MVR (Mechanical Vapor Recompression) evaporative crystallization device

Abstract

The MVR evaporative crystallization device is optimized and improved on the basis of a conventional device, a cyclone hydraulic separator is additionally arranged between a secondary steam outlet and a secondary separator inlet of an evaporative crystallization separator, most of liquid carried by secondary steam is separated in advance, the cyclone hydraulic separator is a circular tank body, and the cyclone hydraulic separator is arranged in the circular tank body. According to the steam compressor, the cyclone liquid inlet is arranged to enter in the circular tangential direction, and the cyclone liquid separator is arranged, so that the liquid content of steam entering the steam compressor is at an extremely low level, corrosion to an impeller of the steam compressor is reduced, and the service life of the steam compressor is greatly prolonged; besides, a shunting pipeline is additionally arranged to take part of material liquid heated by the distilled water preheater, and the material liquid enters the inlet of the discharging pump and is mixed with the material at the inlet of the discharging pump to reduce the temperature of the material, so that the phenomenon that the discharging pump is subjected to cavitation is greatly reduced, the problem that the material is blocked due to cavitation is solved, and the service life of the discharging pump is also prolonged.

Description

Technical Field

[0001] The present application belongs to the technical field of chemical equipment, and specifically relates to an MVR evaporation crystallization device. Background Art

[0002] MVR stands for Mechanical Vapor Recompression, which is an energy-efficient technology used in evaporation and concentration processes. MVR technology uses the secondary steam generated by the evaporation system itself to perform mechanical work through a steam compressor, compressing low-grade steam to a high level, that is, increasing the steam pressure, and the temperature, thereby increasing the thermal enthalpy of the steam. This upgraded steam is then used as a heating medium in the system, replacing the external fresh steam required for traditional evaporation, achieving the recycling of heat energy, energy saving and high efficiency.

[0003] In a production example project of chemical product potassium perchlorate, it is necessary to evaporate and concentrate the by-product brine, and then precipitate the sodium chloride crystals for recycling, so an evaporation and crystallization separation device using MVR technology is equipped. The main equipment of the device includes feed pump, preheater, circulating heat exchanger, evaporation and crystallization separator, discharge pump, thickener, centrifuge, secondary separator, steam compressor, etc. The production process is as follows:

[0004] The raw liquid containing sodium chloride is pumped in by a feed pump, heated by a preheater and a circulating heat exchanger, and then enters an evaporation crystallization separator. After evaporation and concentration, sodium chloride crystals are precipitated, and the concentrated liquid containing crystals is separated by a subsequent thickener and a centrifuge to obtain reusable sodium chloride crystals. In addition, the secondary steam that is heated and evaporated, after removing the liquid component by a secondary separator, enters a steam compressor for pressurization, temperature increase, and enthalpy increase, and then enters a circulating heat exchanger to heat the material, and then the waste heat is recovered and utilized by the preheater, and the condensed water is reused, and the final non-condensable gas is discharged to the atmosphere through a vacuum pump.

[0005] When the device was actually working, it was found many times that the steam compressor vibrated violently. After disassembling the machine, it was found that the root of the impeller blades was cracked and there were obvious corrosion spots on the volute. The reason was analyzed to be that the liquid component in the steam entering the compressor was relatively high, the gas-liquid separation was not thorough, and the entrainment was serious, resulting in unstable operation and large vibration of the compressor. Under high temperature and high pressure environment, water vapor will aggravate the corrosion and rust of metal parts inside the compressor. In addition, the liquid contains residual chloride ion components, which cause corrosion to the secondary steam pipeline, secondary separator and impeller, causing major failures such as impeller cracking, resulting in multiple system shutdowns and related production line shutdowns.

[0006] In addition, the discharge pump frequently experienced cavitation, causing discharge blockage and preventing continuous and normal discharge, greatly affecting the production capacity of the device. It was originally suspected that the diameter of the discharge pump outlet port was too small, but the problem persisted after it was enlarged. Summary of the invention

[0007] In order to solve the above problems, the present application proposes an MVR evaporation crystallization device, which is optimized and improved on the basis of the conventional device, and a cyclone separator and a diversion pipeline are added to solve the problems of corrosion and cracking of the steam compressor impeller and cavitation jamming of the discharge pump.

[0008] To achieve the above objectives, this application provides the following technical solutions:

[0009] A hydrocyclone separator is added between the secondary steam outlet of the evaporation crystallization separator and the secondary separator inlet to pre-separate most of the liquid entrained by the secondary steam. The hydrocyclone separator is a circular tank, and its hydrocyclone inlet is set to enter in the circular tangential direction;

[0010] A branch pipeline is added to take out part of the relatively low-temperature material liquid heated by the distilled water preheater and flow it into the inlet of the discharge pump to mix with its relatively high-temperature inlet material, thereby reducing the material temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of the main process of the MVR evaporation crystallization device described in this application. The arrows in the figure indicate the direction of the fluid in the pipeline and mark the main materials;

[0012] Figure 2 This is a top view cross-sectional schematic diagram of the hydrocyclone separator described in the present application, which shows the flow direction and flow pattern of the secondary steam after entering the hydrocyclone separator tank from the tangential direction.

