Rich Flue Gas Research Articles

Porous Organic Polymers for Efficient and Selective SO2 Capture from CO2‐rich Flue Gas

AbstractThe quest for effective technologies to reduce SO2 pollution is crucial due to its adverse effects on the environment and human health. Markedly, removing a ppm level of SO2 from CO2‐containing waste gas is a persistent challenge, and current technologies suffer from low SO2/CO2 selectivity and energy‐intensive regeneration processes. Here using the molecular building blocks approach and theoretical calculation, we constructed two porous organic polymers (POPs) encompassing pocket‐like structures with exposed imidazole groups, promoting preferential interactions with SO2 from CO2‐containing streams. Markedly, the evaluated POPs offer outstanding SO2/CO2 selectivity, high SO2 capacity, and an easy regeneration process, making it one of the best materials for SO2 capture. To gain better structural insights into the notable SO2 selectivity of the POPs, we used dynamic nuclear polarization NMR spectroscopy (DNP) and molecular modelling to probe the interactions between SO2 and POP adsorbents. The newly developed materials are poised to offer an energy‐efficient and environment‐friendly SO2 separation process while we are obliged to use fossil fuels for our energy needs.

Towards efficient heterotrophic recovery of N2O via Fe(II)EDTA-NO: A modeling study

Efficient recovery of nitrous oxide (N2O) through heterotrophic denitrification with the help of Fe(II)EDTA-NO as a chelating agent has been regarded as an ideal technology to treat nitric oxide (NO)-rich flue gas. In this study, an integrated NO-based biological denitrification model was developed to describe the sequential reduction of the NO fixed in Fe(II)EDTA-NO with organic carbon as the electron donor. With the inclusion of only the key pathways contributing to nitrogen transformation, the model was firstly developed and then calibrated/validated and evaluated using the data of batch tests mediated by the identified functional heterotrophic bacteria at various substrates concentrations and then used to explore the possibility of enhancing N2O recovery by altering the substrates condition and reactor setup. The results demonstrated that the optimal COD/N ratio decreased consistently from 1.5 g-COD/g-N at the initial NO concentration of 40 g-N/m3 to 1.0 g-COD/g-N at the initial NO concentration of 420 g-N/m3. Furthermore, sufficiently increasing the headspace volume of the reactor was considered an ideal strategy to obtain ideal N2O production of 86.6 % under the studied conditions. The production of high-purity N2O (98 %) confirmed the practical application potential of this integrated treatment technology to recover a valuable energy resource from NO-rich flue gas.

Data-driven surrogate modelling and multi-variable optimization of trickle bed and packed bubble column reactors for CO2 capture via enhanced weathering

Enhanced weathering (EW) of minerals could potentially absorb atmospheric CO2 at gigaton scale per year and store it as bicarbonate and carbonate in the ocean. However, this process must be accelerated by engineered reactors, in which optimal reaction conditions maximise the CO2 capture rate and minimise the energy and water consumption. In this work, trickle beds (TBs) and packed bubble columns (PBCs), operated with fresh water and CO2 -rich flue gas, are chosen as typical chemical reactors to perform the EW-based CO2 capture. We firstly develop experimentally validated physics-based mechanistic models then generate data to train data-driven surrogate models to achieve rapid prediction of performance and multi-variable optimization. Two surrogate models, namely, response surface methodology (RSM) and extended adaptive hybrid functions (E-AHF), are developed and compared, in which the effect of five design variables on three objective functions are investigated. Results show that the R2 for the prediction of CO2 capture rate (CR) and water consumption (WC) through RSM and E-AHF is higher than 0.84. For TB reactors, in particular, the calculated R2 is higher than 0.96. The prediction accuracy of energy consumption (EC) through the RSM approach is, however, relatively poor (R2 ∼ 0.79), but is improved by using the E-AHF surrogate model, increasing to R2 ∼ 0.89. The developed data-driven surrogate model can rapidly predict the performance indicators of TB and PBC reactors without solving complex mechanistic models consisting of many partial differential equations. After optimization using the surrogate models, improvements were achieved in the objectives for TB and PBC reactors as follows: CR increased by 37.8 % and 13.1 %, EC reduced by 37.4 % and 23.8 %, and WC reduced by 12.5 % and 40.7 %, respectively.

Multi-objective tailored optimization deciphering carbon partitioning and metabolomic tuning in response to elevated CO2 levels, organic carbon and sparging period.

