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

牛皮纸浆厂熔炼溶解罐运行安全问题的基础研究

• 批准号: RGPIN-2014-04387
• 负责人: Tran, Honghi
• 金额: $ 2.11万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611005
• 关键词: FUNDAMENTAL; STUDIES; SAFETY; ISSUES; SMELT

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.

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。