A Small Scale Biomass Fueled Gas Turbine Engine

A new generation of small scale (less than 20 MWe) biomass fueled, power plants are being developed based on a gas turbine (Brayton cycle) prime mover. These power plants are expected to increase the efficiency and lower the cost of generating power from fuels such as wood. The new power plants are also expected to economically utilize annual plant growth materials (such as rice hulls, cotton gin trash, nut shells, and various straws, grasses, and animal manures) that are not normally considered as fuel for power plants. This paper summarizes the new power generation concept with emphasis on the engineering challenges presented by the gas turbine component.

Combustion Oscillation Analysis of Premixed Flames at Elevated Pressures

A new analytical time lag flame model based on Bloxidge’s flame model was introduced for calculating combustion oscillation of premixed flame to take into account the distribution of heat release rate and flame speed which was calculated by analytical formulas dependent on pressure, temperature, fuel-to-air ratio and velocity. The transfer matrix technique using the new flame model was applied to the calculation of acoustic resonance. To verify the model, combustion oscillation experiments were performed for methane-air premixed flames stabilized by a swirl burner at elevated pressures between 0.6–0.9MPa. Fluctuating pressure had the maximum peak at the specific value of fτf. Here f is the frequency of resonance and τf is the passing time of premixed gas through flame length. The analysis could simulate the dependency of fuel-to-air ratio and static pressure for dynamic pressure local peak.

An Empirical Approach to the Preliminary Design of a Closed Cycle Gas Turbine

This paper investigates the layout and achievable efficiencies of rotating components of a Helium gas turbine. This is done by making a preliminary design of the compressor and turbine needed for the power conversion in a combined heat and power plant with a 40 MWth nuclear high temperature reactor as a heat source. State of the art efficiency values of air breathing gas turbines are used for the first calculations. The efficiency level is corrected by comparing various dimensionless data of the Helium turbomachine with an air gas turbine of similar dimensions. A single shaft configuration with a high speed axial turbine will give highest performance and simple construction. If a generator has to be driven at a conventional speed, a free power turbine configuration must be chosen. The choice of the configuration depends among others on the cost and availability of the asynchrone generator and frequency convertor.

A Parametric Study of CHAT Cycle Performance: Thermodynamic and Design Features

The CHAT (Cascade Humid Air Turbine) cycle introduction has recently been proposed for a more simple and profitable application of the humid air turbine. The very interesting performance announced for this plant has been evaluated in this paper, particular attention is devoted to the multi-stage evaporation process and its thermodynamic limits. A detailed thermodynamic analysis of the most important cycle parameters, like various pressure levels, fire temperatures and blade coolant bleeding can permit the evaluation of better plant performances. The results show a substantial agreement with other published data and they confirm the good efficiency and high specific power of the CHAT cycle. Considering the proposed compressor and turbine for the CHAT plant an off design simulation of the plant is also realized to estimate the real behaviour of turbomachinery components. Moreover this study is based on ESMS code already developed by the authors and the new components model (thermodynamic, design and off-design simulation) introduced for this work are presented.

Biomass/Coal Derived Gas Utilization in a Gas Turbine Combustor

Low calorific value fuel gas, obtained by pressurized fluidized bed gasification of coal/biomass mixtures, is combusted at 0.8 MPa with air or oxygen in a vertical cylindrical chamber (D = 0.28 m, L = 2.0 m). The fuel (T = 1060 K) and oxydizer (air at 350 K, oxygen at 460 K) are injected coaxially, resulting in an essentially axissymmetric flow pattern. Particles have been removed from the fuel gas stream by a cyclone, mounted between the gasifier and the combustor. A two-dimensional model, implemented in the CFD code FLUENT was developed for the calculation of temperatures, flow patterns and species concentrations throughout the combustor. The calculated results are compared with experimental data for two low calorific value fuel gas compositions and two oxidizer compositions at two axial combustor locations (X/L = 0.175 and X/L = 1). The results appear to justify further investigation of the applicability of the model to low calorific value fuel gas fired gas turbine combustors.

Exergy Analysis of Two Second-Generation SCGT Plant Proposals

Two different power plant configurations based on a Semi-Closed Gas Turbine (SCGT) are analyzed and compared in terms of First and Second Law analysis. SCGT plant configurations allow the application of CO2 separation techniques to gas-turbine based plants and several further potential advantages with respect to present, open-cycle solutions. The first configuration is a second-generation SCGT/CC (Combined Cycle) plant, which includes inter-cooling (IC) between the two compression stages, achieved using spray injection of water condensed in a separation process removing vapor from the flue gases. The second configuration (SCGT/RE) combines compressor inter-cooling with the suppression of the heat recovery steam generator and of the whole bottoming cycle; the heat at gas turbine exhaust is directly used for gas turbine regeneration. The SCGT/CC-IC solution provides good efficiency (about 55%) and specific power output figures, on account of the spray inter-cooling; however, with this configuration the cycle is not able to self-sustain the CO2 removal reactions and amine regeneration process, and needs a substantial external heat input for this purpose. The SCGT/RE solution is mainly attractive from the environmental point of view: in fact, it combines the performance of an advanced gas turbine regenerative cycle (efficiency of about 49%) with the possibility of a self-sustained CO2 removal process. Moreover, the cycle configuration is simplified because the HRSG and the whole bottoming cycle are suppressed, and a potential is left for cogeneration of heat and power.

