The LEAT has a wide range of experimental facilities for characterizing the transport and conversion behavior of solid energy carriers. These include, among others:
The reactor allows for the investigation of the thermochemical conversion of individual thermally thick particles with complex shapes fixed in space in a hot gas atmosphere (temperature and composition of the gas atmosphere can be varied, oxyfuel atmospheres are possible). Optical observation of the particle using two high-speed cameras arranged at a 90° angle allows for tracking the particle's conversion. From this, timescales for the conversion of volatile components and char burnout can be determined. The particle temperature is measured through ratio pyrometry. Oxygen concentration in the exhaust gas is determined in situ using a laser, with measurements taken at a rate of 1 Hz. The facility is used, for example, to investigate the conversion of refuse derived fuels, such as those used in the cement industry.
Contact: M.Sc. Robin Streier
To investigate the influence of operating conditions (temperature, gas atmospheres) on the thermochemical conversion of solid and liquid materials (powdered particles, droplets), an isothermal drop-tube reactor is available at the Chair of Energy Systems and Energy Process Engineering.
The reaction zone of the staged reactor consists of a vertically arranged cylindrical ceramic tube with an inner diameter of 150 mm and a total length of 2 meters. Fifty-six tangential silicon carbide heating elements ensure a uniform temperature within the reaction tube. To enable individualized heat supply to each zone, the heating elements are divided into six independent control zones. The maximum operating temperature is 1300°C. Depending on the gas flow rate, the residence time of the particles/droplets can be varied between 1 and 6 seconds. Sixteen measurement ports distributed along the height of the combustion chamber allow for the determination of gas concentrations and gas temperature.
Additionally, samples can be taken to assess, for example, the degree of conversion. Through these ports, secondary materials and additives can also be introduced.
The system offers solid dosing options via screw feeders or suitable atomizing nozzles for liquid materials. The composition of the gas atmosphere can be adjusted through the addition of hot or cold gases, two natural gas burners, or by introducing auxiliary gases.
The reactor design provides a one-dimensional plug flow with negligible radial gradients, as confirmed in previous investigations. Thus, there is a direct correlation between gas residence time and the distance from particle/droplet introduction. The following operating parameters can be varied:
Gas Analytics
Ten different process gas analyzers are used for measuring gas components. The system allows for the measurement of CO, CO2, CxHy, NH3, and HCN. The gas samples are extracted isokinetically from the combustion chambers using compressed-air-cooled probes.
Contact: B.Sc. Linus Pölling
The LEAT is equipped with a drop shaft which serves the aerodynamic characterization of refused derived solid fuels (RDF) using a camera-based method. RDF particles are transported via a conveyor belt to the top of the drop shaft and then fall individually through a pipe that provides an additional path to reach terminal velocity before entering the drop shaft. Inside the drop shaft, the particle trajectories are captured by two stereoscopically arranged cameras. By knowing the image capture rate, it is also possible to determine the settling velocities of the particles. Additionally, a photogrammetry station positioned upstream of the drop shaft creates 3D models of the particles, which are used to determine their frontal areas during the drop shaft experiments.
Using the determined frontal areas and settling velocities, frequency distributions of the drag and lift coefficients of the fuel are derived. These coefficients are then used in CFD simulations to model the flight and combustion behavior of RDF.
The walls of the drop shaft are painted black to ensure a high contrast between the illuminated particle and the background. The lighting system consists of 18 LED modules (104,400 lumens total light flux) and is installed at the top of the drop shaft. At the bottom, there is a drawer with slanted panels that guide the particles, after passing through the drop shaft, into the drawer and out of the camera's field of view. This is crucial to ensure that only one particle is captured per measurement series.
Two high-speed cameras from Baumer (VLXT-28 M.I, 500 fps at 1920 x 1080 px) are used to capture the measurement series. The distance between the cameras and the top of the drawer is 4.8 meters. The cross-sectional area inside the drop shaft is 0.83 m x 0.83 m.
Contact: M.Sc. Robin Streier
To investigate the influence of operating conditions and fuel properties on fuel conversion and the formation of harmful gases in circulating fluidized bed combustion, a pilot plant with a thermal capacity of 100 kW is available at the Chair of Energy Systems and Energy Process Engineering.
The total height of the combustion chamber is approximately 6 meters. Gas velocities in the combustion chamber range between 1.8 m/s and 2.5 m/s, allowing for residence times of up to 3 seconds.
The feed of materials such as coal, biomass, sewage sludge, quartz sand, and lime is carried out using calibrated screw feeders. An additional feeding system has been integrated to enable the introduction of difficult-to-dose materials, such as textile waste, into the combustion chamber. For dosing liquid fuels like heavy oil, the plant is equipped with a heated tank and an injection lance.
