EcoLan Reverse Osmosis System Cleaning and Scale Inhibitor Dosing Case
Project Overview
Product name： A power plant boiler makeup water diagnosis project
Number of UF elements：9 x 64pcs
Water production capacity: 9 x 271m3/h
Number of one-stage RO elements: 8 x 324pcs
Water production capacity: 8 x 208m3/h
Number of two-stage RO elements: 4 x 126pc
Water production capacity:4 x 135m3/h
EDI System：4 x 25pcs
Water production capacity: 4 x 125m3/h
System process flow: Printing and dyeing wastewater → coagulation and sedimentation tank → MBR membrane system → self-cleaning filter → UF membrane system → UF product water tank → One-stage RO membrane system → One-stage RO product water tank → Two-stage RO membrane system → Two-stage RO product water tank → EDI system →Boiler makeup water
System Agent Preparation Method
EcoLan scale inhibitor (CP119) is used to dose the water treatment system, and the following suggestions are given for dosing the system.
The dosing method of reverse osmosis scale inhibitor is continuous online dosing, and the dosing point is before the security filter. The dosing amount is 4.34ppm by software simulation. Considering the water quality fluctuation, suggest dosing 5ppm. The specific preparation is as follows.
The system dosing concentration is 10%, i.e., add 200kg of standard liquid (8 barrels of CP119) when the liquid level of the dosing tank drops to 20cm and add water to the whole liquid level. The scale inhibitor dosing tank is 2000L, equipped with three sets of dosing pumps with a maximum flow rate of 120L/h, two uses, one backup, and one pump corresponding to 4 groups of reverse osmosis system.
Dosage Analysis
| Chemical model | CP119 |
| Max pump flow (L/h) | 120 |
| Stroke(%) | 50% |
| Frequency(%) | 98% |
| Concentration(%) | 10% |
| Total water inlet(m3 /h) | 1180 |
| Dosing(ppm) | 5 |
Fix the stroke of the dosing pump at 50%, and the number of operating sets of the RO system with the corresponding pump frequency is as follows.
| Operating sets | 1 set | 2 set | 3 set | 4 set |
| Corresponding metering pump frequency | 25% | 50% | 75% | 98% |
| Corresponding to the 10% solution metering pump flow | 14.75L/h | 29.5L/h | 44.5L/h | 59L/h |
The formula for calculating the dosage is as follows.
Q × a
X = ——————————
1000× W%×ρ
Q — Reverse osmosis feed water flow (m³/h)
ρ — Density of prepared liquid (kg/m³), generally calculated by 1
W% — Mass fraction of prepared liquid（%）
A — Dosage (ppm, mg/l)
1000 — Unit conversion factor (g/kg)
X — Actual working capacity of the metering pump (L/h)
Operational Data Analysis
1. UF system operating data
| Date | System | Pressure（Mpa） | Flow（m3 /h） | Turbidity（NTU) | |||
| Influent | Concentrated water | Effluent | Influent | Effluent | |||
| 6.01 | 1#UF | 0.06 | / | 0.03 | 281 | 258 | 0.22 |
| 6.01 | 2#UF | 0.06 | / | 0.05 | 268 | 249 | 0.044 |
| 6.01 | 3#UF | 0.07 | / | 0.06 | 279 | 254 | 0.039 |
| 6.01 | 4#UF | 0.08 | / | 0.06 | 283 | 261 | 0.068 |
| 6.01 | 5#UF | 0.06 | / | 0.04 | 276 | 255 | 0.27 |
| 6.01 | 6#UF | 0.08 | / | 0.03 | 275 | 250 | 0.15 |
| 6.01 | 7#UF | 0.07 | / | 0.06 | 275 | 255 | 0.25 |
| 6.01 | 8#UF | 0.07 | / | 0.03 | 274 | 253 | 0.23 |
| 6.01 | 9#UF | 0.06 | / | 0.05 | 279 | 257 | 0.27 |
2. First-stage reverse osmosis operation data
| System | Influent PH | Temperature（℃） | Frequency（HZ） | Pressure（Mpa） | Flow（m3/h） | Conductivity (μs/cm) | Remark | ||||||
| Influent | Intersegment | Pressurization | Concentrated water | Influent | Effluent | Concentrated water | Influent | Effluent | |||||
| 1#RO | / | 37.2 | 50 | 1.04 | 0.87 | 1.03 | 0.94 | / | 211 | 83 | 3425 | 77.5 | |
| 2#RO | / | 35.7 | 50 | 1.0 | 0.87 | 1.03 | 0.99 | / | 191 | 89 | 3201 | 96.6 | |
| 3#RO | / | 34 | 50 | 0.92 | 0.75 | 0.85 | 0.76 | / | 190 | 76 | 3531 | 115 | |
| 4#RO | / | 36 | 59 | 0.99 | 0.84 | 0.99 | 0.91 | / | 213 | 84 | 3581 | 102 | |
| 5#RO | / | 35 | 50 | 0.89 | 0.72 | 0.88 | 0.79 | / | 221 | 81 | 1430 | 79.7 | |
| 6#RO | / | 36 | 50 | 0.98 | 0.8 | 0.97 | 0.84 | / | 189 | 83 | 3291 | 126 | Cleaning |
| 7#RO | / | 37 | 50 | 0.83 | 0.73 | 0.79 | 0.72 | / | 217 | 85 | 3408 | 204 | |
| 8#RO | / | 35 | 0.83 | 0.8 | 0.81 | 0.79 | / | 213 | 76 | 4392 | 192 | ||
Operating data after cleaning
| System | Influent PH | Temperature（℃） | Frequency（HZ） | Pressure（Mpa） | Flow（m3/h） | Conductivity (μs/cm) | Remark | ||||||
| Influent | Intersegment | Pressurization | Concentrated water | Influent | Effluent | Concentrated water | Influent | Effluent | |||||
| 6#RO | / | 37.2 | 50 | 0.89 | 0.8 | 0.96 | 0.87 | 204 | 86 | 3123 | 87 | ||
Summary: This cleaning uses non-oxidizing bactericide + EcoLan special alkaline cleaning agent + EcoLan special acid cleaning agent. After the cleaning, the pressure difference of the first segment is 0.09 MPa, the pressure difference of the second segment is 0.09 MPa, and the water flow rate reaches 204 m3 / h, which has achieved a good cleaning effect.
