Conventional Power Plants Equipped With Systems for CO2 Emission Abatement

Amine scrubbing is the most mature technology for postcombustion carbon capture. Much bench- and pilot-scale work has been focused on CO2 capture from coal-fired flue gas. Because natural gas is inexpensive and readily available in the United States and other countries, the natural gas combined-cycle (NGCC) has been replacing coal for electricity generation. Carbon capture for NGCC is therefore an important technology for the modern power plants. The Piperazine (PZ) Advanced Stripper (PZAS) technology has been established as a benchmark system for second-generation amine scrubbing for CO2 capture from coal-fired flue gas. It has a fast absorption rate, good energy performance, and strong resistance to thermal degradation and oxidation. PZAS was operated with simulated NGCC flue gas (4.3 mol % (dry) CO2) at the National Carbon Capture Center (NCCC) in Wilsonville, Alabama in 2019. This paper presents the absorber performance and model validation for the campaign. The absorber was tested with in-and-out and with pump-around intercooling. The variable operating conditions included lean loading (0.19–0.25 m CO2/mol alkalinity), gas temperature (40, 78 °C), and intercooling temperature (35, 40 °C). Using 5 m PZ CO2 removal from 82% to 96% was achieved with intercooling and only 12 m of packing. A rigorous, rate-based absorber model accurately predicted the CO2 removal and temperature profile. The model shows that the delta loading of the solvent at NGCC conditions for 90% removal is greater than at coal conditions, but high CO2 removal (99%) is more difficult to achieve with NGCC gas than with coal-fired flue gas. The pump-around intercooling was effective, and the intercooling temperature had a large impact on the absorber performance. With pump-around, the delta loading penalty for hot gas feed into absorber without a direct contact cooler was less than 5%.

Climate change issues have led many countries to actively participate to international conventions, with the aim of reducing the impact of human activities on the environment. In this framework the Paris Agreement has established to keep the temperature rise below 2°C above the pre-industrial level. One suitable mitigation option is to remove carbon dioxide, before it is emitted into the atmosphere. Several technologies are available, including chemical processes where acid gases are absorbed by aqueous alkanolamines solutions. Although this process is already widely used in industry, these solvents are characterized by high energy requirements, in addition to other disadvantages such as corrosion and degradation. Recently, alternative solvents are being studied as possible substitutes for traditional amine solutions. Precipitating solvents are considered in chemical absorption processes because of their characteristic of forming a solid phase, which allows the removal of one reaction product from the liquid solution, therefore shifting the equilibrium of the reaction and so enhancing the mass transfer of the CO2 from the vapor phase to the liquid phase. One class of precipitating solvents are amino acids, with several different types which can be used in aqueous solution. Previous studies have identified the most suitable types for the capture of carbon dioxide and have highlighted the additional advantages of low corrosion and high stability towards degradation, in particular for the amino acid species containing a sulfonic group, such as taurine. This work focuses on the use of potassium taurate aqueous solutions for the removal of carbon dioxide from flue gases from natural gas and coal-fired power plants. The aim is to evaluate changes in the solvent performance arising from changes in the flue gases composition and flowrates. The obtained results confirm the possible application of the potassium taurate aqueous solution for CO2 removal both in coal-fired and in NGCC power plants, with different energy requirements.

Recently, it is more necessary to maintain or improve the thermal efficiency of actual thermal power plants to reduce CO2 emission and energy consumption in the world, and it is also important to reduce the maintenance cost of commercial thermal power plants. Thus, it is crucial to investigate power plant performance deterioration factors and solve problems related to these factors promptly when the thermal efficiency decreases. However, it is difficult to understand the internal state of power plants sufficiently and to determine power plant performance deterioration factors only from operation data because actual thermal plants are composed of many components and are very complex systems. In particular, it is more difficult to understand performance deterioration in gas turbine combined cycle (GTCC) power plants than in steam power plants because the performance changes markedly in GTCC power plants depending on atmospheric conditions (temperature, pressure, humidity). In other words, when thermal efficiency changes, it is difficult to determine whether the cause is the change in external factors or that in the performance of the component. Therefore, we develop a method based on heat balance analysis to calculate the immeasurable quantity of state and the efficiency of each component in GTCC power plants, and to correct the performance of each component in a plant to a standard state using the performance function obtained from long-term operation data. Through the method, the analysis of the effects of deterioration factors on thermal efficiency becomes possible, and the performance of a plant can be simulated when the operation conditions are changed. Thus, we can determine the main factor that affects thermal efficiency using our method.

