Xylose Technology

Flash evaporation uses the sensible heat contained in the high-temperature hydrolyzate itself to reduce the boiling point of the hydrolyzate by vacuuming, and part of the water in the hydrolyzate evaporates. During the flash evaporation process, the sensible heat of the hydrolyzate becomes the latent heat of water vapor, and the temperature of the hydrolyzate drops. For every 10°C drop in the temperature of 1 ton of sugar solution, about 18 kg of water can be evaporated.

 

Flash evaporation was originally used for energy saving, but when the hydrolyzate is flashed, some of the highly volatile organic acids also evaporate with the water vapor, which also has a refining effect on the hydrolyzate.

 

 

Filtration is the most commonly used solid-liquid separation method. When the sugar solution passes through the filtration equipment, the solid suspended matter in the sugar solution cannot be intercepted through the fine pores in the filter medium due to its large particle size. The sugar molecules and water molecules in the sugar solution have small particle sizes and can pass through the fine pores in the filter medium, thereby separating the sugar solution from the solid suspended matter and refining the sugar solution. The commonly used filtration equipment in the xylose industry is the plate and frame filter press, and its filtration medium is a fiber woven filter cloth.

 

 

Neutralization is to use calcium salt to react with sulfuric acid to generate calcium sulfate. Calcium sulfate is easy to form precipitation due to its low solubility and can be removed by filtration, thereby achieving the purpose of removing part of the sulfuric acid in the hydrolyzate. The neutralization process brings a small amount of calcium into the hydrolyzate while removing sulfuric acid, so it is important to reasonably control the neutralization end point. Excessive neutralization will not be worth the loss due to the introduction of a large amount of calcium.

 

There are two common calcium salts for neutralization, one is calcium carbonate (i.e. light calcium carbonate powder, commonly known as light calcium powder), and the other is calcium hydroxide (i.e. digested lime powder, commonly known as gray calcium powder). The advantage of using calcium carbonate is that the purity of calcium salt in light calcium powder is high (more than 99%), and less impurity ions are brought into the sugar solution after neutralization; the disadvantage is that the price is high and a large amount of foam is generated during the neutralization process. The advantage of using calcium hydroxide is that the price of gray calcium powder is low, and no foam is generated during the neutralization process; the disadvantage is that the purity of calcium salt in gray calcium powder is low (about 95%), and more impurity ions are brought into the sugar solution after neutralization. Comprehensive comparison, it is recommended to use calcium carbonate as a neutralizer.

 

 

Decolorization is to use the huge active surface of powdered activated carbon to adsorb impurities (mainly organic impurities) and pigments (i.e. organic colored impurities), and then remove the adsorbed impurities together with the activated carbon through filtration to achieve the purpose of sugar solution refining. The process of activated carbon adsorbing impurities is physical adsorption. The ability of activated carbon to adsorb organic matter is much greater than that of inorganic salts, and the ability to adsorb large molecular organic pigments is much greater than that of adsorbing small molecular organic pigments.

 

The commercially available powdered activated carbon is divided into zinc chloride carbon and phosphate carbon according to its manufacturing method. Zinc chloride carbon is manufactured with zinc chloride as a pore-forming agent, while phosphate carbon uses sulfuric acid as a pore-forming agent. Zinc chloride carbon has a lower ash content, more pores and a larger active surface, and has a stronger decolorization ability. Phosphate carbon has a higher ash content, a smaller active surface area, and a weaker decolorization ability. Phosphate carbon also has the problem of false decolorization, that is, the light transmittance test of the sugar solution after decolorization is qualified, but the actual pigment removal rate is not enough, because phosphoric acid has a bleaching effect. Zinc chloride carbon should be used for decolorization in the xylose industry instead of phosphate carbon.

 

The raw materials for producing activated carbon include sawdust (sawdust produced during wood processing), fruit shells and bagasse, etc. Most of them are made from sawdust. There is also recycled carbon for sale on the market, which is recycled from waste activated carbon from various enterprises and regenerated through alkali washing. It has low decolorization power and is very cheap, but it is risky to use (it may contain unknown toxic and harmful substances) and is not suitable for use in the xylose industry. There is also a granular activated carbon on the market, which can be installed in the decolorization column for repeated use, and the decolorization efficiency is restored by alkali washing after each failure. The decolorization power of granular activated carbon gradually decreases during repeated use, and the quality of the decolorized liquid cannot be guaranteed for a long time. The xylose industry generally uses it for the final purification of sugar solution and quality improvement, rather than for the decolorization process with a large decolorization load in the early stage.

 

In xylose production, due to the dark color of the hydrolyzate, the consumption of activated carbon for producing 1 ton of xylose is between 120 and 150 kg. We should not expect that the decolorization requirements can be achieved in one decolorization process. It is advisable to use multiple decolorizations, and each decolorization operation should use semi-countercurrent decolorization to multiple and thorough use of the decolorization power of activated carbon, so as to achieve the purpose of saving carbon.

 

 

Vacuum evaporation is a process that utilizes the boiling point reduction characteristics of sugar solution under vacuum to complete the evaporation of water at a lower temperature. The evaporation process requires steam to continuously heat the sugar solution to provide the latent heat of evaporation required for water to be converted into water vapor. Multi-effect vacuum evaporation utilizes the characteristic that the boiling point of sugar solution is lower under higher vacuum. The evaporation system is evacuated by a vacuum pump to increase the vacuum degree of each evaporation effect, that is, the evaporation temperature (boiling point) of each evaporation effect is reduced. In this way, only one effect needs to use raw steam, and the remaining effects use the water vapor evaporated from the previous effect (commonly known as secondary steam) as the heating heat source, so as to achieve the purpose of saving fresh steam.

 

At present, the first and second evaporation of xylose industry mostly adopts new high-efficiency falling film evaporator. The sugar solution flows over the surface of the heating tube in the form of a thin film, and the heat exchange required for evaporation can be completed in a short contact. Due to the high concentration of sugar solution, the boiling point rise (the temperature higher than the boiling point of water under the same vacuum degree) of the third evaporation of xylose is large, so single-effect evaporation is generally adopted, and single-effect standard evaporator or single-effect falling film evaporator is commonly used. The advantage of using single-effect standard evaporator is that the final concentration and natural crystallization are easy to control, and the disadvantage is that the residence time at high temperature is longer; the advantages and disadvantages of single-effect falling film evaporator are just the opposite of single-effect standard evaporator.

