RU2297580C1 - Method of liquefying natural gas - Google Patents

Abstract

FIELD: liquefying natural gas.

SUBSTANCE: method comprises cooling gas in the heat exchanger by supplying liquid nitrogen. The liquid nitrogen is produced from the air flow by adiabatic expanding and cooling down to a temperature of liquefying of nitrogen. The flow is mixed with the 500-nm carbon particles. The mass of carbon particles is 30-70% of the total mass of the mixture . The mixture is then accelerated up to the velocity exceeding the sound velocity.

EFFECT: enhanced efficiency.

1 dwg

Description

The invention relates to the field of technology for liquefying natural gas.

A known method of producing liquefied natural gas, comprising compressing the source gas in the compressor stage of the turboexpander, injecting methanol into it, cooling the gas, drying and purifying carbon dioxide by contacting with methanol, separating it from the water-condensate-methanol mixture, separating it into components and regenerating separated methanol with its subsequent return to the stage of drying and purification; after cooling, the gas is divided into three streams in the following mass ratio: 1.7: 2.3: 1.0, respectively, while the first stream is directed to heating, and then mixed with the second stream before they are fed to the expansion stage of the expander, the third stream is fed for contacting with chilled methanol, after which it is further cooled, liquid condensate is separated and mixed with the first and second streams at the inlet to the expander, see RU 95117635.

The disadvantage of this method is the need for pre-cooling, the complexity of the implementation due to the need to separate the gas into three streams strictly in predetermined proportions, the high cost of equipment necessary for implementing the method.

A known method of liquefying natural gas supplied under pressure, comprising dividing the initial stream of compressed gas into two parts, cooling the first part in a heat exchanger, and the second part in a cooler, followed by mixing, expansion and separation of the formed liquid phase from the gaseous phase, which is supplied return flow to the heat exchanger; before cooling, the first part of the feed stream is fed into a vortex tube, from which cold and hot flows are removed, the cold stream is mixed with the return flow and sent to the heat exchanger, and the hot stream is sent to the heat exchanger in a direct flow, then it is mixed with the second part of the feed stream cooled in the cooler. before expansion, see RU 2178129.

To implement this method requires complex and expensive equipment, in particular an expander, a compressor, an additional vortex cooler, etc. For gas liquefaction, several cooling cycles are necessary, which significantly increases the energy consumption and time required to produce liquefied gas.

A known method of liquefying natural gas, including its cooling by expansion. Before cooling, natural gas is mixed with an energy-absorbing substance by liquid vapor or a gas with a molar mass of M 40 kg / mol. Vapors of liquid or gas make up 10-50 wt.% Of the total mass of the resulting mixture. Next, the mixture is accelerated to a speed exceeding the speed of sound in it, RU 2212599 C1.

This method is based on the fact that due to the addition of an energy-absorbing substance to natural gas with a very large molecular weight that is more than three times the molecular weight of natural gas, the energy of the obtained gas mixture during its acceleration is divided in proportion to the molecular weights of the components of the mixture. Therefore, during subsequent cooling by expansion, most of the energy is taken away by a component with a higher molecular weight, which provides cooling and liquefaction of the light component (natural gas).

However, this method requires a very high pressure of the source of natural gas (300-500 atm). Therefore, its implementation is advisable in the immediate vicinity of the wells, since such pressure has gas coming from the well. However, in main gas pipelines the gas is at a pressure of no higher than 70 atm and to reduce it by the described method it is necessary to precompress it to a pressure of at least 300 atm. This is due to both large energy costs and serious environmental hazards at gas stations.

A known method of liquefying natural gas under relatively low pressure, comprising cooling it in a heat exchanger with liquid nitrogen supplied thereto, which is obtained from an air stream by expanding and cooling it to a nitrogen liquefaction temperature, RU 2162579.

This technical solution is taken as a prototype of the present invention.

The cooling of the air in the prototype method includes sequentially alternating two isothermal and two isochoric processes.

The working fluid is not consumed, but changes its volume when heated and cooled. The duty cycle includes four clock cycles: compression, heating, stroke, cooling.

This method is very unproductive, since the energy-absorbing substance is a gas having a low energy intensity (any gas). The heat exchange process is very slow. In the prototype method, even fairly large-sized equipment (2 × 2 × 2) m is used, without taking into account the compressor and heat exchanger, it is possible to get only 1-2 kg of liquid nitrogen per hour from the air, which ultimately leads to a low productivity for producing liquefied natural gas.

