Efficiency evaluation of a coal-fired power plant integrated with chilled ammonia process using an absorption refrigerator (original) (raw)
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Applied Energy, 2015
Development of clean coal technologies for power generation is crucial in meeting the European Union 2050 target to reduce greenhouse gas emissions. CO 2 capture technology using chemical solvents currently has the highest potential to decarbonise coal-based power generation. Substitution of amine solvent with NH 3 has been proposed as a viable option to reduce the efficiency penalty. In this study, the scenario of a supercritical coal-fired power plant retrofitted with a chilled ammonia process capture plant and CO 2 compression unit was modelled in a common simulation environment. To fully assess the integration impact on power plant performance, the pressure loss due to steam extraction has been taken into account by using the Stodola ellipse law. Analysis of a basic integration scenario revealed that the efficiency penalty fell between 10.4% and 10.9% points depending on the stripper pressure. The quality of extracted steam became insufficient to meet the reboiler heat requirement above a stripper pressure of 21.8 bar, and the lowest efficiency penalty was obtained when reboiler condensate was returned to the deaerator in the power plant. In evaluating measures to improve integration, the efficiency penalty was reduced to 8.7-8.8% points through the integration of a single-stage or two-stage auxiliary steam turbine, respectively, and a back-pressure turbine. Nevertheless, the analysis has indicated that the net impact on power plant performance is similar to that of an amine-based post-combustion CO 2 capture plant.
In the current trends globally, the excessive utilization of the energy and overconsumption of fuel has resulted in the global warming and environmental pollution. The Absorption cooling offers the possibility of using heat to provide cooling. For cooling purpose the required heat input is obtained from the excessive heat of the boiler or from non conventional power sources like solar energy. NH3-H2O system ammonia used as a refrigerant and water is used as an absorbent, these two liquids served as standard and a refrigerant cycle is produced. The system VARS in environment friendly and does not deplete the atmosphere. Thus it is essential to create awareness in the world for this system for it is an alternative system which is more environmental friendly. The objective of this paper is to present empirical relations for evaluating of the performance of a single stage vapor absorption system.
2011
The continuous increase in the cost and demand for energy has led to more research and development to utilize available energy resources efficiently by minimizing waste energy. Absorption refrigeration systems increasingly attract research interests. Absorption cooling offers the possibility of using heat to provide cooling. For this purpose heat from conventional boiler can be used or waste heat and solar energy. Absorption system falls into two categories depending upon the working fluid. These are the LiBr-H2O and NH3-H2O Absorption Refrigeration system. In LiBr-H2O system water is used as a refrigerant and LiBr is used as an absorbent, while in NH3-H2O system ammonia used as an refrigerant and water is used as an absorbent, which served as standard for comparison in studying and developing new cycles and new absorbent/refrigerant pairs. The objective of this paper is to present empirical relations for evaluating the characteristics and performance of a single stage Ammonia water...
Energies
The interest in employing absorption refrigeration systems is usually related to electricity’s precariousness since these systems generally use thermal rejects for their activation. The application of these systems is closely linked to the concept of energy polygeneration, in which the energy demand to operate them is reduced, which represents their main advantage over the conventional vapor compression system. Currently, the solution pairs used in commercial absorption chillers are lithium bromide/water and ammonia/water. The latter pair has been used in air conditioning and industrial processes due to the ammonia operation’s low temperature. Few review papers on absorption chillers have been published, discussing the use of solar energy as the input source of the systems, the evolution of the absorption refrigeration cycles over the last decades, and promising alternatives to increase the performance of absorption refrigeration systems. There is a lack of consistent studies about ...
Energetic analysis of a commercial absorption refrigeration unit using an ammonia-water mixture
Acta Scientiarum. Technology, 2017
The ROBUR ® absorption refrigeration system (ARS), model ACF60, with a capacity of 17.5 kW, is tested, modeled and simulated in the steady state. To simulate the thermal load a heating system with secondary coolant was used, in which a programmable logic controller (PLC) kept the inlet temperature EVA at around 285.15 K. The mathematical model used was based on balancing the mass, energy and ammonia concentrations and completed by closing equations such as, Newton's cooling equation. The mathematical model was implemented using the Engineering Equation Solver-EES ®. The results obtained after modeling and a numerical permanent simulation are studied using the Duhring diagram. Potential points of internal heat recovery are visualized, and by using graphs of the binary mixture, it is possible to identify the thermodynamic states of all monitored points. The data obtained in the numerical simulation of the ARS was compared with data acquired in the actual tests of the ARS with the ROBUR ® apparatus.
