JPS6337308B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an air liquefaction method using liquefied natural gas (hereinafter referred to as LNG). Utilizing the refrigeration of LNG has been proposed in various fields, and some have already been implemented. Among these, for example, air for combustion support in gas turbine power generation is liquefied and stored using the cooling of LNG for fuel.
There is a method of generating electricity by intensively vaporizing the liquid air during peak electricity demand. This method has the advantage of being able to generate electricity with high efficiency because it saves the power needed to supply air for combustion assistance in gas turbine power generation, but reducing the power required to liquefy and store air reduces power generation costs. Desired because it makes you do something. In addition, when producing liquid air by liquefying air, most of the production cost is power cost, and in order to reduce this power cost,
The reason is that it is proposed to use the refrigeration of LNG, but in reality it is offset by the refrigeration costs of LNG, etc.
The current situation is that it has not been put into practical use. For this reason, the present invention effectively utilizes the cold temperature of LNG, and also uses the increased pressure to drive the expansion turbine to prevent the concentration of high-boiling organic matter contained in LNG, thereby saving power for the compressor. This method has achieved a reduction in electricity costs, which account for the majority of liquid air manufacturing costs. In other words, LNG in excess of the amount of vaporized at a low pressure is supplied to an LNG evaporator that cools and liquefies compressed air, and the vaporized natural gas is repressurized and pumped to the required pressure by a natural gas compressor, and the high-boiling point components are Excess LNG, which has increased in volume, is pressurized above the critical pressure using a pump, heated through indirect heat exchange with compressed air during the pre-cooling process, and, if necessary, heated to room temperature using seawater, heated wastewater, etc. After being heated to the above temperature, it is introduced into an expansion turbine and expanded, and the generated power drives the vaporized natural gas compressor. As a result, the compressed air can be cooled to a low temperature by evaporation of the low-pressure LNG, so the compression pressure of the air can be made relatively low, and the liquefaction power can be saved. At the same time, the required power can be reduced by the recovered power driven by the expansion turbine. Furthermore, in the present invention, when the demand for LNG increases, the increased amount of LNG is pressurized to above the critical pressure using a pump, and after this high-pressure LNG is heated to above room temperature using seawater, hot wastewater, etc., it is expanded using an expansion turbine. It also includes a method for reducing the power required for air liquefaction by generating power and using it as a power source for a raw air compressor. LNG, which is the fuel for thermal power plants, fluctuates depending on the power demand, but the amount of LNG used for cooling air liquefaction is determined based on the minimum demand, that is, the base load value, so that the air liquefaction equipment can operate stably at all times. desirable for. Therefore, since the amount of LNG used increases during the day when the demand for electricity is high, this increased amount of LNG is used to drive the expansion turbine as described above. In other words, the air compressor of the air liquefaction equipment, which is a fairly large power consuming facility, can be driven by both an electric motor and an expansion turbine, and at night when electricity demand is low, the electric motor is driven using cheap nighttime electricity. By using the expansion turbine as the main drive source during the day when the demand for electricity is high, it is possible to significantly reduce the power cost for air liquefaction. Examples of the present invention will be described in detail below. FIG. 1 shows an embodiment of the method of the present invention in which 48,000 Nm ³ of liquid air is produced per hour using LNG supplied to a thermal power plant. 48000Nm ³ /h of air at 30°C is sucked into the cooler 2 through the pipe 1.
By exchanging heat with Freon cooled by LNG
It is cooled down to 5℃ and merges with the air from tube 24.
It becomes 65000Nm ³ /h and is pressurized by compressor 3.
The compressed air at 20 atmospheres and +30°C is introduced into the precooler 7 through the pipe 6. The power required to drive the compressor 3 is 10,000 kW, and the drive source is an electric motor 4 of the same capacity and an expansion turbine 5 installed in series. As will be described later, this expansion turbine 5 uses high-pressure natural gas as a working gas, and during periods of high demand for LNG, the power required for the electric motor is reduced or eliminated by utilizing its driving force. When LNG demand is low, the expansion turbine 5 stops operating and the electric motor 4
The compressor 3 is driven only by the The compressed air introduced into the precooler 7 is cooled again by the refrigerant Freon flowing in the heat exchanger tube 69, and is led out at +5°C.The compressed air is introduced into one of the adsorbers 8a or 8b, which is used selectively, where water and carbon dioxide are removed. Gas is adsorbed and removed.