The combustion chamber temperature can be regulated by adjusting the cooling capacity of the heating surfaces immersed in the fluidized bed. Heating and maintaining the temperature of the combustion chamber is achieved via a natural gas ignition burner.
The supply of primary air, secondary air, and recirculated flue gas is managed separately by individual blowers and gas preheaters. These preheaters allow for the preheating of air or recirculated flue gas up to 430°C. Secondary air can be introduced to the combustion chamber at five different levels, with the flow rates independently controlled for each level. By mixing recirculated flue gas, substoichiometric conditions in the primary zone can be set without altering the fuel amount or the fluidization conditions.
Nineteen sampling ports are distributed along the combustion chamber for flue gas extraction. With flue gas analysis, concentrations of gases such as O2, CO2, CO, CXHY, H2, SO2, NOX, N2O, and NH3 can be measured across the entire height of the combustion chamber.
Combustion Parameters
To minimize pollutant emissions during combustion tests, the plant offers a wide range of independently adjustable combustion parameters. Specifically, the following parameters can be varied:
Contact: M.Sc. Christoph Yannakis
The LEAT operates a non-circulating fluidized bed for the investigation of the cyclic oxidation and reduction of iron ores.
The system has a capacity of approximately 5 kWh. The reactor is electrically heated (Tmax = 1200°C) and can be operated with oxidizing agents such as air, oxygen, and steam, as well as with inert gases or hydrogen (for iron ore reduction) to fluidize the bed material. The system is equipped with sensors for measuring temperature and gas composition, as well as provisions for sampling the bed material.
Contact: M. Sc. Christoph Yannakis
The flash pyrolysis reactor allows the study of the pyrolysis of solid organic dust-like materials, such as biomass.
Key features include:
Ansprechpartner: M.Sc. Erik Freisewinkel
The BORA experimental setup allows for the batch-mode investigation of the combustion of solid, biogenic fuels.
The raw fuel is placed onto a combustion plate, which is then moved into a combustion chamber made of quartz glass. Inside the chamber, the fuel is heated by radiant heat from the chamber's heated walls until it ignites. The system enables variation in air staging (primary and secondary air) as well as agitation of the fuel bed. Two of the three bottom elements of the combustion plate can be moved vertically to achieve this agitation.
During the experiments, gas phase composition and various temperatures are measured. Additionally, a continuous measurement of the fuel bed mass is conducted using a scale, allowing for the determination of the mass conversion rates of the fuel. The combustion process is also visually recorded using an IR camera and a video camera for further analysis.
Contact: M.Sc. Carl Hentschel
The fuel analysis includes proximate analysis, ultimate analysis, determination of calorific value, ash fusion behavior, and sieve analysis. For bed and fly ash samples, loss on ignition tests and occasionally elemental analyses are conducted. To ensure comparability, measurements are referenced to raw (raw), analysis-moist (an), dry (wf), and dry and ash-free (waf) states.
Proximate Analysis (Quick Analysis)
Proximate analysis involves determining the moisture content, ash content, and volatile matter of the fuel.
Moisture Content: Determined using the drying oven method according to DIN 51718. Initially, the surface moisture of the fuel sample is determined by drying it to a constant mass at (30 ± 2) °C (analysis-moist state). To determine the hygroscopic moisture, the sample is dried at (106 ± 2) °C for three hours, transitioning it to the dry state. Moisture content is calculated from the weight difference before and after drying.
Ash Content: Measured according to DIN 51719 in a muffle furnace. The fuel sample is heated in an oxidizing atmosphere, first to 500 °C and then to (815 ± 10) °C, where it is held for at least one hour. After cooling, the completely ashed sample is weighed, and the ash content is determined by the ratio of the dry sample's weight after and before combustion.
Volatile Matter: Determined according to DIN 51720 using a muffle furnace, where the fuel is coked for seven minutes at (900 ± 10) °C in a closed crucible. The weight loss, corrected for analysis moisture, represents the volatile matter content.
Fixed Carbon: Calculated as the difference between the original sample weight and the sum of volatile matter, moisture, and ash.
The analysis can also be performed using a thermogravimetric analysis system (LECO TGA-601), which automatically records and evaluates the change in sample mass as a function of temperature and time in different atmospheres, following corresponding DIN standards.
