Browsing by Subject "Amine scrubbing"
Now showing 1 - 10 of 10
Results Per Page
Sort Options
Item Absorber performance and configurations for CO2 capture using aqueous piperazine(2016-05) Sachde, Darshan Jitendra; Rochelle, Gary T.; Baldea, Michael; Bhown, Abhoyjit; Chen, Eric; Hwang, GyeongAbsorber 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.Item Carbon dioxide solubility and mass transfer in aqueous amines for carbon capture(2015-08) Li, Ph. D., Le; Rochelle, Gary T.; Freeman, Benny D; Sanchez, Isaac C; Svendsen, Hallvard F; Dugas, Ross EAmine scrubbing is the state of the art technology for CO2 capture, and solvent selection can significantly reduce the capital and energy cost of the process. This work presents rigorous CO2 mass transfer and solubility data at expected process conditions for more than 20 aqueous amines and amino acid salts. Amino acid salts are generally not competitive with aqueous amines as solvents for CO2 capture, particularly from coal fired power plants. The capacity of amino acid salts is intrinsically low (0.2 – 0.35 mol/mol alkalinity). Piperazine (PZ) blends have good overall performance. 3.5 m PZ/3.5 m 2-amino-2-hydroxymethyl-propane-1,3-diol (Tris) shows good absorption rates, good capacity, and low solvent viscosity. 6 m PZ/2 m hexamethylenediamine (HMDA) has moderate absorption rates, capacity, and a high viscosity. High solvent viscosity has been shown to reduce CO2 absorption rate and increase sensible heat cost. A simplified speciation model (SSM) was developed in MATLAB to represent CO2 VLE in a mono-amine solvent using only four adjustable parameters. The model can also predict liquid phase speciation. Primary and secondary amines were shown to have different CO2 VLE dependence on amine pKa. At pKa higher than 8, secondary amines have lower carbamate stability than primary amines. A correlation was developed to predict the SSM parameters based on the amine type and amine pKa. The third order overall reaction kinetic expression better explains the mass transfer data at process conditions than the more widely applied second order overall expression. A new Bronsted correlation was developed to represent the third order concentration based kinetic constant at 40 °C for primary and secondary amines: 〖log〗_10 (〖k_(c-3)〗^* )=-11.728+1.113∙p〖K_a〗_amine. This work shows the absorption rate of CO2 at process conditions do not always increase with amine pKa. As the reaction rate constant increases with amine pKa, the free amine available for CO2 absorption decreases. As the result, for primary and secondary mono-amines, the optimum amine pKa for the best mass transfer performance is around 8.7 (at 40 °C).Item Dynamic modeling of post-combustion amine scrubbing for process control strategy development(2016-05) Walters, Matthew Scott; Rochelle, Gary T.; Edgar, Thomas F.; Baldea, Michael; Akella, Maruthi R; Chen, EricIntensified process designs with advanced solvents have been proposed to decrease both capital and operating costs of post-combustion carbon capture with amine scrubbing. These advanced flowsheets create process control challenges because process variables are designed to operate near constraints and the degrees of freedom are increased due to heat recovery. Additionally, amine scrubbing is tightly integrated with the upstream power plant and downstream enhanced oil recovery (EOR) facility. This work simulated an amine scrubbing plant that uses an intercooled absorber and advanced flash stripper configuration with aqueous piperazine to capture CO2 from a 550 MWe coal-fired power plant. The objective of this research was to develop a process control strategy that resulted in favorable closed-loop dynamics and near-optimal conditions in response to disturbances and off-design operation. Two models were created for dynamic simulation of the amine scrubbing system: a medium-order model of an intercooled absorber column and a low-order model of the entire plant. The purpose of the medium-order model was to accurately predict the absorber temperature profile in order to identify a column temperature that can be controlled by manipulating the solvent circulation rate to maintain a constant liquid to gas ratio. The low-order model, which was shown to sufficiently represent dynamic process behavior through validation with pilot plant data, was used to develop a plantwide control strategy. A regulatory control layer was implemented and tested with bounding