Numerical Investigation of Oxy-mild Combustion of Pulverized Coal in a Pilot Furnace☆

Abstract The Conventional coal-fired plants are large contributors to air pollution and greenhouse gas. The combustion generates pollutants such as oxides of sulphur, nitrogen, and carbon as well as fine organic and inorganic particulates. The new technologies able to reduce drastically the pollutant emissions and facilitate to use of coal in an environmentally more friendly way, are commonly known as clean coal technologies (CCT). In this context the CCS technologies play an important role to reduce the CO 2 emissions. The only form with truly zero CO 2 emissions in existence today is pre-combustion gas separation, namely, the combustion of fuel using oxygen instead of air. It is well known that burning pulverized coal in pure oxygen increases the flame temperatures, thus also increases NO x emissions. Therefore, to moderate the flame temperature and reduce NO x the oxygen is mixed with recycled flue gas (RFG). This approach to reduce CO 2 emissions is often called oxy-firing or oxy-fuel combustion. The purified CO 2 stream is then compressed and condensed to produce a manageable effluent of liquid CO 2 , which can be sequestered for storage (CCS) or for use in subsequent processes (CCR). MILD (Moderate or Intensive Low Dilution) or HiTAC (High Temperature Air Combustion) is an innovative combustion technology and probably the most important achievement of the combustion technology in recent years. In MILD combustion the reactions take place in almost the whole volume of the combustion chamber. This leads to temperature and species concentration fields uniform in the chamber. The fuel is oxidized in an environment that contains a substantial amount of inert gases (N 2 , CO 2 , H 2 O) and low oxygen concentrations. This is caused by an internal recirculation of combustion products generated by injecting preheated air jets into the combustion chamber with very high momentum, bringing the temperatures close to the combustion products temperature, reducing the NO x emissions. Because both technologies allow reductions of pollutant emissions, the aim of this work is to demonstrate the advantages of a combination of these two combustion technologies in order to analyze the temperature and specie concentrations field, the CO 2 and NO x emissions by means of CFD. The goal is understand if it is possible to combine the MILD combustion and OXY one in order to reduce the NO x emissions, and capture the CO 2

a comparative energetic analysis of active and passive emission control systems adopting standard emission test cycles

The present work aims at analysing and comparing the thermal performances of active and passive aftertreatment systems. A one-dimensional transient model has been developed in order to evaluate the heat exchange between the solid and the exhaust gas and to estimate the energy effectiveness of the apparatus. Furthermore, the effect of the engine operating conditions on the performances of emission control systems has been investigated considering standard emission test cycles. The analysis has demonstrated that the active flow control presents the higher thermal inertia and it appears more suitable to maintain the converter initial temperature level for a longer time after variations in engine load. Conversely, the traditional passive flow control is preferable when rapid "cooling" or "heating" of the solid phase is requested. Moreover, the investigation has highlighted the significant influence of the cycle time and converter length on the energetic performances of the aftertreatment apparatus

A numerical analysis of energetic performances of active and passive aftertreatment systems

The present work aims to analyze the thermal and the energetic performances of an aftertreatment system with unidirectional and periodic reversal flow within the device. To this purpose a single-channel one-dimensional model was developed in order to assess the heat exchange between the aftertreatment system and the exhaust gas. Furthermore, the temperature profiles of the gas and solid phase were computed and the calculated temperatures were adopted to characterize the energy effectiveness of the aftertreatment system. The comparison between different control modes showed an increase in the heat retention efficiency of the system with reverse flow at low engine load conditions. Conversely, the system with passive thermal management presented higher temperatures of the monolith during the warm-up operations. Furthermore, the influence of unburned hydrocarbons oxidation on the effectiveness of the aftertreatment system was evaluated and the significant influence of the cycle time and the monolith length on the system performance was shown. Finally, the gas residence time was evaluated for different operating conditions. Copyright © 2008 John Wiley & Sons, Ltd

Using a Statistical-Numerical Procedure for the Selection of Pumps running as Turbines to be applied in Water Pipelines: Study Cases

A combined method using statistical and numerical models has been developed by the authors for selecting a pump running as turbine to be applied in micro-hydro plants. The data of the hydrological site chosen for the installation (head and capacity) allow the calculation of two conversion factors which identify the pump to use successfully as turbine in that place. Then, a one-dimensional model, starting from data available on the pumps manufacturers catalogues, reconstructs a virtual geometry of the pump running as turbine, and calculates the performances curves, head vs. capacity, efficiency vs. capacity, useful for identifying the operating point. Two study cases are presented to apply the proposed methodology, concerning the feasibility of the installation of a pump running as turbine in the purifier water plants of Casali and Sersale, located at 1,000 m above sea level (Calabria, South Italy).The assessment of the annual energy yield gives a confirmation of the effectiveness and convenience of using pumps running as turbines

