Heating system for preventing cold box from low-temperature cold brittleness

Abstract

The invention discloses a heating system for preventing a cold box from low-temperature cold brittleness, and belongs to the technical field of cold box protection. The system disclosed by the invention comprises a heating gas buffer tank, a heating gas circulating fan, a heating gas electric heating furnace, a cold box basic heat exchanger and the like. Nitrogen is sent to the electric heating furnace through the circulating fan to be heated, then the nitrogen enters the cold box base heat exchanger to heat the cold box base, and the cooled nitrogen is recycled to the buffer tank. The temperature monitoring unit is arranged at the bottom of the cold box, when it is detected that the temperature is abnormal, heating is controlled through the central control system, it is ensured that the cold box foundation obtains enough heat, and the problems of frost cracking and pulverization of the cold box foundation caused by low temperature are effectively solved. The system is further provided with a pressure maintaining subsystem, the pressure maintaining subsystem comprises a pressure adjusting valve, a flow detection unit, a sealing gas isolating valve, a pressure detection unit and a sealing gas distributor unit and is used for maintaining the pressure in the cold box to be stable, sealing gas is evenly released into the cold box through the sealing gas distributor unit, and the sealing gas pressure maintaining and even distribution effect is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of cold box protection, and in particular relates to a heating system for preventing a cold box from being cold and brittle at low temperatures. Background Art

[0002] With the rapid economic growth of the chemical industry in recent years, projects, particularly in air separation and alcohol-alkane production, have flourished. Cold boxes, as the heart of any project, remain the core technology for every company. They typically consist of containers, piping, and heat exchangers. Due to the low process temperatures, the interior of the cold box is primarily constructed of aluminum, with the shell constructed of stainless steel or carbon steel. Because the cold box operates in a low-temperature environment, pearlescent sand is required for insulation. This low temperature also creates a negative suction effect. Consequently, the cold box, acting as a carrier for the pearlescent sand and cryogenic equipment, simultaneously withstands the negative suction pressure. Furthermore, the cold box's containers and heat exchangers are kept below -100°C. Cryogenic liquids can easily damage the cold box, leading to secondary accidents. This necessitates the development of equipment that can withstand low temperatures and withstand negative pressure adsorption and the large rise in evaporative gases from liquid leakage without causing fatal impacts on the cold box.

[0003] The cold box is a sealed environment. To prevent air from entering the cold box and causing moisture to the pearlescent sand, to prevent deformation caused by negative pressure within the cold box, and to promptly replace leaked process gases within the cold box, the interlayer pressure within the cold box is generally required to remain slightly positive within the normal range. Traditional annular sealing gas distributors are installed at the bottom or middle of the cold box. In actual use, the sealing gas distribution in various parts of the cold box is uneven. In some sections of the cold box, the sealing gas pressure is negative, which easily absorbs moisture in the air and makes the pearlescent sand damp, thus affecting the thermal insulation effect of the pearlescent sand.

[0004] The cold box temperature includes the process temperature within the cold box and the base temperature and foundation temperature within the cold box. During normal production, if the process temperature within the cold box exceeds the normal process range, it may be due to a blockage, in addition to conventional overcooling or insufficient cooling capacity, and needs to be paid attention to by the internal operator. If there is a leak in the cold box pipes or containers, cryogenic liquid will flow down, causing the floor thermometer and the foundation temperature (installed on the cold box foundation) to drop rapidly, exceeding the normal temperature range, and the DCS system will alarm. The internal operator will check the temperature difference between the process temperature and the foundation temperature based on the alarm and historical trends to determine whether there is an internal leak and the approximate leak location. Changes in the cold box foundation temperature usually come from two aspects. First, the leakage of cryogenic liquid will cause the bottom temperature of the cold box to drop. In this case, the process operator needs to analyze the composition of the interlayer gas and check whether the pressure of the sealing gas test gauge is normal to determine. The second reason is the low temperature of the cold box foundation caused by the low temperature environment. Weather changes have a great impact on the cold box foundation. In a low temperature environment, the temperature of the cold box reaches -30℃, which reaches the working limit of the carbon steel cold box. 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 deformation of the cold box bottom plate may affect the cold box bottom plate, resulting in poor sealing and even cold brittleness. When these situations occur, operators should stop production, open the manhole on the top of the cold box, and let the cryogenic liquid evaporate. At the same time, observe the temperature of the cold box foundation to avoid freezing, cracking and powdering of the cold box foundation, and prevent the cold box foundation from powdering and causing collapse accidents. The Yima cold box explosion incident sounded the alarm for air separation and its supporting low-temperature equipment companies. Anti-cold brittleness and anti-collapse measures for cold boxes are urgent. Summary of the Invention

