Dry Coolers For Gas Turbine Power Generation
Dry Coolers for Gas Turbine Power Generation
Gas turbine realizes power generation through "compressor compressed air→combustion chamber mixed fuel combustion→high temperature gas driving turbine to do work", and the core components such as turbine, bearing and generator will generate a large amount of heat (the turbine inlet temperature can be up to 1300-1600℃, and the friction temperature of the bearing is more than 80℃), which needs to be controlled by cooling system to ensure the safety and efficiency of the equipment. The temperature needs to be controlled by a cooling system to ensure the safety and efficiency of the equipment. The dry cooler mainly serves to dissipate heat from the core components of the gas turbine and cool down the auxiliary system.
The efficient operation of gas turbine relies on the precise control of temperature in key parts (e.g. the metal temperature of turbine blades should be lower than the material endurance limit, and the viscosity of lubricating oil should be maintained at 30-50℃), and the application scenario of the dry cooler is directly corresponding to these core requirements:
Secondary Heat Dissipation in Turbine Cooling System
Gas turbine turbine blades, static vanes, etc. are in direct contact with high temperature gas (above 1300℃), and need to reduce the metal temperature by "internal air cooling" (high pressure air is extracted from the pressurizer, passed into the internal channels of the blades to absorb the heat and then discharged). These heat-absorbing "hot air" (temperature of about 300-500 ℃) need to be further cooled and reused in the pressurizer or discharged, where the dry cooler assumes the secondary heat dissipation: the hot air flows through the finned tubes of the dry cooler, and outside the tubes through the forced ventilation of the fan, the air carries away the heat so that the hot air is cooled down to 100-200 ℃, which recovers part of the heat (reducing energy waste), and avoids the need to cool down the metal temperature by "internal air cooling". (This not only recovers part of the heat (reducing energy waste), but also avoids the influence of high temperature gas directly discharged on the environment and equipment.
Cooling of lubricating oil system
The turbine and compressor bearings of gas turbine (rotating at high speed, the rotating speed can be 3000-6000r/min) rely on lubricating oil for lubrication and heat dissipation, and the friction heat will make the temperature of oil rise to 60-80℃, and if it exceeds 55℃, the viscosity of lubricating oil will be decreased significantly, and lubricating performance will be deteriorated. Through the heat exchange between the lubricant inside the tube and the air outside the tube, the dry cooler controls the oil temperature stably at 40-50℃ (the optimal working range), ensures that the friction coefficient of the bearings is stable, and avoids wear and corrosion of the axial tiles due to overheating.
Generator cooling
Gas turbine-driven generator (synchronous generator) generates heat due to electromagnetic induction during operation (stator winding temperature can reach 100-120℃), which will lead to insulation aging if not cooled in time. For medium and high power gas turbines (e.g. above 60MW), some models adopt "air - air heat exchange": the hot air (60-80℃) inside the generator enters the dry cooler, exchanges heat with the external cold air (ambient temperature) and cools down to 40-50℃, then recirculates back to the inside of the generator, to maintain the insulation of the windings.
Compared with traditional water cooling system (e.g. cooling water tower + heat exchanger), dry cooler is more adaptable in gas turbine power generation, especially in the following three aspects:
Breaking through the limitation of "water-scarce environment", expanding the scope of power station site selection
Gas turbine power stations are often built in industrial parks, remote mining areas, deserts and other scenarios, and some areas (e.g. Middle East desert) are water-scarce. Water resources are scarce. The dry cooler does not consume cooling water (only air circulation), and can completely replace the water cooling system, solving the problem of "not being able to build a station due to lack of water". For example, in a desert gas turbine power plant in Saudi Arabia, the application of dry coolers reduces cooling water consumption by more than 95%, and only a small amount of water is needed for equipment cleaning, which greatly reduces the dependence on neighboring water sources.
Simplified System, Reduced O&M and Land Costs
The circulating water pumps, cooling towers, water treatment equipments and water piping network of water-cooled system are eliminated, thus reducing the complexity of the system by more than 40%; the dry cooler can be modularly arranged in the vicinity of the gas turbine (e.g., on the turbine side, next to the generator), and the land area is only 1/3-1/2 that of the water-cooled system with the same cooling capacity. For the O&M, the only thing needed is to clean the fins (to prevent clogging of sand, dust, and oil) on a regular basis, In terms of operation and maintenance, it is only necessary to clean the fins regularly (to prevent sand, dust and oil clogging) and check the fan motors, and there is no need to deal with corrosion of pipelines and scaling of water (especially in areas with high hardness water) like water-cooled systems.
Avoid the risk of "water-cooled leakage" and ensure the safety of equipment
The lubricating oil, turbine cooling air and other media of gas turbines need to be kept clean (if the lubricating oil is mixed with cooling water, it will lead to emulsification and failure). The dry cooler uses air as the medium, which is completely isolated from the cooled medium (through the metal pipe wall for heat exchange), so there is no risk of contamination by leakage;. In contrast, the water-cooled system may lead to the risk of contamination by leakage if the heat exchanger pipe ruptures. If the heat exchanger pipe breaks, the cooling water may penetrate into the lubricating oil or the turbine air system, leading to equipment failure (e.g. bearing wear, corrosion of turbine blades).
