JPS61228268A - Method and device for decompressing pipeline gas with cooling formation - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary of the Invention] High pressure of pipeline gas is passed through two consecutive centrifugal gas compressors driven by two turboexpanders, and the compressed gas is continuously compressed in the turboexpanders. Expansion to low pressure simultaneously produces cooling and reduces pressure to low pressure in the distribution system.

Cooling is recovered from the gas leaving each turboexpander. Methanol is expanded after being injected into the pipeline gas to prevent ice formation. The liquid methanol condensate separated from the expanded gas is distilled to recover methanol for reuse.

FIELD OF INDUSTRIAL APPLICATION This invention relates to the production of refrigeration during the reduction of pipeline gas pressure to the pressure of a gas distribution system. In particular, the present invention relates to a method of maximizing such cooling production.

[Conventional technology]

The pressure of the pipeline gas is reduced at many pressure reduction stations simply by isenthalpic expansion, ie via a line through a pressure reduction valve. Such depressurization wastes valuable energy.

Two possibilities for the use of the energy available in the pipeline gas at the vacuum control station are the generation of electrical energy and the liquefaction of natural gas. Depending on the location of each vacuum control station, generation of electrical energy or production of liquefied natural gas may not be economically attractive.

In such cases, conversion of the available energy in the pipeline gas arriving in bulk at the depressurization station may be a suitable and valuable alternative, especially in local plants where cooling is required, especially where low cost cooling is required.

[Problem that the invention seeks to solve]

Therefore, a primary objective of the present invention is to convert expansion energy, such as that obtained from pipeline gas, into low cost cooling.

Another important objective is to maximize cooling production from isenthalpic expansion of pipeline gas, ie, expansion with work done.

These as well as other objects and advantages of the present invention will become apparent from the following description.

[Means for solving problems]

In accordance with the present invention, pipeline gas typically arriving at a vacuum control station at 100 to 400 psia (about 7.0 to 28.1 kg/cd absolute) is passed through two successive compression steps to at least about 150 psi (about 10.8 kd).
g/elf) increasing the pressure and then work-expanding the doubly expanded gas in two successive steps with intermediate reheating of the gas and generation of cooling from the expanded gas leaving each expansion 111m; desired pressure of, e.g. 30 psia
(2,1 kr/ctA absolute).

Often, the pressure of the pipeline gas reaching the depressurization station is about 150 to 250 psia (about 10.6 to 250 psia).
17.6 kg/-absolute); in such cases it is preferred to increase the pressure at least twice before passing through the second compression step. A centrifugal gas compressor coupled to a turboexpander is used for each compression and expansion step.

As used herein, pipeline gas is defined as having a very high methane content and at least about 950 BTU/cubic foot (standard conditions) (8454,3 Kcal/rd
natural gas or synthetic natural gas with standard conditions). The pipeline gas reaching the depressurization station invariably contains moisture, which will freeze during gas expansion and block the equipment, causing damage. A simple and inexpensive way to remove moisture from pipeline gas is to inject a small amount of methanol into the gas, so that the moisture only condenses during the expansion of the gas, leaving the expanded gas as a water-methanol solution. separated from According to the invention:
This method of methanol usage is integrated with novel refrigeration generation, so that a portion of the energy gained from depressurizing the pipeline gas is used to separate methanol from the water-methanol solution. Thus, the regenerated methanol can be circulated for injection into the pipeline gas, making it work-expandable in accordance with the present invention.

〔Example〕

BRIEF DESCRIPTION OF THE DRAWINGS In order to further clarify the invention, reference will now be made to the accompanying drawings.

FIG. 1 is an illustration of a particular embodiment of the invention in which the pipeline gas used is substantially pure methane containing a small amount of water.

Pressure in line 25 215 psia (15,1 kg/
cnl absolute), the pipeline gas at a temperature of 70°F (21,1°C) is transferred to a centrifugal gas compressor 26. Conduit 27. A pressure of 520 psia (36
, 6 kg/cnT absolute), temperature 260°F (127
℃) into line 29. A branch line 30 with a pressure reducing valve 31 may be used to circulate a small portion of the pipeline gas leaving the compressor 28 back to the inlet line 27; this recycled flow is compressed if necessary. It is used to balance the load work of machine 28 with the power generated in turboexpander 32, which is directly connected to compressor 2g. The control valve 33 diverts about a quarter of the gas in the line 29 to a branch line 34 and a reboiler 35, and then recombines with the gas in the line 29 to a pressure of 518 p.
sia (36,4 kg/aa absolute), 250°F (1
21° C.) and reaches the air cooler 36.

