CA1181957A - Method for heat recovery from internal combustion engines for supplementary power - Google Patents

Abstract

Improved Method of Heat Recovery from Internal Combustion Engines for Supplementary Power ABSTRACT:

Nearly two thirds of the fuel energy consumed in internal combustion engines is expelled as heat in the exhaust gases and coolant. The lower temperature portions of this heat can be upgraded by a heat pump cycle to produce steam which can then be superheated by the higher temperature portion of the exhaust gases. The current pro-posal for achieving this can be improved by superheating the boiler into two sections; directing the high temperature portion of the exhaust gases into the superheating boiler;
and conducting the low temperature portion of the exhaust gases through a heat exchanger in the low temperature boiler; and conducting a controllable portion of the exhaust steam from a driven turbine through the second stage, instead of the first stage of the heat pump cycle.

Description

Improved Me-thod for Hea-t Recovery from Internal Combustion Engines for Supplementary Power _ It is known that approximately one third of the fuel energy in an internal combustion engine is given off as heat in -the exhaus-t gases; and a similar amount of heat is carried away by the engine coo:lant. This invention relates to -the recovery of heat from both the exhaust gases and engine coolant of any internal combustion engine, including diesel engines, to provide supplementary power, such as by heating a fluid to drive a steam or vapour turbine. There is a high temperature stage of heat recovery and a lower temperature stage. Heat from the lower -temperature stage is elevated in temperature by a heat pump cycle and -then del-ivered to the high -temperature stage.
Related patents on this subject may be described as follows:-Combined gas turbine, steam turbine sys-tems have been proposed in United States Patent to Miller, No.

2, 6789 531 and No. 2,678,532 of May 16, 195~, wherein steam is combined wi-th combustion gases in the same comb-ustion chamber, to cool the combustion gases prior to their introduction into the turbine.
There is a United States Patent 3,385,565 -to Aguet of August 15, 1967 wherein a combustion chamber for press-urized gas and air includes a superheater whose steam drives a separate steam turbine; -the combustion gases driv-ing a separate turbine; and the exhaust gas from the gas turbine prehea-ts the liquid. The steam en-ters the combust-ion chamber at two locations, both fed from -the expanded steam exi-ting from the steam turbine.
A ~anadian Patent No. 998,843 issued 76 - lo - 26 to Migneault, describes a combined gas and steam motor comprising two engines operatively connected to jointly drive a power shaft; a combustion chamber in said motor having igni-tion means therein and a boiler means therein.
Thus the boiler is contained within the combustion chamber and combustion is a~ttained by the igni-tion of pressurized fuel and pressurized air, both supplied by pressure ~tanks and pumps. A sui~table liquid such as water is conducted -through jackets around the combus-tion chamber and through a condenser having a baffled tank, pump, shower and supple-mentary burner for preventing freeze-up. The combus-tion gas jet flame is direc-ted in-to the presæure chamber of a motor -to drive same, while steam builds up, whereupon the s-team is also directed in-to -the pressure chamber. The mixing of ~the fluids occurs in -the pressure chamber, not in the com-bus-tion chamber. In one embodimen-t -the s-team and combus-tion gases are conducted in-to -the cylinders of a piston-type engine a~t a pressure of about 800 p. s. i . O~ther embodimen~ts :;nclude a combined gas and s-team mo-tor comprising two turbines~ or a single -turbine housing and a rotor having s-team -turbine vanes on one side and gas je~t vanes on -the o-ther. In both cases -the combus-tion chamber has a boiler means thereirl -to produce s-team -to supplement the gas fuel.
An addi~tiona]. embodimen-t is a relatively small combined s~team condenser, gas and steam engine said engine having a combus-tion chamber, a boiler therein, and an engine housing con-taining a-t leas~t one pressure chamber with a moveable par~t drivingly connected -to a power shaft. The spent steam is condensed and recycled to the boiler.

