### Analysis of Direct and Indirect Air Cooling Technologies

In power plant cooling systems, air cooling technology is widely used due to its high efficiency and water-saving characteristics. Air cooling technology is mainly divided into two categories: direct air cooling and indirect air cooling. Each of these technologies has its own features and is suitable for different environments and requirements. This article will provide a detailed analysis of the working principles, advantages and disadvantages, and application scenarios of direct and indirect air cooling technologies.

**1.** Direct Air Cooling Technology **

Direct air cooling technology uses air as the cooling medium, where mechanical ventilation causes the turbine exhaust steam to condense directly in finned tube air-cooled condensers. The system mainly consists of large-diameter exhaust steam pipes, air-cooled condensers, axial flow cooling fans, and condensate pumps. The working principle of direct air cooling technology is relatively simple: turbine exhaust steam enters the outdoor air-cooled condenser through large exhaust pipes, axial flow cooling fans blow air over the outer surface of the condenser, condensing the exhaust steam into water, which is then pumped back to the boiler.

**Advantages of Direct Air Cooling Technology:**

1. **Water Saving**: Air-cooled units save more than 65% water compared to wet-cooled units, which is especially important in water-scarce areas.

2. **Free Cooling Medium**: Air is freely available with no additional cost.

3. **No Special Site Restrictions**: Since it does not rely on water sources, site selection is more flexible.

4. **Low Maintenance Costs**: Maintenance costs of air-cooled units are 20~30% of those of wet-cooled units.

**Disadvantages of Direct Air Cooling Technology:**

1. **Highly Affected by Environmental Factors**: Temperature, strong winds, rainfall, and other environmental factors affect the heat dissipation performance of air coolers. Especially under high temperature and strong wind conditions, heat dissipation significantly decreases, which may lead to increased turbine back pressure and affect unit safety operation.

2. **High Noise**: The noise from large-diameter axial flow fans is around 85 decibels, which may cause local noise exceedance issues at the power plant boundary.

3. **High Cost**: Although water-saving is significant, the cost of direct air cooling systems is relatively high.

**2.** Indirect Air Cooling Technology **

Indirect air cooling technology, also known as the Hamon system, mainly consists of surface condensers, air coolers, circulating water pumps, nitrogen protection systems, circulating water makeup systems, cooler cleaning systems, and air cooling towers. This system is similar to conventional wet cooling systems but replaces wet cooling towers with air cooling towers and uses a closed circulating cooling water system instead of an open one, with circulating water being demineralized.

**Working Principle of Indirect Air Cooling Technology:**

Circulating water enters the water side of the surface condenser, cooling the turbine exhaust steam on the steam side through surface heat exchange. The heated circulating water is pumped to the air cooling tower, where it exchanges heat with the air via the air cooler. The cooled circulating water then returns to the condenser to cool the turbine exhaust steam, forming a closed loop.

**Advantages of Indirect Air Cooling Technology:**

1. **High Heat Exchange Efficiency**: Using water as the cooling medium, which has a higher specific heat capacity, allows more effective heat absorption and transfer.

2. **Low Water Quality Requirements**: Cooling water and condensate systems are separated and treated according to their own standards, basically eliminating scaling and clogging inside condenser tubes.

3. **Low Noise**: Due to the use of natural draft cooling towers, noise issues are relatively minor.

4. **Low Operating Back Pressure**: Compared to direct air cooling systems, indirect air cooling systems have lower turbine back pressure, providing relatively higher safety during summer operation.

**Disadvantages of Indirect Air Cooling Technology:**

1. **Complex System**: The addition of intermediate cooling stages makes the system more complex and operation more cumbersome.

2. **Large Footprint**: Air cooling towers and related equipment occupy a large area.

3. **High Initial Investment**: The initial investment for indirect air cooling systems is relatively high, mainly due to the cost of heat exchangers and other equipment.

**3. Application Scenarios of Direct and Indirect Air Cooling Technologies**

Direct air cooling technology is suitable for areas with scarce water resources, moderate temperatures, and low noise requirements. Indirect air cooling technology is more suitable for situations with higher water quality requirements, higher temperatures, and strict noise control. In practical applications, the choice of air cooling technology should be based on a comprehensive consideration of specific climate conditions, water resource status, economics, and safety.

In summary, both direct and indirect air cooling technologies have their own advantages and disadvantages. The choice of technology requires comprehensive consideration of multiple factors. With continuous technological progress and cost reduction, the application prospects of air cooling technology in the power generation field will be broader.