Information
-
Patent Grant
-
6663350
-
Patent Number
6,663,350
-
Date Filed
Monday, November 26, 200122 years ago
-
Date Issued
Tuesday, December 16, 200320 years ago
-
CPC
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US Classifications
Field of Search
US
- 417 53
- 417 2975
- 417 213
- 417 286
- 417 298
- 417 521
- 062 481
- 062 506
-
International Classifications
- F04B4902
- F04B49025
- F04B4903
- F04B2304
- F17C1300
-
Abstract
A high pressure pump and delivery system mating to LNG storage and suited for natural gas powered trucks and buses, but also suitable for other cryogenic liquid fuels. The reciprocating pump is comprised of a liquid pumping portion and a vapor compressing portion, operating in concert so that it is possible to locate the pump above a source of saturated LNG and to reliably supply high pressure LNG. The delivery system provides a method of utilizing both the pumped LNG and the compressed NG in a Diesel type fuel injection system, and also to scavenge NG vapor from the LNG storage container so as to extend it's storage life. While especially useful for trucks and buses, the present invention is not limited thereto, as it is also useful for locomotives, automobiles and other vehicles designed to operate through combustion of natural gas, as well as stationary applications.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT OF FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not Applicable
SEQUENCE LISTING
Not Applicable
BACKGROUND
Field of the Invention
This invention relates to the apparatus and methods suitable for very low Net Positive Suction Head (NPSH) cryogenic (and other low temperature boiling liquids) pump systems, either mobile or stationary, able to operate under a wide variety of liquid supply conditions. These conditions include where the pump is above, at or below the source of liquid; whether pumping to low or medium or high pressures; start-stop against discharge pressure; and from zero to low to high NPSH at the pump's intake. Thus it can operate under conditions including where NPSH varies during use from none, to little, to much while pumping. One example of such zero NPSH difficult pumping applications is where the pump is located above a saturated or near saturated cryogenic liquid source carried in a small tank located on a vehicle (the vibration of the vehicle/motor tending to destroy any liquid stratification or pressure building result), thus providing near zero Net Positive Suction Head (NPSH) or less at the intake of the pump's inlet conduit, a condition under which most known cryogenic pumps cannot reliably operate, especially as the tank becomes nearly empty. Furthermore, for many reasons, it may not be desirable to vent to the atmosphere vapor from the cryogenic or liquefied gas storage system; accordingly many traditional methods/techniques utilized in the cryogenic pump industry incorporating pressure building or similar techniques to provide prime or NPSH to a pump are not appropriate. A still further problem is that many such cryogenic systems are self-refrigerating, depending upon the repetitive delivery of cold liquid cryogen to provide the system's refrigeration needs, thus such pressure building methods are undesirable, as they add heat to the system.
One specific application where all these pumping abilities would be desirable is when using LNG (liquefied natural gas) as an on-board fuel for large trucks or buses (or other large mobile powered units), using a LNG fueled engine. Typically the LNG must be delivered by a LNG tank truck or rail car from the producing point to a bulk dispensing station having a large LNG storage vessel; from which the LNG is transferred into each truck's on-board fuel tank. Low pressure fuel storage tanks are desired so as to minimize their weight and costs. Then, as the truck's engine requires fuel, the LNG is vaporized and supplied to the engine at a pre-determined pressure, with the desired pressure being a function of the engine's specific design. Some engines are designed to operate at pressures below about 200 psig while others above about 2,000 psig, and still others at an intermediate pressure. One special difficulty presented at a LNG bulk station is that it is frequently desired for safety reasons to locate the LNG storage vessel underground and thus it is very inconvenient to locate a transfer pump underneath it, as is normal practice with many cryogens when stored in aboveground vessels. Depending upon a number of individual operational factors (and vessel design), the LNG in the underground vessel can be sub-cooled and/or pressurized and the vessel nearly full, thus offering substantial NPSH to an above-ground pump (once primed); or the opposite—at equilibrium conditions and an almost empty vessel, thus offering no NPSH to an above-ground pump; and accordingly the pump is subject to a variety of constantly changing, but normal, operating conditions.
Almost similar type difficulties and conditions are presented on the LNG fueled truck itself in providing NG to the engine. The most favored location on the truck or bus for the on-board fuel (LNG) tank(s) is low, and it would be inconvenient and unsafe to position a pump below the tank in an attempt to provide NPSH to the pump. In addition, the almost constant movement of a truck or bus (and of consequence the LNG fuel tank) causes the LNG throughout the tank to be at near equilibrium conditions, again making the provision of NPSH difficult.
Furthermore, it is desirable to be able to utilize as fuel nearly all the LNG in the tank, thus the ability to pump from a near empty fuel tank is desirable. A special difficulty of cryogenic and liquefied gas systems is that it is desirable to conserve the refrigeration potential of the stored liquid to the greatest extent possible, so that no venting of the cryogen or liquefied gas occurs, either when fuel is being used or when the truck is at rest; accordingly any heat conductive connections to the pump should be such that the heat leak caused by the pump is minimized. A still further difficulty is the wide range of fuel (LNG) supply rates required by trucks or buses and thus pumping capabilities required as the vehicle's engine goes from no use to idle to mid speed and to high speed in highly variable sequences on an as-needed basis. Different engines have different desired supply/injection pressures, but one current desire is to favor injection at higher pressures because of increased efficiency and reduced pollutants in the engine's exhaust gas. While it is theoretically possible to inject the LNG into the engine while in the liquid state (as with diesel fuel), the problems of variable volumetric efficiency associated with cryogenic pumps and the variation in LNG's density associated with its saturation pressure have made this unfeasible. Accordingly, designers have favored vaporizing the LNG after pumping it to the desired pressure and then supplying/injecting the natural gas (NG) to the engine as compressed natural gas (CNG). This typically requires a vaporizer (using the atmosphere and/or waste engine heat or other heat source) for warming the now pressurized LNG thus forming CNG, which is then stored in a small pressure vessel maintained between two pressures, the lower pressure of which is the minimum supply/injection pressure and the upper pressure of which is determined by system capabilities or other factors and delivered through a pressure regulator at the desired pressure; all controlled by a device to monitor the pressures and cause the pump to operate.
