Heat transfer in oxy-fuel fluidized bed boilers

In spite of the stabilization of coal demand in developed countries, the role of coal in the next decades energy mix is still essential. Particularly relevant will be in the great developing economies, such as India or China, where this fuel is abundant and avoid external energy dependences. In parallel, the international community needs to drive its efforts towards politics that commit fossil fuels energetic companies to drop their CO2 emissions drastically for 2015. In this regard, great advances have been made towards gaining plant efficiency and therefore, reducing the tones of CO2 per produced kWh. Still, emissions need a more drastic reduction if we want to avoid an increment of atmosphere temperature higher than 2ºC. Here, the CO2 capture and storage (CCS) technologies will have the potential of reducing up to 25% of CO2 from stationary sources as soon as they will be commercially available. Among the CO2 capture technologies, grouped in pre-combustion, post-combustion and oxy-fuel combustion, this last one is receiving outstanding support by the national and European authorities. The possibility of implementing oxy-fuel combustion into circulating fluidized bed technology, contributes to approaching the concept of clean-coal technology. Fluidized bed combustors have the outstanding feature of offering the possibility of burning a wide variety of fuels They have the possibility to capture SO2 emissions, adding in-bed limestone. Their working temperature is lower than in pulverized fuel boilers, which avoids thermal NOx formation. Additionally to these characteristics, already exploited under air-firing, applying oxy-fuel combustion technology and being able to capture the CO2 emissions from the coal combustion, or even from blends of coal and other fuels, makes oxy-fuel combustion in fluidized bed a great opportunity to turn the coal sustainable in the future power plant designs. About the implications derived of applying oxy-fuel technology to a commercial scale CFB boiler, scarce literature exits, especially when considering high O2 concentrations at inlet. A one dimensional model has been developed. The overall modeling strategy, in which the model has been based on, is explained in the first part of Chapter 2. It is based on the already known and validated air-firing semi-empirical expressions. The model has been divided into three sub-models interacting with each other: fluid-dynamics, combustion and energy balance of plant. For attributing reliability to the developed model, the scarce public experimental measurements of real air-firing boilers have been compared with the model results. Additionally, three studies regarding the modeling of large oxy-fuel CFB boilers have also been used for comparing the model predictions. In spite of having insufficient information about the published models details, the model developed in this work fairly fits the predictions in the literature. This has allowed making the sensibility analysis, trying to draw the main consequences of oxy-fuel deployment in CFB boilers. For retrofitting purposes, i.e. with no changes on an air-firing boiler configuration, the adequate O2 proportion of oxygen at entrance should be around 30%. Higher O2 concentrations lead to smaller cross sectional areas of the boiler. For a given fuel power required in a boiler, feeding 45% O2 in the comburent, would reduce the cross sectional area down to 54% of the original one. This involves a reduction of heat transfer surface along the boiler walls of 23% approximately. The immediate consequence is the need of resorting to external heat transfer surfaces, i.e., external heat exchangers (EHE). This device would need to remove almost 50% of the total heat of combustion in the case of feeding comburent with 60% O2 content. The importance of the EHE resides not only in compensating the reduction of heat transfer surface in the riser, but in managing higher amount of elutriated solids. The simulations have shown that higher solids densities in the boiler will enhance heat transfer coefficients to the riser walls. For certain boiler geometry, if increasing boiler load, higher recycled solids rate will be required. Feeding 60% of O2 at inlet, fuel input can be increased from 600 to 800 MW if elutriated solids increase from 25 to 40 kg/m2s. This refers us again to the higher solids crossing the EHE. An increase of 10% of heat removal will be required in this device for said changing load. Applying EHEs to conventional boilers was not essential during air-firing operation. But for oxy-fuel combustion it was here demonstrated to be crucial for accomplishing the boiler energy balance. However, several operational and design uncertainties will need to be solved, before deploying first demonstration oxy-CFB boiler. The design of the future EHE will imply two relevant distinguishing features of oxy-firing operation: the influence of gas composition on the determination of the heat transfer coefficients and the greater amount of elutriated solids, cooled down in the EHE. The CIRCE bubbling fluidized bed pilot