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I. Air-Cooled Heat Exchangers for Atmospheric and Vacuum Distillation (the Core First Process in Refining)
1. Process Overview
Atmospheric and vacuum distillation is the first stage in crude oil processing. It separates crude oil into fractions such as gasoline, kerosene, diesel, wax oil, and residual oil via atmospheric pressure towers (operating at 100-130°C) and vacuum towers (40-80 kPa negative pressure, operating at 300-380°C). Each fraction and the overhead oil and gas must be rapidly cooled to meet subsequent separation or storage requirements.
2. Air-Cooled Heat Exchanger Application Scenarios
Atmospheric Tower Top Oil and Gas Cooling: Oil and gas discharged from the tower (temperature approximately 110-130°C) are cooled to 40-50°C via an air-cooled heat exchanger, forming a gasoline-water mixture that then enters a separator for oil-water separation.
Vacuum Tower Top Oil and Gas Cooling: Negative-pressure oil and gas at the top of the vacuum tower (temperature approximately 80-100°C) are cooled to 30-40°C via an air-cooled heat exchanger to prevent oil and gas volatilization losses and ensure stable operation of the subsequent vacuum system.
Sidestream Cooling: Sidestream products such as kerosene, diesel, and wax (temperature approximately 200-350°C) from the atmospheric and vacuum towers are initially cooled to 100-150°C via an air-cooled heat exchanger before entering a water cooler for further cooling to storage temperature (40-60°C), reducing the load on the water cooling system.
II. Air-Cooled Heat Exchanger Catalytic Cracking Section (Core Process for Increasing Light Oil Production)
1. Air-Cooled Heat Exchanger Process Overview
Catalytic cracking uses heavy oil (wax oil, residual oil) as feedstock. Catalytic cracking (reaction temperature 480-530°C) cracks heavy oil into lighter products such as gasoline, diesel, and liquefied petroleum gas. These products are then separated in a fractionating tower, and the high-temperature flue gas discharged from the regenerator needs to be cooled to recover heat.
2. Air-Cooled Heat Exchanger Application Scenarios
Fracturing Tower Top Gas Cooling: The liquefied petroleum gas (LPG) and gasoline mixture (approximately 100-120°C) discharged from the top of the fractionating tower is cooled to 40-50°C via an air-cooled heat exchanger before entering the absorption stabilization system to separate the LPG and gasoline.
Crude Gasoline Cooling: The crude gasoline (approximately 180-220°C) drawn from the side of the fractionating tower is cooled to 60-80°C via an air-cooled heat exchanger before being sent to the refining section.
Regenerator Flue Gas Auxiliary Cooling: The high-temperature flue gas (approximately 650-750°C) discharged from the regenerator is first cooled to 200-250°C via a waste heat boiler to recover heat. It is then further cooled to 120-150°C via an air-cooled heat exchanger to prevent low-temperature corrosion of the fan while meeting the inlet temperature requirements of the subsequent desulfurization and denitrification systems.
III. Air-Cooled Heat Exchanger Hydrogenation Unit Section (Product Refining and Heavy Oil Conversion)
1. Air-Cooled Heat Exchanger Process Overview
The hydrogenation unit includes hydrofining (removing sulfur, nitrogen, oxygen, and metal impurities from the oil product) and hydrocracking (converting heavy oil to light oil). The reaction temperature is 280-420°C and the pressure is 6-18 MPa. The reaction products must be cooled before entering the separation system, and the circulating hydrogen must be cooled and recovered.
2. Air Cooler Application Scenarios
Reaction Product Cooling: The high-temperature reaction products (approximately 300-400°C) at the outlet of the hydrogenation reactor are first cooled to 150-200°C via a heat exchanger to recover heat. They are then cooled to 40-50°C via an air-cooled heat exchanger before entering the high-pressure separator (HPS) to separate hydrogen gas and liquid products.
Circulating Hydrogen Cooling: The circulating hydrogen discharged from the top of the HPS (containing a small amount of light hydrocarbons, approximately 40-50°C) is pressurized by a compressor and raised to 80-100°C. It is then cooled to 35-45°C via an air-cooled heat exchanger before being returned to the reactor inlet to ensure a stable reaction temperature.
Low-Pressure Separator (LPS) Outlet Oil Cooling: The refined oil or cracked oil (approximately 60-80°C) discharged from the LPS is cooled to 40-50°C via an air-cooled heat exchanger before being sent to subsequent fractionation or storage systems.
IV. Air-Cooled Heat Exchanger Delayed Coking Section (Key Process for Residue Conversion)
1. Process Overview
Delayed coking uses vacuum residue as feedstock. It is heated to 490-510°C in a furnace and then fed into a coking drum. A “delayed reaction” produces coke and coking gas. The coking gas is then separated into gasoline, diesel, and wax oil in a fractionating tower.
2. Air-Cooled Heat Exchanger Application Scenarios
Fracturing Tower Top Oil and Gas Cooling: The gasoline and liquefied petroleum gas mixture (temperature approximately 100-130°C) discharged from the coking tower is cooled to 40-50°C via an air-cooled heat exchanger before entering a separator to separate the oil, gas, and water.
Wax Oil and Diesel Side Cooling: Wax oil (temperature approximately 320-360°C) and diesel (temperature approximately 250-280°C) extracted from the fractionating tower are initially cooled to 120-160°C via an air cooler and then cooled to storage temperature via a water cooler.
Coking Tower Top Oil and Gas Cooling: During coking tower switching, residual oil and gas discharged from the top of the tower (temperature approximately 300-350°C) are rapidly cooled to 80-100°C via an air-cooled heat exchanger to prevent coking in subsequent pipelines.
V. Air-Cooled Heat Exchanger Catalytic Reforming Section (Gasoline Upgrading and Aromatics Production)
1. Process Overview
Catalytic reforming uses straight-run gasoline as a feedstock. A catalyst (reaction temperature 480-520°C) is used to carry out reactions such as cycloalkane dehydrogenation and alkane cyclization to produce high-octane gasoline or benzene, toluene, and xylene (BTX). The reaction products require cooling and separation.
2. Air-Cooled Heat Exchanger Application Scenarios
Reforming Product Cooling: The reformed oil and circulating hydrogen mixture at the reactor outlet (temperature approximately 480-520°C) is first cooled to 180-220°C via a heat exchanger for heat recovery. It is then cooled to 40-50°C via an air-cooled heat exchanger before entering a high-pressure separator to separate the circulating hydrogen and the reformed oil.
Stabilizer Tower Overhead Oil and Gas Cooling: The reformed oil passes through the stabilizer tower to separate the light components (liquefied petroleum gas and propane). The overhead oil and gas (temperature approximately 90-110°C) is then cooled to 35-45°C via an air-cooled heat exchanger before entering a separator to recover the light hydrocarbons.
VI. Air-Cooled Heat Exchanger Summary
In the refining and petrochemical industries, air-cooled heat exchangers are centrally used for product cooling in various process stages, cooling oil and gas prior to separation, and cooling circulating media. This is particularly true in core processes such as atmospheric and vacuum distillation, catalytic cracking, and hydrogenation. They are crucial equipment for ensuring product quality and separation efficiency, and are also a crucial technical means of reducing water consumption in cooling systems and adapting to the needs of refineries in water-scarce regions.
Their application requires consideration of the process temperature and media characteristics (such as corrosiveness and coking tendency) to determine the appropriate air-cooled heat exchanger structure (e.g., horizontal, inclined-top) and material (e.g., carbon steel, stainless steel).
