A warming system for preventing cold box low temperature cold brittleness

Abstract

The application discloses a kind of heating systems for preventing cold box cryogenic brittle, belong to cold box protection technical field.The system disclosed in the application includes heating gas buffer tank, heating gas circulating fan, heating gas electric heating furnace, cold box basic heat exchanger etc.Nitrogen is sent to electric heating furnace by circulating fan and heated, then nitrogen enters cold box basic heat exchanger to warm up cold box base, and nitrogen after cooling is recycled to buffer tank.Cold box bottom is equipped with temperature monitoring unit, when temperature anomaly is detected, heating is controlled by central control system, to ensure that cold box base obtains enough heat, effectively avoid the problem of cold box base freeze crack and pulverization caused by low temperature.The system is also provided with a pressure maintaining subsystem, including a pressure regulating valve, a flow detection unit, a sealing gas isolation valve, a pressure detection unit and a sealing gas distributor unit, for maintaining the internal pressure of the cold box stable, and evenly releasing the sealing gas into the cold box interior through the sealing gas distributor unit, enhancing the sealing gas pressure maintaining and uniform distribution effect.

Description

Technical Field

[0001] This invention belongs to the field of cold box protection technology, specifically relating to a heating system for preventing cold boxes from becoming brittle at low temperatures. Background Technology

[0002] With the booming development of the chemical industry in recent years, projects focusing on air separation and alcohol / alkanes have flourished. The cold box, as the heart of the project, remains a core technological component for various companies. A cold box typically consists of containers, pipes, and heat exchangers. Due to the low process temperatures, aluminum is primarily used for the interior of the cold box, while the outer shell is made of stainless steel or carbon steel. Because the cold box operates in a low-temperature environment, perlite is needed for insulation, and the low temperature creates a negative pressure effect. Thus, the cold box acts as a carrier for the perlite and the low-temperature equipment, bearing the negative pressure. Simultaneously, the containers and heat exchangers within the cold box are below -100°C, and the cryogenic liquid can easily damage the cold box, potentially causing secondary accidents. This necessitates the development of a device capable of withstanding low temperatures and withstanding negative pressure adsorption and the impact of liquid leakage and the large rise of evaporating gas on the cold box without causing fatal consequences.

[0003] The cold box environment is sealed. To prevent air from entering and causing the perlite to become damp, and to prevent deformation due to negative pressure, as well as to promptly replace leaked process gases, the pressure in the jacket of the cold box is generally required to be maintained at a slightly positive pressure within the normal range. Traditional annular sealing gas distributors, installed at the bottom or middle of the cold box, result in uneven distribution of sealing gas in different parts of the cold box during actual application. Some sections of the cold box have negative sealing gas pressure, which easily absorbs moisture from the air, causing the perlite to become damp and thus affecting its insulation performance.

[0004] The cold box temperature includes the process temperature inside the cold box and the base temperature at the bottom of the cold box. During normal production, if the process temperature inside the cold box exceeds the normal range, besides the usual reasons of overcooling or insufficient cooling, it may be due to blockages, requiring the attention of the operators. When there is a leak in the pipes or containers inside the cold box, the cryogenic liquid flows down, causing the floor thermometer and base temperature (installed on the cold box foundation) to drop rapidly, exceeding the normal temperature range. The DCS system will alarm. Based on the alarm and historical trends, the operators will check the temperature difference between the process temperature and the base temperature inside the cold box to determine if there is an internal leak and its approximate location. Changes in the cold box base temperature usually come from two sources. One is the leakage of cryogenic liquid, leading to a low temperature at the bottom of the cold box. In this case, process personnel need to analyze the composition of the interlayer gas and check the pressure of the sealing gas gauge to make a judgment. Secondly, the low temperature of the cold box foundation is caused by the low-temperature environment. Weather changes have a significant impact on the cold box foundation. In low-temperature environments, the temperature of the cold box can reach -30℃, reaching the working limit of carbon steel cold boxes. Since the bottom of the cold box is in contact with the foundation, the low temperature of the cold box is directly introduced into the foundation. The deformation of the foundation and the cold box bottom plate may affect the cold box bottom plate, leading to poor sealing and even brittleness. In these situations, operators should stop production, open the manhole on the top of the cold box to allow the cryogenic liquid to evaporate, and at the same time monitor the temperature of the cold box foundation to prevent the foundation from freezing, cracking, and pulverizing, which could cause a collapse accident. The Yima cold box explosion incident has sounded the alarm for air separation and related cryogenic equipment companies; measures to prevent brittleness and collapse of cold boxes are urgently needed. Summary of the Invention

