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。对于加拿大的一个典型的硫酸盐纸浆厂，该工艺每天产生多达12，000吨的稀释黑液，其中含有水、溶解的木材组分和废制浆化学品。这种大量的“废物”流必须通过工厂内的化学回收厂进行处理。回收过程包括浓缩黑液并在回收锅炉中燃烧以产生蒸汽和电力，同时将无机燃烧残余物转化回制浆化学品。燃烧导致在回收锅炉的底部形成熔融熔融物。当熔融物从锅炉中流出时，蒸汽喷射将其粉碎成小滴，然后落入下方的溶解罐中，在那里与水相互作用并溶解。 虽然用高压蒸汽射流粉碎熔融熔融物并将粉碎的熔融物溶解在溶解槽中是剧烈且通常危险的过程，但为了有效地处理大量熔融物并产生一致的绿色液体，它们是必要的。溶解槽不断发出巨大的轰鸣声，有时会引起附近地面和建筑物的震动。在严重的情况下，会发生爆炸，导致大量设备损坏和与计划外的锅炉停机相关的生产损失。据报告，爆炸或溶解罐喷出的热/腐蚀性绿色液体淋在人员身上也会造成人员伤亡。在过去的30年里，北美每年大约发生一起爆炸事件，尽管实际数字可能更高，因为许多事件没有报告。毫无疑问，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浆米尔斯厂的首要任务。 该研究计划包括三个主要任务：1）调查熔融熔体的粉碎行为的蒸汽射流，2）调查熔融熔体和水的相互作用和3）开发的在线噪声监测系统。 其目的是获得基本数据的熔融粉碎的蒸汽射流和熔融物-水的相互作用在溶解槽，并系统地检查的熔融粉碎和爆炸的溶解槽的关键操作参数的影响。长期目标是帮助硫酸盐纸浆米尔斯厂开发可行的方法/策略，以确保安全有效的溶解罐操作。 加拿大目前有28家硫酸盐纸浆米尔斯厂。他们将通过更好地了解熔融熔体和水的相互作用以及完全控制爆炸的操作条件，从研究计划中受益匪浅。这将使米尔斯制定可行的指导方针和战略，以提高溶解罐的效率和安全性，并为工厂人员提供一个更安全，更安静的工作环境。研究计划的成功完成还将帮助米尔斯设计减少破碎蒸汽使用的方法，通过更安全和更可预测的操作减少保险费，并避免溶解罐爆炸造成的回收锅炉停机。 该研究计划将帮助培养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提供许多机会，为未来的职业生涯做好准备。

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.