustion techniques applied to natural gas combined cycles. With more detail, the plant configuration here addressed includes: (i) the steam reforming of natural gas, based on an air-blown autothermal process, following a recuperative pre-reforming treatment, (ii) the water gas shift producing CO 2 and H 2, (iii) the separation of CO 2 by means of a mixed physical–chemical absorption system using a MDEA solution, and (iv) a hydrogen fuelled combined cycle. Similar configurations have been studied quite extensively, being among the most attractive for full-scale realizations in a near-mid term future. This paper proposes a detailed thermodynamic study and optimization of the plant configuration, bringing to a reliable performance estimation based on today's best available technology as far as the various plant sections are concerned (gas and steam turbine, natural gas reforming process, CO 2 separation). The predicted LHV efficiency for the base configuration is about 50%. Being this value at the top of the range quoted in the open literature studies (35–50%), the paper includes a quite extensive sensitivity analysis, showing that more conservative assumptions may bring to significantly poorer performance, especially considering the pretty large number of operating parameters involved in the process.

Comparative analysis of CO 2 separation from flue gas by membrane gas absorption technology and chemical absorption technology in China

This paper firstly evaluated the CO 2 absorption performance of a membrane gas absorption system (MAS) and chemical absorption system (CAS) using the overall mass transfer coefficient ( K G a V) as a basis for comparison. MAS selected microporous polypropylene (PP) hollow fiber membrane contactors to capture CO 2 from the simulated flue gas while CAS used a randomly packed column containing stainless Pall packing. Aqueous monoethanolamine (MEA) solution was adopted in both absorbers. Experimental results show that if the fresh membranes were tested, MAS has the higher K G a V values than that of CAS. However, when all the membrane pores were completely wetted or 50% pores were plugged, CAS inversely performs better than MAS in terms of K G a V values. In addition, the economic performance of MAS and CAS was also estimated. Results indicate that if the real operational time of membrane module is reduced to less than the critical value affected by the membrane price, the CO 2 captured cost of MAS is inversely higher than that of CAS. Therefore, the current well-accepted statement that MAS is superior to CAS in any case may be somewhat arbitrary unless membrane pore-wetting and pore-plugging problems, how to reduce the membrane price and how to prolong the membrane lifetime can be solved perfectly in the future.

Decarbonized hydrogen and electricity from natural gas

This paper discusses configuration, attainable performances and thermodynamic features of stand-alone plants for the co-production of de-carbonized hydrogen and electricity from natural gas (NG) based on commercially available technology. We focus on the two basic technologies currently used in large industrial applications: fired tubular reformer (FTR) and auto-thermal reformer (ATR). In both cases we assume that NG is pre-heated and humidified in a saturator providing water for the reforming reaction; this reduces the amount of steam to be bled from the power cycle and increases electricity production. Outputs flows are made available at conditions suitable for transport via pipeline: 60 bar for pure hydrogen, 150 bar for pure CO 2. To reduce hydrogen compression power requirements reforming is carried out at relatively high pressures: 25 bar for FTR, 70 bar for ATR. Reformed gas is cooled and then passed through two water–gas shift reactors to optimize heat recovery and maximize the conversion to hydrogen. In plants with CO 2 capture, shifted gas goes through an amine-based chemical absorption system that removes most of the CO 2. Pure hydrogen is obtained by pressure swing absorption (PSA), leaving a purge gas utilized to fire the reformer (in FTR) and to boost electricity production. For the power cycle we consider conventional steam cycles (SC) and combined cycles (CC). The scale of plants based on a CC is determined by the gas turbine. To maintain NG input within the same range (around 1200 MW), we considered a General Electric 7FA for ATR, a 6FA for FTR. The scale of plants with SC is set by assuming the same NG input of the corresponding CC plant. Heat and mass balances are evaluated by a model accounting for the constraints posed by commercial technology, as well as the effects of scale. Results show that, from a performance standpoint, the technologies of choice for the production of de-carbonized hydrogen from NG are FTR with SC or ATR with CC. When operated at high steam-to-carbon ratios, the latter reach CO 2 emissions chargeable to hydrogen of 10–11 kg of CO 2 per GJ LHV—less than 20% of NG—with an equivalent efficiency of hydrogen production in excess of 77%.

Effect of insoluble substances on absorption removal of ammonia by acidic solutions

An experimental study on the effect of insoluble substances on the exothermic absorption removal of gaseous pollutants with chemical reaction is presented. Ammonia is absorbed into sulfuric acid solution, while oleic acid (OA) is introduced as the insoluble substance, either in the gas flow or in the absorbent liquid. Both the ammonia absorption rate and the surface temperature rise are measured to examine the effect of the insoluble substances on the chemical absorption system. It is observed that the insoluble substance of OA obviously affects the ammonia absorption rate. In general, the presence of insoluble substance of OA tends to reduce the absorption rate and the surface temperature rise in chemical absorption system, for both cases with the insoluble substance in the gas flow and in the absorbent liquid. Although the increase of surface temperature rise may on the one hand increase the reaction rate constant, it may on the other hand reduce the solubility of the gas and hence the absorption rate. ...

Absorption removal of ammonia by acidic chemical absorbent in the presence of soluble surface active agents of IPA

Abstract In this paper, we present an experimental study on the effect of soluble surface active agents (SAA) on the exothermic absorption removal of gaseous pollutants with chemical reactions. Ammonia is absorbed into sulfuric acid solution, and isopropyl alcohol (IPA) is introduced as the soluble SAA in either the gas or in the absorbent liquid. Both the ammonia absorption rate and the surface temperature change are measured to examine the effect of soluble IPA impurities on chemical absorption systems employing a sulfuric acid solution. The results show that the soluble IPA impurities obviously affect the ammonia absorption rate. The soluble impurities of IPA tend to reduce the absorption rate and the surface temperature rise of chemical absorption, in both the cases where there are impurities in the gas flow and in the absorbent liquid. These findings are qualitatively similar to those of physical absorption system with impurities in the gas flow, but are different from those of physical absorption wi...

Mass transfer characteristics of fixed beds with cocurrent upflow and downflow. A special refence to the effect of pressure.

Interfacial areas and liquid-side mass transfer coefficients are determined in a trickle-bed reactor (TBR) and in a flooded-bed reactor (FBR) by means of two chemical absorption systems. The effect of gas and liquid mass flow rates and liquid viscosity is studied for both reactors as well as the influence of pressure (gas density) for TBR. In both TBR and FBR, interfacial area increases with liquid viscosity and fluid mass flow rates. It is also shown that in TBR, at given mass flow rates, interfacial areas and volumetric liquid-side mass transfer coefficients increase with gas density. In the case of FBR, the volumetric liquid-side mass transfer coefficient decreases slightly with the liquid viscosity. A new correlation is proposed for the interfacial area in FBR.

Effect of shape and wettability of packing materials on the efficiency of packed column

Effective interfacial area and mass transfer coefficient were determined by the use of Danckwerts’ plot method for chemical absorption system accompanied by first order reaction to elucidate the effect of shape and wettability of packing materials on these parameters. The liquid phase used in this experiment was K2CO3-KHCO3 buffer solution, and NaOCl was used to catalyze the first order reaction in the liquid phase. Raschig ring, sequare, sphere in shapes, and these were made of ceramic, polypropylene, glass, stainless steel, were used as packing materials. The following correlations were obtained to predict the effective interfacial area and mass transfer coefficient. a/at,=0. 614R0.161(Σc/Σ)0.119 (at,dn (1-e)1/3)-1.01 KL = 0. 0154Re0.24(Σc/Σ) {ie001-01} (atdn)0.18