Search

The refining sector comprises a lot of different processes, since a wide range of final products are obtained in refineries. In any case, CO 2 emissions levels are high and three units can be considered as the main sources accounting the majority of carbon dioxide emissions to the atmosphere: the utility boilers system, the process heaters and the fluid catalytic cracking unit (FCC). In this study, the substitution of the utility boilers system for an oxy-combustion power plant is presented. The power plant is designed to cover the steam thermal and electricity demands of oil refinery. In addition, a heat integration methodology based on pinch analysis is applied to the whole concept for increasing efficiency. Final results show that more than 380,000 tonnes of CO 2 could be avoided. Afterwards, a complete economic approach is carried out. Although profitability is still low with current economic costs, it is expected that in the medium term, oxy-combustion could be economically feasible in refining sector. To this extent, sensitivity analysis shows affordable values for main economic parameters that can be reached in the next years. A 24 €/MWh natural gas price reduces operational cost for oxy-combustion power plant below the conventional refinery value. An electricity price higher than 67 €/MWh and a CO 2 cost around 20 €/tCO 2 also seem to reduce operational cost below reference case ones. The study concludes with the analysis of some realistic future scenarios that prove the oxy-combustion technology both technically and economically feasible and payback periods between 9 and 11 years with IRR values around 7% can be affordable within the following years. [ABSTRACT FROM AUTHOR]

Abstract: High temperature looping cycles, such as carbonation-calcination cycles based on calcium sorbents or chemical looping combustion are being developed and play an essential role in CO2 capture technologies. Among proposed configurations, outstanding schemes make use of a number of interconnected fluidized beds and may operate at bubbling or circulating regime. Fluidized bed behaviour is well-known since they are included in many industrial applications, such as power plants and chemical industries. However, there is a lack of knowledge about their operation when more than one fluidized bed are coupled in the same system. One promising configuration for Ca-based sorption looping systems relies on the use of two circulating beds as carbonator and calciner and two bubbling beds acting as loop-seal valves. Many theoretical and lab experimental studies point out the need of large solid circulation in the system to reach high carbonation efficiencies. The control of this flow in complex CFB looping systems, where also internal recirculation exists in the risers, becomes a difficult task and deserves further studies to characterize them. The challenge to solve, through experimental tests and mathematical modelling, is finding a comprehensive control method to operate two circulating beds in turbulent regime and two bubbling sealing devices. Experimental results supporting high carbonation efficiency or feasibility in scaling-up solid circulation rates and inventories are needed to make the system more reliable. A lab-scale cold flow facility has been designed based on Glicksman’s scaling rules and constructed in order to conduct experimental tests. The mechanical design of the facility and the choice of solid material, fluidizing gas and operating conditions should be such as to ensure the circulation of solids between reactors and the presence of solids inventory in the carbonator which are necessary to achieve high capture efficiencies. Operation of the system has been tested for a long number of hours under very different conditions. Measurements of circulation rate, static pressure, voidage profiles and standpipe height of solids have been used to identify trends in the hydrodynamic behaviour of the whole system while varying gas velocities in the risers, loop-seals, inventories in the reactors or size distribution of the particles. The circulation rates attained in the cold flow plant are comparable, after scaling-up, to solid flows in the loop which lead to high enough carbonation efficiencies of the system. [Copyright &y& Elsevier]

Abstract: Among the main challenges of Carbon Capture and Storage (CCS) technologies, the reduction of energy penalties associated with the capture process and the integration of the new process in the design of a complex system - original power plant and capture facility - are major issues. Traditionally, the Second Law of Thermodynamics is an essential tool for process optimization through the application of exergy and exergy destruction (irreversibility) concepts. An exergy analysis provides a guide for identifying those systems and equipments with larger irreversibility. Modifications in the design of these systems may lead to reduction of thermodynamic inefficiencies in CO2 capture facilities, improving their performance and reducing costs. In this work, some examples of the application of the Second Law of Thermodynamics are presented for postcombustion, oxyfuel combustion and precombustion CO2 capture technologies. The main target is to identify the equipment with larger irreversibilities and to propose items for future optimization. [Copyright &y& Elsevier]

Abstract: One of the important challenges for biomass combustion in industrial applications is the fouling tendency and how it affects to the boiler performance. The classical approach for this question is to activate sootblowing cycles with different strategies to clean the boiler (one per shift, one each six hours,…). Nevertheless, it has been often reported no effect on boiler fouling or an excessive steam consumption for sootblowing. This paper illustrates the methodology and the application to select the adequate time for activating sootblowing in an industrial biomass boiler. The outcome is a control strategy developed with artificial intelligence (Neural Network and Fuzzy Logic Expert System) for optimizing the biomass boiler cleaning and maximizing heat transfer along the time. Results from an optimize sootblowing schedule show savings up to 12GWh/year in the case-study biomass boiler. Extra steam generation produces an average increase of turbine power output of 3.5%. [Copyright &y& Elsevier]

