Ningxia Coal Air Separation Process Flow

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III. Introduction to the Process Flow 1. Air Filter and Air Compression System This system consists of a self-cleaning air filter and a turbine air compressor (driven by a steam turbine). Dusty air enters the air filter, where mechanical particles and dust are removed. The filtered air enters the air compression system, where it is compressed to 0.52 MPa.G before proceeding to the air pre-cooling system. 2. Air pre-cooling system: This system mainly consists of an air cooling tower, a water cooling tower, and four water pumps. The air cooling tower is equipped with two layers of packing. Air at a pressure of 0.52 MPa(G) and a temperature of 105°C is fed into the bottom of the tower, passes through the packing layer from bottom to top, and is cooled by water flowing from top to bottom. This process also removes harmful impurities such as NOx, SO2, and Cl+ from the air. Finally, the air passes through a wire mesh separator at the top before entering the molecular sieve purification system. The temperature of the air exiting the air-cooled tower is approximately 15°C. The moisture entering the air-cooled tower is in two stages. The lower section is fed with 32°C cooling water supplied by the cooling tower in the water supply and drainage section; this water is pressurized by a circulation pump and sent to the middle part of the air-cooling tower, from where it returns to the cooling tower in the water supply and drainage section from the bottom up. The water in the upper section is chilled water at 14°C, obtained through heat exchange cooling of excess nitrogenous gas from the water cooling tower and the distillation tower; after being pressurized by a chilled water pump, it is sent to the top of the air cooling tower, where it joins the cooling water from the middle section and is returned to the cooling tower in the water treatment section. 3. Air purification system: This system is mainly composed of two adsorbers, a steam heater, and an electric heater. The molecular sieve adsorber has a horizontal double-bed structure, with active alumina in the lower layer and molecular sieve in the upper layer; the two adsorbers operate in alternating fashion. The air coming from the air cooling tower is passed through an adsorber to remove water, CO2, and CnHm from it; after that, aside from a portion that is used as feed air for the booster compressor as well as for instrument air and process air, the remaining air all enters the distillation tower to participate in the distillation process. While one adsorber is in operation, the other is being regenerated and cooled as a backup. The contaminated nitrogen gas coming from the fractionation tower is heated to 170°C by a steam heater, then fed into an adsorber for heating and regeneration in order to remove the absorbed water and CO2. After regeneration is complete, it is cooled using contaminated nitrogen gas and set aside for use. During high-temperature activation regeneration, the regeneration gas is heated to 260°C using a steam heater and an electric heater before being fed into the adsorber for heating and regeneration. The moisture content in the air purified by the adsorber is below a dew point of –70°C, with CO2 at ≤1PPm. 4. The booster compressor system: Clean air from the molecular sieve adsorber enters the booster compressor, where it is pressurized to increase its pressure. The pressurized air is divided into two streams; one stream (with a flow rate of 31,500 Nm3/h and a pressure of 2.6 MPa.G) is drawn out from the middle of the booster compressor, cooled, and then fed into the booster driven by an expander ； Another stream (flow rate of 47,000 Nm3/h, pressure of 7.0 MPa.G) is taken from the final stage of the booster compressor, cooled, and then fed into the main heat exchanger. 5. Pressurized expansion turbine system: This system mainly consists of two pressurized turbine expanders, two aftercoolers for the pressurizers, and two oil supply units. The pressurized air, which has been drawn from the booster compressor and cooled, enters the booster driven by an expander; the energy output by the expander is utilized to further increase the pressure of the air. After entering the cooler in the booster, the air is cooled to the desired temperature and then proceeds to the main heat exchanger, where it is cooled to a certain temperature by the returning liquid oxygen, nitrogen, and contaminated nitrogen before entering the turbine expander for expansion. The expanded air then enters the lower column to participate in the distillation process. 