Cooling method and system for spray water of air separation device

Abstract

The invention relates to a cooling method and system for spray water of an air separation device, and belongs to the technical field of energy conservation of an air separation process. According to the method, low-temperature waste nitrogen led out of an air separation low-pressure tower is subjected to sensible heat exchange and evaporative cooling with spraying water in sequence, multi-stage cooling of the spraying water is achieved, the spraying water is recycled into an air separation device, and a closed cooling system is formed. The system comprises a spray water recovery pipeline, a shell and tube heat exchanger, a countercurrent flow heat exchange tower, an air cooling auxiliary tower, a circulating water pump and a waste nitrogen air inducing and pressurizing unit. When the system runs, waste nitrogen is preferentially used as a cold source, dependence on air cooling equipment is reduced, and the overall energy efficiency is improved. According to the scheme, the energy consumption of the system can be obviously reduced, and relatively high resource utilization efficiency and applicability are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of air separation technology, in particular to a cooling method and system for spray water of an air separation device. BACKGROUND

[0002] As a key equipment for industrial gas production, air separation devices are widely used in metallurgy, chemical industry, energy industry, etc. In the process of separating air to produce nitrogen, oxygen and rare gases, a large amount of low-temperature, relatively dry and low-humidity waste nitrogen gas is often produced in addition to high-purity nitrogen. In current processes, waste nitrogen gas has been tried to be used for refrigerated water preparation to achieve partial resource recovery, but overall, this kind of low-temperature gas still has the problem of not being fully utilized and being discharged, resulting in energy waste and low operating efficiency.

[0003] On the other hand, to ensure the stable operation of the air separation device, a circulating spray water cooling system is usually configured in the system for absorbing the heat generated in the equipment and process. The existing cooling system mainly relies on cooling fans to extract external ambient air to exchange heat with the spray water for cooling. However, this air cooling method has the following disadvantages: the cooling efficiency decreases under high-temperature climate conditions, and the spray water temperature is difficult to control; the fans consume a large amount of electricity, and the overall energy consumption level is high; impurities in the external air can easily pollute the water quality, increasing the burden of water treatment; the operation noise of the air cooling tower is large, affecting the environmental quality of the plant.

[0004] In addition, the latent heat evaporation capacity of the ambient air is limited, resulting in significant fluctuations in cooling effect and poor stability of the cooling system. SUMMARY

[0005] The present application proposes a cooling method and circulating water cooling system for spray water of an air separation device, aiming to introduce waste nitrogen gas discharged from a low-pressure column of the air separation device as a cooling source, construct a multi-stage heat exchange process, and efficiently cool the spray water, thereby reducing the load of the traditional air cooling system, reducing energy consumption, and improving the stability of the cooling system.

[0006] The technical solution of the present application is as follows: waste nitrogen gas introduced from a low-pressure column of an air separation device is used as a cooling source to cool spray water through a heat exchange process between the waste nitrogen gas and the spray water, and the cooled spray water is sent back to the air separation device for circulation, forming a closed circulation structure. This solution makes full use of the low-temperature waste nitrogen gas resource produced by the air separation system, reduces the dependence on external cooling air source, and improves the energy efficiency ratio.

[0007] Further, the method specifically includes multiple heat exchange and reflux steps: Step 1: waste nitrogen gas at 10-15℃ and relative humidity not greater than 20% is introduced from the top of the low-pressure column of the air separation device and introduced into the cooling process through an air induction device; Step 2: Recover the high-temperature contaminated spray water at 60-80℃ for subsequent cooling; Step 3: Indirectly exchange heat between the high-temperature spray water and the contaminated nitrogen gas through a shell-and-tube heat exchanger to reduce the temperature of the spray water to 45-50℃; Step 4: Further introduce the contaminated nitrogen gas into a counter-flow heat exchange tower to contact with the spray water in counter-flow to form evaporative cooling to reduce the temperature of the spray water to 30-35℃; Step 5: Continue to introduce the spray water into a wind-cooling auxiliary section to achieve end cooling at 28-30℃ by introducing ambient air; Step 6: Re-transport the cooled spray water back to the top of the air separation tower by a main circulating pump.

