CA1158446A

CA1158446A - Flameless nitrogen skid unit

Info

Publication number: CA1158446A
Application number: CA000373805A
Authority: CA
Inventors: Stanley B. Loesch, Deceased; Danny K. Mints; John Jim C. St.; Allen D. Burmeister
Original assignee: Halliburton Co
Current assignee: Halliburton Co
Priority date: 1980-03-31
Filing date: 1981-03-25
Publication date: 1983-12-13
Also published as: DE3111620C2; NO810967L; NL8101550A; ES500883A0; IT1136833B; DE3111620A1; AR227420A1; IT8120855A0; ES8204926A1; FR2479436A1

Abstract

ABSTRACT
A flameless nitrogen vaporizing unit includes a first internal combustion engine driving a nitrogen pump through a transmission. A second internal combustion engine drives three hydraulic oil pumps against a variable back pressure so that a variable load may be imposed upon the second engine. Liquid nitrogen is pumped from the nitrogen pump driven by the first engine into a first heat exchanger where heat is transferred from exhaust gases from the first and second internal combustion engines to the liquid nitrogen to cause the nitrogen to be trans-formed into a gaseous state. The gaseous nitrogen then flows into a second heat exchanger where it is superheated by an engine coolant fluid to heat the gaseous nitrogen to essentially an ambient temperature. The superheated nitrogen is then injected into the well. The engine coolant fluid flows in a coolant circulation system. Heat is transferred to the coolant fluid directly from the internal combustion engine. Heat is also provided to the coolant fluid from lubrication oil pumped by the three pumps attached to the second internal combustion engine. The coolant fluid circula-ting system includes a comingling chamber for comingling warmer coolant fluid flowing from the internal combustion engines to the second heat exchanger with cooler coolant fluids flowing from the second heat exchanger to the internal combustion engines. Methods of vaporizing nitrogen are also disclosed.

Description

FLAMELESS NITROGEN SKID UNIT
The present invention relates generally to apparatus for heating fluids, and more particularly, but not by way of limitation, to a flameless heater adapted for superheating liquid nitrogen for use in gel fracturing operations on offshore oil and gas wells.
Numerous operations are performed on oil and gas wells which require large volumes of nitrogen gas. These operations may be performed on both onshore and offshore wells. Such operations include foam fracturing operations, acidizing ser-vices, jetting down the tubing or down the tubing-casing annulus, nitrogen cushions for drill stem testing, pressure testing, insulation of the tubing-casing annulus to prevent such problems as paraffin precipitation, jetting with proppant for perforating and cutting operations, reduction of density of well workover fluids, displacement of well fluid from tubing during gun perforation operations to prevent excess hydro-static pressure in the hole from pushing perforation debris into the formation, placing corrosion inhibitors by misting the in-hibitor with nitrogen, extinguishing well fires, and otheroperations. The present invention may be utilized with any of these operations.
One particular such operation with relation to which the following disclosure is made is the fracturing of a sub-surface formation of the well by pumping a fluid under veryhigh pressure into the formation. The fracturing fluid which is pumped into the well often comprises a foamed gel which is produced by the use ~ b of nitro~en gas.
The nitrogen for the foam fracturing operation is generally stored in a liquid form at temperatures of approximately -320F.
Por pressures encountered in these foam fracturing opera-tions, the nitrogen changes state from a liquid to a gas atapproximately -200F. It is, therefore, desirable to heat up the nitroqen gas to a superheated state so that the foam frac-turing fluid being pumped down the well will be at an essentially ambient temperature. This is because of the numerous adverse affects upon mechanical equipment of very low temperature ~hich would otherwise be presented by the nitrogen foam.
For land based wells, the nitrogen-heating equipment generally includes open f]ame heaters. A further problem is however, pre-sented when performing foam fracturing operations on offshore LS wells. For safety and environmental reasons, open flames are not generally allowed on an offshore drilling platfor~. Therefore, it is necessary to provide a he~ter for the nitrogen which does not have an open flame.
~uch flameless nitrogen heaters have previously been ~rovided by utilizing the heat generated by an internal combustion engine and mechanical componen's driven thereby to heat a coolant fluid which transferred that heat to the nitrogen through a coolant fluid-to-nitrogen heat e~changer.
One such prior art device is manufactured by the zwicl~
Energy Research Organization, Inc. of Santa Ana, California.

_. . . .. _ . . . .

