Method for trapping high-purity dry ice

Abstract

The invention discloses a trapping method of high-purity dry ice. The method comprises the steps that firstly, gas is pretreated, air dust, particulate matter and moisture are removed, the gas is compressed to 2.4 Mpa, the compressed gas enters an expansion machine, an internal molded line of the expansion machine is specially designed and matched with an automatic control system, adiabatic expansion cooling is achieved by 100 K, and carbon dioxide in mixed gas is promoted to preferentially reach a supersaturated state and begins to desublimate. A filter screen or a centrifugal dry ice separation device is utilized to efficiently separate and collect dry ice particles from mixed gas, and non-desublimated gas is compressed and recycled for other industrial links or is discharged after being purified to reach the standard. Compared with a traditional dry ice preparation technology, the method has the advantages that an energy recycling mechanism is innovatively constructed, energy generated by external acting of the screw expander is used for driving pretreatment equipment, and the energy utilization rate is increased. The method is suitable for various fields with strict requirements on the purity of the dry ice, such as food preservation, stage special effects, industrial cleaning, medical treatment and the like, and has remarkable economic and environmental benefits.

Description

Technical Field

[0001] The invention relates to the technical field of dry ice preparation, and in particular to a method for capturing dry ice by cooling using a compression and screw expander. Background Art

[0002] Dry ice, or solid carbon dioxide, is widely used in many fields such as food preservation, stage special effects, industrial cleaning, and medical treatment. Traditional methods of preparing dry ice mostly separate carbon dioxide from industrial waste gas, and then obtain it through compression and cooling. However, this method has obvious disadvantages. The composition of industrial waste gas is complex, and it is difficult to remove impurities. It not only increases the complexity and cost of the process, but also limits the separation efficiency. At the same time, conventional refrigeration methods have high energy consumption and large equipment investment, which is not conducive to large-scale, low-cost production of dry ice. With the increasing environmental protection requirements and the continuous growth of demand for dry ice in industrial production, it is urgent to develop efficient, energy-saving and low-cost dry ice capture methods. Summary of the invention

[0003] Purpose of the Invention

[0003] The present invention aims to provide an innovative method for capturing dry ice by cooling using a compression and screw expander, so as to solve the problems of low capture efficiency, high energy consumption and high cost in the existing dry ice preparation technology, and to achieve efficient and energy-saving capture of dry ice from air at normal temperature and pressure.

[0004] Innovative energy recycling mechanism: This method innovatively combines air compression with screw expander cooling to form a unique energy circulation system. During the air compression stage, the outside world does work on the air to increase its pressure to 2.4Mpa, and the temperature rises accordingly. During the screw expander cooling stage, the high-pressure air adiabatically expands to do work externally. This part of energy is not directly dissipated, but is cleverly used to drive other auxiliary equipment, such as filters and dryers in the air pretreatment stage, to achieve cascade utilization of energy and greatly improve energy utilization. This is one of the key innovations that distinguishes it from traditional refrigeration and dry ice preparation technology.

[0005] Precise temperature control and directional desublimation of carbon dioxide: Through the innovative design of the internal profile of the screw expander and the use of an automated control system, the air expansion cooling range can be precisely controlled to reach 100K. This precise temperature control can cause the carbon dioxide in the mixed gas to reach a supersaturated state first and directional desublimation into dry ice particles, reducing the interference of other gases caused by excessive cooling. Compared with traditional processes, it significantly improves the desublimation efficiency of carbon dioxide and the purity of dry ice generation.

[0006] Integrated process design: air pretreatment, compression, cooling, dry ice separation, and non-condensed gas treatment are integrated into an organic whole. Each link works closely together to achieve efficient transmission and conversion of materials and energy. For example, the pretreated air directly enters the compressor, and the compressed high-temperature and high-pressure air seamlessly connects to the screw expander, reducing energy loss and gas leakage risks in the intermediate links, and improving the stability and operating efficiency of the entire system. Specific steps of dry ice capture method

[0007] Air compression steps: Select a suitable type of compressor, such as a piston compressor, screw compressor or centrifugal compressor, and introduce air at room temperature of 20°C and normal pressure. Taking a piston compressor as an example, the air is compressed by the reciprocating motion of the piston, and the air pressure is stably increased to 2.4Mpa through the compressor's own pressure control system. During the compression process, the internal energy of the air increases due to the work done by the outside world on the air. The temperature monitoring device is used to feedback the temperature change in real time. Under normal circumstances, the compressed air temperature will rise to about 130°C-150°C.

