WO2014088592A2

WO2014088592A2 - Waste heat recovery system with centrifugal separator, and method

Info

Publication number: WO2014088592A2
Application number: PCT/US2012/068515
Authority: WO
Inventors: Joel CHAPLIN; Allison ATHEY; Melissa CARDONE
Original assignee: Mack Trucks Inc
Current assignee: Mack Trucks Inc
Priority date: 2012-12-07
Filing date: 2012-12-07
Publication date: 2014-06-12
Anticipated expiration: 2015-06-07
Also published as: WO2014088592A3

Abstract

A waste heat recovery system includes an expander for converting heat energy in a gaseous operating medium to mechanical energy, a condenser downstream of the expander for liquefying the operating medium, and a source of oil for lubricating moving parts of the expander. The expander is of a type that permits at least some mixing of the operating medium and the oil. A centrifugal separator connected downstream of the condenser separates mixed liquid oil and liquid operating medium. A method for waste heat recovery in a waste heat recovery system is a!so provided.

Description

WASTE HEAT RECOVERY SYSTEM WITH

CENTRIFUGAL SEPARATOR, AND METHOD

BACKGROUND AND SUMMARY

The present application relates to waste heat recovery systems and methods and, more particularly, to such systems and methods that require separation of operating medium from lubricating oil that have become mixed in an expander of the system.

A typical waste heat recovery system includes an. expander tor converting heat energy contained in an operating medium, such as ethanol, to mechanical energy. Expanders typically include moving parts such as pistons or turbines that require lubrication and, accordingly, a lubricating oil circuit that is separate from the operating medium circuit is provided. There is typically at least some mixture of oil and operating medium in the expander. Operating medium in the oil circuit presents a risk of insufficient lubrication of the moving parts of the expander and damage to materials used i the oil circuit. Oil i the operating medium cannot typically withstand conditions in the operating medium circuit. Moreover, oil in the operating medium can obstruct heat transfer from the operating medium in the expander, or to the operating medium in the evaporator,

Ethanol is a particularly useful operating medium and typically has a density of 0, 789 g/cm3_., while oil. typically has a density of 0,852-0,864 g em.3. Because of the great similarity in density, th usual technique for separating mixed oil and operating .medium is by one or, more typically, both of a gas-liquid separator downstream of the expander and upstream of a

condenser for separating liquid oil from gaseous operating medium, and a distillation process for boiling ethanol off from lubricating oil. Because ethanol has a low boiling point, distillation, is usually viewed as the easiest method for separating oil and ethanol. However, there is still a large amount of heat needed to boil off the ethanol, which is rather contrary to the overall object of recovering waste heat energy.

it is desirable to removing or reduce the energy demand required by a heating system to improve the efficienc of the system. It is also desirable to provide a waste heat recovery system and method that permits continuous separation of mixed operating medium and oil. it is also desirable to pro vide a waste heat recovery system and method that permits separation of mixed operating medium and oil without the need to supply heat energy.

The inventors have discovered that good results can be provided in a system and method wherein an operating medium such as ethanol that is mixed with oil. having a very great similarity in density by separating them in a ^'liquid-liquid separator. Typically, liquid-liquid separators are used to separate liquids having quite different densities, while liquids with similar densities are ordinarily separated via a gas-liquid separation process.

According to an aspect of the present invention, a waste heat recovery system comprises an expander for converting heat energy in a gaseous operating medium to mechanical energy, a condenser dow nstream of the expander for liquefying the operating medium, a source of oil for lubricating moving parts of the expander, wherein the expander is of a type that permits at least some mixing of the operating medium and the oil, and a centrifugal separator connected downstream of the condenser for separating mixed liquid oil and liquid operating medium.

According to another aspect of the present invention, a method for waste heat recovery in a waste heat recovery system comprises converting heat energy in a gaseous operating medium to mechanical energy in an expander, liquefying the gaseous operating medium in a condenser downstream of the expander, lubricating moving parts of the expander with oil from a source of oil, wherein the expander is of a type that permits at least some mixing of the operating medium and the oil, and separating mixed liquid oil mixed and liquid, operating medium in a centrifugal separator downstream of the condenser.