1~4 `i~

The Zwick ap~aratus includes a single i~ternal cor~ustion engine which drives a hydraulic pump to produce h-~rlraulic fluid under pressure which in turn drives a hydraulically powered nitrogen pump.
The Zwick apparatus uses a single coolant-to-nitrogen heat exchanger means for vaporizing the liquid nitrogen. Zwick does not include a second heat exchanger for transferring heat directly from engine exhaust gases to the nitrogen.
The coolant system of the Zwick device circulates the coolant 0 fluid first through a hydraulic oil-to-coolant heat exchanger where heat from the hydraulic system of the engine and the components driven thereby are transferred to the coolant. ~hen, the coolant fluid stream splits into two parallel portions, one of which flows through the engine block to absorb heat fro~, the engine and the other of which flows throuah a manifold surroundinq the engine exhaust for absorbing heat from the engine exhaust into the coolant _ . . , . ~ _ _ b fluid. After the tTo str~ams pass through the engine block and he exhaust cooling manifolds they once again merge into a single stream which is directed to the coolant fluid-to-nitrogen vaporizer. From the vaporizer the fluid returns to the hyraulic oil cooler therehy completing the loop.
With regard to the nitrogen flow system of zwick the nitrogen flows from the nitrogen pump through the coolant-to-nitrogen heat exchanger and then to the well head. A bypass i9 provided around the coolant-to-nitrogen heat exchanger by means of which liquid nitrogen can be bypassed around the coolant-to-nitrogen heat exchanger to aid in controlling the ,emperature of the nitrogen gas being injected into the ~ell.
The load on the single internal combustion engine of Zwick may be varied by varying the back pressure on the hydraulic pump driven by the engine.
Another prior art flameless nitrogen heating unit is manu-factured by Airco Cryo~enics a division of ~irco Inc. of Irvine California.
The ~irco device also uses a single internal combusion engine driving a hydraulic pump which produces hydraulic fluid under pres-sure for driving a liquid nitrogen pump.
The ~irco device utilizes air as the heat exchange medium for transferrinq hea~ to the liquid nitrogen to varporize the same.
This is accomplished in the following manner. A large plenum chamber is provided into ~hich ambient air is drawn. Disposed in ib the plenum chamber in heat exchange ccntact with the air ,lowing therethrough is a hydraulic oil-to-air heat exchanger ~herein hydraulic fluid heated by the engine and its various ~perating co~ponents is circulated 'hrough the hydraulic oil-to-air heat exchanger tc heat the air.
An enqine coolant fluid-to-air heat exchanger, i.e., the engine radiator, is also disposed in the plenum chamber for 'rans-ferring heat energy from the engine coolant system to the air flo~ing through the plenum chamber.
~dditionally, the exhaust gases produced by the internal combustion engine are dumped dlrectl-y into the plenum chamber to mi,~ with the air flowing therethrough.
The air flo~ing throuah the plenum chamber, after it has ~een heated by the hydraulic oil-to-air cooler and the engine radiator and after it has mixed with engine e~haust gases, then passes over an air-to-nitrogen heat exchanger wherein heat energy is transferred fxom the hot air to the liquid nitrogen to vaporize the same.
The load imposed upon the internal combustion engine of the ~irco device may be varied by var~ing the pressure in the va~porized nitrogen discharge line to raise the pressure against which the nitrogen pump is wor~ing and in turn raise the load on the ~Iydraulic pump driven by the internal combustion engine which in turn increases the load on the internal combustion engine.
Numerous problems are encountered with the Airco type device mainly because of the use of air as a heat transfer medium. Air `tb is a notoriously poor ileat transfer medium as compared to a liquid and the use of ambient air causes the system Lo be very much depenent ~pon ambient air conditions for proper operation.
Additiotlally, due to the large bul~y nature of the plenum chamber required for the use of air as a heat transfer medium, the Airco system is very much larger than a system like that of the present invention of equal ca~acity.
Thus, it is seen that the prior art has recognized the need for a flameless nitrogen vaporizer. The devices of this type included in the pr'ior art, however, have numerous shortcomings particularly with regard to their capability of providing suffi-cient heat for vapori7ing large volumes of nitrogen and with regard to -their capability of accurately controlling the amount of hea~ transferred to the nitrogen and its corresponding temper-ature as it enters the well head.
The flameless nitrogen vaporizing unit of the present invention yreatly improves upon the prior art devices by providing a second internal combustion engine for the sole purpose of providin~
additional leat for the vaporization of the nitrogen. This second ~O internal combustion engine and its associated heat transfer system are so interconnected with a first internal con~ustion engine and its associated heat tr3nsfer system so that the first internal combustion engine ~a~r be used alone for nitrogen production at rates for which sufficient heat may be generated by a single engine for the vaporization thereof, and then for higher rates the second internal combustion engine can be activated and its heat transfer system wor~ing in conjunction t~ith that of the first internal combustion engine provides a total heat transfer sufficient ror ~aporizing nitrogen at these higher rates and superheating it to essentially ambient conditions. ~umerous refinements in the load control systems and temperature control systems as connected to each of the two internal combustion engines are 2rovided also.

The flameless nitrogen vaporizing unit of the present invention includes a first lnternal combustion engine driving a nitrogen pump through a transmission. Connected to the transmission is a transmission retarder for varying the load on the first internal combustipn engine by varying a level of hydraulic fluid oresent in the transmission retarder. A second internal combustion engine drives three hydraulic oil pumps against a variable back pressure so that a variable load may be imposed upon the second engine.
Liquid nitrogen i5 pumped from the nitroqen pump driven by the first engine into a first heat exchanger where heat is trans-ferred fror.l exhaust gases from the f~rst and second internal com-bustion engines to the liqui~1 nitrogen to cause the nitrogen to ~e transformed into a g~seous s~ate. The gaseous nitrogen then flows into a second heat exchanger where it is superheated by an engine coolant fluid to heat the gaseous nitrogen to essentially an amkient temperature. The superheated nitrogen is then injected into the well.

The engine coolant fluid flows in a coolant cir-culation system wherein it receives heat from several sources.
Heat is transferred to the coolant fluid directly from the internal combustion engine. Heat is transferred to the coolant fluid from transmission fluid which flows through the trans-mission of the first internal combustion engine and the trans-mission retarder thereof. Heat is also provided to the coolant fluid from lubrication oil pumped by the three pumps attac~ed to the second internal combustion engine. In an alternative embodiment these three pumps and their related oil to coolant heat exchanger are replaced by a water brake dynamometer which pumps the coolant fluid. The coolant fluid circulating system includes a comingling chamber for comingling warmer coolant fluid flowing from the internal combustion engines to the coolant fluid-to-nitrogen heat exchanger with cooler coolant fluid flowing from the coolant fluid-to-nitrogen heat exchanger to the internal combustion engines. This aids in controlling the temperatures of the internal combustion engines to prevent overcooling of the same.
Numerous features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings.
In one aspect of the 2resent invention there is provided an apparatus for heating a first fluid, comprising, a first internal combustion engine; a second internal combustion engine; a coolant system means for cir-culating a coolant fluid and transferring heat energy from the first and second internal combustion engines to the coolant fluid, a coolant fluid-to-first fluid heat exchanger means for transferring heat energy from the coolant fluid to the first fluid, a main pump means, drivingly connected 4 ~3 to the first internal com~ustion engine, for pumping the first fluid, and a variable load means, connected to the second internal combustion engine, for exerting a varying load on the second internal combustion engine so that an amount of heat energy transferred from the second internal combustion engine to the coolant fluid and from the coolant fluid to the first fluid increases as the load exerted on the second internal combustion engine by the variable load means is increased.
In a further aspect of the present invention, there is provided an apparatus for heating a first fluid, com-prising a first internal combustion engine, a main pump for pumping said first fluid; transmission means connecting said engine and said main pump so that said main pump is driven by said engine, a coolant system means for circulating a coolant fluid and transferring heat energy from said internal combustion engine to said coolant fluid, a coolant fluid-to-first fluid heat exchanger means for transferring heat energy from said coolant fluid to said first fluid, and a transmission retarder means, connected to said transmission means, for exerting a varying load on said engine so that an amount of heat energy transferred from said internal combustion engine to said coolant fluid, and from said coolant fluid to said first fluid, is increased as said load exerted on said engine by said transmission retarder means is increased.
The invention is illustrated by way of example with accompanying drawings wherein:
FIG. 1 is a plan view of the flameless nitrogen unit of the present invention.

-8a-~b FIG. 2 is a left side elevation view of the apparatus of FIG. l;
FIG . 3 is a schematic representation of the nitrogen flow system;
FIG . 4 is a schematic representation of the coolant flo~
circulatina system;
FIG. 5 is a schematic representation of the flow of lube oil from the nitrogen pump to the lube oil-to-coolant fluid exchangers, the flow of the transmission fluid from the trans-mission to the transmission-to-coolant fluid exchanger, and the flow of hydraulic oil from the three pumps attached to the sec-ond internal combustion ensine to the hydraulic oil-to-coolant fluid exchangers;
FIG. 5 is a sectional view of the nitrogen vaporizer discharge 1~ manifold showing the connection of a bypass line thereto for bypassing liquid nitrogen around both the exhaust gas-to-nitrogen heat exchanger and the coolant fluid-to-nitrogen heat exchanger;
FIG. 7 is an elevation view of one of the coolant fluid co-minglin~ chambers;
FIG. 8 is a sectional elevation view along line 8-8 of FIG. 7; and FIG. 9 is a horizontal section view akout line 9-9 of FIG. 8.
FIG. 10 is a schematic representation, similar -to FIG. q, illustrating an alternative embodiment of the present invention wherein ~he second engine drives a water ~rake dynamometer.