Ultimate Analysis
Ultimate analysis examines the elemental composition of solid fuels. The weight percentages of carbon, hydrogen, nitrogen, and sulfur are determined using an automatic elemental analyzer (LECO TrueSpec CHNS Micro), while the oxygen content is calculated by difference. The samples are completely combusted in pure oxygen, and the combustion products (CO2, SO2, H2O) are measured by infrared absorption. The N2 concentration is determined using a thermal conductivity detector after reducing nitrogen oxides to N2 via catalytic conversion. Five analyses are typically performed for each fuel sample.
Additional Fuel Analyses
Calorific Value: Measured in a bomb calorimeter (IKA Type C200) according to DIN 51900 under isoperibolic conditions. The fuel sample is combusted in a sealed vessel under a pure oxygen atmosphere at 30 bar pressure. The calorific value is calculated from the temperature rise of the system, sample weight, and the calorimeter system's heat capacity. The heating value is then derived by combining results from the elemental and proximate analyses.
Particle Size Distribution: Determined using a sieve analysis according to DIN 66165. A vibrating sieve machine (Haver, Type EML 200-80) is used for this purpose.
Loss on Ignition (LOI): Determined for ash samples by combustion at 815 °C, following DIN 51719, similar to the method used for ash content determination.
Ash Fusion Behavior: Analyzed using a Leitz heating microscope, according to DIN 51730. The sample is ashed per DIN 51719, and the resulting ash is pressed into a cylindrical shape. The ash cylinder is heated in an oxidizing atmosphere with a constant heating rate (3...10 K/min). The softening temperature (edges begin rounding), spherical temperature (sample takes a spherical shape), hemispherical temperature (base length is twice its height), and flow temperature (sample collapses to one-third of its original height) are determined.
The LEAT features an optically accessible laminar flow reactor.
Based on a non-premixed Hencken burner, the burner supplies the fuel gas (methane and acetylene) along with CO2 through 100 injection nozzles. The oxidant, a mixture of O2, CO2, and H2O, is introduced via a ceramic honeycomb (50 x 50 mm) with 400 square holes. This ceramic honeycomb positions the fuel nozzles and ensures homogeneous distribution of the oxidant mixture within the combustion chamber. The gas temperature can be measured using a Type S thermocouple with radiation correction.
The reactor uses dust-like particles as fuel, which react individually in the gas atmosphere. The reacting particles can be optically examined using various methods, allowing for the determination of particle size and shape, velocities, and temperature. Soot concentration around the particles can be measured using Laser-Induced Incandescence (LII). Additionally, samples can be collected after different particle reaction times (residence times) for further analysis.
Contact: M.Sc. David Tarlinski
The LEAT features an experimental setup for determining the spectral, normal emissivity of solid surfaces or powders.
The facility at the department consists of a Fourier-Transform Infrared Spectrometer (FT-IR) and an electrical heating unit. The heating unit includes the sample holder and a reference radiator, a blackbody. For the measurements, samples are placed on the sample holder positioned on the blackbody. The heating unit is connected to the FT-IR spectrometer via a gold-coated off-axis parabolic mirror. The temperature of the sample is determined using two Type-K thermocouples (0.25 mm diameter), which are installed 1 and 2 mm beneath the sample surface (along the central axis of the disc-shaped sample). The sample surface temperature is calculated by assuming a linear temperature profile over the height of the sample (the validity of this assumption has been verified by solving the 3D heat conduction equation within the sample).
For blackbody reference measurements, the sample holder is removed, and the blackbody is raised until its aperture is in the same position where the mineral sample was previously located. The reference radiator (blackbody) is designed as a cylindrical cavity radiator (cavity diameter 5 mm, cavity length 135 mm) with an emissivity > 0.9985. The temperature of the blackbody is determined using thermocouples.
Contact: M.Sc. Matthias Tyslik
The LEAT has a laboratory dedicated to investigating the transport and fracture behavior of wood pellets. This laboratory includes the following experimental setups and measurement devices:
Contact: M.Sc. Phil Spatz
The CO2 laser test bench at LEAT provides insights into particle formation from metal chloride droplets. Using an acoustic levitator, a field is created where droplets of an aqueous metal chloride solution, up to 1700 µm in diameter, can be levitated. These droplets are subjected to a CO2 laser with a wavelength of 10.6 µm and a power of up to 40 W, triggering a reaction. The water evaporates, and the metal chloride reacts to form a metal oxide. The diameter change during this process is optically measured, with recording rates of up to 40 Hz. The resulting images provide insights into the timescales of particle formation. This is a crucial factor in developing physico-chemical models for the spray roasting of metal chlorides.
Contact: B. Sc. Linus Pölling
Additional experimental facilities are available. For inquiries, please contact Mr. Dr. habil. M. Schiemann
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Last update: Sep 16, 2024
