Supplementary Firing Research Articles

Optimal design, operation and analytical criteria for determining optimal operating modes of a CCHP with fired HRSG, boiler, electric chiller and absorption chiller

The configuration, design and operation strategy are the main factors that can affect the technical, economic and environmental performances of combined cooling, heating and power (CCHP) system. In this paper, the operation of a CCHP system with fired heat recovery steam generator (HRSG), electric chiller, absorption chiller and a boiler is classified into one of three scenarios which are determined by gas turbine size and magnitude of thermal and electric loads. The optimal operating strategies are presented for these scenarios. For scenario with high cooling loads, we derive analytical expressions for calculation of ratio (electricity price/natural gas price) values which delimit three optimal modes for providing cooling demand in summer, thereby enabling selection of optimal operating strategy without numerical optimization. We examine the optimal design of CCHP system in three climate zones based on the proposed strategy. Supplementary firing as well as a higher coefficient of performance (COP) of the absorption chiller increase system efficiency and enable reduction of gas turbine size. Our case studies show that supplementary firing, (for some values of price ratio, absorption chiller COP and climate zone) the electric chiller and/or the boiler are necessary components to achieve optimal system performance.

Making gas‐CCS a commercial reality: The challenges of scaling up

AbstractSignificant reductions in CO2 emissions are required to limit the global temperature rise to 2°C. Carbon capture and storage (CCS) is a key enabling technology that can be applied to power generation and industrial processes to lower their carbon intensity. There are, however, several challenges that such a method of decarbonization poses when used in the context of natural gas (gas‐CCS), especially for solvent‐based (predominantly amines) post‐combustion capture. These are related to: (i) the low CO2 partial pressure of the exhaust gases from gas‐fired power plants (∼3‐4%vol. CO2), which substantially limits the driving force for the capture process; (ii) their high O2 concentration (∼12‐13%vol. O2), which can degrade the capture media via oxidative solvent degradation; and (iii) their high volumetric flow rates, which means large capture plants are needed. Such post‐combustion gas‐CCS features unavoidably lead to increased CO2 capture costs. This perspective aims to summarize the key technologies used to overcome these as a priority, including supplementary firing, humidified systems, exhaust gas recirculation and selective exhaust gas recirculation. These focus on the maximum CO2 levels achievable for each, as well as the electrical efficiencies attainable when the capture penalty is taken into account. Oxy‐turbine cycles are also discussed as an alternative to post‐combustion gas‐CCS, indicating the main advantages and limitations of these systems together with the expected electrical efficiencies. Furthermore, we consider the challenges for scaling‐up and deployment of these technologies at a commercial level to enable gas‐CCS to play a crucial role in a low‐carbon future. © 2017 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons, Ltd.

Sequential Supplementary Firing in Combined Cycle Power Plant with Carbon Capture: Part-load Operation Scenarios in the Context of EOR

This paper extends previous work on sequential supplementary firing combined cycles (SSFCC) and evaluates their part-load operation in order to define operating strategies to maximise revenue from electricity and Enhanced Oil Recovery (EOR) over a range of fuel input. Sequential supplementary firing consists of burning additional fuel at different stages in the heat recovery steam generator (HRSG) to increase CO2 concentration reduces the volumetric flow of the flue gases. It uses almost all of the oxygen in the flue gas and keeps the maximum gas temperature at around 820°C to avoid large additional capital costs in the HRSG. SSFCC This analysis is important in order to establish ways to maintain a minimum CO2 flow for EOR when the power plant with CO2 capture is at minimum stable generation.Two alternatives to reduce power at part-load are evaluated: a subcritical steam cycle with a combination of variable inlet guide vanes and reduction in supplementary firing; and a strategy where the gas turbine is maintained at full output and the power output is solely reduced by adjusting the amount of supplementary firing in the HRSG.

