US3797248A

US3797248A - Cycle start up system

Info

Publication number: US3797248A
Application number: US00210749A
Authority: US
Inventors: W Witzel; E Doyle
Original assignee: Thermo Electron Corp
Current assignee: Thermo Fisher Scientific Inc
Priority date: 1971-12-22
Publication date: 1974-03-19
Anticipated expiration: 1991-03-19
Also published as: FR2165406A5; IT972534B; JPS4868938A; GB1385539A; DE2255769A1; CA954706A

Abstract

In the starting mode of a closed cycle system, after a period of quiescence, a mixture of working fluid and lubricant is extracted from portions of the system, according to the need for fluid in the cycle, and transmitted into a reservoir where it provides a small pressure head to a starting mode pressurization pump and also provides working fluid for the starting mode. During the starting mode, the prepressurization pump is activated to maintain the static pressure of the fluid exiting through it above its vapor pressure, before it is further pressurized. The mixture is later heated at least to a point where the working fluid is vaporized. The lubricant is removed from the working fluid in a liquid state before the working fluid is recondensed, by a gravity or screen separator. The separated working fluid is retained in the cycle, while the separated lubricant is returned to the point from which it was extracted.

Description

United States Patent 1191 Witzel et a1.

[451 Mar. 19, 1974 RANKINE CYCLE START UP SYSTEM [75] Inventors: Walter H. Witzel, Sudbury; Edward F. Doyle, Dedham, both of Mass.

[73] Assignee: Thermo Electron Corporation,

Waltham, Mass.

21 Appl. NO.2 210,749

52 us. on. 60/646 51 Int. Cl. FOlk 25/08, FOlk 2776'0 [58] Field 6: Search. 60/36, 39, 40, 108 s;

184/1 E, 6 L, 6 A, 6 R

[5 6] References Cited UNITED STATES PATENTS 3,584,457 9/1972 Davoud 60/36 Primary Examiner-Edgar W. Geoghegan Assistant Examiner-Allen M. Ostrager Attorney, Agent, or Firm-James L. Neal 57] ABSTRACT In the starting mode of a closed cycle system, after a period of quiescence, a mixture of working fluid and lubricant is extracted from portions of the system, according to the need for fluid in the cycle, and transmitted into a reservoir where it provides a small pressure head to a starting mode pressurization pump and also provides working fluid for the starting mode. During the starting mode, the prepressurization pump is activated to maintain the static pressure of the fluid exiting through it above its vapor pressure, before it is further pressurized. The mixture is later heated at least to a point where the working fluid is vaporized. The lubricant is removed from the working fluid in a liquid state before the working fluid is recondensed, by a gravity or screen separator. The separated working fluid is retained in the cycle, while the separated lubricant is returned to the point from which it was extracted.

4 Claims, 2 Drawing Figures PATENTEUMAR 19 1974' SHEET 1 [IF 2 INVENTORS WALTER H. WITZEL BY EDWARD F. DOYLE RANKINE CYCLE START UP SYSTEM FIELD OF INVENTION This invention relates in general to closed fluid cycle systems and more particularly to a Rankine cycle engine including specific features for starting up after a long period of quiescence.

BACKGROUND OF THE INVENTION In 'closed fluid cycle systems in general, and in Rankine cycle engines in particular, certain problems are encountered in formulating a design which provides efficient operation not only during normal running, but also in starting up after a long period of time. Systems of this type include an evaporator, an expander, a condenser and a pump. The pump circulates working fluid from the condenser into the evaporator, where it is heated under pressure and is provided at the inlet to the expander, where the expansion of the heated fluid under pressure provides mechanical energy as the output from the system. In many engines of this type the working fluid is a flammable, toxic material. The materials may also be costly, trifluoro ethanol being one such example. Therefore, it is important both from a viewpoint of economics and from a safety viewpoint that the working fluid be conserved within the system. Many of these working fluids have relatively high vapor pressures and hence, when the engine is shut down, there is a great tendency for the working fluid to migrate into the lubricant inthe crankcase of the expander portion of the engine. Attempts to solve similar problems in the past have involved the use of elements, such as heaters in the crankcase to maintain the lubricant at an elevated temperature even during the quiescent state of the engine.