The influence of rotary valve distribution systems on the energetic efficiency of regenerative thermal oxidizers (RTO)

On–off valve systems, commonly used in regenerative thermal oxidizer (RTO) plants, generate, during the opening time, a mass flow rate (MFR) which is constant. On the contrary, rotary valve systems, which are increasingly adopted in RTO plants, are characterized by variable MFR profiles. In this work, the energy requirements of two RTO systems, equipped with on–off or rotary valves, were determined using a home-developed numerical code. Energy performances were evaluated by calculating the thermal efficiency and pressure drop within structured or random packed bed RTO systems, at the same mean MFR. The results demonstrated that thermal efficiency was only moderately influenced by the valve system, and is slightly lower for the RTO with on–off valve. On the other hand, the study revealed that energy requirements of all RTO systems were basically unaffected by cycle duration, allowing valve rotational velocity to be freely set to maximize for other technical requirements. On the contrary, pressure drop was greatly influenced by the valve type and increased as variability in MFR function augmented. Moreover, the type of regenerator, structured or random packed bed, affected differently the total energy requirements (basically pumping energy plus auxiliary fuel). Energy requirements of structured and random regenerators were comparable only when volatile organic compounds concentration was lower than typical values encountered in the industrial practise. In other cases, structured regenerators RTO were more competitive. Finally, structured regenerators are usually the best choice when rotating valve distribution systems are adopted. Copyright © 2007 John Wiley & Sons, Ltd

Numerical Simulation of MILD (Moderate or Intense Low-Oxygen Dilution) Combustion of Coal in a Furnace with Different Coal Gun Positions

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innovative on shore system recovering energy from tidal currents

Abstract An innovative system for the recovering of energy from tidal currents is proposed. The system is composed of a blade submerged in sea waters and connected to a vertical bar which, moving up and down through the tide action, transfers energy to a double effect piston pump. The latter feeds a pressurized reservoir able to provide water flow rate, at a suitable pressure level, to a hydraulic turbine. The basic configuration involves a four-bar linkage connecting the vertical bar and the piston pump. The system can be easily employed in all those sites whose seabed quickly deepens and whose tidal currents are parallel to the coast. The proposed system is a valid alternative to the current tidal energy converters: its big dimensions are necessary to balance the low efficiencies of the overall energy conversion. At any rate, during the working the seabed is not altered, neither is the aquatic fauna damaged

Design and analysis of a new wave energy converter based on a point absorber and a hydraulic system harvesting energy from waves near the shore in calm seas

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hydraulic on shore system recovering energy from sea waves

Abstract The authors propose a new system for recovering energy from sea waves. The system is composed of a large-sized buoy (point absorber), directly connected to a piston pump. The piping, developed underground, allows the water to be moved into a pressurized reservoir, which feeds a hydraulic turbine. The latter discharges the flow in a tank where the hydraulic circuit closes. A sizing methodology developed in the present work, demonstrates the possibility of designing miniaturized components by leaving the possibility of providing an acceptable energy output with low installation costs. A preliminary study demonstrates that a 4.5 m buoy, associated with a small 17 cm diameter Pelton, could be able to recover more than 35,000 kWh/year

Using a Statistical-Numerical Procedure for the Selection of Pumps running as Turbines to be applied in Water Pipelines: Study Cases

A combined method using statistical and numerical models has been developed by the authors for selecting a pump running as turbine to be applied in micro-hydro plants. The data of the hydrological site chosen for the installation (head and capacity) allow the calculation of two conversion factors which identify the pump to use successfully as turbine in that place. Then, a one-dimensional model, starting from data available on the pumps manufacturers catalogues, reconstructs a virtual geometry of the pump running as turbine, and calculates the performances curves, head vs. capacity, efficiency vs. capacity, useful for identifying the operating point. Two study cases are presented to apply the proposed methodology, concerning the feasibility of the installation of a pump running as turbine in the purifier water plants of Casali and Sersale, located at 1,000 m above sea level (Calabria, South Italy).The assessment of the annual energy yield gives a confirmation of the effectiveness and convenience of using pumps running as turbines