Five basic parameters of compressor units

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Basic parameters of the five major compressor units: 1. Air compressor – a multi-axis compressor driven by a extraction steam turbine. In an ammonia synthesis plant, about 21,000 Nm3 of air is required per hour. This air is compressed by air compressors to 3.65 MPa, then sent to an air heater where it is heated to 520°C before entering the two-stage converter for the gas generation reaction. Furthermore, to prevent corrosion of the equipment and pipelines in the urea plant, the oxygen content in the raw material CO2 is required to be at least 0.6% (by volume). Therefore, air with a flow rate of 1172 Nm3 per hour must be drawn from the third-stage outlet of the air compressor and sent to the outlet of the first-stage separator of the CO2 compressor; this air is known as anti-corrosion air (pressure: 0.83 MPa, flow rate: 1172 Nm3). Inlet pressure: 0.017 MPa; Inlet temperature: 19°C; Outlet pressure: 3.65 MPa; Outlet temperature: Steam conditions: 8.6 MPa high-pressure steam drives the turbine. Compressor type: two-stage, six-stage; Flow regulation method: inlet guide vanes + variable speed; Anti-surge bypass: two-stage venting. Turbine power: 4900 KW; Turbine speed: 10500 rpm/min. Requirement for impurities in the air entering the compressor: less than 0.03 mg/m3. 2. Feed gas compressor: multi-axis compressor, driven by a backpressure turbine. In ammonia synthesis, the source of hydrogen is acetylene off-gas, which is the exhaust gas produced when natural gas is partially oxidized to generate acetylene. Its composition mainly consists of H2 (about 60%), CO (about 28%), CO2 (about 3%), CH4 (about 5%), along with small amounts of N2, O2, C2H2, C2H4, Ar, etc. Under normal operating conditions, a 190,000-ton synthetic ammonia plant requires 55,000 Nm3 of feed gas per hour. The feed gas is compressed to 3.85 MPa by a feed gas compressor, after which it undergoes desulfurization, hydrogenation, and heating (to 520°C in a feed gas heater) before entering the second-stage converter for the gas generation reaction. Inlet pressure: 0.9 MPa; Inlet temperature: 30°C; Outlet pressure: 3.85 MPa; Outlet temperature: Steam conditions: 3.6 MPa medium-pressure steam driving the turbine. Compressor type: two-stage, five-stage; Flow regulation method: inlet guide vanes + variable speed; Anti-surge bypass: automatic. Turbine power: 4800 KW; Turbine speed: 6000 rpm/min. 3. Syngas compressor: high and low pressure cylinders, driven by a extraction-type turbine (double-shaft structure). The syngas compressor, also known as a pressure combiner, involves the compression of both fresh syngas and recycled syngas. After the fresh syngas, which has undergone decarburization and medium-low temperature methanation processes, is mixed with the hydrogen recovered by the membrane separation system, it passes through the first and second stage exit coolers as well as the exit separator. Thereafter, it is compressed from 2.94 MPa to 13.5 MPa by the fresh stage of the syngas compressor, and then enters the make-up gas ammonia cooler (in the synthesis process), where it mixes with the recycled gas prior to compression. The recycled gas that comes out of the ammonia synthesis tower, after heat recovery and cryogenic ammonia separation (coming from the heat exchanger at a temperature of about 25°C and a pressure of about 13.2 MPa), is compressed to 14.2 MPa in the compression stage of the syngas compressor before being returned to the synthesis process (via the heat exchangers at the inlet and outlet of the tower) and entering the ammonia synthesis tower. Process flow: The fresh gas from medium-low temperature methanization and the hydrogen recovered by membrane separation are mixed together; the resulting gas is compressed in the fresh gas section of the syngas compressor and then enters the make-up gas ammonia cooler, the make-up gas separator, the No. 2 ammonia cooler, the No. 2 separator, and the heat exchanger at a pressure of 13.5 MPa. It subsequently enters the cycle section at a pressure of 13.2 MPa ； The gas compressed in the circulation section enters the ammonia synthesis tower via the inlet and outlet heat exchangers at a pressure of 14.2 MPa. Inlet pressure: 2.94 MPa; Inlet temperature: 40°C; Outlet pressure of the fresh