Nitrosamine degradation by UV light in post-combustion CO2 capture: Effect of solvent matrix

AbstractPotential production and emission of nitrosamines during post-combustion CO2 capture has drawn some attention due to their toxicity and potential carcinogenicity. One of the possible ways to reduce the concentration of nitrosamines is irradiation of the liquid streams of the capture plant with UV light. This paper shows experimental results of the degradation of nitrosamines such as N-nitroso-diethanolamine (NDELA) and N-mononitroso-piperazine (MNPZ) in different solvent matrices. These solvent matrices include water and laboratory grade monoethanolamine (MEA) aqueous solutions, as well as aqueous MEA solution and wash water that had been used in a CO2 capture pilot plant connected to a coal-fired power plant. Experiments were conducted in dedicated batch set-ups and in a continuous mini CO2 capture plant. Results show that the UV absorbance of impurities (degradation products and/or dissolved metals) present in MEA solvent that had been used in a pilot plant significantly reduces the UV degradation rate of nitrosamines. Furthermore, UV light seems to accelerate the degradation of the capture solvent itself. For these reasons, if UV light treatment is to be used in full-scale post-combustion CO2 capture plants, suitable locations would be the absorber's washing section or the stripper's condensate. At these locations, less interference of degradation products can occur and there is less solvent to be degraded

Analysis of Process Configurations for CO2 Capture by Precipitating Amino Acid Solvents

Precipitating amino acid solvents are an alternative to conventional amine scrubbing for CO2 capture from flue gas. Process operation with these solvents leads to the formation of precipitates during absorption that need to be re-dissolved prior to desorption of CO2. The process configuration is crucial for the successful application of these solvents. Different process configurations have been analyzed in this work, including a full analysis of the baseline operating conditions (based on potassium taurate), the addition of lean vapor compression, multiple absorber feeds, and the use of different amino acids as alternative solvents to the baseline based on potassium taurate. The analysis is carried out with an equilibrium model of the process that approximates the thermodynamics of the solvents considered. The results show that the precipitating amino acid solvents can reduce the reboiler duty needed to regenerate the solvent with respect to a conventional MEA process. However, this reduction is accompanied by an expenditure in lower grade energy needed to dissolve the precipitates. To successfully implement these processes into power plants, an internal recycle of the rich stream is necessary. This configuration, known as DECAB Plus, can lower the overall energy use of the capture process, which includes the energy needed to regenerate the solvent, the energy needed to dissolve the precipitates, and the energy needed to compress the CO2 to 110 bar. With respect to the energy efficiency, the DECAB Plus with lean vapor compression configuration is the best configuration based on potassium taurate, which reduces the reboiler duty for regeneration by 45% with respect to conventional MEA. Retrofitting this process into a coal fired power plant will result in overall energy savings of 15% with respect to the conventional MEA process, including compression of the CO2 stream to 110 bar. Potassium alanate was found to reduce the energy use with respect to potassium taurate under similar process configurations. Therefore, the investigation of potassium alanate in a DECAB Plus configuration is highly recommended, since it can reduce the energy requirements of the best process configuration based on potassium taurat

Calorimetric Studies of Precipitating Solvent System

Calorimetric study of a precipitating solvent system of Potassium-Taurate (KTAU) was performed in the CPA202 calorimeter. Two different experiments were conducted, i.e. heat of absorption of CO2 in KTAU solvent at different conditions (concentration = 1.5 M and 3.0 M), loading up to ∼ 0.8 mol CO2/ mol Taurine and temperature = 25 °C, 40 °C, 80 °C). Moreover, dissolution heats of Taurine/solid were also measured. The result agrees well with the reported data. The procedure developed for the heat of dissolution measurements was verified by measuring heat of dissolution of solid Taurine in water and comparing results with data in literature. The solid formation occurs during the absorption of CO2 in 3.0 M KTAU at low temperatures (25 °C and 40 °C) and at loadings (∼ 0.3 mol CO2/ mol Taurine). The heat of dissolution of the formed solid in pure water is slightly higher than that of Taurine in pure water but less heat is required to dissolve the same solids in unloaded 3.0 M KTAU solution.publishedVersio

Reducing the cost of Post Combustion Capture technology for Pulverized Coal Power Plants by flexible operation

Currently the low carbon prices, low Spreads and regulatory uncertainties hampers the business cases for coal-fired power plants with post-combustion capture (PCC) in Europe. Improvement of the business case of coal-fired power plants with post combustion capture requires a different approach in terms of operational dispatch and in terms of investment planning. Both items have been assessed using a comprehensive power plant valuation model developed by TNO. To change the typical base-load production profile of a coal-fired power plant into a more flexible production profile, a Flexible Operating Mechanisms (FOMs) has been developed for PCC. Based on the results of the techno-economic modeling, FOMs improve the business case. Next to this, FOMs present coal fuelled power plants with additional flexibility. This added flexibility could allow coal plants to provide auxiliary services to the grid and remain competitive in relation to cleaner gas-fired plants. The increase of operational flexibility with FOMs created a significant improvement of the NPV value and, therefore, it is justified to look in much more detail how the operational flexibility of a coal-fired power plant with Carbon Capture can be improved. Running a power plant with a 100% capture unit at base load will require significant amount financial support to close the gap. Starting with a smaller capture unit reduce the financial risk and could improve the business case of the coal-fired power plant without PCC from a marginal cost point of view. The main reason for this is the increase of flexibility, by switching on/off the capture unit. Next to this, the decision to invest is always affected by the opportunity costs of making a commitment now, and thereby, giving up the option of waiting for improved market condition. Increasing the size of the capture plant in stages enables the investor to manage those opportunity cost much better.Process and EnergyMechanical, Maritime and Materials Engineerin