Effect of the Flame Dome Depth and Improvement of the Pressure Loss in the Dump Diffuser

This paper presents the effect of flame dome depth on the total pressure performance and flow behavior in a sudden expansion region of the combustor diffuser without flow entering the dome head. The mean velocity and turbulent Reynolds stress profiles in the sudden expansion region were measured by a Laser Doppler Velocitmetry (LDV) system. The experiments show that total pressure loss is increased, when flame dome depth is increased. Installation of an inclined combuster wall in the sudden expansion region is suggested from the viewpoint of a control of the reattaching flow. The inclined combustor wall is found to be effective in improvement of the diffuser performance. Better characteristics of the flow rate distribution into the branched channels are obtained in the inclined wall configuration, even if the distorted velocity profile is provided at the diffuser inlet.

Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven Oscillations

Lean premixed combustion has emerged as a method of achieving low pollutant emissions from gas turbines. A common problem of lean premixed combustion is combustion instability. As conditions inside lean premixed combustors approach the lean flammability limit, large pressure variations are encountered. As a consequence, certain desirable gas turbine operating regimes are not approachable. In minimizing these regimes, combustor designers must rely upon trial and error because combustion instabilities are not well understood (and thus difficult to model). When they occur, pressure oscillations in the combustor can induce fluctuations in fuel mole fraction that can augment the pressure oscillations (undesirable) or dampen the pressure oscillations (desirable). In this paper, we demonstrate a method for measuring the fuel mole fraction oscillations which occur in the premixing section during combustion instabilities produced in the combustor that is downstream of the premixer. The fuel mole fraction in the premixer is measured with kHz resolution by the absorption of light from a 3.39 μm He-Ne laser. A sudden expansion combustor is constructed to demonstrate this fuel mole fraction measurement technique. Under several operating conditions, we measure significant fuel mole fraction fluctuations that are caused by pressure oscillations in the combustion chamber. Since the fuel mole fraction is sampled continuously, a power spectrum is easily generated. The fuel mole fraction power spectrum clearly indicates fuel mole fraction fluctuation frequencies are the same as the pressure fluctuation frequencies under some operating conditions.

Recuperators in Gas Turbine Systems

The application of recuperators in advanced thermodynamic cycles is growing due to stronger demands of low emissions of pollutants and the necessity of improving the cycle efficiency of power plants to reduce the fuel consumption. This paper covers applications and types of heat exchangers used in gas turbine units. The trends of research and development are brought up and the future need for research and development is discussed. Material aspects are covered to some extent. Attempts to achieve compact heat exchangers for these applications are also discussed. With the increasing pressure ratio in the gas turbine cycle, large pressure differences between the hot and cold sides exist. This has to be accounted for. The applicability of CFD (Computational Fluid Dynamics) is discussed and a CFD–approach is presented for a specific recuperator. This recuperator has narrow wavy ducts with complex cross-sections and the hydraulic diameter is so small that laminar flow prevails. The thermal-hydraulic performance is of major concern.

A Comprehensive Model to Predict Simplex Atomizer Performance

The performance of liquid fuel atomizer has direct effects on combustion efficiency, pollutant emission and stability. Pressure swirl atomizer, or simplex atomizer, is widely used in liquid fuel combustion devices in aircraft and power generation industry. A computational, experimental, and theoretical study is conducted to predict its performance. The Arbitrary-Lagrangian-Eulerian method with finite volume scheme is employed in the CFD model. Internal flow characteristics of the simplex atomizer as well as its performance parameters such as discharge coefficient, spray angle and film thickness are predicted. A temporal linear stability analysis is performed for cylindrical liquid sheets under 3-D disturbance. The model incorporates swirling velocity component, finite film thickness and radius which are essential features of conical liquid sheets emanating from simplex atomizers. It is observed that the relative velocity between liquid and gas phase, density ratio and surface curvature enhance the interfacial aerodynamic instability. As Weber number and density ratio increase, both the wave growth rate and the unstable wave number range increase. Combination of axial and swirling velocity components is more effective than single axial component for disintegration of liquid sheet. A breakup model for conical liquid sheet is proposed. Combining the breakup model with linear stability analysis, mean drop sizes are predicted. The theoretical results are compared with measurement data and agreement is very good.