OXYGEN LIQUEFACTION PROCESS

Abstract

An oxygen liquefaction apparatus may include a heat exchanger that allows oxygen gas to be cooled and condensed with liquid nitrogen. The oxygen liquefaction apparatus may include: a differential pressure gauge that measures the difference in pressure between the hot and cold ends of an oxygen flow path; and an oxygen control unit that calculates the level of oxygen inside the heat exchanger based on the differential pressure gauge reading, that controls an oxygen control valve to adjust the level, and that controls the heat transfer area to control the condensation of the oxygen.

Claims

1. A liquefaction apparatus comprising: a heat exchanger configured to cool and condense a gas using a refrigerant to form a liquefied product, wherein the gas flows through a first path of the heat exchanger, the first path having a cold end and a hot end, wherein the refrigerant flows through a refrigerant flow path having a cold end and a hot end; a first differential pressure gauge configured to measure a difference in pressure between the hot end and the cold end; and a liquefied product control unit configured to calculate a level of the liquefied product inside the heat exchanger based on the differential pressure gauge reading, wherein the liquefied product control unit is further configured to control a liquefied product control valve to adjust the level of the liquefied product, and wherein the liquefied product control unit is further configured to control the heat transfer area to control the condensation of the gas.

2. The liquefaction apparatus according to claim 1, further comprising a second differential pressure gauge configured to measure a difference in pressure between the hot end and the cold end of the refrigerant flow path, wherein the liquefied product control unit is configured to calculate a level of the refrigerant, to control the liquefied product control valve to adjust the level of the refrigerant, and to control the heat transfer area, which allows the liquefied product control unit to control the condensation of the substance that is to be treated.

3. The liquefaction apparatus according to claim 1, further comprising a second differential pressure gauge configured to measure a difference in pressure between the hot end and the cold end of the refrigerant flow path, wherein the liquefied product control unit is configured to control the liquefied product control valve based on the level of the refrigerant and the level of the liquefied product of the gas to adjust the levels of the refrigerant and the liquefied product, and to control the heat transfer area to control the condensation of the gas.

4. The liquefaction apparatus according to claim 1, comprising: a liquefied product discharge line through which the liquefied product is discharged from the cold end of the heat exchanger, and a liquefied product bypass line that is configured to discharge the liquefied product from a part of the liquefied product flow path inside the heat exchanger that is lower than the level of the liquefied product and that merges with the liquefied product discharge line through which the product is discharged from the cold end of the heat exchanger.

5. The liquefaction apparatus according to claim 4, comprising a bypass control unit that controls the opening and closing of a bypass control valve disposed on the liquefied product bypass line so that the temperature of the liquefied product is at a specified value.

6. A liquefied product production method comprising the steps of: providing the liquefaction apparatus of claim 1; introducing the gas into the hot end of the first path of the heat exchanger; introducing the refrigerant the cold end of the refrigerant path of the heat exchanger, wherein the gas is cooled and condensed within the first path of the heat exchanger by exchanging heat with the refrigerant flowing within the refrigerant path, thereby forming the liquefied product; discharging the liquefied product from the cold end of the first path; and controlling an amount of the liquefied product discharged from the cold end of the first path based on the level of liquefied product within the heat exchanger.

7. The liquefied product production method according to claim 6, further comprising controlling the amount of the liquefied product discharged from the cold end of the first path based on the level of the refrigerant9098 within the heat exchanger.

8. The liquefied product production method according to claim 6, further comprising adjusting a temperature within the heat exchanger by discharging a portion of the liquefied product from a part of the heat exchanger that is lower than the level of the liquefied product, and merging with liquefied product that is taken out as the final product, so as to adjust the temperature of the liquefied product.

9. The liquefied product production method according to claim 6, further comprising subcooling the liquefied product using a combination of a primary refrigerant, that primarily effects cooling and condensation, as well as a second refrigerant, that has a lower pressure than the first refrigerant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Other features and advantages of the invention will be further disclosed in the description that follows, and in several embodiments provided as non-limiting examples in reference to the appended schematic drawings, in which:

[0061] FIG. 1 is a diagram illustrating a gas liquefaction apparatus according to Embodiment 1,

[0062] FIG. 2 is a diagram illustrating a gas liquefaction apparatus according to Embodiment 2,

[0063] FIG. 3 is a diagram illustrating a gas liquefaction apparatus according to Embodiment 3, and

[0064] FIG. 4 is a diagram illustrating a gas liquefaction apparatus according to Embodiment 4.