Measurement and prediction of oxygen solubility in post-combustion CO2 capture solvents

This work aims to understand oxygen solubility in pure and aqueous amine solvents for CO2 capture. Commercially available dissolved oxygen sensors were studied to evaluate whether these can be used for measuring oxygen solubility in the carbon capture processes. It also aims to understand the possible discrepancies from realistic concentrations of oxygen when using a dissolved oxygen sensor. Two independent measurement principles were used for this purpose, both electrochemical and optical. Furthermore, a Winkler titration method was used to aid the validation of the sensors as well as understanding salting-out effects. A simple model for predicting oxygen solubility in CO2-loaded ethanolamine solutions was made, which also has potential for predicting oxygen solubility in other loaded amine solutions. The results of the study show that dissolved oxygen sensors may be applied for measurement of oxygen concentrations in amine solutions and that different amines and different concentrations in water only show small variations in oxygen solubility. The sensors may also be used in CO2-loaded amine solutions, but here the increased conductivity of the solution may give a higher measured concentration of oxygen, than it is in reality. In ethanolamine, the consumption of oxygen is faster than the mass transfer of oxygen from gas to liquid phase, giving lower concentrations of oxygen than it should be in absence of a chemical reaction between oxygen and amine

On the Potential of Gallium-and Indium-Based Liquid Metal Membranes for Hydrogen Separation

The concept of liquid metal membranes for hydrogen separation, based on gallium or indium, was recently introduced as an alternative to conventional palladium-based membranes. The potential of this class of gas separation materials was mainly attributed to the promise of higher hydrogen diffusivity. The postulated improvements are only beneficial to the flux if diffusion through the membrane is the rate-determining step in the permeation sequence. Whilst this is a valid assumption for hydrogen transport through palladium-based membranes, the relatively low adsorption energy of hydrogen on both liquid metals suggests that other phenomena may be relevant. In the current study, a microkinetic modeling approach is used to enable simulations based on a five-step permeation mechanism. The calculation results show that for the liquid metal membranes, the flux is limited by the dissociative adsorption over a large temperature range, and that the membrane flux is expected to be orders of magnitude lower compared to the membrane flux through pure palladium membranes. Even when accounting for the lower cost of the liquid metals compared to palladium, the latter still outperforms both gallium and indium in all realistic scenarios, in part due to the practical difficulties associated with making liquid metal thin films

Reference case and test case for benchmarking of HiPerCap technologies

HiPerCap aims to develop high-potential novel and environmentally benign technologies and processes for post-combustion CO2 capture leading to real breakthroughs. The project includes all the main separation categories for post-combustion CO2 capture, absorption, adsorption and membranes. Each technology category is focused on several promising concepts and a key focus in the project is to demonstrate the potential of these various capture technologies. A methodology has been developed for assessment and fair comparison of the various technologies and benchmarking against a state-of-the art capture technology demonstrated in the CESAR project. In the present paper, this methodology is demonstrated for two of the absorption-based concepts involving precipitating solvent systems. Here, the assessment is based on energy efficiency penalty for the total integrated power plant and capture plant process. Though there is a slight improvement compared to the reference plant (0.5 and 7%, respectively) neither of the two precipitating solvent systems assessed here meet the project target of 25% improvement. However, the uncertainty level in the numbers is higher for these two systems compared to the reference case and the models used for the capture process should be improved before a conclusion can be made. The HiPerCap project is just starting the assessment phase and it must be emphasized that additional assessment criteria will be used and other types of technologies will be assessed before completion at the end of 2017.publishedVersio

Online monitoring of the solvent and absorbed acid gas concentration in a CO2 capture process using monoethanolamine

A method has been developed for online liquid analysis of the amine and absorbed CO2 concentrations in a postcombustion capture process using monoethanolamine (MEA) as a solvent. Online monitoring of the dynamic behavior of these parameters is important in process control and is currently achieved only using Fourier transform infrared spectroscopy. The developed method is based on cheap and easy measurable quantities. Inverse least-squares models were built at two temperature levels, based on a set of 29 calibration samples with different MEA and CO2 concentrations. Density, conductivity, refractive index, and sonic speed measurements were used as input data. The developed model has been validated during continuous operation of a CO2 capture pilot miniplant. Concentrations of MEA and CO2 in the liquid phase were predicted with an accuracy of 0.53 and 0.31 wt %, with MEA and CO2 concentrations ranging from 19.5 to 27.7 wt % and from 1.51 to 5.74 wt %, respectively. Process dynamics, like step changes in the CO2 flue gas concentration, were covered accurately, as well. The model showed good robustness to changes in temperature. Combining density, conductivity, refractive index, and sonic speed measurements with a multivariate chemometric method allows the real-time and accurate monitoring of the acid gas and MEA concentrations in CO2 absorption processes.Scopu