Absorber performance and configurations for CO2 capture using aqueous piperazine

Absorber design for CO2 capture with amine solvents is complicated by the presence of temperature gradients and multiple rate controlling mechanisms (chemical reaction and convective mass transfer). The development of rigorous rate-based models has created the opportunity to study the performance limiting mechanisms in detail. A structured approach was developed to validate absorber models, identify limiting phenomena, and develop configurations that specifically address limiting mechanisms. A rate-based model utilizing concentrated aqueous piperazine (PZ) was the focus of model validation and process development. The model was validated using pilot plant data, matching the number of transfer units (NTU) within + 1% while identifying a systematic bias (loading measurement) between the model and pilot plant data. The validated model was used to define limiting cases (isothermal and adiabatic absorbers) to study the effects of operating conditions on the formation of temperature-induced mass transfer pinches. The method allowed for screening of intercooling benefits – high CO2 applications (15% - 27% CO2) require intercooling over the entire practical loading range for PZ and benefit significantly from simple in-and-out intercooling with limited additional benefit expected from advanced design. Low CO2 (4% CO2) applications are expected to benefit the most from improved intercooling, but also have the largest operating window without the need for intercooling (< 0.22 mol CO2/mol alkalinity for 8 m PZ). An analogous approach was developed to study rate mechanisms. A mass transfer parameter sensitivity analysis approach was developed to identify the relative contribution to overall mass transfer resistance of each mechanism as a function of operating conditions and position in the absorber column. The pseudo-first order and instantaneous reaction asymptotic solutions to the reaction-diffusion problem were used to define a dimensionless parameter that quantifies the approach of the modeling results to the limiting conditions and was found to be predictive of the relative liquid film resistance (diffusion vs. reaction) at all conditions. The results of the analysis indicated that the absorber is strongly diffusion controlled, has limited gas-film resistance, and that equilibrium constraints at the rich end of the absorber (depletion of free amine) significantly increase diffusion limitations. Finally, the validation and mechanistic studies provided the basis for four new absorber configurations: 1) integration of a spray nozzle in the intercooling loop, 2) solvent recycle intercooling, 3) integrated flue gas and solvent cooling functions, 4) hybrid intercooling (high intensity contacting with intercooling). Each approach coupled mass transfer enhancement with intercooling and provided new degrees of freedom for operation and design of absorbers for CO2 capture.Chemical Engineerin

Effectiveness of Absorber Intercooling for CO2 Absorption from Natural Gas Fired Flue Gases Using Monoethanolamine Solvent

Chemical absorption using aqueous amine is one of the most feasible options for post-combustion CO2 capture. One of the main challenges of this technology is its high energy requirements. Absorber intercooling was considered as a viable method to offer benefits in terms of solvent absorption capacity and mass transfer efficiency in CO2 absorption processes. However, the effectiveness of absorber intercooling on overall energy requirements depends on other factors such as lean loading and liquid to gas ratio. This study evaluates the benefits of using two different configurations of absorber intercooling, i.e. “in-and-out” and “recycled” intercooling when using 30 wt% aqueous monoethanolamine (MEA) to capture 90% CO2 from a natural gas fired turbine with 4 mol% CO2. The Lean CO2 loading was varied from 0.15 to 0.42 (mol CO2/mol MEA) to determine the lean loading at which the application of intercooling is most significant. Absorber intercooling provides the most benefit at lean loading from 0.30 to 0.34. The use of in-and-out and recycle intercooling at 0.34 lean loading, provided 15.6 and 15.8% reduction in the total equivalent work associated with 32.0% and 36.6% reduction in required packing area when using 1.2 times the minimum liquid flow rate. At lean loading greater than 0.34, the benefit of absorber intercooling is a trade-off between reduction of solvent flow rate and total energy requirement and the drawback of greater packing area in the absorber. The greatest saving in total equivalent work, 17%, was observed at the 0.36 lean loading associated with nearly 60% more packing area when using 1.2 times the minimum solvent flow rate. At very low lean loading and very high lean loading absorber intercooling does not offer significant benefit

Performance evaluation and optimisation of post combustion CO2 capture processes for natural gas applications at pilot scale via a verified rate-based model