[0008] Further, the adjusting valve and temperature control device arranged between the contaminated nitrogen and the wind-cooling cooling section are used to preferentially enable the contaminated nitrogen cooling section according to the temperature and system load to reduce the burden of the wind-cooling.

[0009] Further, the air induction device specifically includes an air induction fan and a compressor for pressurizing the contaminated nitrogen gas to 0.3-0.6 MPa to ensure that it has sufficient flow and pressure to enter the heat exchange unit to improve the heat exchange efficiency.

[0010] Further, in step 4, the contaminated nitrogen gas enters from the lower part of the counter-flow heat exchange tower, and the spray water is sprayed from the upper part to contact with the contaminated nitrogen gas in counter-flow to achieve evaporative heat absorption to strengthen the cooling effect.

[0011] In another aspect of the present application, a circulating water cooling system for air separation devices is provided for implementing the above method, and the system includes: A closed water circulation path composed of the outlet of the spray tower, the spray water pipeline, the shell-and-tube heat exchanger, the counter-flow heat exchange tower, the wind-cooling auxiliary tower, and the main circulating water pump; a contaminated nitrogen gas path composed of the outlet of the low-pressure tower, the contaminated nitrogen air induction fan, the compressor, the heat exchanger inlet, and the exhaust passage; the shell-and-tube heat exchanger and the counter-flow tower are respectively provided with a contaminated nitrogen gas interface, the former is used for sensible heat exchange, and the latter is used for evaporative heat exchange; the spray water is returned to the spray tower after being gradually cooled by multiple heat exchange sections to form a cycle; the wind-cooling auxiliary tower is arranged at the end of the water path to supplement and adjust the temperature.

[0012] Further, the wind-cooling auxiliary tower is provided with a cooling fan for introducing ambient air, and the cooling fan adopts an axial flow fan arranged at the top.

[0013] The cooling method and system have the following beneficial effects: (1) The present application introduces the low-temperature and dry contaminated nitrogen gas discharged from the low-pressure tower of the air separation device to construct a multi-section heat exchange path to replace the traditional single wind-cooling method to cool the spray water, effectively recovers the by-product resources in the air separation process, avoids the direct discharge of the contaminated nitrogen gas, and improves the overall energy utilization efficiency; (2) Compared with the traditional cooling method relying on cooling fan, the present application preferentially uses the waste nitrogen gas to complete the sensible heat and latent heat cooling of the sprayed water, greatly reduces the working load of the air cooling tower and fan, thereby reducing the system operation energy consumption and prolonging the service life of the equipment; (3) The waste nitrogen gas as the cold source has small temperature and humidity fluctuations and is less affected by the environment and climate, and can still maintain high cooling efficiency under adverse weather conditions such as high temperature or high humidity, thereby enhancing the stability and reliability of the cooling system. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The flow chart of the system of the present application. DETAILED DESCRIPTION

[0015] Hereinafter, the technology in the embodiments of the present application will be described clearly and completely in conjunction with the drawings in the embodiments of the present application; obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments; based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts should belong to the protection scope of the present application. It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0016] The present application provides a spraying water cooling method for an air separation device and a system thereof, fully recycles and utilizes the waste nitrogen gas byproduct of the low-pressure tower of the air separation device, uses the waste nitrogen gas as the main cold source in the spraying water cooling process of the air separation device, constructs a composite cooling path integrating sensible heat exchange and evaporative cooling, and replaces the traditional high-energy consumption cooling method relying on the fan ventilation heat exchange. By introducing the low-temperature and low-humidity waste nitrogen gas into the heat exchange unit and performing multi-stage heat exchange with the sprayed water heated due to the cooling of the regenerated gas, the sprayed water temperature is gradually reduced and then sent back to the air separation system for circulation, thereby forming a closed loop. This scheme not only improves the cooling efficiency, but also greatly reduces the running time of the air cooling equipment, significantly reduces the energy consumption, and realizes the high-value utilization of the byproduct resources and the system energy saving optimization.

[0017] The waste nitrogen gas produced by the low-pressure tower of the air separation device has the characteristics of low temperature (10-15℃) and low relative humidity (≤20%), has good heat absorption capacity, and especially when directly contacted with water, can promote water evaporation and absorb a large amount of latent heat. By using it as the spraying water cooling medium, combining sensible heat exchange, evaporative cooling and terminal air cooling compensation, a high-efficiency and energy-saving closed cooling loop is constructed.

