Many pulp processes can be intensified or optimised through the use of oxygen or ozone. We supply oxygen in different modes to suit individual needs, scaling from bulk liquid deliveries through vacuum pressure swing adsorption (VPSA) systems to on-site air separation units (ASUs). Here we work closely with our customers to ensure the best, most cost-effective fit and to maximise the process efficiency gains achievable through the addition of oxygen or ozone. Working with renowned ozone generator manufacturers, we also supply oxygen for ozone generators in the supply modes best suited to individual volume needs.
Some of the key processes that benefit from the use of oxygen are outlined in the following.
The purpose of bleaching is to remove the dark-coloured lignin remaining in the pulp and thus achieve optical quality criteria. Chemical pulp is bleached in several stages. In modern mills, the bleaching starts with oxygen delignification to reduce consumption of more expensive bleaching chemicals and, in turn, the effluent load from the bleach plant.
Oxygen for ozone generation (bleaching)
Ozone is an attractive alternative to chlorine-containing chemicals as a way to bleach pulp and achieve the necessary level of brightness. It is widely used for both TCF and ECF bleaching. As it is an extremely effective bleaching agent, ozone reduces the volume of other bleaching chemicals required.
Oxygen for reinforcement of peroxide bleaching
In TCF bleaching, pressurised peroxide (PO) stages can help achieve the high final brightness required. In ECF sequences, a powerful peroxide stage will reduce the consumption of chlorine dioxide or even replace one chlorine dioxide stage. Addition of oxygen improves the efficiency of the peroxide bleaching stage.
Oxygen for reinforcement of alkaline extraction stages
Oxygen can be added to the pulp in alkaline extraction to intensify the bleaching effect and decrease the volume of more expensive bleaching chemicals required. Oxygen works by improving the dissolution of lignin. The oxygen extraction stage can be intensified by raising the temperature in the stage, increasing the oxygen charge, pressurising the pre-retention tube and adding hydrogen peroxide.
Oxygen enrichment for lime kilns
The production rate of a lime kiln can be increased by adding oxygen, enabling you to increase capacity without having to invest in expensive, high-tech equipment. Oxygen also overcomes the downsides of purchasing more lime and the expense involved in disposing of lime mud surplus. In addition, oxygen enrichment increases combustion efficiency and thus reduces fuel consumption. In fact, the efficiency gains of oxygen enrichment are often sufficient to make this a profitable undertaking even if capacity increases are not required.
Using the same technologies proven in cement kilns and similar installations, we deliver a range of flexible, cost-effective oxygen enrichment and injection systems to improve kiln performance.
Oxygen for white liquor oxidation
In pulp processing, to be able to use white liquor as alkali source for oxygen delignification, the white liquor needs to be oxidised to convert sodium sulfide to sodium thiosulfate (partial oxidation) and/or sodium sulfate (total oxidation). The efficiency of this oxidation process can be greatly enhanced by adding oxygen to the combustion air or by replacing the combustion air entirely with oxygen.
We supply oxygen to several pulp mills for white liquor oxidation. This enables customers to either enhance process efficiency or increase capacity without heavy CAPEX investments.