Network Analysis of Fuel Cell Heat Engine Distributed Energy Systems

A thermodynamic and electrochemical framework transformed into an electrical network is used to analyze the power output and efficiency of high-temperature, ceramic fuel cell heat engine systems for the hydrogen oxidation reaction. It is interesting that the heat engine combustor subsystem performance was able to be recast in electrochemical and electrical network terms. The analysis includes the effect of temperature on the operation and performance of these ceramic, high-temperature systems. The power and efficiency responses of a distributed energy system operated at constant voltage to protect the fuel cell, using supplemental firing of the heat engine, and subjected to a cyclic load demand is presented. These systems are of interest to the emerging renewable energy grid. While the perfect fuel cell would undergo no degradation, practical fuel cells will degrade. The partition of power in a degrading distributed energy system is examined.

Network Analysis of Fuel Cell Heat Engine Distributed Energy Systems

A thermodynamic and electrochemical framework transformed into an electrical network is used to analyze the power output and efficiency of fuel cell heat engine systems for the hydrogen oxidation working reaction. The analysis includes operation of these systems at constant voltage with constant power operation through supplemental firing of the heat engine. It is interesting that the heat engine combustor performance was able to be recast in electrochemical and electrical network terms. The analysis includes the power and efficiency responses of a cyclic load distributed energy system of interest to the renewable energy grid. While the perfect fuel cell would undergo no degradation, practical fuel cells will degrade. The partition of power in a degrading distributed energy system at constant voltage with constant power is examined. Network topology is an important parameter which the electrical network approach is best suited to analyze. For high heat engine exergetic efficiency and low fuel cell operating voltage parallel fuel cell network topology design gives the best performance while for poor heat engine exergetic efficiency and high operating voltage a series fuel cell network topology design gives the best performance design.

Effect of the ambient conditions on gas turbine combined cycle power plants with post-combustion CO2 capture

This paper evaluates the effect of ambient conditions on a natural gas combined cycle power plant (NGCC) with CO2 capture and proposes design options for effective integration and off-design operation. In particular, the study assesses the effect of ambient temperature in the context of the electricity system in Mexico and proposes supplementary firing in the heat recovery steam generator to mitigate reduction in power output. For ambient temperature varying from −5 °C to 45 °C, a typical temperature variation in the north of Mexico, the efficiency of the NGCC with CO2 capture reduces from 50.95% to 48.01% when the temperature increased from 15 °C (ISO design condition) to 45 °C, and reduces from 50.95% to 50.78% when the temperature decreased from 15 °C to −5 °C. The power generated decreases from 676.3 MW at 15 °C to 530 MW at 45 °C. In order to compensate for the loss of output caused by seasonal changes in ambient temperature, supplementary firing in the heat recovery steam generator can be used to generate additional power and return the power output to 640 MW at 45 °C, at the expense of an increase in fuel costs and a drop in efficiency from 50.95% to 43.46%, without and with supplementary firing respectively.

Energy and exergy analyses of pulse combustor integration in air bottoming cycle power plants

Air bottoming cycle (ABC) is a recently recommended waste heat recovery bottoming cycle which can be implemented for small scale power plants. Nonetheless, ABC’s low efficiency is preventing the commercialization of this novel idea. One of the possible modifications is the integration of a pulse combustor in order to improve the ABC’s efficiency. In this paper, integration of pulse combustor in ABC configuration is suggested. For pulse combustor implementation in ABC, two different configurations are proposed comprising pulse combustor integration instead of the topping cycle combustion chamber and as a supplementary firing in the bottoming cycle. Energy analysis is conducted by investigating different design variables’ effects on both thermal efficiency and net specific work output. Furthermore, exergy analysis is accomplished by pinpointing the sources of irreversibility within the configurations. Moreover, thermodynamic optimization is performed to identify the maximum power enhancement due to the implementation of the pulse combustion. Integration of the pulse combustor in the topping cycle can increase the thermal efficiency to 50.8% whereas maximum possible ABC’s efficiency is 43.6%. Additionally, pulse combustor implementation as the supplementary firing in the bottoming cycle led to the maximum efficiency of 41.8%.