Full repowering of existing fuel-oil fired power plant: Modeling and performance evaluation

This study investigates the crucial role of Carbon Capture and Storage (CCS) technology in mitigating CO2 emissions from Poland’s power systems, which is essential not only for meeting climate targets but also for maintaining energy security in the country. Acknowledging natural gas as a transitional fuel, the focus is on evaluating the decarbonization potential of the natural gas combined cycle (NGCC) power plant. The NGCC with and without an amine-based carbon capture unit was modeled using IPSEpro (SimTech, version 7.0). It was found that the annual CO2 emission from 435.68 MWe (net) NGCC can be reduced from 1,365,501 tons (357.8 kgCO2/MWh) to 136,556 tons (42.9 kgCO2/MWh). On the other hand, the CCS reduced the net electric power of the NGCC from 435.68 MW to 363.47 MW and the net energy efficiency from 55.60% to 46.39%. Nonetheless, these results demonstrate the potential of using the amine-based CO2 capture technology in NGCC systems. This is especially important in the context of the decarbonization of the Polish power system.

Extending the operating range and improving the partial load efficiency of the gas turbine combined cycle (GTCC) is becoming increasingly important. This paper proposes a novel method to achieve the two goals simultaneously. To fulfill the research objective, the combination of exhaust heat recuperation and inlet bleed heating (IBH) was adopted and evaluated. A cycle simulation was conducted to confirm whether the research goal could be achieved. A recuperator was installed between the compressor and combustor of the gas turbine, and the degree of heat recuperation was modulated during partial load operation to enhance the cycle efficiency compared to the conventional GTCC plant. In contrast to the conventional GTCC plant, the recuperation ratio was modulated before control of the variable inlet guide vane (VIGV) began. This means that the recuperation control covers the high partial load regime. The gas turbine power remained almost constant in this regime because the inlet flow rate and turbine inlet temperature were kept constant. In contrast, the power of the bottoming cycle decreased with increasing recuperation ratio due to the decrease in exhaust gas energy. After the recuperation ratio reached a limit, the load control was the same, as in conventional plants: VIGV control followed by fuel only control. The purpose of using IBH was to reduce CO emissions in the low load regime. Some of the compressor discharge air was recirculated to the compressor inlet, and the combustion temperature was maintained at a high level. The simulation showed that both IBH and recuperation are effective in extending the operating range. The predicted reduction in the turndown ratio was approximately 10%p. The partial load efficiency improvement by the recuperation was sensible. The efficiency remained higher than the full load efficiency over a wide partial load range. The efficiency of the recuperated GTCC was 4.1%p higher at 50% power than that of the conventional GTCC.

The thermodynamic analyses of the triple-pressure reheat combined cycle gas turbines with duct burner are presented and discussed in this paper. The overall performance of a combined cycle gas turbine power plant is influenced by the ambient temperature, compression ratio and turbine inlet temperature. These parameters affect the overall thermal efficiency, power output and the heat-rate. In this study a thermodynamic model was development on an existing actual combined cycle gas turbine (CCGT) (In this case study, an effort has been made to enhance the performance of the CCGT through a parametric study using a thermodynamic analysis. The effect of ambient temperature and operation parameter, including compression ratio and turbine inlet temperature, on the overall performance of CCGT are investigated. The code of the performance model for CCGT power plant was developed utilizing the THERMOFLEX software. The simulating results show that the total power output and overall efficiency of a CCGT decrease with increase the ambient temperature because increase the consumption power in the air compressor of a GT. The totals power of a CCGT decreases with increase the compression rate, while the overall efficiency of a CCGT increases with increase the compression ratio to 21, after that the overall efficiency will go down. Far there more the turbine inlet temperature increases the both total power and overall efficiency increase, so the turbine inlet temperature has a strong effect on the overall performance of CCGT power plant. Also the simulation model give a good result compared with MARAFIQ CCGT power plant. With these variables, the turbine inlet temperature causes the greatest overall performance variation.

