Application of analytical and CFD models of liquid fuels combustion in a fluidized bed

In Laboratory for Thermal Engineering and Energy of Institute Vinca, University of Belgrade, a 2-D CFD modeling procedure of numerical simulation of unconventional liquid fuel combustion in bubbling fluidized bed has been developed. This procedure is based on a two-fluid Euler-Euler approach modeling a fluidized bed with the determination of the velocities field of gas and particulates in two-phase, granular flows, analog to the kinetic theory of gases. This model describes in detail the unsteady motion of gas and solid phases, the formation and movement of bubbles with the combustion process in the fluidized bed, but temperature profiles calculated by the bed height differ to some extent from the experimentally obtained profiles. This discrepancy is probably due to the inability of a two-fluid CFD model to give a realistic simulation of the liquid fuel mixing in a fluidized bed. Therefore, an analytical model has been developed, where one of the basic assumptions is that the particles are mixed in the vertical direction of fluidized bed mainly by the bubble wakes. The proposed zonal type of calculating procedure is based on Davidson and Harrison two-phase model of the bubbling fluidized bed, where fluidized bed is divided into zones within which material and energy balances are set

Two-dimensional mathematical model of liquid fuel combustion in bubbling fluidized bed applied for a fluidized furnace numerical simulation

Lately, experimental methods and numerical simulations are equally employed for the purpose of developing incineration bubbling fluidized bed (BFB) facilities. The paper presents the results of the 2-D CFD model of liquid fuel combustion in BFB, applied for numerical simulation of a fluidized bed furnace. The numerical procedure is based on the two-fluid Euler-Euler approach, where the velocity field of the gas and particles are modeled in analogy to the kinetic gas theory. The proposed numerical model comprises energy equations for all three phases (gas, inert fluidized particles, and liquid fuel), as well as the transport equations of chemical components that are participating in the reactions of combustion and devolatilization. The model equations are solved applying a commercial CFD package, whereby the user submodels were developed for heterogenic fluidized bed combustion of liquid fuels and for interphase drag forces for all three phases. The results of temperature field calculation were compared with the experiments, carried out in-house, on a BFB pilot facility. The numerical experiments, based on the proposed mathematical model, have been used for the purposes of analyzing the impacts of various fuel flow rates, and fluidization numbers, on the combustion efficiency and on the temperature fields in the combustion zone

Three phase eulerian-granular model applied on numerical simulation of non-conventional liquid fuels combustion in a bubbling fluidized bed

The paper presents a 2-D CFD model of liquid fuel combustion in bubbling fluidized bed. The numerical procedure is based on the two-fluid Euler-Euler approach, where the velocity field of the gas and particles are modeled in analogy to the kinetic gas theory. The model is taking into account also the third liquid phase, as well as its interaction with the solid and gas phase. The proposed numerical model comprise energy equations for all three phases, as well as the transport equations of chemical components with source terms originated from the component conversion. In the frame of the proposed model, user sub-models were developed for heterogenic fluidized bed combustion of liquid fuels, with or without water. The results of the calculation were compared with experiments on a pilot-facility (power up to 100 kW), combusting, among other fuels, oil. The temperature profiles along the combustion chamber were compared for the two basic cases: combustion with or without water. On the basis of numerical experiments, influence of the fluid-dynamic characteristics of the fluidized bed on the combustion efficiency was analyzed, as well as the influence of the fuel characteristics (reactivity, water content) on the intensive combustion zone

Effect of axillary brachial plexus blockade on baroreflex-induced skin vasomotor responses: Assessing the effectiveness of sympathetic blockade

Background: The combination of laser Doppler flowmetry and non-invasive blood pressure monitoring allows the continuous observation of cutaneous vascular resistance (CVR). Continuous recording of unmodulated skin blood flow (SBF) is very sensitive to artefacts, rendering the method unreliable. In contrast, intermittent short lasting challenges of the CVR by cardiovascular autonomic reflexes may provide information about the responsiveness of the sympathetic nervous system in the skin. Methods: Eleven patients with below-wrist hand surgery (six males and five females; aged 35.2 ± 7.1 years) performed Valsalva maneuver following axillary blockade. Skin blood flow was continuously monitored on the forearm of the side axillary blockade, as well as on the contra-lateral forearm, which was used as the control. The responses were expressed as changes compared with the baseline level derived from a resting period of 30s. The maxima

Denitrification techniques for biomass combustion

In order to achieve the main Applicable combustion control systems in grate-fired bogoals of sustainable development through the harmonization of rising energy needs with environmental protection, modern society promotes the use of biomass as a renewable energy source. Biomass, like any taother fuel, emits certain pollutants from combustion, nitrogen oxides (NOx) being one of them. Control of NOx emission, originated in biomass combustion, is becoming a very significant technical challenge due to the imposition of increasingly strict emission limits. The experimental research and industrial experiences (that are not always easily available) were analyzed in order to make an overview of proven and prospective technical solutions, as well as directions for practical applications for reducing NOx emissions originating from biomass combustion. The denitrification techniques according to the broadest classification (pre-combustion, combustion control and post-combustion) have been analyzed. As the NOx emission is more strongly influenced by the nitrogen content of biomass fuels (especially of those with significant nitrogen content) rather than the operating conditions, the emphasis is placed on the post-combustion (secondary denitrification) measures and the most successful among them - selective catalytic (SCR) and non-catalytic reduction (SNCR). The SCR catalysts, as well as commonly used amine-based reagents (in both SCR and SNCR), are analyzed in accordance with various parameters (activity temperature domain, the location of installation and structural configuration). The special challenges for SCR and SNCR application were considered, and a comparative overview of advantages and disadvantages are given, in accordance with several different criteria. In addition, the applicability of deNOx techniques from the aspect of individual biomass combustion technology is given. Guidelines for the selection of denitrification measures are created, depending on the biomass combusted, combustion technology used, and the installation capacity

Capsaicin-sensitive mechanisms are involved in cortical spreading depression-associated cerebral blood flow changes in rats.

