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Mechanism and characteristics of MVR evaporator

Release time：

2020-07-13

MVR is the abbreviation of mechanical vapor recompression (mechanical vapor recompression). The MVR evaporator is an energy-saving technology that reuses the energy of its own secondary steam, thereby reducing the demand for external energy.

1. MVR process introduction

1. MVR principle

The working process of MVR is to compress the low-temperature steam by the compressor, increase the temperature and pressure, and increase the enthalpy, and then enter the heat exchanger for condensation to make full use of the latent heat of the steam. Except for the start-up, there is no need for the secondary steam from the evaporator during the entire evaporation process. After being compressed by the compressor, the pressure and temperature increase, and the enthalpy increases, and then it is sent to the heating chamber of the evaporator to be used as heating steam. Keep the material liquid in a boiling state, while the heating steam itself condenses into water. In this way, the previously discarded steam is fully utilized, latent heat is recovered, and thermal efficiency is improved. The economy of raw steam is equivalent to 30 effects of multi-effect evaporation.

In order to make the manufacture of the evaporation device as simple as possible and easy to operate, centrifugal compressors and Roots compressors can be used. These machines have higher volumetric flow rates in the compression ratio range of 1:1.2 to 1:2.

2. MVR process flow

The system consists of single-effect or double-effect evaporator, separator, compressor, vacuum pump, circulating pump, operating platform, electrical instrument control cabinet, valves, pipelines and other systems, with simple structure and convenient operation and maintenance.

2. Introduction of evaporator

1. MVR falling film evaporator

working principle:

The raw material liquid is added from the upper tube box of the heat exchanger, and the material is distributed into each heat exchange tube through the liquid distributor, and a uniform liquid film is formed along the inner wall of the heat exchange tube. The liquid film in the tube is passed by the shell during the downward flow. The heated steam is heated, boils and evaporates while flowing down. The material at the bottom of the heat exchange tube becomes concentrated liquid and secondary steam.

The concentrated liquid falls into the lower pipe box, and the secondary steam enters the gas-liquid separator. In the gas-liquid separator, the liquid droplets entrained by the secondary vapor are removed, and the pure secondary vapor is transported from the separator to the compressor. The compressor compresses the secondary vapor and sends it to the shell side of the heat exchanger as heating vapor for the evaporator heat source. Realize continuous evaporation process.

Features:

1. High heat exchange efficiency

2. Small footprint

3. The staying time of the material is short, and it is not easy to cause deterioration of the material.

4. Suitable for materials with higher viscosity.

Application range:

The falling film evaporator is suitable for the pre-concentration process of the MVR evaporation crystallization process. It can evaporate materials with higher viscosity. It is especially suitable for heat-sensitive materials, but not suitable for processing crystalline materials.

2. MVR forced circulation evaporator

working principle:

The forced circulation evaporator consists of an evaporation separator, a heat exchanger and a forced circulation pump. The material in the heat exchange tube of the heat exchanger is heated by the steam outside the heat exchange tube to increase the temperature. The material rises to the evaporation separator under the action of the circulating pump, and the material evaporates due to the drop in static pressure of the material in the evaporation separator.

The secondary steam generated by evaporation overflows from the material, and the material is concentrated to produce supersaturation and crystal growth. The supersaturated material enters the forced circulation pump and enters the heat exchanger under the action of the circulation pump. The material circulates in this way and continuously evaporates and concentrates or concentrates and crystals .

The crystal slurry is output from the circulation pipeline with a discharge pump. The secondary steam in the evaporative separator is purified by the separation and defoaming device on the upper part of the evaporative separator, and then sent to the compressor. The compressor compresses the secondary steam and sends it to the shell side of the heat exchanger to be used as the evaporator to heat the steam to achieve heat Continuous evaporation in circulation.

Features:

1. The heat transfer coefficient is low;

2. The heat exchange surface is not easy to form fouling or crystallization.

Application range:

It is suitable for evaporative concentration or evaporative crystallization process of easily fouling, crystallization, high viscosity materials.

3. MVR evaporation OSLO crystallizer

working principle:

OSLO evaporative crystallizer is composed of OSLO evaporator, heat exchanger and forced circulation pump. The material in the heat exchange tube of the heat exchanger is heated by the steam outside the heat exchange tube to increase the temperature. The material rises to the OSLO evaporation crystallizer under the action of the circulating pump, and the material evaporates due to the drop in static pressure of the material in the OSLO evaporation crystallizer.

The secondary steam produced by evaporation overflows from the material, and the material is concentrated to produce oversaturation. The supersaturated solution drops in the central tube of the OSLO evaporation crystallizer and fully contacts the small crystals in the solution to further grow the crystals. The larger crystals undergo scouring. Column elutriation will precipitate large crystals under the elutriation column and transport them to the thickener with a crystal slurry pump. The smaller crystals continue to grow in the OSLO crystallizer.

The clarified liquid is transported to the heat exchanger by the forced circulation pump to continue heating, and the material is continuously evaporated and concentrated or concentrated and crystallized in this way. The secondary steam in the OSLO evaporative crystallizer is purified by the separation and defoaming device on the upper part of the separator and then sent to the compressor. The compressor compresses the secondary steam and sends it to the shell side of the heat exchanger to use as the evaporator heating steam. Realize continuous evaporation of thermal energy cycle.

main feature:

1) Large crystal size and uniform size

2) The equipment has large volume and high cost

Scope of application:

It is suitable for the production of materials requiring large crystal grain size.

4. MVR evaporation DTB crystallizer

working principle:

DTB type crystallizer is a typical crystal slurry internal circulation crystallizer. Since the inner guide tube is set in the crystallizer, a circulation channel is formed, so that the crystal slurry has good mixing conditions, and the supersaturation can be quickly eliminated in the evaporation crystallization, and the supersaturation of the solution can be kept at a relatively low level.

It is especially suitable for products with steep solubility curves. DTB type crystallizer has good performance, high production intensity, can produce larger grains, and is not easy to scar in the crystallizer. It has become one of the main forms of continuous crystallizer.

main feature:

High production intensity, large crystal particles and stable performance.

Scope of application:

It is suitable for the production of materials with large crystal size and high production intensity.

Three, technical summary

In general, the technical characteristics of mvr evaporator are as follows:

(1) Clean energy, high thermal efficiency, low power consumption and no pollution.

(2) "Zero discharge" of industrial wastewater meets national discharge standards.

(3) The material to be processed has a wide application range.

(4) One multi-effect, saving manufacturing cost.

(5) Low temperature evaporation, normal temperature evaporation (non-standard, non-pressure vessel design basis).

(6) It can discharge continuously and intermittently.