Piperazine (PZ) is a cyclic diamine, which means it can absorb two moles of CO2 per mole of amine and potentially has a higher capacity for CO2 capture than monoethanolamine, the current solvent of choice for flue gas treatment. Nitrosamines are formed from the reaction between secondary or tertiary amines and nitrites or nitrogen oxides. Over 80% of nitrosamines are carcinogenic. The reaction of PZ and nitrite can form 1-nitrosopiperazine (also mononitrosopiperazine, MNPZ) and N-N,dinitrosopiperazine (DNPZ). Carcinogenicity of DNPZ is almost 20 times as that of MNPZ. There is also a possibility of nitrosamine formation of PZ in the CO2 capture process because of NOx in input flue gas, with the oxidative and thermal degradation products of PZ. Analytical methods were developed in order to perform kinetic studies of the reaction between a nitrite solution and PZ over a range of temperature from 20 to 150 °C at two different PZ concentrations, 8 and 2 mol/kg of solution, and three levels of CO2 loading, 0.3, 0.2, and 0.1 mole CO2/mole of alkalinity. At less than 75 °C, nitrite reacts with PZ and disappears during the reaction to an equilibrium concentration while at the higher temperature; the concentration of nitrite quickly decreases to a very low value. There is no evidence of DNPZ as a reaction product in all reaction conditions, but MNPZ is formed at the temperature greater than 75 °C. The MNPZ concentration approaches a maximum value consistent with the material balance and nitrite disappearance. By developing the time of reaction at the higher temperature a decomposition of MNPZ has been observed, by either the reverse of the formation reaction or decomposition to other compounds. By increasing the temperature, the maximum value of MNPZ concentration is achieved more quickly and the rate of MNPZ decomposition increases. Reactions follow the same trend at both PZ concentration and at the three different degrees of CO2 loading. A model has been established considering temperature, PZ concentration, and CO2 loading. The calculated activation energies of MNPZ production and decomposition were determined. MNPZ decomposition is more rapid than PZ degradation. / text

Even though the use of renewable energy in electricity generation has significantly increased over time, coal is projected to remain as the primary fuel in electricity generation worldwide in the next decades due to its availability, stability of supply and cost. However, coal-fired power plants are the largest stationary sources of CO2 emissions that contribute to global warming. Several technologies have been developed to mitigate CO2 emissions from coal-fired power plants. Oxy-combustion is a promising pathway to capture CO2 from coal fired power plants that competes favourably with other CO2 capture technology pathways such as post-combustion and pre-combustion. Oxy-combustion has attracted attention because it provides a CO2-enriched flue gas stream which can be further purified using a relatively simple multi-stage compression and cooling processes. Currently, there is no oxy-coal-fired power plant in commercial-scale operation. Thus, the transition towards commercial scale operation is the main challenge for this technology. The CO2 capture and purification unit (CO2CPU) is an important unit in oxy-coal-fired power plants that determine the quality of the CO2 product and energy consumption of the power plants. Several studies published on the CO2CPU process have evaluated the performance of this system at steady state. Insight regarding the dynamic behaviour of the CO2CPU process is very limited and a mechanistic dynamic model of the CO2CPU is not available in open literature. Thus, research on dynamic modelling and control system development is still required to demonstrate the operability and controllability of this technology. This study aims to develop, test and validate a dynamic model of the CO2CPU for oxy-coal-fired power plants. Detailed mathematical models of each unit operation in the CO2CPU are provided in this study. The main challenge was to develop a dynamic model of a multi-stream heat exchanger that involves multiple process streams and encounters both condensing and boiling two phase flows. A dynamic model that is not computationally intensive, to slow down the entire CO2CPU plant model, and that can predict reasonable fluid temperatures in the multi-stream heat exchanger was developed in this study. The proposed multi-stream heat exchanger model was based on a shell and tube configuration that considers only axial changes in flow, i.e., a 1D model. Likewise, the two phase region in this unit was modelled using a homogenous model, which is a simplified discretized two-phase flow model that reduces the computational effort and complexity of the multi-stream heat exchanger process model. The homogenous model takes into account the changes in the fluid properties in the two phase region to calculate the heat transfer coefficients of the multi-stream heat exchanger models. To the author???s knowledge, the model presented in this study represents the first mechanistic process model that describes the transient behaviour of a CO2CPU for oxy-fired power plant. Two design configurations of the CO2CPU were considered in this study, i.e. the Air Products??? CO2CPU and the CanmetENERGY???s proprietary CO2CPU (CanCO2). Both plants are designed based on a two-stage flash separation process. The CanCO2 is an extended design of the Air Products??? CO2CPU. The presence of an external recycle stream , recycling a portion of the CO2 rich effluent gas stream from the first flash drum to the compressor train, in the CanCO2 is a major distinction between the two CO2CPU configurations and enhances the CO2 capture rate for the CanCO2 process. Nevertheless, the addition of this recycle stream makes the CanCO2 plant model convergence more challenging than the Air Products??? CO2CPU since it adds natural feedback into the system. A systematic procedure to perform the process integration of all the unit operations considered in the CO2CPU flowsheets was developed and presented in this study. Stand-alone unit operation models were developed, coded and then connected together one at a time. Dynamic models of the Air Products??? CO2CPU and the CanCO2 were developed and validated at steady state using design data. Reasonable agreement between the developed models and the design data were obtained for both CO2CPU configurations. Several dynamic tests were performed to gain insight into the transient behaviour of the CO2CPU. The results obtained from the transient analyses clearly demonstrate that both CO2CPU plants are highly nonlinear processes. The CO2 recovery and the CO2 product purity obtained from the base case of both plants are similar, approximately at 89 wt% and 95 mol% respectively. The operating conditions of the first flash drum were found to play a key role on the CO2CPU performance of both plants. In addition, both models indicate that the CO2 recovery is more sensitive to the operating conditions than that of the CO2 product purity. The CO2 purity is more sensitive to the flue gas composition and responds to all changes performed in this study faster than the CO2 recovery. Because of the recycle stream, the CanCO2 response to all changes is slower than the Air Products??? CO2CPU. Nevertheless, the use of a recycle stream improves the CO2 recovery and increases the number of manipulated variables in the CanCO2, thus this system has more alternative control structures than the Air Products??? CO2CPU. The models developed in this study can be extended to include the controllability analysis and the control structure design for the CO2CPU; and the integration of oxy-boiler, steam cycle and also air separation unit (ASU) into a complete dynamic model of the oxy-fired power plant that will be very useful for oxyfuel combustion technology scale-up.

