First, a historical review of the recycling of white water for papermaking 20 years ago, that is, in 1979, the papermaking bureau of the former Ministry of Light Industry had issued a document entitled “Promotion of thirteen new technologies for paper industry technological innovation.†The first of these was “Closed recycled water for paper machines. "new technology. The main measures at that time included air floatation, inclined plate (sloped tube) precipitation, and multi-disc filter. The fastest popularization was jet air flotation for the recovery of white water. Bubble diameter was required to be below 50um, and recycled water was recycled per ton of paper. More than 100t, more than 30kg of recovered pulp. The best at that time was Suzhou Huasheng Paper Mill. There are four paper machines in the factory that all use jet air flotation white water recovery device, more than 100 tons of recycled water per ton of paper, more than 30kg of recycled pulp, and each paper machine is equipped with a separate jet air flotation, which facilitates separate assessment and promotes Recovery of recycled water and recycled pulp.
Jet air floes have played a very good role in the recovery of white water. But it also has some weaknesses, such as:
1 The deeper the floatation tank, the general water level is about 2m, which increases the flotation time, reduces the efficiency, and the flotation time is generally 15-30min;
2 The larger the bubble diameter (about 50u), it is easy to break and lose air flotation;
3 Intermittent squeegee, some floating objects will re-sink due to longer residence time, air bubble burst;
4 Head water, horizontal advance, will interfere with the floating effect. The above is a brief description of the old-fashioned air float.
Second, KROFTA super-efficient shallow air flotation technology This technology is the world's most advanced white water recycling technology, in recent years the introduction of more than one Taiwan for the recovery of white paper machine, received good results. The characteristics of this technology are:
1 Dissolved gas is of high quality, and its bubble diameter is generally around 10um, which greatly increases the contact area and contact point between the microbubble and SS, which is beneficial to floating. It has been proved that the smaller the bubble diameter is, the more difficult it is to break. This avoids the problem of suspended matter re-subsidence caused by the collapse of air bubbles in the floating process and the floating of the upper layer. The first key technology for super-efficient shallow air flotation is the manufacture of dissolved air water. The dissolved gas tank has a unique structure and is a patented technology with a small volume, but the dissolved gas has a good effect, which is the key to its superiority to other forms of air floatation.
2 The pond is very shallow, and the general water level is controlled at about 600mm, which greatly shortens the flotation time. Generally, the flotation process can be completed within 3-5 minutes, so the flotation efficiency is more than 5 times higher than that of the jet deep pool.
3 The water distribution is uniform, and the water released directly rises, there is basically no lateral flow, and the influence of the cross flow on the floating action is avoided.
4 It is unique in producing pulp and adopts a continuously operating rotary spoon type pulp extractor, which removes suspended matter accumulated in the upper layer in a timely manner with little interference and avoids re-subsidence of the floating material.
5 The releaser has special characteristics, releasing evenly, which is beneficial to improve the air floatation effect.
6 There is a continuous operation of the sediment removal squeegee near the bottom of the tank to facilitate the timely removal of sediments to ensure that the bottom of the pool is clean and effective.
The advanced nature of KROFTA technology has been valued by many domestic companies. Domestic equipment factories have already digested and absorbed many and produced advanced equipment with the same level as foreign countries. For example, the super-efficient shallow air floater produced by Tianjin Haohui Technology Co., Ltd. and Wuxi Hudong Environmental Engineering Complete Equipment Factory has been successfully run in many paper mills, and the SS removal rate and the quality of recycled water can be comparable to similar foreign equipment. Wuxi Hudong Environmental Engineering Equipment Factory's products have been exported to the United States, Canada and other places, and are welcomed and praised by foreign countries.
Third, on the white water recycling device with the views of the entire plant white machine water pool together, using a larger single super-efficiency air float unified treatment, can reduce the management personnel, but its disadvantage is that the increase of the length of the collection water pipeline and The resistance, as well as the transport distance of recycled water reuse, has a large total power consumption and increases operating costs. The author suggests: Each paper machine is equipped with a separate recovery device, its advantages are:
1Easy to be managed separately, accounted for separately, enhance the sense of responsibility, help improve the quality of recycled water and recovered pulp, and promote recycling of recovered water and recycled pulp;
2 Since each paper machine receives its own use, it can greatly shorten the transmission pipeline, save power consumption and reduce costs;
3 mobility flexibility, one failure, does not affect the operation of other machines;
4 Each paper machine is equipped with a separate recovery device, and the recovery device becomes an organic part of the paper machine, which is convenient for individual accounting and linking with the personal economic benefits of a full-time individual, which is conducive to the maintenance and operation efficiency of the recovery device.