[0005] The purpose of the present invention is to slowly heat the bottom foundation of a cold box by using external heating gas to prevent the cold box foundation from powdering and collapsing, and to provide a heating system for preventing the cold box from being cold and brittle at low temperatures.

[0006] The specific technical solutions adopted in the present invention are as follows:

[0007] In a first aspect, the present invention provides a heating system to prevent a cold box from being brittle at low temperatures, comprising a heating gas buffer tank, a heating gas circulation fan, a heating gas electric heating furnace, a cold box base heat exchanger, and a first temperature monitoring unit for monitoring the temperature of the cold box base. The cold box base heat exchanger and the first temperature monitoring unit are arranged inside the cold box base, and the first temperature monitoring unit is connected to a central control system.

[0008] The air inlet end of the heating gas buffer tank is connected to the nitrogen gas source, and the nitrogen is controlled to enter the heating gas buffer tank through the second valve; the heating gas buffer tank is provided with a gas outlet switch valve, and the discharge of nitrogen is controlled by the gas outlet switch valve; the gas outlet switch valve is connected to the heating gas circulation fan, and the discharged nitrogen is transferred to the heating gas electric heating furnace through the heating gas circulation fan; the air outlet of the heating gas electric heating furnace is connected to the air inlet of the cold box foundation heat exchanger, and the nitrogen heated by the heating gas electric heating furnace enters the cold box foundation heat exchanger, and the cold box foundation is heated by the cold box foundation heat exchanger; the air outlet of the cold box foundation heat exchanger is connected to the heating gas buffer tank, and the nitrogen after cooling is recovered;

[0009] A second temperature monitoring unit is provided at the bottom of the cold box, which is connected to the central control system. The temperature of the bottom of the cold box is detected by the second temperature monitoring unit. If the temperature inside the cold box exceeds the normal temperature range, it is considered that liquid leakage occurs inside the cold box, and the heating is controlled by the central control system.

[0010] Preferably, a heating air temperature detector is provided between the heating gas electric heating furnace and the cold box basic heat exchanger, and PID control is used to perform correlation adjustment between the heating air temperature detector and the heating gas electric heating furnace.

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

[0012] Preferably, the cold box basic heat exchanger adopts a coil heat exchanger.

[0013] Preferably, the cold box is provided with a pressure maintaining subsystem for maintaining the internal pressure of the cold box within a normal range; the pressure maintaining subsystem comprises: 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 the sealing gas source, and the other end of the first valve is connected to the pressure regulating valve for regulating the sealing gas pressure; the sealing gas enters the pressure regulating valve through the first valve for pressure regulation, and the pressure-regulated sealing gas passes through the flow detection unit, the sealing gas isolation valve and the pressure detection unit in turn into the sealing gas distributor unit arranged inside the cold box, and the pressure detection unit is connected to the sealing gas distribution unit inside the cold box through a flange interface; the sealing gas distributor unit is arranged near the side wall and bottom of the cold box, and the sealing gas is released to the internal space of the cold box through the sealing gas distributor unit.

[0014] Preferably, a sealing gas pressure detector is arranged 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 sealing gas distributor and the second sealing gas distributor are arranged vertically and kept parallel to the side of the cold box, and the third sealing gas distributor is arranged horizontally at the bottom of the cold box; the sealing gas that meets the preset pressure range after pressure regulation is divided into three paths and passes through the sealing gas isolation valve of the flow detection unit and the pressure detection unit in turn to enter 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, a first cold box pressure detector, a second cold box pressure detector and a third cold box pressure detector are respectively provided on the top, middle and bottom of the cold box for detecting the internal pressure of the cold box.

[0017] Preferably, an exhalation valve and an intake valve for adjusting the internal pressure of the cold box are provided on the top of the cold box.