~l ~ 7 Canadian Paten-t No. 986,727 issued -to Eggmann in 76 - o4 - o6 describes a h~vbrid motor uni-t wi-th energy s-torage. In substance it is a method of operating an inter-nal combustion engine arranged -to drive a load, wherein a small portion of the engine power drives an air compressor;
the pressurized air is s-tored to meet acceleration require-ments of -the load by supplying said s-tored air through a heat exchanger, which is heated by exhaust gases from the engine -to an air-opera-ted turbine in driving connection with the load. It claims to provide extra power only for acceleration.
In Canadian Patent No. 449, 146 issued to Barr, June 1~, 1948 is described an internal combustion compounded turbine, an included steam turbine and a heat interchanger which extracts heat from the exhaust gases of the lowest pressure internal combus-tion turbine of the compounded series for raising s-team which is used to drive the steam turbine. The water supply of the hea-t in-terchanger is used to cool the compressor/s or intercooler/s, -the feed water being thereby pre-heated. The steam turbine provides supp-lementary power whilst its exhaust steam may be condensed and returned to the feed water supply.
Canadian Paten-t No. 1,112,05~ issued to Hainan, Nov.
lo, 1981 embodies apparatus to generate superhea-ted press-ure steam, an injector-compressor apparatus utilizing the generated steam as motive power to pre-compress the com-bus-tion air, a jacketed cooling system of the engine, through which the air-steam mixture from the injector-compressor flows serving as a coolant, said mixture being thereby superhea~ted and being rammed into the engine's combustion space.
Canadian Patent No. 1, 146, 361 issued to James ~.
Marshall, 17 May 1983 describes a sys~tem for upgrading the coolant heat, and ~the lower temperature portion of the engine exhaust gases by means of a heat pump cycle. This upgraded heat raises the temperature of circulating cond-ensate9 in a boiler, which is then raised to steam or vapour at higher temperature and pressure by the higher-temperature portion of the engine exhaust gases. The said steam is used to drive a turbine whose exhaust steam con-tribu-tes heat to -the first s~tage of a two-stage evapora-tor in the heat pump cycle.
The invention herein differs from known inven-tions, excep-t for -the Marshall Pa~ten-t No. 1, 146, 361, in the followlng ways:
(a) I-t is adap~tible to any in-ternal combustion eng-ine, including diesel engines, and including exis-ting engines, wi-thou-t significant modifica-tion -to those engines.
(b) It recovers hea-t ~rom -three sources: (i) exhaust gases; (li) engine coolant and (iii) exhaust steam from a supplemerl-tary turbine.
(c) I-t uses a hea-t pump cycle -to raise -the temper-ature of hea-t sources which are a-t lower temperature.
(d) I-t uses fluid for the supplementary -turbine in an independen-t circui-t, permi-tting the choice of fluid for optimum f`unc-tional charac~teristics.

