Study of Causticizing Kinetics and Design of Pressurized Reactor

木材主要含有纤维素、半纤维素、木质素和少量抽出物。化学制浆的主要目的是去除束缚木材中纤维的木质素，并释放纤维素纤维。硫酸盐法制浆是制浆造纸工业用来将纤维素纤维从木材结构基质中解放出来的主要化学制浆方法。硫酸盐制浆工艺使用氢氧化钠和硫化钠作为制浆的有效化学物质。化学品和木片一起被装入压力容器(消化器)，内容物以预设的速度被带到反应温度。消化后的薯片被“吹”进水槽中分解，然后送去进行进一步的加工。木片消化和分解产生的纸浆在逆流洗衣机系统中被彻底洗涤，以产生废液或黑液。黑液经过回收循环，通过蒸发和在炉中燃烧，将黑液浓缩到60%-70%的固体。在炉子里，有机物质被完全燃烧以产生蒸汽，钠硫化合物被还原为硫化钠，其余的无机成分被转化为碳酸钠。无机化合物以熔炼的形式从炉子中提取出来，溶解，然后送到苛化部分，通过石灰处理再生氢氧化钠。从苛化部分得到的澄清液，主要含有氢氧化钠、硫化钠和少量未转化的碳酸钠，被称为白液，作为蒸煮液循环回消化器。硫酸盐法制浆工艺成功的主要原因之一是成熟、高效的化学回收工艺，可以回收蒸煮过程中使用的95%以上的化学物质。再生蒸煮液组分的均匀性是生产均匀质量纸浆的关键因素，因此也是整个过程运行的经济性的关键因素。本研究项目的目的是研究硫酸盐法制浆过程中的苛化过程，建立一个可靠的系统动力学模型，最终目的是改善硫酸盐法制浆过程中的化学回收操作。将使用已经设计和制造的能够在较高压力下运行并配备了连续监测主要反应产物组成的半间歇反应器。一种新型的现场在线采样分析系统将被用于饲料绿液浓度的测量。实验平衡数据将得到理论计算的补充。将设计一个管式流动反应器，配备分析器来测试绿液和反应产物。这样的反应器还将允许对石灰添加进行必要的调整，并使白液均匀地进入消化池，从而使消化池稳定运行，改善纸浆质量和提高生产率。

Wood contains mainly cellulose, hemicellulose, lignin and small quantities of extractives. The primary purpose of chemical pulping is to remove the lignin which binds the fibers in the wood and liberate the cellulosic fibers. Kraft pulping is the major chemical pulping process used by the pulp and paper industry for the liberation of cellulosic fibers from the structural matrix of wood. The kraft process uses sodium hydroxide and sodium sulfide as effective chemicals for pulping. The chemicals along with wood chips are charged into a pressure vessel (digester), and the contents are brought to the reaction temperature at a preset rate. After the digestion the chips are disintegrated by being "blown" into a tank and then sent for further processing. The pulp resulting from digestion and disintegration of the wood chips is washed thoroughly in a counter current system of washers to produce spent liquor or "black liquor". This black liquor is sent through a recovery cycle which involves concentration of black liquor to 60-70% solids by evaporation and burning of the concentrated black liquor in a furnace. In the furnace the organic materials are completely burned to generate steam, the sodium-sulfur compounds are reduced to sodium sulfide, and the remainder of the inorganic components are converted to sodium carbonate. The inorganic compounds are withdrawn as smelt from the furnace, dissolved, and then sent to a causticizing section to regenerate sodium hydroxide by treating with lime. The clarified liquor from the causticizing section, containing mainly sodium hydroxide, sodium sulfide and small quantities of unconverted sodium carbonate, is called "white liquor" and is recycled back as the cooking liquor to the digester. One of the major reasons for the success of the kraft pulping process is the established, efficient chemical recovery process whereby more than 95% of the chemicals used in the cooking process can be recovered. Uniformity of composition of the regenerated cooking liquor is a key factor in the production of uniform quality pulp and therefore in the economy of operation of the entire process. The purpose of this research project is to study the causticizing process and develop a reliable kinetic model for the system, with the ultimate goal to improve the chemical recovery operation in the kraft pulping process. A semi-batch reactor already designed and fabricated, capable of operating at higher pressures and equipped to monitor the composition of the main reaction products continuously will be used. A novel in-situ and on-line sampling and analysis system will be used to measure the feed green liquor concentration. Experimental equilibrium data will be supplemented by theoretical calculations. A tubular flow reactor equipped with analyzers to test the green liquor and reaction products will be designed. Such a reactor will also allow necessary adjustment for lime addition and result in uniform white liquor feed to the digester which in turn will allow stable digester operation, improved pulp quality and higher productivity.