The U.S. Dept. of Energy (DOE) in a Small Business Innovation Research Program Solicitation No. DOE/ER0686 identified “Liquid Natural Gas Storage for Heavy Vehicles” as a technical topic in which DOE has a R & D mission. In this Solicitation, on-board medium pressure (about 500 psig) and high pressure (about 3,000 psig) cryogenic pumps for LNG fueled vehicles were identified as specific areas where innovation was specifically desired. A related pump use is where it is desired to also be able to provide CNG or LNG at the bulk dispensing station for charging the truck's small pressure vessel or similar uses, thus a high pressure transfer pump is needed capable of pumping from a LNG source lower than itself (underground).
While LNG in mobile applications is used as an example herein, almost every cryogenic liquid being pumped from storage under conditions wherein a reduction in pressure below the liquid's equilibrium pressure or where the incursion of heat into the liquid, causes part of the intake liquid to vaporize would present similar difficulties. This includes cryogens which vaporize easily from heat incursion, and also liquefied gases, which while less sensitive to heat incursion, vaporize readily from a reduction in pressure.
These problems have generally been addressed by pumps characterized by the term “low NPSH” pumps. Included in previous low NPSH designs are U.S. Pat. No. 3,011,450 issued Dec. 5, 1961; U.S. Pat. No. 3,023,710 issued Mar. 6, 1962; U.S. Pat. No. 3,263,622 issued Aug. 2, 1966; U.S. Pat. No. 3,277,797 issued Oct. 11, 1966; and U.S. Pat. No. 6,006,525 issued Dec. 28, 1999—all to the present inventor. Also U.S. Pat. No. 5,188,519 issued Feb. 23, 1993 to I. S. Spulgis. In particular, these patents illustrate a type of reciprocating pumping mechanism where the intake valve is caused to open by the mechanical action of the piston rod retracting from a center opening in a hollow piston, a type of action commonly referred to as a “lost motion” action, as the piston does not move as far as does the piston rod. This mechanical opening of the intake valve reduces one principal need for NPSH, that of causing the intake valve to open by a reduction in pressure across it. In addition, if the intake valve is located above the compression chamber, vapor in the compression chamber can escape backwards by rising through the open intake valve. These designs require that the pumping chamber be located even with or lower than the source of liquid for optimum low NPSH service.
U.S. Pat. No. 5,411,374 issued May 2, 1999 to A. Gram represents a pump design able to be located above the supply container and able to pump saturated liquid from the container's bottom, a condition described by Gram as “negative feed pressure”. The pump essentially has a double acting piston removing vapor in the pump's inlet conduit at a rate sufficiently fast that liquid rises into the pump; as Gram states “by removing vapor from liquid in an inlet conduit faster than the liquid therein can vaporize by absorbing heat. . . ” However, absorbing heat is but one element in the source of vapor, as equilibrium liquid almost instantaneously releases vapor (and cools itself by evaporative cooling) as its pressure is reduced. In any event, the Gram pump is essentially a pump and/or compressor, handling intermittently under the different conditions that are encountered when pumping such liquids: all vapor, or vapor and liquid mixed, or all liquid. When handling all vapor it becomes a single stage compressor, with all the limitations—when compared to a single stage pump—of a single stage compressor, i.e.: greatly increased power; greatly increased heat generation (heat of compression); greatly reduced capacity; and greatly reduced possible pressure differentials. When handling vapor and liquid mixed (and at low NPSH or “negative feed pressure”), cavitation occurs and the pump's volumetric efficiency (and output) become unpredictably reduced, sometimes to the extent that vapor locking and pumping failure results, especially so when operating at compression ratios of about 10 or more.
U.S. Pat. No. 5,575,626 issued Nov. 19, 1996 to Brown et al is a pump submerged from the top into a container to the bottom. However, the mechanisms represent a serious and constant heat leak and the pump requires positive NPSH to open its spring loaded inlet valve.
U.S. Pat. No. 5,787,940 issued Aug. 4, 1998 to Bonn et al is a pump submerged from the top to the bottom of a separate sump attached to the storage vessel, so that the sump can be flooded with liquid when the pump is in use or not flooded when not in use, so as to reduce the heat leak when not operating. However, the heat gain to the system is substantial due to the heat leak to the sump and pump, even when not filled with liquid; and due to both the sump's and the pump's thermal masses, and the consequent warming of the liquid when it is desired to return the sump and pump to the proper operating temperatures.
U.S. Pat. No. 5,860,798 issued Jan. 19, 1999 to Tschopp is representative of a more common type of cryogenic pump having both spring loaded inlet and outlet valves. The pump is located below its supply container and two connections to the supply container allow liquid to flow down to the pump and vapor to flow back, due to gravity. However, this type of pump cannot pump from a liquid source that is lower than itself, and is not satisfactory at very low NPSH conditions.
U.S. Pat. No. 3,430,576 issued Mar. 4, 1969 to the present inventor is for a low NPSH liquefied gas (liquid carbon dioxide) pump having a spring loaded inlet valve, but creates a temporary increase in suction pressure (NPSH) at the inlet valve during the intake stroke, so as to temporarily provide sufficient NPSH to open the spring loaded inlet valve. Variations of this are also found in the '626, the '940, and the '798 patents. All require that the liquid be supplied to the pump.
U.S. Pat. No. 5,593,288 issued Jan. 14, 1997 to Kikutani is a liquefied gas pump shown in a mobile LNG application, top mounted and submerged to the bottom of the storage vessel; having a leakage path during the initial phase of the compression stroke back to the storage tank intended to allow vapor (bubbles in the liquid) to escape the compression chamber during the initial phase of the compression stroke, and thus avoid cavitation. However, the amount of vapor or bubbles can vary due to a number of factors, and thus excessive bubbles (and liquid) or insufficient bubbles can be allowed to escape, interfering with desirable pump operation.
A container for a cryogenic liquid that is stationary can be referred to as a vessel, and one that is mobile can be referred to as a tank, and tanks are considered to be smaller than vessels, but these terms can be used interchangeably.