Microalgae have garnered much contemplation as candidates to fix CO2 into valuable compounds. Although microalgae have been studied to produce various metabolites, they have not yet proved successful for commercialization. Since, handling such problems practically requires satisfying multiple parameters simultaneously, we put forth a multi-parameter optimization strategy to manipulate the carbon metabolism of Scenedesmus sp. to improve biomass production and enhance CO2 fixation to increase the production of fuel-related metabolites. The Box-Behnken design method was applied with CO2 concentration, CO2 sparging time and glucose concentration as independent variables; biomass and total fatty acid methyl ester (total FAME) content were analyzed as response variables. The strain is supplemented with both CO2 and glucose with an aim to enhance carbon flux and rechannel it towards carbon fixation. As per the results obtained in this study, Scenedesmus sp. could effectively exploit high CO2 concentration (15%) for longer duration under high concentration of glucose supplementation (9g/L) producing a biomass of 635.24±39.9μg/mL with a high total fatty acid methyl ester (FAME) content of 71.29±4.2μg/mg, significant acetyl-CoA carboxylase enzyme activity and a favorable fatty acid profile: 35.8% palmitic acid, 10.5% linoleic acid and 30.6% linolenic acid. The carbohydrate content was maximum at 10% CO2 sparged for the longest duration of 90min under glucose concentration of 9g/L. This study puts forth an optimal design that can provide evidence on comprehending the carbon assimilation mechanism to enhance production of biomass and biofuels and provide conditions to microalgal species to tolerate CO2 rich flue gas.

Simulation of SO2 absorption and performance enhancement of wet flue gas desulfurization system

At the present moment wet flue gas desulfurization systems (WFGD) are widely used in the SO2 emitting industries. With the improvement of the SO2 emission standards and the use of fuel with high sulfur content, there is an urgent need to develop advanced modelling tools to explore the enhancing method of SO2 absorption process on the condition of flue gas with high SO2 concentration. In this study, a detailed mathematical model of tray scrubbers, which are adopted in several China’s power plants in order to treat SO2 rich flue gas, is developed to investigate the influencing factors of the SO2 absorption process. The model is validated by an experiment using pilot-scale WFGD experimental system and can describe the SO2 absorption process in WFGD to a satisfactory level. The influence factors of SO2 absorption of droplets and in spray tower are studied through the model. The effects of pH and tray on desulfurization efficiency are analyzed. Using the tray scrubber is better in order to realize the desulfurization of flue gas with high SO2 concentration rather than adjusting the pH of the slurry. This model can be regarded as a useful tool for equipment selection and operation optimization of WFGD system.

Stepwise Ions Incorporation Method for Continuously Activating PbS to Recover Mercury from Hg0-Rich Flue Gas.

Transition metal elements doping is a conventional strategy for the modification of sulfide-based sorbents to obtain preferable Hg0 adsorption capability. One problem was that such a method could only obtain a temporary promotion to sulfides. To achieve continuous promotion of mercury capture performance, we use the difference of solubility product (Ksp) between sulfides to develop a postsynthesis approach for stepwise doping of PbS by Cu2+ ions. Moreover, it further demonstrated the restoration of PbS surface under a given high temperature, enabled by thermal migration of the foreign Cu2+ ions from outer to interlayer in PbS lattice and rereleased of S sites occupied previously by mercury. The Hg0 adsorption capacity of PbS was enlarged from 0.86 to 2.76 mg·g-1 after the first doping, resulting from the mild oxidization of S2- to S- in the surface layer by foreign Cu2+ ions. Furthermore, regeneration of spent PbS can be implemented by stepwise Cu2+ incorporation due to the renewability of the surface, enabling even better Hg0 adsorption capacity after six cycle tests. This stepwise incorporation method promises the precise utilization of doped elements, as well as offers a tutorial example for the activation and regeneration of sulfide sorbents to recover Hg0 from Hg0-rich flue gas.

Simulation Study of an Oxy-Biomass-Based Boiler for Nearly Zero Emission Using Aspen Plus