[0018] In a second aspect, the present invention provides a heating method to prevent a cold box from being cold and brittle at low temperatures. The method comprises opening a first valve to allow sealing gas to enter a pressure maintaining subsystem, adjusting the pressure by a pressure regulating valve to obtain sealing gas within a target pressure range, detecting the flow rate of the entering sealing gas by a flow detection unit, and if it does not meet the requirements, controlling the flow rate of the sealing gas by a sealing gas isolation valve, and then further detecting the pressure of the sealing gas by a pressure detection unit, allowing the sealing gas that meets the target flow rate and pressure to enter a sealing gas distributor unit through a flange interface, and releasing the sealing gas from bottom to top into the internal space of the cold box through the sealing gas distributor unit, so that the internal pressure of the cold box is maintained in a slightly positive pressure state; detecting whether the pressures in the upper, middle and lower sections of the cold box are in a slightly positive pressure state by a first cold box pressure detector, a second cold box pressure detector and a third cold box pressure detector, controlling the flow rate and pressure of the sealing gas to be adjusted, and at the same time judging whether the low-temperature liquid inside the cold box is leaking in combination with the monitoring data of the second temperature monitoring unit;

[0019] The temperature changes of the cold box base and the bottom of the cold box are monitored by the first temperature monitoring unit and the second temperature monitoring unit. If the temperature of the cold box base and the bottom of the cold box is lower than the operating limit temperature range of the cold box, the gas outlet switch valve is controlled to open by the central control system, and the nitrogen in the heating gas buffer tank is transferred to the heating gas electric heating furnace for heating through 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 heating furnace is controlled to be lowered, otherwise it is increased; the heated nitrogen enters the cold box base heat exchanger to heat the cold box base, and 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 beneficial effects:

[0021] The present invention heats the cold box foundation by providing a cold box foundation heating device and utilizing heated circulating nitrogen to ensure that the bottom of the cold box obtains sufficient heat, effectively avoiding the problems of freezing and pulverizing of the cold box foundation caused by low temperature, thereby ensuring the structural integrity of the cold box foundation. When the temperature inside the cold box is low, the operator can use an external circulating heating system to provide a heat source for the cold box bottom foundation to prevent the foundation from freezing and pulverizing due to low temperature and causing collapse accidents, thereby enhancing the safety and reliability of the cold box, extending the service life of the cold box, and reducing maintenance costs. At the same time, the internal pressure distribution of the cold box is optimized, and sealing gas distributors arranged from top to bottom are added to make the sealing gas distribution in each area of ​​the cold box more uniform, thereby enhancing the sealing gas pressure maintenance and uniform distribution effect, further improving the stability and safety of the cold box operation, and reducing the risk of accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the cold box basic heating system provided in this embodiment;

[0023] Figure 2 A schematic diagram of the cold box pressure maintenance provided in this embodiment;

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

[0025] In the figure: first valve V101, pressure regulating valve PCV101, sealing gas pressure detector PG101, first flowmeter FI210, second flowmeter FI211, third flowmeter FI212, first sealing gas isolation valve V210, second sealing gas isolation valve V211, third sealing gas isolation valve V212, first sealing gas pressure detection gauge PG210, second sealing gas pressure detection gauge PG211, third sealing gas pressure detection gauge 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 detection gauge PIA15A, second cold box pressure detection gauge PIA15B, Third cold box pressure detector 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 circulation fan P101, heating gas electric heating furnace E101, heating gas temperature detector TIA24, cold box base heat exchanger E102, on-site sampling and analysis point AP101, gas analyzer GT101, electric heating furnace starter HS1201, electric heating furnace protector TIAS1212. DETAILED DESCRIPTION

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0027] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the materials described are commercially available unless otherwise specified; in the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connect", "set", and "install" should be understood in a broad sense, for example, they can be fixedly connected or set, or detachably connected or set, or connected or set as a whole. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. The sequential orientation indicated by the terms "in sequence", "through", "through", etc. is based on the sequential orientation shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific sequential orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0028] In the description of the present invention, it should be understood that the terms "first," "second," and "third" are used solely for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly specifying the number of technical features being described. Therefore, a feature identified as "first," "second," or "third" may explicitly or implicitly include at least one of such features.