The definition of a cryogenic liquid as used herein is one found in “Cryogenic Engineering” by R. B. Scott, Van Nostrand Co. 1959 which is that it is a liquid whose critical temperature is below terrestrial temperatures, taken as minus 70° F. Examples include nitrogen, oxygen, argon, methane, hydrogen and natural gas, when in the liquid condition.
The definition of a liquefied gas as used herein includes cryogens but also substances (gases) when stored under conditions where the gas is in the liquid phase and where the storage temperature is below the ambient conditions there/then present. It can be a saturated liquid if it is at both the saturation temperature and pressure; it can be a sub-cooled liquid if the temperature of the liquid is lower than the saturation temperature for the existing pressure; and can be a compressed liquid if the pressure is greater than the saturation pressure for the temperature it is at. Examples include carbon dioxide, ammonia, and other low temperature refrigerants.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a system and method for reliably pumping cryogenic liquids to low, medium or high pressures when the pump is located even with, above or remote from, its source of liquid and the liquid may or may not be saturated. The low NPSH pumping system and method of the present invention provide the suction lift required to bring a saturated liquid (but also less demanding condition liquid) to the pump, and are equally capable of pumping under zero, very low, medium or high NPSH conditions or conditions where the NPSH varies during pumping. The system and method also are able to remove any vapor created by the pumping action, thereby preventing vapor locking or damaging cavitation of the pump. The system and method also offers a number of desirable options for utilizing the removed vapor. As such, they provide the unique versatility necessary to meet the varying conditions encountered in many pumping applications. Depending upon the needs of the entire system the pump is part of, the vapor can be returned to the source container, either below or above the liquid level in that container, or supplied to a vapor using need external to the tank or vessel (such as NG to an engine or other need).
One key element of this system is recognition that the amount of vapor encountered when bringing such liquids to the pump and filling the compression chamber of the pump with a cryogenic liquid or liquefied gas can vary greatly (either increase or decrease). This variation can result from a number of causes, even while pumping, as they are a function of many factors, some of which are: condition or available NPSH of the inlet liquid resulting from storage or flow characteristics of the inlet conduit or other reason, and incoming liquid vaporizing upon contact with warmed pumping chamber elements, the result of frictions. Another factor is residual liquid in the clearance volume expanding to vapor upon the depressurization accompanying the suction stroke as a result of the heat of compression (greater at higher discharge pressures), all resulting in vapor in the inlet side of the pump, which needs to be removed in order to effect reliable high pressure pumping of saturated cryogenic liquids.
Another key element is purposeful vapor removal from a saturated cryogen or liquefied gas located within the inlet conduit of a pump so as to provide suction lift, by causing the remaining cryogen or liquefied gas in the conduit to be cooled by evaporative cooling, thereby providing the differential pressure required for the suction liquid lift for a pump located above, alongside or remote from, the liquid source; and to essentially empty the liquid source. This process is progressive as the liquid in the inlet conduit continues to rise, and also is progressive as new liquid enters the inlet conduit. The cooled cryogen or liquefied gas can continue to be cooled and provided with lift so long as vapor is removed and the resultant evaporative cooling occurs faster than any warming of the evaporative cooled liquid in the conduit. The volume increase occurring when many of these liquids become gas is typically greater than about 40 to 1 under normal storage conditions, so a relatively small volume of liquid becoming vapor can result in a great volume of vapor. While it varies some for each liquid and storage conditions, a lift of over about 10 ft. for some saturated cryogens can result in a greater volume of vapor than liquid.
Accordingly, a pump system is provided that is able to satisfactory function under a wide variety of conditions; instead of the opposite situation, where the conditions must be correct for the pump to operate properly. This eliminates many special conditions and limitations faced in the past at pump installations for the cryogenic liquids and liquefied gases, especially the lower temperature cryogenic liquids. In addition, the dual compressing/pumping nature of this pump uniquely satisfies the requirements of mobile LNG fuel supply for dual injection pressure Diesel type engines and also has the capability to extend the storage life of the on-board LNG storage.
It should be understood that while the invention is described as especially useful for certain LNG applications, there are many other pumping applications involving LNG and other cryogenic liquids or liquefied gases where the dual path arrangement for supplying and pumping liquid and removing vapor from the intake side of the pump and the intake liquid container and other elements of the invention would find valuable use.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
FIGS. 1A
,
1
B,
1
C and
1
D are simplified diagrammatic/sectional views of the invention incorporating both a low, medium or high pressure, lost motion type reciprocating piston pump and a gas/vapor compressor arranged to remove any vapor occurring at the pump's inlet area and to return any compressed vapor to the source liquid container, or to a use outside the container.
FIGS. 2A
,
2
B and
2
C are simplified diagrammatic/sectional views of the pump of
FIGS. 1A
,
1
B,
1
C and
1
D installed above the source of liquid, as at a bulk LNG station (where the bulk LNG storage tank may be below ground level), and illustrating the various locations the compressed vapor may be supplied to.
FIGS. 3A and 3B
are a diagrammatic/sectional partial views of the pump of
FIGS. 1A
,
1
B,
1
C and
1
D; but modified so as to be able to remove vapor from the ullage volume of the source liquid container, as well as that occurring at the pump's inlet area and also able to supply the compressed vapor to a use outside the source liquid container.
FIGS. 4A and 4B
are simplified diagrammatic/sectional views of pump, modified in accordance with
FIGS. 3A and 3B
, installed on a truck or bus (not shown) using LNG as a source for fuel, with the pump above or alongside the on-board LNG tank and the compressed vapor from the pump being supplied to an LNG fueled engine, along with the vaporized/pumped liquid for supplying NG either at a single or at dual pressures for supply to or injection into the truck or bus engine.
In the drawings that follow, an arrow represents a cryogenic liquid (or liquefied gas), an arrow with a circle following the head represents the vapor phase of the cryogenic liquid, a double headed arrow represents a cooled cryogenic liquid, a double headed arrow with a circle following the heads represents a mixture of vapor and the liquid it cooled, a triple headed arrow represents a compressed liquid and a triple headed arrow with a circle following the heads represents a compressed vapor.