Bioenergy integrated CO2 capture is considered to be one of the viable options to reduce the carbon footprint in the atmosphere, as well as to lower dependability on the usage of fossil fuels. The present simulation-based study comprises the oxy bio-CCS technique with the objective of bringing about cleaner thermal energy production with nearly zero emissions, CO2 capture and purification, and with the ability to remove NOx and SO2 from the flue gas and to generate valuable byproducts, i.e., HNO3 and H2SO4. In the present work, a simulation on utilization of biomass resources by applying the oxy combustion technique was carried out, and CO2 sequestration through pressurized reactive distillation column (PRDC) was integrated into the boiler. Based on our proposed laboratory scale bio-CCS plant with oxy combustion technique, the designed thermal load was kept at 20 kWth using maize stalk as primary fuel. With the objective of achieving cleaner production with near zero emissions, CO2 rich flue gas and moisture generated during oxy combustion were hauled in PRDC for NOx and SO2 absorption and CO2 purification. The oxy combustion technique is unique due to its characteristic low output of NO sourced by fuel inherent nitrogen. The respective mechanisms of fuel inherent nitrogen conversion to NOx, and later, the conversion of NOx and SO2 to HNO3 and H2SO4 respectively, involve complex chemistry with the involvement of N–S intermediate species. Based on the flue gas composition generated by oxy biomass combustion, the focus was given to the fuel NOx, whereby different rates of NO formation from fuel inherent nitrogen were studied to investigate the optimum rates of conversion of NOx during conversion reactions. The rate of conversion of NOx and SO2 were studied under fixed temperature and pressure. The factors affecting the rate of conversion were optimized through sensitivity analysiês to get the best possible operational parameters. These variable factors include ratios of liquid to gas feed flow, vapor-liquid holdups and bottom recycling. The results obtained through optimizing the various factors of the proposed system have shown great potential in terms of maximizing productivity. Around 88.91% of the 20 kWth boiler’s efficiency was obtained. The rate of conversion of NOx and SO2 were recorded at 98.05% and 87.42% respectively under parameters of 30 °C temperature, 3 MPa pressure, 10% feed stream holdup, liquid/gaseous feed stream ratio of 0.04 and a recycling rate of the bottom product of 20%. During the simulation process, production of around four kilograms per hour of CO2 with 94.13% purity was achieved.

Oxyfuel CO2 compression: The gas phase reaction of elemental mercury and NOx at high pressure and absorption into nitric acid

Oxyfuel combustion is a technology which combusts coal in oxygen and recycled flue gas, producing a carbon dioxide rich flue gas for sequestration. Oxyfuel flue gas contains trace amounts of elemental mercury, which may corrode brazed aluminium heat exchangers used in the carbon dioxide purification system. International gas vendors have tested the use of the compression system to remove other flue gas impurities such as NOx; however, the reaction mechanism of mercury and its reaction products with NOx and nitric acid formed with condensed water vapour are unclear. This study used lab scale experiments to study the absorption of gaseous elemental mercury into nitric acid and the gas phase reaction between mercury and nitrogen dioxide formed from oxidised NO at pressures up to 25bar. It was observed that mercury has limited absorption into nitric acid and may partially desorb out of solution after depressurisation. On the other hand, mercury reacted readily with nitrogen dioxide (formed from nitric oxide oxidation at high pressure) in the gas phase. These gas phase reactions from the oxidation of nitric oxide to nitrogen dioxide to the subsequent oxidation of elemental mercury by nitrogen dioxide were predicted using existing global kinetic equations. The limited absorption of gaseous elemental mercury in nitric acid and significant oxidation of gaseous elemental mercury by nitrogen dioxide suggests that the primary removal step for elemental mercury is through the gas phase reaction. Oxyfuel compression circuits should therefore allow sufficient residence time for this gas phase reaction to occur.

An Ultra-low Emissions Enhanced Thermal Recovery Process for Oil Sands

Abstract The growth of energy demand over the next few decades with declining conventional fossil fuel production implies that greater reliance will be placed on unconventional fossil fuel energy sources such as heavy oil and extra heavy oil (bitumen). However, unconventional fuels tend to have higher environmental impact than their conventional counterparts. Here, we focus on the oil sands resource of Alberta, Canada whose recovery is both energy and emissions intensive on one hand yet provide economic and social benefits to society on the other hand. There is a drive to improve the energy and emission intensities of oil sands recovery processes. We evaluate the combined application of natural gas decarbonization (NGD) with oxy-combustion and the utilization its CO 2 -rich flue gas to achieve an ultra-low emissions enhanced thermal recovery process for bitumen from oil sands. We used industry-accepted thermal reservoir simulation tools to model steam assisted gravity drainage (SAGD) bitumen recovery using a steam-CO 2 mixture. Our results show that the overall performance of the proposed process when applied to a moderately high oil saturation reservoir is improved over the current practice both from an energy intensity and a CO 2 footprint basis.

Heat Transfer Characteristics of O<sub>2</sub>/CO<sub>2</sub> Pulverized Coal Boiler Furnace

Global warming is currently one of the most serious environmental challenges in the world. The increase of CO2 in the atmosphere is a dominating factor to global warming .O2 / CO2 combustion technology is a new generation of clean coal power generation technology[1],it can directly capture high concentration of CO2 and make the pollutant resource ,so it is one of the most promising feasible technical to reduce CO2 emissions [2]. Compared with conventional pulverized coal combustion boiler, O2 / CO2 combustion technology can be used to produce a CO2 rich flue gas stream. So physical parameters had a very big change, such as flue gas heat capacity, motion viscosity, prandtl number and so on. Thus they affect the heat transfer characteristics [3] inside the furnace.In order to study the heat transfer characteristics of the furnace; this paper established a dynamic mathematical model for the radiation heat transfer progress of the furnace and adequate for control system design.