(e) The steam or vapour -turbine, utilizing the recov-ered hea-t, can supply power con-tinuously, and no-t just for acceleration or other spasmodic loads.
The invention herein differs from -the Marshall Paten-t No. 1, 146, 361 in the following ways:
(a) The boiler is divided into a superheating boiler and a low temperature boiler.
(b) The high-temperature range of engine exhaus-t gases contribute heat to the superheating boiler, and therefrom the lower temperature range of said exhaust gases conduct heat to the low -temperature boiler, ins-tead of to the heat pump evaporator.
(c) The exhaust steam from the driven turbine is con-ducted, in a controllable amount, into ~the second s-tage, that is, the higher temperature s~tage evaporator of the heat pump stage instead of into the first stage evaporator.
The curren-t method in Marshall Paten-t No. 1, 146, 361 for recovering heat from the coolant and exhaus-t gases of an engine with -the employment of a heat pump cycle uses a single boiler; routes some of the exhaust gas heat -through the heat pump circuit; and routes exhaust s~team from a supplementary -turbine through -the first stage of a two-stage evaporator. In operation -this requires that the heat pump circuit carry some of -the exhaust gas heat. The single boiler must have both a superheating heat exchanger and a heat exchanger -~or liquid, and consequen-tly a large -temp-erature gradient, and a complex design. The exhaust steam from the driven turbine is used in the firs-t stage evapor-ator whereas it can be more effectively used in -the second s-tage.
The invention herein conducts -the lower temperature portion of ~the exhaust gas heat directly into a low temp-erature boiler which is more efficient -than directing it through -the heat pump. Secondly the boiler is divided in-to a superheating boiler and a low temperature boiler which results in a lower temperature gradient; a definite div-ision between the lower temperature and higher temperature sections; and a less complex design. Thirdly the exhaust s~team ~rom -the driven turbine, which is at a higher temp-era-ture ~than the engine coolan-t, can be more effec~tively used in -the second s~tage evapora-tor which operates a~t a higher tempera-ture than -the firs-t s-tage. Four-thly, i-t is found -tha-t the ra-te of ~low of steam/condensate -through -the sys-tem is dependen-t upon -the mass of s~team which can be superhea-ted by -the engine exhaust gases. The invention herein provicles for a controllable by-pass valve to limit the portion o~ the exhaus-t s-team from -the driven -turbine entering the second s-tage evaporator o~ -the heat pump so tha-t -the s-team produced in -the low -tempera-ture boiler can be limi-ted -to -the amoun-t which can be adequa-tely super-heated in -the superhea-ting boiler.

Specifica-tion The drawings which lllus-tra-te the embodiments of the invention are:
Figure 1, A schematic diagram of the heat recov-ery system.
Figure 2, The assembly of the heat recovery system and driven turbine, top view.
Figure 3~ The assembly of the heat recovery system and driven turbine, side view.
The heat recovery system comprises four flow circuits which are described as follows:
With reference to Figure 1, (solid line), exhaust gases from the in-ternal combustion engine,1, flow over the surfaces of a superheating heat-exchangert2, within a steam-generating boiler,3, Upon exiting from said boiler the exhaust gases pass through a heat exchanger,4, within low-tempera-ture boiler,30, and exit at 6 to the atmosphere, direc-tly or through a silencer.
The second flow circuit (dashed line) conducts the circulating engine coolant of -the internal combustion engine,1, into a heat exchanger,7, within first stage evap-orator,27, from which it returns -to the internal combustion engine,1.
The third flow circui-t (dash-dot line) comprises a heat pump cycle. The heat pump fluid is compressed by compressor, 8, enters heat exchanger,9, within low temperature boiler, 30, and then passes through expansion valve,10, or alter-na-tive expansion turbine, 11. After expansion the heat pump fluid enters first stage evapora-tor, 27, From said evapOr-ator the heat pump fluid, in a vapour sta~te, flows in-to second stage evaporator, 5, via condui-t 28; and from said evaporator the said fluid returns to compressor, 8, via condui-t 19.
The fourth flow circuit ldash, -two-dot line) con-ducts steam or vapour from boiler, 3, to drive a turbine, 12, or other form of engine via condui-t, 20. A portion of the exhaust fluid from said turbine, con-trolled manually or automatically by boiler pressure, is conducted through heat exchanger, 13, within second s~tage evaporator, ~; the rem-ainder is c~nducted to a condenser 31, or to a heating process; and the condensate is returned to boiler, 30, by pump 14, via condui-t, 29. See Figs. 2 & 3 for operation:
Opera-tion In operation, exhaus-t gases from internal combus-tion engine, 1, flow over hea-t exchanger, 2, in boiler, 3, via conduit 1~ providing direc-t hea-t to superheat steam or vapour in sald boiler. Upon exiting from boiler, 3, the said exhaust gases, a-t reduced -tempera-ture, pass through a hea-t exchanger 4, in -the low -tempera-ture boiler, 30 ! The hea-t pump fluid ex-trac-ts hea-t from -two sources, namely: the coolant of -the interna]. combus-tion engine, and the exhaust fluid from -the supplementary turbine, 12, when i-t is oper-a~ting. The said engine coolant en-ters heat exchanger, 7, in firs-t stage evapora~tor, 27, via conduit 22. Said coolant re-turns -to said engine via conduit, 23. The exhaust fluid from -the supplemen~tary turbine, 12, enters heat exchanger, 13, in second s~tage evaporator, ~, via conduit, 21. A por--tion of said exhaus-t fluid is conducted to condenser, 31, or -to a heating process, by controllable valve, 32. The

