Solid dry ice removing method

Abstract

The invention discloses a method for removing solid dry ice in the technical field of carbon dioxide refrigeration, which comprises the following steps of: acquiring flow, pressure and temperature data of a refrigeration system and a filling pipeline thereof, and judging whether the refrigeration system and the filling pipeline thereof are blocked or not based on the data; during blockage, the pipe sections are sequentially closed in a segmented mode, and if the change amplitude of the upstream and downstream pressure change rate of one pipe section is lower than a set value, the pipe section is judged to be a blocked pipe section; dry ice is removed through heat tracing and gas purging; in the gas purging process, gaseous carbon dioxide is purged at the downstream of the blocked pipe section, so that the gaseous carbon dioxide purges the dry ice in the direction opposite to the blocking direction. According to the method, blockage is judged by comprehensively monitoring changes of flow, pressure, temperature and the like, dry ice blockage is accurately positioned and blocked pipe sections are quickly locked in a manner of closing pipelines in a segmented manner, an accurate target is provided for efficient removal of dry ice, and local pipeline overheating and pressure out-of-control caused when the dry ice is removed are avoided.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide refrigeration, and more specifically to a method for removing solid dry ice. Background Technology

[0002] In industrial systems that utilize liquid carbon dioxide for refrigeration, such as underground coal mine refrigeration systems that include carbon dioxide compressors, throttling devices, and heating and cooling systems, dry ice blockage is a common and troublesome problem. When the pressure inside the pipes or containers is too low, the liquid carbon dioxide rapidly vaporizes and absorbs heat, causing the local temperature to drop sharply below the freezing point, thus forming solid dry ice and causing blockages in the refrigeration system and its filling pipes.

[0003] Traditional methods for handling dry ice blockages are rather passive, typically involving stopping operations, allowing the ice to heat up naturally, or simply baking it after an abnormal flow or equipment alarm is detected. These methods are inefficient, have long defrosting times, and severely impact production continuity. More seriously, traditional methods lack rapid and precise location technology for blockages; blindly attempting to remove the blockage may fail, or even lead to localized overheating or pressure runaway due to improper operation, creating new safety risks. Therefore, there is an urgent need for a method that can quickly respond, accurately locate, and safely and efficiently remove dry ice blockages. Summary of the Invention

[0004] The purpose of this invention is to provide a method for removing solid dry ice, which solves the problems of difficulty in locating dry ice blockages and insufficient pipeline clearing efficiency in existing refrigeration systems and filling pipelines.

[0005] The present invention achieves the above objectives through the following technical solutions: A method for removing solid dry ice, used to remove dry ice from a refrigeration system and its filling pipelines, wherein the refrigeration system and its filling pipelines are divided into multiple pipe sections, includes the following steps: Acquire flow, pressure, and temperature data of the refrigeration system and its filling pipeline, and determine whether there is blockage in the refrigeration system and its filling pipeline based on changes in flow, pressure, and temperature data; When there is a blockage in the refrigeration system and its charging pipeline, each pipeline segment is closed in sequence. If the change rate of the upstream and downstream pressure change of one pipeline segment is lower than the set value after the segment is closed, the pipeline segment is determined to be a blocked pipeline segment. Dry ice in the refrigeration system and its filling lines is removed by heat tracing and / or gas purging to clear blocked sections.

[0006] As a further optimization of the invention, during the heat tracing process, dry ice in the blocked pipe section is removed by the heat tracing device; during the gas purging process, gaseous carbon dioxide is purged downstream of the blocked pipe section, so that the gaseous carbon dioxide is purged in the opposite direction to the blockage direction to the dry ice.

[0007] As a further optimization of the invention, within a first set time period, when the ratio of real-time flow to set flow is continuously lower than the first set value or the real-time flow is zero, it is determined that there is a blockage; within a second set time period, when the upstream pressure change rate is continuously higher than the second set value, it is determined that there is a blockage; within a third set time period, when the ratio of real-time temperature to set temperature is continuously lower than the third set value, it is determined that there is a blockage.

