CORRECT HUMIDITY EQUALS MAXIMUM PRODUCTIVITY
<name>, <job title> at <company name>, explains how dry air can seriously damage
production efficiency as well as tobacco flavour and how best to maintain humidity levels
to avoid these problems.
Tobacco leaves and paper are extremely hygroscopic materials – that is they are both
affected by the ambient moisture content of the surrounding air. If the humidity level of
the surrounding air is low, moisture is drawn from the materials, drying them out and
degrading their properties. This can lead to anything from tobacco shrinking and falling
out of cigarettes to cigar leaves cracking and paper misfeeding onto machines causing
delays on the production line.
Each stage of manufacturing cigars and cigarettes requires very specific humidity levels
to maintain the moisture content of the materials involved, ensuring production efficiency
and product quality.
Primary manufacture
When tobacco is first brought into the factory in bales and opened it is extremely dry.
One of the initial processes, often referred to as softening, involves the tobacco leaves
passing through a large steam-filled rotation cylinder. These areas have a very high
typical humidity of 85-88%RH (relative humidity) at 30-32oC due to moisture leakage
from the process into the ambient air. During this process the tobacco will increase in
moisture from about 1-2% to some 24% moisture by weight dependent on the client
requirement.
After the tobacco has been softened the stems of the leaves are removed. During this
stemming and stripping process the conditions should be about 70-75%RH and 24-29oC
in order to prevent the tobacco from drying out. The tobacco then undergoes its final
process in this area, casing and conditioning, where it is flavoured. In most production
plants the tobacco will leave the Primary area with a moisture content of between 1316%. This requires an ambient equilibrium humidity of between 60-68%RH to prevent
moisture loss.
Due to the fact that steam is involved in this process the humidity in the Primary area
often does not need to be maintained by humidification systems as the leakage from the
process will maintain the ambient humidity at a suitable level. However, in some
factories the processes are so well sealed that there is almost no steam leakage from
the process and therefore humidification systems are needed to maintain the required
conditions.
Tobacco Storage areas
After these initial processes the moistened tobacco is conveyed to large, normally open,
bins or silos, where it is stored until needed by the manufacturing machines. Some
smaller tobacco plants will not have silo storage but will rely on “Box” or “Cut” tobacco
stores.
These areas must be maintained at between 60-70%RH and 21-24oC as they have large
amounts of tobacco exposed to the ambient air. If humidity is not maintained at these
equilibrium levels the tobacco will start to dry.
Filter Production
Filter rod production is one of the few areas that has no real need for humidification as
the material used for the filters is not particularly moisture sensitive. However, if the
humidity drops below 50% electro-static charges can build up. This can cause filters to
stick together and damage the fluidity of their movement to the production area. For this
reason it is advisable to maintain the humidity above 50%RH and around 21oC as this
will totally eliminate static. Static charges will build up when the ambient humidity is
below 45% humidity irrespective of the temperature of the area.
Cigarette production areas
This is probably the most important area as far as humidity control is concerned. The
tobacco is normally delivered to the cigarette machine, via ducts using compressed air,
into a hopper above the maker. The tobacco is forced through a garniture in the shape of
a cigarette and is then wrapped in paper. The amount of moisture the tobacco loses in
this process depends on the speed of the machine and the exposure time to the ambient
and compressed air used to transport it from the storage area.
The paper that the cigarette is wrapped in also has to be kept in equilibrium with the
environment when it is stored on its reel. If its moisture content changes so will the
dimension of the reel of paper along its exposed edges. This can lead to tears, machine
miss-feeds and expensive downtime re-feeding the roll.
Most cigarette production areas in the UK are held at 65-68%RH at 21oC. The relative
humidity in this area is critical as it maintains the equilibrium moisture of the tobacco
around 13% to 16% by weight, the exact moisture content being product and blend
related. If the humidity falls below about 60%RH, the tobacco will start to lose moisture
and dry. This can in severe cases cause the tobacco to drop out of the cigarette when it
is held upside down. If the humidity exceeds 70%, the moisture addition can cause
staining on the paper, which is unacceptable to the end client. Therefore the
maintenance of humidity in production areas at 65%RH +/-5% is critical to the production
and the quality of the product.
During the cigarette manufacture and after the filter is inserted, the filter may be lasered
to burn small holes that allow air to be drawn into the smoke to control the smoking
characteristics of the cigarette. During the lasering process the humidity needs to be
kept at about 55%RH to prevent clogging of the suction holes in the holder. It is
sometimes necessary to dehumidify this section of the machine to achieve this 55%RH
level. This can be easily achieved by using small adsorption dehumidifiers mounted
along side the maker and the “dry” air ducted into the Lasering section.
Once the cigarette is complete it is fed onto a delivery system. From here it will take one
of two routes depending on the type of machine. Older style machines that do not have a
packing machine directly attached will deliver the cigarette to a sorter and then place
them into trays holding around 10,000 cigarettes each. These are then moved on trolleys
to another part of the production area where they are packed into cartons. Most of the
modern machines will have built-in packing sections to take the product directly from the
maker and pack into 20’s and then into cartons of 200.