[0008] Screw expander cooling steps: Introduce compressed high-pressure air into the twin-screw expander. The internal profile of the screw expander has been specially optimized to ensure a high isentropic efficiency, usually up to about 80%. The automatic control system it is equipped with dynamically adjusts the operating parameters of the expander based on the pressure, temperature and other parameters of the inlet air. The high-pressure air adiabatically expands in the expander to do work externally, and its own internal energy is reduced, achieving a precise cooling of 100K, bringing the temperature down to the range of 30℃-50℃. In this temperature range, the carbon dioxide in the mixed gas reaches a supersaturated state first due to its relatively high freezing point, and begins to condense to form dry ice particles.

[0009] Dry ice separation and collection steps: The mixed gas after being cooled by the screw expander, including dry ice particles, uncondensed air and other impurity gases, enters the dry ice separation device. If a separation device with a multi-layer filter structure is used, the gas first passes through a large-aperture filter to initially filter out larger particle impurities, and then passes through a small-aperture filter to capture dry ice particles and collect them in a storage container. If a centrifugal separation device is used, the centrifugal force is used to throw the dry ice particles toward the inner wall of the device, and then they are collected into a storage container through a scraper device. According to testing, the purity of dry ice collected using the method of the present invention can reach 98%-99%.

[0010] Air pretreatment step (optional): Before the air compression step, normal temperature and pressure air is passed through a filter. Different combinations of filter meshes with different filtration precisions can be selected for the filter to effectively remove impurities such as dust and particulate matter in the air. Then the air is passed through a dryer. For example, an adsorption dryer is used, and desiccants are used to adsorb moisture, greatly reducing the humidity of the air and avoiding adverse effects on the equipment operation and dry ice purity caused by water condensation during subsequent compression and cooling processes.

[0011] Ungasified gas treatment step (optional): After the dry ice separation and collection step, for the ungasified gas after separating dry ice particles, it can be compressed to a suitable pressure by a small compressor and then introduced into other gas-using links within the factory that match the gas pressure and composition requirements to achieve resource recovery and reuse. If the composition of the ungasified gas is complex and cannot be directly recycled, it is purified, for example, by chemical absorption, catalytic conversion, etc., and after meeting the environmental protection emission standards, it is discharged into the atmosphere.

[0005] Verified by multiple experiments, under standard working conditions (room temperature 20°C, atmospheric pressure, and the treated air flow rate is 100,000 cubic meters per hour), the dry ice capture efficiency of the method of the present invention is significantly higher than that of traditional methods. Taking the separation of carbon dioxide from the air and the preparation of dry ice as an example, the capture efficiency of the traditional process is about 30%-40%, while the method of the present invention can stably achieve a capture efficiency of 60%-70% for the sublimation of carbon dioxide into dry ice through an optimized compression and cooling process. This means that under the same time and air treatment volume, the method of the present invention can produce more dry ice, greatly improving production efficiency and meeting the growing market demand for dry ice.

[0006] Equipment investment cost: Compared with traditional dry ice preparation technologies, the method of the present invention does not require complex and expensive industrial waste gas impurity treatment equipment and also reduces the dependence on high-energy-consuming refrigeration equipment. For example, the investment cost of multi-stage purification equipment for treating complex components of industrial waste gas in traditional processes is as high as millions or even tens of millions of yuan, while the present invention only needs to configure relatively simple air pretreatment equipment (filters, dryers, etc.) and conventional compressors and screw expanders, and the total equipment investment cost can be reduced by 30%-50%.

[0014] Energy consumption cost: Utilizing the characteristic of the screw expander to do external work for cooling reduces the additional refrigeration energy consumption. Through actual operation measurement, the energy consumption for producing 1 ton of dry ice by traditional refrigeration methods is about 280 kWh, while the energy consumption of the method of the present invention can be reduced to 140 kWh, and the energy consumption cost is reduced by about 40%-60%. In the long-term operation, the cost advantage brought by the energy-saving effect is extremely significant.