 

After the sugar solution is evaporated, part of the water is evaporated, the sugar solution is concentrated, the sugar concentration increases, and the volume of sugar solution is reduced, which reduces the volume of sugar solution that needs to be processed in the subsequent process. The main purpose of sugar solution evaporation is to concentrate, but when the sugar solution evaporates, part of the volatile organic matter (part of organic acids and aldehydes) in the sugar solution is also evaporated and removed, so the evaporation process not only concentrates the sugar solution, but also plays a role in refining the sugar solution.

 

 

Ion exchange is divided into cation exchange and anion exchange. Cation exchange uses cation exchange resin to provide hydrogen ions (H+) to exchange with impurity cations such as calcium (Ca2+), magnesium (Mg2+) and sodium (Na+) in the sugar solution. The hydrogen ions on the resin enter the sugar solution, and the impurity cations in the sugar solution are adsorbed on the resin; anion exchange uses anion exchange resin to provide hydroxide ions (OH-) to exchange with impurity anions such as sulfate (SO42-), chloride (Cl-) and organic acid in the sugar solution. The hydroxide ions on the resin enter the sugar solution, and the impurity anions in the sugar solution are adsorbed on the resin. After the sugar solution is exchanged through cation exchange and anion exchange, the impurity cations and impurity anions in the sugar solution are adsorbed on the ion exchange resin and removed. These impurity ions are components of impurities such as sulfuric acid, organic acid and ash in the sugar solution. The hydrogen ions and hydroxide ions exchanged from the resin into the sugar solution are combined into water.

 

Ion exchange equipment is commonly used for ion exchange. Those filled with cation exchange resin are called cation exchange columns, and those filled with anion exchange resin are called anion exchange columns. The ion exchange columns used in the xylose industry include open atmospheric pressure columns and closed pressure columns. The open columns have low resin loss and are easy to observe, but the regeneration and flushing are slow; the closed columns have fast regeneration and flushing, but the resin loss is relatively large, especially the primary exchange columns due to frequent regeneration.

 

The cation exchange resin brand that is more suitable for the xylose industry is 001×7, which is a strong acid styrene cation exchange resin, which is sodium type when it leaves the factory, and has an exchange capacity of 4.5Mmol/g; the anion exchange resin brands that are more suitable for the xylose industry are D201 and D301, which are strong alkaline styrene anion exchange resin and weak alkaline styrene anion exchange resin, respectively, with exchange capacities of 3.7 and 4.8 Mmol/g. D301 is suitable for the primary and secondary exchanges of xylose due to its strong anti-pollution ability, while D201 is suitable for the tertiary exchange of xylose.

xylose solution is obtained. However, it still contains glucose, arabinose, galactose, ribose and erythropentose. The crystallization of xylose is to extract xylose from the sugar solution in the form of crystals to obtain a solid product that is easy to sell, and to further separate xylose from miscellaneous sugars to obtain a pure xylose product. The extraction of crystalline xylose is the final process of xylose production, including five steps: concentration, crystallization, centrifugal separation, drying and packaging.

 

 

Concentration is to create necessary conditions for crystallization. The concentration of the sugar solution is increased by concentration, which also increases the amount of xylose dissolved in the unit water.

 

The concentration of the purified xylose solution is between 12% and 16%, and it needs to be concentrated to 81% to 83%, with a concentration multiple of 5 to 7. Due to the large concentration multiple and high final discharge concentration, if a set of multi-effect evaporators is used for one-step concentration, the flow rate of the last effect will be too different from that of the first effect, which is not conducive to the operation of the evaporator. In addition, the boiling point of the high-concentration sugar solution increases a lot, which will cause the high temperature of the first effect to harm the sugar. Therefore, the concentration of the purified sugar solution is generally carried out in two stages. The first stage uses a multi-effect (three-effect or four-effect) falling film evaporator to concentrate the sugar solution to 55-60%, and the second stage uses a single-effect evaporator to concentrate the sugar solution from 55-60% to 81-83%.

 

There are generally two types of evaporators used for the second stage of concentration. One is a central falling liquid circulation shell and tube evaporator, commonly known as a standard evaporator, which is a periodically operated intermittent evaporator; the other is a falling film evaporator with continuous discharge. It is recommended to use a standard evaporator because when the high-concentration syrup continues to be concentrated, a small change in the amount of evaporated water will lead to a large change in the concentration of the sugar solution. If a falling film evaporator is used for concentration, the inlet and outlet are continuous, and the concentration rises very quickly, which requires strong operating experience. Otherwise, the instantaneous discharge concentration fluctuates greatly, making it difficult to control the final discharge concentration and the amount of natural crystallization. Due to intermittent operation, a large amount of syrup is always stored in the standard evaporator, and the concentration gradually rises. When it rises to the required concentration, the machine is stopped for discharge, and the final discharge concentration and the amount of natural crystallization are very convenient to control.

 

ENCO Company can add an online concentration meter to the evaporator to display the syrup concentration in the evaporator at any time, making the concentration operation more convenient.

 

In the past, the first stage of the xylose industry was concentrated to 38-40%, but from the perspective of energy saving, the first stage uses multi-effect evaporation, which should be concentrated to 55-60%, so that the multi-effect evaporator can evaporate as much water as possible, and reducing the amount of evaporated water in the single-effect evaporator can obviously save the consumption of fresh steam.

 

Here we need to introduce a few simple professional terms: the unrefined crude xylose solution obtained by hydrolyzing corn cobs in a hydrolysis pot is called hydrolyzate; the hydrolyzate is called xylose liquid after the first step of purification (filtration or decolorization). In production, for the convenience of distinction, it is often named as the first decolorization liquid, the neutralization liquid and the secondary anion exchange liquid (referred to as the second anion liquid) according to the process of the xylose liquid; the xylose liquid becomes more viscous after the concentration rises to more than 55%, which is called xylose syrup; the xylose syrup is further concentrated to supersaturation, and xylose crystals are precipitated. The syrup containing crystals is called xylose paste.

 

 

Crystallization uses the property that the solubility of xylose in water decreases with the decrease of temperature. First, the sugar liquid is concentrated at high temperature to make the amount of sugar dissolved in water reach the limit, and then the solubility decreases by cooling, and the xylose that exceeds the water solubility capacity precipitates to form xylose crystals.

 

When xylose forms crystals and precipitates, other miscellaneous sugars are still dissolved in water and do not precipitate because of their small amount and cannot reach supersaturation. Only a very small amount is mixed with xylose when xylose crystallizes.