CO2 absorption based on chemical reactions is one of the most promising technologies for post combustion CO2 capture (PCC). There have been significant efforts to develop energy efficient and cost effective PCC processes. Given that PCC is still maturing as a technology, there will be a continuing need for pilot scale facilities to support process optimisation, especially in terms of energy efficiency. Pilot scale PCC facilities, which are usually orders of magnitude smaller than those that will be used in future in large scale fossil power plants, make it possible to study details of the PCC process at an affordable scale. However, it is essential that pilot scale studies provide credible data, if this is to be used with confidence to envisage the future large-scale use of the PCC process, especially in terms of energy consumption. The present work therefore establishes and experimentally verifies (using a representative pilot plant as a case study) procedures for analysing the energy performance of a pilot scale amine based CO2 capture plants, focusing on natural gas fired applications. The research critically assesses the pilot plant’s current energy performance, and proposes new operating conditions and system modifications by which the pilot plant will operate more efficiently in terms of energy consumption. The methodology developed to assess and improve the energy performance of the PCC process is applicable, with appropriate inputs, to other plants of this type that employs aqueous 30 wt. % monoethanolamine (MEA) solution as the solvent. A rate based model of the post combustion CO2 capture process using an aqueous solution of 30 wt. % MEA as the solvent was developed in Aspen Plus® V.8.4, and verified using the results of experimental studies carried out using the UK Carbon Capture and Storage Research Centre / Pilot-scale Advanced Capture Technology (UKCCSRC/PACT) pilot plant, as a representative pilot-scale capture plant, and employed for parametric sensitivity studies. Several parameters have been identified and varied over a given range of lean solvent CO2 loading to evaluate their effects on the pilot plant energy requirement. The optimum lean solvent CO2 loading was determined using the total equivalent work concept. Results show, for a given packing material type, the majority of energy savings can be realised by optimising the stripper operating pressure. To some extent, a higher solvent temperature at the stripper inlet has the potential to reduce the regeneration energy requirement. A more efficient packing material, can greatly improve the pilot plant overall energy and mass transfer efficiency

Application of Raman spectroscopy to real-time monitoring of CO2 capture at PACT pilot plant; Part 1: Plant operational data

Process analyzers for in-situ monitoring give advantages over the traditional analytical methods such as their fast response, multi-chemical information from a single measurement unit, minimal errors in sample handing and ability to use for process control. This study discusses the suitability of Raman spectroscopy as a process analytical tool for in-situ monitoring of CO2 capture using aqueous monoethanolamine (MEA) solution by presenting its performance during a 3-day test campaign at PACT pilot plant in Sheffield, UK. Two Raman immersion probes were installed on lean and rich streams for real time measurements. A multivariate regression model was used to determine the CO2 loading. The plant performance is described in detail by comparing the CO2 loading in each solvent stream at different process conditions. The study shows that the predicted CO2 loading recorded an acceptable agreement with the offline measurements. The findings from this study suggest that Raman Spectroscopy has the capability to follow changes in process variables and can be employed for real time monitoring and control of the CO2 capture process. In addition, these predictions can be used to optimize process parameters; to generate data to use as inputs for thermodynamic models, plant design and scale-up scenarios

Uranium extraction from seawater : an assessment of cost, uncertainty and policy implications

textTechnology to recover uranium from seawater may act as a potential backstop on the production cost of uranium in a growing international nuclear industry. Convincing proof of the existence of an effective expected upper limit on the resource price would have a strong effect on decisions relating to deployment of uranium resource consuming reactor technologies. This evaluation proceeds from a review of backstop technologies to detailed analyses of the production cost of uranium extraction via an amidoxime braid adsorbent system developed by the Japan Atomic Energy Agency (JAEA). An independent cost assessment of the braid adsorbent system is developed to reflect a project implemented in the United States. The cost assessment is evaluated as a life cycle discounted cash flow model to account for the time value of money and time-dependent performance parameters. In addition, the cost assessment includes uncertainty propagation to provide a probabilistic range of uranium production costs for the braid adsorbent system. Results reveal that uncertainty in adsorbent performance (specifically, adsorption capacity, kg U/tonne adsorbent) is the dominant contributor to overall uncertainty in uranium production costs. Further sensitivity analyses reveal adsorbent capacity, degradation and production costs as key system cost drivers. Optimization of adsorbent performance via alternate production or elution pathways provides an opportunity to significantly reduce uranium production costs. Finally, quantification of uncertainty in production costs is a primary policy objective of the analysis. Continuing investment in this technology as a viable backstop requires the ability to assess cost and benefits while incorporating risk.Civil, Architectural, and Environmental EngineeringPublic Affair

Absorber Intercooling Configurations using Aqueous Piperazine for Capture from Sources with 4 to 27% CO2

AbstractA systematic evaluation of the solvent capacity and mass transfer benefits of absorber intercooling was conducted for CO2 capture with 8 m piperazine (PZ) for three different flue gas sources: NGCC (4.1% CO2), coal-fired boiler (14.7% CO2), and steel blast furnace (27.4% CO2). The study identified the best intercooling strategy as a function of operating conditions (lean loading, liquid to gas ratio (L/G)). For all applications, operation at low lean loadings did not require intercooling to avoid temperature-related capacity or mass transfer penalties. In a broad intermediate loading range, simple in-and-out intercooling provided large solvent capacity benefits (measured as minimum solvent rate, LMIN) compared to a column without intercooling. LMIN was reduced by 71%, 53%, and 42% for NGCC, coal, and steel, respectively. Finally, the coal and steel applications had a large L/G range at higher loadings where intercooling was once again unnecessary. An enhanced intercooling design for NGCC could yield up to 62% reduction in packing and 46% reduction in solvent capacity at specific conditions (benefits for coal and steel were much lower). A recycle intercooling design for NGCC was introduced to reduce overall column temperatures and enhance mass transfer. For the case evaluated with recycle intercooling, the new design achieved significant packing reductions (>50%) compared to a simple intercooling design and approximated the performance of an isothermal column