plant presents the adequate bubbling working regime to obtain results of heat transfer coefficient for a wide range of oxy-fuel conditions and extracting further conclusions on possible effects of gas composition on heat transfer coefficients. The range of O2 concentration at inlet reached values as high as 60%. Such a high concentration was scarcely achieved in pilot plants due, in most cases, to the limiting bed cooling capacity. Measurements of heat transfer coefficients were taken when cooling was needed to control the combustion temperature. Water could circulate through one or more of the four cooling jackets, depending on the cooling requirements. Heat transfer coefficients were indirectly measured by energy balance with the water mass flow and temperatures. There are no previous results on heat transfer measurements under oxy-fuel combustion, up to date. The pilot plant is characterized by two important performance parameters: the fluidizing velocity and the bed temperature. These two parameters are common for all the fluidized bed plants working on combustion. Particularly for characterizing oxy-fuel combustion, the composition of the oxidant gas is the other key parameter in the plant operation. These three factors have been analyzed and their influence on heat transfer was examined. The three of them are, however, interrelated. O2 concentration and bed temperature varied the gas density and thus, the fluidizing velocity. At the same time, the fluidizing velocity will affect the heat transfer coefficients and consequently, bed temperature would be influenced. For accounting for this kind of dependences, non-dimensional numbers have been used for comparison. It was detected no dominant effect of non-dimensional numbers on the heat transfer. This is mainly offset by the different fluidization velocities in AF and OF operation. In the former, uf was kept over 1 m/s, whereas OF required lower velocities, around 0.9 m/s. It was then determined the adequate semi-empirical correlations for the effective thermal conductivity and the residence time of particles at the heat transfer surface. Hence, a semi-empirical mechanistic approach is recommended for a good agreement with the experimental heat transfer coefficients obtained during oxy-fuel operation. It was demonstrated the relevance of the gaseous film resistance in the oxy-fuel tests, and a new empirical coefficient was deduced for both modes. As examined in Chapter 3, section 3.5, the recommended expressions to predict heat transfer coefficients during oxy-fuel combustion modified the thermal film resistance, fitting the empirical parameter M with experimental data. Where: M=6.51 for oxy-firing and M=11.33 for air-firing The larger amount of solids arriving at the EHE will influence the values and distribution of the average and local heat transfer coefficients, respectively. A review of the difficulties associated with the estimation of heat transfer to the tubes of a heat exchanger has been examined. By the use of a scaled-down EHE, it was possible to experimentally confirm the influence of heat transfer coefficients when horizontal movement of solids took place. The increase of solids rate stressed the inequalities of the local heat transfer coefficient, whereas the longer residence time taken by particles to travel through the EHE allows higher average heat transfer coefficient. The contribution of this parameter to the average heat transfer coefficient was correlated by means of a new expression, as developed in Chapter 4, section 4.4. This expression allows modifying the heat transfer coefficient previously deduced for stationary conditions, and therefore, accounting for the enhancement of heat transfer when recirculation of solids takes place. A real design of an EHE was then simulated and integrated in the existing CFB model previously developed. This is the first time that such a model is developed to predict the heat transfer area required in oxy-fuel operation. The EHE sub-model must fulfill the energy balance requirements previously set for the CFB model. The temperature, at which solids must be recycled back into the boiler, in order to keep the desired boiler temperature, is accomplished with this sub-model. The expressions for the heat transfer coefficient and the enhancement due to recycled mass flow of solids were included in the EHE sub-model. Hence, it was possible to determine the increase on the heat transfer surface, for different O2 concentration in the oxidant stream, and two ranges of boiler temperature required. It was then recognized that, in spite of doubling the heat transfer surface requirements, when O2 concentration increased 10%, the heat transfer surface increases less than expected if solids flow influence were not included in the heat transfer evaluation. This thesis demonstrates that heat transfer surface design, arrangement and allocation, will differ in future oxy-fuel CFB boilers. Particularly, the heat transfer in the EHE will need address the influence of fluidizing gas composition and recycled solids, for an adequate and efficient heat exchanger configuration

