Sappi Ngodwana Mill today announced its wish to “apologise for the inconvenience caused by the unpleasant odour that has been experienced from time to time over the last month.”
In a statement, it said that it is not their intention to cause discomfort to their employees or the community, adding “We are currently busy optimising our plant, but in the process we have had some unforeseen occurrences which have unfortunately adversely impacted the mill odour.”
Here follows some information about the cause of the odour and the effects thereof on people and animals:
What is the smell?
The odour that we have been experiencing sporadically over the past month is worse than the usual smell associated with the kraft pulping process. Usually when the mill cooks wood chips to extract their fibres for making pulp, sulphide compounds are generated. During this process some compound losses occur to atmosphere, and these compounds have an odour. Sulphide compounds are detectable by the human nose at extremely low concentrations. We are so sensitive to the smell that if a drop the size of a pinhead was present in an Olympic size swimming pool, we would immediately be able to detect it. For this reason it will not be possible to totally eliminate the odour from our production process.
However, the recent increase in odour is more unpleasant, and is directly related to the unexpected outage of the mill’s lime kiln. The lime kiln is critical for odour management because it burns or rather incinerates odorous gases collected from the fibre lines and evaporator plant. When the lime kiln is off, for maintenance purposes or due to unscheduled incidents such as now, these gases cannot be incinerated and are then vented or released into the atmosphere. The odorous gases consist of Total Reduced Sulphur gases (TRS gases), which we monitor at our ambient air quality monitoring station. Similar to the smell of boiling cabbage, these gases are not harmful, but they do have an unpleasant odour.
When will the smell improve?
We are working very hard to fix the problem and indications are that the lime kiln will be up and running again by Friday this week which will subsequently reduce the odour. In the short- to medium-term, the mill is also working on several other projects to optimise gas collection and incineration in the lime kiln.
The new Specialised Cellulose Fibre Line is integrated in the existing mill processes, and the start-up of the new plant is a complex process, unlike buying a new car, which drives effortlessly the moment you start the car. We started up the new plant in August 2013, gradually increasing production, whilst simultaneously making adjustments to ensure plant stability at each stage. The aim is to optimise operational efficiency, which would also result in improved odour.
What does Sappi do to reduce the mill’s odour?
The current situation is temporary, and things should return to normal when the Lime Kiln is up and running by May 16.
In general, since 1990 the Mill has spent roughly R2.87 billion to reduce its air emission impact. In general there has been a significant reduction in both the area affected and the concentration of detectable gas particles by implementing new technology. Unfortunately it is still impossible to contain the odour to a specific area, and the problem can be worsened by climatic conditions such as low clouds, wind direction or temperature inversion.
In respect of the new Fibre Line, we are still making alterations to the new plant, as we still have to do the performance run. We believe that once that has been completed, the situation would have improved.
Does the odour pose a health hazard to people or animals?
No, the emissions pose neither a health nor an environmental risk. In fact, the Mill’s gas emissions are significantly below acceptable world health standards. International health organisations have established a Permissible Exposure Limit (PEL) (8 hour time-weighted average) of 10 parts per million (ppm) for these gases. Even during times when the kiln is off, we never recorded values above 0.2 ppm, which is 2% of the PEL and thus not harmful to your health. The odour threshold for these gases is, however 0.00047 ppm and we constantly run above this when the kiln is off.
These values represent the emissions at the point of highest concentration (the point sources), namely the process stacks as well as through the Mill’s ambient air monitoring station. In the measurement and modelling of the air emissions, the mill works with world renowned experts in their fields.
Will this smell be permanent?
The expectation is that the intensity of the smell will drastically improve, and that it should not be an inconvenience to Nelspruit residents once the lime kiln is functioning optimally.
General odour in and around Nelspruit
We do not monitor odorous gasses in Nelspruit. There are various large industries in and around town which all have an impact on the odour in the area and it would not be possible for us to isolate Ngdowana Mill’s impact from the rest.
It is important to remember that these odours are usually more detectable in winter, due to weather conditions such as temperature inversion.
More about our new Specialised Cellulose Plant
Sappi’s increased capacity of Specialised Cellulose is a strategic decision, aimed at securing the company’s future sustainability.
In addition to producing newsprint and Kraft Liner Board, Ngodwana Mill also produces Specialised Cellulose. The new plant will contribute 210,000 tons of specialised cellulose per year to Sappi’s overall capacity of 1,3 million tons per year. Sappi is the world’s largest producer of specialised cellulose with 60% of our production being used in the textiles and clothing industry as viscose, rayon, Lyocell and Tencel. This market grows by at least 6% each year. Our product is also used in many consumer, pharmaceutical and household products and foodstuffs.