[0005] The purpose of this invention is to use external heating gas to slowly heat the foundation of the cold box, preventing the foundation from crumbling and collapsing, and to provide a heating system that prevents the cold box from becoming brittle at low temperatures.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention provides a heating system for preventing low-temperature brittleness in a cold box, comprising a heating gas buffer tank, a heating gas circulating fan, a heating gas electric heater, a cold box foundation heat exchanger, and a first temperature monitoring unit for monitoring the temperature of the cold box foundation. The cold box foundation heat exchanger and the first temperature monitoring unit are disposed inside the cold box foundation, and the first temperature monitoring unit is connected to a central control system.

[0008] The inlet of the heating gas buffer tank is connected to a nitrogen source, and nitrogen is controlled to enter the heating gas buffer tank through a second valve. The heating gas buffer tank is equipped with a gas outlet switch valve, which controls the discharge of nitrogen. The gas outlet switch valve is connected to a heating gas circulation fan, and the discharged nitrogen is transferred to the heating gas electric heater through the heating gas circulation fan. The outlet of the heating gas electric heater is connected to the inlet of the cold box foundation heat exchanger. The nitrogen heated by the heating gas electric heater enters the cold box foundation heat exchanger, which raises the temperature of the cold box foundation. The outlet of the cold box foundation heat exchanger is connected to the heating gas buffer tank to recover the cooled nitrogen.

[0009] A second temperature monitoring unit is installed at the bottom of the cold box. The second temperature monitoring unit is connected to the central control system. The temperature at the bottom of the cold box is detected by the second temperature monitoring unit. If the internal temperature of the cold box exceeds the normal temperature range, it is considered that there is a liquid leak inside the cold box, and then the central control system controls the heating.

[0010] Preferably, a heating gas temperature sensor is provided between the heating gas electric heater and the cold box base heat exchanger, and the heating gas temperature sensor and the heating gas electric heater are correlated and regulated by PID control.

[0011] Preferably, the heating gas buffer tank is equipped with an electric contact pressure gauge; the bottom of the heating gas buffer tank is equipped with a buffer tank drain valve.

[0012] Preferably, the cold box base heat exchanger is a coil heat exchanger.

[0013] Preferably, the cold box is equipped with a pressure-maintaining subsystem for maintaining the internal pressure of the cold box within a normal range. The pressure-maintaining subsystem includes: a first valve, a pressure regulating valve, a flow detection unit, a sealing gas isolation valve, a pressure detection unit, and a sealing gas distributor unit. One end of the first valve is connected to a sealing gas source, and the other end of the first valve is connected to a pressure regulating valve for regulating the sealing gas pressure. The sealing gas enters the pressure regulating valve through the first valve for pressure regulation. The regulated sealing gas then passes through the flow detection unit, the sealing gas isolation valve, and the pressure detection unit in sequence before entering the sealing gas distributor unit located inside the cold box. The pressure detection unit is connected to the sealing gas distributor unit inside the cold box via a flange interface. The sealing gas distributor unit is located near the side wall and bottom of the cold box, and releases the sealing gas into the internal space of the cold box through the sealing gas distributor unit.

[0014] Preferably, a sealing gas pressure detector is provided between the pressure regulating valve and the flow detection unit; the sealing gas distributor unit includes a first sealing gas distributor, a second sealing gas distributor and a third sealing gas distributor, the first and second sealing gas distributors are vertically arranged and parallel to the side of the cold box, and the third sealing gas distributor is horizontally arranged at the bottom of the cold box; after pressure regulation, the sealing gas that meets the preset pressure range is divided into three paths and passes through the sealing gas isolation valve of the flow detection unit and the pressure detection unit in sequence, entering the first sealing gas distributor, the second sealing gas distributor and the third sealing gas distributor.

