The combustion of CO 2 neutral solid fuels like biomass and waste-based fuels with circulating fluidized bed (CFB) boiler designs has become an accepted way to generate electric power and process steam to reduce global CO 2 emissions (i.e. reduce “carbon footprint”) and hence to reduce the potential impact on climate change. In the European Union, for example, there is a co-combustion directive to encourage the use of biomass and waste as energy sources with the co-firing of coal. Quite often biomass and waste combustion in CFB’s have unique technical challenges when compared to fossil fuels. The technical challenges of firing these CO 2 neutral fuels do impact CFB boiler design and may impact plant lifecycle and reliability when compared to coal. Among these are combustion bed agglomeration, furnace and heating surface slagging, and new forms of corrosion potential. However, when co-firing these CO 2 neutral fuels with coal, these challenges can be tempered in a positive way through inherent changes in the flue gas chemistry and other design considerations. Co-firing makes sense. In addition to reducing the carbon footprint of a boiler project through use of biomass and waste, these energy sources can have a significant positive impact on plant financials owing to low cost supply. However these fuels can have wide variations in availability and energy content over the course of the many years of a boiler’s life. As such, maintaining coal as a supplemental fuel or back-up fuel also provides significant benefit in terms of guaranteeing the energy input supply and thereby securing plant availability. This benefit can help lower project financial risk and improve financial attractiveness and viability. This paper describes this type of boiler, its design considerations and operating history. Highlighted herein is the operating facility in Pori, Finland, commissioned in 2008, which is a 60 MWe CFB boiler burning peat, biomass and recycled waste fuel (RDF) with coal as a back-up fuel. Other facilities with similar design and with operating history of over 10 years are included as reference.

The aim of this paper is to study the effect of flow conditions on nanoparticle fraction suspending in base fluid, using water-based TiO 2 nanofluids under laminar flow conditions as an example. With the same initial concentration of nanoparticle (about 0.5% mass fraction), significant deterioration of stability is observed and the deterioration depends on the flow conditions (Reynolds number 500–2000, circulating time). The nanoparticle fraction in nanofluids flowing through bend tube with multi elbows is obviously lower than straight tube with fewer elbows, especially for that at higher Reynolds number. After 8 h, compared with the initial concentration (about 0.5% mass fraction), the relative concentration of nanofluids is 71.5% and 68.5% at Re = 500, for straight tube and bend tube, respectively. Whereas, that is 96.9% and 89.3% at Re = 2000 for straight tube and bend tube, respectively. Sample of nanoparticles in base fluid flowing through bend tube obviously appears the agglomeration (shown in TEM images), larger particle size (measured by laser particle size analyzer) compared with that flowing through straight tube. Moreover, the precipitation of particles can be apparently observed at the out curvature of elbows. These results imply that higher nanoparticle fraction can be maintained for nanofluids at higher Reynolds number and fewer elbows. It maybe helpful for better understanding heat transfer behavior of nanofluids.

Varnish deposits on metal surfaces in turbine lube system results in a number of adverse operational issues, especially the restriction and sticking of moving mechanical parts such as servo or directional control valves. The oil has limited solvency for the material, hence a typical turbine will have the majority of the material as deposits and a relatively small portion as suspended material in the oil phase in quasi-equilibrium with the deposits. The lube system needs to be cleaned by removing the suspended varnish precursors from the oil phase, which allows the deposits to re-entrain into the oil phase, until the majority of the transferable deposits from internal surfaces are removed and the oil carries no significant amount of the material to have any adverse effect. The methods used for the removal of varnish from turbine lube oil systems include chemical cleaning - flushing, and electrostatic charge induced agglomeration - retention and the adsorption of the oil suspended varnish on an adsorbent medium. The paper discusses an absorption based removal method that utilizes a fibrous medium that has pronounced affinity for the removal and retention of the varnish forming material from the oil and the deposits from surfaces that are in quasi-equilibrium with the varnish precursors in the oil. The filtration medium is composite cellulose with specially formulated, temperature cured binder resins. The absorptive medium that exhibits high structural and chemical integrity has been thoroughly tested on operating turbines, showing reduction in varnish levels from critical range to below normal range in a relatively short time. The experiences with the utilization of the absorptive medium in laboratory tests and in two operating turbines are presented.

