Oxygen generators are increasingly used as an oxidant in pulp and paper mills
Paper making typically generates significant streams of wastewater and energy that contain by-products, such as black liquor, from the digestion process. Oxygen is increasingly used as an oxidant in pulp and paper mills within the delignification, bleaching, chemical and energy recovery, and wastewater treatment processes to increase capacity, meet environmental regulations, and improve product quality and energy usage. Read about other industries that use oxygen generators.
The Pulp & Paper Industry has used oxygen generation for a number of well established applications, including:
Oxygen Delignification (O): (Oxygen consumption- 20-30kgO2/BDMT) – is a process between cooking and bleaching sequences, where part of the residual lignin left in pulp after cooking is removed using oxygen and alkali.
Oxygen Alkali Extraction: (Oxygen consumption 5kg/BDMT) – addition of oxygen to the pulp is an efficient method for increasing the bleaching effect and decreasing the consumption of more expensive bleaching chemicals. Oxygen improves the dissolution of lignin in pulp.
White Liquor Oxidation: (Oxygen consumption- 5-10kgO2/BDMT) – oxygen is used to oxidize sodium sulfide into sodium thiosulfate (partial oxidation) and sodium sulfate (total oxidation).
Oxygen Bleaching: (Oxygen Consumption 10-15kg/BDMT) – Oxygen bleaching is essentially a very strong Eo stage and is an alternative to oxygen delignification. The major advantage of the process relative to oxygen delignification is capital investment.
Ozone Bleaching (Z): (Ozone consumption 2-5kg/BDMT, Oxygen requirement 20-40 kgO2/BDMT) – ozone is used to remove lignin and make pulp brighter.
Black Liquor Oxidation: TRS control: (Oxygen consumption, up to 100kg/BDMT) – is used to control total reduced sulfur (TRS) emissions from a “Direct Contact Evaporator” (DCE) recovery boilers. The use of oxygen in black liquor oxidation reduces the discharge of sulfur pollutants into the atmosphere.
Lime kiln enrichment: (Oxygen Consumption, 15-25kg/mt) – is a very standard oxygen application and has been used in the P&P industry for decades to increase lime kiln capacity. Oxygen added to the combustion air increases the production capacity of the soda recovery boiler and the lime-reburning kiln.
Wastewater Treatment – activated sludge treatments purify wastewater by ensuring that organic matter is degraded by aerobic bacteria in the presence of dissolved oxygen.
Oxygen Activated Sludge: (Oxygen consumption, 50+kgO2/BDMT) – UNOX and OASIS are oxygen activated sludge waste water treatment process which are very similar in design. Both systems are in use in the P&P industry. There are a number of claimed advantages over other processes (e.g., ASB), but the major advantage is footprint.
Primary Clarifier Odor Control:(Oxygen consumption, 1-2kg/BDMT) – Hydrogen sulfide can be produced in the pipeline to the primary clarifier, in the primary clarifier and in the wastewater treatment system through the reduction of sulfate by a specific biology.
In Basin Supplemental Oxygen:(Oxygen consumption 3-20+ kg/BDMT) – Oxygen can be added to a waste water treatment plant (e.g., aerated stabilization basin) to raise the DO for BOD removal or to mitigate H2S emissions in anoxic/anaerobic zones. There are numerous injection methods.
Discharge Effluent DO Control:(Oxygen consumptions, 1-3kg/BDMT) – Many mill are required to maintain a specific DO content in the discharged effluent. This typically occurs if the receiving stream/river has a low flow or a marginal DO concentration. In some cases the effluent DO must be equal to the ultimate BOD demand of the discharged effluent. The use of aerators to achieve the required DO is generally not economical and may cause a high effluent nitrogen content that can be detrimental to fish (i.e., causes the bends). Again, there are numerous injection methods available.