[0029] like Figure 1 As shown, as a preferred embodiment of the present invention, this embodiment provides a heating system for preventing a cold box from becoming brittle due to low temperatures. The system includes a heating gas buffer tank T101, a heating gas circulation fan P101, a heating gas electric heater E101, a cold box base heat exchanger E102, and a first temperature monitoring unit for monitoring the cold box base temperature. The cold box base heat exchanger E102 and the first temperature monitoring unit are disposed within the cold box base, and the first temperature monitoring unit is connected to the central control system. The first temperature monitoring unit includes a first base temperature monitor TIA23A, a second base temperature monitor TIA23B, and a third base temperature monitor TIA23C. When the first base temperature monitor TIA23A, the second base temperature monitor TIA23B, and the third base temperature monitor TIA23C detect a rapid drop in the cold box base temperature, exceeding the normal temperature range, the central control system issues an alarm. Based on the alarm and historical trends, the operator verifies the temperature difference between the cold box internal temperature and the cold box base temperature to determine whether an internal leak has occurred and the approximate location of the leak. When the cold box foundation temperature is too low, the cold box foundation heat exchanger E102 is activated to heat the cold box foundation to maintain the cold box foundation temperature and prevent the cold box foundation from pulverizing due to low temperature, which could cause a safety accident. In this embodiment, the cold box foundation heat exchanger E102 uses a coil heat exchanger. Coil heat exchangers have a compact structure, a high heat transfer coefficient, a small footprint, high heat exchange efficiency, and low resistance and pressure drop, maximizing thermal energy utilization.

[0030] In this embodiment, the inlet of the heated gas buffer tank T101 is connected to a nitrogen gas source. An electric contact pressure gauge PG301 is installed on the heated gas buffer tank T101 to monitor the internal pressure of the heated gas buffer tank T101. When the electric contact pressure gauge PG301 detects a decrease in the internal pressure of the heated gas buffer tank T101, nitrogen is controlled to enter the heated gas buffer tank T101 through a second valve V214, thereby maintaining the internal pressure of the heated gas buffer tank T101. A gas outlet on-off valve KV101 is installed on the heated gas buffer tank T101. When the first, second, and third base temperature monitors TIA23A, TIA23B, and TIA23C detect that the cold box base temperature has reached a critical low value, the gas outlet on-off valve KV101 is opened to control the discharge of nitrogen. At the same time, the heated air circulation fan P101 is activated. It initially dries and heats the nitrogen discharged from the heated air buffer tank T101 and transfers it to the heated gas-electric heater E101 for further heating. A heated air temperature detector TIA24 is installed between the heated gas-electric heater E101 and the cold box foundation heat exchanger E102 to monitor the temperature of the nitrogen entering the cold box foundation heat exchanger E102. PID control is used to coordinate and regulate the heated air temperature detector TIA24 and the heated gas-electric heater E101. If the heated nitrogen temperature is too high, the heated gas-electric heater E101 is controlled to reduce the heating temperature to prevent the nitrogen temperature from being too high before entering the cold box foundation, which could lead to excessive temperature fluctuations and thus excessive stress in the cold box foundation. The heating gas-electric heater E101 is equipped with a furnace starter HS1201 for activating the heating gas-electric heater E101 and a furnace protector TIAS1212 for preventing the heating gas-electric heater E101 from burning dry. If the heated nitrogen temperature is detected to be low, the heating gas-electric heater E101 is controlled to increase the heating temperature, thereby improving the heating efficiency of the cold box foundation. The air inlet of the cold box foundation heat exchanger E102, located within the cold box foundation, is connected to the air outlet of the heating gas-electric heater E101. The air outlet of the cold box foundation heat exchanger E102 is also 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 is then returned to the heating gas buffer tank T101 for recycling, reducing nitrogen usage and lowering production costs. A buffer tank drain valve V302 is provided at the bottom of the heating gas buffer tank T101, which is opened regularly to discharge condensed water and other impurities in the heating gas buffer tank T101.