 

At a certain fixed temperature, the maximum amount of xylose that can be dissolved by a unit amount of water is called the solubility of xylose at that temperature. At this time, the xylose solution is a saturated solution and can no longer dissolve xylose. A unit amount of water dissolves xylose that exceeds its solubility, forming a supersaturated solution of xylose, in which the amount of sugar divided by the amount of sugar corresponding to its solubility is the supersaturation (supersaturation coefficient) of the supersaturated solution. Because a saturated solution of xylose can no longer dissolve xylose, a supersaturated solution cannot be obtained by adding excess solid sugar to the solution to dissolve it, but can only be obtained by cooling the saturated solution to reduce its solubility, or by concentrating and continuing to evaporate water from the saturated solution.

 

In a xylose solution with a supersaturation coefficient of 1.0 to 1.3, the xylose crystals present therein can grow, and a xylose solution with a supersaturation coefficient exceeding 1.3 will automatically produce new crystals for precipitation. The process of xylose crystallization is to produce a xylose solution with a supersaturation coefficient exceeding 1.3 by concentrating, automatically produce crystals (natural crystallization), and then enter the crystallizer for cooling. By controlling the cooling rate, the supersaturation coefficient of the xylose paste is kept between 1.1 and 1.2, and the crystals gradually grow.

 

In addition to the natural crystallization method, ENCO Company also has a method of adding seed crystallization, that is, by adding ready-made crushed tiny crystals as seeds, the particle size and uniformity of the seeds after growth are better than those of natural crystallization.

 

The longer the xylose crystallization time is, the slower the speed control, the better the crystal shape of the crystal, the denser the crystals, and the higher the crystallization yield. Experience shows that the best crystallization time for xylose is 60 hours.

After the xylose paste is crystallized, in addition to the xylose that has been precipitated into crystals, there is still a part of the remaining xylose dissolved in water together with other miscellaneous sugars. This part of the syrup solution composed of dissolved sugar and water is called mother liquor.

 

The commonly used crystallization equipment for xylose is a horizontal cooling crystallizer, which relies on a rotating horizontal stirring ribbon to mix the sugar paste and keep the crystals suspended without settling. Small crystallizers (less than 8 cubic meters) rely on cooling water to cool down through the cooling jacket, and large crystallizers (more than 9 cubic meters) have cooling coils added to the stirring ribbon in addition to the cooling jacket.

 

The cooling jacket of the crystallizer is designed for normal pressure, and a breathing port should usually be set. Pressure testing of the crystallizer jacket or letting the jacket bear water pressure should be avoided, but water normal pressure leak test can be used.

In order to ensure the uniform and stable water temperature of the cooling water in the cooling jacket or cooling coil and avoid scaling of the heat exchange surface, each crystallizer should be equipped with a separate circulating cooling water pump to circulate its cooling water, so that the circulating cooling water can exchange heat and cool down with the external cold source through the heat exchanger.

 

The xylose industry often uses a simple primary crystallization to extract crystalline xylose, so various means are taken to increase the crystallization rate by increasing the concentration and extending the crystallization time to increase the total yield of xylose. In fact, the purity of xylose in the refined and purified xylose solution is about 80-87%, and the content of other miscellaneous sugars is 13-20%. As long as the purity of xylose in the xylose paste used for crystallization is greater than 78%, xylose can be crystallized smoothly. That is, we can adjust the purity of xylose syrup before crystallization to 78-80% by recycling a part of the xylose mother liquor to the secondary decolorization, which can improve a part of the crystallization yield. Of course, in order to achieve the recycling of mother liquor to improve the crystallization yield, it is essential to use a high-pressure liquid chromatography analyzer to measure and control the purity of xylose syrup before crystallization.

 

 

Centrifugal separation is the process of separating xylose crystals in the sugar paste from the mother liquor by the centrifugal force generated by the high-speed rotating drum (sieve basket) of the centrifuge. After centrifugal separation, the solid xylose crystals are retained in the filter cloth in the centrifuge drum, and the mother liquor enters the mother liquor pool through the gap between the filter cloth and the drum sieve basket.

 

In the later stage of centrifugal separation, the xylose industry often sprays methanol to wash the xylose crystals. Since methanol does not dissolve xylose, more xylose products can be obtained by eluting with methanol. Methanol is a flammable and explosive dangerous substance, and it is highly toxic. Its vapor is also harmful to the eyes. Therefore, when using methanol, attention should be paid to fire prevention and explosion prevention, and accidental ingestion and volatilization to produce steam should be avoided. Outdoor methanol storage tanks should be cooled with cold water in summer. Because of methanol elution, xylose mother liquor is not allowed to be directly consumed or enter the food processing field.

 

ENCO Company is studying the process of canceling methanol elution, that is, using clean water to wash xylose crystals, and recovering xylose dissolved by elution water by recycling mother liquor.

 

Most of the centrifugal separation equipment currently used by xylose enterprises is SS-type manual top-unloading three-legged centrifuge, which has low separation efficiency and high labor intensity. The reason why high-efficiency top-suspended centrifuges are not used is mainly because the xylose industry is small and the production capacity of a single production line is low. With the rapid development of the xylose industry and the launch of a 5,000 t/a xylose production line, the use of top-suspended centrifuges is an inevitable trend.

 

Packaging is to fill the dried crystalline xylose into the packaging bag after metering for storage, transportation, sales and customer use. Xylose is usually packaged in plastic woven bags lined with plastic film bags, usually in two specifications of 25 kg and 50 kg. Due to the small production capacity of the xylose production line, most companies use manual packaging. With the construction of large-scale production lines, semi-automatic packaging machinery or fully automatic packaging machinery can be used. my country's packaging machinery products are mature. When using manual packaging, use a stainless steel square trough to receive the material at the outlet of the rotary vibrating screen after the dryer, and then use a spoon bucket to fill the packaging bag to avoid leakage to the ground, and it is more convenient for manual weighing.

 

 

The typical process flow of corn cob to produce xylose (D-xylose) is as follows:

Receiving materials→ Loading materials→ Hydrolysis→ Neutralization→ Primary decolorization→ Pre-cation exchange→ Primary anion exchange→ Primary anion exchange→ Primary evaporation→ Secondary decolorization→ Secondary anion exchange→ Secondary anion exchange→ Thirdary anion exchange→ Thirdary series exchange→ Secondary concentration→ Thirdary concentration→ Crystallization→ Centrifugal separation→ Drying→ Packaging→ Waste residue treatment

 

 

 

The work of collecting materials belongs to the preparation work for making xylose. Since collecting materials involves dealing with a large number of farmers, it is very tedious. In order to complete the work of collecting materials with quality and quantity, it is necessary to understand some basic knowledge of collecting materials.