_g_ Referrinq now to the drawings and particularly to FI~S. 1 and 2, the flameless nitrogen vaporizing unit of the present invention is shown and generally designated by the numeral 1~.
The vaporizing unit 10 may generally be referred to as an appa-ratus for heating a first fluid, said fluid being the liquidnitrogen.
The apparatus 10 includes a rectangular transporta~le skid frame 12 havin~ first and second opposed sides 14 and 16, and haviny third and fourth opposed sides 1~ and 20. The first and second sides 14 and 16 define a width of frame 12, which width is approximately 95 inches in a preferred em~odiment. The third and'fourth sides 18 and 20 define a length of frame 12 which lerlath is approximately 168 inches in a preferred e~bodimen'_.
The vaporizing apparatus 10 is surrounded by a protective cage 21 t~hich, in a preferred embodiment, has a 'neight of 9Ç inches.
The protective cage 21 is not shot~n in FI5. 1 so that the other components mav be more clearly illustrated.
~lounted upon the frame 12 are first and second internal comb~stion engines 22 and 24, respectively, which may also be referred to as first and second power sources. In a preferred embodiment, engines 22 and 24 are General Motors ÇV-92T diesel engines. Engines 2, and 24 are oriented upon frame 12 so that the respective axes of rotation, 2h and 23, of the crank shafts of engines 22 and 24 are oriented substantially parallel to third and fourth sides 1~ and 20 of frame 12.

, ~

A compressed air system is provided on the apparatus 10 with an air compressor driven by first engine 22 connected to a compressed air stora~e tank for use with compressed air driven starters on the englnes 22 and 24.
S A nitrogen pump 30, which may also be referred to as a main pump, is located on fra~e 12 between the first engine.22 and second side 16 of frame 12. In a preferred embodiment pump 30 is preferably a Hallil~urton ~T-150 positive displacerllent pump ha~-in~
Linde HP-60 fluid ends.
0 Nitrogen pum~ 30 is drivlngly connected to first en~ine 22 by transmission means 32 and by a gear reduction box 31. In a preferred embodiment transmission 32 is an Allison HT-7;0 transmission, and gear reduction box 31 provides a ~-to-l gear reduction between transmission 32 and pu~p 30.
The transmission 32 is equipped with a hydraulic transmission retarder 33 of a design well known to those skilled in the art which operates in a manner similar to that of a torque convertor with a load exerted on the transmission by the transmission retarder being dependent upon a controllable level of a transmission ~luid 0 present in the transmission retarder. The higher the fluid level in the retarder is, the higher the load exerted will be.
The second engine 24 has a triple pump drive unit 3~ attached to the rear end thereof to which are drivingly connected first, sec-ond and third hydraulic pumps 36, 33 and 40, two of which can ~e seen in FIG. 1.
The exhaust systems from engine 22 and 24 ar~ connected to an exhaust gas-to-nitrogen heat exchanger 4~ which is located b between and abo~7e the engines ~2 and 2~ as shown in FIGS. 1 ar.d 2. The exhaust heat exchanger 42 is a means for transferrin~
h~at energy from the exhaust gases produced by engines 22 and 24 directly to the nitrogen flo~Jing through the tube side of exchanger 44. ~he term "directly" is used to indicate that the heat energy is not passed through any intermediate heat transfer fluid medium bet~een the exhaust gas and the nitrogen.
A coolan-t fluid-to-nitrogen heat exchanger 44 is located behind second engine 24 near the fourth side 20 of frame 12, for transferring lleat from the coolant fluid directly to the nitrogen.
First and second coolant fluid comingling chambers 46 and 48 are located near third and fourth sides 1~ and 20, respectively, of frame 12 just to the rear of first and second engines 22 and 24, respectively.
Located above transmission 3~ are a plurality of heat exchanaers for transferrinc heat energy from various sources on the apparatus 10 to the engine coolant fluid which circulates through the cooling systems of the engines 22 and 24. These heat exchangers include the following.
First and second hydraulic system coolers 50 and 52, respecti~ely, are provided for transferring heat energy from a hydraulic fluid pumped by pumps 36, 38 and 40 to the coolant fluid. Hydraulic coolers 5Q and 52 may also be referred to as hydraulic fluid-to-coolant fluid heat exchangers.
A transmission cooler 54 is provided for transferring heat .. ... . . _ _ energy from the trallsmission fluid circulating through transmission 32, and its associated transmission retarder 33, to the coolant flui~.
First and second nitrogen pump coolers 56 and 58, respectiv-ly, are provided for trans erring heat energy from a lubrica~ing fluid circulating through nltrogen pump 30 to the coolant fluid.
Nitrogen pump coolers 56 and 58 may also be referred to as nitrogen pump lubricating fluid-to-coolant fluid heat exchangers.

Referring now to FIG. 3, a schematic flow diagram is shown for the nitrogen system of the nitrogen heating apparatus 10.
The nitrogen pump 30 takes liquid nitrogen from a liquid nitrogen source 60 which, in a preferred embodim.ent, has a c~pacity of approximately 2,00~ gallons. T.he liquid nitrogen source 60 is 1;, not located on frame 12. A discharge line 62 connects the dis-charge of nitrogen pump 30 to the tube side of exhaust heat exchanger 42.
Ilot exhaust qases from engines 22 and 24 are passed through the shell side of exchanger 42 as indicated by arrows 64 and 66.
2a The liquid nitrogen from pump 30 enters exhaust heat exchanger 42 at a temperature of aporoximately -320F. ~he heat supplied by exhaust exchanger 42 is approximately sufficient to vaporize the nitrogen and the vaporized nitrogen exits exhaust exchanger 42 by means of conduit 68 at a temperature of approximately -200F.
Con~uit 68 directs the vaporize~ nitrogen into the tube side ~ ib of coolant fluid-to-nitrogen heat exchanger 4~. ~Jarm coolant fluicl from the svstem ge!lerallv sho~n in FI~. 4 is passed tnrough the shell side of exchanger '4 as indicated by arrows 70 and 72.
The heat transferred frorn the coolant fluid to the vapori~ed nitrogen in coolant fluid heat exchanger 44 superheats the ~tapori~ed nitroqen to approximately ambient temperatures of 7~F
+ 20F at conduit 73 e~iting exchanger 44.
As is shown in FIG. 3, the exhaust heat exchanger 42 and the coolant heat exchanger 44 are so arranged relative to the direction of flow of the nitrogen that the exhaust heat exchanger 42 is located upstream of the coolant heat exchanger 44.
A first bypass conduit means 74 is provided for bypassing liquid nitro~en past e~haust heat exchanger means 42. Disposed in first bypass conduit 74 is a manually operable control valve 76 which provides a means for controlling the amount of liquid nitrogen which is byPassed around exhaust heat exchanger 42 so that a controlled portion oE nitrogen is so bypassed.
~ second bypass conduit means 78 provides a means for bypassing liquid nitrogen past both the exhaust heat exchanger means 42 and the coolant heat e~changer means 44. Disposed in second bypassing conduit 78 is a manually operable control valve 80, which is a needle valve, by means of whic.l t'ne amount of liquid nitrogen passed through second bypass conduit 78 may be controlled.
The first and second bypass conduit means 74 and 78 are