Dynamic modelling of oxyfuel power plant

Abstract Oxyfuel combustion technology is one of several Carbon Abatement Technologies (CATs) currently being developed. The technology offers a means of generating carbon dioxide rich flue gas requiring minimal treatment prior to sequestration or beneficial application. The oxyfuel process is based on excluding the inert components (mainly nitrogen) of air from the combustion process. In oxyfuel combustion, nitrogen is largely absent from the flue gas, since the fuel is combusted with a mixture of nearly pure oxygen (∼95% O 2 -separated from air in an air separation unit (ASU)) and CO 2 rich recycled flue gas. It is recognised as a leading Carbon Capture technology for new and retrofit power plant. Previous studies undertaken by Doosan Power Systems, Air Products, University of Edinburgh and others have shown that there is significant scope to optimise overall plant efficiency, both at the design stage and during normal operation. Therefore the current work seeks to realise these benefits through the adoption of optimised designs and the development of appropriate control and dynamic optimisation strategies. Recycling flue gas in the Oxyfuel process gives rise to a number of operational and control features not seen in conventional air-fired power plant systems. Comprehensive dynamic models of the Oxyfuel process systems and associated controls are being developed as part of the TSB collaborative project “Optimisation of Oxyfuel PF Power Plant for Transient Behaviour” to study these aspects. The Oxyfuel specific models are coupled to a whole cycle, non-linear, dynamic model of the boiler and turbine systems allowing development of control schemes, which can meet the full range of operational requirements and capabilities of the Oxyfuel plant. Early results from the model suggest that operation in Oxyfuel mode may provide an opportunity to improve plant flexibility and both primary and secondary response, a capability which is of increasing importance as the mix of conventional, nuclear and renewable generation changes.

Near Zero CO2 Emissions in Coal Firing with Oxy‐Fuel Circulating Fluidized Bed Boiler

AbstractCarbon capture and storage is a concept to reduce greenhouse gas emissions of energy production from fossil fuels. In oxy‐fuel combustion, the fuel is burned in a mixture of oxygen and recycled flue gas. This generates CO2‐rich flue gas from which the CO2 is easily separated and compressed. Foster Wheeler Power Group is developing the existing design tools and process models of air‐fired circulating fluidized bed boilers to implement specific features of oxycombustion. The validation data is produced from bench‐scale and pilot‐scale experiments at the VTT, Technical Research Centre of Finland. A three‐dimensional circulating fluidized bed (CFB) furnace model is developed and applied by Lappeenranta University of Technology for predicting the effects of oxycombustion in full scale units. This paper presents concept studies and initial 3D modeling results based on a 460 MWe supercritical CFB power plant at Lagisza, and pilot‐scale studies with flue gas recirculation demonstrating real oxygen combustion conditions.

Coal-fired power plant with calcium oxide carbonation for postcombustion CO2 capture

Abstract In the plant configuration discussed in this paper, CO 2 rich flue gas from an air fired coal boiler is contacted with CaO in a fluidized bed reactor (carbonator) generating CaCO 3 and capturing more than 90% of the CO 2 generated. Sorbent is regenerated in a second fluidized bed (calciner) via oxyfuel combustion of coal, generating a CO 2 rich stream ready for compression and sequestration. Kunii–Levenspiel model, together with correlations for the estimation of sorbent performance after a number of carbonation–calcination cycles were used, in order to estimate carbonator dimensions and pressure losses. A net LHV efficiency of 37.4% was predicted for the selected reference case, with 97% of CO 2 captured. As a comparison, for full oxy-combustion and amine based plants, net efficiency of 36.3% and 32.6% were obtained respectively.

Modeling of oxy-fuel combustion for a western Canadian sub-bituminous coal ☆

The motivation of this research is to develop practical oxy-coal combustion techniques in order to facilitate the conversion of coal-fired utility power plants so as to recover a CO 2 rich flue gas stream for use and/or sequestration. The objective of this study is to ascertain the applicability and accuracy of a modeling tool to assist with future pilot scale oxy-fuel combustion experiments and burner scale-up studies. Two modes of oxy-coal combustion, O 2 enriched air (OEA) and recycled flue gas (RFG), were experimentally tested in a 0.3 MW th pilot-scale combustor using a western Canadian sub-bituminous coal. The computational fluid dynamic tool was utilized to model the combustion, heat transfer and pollutant formation characteristics of these test cases and to examine the impact due to changes in the combustion medium, burner swirl and burner configuration. The model provided insights for the observed variation in NO x production among the test cases: the dramatic increase in the OEA mode, the drop at higher burner swirl settings and the surprisingly small reduction in the RFG mode. Overall the model results compared well with measured data in all test cases and established confidence in using the model to explore new design concepts for oxy-coal combustion.