Production method of liquid carbon dioxide

Abstract

The invention relates to the technical field of carbon dioxide production, in particular to a production method of liquid carbon dioxide, which comprises the following steps: (1) introducing raw material gas containing carbon dioxide into a buffer for pressure stabilization treatment; (2) the raw material gas subjected to pressure stabilizing treatment enters a compressor to be subjected to pressure increasing treatment; (3) the raw material gas subjected to pressure increasing treatment enters a drying tower for desulfurization treatment, and the drying tower is filled with a desulfurizing agent; (4) filtering the desulfurized gas in a filter; (5) precooling the filtered raw material gas by a precooler, feeding the precooled raw material gas into a heavy component removal tower to remove heavy components, and feeding light components at the top of the tower into a condenser to be condensed; (6) performing low-temperature flash evaporation purification treatment on the carbon dioxide obtained after condensation in a purification tower; and (7) the purified liquid carbon dioxide enters a subcooler to be further cooled and liquefied, and then enters a storage tank to be stored. According to the invention, the peculiar smell in the liquid carbon dioxide product can be eliminated, and the purity of the prepared liquid carbon dioxide can reach 99.8% at most.

Description

Technical Field

[0001] The invention relates to the technical field of carbon dioxide production, and in particular to a method for producing liquid carbon dioxide. Background Art

[0002] A large amount of waste gas containing carbon dioxide is generated during the methanol production process. If it is directly discharged without treatment, it will not only aggravate the greenhouse effect, but also cause a waste of resources. Therefore, using liquid carbon dioxide production equipment to greenly recycle methanol plant waste gas is an important way to achieve carbon emission reduction and resource recycling.

[0003] The working principle of liquid carbon dioxide production is mainly based on the physical properties and chemical reaction principles of carbon dioxide. First, through specific absorption and separation technologies, the carbon dioxide in the exhaust gas of the methanol plant is captured and converted into liquid or supercritical state. Then, the liquid carbon dioxide is used for further processing or utilization. This technology has broad application prospects in the chemical industry, especially in the fields of new energy and new materials, where liquid carbon dioxide will play a more important role.

[0004] However, when the downstream products of liquid carbon dioxide produced were applied, it was found that there was an odor in the liquid carbon dioxide products used for dry ice manufacturing or high-grade use. After replacing the adsorbent and desiccant and comparing and analyzing them many times, the odor in the product could not be eliminated. After research, it was determined that the source of the odor in the product was the accumulation of heavy components such as methanol and hydrocarbons in the raw gas. Because the existing production method cannot eliminate the odor in the product, product sales are greatly restricted, it is difficult to develop high-end customers, and the further development of the product market is seriously affected. It is urgent to improve the quality of the existing production method. Summary of the invention

[0005] In view of the technical problem that in the existing liquid carbon dioxide production, heavy components such as methanol and hydrocarbons in the raw gas cannot be effectively removed, resulting in the product producing odor, the present invention provides a method for producing liquid carbon dioxide, which can eliminate the odor in the liquid carbon dioxide product and the purity of the prepared liquid carbon dioxide can reach up to 99.8%.

[0006] The present invention provides a method for producing liquid carbon dioxide, comprising the following steps: (1) The raw gas containing carbon dioxide is passed into the buffer for pressure stabilization treatment; (2) The raw gas after pressure stabilization treatment enters the compressor for pressure-raising treatment; (3) After the pressure-raising treatment, the raw gas enters the drying tower for desulfurization treatment, and the drying tower is filled with a desulfurizer; (4) The gas after desulfurization treatment enters the filter for filtration treatment; (5) The filtered raw gas is precooled in a precooler and then enters a de-weighting tower to remove heavy components. The light components at the top of the tower enter a condenser for condensation. (6) The carbon dioxide obtained after condensation enters the purification tower for low-temperature flash evaporation and purification; (7) The purified liquid carbon dioxide enters the subcooler for further cooling and liquefaction, and then enters the storage tank for storage.

[0007] Furthermore, in step (2), the pressure of the raw gas after being pressurized by a compressor is 2.5 to 2.8 MPa.

[0008] Furthermore, in step (3), the total S content in the raw gas after desulfurization treatment is ≤ 0.1 ppm. Furthermore, in order to improve the desulfurization effect, the desulfurizer can be replaced with a fine desulfurizer.

[0009] Furthermore, in step (5), the heavy components removed by the de-weighting tower are returned to the pre-cooler, and after heat exchange as a refrigerant, they enter the gas-liquid separator, and the separated gas phase and liquid phase are purified and discharged. The top gas phase is merged into the non-condensable gas main pipe for purification and venting, and the bottom liquid phase is recovered to the purification underground tank.