BRIEF DESCRIPTIO OF THE DRAWINGS

The features and ad vantages of the present invention are well understood by reading the following detailed description in conjunction with the drawings in which like numerals indicate similar elements and in which;

FIG. I is a schematic view of a waste heat recovery system according to. an aspect of the present nvention;

FIG, 2 is a cross-sectional side view of a centri fugal separator; and

FIG. 3 is a schematic view of a waste heat recovery system according to another aspect of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows an embodi ment of a waste^' heat recovery system 21 according to an aspect of the present invention.. The system 21 comprises an evaporator 23 arranged, to receive heat from a heat source 25_» such as part of a diesel engine and/or an exhaust after treatment system for a diesel engine. A liquid operating medium, preferably ethanoh absorbs heat energy in the evaporator 23 and is evaporated. The system 21 comprises an expander 27 in an operating medium circuit 29, The expander 27 is disposed downstream of the evaporator and converts heat energy in the gaseous operating medium to mechanical energy. Various types of expanders are known. A condenser 31 is disposed in the operating medium circuit 29 (conduits of which shown by solid lines) downstream of the expander 27 for liquefying the operating medium.

The system 2.1 further comprises a source 33 of oil for lubrica ting moving parts of the expander 27, such as pistons (not shown). Typically, the source 33 of oil is an oil tank in an oil circuit 35 (conduits of which are shown by dashed lines). A pump 37 is typically provided betwee the oil tank 33 and the expander 27 to supply oil to the expander. The expander 27 is of a type that permits at least some mixing of the operating medium and the oil so that., in the expander 27, at least some lubricating oil tends to mix with the operating medium so that lubricating oil enters the operating medium circuit 29. Similarly, some operating medium typically enters the oil circuit 35.

The system 2.1 comprises a centrifugal separator 39 connected downstream of the condenser 31 for, preferably, continuously separating liquid oil mixed with iiquid operating medium. The separator 39 continuously separates liquid oil from liquid operating, medium in the sense that the separation need not involve two discrete separation operations, such as one operation for separating liquid oil from gaseous operating medium, such as by a iiquid separator, and a separate operation for separating operating medium from iiquid oil, such as by distillation of ethanol from an oil/operating gas mixture. Moreover, the separation operation can occur entirely in the Iiquid phase for both the oil and the operating medium.

An embodiment of a centrifugal separator 39 suitable for use m connection with the waste heat recovery system 21 is seen in FIG. 2. The separator 39 includes an inlet 41 for the feed of mixed liquid operating med ium and liquid oil, a bowl 43 that is rotated by any suitable means, such as a. motor 45, an outlet. 47 for a light iiquid fraction, i.e., the operating medium, which, for ethanol, typicall has a density of 0.78 g/cm3, and an outlet 49 for the heavy fraction,, i.e., oil, which typically has a density of 0.852-0.864 g/cm3. The outlet 49 for the heavy fraction is ordinarily disposed slightly lower than the outlet 47 for the light fraction.

When the bowl 43 is rotated, the heavy fraction of the feed will tend to move toward the outer periphery of the howl, while the light fraction will tend to remain closer to the center. The heavy fraction at the outer peripher of the bowl 43 will flow out the lower outlet 49 for the hea vy fraction while the light fraction will flow over the heavy fraction and out the upper outlet for the light fraction. Various alternative centrifugal separator arrangements can be provided.

To further facilitate the separation, an electrostatic coalescing filter 51 (shown schematically in phantom in FIG. 1 ) can be provided downstream of the separator 39 in one or both of the operating medium circuit 29 and the oil circuit 35, a coalescing filter 53 (shown in schematically phantom FIG. .!) can be provi ded upstream of the separator in one or both of the operating medium circuit and the oil circuit, and/or a coalescing filter 55 (shown schematically in phantom in FIG. 1 and in phantom in FIG. 2) can be provided inside the separator. The presently preferred structure of a coalescing filter inside the separator would have a filter material disposed at an expected location of the separation boundary in the separator.

