GB/T 7909-2017Wood chips for pulp (English PDF)

3.1 wood chips for pulp

wood chips for pulping and papermaking in certain specifications and sizes obtained by mechanical processing with wood as raw materials

3.2 mechanical sieve shaker

sieving device in sieve set with sieves of different sieve mesh diameters, driven by mechanical force for vibrating

3.3

weight percent of a certain screen tray percentage of the wood chips remaining on the sieve of a certain mechanical sieve shaker sieve during wood chip sieving in the total weight of wood chips before sieving

3.4

weight percent ratio of accept chips sum of the weight percent of a certain screen tray for chips remaining on sieves with diameters of 4.8mm, 9.5mm, 22.2mm and 28.6mm respectively when sampled and sieved as specified

3.5 accept chips

wood chips meeting the requirements for size and weight percent of each screen tray, and at least meeting the requirements of Grade III

3.6 fines

fine wooden impurities passing through the last layer of sieve of the mechanical sieve shaker

3.7 burned chips

wood chips that have been subjected to slight carbonization reaction after being burned by open fire or heated in high temperature

3.8 rotted chips

wood chips that have been subjected to oxidation, biological damage and erosion for a long time, resulting in changes in wood chip components and decay

3.9 non-wood mixture

non-wood substances such as metal, sand, brick, cement, coal, rubber, plastic products and soil mixed into wood chips

4.1 Wood species

4.1.1 Wood species

All needle-leaved and broad-leaved wood species.

4.1.2 Mixing requirements

The wood species shall be single, and it shall not exceed 2% of the total chips for the mixing quantity of board-leaved wood chips in needle-leaved wood chips, or needle-leaved wood chips in board-leaved wood chips, or single wood species chips in the other single ones specified in the contract.

4.2

The size of accept chips and the limit of weight percent of each screen tray

The size of accept chips and the limit of weight percent of each screen tray shall meet those specified in Table 1.

Table 1 The size of accept chips and the limit of weight percent of each screen tray

Use of wood chips Size of accept chips, mm Weight percent of each screen tray, %

Length Thickness phi4.8mm Sum of phi9.5mm, phi22.2 and phi28.6mm phi31. 8mm Wood chip

Sulphate or sulphite method for pulping 7~45 3~5 <=8 >=80 <=5 <=2

Semi-chemical or chemical-mechanical or mechanical method for pulping 7~45 3~5 <=8 >=70 <=5 <=2

Note: The layers of mechanical sieve shaker and the mesh size of each layer of mechanical sieve shaker may be negotiated by the supplier and the purchaser.

4.3 Grade classification

4.3.1

See Table 2 for the grade classification of wood chips for pulp.

Table 2 Grade classification of wood chips %

Grade classification of wood chips Weight percent ratio of accept chips Bark content Rotted chip content Non-wood mixture content

Grade I >=90 <=1.0 <=1.0 <=0.1

Grade II 85~89.9 <=2.0 <=3.0 <=0.5

Grade III 70~84.9 <=3.0 <=4.0 <=0.5

Note: Other requirements for wood chips may be negotiated by the supplier and the purchaser.

4.3.2

Wood chips for pulp may be divided into three grades (Grade I, Grade II and Grade III) based on quality, and burned chips are not allowed.

5.1 Inspection tools and instruments

Inspection tools and instruments include:

- - balance (with an accuracy of 0.01g);

- - electronic scale (with an accuracy of 0.01g);

- - stopwatch (with an accuracy of 1s);

- - blast drying oven (with a temperature control range of 10°C~300°C and a temperature resolution of 0.1°C).

5.2 Determination of weight percent of a certain screen tray

5.2.1 Mechanical sieve shaker

The mechanical sieve shakers are set in 5 layers, all sieves are of the same mesh shape, the overall appearance of the sieve is also round, and the sieve mesh diameters of each sieve from top to bottom are usually 4.8mm, 9.5mm, 22.2mm, 28.6mm and 31.8mm respectively. The distance between the uppermost sieve and the uppermost edge of the sieve sleeve is 100mm, and that between two neighboring sieves is also 100mm. The sieve sleeve fixes all the sieves and is driven as a whole by mechanical force to carry out nearly circular rotary motion with vibration frequency of >= 220times/min, impact frequency of >= 147times/min, and vibration amplitude of 8mm.

5.2.2 Determination method

Weigh 1,000g of wood chips from the randomly taken specimens with a balance or an electronic scale, put them on the first layer screen of the mechanical sieve shaker, shake for 7min±10s, and then weigh the mass of fines remaining on each screen tray and passing through the bottom screen respectively, accurate to 0.01g, and the weight percent of a certain screen tray is calculated using Equation (1):

(1) where,

Xn - - the weight percent of a certain screen tray, %;

n - - the screen tray (n=1, 2, 3, 4 ...);

m - - the mass of the specimen, g;

mn - - the mass of wood chips remaining on a certain screen tray, g.

5.3 Determination of bark content

Weigh 1,000g of wood chips from the specimens with a balance or an electronic scale, and weigh the bark picked from the weighed wood chips, accurate to 0.01g. The bark contents are calculated using Equation (2):

(2) where,

Xp - - the bark content, %;

m - - the mass of the specimen, g;

mp - - the mass of the bark, g.

5.4 Determination of rotted chip content

Using the specimens with the bark content determined (the mass is still calculated in 1,000g), pick out and weigh the rotted chips, accurate to 0.01g. The rotted chip contents are calculated using Equation (3):