Application of Solar Energy in Reverse Osmosis Systems

1. Background.

As an advanced water treatment technology, reverse osmosis is widely used in seawater desalination, water purifier production and boiler make-up water treatment. At present, the operating pressure of the pump in the reverse osmosis system is very high, usually above 1.8MPa, and the power consumption is large. Therefore, it is of great significance to reduce the reverse osmosis energy consumption.

NEWater company discloses an energy-saving reverse osmosis treatment system, which uses the high-pressure operating conditions of the reverse osmosis treatment system to fully recover and utilize the residual pressure energy of reverse osmosis concentrated water under high-pressure conditions, so as to save energy and improve efficiency.

In addition to the energy-saving technology of recovering the residual pressure energy of reverse osmosis concentrated water, the use of solar energy to reduce power consumption also has the advantages of energy-saving and environmental protection and has a wide application prospect.

In order to more systematically and comprehensively understand the technology related to the combination of solar energy and reverse osmosis, NEWater will introduce the three applications of solar energy in a reverse osmosis system.

2. Solar Driven Membrane Distillation Technology and Equipment.

2.1 Technical Extension.

Reverse osmosis technology is the most commonly used seawater desalination method except the distillation method. It has the advantages of less investment, convenient operation, and a short construction period. However, one of the necessary conditions for the operation of reverse osmosis seawater desalination is the power to drive the high-pressure pump. Generally, the power consumption of the high-pressure pump accounts for about 30% of the system operation cost, which is one of the main factors affecting the cost of seawater desalination.

The solar-driven membrane distillation system is used for seawater desalination or coupled with reverse osmosis to improve the freshwater recovery rate of seawater desalination, which is energy-saving and environment-friendly, in line with the international direction of energy conservation, emission reduction, and carbon dioxide emission reduction. It is very suitable for islands or islands with insufficient power supply systems.

Figure 1 Solar-powered water purifier.

2.2 Technical Principle.

Solar energy is inexhaustible green energy. In essence, it is the conversion of light energy into electric energy. It is a high-tech means to make objects emit electrons to generate current under the irradiation of sunlight according to the principle of the photovoltaic effect of some objects. The normal solar heat collection system can reach the temperature required for membrane distillation operation.

After about half of the water resources are input through reverse osmosis desalination, the remaining salt will not enrich and block the reverse osmosis membrane. Combined with solar energy to provide power for the water pump, the brine with twice the salt content of seawater can be desalinated.

Figure 2 Schematic diagram of solar driving principle.

The principle is that there is a porous plastic film in its seawater desalination system, which can let water vapor pass through and block other substances at the same time. One side of the film is covered with tiny carbon particles, which can absorb the heat of sunlight and make the salt water in contact with it easier to evaporate. After passing through the film, the water vapor will condense into fresh water on the other side.

Moreover, the plastic lens is introduced into the film, which makes the sunlight gather better and generates more heat, which improves the efficiency of the system by 50%.

2.3 Solar Driven Membrane Distillation Technology and Equipment.

Membrane distillation is a new distillation or separation technology combined with the membrane method and thermal method. It has the characteristics of high water quality, compact structure, modular design, low water inlet requirements than reverse osmosis, low operating temperature (50-80℃), can be driven by new solar energy, and is resistant to the corrosion and oxidation of chloride ions, free chlorine, and other substances.

Although the electric energy converted from solar energy through photovoltaic panels can also drive the reverse osmosis system, the photoelectric conversion rate of photovoltaic panels is only 17% to 25%, and the photothermal conversion rate of heat collectors can reach more than 80%. Therefore, the solar-driven membrane distillation seawater desalination system has more economy in operation cost and bright prospects.

NEWater vacuum multi-effect membrane distillation is the only membrane distillation technology in the world to realize engineering applications. In addition to engineering application in the fields of waste acid, industrial concentrated brine, and landfill leachate concentration and reduction, it has also done a lot of promotion and verification work in the field of solar-driven membrane distillation seawater desalination.

NEWater company participated in a pilot project of solar-driven seawater desalination on an island. The project adopts the coupling of reverse osmosis and membrane distillation to improve the freshwater recovery rate. The photovoltaic panel provides electric energy for the coupling system, and the collector provides heat energy for membrane distillation.

Figure 3 Solar-driven reverse osmosis membrane distillation seawater desalination coupling process.

 

Figure 4 Solar-driven reverse osmosis membrane distillation seawater desalination coupling system.

The NEWater membrane distillation equipment uses the steam generated by the solar collector to directly drive the steam turbine pump to provide the water inlet flow and pressure of the reverse osmosis module.

During the pilot test, the operation of the NEWater membrane distillation system is stable, the average flux can reach 4.5L/(M2·h), and the conductivity of produced water is less than 90μS/cm, Figure 5 shows the continuous operation data for 8 days. The pilot test results fully verify the feasibility of a NEWater solar-driven vacuum multi-effect membrane distillation system for seawater desalination or brackish water desalination in outlying islands or island areas.

Figure 5 8-day continuous operation data of solar-driven membrane distillation.

Of course, NEWater solar-driven membrane distillation system can also be applied to other areas suitable for installing solar photovoltaic panels and collectors and is not limited to seawater desalination. NEWater always adheres to the concept of ‘making the best use of people and things’, maximizes and optimizes the application of membrane distillation technology, and gives full play to the advantages of membrane distillation technology.