Carbon capture and storage technologies are required in order to reduce greenhouse gas emissions, while continuing to utilize existing fossil-fueled power generation stations. Of the many developing post-combustion CO2 capture technologies, calcium looping appears promising due to its high thermal efficiency, technical feasibility at commercial-scale, and low sorbent cost. Calcium looping has now been performed at the larger-scale, but there is still a significant quantity of information about sorbent performance, the fate of trace pollutant emissions (specifically SO2 and HCl), dual fluidized bed operating configurations, and impact of realistic operating conditions that still needs to be determined. Based on an economic analysis of the process, three key parameters serve to have the largest potential economic impact: (1) the sorbent deactivation rate, (2) the Ca/C molar ratio, and (3) the rate of sorbent attrition. Therefore, a series of bench-scale, pilot-scale, and continuous pilot-scale testing were conducted to not only explore these parameters from an improvement standpoint, but accurately determine them under conditions expected at the commercial-scale. The presence of HCl did not have a significant impact on sorbent performance provided that steam is present during calcination, although issues with downstream corrosion could be a factor. High CO2 partial pressures during calcination, coupled with high temperatures and the presence of SO2, resulted in dramatically lower cyclic carbonation conversions and a reduced high CO2 capture efficiency regime. Continuous pilot-scale testing generated realistic, and more detrimental, values for sorbent carrying capacity, Ca/C molar ratio, sorbent make-up rates, and rate of sorbent elutriation, that can now be utilized for techno-economic evaluations and scale-up of the technology.

