Multi effect evaporation consumes less power. As the fresh water produced by multi-stage flash depends on the sensible heat absorbed by brine, and the latent heat is far greater than the sensible heat, so the production of the same amount of fresh water requires much more circulation than multi effect evaporation, so multi-stage flash requires more power consumption.
Multi effect evaporation has great operational flexibility. The load range is from 110% to 40%, which can be operated normally without reducing the water production ratio.
The brine is preheated and degassed in the condenser for the first time, and then divided into two streams. One is discharged back to the sea as cooling water, and the other is used as feed for the distillation process.
The feed brine is introduced into the later effects of the evaporator after the scale inhibitor is added. The feed liquid is evenly distributed to the top row tube of the evaporator through the nozzle, and then flows downward along the top row tube in the form of a film. Part of the water absorbs the latent heat of the condensed steam in the tube and evaporates.
The secondary steam is condensed into product water in the next effect, and the remaining feed liquid is pumped to the next effect group of the evaporator. The operating temperature of this group is slightly higher than that of the previous group, and the spraying, evaporation and condensation processes are repeated in the new effect group. The remaining feed liquid is pumped to the high temperature effect group, and then leaves the device in the form of concentrated liquid in the high temperature effect group.
The raw steam is input into the effective evaporation tube and condensed in the tube, and the brine outside the tube produces secondary steam with the same amount of condensation.
Since the operating pressure of the second effect is lower than that of the second effect, the secondary steam enters the heat transfer tube of the next effect after passing through the vapor liquid separator. The evaporation and condensation process is repeated in each effect, each effect produces basically the same amount of distilled water, and the steam of the latter effect is condensed by brine in the condenser.
The concentrated brine flows into a series of concentrated brine flash tanks in the form of steps, and the overheated concentrated brine is flashed to recover its heat. The concentrated brine after flash cooling is discharged back to the sea through the concentrated brine pump.
It can be seen from the above principles that the technical advantages of low-temperature multi effect evaporation are reflected in the following aspects:
Due to low operating temperature, corrosion and scaling of equipment can be avoided or slowed down.
Due to the low operating temperature, the low temperature waste heat of power plants and chemical plants can be fully utilized. For low-temperature multi effect evaporation technology, low-grade steam at 50 ℃ - 70 ℃ can be used as an ideal heat source, which can greatly reduce the impact of back pressure steam extraction on power generation of power plants.
Pretreatment of feed brine is simpler. Another benefit of the system's low-temperature operation is that it greatly simplifies the pretreatment process of brine. Before the brine enters the low-temperature multi effect device, it only needs to be filtered through the screen and added with a small amount of scale inhibitor, instead of acid adding and degassing treatment like multistage flash evaporation.
RO technology is a membrane water treatment technology developed in the late 20th century. It is developed from seawater and brackish water desalination research. It uses the selective permeability of membrane to separate different substances, so as to achieve the role of desalination water. After years of development, RO technology has produced various forms of anti pollution membranes in order to meet different treatment requirements and high pollution and high salinity wastewater. The representatives are reverse osmosis (HERO) and disc tube membrane technology (DTRO), which are commonly used in zero discharge of high salinity wastewater.
HERO technology. HERO technology is a new technology developed on the basis of conventional reverse osmosis. The core principle of HERO technology is to remove the hardness of water by ion exchange, transform the carbonate in water into carbon dioxide and remove it, and then use reverse osmosis to remove salt. The technical feature of HERO is that after all hardness and some alkalinity are removed by pretreatment, reverse osmosis operates under high pH conditions. The characteristics of HERO and conventional reverse osmosis are compared, as shown in Table 3
Heating boiler maintenance and precautions
Content abstract: Corrosion of heating boilers is a major hidden danger in the safe operation of boilers, and its harmfulness has been widely recognized, thus enhancing people's awareness of anti-corrosion, promoting the implementation of boiler anti-corrosion measures, and achieving certain results. However, it should be emphasized that corrosion does not only occur in the operation of the boiler. If proper protective measures are not taken during the shutdown of the boiler, oxygen entering the boiler will cause corrosion on the wet metal surface.
Corrosion is a major hidden danger in the safe operation of boilers, and its harmfulness has been widely recognized, thus enhancing people's awareness of anti-corrosion, promoting the implementation of boiler anti-corrosion measures, and achieving certain results. However, it should be emphasized that corrosion does not only occur in the operation of the boiler. If proper protective measures are not taken during the shutdown of the boiler, the oxygen entering the boiler will cause corrosion on the wet metal surface. The corrosion caused by the shutdown of the boiler is often much more serious than the corrosion in the operation. Therefore, we attach great importance to it.
The series of seawater desalination scale inhibitors developed are mainly composed of chelating agents, functional polymers, non-ionic surfactants, etc. They can effectively prevent the precipitation of calcium carbonate, calcium sulfate and other scales in water in triple concentrated seawater. They have been running continuously for more than 2000 hours on the self-designed dynamic evaluation device based on two-way comparison The LT-MED unit with a capacity of 1000 tons/day has been running continuously for 6 months to verify the performance of the agent. The scale inhibition efficiency is more than 95%. Its performance exceeds that of the agent of foreign water companies, reaching the international level of similar technologies, and has the advantages of low concentration, environmental protection and low price.
Technical features:
1. The developed seawater desalination scale inhibitor has a solid content of more than 40% and a density of more than 1.18g/cm3;
2. At present, seawater concentration is 1.5~2.0 times. The scale inhibitor developed in this achievement has better scale inhibition performance than foreign agents under three times seawater concentration, and its technical level is at the international level.
application area
This achievement is mainly used in the field of seawater desalination water treatment, which can effectively prevent the precipitation of calcium carbonate, calcium sulfate and other scales in water. At present, the national market of seawater desalination water treatment agent has reached more than 100000 tons. The agent developed by this achievement has the advantages of low phosphorus, biodegradable, etc., and has important scientific value and significant social, economic and environmental benefits.