[0008] As a further optimization of the invention, the filling pipeline is provided with a liquid storage tank and a heat exchanger. The liquid storage tank fills the refrigeration system with carbon dioxide through the heat exchanger. A cryogenic liquid pump is provided between the liquid storage tank and the heat exchanger. When the cryogenic liquid pump alarms abnormally, it is determined that there is a blockage in the liquid storage tank or the pipeline between the liquid storage tank and the cryogenic liquid pump.

[0009] As a further optimization of the invention, when the refrigeration system and its filling pipeline are blocked, the filling rate of the filling pipeline is reduced or the liquid storage tank is stopped from discharging liquid before each pipeline segment is closed in sequence.

[0010] As a further optimization of the invention, when purging gaseous carbon dioxide downstream of the blocked pipe section, the gas source for the gaseous carbon dioxide is a storage tank or an external gas source.

[0011] As a further optimization of the invention, when the gas source is a liquid storage tank, the pressure of the liquid storage tank is higher than the set pressure.

[0012] As a further optimization of the invention, the top of the liquid storage tank is provided with an exhaust pipe, which is connected to several pipe sections. An air bladder is provided inside the liquid storage tank, which is used to provide the power to purge gaseous carbon dioxide and maintain the pressure inside the liquid storage tank.

[0013] As a further optimization of the invention, the gas inside the airbag is isolated from the carbon dioxide inside the liquid storage tank.

[0014] As a further optimization of the invention, during the heat tracing process, the insulation layer on the blocked pipe section is removed, and the heat tracing device is fitted onto the blocked pipe section. The heat tracing device is either electric heat tracing or steam heat tracing.

[0015] The beneficial effects of this invention are as follows: This invention provides a systematic dry ice blockage diagnosis and treatment process. It judges the blockage by comprehensively monitoring changes in multiple parameters such as flow rate, pressure, temperature and equipment status, and uses a segmented pipeline closure method to accurately locate the dry ice blockage. It can quickly lock the blockage point to a specific pipeline segment, providing an accurate target for subsequent efficient removal and avoiding situations where local pipeline overheating and pressure runaway occur during dry ice removal due to insufficient positioning accuracy. This invention addresses blockages using two methods: heating and gaseous purging. Heating allows dry ice to sublimate slowly, ensuring safety and reliability. Gaseous purging utilizes airflow and sensible heat transfer to accelerate the decomposition and removal of dry ice. During the purging process, reverse purging is performed from downstream of the blocked pipe section, with the purging direction opposite to the blockage direction, improving the dry ice removal efficiency. Compared to forward purging, reverse purging avoids the dry ice being crushed, making it suitable for scenarios with severe blockages. This invention provides flexible solutions for different scenarios. When the cryogenic liquid pump alarms abnormally, it can be determined first that the blockage is located between the storage tank and the cryogenic liquid pump. The storage tank's own gas phase or an external gas source can be used as the purging gas source to ensure effective purging even when there is no external gas source, thereby improving the on-site availability and reliability of the method. Attached Figure Description

[0016] Figure 1 This is a flowchart of the solid dry ice removal method of the present invention; Figure 2 For liquid carbon dioxide filling systems; In the diagram: 1. Refrigeration system; 2. Liquid storage tank; 3. Heat exchanger; 4. Carbon dioxide input pipe; 5. First liquid outlet pipe; 6. Second liquid outlet pipe. Detailed Implementation