2~ connecte~ in parallel so that the second bypass means 7~ is operable b independent of firs. by?ass means 74 allowing liquid nitroaen to by bv~assed throu~h either one or both of the by~ass means.
Discharge conduit 73 from coolant heat e~changer means 44 and second bypass conduit 73 are bo~h connected to a discharge manifold 82.
Discharge ~anifold 82 is shown in section in FIG. 6. Dis-charge ~anifold ~2 includes a first inlet ~4 to which is con-nected conduit 73, and a second inlet ~6 to which is connected bypass conduit 7~.
A thermowell 33 is disposed in manifold ~2 so that a temp-erature indicating means (not shown) may be connected there.o to measure the temperature of the sul?erheated nitrogen which is discharged from manifold 82 through outlet 90 thereof. The outlet 90 is connected to a nitrogen discharge line 9, which 1~ directs the superheated nitrogen vapors to a foaming unit 96 where the nitrogen gas is used to prcduce the fracturing gel solu-tion which is in turn directed through a conduit 9~ to the well head 100 of the well which is being treated.
Connected to the conduit 73 between coolant heat exchanger means 44 and discharge manifold ~ is a safety~ relief valve 102 and an access flange 104 adjacent an access valve 106.
Referring now to FIG. 4, 'here is thereshown a schema~ic flow diagram for the coolant fluid which flows ~hrough the shell side of coolant .luid heat exchanger 44 as indicated by arrows 70 and 72 on FI5. 3.

In FIG. 4, coolant fluid-to-nitrogen heat e~changer means 44 is sho-~n schematically in a 'manner similar to that in which it is shown in FIG. 3. Conduits leading into and out of the shell side of exchanger 44 are desianated by numerals 70 and 72, res-pectively, corresponding to the arrows 70 and 72 of FIG. 3. The warm coolant fluid enters heat exchanger 44 through conduit 7~
and in the exchanger 44 transfers heat to the nitrogen flowing through the tube side of exchanger 44, as indicated by arrows 6~
I and 73 shown in phantom lines, and a cooler coolant fluid exits ~10 exchanger 44 ~y means of conduit 72.
¦ The other end of conduit 72 is attached to a tube side inlet lOS of hydraulic cooler 50. A tube side outlet 110 of hydraulic cooler 50 is connected to a tube side inlet 112 of second hydraulic cooler 52 by a conduit 114.
A tube side outlet 116 of second hydraulic cooler 52 is con-nected to a tube side inlet 113 of transmission cooler 54 by conduit 120. A tube side outlet 122 of transmission cooler 54 is connected to a conduit 124 which in turn is connected to~draulically parallel conduitsl26 and 12~ leading to tube side inlets 13~ and 132 of first and second nitrogen pu.~p coolers 56 and 58, respec~tively.
A tube side outlet 134 of first nitrogen pump cooler 56 is I connected to a firs~ inlet 137 of first comingling chamber 46 by t a conduit 136. ~ tube side outlet 138 of second nitrogen pump cooler 58 is connected to a first inlet 141 of second comingling chamber 48 by a conduit 140.

.

'~ -16- , ~, l .

The details of construction of comingling chambers 46 and 48 are shown in detail in FIGS. 7-9.
Coolant fluid exits a first outlet 142 of comingling chamber 46 through a conduit 144. The other end of conduit~144 is con-nected to an inlet lq6 to the water jacket of first engine 22. Thecoolant fluid then flows through the water jac~et of engine 22 and exits the water jac~et at outlets 148 and 150. A conduit 15 is connected at one end to outlets 148 and 150 and at the other end to a three-way thermostatically controlled valve 154.
A first outlet 156 of valve 154 is connected to a conduit 1~8 for directing coolant fluid to a radiator 160. A second outlet 162 of valve 154 is connected to a conduit 164 for directing cool-ant fluid to a second inlet 166 of first comingling chamber 146.
Depending upon the temperature of the coolant fluid entering thermostatically controlled val~te 154, the coolant flui~ is directed to one of first and second outle-ts 156 or 162. If the coolant fluid is too hot it is directed to first outlet 1,6 and to conven-tional radiator 150 where the coolant fluid is cooled by heat exchange with air flowing past the outside of radiator 160. ~ther-wise, the coolant fluid is directed to second outlet 162 and dir-ectly to second inlet 166 of first comingling chamber 146.
The coolant fluid directed through conduit 158 to radiator 160 enters the tube side of radiator 160 through inlets 170 and 172.

That coolant fluid then e~its a tube side outlet 174 of radiator 160 and is directed to inlet 146 of the water jacket of first engine 22 by a conduit 176.
An overflow conduit means 17~ is connected to an overflow outlet 180 of radiator 160 and an overflow outlet 182 of first comingling chamber 46. Overflow conduit 178 is connected to a first surge tank 134 from which a coolant fluid make-up conduit 186 directs coolant fluid to a ma~e-up inlet 1~8 of first radiator 160. Surge tank 184 serves to de-aerate the coolant fluid and .o provide make-up fluid.
All of the coolant fluid which flows from first comingling chamher 46 throuyh conduit 144 to the engine 22, or which is recycled through the radiator 160 and then bac~ to the engine 22, eventually returns through the conduit 164 to the second inlet 166 of co-.5 mingling chamber 46 as previously described. The coolant fluid entering second inlet 166 which has just been heated by the first engine 22 is physically mixed with or co~ingled with the cooler coolant fluid entering first inlet 137 within the comingling chamber 96.
A portion of this comingled coolant fluid is tha. which was 0 previously described as exiting first outlet 142 of comingling ~
chamber 46. A second portion of the comingled coolant fluid within the chamber 46 exits second outlet 19~ of comingling chamber 46 by means of conduit 192.
The temperature of the coolant fluid entering first inlet ~5 137, in a pre~ferred embodiment, is approximately 160 to 170F.

