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EXPERIMENTAL STUDY OF CO-FIRING A WOOD BIOMASS WITH PROPANE
The general objective of this
experimental study is to develop a stable, effective and controllable
process of co-firing a fossil fuel (propane, natural gas) with
renewable (wet wood biomass), providing control of a burnout of the
wood char and volatiles, as well as control of the flame dynamics,
processes of the heat/mass transfer and the formation of polluting
emissions by co-firing a fossil fuel with renewable one.
|Fig.1. The digital image (a) and
schematic view (b) of the experimental set-up:
1- gasifier, charged by the wood granules, 2- steel grid, 3- swirling
propane/air burner, 4- air supply, 5- secondary air supply, 6-
water-cooled channel, 7- peepholes for the diagnostic tools, 8- ash
pan, 9- cooling water inlets, 10- cooling water outlets, 11-
measurements of the flame composition using the gas analyzer TESTO
-350XL, 12- peepholes for the radiation measurements.
Laboratory study of co-firing
renewable (wood granules) with fossil fuel (propane) is carried out
using a compact design (Fig.1), which includes a laboratory-scale
premixed propane/air burner (3), a wood biomass gasifier (1), charged
with wood granules and a water-cooled channel (6), downstream of which
the dominant combustion of the volatiles is developing. Combustion
conditions in the system are varied by varying the mass flow rate of
the primary air (4) into the bottom part of the combustor and the mass
flow rate of secondary tangential air flow (5), introduced from the two
tangential air nozzles of inner diameter D=5mm. The primary airflow
ignites the volatiles and initiates combustion, while the secondary
airflow completes the fuel combustion. Between the co-combustor and
water-cooled channel sections and so between the channel sections the
diagnostic sections (7) with peepholes are located to provide the local
injection of the diagnostic tools (Pt/Pt-Rh thermocouples, Pito tube,
gas sampling probe) into the flame of volatiles and so providing the
local measurements of the flame temperature, velocity and composition.
The residual ash is removed from the bottom part of the combustor (8).
The electric control of co-firing the wood granules with propane is
carried out using the central electrode, axially inserted downstream
the flame of volatiles. The bias voltage of the central electrode in
this study could be varied within a range from –3kV to +3kV, while the
ion current is limited to 1 mA, producing the evident variations of the
flame shape (Fig.2), provoked by the field-enhanced variations in a
rate of unsteady heating and volatilisation of wood granules and
burnout of volatiles and wood char.
|Figure 2: The electric field
effect on the shape of the free flame of volatiles: a- U=+3kV, b-U=0,
Basic characteristics of the fuel
- The mass flow rates of primary and secondary airflows could
be varied in a range of 20-90 l/min.
- The rate of stoichiometric propane supply - could be varied
in a range from 0,5 to 0,85 l/min.
- The heat rate released from the propane combustion - from
770 to 1400 J/s.
- The additional energy supply from the propane combustion
varied from 10% up to 25% of the net amount of the total heat released
during the burnout of wood pellets and volatiles.
- The total heat output during the burnout of wood pellets
with propane can be varied in a range from 4 up to 5kWh.
- The measurements of the radial and axial temperature
distributions in the flame are carried out using thermocouples
(Pt/Pt-Rh 10%) and the computerized date processing system with
- The measurements of the flame velocity field – by using the Pitot
tube monitors and LDV;
- The efficiency of heat production is
estimated from the calorimetric measurements in the water-cooled
sections of the experimental channel with computerized data
processing, using PC-20TR;
- The local variations of the temperature, combustion efficiency
and composition of the products (O2, CO2, CO, NO2, NO, NOx, H2) are
registered by using the gas analyzer Testo 350 XL.
- The local composition of the flame is controlled by using the
spectrophotometer SPECORD that provides the measurements of the flame
composition in the infrared spectrum range (2–15μm)
- M. Zake, I. Barmina, A. Desnickijs, Control of pollutant
emissions by co-firing the renewable with fossil fuel, CHISA-2006-17th
International Congress of Chemical and Process Engineering, Praha,
August 2006, CD-ROM with full teksts, P5.95, p. 1-15.
- M. Zake, I. Barmina, A. Meijere, Electric Control of Combustion
and Formation of Polluting Emissions by Co-Firing the Renewable with
Fossil Fuel, Magentohydrodynamics, 2005, N3, pp. 255-271.
- M. Zake, I. Barmina, A. Meijere, The Formation of Polluting
Emissions by the Wood Biomass Co-Firing with Propane, LFTZ, 2005, N1,
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