[0031] Because the bottom of the cold box is in direct contact with the foundation, the cold box's internal low temperatures are directly transferred to the foundation. Deformation of the foundation and the cold box floor can affect the floor, leading to poor sealing and even brittleness. Therefore, in this embodiment, the lower shell of the cold box is made of stainless steel to effectively prevent brittleness. A second temperature monitoring unit is also installed at the bottom of the cold box. This unit is connected to the central control system and detects temperature changes at the bottom of the cold box. If the internal temperature of the cold box exceeds the normal range, it is considered a liquid leak. The central control system then controls the external heating system to heat the cold box foundation. The second temperature monitoring unit is typically a platinum resistance thermometer. Temperature measurement points are located at various locations on the bottom of the cold box, typically at least two. The thermometers must be installed vertically, away from container pipes and away from the internal floor. In this embodiment, two monitoring points are provided: a first bottom temperature monitor TIA21 and a second bottom temperature monitor TIA22. In addition, when the temperature at the bottom of the cold box is too low, the operator should stop production, open the manhole on the top of the cold box to allow the low-temperature liquid to evaporate, and at the same time observe the temperature of the cold box foundation to prevent the cold box foundation from freezing, cracking and powdering.

[0032] like Figure 2As shown, since the cold box is sealed, a pressure-maintaining system is provided in this embodiment to maintain the internal pressure of the cold box within a normal range to prevent air from entering the cold box, which could cause moisture in the pearlescent sand and, in turn, negative pressure deformation within the cold box. 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. Sealing gas enters the pressure-regulating valve PCV101 through the first valve V101, where the pressure is adjusted to approximately 3 kPa. In this embodiment, nitrogen is used as the sealing gas, and the pressure-regulating valve PCV101 is a self-operated regulating valve. A sealing gas pressure detector PG101 is provided 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, all 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, all arranged in parallel. The pressure detection unit includes a first sealing gas pressure detection gauge PG210, a second sealing gas pressure detection gauge PG211, and a third sealing gas pressure detection gauge PG212, all arranged in parallel. The regulated sealing gas is divided into three routes. First, it passes through the first flowmeter FI210, the second flowmeter FI211, and the third flowmeter FI212 to monitor the flow rate of the sealing gas entering the cold box. It then passes through the first sealing gas isolation valve V210, the second sealing gas isolation valve V211, and the third sealing gas isolation valve V212 to control the flow rate of the sealing gas entering the cold box to prevent it from affecting downstream equipment. The first sealing gas pressure detector PG210, the second sealing gas pressure detector PG211, and the third sealing gas pressure detector PG212 detect the pressure of the sealing gas entering the cold box. The regulated and tested sealing gas enters the sealing gas distribution unit inside the cold box through the first flange interface N1, the second flange interface N2, and the third flange interface 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, and a plurality of air outlet holes are densely distributed on the three sealing gas distributors. The first sealing gas distributor FP1, the second sealing gas distributor FP2, and the third sealing gas distributor FP3 are connected through the first flange interface N1, the second flange interface N2, and the third flange interface N3 air inlet pipes respectively. The first sealing gas distributor FP1 and the second sealing gas distributor FP2 are vertically installed from the top of the tower to the bottom of the tower, parallel to the side of the cold box, and the third sealing gas distributor FP3 is horizontally arranged at the bottom of the cold box, and the shape of the third sealing gas distributor FP3 is set to be ring-shaped to ensure that the sealing gas at each end point inside the cold box is evenly distributed. And because the sealing gas runs from bottom to top, it is convenient to drive away the moisture in the pearlescent sand in the cold box.

[0034] In this embodiment, a first cold box pressure gauge (PIA15A), a second cold box pressure gauge (PIA15B), and a third cold box pressure gauge (PIA15C) are respectively provided at the top, middle, and bottom of the cold box for detecting the internal pressure of the cold box. An exhalation valve and an inhalation valve are also provided at the top of the cold box. Normally, the interlayer pressure within the cold box is 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 section within 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 the cryogenic liquid within the cold box is leaking. Simultaneously, the operator adjusts the internal pressure of the cold box by opening the exhalation valve or the inhalation valve.

