What is the difference between an MVR evaporator and a multi-effect evaporator?

Evaporators play a vital role in industry, with two main types being MVR evaporators and multi-effect evaporators. So, what are the differences between MVR evaporators and multi-effect evaporators? Let Jiangsu Gaojie Energy-Saving Equipment Group Co., Ltd. explain the differences between these two types of evaporators.

This is a frequently asked question regarding MVR evaporators and multi-effect evaporators. Homeowners often compare MVR evaporators and multi-effect evaporators when purchasing evaporators and need to understand the differences between them.

MVR evaporators, or mechanical compression evaporators, utilize a steam compressor to recompress the evaporated secondary steam, raising its temperature before sending it back to the evaporation heater for reuse. MVR evaporators consume virtually no live steam, only a portion of electrical energy. Their electrical energy consumption depends primarily on the required temperature rise of the secondary steam and the efficiency of the steam compressor.

A multi-effect evaporator is designed to reuse secondary steam multiple times by utilizing the temperature difference from the first effect to the last effect. Generally, the evaporation temperature of the first effect is controlled by the thermosensitive temperature of the material, while the temperature of the secondary steam in the last effect is determined by the local altitude and the type of vacuum unit selected. Its live steam consumption is inversely proportional to the number of effects.

The main differences between MVR evaporators and multi-effect evaporators are the consumption of heating steam, the amount of cooling water processed, the amount of heat input, the size of the footprint, and the operating system. Overall, MVR evaporators are more energy-efficient than multi-effect evaporators, but for the same processing capacity, MVR evaporators are more expensive than multi-effect evaporators.

Reasons for low vacuum during evaporator operation

Reasons for low vacuum during evaporator operation:

If the concentrator leaks air, the incoming air will add extra pressure to the vacuum system, and in severe cases, it may even prevent the vacuum from being created.

Insufficient cooling water. Besides pump-related issues, the main causes of insufficient cooling water are blocked pipes and damaged valves. Insufficient cooling water will prevent secondary steam from condensing in a timely manner and severely affect the operation of the vacuum system.

If the cooling water temperature is too high, especially the inlet temperature, the large amount of secondary steam generated by the concentrator cannot be maintained in time, causing a sharp drop in the vacuum level of the concentrator. If the heating steam pressure is too high, the evaporation rate of the concentrator will increase rapidly, and due to the generation of a large amount of secondary steam, the load on the cooling device will increase, and the vacuum level will gradually decrease. Lowering the vacuum level will increase the evaporation temperature of the material, affecting not only product quality but also ultimately the production capacity of the equipment.

What are the characteristics of a forced circulation evaporator?

The characteristics of an evaporator include:

1. The speed of liquid circulation is adjusted by the pump.

2. When the feed liquid runs at a high flow rate under the action of external force, the scaling rate is reduced and the turbulence state of the feed liquid is enhanced. At the same time, a certain amount of pressure head is maintained at the outlet end, which can prevent evaporation inside the heat exchanger.

3. In forced circulation evaporation, the circulation of the solution within the equipment relies primarily on forced flow generated by external power. The velocity typically reaches 1.0-3.5 m/s. It offers high heat transfer efficiency and production capacity.

4. The raw material liquid is pumped in from bottom to top by a circulating pump and flows upward along the inside of the heating chamber.

5. The material does not evaporate in the heat exchanger, but flashes in the separator. The vapor is discharged from the top in the separator, while the fluid is obstructed and falls down. It is then sucked into the circulating pump at the bottom of the cone and enters the heating tube to continue circulating.

In summary, the advantages of forced circulation evaporators include: resistance to salt precipitation, resistance to scaling, ease of cleaning, and strong adaptability.

What are the characteristics and applicable scope of forced circulation evaporators?

Evaporators utilize external power for circulation, with a pump forcing the solution through a heater in one direction at a speed of 2-5 m/s. Other evaporators involve vaporization within the evaporator itself. Their common drawback is the low circulation speed of the solution, resulting in poor heat transfer. Forced circulation evaporators can be used when processing solutions with high viscosity, those prone to scaling, or those prone to crystallization.

Features of forced circulation evaporators:

1. Advantages of forced circulation evaporators: high heat transfer coefficient, resistance to salt precipitation and scaling, strong adaptability, and easy to clean.

2. Disadvantages of forced circulation evaporators: higher energy consumption, longer solution residence time; and slightly higher cost and maintenance expenses.

Applications of forced circulation evaporators:

Forced circulation evaporators are suitable for evaporation and concentration in industries such as chemical, food, pharmaceutical, environmental engineering, and waste liquid evaporation and recovery, which require materials that are prone to scaling, crystallization, heat sensitivity (low temperature), high concentration, high viscosity, and contain insoluble solids.