Motor-driven cascade refrigeration compressor unit

Abstract

The utility model discloses a motor-driven cascade refrigeration compressor unit. The motor-driven cascade refrigeration compressor unit comprises an asynchronous motor, a carbon dioxide compressor, an ammonia compressor and the like, the utility model relates to a motor-driven cascade refrigeration compressor unit which is used in the modern coal chemical industry and is driven by a motor under the conditions of the same rotating speed, different working media and different working conditions, namely the cascade refrigeration compressor unit driven by a motor with a deep refrigeration working medium of CO2 / NH3. The unit is a skid-mounted integrated body with a carbon dioxide compressor and an ammonia compressor which are driven by the same asynchronous motor, are coaxial, have the same rotating speed and have the same chassis, and is used for completing cascade refrigeration by coupling two refrigerants CO2 / NH3 in a chemical device instead of an ammonia compressor adopting single ammonia refrigeration under the working condition that the cryogenic temperature is less than or equal to-40 DEG C; in addition, the asynchronous motor is used for providing power, and compared with the mode that a steam turbine is used as a power source, the asynchronous motor is more environmentally friendly and safer in operation.

Description

Technical Field

[0001] This utility model relates to the field of modern coal chemical technology, and in particular to a motor-driven cascade refrigeration compressor unit. Background Technology

[0002] In traditional coal chemical industry, carbon dioxide compressors are mainly used in urea production units of the nitrogen fertilizer industry. CO2 gas is typically compressed to 14.5 MPa before entering the urea synthesis tower as a raw material for urea production. CO2 compressors are also used in the production of liquid CO2 and dry ice. However, CO2 is not currently used as a refrigerant in chemical plants. In modern coal chemical industry's pulverized coal pressurized gasification units, CO2 compressors are used for pressurized conveying of pulverized coal. Ammonia compressors, which use ammonia as a refrigerant, are widely used in chemical plants, especially in the synthetic ammonia production of the nitrogen fertilizer industry, where all refrigeration during ammonia synthesis is handled by ammonia compressors.

[0003] In coal chemical gas purification, the refrigerant in low-temperature methanol washing units for removing sulfur and carbon dioxide is almost always ammonia, and ammonia compressors are used. While ammonia compressors are highly efficient under standard operating conditions (-15℃), they become less efficient at cryogenic temperatures such as -40℃, resulting in a 50% reduction in compression efficiency and a significant increase in energy consumption. Furthermore, ammonia evaporates at ≤-40℃, causing negative pressure at the compressor's suction pressure, which is unsafe. Additionally, ammonia has a relatively small molecular weight. In large-scale coal chemical low-temperature methanol washing units requiring ≤-40℃ refrigeration, using ammonia as the sole refrigerant not only leads to low compressor efficiency but also significantly increases the size of the pipelines, valves, and fittings used to transport ammonia gas.

[0004] With the rapid development and large-scale expansion of modern coal chemical industry, the demand for energy conservation and carbon reduction has become more urgent. However, existing refrigeration units that integrate carbon dioxide compressors and ammonia compressors have high energy consumption and high costs, and cannot meet the requirements of green, energy-saving, and emission-reducing modern production.

[0005] Therefore, whether an improved refrigeration compressor assembly can be provided based on the shortcomings of existing technologies is a technical problem that urgently needs to be solved by those skilled in the art. Utility Model Content

[0006] The technical problem to be solved by this utility model is to overcome the defects in the prior art and provide a motor-driven cascade refrigeration compressor unit.

[0007] The present invention solves the above-mentioned technical problems through the following technical solution:

[0008] A motor-driven cascade refrigeration compressor unit, comprising:

[0009] Asynchronous motor, equipped with a frequency converter;

[0010] A carbon dioxide compressor is used to compress CO2, which is used as a refrigerant.