The separator 39 can be disposed in the operating medium circuit 29 only, in the oil circuit 35 only, or in both the operating medium circuit and the oil circuit. In the embodiment shown in FIG. 1 , the waste heat, recover system 21 comprises an operating medium tank 57 in the operating medium circuit 29 between the condenser 31 and the evaporator 23. A pump 59 may be provided to pump liquid operating medium from the operating medium tank 57 to the evaporator 23. In the embodiment of FIG. I, the separator 39 is disposed in the operating medium circuit 29 between the condenser 3 j and the operating medium tank 57. hi addition, the same separator 39 is disposed in the oil circuit 35 between the expander 27 and the oil tank 33. The liquid operating medium and the liquid oil can enter the separator 39 through separate inlets or can. be merged upstream of a single inlet to the separator,

instead of a single separator 39 for separating the liquid operating medium and the liquid oil in one or both of the operating medium circuit 29 and the oil circuit 35. discrete separators can be provided in each of the operating medium circuit and the oil circuit. For example, FIG. 3 shows an alternative embodiment of the waste heat recovery system 2 in which a separator 39' is disposed in the oil circuit 35' between the oil tank 33' and the pump 37'. Operating medium removed from the feed through the separato 39' can be returned to the operating medium circuit 29' at some suitable point, such as at an operating medium tank 57'. The operating medium 57' can be pumped vi a pump 59^s from the operating medium tank 57^* to the evaporator 23' where it can. recei ve heat energy from the heat source 25'. A liquid separator 61 ' cau.be provided downstream of the expander 27^* for separating liquid, most of which is oil, from the mostly gaseous oil containing operating fluid exiting the expander prior to condensing the operating fluid. The liquid separated at the liquid separator 61 ' can be directed to the oil tank 33'. Any fraction of the liquid directed to the oil tank 33 ' that is operating fluid can be separated by the separator 39' between the oil tank and the pump 37', ^'The mostly operating fluid containing gas exiting the liquid separator 61 ' can then be condensed in a condenser 3 and subjected to a liquid-liquid separation in another separator 39'" with separated liquid operating fluid being directed to the operating medium circuit 29', e.g., to an operating medium tank 57', and separated liquid oil being directed to the oil circuit 35', e.g., to the oil tank 33.

A method for waste heat recovery is described in connection with the waste heat recovery system 21 shown in FIG. 1 , except where otherwise noted. It will be appreciated thai, except where otherwise noted, the description of the method in connection with the system 21 of FIG. 1 is applicable to the system 21 ' of FIG. 3, In the method, heat energy in a gaseous operating medium, preferably ethanol, is converted to mechanical energy in an expander 27. The gaseous operating medium, is liquefied in a condenser 31. downstream of the expander 27. Mo ving parts of the expander 27 are lubricated with oil from a source of oil, i.e.. an oil tank 31. The expander 27 is of a. type that permits at least some mixing of the operatin medium and the oil. Liquid oil is continuously separated from liquid operating medium in a centrifugal separator 39

downstream of the condenser 31.

Liquid oil is filtered from liquid operating medium in a coalescing filter 51 upstream, a coalescing filter 53 downstream, and/or a coalescing filter 55 in the centrifugal separator 39..