DETAILED DESCRIPTION OF THE INVENTION
Shown in
FIGS. 1A
,
1
B,
1
C and
1
D is the pump of the present invention
10
; having a cryogenic pumping portion
11
of the reciprocating mechanically opened intake valve/ lost motion type (depicted as a double lost motion type), also incorporating a separate vapor removal compressing portion
12
connected to the intake side of pumping portion
11
, and a drive portion
13
, all making it possible to pump to high pressures near equilibrium or saturated condition cryogenic liquids or liquefied gases from a source lower than the pump, and also useful for any other liquid conditions and pump or storage locations. The embodiment of the present invention illustrated in
FIGS. 1A and 1B
incorporates as pumping portion
11
a pump of the type described in U.S. Pat. No. 6,006,525 to the present inventor.
As best shown on
FIG. 1A
, pump
10
is comprised of cylindrical casing
14
, mounted at one end to a warm end plate
15
, as could be installed on a typical insulated cryogenic liquid storage tank
16
(or vessel
16
′), on which the reciprocating drive and drive controls
13
are mounted. The single acting pumping portion
11
is just past the beginning of the its suction stroke, and the double acting vapor removal compressing portion
12
is both just past the beginning of a suction stroke and just past the beginning of a discharge stroke. While various drive arrangements can be used with the invention, the depicted drive
13
is a typical reciprocating hydraulic type. Drive
13
is arranged to transmit its reciprocating motion to a piston rod
18
. Suitably mounted near plate
15
and between the inside of casing
14
and rod
18
are warm end packing
20
and warm end guide bushing
22
. At the opposite end of casing
14
, pumping cylinder housing
24
is so connected and contained within lower casing
26
, so as to form sump
28
. Liquid inlet ports
30
and vapor outlet ports
32
provide openings in cylinder
24
for flow of cryogenic liquid
34
, and its vapor phase
35
occupying the space above the liquid phase
34
, with ports
30
and ports
32
acting as conduits between sump
28
and pump intake chamber
36
. Cryogenic liquid
34
is depicted at the bottom of vessel
16
, in sump
28
and in chamber
36
, with it's vapor
35
above, with appropriate arrows indicating liquid and vapor flows as pump
10
operates. Pump
10
is generally mounted either vertically or inclined, with the warm end higher than the cold end, so that liquid
34
readily tends to flow from sump
28
down through ports
30
into chamber
36
and vapor
35
readily tends to flow up through ports
32
from chamber
36
into sump
28
, all due to gravity, once sump
28
contains liquid
34
to a level at least between ports
30
and
32
.
A first cylindrical and hollow pumping piston
37
loosely fits over the cold end of rod
18
, so as to form a conduit between the outside of rod
18
and the inside of piston
37
. Pin
38
which is secured to piston
37
slidably engages and passes through slot
39
of rod
18
. Bushing
40
is fastened to rod
18
so as to loosely guide piston
37
, and contains serrations
41
as illustrated in
FIG. 1B
so as to not impeded flow of vapor
35
or liquid
34
through the conduit between rod
18
and piston
37
.
A second cylindrical and hollow pumping piston
42
fits loosely over piston
37
so as to form a conduit between the outside of piston
37
and the inside of piston
42
. Pin
44
, secured to piston
42
and slidably positioned in slots formed in piston
37
and bushing
40
, engages slot
46
of rod
18
. The cold end nose of rod
18
is tapered so as, when portion
11
is on it's compression stroke, it forms a seal with the also tapered inner nose section of piston
37
by compressing nose end seal
47
. The cold end outer nose of first piston
37
is similarly tapered so as, when pumping portion
11
is on it's compression stroke, it forms a seal by compressing nose end seal
48
with the tapered inner nose of piston
42
. These actions form the opening and closing of pumping portion
11
's intake valve mechanisms.
As the depicted liquid intake stroke begins, slot
39
and slot
46
are arranged so that pin
38
is engaged by slot
39
before pin
44
is engaged by slot
46
. Accordingly, the initial portion of the intake valve action to open is that located at seal
47
. This allows any vapor
35
in the pumping chamber
49
to escape by a dedicated path back to sump
28
before the principal liquid intake action begins through a separate path. Once pin
38
engages the bottom of slot
39
, rod
18
and piston
37
move simultaneously. This action causes piston
37
to rise with respect to piston
42
, so the next intake valve action to open is that located at seal
48
, Once both intake valve actions have occurred and pin
44
has engaged the bottom of slot
46
, piston
37
and piston
42
move as one unit through the remainder of the suction stroke. Liquid cryogen
34
then freely flows between pistons
37
and
42
and into chamber
49
, essentially unimpeded by vapor
35
egressing chamber
49
between piston
37
and rod
18
. As influenced by rod
18
, pins
38
and
44
, pistons
37
and
42
then move simultaneously to Top Dead Center, where the suction stroke ends and the compression stroke begins.
After Top Dead Center is passed, both intake valve mechanisms close in sequence, the first to close that formed by the tapered end of rod
18
and the tapered inner nose section of piston
37
, and then the second to close that formed by the tapered nose end of piston
37
and the tapered inner nose section of piston
42
, and then actual compression of liquid
34
and any attendant vapor
35
occurs in chamber
49
. Pumping chamber
49
is sealed along the exterior of piston
42
by combination bushing and high pressure sliding seals
50
. Upper discharge end plate
52
and lower discharge end plate
54
close chamber
49
and contain discharge check valve
56
. As rod
18
, pistons
37
and
42
then move simultaneously in the compressing stroke, pressurized liquid
34
flows through valve
56
and through discharge line
58
, which exits pump
10
through plate
15
, to use.
Vapor removal compressing portion
12
of pump
10
is comprised of a vapor removal piston
60
, which is slidably positioned within vapor removal housing
61
. Piston
60
features sliding seals
62
and is attached to rod
18
on both sides by retainer rings
63
, so that it, like the pumping portion
11
, also reciprocates in response to the action of drive
13
; in one direction both a suction stroke for causing vapor to enter lower chamber
64
, and a compression stroke for discharging any vapor in upper chamber
65
(as depicted) and the reverse when moving in the other direction. Pump chamber
36
is separated from chamber
64
by lower chamber plate
66
and upper chamber plate
68
separates chamber
65
from the warm end of pump
10
. Lower chamber seals
69
are located in plate
66
and upper chamber seals
70
are located in plate
68
. Compression of vapor
35
by portion
12
occurs as controlled by lower suction check valve
71
and upper suction check valve
72
and lower discharge check valve
73
and upper discharge check valve
74
, all mounted to housing
61
.
