(555c) Black Liquor Gasification Chemical Recovery and Combined Cycle Power at Pulp and Paper Mills Biorefinery

In the areas of chemicals and allied products and energy process engineering, it is of particular interest to design processes with low energy requirements (energy intensive) (preferably renewable materials, e.g., biomass) and the use of minimum raw materials or use of a byproduct as feedstock (materials intensive) and minimum number of equipment (i.e., lean manufacturing). This is the basis from which the area of process intensification (PI) arises. The main objective of PI is to propose production and manufacturing processes in plants as small as possible and with low total energy, materials, water, and other resources.

Pulp and paper are primarily made out of wood fibers originating from natural forests or pulpwood plantations. Recycled fiber and other fiber sources such as agricultural residue are also utilized and recycled fiber is becoming more commonly used in pulp and paper making. There are two significant pulping technologies available that differ greatly in terms of process, i.e., mechanical and chemical pulping. Approximately 30% of the total pulp production in European Union is from mechanical pulping while the rest is produced by means of chemical pulping. North America has major pulp and paper industry, about 21% of the total pulp produced is from mechanical pulping and rest is produced chemically.

A pulp mill that produces bleached kraft pulp generates 1.7-1.8 ton of black liquor (measured as dry content) per ton of pulp. Black liquor thus represents a potential energy source of 250-500 MW per mill. As modern kraft pulp mills have a surplus of energy, they could become key suppliers of renewable fuels in the future energy systems. Today, black liquor is the most important source of energy from biomass. It is thus of great interest to convert the primary energy in the black liquor to an energy carrier of high value. A key advantage of black liquor compared to biofuels and fossil fuels is that it is already at the mill; the handling infrastructure already exists and there are no collection and transport costs.

An extended case study is presented in which black liquor, a byproduct of wood-pulping process, is utilized to make chemicals and biofuels, in particular methanol, dimethyl ether and syngas. Different feedstock, use of byproduct and alternatives and principles of PI are commented (Das, 2020).

Reference: Das, T.K. (2020). Industrial Environmental Management: Engineering, Science and Policy, Wiley, Hoboken, NJ.