3~L9~7 condensate of said fluid is re-turned to boiler, 30, by pump, 14.
The heat pump fluid, after passing -through expansion valve, 10, ex-trac~ts heat in the said first and second evap-ora-tor stages. The heat pump fluid is then drawn in-to compressor, 8, via conduit, 19, where its temperature and pressure are raised; and it is expelled via conduit 17, into heat exchanger, 9, in boiler, 30. The heat pump is the indirec-t mode of providing high -tempera-ture heat to boiler, 30. The steam or vapour superheated in boiler, 3, by heat exchanger, 2, drives supplementary turbine, or other engine, 12, via conduit, 20 and -throttle, 2~.
The characteristics or properties of` the -turbine fluid, the hea-t pump fluid and the engine coolant may be chosen for an optimum -temperature range. The engine coolant9 for example, if circula-ted under pressure, and/or contains e~thylene glycol (anti-freeze) will have a higher boiling temperature than water alone. The heat pump fluid will be chosen to have an evaporating temperature below the boiling temperature of water, for example; and at a practical com-pressor pressure will have a temperature sufficiently high to add heat to the boiler, 30. The heat exchangers will be designed for a low pressure drop and optimum heat -transfer according -to a known art.
The supplementary turbine, 12, may be coupled to the internal combustion engine, 1, by an au-tomatic clutch, of known art, or may be independent; and will have means of control and safety in accordance with known practice.
In very large internal combustion installations an expansion trubine, 11, may be substituted for expansion valve, 10. Said expansion turbine may be used as an auxil-iary power source.

Claims (5)

The embodiments of the invention in which exclusive property or privilege is claimed are defined as follows:

1. Improvements to a mechanical system for recovering heat from an internal combustion engine by external means to produce steam or vapour for supplementary power or pro-cess heat, said heat being extracted from the exhaust gases and from the coolant; employing a heat pump cycle to raise the temperature of the lower temperature heat sources; said improvements comprising the division of the boiler section into a superheating boiler which receives heat from exhaust gases in the upper temperature range and a low temperature boiler which receives heat from exhaust gases in the lower temperature range; and also from the heat pump which extracts heat from the engine coolant only, in its first stage evaporator and from a controllable amount of exhaust steam from a driven turbine or heating process in its second stage evaporator.

2. A mechanical system as described in Claim 1 employing a superheating steam or vapour boiler designed to direct the exhaust gases from the internal combustion engine over the surfaces of a heat exchanger which conducts steam or vapour and connecting to a low temperature boiler which produces wet steam or vapour by having a heat exchanger to conduct the low temperature range of exhaust gases which exit from the superheating boiler; and having a second heat exchanger to conduct the output fluid from a heat pump cycle; and having a pump to return condensate to said boiler.

3. A mechanical system, as described in Claim 1 employ-ing a heat pump cycle comprising an expansion valve, a two-stage evaporator and a single stage or multi-stage com-pressor; wherein the working fluid flows through the exp-ansion valve into the two-stage evaporator and therefrom is drawn into the compressor which delivers the said working fluid, at an elevated temperature and pressure, to a heat exchanger in the low temperature boiler whence it returns to the expansion valve.

4. A mechanical system as described in Claim 1 and Claim 3 employing a heat pump cycle which includes a two-stage evaporator whose first stage contains a heat exchanger conduit which conduct the circulating coolant fluid from the aforesaid internal combustion engine.

5. A mechanical system as described in Claim 1 and Claim 3 employing a heat pump cycle which includes a two-stage evaporator whose second stage contains a heat exchanger conduit which conducts a controllable portion of the exhaust steam of the aforesaid driven steam or vapour turbine, or other mechanism or heating process.