FUNDAMENTAL STUDIES OF SAFETY ISSUES IN SMELT DISSOLVING TANK OPERATION IN KRAFT PULP MILLS

硫酸盐法是制造木浆的主要方法。对于加拿大一家典型的硫酸盐纸浆厂来说，这一过程每天会产生多达1.2万吨的稀释黑液，其中含有水、溶解的木材成分和废纸浆化学品。这些巨大的“废物”流必须通过工厂内的化学回收厂进行处理。回收过程包括将黑液浓缩并在回收锅炉中燃烧以产生蒸汽和电力，同时将无机燃烧残渣转化为制浆化学品。燃烧会在回收锅炉底部形成熔融熔体。当熔融的熔体从锅炉中涌出时，熔融的熔体被蒸汽喷射破碎成小液滴，然后落入下面的溶化池中，在那里它与水相互作用并溶解。虽然用高压蒸汽射流粉碎熔体和在溶解槽中溶解破碎的熔体是激烈且往往是危险的过程，但为了有效地处理大量的熔体熔体，并产生一致的绿色白酒，它们是必要的。正在溶解的坦克不断发出隆隆的响声，有时会引起地面和附近建筑物的震动。在严重的情况下，会发生爆炸，造成大量设备损坏和与计划外锅炉停机相关的生产损失。据报告，人员伤亡也是由爆炸或从溶化罐喷出的热/腐蚀性绿色液体淋浴造成的。在过去的30年里，北美每年大约报告一起爆炸事件，尽管实际数字可能更高，因为许多事件没有报告。不用说，在工作场所安全方面，一次爆炸事件太多了。近年来，随着职业健康和安全法规的日益严格，有效和安全的溶解槽操作已成为硫酸盐纸浆厂的首要任务。建议的研究计划包括三个主要任务：1)研究蒸汽喷射熔体的破碎行为；2)研究熔体与水的相互作用；3)开发在线噪声监测系统。其目的是获得有关蒸汽喷射熔体破碎和熔体-水相互作用的基本数据，并系统地考察溶质池的关键操作参数对熔体破碎和爆炸的影响。长期目标是帮助硫酸盐纸浆厂开发可行的方法/策略，以确保安全高效地运行溶解槽。目前，加拿大有28家硫酸盐纸浆厂。通过更好地了解熔融熔炼和水的相互作用，以及完全控制爆炸的操作条件，他们将从该研究计划中受益匪浅。这将使磨坊制定可行的指导方针和战略，以提高溶解槽的效率和安全性，并为磨坊员工提供更安全、更安静的工作环境。该研究项目的成功完成还将帮助工厂设计出减少破碎蒸汽使用量的方法，通过更安全和更可预测的操作来降低保险费，并避免因溶解储罐爆炸而导致的回收锅炉关闭。该研究项目将帮助培养7名高素质人才(1名博士、4名硕士和2名本科生)。这些研究项目与行业应用密切相关，具有巨大的社会、环境和经济影响，因此将为这些HQP提供许多为未来职业生涯做准备的机会。

The kraft process is the predominant method for making wood pulp. For a typical kraft mill in Canada, the process generates as much as 12,000 tonnes/day of dilute black liquor that contains water, dissolved wood components and spent pulping chemicals. This massive “waste” stream must be processed through the chemical recovery plant within the mill. The recovery process involves concentrating the black liquor and burning it in a recovery boiler to produce steam and power, and at the same time, converting the inorganic combustion residue back into pulping chemicals. The combustion results in the formation of molten smelt at the bottom of the recovery boiler. As it pours out of the boiler, molten smelt is shattered by a steam jet into small droplets before falling into the dissolving tank underneath where it interacts with water and dissolves. While shattering molten smelt with a high pressure steam jet, and dissolving the shattered smelt in the dissolving tank, are violent and often dangerous processes, they are necessary in order to process the large amount of molten smelt effectively, and to produce consistent green liquor. Dissolving tanks constantly rumble loudly, and at times, cause tremors of the ground and buildings nearby. In severe cases, explosions occur, causing substantial equipment damage and production loss associated with unscheduled boiler downtime. Personnel injuries and fatalities have also been reported to be caused by explosion or by being showered with hot/corrosive green liquor ejected from the dissolving tank. Over the past 30 years, there has been about one explosion incident a year reported in North America, although the actual number could be higher as many incidents go unreported. Needless to say, one explosion incident is too many when it comes to workplace safety. As regulations on occupational health and safety have become increasingly stringent in recent years, effective and safe dissolving tank operation has become a top priority for kraft pulp mills. The proposed research program consists of three main tasks: 1) investigation of the shattering behaviour of molten smelt by a steam jet, 2) investigation of molten smelt and water interaction and 3) development of an on-line noise monitoring system. The objectives are to obtain fundamental data on smelt shattering by a steam jet and smelt-water interaction in the dissolving tank, and to systematically examine the effects of key dissolving tank operating parameters on smelt shattering and explosion. The long-term goal is to help kraft pulp mills develop viable means/strategies to ensure safe and efficient dissolving tank operation. There are presently 28 kraft pulp mills in Canada. They will benefit greatly from the research program through a better understanding of how molten smelt and water interact, and the operating conditions under which an explosion can be completely controlled. This will allow mills to develop viable guidelines and strategies for increasing dissolving tank efficiency and safety, and provide mill personnel with a safer and quieter working environment. Successful completion of the research program will also help mills to devise ways to reduce shattering steam usage, reduce insurance premiums through safer and more predictable operation, and avoid a recovery boiler shutdown caused by dissolving tank explosion. The research program will help train 7 highly qualified personnel (1 PhD, 4 MASc and 2 undergraduate students). The research projects are intimately tied to industry applications, with great social, environmental and economical impacts, and thus will provide these HQP with many opportunities to prepare themselves for future careers.