Linked to the packing machine can be a storage/buffer system, which can hold several
thousand cigarettes at any one time. The buffer is used to take the production from the
maker, if making is faster than packing, and conversely it will keep the packing line
supplied if the maker is running slower. The maintenance of between 60-70%RH in and
around the storage system is again critical. The cigarettes can be stored for several
hours in the buffer and being exposed to ambient conditions would change their
equilibrium moisture if the relative humidity is not maintained at a nominal 65%.
Maintenance of humidity in the production area during shutdown periods, weekends,
meal breaks, etc, allows product to be left on the machine without loss of moisture,
weight and quality. This gives the advantage that product is available instantly without
having to wait for the maker to produce stock when production restarts.
There is one final area that is sometimes humidified, the ripping room. This is where
cigarettes that have not been made correctly and production waste are broken up and
the tobacco recovered, with the paper and filter being sent to waste. Any loss in moisture
will lead to poor recovery of tobacco so again these areas are generally maintained at
about 65%RH at 21ºC.
In order to maintain good humidity control in the any of the production and storage
areas, it is vital to maintain the temperature through the heating, ventilating and air
conditioning systems. These systems can introduce large volumes of fresh air to the
production hall depending on how they have been set up. Additionally most of the
cigarette making machines will have dust recovery systems, based on vacuum
extraction. This extraction has to be compensated for by the air handling plant, which will
also lead to large amounts of fresh air being introduced to the production area.
With these large air volumes being constantly introduced, the amount of moisture that
needs to be added can be very high, so great care is needed in the design of the
humidification systems. It is often forgotten that in winter when cold and wet air is drawn
into the building from outside and heated, the air’s relative humidity will fall. For instance,
winter air entering the building at 0ºC and 80%RH, when heated to 21ºC will give a
relative humidity of around 24%. With 65%RH being required to maintain the tobacco’s
moisture content, any air introduced with a relative humidity of 24% would lead to
moisture loss from the tobacco without correct humidification.
Humidity Control
Humidifiers have been around for a number of years in various shapes and forms. They
raise humidity by either releasing cold water or steam into the atmosphere. For large
industrial applications like cigarette production, heating water to produce steam would be
too expensive so cold-water humidifiers are the norm for this industry.
The most common type of cold-water humidifier is a spray atomising system. They come
in a wide variety of types, such as spinning disks, air/water atomising nozzles, highpressure water-only jets and crude spray washers.
Spinning disks and spray washers are relatively rare nowadays due to hygiene concerns
such as Legionella and Humidifier fever. Spinning disk systems typically consisted of a
tank from which water was dripped or drawn onto a spinning disk, distributing it into the
air. Unfortunately, a tank of water provides a good source of contamination and bacteria
can breed readily if the water is stale. This resulted in workers suffering from an illness
known as humidifier fever, which produced flu-like symptoms such as a tight chest,
headaches and sore eyes.
High-pressure water jets are sometimes found in air handling systems but are more
common for mist creation in outdoor situations such as amusement parks, as they were
prone to blockages and drips, which can cause disruption in busy industrial
environments.
Most widely used now are air/water atomisers, such as the JetSpray, which employ
nozzles to combine pressurised air and water to produce a very fine spray. This spray
quickly evaporates raising the humidity to the desired level. The nozzles are strategically
located around the ceiling area of the production plant to give the correct distribution of
moisture whilst also avoiding existing fittings such as lighting, air conditioning or
ductwork.
Nozzle-based humidifiers can cope with a very high capacity, give close control and, in
the case of the JetSpray humidifier, maintenance is minimal due to a self-cleaning
mechanism that avoids blockages. With the correct annual maintenance, this type of
system can give years of trouble free operation, which in a busy working environment is
essential. The nozzle is precision engineered to ensure correct atomization without the
risk of drips. Systems are available with capacities up to 600 litres per hour
These features make this type of system ideal for industrial applications. Even though
many atomising nozzle systems run directly from the potable mains water supply, all
cold-water humidifiers should employ failsafe UV sterilisation or silver ion dosing and
regular automatic water purge cycles to ensure cleanliness.
Any water quality can be used. If mineral dust left behind from the evaporating water is a
problem, which is unusual in most production areas, this can be eliminated using a
demineralised water supply from a reverse osmosis water purification system. In
contrast, the humidifier system also has the added benefit of suppressing existing dust in
the atmosphere and giving a cooling effect, making the working environment more
pleasant for staff.
Depending on where the production facility is in the world, the amount of humidity control
will vary according to seasonal climatic changes. In cooler regions indoor heating will
greatly affect the amount of moisture that is needed so winter seasons will create the
largest humidity demand.
Quality and Productivity
Wherever a factory is located humidity control is always essential. Without it production
is less efficient and product quality suffers. Ensuring that the tobacco and paper maintain
their optimum properties from when they enter the factory to when the cigarettes are
sealed in their protective packaging is a complex but always profitable calculation.
JS Humidifiers has spent over 30 years humidifying the tobacco industry with clients
including BAT, Alfred Dunhill, Imperial Tobacco, Rothmans International, Gallagher and
Altadis Seita. The company offers a comprehensive service of advice, design, supply,
installation and maintenance.
-ENDSFor further information on this article contact:
Duncan Buxton, Marketing Manager, JS Humidifiers, T: 01903 850200. E: dbuxton@jshumidifiers.com.