[0035] This embodiment also provides a heating method to prevent the cold box from being brittle due to low temperature. First, 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 a target pressure range. The flow rate of the entering sealing gas is detected by the flow detection unit. If it does not meet the requirements, the sealing gas flow is controlled by the sealing gas isolation valve. Then, the sealing gas pressure is further detected by the pressure detection unit. The sealing gas that meets the target flow rate and pressure enters the sealing gas distributor unit through the flange interface. The sealing gas is released from the bottom to the top into the internal space of the cold box through the sealing gas distributor unit, 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 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 sealing gas flow rate and pressure are controlled and adjusted. At the same time, the monitoring data of the second temperature monitoring unit is combined to determine whether the low-temperature liquid in the cold box is leaking.

[0036] The temperature changes of the cold box foundation and the cold box bottom are monitored by the first temperature monitoring unit and the second temperature monitoring unit. If the temperature of the cold box foundation and the cold box bottom is lower than the cold box working limit temperature range, the gas outlet switch valve KV101 is controlled to open by the central control system, and the nitrogen in the heating gas buffer tank T101 is transferred to the heating gas electric heating furnace E101 for heating through the heating gas circulation 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 heating furnace E101 is controlled to be lowered, otherwise it is increased; the heated nitrogen enters the cold box foundation heat exchanger E102 to heat the cold box foundation, and the used nitrogen returns to the heating gas buffer tank T101 through the pipeline for reuse.

[0037] In addition, in this implementation, a GT101 gas analyzer is installed at the top interlayer gas collection point of the cold box, directly analyzing flammable, toxic, and oxygen concentration gases within the cold box. When the combustible gas level in the cold box interlayer rises, the DCS system triggers a high alarm, prompting internal operators to confirm. A yellow alarm on the on-site cold box activates with audible and visual signals, while an external operator uses a portable gas detector to verify the instrumentation and process by measuring the gas exiting the on-site interlayer gas vent. If the interlayer gas level consistently reaches the set alarm threshold, the DCS system triggers a high alarm, with a pop-up screen prompting internal operators to confirm and take appropriate action. A red alarm on the on-site cold box activates with audible and visual signals, prompting external operators to evacuate immediately. The small and large nitrogen lines in the cold box are manually opened, while the solenoid valve in the compressed air line remains closed. Displacement occurs at various heights around the cold box and at the bottom, and is vented through a one-way check valve to a flare or safety vent. According to 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 it exceeds the safety range, an alarm will be issued.

[0038] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A heating system for preventing a cold box from being brittle at low temperatures, characterized in that: It includes a heating gas buffer tank (T101), a heating gas circulation fan (P101), a heating gas electric heating furnace (E101), a cold box base heat exchanger (E102) and a first temperature monitoring unit for monitoring the temperature of the cold box base. The cold box base heat exchanger (E102) and the first temperature monitoring unit are arranged inside the cold box base, and the first temperature monitoring unit is connected to the central control system. The air inlet end of the heating gas buffer tank (T101) is connected to the nitrogen gas source, and the nitrogen gas is controlled to enter the heating gas buffer tank (T101) through the second valve (V214); the heating gas buffer tank (T101) is provided with a gas outlet switch valve (KV101), and the discharge of nitrogen is controlled by the gas outlet switch valve (KV101); the gas outlet switch valve (KV101) is connected to the heating gas circulation fan (P101), and the discharged nitrogen gas is discharged through the heating gas circulation fan (P101). 1) Transfer to the heating gas-electric heating furnace (E101); the air outlet of the heating gas-electric heating furnace (E101) is connected to the air inlet of the cold box base heat exchanger (E102), and the nitrogen heated by the heating gas-electric heating furnace (E101) enters the cold box base heat exchanger (E102), and the cold box base is heated by the cold box base heat exchanger (E102); the air outlet of the cold box base heat exchanger (E102) is connected to the heating gas buffer tank (T101), and the nitrogen after cooling is recovered; A second temperature monitoring unit is provided at the bottom of the cold box, which is connected to the central control system. The temperature of the bottom of the cold box is detected by the second temperature monitoring unit. If the temperature inside the cold box exceeds the normal temperature range, it is considered that liquid leakage occurs inside the cold box, and the heating is controlled by the central control system.

2. The heating system for preventing cold box from being brittle at low temperature according to claim 1 is characterized in that: A heating gas temperature detector (TIA24) is provided between the heating gas electric heating furnace (E101) and the cold box basic heat exchanger (E102), and PID control is used to perform correlation adjustment between the heating gas temperature detector (TIA24) and the heating gas electric heating furnace (E101).