[0013] The serial numbers in the figure are explained as follows:

[0014] 1-feed pump, 2-distilled water preheater, 3-non-condensable gas preheater, 4-steam preheater, 5-circulating heat exchanger 1, 6-circulating heat exchanger 2, 7-circulating pump;

[0015] 8-evaporation crystallization separator, 9-discharging pump, 10-secondary separator, 11-steam compressor, 12-hydrocyclone separator, 121-hydrocyclone inlet, 122-steam outlet, 123-liquid outlet, 13-diversion pipeline. DETAILED DESCRIPTION

[0016] In conjunction with the above drawings, the specific implementation of the present application is described as follows:

[0017] like Figure 1 As shown, the main process equipment of the MVR evaporation crystallization device described in the present application includes: a feed pump 1, a distilled water preheater 2, a non-condensable gas preheater 3, a steam preheater 4, a circulating heat exchanger 1 5, a circulating heat exchanger 2 6, a circulating pump 7, an evaporation crystallization separator 8, a discharge pump 9, a secondary separator 10, a steam compressor 11, a hydrocyclone separator 12 and a diversion pipeline 13, and its main process flow is as follows:

[0018] The raw material liquid containing sodium chloride is pumped in by the feed pump 1, and is heated in sequence by the distilled water preheater 2, the non-condensable gas preheater 3, and the steam preheater 4, and then pumped into the circulating heat exchanger 2 6 by the circulating pump 7 to be heated by secondary steam, and then enters the evaporation crystallization separator 8 for evaporation, and part of the material liquid enters the circulating pump 7 through the circulating heat exchanger 1 5 for recirculation and heating, and after continuous evaporation and concentration, sodium chloride crystals are precipitated, and the concentrated liquid containing the crystals is output through the discharge pump 9 and enters the subsequent equipment; and the secondary steam generated by evaporation in the evaporation crystallization separator 8 passes through the cyclone separator 12 and the secondary separator 10 to remove the liquid component, and then enters the steam compressor 11 for pressurization, temperature increase and enthalpy increase, and then enters the circulating heat exchanger 1 5 and the circulating heat exchanger 2 6 to heat the material, and then recovers the waste heat through the non-condensable gas preheater 3 and enters the subsequent equipment.

[0019] The hydrocyclone separator 12 is disposed between the secondary steam outlet at the upper end of the evaporation crystallization separator 8 and the inlet of the secondary separator 10;

[0020] The hydrocyclone separator 12 is a circular tank body, provided with a hydrocyclone inlet 121, a vapor outlet 122 and a liquid outlet 123. The hydrocyclone inlet 121 is set to enter in the direction of a circular tangent, the vapor outlet 122 is set at the center of the tank body, concentric with the tank body, and its lower pipe mouth extends to the middle and lower part of the tank body, and the liquid outlet 123 is located at the center of the bottom of the circular tank body;

[0021] The hydrocyclone inlet 121 of the hydrocyclone separator 12 is connected to the secondary steam outlet at the upper end of the evaporation crystallization separator 8 through a pipeline, and the steam outlet 122 is connected to the inlet of the secondary separator 10 through a pipeline;

[0022] During normal operation, a large amount of secondary steam evaporated in the evaporation crystal separator 8 enters the hydrocyclone inlet 121 of the hydrocyclone separator 12 through the secondary steam outlet and pipeline at its upper end. Figure 2 As shown, the secondary steam rotates around the circle after entering tangentially, and most of the entrained liquid collides and adheres to the inner wall of the tank body under the centrifugal action of its gravity and gathers at the bottom of the tank body, and is discharged from the liquid outlet 123, thereby achieving pre-separation of gas and liquid. It is measured that about 90% of liquid separation can be achieved; the pre-separated secondary steam enters the inlet of the secondary separator 10 from the steam outlet 122 and the subsequent pipeline, and enters the steam compressor 11 after being separated again by the liquid removal filler in the secondary separator 10.

[0023] In addition, the added diversion pipeline 13 is connected between the material outlet of the distilled water preheater 2 and the inlet of the discharge pump 9, and takes out part of the relatively low-temperature material liquid heated by the distilled water preheater 2 and flows into the inlet of the discharge pump 9 to mix with its relatively high-temperature inlet material.

[0024] The beneficial effects of the MVR evaporation crystallization device described in this application are:

[0025] The provision of the hydrocyclone separator 12 ensures that the liquid content of the steam entering the steam compressor 11 is at an extremely low level, reduces corrosion to the impeller of the steam compressor 11, and greatly prolongs the life of the steam compressor 11;

[0026] After the bypass pipeline 13 is provided, the temperature of the material entering the discharge pump 9 is lowered, the cavitation phenomenon of the discharge pump 9 is greatly reduced, the problem of material jamming due to cavitation is solved, and the service life of the discharge pump 9 is extended.

Claims

1. An MVR evaporation crystallization device, characterized in that: A hydrocyclone separator (12) is added between the secondary steam outlet of the evaporation crystallization separator (8) and the inlet of the secondary separator (10); a diversion pipeline (13) is added to separate part of the relatively low-temperature material liquid heated by the distilled water preheater (2) and flow it into the inlet of the discharge pump (9) to mix with the relatively high-temperature inlet material.

2. The MVR evaporation crystallization device according to claim 1 is characterized in that: The hydrocyclone separator (12) is a circular tank, and its hydrocyclone inlet (121) is arranged to enter in the direction of a circular tangent.

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