International Journal of Greenhouse Gas Control, 2012
The use of aqueous ammonia is a promising option to capture carbon dioxide from the flue gas of coal-fired power plants. Compared to a capture process using monoethanolamine (MEA), the use of ammonia can reduce the heat requirement of the CO 2 desorption significantly, although an additional effort is necessary to provide the cooling of the process. To allow for a fair evaluation of the integration of this CO 2 capture process into a power plant process, an overall process evaluation is carried out. The use of detailed models of the power plant, of the compressor and of the CO 2 capture process enables the calculation of the power loss due to the steam extraction as well as due to the required auxiliary power for CO 2 compression, solvent and cooling pumps and mechanical chillers. To study the influence of the cold end of the process, two power plants with different cooling water temperatures are analysed. Additionally, two different process configurations of the capture plant, with either one single absorber or two absorbers connected in series where the first absorber captures the majority of the CO 2 and the second limits the NH 3 slip, are evaluated.
Thermodynamic analysis of one and two stages absorption chiller powered by a cogeneration plant
Thermodynamics models of a single and a noncommon double stage ammonia-water absorption chiller that use waste heat (from three reciprocating engines of 8.7 MW each one) are developed to analyze the performance of the chiller for different operative conditions. A comparison of a single stage refrigeration system with the two stages proposed system is performed in this paper. The coefficient of performance (COP) obtained for both systems are the same, but the heat flux removed from the cooling media with the two-stage system increase from 1.3MW (single stage) until 1.6 MW due to the heat recovered increased with the second generator. The heat recovered used by the chiller was 3.8 MW, and the utilization factor of the cogeneration plant was 58.11%, and the cooling capacity of the equipment was 1,623 kW. Finally, the estimated economics savings for electric power due to the implementation of the absorption chiller that uses exhaust gases in place of a common refrigeration system by vapor compression with the same cooling capacity was 142,000.00 USD/year.
International Journal of Refrigeration, 2008
The Robur absorption-refrigeration water-ammonia (ARWA) system is analyzed using Aspen Plus flowsheet simulator. The results are compared with experimental and some manufacturer data reported in the open literature. Among performance parameters analyzed are coefficient of performance (COP), heat duties of the evaporator, absorber, and the condenser, refrigerant concentration in the weak and strong solution, and flow rates of the weak solution and the flow rate of refrigerant passing through the evaporator. In general, a very good agreement between the simulator's results and the experimental measurements was found. Also, results obtained for the effect of separator (input) heat duty on the COP agree well with the reported experimental data with a maximum percentage deviation of 1.8%. Efficiency of the separator in splitting off the refrigerant at the column top is shown to be of crucial importance; COP increased by 15% in going from 1 to 5 theoretical equivalent mass transfer stages in the separator. Some innovative modifications to Robur cycle aimed at enhancing the separator operation have shown a promising improvement in the COP. In particular, introducing a throttling process directly before the separator can alleviate the separator heat load and enhance the COP by up to 20%. Use of stripping gas injected at the bottom of the boiler is another strategy that has been investigated in this work.
Performance Analysis of Absorption Refrigeration Cycles
— The thermodynamic analysis of a vapor absorption refrigeration system employing ammonia as the refrigerant are presented. The thermodynamic analysis of these three combination of the absorption pairs namely NH3/H2O, NH3/LiNO3, NH3/NaSCN are performed. The best alternative to the ammonia water absorption pair are proposed as ammonia lithium nitrate and ammonia-sodium thiocyanate. It is very much important to select a prominent working substance and their properties have great effect on the system performance. Detailed thermodynamic properties of these fluids are expressed in polynomial equations. Energy and entropy balance equations are applied to analyse each of the process to estimate the individual heat transfer and entropy generation rates for all the systems. Among these three pairs NH3/ NaSCN yields the highest coefficient of performance. Cooling/Heating of the generator/absorber results in significant entropy generation in all the systems. The solution heat exchanger significantly improves the performance of the cycle and yields in the better cooling output.
Modeling of ammonia absorption chillers integration in energy systems of process plants
Applied Thermal Engineering, 1999
A mathematical programming approach is proposed to study the integration of absorption chillers in combined heat and power plants. The aim of this work is to determine the economic viability of the introduction of ammonia absorption chillers in energy systems instead of using the more conventional compression cycles. This procedure selects the best refrigeration alternative taking into account both absorption and compression cycles. To select the most suitable refrigeration cycle for a given refrigeration load, it is not only necessary to model the performance of each cycle, but also to take into account the interactions between the energy system and the considered cycles, optimizing the performance of the global plant. This approach has been implemented in the computer program XV, and tested in an energy plant in the petrochemical complex of Tarragona (Catalunya, Spain). The refrigeration demands to be met are at 0 and À208C. The results highlighted the bene®t obtained with the simultaneous presence of ammonia absorption cycles and a cogeneration based energy plant.