Numerical and experimental study of ethanol combustion in an industrial gas turbine

The application of ethanol as a biomass-derived fuel in OPRA’s 2 MWe class OP16 radial gas turbine has been studied both numerically and experimentally. The main purpose of this work is to validate the numerical model for future work on biofuel combustion. For the experimental investigation a modified OP16 gas turbine combustor has been used. This reverse-flow tubular combustor is a diffusion type combustor that has been adjusted to be suitable for numerical validation. Two series of ethanol burning experiments have been conducted at atmospheric pressure with a thermal input ranging from 16 to 72 kW. Exhaust gas temperature and emissions (CO, CO2, O2, NOx) were measured at various fuel flow rates while keeping the air flow rate and air temperature constant. In addition, the temperature profile of the combustor liner has been determined by applying thermochromic paint. CFD simulations have been performed in Ansys Fluent for four different operating conditions considered in the experiments. The simulations are based on a 3D RANS code. Fuel droplets representing the fuel spray are tracked throughout the domain while they interact with the gas phase. A temperature profile based on measurements has been prescribed on the liner to account for heat transfer through the flame tube wall. Detailed combustion chemistry is included by using the steady laminar flamelet model. The predicted levels of CO2 and O2 in the exhaust gas are in good agreement with the experimental results. The calculated and measured exhaust gas temperatures show a close match for the low power condition, but more significant deviations are observed in the higher load cases. Also, the comparison pointed out that the CFD model needs to be improved regarding the prediction of the pollutants CO and NOx. Chemiluminescence of CH radicals in the flame front indicated that the flame extends up to the liner, suggesting the presence of fuel near the surface. However, this result was not confirmed by liner temperature measurements using thermochromic paint.</jats:p

Effect of char on the combustion process of multicomponent bio-fuel

Combustion of pyrolysis oil has attracted many attention in recent years as a renewable and environmental friendly fuel. However, pyrolysis oil as an multi-component fuel has some differences compared to conventional fossil fuels. One of the main differences is the formation of solid char in the droplet during evaporation. The goal of this work is to study the effect of the solid char on the combustion characteristics of multi-component fuel. An Euler-Lagrange model of three phase gas/liquid/solid combustion is developed to study the detailed information about every phenomena in the process such as: heat, mass and momentum transfer between droplet and gas phase, droplet evaporation, homogeneous and heterogeneous reactions. The results indicate that the presence of the solid char and consequently its combustion elongates significantly the combustion region in a typical spray injection chamber/burner. Moreover, the gas phase reaches higher temperatures as a result of char combustion that creates more heat by heterogeneous oxidation as a kind of afterburner

Characterization of viscous biofuel sprays using digital imaging in the near field region

The atomization of biodiesel, vegetable oil and glycerin has been studied in an atmospheric spray rig by using digital imaging (PDIA). Images of the spray were captured in the near field, just 18 mm downstream of the atomizer, and processed to automatically determine the size of both ligaments and droplets. The effect of the spray structure in this region is of major interest for the combustion of biofuels in gas turbines. The sprays were produced by a pressure-swirl atomizer that originates from the multifuel micro gas turbine (MMGT) setup. Various injection conditions have been tested to investigate the influence of viscosity on the spray characteristics and to assess the overall performance of the atomizer. The spray measurements have been compared to combustion experiments with biodiesel and vegetable oil in the micro gas turbine at similar injection conditions. The results show that the primary breakup process rapidly deteriorates when the viscosity is increased. A higher viscosity increases the breakup length, which becomes visible at the measurement location in the form of ligaments. This effect leads to an unacceptable spray quality once the viscosity slightly exceeds the typical range for conventional gas turbine fuels. The SMD in the investigated spray region was not significantly affected by viscosity, but mainly influenced by injection pressure. The data furthermore indicate an increase in SMD with surface tension. It was found that the penetration depth of ligaments can have major impact on the combustion process, and that the droplet size is not always the critical factor responsible for efficient combustion. The measured delay in primary breakup at increased viscosity shows that pressure-swirl atomization is unsuitable for the application of pure pyrolysis oil in an unmodified gas turbine engin

Techno-economic study of a zero-emission methanol based energy storage system

Within the scope of the energy transition an increasing share of intermittent renewable energy sources demand for grid balancing energy storage technologies, for which a novel zero-emission methanol based energy storage system is introduced. The objective is to establish the feasibility of this system as a grid balancing energy storage method, based on thermal efficiency and cost, at an input power of 50 MW el and boundary conditions that are set to reflect geographically independent operation. The main components are determined to be a PEM electrolyser followed by a recirculating catalytic synthesis reactor for methanol production. Alternatives for power generation are a transcritical carbon dioxide gas turbine (tCO2-GT), a supercritical carbon dioxide gas turbine (sCO2-GT) and a combination of methanol steam reforming and PEM fuel cell (MSR-PEMFC). Modelling of the entire system with respectively tCO2-GT, sCO2-GT and MSR-PEMFC for power generation leads to a system energy efficiency of 30.1%, 26.5% and 24.1%. Levelised cost of storage is estimated to be respectively 0.24 $/kWh, 0.25$/kWh and 0.34 $/kWh based on equipment cost estimations and factorial estimates, provisionally not taking into account the variable operational costs due to the extent of uncertainty in specifically catalyst type and degradation. Hence, based on these results the most efficient and cost effective system configuration is the tCO2-GT which can be competitive with hydrogen seasonal energy storage systems. sCO2-GT thermodynamic efficiency can be improved if cost effective solutions are found for temperature constraints. Furthermore, detailed elaboration of individual components and grid modelling of the system should lead to more accurate results and possibly increased thermodynamic performance. Concluding, when further elaborated the proposed system could be a practical solution to seasonal energy storage