Combined cycle power plants play an important role in the present energy sector. The main challenge in designing a combined cycle power plant is proper utilization of gas turbine exhaust heat in the steam cycle in order to achieve optimum steam turbine output. Most of the combined cycle developers focused on the gas turbine output and neglected the role of the heat recovery steam generator which strongly affects the overall performance of the combined cycle power plant. The present paper is aimed at optimal utilization of the flue gas recovery heat with different heat recovery steam generator configurations of single pressure and dual pressure. The combined cycle efficiency with different heat recovery steam generator configurations have been analyzed parametrically by using first law and second law of thermodynamics. It is observed that in the dual cycle high pressure steam turbine pressure must be high and low pressure steam turbine pressure must be low for better heat recovery from heat recovery steam generator.

Emissions trading systems (ETS) and markets usually do not allow for the inclusion of carbon dioxide removal (CDR) activities and if they do, removal activities are primarily restricted to afforestation. The New Zealand emission trading system (NZ ETS), for examples, integrates afforestation, and the California Low-Fuel Standard, the Quebec ETS and the Chinese ETS permit the restricted inclusion of afforestation offsets. Furthermore, the California Low-Carbon Fuel Standard System allows for the inclusion of removal via Direct Air Capture. In combination with the 45Q tax credit program, the largest incentives for CDR via Negative Emissions Technologies (NETs) are currently provided in the US. However, both do not yet allow for the inclusion of ocean-based carbon removal. Hence, we provide first a brief overview about the NZ ETS and its inclusion of afforestation, pointing out that the concept will likely not be applicable to ocean-based CDR with the potential exemption of blue carbon projects. Second, we discuss the 45Q tax credit program, the California Low-Fuel Standard System, and the California Compliance Offset Scheme. Third, we provide an overview about the company database related to ocean-based carbon removal. Fourth, we briefly look at the voluntary carbon market, providing some insights for carbon removal accounting.

Objective. In order to evaluate environmental loads, we studied the effects on energy efficiency and CO2, SO2 emissions in each advanced thermal power generation technologies in China and India using the energy chain life cycle assessment (LCA) model. Integrated coal gasification combined cycle (IGCC), ultra super critical power plant (USC) and natural gas combined cycle (NGCC) were chosen as new power generation technologies.Results and Discussion. NGCC with a natural gas pipeline for transport is most effective in reducing CO2, SO2 emissions. Advanced coal-fired technologies are advantageous in lowering the fueling cost. IGCC and USC are desirable for Shanxi which is the coal producing region. The cost of CO2 emission reduction that will be generated by NGCC amounts 102 USD/t-CO2 in Shanghai province, which is lower than the comparable cost of 492 USD/t-CO2 for the case of IGCC with coal transportation by truck.Conclusions. NGCC with pipeline transportation has a higher energy profit ratio (EPR), and NGCC with a natural gas pipeline for transport is most effective in reducing CO2 emission. From the results obtained by evaluating the energy cost, it was found that IGCC and USC are advantageous in lowering the fueling cost of coal. Meanwhile, the energy cost in natural gas-fired power generation depends on the fuel transport method. The fuel transport cost is high when LNG trucks are used over long distance: hence, developing natural gas pipelines would be most important.