DETAILED DESCRIPTION OF THE INVENTION

[0065] Several embodiments of the present invention will be described below. The embodiments described below are given as examples of the present disclosure. The present disclosure is in no way limited by the following embodiments, and also includes a number of variants that can be implemented within a scope that does not alter the gist of the present disclosure. It should be noted that not all the configurations described below are necessarily essential to the present disclosure. Upstream and downstream are based on the direction in which the fluid flows.

Embodiment 1

[0066] A liquefaction apparatus A1 according to Embodiment 1 will be described with the aid of FIG. 1.

[0067] The oxygen liquefaction apparatus A1 comprises a single heat exchanger 1. In the oxygen liquefaction apparatus A1, oxygen gas (GOX) flows down into the hot end, and liquefied oxygen (LOX) is discharged from the cold end. Liquefied nitrogen (LIN) also flows upward via the cold end, and nitrogen gas (GAN) is discharged from the hot end. The nitrogen line L1 is a nitrogen flow path for introducing liquefied nitrogen (LIN) through the cold end and discharging nitrogen gas (GAN) from the hot end of the heat exchanger 1. The oxygen line L2 is an oxygen line for introducing oxygen gas (GOX) from the hot end and discharging liquefied oxygen (LOX) from the cold end of the heat exchanger 1.

[0068] A gate valve V1 is disposed upstream from the cold end of the heat exchanger 1 in the nitrogen line L1.

[0069] A nitrogen gas pressure measurement unit 101 measures the pressure of the nitrogen gas downstream from the cold end of the heat exchanger 1 in the nitrogen line L1.

[0070] A nitrogen control unit 21 controls the opening and closing (adjusts the opening) of a nitrogen control valve V2 disposed in the nitrogen line L1 when, for example, within a predetermined range, or below a predetermined threshold value, or at or over the predetermined threshold value, based on the pressure value measured by the nitrogen gas pressure measurement unit 101.

[0071] A gate valve V3 is disposed upstream from the hot end of the heat exchanger 1 in the oxygen line L2.

[0072] An oxygen differential pressure measurement unit 102 measures the difference in pressure between the pressure of oxygen gas upstream from the hot end of the heat exchanger 1 in the oxygen line L2 and the pressure of liquefied oxygen downstream from the cold end of the heat exchanger 1 in the oxygen line L2.

[0073] An oxygen control unit 22 controls the opening and closing (adjusts the opening) of an oxygen control valve V4 disposed in the oxygen line L2 when, for example, within a predetermined range, or below a predetermined threshold value, or at or over the predetermined threshold value, based on the pressure value measured by the oxygen gas pressure measurement unit 102.

[0074] The oxygen control unit 22 calculates the level of liquefied oxygen inside the heat exchanger 1 based on the difference in pressure measured by the oxygen differential pressure measurement unit 102, controls the oxygen control valve V4 to adjust the liquid level, and controls the heat transfer area to control condensation of the oxygen.

[0075] The liquefied oxygen in the heat exchanger 1 is subcooled by heat exchange with the liquefied nitrogen. When attempting to control the temperature of the liquefied nitrogen in cases where the liquefied oxygen is under-or over-cooled, the nitrogen pressure must be adjusted, but energy will be needed to compress and decompress the nitrogen. The level of the oxygen is therefore adjusted to adjust the heat transfer area involved in subcooling the liquefied oxygen. This allows the liquefied oxygen temperature to be adjusted without changing the nitrogen operating pressure. The nitrogen line L1 pressure control (101, 21) is configured so that the nitrogen that is evaporated via heat exchange with oxygen is discharged through the piping and out of the system.

Embodiment 2

[0076] An oxygen liquefaction apparatus A2 according to Embodiment 2 will be described with the aid of FIG. 2. The oxygen liquefaction apparatus A2 according to Embodiment 2 has the functions of the oxygen liquefaction apparatus A1 according to Embodiment 1, and additional functions are described below. Reference symbols which are the same denote the same functions.