[0011] Ammonia compressor, used to compress NH3 as a refrigerant;

[0012] The carbon dioxide compressor and the ammonia compressor share the same asynchronous motor for drive. The asynchronous motor, the carbon dioxide compressor, and the ammonia compressor are configured to be coaxial and have the same rotation speed, and their chassis are integrated into a single structure.

[0013] The first compressor inlet gas-liquid separator is connected to the inlet of the carbon dioxide compressor;

[0014] The second compressor inlet gas-liquid separator is connected to the inlet of the ammonia compressor;

[0015] The CO2 / NH3 condenser-evaporator is connected to the outlet of the carbon dioxide compressor and to the inlet gas-liquid separator of the second compressor.

[0016] An ammonia condenser is connected to the outlet of the ammonia compressor;

[0017] A liquid ammonia tank is connected to the outlet of the ammonia condenser;

[0018] The NH3 power-saving device is connected to the liquid ammonia tank, the gas-liquid separator at the inlet of the second compressor, and the CO2 / NH3 condenser-evaporator.

[0019] The CO2 economizer is connected to the CO2 / NH3 condenser-evaporator and to the gas-liquid separator at the inlet of the first compressor.

[0020] A liquid CO2 tank, connected to the CO2 economizer;

[0021] The asynchronous motor has a single output shaft, and the carbon dioxide compressor and the ammonia compressor are configured on the same side of the asynchronous motor. Alternatively, the asynchronous motor has two output shafts, with one shaft directly connected to the carbon dioxide compressor and the other shaft directly connected to the ammonia compressor.

[0022] Preferably, the carbon dioxide compressor is a single-stage centrifugal compressor or a multi-stage centrifugal compressor.

[0023] Preferably, the ammonia compressor is a multi-stage centrifugal compressor.

[0024] Preferably, the inlet pressure of the carbon dioxide compressor is 0.8-1.0 MPa, and the outlet pressure is 2.6-2.8 MPa.

[0025] Preferably, the load of the ammonia compressor is matched with that of the carbon dioxide compressor to operate NH3 as a refrigerant at -15°C.

[0026] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of this utility model.

[0027] The positive and progressive effects of this utility model are as follows: The motor-driven cascade refrigeration compressor unit of this utility model includes an asynchronous motor, a carbon dioxide compressor, an ammonia compressor, a first compressor inlet gas-liquid separator, a second compressor inlet gas-liquid separator, a CO2 / NH3 condenser-evaporator, an ammonia condenser, a liquid ammonia tank, an NH3 economizer, a CO2 economizer, and a liquid CO2 tank. This motor-driven cascade refrigeration compressor unit is used in modern coal chemical industry for motor-driven cascade refrigeration compressor units operating at the same speed with different working media and under different conditions; specifically, it is a motor-driven cascade refrigeration compressor unit with CO2 / NH3 as the deep refrigeration working media. This unit is a skid-mounted integrated unit with a carbon dioxide compressor and an ammonia compressor driven by the same asynchronous motor, coaxial, rotating at the same speed, and on the same chassis. It achieves cascade refrigeration using the coupling of two refrigerants, CO2 and NH3, in chemical plants, replacing the use of a single ammonia compressor for cryogenic temperatures ≤-40℃, thereby achieving energy saving, reduced investment, and reduced carbon emissions. Furthermore, this invention uses an asynchronous motor for power, which is more environmentally friendly and safer to operate than using a steam turbine as a power source. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the motor-driven cascade refrigeration compressor unit of Embodiment 1 of this utility model.

[0029] Figure 2 This is a schematic diagram of the motor-driven cascade refrigeration compressor unit of Embodiment 2 of this utility model.

[0030] Explanation of reference numerals in the attached figures:

[0031] Carbon dioxide compressor 1

[0032] Ammonia compressor 2

[0033] Asynchronous motor 3

[0034] Axis 4

[0035] Skid-mounted structure 5

[0036] CO2 / NH3 condenser evaporator 6

[0037] CO2 Economizer 7

[0038] Liquid CO2 tank 8

[0039] Ammonia condenser 9

[0040] 10 liquid ammonia tanks

[0041] NH3 power saving device 11

[0042] First compressor inlet gas-liquid separator 12

[0043] Second compressor inlet gas-liquid separator 13

[0044] Chemical Cold Zone 14 Detailed Implementation

[0045] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present utility model or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present utility model without creative effort are within the scope of protection of the present utility model.