FIG. 1C
depicts valves
71
and
72
, with clack
75
held against seat
76
by the action of spring
77
against retainer
78
. Retainer
78
is made of a material that is attracted by a magnet, and if retainer
78
is attracted sidewise by a magnet, clack
75
is held in a cocked position and is not able to close, thereby disabling (unloading) the compressing action of the chamber it serves (as depicted by the alternate center line). Other methods of unloading compressing portion
12
are well known in the compressor industry and can be substituted without departing from the present invention.
FIG. 1D
is a simplified view along line A-A′ of
FIG. 1A
, showing the control elements and valves of vapor removal portion
12
of pump
10
; at a time when sufficient liquid
34
is in sump
28
, but some vapor
35
is being released from chamber
49
. Valve
72
communicates with suction cavity
79
, which communicates with sump
28
. Valve
74
communicates with discharge cavity
80
and discharge vapor line
81
in turn. Accordingly, valve
72
communicates with the upper portion of sump
28
, containing float type level control
82
, which is equipped with magnet
84
that as control
82
rises, magnet
84
also rises and attracts suction valve
72
so that it is held open in the manner illustrated in
FIG. 1C
, by the magnetic action of control
82
. Magnet
84
is located so as to progressively disable the action of compressing portion
12
by disabling in turn, valve
71
and valve
72
, and thus compensate for the varying amounts of vapor
35
created in pumping portion
11
or arriving at sump
28
through seperator
88
, possibly from all vapor during pumping portion
11
's cool-down to no vapor when tank
16
(or vessel
16
′) are full, or when there is NPSH available. If control
82
then rises to where the point that magnet
84
has attracted valve
71
so that it is cocked and remains open (disabled), but not valve
72
, thereby causing partial unloading of compressing portion
12
. If control
82
continues to rise, valve
72
is also attracted by magnet
84
so as to remain open, and no vapor
35
is removed from sump
28
. This condition results in compressing portion
12
becoming vapor trapped, so that no liquid
34
reaches valve
71
and valve
72
. If control
82
sinks, magnet
84
allows both valve
71
and valve
72
to function normally, and vapor
35
to be removed from sump
28
at the full capacity of compressing portion
12
. If desired, magnet
84
can be separated into two halves and each half so located in control
82
that the order in which valve
71
and valve
72
become disabled is reversed (not shown); or alternately valve
71
and valve
72
become disabled simultaneously (not shown). Other type known level controls can be substituted without departing from the present invention.
As shown in
FIGS. 2A
,
2
B and
2
C, discharge vapor line
81
can be extended, line
81
a
or line
81
b
or line
81
c
, so as to direct any compressed vapor
35
to where it is most useful, depending upon the supply and use circumstances of the entire facility pump
10
is a part of.
FIG. 2A
shows pump
10
as located above storage tank
16
(or vessel
16
′), wherein pump
10
is inserted into tank
16
(or vessel
16
′) through an opening in it's top, utilising plate
15
for mounting. A tank generally refers to a liquid container that in some fashion is (or can be) mobile, and vessel to a liquid container that is stationary. Line
58
takes the compressed liquid
34
to use (not shown). Inlet line
86
extends to near the bottom of tank
16
(or vessel
16
′), so tank
16
(or vessel
16
′) may be nearly emptied by pump
10
, and vapor return line
81
a
extends not quite as far as does line
86
, so that the returning vapor
35
does not unduly agitate the stored liquid
34
or dissipate any NPSH at the inlet of line
86
. When tank
16
(or vessel
16
′) contains liquid
34
to a level above L-2, such as L-1, vapor
35
returning tends to be cooled as it bubbles up through liquid
34
so as to return to the vapor space in tank
16
(or vessel
16
′). This action both reduces the volume of vapor
35
and warms liquid
34
as it bubbles through, as well as reducing any temperature related stratification of liquid
34
and consequent high pressure in tank
16
(or vessel
16
′). Moreover, this warming of liquid
34
extends the fill life of tank
16
(or vessel
16
′), as much of the heat gain of pump
10
and tank
16
(or vessel
16
′) then tends to be removed with the pumped liquid
34
. When the level of liquid
34
falls to level L-2, such action would no longer occur. Pump
10
and tank
16
(or vessel
16
′) are not shown to the same scale, as if tank
16
(or vessel
16
′) is large, pump
10
benefits by being located in the ullage volume of tank
16
(or vessel
16
′), thereby tending to remain cold during non-use, and not imposing as large a heat leak to the system. A small extension on the top of tank
16
(or vessel
16
′) could be provided to accept pump
10
(not shown).
Turning next to
FIG. 2B
, typically used for larger vessels
16
′, where it is frequently desired to mount a pump external to the vessel, pump
10
is connected in such a manner that pump
10
may be disconnected from vessel
16
′ without depressurizing vessel
16
′, even through liquid
34
may be in it. In this case, pump
10
can be mounted inclined (or vertical if preferred) inside an insulated enclosure
90
, and vapor line
81
b
may only extend partially below the safe fill line for vessel
16
′. Line
58
takes the compressed liquid
34
to use (not shown). A spray header
92
is typically used during liquid replenishment, condensing vapor
35
with the cold, low pressure liquid
34
typically being supplied, so as to reduce the pressure of vessel
16
′and thus prevent venting of vapor
35
. If desired, pump
10
could be remote from vessel
16
′, including inlet line
86
being external to vessel
16
′ and containing trap(s) (not shown).
Turning next to
FIG. 2C
, pump
10
is depicted as in
FIG. 2A
, except it is supplying both compressed vapor
35
with line
81
c
, and pumped liquid
34
with line
58
, either to one use or to two uses, outside tank
16
or vessel
16
′.
