Why the black liquor route for biomass conversion is superior
Black liquor properties
Black liquor is a biomass feedstock with unique properties.
First of all, it is available at existing industrial sites in large quantities.
Secondly it is a liquid. This makes it possibly to easily feed it by pumping into the pressurized gasifier. With biomass in solid or pulverized form this becomes significantly more difficult. The liquid state also makes the black liquor easy to atomize into a fine mist that reacts very fast in the gasifier.
Thirdly, the gasification of black liquor char is more rapid than for any other feedstock as the inherently high sodium and potassium content of black liquor acts as a catalyst.
These properties makes it possible to apply the high temperature, entrained flow gasification principle to black liquor. This type of gasification process provides many advantages over alternative gasification technologies:
- It is a very rapid, single-stage gasification process with low reactor volume
- It minimizes the need for raw syngas clean-up as the Chemrec process directly provides a raw syngas of excellent quality with
- Complete carbon conversion
- No tar formation
- Low methane content
Investment cost and energy efficiency
Black liquor gasification fulfills two investment-intensive duties with a single process; it provides the pulp mill with needed black liquor recovery capacity at the same time as it produces syngas for biofuels production. In this way the total investment demand decreases.
The Chemrec gasification process also has a substantially higher thermal efficiency than the process it replaces - the Tomlinson recovery boiler.
The location within a pulp mill complex gives other benefits. First, permitting is generally easier than for a greenfield industrial activity. Secondly, the pulp mill infrastructure for raw material supply, utilities and energy reuse further reduces investment and provides the opportunity for net energy cost reduction.