Combustion of Waste in Pilot Scale Incinerators at the Research Centre
Karlsruhe
Matthieu Freyder, Hans-Georg Dittrich, Ulrike Santo, Stefan Bleckwehl, Michael Nolte, Mark Eberhard,
Thomas Kolb, Helmut Seifert
Research Center Karlsruhe GmbH, Institute for Technical Chemistry,
Thermal Waste Treatment Division,
PO Box 36 40, D-76021 Karlsruhe, Germany
Abstract
At the Research Centre Karlsruhe high temperature processes for waste treatment are a major research topic.
Research is done both experimentally from laboratory to pilot scale and also theoretically using various model
approaches for numerical simulations of transport processes, heterogeneous reactions in the fuel bed and the
burn-out of gaseous and solid phases. The main R&D objective is the optimisation of the processes with respect
to a high ecoefficiency.
Besides lab scale experimental equipment, the semi-technical pilot plants TAMARA (grate combustion) and
THERESA (rotary kiln combustion) are incineration plants for municipal solid and hazardous waste respectively
with a complete flue gas cleaning system, according to the German regulations (17. BImSchV).
TAMARA is a 1/100 scale of a grate furnace for municipal solid waste. The basic fuel burnt in it is municipal
solid waste. The heating value can be adjusted by addition of a higher heating value waste like refuse derived
fuel (RDF). Throughput of solid waste on the 3.2 meter long grate is between 150 and 300 kg/h. The 0,5 MW
boiler produces saturated steam at 5 to 30 bar.
THERESA is a rotary kiln/secondary combustion chamber pilot plant (scale 1/10) equipped with a boiler for heat
recovery and flue gas cleaning system. The waste to be treated covers an extremely wide spectrum of physical
and chemical properties, comprising gaseous, liquid, pasty and solid matter. The heating value ranges from highcalorific substances like organic solvents to inert materials like contaminated soil and even to fractions with a
negative calorific value, such as polluted waste water. Solid and sludge can be burnt in the rotary kiln (diameter
1,4 m length 8,4m), at temperatures up to 1200°C. In the secondary combustion chamber, liquid wastes and off
gases are injected through 2 atomization burners.
Keywords: Waste, Pilot, Combustion, Incineration, Gasification
1. Introduction
Despite all efforts of waste prevention and of closing material cycles by waste treatment, each year 165 million
tons of municipal solid waste (24 million t of which in Germany) as well as about 23 million t of hazardous
waste (5 million t of which in Germany) must be disposed of in Europe. Presently, about 70 % of municipal solid
waste (in Germany about 50 %) is still landfilled without treatment. Worldwide, particularly in countries of the
Third World, the shares are even higher. In the long run, such type of disposal involves a high risk potential for
man and environment through the contamination of soil and groundwater, and through an increase of the
greenhouse effect. Area contamination resulting from anthropogenic, especially industrial use and old disposal
sites represent a similar threat. Based on European and national legislative regulations, sustainable problem
solutions and technological procedures for waste management and area remediation, which reliably prevent any
aftercare, have to be developed.
With regard to waste, thermal processes with energy and material use are extremely suitable for achieving this
goal. The present paper brings up the strategy of the Research Centre Karlsruhe in the field of thermal waste
treatment. Technical means available at the Research Centre Karlsruhe as well as the research carried out will
also be presented.
2. Thermal waste Treatment at the Research Centre Karlsruhe
Forschungszentrum Karlsruhe is one of the biggest independent science and engineering research institution in
Germany. Its tasks are concentrated in five research areas: structure of matter, earth and environment, health,
energy and key technologies. As the next figure shows, the challenges of the ITC-TAB (Institute for Technical
Chemistry-Thermal Waste Treatment Division) are integral part of the Energy and the Earth and Environment
research programs of the Helmoltz-Association of National Research Centers.
