## I. Project Abstract

Evaporators, as material concentration equipment, are widely used in many industries. Our company has conducted in-depth research on the existing problems of the equipment and technology for the evaporation of sodium aluminate solution in the alumina industry, and has developed the low-energy-consumption seven-effect two-stage sectional evaporation technology for sodium aluminate solution.

Currently, for the evaporation of alumina production mother liquor (sodium aluminate solution) worldwide, there are three-effect natural circulation evaporator units, four-effect natural circulation evaporator units, five-effect natural circulation evaporator units, five-effect falling film evaporator units, and six-effect falling film evaporator units. Most of the old production lines adopt three-effect, four-effect, or five-effect operations, while newly built or expanded production lines in old factories use six-effect operations. The steam consumption of the three-effect evaporator unit operation reaches 0.5-0.6t of steam per ton of water, that of the four-effect evaporator unit operation reaches 0.45-0.5t of steam per ton of water, and that of the six-effect evaporator unit operation reaches 0.3-0.35t of steam per ton of water. The relatively high steam consumption leads to high production costs.

The disadvantages of the existing falling film evaporators are as follows:

1. The heating chamber and the separation chamber are integrated up and down. The heating chamber inserted into the separation chamber occupies most of the separation space, resulting in a small vapor-liquid separation space, a short separation path, a high superficial gas velocity in the empty tower, insufficient vapor-liquid separation, a high alkali content in the condensed water, and a series of problems brought to the production by a large amount of unqualified condensed water.

2. The distributor of the evaporator uses multiple umbrella-shaped distribution heads to distribute the material. This distributor cannot distribute all the material to the hole bridges between the tubes. Most of the material directly falls into the middle of the tubes, and the material enters the separation chamber at the lower part of the heating chamber without being heated or evaporated. The heat transfer effect is poor, increasing the power of the circulation pump and the consumption of steam.

3. The flash evaporator is not reasonably designed, with a poor cooling effect, and its role in reducing gas consumption is not obvious.

4. The number of effects and the process of the evaporator have not reached the optimal energy-saving mode, directly affecting energy conservation and consumption reduction.

The newly developed split-type seven-effect two-stage energy-saving evaporator of our company has a slightly higher overall investment for the evaporator with the same evaporation capacity compared to the integrated six-effect falling film evaporator, but it can save more than 30% of energy during operation. After adopting the new split-type seven-effect falling film evaporator, the steam consumption is 0.18-0.22t of steam per ton of distilled water (currently, for the evaporators used in alumina production worldwide, the best steam consumption is still above 0.28t of steam per ton of distilled water). The liquid level of the evaporator, the gate valve (pneumatic), and the evaporation return water can all be automatically controlled. The qualification rate of the condensed water of the evaporator is 100%. This technology is a proprietary technology independently developed by our company with independent intellectual property rights.

## II. Significance and Necessity of the Project

With the continuous increase in energy prices, the current competition in the alumina industry is becoming increasingly fierce. Facing the current situation of rising prices of raw materials, materials, and energy, as the energy consumption accounts for nearly half of the cost in the alumina industry, energy conservation and consumption reduction are particularly important and urgent. Reducing energy consumption and improving energy utilization rate have become the most effective way to reduce costs. Currently, in alumina production, the steam consumption in the evaporation process accounts for about 30-50% of the total steam consumption. Therefore, how to reduce the evaporation steam consumption is of great significance for energy conservation and consumption reduction in alumina production. Thus, researching and developing high-efficiency energy-saving evaporation technologies and equipment is a necessity for the survival and development of the alumina industry, with a large market demand.

Against this background, in accordance with market demand, our company has organized technical personnel to tackle key problems and developed the seven-effect two-stage energy-saving evaporator that meets the needs of alumina production. If this evaporator is popularized and applied in the alumina industry, based on China's current alumina production capacity of 50 million tons per year, it will save 20-30 million tons of steam annually. Calculated according to the current price, it will save 2.4-3.6 billion yuan. The popularization and application of this project can not only generate huge economic benefits but also achieve significant environmental and social benefits, conforming to the sustainable development industrial policies encouraged and supported by the state.

## III. Main Technical Features and Innovation Points of the Project

This falling film evaporator adopts a split layout of the heating chamber and the separation chamber. The secondary steam enters the separation chamber tangentially and spirally, playing the role of two vapor-liquid separations. The separation space is also larger than that of the integrated evaporator, ensuring sufficient vapor-liquid separation. The film distributor adopts a multi-layer sieve plate structure for positioning and fixing, enabling the uniform distribution of materials on the hole bridges of the tube sheet and overflowing into the inner wall of the tubes, resulting in uniform film formation. An expansion ring is used at the steam inlet of the heating chamber. The expansion ring and the inner baffle cylinder form a jacket, enabling the circumferential uniform distribution of the steam flow and its axial inflow into the heating chamber, greatly reducing the impact of the steam flow on the tubes. At the same time, the expansion ring can reduce the damage to the equipment caused by the temperature difference stress.

The evaporator unit adopts a seven-effect split-type falling film evaporator, with a five-stage flash evaporator for two-stage evaporation and a countercurrent operation process. The first-stage evaporation is composed of Effect VII and Effect VI, and the second stage is composed of Effect V, Effect IV, Effect III, Effect II, Effect I, and the five-stage flash evaporation. The material for the first-stage evaporation (original evaporation liquid) enters from Effect VII and exits from Effect VI; the material for the second-stage evaporation (original evaporation liquid) enters from Effect V and successively passes through Effect IV, Effect III, Effect II, Effect I, and the five-stage flash evaporation for discharging. The discharged materials from the two-stage evaporation both enter the evaporation mother liquor tank for mixing.

## IV. Analysis of Expected Economic, Social, and Environmental Benefits of the Project

### Economic Benefit Analysis

The benefit calculation is only based on the savings in steam:

The steam consumption of the newly developed new film distributor, high-efficiency flash steam, and the new seven-effect two-stage evaporator is 0.2 tons of steam per ton of water, while the lowest steam consumption of the six-effect integrated evaporator is still 0.3 tons of steam per ton of water. 0.1 ton of steam can be saved for every ton of water evaporated. For an annual alumina production of 1 million tons, 2 sets of 240t/h evaporators are required. Calculated based on the operation of one set, with an equipment operation rate of 90% and a price of 130 yuan per ton of steam, the value of steam saved annually is approximately 0.1×240×8760×0.9×130 = 24.6 million yuan.

### Social Benefit Analysis

For each set of this technical device put into operation in an alumina plant, 24 tons of steam can be saved per hour, which is equivalent to not putting into operation a 20t/h pulverized coal boiler, reducing the dust and flue gas emissions to the surrounding environment, and having significant social benefits.

Developing Unit: Henan Jiuye Chemical Equipment Co., Ltd.

Project Leader: Ju Lirang