[0017] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0018] Example like Figure 1 and Figure 2 As shown, this embodiment relates to a method for removing solid dry ice, which is applied to a coal mine refrigeration project, specifically for removing dry ice from a refrigeration system 1 and its filling pipeline. A storage tank 2 and a heat exchanger 3 are provided on the filling pipeline. The storage tank 2 fills the refrigeration system 1 with carbon dioxide through the heat exchanger 3. A carbon dioxide input pipe 4 is provided at the bottom of the heat exchanger 3, and a carbon dioxide output pipe is provided between the heat exchanger 3 and the refrigeration system 1. A first outlet pipe 5 and a second outlet pipe 6 are provided between the carbon dioxide input pipe 4 and the storage tank 2. Both the first outlet pipe 5 and the second outlet pipe 6 are equipped with outlet valves, and a cryogenic liquid pump is provided on the second outlet pipe 6. When the pressure in the pipeline of the refrigeration system 1 or the storage tank 2 is lower than 0.8 MPa, the liquid carbon dioxide rapidly vaporizes and absorbs heat, causing a sudden drop in local temperature in the refrigeration system 1 and its filling pipeline, thereby forming solid dry ice and causing pipeline blockage. The solid dry ice removal method includes the following steps: Step 1: Determine if there is dry ice blockage. The refrigeration system 1 and its filling pipeline are divided into multiple pipe sections. Flow meters, pressure sensors, and temperature sensors are installed on each pipe section. During the carbon dioxide filling and operation of the refrigeration system 1, the data collected by the flow meters, pressure sensors, and temperature sensors are used to determine whether there is a blockage. When the data changes abnormally, a blockage is determined to exist.

[0019] The above-mentioned abnormal data changes include the following situations: Scenario 1: Flow rate drops sharply or becomes zero: If the ratio of real-time flow rate to set flow rate remains below the first set value or the real-time flow rate becomes zero within a first set time period, a blockage is determined to exist. The first set time period is preferably 30-50 seconds, the first set value is preferably 40%-60%, and the sampling interval of the flow sensor does not exceed 10 seconds.

[0020] Scenario 2: Continuous Increase in Upstream Pipeline Pressure: If the rate of change of upstream pressure remains higher than the second set value within a second set time period, a blockage is determined. The second set time is preferably 45s to 75s, the second set value is preferably 0.06 to 1MPa / min, and the sampling interval of the pressure sensors does not exceed 15s. Furthermore, the rate of change of pressure is the rate of change of pressure between two consecutive samples. If the rate of change of pressure from multiple pressure sensors located relatively upstream is higher than the second set value within the second set time period, it indicates that the upstream pipeline pressure is continuously increasing.

[0021] Scenario 3: Sudden Temperature Drop: If the ratio of the real-time temperature to the set temperature remains below the third set value within the third set time period, a blockage is determined to exist. The third set time is preferably 3 to 6 minutes, the third set value is preferably 70% to 90%, and the sampling interval of the temperature sensor does not exceed 1 minute.

[0022] Scenario 4: Cryogenic Liquid Pump Malfunction: The cryogenic liquid pump is unable to deliver liquid carbon dioxide normally. Specifically, sensors such as the pump inlet and outlet differential pressure sensor and the pump body vibration sensor are used to detect whether the cryogenic liquid pump is malfunctioning. If an malfunction is detected, an alarm will be triggered, indicating that there is dry ice blockage in the storage tank 2 or the pipeline between the storage tank 2 and the cryogenic liquid pump.

[0023] Step 2: Locate the blockage During the process of locating the blockage, valves at both ends of each pipe segment are closed sequentially from upstream to downstream, and the blockage status is determined based on changes in pressure sensor data. If the change in the upstream and downstream pressure change rate is lower than a set value after a certain pipe segment is closed, it indicates that the blockage area is within that pipe segment, and that pipe segment is considered blocked. The preferred set value is 0.02–0.05 MPa / min. When the cryogenic liquid pump alarms abnormally, the blockage location is determined to be either at the outlet of storage tank 2 or on the pipeline between the outlet of storage tank 2 and the cryogenic liquid pump.

[0024] When a blockage occurs, immediately reduce the filling rate or directly close the liquid outlet valve to stop supplying liquid carbon dioxide to the blocked area before the sectional pipe is closed. Refrigeration system 1 and its filling lines are equipped with pressure relief valves. When a blockage occurs, open the pressure relief valves to prevent pressure buildup.