The air purified by adsorption is introduced into the feed air precooling heat exchanger 10 through the tube 9, where it is cooled down to -130°C by exchanging heat with low-temperature vaporized air from the gas-liquid separator 18 and circulating Freon, which will be described later. 11 and is introduced into the LNG evaporator 12. In the LNG evaporator 12, the compressed purified air exchanges heat with LNG at atmospheric pressure, is cooled to -155°C, and is liquefied. The liquefied air is introduced into the LNG evaporator 14 through the pipe 13,
It exchanges heat with LNG at 0.5 atm (absolute), is subcooled to -168°C, and is discharged from pipe 15. The supercooled liquid air is further introduced into a heat exchanger 16, where it exchanges heat with vaporized air from a gas-liquid separator 18 (to be described later), is further supercooled, and then discharged, and expanded to 1.5 atmospheres at an expansion valve 17. The gas is introduced into the gas-liquid separator 18. 48,000 Nm ³ /h of liquid air is taken out from the bottom of the gas-liquid separator 18 via a pipe 19 and stored in a liquid air storage tank 21 via a valve 20. On the other hand, the low temperature vaporized air of the gas-liquid separator 18
17000Nm ³ /h enters the heat exchanger 16 from the pipe 22, subcools the liquid air, raises its temperature and draws it out, and is further introduced into the heat exchanger 10 through the pipe 23, cools the compressed purified air, and cools the liquid air itself. The temperature of tube 2 was increased to approximately room temperature.
4, joins with the raw material air from the pipe 1, and is returned to the suction side of the compressor 3. LNG for cold use is pipe 25 at 10 atm and -155℃.
80000Nm ³ /h
is provided through the pipe 26 for the aforementioned liquefaction of the air. That is, the LNG in the pipe 26 is further divided into two parts, a part of which is reduced in pressure to atmospheric pressure through the valve 27, and introduced into the LNG evaporator 12 at -160°C, where it is evaporated by exchanging heat with air. In this case the LNG regulated by valve 27
The amount of LNG supplied to the evaporator 12 is
Make sure the amount is in excess of the amount that will evaporate. accordingly
The LNG led out of the LNG evaporator 12 and flowing through the pipe 28 is in a gas-liquid mixed state, and this enters the gas-liquid separator ²⁹ where it is separated into gas and liquid.
It is derived from On the other hand, the branched flow of LNG for air liquefaction is introduced into the LNG evaporator 14 via the valve 31,
Here, the LNG is evaporated at 0.5 atm (absolute) and -170°C, but in this case as well, the amount of LNG supplied that is adjusted by the valve 31 is set to be in excess of the amount evaporated by the LNG evaporator 14. Therefore, LNG in a gas-liquid mixed state is introduced into the gas-liquid separator 33 through the pipe 32, and the separated gas is
12000 Nm ³ /h is compressed by a vacuum pump 35 driven by an electric motor 34, and merges with the gas from the pipe 30 through a pipe 36 at an atmospheric pressure of -110°C. The combined gas becomes 45,000 Nm ³ /h and is passed through a pipe 39 as natural gas at 10 atmospheres and +10°C by a compressor 38 driven by an expansion turbine 37, and then from other pipes 52 and 60, which will be described later. After combining with the natural gas of The liquid separated by the gas-liquid separators 29 and 33 generally contains concentrated high-boiling components such as hydrocarbons contained in LNG, and their precipitation causes the inconvenience of clogging the evaporator. To prevent this, high boiling point components are concentrated.
By pressurizing and heating LNG, LNG
It is necessary to reduce the relative volatility of methane, which is the main component, and high-boiling components so that they can be uniformly vaporized in the methane stream. For this reason, the gas-liquid separator 29
The LNG separated at and 33 is introduced into pumps 44 and 45 through pipes 42 and 43, respectively.