[0007] Operation and maintenance cost: Due to the relatively simple equipment structure and high integration degree of each link, the number of failure points is reduced, and the maintenance difficulty and frequency are decreased. For the traditional process, due to the complex equipment, the annual maintenance cost accounts for 10%-15% of the equipment investment, while the operation and maintenance cost of the method of the present invention can be controlled within 5%-8% of the equipment investment, further reducing the overall cost. Beneficial effects

[0008] Efficient capture: The unique compression and screw expander cooling process can effectively capture dry ice from the air. Compared with the traditional method of capturing carbon dioxide from complex industrial waste gas, the process is more concise and the capture efficiency is higher.

[0017] Energy conservation and consumption reduction: Using the screw expander to do external work to achieve cooling, fully recovering energy, reducing additional refrigeration energy consumption. Compared with conventional refrigeration means, the energy consumption is significantly reduced, and the production cost is decreased.

[0018] Cost reduction: The entire process equipment is relatively simple, reducing complex impurity treatment equipment and high-energy-consuming refrigeration equipment. The equipment investment cost is low, and the long-term operation cost reduction brought by energy conservation makes the overall cost advantage obvious.

[0019] High product purity: Pretreating the air to reduce the influence of impurities and moisture. Using a suitable separation device in the dry ice separation process can effectively improve the dry ice purity, meeting the strict requirements for dry ice quality in different fields.

[0020] Environmental protection and sustainability: Realizing the resource utilization of carbon dioxide in the air, reducing carbon emissions. At the same time, recycling or purifying the uncondensed gas, which conforms to the environmental protection concept and has good environmental benefits and sustainability. Description of the drawings

[0009] Figure 1 For the relevant equipment structure and process flow of the present invention, refer to the attached Figure 1 .

[0010] 1. Gas input port 2. Compressor 3. High-pressure gas output port 4. Screw expander 5. Low-temperature gas output port 6. Dry ice trap 7. Exhaust gas discharge port 8. Dry ice cold box 9. Dry ice manufacturing workshop Specific implementation manners

[0011] Air compression: Select a piston compressor with a rated pressure of up to 3 Mpa and a flow rate meeting the process requirements. Introduce the air at normal temperature of 20°C and normal pressure into the piston compressor, and compress the air through the reciprocating motion of the piston. During the compression process, the pressure control system of the compressor stably controls the pressure at 2.4 Mpa, and at the same time, the temperature monitoring device real-time feedbacks the temperature change. The temperature of the compressed air rises to about 150°C.

[0023] Temperature reduction of the screw expander: The compressed high-pressure air is introduced into the twin-screw expander. The internal profile of the screw expander has been optimized, and the isentropic efficiency can reach 80%. The automatic control system adjusts the operating parameters of the expander according to the inlet air parameters, enabling the air to expand and do work fully in the expander, with the temperature reduced by 100K to about -50°C. During this process, carbon dioxide begins to sublime and form dry ice particles.

[0024] Dry ice separation and collection: The cooled mixed gas enters the dry ice separation device with a multi-layer filter structure. The large-aperture filter first filters out larger particle impurities, and then the small-aperture filter captures the dry ice particles and collects them into the storage container. After detection, the purity of the collected dry ice reaches 98%.

[0025] Treatment of non-sublimed gas: The non-sublimed gas after dry ice separation is compressed to an appropriate pressure by a small compressor and then introduced into other air-using processes in the factory to achieve resource recovery and utilization. Example 2

[0026] Air pretreatment: First, the normal-temperature and normal-pressure air is passed through a filter to remove impurities such as dust and particulate matter, and then through a dryer to reduce the humidity.

[0027] Air compression: A combination of a screw compressor and a centrifugal compressor is used. First, the screw compressor performs preliminary compression, and then the centrifugal compressor further compresses it to 2.4 Mpa. During the compression process, the pressure and temperature are stable and controllable, and the temperature of the compressed air is about 130°C.

[0028] Temperature reduction of the screw expander: The compressed air enters the screw expander equipped with an auxiliary spray cooling device. When the expander operates, the spray device also works, spraying low-temperature coolant on the gas before and after expansion to accelerate the temperature reduction. Finally, the air temperature is reduced by 100K to about -30°C, and a large amount of carbon dioxide sublimes into dry ice particles.