From there, the gas is 508 psia (35,7 kg/
co! line 2 at a temperature of 163°F (72,8°C)
9 continues to flow into the contact column 38. Control valve 39 diverts approximately 1% of the gas in line 29 through branch line 40 and heat exchanger 41 before entering contact column 38 at a pressure of 505 ml.
psia (35.5 kg/cal absolute), temperature 13
Recombine at 5°F (57,2°C).

The methanol in tank 42 flows through line 43 and pump 44 at approximately 575 bonds per million cubic feet of gas (Standard B) passing through column 38.
g/million standard conditions) into column 38. The vaporized methanol-containing gas is sent from the column 38 through a pipe 45 and a heat exchanger 46 to a separator 47 at a pressure of 500 psia.
(35,2 kg/c++! Absolute), temperature 65°F (1
8.3° C.) where the condensate is separated from the gas before entering the expander 32 via line 48. The inflation gas is pumped through the expander 32 to a pressure of 125 psi without substantially liquefying it.
a (8,8 kg/cd absolute), temperature -65°F
(-53.9 DEG C.) and flows from line 49 into separator 50 where the methanol condensate aqueous solution is removed from the cold partially expanded gas and then exits via line 51 and cold recovery exchanger 52. From there, the gas is at 123 psia (8,
7 kg/cm2 (absolute) and a temperature of -10°F (-23°C) through the exchanger 46 and enters the turboexpander 53 at a pressure of 12°C.
0 psia (8,4 kg/cn absolute), temperature 33°
F (2,3 °C).

Furthermore, the expanded gas has a pressure of 40 psia (2,8
ky/ctA absolute), temperature -65°F (-53,
9°C) from the expander 53 to the conduit 54 and the cooling recovery exchanger 55.
from there to a pressure of 37 psia (2,6 kg/
cnl absolute) and exit at a temperature of -10°F (-23°C).

From there, the gas passes through exchanger 46 to a pressure of 33 psia.
(2,3 kg/crA absolute), temperature 33°F (0,5
6° C.) through line 54 and exchanger 37.

A control valve 56 is used to divert a small portion of the gas in line 54 through branch line 57 and condenser 58; the small stream in line 57 then joins the gas in line 54. All process gases according to the invention are placed at point 59 at a pressure of 30 psia (
2,1 kg/cnl absolute), temperature 80°F (26,
7°C) and can be used directly in distribution systems.

The methanol portion added to the gas in column 38 is transferred to separator 47
It is separated and dripped as a condensate in the separator 47 to the pipe 60.
and is discharged into the tank 42 via the pressure reducing valve 61. The methanol portion remaining in the gas is removed from the cold expanded gas flowing into the separator 50 as a methanol condensate solution. This condensed aqueous solution contains 95% by weight methanol, and line 62. It flows through exchanger 64 and exchanger 41 and reaches pressure reducing valve 63 at a pressure of 120 psia (8.4 kg/cd absolute) and a temperature of 80°F (26.7°C). The condensed aqueous solution enters the separator 64 at a pressure of 20 psia (1,4 k
g/cIa absolute) at a temperature of 60°F (15.6°C). Trace amounts of inert gas are released from the condensate in the fractionator 64 and exit through valved line 65.

The condensate flows from the separator 64 via line 66 into the middle part of distillation column 67. Methanol vapor exits the top of column 67 via line 68 and condenses in condenser 58. Liquid methanol is pumped by pump 69 via line 70 to tank 42 and is reused for dehydration of the pipeline gas supplied by line 25. A control valve 71 in line 70 is used to control the amount of methanol returned via line 72 as it returns to column 67.

The water that collects at the bottom of the column circulates via line 73 and reboiler 35 and supplies heat to column 67. Valved line 74 is used to drain water from column 67 as required. A very small amount of the methanol injected into the pipeline gas remains in the gas in line 59 feeding the distribution system.

This methanol loss is per million cubic feet (normal conditions) of pipeline gas dewatered.

Approximately 6.5 bonds (approximately 104.1 kg/million d standard conditions) is replenished by fresh methanol added to tank 42 via line 75.

Cooling is provided by the present invention at approximately 105 tons of exchanger 52 per million cubic feet of pipeline gas processed per hour (standard conditions).
10,000 M (standard condition), and the exchanger 55 has a weight of approximately 100 tons (approximately 3,531.4 tons). Isenthalpic expansion, as practiced in many vacuum control stations, therefore produces enormous tonnage of heavy cooling from energy that would be wasted if the pressure of the pipeline gas were reduced.

FIG. 2 shows an improvement to the process diagram of FIG. 1, which allows the method of the invention to obtain cooling at two levels.