[0046] It should be noted that in the claims and specification of this patent, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0047] Example 1

[0048] like Figure 1 As shown, this embodiment discloses a motor-driven cascade refrigeration compressor unit, which includes an asynchronous motor 3, a carbon dioxide compressor 1, an ammonia compressor 2, a first compressor inlet gas-liquid separator 12, a second compressor inlet gas-liquid separator 13, a CO2 / NH3 condenser-evaporator 6, an ammonia condenser 9, a liquid ammonia tank 10, an NH3 economizer 11, a CO2 economizer 7, and a liquid CO2 tank 8.

[0049] In this embodiment, the asynchronous motor 3 has two output shafts, with one shaft 4 directly connected to the carbon dioxide compressor 1 and the other shaft 4 directly connected to the ammonia compressor 2.

[0050] Carbon dioxide compressor 1 is used to compress CO2, the refrigerant. Compressor 1 is a single-stage or multi-stage centrifugal compressor. It can regenerate and desorb CO2 removed from the low-temperature methanol washing unit in coal chemical industry, sending high-, medium-, and atmospheric-pressure CO2 gases to different stages of compressor 1 respectively. Finally, the pressure is increased to 2.6 MPa, where the refrigerant from ammonia compressor 2 is used to completely liquefy the CO2, enabling CO2 capture, utilization, and storage (CCUS) in coal chemical industry. The medium in carbon dioxide compressor 1 is CO2, which provides deep cooling (temperature ≤ -40℃) to external chemical plants. The compressor inlet pressure is 0.8–1.0 MPa, and the outlet pressure is 2.6–2.8 MPa. The compressor load is determined based on the required deep cooling capacity from the external environment.

[0051] Ammonia compressor 2 is used to compress NH3 as a refrigerant. Ammonia compressor 2 is a multi-stage centrifugal compressor, and its load is matched with that of carbon dioxide compressor 1 to operate NH3 as a refrigerant at -15℃. The NH3 refrigerant in ammonia compressor 2 is condensed into liquid by a shared CO2 / NH3 condenser-evaporator 6, which condenses the gaseous CO2 from carbon dioxide compressor 1. Its load is matched with that of carbon dioxide compressor 1 to ensure that the NH3 refrigerant operates under standard conditions (-15℃). The NH3 refrigerant circulates only within the cascade refrigeration unit system, thus meeting the cryogenic temperature requirements of chemical plants while saving energy and reducing consumption. Furthermore, the entry of CO2 into the chemical refrigeration zone 14 is safer and more reliable.

[0052] In this system, carbon dioxide compressor 1 and ammonia compressor 2 share a single asynchronous motor 3. The asynchronous motor 3, carbon dioxide compressor 1, and ammonia compressor 2 are configured coaxially (same shaft 4), operate at the same speed, and their chassis are integrated into a single structure, sharing a single skid-mounted structure 5. Carbon dioxide compressor 1 and ammonia compressor 2 are driven by the asynchronous motor 3 on the same shaft and operate at the same speed. Under given operating conditions, the speed of ammonia compressor 2 is first set, and then matched to the speed of carbon dioxide compressor 1. Then, based on the same speed, the impeller structure of each centrifuge is optimized to achieve matched control of the two compressors under different working fluids and operating conditions at the same speed. The three machines are integrated into a single skid-mounted structure 5. Within the rated speed, maximum speed, and operating speed range, thermodynamic analysis of the unit shows that the overall vibration value is minimized during acceleration and deceleration when the load changes, ensuring stable operation. Furthermore, the compact design minimizes shaft vibration and displacement, ensuring stable operation of the unit.