[0029] Dry ice separation and collection: A centrifugal separation device is used to use centrifugal force to throw the dry ice particles towards the inner wall of the device and collect them into the storage container through a scraping device. After detection, the purity of the dry ice reaches 99%.

[0030] Treatment of non-sublimed gas: The non-sublimed gas is treated and purified to meet the environmental protection discharge standards and then discharged into the atmosphere.

Claims

1. A method for capturing dry ice from air at normal temperature and pressure, characterized in that, The steps include the following: Air compression step: Use a compressor to compress the air at normal temperature and pressure, increasing the gas pressure to 2.4 Mpa. During the compression process, the air temperature rises due to the work done by compression. Screw expander cooling step: Introduce the compressed high-pressure air into the screw expander. Utilize the working principle of the screw expander to make the air expand and do work within the expander. The air doing work externally leads to a reduction in internal energy and a temperature drop of 100 K. During this process, since the freezing point of carbon dioxide is relatively high, as the temperature drops, carbon dioxide will gradually reach supersaturation and start to sublime to form dry ice particles. Dry ice separation and collection step: The mixed gas (containing dry ice particles, un-sublimed air, and other impurity gases) after passing through the screw expander enters the dry ice separation device. Through physical separation means such as filtration and centrifugation, the dry ice particles are separated from the mixed gas and collected.

2. The method according to claim 1, wherein The compressor is one or a combination of a piston compressor, a screw compressor, or a centrifugal compressor, and the compressor has good pressure control and temperature monitoring functions, capable of stably compressing the air to 2.4 Mpa and providing real-time feedback on the temperature changes during the compression process for subsequent process adjustment.

3. The method according to claim 1, characterized in that, The screw expander uses a twin-screw expander, which has a high-precision clearance seal between the screw rotor and the casing to ensure airtightness during the expansion process. The internal profile of the screw expander is specially designed to ensure a high isentropic efficiency during the air expansion and cooling process, achieving efficient cooling. At the same time, the screw expander is equipped with an automatic control system that can automatically adjust the operating parameters of the expander according to the pressure and temperature of the inlet air and the required cooling range.

4. The method according to claim 1, wherein In the dry ice separation and collection step, the dry ice separation device adopts a multi-layer filter screen structure, and the filter screen pore size gradually decreases from the inlet to the outlet. First, the larger particle impurities are preliminarily filtered out through the large-pore filter screen, and then the dry ice particles are captured through the small-pore filter screen. Or a centrifugal separation device is used, and the dry ice particles are thrown towards the inner wall of the device by centrifugal force to achieve separation from the gas. The separated dry ice particles are collected into a storage container through a scraping device.

5. The method according to claim 1, wherein Before the air compression step, an air pretreatment step is also included. The air at normal temperature and pressure is passed through a filter to remove impurities such as dust and particulate matter in the air; through a dryer to reduce the humidity of the air, so as to reduce the adverse effects caused by water condensation during the subsequent compression and cooling processes, and ensure the stability of the entire capture process and the purity of dry ice.

6. The method according to claim 1, characterized in that, After the dry ice separation and collection step, an un-sublimed gas treatment step is also included. The un-sublimed gas after separating the dry ice particles is recycled. It can be compressed to a suitable pressure by a compressor and then re-introduced into other gas-using links in industrial production, or further purified before being discharged into the atmosphere to meet environmental protection requirements.

7. The method according to claim 1, characterized in that, During the entire process of capturing dry ice, parameters such as the pressure, temperature, and flow rate of the gas at each stage are monitored in real time through sensors, and the data is transmitted to the control system. The control system automatically adjusts the operating frequency of the compressor, the expansion ratio of the screw expander, and the operating state of the dry ice separation device according to the preset parameter range to achieve automated and intelligent dry ice capture operations.

8. The method according to any one of claims 1-7, characterized in that, In the step of cooling the screw expander, in order to further improve the cooling effect and the dry ice capture efficiency, an auxiliary cooling device, such as a spray cooling device, can be set at the inlet or outlet of the screw expander. The low-temperature liquid (such as water or other coolant) is used to spray-cool the gas before and after expansion to accelerate the gas cooling process.

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