[0077] A liquefied oxygen bypass line L21 is a line by which a portion of the hot liquefied oxygen is discharged from a point midway in the heat exchanger 1 and is merged with liquefied product downstream from the cold end of the heat exchanger 1 of the oxygen line L2 so as to adjust the temperature of the liquefied oxygen taken out as the final product.

[0078] A liquefied oxygen temperature measurement unit 103 measures the temperature of the liquefied oxygen downstream from the cold end of the heat exchanger 1 in the oxygen line L2.

[0079] A hot oxygen control unit 23 controls the opening and closing (adjusts the opening) of a hot oxygen control valve V5 disposed in the liquefied oxygen bypass line L21 when, for example, within a predetermined range, or below a predetermined threshold value, or at or over the predetermined threshold value, based on the temperature value measured by the liquefied oxygen temperature measurement unit 103. This allows the temperature of the liquefied oxygen product to be controlled to a specified value, thereby allowing liquefied oxygen having a stable temperature to be produced at a low cost.

[0080] With this configuration, hot liquefied oxygen is discharged from a point midway in the flow path of the oxygen line L2 of the heat exchanger 1 and is mixed with liquefied oxygen discharged from the cold end of the heat exchanger 1 to thereby produce the liquefied oxygen product. This allows liquefied oxygen of a suitable temperature to be supplied on demand. The subcooling temperature is preferably approximately at least 1 C. lower than the temperature of the saturated liquid at operating pressure in order to prevent the discharged hot liquid oxygen from flowing in two layers as a result of partial evaporation due to reduced pressure or heat coming from the environment. This is because partial evaporation due to loss of pressure may result in a two-layered flow.

Embodiment 3

[0081] An oxygen liquefaction apparatus A3 according to Embodiment 3 will be described with the aid of FIG. 3. The oxygen liquefaction apparatus A3 according to Embodiment 3 has the functions of the oxygen liquefaction apparatus A1 and A2 according to Embodiments 1 and 2, and additional functions are described below. Reference symbols which are the same denote the same functions.

[0082] Intermediate-pressure liquefied nitrogen (MP LIN) is supplied to the nitrogen line L1.

[0083] A low-pressure nitrogen line L11 is a line for introducing low-pressure liquefied nitrogen (LP LIN) through the cold end of the heat exchanger 1 and discharging low-pressure nitrogen gas (LP GAN) from the a point midway in the heat exchanger 1.

[0084] A low-pressure nitrogen gas pressure measurement unit 104 measures the pressure of low-pressure nitrogen gas downstream from a point midway in the heat exchanger 1 in the nitrogen line L11.

[0085] A low-pressure nitrogen control unit 24 controls the opening and closing (adjusts the opening) of a low-pressure nitrogen control valve V12 disposed in the low-pressure nitrogen line L11 when, for example, within a predetermined range, or below a predetermined threshold value, or at or over the predetermined threshold value, based on the pressure measured by the low-pressure nitrogen gas pressure measurement unit 104.

[0086] This will allow liquefied nitrogen to be used to cool and liquefy oxygen gas, and will allow low-pressure liquefied nitrogen to be used in the subcooling of liquefied oxygen.

[0087] With this configuration, liquefied oxygen is subcooled by low-temperature liquefied nitrogen. The intermediate-pressure liquefied nitrogen can be optimized for cooling and liquefying oxygen gas, and the low-temperature liquefied nitrogen can be used to optimize the subcooling of liquefied oxygen, resulting in more efficient heat exchange.

Embodiment 4

[0088] An oxygen liquefaction apparatus A4 according to Embodiment 4 will be described with the aid of FIG. 4. The oxygen liquefaction apparatus A4 according to Embodiment 4 has the functions of the oxygen liquefaction apparatus A1, A2, and A3 according to Embodiments 1, 2, and 3, and additional functions are described below. Reference symbols which are the same denote the same functions.

[0089] The oxygen liquefaction apparatus A4 comprises a nitrogen liquefier E2 for liquefying nitrogen gas (Feed N.sub.2) sent from a supply source via a line L4. The nitrogen liquefier E2 is composed of a heat exchanger, for example.

