Research on chemical cleaning of filter material in turbid ring water system of rolling steel

Steel rolling turbid circulating water system of chemical cleaning filterDong   Enchuan1, Liu   Wuwen1, Shu Chun2, Yu   Qin2, Xu   Fengwu2(1.Hubei Haili Chemical Technology Co., Ltd., Wuhan 430074, China;2.Wuhan Iron and Steel Company Power Company, Wuhan 430083, China)

Abstract：Three hot water supply plant in WISCO station 1580 circulating water system filter pollutantsas object,Simulated field condition of filter line chemical cleaning experiment, selected the suitableHL-610B cleaning agent formulations,   and Through field application experiments determined thecleaning agent using the best qualityconcentrationof 1%,   the time required for cleaning is about 24h. Chemical cleaning can be realized through the filter regeneration.Key words：Turbid circulating water system；Filter；The filter pollution；Chemical cleaning

In the treatment of turbid ring water in steel rolling, the application of filter greatly improves the water quality of water supply, and provides a reliable guarantee for the direct cooling of products and equipment in steel rolling production. The 1580 turbid-ring water system filter of the three-hot rolling water station of WisCO water supply plant has been put into operation for nearly four years, although it is equipped with hydraulic backwashing system, but the filter material blockage, weathering, hardening and other conditions are more serious, and even some filters have appeared cut-off phenomenon, which seriously affects the effluent water quality, and water quality indicators such as turbidity, oil content and iron ions are out of control. The rate of water quality reaching the standard has decreased greatly, which brings potential harm to the normal operation of turbidity water system equipment, pipelines and the daily production of steel rolling. Sample and test 26 sets of high-speed filter filter material (diameter 5m, anthracite, quartz sand and other multi-media filter material, filter material filling height of 3.5m, of which anthracite filter material accounted for 60%) of the system. The main components and quality of pollutants attached to the filter material are shown in Table 1.

    Table 1 Main components and mass ratio of filter material pollutants             

It can be seen from Table 1 that the main components of the pollutants attached to the filter material of the system are iron oxide, oily mud and sediment. These pollutants mixed together will form sludge, permeate into the gap between the filter material causing blockage, and easy to adhere to the filter material, a long time can lead to filter material corrosion, weathering, etc., filter water quality significantly decreased, directly affect the production of water supply quality, need to replace the filter material in time [1]. In order to extend the replacement time of the filter material, save costs, and better ensure the quality of the filter water, it is necessary to carry out chemical cleaning of the filter material to achieve the regeneration of the filter material.

In this paper, the filter material of the turbidity ring water system of 1580 hot rolling water station in WISCO water supply plant is taken as the object, and the offline chemical cleaning experiment is carried out to simulate the field conditions, and the suitable cleaning agent formula is selected, and the best concentration and cleaning time are determined through the field application experiment, which provides a scientific basis for the filter cleaning work of WISCO water supply plant.

1 Offline cleaning experiment

1.1 Experimental principle and purpose

Under the condition of intermittent blowing and stirring, the pollutants attached to the filter material are removed by the chemical action of the cleaning agent, such as dissolution, penetration, stripping and emulsification, and the regeneration of the filter material is realized. The upper cleaning solution was taken to determine its pH value, suspended matter content (SS), total iron, oil content and other indicators to determine the appropriate cleaning agent formula.

1.2 Experimental process

Three pieces of blocky filter material with similar size and appearance were selected as experimental samples, and in order to ensure the consistency of experimental conditions, the mass of filter material samples was between 5.4 and 5.6Kg. Three kinds of cleaning agents HL-610A, HL-610B and HL-610C were selected, and the cleaning agents of these three formulas were diluted with water respectively to form a cleaning solution with a mass concentration of 1%. Then put the filter material sample into the corresponding 50L cleaning solution until completely immersed. At the same time, the air pipe is connected, and the air is pumped every 3 hours for 30 minutes each time, so the cycle operation is 24 hours. Then access clean water to wash twice, and finally observe the surface condition of the filter material after cleaning. During the period of regular sampling and testing, analysis of the upper cleaning fluid pH value, suspended matter content (SS), total iron, oil content and other indicators.