[0010] Furthermore, in step (5), the temperature in the de-weighting tower is controlled at -90 to -100° C. At this temperature, heavy components such as methanol and heavy hydrocarbons are deposited at the bottom of the tower due to their higher boiling points, forming bottom liquid, while the light component carbon dioxide gradually rises and is discharged through the top of the tower.

[0011] Furthermore, in step (6), the non-condensable gas generated by the purification tower is combined with the heavy components removed by the de-weighting tower and then returned to the pre-cooler, and then enters the gas-liquid separator after heat exchange as a refrigerant, and the separated gas phase and liquid phase are purified and discharged.

[0012] Furthermore, in step (6), the temperature of the low-temperature flash evaporation is -70°C.

[0013] Furthermore, in step (7), the carbon dioxide enters a supercooler and is cooled to -25°C.

[0014] Furthermore, in step (7), part of the liquid carbon dioxide after cooling and liquefaction in the cooler is introduced into the top of the deweighting tower to wash the raw gas in step (5).

[0015] The principle of the present invention is as follows: the present invention replaces the original adsorbent in the drying tower with a desulfurizing agent for desulfurization, the equipment modification is simple and the desulfurization effect is good, and the raw gas containing heavy substances enters the deweighting tower from the bottom, and in the tower, it is fully countercurrently contacted with the liquid carbon dioxide coming down from the top of the tower, and the methanol, heavy hydrocarbons and other odor components in the raw gas are washed and removed. At the same time, the principle of low-temperature distillation in the tower is utilized, and the heavy components such as methanol and heavy hydrocarbons are deposited at the bottom of the tower due to their higher boiling points to form a kettle bottom liquid, while the light component carbon dioxide gradually rises and is discharged through the top of the tower.

[0016] The beneficial effect of the present invention is that the production method of liquid carbon dioxide provided by the present invention can eliminate the odor in the liquid carbon dioxide product, and the purity of the prepared liquid carbon dioxide can reach up to 99.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 It is a process flow chart of a specific implementation mode of the present invention. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0020] Example 1 Combination Figure 1 , a method for producing liquid carbon dioxide, comprising the following steps: (1) The raw gas containing carbon dioxide is passed into the buffer for pressure stabilization treatment; (2) The raw gas after pressure stabilization treatment enters the compressor for pressure-raising treatment. The pressure of the raw gas after pressure-raising treatment by the compressor is 2.5MPa; (3) After the pressure-raising treatment, the raw gas enters the drying tower for desulfurization treatment. The drying tower is filled with a desulfurizer. After the desulfurization treatment, the total S content (including sulfur and carbonyl sulfide in hydrogen sulfide) in the raw gas is controlled to be ≤0.1ppm; (4) The gas after desulfurization treatment enters the filter for filtration treatment to filter out solid impurities and oil substances in the raw gas; (5) The filtered raw gas is precooled in a precooler and then enters a de-weighting tower to remove heavy components. The temperature in the de-weighting tower is controlled at -90°C. The raw gas enters from the bottom of the de-weighting tower and countercurrently contacts with the liquid carbon dioxide flowing downward from the top of the de-weighting tower to wash and remove odor components such as methanol and heavy hydrocarbons in the raw gas. The heavy components such as methanol and heavy hydrocarbons at the bottom of the tower are deposited at the bottom of the tower due to their higher boiling points to form a bottom liquid, while the light component carbon dioxide gradually rises and is discharged from the top of the tower together with the raw gas and enters the condenser for condensation. The heavy components removed by the de-weighting tower are returned to the precooler and enter the gas-liquid separator after heat exchange as a refrigerant. The separated gas phase and liquid phase are purified and discharged externally. (6) The carbon dioxide obtained after condensation enters a purification tower for low-temperature flash distillation and purification. The temperature of the low-temperature flash distillation is -70°C, and the impurities are flashed out. At the same time, a qualified liquid carbon dioxide product is obtained at the bottom of the tower. The non-condensable gas produced by the purification tower is combined with the heavy components removed by the de-weighting tower in step (5) and returned to the pre-cooler; (7) The purified liquid carbon dioxide enters a subcooler and is further cooled to -25°C for liquefaction. A portion of the liquefied liquid carbon dioxide is introduced to the top of the deweighting tower in step (5) to flow downward to wash the raw gas, and the remaining liquid carbon dioxide is sent to a storage tank for storage.

[0021] The liquid carbon dioxide obtained in the storage tank was sampled and analyzed, and the purity of the carbon dioxide was 99.8% with no odor.