Comparative exergoeconomics of power utilities: Air-cooled gas turbine cycle and combined cycle configurations

Gas separation using polymeric membranes is generally believed to be poorly suited for CO2 capture from gas turbine based power plants, because the high air-to-fuel ratios produce large amounts of exhaust gas containing strongly diluted CO2. The driving force for selective permeation is obtained by compressing the entire exhaust stream, resulting in a significant energy penalty. Additional energy is required for permeate compression, which is impaired by the other gases emitted with CO2. In spite of these difficulties, the present study is concerned with membrane systems, which the authors believe warrant further investigation. The attention was focused on natural gas combined cycles (NGCC), so as to have a starting point with high energy efficiency and low baseline emissions. To reduce the exhaust gases and to concentrate the CO2, the NGCC is fitted with a flue gas recirculation system, which has proven to leave plant performance substantially unaffected. The energy requirements for exhaust gas compression are reduced by introducing a heat exchanger between the compressed and residual exhaust gas and recovering heat from the latter. The membrane separator has been modeled using conservative data reported in the literature. Various configurations, such as multiple compression-expansion and multistage membrane units, are considered. Permeate compression is also modeled, so as to highlight the influence of permeate purity on this process. The results show a rather moderate performance penalty. A specific emission of 100 g CO2/kWh corresponds to 48 percent efficiency. Admittedly a CO2 separator for a power plant would be larger than any other membrane system designed for other purposes. However, the system appears technically feasible and would offer valuable benefits in terms of emissions.

Novel process design for waste energy recovery of LNG power plants for CO2 capture and storage

This article illustrates aspects of heat recovery steam generator (HRSG) design when employing process integration in an integrated reforming combined cycle (IRCC) with pre-combustion CO2 capture. Specifically, the contribution of the paper is to show how heat integration in a pre-combustion CO2 capture plant impacts the selection of HRSG design. The purpose of such a plant is to generate power with very low CO2 emissions, typically below 100 g CO2/net kWh electricity. This should be compared to a state-of-the-art natural gas combined cycle (NGCC) plant with CO2 emissions around 380 g CO2/net kWh electricity. The design of the HRSG for the IRCC process was far from standard because of the significant amount of steam production from the heat generated by the auto-thermal reforming process. This externally generated steam was transferred to the HRSG superheaters and used in a steam turbine. For an NGCC plant, a triple-pressure reheat steam cycle would yield the highest net plant efficiency. However, when generating a significant amount of high-pressure steam external to the HRSG, the picture changed. The complexity of selecting a HRSG design increased when also considering that steam can be superheated, and low-pressure and intermediate-pressure steam can be generated in the process heat exchangers. For the concepts studied it was also of importance to maintain a high net plant efficiency when operating on natural gas. Therefore the selection of HRSG design had to be a compromise between NGCC and IRCC operating modes.

The system-level simulation model for Natural Gas Combined-Cycle (NGCC) plant combines advanced G class turbine with various fuels was performed in the study. The commercial chemical process simulator, Pro/II® V8.1.1, is used in the study to build the analysis model. There are three major sections which are gas turbine (GT), heat recovery steam generator (HRSG) and steam turbine (ST).The study envisages two analyses as the basic and feasibility cases. The former is the benchmark case which is verified with the reference data of exist NGCC power plant located in Dah-Tarn, Taiwan. The Dah-Tarn NGCC power plant introduces the advanced M501G gas turbine from Mitsubishi Heavy Industries, Ltd. (MHI) and the system efficiency of the combined-cycle is 58.75 % (LHV). The latter introduces a feasibility study with advanced gas turbine and actual parameters in Taiwan. The SNG from carbonate fuel feed to M501G based combined-cycle is evaluated in the feasibility study cases first, and the mixture gas of SNG and syngas is also evaluated to compare the different of overall performance with the pure SNG case.The results show that the system efficiency of pure SNG case is around 57 % (LHV). For the mixture gas case, the maximum ratio of syngas to SNG is 1:19, due to keep the same composition of methane is 85.9 % with the Dah-Tarn NGCC power plant. The efficiency of mixture gas case is 55.75 % (LHV).The study shows the possibility way to use coal and reduce the CO2 emission. The another advantage is the using of SNG could increases the usage of combined-cycle in Taiwan, due to the prices of natural gas is higher than coal in Taiwan and results in the higher idle capacity.