IV. Other uses of KROFTA super-efficient shallow air floater The main feature of super-efficient shallow air floater is the high removal rate of suspended solids (SS). The white water in paper machine contains high organic suspended matter (high-grade filler paper in white water. Contains a high inorganic filler suspension, so it was first used successfully for white water recycling in paper machines. For this reason, any wastewater containing SS with high suspended solids is effective in super-efficient shallow air flotation. The clinker-waste paper and commercial pulp-based paper mills, whose integrated wastewater (some plants are also referred to as "middle-stream wastewater") contain a high proportion of suspended solids, using super-efficient shallow air flotation and suitable flocculants. , you can achieve a very good treatment effect. When no flocculant is added, the removal rate of SS can reach 70% or more; with flocculants, the removal rate of SS can reach 90% or more, and the highest can reach 95% or more. The addition of flocculants not only helps to improve the flotation effect, but also remove some of the soluble COD and BOD. In this regard, there have been successful experiences in China, such as Wuxi Longda Rongcheng Paper Company and Shanghai Baohua Paper Company.
For paper mills with self-slurry, the traditional practice is to use the precipitation method in the first stage, which is commonly known as primary sedimentation. The main purpose is to remove suspended solids SS. However, there are many small fibers, fiber fragments, and heterocells in the waste water of straw pulp, and most of them have high degree of hydration and are not easily precipitated. The author believes that the use of air flotation to remove suspended solids SS may be better and more effective, especially the first-stage flotation plus flocculation, SS removal rate can be very high, which can greatly reduce the secondary biochemical processing load and operation cost.
For alkaline chemical pulping, increasing the black liquor extraction rate is an effective way to reduce the mid-water treatment load. Similarly, improving the recovery of white water and increasing the removal rate of SS is also an effective way to reduce the processing load of mid-stage water (actually, the overall plant-wide wastewater).
5. The recovery of white water should be an essential measure for all wet papermaking companies. At present, domestic water resources are becoming increasingly scarce, and water shortages have already occurred in many cities. Beijing has new provisions for water use this year: the use of limited quantities of water, and excessive measures to increase prices. Therefore, it is imperative to save water and improve the recycling rate of water. Doing a good job of recycling and recycling of white water can not only ease the tension in the use of paper, but also reduce the water extraction fee and waste water discharge fee. This is a good measure to win more. At present, the cost of clean water for domestic paper mills is mostly around 0.30 yuan/t, and the high one is about 0.50 yuan/t, and the highest one is about 1.00 yuan/t. This has already explained the high cost of wasting water.
Super-efficient shallow air-float white water recovery, for each ton of paper, can be recycled 50-100t water recycling, recycling the cost per ton of water is about 0.12-0.22 yuan, that is, reuse of 1t water can save at least 0.10 yuan. Therefore, do a good job of white water recycling, not only can guarantee the use of paper, but also reduce the cost of paper.
At present, some domestic super-efficient shallow air floater manufacturing facilities have reached international advanced level (for example, Tianjin Haohui Technology Co., Ltd., Wuxi Hudong Environmental Engineering Equipment Factory), and the price is more than half of that of imported equivalent equipment. Super-efficient shallow air floatation equipment can be fully domesticated. Therefore, the promotion of the effective material foundation of the ultra-efficient air floatation technology can be fully promoted throughout the country.
Sixth, Linqing Yinhe Paper Co., Ltd. has achieved remarkable results in the treatment of wastewater from the entire plant. Linqing Yinhe Paper is a large-scale wheat straw pulp and papermaking enterprise, and wheat straw alkali recovery, mid-stage water, and white water recovery are all the most difficult problems in the current pollution control. However, the leadership of the plant dared to meet difficulties and make decisive decisions. He did not hesitate to make high investment in the selection of advanced technologies and equipment at home and abroad so that the recycling of black liquor, middle water and white water in all three parts of the plant was effectively managed and created. A wheat straw pulp mill is typical of comprehensive pollution control standards.
