Prevention of mist formation in amine based carbon capture : field testing using a Wet ElectroStatic Precipitator (WESP) and a Gas-Gas Heater (GGH)

This study presents the results of two field tests that aimed at evaluating two countermeasures (WESP and GGH) to avoid acid mist formation. A WESP is shown to be very efficient for the removal of nuclei from the flue gas (100 % efficient) and thus can prevent aerosol formation inside an amine based absorber. This is however only valid in the absence of SO2 in the flue gas entering the WESP. A decreasing WESP efficiency is noted in the presence of SO2 with increasing voltages as a result of newly formed aerosols inside the WESP. This implies that no or very low levels of SO2 should be present in the flue gas entering the WESP. Since most of the amine carbon capture installations have a pre-scrubber (usually using NaOH to remove residual SO2 in the flue gas leaving the power plant's Flue Gas Desulphurisation) in front of their amine absorber, the WESP must be installed behind this pre-scrubber and not in front of it. Having a Gas-Gas Heater (or any type of flue gas cooling such as a Low Temperature Heat Exchanger) installed upstream of the wet scrubbing may prevent homogenous nucleation and thus prevent the conversion of H2SO4 into sulfuric acid aerosols and consequently mist formation issues in the amine based carbon capture installation. Which option to choose amongst the two countermeasures presented in this study will depend on whether a new built installation is being considered or whether a carbon capture is planned as a retrofit into an existing installation. (C) 2017 The Authors. Published by Elsevier Ltd

Prevention of Mist Formation in Amine Based Carbon Capture: Field Testing Using a Wet ElectroStatic Precipitator (WESP) and a Gas-Gas Heater (GGH)

This study presents the results of two field tests that aimed at evaluating two countermeasures (WESP and GGH) to avoid acid mist formation. A WESP is shown to be very efficient for the removal of nuclei from the flue gas (100 % efficient) and thus can prevent aerosol formation inside an amine based absorber. This is however only valid in the absence of SO2 in the flue gas entering the WESP. A decreasing WESP efficiency is noted in the presence of SO2 with increasing voltages as a result of newly formed aerosols inside the WESP. This implies that no or very low levels of SO2 should be present in the flue gas entering the WESP. Since most of the amine carbon capture installations have a pre-scrubber (usually using NaOH to remove residual SO2 in the flue gas leaving the power plant's Flue Gas Desulphurisation) in front of their amine absorber, the WESP must be installed behind this pre-scrubber and not in front of it. Having a Gas-Gas Heater (or any type of flue gas cooling such as a Low Temperature Heat Exchanger) installed upstream of the wet scrubbing may prevent homogenous nucleation and thus prevent the conversion of H2SO4 into sulfuric acid aerosols and consequently mist formation issues in the amine based carbon capture installation. Which option to choose amongst the two countermeasures presented in this study will depend on whether a new built installation is being considered or whether a carbon capture is planned as a retrofit into an existing installation. (C) 2017 The Authors. Published by Elsevier Ltd

Operational flexibility options in power plants with integrated post-combustion capture

Flexibility in power plants with amine based carbon dioxide (CO2) capture is widely recognised as a way of improving power plant revenues. Despite the prior art, its value as a way to improve power plant revenues is still unclear. Most studies are based on simplifying assumptions about the capabilities of power plants to operate at part load and to regenerate additional solvent after interim storage of solvent. This work addresses this gap by examining the operational flexibility of supercritical coal power plants with amine based CO2 capture, using a rigorous fully integrated model. The part-load performance with capture and with additional solvent regeneration, of two coal-fired supercritical power plant configurations designed for base load operation with capture, and with the ability to fully bypass capture, is reported. With advanced integration options configuration, including boiler sliding pressure control, uncontrolled steam extraction with a floating crossover pressure, constant stripper pressure operation and compressor inlet guide vanes, a significant reduction of the electricity output penalty at part load is observed. For instance at 50% fuel input and 90% capture, the electricity output penalty reduces from 458 kWh/tCO2 (with conventional integration options) to 345 kWh/tCO2 (with advanced integration options), compared to a reduction from 361 kWh/tCO2 to 342 kWh/tCO2 at 100% fuel input and 90% capture. However, advanced integration options allow for additional solvent regeneration to a lower magnitude than conventional integration options. The latter can maintain CO2 flow export within 10% of maximum flow across 30–78% of MCR (maximum continuous rating). For this configuration, one hour of interim solvent storage at 100% MCR is evaluated to be optimally regenerated in 4 h at 55% MCR, and 3 h at 30% MCR, providing rigorously validated useful guidelines for the increasing number of techno-economic studies on power plant flexibility, and CO2 flow profiles for further studies on integrated CO2 networks

Aerosol-based Emission, Solvent Degradation, and Corrosion in Post Combustion CO2 Capture