Recent price increases for various forms of energy along with projected shortages of supply have resulted in renewed interest in alternative fuels. Biomass gasification provides a renewable basis for supplying electric power and also a broad suite of chemicals such as Fisher-Tropsch liquids as well as hydrogen. The Taylor gasification process, being developed by Taylor Biomass Energy is a biomass gasification process that produces a medium calorific value (MCV) gas. The Taylor gasification process provides improvements over currently available gasification processes by integrating improvements to reduce issues with ash agglomeration and provide in-situ destruction of condensable hydrocarbons (tars), an essential element in gas cleanup. The gas conditioning step integrated into the Taylor Gasification Process provides a unique method to convert the tars into additional synthesis gas and to adjust the composition of the synthesis gas. Taylor Biomass Energy has developed and refined a sorting and recycling process that can produce a clean feedstock for energy recovery from abundant residue materials such as construction and demolition residuals and municipal solid wastes (MSW). The sorting and separating process can then be coupled to the Taylor gasification process to produce clean, sustainable energy. The development process including integration with a gas turbine based combined cycle system, connection into the New York ISO, and identification of renewable energy credit options is discussed along with a discussion of the Taylor Gasification Process, its modular design, and implementation into the commercial Biomass Integrated Gasification Combined Cycle (BIGCC) system in Montgomery, NY.

Ash related operational problems are very common in biomass fired boilers. Biomass naturally contains both sodium chloride and potassium chloride and theses compounds lower the melting temperature of the ash which may cause large operational problems with agglomeration and defluidization in Circulating Fluidized Bed (CFB) boilers. The number of biomass fired CFB-boilers for combined heat and power (CHP) production in the Scandinavian market is growing due to their good combustion efficiency, fuel flexibility and low emissions. The power companies are asking for a method to calculate the internal and external circulation flows of solids in the boiler and an accurate diagnostic method to detect initial agglomeration in order to be able to prevent the problem of defluidization that leads to large costs and loss of revenue when the boiler has to be shut down for cleaning. Two heat and mass balance based models have been developed in order to calculate the fuel flow and the internal and external solids circulation flows in a CFB boiler with internal heat exchangers (INTREX). The solids circulation model is divided into three parts: cyclone, combustion and INTREX chambers. Measurements used in the calculation are from commissioning tests on CFB-boiler 5 at Ma¨larEnergi in Va¨stera˚s, Sweden. The boiler was manufactured by Foster Wheeler OY in Finland and has a thermal heat output of 157 MW. The external solids flow at 100% load, with and without air humidification, is 215 kg/s and the internal solids circulation is 93 kg/s. The external solids circulation flow at 60% load is 30 kg/s and the internal solids circulation flow is 486 kg/s. At 60% load, there is no data available for validation, which means that this is more an estimate then a calculation. The calculated internal flow of solids is very sensitive to changes in the total heat flow in the INTREX chamber caused by agglomeration or combustion, whereas the external solids flow is not affected. Hence initial agglomeration and combustion can be detected. A simulated agglomeration in the INTREX chambers by decreasing the total heat flow by 1%, led to a decrease in the internal solids circulation flow by 11%. A simulation of combustion in the INTREX chamber of 0.5 kg/s of fuel entering the chamber corresponds to an increase in the total heat flow of 22% and a decrease in the calculated internal mass flow of 16%. The potential for using this method of diagnostics for detecting initial agglomeration is very promising.

At present Flue Gas Desulphurization by Circulating Fluidized Bed (CFB FGD) has been widely used to partly take the place of the Spray Dry Absorbers (SDA) due to its simple system, excellent performance, occupying less area, and less cost, etc. It has been considered internationally as one of the most promising FGD technologies. The mechanism of FGD in CFB is introduced in the paper. Based on the mass transfer theory of two-phases, the fundaments of absorption and adsorption in CFB are analyzed. The influence of particle attrition on mass transfer coefficient of liquid phase is analyzed in terms of the special phenomenon in CFB. The result indicates that abrasion is beneficial to completely utilization of absorbents and further absorption, and it also has an inconspicuously enhanced effect on mass transfer. Fine particle agglomeration is analyzed in the paper and the study results show that the main course of FGD in CFB is absorbing process. Based on the gas absorption, the key parameters that influence desulphurization efficiency are analyzed finally. Mechanism study and influence factors analysis of FGD in CFB could be provided as the references for improving desulphurization.