An additional problem encountered in these engines as a result of long periods ofinaction arises from the requirement that the circulating pump, feeding the working fluid into the boiler must have a static positive pressure at its imput, in excess of the vapor pressure of the working fluid, in order to operate. Without such a positive pressure the pump would cavitate and not operate. During normal running the vapor pressure of the working fluid throughout the system provides this positive pressure. One solution to this problem involves the use of a booster pump as a prior stage to the circulating pump providing pressurized fluid at the input to the circulating pump after the engine has been quiescent for an extended period. In order to use such a system, however, there must be available at the input to the booster pump a supply of fluid.

BRIEF SUMMARY OF THE INVENTION Broadly speaking, in the engine of this invention, the crankcase lubricant is miscible with the working fluid and the sealing arrangements in the expander are such that in the quiescent state the working fluid is allowed to migrate into the crankcase and mix with the lubricant. The engine includes an expander which is supplied working fluid at elevated pressures and temperatures from the boiler. The working fluid at lower pressures and temperatures is exhausted from the expander and passes through a regenerator to a condenser for cooling and liquefying the fluid. The output from the condenser is supplied to a reservoir which in turn provides fluid to the input of a booster pump supplying fluid at an elevated pressure to the input of the circulating feed pump, which is normally driven by the mechanical output of the expander. The feed pump pres surizes the fluid and circulates it to the boiler where it passes again to the expander. Between the boiler and the expander, there is included a separator, which separates lubricant from working fluid, draining the lubricant into the crankcase of the expander while the working fluid is allowed to pass directly through into the expander volume. The reservoir between the condenser and the booster pump also has an inlet directly from the crankcase or lubricant sump of the expander and this latter inlet is under the control of a float valve which keeps the inlet from the crankcase closed unless the level of fluid within the reservoir falls below a predetermined level.

Once the engine has started up this system operates in substantially the same manner as the conventional Rankine cycle engine, that is the working fluid, heated and pressurized at the boiler, is passed into the expander where its expansion generates mechanical energy, the somewhat cooled working fluid, at lower pressure, then being exhausted to a regenerator where it serves to preheat working fluid passing from the condenser into the boiler. The fluid from the regenerator is passed into the condenser where it is cooled and liquefied and thence through the booster pump (operating merely as a conduit under these conditions) to the circulating pump and thence to the boiler.

It is in the start-up mode,however, that the present invention operates in an effective and unusual fashion. When the engine has been quiescent for a prolonged period, the fluid in the crankcase :is a mixture of working fluid and lubricant and also the fluid in the reservoir is a mixture of these two materials. At start-up the mixture in the reservoir supplies fluid pressure for the booster pump, which pressurizes it and supplies it with an increased pressure head to the circulating pump initiating the circulating action of fluid in the engine. As the mixture passes through the boiler the working fluid is vaporized, while the lubricant. is not and, consequently, at the separating stage the lubricant, being in a liquid state, can readily be separated from the working fluid in the vapor state and the lubricant is thus drained into the crankcase. Hence, in the initial cycles after start-up, there is circulated a mixture of lubricant and working fluid which are quickly separated from one another, until the lubricant is all in the crankcase and the working fluid is in the normal cycling path. Once the system is up to sufficient pressure, the reservoir fills only with the circulating working fluid and hence the float valve keeps lubricant from draining from the crankcase into the fluid cycle. On the other hand during the start-up process itself, both the liquid working fluid and the liquid lubricant are available to serve as liquid for initiating the action of the pump with the working fluid from the crankcase assisting in the start of the process. Thus, these two features provide for efficient start-up, eliminate the necessity for an effective seal during long periods of inactivity of the engine, between the miscible lubricant and working fluid and do not require extra supply of working fluid to be available for start-up of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS ing detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic representation of an overall engine design in accordance with the invention; and

FIG. 2 is a state diagram showing the state of the working fluid at various points in the working cycle, in accordance with this invention.

