Sugarcane sugar-making technology

There are two methods to extract sugarcane juice from sugarcane: squeezing method and exudation method. Squeezing is a method of extracting sugarcane juice through pretreatment and squeezing equipment combined with osmotic system. Percolation is a method that sugar cane is pretreated and crushed, and then sugar cane materials are leached with water and dilute sugar juice through percolation equipment and a certain juice flow system, so that sugar cane is continuously leached and washed out.

Sugarcane pressing method

The principle of squeezing juice is mainly to cut sugarcane into filiform and flaky sugarcane materials and put them into a squeezing machine, so that the cell wall of sugarcane cells filled with sugarcane juice is broken under the pressure of the squeezing roller and oil pressure, the sugarcane materials are compressed, the cells are crushed and the sugarcane juice is discharged; With the aid of the osmotic system, the bagasse discharged from the extruder and started to swell was infiltrated with water or dilute juice to dilute the sugar in the cells and extract more sugarcane juice.

Sugarcane has been squeezed several times by several three-roll presses. Before the sugarcane raw materials enter the last press, water is added for infiltration. The added water is called soaking, and the general dosage is 15 ~ 25% of sugarcane. The juice squeezed from the last press is called the juice squeezed from the last press, which is immediately pumped into the previous press as leachate to percolate the sugarcane materials entering this press, and the diluted juice squeezed out is used as the leachate of the previous press, thus reaching the second press. This is the common composite percolation method in sugar mills. The juices squeezed by the first and second juicers are combined into mixed juice and sent to be cleaned. The raw material of sugarcane discharged from the last press is called bagasse. Bagasse contains 45-50% water, 1-4% sugar, 45-52% fiber and 1.5-6% soluble solids. Bagasse is sent to boilers as fuel or used as other industrial raw materials. Sugar extraction rate is used to measure the sugar extraction efficiency of juice extraction method, which is defined as the mass percentage of sucrose extracted from sugarcane to sucrose in sugarcane. The sugar yield of cane sugar mills is between 92% and 97%.

The main equipment for squeezing juice includes sugarcane cutter, squeezing and its driving device, infiltration system and corresponding conveying equipment. The sugarcane cutter consists of a sugarcane cutter and a driving device. The printing machine consists of three rollers and a frame. The rollers of a three-roller press are embedded in a triangle, which are called top roller, front roller and back roller respectively according to their positions. There is a certain gap between the upper roller and the front and rear rollers. The shaft ends of the three pressure rollers are provided with transmission teeth, and the top roller is driven by a motor, a steam turbine or a steam engine through a reducer, so that the three pressure rollers rotate at the same speed.

The production capacity of sugar cane sugar factory is expressed by the tonnage of sugar cane squeezed by sugar factory every day. The ability to treat sugarcane is related to the times of pressing, the crushing degree of sugarcane, the diameter and length of pressing roller, the speed of roller, the fiber content of sugarcane and the requirements for sugar extraction. Usually, sugar factories use 4-6 presses to form a press train. There are 2 rows and 3 rows to meet the production needs.

The chemical composition of sugarcane juice varies with the chemical composition of sugarcane, storage time and post-harvest environment. Table 1 [Components of sugarcane juice] Chemical components of sugarcane juice.

Since the late 1980s, on the one hand, the extraction technology of sugarcane juice tends to strengthen the pretreatment of sugarcane, so that the crushing degree can be increased to 70-80%; Pay attention to the use of high feed trough, or use two pressure feed rollers (also known as toothed feed rollers) and a traditional three-roller press to form a five-roller press, so as to strengthen the feeding and preloading of the press and improve the production capacity of the press; On the other hand, in the percolation process, on the basis of the composite percolation system, most of the dilute juice from squeezing is refluxed to squeezing, and the amount of leachate is increased without increasing the amount of percolation water, so that the liquid content of bagasse reaches saturation and the residual sugar of sugarcane is fully percolated and diluted, thereby further improving the sugar yield.

Squeezing method consumes more steel and electricity, but it has the advantages of strong adaptability, convenient technical management and reliable operation, and is still the main method of sugarcane juice extraction.

Sugarcane exudation method

The basic principle of sugarcane exudation method is that there is a plasma membrane between cytoplasm and cell wall in sugarcane cells, which can selectively absorb extracellular substances. Therefore, the leaching operation of solid-liquid extraction can be used to transfer sucrose molecules in sugarcane to the leachate through washing, dilution, infiltration and diffusion, so as to extract sugar. Sugarcane percolation juice extraction technology mainly includes sugarcane pretreatment, sugar infiltration and wet bagasse dehydration. The exudation process can be divided into two categories: one is the exudation of sugarcane shreds, which are pretreated into sugarcane shreds and then enter the exudation device, and the exudation juice is obtained by exudation water and dilute juice; One is bagasse squeezing, in which the pretreated sugarcane shreds are squeezed to extract the original sugarcane juice equivalent to 60-80% of the sugar content of sugarcane, and then the juice is further squeezed in a squeezing device, and the squeezed original sugarcane juice and squeezed juice are combined into a mixed juice for purification. The sugarcane material coming out of the percolator is called wet bagasse, and its water content is about 85%. Dehydrate in dehydration equipment, the water content is reduced to below 50%, and then send it to the boiler for fuel or other industrial raw materials. The dilute juice obtained by dehydration equipment is called dehydrated juice, which is usually purified by chemical and physical methods such as adding phosphoric acid, lime and heating, and the clear juice is led back to the exudation device to help extract and recover more sugar. The extraction rate of sugar by exudation method is roughly the same as that by pressing method.