 

In most corn-producing areas in my country, the yield of dry corn (grains) per mu is 500 kg, and the by-product corn cobs are 125-150 kg. The moisture content of fully dried corn cobs is below 14%, while the moisture content of wet corn cobs is as high as more than 40%. The pile specific gravity of dry corn cobs is between 0.15 and 0.18, that is, the stacking volume of each ton of corn cobs is between 5.5 and 6.5 cubic meters.

 

The stacking height of corn cobs is generally 6 to 7 meters, and they are generally stacked in the open air. Open-air stacking has better ventilation, convenient fire fighting, and no need to build a large-scale roof. The top layer can be quickly re-dried or air-dried when it is rained, so long-term stacking generally only damages a small part of the top layer.

 

It takes about 15 acres of land to stack 10,000 tons of corn cobs. In areas with abundant rainfall, cement sites (cement thickness of 8 to 10 cm is sufficient) should be used, and drainage facilities should be unobstructed; in areas with less rainfall, compacted mud land can be used.

 

When stacking corn cobs, mobile inclined belt conveyors can be used to stack them high to reduce manpower. It is best to stack newly harvested corn cobs for 20 days before sending them to the workshop for use. The stacking process of corn cobs will produce natural fermentation to degrade some adhesive substances. Wet corn cobs are more likely to rot when stacked, so it is best not to stack them in large piles and arrange for workshop use as soon as possible.

 

When stacking corn cobs in large piles, it is best to arrange some air vents at a fixed distance (about 6 meters) to avoid the heat generated by natural fermentation accumulating at the bottom of the pile to cause fire or carbonization of corn cobs.

 

When collecting materials, it is advisable to collect as many dry and fresh corn cobs as possible, and not to collect wet and moldy corn cobs. Dry and fresh corn cobs are bright and shiny in color, not easy to break, and the sugar concentration of the hydrolyzate after hydrolysis is higher; wet and moldy corn cobs are gray and dark in color, easy to break, and the sugar concentration of the hydrolyzate after hydrolysis is lower. When collecting materials, care should be taken to avoid carrying debris, which can be checked during the unpacking process before stacking.

 

Corn cobs are generally packed in nylon net bags and then loaded for transportation. Enterprises can also sign an agreement with large purchasers and have them organize the supply. With the rapid development of the xylose industry, the price of corn cobs is getting higher and higher. Enterprises should take the opportunity to establish a high-quality and high-price purchase mechanism to guide farmers not to sprinkle water or adulterate. It is also a good idea to consider pricing by volume in terms of measurement.

 

 

The first step of loading is to transport the corncob raw materials from the material yard to the receiving hopper of the workshop feeding belt. Small enterprises generally use manual loading into small three-wheel dump trucks, and then transport them to the inter-vehicle hopper, or use small loaders to load materials into small dump trucks; large enterprises use medium or large loaders to load materials from corncob stacks into dump trucks, and then transport them from dump trucks to inter-vehicle hoppers.

 

After the corncobs enter the receiving hopper of the workshop feeding belt, they are sent to the vibrating screening conveyor by the belt to screen out some of the silt and debris before entering the washing machine. In the past, corncob washing machines generally used hydraulic pulp breakers in the papermaking industry. The paddle wheel washing machine designed by ENCO Company not only has a good washing effect, but also consumes much less water and electricity than hydraulic pulp breakers. The corncob washing machine should regularly remove the silt in its sand settling hopper.

 

After washing, the corn cobs are dehydrated through a vibrating dehydration screen and then enter a bucket elevator or a high-angle belt conveyor with sidewalls. They are then lifted and transported to the horizontal belt conveyor on the top of the hydrolysis pot, and then controlled by a distribution plug plate to be sent through a chute into the hydrolysis pot that needs to be loaded.

 

 

After the hydrolysis pot is filled with materials (generally slightly lower than the joint between the straight cylinder and the conical top cover of the hydrolysis pot body), hydrolysis begins.

 

The first step of hydrolysis is dilute acid pretreatment. The honeycomb outer layer of the corn cob entering the hydrolysis pot is still inevitably attached with firm soil, and the corn cob also contains non-hemicellulose sugars, pigments, pectin, nitrogen-containing substances and fats, etc. These substances entering the hydrolyzate will greatly increase the burden of the subsequent refining process. Therefore, the corn cob needs to be pretreated with dilute acid before hydrolysis to remove these impurities in advance. The treatment conditions are 0.1% sulfuric acid (the concentration of the raw material dilute sulfuric acid solution added to the pot is 0.2%) and 120℃ for 1 hour. This condition basically does not cause hemicellulose hydrolysis and loss of xylose, but after dilute acid treatment, the quality of the hydrolyzate is greatly improved.

 

After the corn cob is pretreated with dilute acid, the washing liquid from the previous pot with sulfuric acid added is added as raw material, and the temperature is raised to the specified temperature (128-132°C) by steam, and the temperature is kept for the specified time (2.5 hours) to complete the hydrolysis. Most xylose companies control the hydrolysis temperature by looking at the pressure of the hydrolysis pot. Although the saturated steam pressure in the hydrolysis pot has a corresponding relationship with the temperature, the actual temperature will be lower than the temperature corresponding to the pressure if the air in the pot is not completely exhausted. Therefore, the drain valve of the hydrolysis pot needs to be slightly opened during the hydrolysis process to fully exhaust the air. ENCO Company uses corrosion-resistant thermal resistance thermometers to measure the temperature in the hydrolysis pot, and the displayed temperature is no longer affected by the residual air in the pot.

 

After the hydrolysis is completed and the hydrolysis liquid is discharged, a large amount of hydrolysis liquid still remains on the corn cob residue in the hydrolysis pot. Whether the xylose in this part of the residual liquid can be fully washed out with water will directly affect the sugar yield of the corn cob and the sugar concentration of the hydrolysis liquid. A better method is to add the clean slag water from the waste slag treatment section to the hydrolysis pot that has just completed hydrolysis, heat it to full boiling with steam, and then discharge it with compressed air to obtain the washing liquid for the raw material of the next pot of hydrolysis.

 

After the washing liquid is made, the hydrolysis pot is pressurized with compressed air, and then the slag discharge valve is opened to empty the residue. For each hydrolysis pot, the hydrolysis operation is intermittent, but if several hydrolysis pots with evenly staggered time intervals are operated together, the feed and hydrolysis liquid discharge of the hydrolysis section will become more uniform and continuous.