DETAILED DESCRIPTION OF INVENTION Referring to FIG. 1, a Rankine cycle engine utilizing working fluid miscible with lubricant-is shown. The engine includes several features operative only during start-up as well as those elements needed for normal operation. A boiler feed pump 46 is connected, through line 48 to a regenerator 50, where working fluid is preheated in a coil 52. The fluid then flows through pipe 54 into the boiler 6. A fuel-and-air mixture introduced through line 2 into the burner 4 is ignited and heats the working fluid in the coil 8, where the working fluid is boiled and vaporized and exits from the boiler 6 through line 10. Working fluid enters into a separating chamber through inlet 12 and then passes out of said chamber through line 18 and through throttle valve 20 into the expander 22. Expander 22 is illustrated as a reciprocating piston expander by way of example. Other expanders may be employed. Typical are rotary piston or turbine devices. In these expanders, a lubricant reservoir is provided. In the reciprocating piston it may be the crank case. In the other devices it could be a lubricant sump. In the expander 22 shown, the working fluid reacts upon the pistons indicated at 24, which deliver energy to an external source and also drive feed pump 46. The pistons 24 then drive the expanded working fluid out through an exhaust line 64 into regenerator 50 where the residual heat contained in the expanded gas is used to preheat the working fluid passing through coil 52. The gaseous working fluid which entered through line 64 now exits from the regenerator 50 through line 62 and passes into the condenser 56 where it is cooled in the heat exchanger 58 condensing into a liquid. The condenser 56 is connected through line 60 to a fluid receiver 38 which drains out through line 40. During normal operation, the pump 42 is not activated and the fluid entering through line 40 into the pump 42 exits through line 44, without substantial loss of static pressure head, into the boiler feed pump indicated at 46, thus completing the normal operating cycle of a closed cycle engine.

FIG. 2 is a representation of the pressure and enthalpy characteristic properties of trifluoroethanol as a working fluid operated in the engine of FIG. 1. The fluid is pressurized by the boiler feed pump from Point H to Point C at almost constant enthalpy. Without substantial pressure loss, the enthalpy of the fluid increases as it is heated in the regenerator as indicated between Points C and D and then in the boiler as indicated between Points D and E. The pressure and the enthalpy of the fluid decreases as it produces useful work in the expander as indicated between Points E and F. The

until it is boiled and vaporized in the boiler. As indicated by the saturated vapor line, the fluid remains in a totally gaseous state from a point in the boiler to a point in the condenser, where it is further cooled to a liquid state. When the engine is shut down, no more heat is being applied to the working fluid and the system will cool and consequently the pressure of the fluid in the system will decrease.

The dotted line in FIG. 2 indicates the state of the working fluid as it passes through the start up process before entering into the regenerator at Point C. Assuming that the system has cooled so that the working fluid is at an average temperature of lOOF and at the pressure and enthalpy indicated at Point A in the diagram, in the start up process according to this invention, a booster pump is activated to increase the static pressure of the liquid working fluid before it enters into the boiler feed pump as indicated by the dotted line between Points A and B. The boiler feed pump then increases the fluid pressure to the pressure level indicated at C, which in this case will also represent the pressure and enthalpy of the fluid as it leaves the regenerator, since in the starting process the regenerator is normally unable to preheat the working fluid prior to its entry into the boiler. When steady state operation is achieved, the fluid working cycle will follow the solid line closed loop diagram as described above.

Referring to FIG. 1, after the system has shut down and begun to cool, the working fluid in the system will tend to migrate to the expander crankcase 26 which contains the lubricant necessary for expander operation. Expander crankcase 26 now contains a fluid 28, which is a mixture of lubricant and working fluid. In normal operation, however, the crankcase should contain only pure lubricant; otherwise the fluid lubricating the expander will not be at the proper viscosity, which could result in shortened engine life. Typical lubricants and working fluids used in closed cycle systems are miscible; it is therefore necessary to provide a means for separating these two miscible liquids.

While, in a properly designed closed cycle engine the residual pressure of the expanded gas as it enters into the condenser 56 plus the static head of the liquid in the condenser 56 relative to the inlet to the boiler feed pump 46, will be sufficient to avoid cavitation at the boiler feed pump inlet, typical engine geometry requirements do not permit the condenser 56 to be placed high enough above the boiler feed pump 46 so that, at start up, the static head of the liquid working fluid alone will provide a sufficient pressure at the boiler feed pump inlet to avoid cavitation.