3. Second-stage reverse osmosis operation data
| System | Influent PH | Temperature（℃） | Frequency（HZ） | Pressure（Mpa） | Conductivity (μs/cm) | |||||||
| Influent | Intersegment | Concentrated water | Effluent | Influent | Effluent | Concentrated water | Influent | Effluent | ||||
| 1#RO | 8.7 | 36.5 | 50 | 0.8 | 0.7 | 0.62 | / | 180 | 150 | 30 | 115 | 6.1 |
| 2#RO | 8.6 | 34.3 | 50 | 0.92 | 0.81 | 0.75 | / | 175 | 151 | 24 | 114 | 4.1 |
| 3#RO | 8.4 | 37.9 | 50 | 0.77 | 0.68 | 0.62 | / | 174 | 150 | 24 | 149 | 5.6 |
| 4#RO | 8.4 | 36 | 59 | 0.82 | 0.72 | 0.68 | / | 177 | 153 | 24 | 123 | 5.4 |
Conclusion: The ultrafiltration system usually runs according to the above data and on-site operation analysis. The first segment of the one-stage reverse osmosis device has a high-pressure difference. After on-site communication, it is found that the pressure difference increases rapidly and returns to normal after cleaning, but the pressure difference rises again after about 10 days. On-site disassembly of a pressure vessel in the first section of 6# reverse osmosis unit revealed a fishy smell of slimy stuff. At the same time, it was observed that the RO membrane element was also fouling rapidly. The odor was more severe after the RO membrane element was disassembled overnight, so it was considered organic contamination.
Since the customer also uses non-oxidizing biocides, but they are poured in the main pipe, far from the security filter, some of the bacteria not killed by the non-oxidizing biocides will multiply at the back end, causing the first segment of the RO membrane element to become organically contaminated. Therefore, we suggest moving the biocide and scale inhibitor to the security filter inlet water, which can alleviate some pressure differential increases.
Diagnostic Recommendations
- Testing the SDI value once per shift and keeping detailed records is recommended.
- It is recommended that the 6# RO unit be dosed separately for testing and that the scale inhibitor and non-oxidizing biocide dosing point be moved to the front of the security filter.
- At present, one dosing metering pump corresponds to 4 sets of reverse osmosis systems, and the distance of non-oxidizing biocide dosing is far, which is easy to cause unsatisfactory results of pharmaceutical dosing, so it is suggested to change the dosing mode to 1 dosing pump corresponding to 1 set of reverse osmosis equipment.
- Control the residual chlorine in reverse osmosis system feed water. Reverse osmosis feed water residual chlorine should be ≤ 0.05ppm.
- The feed water temperature is too high, long-term operation at high temperatures, the reverse osmosis membrane element desalination rate will be reduced, and the service life will be shortened. Therefore, it is recommended to reduce the front-end water temperature. Although the reverse osmosis membrane manufacturer gives the highest temperature at 45℃, and the general site operating temperature is controlled between 25℃~30℃, the reverse osmosis membrane element works best.
- It is recommended to control the water quality in the front-end pretreatment system to ensure that the TDS value of the feed water to the reverse osmosis system is not very different so that the reverse osmosis membrane element can work under the condition that the water quality does not fluctuate much and the pressure is stable.
- In daily operation, the liquid level of each dosing tank should be closely observed, whether the dosing pump is standard, and whether the dosing amount is in place. For example, suppose it is found that the tank’s liquid level is low or the metering pump cannot be filled with chemicals. In that case, it is necessary to prepare chemicals or exhaust the metering pump in time to ensure that the chemicals can be filled typically and prevent the reverse osmosis system from clogging because the chemicals cannot be loaded.
In daily operation, if you find that the differential pressure of the system increases by 10%~15%, or the flow rate of product water decreases by 10%~15%, or the desalination rate of the system decreases by 10%~15%, you should immediately check the reverse osmosis system and determine the cause. If you need help solving the problem, please contact EcoLan service engineers in time. We will give guidance according to the operation situation or go to the site to solve the problem if necessary.