Sugarcane pretreatment technology requires that the sugarcane crushing degree of bagasse infiltration method is 75-80%, and that of sugarcane silk infiltration method is 85-90%. Sugarcane shreds should be thin and flaky, and there should not be too much sugarcane crumbs, which is conducive to the more effective seepage of sugarcane sugar. Pretreatment equipment commonly used tearing machine or heavy hammer tearing machine, sugarcane cutter or their combination equipment. The dewatering equipment uses a three-roll press. There are many forms of exudate, mainly silver type, BMA type, dessmet type, DdS type and Saturne type. Different forms of exudates have their own characteristics, but the process effect is roughly the same. All kinds of exudators have moving parts and graded infiltration systems, so that sugarcane materials can move forward continuously or rotationally. Pretreated sugarcane raw materials are sent to one end of a percolator, and percolating water accounting for 25% of sugarcane quantity is added to the other end, sugar is extracted by percolating, and wet bagasse is discharged from this end. With the help of multi-stage percolation system, the sugarcane material and the extraction solution are subjected to multi-stage countercurrent percolation, and the percolated juice is discharged from the end of the sugarcane material. Infiltration system grade, sugarcane silk seepage grade 12 ~ 18, seepage time 20 ~ 35 minutes; The leaching grade of bagasse is 8 ~ 12, and the leaching time is 16 ~ 26 minutes. The exudation temperature is to keep the exudation temperature in the thermal cracking area of the exudation device at 80 ~ 90℃ by heating the dilute juice, and the final exudation temperature is 50 ~ 65℃. The main factors affecting the extraction efficiency of percolated sugar are sugarcane crushing degree, percolating temperature, percolating time and percolating water quantity. The production capacity of the percolator mainly depends on its standard size and the flow rate of sugarcane juice flowing through the sugarcane bed. The factors affecting the speed of sugarcane juice flowing through sugarcane bed are sugarcane quality, pretreatment crushing degree, sugarcane bed thickness, dehydrated juice quality and seepage temperature.

Juice extraction by exudation has the advantages of saving steel, electricity, investment and maintenance costs. But the technical management requirements are higher and the steam consumption is more. With the help of chemical and physical-chemical actions of detergent and heating, various non-sugar substances affecting sucrose crystallization in mixed juice were removed as much as possible by solid-liquid separation, and clear juice with low color value was obtained.

The sugar-making method of sugarcane is named after the main detergent used in the cleaning process. The common cleaning methods for sugar cane production in various sugar-producing countries are mainly sulfite method, lime method and carbonic acid method.

The sulfuric acid process uses lime and sulfur dioxide as the main detergents. The mixed juice is pre-soaked in ash (Figure 2 [sulfuric acid process flow]), heated once, neutralized by sulfur fumigation, and heated twice, and then enters the settler. Filtering the separated clear juice and mud juice to obtain filtered juice, mixing with the clear juice, heating, multi-effect evaporation into syrup, and sulfur fumigation with syrup to obtain clear syrup as crystallization raw material.

Fig. 2 [Sulfuric acid process] Sulfur fumigation intensity is an index of SO absorption by sugarcane juice, which is generally expressed by iodine titration and expressed by the number of milliliters of N/32 iodine solution consumed by 10 ml sulfur fumigation juice.

The principle of sulfurous acid method is mainly to use sulfite ions to react with calcium ions to generate calcium sulfite particles and adsorb the pigments in sugarcane juice. Heating coagulates colloidal substances and accelerates sedimentation; Adjust the neutralization pH value to make some non-sugar substances reach the condensation point and produce chemical and physical-chemical effects such as precipitation, so as to achieve the purpose of cleaning. Pre-liming and primary heating can also inhibit the proliferation of microorganisms in sugarcane juice.

Sulfuric acid is a reducing agent and bleaching agent. It temporarily reduces the pigment to a colorless substance, which will gradually change color when exposed to air for a long time. This is also one of the reasons why white sugar prepared by sulfurous acid method will turn yellow if it is left for a long time.

Sucrose will be hydrolyzed into a mixture of glucose and fructose under acidic conditions, which is called invert sugar. Because of its reducibility, the sugar industry is also called reducing sugar. Reducing sugar is stable in acidic solution, but it decomposes rapidly in alkaline solution at high temperature to produce organic acids such as hexosalicylic acid, gluconic acid and dark complex. These substances are not easy to remove. Dark color complex also affects the color value of products. The purpose of controlling the pH value of syrup by sulfur fumigation is to prevent the decomposition of reducing sugar during crystallization, improve the color value, and reduce the color value and viscosity by bleaching with sulfurous acid.