Global greenhouse gas emissions, especially of CO2, have been increasing tremendously over the past century. This is known to cause not only an increase of temperature, but also a change in our climate. Along with a shift to renewable sources of energy, Carbon Capture and Storage is necessary to mitigate climate change. Power plants are the largest point source of CO2 emissions and therefore, capture of CO2 from such sources is a must. Post Combustion CO2 Capture (PCCC), and specifically absorption-desorption based technology is the preferred choice of technology for CO2 capture from flue gases. It has been extensively used in the oil and gas industry for gas treatment. Its application for CO2 capture from flue gases is not straightforward, mainly due to different flue gas composition and operating conditions. Other aspects such as solvent degradation, solvent emissions and corrosion become even more critical. In Chapter 1, the state-of-the-art in PCCC is explained with further details on the current knowledge and understanding of these aspects. In Chapter 2, the aspect of solvent ageing is studied over two test campaigns in a CO2 capture pilot plant using 30 wt.% MEA. Solvent degradation occurs via thermal and oxidative routes, with the latter being more prominent. Ammonia is known to be a major oxidative degradation product, while the remaining degradation products are known to be corrosive. Therefore, solvent degradation is expected to have a significant impact on the corrosion in the plant and the resulting emissions of ammonia. The link between these three parameters was confirmed using online monitoring probes. Moreover, an autocatalytic behaviour was observed resulting in an rapid increase of the solvent metal content and ammonia emissions. The solvent iron content was above 500 mg/kg, while the ammonia emissions exceeded 150 mg/m3 STP (STP; 0°C and 101.325 kPa). By correlating the process conditions to the underlying degradation and corrosion mechanisms, online monitoring tools can be used to assess and manage the lifetime of the solvent. Even if the state of the solvent is kept in check by reclaiming methods, there could be instances where ammonia emissions could increase. Therefore, it is necessary to have an end of pipe countermeasure for such emissions. Chapter 3 presents the results from a test using an acid wash scrubber for ammonia emissions in a pilot plant test campaign. Several parametric tests were conducted in order to test the efficiency of the acid wash. Moreover, the ammonia concentration in the gas inlet to the acid wash was increased artificially (~150 mg/m3 STP). The acid wash scrubber reduced ammonia emission to very low levels, below 5 mg/m3 STP and mostly below 1 mg/m3 STP. Moreover, the MEA content was also reduced to mostly below 1 mg/m3 STP. A comparison between a model made in Aspen Plus and the experimental results showed good agreement, with deviations only at pH above 5 to 6. Aerosol based emissions are known to be a concern in PCCC. In Chapter 4, the impact of flue gas particles such as soot and sulphuric acid aerosol droplets on solvent emissions was studied in a mobile CO2 capture plant. These tests confirmed that solvent emissions can be in the order of grams per m3 STP, which is several orders of magnitude higher than volatile emissions. The number concentration of these particles had a direct relation to the extent of emissions. Particle number concentrations in the range of 107-108 per cm3 led to emissions of MEA in the range of 600-1200 mg/m3 STP. In Chapter 5, further tests were performed on the same setup in order to assess the impact of operating conditions of the CO2 capture plant on aerosol based emissions. Increasing the temperature of the lean solvent resulted in lowering of the aerosol based emissions. However, the total solvent emission increased as a result of increased volatile emissions. Aerosol based emissions were observed also for AMP-Pz as the capture solvent. The pH of the lean solvent was decreased by lowering the stripper temperature and thereby, changing the CO2 loading of the solvent. This resulted in an increase in the aerosol based emissions as the activity of the amine increased in the solvent. As the CO2 content in the flue gas was reduced from 12.7 vol.% to 0.7 vol.%, a maximum in the emissions was observed between 6 and 4 vol.%. When a mixture of a slow reacting volatile amine, AMP, with a fast reacting non-volatile, taurate, was used, no aerosol based emissions were observed. This led to the important conclusion that in reactive absorption, along with supersaturation and particle number concentration, the reactivity of the amine plays an important role in aerosol based emissions. A Brownian Demister Unit (BDU), consisting of multiple polypropylene fibre elements, can be potentially used as a countermeasure for aerosol based emissions. This was tested in a pilot plant campaign using MEA and is discussed in Chapter 6. The BDU reduced emissions from about 85–180 mg/m3 STP to about 1–4 mg/m3 STP. A water wash was found to be effective against vapour based emissions, while the BDU was effective against aerosol based emissions. A BDU is not effective against ammonia emissions, as they are present in the vapour form. From the measured nitrosamines, NDELA was found to be in the solvent in the order of 2000 ng/ml, while in the water wash it was ca. 1 ng/ml. Gas phase nitrosamine concentrations were in the range of tens of ng/m3 STP. The BDU results in a significant additional pressure drop of ca. 50 mbar, for the configuration and type of BDU used here. This translated to an additional consumption of electricity by the blower in the range 26–52%. A system containing three distinct phases, gas, liquid and aerosol droplets, are complex to understand and model. In Chapter 7, a methodology is presented with which such a complicated system can be modelled in commercially available software such as Aspen Plus. The mass and energy exchanges are split into two distinct interactions, gas-liquid and gas-aerosol. Aerosol droplets are considered to be as bulk liquid without any direct interaction with the solvent. The different parameters that were varied were the CO2 concentration in the flue gas, temperature of the lean solvent and CO2 loading of the lean solvent. The resulting trends were in good agreement with the experimental results presented in Chapter 5. The model did not predict a maximum in the emissions as the CO2 content in the flue gas was varied. Although absorption desorption based process for CO2 capture is well known, several operating issues needs to be addressed for its application in PCCC, as evident in this thesis. It is important to monitor the degradation of the solvent and deploy appropriate methods at the right time, to minimize its detrimental effect on the corrosion of the plant and avoid high emissions of ammonia. Aerosol based emissions in a PCCC process is a serious issue. The experimental results, proposed mechanism and modelling methodology will enable the design of appropriate counter-measures against aerosol based emissions. It is recommended to devise appropriate strategy and innovative solutions based on the understanding of the various operational aspects of absorption-desorption based PCCC as presented in this thesis. This will increase the confidence level in the technology and lead to its successful deployment for mitigating climate change in the short term.Process and EnergyMechanical, Maritime and Materials Engineerin