Best Available Techniques (BAT) Reference Document for Large Combustion Plants. Industrial Emissions Directive 2010/75/EU (Integrated Pollution Prevention and Control)

The BAT Reference Document (BREF) for Large Combustion Plants is part of a series of documents presenting the results of an exchange of information between the EU Member States, the industries concerned, non-governmental organisations promoting environmental protection, and the Commission, to draw up, review, and -where necessary- update BAT reference documents as required by Article 13(1) of Directive 2010/75/EU on Industrial Emissions. This document is published by the European Commission pursuant to Article 13(6) of the Directive. This BREF for Large Combustion Plants concerns the following activities specified in Annex I to Directive 2010/75/EU: - 1.1: Combustion of fuels in installations with a total rated thermal input of 50 MW or more, only when this activity takes place in combustion plants with a total rated thermal input of 50 MW or more. - 1.4: Gasification of coal or other fuels in installations with a total rated thermal input of 20 MW or more, only when this activity is directly associated to a combustion plant. - 5.2: Disposal or recovery of waste in waste co-incineration plants for non-hazardous waste with a capacity exceeding 3 tonnes per hour or for hazardous waste with a capacity exceeding 10 tonnes per day, only when this activity takes place in combustion plants covered under 1.1 above. In particular, this document covers upstream and downstream activities directly associated with the aforementioned activities including the emission prevention and control techniques applied. The fuels considered in this document are any solid, liquid and/or gaseous combustible material including: - solid fuels (e.g. coal, lignite, peat); - biomass (as defined in Article 3(31) of Directive 2010/75/EU); - liquid fuels (e.g. heavy fuel oil and gas oil); - gaseous fuels (e.g. natural gas, hydrogen-containing gas and syngas); - industry-specific fuels (e.g. by-products from the chemical and iron and steel industries); - waste except mixed municipal waste as defined in Article 3(39) and except other waste listed in Article 42(2)(a)(ii) and (iii) of Directive 2010/75/EU. Important issues for the implementation of Directive 2010/75/EU in the Large Combustion Plants sector are the emissions to air of nitrogen oxides, sulphur dioxide, hydrogen chloride and fluoride, organic compounds, dust, and metals including mercury; emissions to water resulting especially from the use of wet abatement techniques for the removal of sulphur dioxide from the flue gases; resource efficiency and especially energy efficiency. This BREF contains 12 Chapters. Chapters 1 and 2 provide general information on the Large Combustion Plants industrial sector and on the industrial processes used within this sector. Chapter 3 provides data and general information concerning the environmental performance of installations within the sector in terms of water consumption, the generation of waste and general techniques used within this sector. It also describes in more detail the general techniques to prevent or, where this is not practicable, to reduce the environmental impact of installations in this sector that were considered in determining the BAT. Chapters 4 to 9 provide the following information given below on specific combustion processes (gasification, combustion of solid fuel, combustion of liquid fuel, combustion of gaseous fuel, multi-fuel combustion and waste co-incineration). Chapter 10 presents the BAT conclusions as defined in Article 3(12) of the Directive. Chapter 11 presents information on 'emerging techniques' as defined in Article 3(14) of the Directive. Concluding remarks and recommendations for future work are presented in Chapter 12.JRC.B.5-Circular Economy and Industrial Leadershi

Identification of atmospheric pollutants control mechanisms during co-combustion of coal and non-toxic wastes

Doctoral dissertation for Ph.D. degree in Sustainable Chemistr

Advances in Theoretical and Computational Energy Optimization Processes

The paradigm in the design of all human activity that requires energy for its development must change from the past. We must change the processes of product manufacturing and functional services. This is necessary in order to mitigate the ecological footprint of man on the Earth, which cannot be considered as a resource with infinite capacities. To do this, every single process must be analyzed and modified, with the aim of decarbonising each production sector. This collection of articles has been assembled to provide ideas and new broad-spectrum contributions for these purposes

Online Laser Diagnostics for High-Temperature Chemistry in Biomass Combustion

Increasing concern over environment and new energy policies are driving the thermal heat and power industry towards new CO2 neutral fuels, such as biomass, and novel combustion schemes. Therefore new operational control and monitoring concepts are required to provide information of the combustion processes. Alkali elements and compounds have been identified to be one of the greatest challenges associated with thermal conversion of biomass as they cause severe operational problems in power plant boilers. In this Thesis, a new method to monitor temperature and O2 concentration during thermal conversion of biomass is developed. Collinear Photofragmentation and Atomic Absorption Spectroscopy (CPFAAS) is utilized to measure potassium reaction kinetics in lean combustion conditions, which provides valuable information for high temperature reaction models and simulations. The new information on potassium reaction kinetics with O2 enables online monitoring of temperature and O2 concentration utilizing the CPFAAS signal.Microwave-Assisted Laser-Induced Breakdown Spectroscopy (MW-LIBS) is demonstrated for the first time at ambient atmospheric conditions with impressive 93fold enhancement in limit of detection (LOD). MW-LIBS is further applied for online elemental monitoring during thermal conversion of biomass fuels as it improves detection of trace elements and reduces adverse self-absorption effects in high-concentration conditions. To enable the benefits of MW-LIBS, a novel burner for flame calibration is introduced. The burner allows calibration of LIBS for extended concentration range enabling quantitative elemental release monitoring during thermal conversion of different biomass fuels with varying elemental content. The elemental release behavior of biomass fuels is paramount for thermal conversion models and simulations that provide boiler operators and manufacturers crucial information on how to optimize the thermal processes and mitigate the alkali associated problems. Furthermore, as the novel MW-LIBS approach requires no or minimal sample preparation, it has great application potential for online elemental monitoring in different fields of science where low LOD or high sensitivity is required.The novel CPFAAS and MW-LIBS approaches provide simple and versatile methods for online high-temperature chemistry monitoring from laboratory-scale systems up to full-scale power plant boilers. Laser diagnostics will play a significant role in optimization and in process control of future thermal power generation as it enables development of online sensor networks to monitor and forecast the plant behavior