Specific results include:
1 The 100t/d wheat straw alkali recovery operation of this plant was very successful. From January to June this year, the factory has recovered more than 4100 tons of alkali, and the average daily recovery of 25 tons of alkali, the average monthly recovery of more than 700 tons of alkali, the recovery of the comprehensive cost of 1300 yuan / t, in July to create a new level of 780 tons of alkali production (total alkali synthesis costs Has been reduced to 1100 yuan, in July a month alkaline recovery profit 280,000 yuan, the annual recovery of alkali can be expected to exceed 8000t, if it can be expected to achieve, it will be 100t / d wheat straw alkali recovery of the crown.
2 The middle section of the plant is running normally. Design capacity Daily processing water 50,000 tons, a total investment of 48.5 million yuan, the current treatment of water volume has reached 4t million, the effluent COD 300mg / L or less, BOD100mg / L or less, SS200mg / L or less. According to the new standard, COD and BOD have all reached the standard, and only the SS is higher than the new standard 100mg/L. The plant plans to add a super-efficient air floater in the mid-stage water treatment plant, and it is expected that the SS can also reach below 100 mg/L. At present, some of the treated mid-stream water has been used for wet preparations to wash the grass and water conservation has also been received.
The mid-segment water sludge dewatering has been introduced into German Hupe Company's oblique spiral extrusion dewatering, and the sludge dryness can reach more than 30%. This is also very advanced in the dewatering of the water sludge in the middle section of wheat straw pulp. Tons of water treatment costs about 0.60 yuan, which is also more advanced.
3 white water recycling. The plant used two domestic KROFTA super-efficient shallow air floaters, one for 10,000 t/d and one for 700 t/d, and the total amount of water recovered daily reached 18,000 t. SS removal rate: up to 70% when no flocculant is added. When 2×10-6 PAM is added, the SS removal rate is about 90%. When 4×10-6 PAM is added, the removal rate is about 95%. Recovery water cost: 0.12 yuan/t water when PAM is not added; 0.22 yuan/t water when PAM2*10-6 is added. The cost of self-supplied clean water in the plant is above 0.30 yuan/t water, and the recovered water has been economically beneficial.
VII. Ideas for the compliance of wastewater from papermaking enterprises 1. Alkaline chemical pulping: Alkaline recovery should be done first, and the corresponding mid-stage water treatment and whitewater recovery should be implemented to achieve the discharge of standards.
2, acid and ammonium slurry pulp: First of all to do a good job of comprehensive utilization of red liquor, and the corresponding provision of water treatment and white water recovery.
3. The middle-stage water treatment of chemical pulping should adopt two-stage treatment. That is, one-level removal of SS, sedimentation, air floatation can be; two should adopt biochemical methods, mainly biological aeration.
4. Paper-making enterprises based on waste paper and commercial pulp can use super-efficient air flotation and flocculation.
5. All wet papermaking enterprises should do a good job of white water recycling. The super-efficient shallow air floatation has proved to be effective.
Jet air floes have played a very good role in the recovery of white water. But it also has some weaknesses, such as:
1 The deeper the floatation tank, the general water level is about 2m, which increases the flotation time, reduces the efficiency, and the flotation time is generally 15-30min;
2 The larger the bubble diameter (about 50u), it is easy to break and lose air flotation;
3 Intermittent squeegee, some floating objects will re-sink due to longer residence time, air bubble burst;
4 Head water, horizontal advance, will interfere with the floating effect. The above is a brief description of the old-fashioned air float.
Second, KROFTA super-efficient shallow air flotation technology This technology is the world's most advanced white water recycling technology, in recent years the introduction of more than one Taiwan for the recovery of white paper machine, received good results. The characteristics of this technology are:
1 Dissolved gas is of high quality, and its bubble diameter is generally around 10um, which greatly increases the contact area and contact point between the microbubble and SS, which is beneficial to floating. It has been proved that the smaller the bubble diameter is, the more difficult it is to break. This avoids the problem of suspended matter re-subsidence caused by the collapse of air bubbles in the floating process and the floating of the upper layer. The first key technology for super-efficient shallow air flotation is the manufacture of dissolved air water. The dissolved gas tank has a unique structure and is a patented technology with a small volume, but the dissolved gas has a good effect, which is the key to its superiority to other forms of air floatation.
2 The pond is very shallow, and the general water level is controlled at about 600mm, which greatly shortens the flotation time. Generally, the flotation process can be completed within 3-5 minutes, so the flotation efficiency is more than 5 times higher than that of the jet deep pool.
3 The water distribution is uniform, and the water released directly rises, there is basically no lateral flow, and the influence of the cross flow on the floating action is avoided.
