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US 2025/0075973 A1Published application
Natural gas liquefaction process and plant to carry it out
AssigneeUniversidad Nacional De Itapua
InventorsEugenio Jose Cano Coscia, Jorge Alberto Mellid Samusik, Fernando Luis Galeano Flores
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Abstract
Gas liquefaction process, preferably natural gas in a small-scale plant that includes compression cycles, refrigeration with various refrigerants and expansion, and a small-scale plant that includes of 4 loops to carry it out.
Claims23
A gas liquefaction process for, a natural gas pre-treated for liquefaction, the process comprising the steps of:
- conveying said pre-treated gas at a pressure between 150 and 200 psia, and a temperature between 15 and 20° C., to a first pre-cooling heat exchanger, wherein the pre-treated gas is cooled by exchanging heat in counter-stream with a cycle of propane, thus being refrigerated to a temperature between −10 and −15° C.,
- directing the gas from the previous step to a higher hydrocarbon separator to separate a fraction of liquefied gas at the bottom, when there are condensable traces and the dry gas is released at the top,
- conveying the gas separated from said upper part of the previous step to a cool box, to circulate it through a second recuperative type counter-stream heat exchanger, thus producing cooling to a range of −15 to −20° C.,
- conveying the natural gas from the previous step to a third counter-stream heat exchanger, producing additional counter-stream cooling with a mixed refrigerant loop, until partial liquefaction of said gas is achieved at a temperature between −130 and −140° C.,
- conveying the gas from the previous step partially or completely liquefied to a fourth recuperative heat exchanger, increasing the gas percentage of liquefaction or sub-cooling, within a temperature gradient of 0.5 to 1° C., as heat is exchanged in counter-stream with the gas itself at low pressure,
- passing the flow of liquid natural gas thus achieved through a throttle valve, producing its expansion in a cryogenic collector tank, wherein its pressure decreases to a range between 45 and 50 psia, and reaches a temperature of −148 to −150° C., producing partial vaporization,
- collecting and storing the liquid fraction in said cryogenic collector tank, and conveying the vapors from the previous step to the fourth recuperative heat exchanger and then to the second natural gas exchanger mentioned above to achieve recuperative cooling,
- extracting the liquefied natural gas from the cryogenic collector tank, and
- compressing said portion of partially vaporized gas that produced the recuperative cooling in a compressor, to be injected together with the pre-treated natural gas from the first stage, thus re-starting the process.
6 more elements
A gas liquefaction plant for natural gas comprising:
- a) a first loop of pre-treated natural gas that is supplied at a pressure of 150 to 200 psia and is led to a first heat exchanger that pre-cools the natural gas with a propane cycle, then the gas is led to a separator of phases that retains the condensable traces if there are higher hydrocarbons and the gas fraction is directed to a cool box that has a liquefaction column made up of a second recuperative type counter-stream heat exchanger, a third counter-stream heat exchanger that exchanges heat with a mixed refrigerant loop and a fourth recuperative heat exchanger, connected in series in that order, said fourth heat exchanger being connected through a throttle valve with the inlet of a cryogenic collector tank that accumulates the gas fraction liquefied natural gas, and the gas fraction is vented from the tank to produce recuperative cooling, passing through the forth and then the second exchanger respectively at low pressure, to finally be re-injected by a compressor along with the pre-treated gas stream,
- b) a second mixed refrigerant loop that has a low pressure compressor for the mixed refrigerant, the same being connected, through an oil separator and a first mixed refrigerant heat exchanger, with a high pressure compressor for the mixed refrigerant having an outlet connected to an oil separator in series with a second mixed refrigerant heat exchanger or a two-stage compressor with intermediate cooling and a high pressure oil separator extending from said second exchanger of heat to a coalescing filter that leads the mixed refrigerant to a third recuperative type heat exchanger that we call mixed refrigerant heat recovery which has an outlet that leads the mixed refrigerant to a fourth exchanger that acts as a pre-cooler for the mixed refrigerant with an auxiliary propane cycle, which leads to a fifth recuperative exchanger that acts as a liquefier for the mixed refrigerant, extending from its outlet a condensate line that passes through a throttle valve that allows the expansion of the mixed refrigerant in an heat exchanger or mixed refrigerant evaporator through which the natural gas passes in counter-stream as mentioned above, wherein the mixed refrigerant then passes at low pressure through the mixed refrigerant liquefier and subsequently through the mixed refrigerant heat recovery, producing recuperative refrigeration in both and from there it returns to the low-pressure compressor, said mixed refrigerant heat recovery being said mixed refrigerant pre-cooler, said mixed refrigerant liquefier and mixed refrigerant evaporator arranged within said cool box,
- c) a third pre-cooling loop with propane that comprises a single-stage compressor that draws in the refrigerant at low pressure and drives it to an oil separator connected to a condenser cooled by forced air and from there a streamline emerges in liquid state that is divided into two, one of them goes to the natural gas pre-cooler to which it enters through a thermostatic valve that allows its expansion therein and the second line goes to another thermostatic valve that expands the refrigerant in the mixed refrigerant pre-cooler, wherein the low-pressure propane outlets of both exchangers are unified again and absorb residual heat from an auxiliary water-glycol refrigerant, over-heating before being drawn in again by the compressor, and
- d) a fourth loop with R22 Refrigerant or another similar one intended to cool the mixed refrigerant after each compression stage through a water/glycol auxiliary fluid, wherein the loop comprises a compressor that receives the R22 refrigerant vapors at low pressure and discharges them compressed into an oil separator associated in series with a condenser cooled by forced air, whose outlet leads to a thermostatic expansion valve that expands in refrigerant in an evaporator and subsequently the R22 refrigerant is drawn in again by the compressor, wherein the evaporator cools the water/glycol auxiliary fluid and maintains it between 5 and 9° C., which is pumped from a tank and is diverted into two for the first and second mixed refrigerant heat exchangers, which are in parallel and return the auxiliary fluid later to the tank.
1 more element
Dependencies are inferred from the claim text.