The work presented in this report was done in order to design a pressurized
test facility for droplet analysis with a laser measurement technique, Phase
Doppler Anemometry. The test facility was a development work within
Chemrec's pressurized black liquor gasification (BLG) project. BLG is a
complex process where black liquor is atomized and sprayed into a reactor
and gasified using pure oxygen. In the process it is crucial that all
organic material is consumed to produce combustible gases using three stages
of conversion: drying, pyrolysis and char gasification.
In the end of the conversion, only an inorganic smelt is supposed to remain
(ideally). For the gasification process, it is important to be fully aware
of the spray characteristics created by the nozzle that yields an ideal
conversion. Therefore a pressurized spray test facility with optical access
windows for measurements was developed. Parameters that are important and
interesting to study are droplet size and their velocity. The purpose of the
facility is to gain quantitative information to optimize the black liquor
gasification (BLG) process.
For measuring droplets, a non-intrusive laser measurements system is used
called Phase Doppler Anemometry (PDA). PDA is the most advantageous
technique for measuring droplet velocity and size distribution.
The first stage in the work of developing this spray test facility was a
brief feasibility study of other pressurized spray testing facilities using
PDA, to get information of different concepts.
Concepts and configurations of the different parts for the pressurized test
facility have been analyzed and investigated with a variety of engineering
tools. Because measurements with PDA are very depending on certain receiving
angles a deep review of PDA was performed, all to achieve correct placement
of the transmitting and receiving optical access windows.
The final design resulted in a standing pressure vessel with height 5600 mm
and a diameter of 500 mm. The test facility was tested and is approved for a
working pressure of 15 bar. To prevent corrosion due to the future
application of black liquor atomization, it was made of stainless steel
(SS2343). Four optical access side ports were placed approximately 500 mm
from the top of the vessel. The side port for the transmitter probe is
located at 0 degrees and the three receiving side ports at 106.3, 120 and
270 degrees.
These angles were chosen to fulfill the requirements and demands essential
for PDA.
Simulations using CFD have contributed with useful information for the flow
behavior inside the vessel and how droplets are affected by it. These
simulations gave information about the flow near the optical access side
ports and the necessity of optical clearance. The simulations show that
recirculated flow carries droplets from the spray that reaches the glass
windows, which is not preferable as it may interfere during laser
measurements. Initial test runs and experiments confirm the results obtained
from the simulations. The outcome of this study became a development of a
purging air wall to prevent droplets reaching the glass windows.
Fine polished fused quartz glass, especially suitable for laser measurements
is used for the glass windows. These glasses are free from inclusions and
are distinguished from other glasses by good transmission in UV- and the
visible spectral range. A solid mechanic calculation of the glass specimen
was performed to determine the thickness of the glass in order to withstand
a maximum pressure of 15 bar.
An evacuation port was placed in the middle of the vessel to perform
evacuation of gas. The evacuation is used for both atmospheric and
pressurized conditions. During pressurized runs, a flange lid with a
pressure control valve can be attached to this side port to regulate the
pressure.
Connections for adding a fluid level gauge were placed on the vessel side.
On the top of the vessel a unique designed spray la...