[0015] Preferably, the pressure regulating valve is a self-operated regulating valve.

[0016] Preferably, the top, middle and bottom of the cold box are respectively provided with a first cold box pressure gauge, a second cold box pressure gauge and a third cold box pressure gauge for detecting the internal pressure of the cold box.

[0017] Preferably, the top of the cold box is provided with a breather valve and a suction valve for adjusting the internal pressure of the cold box.

[0018] Secondly, this invention provides a heating method to prevent low-temperature embrittlement in a cold box. A first valve is opened to allow sealing gas to enter the pressure-maintaining subsystem. The pressure is adjusted by a pressure regulating valve to obtain sealing gas within the target pressure range. A flow detection unit detects the flow rate of the entering sealing gas. If it does not meet the requirements, the flow rate is controlled by a sealing gas isolation valve. Then, a pressure detection unit further detects the sealing gas pressure. Sealing gas meeting the target flow rate and pressure is introduced into a sealing gas distributor unit through a flange interface. The sealing gas distributor unit releases the sealing gas from bottom to top into the internal space of the cold box, maintaining the internal pressure of the cold box in a slightly positive state. A first, second, and third cold box pressure gauge detects whether the pressure in the upper, middle, and lower sections of the cold box is in a slightly positive state. If not, the flow rate and pressure of the sealing gas are adjusted. Simultaneously, the monitoring data from a second temperature monitoring unit is used to determine whether there is leakage of the low-temperature liquid inside the cold box.

[0019] The temperature changes of the cold box foundation and bottom are monitored by the first and second temperature monitoring units. If the temperature of the cold box foundation and bottom is lower than the working limit temperature range of the cold box, the gas outlet switch valve is opened by the central control system. The nitrogen in the heating gas buffer tank is transferred to the heating gas electric heater by the heating gas circulation fan. The temperature of the heated nitrogen is detected by the heating gas temperature detector. If the temperature is too high, the heating temperature of the heating gas electric heater is controlled to be reduced, and vice versa. The heated nitrogen enters the cold box foundation heat exchanger to heat the cold box foundation. The used nitrogen returns to the heating gas buffer tank through the pipeline for reuse.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] This invention utilizes a cold box foundation heating device, employing circulating nitrogen gas to heat the foundation. This ensures sufficient heat is supplied to the bottom of the cold box, effectively preventing freezing cracks and pulverization due to low temperatures, thus protecting the structural integrity of the foundation. When the cold box is at low temperatures, operators can use an external circulating heating system to provide a heat source to the foundation, preventing collapse caused by freezing cracks or pulverization. This enhances the safety and reliability of the cold box, extends its service life, and reduces maintenance costs. Simultaneously, the internal pressure distribution is optimized by adding a top-down sealing gas distributor, resulting in more uniform sealing gas distribution across all areas of the cold box. This enhances the pressure retention and distribution of the sealing gas, further improving the stability and safety of the cold box operation and reducing the risk of accidents. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the cold box basic heating system provided in this embodiment;

[0023] Figure 2 This is a schematic diagram of the pressure holding process in the cold box provided in this embodiment;

[0024] Figure 3 This is a schematic diagram of the distribution of the sealing gas distributor provided in this embodiment;

[0025] In the diagram: First valve V101, pressure regulating valve PCV101, sealing gas pressure detector PG101, first flow meter FI210, second flow meter FI211, third flow meter FI212, first sealing gas isolation valve V210, second sealing gas isolation valve V211, third sealing gas isolation valve V212, first sealing gas pressure sensor PG210, second sealing gas pressure sensor PG211, third sealing gas pressure sensor PG212, first flange interface N1, second flange interface N2, third flange interface N3, first sealing gas distributor FP1, second sealing gas distributor FP2, third sealing gas distributor FP3, first cold box pressure sensor PIA15A, second cold box pressure sensor PIA15B. The following equipment is listed: third cold box pressure gauge PIA15C, first bottom temperature monitor TIA21, second bottom temperature monitor TIA22, first base temperature monitor TIA23A, second base temperature monitor TIA23B, third base temperature monitor TIA23C, second valve V214, heating gas buffer tank T101, electric contact pressure gauge PG301, buffer tank drain valve V302, gas outlet switch valve KV101, heating gas circulating fan P101, heating gas electric heater E101, heating gas temperature gauge TIA24, cold box base heat exchanger E102, on-site sampling and analysis point AP101, gas analyzer GT101, electric heater starter HS1201, electric heater protector TIAS1212. Detailed Implementation

[0026] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in the various embodiments of the present invention can be combined accordingly without mutual conflict.

