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卡夫工厂来说，这一过程每天产生多达1.2万吨的稀释黑液，其中含有水、溶解的木材成分和废制浆化学品。这种巨大的“废物”流必须通过工厂内的化学回收装置进行处理。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，同时将无机燃烧残留物转化为制浆化学品。燃烧导致在回收锅炉底部形成熔融熔体。当熔体从锅炉中流出时，蒸汽喷射将熔体粉碎成小液滴，然后落入下面的溶解罐中，在那里它与水相互作用并溶解。用高压蒸汽射流粉碎熔融熔体，并将破碎的熔体溶解在溶解罐中，这是一个暴力且往往危险的过程，但为了有效地处理大量熔融熔体，并产生一致的绿色液，这是必要的。溶解的坦克不断发出巨大的隆隆声，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，造成大量设备损坏和与锅炉计划外停机有关的生产损失。据报告，也有人员受伤和死亡是由于爆炸或被从溶解罐中喷出的热/腐蚀性绿色液体淋湿造成的。在过去的30年里，北美每年大约有一起爆炸事件被报道，尽管实际数字可能更高，因为许多事件没有被报道。不用说，就工作场所安全而言，一起爆炸事故已经太多了。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。提出的研究计划包括三个主要任务：1)研究熔体在蒸汽射流下的破碎行为，2)研究熔体与水的相互作用，3)开发在线噪声监测系统。目的是获得熔体在蒸汽喷射和熔体-水相互作用下破碎的基本数据，并系统地研究溶解池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制定可行的手段/策略，以确保安全和有效的溶解罐操作。目前加拿大有28家卡夫纸浆厂。通过更好地了解熔融熔体和水如何相互作用，以及爆炸可以完全控制的操作条件，他们将从研究计划中受益匪浅。这将允许工厂制定可行的指导方针和策略，以提高溶解罐的效率和安全性，并为工厂人员提供更安全和更安静的工作环境。研究项目的成功完成还将有助于工厂设计出减少破碎蒸汽使用量的方法，通过更安全、更可预测的操作降低保险费用，并避免因溶解罐爆炸而导致回收锅炉关闭。培养高层次人才7人（博士1人、硕士4人、本科生2人）。这些研究项目与工业应用密切相关，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，为他们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.