cases that represent either electricity generation requirements, CO2 emission regulations, or EOR constraints dominating the control strategy. Satisfying the operational and economic objectives of one system component was found to result in unfavorable dynamic performance for the remainder of the system. Self-optimizing control variables were identified for the energy recovery flowrates of the advanced flash stripper that maintained good energy performance in off-design conditions. Regulatory control alone could not satisfactorily achieve the set point for CO2 removal rate from the flue gas. A supervisory model predictive controller was developed that manipulates the set point for the stripper pressure controller in order to control removal. The straightforward single-input, single-output constrained linear model predictive controller exhibited a significant improvement compared to PI control alone.Item Modeling advanced flash stripper for carbon dioxide capture using aqueous amines(2016-08) Lin, Yu-Jeng; Rochelle, Gary T.; Baldea, Michael; Chen, Eric; Hwang, Gyeong S.; Miller, DavidThe intensive energy use is the major obstacle to deployment of CO2 capture. Alternative stripper configurations is one of the most promising ways to reduce the energy consumption of CO2 regeneration and compression. The advanced flash stripper (AFS) proposed in this work provides the best energy performance among other alternatives. A systematic irreversibility analysis was performed instead of examining all the possible alternatives. The overhead condenser and the cross exchanger were identified the major sources of lost work that causes process inefficiencies. The AFS reduces the reboiler duty by 16% and the total equivalent work by 11% compared to the simple stripper using aqueous piperazine. The AFS was demonstrated in a 0.2 MW equivalent pilot plant and showed over 25% of heat duty reduction compared to previous campaigns, achieving 2.1 GJ/tonne CO2 of heat duty and 32 kJ/mol CO2 of total equivalent work. The proposed bypass control strategy was successfully demonstrated and minimized the reboiler duty. Approximate stripper models (ASM) were developed to generalize the effect of solvent properties on energy performance and guide solvent selections. High heat of absorption can increase partial pressure of CO2 at elevated temperature and has potential to reduce compression work and stripping steam heat. The optimum heat of absorption was quantified as 70–125 kJ/mol CO2 at various conditions, which is generally higher than existing amines with 60–80 kJ/mol. The energy performance of AFS is not sensitive to the heat of absorption. A techno-economic analysis with process optimization that minimizes the annualized regeneration cost was performed to demonstrate the profitability of the AFS. The AFS reduces the annualized regeneration cost by 13% and the major savings come from the reduction of the OPEX, which counts for over 70% of the regeneration cost. The compressor and the cross exchanger are the major components of the CAPEX. The optimum lean loading is around 0.22 mol CO2/mol alkalinity for PZ but is flat between 0.18 and 0.24 with less than 1% difference. The AFS was demonstrated as a flexible system that can be applied to a wide range of solvent properties and operating conditions while still maintaining remarkable energy performance. Further improvement of energy efficiency by process modifications is expected to be marginal. Increasing solvent capacity will give the most energy and cost reduction in the future.Item Modeling of carbon dioxide absorption/stripping by aqueous methyldiethanolamine/piperazine(2014-05) Frailie, Peter Thompson, II; Rochelle, Gary T.Rigorous thermodynamic and kinetic models were developed in Aspen Plus® Rate SepTM for 8 m PZ, 5 m PZ, 7 m MDEA/2 m PZ, and 5 m MDEA/5 m PZ. Thermodynamic data was regressed using a sequential regression methodology, and incorporated data for all amine, amine/water, and amine/water/CO₂ systems. The sensitivity of CO₂ absorption rate was determined in a wetted wall column simulation in Aspen Plus®, and the results were used in Microsoft Excel to determine the optimum reaction rates, activation energies, and binary diffusivities. Density, viscosity, and binary diffusivity are calculated using user-supplied FORTRAN subroutines rather than built-in Aspen Plus® correlations. Three absorber configurations were tested: adiabatic, in-and-out intercooling, and