Optimization of Anthraquinone Pulping Through Computer Modelling, 1995 Pulping Conference Proceedings

L. G. Sturgeoff

J. T. Burton

C. J. Kanters

ICI Forest Products

Anthraquinone (AQ) is added to alkaline pulping to enhance the process. The well-known effects of AQ are acceleration of the pulping process and increased pulp yields. These effects are accomplished in a cyclic chain of reactions in which AQ or its reduced form, anthrahydroquinone, reacts sequentially with the wood cellulose and the lignin. From these two basic effects, many uses can be found at various mills. Thus AQ can be used to increase pulp production under varying different scenarios by removing production bottlenecks and by increasing yield. Typical "AQ-able" production bottlenecks are: the recovery furnace that can be limiting in the handling of black liquor solids or in the total heat produced; the white liquor loop; the digester cooking time. AQ can also be used to attain lower brownstock kappa numbers or to permit a reduction in pulping sulfidity. These applications of AQ result in substantial changes in the pulp mill. By increasing pulp yield, the nature of the organic component of the black liquor is altered, as the 1ignin:carbohydrate ratio is changed. When AQ is used to reduce white liquor requirements, the black liquor characteristics are again altered as the component comprising the inorganic solids diminishes. To quantify the economic benefit of AQ for a particular mill, these process changes must be taken into account as well as the cost of mill inputs and of any liquor shipments and the value of any incremental pulp produced. Hidden benefits and costs may come to light when the use of AQ is examined in terms of how it affects the total mill operation. These factors combine to make the optimization of AQ pulping exceedingly complex and time consuming, involving the simultaneous solution of hundreds of interrelated equations. Such a job is well suited to the capabilities of a computer. A computer model that takes all of these factors into account allows a mill to put the different possible applications of AQ into perspective to identify the most cost-effective application. The mill can identify secondary bottlenecks. A well-designed...