The objective of the invention is to increase the productivity of the method of liquefying natural gas.

According to the invention, this problem is solved due to the fact that in the method of liquefying natural gas by cooling it in a heat exchanger with liquid nitrogen supplied therein, which is obtained from the air stream by adiabatic expansion of the latter and, accordingly, cooling it to a nitrogen liquefaction temperature, the air stream is mixed with carbon particles no larger than 500 nm in size, while carbon particles make up 30-70 wt.% of the total mass of the air mixture with these particles, after which the mixture is accelerated to a speed exceeding soon be sound in it.

The applicant has not identified sources containing information about technical solutions identical to the present invention, which allows us to conclude that it meets the criterion of "novelty."

If in the prototype method the energy-absorbing substance in the production of liquid nitrogen is a gas having a low energy intensity, then in the claimed method, the energy-absorbing substance are particles of a solid substance - carbon, the energy intensity of which is ten times greater than any gas. In this case, the carbon particles should have a size of not more than 500 nm, otherwise they behave similarly to macroscopic droplets, which causes a violation of the uniformity of the flow velocity field; carbon particles should be at least 30 wt.% and not more than 70 wt.% of the total mass of the mixture of air with these particles. If the proportion of carbon particles is less than 30 wt.%, Then the energy absorption is too small, and effective cooling of the air and, especially, nitrogen condensation does not occur. If the proportion of carbon particles exceeds 70 wt.%, Then there is not enough air in such a mixture, and the amount of condensed nitrogen is also small. Accordingly, the yield of the final product — liquefied gas — is small.

The applicant has not found any sources of information containing information about the impact of the claimed distinctive features on the technical result achieved as a result of their implementation. This, according to the applicant, indicates that this technical solution meets the criterion of "inventive step".

The claimed method is illustrated in the drawing, which shows a diagram of its implementation.

Compressed air from the compressor is supplied to mixer 1. Carbon particles are introduced into the same mixer through pipe 2, which are mixed with air; carbon particles have a size of not more than 500 nm and comprise from 30 to 70 wt.% of the total weight of the mixture. In a specific example, parts of intercalated graphite are used.

Then open the nozzle 3 - supersonic Laval nozzle and accelerate the mixture to a speed exceeding the speed of sound in this mixture. At the exit of the nozzle 3, adiabatic expansion of the mixture occurs, the pressure drops, the mixture cools and its components separate. At t ° - 195.8 ° C, liquid nitrogen condenses in the condensation chamber 4, which flows into the collector 5 and then enters the radiator 6 of the heat exchanger 7. The non-condensed air residue enters the atmosphere through the pipe 8 with a non-return valve. The carbon particles fly through the chamber 4 and settle in the collector 9, after which, by re-intercalation can be restored to its original state for reuse.

A source of natural gas is supplied to the heat exchanger 7 through a pipe 10, which is cooled by a radiator 6. A radiator 6 is connected to a radiator 11, which pre-cools the air entering the mixer 1. The spent nitrogen enters the atmosphere.

In a specific example, compressed air was supplied to the mixer at a pressure of 300 atm at a temperature after pre-cooling of 18 ° C in an amount of 40 kg / s. Powder of intercalated graphite in the amount of 50 wt.% Of the total mass of the mixture with a particle size of not more than 500 nm was introduced into the flow of air entering the mixer. Natural gas, methane, was supplied to the heat exchanger 7 from a transition gas station at a pressure of 70 atm in the amount of 8 kg / s at t ° 20 ° C. The output of liquefied gas is 62% by weight of the source of natural gas. The energy consumption per unit of the final product is 610 kJ / kg.

A unit implementing this method with dimensions (excluding compressor and heat exchanger) of not more than 1 × 0.7 × 0.7 m provides a capacity of up to 500 kg of liquefied natural gas per hour.

Claims (1)

A method of liquefying natural gas by cooling it in a heat exchanger with liquid nitrogen supplied therein, which is obtained from an air stream by adiabatic expansion of the latter and, accordingly, cooling to a nitrogen liquefaction temperature, characterized in that the air stream is mixed with carbon particles no larger than 500 nm, while carbon particles make up 30-70% of the total mass of the air mixture with these particles, after which the mixture is accelerated to a speed exceeding the speed of sound in it.