Experimental Study of Air Pump Backwash with Jet Pump

Key words: jet pump, experimental study

Abstract: Jet pump instead of air compressor or blower for air and water filter backwash, can greatly reduce the cost of equipment deduction. Semi-productive tests show that this process works well and is technically feasible. This paper describes the experimental results of the new technology in the aspects of equipment composition, process parameters, flushing effect and so on.

Filter is the most commonly used equipment in water treatment projects. Filter rinse was good or bad, the filter effect of the filter and the economy have a significant impact. Air-water backwash filter than the backwash water alone is good, but the need to set large-capacity air compressors or blowers, due to the high cost of equipment, complex operation, and work vibration, noise, slow promotion. Jet pump filter air and water backwash, you can greatly reduce equipment and operating costs, simplify operations, reduce noise, is conducive to the promotion. The technology has been patented. This article focuses on the results of semi-productive pilot studies.

1. Semi-productive test equipment

The semi-productive test of jet pump suction air-water backwash filter is based on the indoor small-scale test. Test filter located in Chongqing Municipality hit dam water plant. There are two experimental filter, filter area is lm2, square. A filter with long-handled filter for water distribution system. Figure l (1). The filter head is installed on the diaphragm at the lower part of the filter. The filter heads are arranged in checkerboard with a pitch of 0.14m. Under the partition with a water chamber height of 0.45m. The separator is provided with a thickness of 0.05m of coarse sand (particle size 2 ~ 4mm), on which is 0.3m thick quartz sand filter (particle size 0.5 ~ 1.0mm) and 0.4m thick anthracite filter layer ~ 1.7mm). Drains, the roof from the sand 0.68m. Drainage top with 40 mesh nylon sand control, to prevent air and water backwash filter loss. The total height of the filter is 3.5m. The jet pump is mounted vertically on the filter backwash hose. Jet pump factory water as the pressure water source. Filter backwash, the pressure water jet nozzle jet, the air inhalation, the formation of gas-water mixture, into the lower part of the water distribution chamber filter; gas-water separation, the long-handled filter evenly distributed in the filter plane On the bottom of the filter layer of gas and water at the same time backwash; backwash gas and water, then separate water backwash to exclude the filter layer of bubbles, and the double layer filter layered. After the backwashing wastewater, collected by the upper drain and discharged from the pool.

Another experimental filter with perforated pipe for water distribution and gas distribution system, as shown in Figure 1 (2). Perforated water distribution pipes are arranged at the bottom of the pool and are provided with a pebble supporting layer (particle size: 32-16mm, 16-8mm, 8-4mm, 4-2mm. The thickness of each layer is 0.15m, 0.10m, 0.10m and 0.13m ). Perforated gas pipe located in the particle size of 4 ~ 2mm support layer. Support layer double filter layer, particle size and thickness with the former. Drainage from the sand roof is 0.45m. The total height of the filter and other dimensions with the former. The filter and the aforementioned filter share a jet pump. And after the jet pump set up a gas-water separation tank, the water and gas were separated into the perforated pipe water distribution and gas distribution system, bottom-up gas-water filter at the same time backwash. With perforated pipe for water distribution and gas distribution, not only for the new filter, and is particularly suitable for ordinary fast filter transformation.

2. Test results and analysis

The experiment began in July 1987 and ended in December, which lasted more than five months and experienced the flood period and the flat water period of the Jialing River. Sedimentation into the filter water turbidity minimum 3 degrees, up to 25 degrees, an average of 13 degrees; water temperature is 17.5 ~ 26.5 ° C. The test results are as follows:

2.1 air and water backwash the best process parameters of the experimental study

In order to determine the process parameters of semi-productive test, two orthogonal experiments were carried out with 10 filter columns. Filter column diameter of 150mm, length 4m, the lower part of the installation of long-handled filter as water distribution system, the upper part of the filter diameter of 0.5 ~ 1.2mm quartz sand filter, thickness 0.4m, and 0.8 ~ 1.8mm of anthracite filter Material, thickness 0.3m. The test is also being carried out at a dam dam factory, with the same test conditions as the semi-production test. Filter column to the constant velocity filtration, filtration rate control in 13 ~ 16m / h. When the filter head loss reached 1.7m, backwashing. Backwash water from the factory pressure water supply, backwash air supply from the air compressor. First with air and water backwash several minutes at the same time, and then separate water backwash 2min. The first batch of orthogonal test selected gas-water simultaneous backwash gas-water ratio, the total strength of backwash gas and water and air backwash time, and water backwash strength of four factors were investigated to filter period as an indicator. Choose 3 levels for each factor. The test results are shown in Figure 2. According to the results of orthogonal test and Fig. 2, the main factors influencing the filtration cycle are single water backwash intensity, followed by gas-water ratio and gas-water simultaneous backwashing time, while the total strength of backwash gas- Less affected. This is because when gas and water are backwashed at the same time, the anthracite and quartz sand are almost completely mixed. Increasing the intensity of the single water backwash can make the coal sand well layered and increase the filtration period. The second batch of orthogonal test, air-water ratio of 2: 1 fixed, select the total strength of air and water backwash and backwash time, single water backwash strength and backwash time to examine four factors, each factor choice 3 A level. The test results are shown in Figure 2. From the analysis, it can be seen that the main factor affecting the filtration cycle is still the single water backwash intensity; the other factors are the single water backwash time, air and water backwash time and the total backwash strength.

The first batch and the second batch of experiments, we can see the process parameters should be selected air-water ratio of 1.5: l ~ 2: 1, air and water backwash total strength of about 12L / (s.m2), gas and water backwash time For 5 ~ 7min, water backwash intensity of 15 L / (s.m2) or so, separate water backwash time to 2min better.

2.2 semi-productive filter operating mode and operating conditions

Experimental filter by constant head deceleration filter. Pre-filter water level remained above the surface of the sand 1.7m or so. Initial filtration rate control at 14 ~ 17m / h. Filter backwash once every 2d, filtration cycle average of 47h. At the end of the cycle, the final filtration rate is only 3-4 m / h less than the initial filtration rate. The average filtration rate of the filter, perforated pipe water distribution filter for the 13.4m / h, the filter with water distribution filter 14.5m / h.

As the pressure of the factory water changes frequently, the water pressure before the jet pump is different during each backwashing of the filter, and generally varies between 2.2 and 3.5 atmospheres. The backwashing strength of water was 4.8 ~ 5.7L / (sm 2 ) with an average of 5.3 L / (sm 2 ) when air-water backwashing was carried out simultaneously. The backwashing strength of gas was 4 ~ 10.6 L / (sm 2 ) It was 7.2 L / (sm 2); gas-water ratio of 0.83: 1 to 2: 1, an average of 1.36: 1; air-water backwashing total intensity of 8.8 ~ 16.3 L / (sm 2 ), an average of 12.6 L / ( sm 2 );

The backwash time of gas and water was 5min at the same time; the backwashing intensity of water alone was 12 ~ 17 L / (sm 2 ) with an average of 15 L / (sm 2 ); Backwash water consumption rate of perforated pipe water distribution filter is 0.6%, the filter with water distribution filter is 0.59%.

Filter backwash, the jet pump is working properly, gas-water separation tank separation effect is good; whether long-handled filter or perforated pipe, with water distribution are more uniform; separate water backwashing, coal sand stratification layer is good, Sand surface smooth.

2.3 Test filter drainage turbidity, sewage rate and filter mud content

Filter drainage turbidity, sewage and filter mud content from different aspects of the filter to reflect the flushing effect.

Tests show that the beginning of filter air-water backwash, the turbidity increased drastically, 0.5min before and after the maximum occurs, the turbidity up to 8000 ~ 10000 degrees, then quickly reduce turbidity turbidity at the end of the backwash Can be reduced to 30 to 120 degrees. The removal rate of contaminants can reach 80-88% at the end of gas-water simultaneous backwashing, and can be up to 97.5-99.6% through backwashing with separate water for 2min. Table 1 for the three filter layer during the test mud content measurement results, the table shows that after several months of operation of the filter, the filter mud content is still low. In addition, with the naked eye, the filter cloth has the same luster as the new filter after being washed, no mud film is found on the filter material, and there is no mud ball at the interface of the coal sand, which shows that the flushing effect is good.