After being pressurized to 200 atmospheres, they join together and enter a heat exchanger 47 via a pipe 46. In the heat exchanger 47, it exchanged heat with circulating freon, which will be described later, and was heated to -40°C and led out, introduced through a pipe 48 to a heater 49, where it was heated to +100°C by a waste heat source 50. rear,
It enters the expansion turbine 37 through the pipe 51, expands from 200 atm to 10 atm, generates power, and leads out to the pipe 52. In this case, the expansion turbine 37 is set to two or more stages, and the first high-pressure natural gas heated above room temperature is first expanded to an intermediate pressure in the first stage turbine, and the outlet gas whose temperature has dropped at that time is heated again by hot waste water or the like. Efficiency can be further improved by employing a multi-stage turbine in which the gas is heated to above room temperature and expanded in the next stage turbine, and the outlet gas of the final stage turbine is sent to the natural gas pressure feeding pipe 52. The flow of LNG for air liquefaction described above uses so-called base load LNG, which is constantly supplied regardless of changes in the amount of LNG due to fluctuations in electricity demand. This flow utilizes LNG, which is flown only during peak electricity demand. In other words, this is the increase when the power plant's LNG consumption increases, and it utilizes the flow of LNG that is virtually not flowed at night but is flowed during the day according to the amount used. The other portion of the LNG, which is supplied through the pipe 25 and divided into two parts, is introduced into the pump 55 through the pipe 54, is pressurized to 200 atmospheres, and reaches the valve 56. valve 56
The amount of electricity used is adjusted according to the electricity demand, enters the heater 57, is heated to +100°C by the waste heat source 58, and is introduced into the expansion turbine 5 via the tube 59, where the temperature is increased from 200 atm to 10 atm. The power generated at this time is used as part or most of the power required for the connected air compressor 3. The expansion turbine 5 may have two or more stages, and may be of a multi-stage reheating type in which the gas whose temperature has been lowered by expansion in the first stage turbine is heated again by hot waste water or the like to rise above room temperature and then introduced into the second stage turbine. It is. The outlet gas of the expansion turbine 5 passes through a pipe 60, joins the gas from the pipes 39 and 52, and is sent to the thermal power plant 4, which is the demand destination.
Sent to 1. Next, in the method of the present invention, a Freon refrigerant circulation system is provided in order to utilize the refrigeration of LNG more effectively and safely. 10 atmospheres flowing through pipe 61, -
Liquid Freon at 150°C is pumped by a pump 62 and introduced into the heat exchanger 10 through a pipe 63. The heat exchanger 10 is used as a cooling source for purified compressed air, and the purified compressed air itself is heated to -20°C and is led out through the pipe 64. Next, this flow of Freon is divided into two parts, and a part of it flows through the tube 65 and inside the heat transfer tube 66 of the cooler 2, exchanging heat with the raw material air and cooling it, so that the temperature itself reaches 0°C.
The temperature is raised to a temperature of 100.degree. On the other hand, the other part, which is divided into two parts, flows through the tube 68 and inside the heat transfer tube 69 of the precooler 7.
The compressed raw material air is cooled and its temperature rises to 0° C. and is led out to the pipe 70. The tube 70 joins the tube 67 to the heat exchanger 47, where the Freon is heated to high pressure.
It is cooled by LNG to −150° C. and circulated by a derivation pump 62. Note that it is of course possible to directly exchange heat between compressed air and LNG without using this Freon circulation system. Next, other embodiments of the present invention will be described. As described above, in the present invention, the expansion turbine is multi-staged and a reheating circuit is combined between each stage, thereby increasing the power generated in the high-pressure natural gas expansion turbine and further increasing the power saving effect. It is possible to make it big. FIG. 2 shows an example of this case. Natural gas at 200 atm and -40°C supplied from pipe 48 is heated to + by waste heat source 50 in heater 49A.
After being heated to 100°C, it is introduced into the expansion turbine 37A through the pipe 51A, where it is expanded to a state of 45 atmospheres and 20°C, passes through the pipe 52A, enters the heater 49B, is heated to 100°C again, and is expanded through the pipe 51B. It is introduced into the turbine 37B. Here, it expands again to a state of 10 atmospheres and +20°C, and is led out to the pipe 52B.
The power generated by the expansion turbines 37A and 37B is used as power to drive the compressor 38 connected together. On the other hand, the LNG at 10 atm and -155°C supplied from the pipe 54 is pressurized to 200 atm by the pump 55, and then reaches the valve 56, where it is supplied to the upper heater 57A where the supply amount is adjusted according to the electricity demand. It is heated to 100° C. by the input heat source 58 and introduced into the expansion turbine 5A through the pipe 59A. Here the high pressure
The LNG expands to 45 atmospheres and +20°C, enters the heater 57B from the pipe 60A, is heated again to +100°C by the heat source 58, passes through the pipe 59B, enters the expansion turbine 5B, and expands again to 10 atmospheres. It reaches a state of +20°C and is led out to the pipe 60B. The pipe 60B merges with the above-mentioned 52B and 39, becomes the pipe 40, and reaches the thermal power plant of the demand destination. The expansion turbines 5A and 5B transmit the generated power to the air compressor 3 connected thereto, and supply part or most of the power necessary for compressing the raw material air. As described above, in order to solve the inconvenience that high boiling point organic substances normally contained in LNG are concentrated and precipitated during the vaporization process, the present invention focuses on pressurizing LNG in which the organic substances are concentrated, and makes effective use of this pressure. By doing so, we can reduce the power consumption of the compressor and
This method makes it possible to improve the liquefaction rate of air by making maximum use of the cold temperature of air.Comparing the unit consumption of liquid air produced by this method with that of the conventional method, it is as follows. The consumption at thermal power plants, which are the final demand for LNG, is now 80,000 Nm ³ /h at night.