Modelling and exergoeconomic-environmental analysis of combined cycle power generation system using flameless burner for steam generation

To have an optimum condition for the performance of a combined cycle power generation, using supplementary firing system after gas turbine was investigated by various researchers. Since the temperature of turbine exhaust is higher than auto-ignition temperature of the fuel in optimum condition, using flameless burner is modelled in this paper. Flameless burner is installed between gas turbine cycle and Rankine cycle of a combined cycle power plant which one end is connected to the outlet of gas turbine (as primary combustion oxidizer) and the other end opened to the heat recovery steam generator. Then, the exergoeconomic-environmental analysis of the proposed model is evaluated. Results demonstrate that efficiency of the combined cycle power plant increases about 6% and CO2 emission reduces up to 5.63% in this proposed model. It is found that the variation in the cost is less than 1% due to the fact that a cost constraint is implemented to be equal or lower than the design point cost. Moreover, exergy of flow gases increases in all points except in heat recovery steam generator. Hence, available exergy for work production in both gas cycle and steam cycle will increase in new model.

Investigation of Different Operation Strategies to Provide Balance Energy With an Industrial Combined Heat and Power Plant Using Dynamic Simulation

Intermittency of renewable electricity generation poses a challenge to thermal power plants. While power plants in the public sector see a decrease in operating hours, the utilization of industrial power plants is mostly unaffected because process steam has to be provided. This study investigates to what extent the load of a combined heat and power (CHP) plant can be reduced while maintaining a reliable process steam supply. A dynamic process model of an industrial combined CHP plant is developed and validated with operational data. The model contains a gas turbine (GT), a single pressure heat recovery system generator (HRSG) with supplementary firing and an extraction condensing steam turbine. Technical limitations of the gas turbine, the supplementary firing, and the steam turbine constrain the load range of the plant. In consideration of these constraints, different operation strategies are performed at variable loads using dynamic simulation. A simulation study shows feasible load changes in 5 min for provision of secondary control reserve (SCR). The load change capability of the combined cycle plant under consideration is mainly restricted by the water–steam cycle. It is shown that both the low pressure control valve (LPCV) of the extraction steam turbine and the high pressure bypass control valve are suitable to ensure the process steam supply during the load change. The controllability of the steam turbine load and the process stability are sufficient as long as the supplementary is not reaching the limits of the operating range.

Hydrogen production from heavy fraction of bio-oil using iron-based chemical looping process: Thermodynamic simulation and performance analysis

The purpose of this work is to investigate the overall performance of the iron-based chemical looping hydrogen (CLH) production from the heavy fraction of bio-oil (HFB). The multiple ASPEN models are employed to simulate a two-stage fluidized bed reduction reactor considering the thermodynamic equilibrium limit. Several important factors are discussed to determine the suitable reactor operation conditions for the process simulation of two operation modes. The results show HFB CLH process has a maximum hydrogen efficiency of 73.1% (LHV) and a total thermal efficiency of 59.2% (LHV) at the cost of decreasing the CO2 capture efficiency under the condition of supplementary firing. Within the complete self-sustaining operation range, the highest hydrogen thermal efficiency is 57.8% (LHV) corresponding to a total thermal efficiency of 58.3% (LHV) and a CO2 capture efficiency of nearly 100%. This study indicates the CLH process has significant advantages over the conventional coal gasification (CG) for hydrogen production owing to its high energy conversion efficiency and high-efficient CO2 capture with low cost.

Sequential supplementary firing in natural gas combined cycle with carbon capture: A technology option for Mexico for low-carbon electricity generation and CO2 enhanced oil recovery

