Pulp & Paper

'Pulp and Paper' is the generic name for the industry in which wood is processed into paper, pulp, paperboard, and other cellulose-based products. Lime is one of the most essential products used in this application. It is applied in the cellulose extraction process, in bleaching (formation of calcium hypochlorite) and in water treatment processes. This reagent is the key in kraft pulping, also known as the sulfate process, where lime is used in a closed loop as part of the causticization process.

The causticization process involves transforming waste sodium carbonate into sodium hydroxide, also known as caustic soda, by reacting it with high calcium lime. The recovered caustic soda is then re-used in the process. The reaction also forms a waste calcium carbonate, which can be calcined to recover a lime yield of 90-97%. To compensate for the losses, a replenishment of high purity quicklime from an external source is required.

Quicklime recalcination and the causticizing circuits in kraft mills are difficult processes for even the most well-run plants. Non-process element (NPE) buildup can cause inefficiencies in the causticizing circuit, reducing plant throughput. These elements can build up causing kiln ringing and filter blinding, which reduces recalcination rates and can lead to expensive outages and frequent maintenance. High quality quicklime can help to reduce this NPE loading.