[0027] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are conventional methods, and the materials described are commercially available unless otherwise specified. In the description of this invention, it should be noted that, unless otherwise explicitly stated and limited, the terms "connection," "setting," and "installation" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The terms "in sequence," "through," and "after" indicate the sequential orientation based on the sequential orientation shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific sequential orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0028] In the description of this invention, it should be understood that the terms "first," "second," and "third" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," and "third" may explicitly or implicitly include at least one of those features.

[0029] like Figure 1 As shown in the preferred embodiment of the present invention, this embodiment provides a heating system to prevent low-temperature brittleness in a cold box, including a heating gas buffer tank T101, a heating gas circulating fan P101, a heating gas electric heater E101, a cold box foundation heat exchanger E102, and a first temperature monitoring unit for monitoring the temperature of the cold box foundation. The cold box foundation heat exchanger E102 and the first temperature monitoring unit are located inside the cold box foundation, and the first temperature monitoring unit is connected to the central control system. The first temperature monitoring unit includes a first foundation temperature monitor TIA23A, a second foundation temperature monitor TIA23B, and a third foundation temperature monitor TIA23C. When the first foundation temperature monitor TIA23A, the second foundation temperature monitor TIA23B, and the third foundation temperature monitor TIA23C detect a rapid drop in the cold box foundation temperature, exceeding the normal temperature range, the central control system issues an alarm. The operator checks the temperature difference between the internal temperature of the cold box and the temperature of the cold box foundation based on the alarm and historical trends to determine whether there is an internal leak and the approximate location of the leak. When the temperature of the cold box foundation is too low, the foundation is heated by turning on the cold box foundation heat exchanger E102 to maintain its temperature and prevent it from pulverizing due to low temperature, which could lead to a safety accident. In this embodiment, the cold box foundation heat exchanger E102 is a coil-type heat exchanger. Coil-type heat exchangers have a compact structure, a large heat transfer coefficient, a small footprint, high heat exchange efficiency, and low pressure drop, maximizing the utilization of thermal energy.

[0030] In this embodiment, the inlet of the heating gas buffer tank T101 is connected to a nitrogen source. An electrical contact pressure gauge PG301 is installed on the heating gas buffer tank T101 to detect the internal pressure. When the pressure gauge PG301 detects a decrease in the internal pressure of the heating gas buffer tank T101, nitrogen is introduced into the heating gas buffer tank T101 via the second valve V214, thereby maintaining the internal pressure of the heating gas buffer tank T101. The heating gas buffer tank T101 is equipped with a gas outlet switch valve KV101. When the first base temperature monitor TIA23A, the second base temperature monitor TIA23B, and the third base temperature monitor TIA23C detect an extremely low base temperature in the cold box, the gas outlet switch valve KV101 is opened to control the discharge of nitrogen. Simultaneously, the heating gas circulation fan P101 is activated. The fan initially dries and heats the nitrogen gas discharged from the heating gas buffer tank T101 and transfers it to the heating gas electric heater E101 for further heating. A heating gas temperature sensor TIA24 is installed between the heating gas electric heater E101 and the cold box foundation heat exchanger E102 to detect the temperature of the nitrogen gas entering the heat exchanger. The heating gas temperature sensor TIA24 and the heating gas electric heater E101 are correlated and regulated using PID control. If the heated nitrogen gas temperature is too high, the heating gas electric heater E101 is controlled to lower the heating temperature to prevent excessively high nitrogen gas temperature entering the cold box foundation, which could lead to excessive temperature fluctuations in the cold box foundation and consequently, excessive stress on the foundation. The heating gas electric heater E101 is equipped with an electric heater starter HS1201 for starting the heater and an electric heater protector TIAS1212 for preventing the heater from dry-burning. If the temperature of the heated nitrogen is detected to be low, the heater E101 is controlled to increase the heating temperature, thereby improving the heating efficiency of the cold box foundation. The inlet of the cold box foundation heat exchanger E102, located inside the cold box foundation, is connected to the outlet of the heating gas electric heater E101, and the outlet of the cold box foundation heat exchanger E102 is connected to the heating gas buffer tank T101. The nitrogen heated by the heating gas electric heater E101 enters the cold box foundation heat exchanger E102, where it exchanges heat and raises the temperature of the cold box foundation. The cooled nitrogen returns to the heating gas buffer tank T101 for recycling, reducing nitrogen usage and lowering production costs. The bottom of the heating gas buffer tank T101 is equipped with a buffer tank drain valve V302, which is opened periodically to drain the condensate and other impurities inside the heating gas buffer tank T101.

