Oxy-combustion Boiler Research Articles

Thermodynamic analysis of tri-reforming of oxy-fuel combustion exhaust gas

A thermodynamic equilibrium analysis of the tri-reforming of oxy-combustion exhaust gases based on the minimisation of the Gibbs energy, was performed. To capture the effect of air leakage into the oxy-combustion boiler, two cases were investigated, representing 10 % and 1% combustion air leakage. The effects of temperature, pressure, and the ratio of methane to carbon dioxide (CH4/CO2) on the tri-reforming of the exhaust gases was studied. The domain of the practical operating regime for the tri-reforming of exhaust gases which is circumscribed by the maximum operating temperature, minimum CO2 conversion and zero-coke equilibrium was identified. In addition, three reactions (steam reforming, dry reforming and reverse water gas shift) were identified to be dominating in the temperature domain above the zero-coke equilibrium temperature. Within the boundaries of the practical operating regime, the tri-reforming of coal oxy-combustion exhaust gas results in more than three times the net conversion of CO2/kg CH4, when compared to the tri-reforming of conventional coal combustion exhaust gas.

Dynamic Exergy Method for Evaluating the Control and Operation of Oxy-Combustion Boiler Island Systems.

Exergy-based methods are widely applied to assess the performance of energy conversion systems; however, these methods mainly focus on a certain steady-state and have limited applications for evaluating the control impacts on system operation. To dynamically obtain the thermodynamic behavior and reveal the influences of control structures, layers and loops, on system energy performance, a dynamic exergy method is developed, improved, and applied to a complex oxy-combustion boiler island system for the first time. The three most common operating scenarios are studied, and the results show that the flow rate change process leads to less energy consumption than oxygen purity and air in-leakage change processes. The variation of oxygen purity produces the largest impact on system operation, and the operating parameter sensitivity is not affected by the presence of process control. The control system saves energy during flow rate and oxygen purity change processes, while it consumes energy during the air in-leakage change process. More attention should be paid to the oxygen purity change because it requires the largest control cost. In the control system, the supervisory control layer requires the greatest energy consumption and the largest control cost to maintain operating targets, while the steam control loops cause the main energy consumption.

Plantwide control and operating strategy for air separation unit in oxy-combustion power plants

To ensure that air separation unit can bear high ramp rate and flexible operations when integrated into oxy-combustion power plant, this paper focuses on the investigations of plantwide control design and operating strategy for double-column air separation unit without or with liquid oxygen storage drum through dynamic simulation. It is found that three air separation unit types (normal, oversize, and downsize) with the proposed control structure configured with logic control loops (strategies 1, 2, and 3) can achieve 5%/min of high ramp rate and flexible operations such as peak and off-peak or/and energy storage. Compared between the latter two logical controls, strategy 2 would be better because its oxygen product qualities can be maintained closer to their targets. Three integrated patterns between air separation unit and oxy-combustion boiler are proposed to improve operating flexibility, among which oversize case would be more suitable for oxy-combustion power plant since its energy saving (20.33MW) is larger and operating strategy is more flexible than those in downsize (10.76MW) and normal cases. Process control for flexible operations would be an opportunity for engineering, and comprehensive dynamic model with specified control system provides possibility to integrate air separation unit with full-train oxy-combustion power plants.

Corrosion Resistance of Novel Coatings on Ferritic Steels for Oxycombustion–Supercritical Steam Boilers: Preliminary Results

Increasing the efficiency of coal fired steam power plants is an important contribution towards clean coal power. In fact, new ferritic steels are expected to withstand 325 bar and 650 °C. Moreover, in order to facilitate CO2 capture oxygen can be used instead of air for combustion (oxycombustion) so that no NOX emissions are produced. Boiler components, such as superheater tubes, are exposed to both steam and fireside corrosion and at higher temperatures, ferritic steels corrode at very fast rates under both atmospheres. A solution can be found in the use of protective coatings, a number of which, applied by techniques capable of depositing said coatings both on the inner and outer surfaces of tubes, are being studied within nationally and European funded projects. In particular, two new Ni and Cr modified aluminide coatings deposited on P92 by non-line-of-sight hybrid processes have been produced and the preliminary results of on-going laboratory testing, both under oxycombustion model atmospheres as well as under pure steam at 650 °C are promising, in particular those exhibited by the Cr enriched aluminide coating. Moreover, results obtained in a pilot oxycombustion boiler operated by CIUDEN in Leon, Spain are also shown.

Dynamic modeling and control for pulverized-coal-fired oxy-combustion boiler island

Oxy-fuel combustion is one of competitive and promising carbon capture technologies for restraining CO2 emissions from power plants. Dynamic simulation of oxy-combustion system, which is essential for gaining its dynamic characteristics, can help to evaluate and improve process design, and to develop control system and operational strategies. This paper focuses on dynamic simulation and control design for a conceptual 600MWe oxy-combustion pulverized-coal-fired boiler. The steady-state model using a pseudo coal to substitute real coal is established, validated, and then transformed into the dynamic model which uses pressure-driven solution. The control system, which aims to automatically regulating flue gas O2 concentration within reasonable range (2–7mol.% in this study), is designed and applied to the dynamic boiler model. Three planned disturbances of load change, oxygen purity (from cryogenic air separation unit) ramp change and air in-leakage (from boiler) step change are conducted. Detailed dynamic behavior from water side and flue gas side is obtained and analyzed to help engineering operation in real plant. Mode switching process and alternative control strategy are simulated and discussed. Comprehensive dynamic model with specified control system provides possibility to study the dynamic characteristics of full-train oxy-combustion power plants.