pump-around intercooling. The two intercooled configurations demonstrated comparable improvement in capacity and packing area, with the greatest improvement in 8 m PZ occurring between lean loadings of 0.20 and 0.25 mol CO₂/mol alkalinity. The effects of absorber temperature and CO₂ removal were tested in the adiabatic and in-and-out intercooled configurations. For 7 m MDEA/2 m PZ at a lean loading of 0.13 mol CO₂/mol alkalinity reducing the absorber temperature from 40 °C to 20 °C increases capacity by 64% without an appreciable increase in packing area. Increasing CO₂ removal from 90% to 99% does not double the packing area due to favorable reaction rates at the lean end of the absorber. Two stripper configurations were tested: the simple stripper and the advanced flash stripper. For all amines, absorber configurations, and lean loadings the advanced flash stripper demonstrated the better energy performance, with the greatest benefit occurring at low lean loadings. An economic estimation method was developed that converts purchased equipment cost and equivalent work to $/MT CO₂. The method is based on economic factors proposed by DOE-NETL and IEAGHG. The total cost of CO₂ decreases as lean loading decreases for all amines and configurations. Increasing CO₂ removal from 90% to 99% results in a 1% increase in the total cost of CO₂ capture. Decreasing absorber temperature for 7 m MDEA/2 m PZ from 40 °C to 20 °C decreases total cost of CO₂ capture by up to 9.3%.Item Modeling of stripper configurations for CO₂ capture using aqueous piperazine(2013-05) Madan, Tarun; Rochelle, Gary T.This thesis seeks to improve the economic viability of carbon capture process by reducing the energy requirement of amine scrubbing technology. High steam requirement for solvent regeneration in this technology can be reduced by improvements in the regeneration process. Solvent models based on experimental results have been created by previous researchers and are available for simulation and process modeling in Aspen Plus®. Standard process modeling specifications are developed and multiple regeneration processes are compared for piperazine (a cyclic diamine) in Chapter 2. The configurations were optimized to identify optimal operating conditions for energy performance. These processes utilize methods of better heat recovery and effective separation and show 2 to 8% improvement in energy requirement as compared to conventional absorber-stripper configuration. The best configuration is the interheated stripper which requires equivalent work of 29.9 kJ/mol CO₂ compared to 32.6 kJ/mol CO₂ for the simple stripper. The Fawkes and Independence solvent models were used for modeling and simulation. A new regeneration configuration called the advanced flash stripper (patent pending) was developed and simulated using the Independence model. Multiple complex levels of the process were simulated and results show more than 10% improvement in energy performance. Multiple cases of operating conditions and process specifications were simulated and the best case requires equivalent work of 29 kJ/mol CO₂. This work also includes modeling and simulation of pilot plant campaigns carried out for demonstration of a piperazine with a 2-stage flash on at 1 tpd CO₂. Reconciliation of data was done in Aspen Plus for solvent model validation. The solvent model predicted results consistent with the measured values. A systematic error of approximately +5% was found in the rich CO₂, that can be attributed to laboratory measurement errors, instrument measurement errors, and standard deviation in solvent model data. Stripper Modeling for CO₂ capture from natural gas combustion was done under a project by TOTAL through the Process Science and Technology Center. Two configurations were simulated for each of three flue gas conditions (corresponding to 3%, 6% and 9% CO₂). Best cases for the three conditions of flue gas require 34.9, 33.1 and 31.6 kJ/mol CO₂.Item Modeling the advanced flash stripper for CO2 capture using 5 m piperazine(2016-12) Ding, Junyuan; Rochelle, Gary T.Amine scrubbing is the most mature technology for post-combustion CO2 capture. Several studies have demonstrated that the advanced flash stripper (AFS) consumes less energy among stripper alternatives. This thesis seeks to demonstrate the AFS energy performance and cost over a wide range of CO2 loading. Solvent models based on experimental results have been created by previous researchers