Double quadruple effect evaporator

1. Core Concepts and Design Philosophy 

The double quadruple-effect evaporator consists of two independent quadruple-effect evaporation systems connected in parallel or series. They share some common utilities (such as feed pretreatment, vacuum system, and control system) and are often enhanced using thermal compression pumps (TVR) or mechanical vapor recompression (MVR) technology. Its design philosophy is to push the economic efficiency of steam to its theoretical limit through large-scale operation and energy integration, based on the traditional quadruple-effect evaporator. It can typically achieve the effect of evaporating more than 6.5 tons of water from 1 ton of live steam, far exceeding the ordinary quadruple-effect evaporator (approximately 4.2 tons of water/ton of steam).

2. Process Flow and Configuration Mode

Parallel Double Quadruple-Effect (Mainstream Mode):

Process: The pretreated feed liquid is fed in parallel into two independent quadruple-effect evaporation sequences (System A and System B) through a distribution system. The two systems are completely identical in operating parameters (temperature, pressure, concentration).

Heat Source: Live steam is pumped through one or more thermal compression pumps (TVR) to extract a portion of the secondary steam generated by systems A and B, respectively. After pressurization and heating, this serves as the heat source for the first effect. This significantly reduces the total consumption of fresh steam.

Advantages: The system is symmetrical, the process is clear, control is relatively simple, and it is easy to scale up. It has a huge capacity and is suitable for processing single, stable, high-flow-rate materials, such as alkali evaporation in large alumina plants and large-scale seawater desalination.

Series-Type Double Quadruple Effect (Stage Processing):

• Process: The material enters the first quadruple effect system for preliminary concentration. The resulting concentrate is then used as feed to the second quadruple effect system for final concentration and crystallization.

• Features: The operating parameters of the two systems can be set independently to adapt to the different characteristics of the material at different concentration stages (such as boiling point rise, viscosity, and scaling tendency). The second system can be specifically optimized for high-concentration, high-boiling-point-rise materials.

• Advantages: Suitable for complex operating conditions with large variations in material concentration and significant differences in physical properties between early and late stages, achieving cascaded energy utilization and refined process control.

3. Core Advantages

Extreme Energy Efficiency: The combination of dual quadruple-effect evaporators and TVR/MVR technology represents the pinnacle of current evaporation energy-saving technologies, resulting in extremely low unit steam consumption and unparalleled economic efficiency in ultra-large-scale models.

Large Processing Capacity: A single system can achieve an evaporation capacity of over 100 tons per hour, meeting the massive production demands of modern chemical, metallurgical, and seawater desalination industries.

Relatively Optimized Footprint: Although the equipment is large, through shared utilities and a compact design, the footprint per unit evaporation capacity is less than that of building two independent quadruple-effect units.

Operational Flexibility: During partial load operation, the operating status of one system can be adjusted according to production demand (e.g., load reduction or suspension), while the other maintains rapid operation, improving the overall plant's production scheduling flexibility.

4. Application Areas

This system involves huge investments and complex technology, and is only suitable for specific scenarios:

Large-scale alumina plants: Handling the massive demand for seed mother liquor evaporation.

Giant seawater desalination projects: Serving as a pre-concentration stage for high-concentration brine.

Ultra-large-scale chemical industrial parks: The core evaporation unit for centralized treatment of high-salinity wastewater within the park, achieving zero-discharge ZLD .

Paper industry: Large-scale black liquor concentration.

5. Challenges and Considerations

Huge Initial Investment: The large number of equipment, high material requirements, and complex control systems result in very high fixed asset investment.

Highly Complex System Control: The strong coupling between the two systems means that fluctuations at any point will affect each other, placing extremely high demands on the reliability, accuracy, and anti-interference capabilities of the automatic control system.

Cumbersome Start-up and Shutdown Procedures: Strictly sequential start-up and shutdown procedures are required, resulting in long processing times.

Stringent Design Requirements: Extremely precise process calculations and system integration design are required; any design deviation may lead to substandard overall performance.