Online Laser Diagnostics for High-Temperature Chemistry in Biomass Combustion

Increasing concern over environment and new energy policies are driving the thermal heat and power industry towards new CO2 neutral fuels, such as biomass, and novel combustion schemes. Therefore new operational control and monitoring concepts are required to provide information of the combustion processes. Alkali elements and compounds have been identified to be one of the greatest challenges associated with thermal conversion of biomass as they cause severe operational problems in power plant boilers. In this Thesis, a new method to monitor temperature and O2 concentration during thermal conversion of biomass is developed. Collinear Photofragmentation and Atomic Absorption Spectroscopy (CPFAAS) is utilized to measure potassium reaction kinetics in lean combustion conditions, which provides valuable information for high temperature reaction models and simulations. The new information on potassium reaction kinetics with O2 enables online monitoring of temperature and O2 concentration utilizing the CPFAAS signal.Microwave-Assisted Laser-Induced Breakdown Spectroscopy (MW-LIBS) is demonstrated for the first time at ambient atmospheric conditions with impressive 93fold enhancement in limit of detection (LOD). MW-LIBS is further applied for online elemental monitoring during thermal conversion of biomass fuels as it improves detection of trace elements and reduces adverse self-absorption effects in high-concentration conditions. To enable the benefits of MW-LIBS, a novel burner for flame calibration is introduced. The burner allows calibration of LIBS for extended concentration range enabling quantitative elemental release monitoring during thermal conversion of different biomass fuels with varying elemental content. The elemental release behavior of biomass fuels is paramount for thermal conversion models and simulations that provide boiler operators and manufacturers crucial information on how to optimize the thermal processes and mitigate the alkali associated problems. Furthermore, as the novel MW-LIBS approach requires no or minimal sample preparation, it has great application potential for online elemental monitoring in different fields of science where low LOD or high sensitivity is required.The novel CPFAAS and MW-LIBS approaches provide simple and versatile methods for online high-temperature chemistry monitoring from laboratory-scale systems up to full-scale power plant boilers. Laser diagnostics will play a significant role in optimization and in process control of future thermal power generation as it enables development of online sensor networks to monitor and forecast the plant behavior

Online Laser Diagnostics for High-Temperature Chemistry in Biomass Combustion

Increasing concern over environment and new energy policies are driving the thermal heat and power industry towards new CO2 neutral fuels, such as biomass, and novel combustion schemes. Therefore new operational control and monitoring concepts are required to provide information of the combustion processes. Alkali elements and compounds have been identified to be one of the greatest challenges associated with thermal conversion of biomass as they cause severe operational problems in power plant boilers. In this Thesis, a new method to monitor temperature and O2 concentration during thermal conversion of biomass is developed. Collinear Photofragmentation and Atomic Absorption Spectroscopy (CPFAAS) is utilized to measure potassium reaction kinetics in lean combustion conditions, which provides valuable information for high temperature reaction models and simulations. The new information on potassium reaction kinetics with O2 enables online monitoring of temperature and O2 concentration utilizing the CPFAAS signal.Microwave-Assisted Laser-Induced Breakdown Spectroscopy (MW-LIBS) is demonstrated for the first time at ambient atmospheric conditions with impressive 93fold enhancement in limit of detection (LOD). MW-LIBS is further applied for online elemental monitoring during thermal conversion of biomass fuels as it improves detection of trace elements and reduces adverse self-absorption effects in high-concentration conditions. To enable the benefits of MW-LIBS, a novel burner for flame calibration is introduced. The burner allows calibration of LIBS for extended concentration range enabling quantitative elemental release monitoring during thermal conversion of different biomass fuels with varying elemental content. The elemental release behavior of biomass fuels is paramount for thermal conversion models and simulations that provide boiler operators and manufacturers crucial information on how to optimize the thermal processes and mitigate the alkali associated problems. Furthermore, as the novel MW-LIBS approach requires no or minimal sample preparation, it has great application potential for online elemental monitoring in different fields of science where low LOD or high sensitivity is required.The novel CPFAAS and MW-LIBS approaches provide simple and versatile methods for online high-temperature chemistry monitoring from laboratory-scale systems up to full-scale power plant boilers. Laser diagnostics will play a significant role in optimization and in process control of future thermal power generation as it enables development of online sensor networks to monitor and forecast the plant behavior