ENERGY
mixed solid
W industrial
A
S construction /
T demolition
E
agricultural
gas treatment
particle technology
incineration
pyrolysis
gasification
silicatic
products
metals
organic
products
halogens
co-combustion /
combination with power plant
residues
P
R
O
D
U
C
T
S
salts
emissions
Figure 1. Research activities of the ITC-TAB
Research is focused on the R&D areas incineration and pyrolysis/gasification of wastes, as well as gas
treatment/particle technology. To take up the challenge, the problematic is tackled from the following angles:
high temperature
processes
pollutant formation control
transient processes
gas cleaning /
heat recovery
treatment
emission
aerosol
& health
integration of stages
memory effects
particle formation / particle size measurement
numerical simulation / process control
catalytic conversion
high temperature gas cleaning
residues to products
deposits / corrosion
residues to products
processes for contaminated sites
Figure 2. Technical Know-how of the ITC-TAB
The work in all areas benefits from the unique combination of experimental facilities ranging from laboratory
scale for basic research to semi-technical scale for application which are often complemented by tests in full
scale facilities. The pilot-plants as well as the research areas will be presented in the following chapters.
3. Pilot Scale Incinerators of the Research Centre Karlsruhe
3.1 Pilot Plant KLEAA
Experimental studies for investigation of the combustion behaviour of solid fuels were carried out in KLEAA, a
fixed bed reactor. The unit comprises three main components, i.e. the combustion chamber with a fixed bed and
a heated furnace, the afterburning chamber and the flue gas cleaning system consisting of a heat exchanger, a
filter chamber and a carbon adsorber. The fuel bed has a volume of 10 l. Compared to thermogravimetric
methods, where sample volumes in the gram range are applied, the fixed bed reactor KLEAA is suitable for the
investigation of technical fuels like municipal waste or RDF. The furnace and afterburning chamber can be
heated electrically up to a maximum temperature of 1100 °C. Primary air is supplied from below through a
sintered metal plate and can be pre-heated up to a maximum temperature of 300 °C. The major components of
the facility are represented schematically in Fig. 1.
The solid fuel is ignited by radiant heat from the furnace and burns down in opposite direction to the primary air
flow i.e. from top down. The concentrations of the main flue gas components CO2, CO, organic carbon, H2O,
and O2 are measured at three different measuring point right above the fuel. The temperatures are recorded at
several locations in the fuel bed and along the gas path. To measure the temporal reduction of the fuel mass a
Camera
load cell is placed under the fuel containing pot. 2 m above the fuel pot a camera is located for optical
monitoring.
Gas Sample
.
Gas Sample
.
VSA
VN
2
Heat Exchanger
T102
T101
Heated
(up to 1100°C)
Filter Chamber
T100
Gas Sample
T2
to
T12
T3
to
T13
Coal Adsorber
Blower
Fixed Bed
Sinter Metal Plate
.
Load Cell
VPA
Burning Chamber
Afterburning Chamber Flue Gas Cleaning
Figure 3. Schematic diagram of the fixed bed reactor KLEAA
Major research topics
The detailed combustion behaviour of various waste-based fuels and the influence of several operating
parameters (e.g. primary air amount, combustion chamber temperature, primary air temperature) and material
properties (e.g. fly ash and fixed carbon, heating value, water content) are investigated. In the described test
facility KLEAA, combustion characteristics will be determined from the characterization of the combustion
behaviour of heterogeneous technical fuels. Based on these parameters, the combustion behaviour of various
waste-based fuels will be assessed quantitatively in comparison to standard fossil fuels (e.g. coal). Moreover the
experimental studies shall serve as a basis to describe the combustion process of solid fuels in technical systems
like grate incinerator plants or biomass power plants. Finally by means of the study of the combustion behaviour
a mathematical model for the calculation of the combustion process will be build.
3.2 Pilot plant TAMARA
Since relevant research in the field of waste combustion cannot be performed in laboratory scale only, the
TAMARA test facility was built up and taken into operation in 1987. TAMARA is a German acronym and
stands for “test facility for waste combustion, flue gas cleaning, residue treatment and water purification”. It
models a grate combustion plant equipped with a flue gas cleaning line.
Stack
Boiler
Prequench
Quench
Scrubber 1 Scrubber 2
H2 O
SCR
Bag Filter
Waste
Ammonia
Liquor
pH<1
pH<1
pH=7
pH=7
Adsorber
Slag
Fly Ash
Air
H2O
NaOH
Preheater
Figure 4. Schematic diagram of the grate incineration pilot plant TAMARA
Combustion chamber
The fuel load ranges between 150 and 300 kg/h, maximum flue gas flow is 1000 Nm³/h. The maximum thermal
load is limited to 0,5 MW and steam is delivered at pressure between 5 an 30 bar. The advancing grate with a
length of 3200 mm and a width of 800 mm is divided into 4 primary air zones, for which the grate kinematics
and the residence time of the fuel respectively, is controlled independently. Secondary air is optional at 3
different levels above the combustion chamber via nozzles at each secondary air inlet. Raw and cleaned flue gas
can be recycled to all air ports.As geometry of the combustion chamber, a contra, centre and parallel flow
configuration may be chosen by installing variable roof elements. The walls are made of SiC.
