There are many types of filter tanks, and the ordinary fast filter tank with quartz sand as the filter material has a long history of use. On this basis, people from different process perspectives to develop other types of fast filtration tanks, V-type filter is based on this by the French Deliman company in the 1970s developed. v-type filter using a thicker, thicker, uniform particles of the quartz sand filter layer; the use of the layer does not make the expansion of the air, water backwashing and the surface of the water to be filtered sweeping; the use of air cushion distribution of air and a special long-handled filter head for air, water distribution and other processes. It adopts air cushion to distribute air and special long-handled filter head to distribute air and water. It has good water quality, high filtration rate, long operation cycle, good backwashing effect, energy saving and easy to automate the management and other characteristics. Therefore, it has been widely used in mainland Europe in the 70's. In the late 80's, Nanjing, Xi'an, Chongqing and other places in China began to introduce the use of the 90's, China's newly built large and medium-sized water purification plants almost all use the V-shaped filter pool this water filtration process, especially in Guangdong Province, almost all of the newly built water purification plants use the V-shaped filter pool. 91-94 our company in the construction of Shakou Water Treatment Plant (500,000 m3/d), the first time to design, construct and install their own water treatment plant, and the first time to design, construct and install their own water treatment plant. In 91-94, our company in the construction of Shakou water plant (500,000m3/d), for the first time to design, construction and installation of their own V-shaped filter. Since then, we have carried out the design and installation of V-shaped filter tanks. We have helped design and install V-filter tanks in Gaoming, Zhongshan Xiaolan, Zhongshan Shanfeng, Shunde Longjiang, Sanshui, Guangning, Shantou, Huizhou and other sister water companies. In nearly a decade of V filter design, construction and installation, as well as automatic control process, we have gained a certain amount of practical experience, there are the following points of experience:
A study to master the structure of the V filter, the principle of operation, process characteristics
Filter is an important link in the water purification process in the water treatment plant, and the regeneration of the filter capacity, the filter is the key to the stable and efficient operation of the key. If you use better backwashing technology, so that the filter cell is often in the optimal conditions of work, not only can save water and energy, but also improve water quality, increase the dirt trapping capacity of the filter layer, prolong the working cycle, improve water production. The regeneration of the filtration capacity of the V-shaped filter tank adopts the technology of advanced gas and water backwashing and surface sweeping. Therefore, the filtration cycle of the filter tank is extended by about 75% compared with that of the simple water rinsing filter tank, and the sewage intercepting capacity can be increased by 118%, while the consumption of backwashing water can be reduced by more than 40% compared with that of the simple water rinsing filter tank. Filter tank in the air rinse, due to the blower will be pressed into the filter layer of air, and thus from the following aspects to improve the filter performance of the filter tank:
① The addition of compressed air to increase the shear force of the surface of the filter media, which makes it easy to peel off the dirt in the usual water rinsing in the bubbles of the bubble rises dramatically in high shear can be flaked off to improve the effect of the backwash.
②The movement of bubbles in the filter layer produces a mixture of particles in the filter media can make the particles continue to vortex diffusion, promoting the filter layer particles circulating mixing, thus obtaining a graded uniform mixed filter layer, its porosity is higher than that of the graded filter media graded filter layer, improving the filtration performance, thereby improving the filter layer's dirt trapping capacity.
3 compressed air, bubbles in the particles of the filter media burst, so that the collision between the particles of the filter media friction intensified, in the water flushing, the shear effect on the surface of the particles of the filter media can also be given full play to strengthen the effectiveness of the water flushing dirt.
4. The movement of bubbles in the filter layer reduces the resistance of mutual contact between the particles of the filter media during water rinsing, which greatly reduces the intensity of water rinsing, thus saving the energy consumption of rinsing.
In summary, the gas and water backwashing, due to the bubble's intense Trenton action, greatly strengthened the dirt flaking ability and intercepting capacity. In the actual backwashing of the filter tank, we observed that: when the backwash time of about 5 minutes when the filter layer of dirt stripping up to 95% or more, so the V-shaped filter tank backwashing effect is certain. In addition, backwashing, raw water through the backwash drain tank opposite the two V-slot bottom of the hole into the filter tank, it sweeps the surface of the filter layer, and the filter layer backwash up the dirt, impurities pushed to the drain tank, while sweeping the level of speed is equal to zero in some places, in which the sand floated up to re-sedimentation. In addition, the surface of the filter sweeping, but also to speed up the backwash water rinsing speed, with raw water to feed the backwash after filtering the amount of water and electricity, but also saves the amount of rinsing water. Feeding rinse water is a special advantage of raw water surface sweeping, in fact, it also plays a role in a filter backwash to prevent the other filters in the maximum output load operation.