Dynamic simulation for mode switching strategy in a conceptual 600 MWe oxy-combustion pulverized-coal-fired boiler

Oxy-fuel combustion as a promising CO2 capture technology is ready for commercial demonstration. Dynamic simulation of oxy-combustion system, which is essential for gaining its dynamic characteristics, can help to evaluate and improve process design, and develop control system and operational strategies. This paper focuses on dynamic simulation of a 600MWe oxy-combustion pulverized-coal-fired boiler. The steady-state model using a pseudo coal to substitute real coal is firstly established, validated, and then transformed into the dynamic model which uses pressure driven solution. Mode switching processes between air-combustion and oxy-combustion are particularly investigated for reasonable and effective switching strategy. It is found that manipulating oxygen and recycled flue gas streams with different ramp rates of corresponding valve positions during different switching stages while manipulating air stream with a constant ramp rate of air valve position throughout the switching process could be an effective switching strategy. The switching time of 17min could realize a stable mode switching either from the air-combustion to the oxy-combustion or from the oxy-combustion to the air-combustion. The dynamic model provides powerful tool to study the dynamic behavior and mode switching characteristics of oxy-combustion boiler.

Oxy-combustion CPU – From Pilots Towards Industrial-scale Demonstration

The CPU (Compression and Purification Unit) is used to capture, purify and compress the CO2 contained in oxy-combustion boiler flue gas. Therefore, it plays a key role in the oxy-combustion route for carbon capture and storage (CCS). Over the last ten years Air Liquide has been developing this technology from a conceptual stage towards industrial maturity.Since the last GHGT conference in 2012 [1], significant progress has been made. The objective of this paper is to present an overview of the progress made in developing the technology with a particular focus on results from pilot plants, and the intended application of key technology developments to the FutureGen 2.0 project.

Lacq Carbon-Capture and -Sequestration Pilot

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 157157, ’The Lacq CCS Pilot, a First,’ by Jacques Monne, SPE, Total, prepared for the 2012 SPE/APPEA International Conference on Health, Safety, and Environment in Oil and Gas Exploration and Production, Perth, Australia, 11-13 September. The paper has not been peer reviewed. Carbon capture and sequestration (CCS) holds promise for use on an industrial scale. Total has been involved in CO2 injection and geological storage for more than 15 years, in Canada (Weyburn oil field) for enhanced oil recovery and in Norway (Sleipner and Snohvit fields) for aquifer storage. In 2006, the company decided to set up an experiment for CO2 capture, transportation, and injection in a depleted gas reservoir. The pilot is in the Lacq basin in southwestern France, 800 km from Paris, and has been on stream since January 2010. Introduction This CCS project entailed converting an existing air/fuel-gas combustion boiler into an oxygen/fuel-gas combustion (oxy-combustion) boiler using oxygen delivered by an air-separation unit (ASU) to obtain more-efficient combustion and a more-concentrated flue-gas-CO2 stream. The 30-MW oxy-combustion boiler can deliver up to 38 t/h of steam to the high-pressure steam network of the Lacq sour-gas-production and -treatment plant. After quenching the flue-gas stream, the rich CO2 stream is compressed to 27 barg, dried, and transported in gaseous phase by use of existing pipelines to a depleted gas field, 29 km away, where it is injected into the deep Rousse reservoir. Over a 3½-year period, up to 90 000 t of CO22 could be injected. The main objectives in this experiment were: To demonstrate the technical feasibility and reliability of an integrated chain comprising steam production and CO2 capture, transportation, and injection into a depleted gas reservoir. To acquire operating experience and data to scale up the oxy-combustion technology from pilot scale (30 MW) to industrial scale (200 MW) while reducing costs. To develop on-site monitoring methods and technologies to serve future onshore storage-monitoring programs that will be larger in scale, longer in term, and economically and technically viable (i.e., microseismic and environmental monitoring). Technical Description The CCS pilot installation, shown in Fig. 1, consists of an ASU, an oxy-combustion boiler, a direct-cooling contactor, a CO2 compressor, a dryer system, a transportation pipeline, and an injection site (i.e., compressor, injection well, reservoir, and a subsurface-seismic network). ASU. A dedicated ASU, the oxygen-production unit, was installed on the Lacq gas-treatment complex to produce 240 t/d of low-pressure oxygen (1.8 bara) at 95 to 99.5 vol% purity. Only 99.5% pure oxygen is used to feed the oxy-combustion boiler. The nitrogen rejected by the ASU is partially used for regenerating the dryer system.

Exergy Analysis of a 600 MWe Oxy-combustion Pulverized-Coal-Fired Power Plant

In an oxy-combustion pulverized-coal-fired power plant (PC), a high CO2 content flue gas could be obtained, and this allows CO2 sequestration in an efficient and energy-saving way. To better understand the thermodynamic characteristics of the oxy-combustion process, a detailed exergy analysis of a 600 MWe oxy-combustion PC was carried out. The whole oxy-combustion PC system was divided into four models: boiler, turbines and feedwater heaters (FWHs), air separation unit (ASU), and flue gas treatment unit (FGU). The exergy (including physical exergy and chemical exergy) of each model was obtained, showing that the oxy-combustion boiler could reach higher exergy efficiency than the conventional combustion boiler. There is a significant difference between the exergy efficiencies of furnaces in the two boiler models, and the combustion exergy efficiency in the oxy-combustion furnace is about 4% higher. In each boiler model, the combustion process contributes nearly 60% exergy destruction. The exergy efficiency of the air heater in the oxy-combustion boiler is 10.3% higher than that in the conventional combustion boiler because of the flue gas recycle in the oxy-combustion boiler. The exergy destruction in the turbine and FWH model is just 9.01% of the total fuel exergy, and the turbines contribute about half. The exergy efficiencies of the ASU and FGU processes are 15.84 and 73.45%, respectively. The exergy efficiency of the oxy-combustion system is 37.13%, which is 4.08% lower than that of the conventional system.