Combined cycle gas turbine power plants with sequential supplementary firing in the heat recovery steam generator could be an attractive alternative for markets with access to competitive natural gas prices, with an emphasis on capital cost reduction, and where supply of carbon dioxide for Enhanced Oil Recovery (EOR) is important. Sequential combustion makes use of the excess oxygen in gas turbine exhaust gas to generate additional CO2, but, unlike in conventional supplementary firing, allows keeping gas temperatures in the heat recovery steam generator below 820°C, avoiding a step change in capital costs. It marginally decreases relative energy requirements for solvent regeneration and amine degradation. Power plant models integrated with capture and compression process models of Sequential Supplementary Firing Combined Cycle (SSFCC) gas-fired units show that the efficiency penalty is 8.2% points LHV compared to a conventional natural gas combined cycle power plant with the same capture technology. The marginal thermal efficiency of natural gas firing in the heat recovery steam generator can increase with supercritical steam generation to reduce the efficiency penalty to 5.7% points LHV. Although the efficiency is lower than the conventional configuration, the increment in the power output of the combined steam cycle leads a reduction of the number of gas turbines, at a similar power output to that of a conventional natural gas combined cycle. This has a positive impact on the number of absorbers and the capital costs of the post combustion capture plant by reducing the total volume of flue gas by half on a normalised basis. The relative reduction of overall capital costs is, respectively, 15.3% and 9.1% for the subcritical and the supercritical combined cycle configurations with capture compared to a conventional configuration. For a gas price of $2/MMBTU, the Total Revenue Requirement (TRR) – a metric combining levelised cost of electricity and revenue from EOR – of subcritical and supercritical sequential supplementary firing is consistently lower than that of a conventional NGCC by, respectively, 2.2 and 5.7 $/MWh at 0 $/t CO2 and by 4.9 and 6.7 $/MWh at $50/t CO2. At a gas price of $4/MMBTU and $6/MMBTU, the TRR of a subcritical configuration is consistently lower for any carbon selling price higher than 2.5 $/t CO2 and 37 $/t CO2 respectively.

Performance Comparison on Repowering of a Steam Power Plant with Gas Turbines and Solid Oxide Fuel Cells

Repowering is a process for transforming an old power plant for greater capacity and/or higher efficiency. As a consequence, the repowered plant is characterized by higher power output and less specific CO2 emissions. Usually, repowering is performed by adding one or more gas turbines into an existing steam cycle which was built decades ago. Thus, traditional repowering results in combined cycles (CC). High temperature fuel cells (such as solid oxide fuel cell (SOFC)) could also be used as a topping cycle, achieving even higher global plant efficiency and even lower specific CO2 emissions. Decreasing the operating temperature in a SOFC allows the use of less complex materials and construction methods, consequently reducing plant and the electricity costs. A lower working temperature makes it also suitable for topping an existing steam cycle, instead of gas turbines. This is also the target of this study, repowering of an existing power plant with SOFC as well as gas turbines. Different repowering strategies are studied here, repowering with one gas turbine with and without supplementary firing, repowering with two gas turbines with and without supplementary firing and finally repowering using SOFC. Plant performances and CO2 emissions are compared for the suggested repowered plants.

Performance analysis of a micro gas turbine and solar dish integrated system under different solar-only and hybrid operating conditions

A hybrid energy system comprising a parabolic dish solar energy concentrator (Solar Dish) and a micro gas turbine is investigated in the study. A thermodynamic model of the system is presented, able to simulate both on-design and off-design performance of the system and accounting for the main technical aspects of the concentrator, receiver and gas turbine engine. Then, simulations are performed for various system sizes and operating strategies, with and without supplementary firing and for a reference location (Seville, Spain), yielding solar-to-electric power conversion efficiencies between 16.78% and 18.35% (rated conditions), depending on size. Annual performances result in a capacity factor of about 29% (2540 full operating hours) in solar only operation and annual average efficiency at 95% of the nominal value.The main results indicate that moderate supplementary firing is interesting for it increases the average efficiency of the system and the annual yield, whilst still keeping the carbon footprint within reasonable values. Nevertheless, as heavy fossil fuel firing is adopted, the system becomes less competitive against conventional, standard distributed generation power systems either for natural gas or diesel fuel. Whilst these trends were somehow to be expected, the interest of this paper is to provide the reader with a fundamental analysis from which a technical and economic analysis can be performed, aimed at identifying the most leveraged solar share (i.e., fuel utilisation).