The pilot plant is equipped with sensors which allow monitoring online parameters of the process like
temperature, pressure, gas flow rate, pH values or also concentration of the major constituents of the raw gas and
in the stack. Furthermore, openings in the combustion chamber and in the first post-combustion chamber path
allows to measure concentrations and temperatures on specific points by the use of appropriates lances.
The gas cleaning line is composed of a prequencher which enables to adjust the gas temperature to
approximately 180°C and prevent low-temperature formation of PCDD/F in the fabric filter. For the abatement
of acid gases and Hg a separate ceramic and two Venturi scrubbers are implemented: for improved Hg removal
the pH value of the scrubbing solution is kept <1, although the second scrubber is operated at pH=7 for SO 2
removal. At the end of the flue gas cleaning line, a Selective Catalytic Reduction reactor (SCR) removes NO x
from exhaust gas.
The Basic fuel burnt in TAMARA comprises a homogenized and sieved (<800mm) residential waste the heating
value of which can be adjusted by addition of a pelletized refuse derived fuel (RDF). The typical feed
composition of the fuel mix is well representing the today’s Central European municipal solid waste. The
feeding of the fuel is controlled by the central control system. Additional feeders for shredded, granular or fine
grained matter allow the co-feeding of various fuels and waste fractions such as wood chips, straw pellets, post
consumer mixed plastic waste, PVC, automotive shredder residues, electric and electronic (E+E) waste, textiles
or plastic foams.
Major research topics
TAMARA has proven to be a powerful tool for the research of waste combustion due to his high flexibility
concerning the adjustment of any parameters in the furnace as well as in the entire process chain following the
combustion. The combination with the engineering, chemical and analytical expertise of the Institute of
Technical Chemistry allows successful investigations into a wide range of research areas. The major objective of
all research is to close relationship to real life problems.
The present researches and developments focus on the study and the modelling of combustion behaviour of
heterogeneous solid fuels and on the study of unstationary combustion. Several works also target to reduce the
emission of different pollutants. In this way, many works are done on the reduction of NO x -emission by primary
measures and the reduction of trace-elements emission.
3.3 Pilot Plant THERESA
The ITC-TAB operates a modern rotary kiln test facility equipped with a boiler for heat recovery and a complete
flue gas cleaning system which complies with the German regulations of emissions (17. BImSchV). The pilot
plant THERESA provides the opportunity to work on different topics and problems from industry.
Fuel
Rotary
PostKiln
Combustion
Chamber
Waste
Heat
Boiler
Spray
Drier
SCR Stack
Flue Gas Scrubber
Scrubber 1 Scrubber 2 Catalyst
Fabric
Filter
H2O
Process Steam
40 bar, 250 °C
Air
Gas
Adsorbent
H2O
Steam
Liquid
Paste
Solid
Precipitating
Agent
Salts,
Flue Dust
Air
Loaded
Adsorbent
Induced
Draught
NaOH
Boiler Ash
Slag
Figure 5. Schematic diagram of the rotary kiln incineration pilot plant THERESA
The waste materials to be treated in THERESA cover an extremely broad spectrum of physical and chemical
properties, comprising gaseous, liquid, pasty and solid matter. Their heating value ranges from high-calorific
substances like organic solvents to inert materials. Combustibles are fed to the kiln through different inlets:
Chute for bulk materials of up to 40 mm grain size, combined burner for gases and liquids, atomizer lance for
liquids, transfer lock for barrels containing a maximum of 5l.
The revolution (0,1-2 rpm) and the inclination of the kiln (0,5-3°) cause the solid and pasty materials to travel
slowly downwards through the rotary kiln (Length 8,4 m, inside diameter 1,4m) as it is degasified, incinerated
and at the end discharged into the wet de-slagger system. Depending on the temperature in the rotary kiln (up to
1200°C), the combustion residues may be either solid or molten when discharged. The adjustment of the angle of
inclination and the revolution speed of the kiln controls the residence time of the solid waste in the rotary kiln.