4 It is unique in producing pulp and adopts a continuously operating rotary spoon type pulp extractor, which removes suspended matter accumulated in the upper layer in a timely manner with little interference and avoids re-subsidence of the floating material.
5 The releaser has special characteristics, releasing evenly, which is beneficial to improve the air floatation effect.
6 There is a continuous operation of the sediment removal squeegee near the bottom of the tank to facilitate the timely removal of sediments to ensure that the bottom of the pool is clean and effective.
The advanced nature of KROFTA technology has been valued by many domestic companies. Domestic equipment factories have already digested and absorbed many and produced advanced equipment with the same level as foreign countries. For example, the super-efficient shallow air floater produced by Tianjin Haohui Technology Co., Ltd. and Wuxi Hudong Environmental Engineering Complete Equipment Factory has been successfully run in many paper mills, and the SS removal rate and the quality of recycled water can be comparable to similar foreign equipment. Wuxi Hudong Environmental Engineering Equipment Factory's products have been exported to the United States, Canada and other places, and are welcomed and praised by foreign countries.
Third, on the white water recycling device with the views of the entire plant white machine water pool together, using a larger single super-efficiency air float unified treatment, can reduce the management personnel, but its disadvantage is that the increase of the length of the collection water pipeline and The resistance, as well as the transport distance of recycled water reuse, has a large total power consumption and increases operating costs. The author suggests: Each paper machine is equipped with a separate recovery device, its advantages are:
1Easy to be managed separately, accounted for separately, enhance the sense of responsibility, help improve the quality of recycled water and recovered pulp, and promote recycling of recovered water and recycled pulp;
2 Since each paper machine receives its own use, it can greatly shorten the transmission pipeline, save power consumption and reduce costs;
3 mobility flexibility, one failure, does not affect the operation of other machines;
4 Each paper machine is equipped with a separate recovery device, and the recovery device becomes an organic part of the paper machine, which is convenient for individual accounting and linking with the personal economic benefits of a full-time individual, which is conducive to the maintenance and operation efficiency of the recovery device.
IV. Other uses of KROFTA super-efficient shallow air floater The main feature of super-efficient shallow air floater is the high removal rate of suspended solids (SS). The white water in paper machine contains high organic suspended matter (high-grade filler paper in white water. Contains a high inorganic filler suspension, so it was first used successfully for white water recycling in paper machines. For this reason, any wastewater containing SS with high suspended solids is effective in super-efficient shallow air flotation. The clinker-waste paper and commercial pulp-based paper mills, whose integrated wastewater (some plants are also referred to as "middle-stream wastewater") contain a high proportion of suspended solids, using super-efficient shallow air flotation and suitable flocculants. , you can achieve a very good treatment effect. When no flocculant is added, the removal rate of SS can reach 70% or more; with flocculants, the removal rate of SS can reach 90% or more, and the highest can reach 95% or more. The addition of flocculants not only helps to improve the flotation effect, but also remove some of the soluble COD and BOD. In this regard, there have been successful experiences in China, such as Wuxi Longda Rongcheng Paper Company and Shanghai Baohua Paper Company.
For paper mills with self-slurry, the traditional practice is to use the precipitation method in the first stage, which is commonly known as primary sedimentation. The main purpose is to remove suspended solids SS. However, there are many small fibers, fiber fragments, and heterocells in the waste water of straw pulp, and most of them have high degree of hydration and are not easily precipitated. The author believes that the use of air flotation to remove suspended solids SS may be better and more effective, especially the first-stage flotation plus flocculation, SS removal rate can be very high, which can greatly reduce the secondary biochemical processing load and operation cost.
For alkaline chemical pulping, increasing the black liquor extraction rate is an effective way to reduce the mid-water treatment load. Similarly, improving the recovery of white water and increasing the removal rate of SS is also an effective way to reduce the processing load of mid-stage water (actually, the overall plant-wide wastewater).
5. The recovery of white water should be an essential measure for all wet papermaking companies. At present, domestic water resources are becoming increasingly scarce, and water shortages have already occurred in many cities. Beijing has new provisions for water use this year: the use of limited quantities of water, and excessive measures to increase prices. Therefore, it is imperative to save water and improve the recycling rate of water. Doing a good job of recycling and recycling of white water can not only ease the tension in the use of paper, but also reduce the water extraction fee and waste water discharge fee. This is a good measure to win more. At present, the cost of clean water for domestic paper mills is mostly around 0.30 yuan/t, and the high one is about 0.50 yuan/t, and the highest one is about 1.00 yuan/t. This has already explained the high cost of wasting water.