As can be seen from
FIGS. 2A
,
2
B and
2
C, the amount of lift, that is the distance from the point in tank
16
or vessel
16
′ where the actual inlet of the line
86
occurs to the liquid level desired within sump
28
can vary with the dimensions of tank
16
or vessel
16
′, as well as the method chosen to mount pump
10
to tank
16
or vessel
16
′. For the same condition saturated or near saturated liquid, the greater this lift distance, the greater the capacity of compressing portion
12
of pump
10
should be. This occurs because the greater the lift, the higher the percentage of vapor formed in lifting saturated liquid by causing a reduced pressure, so as to produce the needed lift. Also, vapor is formed in the pump itself as caused by heat leak from pump
10
's surroundings and from residual heat caused by friction and from residual heats of compression, or other reasons. Thus the higher the discharge pressure of pumping portion
11
and to a lesser degree compressing portion
12
, the greater the quantity of vapor
35
formed. To accommodate such higher lifts and higher pressures, resulting in greater amounts of vapor
35
that is to be removed, the capacity of compressing portion
12
can be increased by increasing the diameters of chamber
64
and chamber
65
, piston
60
and casing
14
, and casing
26
to match. Vapor
35
returned to tank
16
or vessel
16
′ by compressing portion
12
can be returned to about the top, about the middle, or about the bottom of tank
16
or vessel
16
′ by line
81
a
or
81
b
, as individual circumstances dictate as to any desired point of return inside tank
16
or vessel
16
′ or outside tank
16
or vessel
16
′ by line
81
c
to various uses (not shown). A foot valve (not shown) can be used with line
86
, if the dimensions and flow dynamics require such, so as to prevent back-flow of liquid
34
in line
86
when pump
10
is operating.
FIGS. 3A and 3B
are simplified views of an alternate compressing portion
12
′ of pump
10
′, having an arrangement whereby vapor
35
is removed first from the sump
28
and then once sufficient vapor
35
has been removed from sump
28
, removes vapor
35
from the ullage volume of tank
16
(or vessel
16
′), and the compressed vapor
35
is supplied to a use outside tank
16
(or vessel
16
′), along with the pumped liquid
34
, with the discharge arrangements as depicted in FIG.
2
C. The removal of vapor
35
from the ullage volume of tank
16
or vessel
16
′ has the desirable effect of extending the fill life of tank
16
or vessel
16
′.
FIG. 3A
depicts alternate float type liquid level control
96
arranged so as to change the source of vapor
35
supplying compressing portion
12
′ from the top of sump
28
to the ullage volume of tank
16
(or vessel
16
′), utilizing line
98
and valve
100
, which modulates the opening of line
98
in response to control
96
, so that whenever liquid
34
in sump
28
is at the desired level, compressing portion
12
′ then removes vapor
35
from the ullage volume of tank
16
(or vessel
16
′). Thus once the desired level of liquid
34
is present in sump
28
, the action of control
96
provides a conduit between the ullage volume of tank
16
or vessel
16
′, and modulates the flow of vapor
35
through line
98
in response to the level of liquid
34
in sump
28
as sensed by control
96
, so as to provide sufficient vapor
35
to removal portion
12
′. Should it be desired (not shown), a valve can be installed in line
98
so that flow of vapor from the ullage volume of tank
16
or vessel
16
′ can be blocked and the functions of control
82
and control
96
combined so that valve
71
and valve
72
are disabled by the same means as described in
FIGS. 1A
,
1
C and
1
D in the event the flow of vapor
35
through line
98
is caused to cease.
FIG. 3B
depicts valve
100
which modulates the size of the passageway in line
98
between sump
28
and the ullage volume of tank
16
(or vessel
16
′). Sleeve
102
cooperates with control
96
, and is slidably attached to line
98
. Opening
104
in line
98
is closed by sleeve
102
, unless control
96
has risen, and caused sleeve
102
to also rise, to the extent that opening
106
in sleeve
102
is aligned with opening
104
, thereby allowing vapor
35
to flow through line
98
from the ullage volume of tank
16
(or vessel
16
′) to sump
28
.
Turning next to
FIGS. 4A and 4B
, of special use when pump
10
′ is utilized to supply the cryogen (LNG) as a gaseous fuel (NG) to engine
110
of truck
108
. The compressed vapor
35
and pressurized liquid
34
are warmed to about ambient temperature, either with waste heat from engine
110
or from ambient, then supplied to engine
110
of truck
108
as NG fuel. Tank
16
is shown mounted in saddle tank fashion from frame
112
to tractor type truck
108
, and between cab
114
and tire
116
.
FIG. 4A
is a generalized view which depicts a case where engine
110
does not require NG fuel supplied at a pressure higher than about 500 psig. Pump
10
′ is located above and mounted to tank
16
in a manner similar to that shown in
FIG. 2C
, with lines
58
and
81
c
exiting tank
16
through plate
15
. Pump
10
′ is modified in accordance with
FIGS. 3A and 3B
and alternate control
96
, making it possible to also scavenge vapor
35
from the ullage volume of tank
16
through line
98
. After exiting tank
16
, lines
58
and
81
c
can be combined (not shown) or routed separately to vaporizers and use in engine
110
of truck
108
. In this case, fuel (NG) supply pressure required by engine
110
is less than about 500 psig, a pressure that compressing portion
12
′ can readily provide if the pressure in tank
16
is above 50 psig, a normal condition. Accordingly, line
58
carrying pumped liquid
34
passes through vaporizer
120
to NG storage
122
, whose pressure is monitored by control
124
, which causes pump
10
′ to operate when the pressure in storage
122
is below a pressure of about 750 psig and causes pump
10
′ to cease operation when the storage pressure reaches a higher figure (about 1,000 psig), indicating engine
110
is requiring NG fuel at a slower rate than pump
10
′ is supplying it. Pressure regulator
126
maintains line
128
at the desired supply pressure to engine fuel control
130
, which then supplies the NG fuel to engine
110
. Line
81
c
carrying compressed vapor
35
passes through vaporizer
132
to storage
134
, whose pressure is also monitored by control
124
and causes pump
10
′ to cease operation if the pressure becomes excessive or will cause line
98
to close. Storage
134
utilizing line
136
by itself provides fuel (NG) to line
128
until the pressure in line
128
drops below the setting of pressure regulator
126
. When this ocurs, pressure regulator
126
opens so that NG fuel from storage
122
supplements the NG from storage
134
50
that the pressure in line
128
returns to the proper level. NG will be supplied to fuel control
130
through line
128
from both storage
134
and storage
122
until the pressure within storage
122
drops below approximately 750 psig. At that time, pump
10
′ will be caused to operate so as to replenish both storage
134
and storage
122
. Storage
134
then returns to being the sole source of NG for line
128
after regulator
126
closes. Line
136
connects storage
134
with line
128
, so both the compressed vapor
35
and the pumped liquid
34
supply the fuel needs of engine
110
. Alternately, pump
10
′ could be mounted to tank
16
in the manner illustrated in FIG.