Reference numerals shown in FIG. 1 are used for the same elements in FIG. The two new elements in Figure 2 are reference numbers 80 and 8.
1 is a high-level cooling recovery exchanger. If one compares FIG. 2 with the portion of FIG. 1 which it replaces, it is apparent that elements 37, 39, 40 and 41 of FIG. 1 have been omitted. After passing through the low level refrigeration recovery exchanger 52, the expanded gas in line 51 enters the high level refrigeration recovery exchanger 80 rather than exchanger 46 before entering the expander 53.

Additional expanded gas in line 54 is supplied to a low level cooling recovery exchanger 55.
After passing through the high-level cooling recovery exchanger 81, the exchange f11! ! Pass through B46.

[Effect]

The exchanger 52 is set to a pressure of 123 psia (8.7 kg/-
absolute), the gas leaving at a temperature of -1°0°F (-23°C) is (
Pressure 120 psia (8,4 kg/
-absolute), exits at a temperature of 33°F (0.56°C). Similarly, the exchanger 55 is set to a pressure of 37 psia (2.6 kg/
cn absolute), temperature -10°F (-23°C), leaves exchanger 8I at a pressure of 34 psia (2.4 kg/
cnl absolute), exits at a temperature of 33°F (0,56°C).

What should be noted is that based on Figure 1, 1 million cubic feet of pipeline gas is processed per hour according to the example.
As mentioned above, the cooling obtained per unit (standard condition) is 105 tons (3708,0) tons/1,000,000 standard conditions) in the exchanger 52, and further 100 tons (3531,0) tons in the exchanger 55.
, 4) tons per million standard conditions) and this amount can be obtained essentially unchanged in the corresponding exchanger with the improved method shown in FIG. 2, and according to FIG. Approximately 81 tons (2860,4 tons/million d) per million cubic feet of pipeline gas in exchanger 80
standard condition) and exchanger 81, approximately 79 tons (2789,
8) n/1,000,000 M standard state) is additionally obtained. The embodiment of FIG.
5 tons (7239,4) tons/million standard conditions), whereas the embodiment of FIG. d standard conditions) as well as a total high level cooling of approximately 160 tons (5650,2 tons/1 million M standard conditions) for 1 million cubic feet per hour of pipeline gas.

〔effect〕

Therefore, Figure 2 shows that the additional cooling is approximately -5°F (-20,6
80% more cooling than in Figure 1 is obtained at temperatures close to -60°F (-5
can be obtained at temperatures close to 1"C). In summary:
Figure 2 is justified if there are customers who require cooling in their respective operations at different temperature levels, for example, some customers use low level cooling for deep freezing, and some customers have cold storage warehouses. This is the case when using high level cooling. Generally, low-level cooling is recovered at temperatures below about -40°F (-40°C), and high-level cooling is recovered at temperatures below about 20°F (-6,7°C).
℃) or below.

Many variations and modifications of this invention will be apparent to those skilled in the art without departing from its spirit and scope. For example, conduit 5
The gas streams 1 and 54 may be passed through a single cooling exchanger in place of exchangers 52 and 55 in countercurrent relation to one heat transfer fluid, which fluid is connected to one or more utilization sides. On the other hand, it is used to convey cooling. Similarly, in FIG. 2, the cold gas in line 51 may exit in countercurrent relation to a heat transfer fluid through a single cooling exchanger instead of exchangers 52 and 80, which fluid is exchanged. It will enter at the warm end of the vessel and exit at the middle of the exchanger, where another heat transfer fluid will flow into and be withdrawn from the cold end of the exchanger.

The first heat transfer fluid would be delivered to a customer requiring high level cooling, and the other heat transfer fluid would be delivered to a customer requiring low level cooling. Exchangers 55 and 81 may similarly be replaced by a single exchanger.

In FIG. 1, the gas in line 48 may be passed through expander 53, in which case the gas in line 51 would be passed through expander 32.

Of course, only such limitations should be placed on the claimed invention.

[Brief explanation of the drawing]

FIG. 1 is a process flow diagram of a preferred embodiment for producing low-level cooling according to the present invention; FIG.
FIG. 1 is a process diagram showing improvements in the portions indicated by FIG. 2; FIG. It is a diagram. 26.2B, Centrifugal gas compressor 32.53. ,,Turbo expander 35. ,, reboiler 36
,,, air cooler 37. ,, heat exchanger 38°9.
Contact tower 41. , , heat exchanger 42 , , methanol tank 46. ,, heat exchanger 47.50. ,,
Separator 52, 55. ,,low level cooling recovery exchanger80.
81. ,, High level cooling recovery exchanger FIG, 1

Claims (12)

