Agglomeration of Bed Particles in Low-Temperature Black Liquor Gasification Agglomeration of Bed Particles in Low-Temperature Black Liquor Gasification

by Woodruff, Mark A

The increasing concern for emissions and pollutants from power generation plants has increased the desire for and the study of biomass fuels. Biomass combustion produces less carbon monoxide as well as other greenhouse gases. Black liquor is a byproduct from the Kraft process in making paper. Black liquor can be gasified and used as a fuel in recovery boilers and fluidized bed steam reformers. Recovery boilers have a low efficiency and are used today because of their reliability. Steam reformers have a much higher efficiency but they are a relatively new science and are not as reliable.

One of the reasons why steam reformers are not reliable is due to the agglomeration of the particles in the fluidized bed. The particles will stick together, agglomerate, at temperatures much lower than their melting temperature. The strength of these bonds and the temperature at which the bed agglomerates were studied as well as the effect of particle size on the heat transfer coefficient from the heaters to the bed material by means of experimentation and analysis.

As the carbon content decreases, the agglomeration temperature also decreases. For 0.3% carbon content coated particles, the agglomeration temperature is approximately 490 ºC. The temperature at which the inter-particle bond strength increases dramatically also decreases. By comparing the inter-particle force with the collision force between particles, it was observed that when the velocity of the particles decreases below 1/500th of the free stream velocity, the particles will agglomerate.