 

 

 

Use a pump to send the hydrolyzed liquid into the neutralization tank, and gradually add light calcium carbonate powder to the neutralization tank while stirring. Continuously test with precision PH test paper until the PH rises to 3.3-3.6. Take samples for testing, and the inorganic acid should be 0.09-0.12%. Then add the secondary old carbon used in the subsequent decolorization process, stir thoroughly and send it to the plate and frame filter press for filtration. Since the neutralization of light calcium powder produces carbon dioxide, a large amount of foam is generated. In order to avoid the influence of foam on the neutralization process, there are two solutions.

 

One is to mix the light calcium powder with water to form an emulsion and slowly add it to the neutralization tank. The other is to add a baffle to the inlet pipe of the neutralization tank so that the hydrolyzed liquid flows into the neutralization tank in a film shape. At the same time, according to experience, most of the light calcium powder to be added is sprinkled on the hydrolyzed liquid film with a shovel. The remaining small amount of light calcium powder is slowly added according to the PH test results after the full slam.

 

Neutralization temperature also affects the neutralization effect. The solubility of calcium sulfate is greater at a lower temperature, which will lead to an increase in the residual amount of calcium in the neutralization solution. Before neutralization, the sugar solution should be heated to 80-82℃.

 

 

Because the color of the neutralization solution is darker, the consumption of activated carbon for primary decolorization is large, accounting for about one-fourth of the total carbon consumption. In order to make full use of the decolorization capacity of activated carbon and save activated carbon, a semi-countercurrent decolorization process is generally adopted. Three stirring tanks are required for primary decolorization: neutralization liquid storage tank, intermediate liquid storage tank and decolorization tank. The volume of the neutralization liquid storage tank can be larger, but the volume of the intermediate liquid storage tank and the decolorization tank is the same.

 

After the decolorization tank is filled with sugar solution, fresh activated carbon is added to fully stir and decolorize, and then it is sent to the new plate-frame filter press that has been disassembled and washed for complete filtration, and then the filtrate is sent to the decolorization liquid storage tank. After the filtration, the plate frame is not disassembled and washed first, and the sugar solution in the intermediate liquid storage tank is completely filtered through the plate frame filled with carbon cakes, and then the filtrate is sent to the decolorization tank. After the filtration, the sugar solution in the neutralization liquid storage tank is filtered through the plate frame, and then the filtrate is sent to the intermediate liquid storage tank until the tank is full. Two plate-frame filter presses, one for filtering and one for disassembly and washing, are used alternately. The neutralizing liquid is filtered batch by batch from the neutralizing liquid storage tank and gradually reaches the intermediate liquid storage tank, decolorizing tank and decolorizing liquid storage tank in turn, completing a decolorization filtration. The plate-frame filter press can adjust its filtration area by adding or subtracting the number of plates and frames, so that in most cases, after filtering a whole tank of sugar liquid in the decolorizing tank, the filter cake is basically filled with the plate frame.

 

When the decolorization is newly started, only the neutralizing liquid storage tank has material, and the intermediate liquid storage tank and the decolorizing tank are empty. The discharge tanks of the neutralizing liquid storage tank, the intermediate liquid storage tank and the decolorizing tank can be opened at the same time to connect the three tanks, and the neutralizing liquid fills the intermediate liquid storage tank and the decolorizing tank by gravity.

 

The amount of fresh activated carbon added to the decolorizing tank is controlled according to the transmittance (commonly known as light transmittance) index of the decolorizing liquid. If the decolorizing tank sample is filtered by filter paper and the light transmittance is not enough, fresh activated carbon needs to be added until the sampling test is qualified.

 

Since many pigments in the xylose solution are more easily adsorbed by activated carbon at relatively low temperatures, the sugar solution should be cooled to 50-52°C before entering the decolorization tank. Another advantage of this temperature is that the decolorized solution does not need to be cooled down when entering the pre-cation exchange.

 

 

The ash, organic acid and organic acid contained in the primary decolorized solution need to be removed by ion exchange. The pH of the primary decolorized solution is about 3.2, which is obviously acidic. From the perspective of fully utilizing the resin exchange capacity, it should first enter the anion exchange column for exchange. However, due to the high calcium content in the primary decolorized solution of the neutralization process, the sugar solution has a high hardness, and directly entering the anion exchange column will cause great toxicity to the anion exchange resin. Therefore, the primary decolorized solution needs to be softened by pre-cation exchange. During the pre-cation exchange process, the cations (mainly Ca2+) in the sugar solution are replaced by hydrogen ions (H+), and the pH drops by 1.5-2.0. The inorganic acid content is detected, and it is significantly greater after the exchange than before the exchange.

 

The xylose hydrolysate has a characteristic that its transmittance increases with the decrease of pH, mainly because the light absorption characteristics of the coloring substances are affected by pH. In the process of pre-cation exchange, the resin absorbs part of the pigment and the pH decreases at the same time, so the transmittance increases significantly. As the exchange capacity of the resin decreases, its ability to absorb pigments also decreases, so the transmittance of the output also decreases synchronously. The loss of the resin exchange capacity can also be seen from the decrease in the transmittance of the output.

 

The detection of calcium ion content in sugar solution is relatively complicated and time-consuming. Usually, the inorganic acid content of the input and output and the transmittance of the output are measured to detect whether the resin is invalid. In order to ensure the softening effect of the sugar solution, in addition to using the detection of inorganic acid and transmittance to determine the exchange end point, it is generally stipulated according to experience that the excess liquid volume of the pre-cation exchange shall not exceed 8 times the volume of the resin.

 

After the exchange column reaches the exchange end point, the exchange capacity of the resin is basically lost, and the process of washing the resin with a dilute acid solution to restore the exchange capacity of the resin is called regeneration. The dilute acid solution contains a high concentration of hydrogen ions. During the regeneration process, hydrogen ions are exchanged with impurity cations adsorbed on the resin. The impurity cations are discharged with the regeneration waste liquid, and the hydrogen ions enter the resin. The regeneration of the front cation exchange is typically different from other cation exchange processes in that sulfuric acid cannot be used for regeneration, but only hydrochloric acid. Because a large amount of calcium ions are adsorbed on the resin after the front cation exchange fails, the calcium ions combine with sulfate to form calcium sulfate precipitation adsorbed on the resin and difficult to elute, which causes the resin to harden in severe cases. Other cation exchange processes can be regenerated with either sulfuric acid or hydrochloric acid because there are fewer calcium ions on the resin. The advantage of regeneration with sulfuric acid is that the cost is slightly lower than that of hydrochloric acid, and the advantage of regeneration with hydrochloric acid is that the regeneration effect is better than that of sulfuric acid. Considering all factors, hydrochloric acid regeneration is recommended.