,~ . . .

~L~

The teml~erature of the _0012llt rluid entering second inlet lfi6 is approximately 190~. The temperature of the coolant fluid exiting first and second outlets 142 and l~0 is approximatel~f~ 180~ for each outlet.
The comingling chamber 46 serves to raise tlle temperature of the coolant fluicl directed to the coolant system of first engine 22 higher than it would be if the comingling chamber a~
were eliminated and the conduit 136 were connected directly to the conduit 144. This hel~s prevent over-cooling of the first L0 engine 22 and Prevents the mechanical problems which can arise as a natural consequence of over-cooling an internal cor,lbustion engine.
The entire system shown in FIG. 4 may generally be referred to as a coolant system means.
The various conduits which return the coolant fluid from engines 22 and 24 to the heat e,cchanaer 44 may generally be described as a first coolant fluid conducting means, and the various conduits conducting coolant fluid from coolant fluid heat e~changer 44 to the first and second engines 22 and 24 may gerlexally be described as a second coolant fluid conducting means.
All of the various heat exchangers, comingling chambers, radiators, surge tanks, pumps and tlle like shown in FIG. 4 mav generally be described as being disposed in one of these first or second coolant fluid conducting means.
The second coolant fluid conducting means supPlying fluid _ _ _ _ b from exchanger 44 to the engines 22 and 24 s~lits in~o two parallel streams at the tee 125. The two parallel st`reams are again combined at the tee 204 in the first coolant fluid con-ducting means. The first and second engines 22 and 2a may therefore, be said to be connected in parallel between the first and second coolant fluid conducting means, so that the coolant fluid flowing from the second coolant fluid conducting means to the first coolant fluid conducting means is split in~o first and second coolant fluid streams flowing past said first and second internal combustion engines 22 and 24, respectively.
The cominglins chambers 46 and 4~ may each ~e ~enerally referred to as a transfer means, connected to the first and second coolant fluid conducting ;neans between the engines 22 ancl 24 and the heat exchanger means 44, for transferring heat ~15 energy from coolant fluid in the first coolant fluid conducting means to coolant fluid in the second coo~ant fluid conducting means.
The ccmingling chamber 46 could be replaced by a more conventional heat exchanger which does not mix the fluid flowing to and from engine 22, but due to the fact that the fluids are identical and the temperature differential is small the comingling chamber is preferred because it provides a much larger heat e~change than ould a conventional shell and tube exchanger of similar physical size.

I

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b The conduits connectina second comingling chamber 43 with second engine 24 ~re similar to that just described between first comingling chamber 46 and first ensine 22.
The second cominglins cnamber 4~ includes the first in-S let 141 and a second inlet 194. It also includes first and secondoutlets 196 and 198. Second outlet 198 is connected to a conduit 200.
Conduits lg2 and 200 returning coolant fluid from cominglinu chambers 46 and 48 both connect to a comnlcn return line 202 at a tee connection 204.
Return conduit 20 is connected to a suction side of a coolant fluid pump 206. The discharge 5ide of coolant fluid pump 206 is connected to the conduit 70 which has previouslv been described as connected to the inlet of the shell side of L~ coolant fluid heat exchanger 44. Pump 206 is a hydraulically powered pump which is driven by a hydraulic motor.
Although not illustrated in FIG. 4, it is desirable to conduct a smaller portion of the flow of warm coolant fluid ~: from the discharge of pump 206 throush a heating jac~et around the fluid end o nitrogen pump 30 to heat the same.

.~

_ . . . _. . . _ . =~ '=Y

~15~ ib The details of construction of comingling chamber 46 are shown in FIGS. 7-9. Second comingling chamber 48 is similarly constructed. FIG. 7 is an outer elevation view of comingling chamber 45.
Cominglinq chamber 46 includes a vertically oriented cylin-drical housing 208 to which tlle inlets 137 and 166 and the outlets 142 and 190 are connected.
A cap 210 is connected to the upper end of housing 208 by a locking collar 212. The overflow outlet 182 is attached to L0 cap 210.
Referring now to FIG. 3 a sectional elevation view about line 8-8 of PIG. 7 is thereshown. A base plate 214 seals the lower end of cylindrical housing 20~. First and second mounting brackets 216 and 218 are attached to the outer surface of housing 208 for attaching the same to the frame 12 of the flameless nitro-gen vaporizing unit 10.
Inside the housing 20S are first, second and third baffles 220, 222 and 224.
As is best shown in FIG. 9 which is a horizontal section ) view along line 9-9 of FIG. 8, the baf~les are attached to two central vertica].ly oriented parallel support legs 226 and 228 which set in rectangular cut-out spaces in the baffles. The baffles are attached to the support legs 226 and 228 by welding or other suitable means.
j The operation of the cor~lingling chamber 46 is as follows.

, _ _ . . _, . . .

`}b The cooler coolant fluid enters first inlet 137 and the warmer coolant fluid en~_ers second inlet 166 and the two streams of fluid begin comingling with each other above firs~ baffle 220.
As the comingled fluid flows downward through comingling chamber ~6 to the outlets 142 and 130, the direction of the fluid is deflected twice by the second and third baffles 222 and 224 to insure thorough mixing or comingling or the two liquid streams so that the liquid exiting the two outlets 142 and 190 is essen-tially of the same te~perature at each of those outlets.
Referring now to FIG. 5, a schematic flow diagram is shown for the shell side fluids of the hydraulic coolers 50 and 52, the transmission cooler 54 and the nitrogen pump coolers 56 and 58. ~he flow of coolant fluid through 'the tube sides of t~ose exchangers is represented b'y phantom lines in a manner lS similar to that shown in FIG. ~ for aid in correlation of the two drawings.
In the lower portion of FIG. 5, the three hydraulic pumps 36, 38 and 40 which are driven by second engine 22 are thereshown.
The discharge sides 226, 2 3 and 230 of pumps 36, 38 and 40, respectively, are connected to a common discharge line 232. Dis-posed in discharge line 232 is a pilot controlled relief valve 234 which allows the discharge pressure in discharge line 232 to be controlled and varied. The pilot controlled relief valve 234 includes a relief valve which may be set at the desired operating backpressure for the discharge line~32, The relief valve remains b closed for a very short period of tir.le after the positive dis-placement pumps '26, 228 and 230 have begun operating until the pressure in discharge 232 reaches the preset value at ~hich the relief valve isdesigned to open. Lhe relief val~e opens at that point and maintains a constant backpressure against the pumps 226, 223 and 230 at the ~reset level.
In a control consol~ (not shown) supported from the frame 12 of flameless nitrogen heating unit 10, there is located an overriding relief valve which is interconnected with pilot controlled relief valve 23~ so that the setting of pilot con-trolled relief valve 234 may be overriden and changed by operation of the relief valve located in the control con.sole.
Heat is generated and transferred to the hydraulic fluid as it is pumped through the pumps 36, 38 and ~0 and as it drops across the restriction in pilot controlled relief valve 234.
The pumps 36, 38 and 40 along with pilot controlled relief valve 234 provide a variable load means, connected to second internal co~bustion engine 24, for exerting a varying load on second internal combustion engine 24, so that an amount of heat energy transferred from engine 24 to the coolant fluid in the system illustrated in FIG. 4, and then from the coolant fluid to the liquid nitrogen in the coolant fluid heat exchanger 44, increases as the load exerted on second internal combustion engine 24 is increased by raising the backpressure controlled by pilot controlled relief valve 234.

