**8. Conclusion**

**7. Desilication and chemical recovery of black liquor**

did not always increase with the rise of system pH. The O<sup>2</sup>

investigated. In addition, the pulp yield, alkali concentration, and O<sup>2</sup>

ferential state expressions of two phases were deduced [8, 29].

ing were studied. The results showed that desilication reaction from the O<sup>2</sup>

Two different kappa number pulps of wheat straw soda-AQ cooking were studied followed

pulp did not always decrease with the rise of system pH and silica content of black liquor

cooking cannot only successfully desilicate from the black liquor but also delignify effectively

liquor could be divided into two phases, a rapid initial desilication phase followed by a slow final desilication phase. They both follow pseudo-first-order reaction toward the silica concentration in black liquor with the reaction energy 64 and 79 kJ/mols, respectively. The dif-

Studies also indicated that under the experiment conditions, the pulp yield increased by

 cooking process. The successful experiences for chemical recovery in China's wheat straw chemical pulping mills indicate the following: (1) to enhance the loss of wheat straw preparation is helpful to decrease the silica content and viscosity of black liquor; (2) rapid cooking at lower temperature

pressure and alkali concentration in the system decreased with the extend-

stage in the wheat straw soda-AQ/O<sup>2</sup>

sure ranges for the desilication, the pulp yield, and the black liquor viscosity in the O<sup>2</sup>

system at given other conditions. The results also showed that silica content in the O<sup>2</sup>

 cooking for elucidating the effects of alkali charge, temperature and oxygen pressure on the black liquor desilication, pulp yield, and pulp delignification. The results showed that the soda-AQ cooking conditions had an influence on the properties of the pulp and the black

cooking stage. And, there were proper alkali charge, temperature and pres-

cooking in soda-AQ/O<sup>2</sup>

cooking process could be an environmentally friendly potential

cooking

cooking

two-stage

cook-

cooking black

two-stage cooking were

pressure in the O<sup>2</sup>

**7.1. Desilication in wheat straw cooking**

**Figure 7.** Diagram of an effluent treatment plan [24].

by O<sup>2</sup>

liquor in the O<sup>2</sup>

234 Global Wheat Production

itself. Hence, the soda-AQ/O<sup>2</sup>

Desilication kinetics of the O<sup>2</sup>

ing time at given temperature in the O<sup>2</sup>

pulping process [29].

0–3.5% and the O<sup>2</sup>

Wheat is a kind of annual vascular-bundled herbal arthrophyte with only internodes of about 68%w/w of the whole stalk being acceptable for pulping and the remainder of 20–30%, i.e., leaves-sheaths, leaves-blade, nodes, grain, debris, etc., being removed for chemical saving and pulp quality improvement as well as silica content decrements of black liquor from cooking at a commercial pulping process line. There are a series of pulping processes, such as the soda, soda-AQ, KP, NS and AS process, etc., successfully employed by wheat straw pulping practices for production of brown pulps or bleached pulps, among which the soda-AQ (anthraquinone) process is most commonly applied in producing the bleached pulps from wheat straw, for AQ to be used in improving selectivity of delignification.

**Acknowledgements**

province, China.

**Author details**

**References**

p. 54

2007;**26**(12):71-74

drind.2016.1603

Guigan Fang\* and Kuizhong Shen

Pulp & Paper. 2011;**30**(11):55-63

\*Address all correspondence to: fangguigan@icifp.cn

Biomass Energy and Material of Jiangsu, Nanjing, PR China

China. China Pulp & Paper Industry. 2005;**26**(5):22-26

**67**(2):119-125. DOI: 10.5552/drind.2016.1446

This work was funded the Fundamental Research Funds for the Central Non-profit Research Institution of CAF (CAFYBB2017ZX003–08) and the Le'an Scholarship Program, Shandong

Wheat Straw Pulping for Paper and Paperboard Production

http://dx.doi.org/10.5772/intechopen.77274

237

Institute of Chemical Industry of Forestry Products (CAF), Key Lab of Forest Chemical Engineering (SFA), National Engineering Lab for Biomass Chemical Utilization, Key Lab of

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The first installation of continuous cooking system with an annual capacity of 100,000 metric tons of wheat straw pulps was successfully operated in China, scaling up an individual pulp production line capacity from non-wood materials in the world, with the tensile strength of wheat straw pulp up to 6000 m, the mid-water discharge amount of less than 50m3 /t o.d. pulp, COD less than 60 mg/L of treated effluent, and the black liquor extraction rate up to 94.6%.

The first mid-consistency and shortened TCF bleaching sequence in the world, namely, OQPo (oxygen delignification—chelating metal ions—peroxide bleaching assisted with oxygen) sequence, was successfully commercially operated in China in 2008, with the brightness of bleached wheat straw pulps (BWSPs) of more than 80%ISO, the pulp viscosity of 653 ml/g, breaking length of more than 7000 m, less amount bleaching effluent generated about 30 m3 /t pulps, and decrease by more than 60% of a traditional CEH bleaching process. The BWSPs can be used to manufacture a wide range of paper and paperboard grades as the full or part furnishes, such as light-weighted printing paper, letterpress printing paper, typing paper, writing paper, aluminum foil base paper, cylinder polished paper, tissue and sanitary papers, white board, coated ivory board, and almost all grades of paper and paperboard grades.

Chemi-mechanical pulps, meeting the requirement of manufacturing A-grade corrugated medium, A-grade linerboard, etc., can be produced from wheat straw using a small amount of caustic soda with advantages as high pulp yield (73.1–78.9%), good physical strength (a tensile strength of 19.49–41.27 N.m/g), and proper biodegradable effluents. A relationship between COD load (y) and pulp yield (x) of wheat straw pulping, i.e., y = 4929.58426– 104.0789x + 0.5883x<sup>2</sup> , r<sup>2</sup> = 0.910, is summarized, and it is proven that effluent from wheat straw chemi-mechanical pulping has a good biodegradability contrasting with that from OCC (old corrugated container) pulping.

The O<sup>2</sup> cooking in soda-AQ/O<sup>2</sup> two-stage cooking is benefited for the desilicate of black liquor from wheat straw chemical pulping line. The successful experiences for chemical recovery in China's wheat straw chemical pulping mills indicate the following: to enhance the loss of wheat straw preparation being helpful to decrease the silica content and viscosity of black liquor, rapid cooking at lower temperature preventing the degradation of cellulose and providing wheat straw chemical pulps with good physic strength and drainability, and high efficient extraction washer for black liquor added to increase the initial concentration of black liquor and to result in steam savings during thickening black liquor and also decrement of fresh water consumption in pulp washing stage. SFP lignin, a kind of lignosulfonate in the waste liquor from the pulping of wheat straw with Na<sup>2</sup> SO3 , HCHO, and AQ and its modified products, can be used as a thinning and foaming agent for drilling fluids, as well as a flocculating agent for treating waste drilling fluids.