and are available for simulation and process modeling in Aspen Plus®. In collaboration with Membrane Technology and Research Inc., various hybrid amine/membrane configurations were studied to minimize the total CO2 capture cost. CO2 in the flue gas is enriched by membranes from 12% to 18 and 23% for coal-fired power plant, and from 6% to 12~18% for natural gas combined cycle power plant (NGCC). The CO2 loading covers the range of flue gas CO2 from coal-fired power plants and NGCC. For each configuration, the cold and warm rich bypasses are optimized to minimize the energy cost. The cost optimization is also demonstrated on 5 m PZ, 5 m MDEA/5 m PZ, and 2 m PZ/3 m HMPD. The most cost-effective solvent varies with the flue gas CO2. When applied to a coal-fired power plant, hybrid parallel amine/membrane designs with 99% and 95% CO2 removal cost less than hybrid series with 60% CO2 removal. The equivalent work of the parallel configuration with 99% CO2 removal using 5 m MDEA/5 m PZ (32.3 kJ/mol CO2) is less than using 5 m PZ (34.0 kJ/mol CO2). The equivalent work with 95% CO2 removal (Case 19) using 5 m MDEA/5 m PZ (32.5 kJ/mol CO2) is less than using 5 m PZ (33.3 kJ/mol CO2). The capital cost with 99% CO2 removal using 5 m MDEA/5 m PZ ($70.5MM) is more than using 5 m PZ ($67.5MM). The capital cost with 95% CO2 removal using 5 m MDEA/5 m PZ ($73.5MM) is less than using 5 m PZ ($79.5MM). The total annual cost with 95% CO2 removal using 2 m PZ/3 m HMPD ($38.7/tonne CO2) is less than using 5 m PZ ($41.5/tonne CO2). When applied to NGCC, the cost of amine scrubbing is reduced by increasing absorber inlet CO2 by membranes. However, this is offset by the membrane cost. As absorber inlet CO2 increases from 6% to 18%, the operating cost decreases from $18.8 to $15.4/tonne CO2, while total regeneration cost decreases from $35.6 to $33.1/tonne CO2.Item Oxidation and thermal degradation of methyldithanolamine/piperazine in CO₂ capture(2011-12) Closmann, Frederick Bynum; Rochelle, Gary T.; Bedell, Stephen; Lawler, Desmond F.; Ekerdt, John G.; Willson, Carlton G.The solvent 7 molal (m) methyldiethanolamine (MDEA)/2 m piperazine (PZ) presents an attractive option to industry standard solvents including monoethanolamine (MEA) for carbon dioxide (CO₂) capture in coal-fired power plant flue gas scrubbing applications. The solvent was tested under thermal and oxidizing conditions, including temperature cycling in the Integrated Solvent Degradation Apparatus (ISDA), to measure rates of degradation for comparison to other solvents. Unloaded 7 m MDEA/2 m PZ was generally thermally stable up to 150 °C, exhibiting very low loss rates. However, at a loading of 0.25 mol CO2/mol alkalinity, loss rates of 0.17 ± 0.21 and 0.24 ± 0.06 mM/hr, respectively, for MDEA and PZ were measured. No amine loss was observed in the unloaded blend. Thermal degradation was modeled as first-order in [MDEAH⁺], and a universal Ea for amine loss was estimated at 104 kJ/mol. An oxidative degradation model for 7 m MDEA was developed based on the ISDA data. From the model, the rate of amine loss in 7 m MDEA/2 m PZ was estimated at 1.3 X 10⁵ kg/yr, based on a 500 MW power plant and 90% CO₂ capture. In terms of amine loss, the solvent can be ranked with other cycled solvents from greatest to least as follows: 7 m MDEA>7 m MDEA/2 m PZ>8 m PZ. Thermal degradation pathways and mechanisms for 7 m MDEA/2 m PZ include SN2 substitution reactions to form diethanolamine (DEA), methylaminoethanol (MAE), 1-methylpiperazine (1-MPZ), and 1,4-dimethylpiperazine (1,4-DMPZ). The formation of the amino acids bicine and hydroxyethyl sarcosine (HES) has been directly tied to the formation of DEA and MAE, respectively, through oxidation. As a result of the construction and operation of the ISDA for cycling of solvents from an oxidative reactor to a thermal reactor, several practical findings related to solvent degradation were made. The ISDA results demonstrated that increasing dissolved oxygen in solvents leaving the absorber will increase the rate of oxidation. A simple N2 gas stripping method was tested and resulted in a reduction to 1/5th the high temperature oxidation rate associated with dissolved oxygen present in the higher temperature regions of an absorber/stripper system. The ISDA experiments also demonstrated the need to minimize entrained gas bubbles in absorber/stripper systems to control oxidation. When the ISDA was modified to intercept entrained gas