Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With regeneration – reclamation – reuse – recycling or...
Reexamination Certificate
2001-10-03
2003-01-07
Nguyen, Dean T. (Department: 3629)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With regeneration, reclamation, reuse, recycling or...
C162S030100, C162S030110, C162S090000
Reexamination Certificate
active
06503369
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns production of cellulose. In particular, the invention relates to such a process for producing cellulose in which process waters can be completely recycled and cooking and bleaching chemicals can either be recycled or utilized as commercial products. Also lignin and other organic matter obtained from pulp production as a by-product can be utilized. The invention also relates to a by-product obtained from the process, the by-product being useful as a fertilizer, especially as a potash fertilizer. The invention further relates to production of a fertilizer.
A complete circulation of chemicals and process waters of a cellulose process has not yet succeeded. The reasons have been both economical and technical. Although many partial solutions have been taken into use, pulp mill bleach waters must, however, still be treated separately by an activated sludge process, for example, before they are led to water systems. Water consumption is still relatively high in the cellulose and paper industries.
The economical water use is particularly difficult in alkaline strawpulp processes, since silicon compounds of plants complicate the recovery of chemicals and cause big environmental problems.
Finnish Patent 960275 describes a process for pulp production based on formic acid, in which process a closed chemical and water cycle is implemented. Formic acid is used as a cooking chemical and the pulp is bleached by an alkaline peroxide process (NaOH is used as alkali). Nutrients are recovered from power plant ashes and silicate compounds are separated from bleach waters as sodium silicate, which is a versatile product in the chemical industry. The markets of the sodium silicate are, however, limited.
Potassium is one of the basic nutrients of fertilizers. Plants need potassium for various reasons. It participates in many functions of plants e.g. by controlling the water economy of plants, delivering other substances necessary for photosynthesis and participating in protein production and by functioning as an enzyme activator.
The utilization of by-products obtained from pulp production for fertilizing purposes, for example, has been suggested by many. The publication Meier D. et. al., Conversion of Technical Lignins into Slow-release Nitrogenous Fertilizers by Ammoxidation in Liquid Phase, Bioresource Technology 49 (1994), 121-128 has described the utilization of residual lignin obtained as a wood processing industry by-product in slow-release fertilizers.
It has also been suggested that potassium compounds used in potassium-based pulping processes would be recovered and utilized as fertilizers. For example, the publication Wong, A. et. al., Potassium-based Pulping of Wheat Straw, TAPPI Pulping Conference, 1989, p. 477-479 describes a potassium-based sulphite cooking process, which can be applied to agricultural wastes. The publication also suggests that spent liquor would be used directly in liquid form as a potassium-sulphur fertilizer containing organic matter of arable land. Used as liquid, a considerable amount of nutrients will not be used by plants, but the nutrients are easily leached from fields and may get into ground water. In addition, the energy value of cooking liquor is lost by delivering lignin and other organic substances with the cooking liquor to fields. Further, a drawback of the process is its poor usability. Storage of diluted liquid fertilizers is difficult, since the fertilizer use is seasonal.
The publication Sameshima, K. & Ohtani, Y., What should be done between Forestry and Agriculture? A Need for Research and Development on Kenaf as a new Model, TAPPI Pulping Conference 1995, p. 273-276 suggests that if alkaline hydrogen peroxide pulping were performed by using KOH, the formed waste material could be utilized as a potassium fertilizer and the ammonium oxalate could be used as a nitrogen fertilizer. The publication does not include a more specific description of waste material treatment into a potassium fertilizer.
The prior art has not described a process, however, in which all cooking chemicals used in pulping would be regenerated and the waste material formed as a by-product would be efficiently utilized either for energy production or as a fertilizer at the same time as the bleaching chemicals are utilized and the bleach waters are recycled.
BRIEF DESCRIPTION OF THE INVENTION
The invention is based on the idea that sodium hydroxide to be used in alkaline pulp bleaching is at least partly replaced with potassium hydroxide, whereby a bleach water concentrate rich in potassium is obtained from the bleach water treatment. This concentrate is then combined with ashes obtained from the burning of lignin and other organic matter recovered from pulp production as a by-product, in order to be used as raw material for a potash fertilizer. The bleach water concentrate can also be used as such as raw material for a potash fertilizer.
In the process of the invention, organic compounds dissolved during cooking are utilized in energy production (the burning of lignin) in a mill power plant, and the power plant ashes and bleaching chemicals are utilized in the fertilizer production. The bleach waters are also completely recycled.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to a process for producing cellulose and a fertilizer by-product by using a closed cycle of cooking chemicals and process waters, which process comprises
(1) cellulose cooking, washing and bleaching, the bleaching comprising alkaline stages,
(2) recovery of cooking chemicals and wash waters as well as lignin and other organic matter formed as a by-product in pulp production,
(3) recycling of the recovered cooking chemicals and process waters, and
(4) burning of the recovered lignin and other organic matter recovered from pulp production as a by-product.
The process is characterized by
(i) at least partly using potassium hydroxide as alkali in the bleaching,
(ii) separating the used bleach liquor into an aqueous fraction and a potassium-containing bleach concentrate,
(iii) returning the aqueous fraction to the bleaching and
(iv) recovering the potassium-containing bleach concentrate to be used as raw material for a potash fertilizer.
In an alternative embodiment of the invention, in step (iv) the potassium-containing bleach concentrate is mixed with ashes obtained from the burning of lignin and possibly other organic matter recovered from pulp production as a by-product, in order to be used as raw material for a potash fertilizer.
The process of the invention comprises cooking, washing and bleaching stages known per se. A bleaching sequence comprising alkaline stages is used in the process. Cooking chemicals and wash waters are recovered in manners known per se and they are recycled into the cooking and washing stage. A lignin fraction, which may also contain other organic substances and which is recovered from the cooking and washing stage, is led to a biopower plant of the pulp mill to be burnt. Organic waste obtained from the pretreatment of cellulose raw material, e.g. from straw screening, is also typically led to the biopower plant. The biopower plant produces energy, which is typically utilized as steam in the process, and an ash fraction. In the process of the invention, the ash is utilized in fertilizer production.
A bleaching sequence comprising alkaline stages is used in the process of the invention. The bleaching is typically an alkaline hydrogen peroxide bleaching. Before the peroxide stage, the bleaching sequence can further comprise an oxygen stage, an ozone stage (pH=1.5 to 3) or a peracetic acid stage (pH=1.5 to 7).
The process of the invention is characterized by replacing sodium hydroxide generally used at the alkaline stages of the bleaching either entirely or partly with potassium hydroxide (step i). Potassium hydroxide can also be used to increase pH before the bleaching. When potassium hydroxide is used instead of sodium hydroxide to increase pH or as a bleaching chemical, a potassium-containing concentr
Rousu Esa J.
Rousu Päivi P.
Rousu Pasi P.
Alston & Bird LLP
Chempolis Oy
Nguyen Dean T.
LandOfFree
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