Online Laser Diagnostics for High-Temperature Chemistry in Biomass Combustion

Increasing concern over environment and new energy policies are driving the thermal heat and power industry towards new CO2 neutral fuels, such as biomass, and novel combustion schemes. Therefore new operational control and monitoring concepts are required to provide information of the combustion processes. Alkali elements and compounds have been identified to be one of the greatest challenges associated with thermal conversion of biomass as they cause severe operational problems in power plant boilers. In this Thesis, a new method to monitor temperature and O2 concentration during thermal conversion of biomass is developed. Collinear Photofragmentation and Atomic Absorption Spectroscopy (CPFAAS) is utilized to measure potassium reaction kinetics in lean combustion conditions, which provides valuable information for high temperature reaction models and simulations. The new information on potassium reaction kinetics with O2 enables online monitoring of temperature and O2 concentration utilizing the CPFAAS signal.Microwave-Assisted Laser-Induced Breakdown Spectroscopy (MW-LIBS) is demonstrated for the first time at ambient atmospheric conditions with impressive 93fold enhancement in limit of detection (LOD). MW-LIBS is further applied for online elemental monitoring during thermal conversion of biomass fuels as it improves detection of trace elements and reduces adverse self-absorption effects in high-concentration conditions. To enable the benefits of MW-LIBS, a novel burner for flame calibration is introduced. The burner allows calibration of LIBS for extended concentration range enabling quantitative elemental release monitoring during thermal conversion of different biomass fuels with varying elemental content. The elemental release behavior of biomass fuels is paramount for thermal conversion models and simulations that provide boiler operators and manufacturers crucial information on how to optimize the thermal processes and mitigate the alkali associated problems. Furthermore, as the novel MW-LIBS approach requires no or minimal sample preparation, it has great application potential for online elemental monitoring in different fields of science where low LOD or high sensitivity is required.The novel CPFAAS and MW-LIBS approaches provide simple and versatile methods for online high-temperature chemistry monitoring from laboratory-scale systems up to full-scale power plant boilers. Laser diagnostics will play a significant role in optimization and in process control of future thermal power generation as it enables development of online sensor networks to monitor and forecast the plant behavior

ECOS 2012

The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology

XVIII International Coal Preparation Congress

Changes in economic and market conditions of mineral raw materials in recent years have greatly increased demands on the ef fi ciency of mining production. This is certainly true of the coal industry. World coal consumption is growing faster than other types of fuel and in the past year it exceeded 7.6 billion tons. Coal extraction and processing technology are continuously evolving, becoming more economical and environmentally friendly. “ Clean coal ” technology is becoming increasingly popular. Coal chemistry, production of new materials and pharmacology are now added to the traditional use areas — power industry and metallurgy. The leading role in the development of new areas of coal use belongs to preparation technology and advanced coal processing. Hi-tech modern technology and the increasing interna- tional demand for its effectiveness and ef fi ciency put completely new goals for the University. Our main task is to develop a new generation of workforce capacity and research in line with global trends in the development of science and technology to address critical industry issues. Today Russia, like the rest of the world faces rapid and profound changes affecting all spheres of life. The de fi ning feature of modern era has been a rapid development of high technology, intellectual capital being its main asset and resource. The dynamics of scienti fi c and technological development requires acti- vation of University research activities. The University must be a generator of ideas to meet the needs of the economy and national development. Due to the high intellectual potential, University expert mission becomes more and more called for and is capable of providing professional assessment and building science-based predictions in various fi elds. Coal industry, as well as the whole fuel and energy sector of the global economy is growing fast. Global multinational energy companies are less likely to be under state in fl uence and will soon become the main mechanism for the rapid spread of technologies based on new knowledge. Mineral resources will have an even greater impact on the stability of the economies of many countries. Current progress in the technology of coal-based gas synthesis is not just a change in the traditional energy markets, but the emergence of new products of direct consumption, obtained from coal, such as synthetic fuels, chemicals and agrochemical products. All this requires a revision of the value of coal in the modern world economy