[0053] The first compressor inlet gas-liquid separator 12 separates the liquid droplets carried during the evaporation of liquid CO2 to prevent liquid from being carried into the carbon dioxide compressor 1 and causing liquid hammer. The first compressor inlet gas-liquid separator 12 is connected to the inlet of the carbon dioxide compressor 1. The second compressor inlet gas-liquid separator 13 separates the liquid droplets carried during the evaporation of liquid NH3 to prevent liquid NH3 from being carried into the ammonia compressor 2 and causing liquid hammer. The second compressor inlet gas-liquid separator 13 is connected to the inlet of the ammonia compressor 2. The CO2 / NH3 condenser-evaporator 6 liquefies the pressurized gaseous CO2 through NH3 evaporation and cooling. The CO2 / NH3 condenser-evaporator 6 is connected to the outlet of the carbon dioxide compressor 1 and to the second compressor inlet gas-liquid separator 13. The ammonia condenser 9 liquefies the pressurized gaseous NH3 through water cooling. The ammonia condenser 9 is connected to the outlet of the ammonia compressor 2. The liquid ammonia tank 10 is connected to the ammonia condenser 9. The NH3 energy-saving device 11 is connected to the liquid ammonia tank 10, the second compressor inlet gas-liquid separator 13, and the CO2 / NH3 condenser-evaporator 6. The CO2 economizer 7 is connected to the CO2 / NH3 condenser-evaporator 6 and to the inlet gas-liquid separator 12 of the first compressor. The liquid CO2 tank 8 is connected to the CO2 economizer 7. The carbon dioxide compressor 1 is equipped with the CO2 economizer 7, and the ammonia compressor 2 is equipped with the NH3 economizer 11, which can achieve energy saving.

[0054] Before the motor-driven cascade refrigeration compressor unit in this embodiment is put into operation, the sealing system, the oil system, the power supply to the asynchronous motor 3, and the shaft seal system are established. Both the carbon dioxide compressor 1 and the ammonia compressor 2 are purged with nitrogen and pressurized to 0.4 MPa. Then, the asynchronous motor 3 is controlled by the frequency converter to run at low speed and start according to the start-up procedure, matching and controlling the operation of the carbon dioxide compressor 1 and the ammonia compressor 2.

[0055] First, ammonia compressor 2 is loaded and liquid CO2 is prepared. Low-pressure CO2 (1.0 MPa) gas is introduced from outside the chemical cold zone 14 to carbon dioxide compressor 1, pressurized to 2.6 MPa, and sent to the tube side of CO2 / NH3 condenser-evaporator 6. Liquid ammonia, which has been pre-filled into liquid ammonia tank 10, is sent to the shell side of CO2 / NH3 condenser-evaporator 6 via NH3 economizer 11. NH3 and CO2 exchange heat, gaseous CO2 condenses and liquefies, and liquid ammonia evaporates. The -15℃, 0.24 MPa gaseous ammonia enters the first stage of ammonia compressor 2. The outlet of ammonia compressor 2 is vented to remove nitrogen. After outlet gas analysis, when the ammonia concentration is ≥98%, it is sent to ammonia condenser 9. The condensed liquid ammonia enters liquid ammonia tank 10. The -10℃ liquid CO2 prepared by CO2 / NH3 condenser-evaporator 6 is cooled to -15℃ by CO2 economizer 7 and sent to liquid CO2 condenser 9. In the O2 tank, liquid CO2 is drawn from the tank and sent to the chemical plant area as a refrigerant, such as the low-temperature methanol washing unit or the ammonia synthesis unit. The liquid CO2 evaporates at -40℃ to -42℃ and 0.9 to 1.0 MPa. The gaseous CO2 returns to the CO2 economizer 7 of the motor-driven cascade refrigeration compressor unit to pre-cool the liquid CO2 from the CO2 / NH3 condenser-evaporator 6. The gaseous CO2 is heated to -25℃ and enters the carbon dioxide compressor 1, which pressurizes it to 2.6 to 2.8 MPa. The CO2 gas then enters the CO2 / NH3 condenser-evaporator 6 to exchange heat with the ammonia refrigerant provided by the ammonia compressor 2. The NH3 is refrigerated and vaporized under standard operating conditions (-15℃), and the gaseous CO2 is liquefied. This cycle continues.