[0022] Example 2 A method for producing liquid carbon dioxide comprises the following steps: (1) The raw gas containing carbon dioxide is passed into the buffer for pressure stabilization treatment; (2) The raw gas after pressure stabilization treatment enters the compressor for pressure-raising treatment. The pressure of the raw gas after pressure-raising treatment by the compressor is 2.8MPa; (3) After the pressure-raising treatment, the raw gas enters the drying tower for desulfurization treatment. The drying tower is filled with a desulfurizer. After the desulfurization treatment, the total S content (including sulfur and carbonyl sulfide in hydrogen sulfide) in the raw gas is controlled to be ≤0.1ppm; (4) The gas after desulfurization treatment enters the filter for filtration treatment to filter out solid impurities and oil substances in the raw gas; (5) The filtered raw gas is precooled in a precooler and then enters a de-weighting tower to remove heavy components. The temperature in the de-weighting tower is controlled at -100°C. The raw gas enters from the bottom of the de-weighting tower and countercurrently contacts with the liquid carbon dioxide flowing downward from the top of the de-weighting tower to wash and remove odor components such as methanol and heavy hydrocarbons in the raw gas. The heavy components such as methanol and heavy hydrocarbons at the bottom of the tower are deposited at the bottom of the tower due to their higher boiling points to form a bottom liquid, while the light component carbon dioxide gradually rises and is discharged from the top of the tower together with the raw gas and enters the condenser for condensation. The heavy components removed by the de-weighting tower are returned to the precooler and enter the gas-liquid separator after heat exchange as a refrigerant. The separated gas phase and liquid phase are purified and discharged externally. (6) The carbon dioxide obtained after condensation enters a purification tower for low-temperature flash distillation and purification. The temperature of the low-temperature flash distillation is -70°C, and the impurities are flashed out. At the same time, a qualified liquid carbon dioxide product is obtained at the bottom of the tower. The non-condensable gas produced by the purification tower is combined with the heavy components removed by the de-weighting tower in step (5) and returned to the pre-cooler; (7) The purified liquid carbon dioxide enters a subcooler and is further cooled to -25°C for liquefaction. A portion of the liquefied liquid carbon dioxide is introduced to the top of the deweighting tower in step (5) to flow downward to wash the raw gas, and the remaining liquid carbon dioxide is sent to a storage tank for storage.

[0023] The liquid carbon dioxide obtained in the storage tank was sampled and analyzed, and the purity of the carbon dioxide was 99.7% with no odor.

[0024] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for producing liquid carbon dioxide, characterized in that: The steps include: (1) The raw gas containing carbon dioxide is passed into the buffer for pressure stabilization treatment; (2) The raw gas after pressure stabilization treatment enters the compressor for pressure raising treatment; (3) After the pressure-raising treatment, the raw gas enters the drying tower for desulfurization treatment, and the drying tower is filled with a desulfurizer; (4) The gas after desulfurization treatment enters the filter for filtration treatment; (5) The filtered raw gas is precooled in a precooler and then enters a de-weighting tower to remove heavy components. The light components at the top of the tower enter a condenser for condensation. (6) The carbon dioxide obtained after condensation enters the purification tower for low-temperature flash evaporation and purification; (7) The purified liquid carbon dioxide enters the subcooler for further cooling and liquefaction, and then enters the storage tank for storage.

2. The method for producing liquid carbon dioxide according to claim 1, characterized in that: In step (2), the pressure of the raw gas after being pressurized by the compressor is 2.5-2.8 MPa.

3. The method for producing liquid carbon dioxide according to claim 1, characterized in that: In step (3), the total S content in the raw gas after desulfurization treatment is ≤0.1ppm.

4. The method for producing liquid carbon dioxide according to claim 1, characterized in that: In step (5), the heavy components removed by the de-weighting tower are returned to the pre-cooler and enter the gas-liquid separator after heat exchange as a refrigerant. The separated gas phase and liquid phase are purified and discharged.

5. The method for producing liquid carbon dioxide according to claim 1, characterized in that: In step (5), the temperature in the deweighting tower is controlled at -90 to -100°C.

6. The method for producing liquid carbon dioxide according to claim 4, characterized in that: In step (6), the non-condensable gas produced by the purification tower is combined with the heavy components removed by the de-weighting tower and then returned to the pre-cooler. After heat exchange as a refrigerant, it enters the gas-liquid separator, and the separated gas phase and liquid phase are purified and discharged.

7. The method for producing liquid carbon dioxide according to claim 1, characterized in that: In step (6), the temperature of the low-temperature flash evaporation is -70°C.

8. The method for producing liquid carbon dioxide according to claim 1, characterized in that: In step (7), the carbon dioxide enters a supercooler and is cooled to -25°C.

9. The method for producing liquid carbon dioxide according to claim 1, characterized in that: In step (7), part of the liquid carbon dioxide that has been cooled and liquefied by the cooler is introduced into the top of the deweighting tower to wash the raw gas in step (5).

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