It is assumed that the peak power consumption during the daytime is 150000Nm ³ /h. That is, in the embodiment shown in FIG.
Assuming that 80000Nm ³ /h of LNG constantly flows through pipe 26 for air liquefaction, while the amount of LNG flowing through pipe 54 is negligible at night and reaches 70000Nm ³ /h during the daytime peak hours, each The following table shows the power consumed by the equipment, the power generated by the expansion turbine of the method of the present invention, and the required power when the power generated by the turbine is used as the drive source for the compressor.

[Table] Therefore, the electricity consumption rate when manufacturing liquid air at 48000Nm ³ /h is 13700/48000 = 0.285kWH/Nm ³ in the conventional method, whereas in the case of Example 1 it is 7000/48000 = 0.146 kWH/ ^Nm3 . That is, the method of the present invention provides a great economical effect in that the power consumption rate is about half that of the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing one embodiment of the method of the present invention, and FIG. 2 is a system diagram showing another embodiment. 2 is a cooler, 3 is a compressor, 4 is an electric motor, 5,5
A and 5B are expansion turbines, 7 is a precooler, 8a and 8b are adsorbers, 10 is a heat exchanger for precooling raw air,
12 and 14 are LNG evaporators, 16 is a heat exchanger,
17 is an expansion valve, 18 is a gas-liquid separator, 21 is a liquid air storage tank, 29 and 33 are gas-liquid separators, 34 is an electric motor, 35 is a vacuum pump, 37, 37A, 37B is an expansion turbine, 38 is a compressor, 41 is a thermal power plant, 44 and 45 are pumps, 47 is a heat exchanger, 4
9, 49A, 49B are heaters, 55 is a pump, 5
7, 57A, 57B are heaters, and 62 is a pump.

Claims (1)

[Claims] 1. In a method of liquefying air using liquefied natural gas, raw air is compressed with a compressor, and after being pretreated, it is introduced into a liquefied natural gas evaporator and the A step of cooling and expanding the liquefied natural gas with the supplied liquefied natural gas, storing the generated liquefied air and collecting the separated low-temperature air, and then combining the liquefied natural gas with the raw material air sucked into the compressor. The evaporated gas of the liquefied natural gas that has been supplied to the gas evaporator in excess of the evaporation amount is pressurized and supplied to the consumer, and the excess liquid is pressurized to a critical pressure or higher, heated, and then introduced into an expansion turbine to absorb the evaporated natural gas. An air liquefaction method using liquefied natural gas, characterized by comprising a step of expanding the gas as a power source for pressurizing the gas. 2. Air liquefaction using liquefied natural gas according to claim 1, characterized in that the natural gas pressurized above the critical pressure and heated is expanded by an expansion turbine consisting of multiple stages. Method. 3 In a method of liquefying air using liquefied natural gas, raw air is compressed with a compressor, pre-treated, and then introduced into a liquefied natural gas evaporator to supply liquefied natural gas in excess of the evaporation amount. The liquefied natural gas is cooled and expanded by the liquefied natural gas evaporator. The evaporated gas of the liquefied natural gas supplied above is pressurized and supplied to the consumer, and the surplus liquid is pressurized to a critical pressure or higher and heated, and then introduced into an expansion turbine, which generates power for pressurizing the evaporated natural gas. and a step of pressurizing separately supplied liquefied natural gas to a critical pressure or higher, heating it, introducing it into an expansion turbine, and expanding and supplying it as a power source for pressurizing the raw material air. An air liquefaction method using liquefied natural gas characterized by: 4 Utilizing the liquefied natural gas according to claim 3, wherein the separately supplied natural gas pressurized to the critical pressure or higher and heated is expanded by an expansion turbine consisting of multiple stages. air liquefaction method.