 

In order to save the amount of hydrochloric acid, the regeneration of the front cation exchange can be first soaked in recycled hydrochloric acid, then soaked in fresh dilute hydrochloric acid, and then rinsed with water. Because there are more calcium ions on the resin after the front cation exchange, the used dilute hydrochloric acid solution rinsed with water cannot be recycled, but directly discharged to the sewage treatment station. This is also different from other cation exchange processes.

 

 

After the pre-cation exchange, a large part of the impurity cations in the sugar solution are removed, and the pH drops to 1.5-2.0. It is passed into the anion exchange column, and the anions in the sugar solution (mainly sulfate ions and organic acid ions) are quickly exchanged with the hydroxide ions on the anion exchange resin and removed. The pH of the discharged sugar solution rises sharply to 7.5-9.0, and the sample detection of inorganic acid is <0.01%.

 

During the anion exchange process, the pH rises sharply while the resin adsorbs a part of the pigment. As a result of the combined effect, the transmittance of the discharge in the early stage of the anion exchange is significantly higher than that of the feed. As the exchange proceeds, the ability of the resin to adsorb pigments also decreases, and the transmittance of the discharge also gradually decreases, and the final transmittance is even slightly lower than that of the feed. The decrease in the transmittance of the anion exchange discharge also reflects the loss of the resin's exchange capacity.

 

After the anion exchange column reaches the end of the exchange, the anion resin fails and needs to be washed and regenerated with a dilute alkali solution. The xylose industry usually uses caustic soda (sodium hydroxide). The dilute alkali solution contains a high concentration of hydroxide ions. During the regeneration process, the hydroxide ions are exchanged with the impurity anions adsorbed on the resin. The impurity anions are discharged with the regeneration waste liquid, and the hydroxide ions enter the resin.

 

In order to save the amount of caustic soda, the regeneration of the single anion exchange can be soaked in the recycled alkali solution first, then washed with fresh dilute alkali solution, and then rinsed with water. The waste alkali solution discharged after the recycled alkali solution is reused has no value for reuse and is discharged to the sewage treatment station; but the dilute alkali solution discharged after washing with fresh dilute alkali solution enters the recycled alkali pool for later use.

 

 

After the single anion exchange, most of the impurity ions in the sugar solution are removed, but to completely remove the impurity ions in the sugar solution, it is necessary to further repeatedly pass through cation exchange and anion exchange to obtain high-quality purified sugar solution. After the anion liquid is passed into the cation exchange column, the remaining small amount of cations (mainly calcium ions) in the sugar solution are exchanged with the hydrogen ions on the cation exchange resin and removed. The pH of the discharged sugar solution drops to 2.5-3.0. The inorganic acid content is detected. It cannot be detected before the exchange, but it is between 0.01% and 0.05% after the exchange.

 

During the anion exchange process, the resin adsorbs part of the pigment and the pH drops at the same time, so the light transmittance of the discharged material also decreases synchronously. The loss of the resin exchange capacity can also be seen from the light transmittance of the discharged material in the anion exchange.

 

After the anion exchange column reaches the end of the exchange, the anion resin fails and needs to be regenerated by washing with dilute hydrochloric acid. In order to save the amount of hydrochloric acid, the regeneration of the anion exchange can be first soaked in recycled hydrochloric acid, then washed with fresh dilute hydrochloric acid, and then rinsed with water. The waste acid discharged after the recycled hydrochloric acid solution is reused has no value for reuse and is discharged to the sewage treatment station; but the dilute hydrochloric acid solution discharged after the fresh dilute hydrochloric acid solution is washed into the recycled acid pool for later use.

 

 

The sugar concentration in the hydrolyzate (commonly known as sugar concentration) is generally 6.0-8.5% refractive index. Since the new ion exchange column will be diluted when it is used and when it is disabled, the sugar solution concentration drops to 4.5-6.0% refractive index after the exchange of the front positive, one negative and one positive. The concentration of the sugar solution is increased to 26.0-28.0% refractive index through primary evaporation, and the volume of the sugar solution is greatly reduced, which reduces the refining burden of the subsequent process. At the same time, the concentration of impurities in the sugar solution is also greatly increased, which provides convenience for the subsequent purification process and ensures the quality of the sugar solution after the subsequent purification (under the same impurity content, the higher the sugar concentration, the higher its purity).

 

The primary positive liquid is pumped into the first, second, third and fourth effects of the four-effect falling film evaporator in sequence, and then sent to the secondary decolorization after coming out of the fourth effect. When the sugar liquid flows through each effect, each effect evaporates and removes a part of the water, and the sugar concentration increases with each effect. The sugar concentration of the evaporation discharge can be controlled by adjusting the amount of heated fresh steam entering the first effect. ENCO

 

Company can provide automatic control devices for the four-effect falling film evaporator to realize the fully automatic operation of evaporation, thereby eliminating the operator of evaporation.

A part of the isovolatile organic acids contained in the sugar liquid are also evaporated and removed during the evaporation process, some of which are pumped away by the vacuum pump, and some enter the condensate water. The condensate water produced by the primary evaporation contains a large amount of organic acids, so it is not suitable for recycling and is generally discharged directly to the sewage treatment station.

 

 

After the sugar liquid passes through the primary evaporation, the concentration increases, and the concentration of the colored substances in it also increases at the same time. In addition, some organic substances produce new colored substances under the action of the high temperature of evaporation. The light transmittance of the sugar liquid drops to about 20% after the primary evaporation.

 

Secondary decolorization can also use semi-countercurrent decolorization process like primary decolorization to reduce activated carbon consumption. After the first evaporation, the temperature of the sugar solution is between 60 and 65℃. Unlike the primary decolorization, the secondary decolorization does not need to cool the sugar solution.

 

 

After the secondary decolorization, the pH of the sugar solution is between 1.8 and 2.3, and it is sent to the secondary ion exchange process to continue to remove impurity ions.

 

The load of the secondary exchange is much smaller than that of the primary exchange. There are many ways to perform secondary exchange in the xylose industry: one is to first pass through two anions and then two yangs; the other is to first pass through two yangs and then two anions; and the other is to use the yang column and the anion column in series, put them into use at the same time, and regenerate them at the same time. The first method has the lowest acid and alkali consumption, the second method has better protection for the anion resin, and the third method is the most convenient to operate. It is recommended to use the first method.