Sulfur dioxide in the process of sulfur fumigation and neutralization is produced when sulfur is burned in a sulfur-burning furnace. Gaseous sulfur dioxide is pumped by a multi-nozzle vertical pipeline sulfur fumigation neutralizer which is similar to a water jet vacuum extractor. Fully contacted with the sprayed sugarcane juice in the pipeline, and reacted to generate sulfurous acid. At the same time, lime is added at several points in the tail pipe and juice storage box for neutralization, thus completing the process of sulfur fumigation neutralization.

Most heating equipment adopts multi-pass tube heaters. Mud juice filtration generally adopts drum vacuum suction filter, and there are also general plate-and-frame filter presses. Stirred continuous settler (also known as Dor settler) is one of the sedimentation and separation equipment. It is divided into four or five layers by the partition, the top layer is the adhesive layer, the bottom layer is the slurry thickening layer, and the middle layer is the precipitation layer. Clear juice is mainly discharged from each precipitation layer. Mud juice slowly drives its mud juice rake by means of the central shaft of the device, so that it flows to the bottom and is released, thus achieving the purpose of precipitation and separation.

In the sulfurous acid process, phosphoric acid is usually used as an auxiliary detergent. It reacts with lime to form flocculation precipitation. It has a strong adsorption effect on some non-sugar substances and pigments. The sugar industry generally believes that the mixed juice contains 300 ~ 400 ppm of effective phosphorus pentoxide, which can achieve good results.

2002-20 12 A synthetic polyelectrolyte, also known as flocculant, is widely used in sugar factories. It is a polymer compound. Polyacrylamide is commonly used, and its molecular weight is about 2 million to 20 million. Its dosage is very small, a few ppm is enough to promote particles to gather into coarse flocculent aggregates, and accelerate sedimentation and filtration.

On the basis of sulfurous acid method, a large number of colloids, pigments and some inorganic salts can be separated from sugarcane juice under alkaline conditions by using flocculant. A new process of removing most non-sugar substances from agglomerated particles by air flotation separation technology, then neutralizing their alkaline clear juice with phosphoric acid and putting it into a settler. The color value of the purified juice is 30 ~ 40% lower than that of the original sulfite method, thus improving the quality of white sugar. Using air flotation separation technology to purify sulfite syrup can also improve the quality of syrup and white sugar.

Lime method uses lime as the main detergent. Pre-liming the mixed juice to pH6.4, heating to 60℃, adding ash to neutralize to pH 7.6 ~ 8.0, heating to 100 ~ 102℃, and separating clear juice and mud juice in a settler. Filtering the mud juice to obtain filtered juice, mixing with purified juice, and crystallizing by multi-effect evaporation to obtain syrup.

Lime process is simple, less equipment, only relying on adding ash to neutralize sugarcane juice to produce a small amount of precipitation and heating coagulation, and less non-sugar substances and pigments are removed in the cleaning process, which is suitable for producing coarse sugar. Cane juice purification by carbonation with lime and carbon dioxide as main detergents. The process flow (Figure 3 [Carbonation process flow]) is as follows: the mixed juice is heated and pre-ashed once, then carbon dioxide is introduced, and excessive lime milk is added to precipitate a large number of calcium salts, then heated and filtered to obtain a clear carbon juice, then heated and filtered for the second time to obtain a clear carbon juice, then smoked with sulfur, and heated and evaporated into syrup. Then sulfur bleaching is carried out, the pH value is reduced to 5.8 ~ 6.4, and crystallization is carried out.

The principle of carbonation process is mainly to use a large number of calcium carbonate particles generated in the process of one-carbon saturation to adsorb colloid, pigment and other non-sugars, reduce the color value and improve the purity of clear juice. However, because sugarcane juice contains more reducing sugar, in order to avoid decomposition under high temperature and strong alkali conditions, the amount of lime added to one carbon is 1.5 ~ 2.0% of sugarcane juice, and the suitable pH of one carbon is 10.5 ~ 65433. The following carbonation is to control the pH at 8.0 ~ 8.4. Carbonization means that lime and calcium salt dissolved in single-carbon clear juice are precipitated as completely as possible by entering CO, and some impurities and pigments are adsorbed to further improve the quality of clear juice.

When SO is introduced into the clear juice, the clear juice evaporates into syrup under the condition of near neutrality, which avoids the destruction of reducing sugar, increases the color value and reduces the viscosity of syrup. When carbon dioxide is full, the introduction of excessive CO can not achieve the effect of this process, because it will increase the content of calcium salt and affect the cleaning effect.

The carbonation sugar factory is equipped with a lime kiln, and the CO and CaO produced by calcining limestone in the kiln are needed in the production process of this method.

The cleaning effect of carbonic acid method is better than that of sulfurous acid method, and the product quality is better. However, cleaning consumes a lot of materials, has high cost and is difficult to treat sludge. The sulfuric acid process of fabia carbonate is more complicated and requires higher operation technology.