Waste heat recovery cycle for producing power and fresh water

Steam is produced from aqueous brine, by a process that employs hot fluid, nozzle means and rotary separator means. Process steps include: PA1 (a) transferring heat from said hot fluid to said brine, PA1 (b) passing the heated brine in pressurized state to the nozzle means for flow therethrough, and expanding the flow therein thereby to form steam and liquid droplets, and PA1 (c) causing said expanded flow to rotate the rotary separator means for forming a layer of said brine on the separator means and accompanied by steam separation and for subsequent removal. The liquid from the rotating layer and/or the separated steam may be used to drive turbine means; the hot fluid may comprise combustion products from a combustion source; and several stages of separators may be employed.

BACKGROUND OF THE INVENTION 
This invention relates generally to systems to recover waste heat for 
producing power and/or fresh water; more particularly it concerns use of 
rotary separator and turbine elements in a cycle to achieve these 
objectives. 
There is a constant requirement and need for efficient systems to recover 
waste heat, to produce power and to produce fresh water from brine such as 
sea water. While many heat recovery cycles and fresh water producing 
systems have been proposed in the past, none are believed to embody the 
many unusual advantages in construction, mode of operation, and results as 
are now achievable through use of the present invention. 
SUMMARY OF THE INVENTION 
Basically the invention provides an efficient and simple method of 
recovering "waste heat" in the exhaust gas from diesel engines, gas 
turbines, boiler plants and the like. Heat is recovered from the 
relatively low level of engine exhaust by transfer to a liquid, which is 
then expanded in a nozzle to produce a "biphase" fluid (mixture of liquid 
drops and gas). The kinetic energy of the expanding gas is largely 
imparted to the liquid, where the energy is available to drive a liquid 
turbine. A nozzle, and rotary separator and liquid turbine components are 
provided, and the cycle as a whole, has significant advantages over 
Rankine cycles, which evaporate a fluid to operate a gas turbine. These 
advantages include simplicity and reliability, low temperature operation 
of rotating parts, lower speeds, more efficient heat transfer, and 
potentially improved thermodynamic efficiency. In this regard, a simple 
system embodying the invention typically costs between 50 and 60 percent 
of the comparable cost of a Rankine system. 
While the basic system as referred to possesses all of the advantages 
mentioned above in a marine application, and in addition produces a supply 
of fresh water, it can also be used to concentrate brine in certain 
industrial applications while producing power from waste heat. The cycle 
power production efficiency is competitive with the more costly Rankine 
cycle, and a fraction of the brine or sea water used in the cycle is 
delivered as potable water while concomitantly concentrating the brine. 
Basically, the method of the invention involves transferring heat from hot 
fluid (such as hot products of combustion) to liquid such as brine; 
passing the brine in pressurized state to nozzle; means for expansion 
therein to produce steam and liquid droplets in a jet; and employing the 
kinetic energy of the jet to rotate a rotary separator to form a rotating 
layer or ring of liquid on the separator accompanied by separation of the 
vapor or steam in usable form (i.e. to produce fresh water after 
condensation). The energy of the rotating ring of liquid on the separator 
is then typically employed to drive a turbine to derive shaft power 
output, and the rejected brine may be re-used as will be described. 
Several separator and turbine stages may be employed to increase 
efficiency, in the manner as will be described.

DETAILED DESCRIPTION 
The basic waste heat recovery cycle for producing power and fresh water is 
shown in FIG. 1. Brine, such as sea water for example, (or other liquid) 
is supplied at 10, and its pressure is elevated if need be by pump 11. The 
relatively cool brine then flows at 12 through heat transfer means such as 
condensers 13 and 14 containing coils 15 and 16, wherein it is heated by 
heat transfer from coils 17 and 18. Vapor passed at 19 through the latter 
coil is condensed to supply such heat, and in the case of steam, the 
resultant fresh water condensate is removed at 20 for use. 
The heated liquid or brine then enters the primary heat exchanger 21 
wherein it picks up heat from waste hot fluid, as for example hot products 
of combustion produced by a source 22 such as an internal combustion 
engine. The overall system has special utility in marine applications, 
where for example Diesel engines are widely used. In this regard, the 
brine may flow through a coil 23 over which the hot products of combustion 
flow, as indicated. 
The heated liquid or brine is then conducted at 12a to nozzle means (as for 
example nozzle 24) connected or located to receive that liquid for flow 
through the nozzle means and expansion therein to form vapor and liquid 
droplets in a jet 25 discharged from the nozzle. Such a nozzle is 
described in U.S. Pat. No. 3,879,949 to Hays et al. The expansion imparts 
kinetic energy to the liquid drops, and the two-phase mixture in the jet 
impinges on the rim of a rotary separator 26. The latter is located in the 
path of the jet to be rotated by the jet for producing a layer of liquid 
on the separator rim, as described in U.S. Pat. No. 3,879,949. Vapor 
separation from the jet and from the liquid also occurs, the vapor being 
accumulated within a housing 27 containing the separator, and exiting from 
the housing at 28. That vapor then flows to the condensers 14 and 13 as 
referred to above. 