We tested the hypothesis that capsaicin-sensitive mechanisms play a role in the cortical spreading depression (CSD)-related changes in cortical blood flow (CBF). CBF was measured with laser Doppler flowmetry in anesthetized rats. The animals were treated with capsaicin before (48 h-2 weeks) or during the experiments. This agent is thought to stimulate small-diameter sensory nerve fibers selectively and to deplete stored peptides. In the vehicle-treated group (n=8), the peak value of the CSD-associated hyperperfusion was 257+/-12% above the baseline (mean+/-SEM, P<0.05). In the groups treated with 20 and 40 microg/kg or 20 mg/kg capsaicin, there were only small decreases in CBF. In the groups treated with 100 mg/kg capsaicin, the CSD-associated hyperemia was reduced at 48 h (158+/-7%, P<0.05). However, at 96 h a transient hyperresponsiveness (390+/-38%, P<0.05) was observed, which had disappeared by 2 weeks. These results indicate that the manipulation of sensory neuropeptide stores results in a biphasic effect on CSD-induced CBF responses

Hemodynamic effects of slow breathing: Does the pattern matter beyond the rate?

Purpose: Patterned breathing allows standardized serial measurements of heart rate variability and baroreflex indices. The slow breathing augments these parameters, and regular exercises, including yoga breathing practices with even respiratory rates have long-term beneficial effects in cardiovascular diseases. The role of temporization of breathing phases, i.e. the ratio of expiration to inspiration, is not known. In order to characterize the hemodynamic and autonomic responses during varying breathing phases 27 volunteers performed three short breathing sessions at 6/minutes frequency with 5:5, 3:7 and 7:3 inspiration expiration ratios. Results: The immediate responses in arterial pressure and heart rate were negligible. The time domain parameters of heart rate variability (SDRR, PNN50, RMSSD) increased significantly with patterned breathing. So did the spontaneous baroreflex gain of increasing sequences (up-BRS, from 12 ± 7 to 17 ± 10 ms/mmHg, p < 0.05), and the cross-spectral low frequency gain, the LF alpha (from 11 ± 7 to 15 ± 7 ms/mmHg, p < 0.05). None of these parameters differed significantly from each other while using any of tested inspiratory-expiratory patterns. Conclusion: The major determinant of autonomic responses induced by slow patterned breathing is the breathing rate itself. From our observations, it follows that slow breathing exercises performed either with diagnostic or therapeutic purpose could be simplified, allowing more extensive investigations. Keywords: non-invasive finger blood pressure monitoring, respiratory sinus arrhythmia, baroreflex sensitivity inde

Two-dimensional mathematical model of liquid fuel combustion in bubbling fluidized bed applied for a fluidized furnace numerical simulation

Lately, experimental methods and numerical simulations are equally employed for the purpose of developing incineration bubbling fluidized bed (BFB) facilities. The paper presents the results of the 2-D CFD model of liquid fuel combustion in BFB, applied for numerical simulation of a fluidized bed furnace. The numerical procedure is based on the two-fluid Euler-Euler approach, where the velocity field of the gas and particles are modeled in analogy to the kinetic gas theory. The proposed numerical model comprises energy equations for all three phases (gas, inert fluidized particles, and liquid fuel), as well as the transport equations of chemical components that are participating in the reactions of combustion and devolatilization. The model equations are solved applying a commercial CFD package, whereby the user submodels were developed for heterogenic fluidized bed combustion of liquid fuels and for interphase drag forces for all three phases. The results of temperature field calculation were compared with the experiments, carried out in-house, on a BFB pilot facility. The numerical experiments, based on the proposed mathematical model, have been used for the purposes of analyzing the impacts of various fuel flow rates, and fluidization numbers, on the combustion efficiency and on the temperature fields in the combustion zone. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR33042: Improvement of the industrial fluidized bed facility, in the scope of technology for energy efficient and environmentally feasible combustion of various waste materials in fluidized bed

Three phase Eulerian-granular model applied on numerical simulation of non-conventional liquid fuels combustion in a bubbling fluidized bed

The paper presents a two-dimensional CFD model of liquid fuel combustion in bubbling fluidized bed. The numerical procedure is based on the two-fluid Euler-Euler approach, where the velocity field of the gas and particles are modeled in analogy to the kinetic gas theory. The model is taking into account also the third - liquid phase, as well as its interaction with the solid and gas phase. The proposed numerical model comprise energy equations for all three phases, as well as the transport equations of chemical components with source terms originated from the component conversion. In the frame of the proposed model, user sub-models were developed for heterogenic fluidized bed combustion of liquid fuels, with or without water. The results of the calculation were compared with experiments on a pilot-facility (power up to 100 kW), combusting, among other fuels, oil. The temperature profiles along the combustion chamber were compared for the two basic cases: combustion with or without water. On the basis of numerical experiments, influence of the fluid-dynamic characteristics of the fluidized bed on the combustion efficiency was analyzed, as well as the influence of the fuel characteristics (reactivity, water content) on the intensive combustion zone. [Projekat Ministarstva nauke Republike Srbije, br. TR33042: Improvement of the industrial fluidized bed facility, in scope of technology for energy efficient and environmentally feasible combustion of various waste materials in fluidized bed