_, _ . . . _ _ ,_~" . _ . _ .. ____ :_ ,, T~ I _ - , ' ' -- ' b ~ conauit 236 connec-s pilot controlled relief valve 234 to a shell side inlet 23, or second hy~raulic cooler 52.
conduit 240 connects a shell side outlet 242 of second hydraulic cooler 25 with a shell side inlet 244 of first hydraulic cooler ~0. A shell side outlet 246 of first hydraulic cooler 50 is connPcted to a conduit 248.
Conduit ,48 is connected to two parallel conduits 250 and 252 which are connected to first and second filters ?.54 and 255.
The outlets of filters 25~ and 256 are connected to conduits L0 253 and 260 which are connected to a common return conduit 262.
Suction sides 264, 266 and 268 of pumps 36, 38 and 40, respectiveiy, are all connected ~o the return line 262 thereby completing the circuit for the hydraulic fluid through the shell side of hydraulic coolers 50 and 52.
Return line 262 is connected to a hydraulic oil reservoir 263 by a conduit 265 and a back pressure check valve 267. Another hydraulic fluid return line 269 from a hydraulic motor (not shown) which drives coolant pump 206, see FIG. 4, connects to conduit 265 between check valve 267 and conduit 262.
8ack pressure check valve 267 maintains a constant back pressure of 22 psi on conduits 265 and 269. This provides a constant pressure supply of hydraulic fluid to the suction sides of pumps 36, 38 and 40.
Referring now to the middle portion of FIG. 5, the first internal combustion enyine 22, the transmission 32 and transmission retarde- 33 are there schematically illustrated.

~ l outlet 270 from transmission 32 and transmission retarder 33 is connected to a suction side of transmission fluid pump 272 by a conduit 274. The discharge from pump 272 is connected to a shell side inlet 276 of transmission cooler S4 by a conduit 278.
A shell side outlet 2~0 of transmission cooler 54 is connected to a conduit 282 the other end of which is connected to a filter 284.
The outlet from filter 2~4 is connected to a return conduit 286 which is connected to an inlet 288 of transmission 32 and trans-mission retarder 33. The transmission fluid is heated by the friction incurred in the tra~smission 32 and transmission retarder 33 and that heat is transferred to the coolant fl~id by means of transmission cooler 54.
Referring now to the upper portion of FIG. 5, the circulation system for lubricating oil for the nitrogen pump 30 is thereshown.
A lubricating oil manifold which distributes lubrica-ting oil to the various moving parts of nitrogen pump 32 is represented schema-tically by nitrogen pump lube manifold 290. The lubrication oil is heated as it flows through the manifold 290. The lubrication oil from manifold 290 is carried by a conduit 292 to the gear reduction bo~ 31 which was previously described with relation to FIG. 1. The gear reduction box 31 connects transmission 32 to nitrogen pump 30. The lubrication oil is then carried from ~ear reduction box 31 by a conduit 294 to a lubricating oil reservoir 296.
. 25 : -j! -26-,' l . ~
~ T

, . . ~

A lube oil pump 298 has a suction t`nereof connected to the lube oil reservoir 296 by a conduit 300. A discharge side of pump 298 is cor.nected to a shell side inlot 302 of first nitrogen pump cooler ~6 by a conduit 304.
A shell side outlet 306 of first nitrogen pump cooler ~6 is connected to a shell side inlet 308 of second nitrogen pump cooler 58 by a conduit 310. A shell side outlet 312 of second nitroqen pump cooler 58 is connected to a conduit 314.
Conduit 314 is connected to an inlet of filter 316. The outlet of filter 316 is connected to the inlet of nitrogen pump lube manifold 290 by a conduit 318, thereby completing the circu-lating loop for the lube oil.
A safety relief valve 320 is connected to conduit 314 by a conduit 322 and the outlet of relief valve 320 is connected to lube oil reservoir 296 by a conduit 324.
The operation of the flameless nitrogen vaporizing unit 10 ¦ is generally as follows.
¦ For relatively low pumping rates of nitrogen, only the first ~ internal combustion engine 22 need be utilized. The engine 22 is i ~ started and it drives the nitrogen pump 30 which pumps the nitrogen through the flow system illustrated in FIG. 3. The flow rate of nitrogen pumped by pump 30 is controlled by controlling the speed of engine 22 and by the transmission gearing in transmission 32.
Simultaneously, exhaust gases from the engine 22 flow throug~
the shell s-ide of eY.haust heat exchanger 42 and heat the liquid -:27-; ~

nitrogen. If too much heat is being provided by the exhaust exchanger 42 it may be partially or entirely bypassed by means of bypass conduit 74 and con~rol valve 76.
The nitrogen then flows into coolant fluid heat exchanger 44 ~here it is further heated by heat transferred from the cool-ant fluid. Both the exchanger 42 and the coolant fluid exchanger 44 may be bypassed by means of second bypass conduit 78 and control valve 80. By watching the temperature indicated by a temperature indicator (not shown) disposed in thermowell 88, an operator may utilize the valves 76 and 80, primarily the valve 80, for fine adjustment of the temperature of the nitrogen flowing out the outlet 90 of the discharge manifold 8 A larger but less accurate adjustment of the temperature of the nitrogen can be made by varying the load on transmission retarder 33 so as to vary the load on engine 22 and correspondingly vary the heat generated thereby in the various heat exchange systems. Simultaneously with all of this, of course, heat is transferred from the transmission 32 and transmission retarder 33 to transmission fluid and then to the coolant fluid ~y means of transmission cooler 54. Also, heat flows in the nitrogen pump lube oil system shown in the upper part of FIG. 5 to the nitrogen pump coolers 56 and 58.
If all the systems connected to the first internal combustion engine 22 are not capable of providing sufficient heat for the vaporization of the desired flow rates of liquid nitrogen, then -2~-_ _ _ _ _ _ _ _ _ _ ~

the second internal combustion engine 24 is activated. The second internal combustion engine 24 is operable independently of first internal combustion engine 22, so that the second internal combustion en~ine 24 may be selectively used as an auxiliary heat source in addition to first internal combustion engine 22 when the amount of heat energy transferred from the first engine 22 to the coolant fluid is insufficient to provide sufficient heat energy for heating the nitrogen to a desired temperature in the coolant heat exchanser means 44.
o Once the second internal combustion engine 24 is activated, the amount of heat provided thereby may be grossly adjusted by varying theback pressure on the pumps 36, 38 and 40 by means of the pilot controlled relief valve 234. The fine temperature adjustment is still provided by the bypass means 73 and control valve 80.
The apparatus 10 provides pumping rates in the overall ran~e of from 15,000 to 230,000 standard cubic feet per hour at a pump pressure of 10,000 psi.