Two, a reasonable choice of design parameters
After understanding and mastering the working principle of the above V filter, to be designed to give full play to its superiority of the V filter. It is necessary to strictly guarantee the structural dimensions of the process requirements. Therefore, a reasonable choice of design parameters to carry out the process design of the filter is essential. Over the past decade by our design of a number of V-shaped filter, built and put into operation after the actual operating results are generally better. This proves that the design parameters we have chosen are ideal, the introduction is as follows:
1, the use of the main design parameters
Filter media: quartz sand, preferably selecting the seawater flushing strength of the seaside sand quarry quartz sand. Grain size 0.95～1.35mm; uneven coefficient K80=1.0～1.3; thickness of filter layer 1.2～1.5m.
Filtering speed: 7～15m/h. Depth of water on the sand is 1.2～1.3m.
Backwashing intensity: compressed air 15～161/m2.s; water backwash 4～51/m2.s; water surface sweeping 1.5～1.8/ m2.s.
Filter head: QS-type long-handle filter head is used, with a length of 28.5cm; 36 slits on the filter cap; φ2mm air holes on the upper part of the filter handle, and 65mm-long and 1mm-wide slits on the lower part; the material is ABS engineering plastics. The filter head is evenly distributed on the filter plate, with 48-56 per square meter.
The filter plate and filter beam are prefabricated steel reinforced concrete parts. The filter plate is made of rectangle or square, but the side length should not exceed 1.2 m. The width of the filter beam is 10cm, and the height and length are decided according to the actual situation.
2, the size and elevation of the filter tank structure
According to the flow characteristics of the fluid, in order to ensure that the backwash filter tank plane gas, water distribution uniformity, the filter tank plane dimensions of the aspect ratio of a little larger than the best. Generally: length: width = 4:1 ~ 3.5:1 (width does not include the central gas and water distribution tank, the central gas and water distribution tank width is generally 0.7 ~ 0.9 meters). In general, the length of the pool should preferably not be less than 11 meters. The central air-water distribution tank of the pool will be divided into two halves of the width of the pool, each half of the width should not be more than 4 meters.
In order to ensure equal pressure at any point under the filter plate during backwashing, and so that the air pressed under the filter plate can form a cushion of air as soon as possible, there should be a space of appropriate height between the filter plate and the bottom of the pool. We put the height of the clear water reservoir under the filter plate is generally designed for 0.85 to 0.95 meters. This height is enough to make the air through the holes and seams of the filter head to get fully mixed and evenly distributed over the entire area of the filter pool, thus ensuring the normal filtration of water filtering work and regeneration effect of the filter pool.
The water to be filtered passes through the main inlet channel, through two pneumatic rubber valves and a manual gate valve, and then through the overflow weir by two side holes into the V-shaped tank and then flows into the filter compartment. We design the square hole in the center (denoted by W1) as an inlet hole controlled by a manual gate valve, which is normally open (only closed when the filter compartment is being repaired), and the surface cleaning water enters through the overflow weir from this square hole when the filter tank is backwashed. We take the two sides of the water inlet holes (W21 and W22, respectively, W1 = W2), designed as two equal size, pillow-shaped inflatable rubber valve to control the square hole to be filtered water into the filter tank backwash, these two holes by the pillow-shaped inflatable rubber valve plugged. We design the ratio of the size of the area of these three inlet holes as follows: W1:W21=W1:W22=1:3; the flow rate of the inlet holes is controlled at 0.40-0.5m/s; these two principles are used to revise each other and finally determine the size of the inlet holes.
Surface sweeping is realized by the jet sprayed from the small hole at the bottom of the V-groove. According to the nature of the jet, in order to make the best surface cleaning effect, this jet is preferably semi-flooded jet. Therefore, the determination of the center elevation of the small hole at the bottom of the V-groove is very critical. According to our experience, the small hole center elevation than the backwash water level is 0.8 ~ 1.2cm lower than the best. We have visited a water plant designed by the French company Deliman, they designed the center of the hole elevation than the backwash water level is lower than 1.3cm. filter tank backwash, the surface of the sweeping effect is not as good as our design of the filter tank.
The other aspects of the design of the filter tank we introduced with the relevant information is basically the same, not much to repeat here.