2
B.
FIG. 4B
depicts a specific application utilizing pressurized and vaporized LNG as an on-vehicle fuel, wherein the unique capabilities of the present invention are displayed. Pump
137
, tank
138
, pressure control
140
, fuel injection control
142
and engine
144
, are installed on a large heavy duty truck or tractor truck
108
or intra-city bus (not shown) making multiple stops in a large, densely populated metropolitan area, using expressways for a portion of its run, such as the grater Los Angeles area. Pump
137
is as described in
FIGS. 3A and 3B
; having the ability to both pump liquid
34
to high pressure from tank
138
and when desired, to scavenge vapor
35
from the ullage volume of tank
138
so as to provide extended hold time for the LNG therein, without requiring a very high pressure capability for tank
138
. Management of the internal pressure of tank
138
and of the supply pressures to engine
144
is by system gas (NG) storage and control
140
; which can change the speed of pump
137
(if drive portion
13
is so equipped), or stop or stop pump
137
; block line
98
, open line
81
a
or
81
b
(not shown), and store a small amount of NG in gas storage at a suitable pressure for instant use as fuel in engine
144
. For the purposes of this example, engine
144
is Diesel cycle, fuel injected requiring about 3,000 psig NG when the engine is under heavy load and about 500 psig NG when under light load or idling; and the response to the operator's input is to be immediate. Pump
137
can be mounted to tank
16
in a similar manner to that depicted in
FIG. 4A
; but for space convenience and thermal isolation, is located alongside tank
138
, utilizing a head end opening in tank
138
for connecting insulated sump
145
into the top of which pump
137
is inserted. Pump
137
is modified in accordance with FIG.
3
A and FIG.
3
B. After exiting sump
145
, line
58
carrying liquid
34
pumped to a high pressure, passes through vaporizer
120
′ to NG storage
122
′, whose pressure is monitored by control
140
, which causes pump
137
to operate when the pressure in storage
122
′ is below about 110% of the minimum selected high injection pressure (about 3,300 psig) and causes pump
137
to cease operation when the pressure in storage
122
′ reaches a pressure about 120% higher than the selected minimum high injection pressure (about 3,600 psig), indicating engine
144
is requiring fuel at a slower rate than pump
137
is supplying. Pressure regulator
126
′ maintains line
128
′ at the selected high injection pressure to engine fuel control
142
, which then supplies the high pressure NG fuel for injection into Diesel engine
144
when required. Line
81
c
carrying compressed vapor
35
passes through vaporizer
132
′ to storage
134
′, whose pressure is also monitored by by control
140
. Regulator
150
maintains line
151
at the selected low injection pressure, supplying control
142
. In the event that a greater quantity of low pressure NG fuel is required than that available in storage
134
′, regulator
152
, located in line
153
, supplies low pressure NG fuel from storage
122
′, should the supply of NG from storage
134
′ be insufficient.
A gas intensifier, which uses a higher pressure stream to raise the pressure of a lower pressure stream, and then joins it, can be added in either line
136
between storage
134
and line
128
, with high pressure gas supply from storage
122
(
FIG. 4A
) should a higher pressure compressed NG be desired than pump
10
′ provides (not shown). Similarly, an intensifier can be added in line
151
between storage
134
′ and the junction of line
153
, with high pressure gas supply from storage
122
′ (FIG.
4
B), should a higher pressure compressed NG be desired than pump
137
provides (not shown).
Single lost motion pumps, such as U.S. Pat. Nos. 3,023,710 and 3,263,622 to the present inventor, have similar characteristics to the depicted double lost motion pump except there is only one piston. A number of low NPSH reciprocating piston pumps are available which provide assistance in opening the intake valve by inertia of the intake valve or momentary creation of a higher pressure regime at the entrance to the intake valve or by magnetic force or by a combination of these. Such pumps are able to reliably pump low NPSH, or very low NPSH cryogenic liquids as long as the pump's intake is covered with liquid and any vapor there is able to escape; and for the purposes of this invention, are all considered as benefiting the same as the depicted double lost motion pump.
Cryogenic liquids and liquefied gases are characterized by being typically stored under pressure above atmospheric. Some, (the cryogens) are manufactured at pressures only slightly above atmospheric, but are allowed to increase in pressure (by warming) in steps as the cryogen progresses along the distribution and use chain. Accordingly, pump
10
,
10
′ or
137
can be operating at a varying number of intake pressures, as the pressure in sump
28
relates to the pressure of the liquid in tank
16
, vessel
16
′ or tank
138
.
Although the invention has been described with regard to what is believed to be the preferred embodiment, changes and modifications as would be obvious to one having ordinary skill in both pump design, cryogenic and liquefied gas engineering and compressed gas use can be made to the invention without departing from its scope. Particular features are emphasized in the claims that follows. The term conduit in the following claims should be interpreted broadly to include pipe, tube, valve and other devices used in the transfer of liquid or vapor.
Claims
- 1. A pump for a cryogenic liquid comprising:a. a casing defining a sump having an inlet for containing a supply of the cryogenic liquid with a head space above; b. a pumping cylinder housing postioned in said sump and defining a pumping cylinder having an inlet for communication with the supply of cryogenic liquid and an outlet; c. a pumping piston slidably disposed within said pumping cylinder; d. a rod connected to said pumping piston; e. a vapor removal compressor including: i. a vapor removal housing positioned above said sump and defining a vapor removal chamber having an inlet for communication with said head space and an outlet; ii) a vapor removal piston slidably disposed within said vapor removal chamber; iii) a suction valve in said vapor removal housing inlet; iv) a discharge valve in said vapor removal housing outlet; v) a level control positioned with respect to said sump for determining the level of a cryogenic liquid therein; and f. means responsive to said level control for disabling the vapor removal compressor whereby vapor is not removed from said sump.
