Research Progress of Pretreatment Technology and Equipment for Raw Materials of Reconstituted Tobacco

Zhen XIONG Guiyuan ZHOU Wenjun ZHANG Rui LI Xiaosheng WANG Kechao SHANG Yu QIN

Abstract The purpose of pretreating raw materials of reconstituted tobacco is to improve the quality of raw materials as well as product quality and production efficiency. In recent years, the research achievements and equipment status of the pretreatment technology of reconstituted tobacco raw materials in China were systematically reviewed, and the research and equipment development prospects of the pretreatment technology of reconstituted tobacco raw materials were prospected.

Key words Reconstituted tobacco; Raw material; Pretreatment technology

Received: September 23, 2020  Accepted: November 29, 2020

Zhen XIONG (1988-), female, P. R. China, engineer, devoted to research about reconstituted tobacco.

*Corresponding author. E-mail: xiongzhen@cts-yn.com.

Reconstituted tobacco is obtained from the industrial recombination and processing of tobacco waste (fragments, cigarette ends, tobacco stalks, non-applicable tobacco leaves for industry, etc.). The physical and chemical characteristics of reconstituted tobacco are similar to natural tobacco［1-4］, which have significant effects on reducing coke and harm of cigarettes and have been recognized by people. However, most of the raw materials are produced in the threshing & redrying and cigarette processing. The size of tobacco stalk is uneven, the water content is greatly different, and the chemical composition of tobacco stalk fluctuates greatly in the threshing & redrying. The degree of homogenization of smoke dust and debris is low, and there are many sundries such as stalk stick, dust and hemp rope. The soot sticks produced during the process of making silk rolls are poor in purity. The stems and leaves are not separated, and some raw materials mildew. The overall stability of raw materials is poor, and if directly used in the production of reconstituted tobacco, it will have a great impact on product quality［5］. In order to improve the quality of reconstituted tobacco, it is important to ensure the uniformity, stability and safety of raw materials. Therefore, many scholars have paid attention to the pretreatment technology and equipment of reconstituted tobacco raw material. This article summarizes the typical raw material pretreatment technology and equipment for reconstituted tobacco production, including raw material classification, leaf and stem separation, water regulation and purification and removal of impurities, etc., to provide a raw material basis for subsequent formulation modular processing, and a brief introduction to raw material pretreatment Processing technology and equipment. It aims to provide a reference for the selection of pretreatment technology and equipment for the production of raw materials for reconstituted tobacco.

Finishing Classification

There are many batches and uneven quality of reconstituted tobacco raw materials. However, raw materials are one of the factors to guarantee the quality of reconstituted tobacco, so it is important to control the quality of raw materials before feeding. According to the characteristics of the raw materials, they are pretreated by different sorting and grading methods. For example, For industrial tobacco, the current common method is to manually remove the packaging bag ［6-7］, combined with the demand of tobacco leaf raw materials, moldy and carbonized raw materials were removed by manual solution. Fragments, tobacco powder and tobacco soot can pass screening technology, and the reference equipment is a vibrating screen［8］, through which tobacco by-products with the required size can be screened. After the tobacco leaves are measured, they are transported into the waste tobacco crushing device. After being crushed to a size suitable for the production of reconstituted tobacco, the mixed raw materials transported to the air separation chamber are neutralized and thrown. The weight of the stems, leaves and impurities are adjusted by adjusting the wind and wind speed. Substances with different shapes are separated and flow out from different blanking openings. The tobacco leaf treatment stem and leaf separation process ensures the stable quality of raw materials ［9］.

Stems and Leaves Separated

At present, discarded tobacco is widely used as raw materials for the production of reconstituted tobacco, and the overall quality of discarded tobacco is uneven. If it is applied to the production of reconstituted tobacco, it will inevitably affect the quality of reconstituted tobacco, which needs to be treated［10］. Zhang et al.［11］ invented a paper-making method for reconstituted tobacco raw material stem and leaf separation system, which consists of a hoist, a stem leaf cracking machine, a wind separator, and a blanking device in turn to form a system. William. Cunningham［12］ invented a device for tobacco threshing , including a rotatable tearing device and a feeder. The feeder includes a pair of elements for feeding tobacco into the tearing device that cooperate with each other and can rotate in opposite directions. The feeder and the tearing device are configured to be subjected to a shearing force when the tobacco leaves pass through the counter-rotating element and the rotating tearing device, and the shearing force can tear at least a part of the tobacco leaves from the tobacco stems.

Moisture Adjustment

The characteristics of large difference in moisture of tobacco stalks and leaves in commercial purchase during the threshing & redrying are described. Water is one of the important detection indexes of raw materials and reconstituted tobacco products. Therefore, water should be strictly controlled in the storage of reconstituted tobacco raw materials. At present, the water control of reconstituted tobacco raw materials in China refers to the development and design of the threshing & redrying technology for water adjustment equipment, that is, drum dryer［13］. The objective is to effectively control the moisture uniformity of tobacco raw materials and avoid mildew and insect pests caused by high moisture content. The wind speed of conveying network belt and network surface is adjusted by the wind guide plate and circulator frequency conversion, so that the wind speed of the network surface is close to uniform. Through the hot air recycling system, the steam consumption is reduced, and the energy consumption of the flue gas the threshing & redrying machine is effectively reduced［14］.