Exergetic Analysis of Triple-Level Pressure Combined Power Plant with Supplementary Firing

AbstractThis work presents a thermodynamic analysis of a triple-level pressure combined power plant with supplementary firing. The supplementary firing is a technological development for improving and increasing the output power of a combined-cycle (CC) power plant. In Mexico, there is a plant operating with this configuration, which generates a net power of 1,170 MW, with a power ratio of the gas turbine (GT) to the steam turbine (ST) of 1.35∶1. This plant is composed of four combined-cycle units with supplementary firing, each providing an output power of 292.5 MW. The energetic and exergetic analyses of the combined cycle with and without supplementary firing are pursued, taking into account the combustion process of natural gas and humid air. These analyses are also carried out for the heat recovery steam generator, considering the waste gases of the gas turbine and of the supplementary firing as the energy sources. The obtained results are fuel, steam, and humid air flows; excess of air; gas and stea...

Control Strategies for Irreversible Fuel Cell Heat Engine Systems

A novel thermodynamic and electrochemical framework for the analysis of irreversible fuel cell heat engine systems is introduced in this paper and used to begin to explore the possibility of operating these systems at constant voltage operation and at constant voltage operation with constant power operation through supplemental firing for the hydrogen oxidation working reaction. It is interesting that the heat engine combustor performance was able to be recast in electrochemical terms. While the perfect fuel cell would undergo no degradation, practical fuel cells with irreversibilities will degrade. For several reasons it is desirable to operate these degrading systems at constant voltage. The limits of the performance of the basic fuel cell heat engine system is discussed.

Advanced exergy and environmental analyses and multi objective optimization of a real combined cycle power plant with supplementary firing using evolutionary algorithm

This paper deals with an advanced exergy analysis and optimization of a real CCPP (combined cycle power plant) with DBs (duct burners) located in Iran. The endogenous/exogenous exergy destruction parts of each component as well as their combinations with avoidable/unavoidable parts are determined. A parametric study is carried out to assess the sensitivity of total avoidable exergy destruction and CO2 emission to TIT (turbine inlet temperature), compressor pressure ratio (rc) and DB fuel mass flow rate (m˙DB). Parametric results reveal that the increments in TIT and rc improve the CO2 emissions by about 6.8% and 17%, respectively and the total avoidable exergy destruction rate increases within 19% when rc is in the range of 9–14. In addition, NSGA-II (Non-dominated Sort Genetic Algorithm-II) is applied to obtain the final solutions in the multi-objective optimization of the CCPP. The optimum value of total avoidable exergy destruction rate and CO2 emission indicates 10.6% and 8.3% improvements, respectively, relative to the base case. Furthermore, the values of TIT and m˙DB decrease to 1.7% and 32.5%, respectively and rc increases 38% compared with the base case.

Analytical Off-design Characteristics of Gas Turbine-Based CCHP System

Grounded on the typical analytical off-design performances of some basic CCHP (combined cooling, heating and power) components, off-design characteristics of a gas turbine-based CCHP system were analyzed and summarized. The results and discussion show that, at full power load of the gas turbine, the CCHP relative cold output Qrc varies from 0∼1.2, and the corresponding relative heat output Qrh from 1∼0. The CCHP system supplies 23.7% of the design cold capacity or 22.7% of the design heat capacity at empty power load. CCHP economic exergy efficiency and thermal efficiency both rise with the increase of power output, and trend towards a slight decline at a near-full cooling load of chiller. In a wide operation range of CCHP, economic exergy efficiency and thermal efficiency both rise with the increase of cooling load. Higher ambient temperature results in lower relative capacity of cold, heat and power. It is proposed that renovation technologies such as gas turbine inlet air cooling, steam injected gas turbine and HRSG supplementary firing be applied to weaken the effect of the ambient temperature on CCHP system. The quantitative results are meaningful for optimal configuration and economical operation of the energy systems.