Also provided is liquid turbine means indicated schematically at 29, the 
common axis of the rotary separator 26, rotary turbine 29, and output 
shaft 30 appearing at 31. Liquid from the rotating ring or layer formed on 
the separator rim is removed to drive the turbine, in the manner described 
in U.S. Pat. No. 3,879,949, and also below, in FIGS. 4-8, power produced 
by the turbine being taken out at shaft 31. Spent liquid such as 
concentrated brine exits from the turbine at 32, and may be returned to 
the sea. The amount of fresh water obtainable in this way is a substantial 
fraction of the volume of brine entering the cycle. 
FIGS. 4-8 illustrate typical nozzles 167, separator wheel 168 rotating 
within casing 180, and radial-flow turbine 169, shown as coaxially 
rotatable within the casing. The liquid and vapor or gas mixture is 
supplied at high pressure to the nozzle inlets 170. The mixture expands to 
low pressure at the nozzle exits 171, and the resulting high-velocity 
two-phase jets 172 impinge on the inner surface 173 of the rim 174 of the 
rotating separator at locations 175, seen in FIG. 8. The briny liquid 
becomes concentrated in a layer 176 on the inner surface 173 due to the 
inertia of the liquid and to centrifugal force, while the gas or steam 
separates and flows radially inward through passages 177 and enters the 
discharge pipe 178 through ports 179 in the stationary casing or housing 
180. The rotating separator is supported by bearings 181 mounted in the 
housing 180, and receiving a separator wheel axle 168a. 
The rotation of the separator 168 is impeded only by windage and bearing 
friction losses which can be very small. Thus only a very small relative 
velocity between the impinging jet 172 and the surface 173, aided by the 
torque imparted to the rotating separator by the inward flow of the gas 
through passages 177, serves to maintain the speed of the liquid layer 176 
at a value nearly equal to that of the jets 172. 
The liquid flows from the liquid layer 176 through passages 182 in the rim 
of the rotating separator 168 and then into annular chamber 183 which 
forms an integral part of the separator wheel 168. As a result another 
liquid layer 184 is formed, held against the surface 185 by centrifugal 
force. This layer furnishes the fluid energy source for the turbine rotor 
169 rotating concentrically within the separator wheel and having turbine 
inlet passages 186 immersed in the liquid layer 184. 
The turbine 169 may have blades or passages arranged to intercept the 
liquid layer 184, and FIGS. 5 and 6 show a radial-flow type turbine. The 
turbine rotor 169 typically rotates at a lower angular velocity than the 
separator wheel 168, causing liquid from the layer 184 to enter the inlets 
186, flow radially inward through passages 187, and flow to liquid outlet 
pipe 188 via axial passage 187a in shaft 190 and apertures 189 in the wall 
of the turbine shaft 190. The shaft 190 is connected to the load to be 
driven. The turbine 169 is supported on bearings 191. 
Each turbine passage 187 can optionally incorporate a diffuser 192 in which 
the velocity of the liquid entering inlet 186 can be partially converted 
to pressure such that, even allowing for the pressure drop in the radial 
passages 187 due to centrifugal force, the liquid pressure in discharge 
pipe 188 is substantially higher than the pressure in the turbine casing 
180, and, in fact, greater than the pressure at the nozzle inlets 170. 
Thus the diffusers 192 can supply any need for pumping of the liquid. 
For operation with high pressure at the discharge 188, the leakage of 
liquid between the shaft 190 and the housing 180 is reduced by labyrinth 
seals 193 and drains 194 which return liquid leakage to the bottom 195 of 
the housing 180, where the liquid from this and other internal leakage 
sources is picked up by slinger blades 196 and thrown back into the jets 
172. Leakage to the outside of housing 180 is prevented by a shaft seal 
197. 
The external shape of the turbine inlet ports 186 must be such as to 
minimize external drag and turbulence that could disturb and retard the 
liquid layer 184. The design shown in FIG. 7 employs a wedge-shaped strut 
198 for the portion of the turbine inlet which intercepts the surface of 
the liquid layer 184 so that the flow intercepted by the strut is split at 
199 with minimum disturbance and returned with little velocity loss to the 
liquid layer in the wake region 200 behind the turbine inlet 186. 
To allow for operation at different liquid flow rates, the passage 192 may 
be equipped with moveable walls 201 which serve to vary the area of the 
turbine inlets 186. 
Accordingly, the FIGS. 4-8 embodiment provide, essentially, a moving 
surface to enable separation of the gas and liquid phases with extremely 
low friction, said surface comprising a first wheel having a periphery 
toward which the jet is tangentially directed, which is free to rotate, 
and including means to capture first fluid which has been separated from 
the second and has acted to impart rotation to the wheel but with 
essentially no power transfer. Also, they provide a second wheel having a 
periphery extending in proximity with the periphery of the first wheel 
whereby the two wheels define a gap therebetween to receive the separated 
first fluid and supply the fluid to the second wheel wherein the kinetic 
energy of the fluid is converted partly to shaft power and partly to 
pumping power. 