As noted above, after shut down the system will cool and the overall pressure in the system will decrease. In order then, to provide a sufficient static pressure at the boiler feed pump inlet, a prepressurization booster pump 42 is introduced into the line between condenser 56 and the boiler feed pump 46. This pump is activated by a DC motor during the start up process through power line 82 to provide a supply of fluid at sufficient pressure to the boiler feed pump 46. It is necessary, in the starting process to provide a reservoir of working fluid to supply booster pump 42 until steady state operation is achieved. If the working fluid contained in the expander crankcase 26 could not be used during the start up process, a greater reservoir of working fluid would be necessary to assist in this process.

According to this invention, then, the start up process proceeds as follows: The DC motor 88 through power line 86 drives the expander 22 which in turn drives the boiler feed pump 46 through shaft 84. Simultaneously DC motor 80 is activated and it in turn drives the prepressurization booster pump 42 through power line 82. The prepressurization pump 42 can be a radial centrifugal design and can receive its power input through a magnetic clutch from power line 82, which thereby allows disengagement from power line 82, while maintaining a hermetic seal against the atmosphere. Working fluid is drained from the receiver 38. As the level of the working fluid in the receiver decreases, a float 34 will activate a valve 32 which will allow the fluid mixture 28 contained in the crankcase 26 to drain through line 30 into the working fluid receiver 38. When this mixture reaches the boiler 6 through line 54, the working fluid will be boiled and vaporized and therefore be useful for supplying energy to the expander 22. The lubricant which enters with the working fluid into the boiler 6 is usually not vaporized. If the lubricant remains in a liquid state, it will be carried along by the gaseous working fluid from the boiler 6 out through line 10.

A gravity and screen separator extracts the liquid lubricant from the gaseous working fluid. In this design the liquid separator is located between the boiler 6 and the expander 22. The mixture of gaseous working fluid and liquid lubricant enters into the chamber beneath screens 14 and the droplets of lubricant collect, as indicated at 16, while the gaseous fluid passes from the top of the chamber 15 above the screens indicated at 14. In this manner the screens collect any of the finer droplets of lubricant that would have been carried along by the flow of gas and which do not fall to the bottom of the chamber of their own weight. A float 66 in chamber 15 operates valve 68 when this fluid reaches a predetermined level and lubricant will drain through line 70 into the crankcase 26. This separating chamber can be placed in a position anywhere in the system where the lubricant is in a liquid state and the working fluid remains in a gaseous state. While it has been assumed that the lubricant is not vaporized, the system can be operated such that the lubricant is vaporized in the boiler 6 provided that the separation chamber 15 is placed at a point in the system where the lubricant has recondensed and where the working fluid has not recondensed. By this technique the working fluid which mixed in the crankcase 26 with the lubricant is removed from the crankcase during the start up process. This working fluid lubricant mixture from the crankcase 26 is available for the start up process, thereby reducing the total working fluid volume in this system necessary for the start up process.

Once sufficient residual pressure from the gaseous working fluid reaches the condenser 56 and a sufficient static head of liquid working fluid has been developed in the condenser 56, so that prepressurization by the booster pump 42 is no longer required, the DC motor 80 will be shut down and the pump 42 will simply serve as a conduit between the reservoir 38 and the boiler feed pump 46. Once the expander begins to operate in a self-sustaining mode, with sufficient energy to drive the boiler feed pump 46, at least, the DC motor 88 will also be shut down. When steady state operation has been achieved, the working fluid receiver will contain enough working fluid so that valve 32 is no longer open and the lubricant is no longer free to drain from the crankcase 26 through line 30 into the working fluid receiver 38. Eventually all the lubricant originally present in the crankcase 26 will be returned to the crankcase in a pure condition and be available for normal expander lubrication operations.

Typical working fluids can be CJ-LS known by its chemical name throphene, pyridine, trifluoro-ethanol, as mentioned above, or water. Typical lubricants may be SUNISO-3 G S, a tradename for a lubricant sold by the Sun Oil Company; HUMBLETHERM 500; or TE- RESSO-43, tradenames for lubricants sold by the Humble Oil Company; or MONSANTO OS 124, a tradename for a lubricant sold by the Monsanto Company.

Furthermore, this invention will have application not only in closed cycle power producing devices but any closed cycle system consisting of an evaporator, expander, and condenser, such as an air-conditioning or refrigeration system.