Three, construction and installation practices
The construction and installation of the filter pool is directly related to the completion of the filter pool after the commissioning of the normal operation of the process to meet the design requirements. v-type filter pool on the construction and installation of the requirements of the more stringent provisions: the level of the filter plate error shall not be greater than ± 2 mm; the level of the filter pool shall not be greater than the error of ± 5 mm; the center of the beams and the anchoring bars between the distance between the error ± 2 mm; plate size production error ± 2 mm; the error in the size of the plate shall not be greater than ± 2 mm. 2 millimeters; plate size production error of ± 2 millimeters; it requires the central drain weir top of the level of error can not be greater than ± 2 millimeters; all the inner edges of the filter pool size are required to be strictly controlled. Therefore, to ensure that the construction and installation of the filter pool quality requirements, in addition to the strict management and control of the whole pool of civil construction, the most critical also have to strictly control the production and installation of the filter plate and filter beam, only the filter plate, filter beam leveled, the filter head essentially also leveled. The filter plate and filter beam are often made into prefabricated parts. In the prefabrication yard, we use steel molds, steel bars and concrete to carefully make filter plate and filter beam, to ensure the level of the single filter plate and filter beam and the thickness of the filter plate, and to maintain it, and to keep the quality of the first gate. To make the whole pool filter plate surface level, the key is in the installation of the filter beam. We will install the filter beam with the buried iron accurately and smoothly buried in the bottom of the pool, and then in this piece of buried iron welded a DN100 steel pipe, and in the prefabricated filter beam below the buried iron welded a DN80 steel pipe, DN80 steel pipe into the DN100 steel pipe, with the level meter school level, leveling, and then welded the pipe into a whole. Then use DN200 pipe as a mold, cement mortar into the mold, so that in DN100, DN80 pipe outside the formation of a layer of protective film to prevent the steel pipe support rust, but also to strengthen the strength of its support. In the filter beam installed on the basis of good, and then use the level meter to strictly control the level of the filter plate installation. Really achieve the whole pool filter plate surface level error of not more than ± 5 mm. We use the Ministry of Electric Power, East China Survey and Design Institute of the development and production of 905 joints special sealant (according to cement: sand: 905 glue = 1:1:0.5 ratio formulated into 905 mortar) between the filter plate and the filter plate and the wall of the gap between the seal. Ensure the sealing performance of no water leakage and no air leakage, thus also ensuring the success of gas and water backwashing.
Four, the automatic control of production operation
The automatic control of filtration and regeneration of the V-type filter pool is the guarantee of normal production operation of the filter pool. We use a programmable controller and industrial computer (PLC + IPC) composed of real-time multi-task distributed control system to control the filtration and backwashing of the filter tank.
1, filtration control
We have installed water level sensors and head loss sensors in the corresponding parts of the filter tank. The filtration of the filtering tank is measured through their water level and head loss of the filtering tank, the water level value and the opening degree of the valve of the filtered water is sent to a special module installed in each PLC cabinet, and the adjustment module can be adjusted to adjust the opening degree of the valve, so that the filtering tank reaches the inlet and outlet of the water balance, so as to realize the automatic filtration of the constant water level and the constant filtration speed.
2. Backwashing control
The backwashing of a group of filter tanks is controlled by a common PLC. When filtration reaches the filtration cycle or filter tank differential pressure (head) set value, the filter tank backwash request, PLC according to the priority order of the filter tank, composed of a request backwash queue. Once the response to the request of a filter cell, PLC implementation of the entire process of backwash, in a group of filter plate, not allowing two filter cells at the same time backwash, when a filter cell is backwashing, other filter cell request backwash signal is stored in the common PLC, and then in accordance with the order of the storage, the filter cell in order to carry out backwash.
When the filter backwash, the public PLC control process is: ① Close the water inlet valve to be filtered, when the water level of the filter tank drops to the top of the sand washing drainage tank, close the post-filtering water control valve, open the backwash drain valve; ② start the blower, after 5 seconds, open the filter tank backwash valve, the filter tank for 1 minute of gas pre-purge; ③ open the backwash water valve, start the backwash pump, the gas and water for 7 minutes; ④ close the blower, after 5 seconds, open the filter tank backwash valve, pre-wash for 1 minute; ③ open the backwash valve, start the backwash pump, backwash for 7 minutes. At the same time backwash; ④ close the backwash valve, 5 seconds later, stop the blower, open the air diaphragm valve exhaust, 5 minutes of water backwash rinse, stop the backwash pump. 5 seconds later, close the water backwash valve, and then close the backwash drain valve, open the water inlet valve to be filtered water, the filter tank to resume filtration. The entire backwashing process lasted about 25 minutes.