gas section: 13.5 MPa; Inlet pressure/temperature of the circulation section: 13.2 MPa/25°C; Outlet pressure of the circulation section: 14.2 MPa; Steam conditions: 8.6 MPa high-pressure steam driving the turbine. Compressor type: two-cylinder, three-stage design, with 9+8+1 stages (the first stage is a low-pressure cylinder, while the second and circulation stages are high-pressure cylinders). Flow regulation method: variable speed. Anti-surge bypass systems: backflow in the low-pressure and high-pressure cylinders, as well as backflow in the circulation section. Turbine power: 7106 KW; Turbine speed: 12214 rpm/min. 4. Ammonia compressor: multi-shaft compressor, driven by an electric motor. After the synthetic cycle gas and make-up gas (fresh gas) are cooled in the ammonia cooler, the liquid ammonia separated in the ammonia separator enters the shell side of the ammonia cooler after depressurized flashing. The liquid ammonia coming out of the shell side of the ammonia cooler (Ammonia Cooler No. 2) is the finished ammonia. The gaseous ammonia coming out of the shell sides of the ammonia coolers (Ammonia Cooler No. 1, Ammonia Cooler No. 2, and Make-up Gas Ammonia Cooler), as well as the gaseous ammonia vaporized from the liquid ammonia storage tank, enters the ammonia compressor where it is compressed to 1.65 MPa before being cooled to become liquid ammonia ready for use. Gaseous ammonia coming from the shell side of the No. 1 ammonia cooler and the liquid ammonia storage tank enters the first stage of the ammonia compressor, while gaseous ammonia coming from the shell side of the No. 2 ammonia cooler enters the make-up air section of the compressor. Inlet pressure: 0.24 MPa; Inlet temperature: -12°C; Make-up air pressure: 0.5 MPa; Make-up air temperature: 4°C; Outlet pressure: 1.65 MPa; Outlet temperature: Compressor type: two-stage, four-speed; Flow regulation method: inlet guide vanes + variable speed; Anti-surge bypass: automatic; Motor power: 2300 KW. 5. CO2 compressor: High and low-pressure cylinder compressors, driven by a fully condensed steam turbine. The CO2 gas from the decarburization process of the ammonia synthesis plant is sent to the urea plant as one of the raw materials for urea production. In addition to being used for urea production, some of the CO2 gas is sent to the potassium carbonate plant in the potash industry, while the remaining excess CO2 gas is vented. CO2 from the decarburization process in ammonia synthesis (the CO2 regeneration tower of the decarburization unit) enters the inlet separator, then proceeds to the first stage of the CO2 compressor. After passing through the inter-stage cooler and inter-stage separator of stage 1, it moves on to the second stage of the compressor; from there, it goes through the inter-stage cooler and inter-stage separator of stage 2 before reaching stage 3 of the compressor. Subsequently, it passes through the dehydrogenation reactor, inter-stage cooler, and inter-stage separator to reach stage 4, and finally the compressed gas is sent to the CO2 stripping tower in the synthesis and recycling process of the urea plant. Therein, anti-corrosion air from the third stage of the air compressor (pressure: 0.83 MPa, flow rate: 1172 Nm3/h) is added at the outlet of the inter-stage separator of the first stage of the CO2 compressor, and enters the second stage along with the gaseous CO2. The gas from the third stage outlet of the CO2 compressor (with a temperature of approximately 190°C and a pressure of approximately 8.25 MPa) enters the dehydrogenation reactor; after dehydrogenation, cooling, and separation, it proceeds to the fourth stage of the compressor for further compression. Due to its high pressure ratio (compressing from 0.14 MPa to 14.8 MPa) and low flow rate (the exhaust volume under normal operating conditions is less than 18,000 Mm3/h), CO2 compressors require very high standards in terms of their pneumatic design. Inlet pressure: 0.14 MPa; Inlet temperature: 40°C; Outlet pressure: 14.8 MPa; Outlet temperature: Steam conditions: Medium-pressure steam at 3.6 MPa driving the turbine. Compressor type: Two-cylinder, four-stage, 13-stage. Flow regulation method: Variable speed. Anti-surge bypass: Two-in-one (one set), four-in-three (one set), four-stage outlet venting. Turbine power: 5916 KW; Turbine speed: 9180 rpm/min