bubbles, the oxidation rate was reduced 2 to 3X.Item A techno-economic plant- and grid-level assessment of flexible CO2 capture(2012-08) Cohen, Stuart Michael, 1984-; Rochelle, Gary T.; Webber, Michael E., 1971-; Baldick, Ross; Schmidt, Philip S.; Bickel, EricCarbon dioxide (CO₂) capture and sequestration (CCS) at fossil-fueled power plants is a critical technology for CO₂ emissions mitigation during the transition to a sustainable energy system. Post-combustion amine scrubbing is a relatively mature CO₂ capture technology, but barriers to implementation include high capital costs and energy requirements that reduce net power output by 20-30%. Capture energy requirements are typically assumed constant, but work investigates whether flexibly operating amine scrubbing systems in response to electricity market conditions can add value to CO₂ capture facilities while maintaining environmental benefits. Two versatile optimization models have been created to study the electricity system implications of flexible CO₂ capture. One model assesses the value of flexible capture at a single facility in response to volatile electricity prices, while the other represents a full electricity system to study the ability of flexible capture to meet electricity demand and reliability (ancillary) service requirements. Price-responsive flexible CO₂ capture has limited value at market conditions that justify CO₂ capture investments. Solvent storage can add value for price arbitrage by allowing flexible operation without additional CO₂ emissions, but only with favorable capital costs. The primary advantage of flexible CO₂ capture is an increased ability to provide grid reliability services and improve grid resiliency at minimum and maximum electricity demand. Flexibility mitigates capacity shortages because capture energy requirements need not be replaced, and variable capture at low demand helps respond to intermittent renewable generation.Item Thermodynamic and mass transfer modeling of aqueous hindered amines for carbon dIoxide capture(2016-05) Sherman, Brent Joseph; Rochelle, Gary T.; Baldea, Michael; Chen, Chau-Chyun; Chen, Eric; Hwang, GyeongWith the detrimental effects of global climate change beginning to be felt, there is a growing consensus that something must be done. One part of the solution is carbon capture and storage using amine scrubbing to capture 90% of the CO2 from power plants burning coal and natural gas. To actualize this solution, process models are necessary. A process model requires an accurate thermodynamic and mass transfer model with physically meaningful parameters. While hindered amines are commercially used, the reason for their mass transfer rates is still an open question. These two needs are addressed in this work. To improve thermodynamic modeling, the physical significance of the electrolyte non-random two-liquid (eNRTL) regressed binary interaction parameters were examined. To improve mass transfer modeling, a response surface methodology (RSM) approach was used to give statistically significant regressed parameters. The mass transfer of two hindered amines, 2-amino-2-methyl-propan-1-ol (AMP) and 2-piperidineethanol (2PE) was studied to determine the role of carbamate. The absolute difference in eNRTL binary interaction parameters was found to moderately correlate with the pKa of the amine. An analogy method was developed to enable thermodynamic model creation for amines in the absence of some physical property data. The carbamate reaction plays a determining role in mass transfer of hindered amines. Based on Bronsted plots, 2PE appears to form carbamate using the same mechanism as unhindered, cyclic secondary amines, while AMP does not seem to use the same mechanism as unhindered, primary amines. The rate constant for bicarbonate formation for both amines is a factor of twelve faster than predicted from tertiary amine bicarbonate formation, indicating that neither seems to form bicarbonate using the tertiary amine mechanism. The six models constructed in this work enable process modeling and economic comparisons of solvents. Four binary interaction parameters were the most physically significant and should be regressed for future solvents. The high bicarbonate reaction rate of the hindered amines should be further investigated to determine if the mechanism is different or if this is model artifice, as either outcome will substantially improve mass transfer modeling for all amines.