The challenge of measuring sulfuric acid aerosols : number concentration and size evaluation using a condensation particle counter (CPC) and an electrical low pressure impactor (ELPI+)

In this study, two different methods for the measurement of the sulfuric acid aerosol which is formed in wet flue gas cleaning processes have been investigated. The condensation particle counter (UFCPC, PALAS GmbH) provides information about the number concentration. With the electrical low pressure impactor (ELPI+, Dekati Ltd.) also the size evaluation is possible. Both measurement methods reveal number concentrations above 108cm-3 under well controlled conditions in a pilot plant and the good conformance of the both methods is shown. With the ELPI+ the effect of dilution on the size of the volatile aerosol can be observed. The predicted trend of an existing simulation tool can be verified: the higher the sulfuric acid concentration, the larger are the droplet sizes. The number concentration, however, doesnD́t change considerably when altering the sulfuric acid concentration. © 2013 Elsevier Ltd

Effect of a gas-gas-heater on H2SO4 aerosol formation: implications for mist formation in amine based carbon capture

This study is to our knowledge the first to describe the effect of a Gas-Gas Heater (GGH) of a coal fired power plant's has on (i) the H2SO4 concentration and (ii) the particle/aerosol number concentration and particle size distribution present in the flue gas. In the absence of a GGH, homogenous nucleation takes places inside the Wet Flue Gas Desulphurisation (WFGD) converting the gaseous H2SO4 into aerosol H2SO4. This leads to a high aerosol number concentration behind the WFGD with 80% of the aerosols being smaller than 0.02 μm. This implies that an amine based carbon capture (CC) installation treating this flue gas can suffer from amine mist formation due to the high amount of available nuclei (i.e., H2SO4 aerosols) resulting in high amine emissions. In contrast, in the presence of a GGH not only 70% of the H2SO4 is removed from the flue gas (measured at the Nijmegen powerplant), but also homogenous nucleation in the WFGD is prevented resulting in low particle number concentrations. The flue gas leaving the GGH will not create any mist formation issues in an amine based CC installation due to the low amount of nuclei present in the flue gas. It is not the reduction in H2SO4 concentration by 70% inside the GGH as such that prevents mist formation but absence of H2SO4 in its aerosol form. These results are most likely quite widely transformable to other power plants that burn low sulfur coal i.e., around 0.7 weight%. This information will serve future pilot and demo CC installation around the world; in particular when retrofitted on power plants that have a GGH

A wet electrostatic precipitator (WESP) as countermeasure to mist formation in amine based carbon capture

This study is to our knowledge the first to evaluate the potential of a wet electrostatic precipitator (WESP) to prevent aerosol formation issues inside amine based carbon capture installations. A WESP is a suitable option since this study proves that it is very efficient for the removal of the mist precursors inside the flue gas to be treated. Although a significant capital investment cost may be involved, energy requirements (i.e. low pressure drop), maintenance and therefore operational costs are expected to be very low. However, it is shown here that the WESP must be installed at the right location, i.e. the flue gas to be treated must contain no or very low levels of SO2. The reason is that the WESP's aerosol removal efficiency decreases strongly in the presence of SO2 gas and in a certain range also with increasing voltages. This limits the positive effect that the WESP has on reducing the MEA emissions from the absorber since a large number of mist formation precursors remain in the flue gas. In the presence of SO2, a WESP can actually produce H2SO4 aerosols. It is shown that these newly created aerosols are very small (low nanometre range). This information is very important for future pilot and demo amine carbon capture installations thinking of implementing a WESP as countermeasure to aerosol formation issues. It implies that no or very low levels of SO2 should still be present in the flue gas before entering the WESP. Since most of the amine carbon capture installations have a pre-scrubber (usually using NaOH to remove residual SO2 in the flue leaving the power plant's FGD) in front of their amine absorber, the WESP must be installed behind this pre-scrubber and not in front of it