We claim:

1. In a process for a closed fluid cycle system containing working fluid and lubricating fluid wherein in operation said working fluid is circulated through a feed pump, an evaporator, an expander and a condenser and wherein at least a portion of said lubricating fluid is present in a reservoir within said system and is therein substantially isolated from circulating working fluid, a starting process comprising the steps of:

extracting fluid including at least some lubricant from said reservoir while retaining said extracted fluid in said closed system;

draining said extracted fluid from said reservoir to a receiver by gravity to establish a predetermined fluid level in said receiver; supplying said extracted fluid from said receiver to a boost pump with a pressure head functionally related to the fluid level in said receiver, said reservoir, receiver and boost pump being positioned relative to each other so that said extracted fluid will flow from said reservoir to said receiver and from said receiver to said boost pump by gravity;

supplying said extracted fluid from the boost pump to said feed pump with a pressure head and operating said feed pump to circulate said extracted fluid at an elevated pressure whereby said extracted fluid circulates with said working fluid and mixes therewith;

heating the circulated mixture to a temperature where at least the working fluid is boiled and vaporized;

thereafter separating said lubricant from said working fluid, retaining said vaporized working fluid in circulation within the system and returning the separated lubricant to said reservoir.

2. In a closed fluid cycle system containing working fluid and lubricating fluid, said system including in fluid connected series a pump, an evaporator, an expander and a condenser through which said working fluid circulates during operation of said system, said system including lubricant reservoir means for substantially isolating lubricating fluid therein from circulating working fluid,

the improved apparatus for assisting in the start up of said system after a period of quiescence compriss;

fluid receiving means positioned relative to said lubricant reservoir means so that lubricating fluid will drain from said lubricant reservoir means to said receiving means;

a valved conduit connecting said lubricant reservoir means to said receiving means for controlling the drainage of said lubricating fluid from said lubricant reservoir means to said receiving means;

means connecting said condenser to said receiving means permitting working fluid to flow from said condenser to said receiving means, whereby when lubricating fluid is present in said receiving means it mixes with said working fluid;

prepressurizing boost pump means connecting said receiving means to said pump for providing fluid at elevated pressures from said receiving means to said pump; and

means for separating lubricating fluid from said working fluid and for retaining said separated working fluid in said fluid connected series while providing said separated lubricating fluid to said lubricant reservoir means.

3. In a closed fluid cycle system containing working fluid and lubricating fluid, said system including in fluid connected series a pump, an evaporator, an expander and a condenser through which said working fluid circulates during operation of said system, said system including lubricant reservoir means for substantially isolating lubricating fluid therein from circulating working fluid,

the improved apparatus for assisting in the start up of said system after a period of quiescence comprising:

a valved conduit connecting said lubricant reservoir means to said receiving means for controlling the drainage of said lubricating fluid from said lubricant reservoir means to said receiving means, said valved conduit being controlled by means within said receiving means shutting off said conduit whenever a predetermined volume of fluid is contained within said receiving means;

means including a pressure increasing device connecting said receiving means to said pump for providing fluid at elevated pressures from said receiving means to said pump; and

4. In a closed vapor cycle engine containing lubricating fluid and working fluid, said engine comprising in fluid connected series a pump, an evaporator, an expander and a condenser through which said working fluid circulates during power producing operation, apparatus for assisting in the start up of said engine comprising:

lubricant reservoir means for substantially isolating lubricating fluid therein from circulating working fluid;

means connecting said condenser to said pump for supplying working fluid from said condenser to said P p;

boost pump means for providing initial fluid input to said pump, said boost pump means being situated to permit lubricating fluid to drain thereto from said lubricant reservoir means;

a valve controlled connection means between said lubricant reservoir means and the inlet to said boost pump means for providing lubricating fluid at elevated pressure to said boost pump means from said lubricant reservoir means, whereby the lubricating fluid supplied to said boost pump means and the working fluid supplied to said pump are mixed; and

means for separating lubricating fluid from said working fluid and returning separated lubricating fluid to said lubricant reservoir means.