Referring now to FIG. 2, sea water enters the modified system at 110, is 
pressurized by pump 111 and passes at 112 through coil 115 in condenser 
113 and through coil 116 in condenser 114. The brine then passes through 
coil 123 in primary heat exchanger 121 corresponding to exchanger 21 in 
FIG. 1. An engine 122 corresponds to engine 22 in FIG. 1. 
The heated sea water is then passed at 112a to first stage nozzle means at 
124 for flow and expansion therein to form vapor such as steam, and liquid 
droplets, in a first stage jet. A first stage rotary separator means 126 
is located in the path of that jet to be rotated by kinetic energy of the 
jet for producing a layer of liquid on the separator means (as described 
above), accompanied by vapor or steam separation. Steam passes at 119 from 
the separator housing 128 to coil 117 in condenser 114, where it is partly 
condensed and passed as pressurized steam and water droplets to nozzle 324 
associated with a third rotory separator means 326. 
A first stage turbine 129 is associated with separator 126 and receives 
liquid brine from the rotating layer on separator 126 to drive that first 
turbine stage, an output shaft being indicated 131. Brine at reduced 
pressure that has passed through turbine 129 is passed at 200 to second 
stage nozzle means 224 for flow and expansion therein to form steam and 
liquid droplets in a second stage jet. The latter impinges on a second 
stage rotary separator means 226 (in the path of the jet) to rotate that 
separator and produce a layer of brine on that separator and rotating 
therewith. Separated steam is passed at 219 from housing 228 to coil 218 
of condenser 113, for condensation and removal at 120 as fresh water. A 
second stage turbine means 229 communicates with the separator 226 (in the 
manner described above) to receive liquid brine from the rotating layer, 
such kinetic energy driving the second stage turbine. Brine that has 
passed through that turbine is rejected at 300. A second stage turbine 
output shaft is indicated at 231. 
A third stage rotary turbine is indicated at 329 and as communicating with 
the third stage rotary separator 326. Liquid separated by the separator 
326 is employed to drive turbine 329, in the same manner as in the 
described first and second stages. In this case, the liquid passing 
through the separator and turbine is typically fresh water, so that such 
water that is rejected by the turbine at 120a may be combined with fresh 
water stream 120. A turbine output shaft is indicated at 331. 
All the turbine stages 129, 229 and 329 may be located on a common shaft, 
or their shafts 131, 231 and 331 may be interconnected. Further, all 
separator and turbine stages in FIG. 2 may be coaxial. FIG. 2 also shows a 
parallel system 400 of separator turbine stages 1129, 1229 and 1329 
corresponding to stages 129, 229 and 329, with connections to condensers 
114 and 113 as shown. System 400 is otherwise the same as the FIG. 2 
systems described means, with corresponding elements preceded by an added 
digit. 
In a typical installation employing an internal combustion engine producing 
hot products of combustion at 700.degree. F., the sea water working fluid 
can be heated to 600.degree. F., and delivered to the first nozzle as 
saturated liquid water at 1534 psia. The intermediate stage temperature is 
a variable; and using the conservative assumptions incorporated in FIG. 3, 
this temperature can be chosen at 340.degree. F., giving a second stage 
pressure of 118 psia. The cycle illustrated has cycle efficiency of 23%. 
The overall cycle efficiency, defined as net turbine power output divided 
by net power output plus heat rejected, h.sub.c =P.sub.n /(P.sub.n 
+Q.sub.c), has been estimated for the waste heat conditions outlined 
above. This is plotted in FIG. 3 as a function of the intermediate stage 
temperature, and for various degrees of conservatism in the assumptions. 
The quality of entering fluid (percent steam), X, varies from 0 to 20. 
Turbine nozzle efficiency, h.sub.n, is taken as 80 to 90%, with turbine 
efficiency, h.sub.t, at 75% to 80%. The estimates, which represent 
currently demonstrated parameters, show cycle efficiency levels up to 23 
percent. This cycle efficiency competes with well-developed organic 
Rankine cycles (which do not deliver by-product water). 
The described cycle tranfers heat to the sea water at normal concentration. 
A special feature of the cycle is that the more concentrated brine 
contacts the nozzles and separators in a transistory manner which 
precludes corrosion. This has been domenstrated with highly corrosive 
geothermal brines. The cycle can be operated so that no water is 
evaporated from surfaces, to eliminate buildup and corrosion problems, at 
a slight sacrifice of cycle efficiency, i.e. the dotted curve in FIG. 3. 
The cycle is also readily scalable from very small sizes to very large 
sizes. 
In summary, the described marine cycle will conserve the "waste heat" of 
ship's engine exhaust gas, producing shaft power to run electrical 
auxiliaries and also fresh water. The shaft power produced is equivalent 
to that from the more complicated and expensive organic Rankine cycle 
boilers which do not deliver fresh water. 
Advantages also include: 
1. Low first cost; low operating cost. 
2. Simplicity, and reliability. Very few close tolerances required. 
3. No additional fluids required; no problems with toxid materials. 
4. Scalable in size. 
5. Efficient countercurrent heat exchange (smaller exchangers) because of 
reduced vaporization duty. 
6. Low turbine RPM (eliminates gearboxes). 
7. No concentrated brine handled in heat exchangers (relative to other 
water makers).