- 2. The pump of claim 1 wherein said vapor removal piston divides said vapor removal chamber into an upper and lower chamber, each having a suction valve and an intake valve.
- 3. The pump of claim 1 wherein said level control is a float control positioned within said sump so as to float in any cryogenic liquid there, said float control having a magnet mounted thereto, and said magnet to disable said suction valve when said magnet is positioned near said suction valve.
- 4. The pump of claim 1 wherein said inlet of said sump includes an inlet conduit.
- 5. The pump of claim 4 further comprising a vapor liquid separator positioned within said sump and in communication with said inlet conduit.
- 6. The pump of claim 1 where said vapor removal piston is connected to said rod and further comprising a drive mechanism connected to said rod, said drive mechanism reciproating said rod so that said pumping and vapor removal pistons may be reciprocated.
- 7. The pump of claim 1 wherein said casing also defines a suction cavity above said sump in communication with said vapor removal suction valve.
- 8. The pump of claim 1 wherein said casing also defines a discharge cavity in communication with said discharge valve and a discharge line.
- 9. The pump of claim 1 wherein said pumping cylinder housing outlet is a vapor outlet port in communication with the head space and the pumping cylinder.
- 10. The pump of claim 1 wherein said pumping cyinder housing inlet is a liquid inlet port in communication with the head space and the pumping cylinder.
- 11. The pump of claim 10 wherein a pumping chamber is defined within said pumping cylinder by said pumping piston and said pumping cylinder housing; and further comprising a check valve within said pumping cylinder housing and in communication with said pumping chamber and a use line.
- 12. The pump of claim 11 wherein said pumping piston is hollow with said rod received therein and said rod has a slot formed therein; and further comprising a pin connected to said pumping piston, said pin received in said slot of said rod, and said slot sized so that said rod may move to a limited extent independent of said pumping piston so that vapor may exit from said pumping chamber between the rod and the pumping piston when they are separated as the suction stroke of the pumping piston commences and that liquid may subsequently enter the pumping chamber.
- 13. The pump of claim 1 wherein said means responsive to said level control for disabling the vapor removal compressor disables the suction valve of the vapor removal compressor.
- 14. A device for removing vapor from a sump containing a cryogenic pump and a cryogenic liquid with a head space there above comprising:a. a vapor removal housing positioned above the sump; b. a vapor removal piston slidably disposed in said vapor removal housing so that upper and lower chambers are defined therein; c. a rod connected to the piston; d. a drive mechanism connected to said rod so that said vapor removal piston is moved by said rod in a reciprocating fashion; e. upper and lower suction valves in communication with the upper and lower chambers, respectively, and adapted to communicate with the head space of said sump; f. upper and lower discharge valves in communication with the upper and lower chambers, respectively, and a discharge line so that vapor from the head space flows through the discharge line when said vapor removal piston is reciprocated by said rod; and g. level control means sensing the level of cryogenic liquid within the sump and valve disabling means for disabling the suction valves before the level of cryogenic liquid reaches them.
- 15. The device of claim 14 wherein said level control is a float control positioned within said sump so as to float in any cryogenic liquid there, said float control having a magnet mounted thereto; and said magnet to disable said suction valves when said magnet is positioned near said suction valves.
- 16. The device of claim 14 wherein an inlet of said sump includes an inlet conduit.
- 17. The device of claim 14 further comprising a vapor liquid separator postioned within said sump and in communication with said inlet conduit.
- 18. The device of claim 14 further comprising a casing that defines a suction cavity that is in communication with said upper and lower suction valves and adapted to communicate with the head space of the sump.
- 19. The device of claim 18 wherein said casing also defines a discharge cavity that is in communication with said upper and lower discharge valves and said discharge line.
- 20. A method for lifting a cryogenic liquid through an inlet conduit of a pump, where the inlet conduit has an upper end and a lower end, comprising the steps of:a. directing the cryogenic liquid through the lower end of the inlet conduit so that cryogenic liquid enters the inlet conduit; b. reducing a pressure at the upper end of the conduit so that vapor is formed from the cryogenic liquid in the inlet conduit and removing the vapor from the upper end of the conduit so that a portion of the cryogenic liquid nearest the upper end of the ilet conduit is cooled by evaporative cooling so that a pressure differential is formed between the cooled portion of the cryogenic liquid and a warmer portion of the cryogenic liquid beneath the cooled portion so that lift for the cryogenic liquid through the inlet conduit is provided.
- 21. The method of claim 20 further comprising the step of combining the vapor removed from the inlet conduit with vapor removed from the pump and directing the vapor removed from the inlet conduit and the vapor removed from the pump to a use device.
- 22. The method of claim 20 further comprising the step of directing the vapor removed from the inlet conduit to a source of the cryogenic liquid that is providing the cryogenic liquid to the inlet conduit.
- 23. A method of separately withdrawing a gaseous phase and a liquid phase of a liquid cryogen fuel from a storage tank for supply to an engine comprising the steps of:a. providing a vapor removal compressing device; b. providing a liquid pumping device having an inlet conduit and a low Net Positive Suction Head reciprocating piston pump with an inlet; c. withdrawing the liquid phase from the storage tank with the liquid pumping device; and d. withdrawing the gaseous phase from the storage tank with the vapor removal compressing device so that the liquid phase in said tank flows through the inlet conduit to at least the inlet of the pump.
- 24. The method of claim 23 further comprising the step of removing the gaseous phase from a head space of the storage tank with the vapor removal compressing device so that the pressure in the storage tank is reduced whereby a storage life of the storage tank is extended.
- 25. The method of claim 23 further comprising the step of warming both the gaseous phase and the liquid phase of the liquid cryogen fuel before supplying it to the engine, whereby it is supplied to the engine at an anticipated density.
- 26. The method of claim 25 further comprising the step of storing the warmed cryogen as a gas at a higher pressure than a minimum pressure desired for subsequent supply as fuel to the engine whereby the fuel is quickly available for use.
- 27. The method of claim 26 further comprising the step of supplying the gaseous phase to the engine at a lower pressure than the liquid phase, whereby both phases of the liquid cryogen fuel may be burnt as fuel.
US Referenced Citations (17)