~0 In FIG. 10 an alternative embodiment of .he present invention is illustrated, in which the pumps 226, 22~ and 230 and the ~ attached system shown in the lower portion of FIG. S are replace,d 1~ b~ a water brake dynamometer 400 which is driven by a second engine 24. ~7ater brake dynamometer 400 is an alternative means for exerting a varying load on engine 24 so that the amo~nt of heat --2g--I

b transferred from engine 24 to the coolant fluid, and then from the coolant fluicl to the liquid nitrosen in the coolant fluid heat exchanger 44, increases as the load exerted on engine 24 is increased.
In the embodiment of FIG. 10, coolant fluid exiting the shell side of heat exchanger 44 is carried by a conduit 402 to an inlet 404 of water brake dynamometer 400. Water brake dyna-mometer 400 acts as an inefficient centrifugal pump to convert mechanical energy from engine 24 into heat energ~l~ in the coolant L0 fluid. The load exerted on engine 2a is varied by varying the bac~c pressure against which dynamometer 400 is pumping. This is done by means of a bac~c pressure valve 406.
Coolant fluid e~iting back pressure valve 406 is at approxi-mately ~1 psig and is carried h-~ conduit 403 to a sump 410.
L5 The coolant fluid is tal;en from sump 410 bv a suction line 412 leading to a coolant fluid booster pump 414 which boosts the pressure of the coolant fluid up to approximately 8 psig as is required for proper operation of the remainder of the system.
A conduit 416 carries the coolant fluid from pump 414 to tube side inlet 113 of transmission cooler 54. Tl e remainder of the system shown in FIG. 10 is similar to that of FIG. 4.
Thus it is seen that the flameless nitrogen vaporizing skid unit of the present invention is readily adapted to attain the ends and advantages m~entioned as well as those inherent therein.
2~ ~hile presently preferred embodiments of the invention have been --3û--'}b illustrated for the purposes of the present disclosure, nu~erous changes in the construction and arrangement of parts may be made by those skilled in the art which changes are encom~assed within the spirit and scope of this invention as defined by the appended claims.

_ _ . . . . .

Claims

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

1. An apparatus for heating a first fluid, comprising:
a first internal combustion engine;
a second internal combustion engine;
a coolant system means for circulating a coolant fluid and transferring heat energy from said first and second internal combustion engines to said coolant fluid;
a coolant fluid-to-first fluid heat exchanger means for transferring heat energy from said coolant fluid to said first fluid;
a main pump means, drivingly connected to said first internal combustion engine, for pumping said first fluid; and a variable load means, connected to said second internal combustion engine, for exerting a varying load on said second internal combustion engine so that an amount of heat energy transferred from said second internal combustion engine to said coolant fluid and from said coolant fluid to said first fluid increases as said load exerted on said second internal combustion engine by said variable load means is increased.

2. The apparatus of claim 1, wherein:
said second internal combustion engine is operable independent of said first internal combustion engine, so that said second internal combustion engine may be selectively used as an auxiliary heat source in addition to said first internal combustion engine when an amount of heat energy transferred from said first internal combustion engine to said coolant fluid is insufficient to provide sufficient heat energy for heating said first fluid to a desired temperature in said coolant fluid-to first fluid heat exchanger means.

3. The apparatus of claim 1, wherein:
said variable load means includes a hydraulic pump means, driven by said second internal combustion engine, for pumping a hydraulic fluid against a controlled variable dis-charge pressure, so that the load on said second internal com-bustion engine is increased by increasing said discharge pressure.

4. The apparatus of claim 3, further comprising:
hydraulic fluid-to-coolant fluid heat exchanger means for transferring heat energy from said hydraulic fluid to said coolant fluid.

5. The apparatus of claim 4, further comprising:
a main pump lubricating fluid circulation system for providing lubricating fluid to said main pump; and lubricating fluid-to-coolant fluid heat exchanger means, connected between said main pump lubricating fluid cir-culation system and said coolant system means, for transferring heat energy from said lubricating fluid to said coolant fluid.

6. The apparatus of claim 5, wherein:
said hydraulic fluid-to-coolant fluid heat exchanger means and said lubricating fluid-to-coolant fluid heat exchanger means are located, relative to a direction of flow of said coolant fluid in said coolant system means, downstream from said coolant fluid-to-first fluid heat exchanger means and upstream of said first and second internal combustion engines.

7. The apparatus of claim 6, wherein:
said coolant system means includes a first coolant fluid conducting means for conducting said coolant fluid from said first and second internal combustion engines to said coolant fluid-to-first fluid heat exchanger means and a second coolant fluid conducting means for conducting said coolant fluid from said coolant fluid-to-first fluid heat exchanger means to said first and second internal combustion engines, said hydraulic fluid-to-coolant fluid heat exchanger means and said lubricating fluid-to-coolant fluid heat exchanger means being disposed in said second coolant fluid conducting means.

8. The apparatus of claim 7, wherein:
said first and second internal combustion engines are connected in parallel between said first and second coolant fluid conducting means, so that said coolant fluid flowing from said second coolant fluid conducting means to said first coolant fluid conducting means is split into first and second coolant fluid streams flowing past said first and second internal combustion engines, respectively.

9. The apparatus of claim 8, further comprising:
comingling chamber means, connected to a portion of said first and second coolant fluid conducting means within which said first stream of coolant fluid flows, for comingling coolant fluid from said first coolant fluid conducting means with coolant fluid from said second coolant fluid conducting means and thereby transferring heat energy from said coolant fluid in said first coolant fluid conducting means to coolant fluid in said second coolant fluid conducting means.

10. The apparatus of claim 1, wherein:
said variable load means includes a water brake dynamometer means, driven by said second internal combustion engine, for converting mechanical energy of said second internal combustion engine into heat energy in said coolant fluid as said coolant fluid is moved through said water brake dynamometer.