Filter average clay content (%) Table 1

2.4 filter filter head loss and effluent quality

The initial head loss of the filter is a measure of the filter backwash effect. Figure 3 shows the initial filter head loss with the filter cycle changes. In order to avoid head loss by the initial filtration rate. In Figure 3, the ratio of initial head loss to initial filtration rate H0 / V0 is the ordinate. It can be seen from the figure that the initial head loss of the filter layer only fluctuates within a small range without the tendency of increasing with the number of cycles, which shows that the filter layer washing effect is good.

Filter filter process, the head loss changes, but also to some extent, reflect the filter backwash effect is good or bad. Figure 4 is the average of two experimental filter head loss changes in the situation. As can be seen from the figure, the head loss of the filter layer increases slowly during the filtration process. Under the condition of higher filtration speed, the loss of the head of the filter is less than 1.60m at the end, which is much smaller than the limit head loss provided by the filter. The fact shows that the filtration period of the filter can greatly exceed the test value. Tests showed that the filter head loss did not increase with the number of filtration cycles, which also reflects the good filter flushing effect.

Figure 4 also plots the change in turbidity of the two test filters (average of multiple runs). As can be seen from the figure, the turbidity of the filter effluent is stable and variable throughout the filtration period, and generally less than 2 degrees, the effluent quality is good. Figure 5 plots the frequency distribution curve of the influent turbidity and effluent turbidity of the test filter. As can be seen from the figure, the median turbidity (50%) is about 13 degrees, and the median turbidity of the water is about 1 degree, indicating that the interception of the filter layer is always strong.

2.5 prevent the loss of filter material measures

Gas and water backwash filter layer, the filter can be carried up to the surface of the air bubbles and water loss. In order to understand the height of the material to be carried, a special test was carried out in the filter column. The filter column is filled with quartz sand filter with particle size of 0.5-1.0mm, the filter layer is 0.7m thick, and the lower part of the filter layer is equipped with long-handled filter with water distribution. To the lower part of the filter into the different flow of air and water, the filter layer of air backwash. And observe the maximum carrying height of the filter. Figure 6 shows the test results. In the figure, the vertical axis is the height of the filter media carrying the filter media to the surface of the expansion filter, and the horizontal axis is the backwashing intensity of air. Can be seen from the figure, when the water backwash intensity remains unchanged, the maximum carrying height of the filter increases with the backwash intensity. When gas and water are rinsed at the same time, the carry-on height of the filter material is obviously increased compared with that of the single gas backwashing (that is, the water backwash intensity is zero). However, within the range of water backwash intensity (5 ~ 20L / (s.m2)), the backwashing intensity of water has little effect on the carrying height of filter media. It can be seen from the figure that the maximum carrying height of the filter material shows that for the conventional installation height of the drainage groove, the loss of the filter material is inevitable when the air and water are backwashed at the same time. solved problem.

In a semi-productive test, a nylon web interception method was used to prevent the loss of the filter material. Nylon mesh diameter of 40 mesh, net height of 250mm, tilt installed in the drainage outside the top of the top of the top of the drainage 50 ~ l00 mm. In order to observe the interception effect of the nylon net, the drainage grooves of the two experimental filters adopted different installation heights, one of which was close to the normal value of 0.68 m and the other was much lower than the conventional value of 0.45 m. After nearly six months of operation observation, nylon mesh to prevent the loss of the filter effect is good, indicating that this method is entirely feasible in the production.

A few conclusions

1. Semi-productive tests have shown that it is possible to backflush the filter air and water with a jet pump, which can greatly reduce equipment and operating costs and is easy to popularize.

2. In nearly half a year of running time, semi-productive test filter, the average water turbidity of about 13 degrees, the average filtration rate of 13.4 ~ 14.5m / h, the average filter cycle 47h, air and water backwash simultaneously water backwash The backwash intensity was 15 L / (s.m2), the backwash intensity was 5.3 L / (s.m2), the gas backwash intensity was 7.2 L / (s.m2) and the backwash time was 5 min. 2min conditions, the filter flushing effect is good, the initial loss of the filter head and the change of the filter head with the number of cycles did not increase, the average turbidity after filtration is about 1 degree, the water quality is good.

3. Semi-productive test using 40 mesh nylon mesh interception to prevent the loss of filter media, after nearly six months of tests showed that the effect is good, is feasible in production.