3. Application of Solar Powered Reverse Osmosis Systems

3.1 New Portable Solar Desalination Sevice.

At present, the seawater desalination technology has been basically mature, the seawater desalination market is in an active cultivation period, and the desalination equipment and technology have been vigorously promoted in the international market, but they have not been applied on a large scale.

At the same time, because the working pressure of reverse osmosis equipment is related to the salinity level, the average salinity of seawater is 3.5%, the reverse osmosis pressure is high, the freshwater recovery rate is low, and the energy demand is relatively high. In addition, there is a shortage of energy in the marine working environment. There is an urgent need for an energy recovery device to solve the energy consumption problem of small-scale seawater desalination.

Small seawater desalination device is a device for treating seawater or brackish water into fresh water and drinking water. It has the advantages of a small floor area, easy preparation, and easy relocation. The new portable solar desalination device currently studied by NEWater company is a device that can convert light energy into electric energy through its own solar panel and store it in the battery.

Figure 6 Small solar desalination device.

The solar desalination device designed by NEWater adopts folding solar photovoltaic panels. The photovoltaic panel is equipped with the maximum solar power tracking servo system, which can rotate the solar photovoltaic panel with the offset of the sun, so as to be at the maximum electrical power status at all times. The solar photovoltaic panel converts solar energy into direct current and stores it in the battery to provide energy for the booster pump of the device. The booster pump pumps the water into the water purification device and sends the clean water out through a series of treatment processes such as filtration and disinfection.

Process flow of NEWater portable seawater desalination unit:

Seawater→Water Tank→Solar Driven Water Pump→Multi-Media Filter→Activated Carbon Filter→Soft Water Processor→Precision Filter→Solar Driven High-Pressure Pump→Primary Reverse Osmosis→Purified Water Tank→Solar Driven High-Pressure Pump→Secondary Reverse Osmosis→Ultraviolet Sterilization Device→Pure Water.

Figure 7 NEWater portable solar desalination device.

In the process, without tap water pressure, the water pump is driven by the battery power supply to suck seawater into the equipment for filtration and distillation to remove harmful substances. At the same time, it can effectively filter bacterial pathogens, so as to effectively improve people’s drinking water safety.

3.2 Solar Reverse Osmosis Boiler Water Equipment.

At present, the boiler water used in hospitals, schools, and bathing places basically adopts nonrenewable energy such as gas and coal. The whole process consumes a lot of energy, is harmful to the environment, and has a low degree of environmental protection. At the same time, the purification degree of traditional boiler water is low, and there are certain hidden dangers in water quality. If solar energy and reverse osmosis are combined and applied to the preparation of boiler water, it can not only save energy and promote environmental protection but also purify boiler water and ensure the quality of water.

Figure 8 Solar reverse osmosis boiler water equipment.

The solar reverse osmosis boiler water equipment prepared by NEWater company is mainly composed of a pretreatment system, solar collector, thermal insulation water tank, water pump and reverse osmosis unit.

The process flow of the equipment is: Raw Water→Solar Heating to 30 ~ 40℃→Solar Raw Water Pump→Medium Filter→Activated Carbon Filter→Precision Filter→Solar Driven High-Pressure Pump→Reverse Osmosis Unit→Solar Collector→Insulated Water Tank→Water Outlet.

Figure 9 Schematic diagram of water equipment of solar reverse osmosis boiler.

3.2.1 Benefit Analysis of Energy Conservation and Emission Reduction.

Cost Analysis.

  1. a. Energy formula required for water heat absorption: q=cm(t-t0), where C – specific heat capacity of water, value is 4.2×103J/kg℃; M – Mass of Water, kg; T – Final Temperature of Water ℃; T0– Initial Temperature of Water ℃. When the water temperature rises from 20℃to 30℃, the heat to be absorbed is Q1: Q1 = 4.2×103×5×103×8×(30-20)=1.68×109J;
  2. The proposed specification of solar collector vacuum tube is Φ 70×2000mm, endothermic Q2: Q2= 2.31×106J;
  3. Number of solar collector pipes required n: n = Q1/ Q2= 1.68×109/2.31×106≈728;
  4. According to the market survey, the price of each solar vacuum tube is about 60 yuan, and the initial investment of solar collectors will increase by about 60000 yuan (including installation fee).
3.2.2 Power Saving Analysis.

Solar energy heats the water entering the boiler. The experimental data show that increasing the inlet water temperature will reduce the operating pressure of the reverse osmosis device (1.8MPa to 1.2MPa), so that the power consumption of the reverse osmosis device can be reduced by about 30%.

When the reverse osmosis device operates alone, the power consumption per hour is 4kw·h. After using the solar-assisted reverse osmosis water treatment device, the power consumption per hour is 2.8KW·h, then 1.2kW·h can be saved per hour.

During the operation time of the solar-assisted reverse osmosis device, the reverse osmosis device can save power in one year: W1 =1.2×220×8 = 2112kw·h, about 0.52 yuan per kilowatt-hour, then the electricity expenditure can be reduced in one year: N1 = 2112×0.52 = 1098.24 yuan.

The above data show that the solar reverse osmosis boiler water equipment prepared by NEWater can greatly save energy and reduce emissions, which calls for the response of the times to environmental protection and meets the needs of people’s production.

 

If you have any needs or problems in the process of seawater desalination, water purifier production, boiler make-up water treatment, etc., contact NEWater directly, and our technical engineers will provide one-to-one powerful water treatment scheme and equipment support for solar applied reverse osmosis system, so as to realize energy conservation and environmental protection and create water for life with you!

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