[0031] Because the bottom of the cold box is in direct contact with the cold box foundation, the low temperature inside the cold box is directly introduced into the foundation. Deformation of the foundation and the cold box bottom plate may affect the cold box bottom plate, leading to poor sealing or even brittleness. Therefore, in this embodiment, the lower shell of the cold box is made of stainless steel, which can effectively avoid brittleness. A second temperature monitoring unit is also installed at the bottom of the cold box, connected to the central control system. This unit detects temperature changes at the bottom of the cold box. If the internal temperature exceeds the normal range, it is considered that there is a liquid leak inside the cold box, and the central control system then controls an external heating system to heat the cold box foundation. The second temperature monitoring unit typically uses a platinum resistance thermometer. Temperature measurement points are set in various directions on the bottom of the cold box, generally no fewer than two. The thermometers must be installed vertically, not near container pipes, and not in contact with the internal bottom plate of the cold box. In this embodiment, two monitoring points are set: a first bottom temperature monitoring meter TIA21 and a second bottom temperature monitoring meter TIA22. In addition, when the temperature at the bottom of the cold box is too low, the operator should stop production, open the manhole at the top of the cold box to allow the cryogenic liquid to evaporate, and at the same time monitor the temperature of the cold box foundation to prevent the foundation from freezing, cracking and pulverizing.

[0032] like Figure 2As shown, due to the enclosed environment inside the cold box, to prevent air from entering and causing the perlite to become damp, which could lead to negative pressure deformation inside the cold box, this embodiment also includes a pressure-maintaining system to keep the internal pressure of the cold box within a normal range. The pressure-maintaining system includes a first valve V101, a pressure regulating valve PCV101, a flow detection unit, a sealing gas isolation valve, a pressure detection unit, and a sealing gas distributor unit. One end of the first valve V101 is connected to the sealing gas source, and the other end is connected to the pressure regulating valve PCV101, which regulates the sealing gas pressure. The sealing gas enters the pressure regulating valve PCV101 through the first valve V101, and the pressure is adjusted by the pressure regulating valve PCV101 to obtain a sealing gas pressure of approximately 3 kPa. In this embodiment, nitrogen is used as the sealing gas, and the pressure regulating valve PCV101 is a self-regulating valve. A sealing gas pressure detector PG101 is installed between the pressure regulating valve PCV101 and the flow detection unit to detect whether the regulated sealing gas has reached the target pressure range. In this embodiment, the flow detection unit, the sealing gas isolation valve, and the pressure detection unit are connected in series. The flow detection unit includes a first flow meter FI210, a second flow meter FI211, and a third flow meter FI212, which are arranged in parallel. The sealing gas isolation valve includes a first sealing gas isolation valve V210, a second sealing gas isolation valve V211, and a third sealing gas isolation valve V212, which are arranged in parallel. The pressure detection unit includes a first sealing gas pressure gauge PG210, a second sealing gas pressure gauge PG211, and a third sealing gas pressure gauge PG212, which are arranged in parallel. The pressure-regulated sealing gas is divided into three streams. First, it passes through flow meters FI210, FI211, and FI212 to monitor the flow rate entering the cold box. Then, it passes through three isolation valves V210, V211, and V212 to control the flow rate and prevent impact on downstream equipment. Finally, pressure gauges PG210, PG211, and PG212 detect the pressure of the sealing gas entering the cold box. After adjustment and detection, the sealing gas enters the sealing gas distribution unit inside the cold box through flange interfaces N1, N2, and N3.