The iron and steel industry is the largest energy-consuming sector in the world. It is responsible for emitting 4–5% of the total anthropogenic CO2. As an energy-intensive industry, it is essential that the iron and steel sector accomplishes important carbon emission reduction. Carbon capture is one of the most promising alternatives to achieve this aim. Moreover, if carbon utilization via power-to-gas is integrated with carbon capture, there could be a significant increase in the interest of this alternative in the iron and steel sector. This paper presents several simulations to integrate oxy-fuel processes and power-to-gas in a steel plant, and compares gas productions (coke oven gas, blast furnace gas, and blast oxygen furnace gas), energy requirements, and carbon reduction with a base case in order to obtain the technical feasibility of the proposals. Two different power-to-gas technology implementations were selected, together with the oxy blast furnace and the top gas recycling technologies. These integrations are based on three strategies: (i) converting the blast furnace (BF) process into an oxy-fuel process, (ii) recirculating blast furnace gas (BFG) back to the BF itself, and (iii) using a methanation process to generate CH4 and also introduce it to the BF. Applying these improvements to the steel industry, we achieved reductions in CO2 emissions of up to 8%, and reductions in coal fuel consumption of 12.8%. On the basis of the results, we are able to conclude that the energy required to achieve the above emission savings could be as low as 4.9 MJ/kg CO2 for the second implementation. These values highlight the importance of carrying out future research in the implementation of carbon capture and power-to-gas in the industrial sector. [ABSTRACT FROM AUTHOR]

Power to Gas (PtG) has appeared in the last years as a potential long-term energy storage solution, which converts hydrogen produced by renewable electricity surplus into synthetic methane. However, significant economic barriers slow down its massive deployment (e.g. operating hours, expensive investments). Within this framework, the PtG-Oxycombustion hybridization can palliate these issues by improving the use of resources and increasing the overall efficiency. In this study we assess the requirements for electrolysis, depending on the size of the oxycombustion plant, the fuel physical and chemical properties and the final application of the hybrid system. Most suitable heat demanding options to implement this PtG-Oxycombustion hybridization are district heating, industrial processes and small combined cycled power plants. The latter case is modelled and simulated in detail and thermally integrated. The global efficiency of this hybrid system increases from 56% to 68%, thanks to avoiding the requirement of an air separation unit and integrating up to 88% of the available heat from methanation in a LP steam cycle. [ABSTRACT FROM AUTHOR]

Air-staged combustion is a known, successful way to reduce NOx emission in solid-fired systems. Despite this measure has been more frequently applied in pulverized fuel units, it can also be found in fluidized bed boilers. In this case, air-staging affects the fluid dynamics and other closely related issues, like combustion efficiency or desulphurization. The extent of these effects is still to be completely determined in oxy-fired boilers. This paper discusses the influence of gas-staging on CO, NOx and SO2 emissions in fluidized bed oxy-firing. An experimental plan was carried out in a 90 kWth bubbling fluidized bed with two secondary gas inlets located at different heights. The tests were conducted firing two Spanish coals (anthracite and lignite) for a variety of O2/CO2 atmospheres and secondary flow rates. The secondary gas ratio has been revealed as the key variable, since solid mixing and particle conversion in the dense zone are directly affected. While gas-staging is shown to be an effective measure to reduce NOx emissions for all the coals and atmospheres tested, SO2 is however penalized, so finally a trade-off solution is needed. These trends are deepened for the higher values of CO2 concentration. [ABSTRACT FROM AUTHOR]

A comprehensive experimental characterization of Spanish anthracite oxy-combustion has been conducted, and the results are discussed in this paper, encompassing combustion efficiency, heat transfer, and pollutant emissions. The experimental work has been carried out in a 90 kW th bubbling fluidized reactor under a variety of O 2 /CO 2 atmospheres and operating conditions (fluidization velocity, Ca:S ratio, and secondary oxidant supply). Combustion efficiency is improved under oxy-firing compared to air-firing, mainly due to the multiple-bubble regime and the lower fluidization velocities. The share of radiative heat transfer also rises, since O 2 /CO 2 operation leads to an increase of the temperature in the dense zone of the reactor. Concerning SO 2 emissions, the minimum values are found under the richest O 2 atmosphere, yielding maximum values of sulfur capture efficiency in the temperature range of 880–890 °C. A decrease of NO x emissions is also observed under oxy-firing conditions, while the benefit of secondary oxidant supply has to be optimized for every specific O 2 concentration. [ABSTRACT FROM AUTHOR]

Highlights: [•] A model has been developed to predict oxy-coal combustion in fluidized beds. [•] Model comprises fluid-dynamics, coal combustion, sulfur capture and heat transfer. [•] Validation is accomplished for three coals, under a variety of operating conditions. [•] Pressure, temperature and emissions patterns are simulated. [Copyright &y& Elsevier]

Abstract: This paper addresses the mathematical development and the experimental validation of a semi-empirical model designed to characterize the fluid-dynamic response of a fluidized bed reactor under oxy-fuel operation. The objective is to survey the main differences between a conventional air operation and a novel O2/CO2 operation, as for the interactions of solid-phase and gas-phase. The model provides all the relevant variables describing the fluid-dynamics, and it is conceived to simulate the performance of a lab-scale facility. Data gathered from the cold- and hot-operation of a 90kWth oxy-fired fluidized bed are used for validation purposes. Bed porosity, minimum fluidization velocity and bubbles’ size are detected to change under oxy-firing conditions. Once validated, the tool will be used to predict the performance under new fluidizing atmospheres and will be integrated within an entire model coupling fluid-dynamics, combustion and heat transfer phenomena. [Copyright &y& Elsevier]