The impact of spray quality on the combustion of a viscous biofuel in a micro gas turbine

The relation between spray quality and combustion performance in a micro gas turbine has been studied by burning a viscous biofuel at different fuel injection conditions. Emissions from the combustion of a viscous mixture of straight vegetable oils have been compared to reference measurements with diesel No. 2. The effect of fuel viscosity on pollutant emissions is determined by adjusting the injection temperature. The measurements confirm that a reduction in fuel viscosity improves the spray quality, resulting in faster droplet evaporation and more complete combustion. CO emission levels were observed to decrease linearly with viscosity in the tested range. For the pressure-swirl nozzle used in the tests, the upper viscosity limit is found to be 9 cP. Above this value, droplet evaporation seems to be incomplete as the exhaust gas contains a considerable amount of unburned fuel. Additionally, the influence of increased injection pressure and combustor temperature is evaluated by varying the load. Adding more load resulted in improved combustion when burning diesel. In case of vegetable oil, however, this trend is less consistent as the decrease in CO emissions is not observed over the full load range. The outcome of this study gives directions for the application of pyrolysis oil in gas turbines, a more advanced biofuel with high viscosit

Hydrothermal carbonization of wet biomass from nitrogen and phosphorus approach: A review

With increasing energy and resource consumption due to population growth, the biorefinery concept is becoming popular. This concept aims to harness all the properties of biomass by producing energy and recovering useful chemical products. Nutrients such as nitrogen and phosphorus play a key role in the world’s food production because they are the main elements used in fertilizer production. Hydrothermal carbonization (HTC) has been presented as a suitable option for energy recovery that can also be used as a pre-treatment for enhanced nutrient recovery. During the HTC process, part of the nitrogen and phosphorus are solubilized into the process water and the other part remains within the hydrochar. Hydrochars are mainly used as soil amendments due to their high content of phosphorus and nitrogen, but in this process, water still contains a considerable concentration of these compounds making it a potential source for their recovery. Therefore, HTC may boost the nutrient recovery strategy by extraction (process water) or densification (hydrochar) from biomass if it is coupled with another nutrient recovery process. This review presents an overview of the phosphorus and nitrogen fate during the HTC process from a perspective of nutrient recovery, presenting existing technologies and future trends

Experimental and numerical investigation of the application of fast pyrolysis oil in a gas turbine combustor

The growing demand for more economical and environmentally friendly power generation forces the industry to search for fuels that can replace conventional fossil fuels. Fast pyrolysis oil is an example of these alternative fuels. Pyrolysis of biomass is one of the most promising ways to directly generate liquid fuels from biomass. However, pyrolysis oil may have several major drawbacks which suppress its application. Within the ERA-NET EnCat project several aspects of pyrolysis oil comprising production processes, characterization as well as combustion in gas turbines and engines are approached. The present work focusses on the application of fast pyrolysis oil in a gas turbine. A combined numerical and experimental approach has been applied to a real scale gas turbine combustor for the OPRA OP16 gas turbine. This includes full scale combustor tests with various fuels and advanced CFD simulations. When operating on solely pyrolysis oil, it was found that stable operation could be achieved in the 30-100% load. Advanced char burnout simulations have been performed, which determined the optimal conditions for pyrolysis oil combustion. The newly developed NOx formation and pyrolysis oil combustion model show a good agreement with experimental data

Effect of char on the combustion process of multicomponent bio-fuel

Combustion of pyrolysis oil has attracted many attention in recent years as a renewable and environmental friendly fuel. However, pyrolysis oil as an multi-component fuel has some differences compared to conventional fossil fuels. One of the main differences is the formation of solid char in the droplet during evaporation. The goal of this work is to study the effect of the solid char on the combustion characteristics of multi-component fuel. An Euler-Lagrange model of three phase gas/liquid/solid combustion is developed to study the detailed information about every phenomena in the process such as: heat, mass and momentum transfer between droplet and gas phase, droplet evaporation, homogeneous and heterogeneous reactions. The results indicate that the presence of the solid char and consequently its combustion elongates significantly the combustion region in a typical spray injection chamber/burner. Moreover, the gas phase reaches higher temperatures as a result of char combustion that creates more heat by heterogeneous oxidation as a kind of afterburner