Investigating the effect of duct burner fuel mass flow rate on exergy destruction of a real combined cycle power plant components based on advanced exergy analysis

In this research, an advanced exergy analysis of a real combined cycle power plant (CCPP) with supplementary firing is investigated. The endogenous/exogenous irreversibilities of each component and their combination with avoidable/unavoidable irreversibilities are identified. Furthermore, parametric study of the total exergy destruction, thermal and exergetic efficiencies and different parts of exergy destruction of each component are examined as a function of duct burner fuel mass flow rate (ṁDB). It is revealed that the avoidable exergy destruction of CCPP decreases within 23.9% while its unavoidable part increases by about 50% as ṁDB increases. In addition, the endogenous avoidable exergy destruction of CCPP gets 3 times while its exogenous part of avoidable is reduced within 86% by increasing ṁDB. It is found that the growth of ṁDB elevates the potential improvement of high pressure superheater (HP.SUP), low pressure evaporator (LP.EVAP) and low pressure steam turbine (LP.ST), and decreases the avoidable exergy destruction of the high pressure evaporator (HP.EVAP) and duct burner (DB). Moreover, the increment of ṁDB, decreases the unavoidable exergy destruction just in high pressure steam turbine (HP.ST) and dearator (DEAR) by about 8.2% and 5%, respectively, and increases the exogenous of avoidable exergy destruction of DB (ĖD,DBAV) within 166%. It means that the effect of other components irreversibilities on avoidable exergy destruction of DB is increased while inefficiency of this component has considerable decrement on its avoidable exergy destruction.

Investigation of Alternative Strategies for Integrating Post-combustion CO2 Capture to a Natural Gas Combined Cycle Power Plant

With increasing urgency for global action toward climate change mitigation, this study is undertaken to evaluate integration options for post-combustion CO2 capture (PCC) on gas-fired power plants. High-fidelity models of a natural gas combined cycle power plant, a PCC plant, and a CO2 compression train are integrated for a 90% CO2 capture level. Three options to provide steam for solvent regeneration are explored: extracting steam from the intermediate-pressure (IP)/low-pressure (LP) crossover, using a gas-fired package boiler, and extracting steam from the LP drum. The effect of pressure losses because of steam extraction, a factor ignored in previous analyses, is also considered. The integrated plant net efficiency is 47.8, 40.4, and 44.9%, respectively, for the aforementioned scenarios. Next, supplementary firing of gas turbine exhaust is employed to generate an ample amount of steam to preserve plant net output under a sliding pressure scenario and meet solvent regeneration requirements. It is observed that the net plant efficiency converges to a value of 43.5% for the options considered.

Sensitivity analysis of exergy destruction in a real combined cycle power plant based on advanced exergy method

The advanced exergy analysis extends engineering knowledge beyond the respective conventional methods by improving the design and operation of energy conversion systems. In advanced exergy analysis, the exergy destruction is splitting into endogenous/exogenous and avoidable/unavoidable parts. In this study, an advanced exergy analysis of a real combined cycle power plant (CCPP) with supplementary firing is done. The endogenous/exogenous irreversibilities of each component as well as their combination with avoidable/unavoidable irreversibilities are determined. A parametric study is presented discussing the sensitivity of various performance indicators to the turbine inlet temperature (TIT), and compressor pressure ratio (rc). It is observed that the thermal and exergy efficiencies increase when TIT and rc rise. Results show that combustion chamber (CC) concentrates most of the exergy destruction (more than 62%), dominantly in unavoidable endogenous form which is decreased by 11.89% and 13.12% while the avoidable endogenous exergy destruction increase and is multiplied by the factors of 1.3 and 8.6 with increasing TIT and rc, respectively. In addition, TIT growth strongly increases the endogenous avoidable exergy destruction in high pressure superheater (HP.SUP), CC and low pressure evaporator (LP.EVAP). It, also, increases the exogenous avoidable exergy destruction of HP.SUP and low pressure steam turbine (LP.ST) and leads to the high decrement in the endogenous exergy destruction of the preheater (PRE) by about 98.8%. Furthermore, rc growth extremely rises the endogenous avoidable exergy destruction of gas turbine (GT), CC and high pressure evaporator (HP.EVAP); it also increases the exogenous exergy destruction in LP.EVAP, GT, air compressor (AC) and PRE and causes the most increment in endogenous exergy destruction of GT by about 28.4%. Therefore, an increase in TIT and rc has positive effect on most of the component’s potential improvements to have a CCPP with higher efficiency and lower exergy destruction.