[Claims] (1) A method for reducing the high pressure of a pipeline gas to a predetermined lower pressure in a distribution system while producing cooling solely from the energy obtained from the reduced pressure, wherein the gas is compressed in two successive steps to a pressure of at least about 150 psi ( 10.6k
g/cm^2) Increase the gas pressure, inject methanol into the compressed gas, cool the methanol-containing compressed gas by exchanging heat with the expanded gas described below, and substantially liquefy this cooling gas. Expansion is carried out with work carried out without any process, said work being used in one of said two steps of compression, separating condensed liquid methanol from the expanded gas, and then distilling said condensate to recover said methanol. and reuse, the distillation cools the compressed gas after receiving reboiler heat from the compressed gas, thus recovering low-level cooling from the dehydrated expanded gas, and then additionally expanding the dehydrated expanded gas to produce substantially to perform additional work without liquefying the gas,
The additional work is used in the other of the two compression steps to recover low level cooling from the additional expanded gas, and then the additional expanded gas is passed in countercurrent heat exchange relationship with the compressed gas to produce the compressed gas as described above. 2. A method of producing refrigeration, comprising: producing refrigeration of , using said additional expanded gas to provide reflux cooling to said distillation, and then discharging said additional expanded gas at said predetermined low pressure into said distribution system. (2) The cooling generation method according to claim 1, wherein the high-level cooling is recovered from the expanded gas after the low-level cooling is recovered, and the high-level cooling is recovered from the additionally expanded gas after the low-level cooling is recovered. (3) Cooling generation according to claim 1, wherein the work performed by expansion of the cooling gas is used for the two steps of compression, and the additional work performed by the additional expansion of the expanded gas is used for the first step of compression. Method. (4) The high pressure of pipeline gas is approximately 100 to 400 ps
A cooling production method according to claim 1, 2 or 3 in the range of ia (7.0 to 28, 1 kg/cm^2 absolute). (5) The high pressure of pipeline gas is approximately 150-250p
sia (10.6 to 17.6 kg/cm^2 absolute), and the high pressure is at least doubled after compressing the high pressure gas in two successive steps.
, 2 or 3. The cooling production method according to item 2 or 3. (6) The cooling production method according to claim 1, 2 or 3, wherein the separated liquid methanol condensate is heated by exchanging heat with compressed gas, and then the condensate is distilled. (7) recover low-level cooling at a temperature below about -40°F (-40°C) and recover high-level cooling at a temperature of about 20°F (-6.7°C) or less;
) The cooled production method according to claim 2, wherein the product is recovered at a temperature of: (8) A method of producing refrigeration according to claim 1 or 3, wherein the expanded gas is passed therein in a countercurrent heat exchange relationship with the compressed gas after recovering low-level refrigeration therefrom, and the compressed gas is then expanded. (9) In an apparatus for reducing the high pressure of pipeline gas to a predetermined low pressure in a distribution system and further recovering cooling produced solely by the energy obtained from the pressure reduction, a first centrifugal gas coupled to a first turboexpander; a first centrifugal gas compressor, the inlet of the first compressor being connected to an inlet of pipeline gas; a second centrifugal gas compressor coupled to a second turboexpander; a second centrifugal gas compressor in which an inlet of the second compressor is connected to an outlet of the first compressor; a distillation column having a reboiler connected to a passage through which compressed gas from the second compressor passes; ; means for injecting methanol into the compressed gas; a heat exchanger having a first flow path connected to an outlet of the second compressor and an inlet of one of the first and second turboexpanders; a gas-liquid separator connected to an outlet of one of the turboexpanders, the liquid outlet of the separator being connected to a gas-liquid separator connected to an intermediate part of the distillation column; a first cooling recovery exchanger connected to the other inlet of the first and second turboexpanders; a second cooling recovery exchanger connected to the outlet of the other turboexpander and a second flow path to the heat exchanger; A cooling recovery exchanger,
The second flow path counterflows the first flow path and connects to and passes gas leaving the second flow path via a reflux condenser of the distillation column and discharges gas into the distribution system. A recovery device for the generated cooling, comprising a second cooling recovery exchanger. (10) Claims in which the first auxiliary cooling recovery exchanger is connected in series with the first cooling recovery exchanger, and the second auxiliary cooling recovery exchanger is connected in series with the second cooling recovery exchanger. 10. The apparatus for recovering the generated cooling according to claim 9. (11) The outlet of the first cooling recovery exchanger is the third cooling recovery exchanger in the heat exchange tower.
9. Recovery of the produced cooling as claimed in claim 9, wherein the third flow path is in counter flow with the first flow path and is connected to the other inlet of the first and second turboexpanders. Device. (12) The first flow path of the heat exchanger connected to the outlet of the second compressor is connected to the inlet of the second turbo expander, and the first cooling recovery exchanger is connected to the outlet of the second turbo expander. , and the first
11. The produced cooling recovery apparatus as claimed in claim 10, wherein the auxiliary cooling recovery exchanger is connected to the inlet of the first turboexpander.