 

After the two-anion exchange, the pH of the secondary decolorized liquid rises to 7.0-8.0. The transmittance of the early discharge is significantly higher than that of the feed, but as the exchange proceeds, the ability of the resin to adsorb pigments also decreases, and the transmittance of the discharge gradually decreases, and finally the transmittance is close to that of the feed.

 

After the two-anion exchange column reaches the end of the exchange, it is regenerated with caustic soda (sodium hydroxide) dilute alkali solution. Because the quality of the sugar solution reaching the two-anion exchange is already very good, the two-anion regeneration can no longer be soaked in recycled alkali solution, but can only be soaked in fresh dilute alkali solution and then rinsed with water. The dilute alkali solution discharged after the fresh dilute alkali solution is washed and enters the recovery alkali pool for later use.

 

 

After two-yin exchange, the pH of the two-yin liquid drops back to 3.5-5.0, and the transmittance of the output material rises to more than 90%.

After the two-yang exchange column reaches the end of the exchange, it is regenerated with dilute hydrochloric acid. The two-yang regeneration can no longer be soaked in recycled acid, but can only be washed with fresh dilute acid and then rinsed with water. The dilute acid discharged after the fresh dilute acid wash enters the recycled acid pool for later use.

 

 

After the sugar solution enters the three-time exchange, it is already very pure. The load of the three-time exchange is extremely small, but the three-time exchange plays a great role in fully guaranteeing the quality of the sugar solution. Because the load of the three-time exchange is small, there is no need to exchange in steps, and the yin and yang columns are usually exchanged in series.

 

ENCO Company has introduced a special series exchange method that can better guarantee the quality of the sugar solution and make full use of the exchange capacity of the ion exchange resin. That is, six ion exchange columns are used:

 

No. 1 negative column, No. 2 positive column, No. 3 negative column, No. 4 positive column, No. 5 negative column and No. 6 positive column.

 

The conductivity index of the discharge of columns 2, 4 and 6 is used to judge the failure of the exchange column.

 

The sugar solution is first exchanged through No. 1-→No. 2-→No. 3-→No. 4. Columns 1 and 2 fail first, and the exchange is stopped for regeneration; the flow direction of the sugar solution is changed to No. 3-→No. 4-→No. 5-→No. 6 for exchange.

 

Columns 3 and 4 fail first, and the exchange is stopped for regeneration; the flow direction of the sugar solution is changed to No. 5-→No. 6-→No. 1-→No. 2 for exchange. Columns 5 and 6 fail first, and the exchange is stopped for regeneration. This cycle is repeated, and exchanges and regeneration are performed in sequence.

 

After three series exchanges, the pH of the sugar solution is 5.0-6.0, and the transmittance of the discharge rises to more than 95%. The regeneration of the tertiary exchange column can only use fresh dilute caustic soda solution or fresh dilute hydrochloric acid solution. The dilute caustic soda solution or fresh dilute hydrochloric acid solution discharged after use enters the recovery alkali pool and the recovery acid pool respectively.

 

 

 

The three-phase liquid is pumped into the multi-effect falling film evaporator for secondary concentration. When the sugar solution flows through each effect, each effect evaporates and removes a part of the water, and the sugar concentration increases with each effect. The sugar concentration of the evaporation discharge can be controlled by adjusting the amount of fresh heating steam entering the first effect. After the sugar solution is concentrated to a refractive index of 55-60%, it is sent to the third concentration.

 

Since the feed sugar solution is very pure in the second concentration, the non-sugar organic impurities in it are removed more thoroughly. Therefore, the condensed water produced by evaporation is also relatively pure and can be recycled. It is generally sent to the waste residue treatment section as slag washing water.

 

 

The syrup after secondary concentration is vacuum-absorbed into the standard evaporator for third concentration. While concentrating and adding materials, the syrup concentration and liquid level gradually increase. The speed of evaporation of water can be controlled by adjusting the amount of heating steam, and the speed of concentration and liquid level rise can be controlled by adjusting the amount of feeding. It is best that the concentration is close to the discharge concentration when the evaporator reaches the full liquid level. Stop feeding at the full liquid level and continue concentrating for a period of time until the concentration reaches the discharge concentration, and the amount of crystals produced by natural crystallization is sufficient. Then turn off the heating steam, stop the vacuum pump, break the vacuum, and discharge the material into the crystallizer to complete a concentration cycle.

 

After the standard evaporator completes a concentration cycle, you can start the vacuum pump to evacuate, re-inhale the sugar solution, and then turn on the heating steam for re-concentration. This cycle is repeated to complete the process of concentrating the sugar solution.

 

When using a standard evaporator for concentration, the feed syrup concentration can be relatively high, as long as it does not block the feed pipe due to excessive thickness. In this way, most of the water in the concentrated sugar solution is removed by the multi-effect evaporator for secondary concentration, and only a small part is removed by the single-effect standard evaporator for tertiary concentration.

 

 

After the sugar paste with crystals produced after three concentrations enters the crystallizer, the cooling speed of the sugar paste can be controlled by adjusting the temperature of the circulating cooling water in the crystallizer jacket and the central cooling coil.

 

At the beginning of crystallization, because the crystal grains are still small and the total surface area of ​​the crystals is also small, the crystallization speed is also slow, and a slower cooling speed needs to be controlled; in the later stage of crystallization, because the crystal grains have grown and the total surface area of ​​the crystals is also large, the crystallization speed is also fast, and a faster cooling speed can be controlled.

 

 

After crystallization is completed, the sugar paste flows into the feed trough by gravity, and then flows from the feed trough to each centrifuge. To prevent the sugar paste from sedimentation, the feed trough needs to be continuously stirred and the jacket is kept at a constant temperature circulating water. After the sugar paste enters the centrifuge, it is driven by the centrifuge to rotate at a high speed, generating a centrifugal force of hundreds or even thousands of times the weight of the sugar paste. Under the action of centrifugal force, the mother liquor of the sugar paste is thrown out through the screen on the centrifuge drum, and the crystals are blocked in the drum. In the later stage of separation, the crystals are washed with clean water, and the washing liquid is returned to the production line. After washing, continue to centrifuge for a period of time to completely dry the washing water, then stop the centrifuge to unload the xylose crystals and send them to dry through a screw conveyor.

 

 

After entering the dryer, the xylose crystals are blown up by the hot air and semi-suspended in the hot air in a fluidized state. The xylose crystals are fully in contact with the hot air when passing through the dryer. The moisture content of the crystallized xylose after drying can be controlled by adjusting the feed speed, air volume and air temperature. The slower the feed speed or the larger the air volume, the more fully the material contacts the hot air, and the lower the moisture content of the discharged material; the higher the air temperature, the faster the moisture evaporates, and the lower the moisture content of the discharged material.