The oil tank 33 is preferabl in an oil circuit 35 that further comprises a pump 37 between the oil tank and the expander. As seen in FIG. 3, separator 39^! can separate the liquid oil from the liquid operating medium in the oil circuit 35 ' between the oil tank 33 ' and the pump 37',

The waste heat recovery system 21 typically comprises an operating medium circuit 29 comprising an operating medium tank 57 between the condenser 31 and the evaporator 23. A separator 39 can separate the liquid oil from the liquid operating medium in the operating medium circuit 2 between the condenser 1 and the operating medium tank 57. As seen in FiG, 3, a separate separator 39" can be provided in the oil circuit. 35'. as well. In the embodiment of FIG. .1 , the separator 39 separates the liquid oil from the liquid operating medium in the oil circuit 35 between the expander 27 and the oil tank 33, however, an additional separator (not shown) might be provided in the embodiment of FIG. 1 to separate oil and operating medium downstream of the oil tank. In the present application, the use of terms such as 'including" is open-ended and is intended to have the same meaning as terms such as "comprising" and not preclude the presence of other structure, materia! , or acts. Similarly, though the use of terms such as "can" or "may" is intended to be open-ended and to reflect thai structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presentl considered to be essential, they are identified as such.

While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.

Claims

WHAT IS CLAIMED IS:

1. A waste heat recovery system, comprising;

an expander for eon veiling heat energy in a gaseous operating medium to mechanical energy;

a condenser downstream of the expander for liquefying the operating medium;

a source of oil for lubricating moving parts of the expander, wherein the expander is of a type tha permits at least some mixing of the operatin g medium and the oil; and

a centrifugal separator connected downstream of the condenser for separating mixed liquid oil and liquid operating medium,

2. The waste heat recovery system, as set forth in claim 1 , wherein the operating medium is ethano!.

3. The waste heat recovery system as set forth in claim I , comprising a coalescing filter downstream of the separator.

4. The waste heat recovery system as set forth in claim I comprising a coalescing filter upstream of the separator .

5. The waste beat recovery system as set forth in claim i, comprising a coalescing filter inside the separator.

6. The waste heat recovery system as set forth in claim i , wherein the source of oil comprises an oil tank in an oil circuit that further comprises a pump between the oil tank and the expander.

?. The waste heat recovery system as set forth hi claim 6, wherein the separator is disposed in the oil circuit between the oil tank and the pump.

8, The waste heat recovery system as set forth in claim 6, comprising an operating medium circuit comprising an operating medium tank between the condenser and the evaporator.

9, The waste heat recovery system as set forth in claim 8, wherein the separator is disposed in the operating medium circuit betwee the condenser and the operating medium lank.

10. The waste heat recovery system as set forth in claim 9, wherein the -separator is disposed in the oil circuit between the expander and the oil tank.

1 1 . Tire waste heat recovery system as set forth in claim 6, wherein the separator is disposed in the oil circuit between the expander and the oil tank,

.

12. A method for waste heat recovery m a waste heat recovery system, comprising:

converting heat energy in a gaseous operating medium to mechanical energy in an expander;

liquefying the gaseous operating medium in a condenser downstream of the expander; lubricating moving parts of the expander with oil from a source of oil, wherein the expander is of a type that permits at least some mixing of the operating medium and the oil; and separating mixed liquid oil mixed and liquid operating medium in a centrifugal separator downstream of the condenser.

.

13. The method as set forth in claim 12, wherein the operating medium is ethanol.

14. The method as set forth in claim 12, comprising filtering liquid oil from, liquid operating medium in a coalescing filter.

.15. The method as set forth in claim 12, wherein, the source of oil comprises an oil tank in an. oil. circuit that further comprises a pump between the oil tank and the expander.

1 . The method as set forth in claim 15. wherei the separator separates the liquid oil from the liquid operating medium in the oil circuit betwee the oil tank and the pump.

17. The method as set forth in claim 15, wherein the waste heat recovery system comprises an operating medium circuit comprising a operating medium tank between the condenser and the evaporator, and wherein the separaior separates the liquid oil from the liquid operating medium in the operating medium circuit between the condenser and the operating medium tank.

18. The method as set forth in claim 17. wherei the separator separates the liquid oil from the liquid operating medium in the oii circuit between, the expander and the oil tank. 19, The method as set forth in claim 15, wherein the separator separates the liquid oil from the liquid operating medium in the oil circuit between the expander and the oil tank.

20, The method as set forth in claim 12, wherein the liquid oil is continuously separates.! from the liquid operating medium m the separator.