[0090] A recycled nitrogen compressor C1 and feed nitrogen compressor C2 are connected in series via a line L12. The first recycled nitrogen compressor C1 is disposed downstream from the hot end of the nitrogen liquefier E2 in the first recycled nitrogen line L12, and compresses the recycled low-pressure nitrogen. The feed nitrogen compressor C2 compresses nitrogen gas (MP GAN) discharged from the hot end of the heat exchanger 1 and nitrogen gas (Feed N.sub.2) from a supply source. The feed nitrogen compressor C2 compresses the nitrogen gas compressed by the recycled nitrogen compressor C1. The feed nitrogen compressor C2 also compresses nitrogen gas that has been expanded by the first expansion turbine 52 described below and introduced into the nitrogen liquefier E2. The feed nitrogen compressor C2 also compresses nitrogen gas that has been separated in the gas-liquid separator 7 described below and introduced into the nitrogen liquefier E2.

[0091] A first booster 51 and the second booster 61 are connected in series via the line L12 and a line L13.

[0092] The first booster 51 boosts the pressure of the nitrogen gas that has been compressed by the feed nitrogen compressor C2. The second booster 61 further boosts the pressure of a portion of the nitrogen gas pressure-boosted by the first booster 51.

[0093] A first expansion turbine 52 is provided, whereby the remainder of the nitrogen gas (remainder of the portion of nitrogen gas sent to the second booster 61) that has been pressure-boosted by the first-stage first booster 51 is introduced via the first recycled nitrogen line L12 into the hot end of the nitrogen liquefier E2, and nitrogen gas discharged from a point midway therein is expanded. The expanded nitrogen gas is introduced via the first recycled nitrogen line L12 into a point midway in the nitrogen liquefier E2 and is merged in a second recycled nitrogen line L13b.

[0094] A second expansion turbine 62 is provided, by which the nitrogen gas that has been pressure-boosted by the second booster 61 is introduced into the hot end of the nitrogen liquefier E2, and a portion of the nitrogen gas discharged from a point midway in the nitrogen liquefier E2 is expanded via a line L13a. The expanded nitrogen gas merges, via the line 13a, in a second recycled nitrogen line L13b by which separated nitrogen gas is introduced from the gas-liquid separator 7 into the cold end of the nitrogen liquefier E2.

[0095] A first expansion valve V13 is disposed in the line L13 downstream from the cold end of the nitrogen liquefier E2. The first expansion valve V13 introduces nitrogen gas that has been pressure-boosted by the second booster 61 into the hot end of the nitrogen liquefier E2 and expands the remainder of the nitrogen gas discharged from the cold end (the remainder of the portion of nitrogen gas sent to the second expansion turbine 62).

[0096] The first nitrogen gas-liquid mixture expanded by the first expansion valve V13 is introduced into a gas-liquid separator 7 where the gas and liquid are separated. The separated nitrogen gas is introduced via the first recycled nitrogen line L13b into the cold end and discharged from the hot end of the nitrogen liquefier E2 and is merged in the second recycled nitrogen line L12. A portion of the separated liquefied nitrogen is introduced as thermal energy via the liquefied nitrogen line L1 into the heat exchanger 1, and the remainder is introduced into a second heat exchanger E3 described below.

[0097] The second heat exchanger E3 is such that the remainder of the liquefied nitrogen (MP LIN) separated in the gas-liquid separator 7 (the remainder of the portion of liquefied nitrogen introduced into the heat exchanger 1) is cooled by being introduced into the hot end and discharged from the cold end. A portion of the liquefied nitrogen (LP LIN) that has been cooled in the second heat exchanger E3 is introduced as subcooling thermal energy via the low-pressure liquefied nitrogen line L11 into the heat exchanger 1.

[0098] A second expansion valve V14 is disposed in the first recycled nitrogen line L12 branching off from the low-pressure nitrogen discharge line L11a, and expands the remainder of the low-pressure liquefied nitrogen (the remainder of the portion introduced into the heat exchanger 1).

[0099] The low-pressure nitrogen discharge line L11a is a line for discharging liquefied nitrogen (LP LIN) cooled in the second heat exchanger E3 and sending a portion thereof to the low-pressure liquefied nitrogen line L11.

[0100] The first recycled nitrogen line L12 is a line through which the second nitrogen gas-liquid mixture expanded by the second expansion valve V14 is introduced into the cold end and discharged from the hot end of the second heat exchanger E3, merged in the low-pressure nitrogen line L11, and then introduced into the cold end and discharged from the hot end of the nitrogen liquefier E2.