[0018] The specific implementation steps are as follows: Firstly, the dirty nitrogen gas with temperature of 10-15℃ and relative humidity of no more than 20% is drawn from the top of the low-pressure tower of the air separation device, and the gas is drawn into the cooling process by the induced draft device. The induced draft device includes a low-temperature induced draft fan and a multi-stage compressor, which is used to raise the pressure of the dirty nitrogen gas to 0.3-0.6 MPa, so as to ensure the flow rate and heat exchange efficiency in the subsequent heat exchange process.

[0019] Meanwhile, the spray water heated by cooling the high-temperature regenerated gas or the dirty nitrogen gas is recovered from the outlet of the spray tower of the air separation device, and the temperature of the spray water ranges from 60-80℃. The spray water is first introduced into the shell-and-tube heat exchanger to exchange the sensible heat with the dirty nitrogen gas, so that the temperature of the water is reduced to 45-50℃, and the dirty nitrogen gas is heated to 20-25℃.

[0020] Subsequently, the heated dirty nitrogen gas flows into the direct-contact countercurrent heat exchange tower, and a multi-stage spray device is arranged at the top of the tower body, so that the spray water is sprayed from top to bottom, and the dirty nitrogen gas flows reversely from bottom to top, forming a countercurrent contact structure. In this process, the dirty nitrogen gas promotes the evaporation of water due to its dry and unsaturated characteristics, absorbs latent heat, and further reduces the temperature of the spray water to 30-35℃.

[0021] The cooled spray water continues to flow into the air-cooled auxiliary section. The section is provided with an axial flow cooling fan arranged at the top, which is used to introduce ambient air, and the water temperature is finally adjusted to 28-30℃ by the evaporation heat exchange between air and water in the filler layer. The fan can be a variable frequency structure, which automatically adjusts the air volume according to the system load to realize energy-saving operation.

[0022] After the cooling is completed, the spray water is delivered back to the air separation system by the main circulating water pump, including the air separation tower condenser, the molecular sieve regenerator, the compressor intercooler and the top of the spray tower, to form a continuous closed loop circulation, so as to guarantee the process cooling demand.

[0023] Specifically, in the spray water cooling loop, an electric regulating valve and a temperature control device are arranged between the dirty nitrogen gas heat exchange path and the air-cooled path, which can realize dynamic switching and flow proportional adjustment according to the set water temperature and system cooling load. When the system is running, the dirty nitrogen gas cooling section is preferentially started, and the air-cooled auxiliary section is automatically started when the capacity is insufficient or the water temperature is out of limit, so as to meet the cooling demand while significantly reducing the running time and energy consumption of the fan.

[0024] Reference Figure 1The embodiment also comprises a closed water circulation path formed by the outlet of the spray tower 1, a spray water pipeline, the shell-and-tube heat exchanger 2, the counterflow heat exchange tower 3, the air-cooled auxiliary tower 4 and a main circulating water pump; and a contaminated nitrogen gas path formed by the outlet of the low-pressure tower 5, a contaminated nitrogen air blower 6, a compressor 7, the inlet of the heat exchanger 2 and an exhaust passage. The shell-and-tube heat exchanger 2 and the counterflow heat exchange tower 3 are respectively provided with contaminated nitrogen gas interfaces for realizing indirect sensible heat exchange and direct evaporation heat exchange. The cooled spray water is returned to the spray tower to form a closed loop circulation after being gradually cooled in multiple heat exchange stages.

[0025] The air-cooled auxiliary tower 4 is provided with a top axial flow cooling fan, which forcibly introduces external ambient air to perform end cooling with the spray water, and serves as a supplementary adjustment section of the contaminated nitrogen cooling path, and is automatically started when the system cooling load fluctuates or the contaminated nitrogen gas supply is insufficient, so as to stabilize the outlet water temperature of the spray water and meet the air separation process requirements.