This work considers the value of flexible power provision from natural gas-fired combined cycle (NGCC) power plants operating post-combustion carbon dioxide (CO2) capture in low carbon electricity markets. Specifically, the work assesses the value of the flexibility gained by varying CO2 capture levels, thus the specific energy penalty of capture and the resultant power plant net electricity export. The potential value of this flexible operation is quantified under different electricity market scenarios, given the corresponding variations in electricity export and CO2 emissions. A quantified assessment of natural gas-fired power plant integrated with amine-based post-combustion capture and compression is attempted through the development of an Aspen Plus simulation. To enable evaluation of flexible operation, the simulation was developed with the facility to model off-design behaviour in the steam cycle, amine capture unit and CO2 compression train. The simulation is ultimately used to determine relationships between CO2 capture level and the total specific electricity output penalty (EOP) of capture for different plant configurations. Based on this relationship, a novel methodology for maximising net plant income by optimising the operating capture level is proposed and evaluated. This methodology provides an optimisation approach for power plant operators given electricity market stimuli, namely electricity prices, fuel prices, and carbon reduction incentives. The techno-economic implications of capture level optimisation are considered in three different low carbon electricity market case studies; 1) a CO2 price operating in parallel to wholesale electricity selling prices, 2) a proportional subsidy for low carbon electricity considered to be the fraction of plant electrical output equal to the capture level, and 3) a subsidy for low carbon electricity based upon a counterfactual for net plant CO2 emissions (similar to typical approaches for implementing an Emissions Performance Standard). The incentives for variable capture levels are assessed in each market study, with the value of optimum capture level operation quantified for both plant operators and to the wider electricity market. All market case studies indicate that variable capture is likely to increase plant revenue throughout the range of market prices considered. Different market approaches, however, lead to different valuation of flexible power provision and therefore different operating outcomes.

Sulfate accumulates in the post-combustion CO₂ capture system and must be removed to re-use amine efficiently. Removal of sulfate from the amine-based postcombustion CO₂ capture system through a solvent reclaiming process may reduce CO₂ capture costs. This work determines the solubility of K₂SO₄ and Na₂SO₄ in 2 to 8 m PZ loaded with CO₂ and develops a thermodynamic and process model for the reclaiming process. At 40°C the solubility of Na2SO₄ in 8 m PZ with a CO₂ loading of 0.3 is 0.3 m Na2SO₄ and that of K₂SO₄ is 0.1 m K₂SO₄. Sulfate solubility in PZ solutions is represented by the empirical models: K₂SO₄: ln(Ksp) = 10.53I[superscript 0.3] - 0.98[PZ][subscript T] -3440/T - 2.42 ; Na₂SO₄: ln(Ksp) = 2.137I[superscript0.3] - .6505[PZ][subscript T] -826/T + 265 where [PZ][subscript T] = 2*(molality of PZ). A K₂SO₄ and Na₂SO₄ solubility thermodynamic model was developed in the eNRTL framework in the Fawkes model for PZ/CO₂/H₂O in Aspen Plus[trademark]. The energy cost of the Na process when removing the equivalent of 100 ppm SO₂ from the flue gas, ranging from $0.1-0.5/ton CO₂, was practically the same as the K process(ranging from $0.1-0.8/ton CO₂). The K₂SO₄ recovered in the process can be used as fertilizer. However, the KOH will still cost $0.6/tonne CO₂. If it is not possible to sell the K₂SO₄ as fertilizer because of the impurities that may be present on the K₂SO₄crystals, the chemical cost of the process would increase to $2/tonne CO₂. The chemical cost for the Na case is $0.7/tonne of CO₂. / text

The focus of this work is to investigate the feasibility of oxygen extraction from CO2 by doped ceria in chemical looping process. In order to increase the oxygen capacity and oxygen release rates, Cerium- based oxygen carriers are doped with ZrO2. Additionally, the zirconia-doped ceria is modified by iron and copper to boost the oxygen release in the fuel reactor. It should be noted that the level of doping allows the solids to maintain the cubic fluorite structure of CeO2. The redox activity of oxygen carriers is studied in order to determine the most promising material due to the oxygen transfer capacity and methane conversion. The chemical looping dry reforming in a quartz fixed-bed reactor is carried out in two steps. In the first step, the oxygen carriers are reduced by methane through the combustion reaction. In the second step, CO2 is used for oxidation of reduced metal oxides. The obtained results at different doping levels were compared to determine the optimal oxygen carrier. The results indicate that doping ceria can boost the reactivity with methane and enhance the methane conversion during combustion reaction. CeO2 modified by Fe presents a progress in both oxygen release and uptake with an increase in oxygen capacity of metal oxide. However, zirconia and copper ceria show different effect on reduction and oxidation. This means that zirconia doped ceria results in an increase in oxygen release during reduction and decrease in oxygen uptake during oxidation with CO2. In contrast, addition of copper to ceria metal oxides shows a negative effect on oxygen release, while it enhances the ability of oxygen uptake. Out of all mixed cerium oxides investigated in this study, cerium oxide containing 10% mole iron is determined as the most promising oxygen carrier for CLDR due to the methane conversion, facilitating oxygen release, increasing the level of reduction and improving the oxidation uptake of the metal oxide in the reaction with CO2.