11. The apparatus of claim 10, wherein:
said water brake dynamometer means includes a variable back pressure valve means for varying a back pressure against which said water brake dynamometer pumps said coolant fluid so that a load exerted on said second internal combustion engine is varied as said back pressure is varied.

12. The apparatus of claim 11, further comprising:
sump means for receiving coolant fluid from said back pressure valve means; and booster pump means for taking said coolant fluid from said sump means and pressurizing said coolant fluid.

13. The apparatus of claim 10, further comprising:
a main pump lubricating fluid circulation system for providing lubricating fluid to said main pump; and lubricating fluid-to-coolant fluid heat exchanger means, connected between said main pump lubricating fluid cir-culation system and said coolant system means, for transferring heat energy from said lubricating fluid to said coolant fluid,

14. The apparatus of claim 13, wherein:
said water brake dynamometer and said lubricating fluid-to-coolant fluid heat exchanger means are located, relative to a direction of flow of said coolant fluid in said coolant system means, downstream from said coolant fluid-to-first fluid heat exchanger means and upstream of said first and second internal combustion engines.

15. The apparatus of claim 14, wherein:
said coolant system means includes a first coolant fluid conducting means for conducting said coolant fluid from said first and second internal combustion engines to said coolant fluid-to-first fluid heat exchanger means and a second coolant fluid conducting means for conducting said coolant fluid from said coolant fluid-to-first fluid heat exchanger means to said first and second internal combustion engines, said water brake dynamometer and said lubricating fluid-to-coolant fluid heat exchanger means being disposed in said second coolant fluid conducting means.

16. The apparatus of claim 15, wherein:
said first and second internal combustion engines are connected in parallel between said first and second coolant fluid conducting means, so that said coolant fluid flowing from said second coolant fluid conducting means to said first coolant fluid conducting means is split into first and second coolant fluid streams flowing past said first and second internal combustion engines, respectively.

17. The apparatus of claim 16, further comprising:
comingling chamber means, connected to a portion of said first and second coolant fluid conducting means within which said first stream of coolant fluid flows, for comingling coolant fluid from said first coolant fluid conducting means with coolant fluid from said second coolant fluid conducting means and thereby transferring heat energy from said coolant fluid in said first coolant fluid conducting means to coolant fluid in said second coolant fluid conducting means.

18. The apparatus of claim 1, wherein:
said coolant system means includes a first coolant fluid conducting means for conducting said coolant fluid from said first and second internal combustion engines to said coolant fluid-to-first fluid heat exchanger means and a second coolant fluid conducting means for conducting said coolant fluid from said coolant fluid-to-first fluid heat exchanger means to said first and second internal combustion engine.

19. The apparatus of claim 18, wherein:
said first and second internal combustion engines are connected in parallel between said first and second coolant fluid conducting means, so that said coolant fluid flowing from said second coolant fluid conducting means to said first coolant fluid conducting means is split into first and second coolant fluid streams flowing past said first and second internal com-bustion engines, respectively.

20. The apparatus of claim 19, further comprising:
comingling chamber means, connected to a portion of said first and second coolant fluid conducting means within which said first stream of coolant fluid flows, for comingling coolant fluid from said first coolant fluid conducting means with coolant fluid from said second coolant fluid conducting means and thereby transferring heat energy from said coolant fluid in said first coolant fluid conducting means to coolant fluid in said second coolant fluid conducting means.

21. The apparatus of claim 1, further comprising:
an exhaust-to-first fluid heat exchanger means for transferring heat energy from exhaust gases produced by said first and second internal combustion engines directly to said first fluid.

22. The apparatus of claim 21, wherein:
said exhaust-to-first fluid heat exchanger means and coolant fluid-to-first fluid heat exchanger means are so arranged relative to a direction of flow of said first fluid that said exhaust-to-first fluid heat exchanger means is located upstream from said coolant fluid-to-first fluid heat exchanger means.

23. The apparatus of claim 22, further comprising:
first bypass means for bypassing said first fluid past said exhaust-to-first fluid heat exchanger means.

24. The apparatus of claim 23, wherein:
said first bypass means is further characterized as being a controllable bypass means for bypassing a controlled portion of said first fluid.

25. The apparatus of claim 23, further comprising:
second bypass means for bypassing said first fluid past said exhaust-to-first fluid heat exchanger means and said coolant fluid-to-first fluid heat exchanger means.

26. The apparatus of claim 25, wherein:
said second bypass means is operable independent of said first bypass means.

27. The apparatus of claim 22, further comprising:
bypass means for bypassing said first fluid past said exhaust-to-first fluid heat exchanger means and said coolant fluid-to-first fluid heat exchanger means.

28. The apparatus of claim 27, wherein:
said bypass means is further characterized as being a controllable bypass means for bypassing a controlled portion of said first fluid.

29. The apparatus of claim 22, further characterized as being an apparatus for heating a liquid first fluid sufficiently to transform said first fluid to a superheated gaseous state, wherein:
said exhaust-to-first fluid heat exchanger means is further characterized as being a means for transferring approxi-mately enough heat energy from said exhaust gases to said liquid first fluid to transform said first fluid to a gaseous state; and said coolant fluid-to-first fluid heat exchanger means is further characterized as a means for superheating said gaseous first fluid.

30. The apparatus of claim 1, further comprising:
a rectangular frame having first and second opposed sides and third and fourth opposed sides, said first and second internal combustion engines being mounted upon said frame with axes of rotation of crankshafts of said first and second internal combustion engines being oriented substantially parallel to said third and fourth sides of said frame.

31. The apparatus of claim 30, further comprising:
said main pump being located on said frame between said first internal combustion engine and said second side of said frame; and transmission means for connecting said first in-ternal combustion engine to said main pump, so that said main pump is driven by said first internal combustion engine.

32. The apparatus of claim 30, wherein:
said rectangular frame is further characterized as being a transportable skid frame.

33. The apparatus of claim 1 for heating a first fluid, comprising:
transmission means connecting said first internal combustion engine and said main pump so that said main pump is driven by said first engine; and a transmission retarder means, connected to said transmission means, for exerting a varying load on said first internal combustion engine so that an amount of heat energy transferred from said first engine to said coolant fluid, and from said coolant fluid to said first fluid, is increased as said load exerted on said first engine by said transmission retarder means is increased.

34. The apparatus of claim 33, wherein:
said transmission retarder means has a transmission fluid circulating therethrough; and said apparatus further comprises a transmission fluid-to-coolant fluid heat exchanger means for transferring heat energy from said transmission fluid to said coolant fluid.

35. The apparatus of claim 34, wherein:
said transmission fluid-to-coolant fluid heat ex-changer means is located, relative to a direction of flow of said coolant fluid in said coolant system means, downstream from said coolant fluid-to-first fluid heat exchanger means and upstream of said internal combustion engine.