[0025] Step 3: Clear the blockage Methods for handling blockages include heat tracing and gas purging. During heat tracing, dry ice is removed from the blocked pipe section using a heat tracing device. During gas purging, gaseous carbon dioxide is purged downstream of the blocked section, causing the gaseous carbon dioxide to blow away the dry ice in the opposite direction of the blockage. Both methods can be used individually or simultaneously.

[0026] Specifically, during the heat tracing process, the insulation layer of the blocked pipe section is first removed, and then the heat tracing device is tightly fitted to the blocked pipe section to transfer heat into the blocked pipe section and promote the sublimation of dry ice.

[0027] The heat tracing device can be electric heat tracing, steam heat tracing, etc. In this embodiment, the heat tracing device is preferably electric heat tracing, and the set heating temperature of electric heat tracing is 60℃~120℃, preferably 80℃. In addition, in some other embodiments, if the blockage is not severe, the insulation layer on the blocked pipe section can be left unremoved, and the heat tracing device can be attached to the insulation layer.

[0028] During the gas purging process, a gaseous carbon dioxide source is connected to the blocked pipe section, and the gas source pressure is adjusted to 1.0 MPa to 1.2 MPa. Multiple purging ports are provided on the refrigeration system 1 and its filling pipeline. Purging is performed through the purging port downstream of the blocked area, in the opposite direction to the blockage. The heat and flow of the gaseous carbon dioxide accelerate the sublimation of dry ice and remove residual gas. The gas source is either the liquid storage tank 2 or an external gas source.

[0029] The storage tank 2 contains liquid carbon dioxide, with gaseous carbon dioxide at its top. When the gas source is the storage tank 2, an exhaust pipe is installed at the top of the storage tank 2. All pipe sections or portions of the refrigeration system 1 and its filling pipelines are equipped with purge ports, and the exhaust pipe is connected to each purge port. An on / off valve is installed at the connection between the exhaust pipe and the purge port. During purge, the on / off valve of the purge port downstream of the blocked pipe section is opened, using the pressure of the storage tank 2 itself to purge the gaseous carbon dioxide into the blocked pipe section. During the purge process, the pressure of the storage tank 2 itself needs to be higher than the set pressure of the storage tank, preferably 0.8–1.2 MPa. If the pressure of the storage tank 2 itself is lower than the set pressure, the on / off valve is closed.

[0030] In other embodiments, an airbag is installed inside the liquid storage tank 2. The space inside the airbag is not connected to the space inside the liquid storage tank 2 except for the airbag itself, preventing the gas inside the airbag from mixing with the carbon dioxide inside the liquid storage tank 2. By inflating the airbag, the gaseous carbon dioxide in the liquid storage tank 2 is expelled, purging the blocked pipe section. This airbag provides the power to purge the gaseous carbon dioxide while maintaining the pressure inside the liquid storage tank 2, ensuring that the pressure inside the liquid storage tank 2 is greater than a set pressure. This purging method avoids introducing other gases into the refrigeration system 1 and its filling pipelines, ensuring the purity of the gas composition.

[0031] Step 4: Refill The temperature and pressure data of the refrigeration system 1 and its charging pipeline are monitored in real time. When the pressure and temperature data stabilize, it is determined that the dry ice removal is complete. Additionally, if the liquid storage tank 2 is clogged, the liquid level and pressure data of the liquid storage tank 2 also need to be monitored. When the liquid level, pressure, and temperature data stabilize, it is determined that the dry ice removal is complete. After the dry ice removal is complete, the heating device and carbon dioxide gas source are turned off. The equipment and pipelines are checked according to the pre-filling preparation procedure. After confirming that there are no abnormalities, carbon dioxide is refilled. The solid dry ice removal method of this embodiment can effectively remove dry ice from the refrigeration system 1 and its charging pipeline.

[0032] In addition, the aforementioned refrigeration system 1 includes a refrigeration unit consisting of a carbon dioxide compressor and a throttling device, as well as a heating device and a cooling device. On the coal mine surface, the carbon dioxide compressor compresses gaseous carbon dioxide into a supercritical fluid, which is then transported to the heating device to provide heat to users. After flash evaporation within the heating device, the supercritical fluid is cooled by the cooling device and throttled by the throttling device to form cryogenic liquid carbon dioxide. The carbon dioxide refrigeration unit uses this cryogenic liquid carbon dioxide as a cooling medium to transport it underground. The cooling medium exchanges heat with chilled water, lowering the temperature of the chilled water, which is then sent to the final air cooler to cool the working environment.