6. Oxygen and nitrogen distillation: This system mainly consists of a lower column, a main condensation evaporator, an upper column, a subcooler, and an liquid oxygen pump. The process air coming from the purification system is cooled to near the dew point in the low-pressure main heat exchanger, after which it is divided into two streams. One stream enters the nitrogen booster where it is liquefied and then sent to the lower column, while the other stream combines with the expanded air and the high-pressure air from the final stage cooler of the booster compressor; together these gases are liquefied in the high-pressure main heat exchanger before being sent to the lower column. Through distillation in this column, nitrogen is obtained at the top. Apart from a portion that is used as a heat source for the pure argon column, the remaining nitrogen is condensed in a condensing evaporator. Part of the condensed liquid serves as reflux for the lower column, while another portion is sent to the nitrogen booster where it is vaporized by air and then reheated in the high-pressure main heat exchanger to be used as a product. The rest of the liquid is subcooled in a cooler; part of it is taken out of the cryogenic tank as liquid nitrogen product, a small amount is used as a heat source for the pure argon condenser, and the remaining portion is throttled and used as reflux for the upper column, sent to the top of that column. The contaminated liquid nitrogen obtained at the lower part of the lower column is subcooled in a cooler and then throttled to the upper part of the upper column to participate in distillation. At the bottom of the lower column, oxygen-enriched liquid air is obtained; after being subcooled in a cooler, part of it serves as a cooling source for the crude argon column, while the rest is throttled to the middle section of the upper column to participate in distillation. Through rectification in the upper tower, contaminated nitrogen gas is obtained at the top. After being reheated in a cooler, this gas is divided into two streams: one stream enters the water-cooled tower for cooling via the high-pressure main heat exchanger, while the other stream is reheated in the low-pressure main heat exchanger; aside from a portion that is used as gas for the regeneration of the purification system, the remaining part is also sent to the water-cooled tower for cooling. Liquid oxygen is drawn from the bottom of the main condensation evaporator; part of it is taken out as liquid oxygen product from the cryogenic tank, while the remaining part is pressurized by a liquid oxygen pump and sent to the high-pressure main heat exchanger for reheating before being fed into the vaporization furnace. To facilitate argon adjustment, a bypass valve for oxygen gas (to waste nitrogen gas) has also been installed. 7. Argon distillation: This system mainly consists of crude argon column I, crude argon column II, crude argon condenser, pure argon column along with its condenser and evaporator, as well as process liquid argon pumps. The argon fraction gas drawn from the middle part of the upper tower enters crude argon column I for distillation, thereby reducing the oxygen content. The reflux liquid of Crude Argon Column I is liquid crude argon drawn from the bottom of Crude Argon Column II and transported by a process liquid argon pump. The liquid at the bottom of Column I for crude argon is returned to the upper column to participate in distillation. The gas drawn from the top of crude argon column I enters the bottom of crude argon column II, where further separation of argon and oxygen takes place within the column. As a result, crude argon with O2 ≤ 2 PPm is obtained at its top. After being condensed into a liquid by the crude argon condenser, the crude argon is returned to Column II as a reflux stream. The cooling source for the crude argon condenser comes from the oxygen-enriched liquid air drawn out after the subcooler; this oxygen-enriched liquid air exchanges heat (evaporates) with the crude argon gas before returning to the upper column to participate in the distillation there. An appropriate amount of crude argon with O2 content ≤ 2 PPm is drawn from the plate-type unit of the crude argon condenser and fed into the middle section of the pure argon column. Through distillation in this column, qualified liquid argon is obtained at its bottom. While a portion of this liquid argon is sent as a product out of the cryogenic tank via a control valve and into the liquid argon storage system, the remaining portion exchanges heat with medium-pressure nitrogen coming from the lower part of the column inside the evaporator of the pure argon column, thereby vaporizing and becoming gas that participates in the distillation process within the column. The liquefied liquid nitrogen then returns to the top of the upper column to participate in the distillation there. The top of the pure argon column is equipped with a condenser that condenses the rising gaseous argon into a liquid, which serves as the reflux fluid for the pure argon column. The cooling source for this condenser is liquid nitrogen coming from the subcooler; after evaporating, this liquid nitrogen returns to the pipeline leading to the column outlet.