1.3 Experimental results and analysis

In the cleaning process, the upper cleaning liquid is taken every 6 hours to determine its pH value, suspended matter (SS), total iron, oil content and other indicators, and the cleaning effect of these three cleaning agent formulas is judged by the change amplitude of these indicators, so as to screen out the better cleaning agent formula. The change curve of each indicator is as follows:

FIG. 1 pH value change curve during the offline cleaning experiment

Figure 2. Variation curve of suspended solids (SS) content in the process of offline cleaning experiment

Figure 3. Variation curve of total iron ion content in the process of underground cleaning experiment

FIG. 4 Variation curve of oil content in the process of offline cleaning experiment

Based on various analysis indicators, it can be seen that the cleaning effect of the HL-610B cleaning agent formula is the best, and the SS, total iron, oil content and other indicators of the cleaning solution increase the most, which indicates that the pollutants attached to the filter material are gradually stripped into the cleaning solution, and the cleaning is more thorough [2]. At the same time, judging from the surface condition of the three filter samples after cleaning, the filter particles cleaned by the HL-610B formula can be seen, the clumps completely disintegrated, and there were basically no obvious pollutants attached to the surface. However, there are still some lumps in the HL-610A and HL-610B formulations, among which the lumps in the HL-610C formulations are larger, and the mass is only 52% less than that before cleaning, and the sludge is still clearly visible. Moreover, with the extension of cleaning time, the surface foam of the cleaning solution of HL-610B formula was reduced, and there was basically no foam after 24 hours, and the color of the cleaning solution was the darkest, and there was obvious odor overflow.

2. Field application experiment

The field application experiment is mainly to determine the best concentration and cleaning time of HL-610B cleaning agent.

2.1 Preparation before the experiment

（1）Confirm the discharge flow and water quality indicators such as SS, total iron and oil content of the cleaned filter before it is discontinued.

（2）Confirm that the filter is in shutdown state, the backwash system is normal, and the necessary water, power, and air sources are available.

（3）Open the filter cover and check the surface condition of the filter material.

（4）Estimate the static capacity of a single filter.

（5）Verify that the dosing device is fully connected.

2.2 On-site cleaning experiment process

Three turbidity ring water system filters C21, C22 and C23 of the three-hot rolling water station of WISCO Water Supply plant were selected as the filters for on-site cleaning experiments. The surface pollution of each filter material was similar, and the static water retention was calculated by 25 tons.

（1）Add 125Kg of HL-610B cleaning agent to C21 filter at the mass concentration of 0.5%; Add 250Kg of HL-610B cleaning agent to C22 filter at 1% mass concentration; Add HL-610B cleaning agent 500Kg to C23 filter at 2% mass concentration. The reagent is added to the tank through the filter top at one time, and then enough water is added through the backwash system to completely immerse the filter material.

（2）Open the normal air washing procedure of the filter, blow once every 210 minutes on average, and each blow lasts for 15 minutes (wind pressure is about 0.07MPa), so the cycle operation. During the period, regular sampling and testing were conducted to analyze the pH value, suspended matter content (SS), total iron, oil content and other indicators of the upper cleaning liquid in the filter.

（3）After confirming the completion of chemical cleaning, the cleaning solution is discharged through the backwashing system and flows to the backwashing advection pool. A small amount of defoamer is added at the water outlet to inhibit foam according to the amount of foam.

（4）After draining the cleaning solution, rinse the filter twice with clean water through the backwash system.

2.3 Experimental results of on-site cleaning

During the cleaning process, the upper cleaning liquid of the filter is taken every 4h to determine its pH value, suspended matter (SS), total iron, oil content and other indicators, and the cleaning effect of HL-610B cleaning agent under different concentration conditions is determined by the change amplitude of these indicators, so as to determine the best cleaning agent concentration range and cleaning time. The change curve of various indicators in the field cleaning process is as follows:

FIG. 5 pH value change curve during field cleaning experiment

Figure 6. Variation curve of suspended matter (SS) content during field cleaning experiment

Figure 7. Variation curve of total iron ion content during field cleaning experiment

FIG. 8 Variation curve of oil content during field cleaning experiment

It can be seen from the index changes of sampling analysis during the cleaning process that HL-610B cleaning agent can meet the cleaning requirements when the dosing mass concentration reaches 1%, and can effectively remove various pollutants attached to the filter material, and achieve a good cleaning effect 24h after dosing, and then the index changes little with the extension of time. At the same time, the effluent quality and flow of these three filters before and after cleaning were further analyzed, and the results were shown in Table 2.

Table 2 Comparison of effluent quality and flow of C21 filter before and after cleaning

Table 3 Comparison of effluent quality and flow of C22 filter before and after cleaning

Table 4 Comparison of effluent quality and flow of C23 filter before and after cleaning

As can be seen from the effluent water quality data in the above table, the effluent water quality of the three filters after chemical cleaning is significantly better than that before cleaning, and the effluent water quality of the C22 and C23 filters can meet the requirements of production water supply quality, and the effluent flow rate is significantly improved after cleaning. In addition, from the filter material removed from the filter tank after cleaning, after 24 hours of cleaning when the dosage concentration is 1%, there is basically no obvious contaminant attachment on the surface of the filter material in the C22 filter tank (see Figure 10), which is significantly different from the surface of the filter material before cleaning (see Figure 9).

   Figure 9 Appearance of filter material before C22 filter cleaning                    Figure 10 Appearance of filter material after C22 filter cleaning   

3 Economic benefit analysis