IPUL >> wood_cofire         



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.

Experimental set-up
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, c-U=-3kV

Basic characteristics of the fuel mixture compounds:

  • 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 can be 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.

Diagnostic tools:
  • 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 PC-20TR;
  • 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)
Main publications:

  1. 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.
  2. 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.
  3. M. Zake, I. Barmina, A. Meijere, The Formation of Polluting Emissions by the Wood Biomass Co-Firing with Propane, LFTZ, 2005, N1, pp. 33-42.