Purify and Remove Impurities

Physical elimination

With the expansion of the production scale of reconstituted tobacco and the increase in production capacity, raw materials have been difficult to meet production needs. Raw materials with different quality are used as raw materials, and these raw materials are difficult to be screened and quality controlled［15］. After conventional treatment, the requirements for use are not met, which affects the application of reconstituted tobacco products in the formulation of leaf groups. To this end, the ash bar is used for microwave irradiation with a microwave device, so that the ash bar is loosely broken and subjected to fine tobacco stem and soot sorting to meet the needs of subsequent production and processing. The use of microwave equipment for microwave irradiation causes the tobacco rods to be loosely broken. The fine tobacco stems and tobacco dust are sorted to meet the needs of subsequent production and processing. Microwave irradiation can improve the quality of tobacco rods, including the smoking quality and kill the content of the tobacco rods. Harmful insects, bacteria) The separation of fine tobacco stems and tobacco dust improves the availability of tobacco sticks［16］.The automatic removal and collection of iron impurities in the reconstituted tobacco material can also be carried out by using an automatic electromagnetic impurity removal technique, which systematically and efficiently removes a large amount of iron impurities contained in the reconstituted tobacco leaf material［17］. The separation principle can be used to separate impurities by the weight and traits of stems, leaves and debris through the wind selection chamber［18］.

Methods of water washing, microwave and high pressure treatment

The impurities in tobacco stalks are removed by means of water washing, microwave and high pressure treatment, so as to improve the wood gas and scorched gas brought by tobacco stalks to remanufactured tobacco leaves. Stem washing process is to use constant temperature circulating water to treat tobacco stalks online after beating. Sun et al.［19］ adopted the core technology to improve the quality of tobacco stalk pulping through stem washing, and the specific process was carried out in sequence: stem washing, extraction,  pulping, and pretreatment of tobacco stalks with a screw conjugate grinding multifunctional pulping machine. Through the introduction of the water stem washing equipment produced by Henan Gongyi Machinery Factory, the tobacco stems after being beaten are processed on-line with constant temperature circulating water. The corrugated tank bottom of the equipment is convenient for the water to form ripples at a certain flow rate to impact the tobacco stems, so that the tobacco stems are rolled in the water tank for sufficient cleaning; at the same time, some metal stones and other sundries sink into the bottom of the tank. After the tobacco stems exit the water tank, they enter the stem storage cabinet through the water filter belt for softening. This method confirms the final stalk washing process, which is more effective than the moistening stalk process［20-21］. Zhao et al.［22］ invented a pretreatment method of microwave expanded stem. The specific process flow is as follows: raw material preparation, quantitative feeding, tobacco stem warming, microwave expansion, microwave moisture removal, cooling and shaping, and stem silk production., Some researchers have designed a new type of tobacco stem pretreatment equipment, that is, a microwave stem humidifier using microwave technology［23］ and verified the production of key technological parameters in the tobacco stalk pretreatment process. The tobacco stalks are heated by superheated steam under conventional pressure, and then a small amount of superheated steam with pressure not less than 1.2 mpa is injected into the air lock cavity released by the expansion of the tobacco stalks to realize the expansion of the tobacco stalks［24］. The equipment includes the successively connected feed air lock, the tobacco stalk heating device and the discharge expansion air lock.

Recipe Module Technology

The blending uniformity of raw materials and formulas plays a decisive role in the physical quality, internal quality and stability of remanufactured tobacco leaves.  The raw material mixing process generally budgets the raw materials of each batch according to the production batch. However, the reconstituted tobacco products use many types of raw materials, and the nature of the production requires a small amount of material to be discharged, and at the same time, it is difficult to ensure that the quality of each batch is uniform. Accurate control is not conducive to the organization and production of formula feeding, and it is not conducive to the stability of product quality. At the same time, the labor intensity of batching and discharging is high. Liu et al.［25］ made full pretreatment of tobacco stalks and tobacco leaves before raw material premixing through the integrated process of raw material pretreatment and automatic control of production feeding for remanufactured tobacco leaves, and determined the ratio of production feeding structure and feeding mixing technology to form the pretreatment technology of raw material uniformity of components. Wang［26］ designed a pre-treatment and blending system for tobacco flake raw materials, which effectively realized that raw materials were put from the feeding port according to the process menu to the discharge according to the batching procedure. It can effectively improve the efficiency of the production site, while ensuring the uniformity of the materials and the stability of the quality are of great significance, and the operation is simple and convenient.

Agricultural Biotechnology2021

Comparison of Pretreatment Methods Abroad

With the development of domestic pretreatment technology for remanufactured tobacco raw materials, the application of tobacco by-products in the formula of remanufactured tobacco raw materials has been solved, and the comprehensive domestic pretreatment technology covers physical method, chemical method and biological method, etc. ［27-28］. However, the pretreatment of remanufactured tobacco leaves in foreign countries mainly adopts chemical methods to reduce the material content regardless of product quality. In 1999, American Brown&Wlilliamson tobacco company used ammonium salt and urea to treat the raw material of remanufactured tobacco leaves, and then placed it under the steam pressure of 60 psi for 1-5 min to remove the components that did not care about smoking［29］. In 2001, British American tobacco company added acetate or alkaline solution to treat the raw material in the production process of remanufactured tobacco leaves to reduce the protein content of the product ［30］.

Conclusions and Prospects

Various pretreatment processes and the current equipment development in China are analyzed and compared with the pretreatment of raw materials abroad. Although these methods have their own advantages, the existing pretreatment technology has many shortcomings, a single technology has a high cost, low efficiency and other disadvantages. Through the analysis of common raw material classification, petiole separation, moisture adjustment and purification and impurity removal, formula mixing and other technologies, such as a reasonable combination of different pretreatment technologies, a complete set of reconstituted tobacco raw material pretreatment production lines will be realized, which will be effective. The reduction of reconstituted tobacco leaves the stability of product quality due to fluctuations in the production raw materials.

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