High vacuum system for vacuum salt making

A new type of high vacuum combined technology for vacuum salt making is introduced. The process flow and working principle of the technology and the functions of cooling tower and vacuum pump are introduced. The high vacuum combined technology can ensure that the temperature of the cooling water is less than 32 ℃ under low pressure, and the non condensable gas in the secondary steam can be basically exhausted, so as to improve the vacuum degree of the final effect. The application results show that, compared with the traditional open water cooling vacuum technology, this high vacuum combination technology can increase the end effect vacuum degree by 0.011mpa, further reduce the steam consumption and improve the production capacity.

Whether it is sea lake salt or well salt, vacuum salt production method is multi effect negative pressure evaporation. One of the more important processes is the vacuum system. Its effect directly affects the production capacity and production cost of the whole salt making plant. At present, the domestic salt industry mostly adopts the open water cooling vacuum technology, that is, the cooling water from the circulating water field is sent to the air mixing condenser, the water is discharged into the water sealed pool, and then pumped to the circulating water plant for cooling. To a certain extent, this technology can meet the vacuum degree required for salt making, but this technology has its limitations. The final effect vacuum degree is not high, In production, only by increasing the first effect steam pressure to maintain a high heat transfer driving force, so that the steam consumption increases; the water temperature from the mixing condenser is higher, which increases the load of the circulating water field, so that the low temperature of the cooling water upper water can not be guaranteed. Especially in summer, the outlet water temperature of the circulating water field is as high as 40 ℃, which seriously affects the effect of the vacuum system, This will further reduce the already low vacuum. Therefore, according to the characteristics of vacuum salt making, the author designs a new type of high vacuum combination technology, which effectively overcomes the above shortcomings and has good effect in production and application.

1. Device flow and working principle

Unit flow

In the production of vacuum salt, the key factors that affect the vacuum degree are: the temperature of cooling water supply and the extraction amount of non condensable gas. In order to improve the vacuum degree, it is necessary to reduce the water temperature of cooling water and use a vacuum equipment with low steam consumption, high efficiency and large steam extraction capacity. At present, the open water cooling vacuum technology used in the salt making industry completely relies on the direct contact of water vapor to produce negative pressure, which will lead to the accumulation of non condensable gas and the decrease of vacuum degree. In order to eliminate non condensable gas, some domestic salt making enterprises install steam jet pump next to the mixed condenser. However, this requires a steam pressure of 1MPa, which has large steam consumption, high noise and unstable extraction capacity, so it is of little significance to popularize.

High vacuum combined technology is based on the open water cooling vacuum technology, adding cooling tower and vacuum pump, from open water cooling process to closed-circuit circulating cooling.

working principle

The water in the air mixing condenser is cooled by the pumping cooling tower, and then the water is cooled in two ways: one is into the water jet tower and steam jet tower of the vacuum pump; the other is used as the cooling water and sent to the mixing condenser. After the final effect secondary steam enters the air mixing condenser, the non condensable gas is pumped away by vacuum pump, and the remaining steam is dissolved and liquefied by a large amount of cooling water to produce vacuum. The whole cooling circulating water becomes an independent operation system, and is no longer sent to the circulating water field.

2. Design and function of main equipment

Cooling tower

The cooling tower is equipped with spray cooling tower, which is composed of tower body, air duct, water screen, water collector and spray propulsion atomizer. The key component of the spray propulsion atomizer is a new type of spray driven jet element driven by hydraulically, which takes the place of traditional filler and fan. As a result, the flow rate of the spray nozzle is increased, and the rotation speed of the spray nozzle is enhanced, and the rotation speed of the spray nozzle is enhanced. This design ensures that the working parameters of the atomizer are always in a state of matching, so as to achieve the goal of adequate heat and mass transfer under hot fog conditions. In addition, the new type of wind blades, air channels, water screen and water collector, which are designed in the tower, are in harmony with the sprayer, thus achieving the effect of efficient cooling of circulating water.

Vacuum pump

The vacuum pump is a cascade vacuum pump with steam jet tower as main pump and water jet tower as front stage pump. At the same time, it has the advantages of water jet pump and steam jet pump, that is, it has large steam extraction capacity and high working efficiency under high vacuum degree. The water jet tower is designed as the front stage pump, which not only increases the steam extraction stability of the whole vacuum pump, but also overcomes the disadvantages of the steam jet pump, such as high steam consumption, high working steam pressure and high noise.

3. Performance characteristics

The high vacuum combination technology has the following performance characteristics:

(1) The vacuum degree of the final effect of vacuum salt making is improved and the production capacity is increased. The spray cooling tower is used to solve the problem that the temperature of the upper cooling water of the circulating cooling water is high and fluctuating. It is no longer concerned about the influence of the high temperature of summer on the cooling water temperature. The vacuum pump with a strong extraction capacity can basically exhaust the two condensate steam in the steam and ensure the stability of the final vacuum degree. With the increase of vacuum degree, the driving force of heat transfer is increased and the production capacity is increased.

(2) The cooling effect is good and the temperature of cooling water is stable. In the cooling tower, the heat exchange between hot water and cold air is carried out in the cooling tower, and the upper spray type is used. The water mist rises to the drop of water droplets and can be transported with the cold air. Besides, the water draught screen is used to separate the intake zone from the tower body, avoiding the return air and mutual interference. At the same time, the spray flow generates two ejection winds, and the superposition effect makes the ratio of steam to water increase. Therefore, the cooling effect is better than the traditional packed tower. In addition to the problems of packing aging, deformation, collapse and blockage and fan failure, the tower solution can operate for a long time with stable cooling effect, so that the water temperature of cooling water can be kept below 32 ℃, and the phenomenon of water vaporization is completely avoided.

(3) The operation is simple. There is no electric equipment in the whole device, which is driven by water pressure and steam pressure. The water pressure and steam pressure can be automatically controlled by PLC according to the working conditions, so that they are always in the set safety range.

(4) Low investment and high efficiency. As the cooling water is no longer sent to the circulating water plant for cooling, but is pumped to the cooling tower for cooling, so the huge circulating water field is saved, the investment and operation cost are saved, and the benefit is improved.