The combustion gases from the rotary kiln are fed into the post combustion chamber which is equipped with two
combined burners for gases and liquids and an air nozzle for secondary combustion air. The burners are
staggered anti-parallel to each other. This configuration cares for high turbulence and, consequently, improved
mixing of the combustion gases. The post-combustion chamber is designed for gas temperatures up to 1300°C.
With the exception of barrels, all materials are fed continuously to the rotary kiln and the post-combustion
chamber. All partial flows are measured and recorded for mass balancing.
The hot flue gas leaving the post-combustion chamber enters the boiler and generates saturated steam of 40 bar
and 250°C.The complete gas cleaning line comprises a spray dryer, a fabric filter, two scrubbers and an SCR
reactor.
Major research topics
With the aid of in-situ measurements and control of the combustion process, CO-peaks realesed by barrel
combustion in rotary kilns can be significant reduced. This provides the opportunity to increase the capacity of
barrels in rotary kilns at constant high thermal outputs without emission problems.
The implementation of a measurement technique using inactive tracers (alkaline salts) enables to study the
residence time of the gas phase in the process. The evolution of concentration in alkali atoms during time is
followed by diode-laser or emission spectroscopy.
Furthermore, the combined-burners flame behaviour is studied by the use of digital video recording. Several
pictures of the flame are grabbed. After image processing, each frame can be analysed. Characteristic parameters
are then deduced from the fluctuations of the flame in different ranges of visible wave lengths.
3.4 Entrained Flow Gasifier
The electrically heated and top-down-fed vertical entrained flow gasifier was originally designed for combustion
of low-calorific liquid waste materials. It has been modified to operate particle containing fluids such as highdensity slurries. Length of the reactor is 3m, the inner diameter is 0.28m. The reactor is used under atmospheric
pressure at temperature up to 1600°C and provides 60kW thermal load. The maximum flue gas flow is
approximately 100 Nm³/h.
Slurries are prepared and stored in a tank, where they are mixed and recirculated in order to prevent decanting.
They are then injected into the reactor which can be operated at sub-stoichiometric conditions only in the upper
area of the combustion chamber, thanks to a staged air supply. The syngas is burnt in the combustion zone. The
gas is then treated in the gas cooling and cleaning part. For testing new burner nozzles for slurries, a vertically
movable burner unit is installed.
The process is monitored online and gasification can be investigated by using several types of analytical
equipment. Gas phase is analysed with standards techniques like IR, paramagnetic (oxygen) or FID
measurements. Laser Doppler anemometry and Prandtl tube are used to determine velocity field in the
combustion chamber. Tests of laser diode technique are planned for measurement of concentrations of particles
and temperatures.
Primary air /
oxygen
Natural gas
Slurry of
biomass
pyrolysis
Burner
(movable)
Inert gas
Gas analysis
Gasification
zone
Optical
Synthesis
gas
HT synthesis gas
conditioning +
synthesis
Flue gas
Water
Clean gas
measurements
Controlling
+
Data logging
Secondary air
+ Ignition burner
Combustion zone
Electrical heating
Flue gas
cooler
Combustion
Chamber
Flue gasscrubber
Activated carbon
adsorber
Slag
Figure 6. Schematic diagram of the entrained flow gasifier pilot plant
Major research topics
The main goal of our research is the study of the atomisation and ignition of slurries in vertical entrained flow
gasifiers. That way spray behaviour of slurries, as well as trajectories and velocity profiles are investigated. The
gasification process is also studied. Data from the process (like concentration or temperature profiles) are used
for to build and check numerical simulation models. Soon, a syngas converter has to be implemented in order to
work on conditioning and synthesis of high-temperature syngas.
3. Conclusion
At the Research Centre Karlsruhe, research is done both experimentally from laboratory to pilot scale and also
theoretically. The overall goals of our research work are:
- Protection of human health and environment through inertisation of wastes or residues,
- Pollutant destruction (e. g. organic materials) or separation (e. g. heavy metals),
- Preservation of resources through utilisation of residues,
- Substitution of fossil fuels,
- Climate protection through avoidance of organic emissions (e. g. methane, CFC),
- CO2-neutral energy use.
The most important challenge for all processes under investigation is improving economy (minimization of
costs) by sustaining the high ecological standards of modern high temperature waste treatment processes, i.e.
increase eco-efficiency.
References
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