Super-efficient shallow air-float white water recovery, for each ton of paper, can be recycled 50-100t water recycling, recycling the cost per ton of water is about 0.12-0.22 yuan, that is, reuse of 1t water can save at least 0.10 yuan. Therefore, do a good job of white water recycling, not only can guarantee the use of paper, but also reduce the cost of paper.
At present, some domestic super-efficient shallow air floater manufacturing facilities have reached international advanced level (for example, Tianjin Haohui Technology Co., Ltd., Wuxi Hudong Environmental Engineering Equipment Factory), and the price is more than half of that of imported equivalent equipment. Super-efficient shallow air floatation equipment can be fully domesticated. Therefore, the promotion of the effective material foundation of the ultra-efficient air floatation technology can be fully promoted throughout the country.
Sixth, Linqing Yinhe Paper Co., Ltd. has achieved remarkable results in the treatment of wastewater from the entire plant. Linqing Yinhe Paper is a large-scale wheat straw pulp and papermaking enterprise, and wheat straw alkali recovery, mid-stage water, and white water recovery are all the most difficult problems in the current pollution control. However, the leadership of the plant dared to meet difficulties and make decisive decisions. He did not hesitate to make high investment in the selection of advanced technologies and equipment at home and abroad so that the recycling of black liquor, middle water and white water in all three parts of the plant was effectively managed and created. A wheat straw pulp mill is typical of comprehensive pollution control standards.
Specific results include:
1 The 100t/d wheat straw alkali recovery operation of this plant was very successful. From January to June this year, the factory has recovered more than 4100 tons of alkali, and the average daily recovery of 25 tons of alkali, the average monthly recovery of more than 700 tons of alkali, the recovery of the comprehensive cost of 1300 yuan / t, in July to create a new level of 780 tons of alkali production (total alkali synthesis costs Has been reduced to 1100 yuan, in July a month alkaline recovery profit 280,000 yuan, the annual recovery of alkali can be expected to exceed 8000t, if it can be expected to achieve, it will be 100t / d wheat straw alkali recovery of the crown.
2 The middle section of the plant is running normally. Design capacity Daily processing water 50,000 tons, a total investment of 48.5 million yuan, the current treatment of water volume has reached 4t million, the effluent COD 300mg / L or less, BOD100mg / L or less, SS200mg / L or less. According to the new standard, COD and BOD have all reached the standard, and only the SS is higher than the new standard 100mg/L. The plant plans to add a super-efficient air floater in the mid-stage water treatment plant, and it is expected that the SS can also reach below 100 mg/L. At present, some of the treated mid-stream water has been used for wet preparations to wash the grass and water conservation has also been received.
The mid-segment water sludge dewatering has been introduced into German Hupe Company's oblique spiral extrusion dewatering, and the sludge dryness can reach more than 30%. This is also very advanced in the dewatering of the water sludge in the middle section of wheat straw pulp. Tons of water treatment costs about 0.60 yuan, which is also more advanced.
3 white water recycling. The plant used two domestic KROFTA super-efficient shallow air floaters, one for 10,000 t/d and one for 700 t/d, and the total amount of water recovered daily reached 18,000 t. SS removal rate: up to 70% when no flocculant is added. When 2×10-6 PAM is added, the SS removal rate is about 90%. When 4×10-6 PAM is added, the removal rate is about 95%. Recovery water cost: 0.12 yuan/t water when PAM is not added; 0.22 yuan/t water when PAM2*10-6 is added. The cost of self-supplied clean water in the plant is above 0.30 yuan/t water, and the recovered water has been economically beneficial.
VII. Ideas for the compliance of wastewater from papermaking enterprises 1. Alkaline chemical pulping: Alkaline recovery should be done first, and the corresponding mid-stage water treatment and whitewater recovery should be implemented to achieve the discharge of standards.
2, acid and ammonium slurry pulp: First of all to do a good job of comprehensive utilization of red liquor, and the corresponding provision of water treatment and white water recovery.
3. The middle-stage water treatment of chemical pulping should adopt two-stage treatment. That is, one-level removal of SS, sedimentation, air floatation can be; two should adopt biochemical methods, mainly biological aeration.
4. Paper-making enterprises based on waste paper and commercial pulp can use super-efficient air flotation and flocculation.
5. All wet papermaking enterprises should do a good job of white water recycling. The super-efficient shallow air floatation has proved to be effective.
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