[0033] like Figure 2 and Figure 3As shown, in this embodiment, the sealing gas distributor unit includes a first sealing gas distributor FP1, a second sealing gas distributor FP2, and a third sealing gas distributor FP3, each with multiple air outlets. The first sealing gas distributor FP1, the second sealing gas distributor FP2, and the third sealing gas distributor FP3 are connected via air inlet pipes through a first flange interface N1, a second flange interface N2, and a third flange interface N3, respectively. The first sealing gas distributor FP1 and the second sealing gas distributor FP2 are installed vertically from the top to the bottom of the tower, parallel to the side of the cold box. The third sealing gas distributor FP3 is horizontally positioned at the bottom of the cold box, and its shape is annular to ensure uniform distribution of sealing gas at each end point inside the cold box. Furthermore, because the sealing gas flows upwards, it facilitates the removal of moisture from the perlite inside the cold box.

[0034] In this embodiment, the top, middle, and bottom of the cold box are respectively equipped with a first cold box pressure gauge PIA15A, a second cold box pressure gauge PIA15B, and a third cold box pressure gauge PIA15C for detecting the internal pressure of the cold box. The top of the cold box is also equipped with a breather valve and a suction valve. The internal pressure of the cold box is normally required to be maintained at a slightly positive pressure. When the first cold box pressure gauge PIA15A, the second cold box pressure gauge PIA15B, or the third cold box pressure gauge PIA15C detects an abnormal pressure in a certain section of the cold box, the flow rate and pressure of the sealing gas entering the cold box are controlled to adjust the pressure and determine whether a leak of the cryogenic liquid has occurred. Simultaneously, the operator adjusts the internal pressure of the cold box by opening the breather valve or the suction valve.

[0035] This embodiment also provides a heating method to prevent cryogenic embrittlement of the cold box. First, the first valve V101 is opened to allow sealing gas to enter the pressure-holding subsystem. The pressure is adjusted by the pressure regulating valve PCV101 to obtain sealing gas within the target pressure range. The flow rate of the incoming sealing gas is detected by the flow detection unit. If it does not meet the requirements, the flow rate of the sealing gas is controlled by the sealing gas isolation valve. Then, the pressure detection unit further detects the sealing gas pressure. The sealing gas that meets the target flow rate and pressure is introduced into the sealing gas distributor unit through the flange interface. The sealing gas distributor unit releases the sealing gas from bottom to top into the internal space of the cold box, so that the internal pressure of the cold box is maintained in a slightly positive pressure state. The first cold box pressure detector PIA15A, the second cold box pressure detector PIA15B, and the third cold box pressure detector PIA15C detect whether the pressure in the upper, middle, and lower sections of the cold box is in a slightly positive pressure state. If not, the flow rate and pressure of the sealing gas are adjusted. At the same time, the monitoring data of the second temperature monitoring unit is used to determine whether there is a leak of cryogenic liquid inside the cold box.

[0036] The temperature changes of the cold box foundation and bottom are monitored by the first and second temperature monitoring units. If the temperature of the cold box foundation and bottom is lower than the working limit temperature range of the cold box, the gas outlet switch valve KV101 is opened by the central control system. The nitrogen in the heating gas buffer tank T101 is transferred to the heating gas electric heater E101 for heating by the heating gas circulating fan P101. The temperature of the heated nitrogen is detected by the heating gas temperature detector TIA24. If the temperature is too high, the heating temperature of the heating gas electric heater E101 is controlled to decrease, and vice versa. The heated nitrogen enters the cold box foundation heat exchanger E102 to heat the cold box foundation. The used nitrogen returns to the heating gas buffer tank T101 for reuse through the pipeline.