[0056] The speed of the motor-driven cascade refrigeration compressor unit is determined by the load of the ammonia compressor 2, and the operation of the carbon dioxide compressor 1 is matched and controlled. The matching program follows the principle of "increasing speed before increasing pressure and decreasing pressure before decreasing speed" to adapt to the load changes of the chemical plant and ensure long-term stable operation.

[0057] In this embodiment, the motor-driven cascade refrigeration compressor unit uses both CO2 and NH3 as refrigerants. The CO2 compressor provides deep cooling to the chemical plant, and the discharged liquid CO2 evaporates at -40℃ to -42℃ at a pressure of 0.8 to 1.0 MPa. The gaseous CO2 returned from the chemical plant is pressurized to 2.6 to 2.8 MPa by the CO2 compressor 1. The ammonia compressor 2 in the motor-driven cascade refrigeration compressor unit provides ammonia refrigerant. In the CO2 / NH3 condenser-evaporator 6, liquid ammonia evaporates at -14℃ to -15℃ at a pressure of ~0.24 MPa to provide cooling, condensing and liquefying the gaseous CO2. The gaseous ammonia is then pressurized to 1.7 MPa by the ammonia compressor 2 and cooled and condensed into liquid ammonia by circulating water. The CO2 compression and ammonia compression operate cyclically under different operating conditions. CO2 is an inert medium with a molecular weight of 44. It provides a relatively high gas phase pressure (1.0 MPa) at ultra-low temperatures (-40℃ to -42℃) and is suitable for use in chemical plants. Ammonia, on the other hand, is a toxic, flammable, and explosive medium with a molecular weight of 17. It only circulates within the cascade refrigeration unit and operates under standard conditions (-15℃), exhibiting high compression efficiency. CO2 has a higher pressure and larger molecular weight at ultra-low temperatures than ammonia, resulting in significantly smaller gas delivery pipelines, valves, and fittings for the same cooling capacity. This allows the motor-driven cascade refrigeration compressor unit to achieve energy savings, reduced investment, and safer operation compared to traditional single-ammonia refrigeration compressors. Furthermore, this invention uses an asynchronous motor for power, which is more environmentally friendly and safer than using a steam turbine as a power source. In the ammonia synthesis unit of the nitrogen fertilizer industry, a motor-driven cascade refrigeration compressor unit replaces the single ammonia refrigeration system. The carbon dioxide compressor 1 provides -42℃ cooling capacity, which can cool the ammonia synthesis cycle gas to -35℃. The ammonia content in the gas entering the ammonia synthesis tower is reduced from the traditional 2.6% to 0.6%, improving the net ammonia value. The synthesis cycle gas volume is reduced by 20%, and the NH3 refrigerant only exchanges heat with the CO2 refrigerant efficiently within the cascade refrigeration compressor unit boundary, which saves energy and reduces investment.