In addition, the PLC can also control the number of open filter pools, it is based on the number of filter pools to determine the number of open filter pools, according to the first to stop the first to open, the first to open the first to stop the principle of determining the opening of a grid filter pools, stop.
V. Selection of the main equipment of the V filter
Specialized instrumentation and the selection of pneumatic valves, is the key to achieve fully automatic control of the V filter, the normal operation of the V filter backwash water valves, air valves; fresh water valve, sewage valve, we have adopted a pneumatic butterfly valve. These valves can be based on their own water companies decide to use domestic or imported, but must choose a good quality. At present, some domestic manufacturers of the quality of the world's advanced level, not worse than imported valves, good value for money, it is worth a trial. We believe that the water inlet valve to be filtered using pillow pneumatic rubber valve is better, simple production, reliable action. Other supporting equipment: blowers, air compressors, pumps and other domestic can meet the requirements, there is no need to import.
In summary, we believe that the V-shaped filter advanced, lies in the use of homogeneous filter media and advanced gas, water backwash and surface cleaning technology. In addition to the application of this technology in the new water purification plant, we can also promote this technology to the old plant renovation, relying on scientific progress, the use of new science and technology, technological transformation, to give full play to its fullest potential, can be in a short period of time to make a substantial increase in the amount of water production, is to realize the water supply industry, "to improve the quality of water supply, improve the safety and reliability of water supply, reduce the consumption of medicines, reduce energy consumption, reduce leakage. Reduce leakage." A better way. Its main features are: the use of relatively coarse particle size quartz sand homogeneous filter material and thicker filter layer of the interception of dirt, dirt-holding capacity, and to extend the working cycle of the filter tank; air-water backwash plus surface sweeping, the filter layer does not swell or slightly swollen; its water distribution system for the long handle filter head distribution system; operation to realize the "communal rinsing PLC + the filter tank PLC" of the automatic control mode. The operation realizes the automatic control mode of "common rinsing PLC + each filter tank PLC". The main design parameters are as follows: the plane size is 12 m×7 m; the designed filtration speed is 8.04 m/h; the density of filter head is 54/m2; and the thickness of filter material layer is 1.2 m.
When the V-type filter tank operates in automatic mode, the PLC controls the constant liquid level of the filter tank by controlling the openness of the after-filtering water outflow gate, and the backwashing starts when one of the following conditions is met: the running time of the filter tank reaches the set value; The head loss of filtration reaches the set value; the flushing command from the PLC-XBT keyboard at the console site or the monitoring computer in the central control room.
V-type filter backwash is more distinctive, rinsing three processes: ① gas pre-scrub [a blower, send gas 1 min, q gas = 22.5 m3/(m2-h)]; ② gas and water mixing rinsing [two blowers, a rinse pump, rinse 6 min, q gas = 55 m3/(m2-h), q water = 7.5 m3/(m2-h)]; ③ water rinsing [two rinsing pumps, rinsing 6 min, q water = 15 m3/(m2-h)]; always transverse surface sweeping intensity q water = about 5.2 m3/(m2-h).
In the operation and management, it is found that: the elevation of the horizontal surface washing hole in the V-shaped tank of the filter tank inlet is too low, and the surface washing intensity is slightly low, which leads to the poor effect of the horizontal washing, and the foam and scum are floating and retained; there is a blockage of the filter head, and it is extremely inconvenient to clean it; the regulation failure of the filter tank occurs frequently, and the main countermeasures are to regularly clean the water level meter and the head loss meter of the filtration layer, to keep the sensitivity, and to control the filter tank appropriately. Stability of water intake, filter tank maintenance and management workload is large.
In addition, in the production of low-turbidity period (raw water turbidity <20 NTU) of the V-type filter direct filtration performance and polymerization of aluminum dosage on the direct filtration of the impact. The results show that reasonable control of PAC dosage will produce the following effects: ① slow down the growth of filtration head loss, head loss over time curve approximate straight line, can effectively prevent premature clogging of the filter layer; ② increase the depth of penetration of flocs in the filter layer, to give full play to the homogeneous filtration media of the V-type filtration tank, the advantages of the deep filtration bed of the interception of dirt and dirt.
This article is from: Environmental Technology Network (www.cnjlc.com) Detailed source reference: jlc.com/h2o/3/20070706626.html