[0037] In addition, in this implementation, a GT101 gas analyzer is installed at the gas collection point in the top interlayer of the cold box, which can directly analyze the combustible, toxic, and oxygen concentrations in the top of the cold box. When the combustible gas detection value in the cold box interlayer rises, the DCS system will trigger a high alarm, reminding the internal operators to confirm. A yellow alarm on the cold box will sound with both sound and light, while external operators will use a handheld portable gas detector to detect the gas coming from the local exhaust port in the cold box interlayer for secondary instrument and process confirmation. When the gas detection value in the cold box interlayer continuously reaches the set alarm value, the DCS system will trigger a high-high alarm, with a pop-up alarm display, reminding the internal operators to confirm and perform appropriate operations. A red alarm on the cold box will sound with both sound and light, reminding external operators to evacuate immediately. The small and large nitrogen pipelines in the cold box will be manually opened, while the compressed air pipeline solenoid valve will remain closed. The compressed air will be purged from different heights around the cold box and from the bottom of the cold box, and then released through a one-way check valve to the flare or safety vent. Based on actual production needs, an on-site sampling and analysis point AP101 can be set on the top of the cold box to sample the gas inside the cold box and send it to the central control system for detection and analysis. If the gas exceeds the safe range, an alarm will be triggered.

[0038] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A heating system for preventing low-temperature brittleness in cold boxes, characterized in that, It includes a heating gas buffer tank (T101), a heating gas circulating fan (P101), a heating gas electric heater (E101), a cold box foundation heat exchanger (E102), and a first temperature monitoring unit for monitoring the temperature of the cold box foundation. The cold box foundation heat exchanger (E102) and the first temperature monitoring unit are installed inside the cold box foundation, and the first temperature monitoring unit is connected to the central control system. The inlet of the heating gas buffer tank (T101) is connected to a nitrogen source, and nitrogen is controlled to enter the heating gas buffer tank (T101) through a second valve (V214). The heating gas buffer tank (T101) is equipped with a gas outlet switch valve (KV101), which controls the discharge of nitrogen. The gas outlet switch valve (KV101) is connected to a heating gas circulating fan (P101), and the discharged nitrogen is discharged through the heating gas circulating fan (P101). 1) The gas is transferred to the heating gas electric heater (E101); the outlet of the heating gas electric heater (E101) is connected to the inlet of the cold box foundation heat exchanger (E102). The nitrogen gas heated by the heating gas electric heater (E101) enters the cold box foundation heat exchanger (E102) and raises the temperature of the cold box foundation; the outlet of the cold box foundation heat exchanger (E102) is connected to the heating gas buffer tank (T101) to recover the cooled nitrogen gas; A second temperature monitoring unit is installed at the bottom of the cold box. The second temperature monitoring unit is connected to the central control system. The temperature at the bottom of the cold box is detected by the second temperature monitoring unit. If the internal temperature of the cold box exceeds the normal temperature range, it is considered that there is a liquid leak inside the cold box, and then the central control system controls the heating.

2. The heating system for preventing low-temperature brittleness in a cold box according to claim 1, characterized in that, A heating gas temperature sensor (TIA24) is installed between the heating gas electric heater (E101) and the cold box base heat exchanger (E102). The heating gas temperature sensor (TIA24) and the heating gas electric heater (E101) are correlated and regulated by PID control.

3. The heating system for preventing low-temperature brittleness in a cold box according to claim 1, characterized in that, The heating gas buffer tank (T101) is equipped with an electric contact pressure gauge (PG301); the bottom of the heating gas buffer tank (T101) is equipped with a buffer tank drain valve (V302).

4. The heating system for preventing low-temperature brittleness in a cold box according to claim 1, characterized in that, The cold box base heat exchanger (E102) is a coil-type heat exchanger.