3. The heating system for preventing cold box from being brittle at low temperature according to claim 1 is characterized in that: The heating gas buffer tank (T101) is provided with an electric contact pressure gauge (PG301); and a buffer tank drain valve (V302) is provided at the bottom of the heating gas buffer tank (T101).

4. The heating system for preventing cold box from being brittle at low temperature according to claim 1 is characterized in that: The cold box basic heat exchanger (E102) adopts a coil heat exchanger.

5. The heating system for preventing cold box from being brittle at low temperature according to claim 1 is characterized in that: The cold box is provided with a pressure maintaining subsystem for maintaining the internal pressure of the cold box within a normal range; the pressure maintaining subsystem comprises: 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 of the first valve (V101) is connected to the pressure regulating valve (PCV101) for regulating the sealing gas pressure; the sealing gas enters the pressure regulating valve (PCV101) through the first valve (V101) for pressure regulation, and the pressure-regulated sealing gas passes through the flow detection unit, the sealing gas isolation valve and the pressure detection unit in sequence and enters the sealing gas distributor unit arranged inside the cold box, and the pressure detection unit is connected to the sealing gas distribution unit inside the cold box through a flange interface; the sealing gas distributor unit is arranged 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.

6. The heating system for preventing a cold box from being brittle at low temperatures according to claim 5 is characterized in that: A sealing gas pressure detector (PG101) is arranged 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 arranged vertically and kept parallel to the side of the cold box, and the third sealing gas distributor (FP3) is arranged horizontally at the bottom of the cold box; the sealing gas that meets the preset pressure range after pressure regulation 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 to 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 a cold box from being brittle at low temperatures according to claim 6 is characterized in that: The pressure regulating valve (PCV101) is a self-operated regulating valve.

8. The heating system for preventing a cold box from being brittle at low temperatures according to claim 6 is characterized in that: The top, middle and bottom of the cold box are respectively provided with a first cold box pressure detection gauge (PIA15A), a second cold box pressure detection gauge (PIA15B) and a third cold box pressure detection gauge (PIA15C) for detecting the internal pressure of the cold box.

9. The heating system for preventing a cold box from being brittle at low temperatures according to claim 6, characterized in that: An exhalation valve and an inhalation valve for adjusting the internal pressure of the cold box are provided on the top of the cold box.

10. A heating method for preventing a cold box from being brittle at low temperatures as claimed in claim 9, characterized in that: Open the first valve (V101) to allow the sealing gas to enter the pressure maintaining subsystem, adjust the pressure through the pressure regulating valve (PCV101) to obtain sealing gas within the target pressure range, detect the flow rate of the entering sealing gas through the flow detection unit, and if it does not meet the requirements, control the sealing gas flow through the sealing gas isolation valve, and then further detect the sealing gas pressure through the pressure detection unit, and allow the sealing gas that meets the target flow rate and pressure to enter the sealing gas distributor unit through the flange interface, and release the sealing gas from bottom to top into the internal space of the cold box through the sealing gas distributor unit, so that the internal pressure of the cold box is maintained in a slightly positive pressure state; use the first cold box pressure detector (PIA15A), the second cold box pressure detector (PIA15B) and the third cold box pressure detector (PIA15C) 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, control the sealing gas flow and pressure to adjust, and at the same time, combine the monitoring data of the second temperature monitoring unit to determine whether the low-temperature liquid in the cold box is leaking; The temperature changes of the cold box base and the cold box bottom are monitored by the first temperature monitoring unit and the second temperature monitoring unit. If the temperature of the cold box base and the cold box bottom is lower than the cold box working limit temperature range, the gas outlet switch valve (KV101) is controlled to open by the central control system, and the nitrogen in the heating gas buffer tank (T101) is transferred to the heating gas electric heating furnace (E101) for heating through the heating gas circulation 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 heating furnace (E101) is controlled to be lowered, otherwise it is increased; the heated nitrogen enters the cold box base heat exchanger (E102) to heat the cold box base, and the used nitrogen returns to the heating gas buffer tank (T101) through the pipeline for reuse.

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