Digesters batch

By-Products. There are three stages within the pulping operation at which wood-derived chemicals can be recovered as by-products. Turpentine is obtained from the reHef of gases after an initial steaming of chips in the digester. Better yields of turpentine are obtained from batch digesters than from continuous systems. Pines and firs give the best yields. Turpentine is composed principally of unsaturated bicycHc hydrocarbons, of which ca 90% are a- and P-pinenes and 5—12% other terpenes. 

Continuous digester, displacement heating/batch digesters, chemi-mechanical pulping... 

Batch Digester Advantages Continuous Digester Advantages... 

Hvala, N., Strm...nik, S., and emeti...,J., Scheduling of Batch Digesters According to Different Control Targets and Servicing Limitations, Computers Chem. 

Most applications of USASD are discrete In nature. This can be ascribed to the fact that few research groups have so far worked on continuous approaches despite such major advantages as automation and reduced chemical consumption. Because automation Is one of the main goals In developing continuous systems, the best way of performing batch digestion steps In an automated manner Is by using a robot to mimick the operations carried out manually by an operator [14],... 

The described sequence would be expected if reactions tended to occur in order of their thermodynamic possibility. The reductant (CH2O) will supply electrons to the lowest unoccupied electron level (O2) with more electrons available, successive levels—NOf, NO, Mn02(s) and so on—will be filled up. The described succession of reactions is mainly reflected in the vertical distribution of components in a nutrient-enriched (eutrophied) lake and in general also in the temporal succession in a closed system containing excess organic matter, such as a batch digester (anaerobic fermentation unit). 

Historically chemical pulping was carried out in large batch digesters (200-400 m ). However, the trend is towards the use of continuous digesters, now accounting for about 65% of kraft production. The largest in operation have production capacities of more than 2000 tonnes of pulp a day. 

Steam Explosion Steam explosion was conducted in a two-cubic foot batch digester equipped with steam injection and ball valves providing for rapid decompression. Approximately 2 kg of yellow poplar (Liriodendron tulipifera) wood chips were loaded batchwise into the vertical reaction vessel and treated with live steam (232 C) for 2.5 minutes. Using the method of Overend and Chomet (34), these conditions corresponded to a severity of log R 4.3. Following decompression, the exploded fibrous mulch was collected from a cyclone steam separator. 

Stainless steel or nickel-base alloy weld overlays have been used to extend the life of both continuous and batch digesters. Other corrosion protective measures for digesters include anodic protection and thermal spray coating [1161. 

The NaOH is consumed during either batch or continuous cooking. In a batch digester, the NaOH concentration decreases over the duration (approximately 2 h) of a batch cook, and the NaOH may eventually be completely depleted. Despite the depletion of NaOH in batch cooking, there have been rare occurrences of SCC in batch digesters. 

LPR testing is typically done in accordance with ASTM Standard G 96. Yeske [154] measured the corrosion rates of carbon steels in alkaline sulfide environments using the LPR technique and described the use of the silver/silver sulfide reference electrode. These techniques were develop>ed further by Crowe and Yeske [755] and used with real mill liquors for on-line monitoring of corrosion rates. The corrosion rates were found to be related to liquor composition with a strong flow effect. Crowe [156] also used LPR testing for on-line corrosion monitoring in white liquor clarifiers. Leinonen et al. [757] used the LPR method to monitor corrosion in a batch digester. 

Audouard et al. and Dupoiron [758-760] simulated the p)er-formance of stainless steels in batch digesters during filling after a cook. Their studies were conducted under heat transfer conditions where white liquor was sprayed onto metal surfaces heated above the boiling point. They measured corrosion potentials, redox potentials, and polarization resistance and performed polarization tests in white and black liquors and mixtures of both at temperatures up to 170°C. 

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