TESTS WITH PO IN A LARGE BOILER
The aim of the test was to verify the combustion behaviour and the
emissions level with pyrolysis oil (PO) in a large scale boiler.
The combustion test was carried out in a 9 MW boiler at the Årsta
District Heating Plant in Stockholm. The test was performed 1st and
2nd of April 2004 by Fortum Värme.
Årsta District Heating Plant is one of several production plants
in the south district heating net of Stockholm. The plant is used
as peak load and stand by plant within the net.
It is situated in a built up area and dwelling houses are on a distance
less than 50 m.
Årsta District Heating Plant is equipped with four hot water
boilers and one boiler producing steam for soot blowers. The used
fuels are fossil and bio oils. The plant is operating from October
until the middle of May.
The test was carried out in boiler 1 in Årsta District Heating
Plant. The 9 MW boiler was originally designed for heavy fossil fuel
but it is now adapted to different bio oils. The boiler has forced
circulation with temperature regulated at 160 °C and no flue gas
The burner is a rotating cup burner manufactured by Petrokraft AB.
The fuel is added inside a rotating cone (5000 rpm) and the rotation
together with the primary air added outside the cone, atomises the
fuel. When using different fuels it helps in mixing them.
The fuel was produced in the pilot-scale production plant in Porvoo,
Finland, during the autumn 2003, shipped to Stockholm September 2003
and stored for 8 months in 1 m3 plastic containers.
When the test was run the fuel was pumped from the containers to a
storage tank. There were no sediment layer and viscosity was good
at room temperature. The liquid was pumped easily, but a problem was
the characteristic smell.
Having the PO a low heating value, 21.10 MJ/Kg, it was necessary to
co-fire it with a support fuel. In this test fatty acid was used but
it could also have been tall pitch oil or heavy oil. Its heating value
was 45 MJ/Kg.
The support fuel was delivered to the mass flow meter, filtered and
preheated in the normal fuel system. The PO was handled in a separate
test unit - an air tight, stainless, 10 m3 tank with stirring device.
The PO was lead from the tank to a loop - rotor pump with controlled
rpm and further to a 400 micrometer filter, a pre heater and through
a mass flow meter.
The boiler was started up with 100 % support fuel. After a while
PO was added. During the test burning PO was mixed with a decreasing
amount of fatty acid. When the combustion began to be unstable the
flame started to pulsate and the CO-level increase. The amount of
PO was then reduced until stable conditions appeared again. The emissions
measurement was started up.
It was noticed that the combustion was stabilized from an higher O2
During the two days the boiler was operating with PO approximately
six hours and the total consumption of PO was about 4 m3.
The result of the measurements in the flue gas is:
|| vol % tg
|| vol % tg
| CO content
|| ppm tg
| Dust content
| Spec dust emission
| Spec gasflow*
|| m3ntg/MJ fuel
* Theoretically from oil analysis and measured O2
· Handling of the PO was easy and the test
worked out well;
· Emissions measurements indicated a dust content higher
than expected while the NOx level was more or less the same than
with pure fatty acid;
· Further tests are needed.
In order to have an industrial use of pyrolysis oil his heating value
has to be increased or the combustion conditions have to be modified.
The latter could be done adding some refractory bricks at the bottom
of the boiler and close to the burner to create a radiating shield.
Another option could be air preheating.