ACKNOWLEDGEMENTS

First and foremost, I would like to thank my advisor, Dr. Sharma Chakravarthy, for his constant guidance and support, and for giving me a wonderful opportunity to work on such a challenging project. I am also grateful to Dr. Alp Aslandogan and Dr. Lynn Peterson for serving on my committee. I would like to thank Ajay Eppili and Shravan Chamakura for helping me throughout the design and implementation of this work. Thanks are due to my seniors Jyoti Jacob and Naveen Pandrangi and Anoop Sanka for their fruitful discussions and guidance. I would like to thank my roommate Swapna Rao and my friends Sridhar Varakala, Hima Valli Kona and others for their help. I also thank my friends L.Stephen Lobo, Laali Elkhalifa and Raman Adaikkalavan and Manu Aery for their support and encouragement in ITLAB

The Radial Bow following Square Nailing in Radius and Ulna Shaft Fractures in Adults and its Relation to Disability and Function

One of the points made against nailing in radius and ulna shaft fractures has been the loss of radial bow and its impact on function. The aims of the study were to assess the change in magnitude and location of the radial bow in radius and ulna shaft fractures treated with intramedullary square nails and to assess the impact of this change on functional outcome, patient reported disability and the range of motion of the forearm. We measured the magnitude of radial bow and its location in the operated extremity and compared it to the uninjured side in 32 adult patients treated with intramedullary square nailing for radius and ulna shaft fractures at our institute. The mean loss of magnitude of maximum radial bow was 2.18 mm which was statistically significant by both student-T test and Mann-Whitney U test with p value less than 0.01. The location of maximum radial bow shifted distally but was statistically insignificant. The magnitude of maximum radial bow had a negative correlation with DASH score that was statistically insignificant (R=- 0.22, p=0.21). It had a positive, statistically significant correlation to the extent of supination in the operated extremity (R = 0.66, p = 0.0004). A loss of up to 2mm of radial bow did not influence the functional outcome as assessed by criteria reported by Anderson et al. The magnitude of radial bow influenced the supination of the forearm but not the final disability as measured by DASH score. Intramedullary nailing did decrease the magnitude of radial bow but a reduction of up to 2mm did not influence the functional outcome

Study of management of postburn flexion contracture of finger by glabrous versus nonglabrous split skin graft

Aims and Objectives: This prospective study was designed to determine the outcome of split-thickness glabellar and nonglabellar skin graft for the coverage of defects on palmar aspect of hand after release of postburn contracture in terms of graft take, complications, recurrence, and patient satisfaction for color and texture match. Materials and Methods: This prospective comparative study was carried out on patients from December 2018 to December 2020. Fifty patients were randomly divided into two groups by simple randomization method. Group A was offered treatment with split-thickness graft from glabellar region and other Group B was offered treatment with split-thickness graft from nonglabellar skin. Frequencies and percentages of both recipient and donor sites complications such as infection, hypertrophic scarring on the Vancouver scar assessment scale, recurrence, and difficulty in walking were noted. Patient satisfaction for colour and texture match to neighboring skin at recipient site were assessed 3 months after the operation using five points Likert scale. Results: At follow-up of the Group A, the donor areas were completely healed in all the cases 100%. The grafted area showed excellent color and texture match with the adjacent palmer skin. The graft was mobile, stable and without any pigmentation. There was also no hypertrophic scarring, hyperpigmentation or pain at the donor site as compared to ordinary skin graft. Walking and weight bearing were smooth and the instep curvature appeared normal. In Group B, 100% of patients had hyperpigmentation, 20% had marginal scarring and scar hypertrophy at hand. While 40% had scar hypertrophy at 80% had hyperpigmentation over the donor site. Recurrence was noted in 32% of patients in Group B as compared to 8% in Group A. Conclusions: Glabellar skin of the instep is the best replacement for the palmar skin of the digits and hand because of the similarities in their characteristics. Results are excellent in terms of color and texture match, no hyperpigmentation, less marginal scarring, scar hypertrophy, and less recurrence of contracture in patients with area grafted with glabellar skin. Donor site morbidity is very low and hardly any donor site scar is visible. So in conclusion for the management of postburn flexion contracture of the finger. An ideal skin substitute is glabellar skin grafts from the instep region of foot