How to calculate the recovery rate of reverse osmosis equipment

How to calculate the recovery rate of reverse osmosis equipment?

The reverse osmosis process determines that it must discharge a certain amount of high-salt concentrated water to produce a low-salt desalinated water. The system recovery rate refers to the total recovery rate of the reverse osmosis unit in actual use. The system recovery rate mainly depends on various factors such as the length of the membrane elements connected in series, the number and arrangement of the water-receiving membrane elements, the presence or absence of concentrated water circulation, and the size of the circulating flow.

In general, in order to increase the recovery rate of reverse osmosis equipment, the membrane elements will be connected in series, but if there are many membrane elements in the system, they cannot be connected in series. If so, the water supply flow rate of the *support film will be very high. Large, system pressure is too large, and the distribution of water production is not balanced. Therefore, in actual use, a certain number of membrane elements are placed in a pressure vessel, and then the pressure vessels are arranged in a certain arrangement, according to the flow of pure water and concentrated water to one side, respectively, the concentrated water of the * group water supply device The flow into the next pressure vessel is * segment, and the water supply in the * section is re-flowed to the next pressure vessel as the second section, and in turn to other sections, so that the equipment can be increased in proportion and the original water cost can be reduced.

However, for various reverse osmosis equipment, more than one reverse osmosis membrane element is often required. At this time, there is a problem of how to arrange the membrane elements. As described above, the actual recovery rate of the membrane element is the recovery rate of the membrane element in actual use. Small-scale reverse osmosis equipment has a low system feed rate due to the small number of membrane elements, and the system recovery rate is generally low. However, the large-scale reverse osmosis unit for industrial use has a long water supply process, so the actual recovery rate is generally above 65%. That is to say, for every 65 tons of desalinated water, about 35 tons of reverse osmosis concentrated water need to be discharged, and sometimes even 90%.

For the first-stage reverse osmosis, the * level recovery rate R1 = * level water production / * level water intake × 100%; the second level reverse osmosis recovery rate R2 = second level water production / second stage water intake × 100% . The recovery rate of the secondary reverse osmosis is not the product of the recovery rate of the two-stage reverse osmosis system. The concentrated water of the second-stage reverse osmosis system is not discharged, but is returned to the inlet of the first-stage reverse osmosis. Therefore, the recovery of multi-stage reverse osmosis equipment should be calculated according to the following criteria: system recovery rate = total water production / total water intake × 100%.

What are the main factors affecting the recovery rate?

1. The index of insoluble salts in the quality of the feed water constitutes the limit recovery rate of the insoluble salts of the reverse osmosis membrane system.

2. The number, variety and arrangement of the components of the reverse osmosis membrane system have the concentration polarization recovery.

3. The concentrated water flow at the end of the system constitutes the limit recovery rate of the concentrated water flow of the system.

4. The flux balance requirement of reverse osmosis membrane constitutes the equilibrium recovery rate of the system equilibrium flux.

The lower value of the value zui in the four ultimate recovery rates constitutes the actual limit for system design recovery. Increasing the zoi low value in the four ultimate recovery rates can effectively increase the actual recovery rate of reverse osmosis equipment.

In particular, in recent years, the government has become increasingly strict with the indicators on total control and recycling rate, forcing companies to consider various water reuse technologies. Compared with the high and high cost of wastewater recycling, the recycling of reverse osmosis concentrated water, which accounts for 1/3 of the water production, is more advantageous. Increasing the recovery rate of the system not only makes full use of water resources, but also reduces the investment scale and operating cost of the pretreatment process, reduces the scale and energy consumption of the high pressure pump of the membrane system, and thus effectively improves the efficiency of the whole system.