5. The heating system for preventing low-temperature brittleness in a cold box according to claim 1, characterized in that, The cold box is equipped with a pressure-maintaining subsystem for maintaining the internal pressure within a normal range. This subsystem includes a first valve (V101), a pressure regulating valve (PCV101), a flow detection unit, a sealing gas isolation valve, a pressure detection unit, and a sealing gas distributor unit. One end of the first valve (V101) is connected to a sealing gas source, and the other end is connected to the pressure regulating valve (PCV101) for adjusting the sealing gas pressure. The sealing gas enters the pressure regulating valve (PCV101) through the first valve (V101) for pressure regulation. After pressure regulation, the sealing gas sequentially passes through the flow detection unit, the sealing gas isolation valve, and the pressure detection unit before entering the sealing gas distributor unit located inside the cold box. The pressure detection unit is connected to the sealing gas distributor unit inside the cold box via a flange interface. The sealing gas distributor unit is positioned near the side wall and bottom of the cold box, releasing the sealing gas into the internal space of the cold box.

6. The heating system for preventing low-temperature brittleness in a cold box according to claim 5, characterized in that, A sealing gas pressure detector (PG101) is installed between the pressure regulating valve (PCV101) and the flow detection unit; the sealing gas distributor unit includes a first sealing gas distributor (FP1), a second sealing gas distributor (FP2), and a third sealing gas distributor (FP3). The first sealing gas distributor (FP1) and the second sealing gas distributor (FP2) are vertically arranged and parallel to the side of the cold box, while the third sealing gas distributor (FP3) is horizontally arranged at the bottom of the cold box; after pressure regulation, the sealing gas that meets the preset pressure range is divided into three paths, which pass through the sealing gas isolation valve of the flow detection unit and the pressure detection unit in sequence, and then enter the first sealing gas distributor (FP1), the second sealing gas distributor (FP2), and the third sealing gas distributor (FP3).

7. The heating system for preventing low-temperature brittleness in a cold box according to claim 6, characterized in that, The pressure regulating valve (PCV101) is a self-operated regulating valve.

8. The heating system for preventing low-temperature brittleness in a cold box according to claim 6, characterized in that, The top, middle and bottom of the cold box are respectively equipped with a first cold box pressure gauge (PIA15A), a second cold box pressure gauge (PIA15B) and a third cold box pressure gauge (PIA15C) for detecting the internal pressure of the cold box.

9. The heating system for preventing low-temperature brittleness in a cold box according to claim 6, characterized in that, The top of the cold box is equipped with a breather valve and a suction valve for adjusting the internal pressure of the cold box.

10. A heating method based on the heating system for preventing low-temperature embrittlement of a cold box as described in claim 9, characterized in that, The first valve (V101) is opened to allow sealing gas to enter the pressure-maintaining subsystem. The pressure is adjusted by the pressure regulating valve (PCV101) to obtain sealing gas within the target pressure range. The flow rate of the incoming sealing gas is detected by the flow detection unit. If it does not meet the requirements, the flow rate of the sealing gas is controlled by the sealing gas isolation valve. Then, the pressure detection unit further detects the sealing gas pressure. The sealing gas that meets the target flow rate and pressure is introduced into the sealing gas distributor unit through the flange interface. The sealing gas distributor unit releases the sealing gas from bottom to top into the internal space of the cold box, so that the internal pressure of the cold box is maintained in a slightly positive pressure state. The first cold box pressure sensor (PIA15A), the second cold box pressure sensor (PIA15B), and the third cold box pressure sensor (PIA15C) are used to detect whether the pressure in the upper, middle, and lower sections of the cold box is in a slightly positive pressure state. If not, the flow rate and pressure of the sealing gas are controlled and adjusted. At the same time, the monitoring data of the second temperature monitoring unit is used to determine whether there is a leak of the cryogenic liquid inside the cold box. The temperature changes of the cold box foundation and bottom are monitored by the first and second temperature monitoring units. If the temperature of the cold box foundation and bottom is lower than the working limit temperature range of the cold box, the gas outlet switch valve (KV101) is opened by the central control system. The nitrogen in the heating gas buffer tank (T101) is transferred to the heating gas electric heater (E101) for heating by the heating gas circulating fan (P101). The temperature of the heated nitrogen is detected by the heating gas temperature detector (TIA24). If the temperature is too high, the heating temperature of the heating gas electric heater (E101) is controlled to decrease, and vice versa. The heated nitrogen enters the cold box foundation heat exchanger (E102) to heat the cold box foundation. The used nitrogen returns to the heating gas buffer tank (T101) through the pipeline for reuse.

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