 

Before the xylose crystals enter the dryer, the dryer should be started first and the air volume and air temperature have been adjusted to be stable. The dryer and hot air can be turned off only after all the crystallized xylose is dried and emptied.

 

 

The xylose industry currently mostly uses manual packaging. After the dried crystallized xylose comes out of the dryer, it falls into the stainless steel receiving square trough, and then is scooped up with a spoon bucket and filled into the packaging bag that has been covered with a plastic film inner bag. At the same time, it is weighed by a scale. When the filling weight reaches the required weight, the inner bag is tied with a plastic rope and the outer bag is sealed with a sewing machine. During packaging, samples should be taken from the receiving square trough for finished product analysis and testing.

 

After the crystallized xylose is packaged, it becomes a finished product and is sent to storage or sold directly.

 

 

 

 

 

A notable feature of the xylose industry is its high water consumption. Before 2003, some enterprises consumed more than 1,000 tons of water to produce 1 ton of xylose, and some consumed more than 600 tons. After 2003, all enterprises began to pay attention to water conservation. Most enterprises have reduced their water consumption per ton of xylose to less than 400 tons, and some enterprises have even reduced it to about 260 tons. At present, the price of xylose is high, and the supply of xylose and xylitol is in short supply.

 

The price of xylose has exceeded 30,000 yuan/ton, and it has an absolute advantage over the furfural industry in the competition for corn cob raw materials. Water consumption and wastewater discharge have become key factors restricting the rapid development of the xylose industry. Therefore, xylose enterprises should pay full attention to water conservation and increase investment in water-saving facilities. Common water-saving measures in the xylose industry are listed below:

 

 

Most xylose companies use hydraulic pulp crushers introduced from the papermaking industry to wash corn cobs. For a 3,000 t/h xylose production line, the hydraulic pulp crusher consumes about 70 t/h of water during operation, and the supporting motor power is 55KW. The hydraulic pulp crusher is replaced by a mechanical paddle wheel washing machine to wash corn cobs. The water consumption during operation is about 20 t/h, and the supporting motor power is 2.2KW, which saves both electricity and water. In this way, the washing water recovered from the ion exchange process and the evaporation process can meet the needs of corn cob washing without adding fresh water.

 

 

According to the characteristics of the regeneration of the ion exchange column, some equipment is added to separate the clean and dirty water from the regeneration of the ion exchange column and store it in categories. At the beginning, the effluent from the ion exchange column cannot be recycled due to its high COD and is discharged as sewage. The effluent COD in the middle period is between 500 and 1000, which is recycled and sent to wash corn cobs. The effluent COD in the last period is below 500 and collected for the early flushing water of the next batch of ion exchange column regeneration, thereby realizing the recycling of process water and saving clean water.

 

 

The cooling water for the condenser in the evaporation process no longer uses fresh water but circulating cooling water. The circulating cooling water is cooled by the cooling tower, and the replenishment water relies on the alkaline washing water generated by the anion exchange column; a plate heat exchanger is added to the circulating cooling water system of the evaporation process to allow the ion exchange flushing water to exchange heat with the circulating cooling return water, reducing the cooling load of the cooling tower, while reducing the evaporation amount of the cooling tower and saving the replenishment of circulating cooling water.

 

 

 In the first effect of the evaporator, add a steam-water separator and a condensate storage tank and a matching pump to recover the steam condensate and send it to the boiler, which can reduce the water consumption of the boiler. At the same time, the high temperature of the condensate can also reduce coal consumption.

 

 

The water supply workshop uses new water treatment equipment such as electrodialysis or reverse osmosis to produce desalted water. The desalted water is used for boiler water or water for washing the ion exchange column in the xylose workshop, which can significantly reduce the burden of the ion exchange column and extend the service life of the ion exchange column, thereby reducing the number of ion exchange column regenerations and reducing the water used for washing the ion exchange column.

 

 

The xylose workshop mainly has three processes, hydrolysis, evaporation and drying, as well as steam energy consumption for workshop heating. By saving steam consumption in these processes, energy conservation can be achieved. Of course, sending waste slag to the slag-coal mixed combustion boiler for incineration to reduce coal consumption is also an important energy-saving measure. Common energy-saving measures are as follows:

 

 

 The hydrolysis process is a major energy consumer in the xylose production line. Using the waste heat of each process to fully preheat the liquid entering the hydrolysis pot can reduce the steam consumption of hydrolysis; the heat source discharged during the hydrolysis process, including the heat source emitted when the high-temperature wastewater and the high-temperature hydrolysis liquid are discharged, can obtain secondary steam through flash evaporation, which is used for heating steam in the latter effects of the multi-evaporation system; the steam discharged from the upper exhaust pipe during the hydrolysis insulation process can also be recovered to the multi-evaporation system for heating steam in the latter effects; the high-temperature waste slag sprayed out by the hydrolysis can be used to heat the liquid that needs to be heated through the heating coil.

 

 

Raising the boiler steam pressure above 0.6MPa and using a four-effect vacuum falling film evaporator with a heat pump can fully save evaporation steam consumption. Increasing the sugar solution concentration entering the three-time single-effect standard evaporator and using the secondary steam from the first effect of the secondary evaporator as the heat source for the three-time evaporation can save evaporation steam consumption.

 

 

The drying process uses a more advanced fixed fluidized bed or vibrating fluidized bed to reduce the short-circuiting phenomenon of xylose crystals, which can save evaporation steam consumption.

 

 

 Incineration of waste slag cannot reduce steam consumption, but it can reduce coal consumption and reduce the energy cost of the enterprise. By incinerating waste slag, the 5000 kcal coal consumed in producing 1 ton of xylose can be reduced from 6 to 7 tons to 2 to 3 tons.

 

 

To do a good job in environmental protection of xylose enterprises, we must start from the source of pollution. Not only should the pollutants produced be treated to meet the standards, but the generation of pollutants should also be reduced as much as possible to save limited social resources. At this stage, my country's environmental protection has implemented total pollution control. Not only must the discharge meet the standards, but the total COD discharge is also controlled by region.

 

The COD of the comprehensive wastewater generated by the xylose industry is generally between 5000 and 8000. Through anaerobic fermentation, COD can be reduced to between 1200 and 1500, and the biogas produced can be sent to the boiler for incineration.

 

After anaerobic fermentation, aerobic fermentation and aeration, COD can be reduced to below 100, reaching the first-level discharge standard for industrial wastewater.