New phosphonium and ammonium ionic liquids were prepared for use in two green applications. Ionic liquids are generating considerable current interest as media for electrochemical processes such as electrodeposition, which can be used to create thin films of a variety of compounds. For the first time, silicon deposition has been achieved in the phosphonium ionic liquid triethyl(2-methoxyethyl)phosphonium bis(trifluoromethylsulfonyl)amide (P201-TFSI). Subsequently, silicon has been deposited from a wide variety of precursors in order to optimize the thickness and morphology of the deposited films. The silicon films electrodeposited in the phosphonium ionic liquid show marked differences from those deposited in organic solvents, imidizolium and pyrrolidinium based ionic liquids. Phosphonium and ammonium ionic liquids were also investigated for use in carbon dioxide capture. Task-specific ionic liquids have shown great promise as agents for the physisorption and chemisorption of CO2 from combustion gas streams. Efforts to synthesize new task specific ionic liquids with multiple amine functionalities for CO2 capture are reported. Four different reaction pathways were explored for the synthesis of these materials. While this goal was not achieved in this work, task-specific phosphonium and ammonium ionic liquids offer the promise of opening up new areas in ionic liquid research. / text

With the emission of carbon dioxide (CO2) becoming an international worry due its role in climate change, solutions such as CO2 capture and storage technologies are needed to decrease the emissions. The main proportion of CO2 gas emissions is from fossil fuel combustion in a range of industries, including power generation. To develop the CO2 capture system for these operations, new materials are needed for CO2 capture. Metal-organic framework (MOF) materials have porous crystal structures containing organic molecules (organic ligands) linked to each other by metalcontaining nodes. The large internal surface area can be exploited for the adsorption of small gas molecules, and for this reason MOFs may be ideal candidate materials for CO2 capture and gas separations. Thousands of MOF materials have been reported, with different combinations of the ligands and metals and with the capability of forming many different network topologies. Experimentally it is very difficult to study the gas absorption dynamics, interaction and gas adsorption capacity for the large number of materials. This problem can be solved by simulations. The aim of the thesis is to develop a systematic simulation method to screen the MOF properties and CO2 adsorption capacity and interaction dynamics at different environment. The molecular dynamics (MD) method with parameterised force fields was used to study the interactions between CO2 molecules and one class of the MOFs, zeolitic imidizolate frameworks (ZIFs) with zinc as the metal cation. To develop the model, the atom charges have been developed by using the distributed multipole analysis (DMA) method based on ab initio DFT calculations for molecules and clusters. The intermolecular forces were developed by fitting against the MP2 calculations of small clusters of the metal cations and molecular ligands. In order to evaluate the models I simulated the gas-liquid coexistence curve of CO2 and showed that it is consistent with experiments. I also simulated the pure ZIF structures on changing both temperature and pressure, demonstrating the stabilities of the structures but also showing the existence of displacive phase transitions. I have used this approach to successfully study CO2 absorption in a number of ZIFs (from ZIF-zni, ZIF-2, ZIF-4, ZIF-8 and ZIF-10) using MD. The gas absorption capacity and dynamics have been investigated under 25 bar and 30 bar, 200 , showing a promising uptake of CO2. The results have shown that CO2 capacity is mainly determined by the pore sizes and pore surfaces, in which a higher capacity is associated with a higher pore surface. The intermolecular distance of CO2 inside the pores and channels have been investigated in the saturation state. It has been shown that the distance is approximately 4 Å. The attraction force is from the interaction between CO2 and the imidazolate ligands. In addition, the systematic studies of the saturated ZIF system gave the minimum diameters for CO2 adsorption which is approximately 4.4 Å. This interaction has caused the gate opening effects, with the imidazolate ligands being pushed to be parallel to the CO2 molecules and opening up to allow more gas molecules go through the channels that connect the pore structures. This gate opening effect also explains the phase transition in ZIF-10 caused by CO2 molecules in our simulation, and can be applied to predict phase transitions in other materials with similar structure such as ZIF-7 and ZIF-8. The dynamics have also shown that the gas diffusion velocity is determined by the pore structure as well and by the accumulated layers of CO2 on the surface prior to being pushed in toward the centre of the material layer by layer. The de-absorption processes have also been studied in these materials by decreasing the pressure from 25 bar to 1 bar under at same temperature. The results indicate that the de-absorption is a reverse process of absorption. The structure of ZIF-10 went through a phase transition induced by CO2 recovered after the guest molecules had been released. The de-absorption can be accelerated by increasing the temperature.

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