[0101] The second recycled nitrogen line L13b is a line through which the intermediate-pressure nitrogen gas separated in the gas-liquid separator 7 is introduced into the cold end and discharged from the hot end of the nitrogen liquefier E2, and is merged between the recycled nitrogen compressor C1 and the feed nitrogen compressor C2 of the first recycled nitrogen line L12.

[0102] With this configuration, intermediate-pressure liquefied nitrogen and low-pressure, low-temperature liquefied nitrogen are each supplied from a nitrogen liquefaction cycle, and the gasified products are each returned to the liquefied nitrogen cycle. The nitrogen gas discharged from the heat exchanger 1 can thus be recovered efficiently in terms of heat and mass balance.

[0103] In the above embodiments, argon can be liquefied instead of oxygen as the liquefied product or liquefied gas.

EXAMPLE

[0104] A simulation was performed with the configuration of Embodiment 3 (FIG. 3).

[0105] Oxygen gas was introduced through the hot end of a heat exchanger 1 at 21 C., 6.8 barA, and 6500 Nm.sup.3/h, and was discharged in the form of liquefied oxygen from the cold end at 184 C. As the boiling point of oxygen at 6.8 barA is approximately 160 C., intermediate-pressure liquefied nitrogen that would result in subcooling at 24 C. was introduced at 180 C., 4.81 barA, and 7079 Nm3/h, and was discharged in the form of intermediate-pressure nitrogen gas at 9.1 C.

[0106] Low-pressure liquefied nitrogen was introduced at 192 C., 3.26 barA, 1622 Nm.sup.3/h, and was discharged in the form of low-pressure nitrogen gas at 185 C.

[0107] When the temperature of low-pressure liquefied nitrogen falls at reduced pressure, for example, there is a corresponding decrease in the temperature of liquefied oxygen. A fall in the liquid oxygen temperature to below the set value of 2 C. would result in subcooling at 26 C. and thus approximately 8.3% over-cooling.

[0108] In one example, the heat exchanger 1 has a 4000-mm high first section (cooling/condensing area 1a) for cooling and condensing oxygen gas, and a 900-mm second section (subcooling area 1b) for subcooling liquefied oxygen, where the level of the liquefied oxygen in the heat exchanger 1 is, by design, at the boundary between the first and second sections. In the event of 8.3% over-cooling, the level of the liquefied oxygen is controlled to 900 mm(100%8.3%)=825 mm. As the specific gravity of liquefied oxygen is 1.11, valve 4 on the liquefied oxygen product discharge line L2 is controlled so as to result in a measured differential pressure of between 100 mbar and 92 mbar.

[0109] To furthermore prevent an over-cooled liquefied oxygen product from being supplied during the above level-controlling procedure, hot liquefied oxygen having a temperature of 176 C. can be discharged at 1300 Nm.sup.3/h from the hot liquefied oxygen bypass line L21 as cold liquefied oxygen having a temperature of 186 C. is discharged at 5200 Nm.sup.3/h, and they can be mixed in order to produce liquefied oxygen at 6,500 Nm.sup.3/h, thereby producing a liquefied oxygen product having a temperature of 184 C. Liquefied oxygen of stable temperature and quality can thus be produced while reducing the thermal energy consumption of the liquefied nitrogen refrigerant corresponding to the 8.3% over-cooling noted above.

[0110] (Other embodiments) (1) Although not explicitly stated, pressure regulating devices and flow rate control devices, etc. may be installed in each pipeline in order to regulate pressure and regulate flow rate.

[0111] (2) Although not explicitly stated, control valves and gate valves, etc. may be installed in each line.

[0112] (3) A nitrogen differential pressure measurement unit may be provided instead of the oxygen differential pressure measurement unit 102, the level of the nitrogen may be calculated based on the differential pressure value, the oxygen control valve V4 may be controlled to adjust the level, and the heat transfer area may be controlled to control the condensation of oxygen.

[0113] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0114] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0115] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0116] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0117] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0118] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

KEY TO SYMBOLS

[0119] 1 Heat exchanger [0120] 22 Oxygen control unit [0121] 23 Hot liquefied oxygen control unit [0122] 102 Oxygen differential pressure measurement unit [0123] 103 Liquefied oxygen temperature measurement unit [0124] A1, A2, A3, A4 Oxygen liquefaction apparatus [0125] V4 Oxygen control valve [0126] V5 Hot oxygen control valve