In the alumina production process, evaporators play a vital role, and the key to ensuring negative-pressure evaporation in evaporators lies in the cooling method of the steam from the last effect. There are three cooling forms for the steam from the last effect of evaporators in the alumina industry. Each has its own advantages and plays a unique role in different scenarios. Let's explore them together!

1. Direct Condenser: The Traditional yet Efficient "Veteran"
   

   
   

Direct Condenser: The most traditional cooling method for final-effect steam in the alumina industry.
Its principle is straightforward: low-temperature circulating water directly contacts the final-effect steam in a large steam condenser. As the circulating water absorbs the steam's heat, the steam volume shrinks. With the aid of a vacuum pump, this process creates the vacuum required for the final effect. After absorbing heat, the circulating water temperature rises, and the high-temperature effluent is sent to a cooling tower. By volatilizing part of the water, the cooling tower reduces the water temperature, enabling cyclic reuse.

This cooling method excels in simple structure and convenient operation, but its disadvantages are also obvious. Since the circulating water needs to absorb a large amount of steam heat, the water consumption is extremely high, leading to relatively high power consumption. However, with its mature technology and stable performance, the direct condenser remains a reliable choice in scenarios where cost control requirements are relatively lenient.

2. Indirect Condenser: The "Smart Choice" for Energy and Water Saving

Unlike direct condensers, indirect condensers adopt a water-cooling method where circulating water does not directly contact the final-effect steam. They also rely on the lower inlet temperature and higher outlet temperature of the circulating water to carry away heat, condense the final-effect steam, and thus form a vacuum.

The greatest advantage of indirect condensers lies in that since the steam does not directly contact the circulating water during condensation, the condensed water is relatively pure and can be used for production or other processes. This effectively realizes the recycling of secondary condensed water and greatly reduces water resource waste. However, this method requires additional heat exchangers, and the area of the heat exchanger must be accurately calculated based on heat, so the initial investment is relatively large. Nevertheless, in areas with water shortages and high water-saving requirements, indirect condensers have become the preferred choice for many enterprises due to their water-saving advantages.

3. Evaporative Condenser: The Trend-setting "Industry Rising Star"

The evaporative condenser can be regarded as an innovative achievement in the field of evaporator cooling technology. It is actually the application of closed-circuit cooling towers in the evaporation sector. Jiuye Chemical has promoted this technology for many years and achieved good application effects in small evaporators.

At the Huasheng Alumina Plant of Chinalco Fangchenggang, a 500-ton large-scale evaporator equipped with an evaporative condenser is currently operating with excellent performance. The calculation process is relatively complex, requiring comprehensive consideration of local factors such as temperature and humidity. The successful application in subtropical regions like Fangchenggang—characterized by high humidity and temperature—indicates the feasibility of this technology in other domestic areas.

Compared with other cooling methods, evaporative condensers show particularly significant energy-saving effects, saving 2 to 3 kWh of electricity for every ton of water evaporated. With their outstanding energy-saving advantages, evaporative condensers have gradually emerged in the application of large-scale evaporators in alumina plants, becoming a new trend in industry development.

The three final-effect steam cooling methods each have their advantages and disadvantages. Direct condensers are simple and efficient, indirect condensers are water-saving and environmentally friendly, and evaporative condensers excel in energy conservation. When selecting a method, enterprises need to comprehensively consider their production requirements, cost budgets, and local resource environments. With the continuous technological development and increasing requirements for environmental protection and energy conservation, it is believed that evaporative condensers will be more widely applied in the alumina industry, injecting new momentum into the green and efficient development of the industry!