Biomass is a key resource in a future
sustainable energy supply. However,
many types of biomass are not easy to
convert into useful energy in terms of
power and heating.
There is a constant need for development of more efficient, reliable and
cost-effective technological solutions
for biomass-based energy plants.
New biomass technologies
A major challenge of biomass energy
plants is fouling and corrosion of the
gas cooler.
Dall Energy provides a new method
to cool and clean gases and recover
the heat from the cooled gases, which
overcomes the problems of fouling
and corrosion.
Dall Energy integrates a simple cooling technology “Evaporative Cooling”
into biomass energy plants. Evapo-
rative cooling is used within heavy
industry: cement and steel, where it
is necessary to cool and clean the gas
before it is led to the stack.
Dall Energy integrates air moisturizing into biomass energy plants. Several advantages are hereby achieved, e.g.
an increase in efficiency of 10-15%.
Patents are pending.
A full-scale demonstration project in
Denmark is being prepared.
Dall Energy
Dall Energy develops and implements
innovative solutions for biomassbased energy plants.
Dall Energy’s activities include combustion plants for heat production and
gasification plants for heat and power
production.
Dall Energy is a specialist company
with comprehensive theoretical and
practical expertise.
Dall Energy cooperates with universities, research institutes and industrial partners.
Evaporative cooling
Air moisturizing
In an evaporative cooler, fine droplets
of water are sprayed into the hot gas.
Due to the high evaporation energy
of water (2.2 MJ/kg), the gas is cooled
fast to 150-250°C.
In an air moisturizer, the air for
combustion or for gasification is
preheated and moisturized.
Air moisturizers result in several advantages: An increase in
thermal efficiency of 10-15% and
lower combustion/gasification
temperature, which means less
slagging and less NOx.
Strategic
partners:
Combustion plants
In standard biomass combustion
plants, the flue gas is cooled from
about 800°C to about 150°C in a “shell
and tube” heat exchanger where the
flue gas flows inside the tubes and
water on the outside of the tubes.
When the biomass contains chlorine, potassium or other contaminants, such heat exchangers suffer
from corrosion and fouling. The lifetime of such heat exchangers is often
short, and the maintenance costs are
often high.
Quench
Standard biomass combustion plant with condensation.
Simple cooling
Dall Energy offers a new simple and
reliable solution to cool flue gases in
biomass-based district heating plants.
In a Dall Energy biomass combustion plant, the flue gases are cooled in
an evaporative cooler.
The cooling is done by injection of
water droplets into the hot gas. As
water has a high evaporation energy,
the gases are cooled effectively, while
the water evaporates.
Due to the water injection, the flue
gas now has a high content of water
vapours: The water dew point has
been increased to about 80°C.
Heat recovery
After the evaporative cooler, the
energy of the flue gas is recovered in a
condensation unit. Such condensation
unit may be a scrubber unit or a shell
and tube heat exchanger.
Similar condensation units are
known in energy plants, but Dall Energy units are unique:
•Due to the high moisture content
and the high water dew point in
the flue gas, the amount of energy
produced in the condensation unit
is much higher (up to 5 times) compared to traditional condensation
units;
Quench
Dall Energy combustion plant.
•Due to the high water dew point,
the condensation unit can produce
district heating water at much
higher temperatures than normal
condensation units:
– In scrubber units up to 90°C
– In shell and tube units above 100°C
•Due to the air moisturizing system,
the flue gas is cooled to about 35°C
resulting in very little fume and a very
high energy efficiency of the plant.
Standard
Dall Energy
Efficiency (LHV):
wood / waste
105 %
115%
Efficiency (LHV):
straw / pellets / coal
90%
105%
Corrosion boiler
Yes
No
Fouling boiler
Yes
No
Water system
Complex
Simple
NOx reduction
No
Yes
Slagging in furnace
Yes
Less
Hundested Heating Plant. A 10MW demonstration plant is being prepared.
Gasification plants
Flue gas
to stack
Flue gas cooling
Hot product gas
As the gasifier operates at about
800°C, the alkali metals and chlorine are in gas phase. When the gas
is cooled after the gasifier, the alkali
metals and chlorine form salts. These
salts are sticky, and they build up and
clog in traditional heat exchangers.
District heating
Bag filter
Air
Gas engine
~
200°C
Ash
Condensate
District heating
Standard gasification plant.
Flue gas
to stack
Flue gas cooling
Hot product gas
Air
District heating
or industrial steam
District heating
Gasification
Bag filter
Fuel
Cold gas cooling
Gasifier
800°C
Evaporative cooler
Agricultural residues are characterized by being cheap and plentiful in
many regions. Hence there is a strong
interest in having reliable systems that
can utilise agricultural residues as
fuel. However, these fuels often have
a high content of ashes with alkali
metals (e.g. potassium) and chlorine,
which cause technical problems in the
gas cooler.
District heating
or industrial steam
Air
Dall Energy provides simple and reliable gas cooling and cleaning technologies for gasification plants.
Agricultural residues
Cold gas cooling
Gasification
Hot gas cooling
Fuel
Water or air heating
800°C
Gasifier
Biomass gasification may become a
key technology in the future energy
market.
Electricity, biofuels and heat can be
produced with high efficiencies by use
of biomass gasification.
Several different biomass gasification technologies are under development, aiming at different applications
and markets. For many applications,
such as gas turbines, gas engines, synthesis processes as well as fuel cells, it
is important that the produced gas is
cooled and cleaned.
Air
Gas engine
~
200°C
Ash + salts
Condensate
District heating
Dall Energy gasification plant.
Simple cooling
Gas cleaning
Dall Energy offers a new simple and
reliable solution to cooling product
gas in biomass gasifiers.
In a Dall Energy solution, the product gas is cooled by use of evaporative
cooling.
The cooling is done by injection of
water droplets into the hot gas. As
water has high evaporation energy, the
gases are cooled effectively, while the
water evaporates.
The cooled gas can be cleaned with
traditional gas cleaning technologies,
e.g. bag filters.
Typical grouping of biomass gasifiers with their advantages and disadvantages
Technology
Advantage
Disadvantage
Fluid bed
• Reliable
• Can be upscaled
• Fuel flexible
• Medium-high tar levels
• Salt condensation if agricultural residues are used
Updraft
• Reliable
• High cold gas efficiency
• Can operate on moist fuel
• Limited upscale potential
• Limited to wood fuels
• High tar level
Entrained flow
• Large scale
• Extensive fuel preparation
• Poor cold gas efficiency
Down draft
• Low tar content
• Simple gas cleaning
• Limited upscale potential
• Limited to wood fuels
Heat recovery
After the gas cleaning unit, the energy
of the product gas can be recovered in
a condensation unit such as a scrubber system or a shell and tube heat
exchanger.
Dall Energy develops design tools
for innovative solutions of biomass
energy plants.
The design tools include mass and
energy balance programmes for complete plants and design tools for key
components.
The design tools are programmed in
commercial software.
Dall Energy software includes:
•Mass and energy balance programme
for combustion plants
•Mass and energy balance programme
for gasification plants
•Layout of scrubbers for heat recovery
•Layout of shell and tube heat exchanger in condensing mode.
Screen of energy-mass balance programme for biomass combustion plant with evaporative cooling and heat recovery in scrubber system.
Dall Energy • Telephone: +45 2987 2222 • [email protected] • www.dallenergy.com
© Dall Energy February 2008 Photos: Biopress & Tao Lytzen Diagrams: COWI Layout: Marusa Design
Software