Claims

1. In a process for a closed fluid cycle system containing working fluid and lubricating fluid wherein in operation said working fluid is circulated through a feed pump, An evaporator, an expander and a condenser and wherein at least a portion of said lubricating fluid is present in a reservoir within said system and is therein substantially isolated from circulating working fluid, a starting process comprising the steps of: extracting fluid including at least some lubricant from said reservoir while retaining said extracted fluid in said closed system; draining said extracted fluid from said reservoir to a receiver by gravity to establish a predetermined fluid level in said receiver; supplying said extracted fluid from said receiver to a boost pump with a pressure head functionally related to the fluid level in said receiver, said reservoir, receiver and boost pump being positioned relative to each other so that said extracted fluid will flow from said reservoir to said receiver and from said receiver to said boost pump by gravity; supplying said extracted fluid from the boost pump to said feed pump with a pressure head and operating said feed pump to circulate said extracted fluid at an elevated pressure whereby said extracted fluid circulates with said working fluid and mixes therewith; heating the circulated mixture to a temperature where at least the working fluid is boiled and vaporized; thereafter separating said lubricant from said working fluid, retaining said vaporized working fluid in circulation within the system and returning the separated lubricant to said reservoir.

2. In a closed fluid cycle system containing working fluid and lubricating fluid, said system including in fluid connected series a pump, an evaporator, an expander and a condenser through which said working fluid circulates during operation of said system, said system including lubricant reservoir means for substantially isolating lubricating fluid therein from circulating working fluid, the improved apparatus for assisting in the start up of said system after a period of quiescence comprising; fluid receiving means positioned relative to said lubricant reservoir means so that lubricating fluid will drain from said lubricant reservoir means to said receiving means; a valved conduit connecting said lubricant reservoir means to said receiving means for controlling the drainage of said lubricating fluid from said lubricant reservoir means to said receiving means; means connecting said condenser to said receiving means permitting working fluid to flow from said condenser to said receiving means, whereby when lubricating fluid is present in said receiving means it mixes with said working fluid; prepressurizing boost pump means connecting said receiving means to said pump for providing fluid at elevated pressures from said receiving means to said pump; and means for separating lubricating fluid from said working fluid and for retaining said separated working fluid in said fluid connected series while providing said separated lubricating fluid to said lubricant reservoir means.

3. In a closed fluid cycle system containing working fluid and lubricating fluid, said system including in fluid connected series a pump, an evaporator, an expander and a condenser through which said working fluid circulates during operation of said system, said system including lubricant reservoir means for substantially isolating lubricating fluid therein from circulating working fluid, the improved apparatus for assisting in the start up of said system after a period of quiescence comprising: fluid receiving means positioned relative to said lubricant reservoir means so that lubricating fluid will drain from said lubricant reservoir means to said receiving means; a valved conduit connecting said lubricant reservoir means to said receiving means for controlling the drainage of said lubricating fluid from said lubricant reservoir means to said receiving means, said valved conduit being controlled by means within said receiving means shutting off said conduit whenever a predetermined volume of fluid is contained withiN said receiving means; means connecting said condenser to said receiving means permitting working fluid to flow from said condenser to said receiving means, whereby when lubricating fluid is present in said receiving means it mixes with said working fluid; means including a pressure increasing device connecting said receiving means to said pump for providing fluid at elevated pressures from said receiving means to said pump; and means for separating lubricating fluid from said working fluid and for retaining said separated working fluid in said fluid connected series while providing said separated lubricating fluid to said lubricant reservoir means.

4. In a closed vapor cycle engine containing lubricating fluid and working fluid, said engine comprising in fluid connected series a pump, an evaporator, an expander and a condenser through which said working fluid circulates during power producing operation, apparatus for assisting in the start up of said engine comprising: lubricant reservoir means for substantially isolating lubricating fluid therein from circulating working fluid; means connecting said condenser to said pump for supplying working fluid from said condenser to said pump; boost pump means for providing initial fluid input to said pump, said boost pump means being situated to permit lubricating fluid to drain thereto from said lubricant reservoir means; a valve controlled connection means between said lubricant reservoir means and the inlet to said boost pump means for providing lubricating fluid at elevated pressure to said boost pump means from said lubricant reservoir means, whereby the lubricating fluid supplied to said boost pump means and the working fluid supplied to said pump are mixed; and means for separating lubricating fluid from said working fluid and returning separated lubricating fluid to said lubricant reservoir means.