Production of cellulose by removing non-cellulose substances from cellulose containing material. This subclass also embraces the after treatment of cellulose pulp and the regeneration of pulp liquors. It further also covers different aspects of digesters for pulping cellulosic material.

D21B covers fibrous raw material or their mechanical treatment.

D21D covers treatment of materials before passing to the paper-making machine.

D21F covers papermaking machines and methods for producing paper thereon.

D21H covers Pulp compositions (not covered by subclasses of D21C and D21D), impregnating or coating of paper, treatment of finnished paper and paper not otherwise provided for.

The main aspect(s) of the invention is/are given a class according to the classification scheme. The invention per se should be classified in the last appropriate class(es), if possible. Ideally, one class should be given for covering the main aspect of the invention per se. Exceptionally, the core of the invention may also be classified by using several classes (up to three)

Classification of additional information

In this subclass, it is highly desirable to add Indexing Codes for secondary aspects of the invention (e.g. the features of the dependent claims) or for additional information, which is not considered to form the claimed invention per se, but which might be of interest for the search. For the Indexing Codes the "D" is replaced with an "N", e.g. to classify the additional information that the pulp is treated by an enzyme (or microorganisms ) should read D21C 5/005 (instead of D21C 5/005).

Different pre-treatments (e.g. impregnation) of finely divided cellulosic containing material using e.g. water, steam, acids, alkaline compounds, oxygen generating compounds or physical methods for facilitating impregnation.

Pulping with inorganic bases or alkaline reacting compounds, e.g. the sulphate process

Pulping with acid, acid salts or acid anhydrides

Pulping with sulphur dioxide, sulphurous acid, bisulphites or sulphites

Pulping with nitrogen oxides, nitric acid, nitrates or nitrites

Pulping with organic solvents or in solvent environment

Other features of the pulping process

Other processes for obtaining cellulose such as:

This group refers to structural features of the digester, i.e. defining different types or parts of the digester, e.g. rotary digesters, linings, feeding devices, discharge devices, heating devices, devices for regulating or controlling, means for circulating the lye (e.g. white or black liquor) or safety devices.

Modification of pulp properties

Washing

Displacing cooking or pulp-treating liquors contained in the pulps by fluids, e.g. wash water or other pulp treating agents

Removal of fats, resin pitch or waxes

Chemical or physical purification i.e. refining of crude cellulose by removing non-cellulose contaminants, optionally in combination with bleaching

Bleaching, e.g with halogen or halogen containing compounds, with ClO2 or chlorites, with oxygen or its allotropic modifications, with ozone, with per compounds such as peroxides or peracids

Apparatus for bleaching

De-watering

Elimination of cooking or pulp-treating liquors from the pulp

Aspects concerning the production and the treatment of green and white liquors, e.g. causticizing green liquor

Combustion of pulp liquors

Concentration spent liquors by evaporation

Deodorisation or elimination of malodorous compounds, e.g. sulphur compounds such as hydrogen sulphide and mercaptans, for gas streams

Introduction of auxiliary substances into the regenerating system in order to improve the performance of certain steps of the latter, the presence of these substances being confined to the regeneration cycle

Recovery of by-products, i.e. compounds other than those necessary for pulping

Regeneration of alkali lye, of pulp liquors or effluent waste waters, of acid, neutral or alkaline sulphite lye

Treatment of pulp gases or of gases arising from various sources in pulp and paper mills

Recovery of the heat content in the gases

Regeneration of gaseous SO2, e.g. arising from liquors containing sulphur compounds

Wet combustion

Treatment of pulp liquor without previous evaporation, by oxidation of liquors remaining at least partially in the liquid phase, e.g. by application of pressure