[0033] In addition, in some other embodiments, the blockage location can be located in step two in the following way. The location process is as follows: when there is a blockage in the refrigeration system 1 and its charging pipeline, if the pressure difference between the two ends of one of the pipe sections is greater than the set pressure difference, the pipe section is determined to be the blocked pipe section. The set pressure difference is preferably 0.8 to 1.2 MPa.

[0034] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for removing solid dry ice, the method being used to remove dry ice from a refrigeration system and its filling pipelines, wherein the refrigeration system and its filling pipelines are divided into multiple pipe sections, characterized in that, Includes the following steps: Acquire flow, pressure, and temperature data of the refrigeration system and its filling pipeline, and determine whether there is blockage in the refrigeration system and its filling pipeline based on changes in flow, pressure, and temperature data; When there is a blockage in the refrigeration system and its charging pipeline, each pipeline segment is closed in sequence. If the change rate of the upstream and downstream pressure of a pipeline segment is lower than the set value after the segment is closed, the pipeline segment is determined to be a blocked pipeline segment. Dry ice in the refrigeration system and its filling lines is removed by heat tracing and / or gas purging to clear blocked sections.

2. The solid dry ice removal method according to claim 1, characterized in that: During the heat tracing process, dry ice in the blocked pipe section is removed by the heat tracing device; during the gas purging process, gaseous carbon dioxide is purged downstream of the blocked pipe section, so that the gaseous carbon dioxide is purged in the opposite direction to the blockage direction to remove the dry ice.

3. The solid dry ice removal method according to claim 1, characterized in that: Within a first set time period, if the ratio of real-time flow to set flow is consistently lower than the first set value or the real-time flow is zero, a blockage is identified. Within a second set time period, if the upstream pressure change rate is consistently higher than the second set value, a blockage is identified. Within a third set time period, if the ratio of real-time temperature to set temperature is consistently lower than the third set value, a blockage is identified.

4. The solid dry ice removal method according to claim 1, characterized in that: The filling pipeline is equipped with a liquid storage tank and a heat exchanger. The liquid storage tank fills the refrigeration system with carbon dioxide through the heat exchanger. A cryogenic liquid pump is installed between the liquid storage tank and the heat exchanger. When the cryogenic liquid pump alarms abnormally, it is determined that there is a blockage in the liquid storage tank or the pipeline between the liquid storage tank and the cryogenic liquid pump.

5. The solid dry ice removal method according to claim 4, characterized in that: When there is a blockage in the refrigeration system and its filling pipeline, reduce the filling rate of the filling pipeline or stop the liquid discharge from the storage tank before closing each pipeline segment in sequence.

6. The solid dry ice removal method according to claim 4, characterized in that: When purging gaseous carbon dioxide downstream of a blocked pipe section, the gas source for the gaseous carbon dioxide is a storage tank or an external gas source.

7. The solid dry ice removal method according to claim 6, characterized in that: When the gas source is a liquid storage tank, the pressure of the liquid storage tank is higher than the set pressure.

8. The solid dry ice removal method according to claim 7, characterized in that: The top of the liquid storage tank is equipped with an exhaust pipe, which is connected to several pipe sections. An air bladder is installed inside the liquid storage tank to provide the power to purge gaseous carbon dioxide and maintain the pressure inside the liquid storage tank.

9. The solid dry ice removal method according to claim 8, characterized in that: The gas inside the airbag is isolated from the carbon dioxide in the storage tank.

10. The solid dry ice removal method according to claim 1, characterized in that: During the heat tracing process, the insulation layer on the blocked pipe section is removed, and the heat tracing device is fitted onto the blocked pipe section. The heat tracing device is either electric or steam heat tracing.

Images