Increasing pulp wash efficiency using carbon dioxide
Pulp wash is a pulping process where the objective is to achieve a maximum separation of wood fibers from pulping liquor which contains dissolved wood components and cooking chemicals. AGA has developed and patented a method which can improve pulp washing results and washer runnability through the addition of carbon dioxide.
Our method is environmentally friendly and cost-efficient, and can achieve several benefits depending on the need of individual mills. Carbon dioxide can be used to increase wash efficiency in the production of both non-bleached and bleached pulp. The method does not require major investments.
Oxygen delignification
Bleached chemical pulp is formed of cellulose fibers, from which practically all lignin has been removed. Lignin is removed during cooking, oxygen delignification and final bleaching using various chemicals.
From cooking and oxygen delignification the chemicals and dissolved organic matter can be recovered. The amount of chemicals used for final bleaching, such as ozone, chlorine dioxide, oxygen and/or peroxide, depends on the amount of lignin surviving oxygen delignification and cooking.
That is why it is both environmentally and economically profitable to take cooking and oxygen delignification as far as possible without endangering pulp quality. In order to optimize the physical and optical characteristics of pulp and pulp yield, it is naturally important to strike a balance between cooking, oxygen delignification and bleaching.
Modern dual-stage methods can reach delignification rates of over 70% in oxygen delignification. The extensive use of oxygen is a requirement for closing pulp manufacturing process cycles, i.e. reducing environmental emissions.
Ozone bleaching
The use of ozone, combined with oxygen and hydrogen peroxide, enables the manufacture of fully bleached pulp without chlorine-containing chemicals. Ozone is also used in combination with chlorine dioxide to reduce consumption of chlorine dioxide.
Ozone is a powerful oxidant and, in the right conditions, an effective delignification chemical and bleaching agent. Ozone cannot be stored, which is why it is always produced from oxygen in the immediate vicinity of the pulp mill.
The production and use of ozone requires a high level of expertise in gas engineering, equipment and safety.
After ozone bleaching the residual gas, containing oxygen can be utilized after treatment in, for example, oxygen delignification, bleaching or waste water treatment. The oxygen can also be returned to the ozone generators.
Process optimization using a tracer gas technology
An important requirement for the efficient operation of the oxygen or ozone stage is that a sufficient amount of gas necessary for the reactions is thoroughly mixed with the pulp. Furthermore, the gas must remain dispersed.
In our method, the distribution of gas retention time in the reactor is measured using a tracer gas. The results are used to optimize the stage in question or the entire process, both from the technical and financial perspective.
The method has been applied to the analysis of oxygen delignification, oxygen alkaline and ozone bleaching stages.