[0026] In summary, the present application realizes efficient cooling and closed circulation of the spray water by constructing a multi-stage cooling path with contaminated nitrogen gas as a core cooling source, combining temperature control and path adjustment mechanisms, has significant energy-saving effect and system stability, and is suitable for spray water cooling control system design in energy-saving reconstruction and new projects in the air separation industry.

Claims

1. A cooling method of spray water of an air separation plant, characterized by, The method comprises the following steps: The dirty nitrogen gas drawn from the low-pressure tower of the air separation device is used as a cold source to cool the spray water by heat exchange between the dirty nitrogen gas and the spray water, and the cooled spray water is sent back to the air separation device for recycling.

2. The cooling method of the spray water of the air separation apparatus according to claim 1, wherein The method comprises the following steps: S1. Dirty nitrogen gas with a temperature of 10-15℃ and a relative humidity of not more than 20% is drawn from the top of the low-pressure tower of the air separation device and enters a dirty nitrogen cooling section through a draft device; S2. Spray water recovered from the air separation spray tower is heated to 60-80℃ by cooling high-temperature dirty nitrogen gas or regenerated gas, and enters the dirty nitrogen cooling section to exchange heat with the dirty nitrogen; S3. The dirty nitrogen cooling section comprises a shell-and-tube heat exchanger, the recovered spray water is introduced into the shell-and-tube heat exchanger to exchange heat with the low-temperature dirty nitrogen gas, the temperature of the spray water is reduced to 45-50℃, and the dirty nitrogen gas is heated to 20-25℃; S4. The dirty nitrogen cooling section further comprises a counterflow heat exchange tower, the heated dirty nitrogen gas is introduced into the lower part of the counterflow heat exchange tower to be in counterflow contact with the spray water sprayed from the top of the tower, and the spray water is further cooled to 30-35℃ by evaporation and heat absorption; S5. The spray water is continuously introduced into the air cooling section to be finally cooled to 28-30℃ by introducing ambient air through a cooling fan; S6. The cooled spray water is sent back to the top of the air separation device spray tower through a main circulating pump to form a closed circulation loop.

3. The cooling method of the spray water of the air separation apparatus according to claim 2, characterized by, The draft device used in S1 comprises a draft fan and a compressor for increasing the pressure of the dirty nitrogen gas to 0.3-0.6 MPa.

4. The cooling method of the spray water of the air separation apparatus according to claim 2, wherein The evaporation heat exchange between the spray water and the dirty nitrogen gas in S4 is carried out in the counterflow heat exchange tower, the dirty nitrogen gas flows upward from the bottom of the tower, and the spray water is sprayed downward from the top of the tower to be in counterflow contact.

5. An air separation unit recycle water cooling system for implementing the method of any one of claims 1-4, wherein, The high-temperature spray water drawn from the outlet of the air separation device spray tower sequentially flows through a shell-and-tube heat exchanger, a counterflow heat exchange tower and an air cooling auxiliary tower, is gradually cooled in multiple heat exchange units, is transported back to the top of the spray tower through a return pipeline to form a closed loop circulation, and is driven to flow by a circulating water pump arranged in the loop; The shell-and-tube heat exchanger and the counterflow heat exchange tower are respectively provided with a dirty nitrogen gas inlet for introducing the dirty nitrogen gas drawn from the top of the low-pressure tower of the air separation device; A draft device and a compression device connected to the dirty nitrogen gas inlet are arranged in the system to increase the flow pressure of the dirty nitrogen gas; The dirty nitrogen gas sequentially flows through the shell-and-tube heat exchanger and the counterflow heat exchange tower, exchanges heat with the spray water in the shell-and-tube heat exchanger by indirect sensible heat exchange, and exchanges heat with the spray water in the counterflow heat exchange tower by direct counterflow contact for evaporation cooling, and the dirty nitrogen gas after heat exchange is discharged from the system through an exhaust passage; The air cooling auxiliary tower is arranged at the end of the spray water cooling, uses ambient air to further adjust the temperature of the spray water, and is used as a supplementary cooling section.

6. A water cooling system for an air separation plant recycle according to claim 5 wherein, The air cooling auxiliary tower is provided with a cooling fan for introducing ambient air.

7. A water cooling system for an air separation plant recycle according to claim 6 wherein, The cooling fan adopts an axial flow fan arranged at the top.

Images