Tobacco Leaf Processing
The world grows 7.5 million metric tons of tobacco, which is then used to make 5.5 trillion cigarettes. As a highly valued crop, tobacco leaf has to go through a lot of steps before it can be made into things like cigarettes, cigars, pipe tobacco, and other things. The first step is to process the tobacco leaves.
Whole tobacco leaves have a central stem (called a midrib) and a leaf (called a lamina). The midrib and leaf are separated mechanically at the leaf processing plant because they are used in different ways at the primary processing plant. The amount of moisture in these two parts is important for separating them (called “threshing”) and packing them into storage cases before making finished tobacco products. Moisture affects the taste, burn, fill, waste, and how the machine works.
Steps in Making Tobacco Leaves
Taking care of green leaves and stems
To get the harvested tobacco leaves ready for the mechanical threshing process, hot air and steam are used to make the leaves more flexible in cylinders. The conditioning cylinder is a rotating drum with steam jet nozzles that add moisture to the tobacco. Each steam jet nozzle can be controlled separately. The threshing process is next for the tobacco that has been cured.
How Tobacco Is CrushedMCT460-T A moisture sensor for tobacco leaves
The leaf that has been cleaned and dried goes through a series of mechanical threshers and air separators. The drums and blades of the thresher pull the lamina off the stems, and the thresher makes a mix of lamina, stems, and leaves that haven’t been threshed. This mix is put into a classifier, which separates the lamina from the leaf that hasn’t been threshed and the stem. The lamina moves on to the next step, while the leaf and stem parts that haven’t been threshed go into the next thresher. Repeat threshing and sorting until all of the stems and leaves are separated.
The stem is now on the stem conditioning line, which makes the stem more moist than the green leaf. The stem is then cut with a stem cutter to make a uniform cut, and the drying process begins, which is the same as for the lamina.
Lamina from different classifiers has different amounts of moisture, so the moisture needs to be made the same so that the lamina can be stored well. First, the lamina goes through a drying chamber to make sure the moisture level is the same everywhere. The dried lamina is cooled, and then it goes into a chamber with high humidity where it soaks up water and reaches equilibrium. The lamina is then put into packages and put away until it needs to be used. Stems are treated the same way and dried on a separate line so that they can be stored the same way.
Quality Metrics and Points of Measurement
Taking care of green leaves and stems
For tobacco green leaf threshing (GLT) to work well, the leaf must have between 17 and 22% moisture. To get the right amount of moisture, green leaf tobacco is conditioned in cylinders with steam that can be changed to control how much moisture comes out. To optimize GLT and get the desired strand length, it’s important to measure the moisture level accurately.
By controlling the amount of steam, the moisture level of the stem is brought up to about 40%. This makes it more flexible for the cutting process.
To store tobacco safely for a long time and make sure it is of good quality, the lamina and stems must have a moisture level between 11 and 12%. When the lamina comes out of the drying chamber, it is somewhere between 6 and 8% moisture, and when it comes out of the humidity chamber, it is between 11 and 12% moisture. Usually, the packed leaves and stems are put away for at least 6 months to age or soften.
Temperature: In addition to measuring moisture, you can also measure temperature in real time to see how well drying and conditioning are going.
Measuring Points: Conditioning and Drying of Green Leaves and Stems
The Pioneer Tobacco (PT) MCT460-T Tobacco NIR Moisture Sensor can be placed at the entrance or exit of the conditioning cylinder and the drying chamber to measure moisture in real time. Closed loop process control makes it possible to get the most out of conditioning and drying by using the standard 4-20mA/0-10v output or an optional digital output (ProfiNet, ProfiBus, Ethernet IP, Modbus TCP, or DeviceNet).
The sensor is placed 8 to 10 inches above and far enough down the conveyor so that water vapor from the tobacco doesn’t affect measurements. A built-in IR temperature sensor can be added to the MCT460-T so that the temperature of the tobacco can be monitored during both drying and conditioning.
Price and value
Moisture control is a very important part of the process of turning a green tobacco leaf into a finished lamina and stem. With a Pioneer Tobacco MCT460-T moisture analyzer for closed loop process control, all parts of the process will work as well as possible. It will help make a consistent, high-quality finished product that can be stored safely for months until it is used at a second processing plant to make a finished product.
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