[0058] This embodiment of the motor-driven cascade refrigeration compressor unit uses both CO2 and NH3 as refrigerants. It innovatively integrates a carbon dioxide compressor 1 and an ammonia compressor 2 into a cascade refrigeration unit, thus solving the problems associated with using only ammonia as a refrigerant. This not only results in low efficiency for the ammonia compressor 2 but also significantly increases the size of the pipelines, valves, and fittings used to transport gaseous ammonia. This achieves substantial energy savings, carbon reduction, and lower investment. The carbon dioxide compressor 1 provides deep cooling (-40℃ to -42℃) to the chemical plant, while the ammonia compressor 2 operates under standard conditions (-15℃), compressing and boosting carbon dioxide to condense CO2 gas back into liquid CO2, repeating the cycle. This unit is driven by an asynchronous motor 3, and is a skid-mounted cascade refrigeration compressor unit with three coaxial (same shaft 4), same speed, different refrigerants, and different operating conditions. Modern coal chemical processes, whether pulverized coal gasification or coal-water slurry gasification, are generally equipped with gas purification devices, namely low-temperature methanol washing. Cascade refrigeration units not only provide deep cryogenic cooling capacity but also capture almost all of the CO2 gas desorbed from the low-temperature methanol washing regeneration system. This CO2 is then liquefied and utilized or stored by a motor-driven cascade refrigeration compressor unit, playing a role in the field of (CCUS). Motor-driven cascade refrigeration compressor units can also provide deep cooling capacity of -42°C to ammonia synthesis units, cooling the temperature of ammonia-containing synthesis gas to -35°C. This reduces the NH3 content in the inlet gas of the synthesis tower from 2.6-2.7% to 0.6%, increasing the net value of synthesized ammonia by 2% and reducing the circulating gas volume of ammonia synthesis by 20%, significantly reducing energy consumption.

[0059] Example 2

[0060] like Figure 2 As shown, the difference between this embodiment and Embodiment 1 is that:

[0061] The asynchronous motor 3 has a single output shaft, with the motor on one side and the shaft 4 on the other side directly connected to the carbon dioxide compressor 1 and the ammonia compressor 2.

[0062] Everything else is the same as in Example 1, and will not be repeated here.

Claims

1. A motor-driven cascade refrigeration compressor unit, characterized in that, include: Asynchronous motor, equipped with a frequency converter; A carbon dioxide compressor is used to compress CO2, which is used as a refrigerant. Ammonia compressor, used to compress NH3 as a refrigerant; The carbon dioxide compressor and the ammonia compressor share the same asynchronous motor for drive. The asynchronous motor, the carbon dioxide compressor, and the ammonia compressor are configured to be coaxial and have the same rotation speed, and their chassis are integrated into a single structure. The first compressor inlet gas-liquid separator is connected to the inlet of the carbon dioxide compressor; The second compressor inlet gas-liquid separator is connected to the inlet of the ammonia compressor; The CO2 / NH3 condenser-evaporator is connected to the outlet of the carbon dioxide compressor and to the inlet gas-liquid separator of the second compressor. An ammonia condenser is connected to the outlet of the ammonia compressor; A liquid ammonia tank is connected to the outlet of the ammonia condenser; The NH3 power-saving device is connected to the liquid ammonia tank, the gas-liquid separator at the inlet of the second compressor, and the CO2 / NH3 condenser-evaporator. The CO2 economizer is connected to the CO2 / NH3 condenser-evaporator and to the gas-liquid separator at the inlet of the first compressor. A liquid CO2 tank, connected to the CO2 economizer; The asynchronous motor has a single output shaft, and the carbon dioxide compressor and the ammonia compressor are configured on the same side of the asynchronous motor. Alternatively, the asynchronous motor has two output shafts, with one shaft directly connected to the carbon dioxide compressor and the other shaft directly connected to the ammonia compressor.

2. The motor-driven cascade refrigeration compressor unit as described in claim 1, characterized in that, The carbon dioxide compressor is a single-stage centrifugal compressor or a multi-stage centrifugal compressor.

3. The motor-driven cascade refrigeration compressor unit as described in claim 1, characterized in that, The ammonia compressor is a multi-stage centrifugal compressor.

4. The motor-driven cascade refrigeration compressor unit as described in claim 1, characterized in that, The carbon dioxide compressor has an inlet pressure of 0.8–1.0 MPa and an outlet pressure of 2.6–2.8 MPa.

5. The motor-driven cascade refrigeration compressor unit as described in claim 1, characterized in that, The load of the ammonia compressor is matched with that of the carbon dioxide compressor to operate NH3 as a refrigerant at -15°C.

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