ENERGY RECOVERY SYSTEM AND METHOD
10 TECI-INICAL FIELD
The subject invention relates generally to an econolnical means for the conversion
of otherwise wasted heat energy produced by industrial furnaces into electrical energy.
More particularly, a system and method are disclosed for increasing the efficiency of a
steel mill plant by recovering part of the wasted heat energy and transforming it into
15 electrical energy that can be reused inside the same plant.
BACKGROUND OF THE lNVENTION
Steel mills incorporate different types of furnaces. Slab reheating furnaces,
annealing furnaces and other type of furnaces are typical in steel mill plants. The furnaces
20 in general have a relatively low efficiency and an important portion of the heat produced
as a result of the combustion of gas or other means, can't be transferred to the steel and is
finally dissipated into the atmosphere.
Steel mills are major consumers of electrical energy. Most of the power plants in
the world use fossil f~leltsh at generate C02 emissions. Therefore, it is important to
25 reduce the electrical energy consumption to minimize C02 emissions.
In some furnaces, a recuperator is included in the stack in order to heat the
combustion air for the fuel or gas that is used to produce the heat required by the process.
In other cases, the heat is used to heat water that is later used to heat buildings. A
schematic diagram of a typical such system known in the art is presented in FIG. 1 in
30 which primary exhaust gases 5 from furnace 10 are fed into a recuperator 15 through
which incoming air or liquids 20 are cycled so as to transfer and capture heat energy in
output air or liquids 25. The remaining secondary exhaust gases 30 are disposed of
through stack 35. Even though these systems normally recover a significant amount of
1
5 heat, some significant portion of the heat is still wasted by releasing hot gases to the
atmosphere. The temperature of these exhaust gases remain high enough to warrant
efforts to transform that heat energy into electrical energy.
SUMMARY OF THE INVENTION
10 The invention relates to a system and method for recovering otherwise wasted
energy generated in the form of waste gases as a byproduct of an industrial process.
Waste gases are produced by a fuel-powered device and these gases are expelled into an
exhaust structure. At least a part of these waste gases are diverted into a gas input of a
heat exchanger which also includes a gas output, a heat source liquid input and a heat
15 source liquid output. The input of an evaporator of an organic Rankine cycle (ORC)
system is connected to the heat source Liquid output of the heat exchanger while the output
of the ORC is connected to the heat source liquid input of the heat exchanger. The amount
of waste gases circulated through the heat exchanger and back into the exhaust structure
through the gas output in the gas circuit is regulated by an exhaust fan connected to a first
20 electric motor controlled by a first variable frequency drive (VFD). The amount of heat
source liquid circulated through the heat exchanger and an evaporator in the ORC in a heat
source liquid circuit is regulated by a pump connected to a second electric motor and a
second variable frequency drive (VFD). The heat source liquid incorporates a pressurized
expansion tank. A first controller which incorporates a Proportional-Integral regulator
25 monitors the operation of both the gas circuit and the heat source liquid circuit and
regulates the amount of gas and liquid, respectively, circulating through each circuit. A
second controller connected to the fuel-powered device provides data to the first controller
on the fuel consumption rate of the fuel-powered device. The fuel consumption data is
used by the first controller to regulate gas and heat source liquid flows. An expander in
30 the ORC is connected to a generator in the ORC and produces electricity which is
measured by a transducer.
The invention also relates to a method for regulating the generation of electrical
power from heated waste gases emitted from a fuel-powered industrial device using the
system described above. The optimum target temperature for the heat source liquid is
35 calculated based on a function having as input variables the temperature feedback of
5 heated gases entering the gas input of the heat exchanger and the device fuel consumption
as indicated by the second controller, if such data is available, added to the heat source
liquid initial target temperature. Then, a desired speed feed forward command for the first
VFD is further calculated based on a function having as input variables the optimal heat
source liquid temperature and a target speed reference for the second variable frequency
10 drive. Yet a further calculation is then made of a speed adjustment for the exhaust gases
fan based on the measured temperature of the heat source liquid and the proportional and
integral gains of the Proportional-Integral regulator incorporated into the first controller.
The target speed of the first VFD is then set along with its calculated maximum allowable
speed. If the fan speed target exceeds the maximum allowable speed, it is clamped to the
15 maximum allowable speed. Next, the target speed for the second VFD is subsequently
calculated based on a function having as input variables the heat source liquid target
temperature at the heat source liquid outlet of the heat exchanger and the temperature of
the ORC system cooling fluid based on a feedback signal from a temperature sensor. The
maximum allowable speed for the second VFD is determined based on a function having
20 as an input variable the power output of the ORC as measured by the transducer. If the
maximum allowable speed for the second VFD is exceeded, its target speed is clamped to
the allowed level. Until the fuel-powered device is shut down, the method returns to the
point where a determination is made whether fuel co~~sumptiodna ta is available.
2 5 BRIEF DESCRIPTION OF TIlE DRAWINGS
The foregoing and other objects, aspects and advantages of the invention will be
better understood from the following detailed description of the invention with reference
lo the drawings, in which
FIG. 1 is a schematic diagram of a gas heat recuperator system known in the art.
30 FIG. 2 is a schematic diagram showing the main elements of an industrial energy
recovery system.
FIG. 3 is a block diagram of the method used to implement the industrial energy
recovery system of this invention.
5 FIG. 4 is a schematic diagram of an alternative arrangement showing the main
elements of an industrial energy recovery system.
DETAlLED DESCRIPTION OF THE INVENTION
10 FIG. 2 illustrates in schematic diagram form the functional elements of the system
of this invention. The same elements are present as shown in FIG. 1 but, in addition,
furnace controller 40 is required to monitor the operation of furnace 10 and to provide data
concerning furnace fuel consumption to controller 90, as discussed below. Tap 45 is
added to divert at least a portion of the secondary exhaust gases 30 prior to their
15 evacuation through an exhaust structure such as stack 35 into a tertiary exhaust gas stream
50. Tap 45 feeds tertiary exhaust gas stream 50 into first heat exchanger 55. This heat
exchanger is designed based on the temperature range of the exhaust gases, the acceptable
temperature range for the heat source liquid, the amount of heat to be transferred to the
heat source liquid and the acceptable pressure drop on both circuits that will provide an
20 economic solution based on the cost of the heat exchanger and the energy to be consumed
by exhaust gases fan and the heat source liquid circulating pump. The material of the heat
exchanger has to be suitable for the chemical composition of the exhaust gases. Tertiary
exhaust gas stream 50 is circulated through first heat exchanger 55 by using exhaust gases
fan 60 which is driven by first electric motor 65 controlled by first variable frequency
25 drive (VFD) 70. Exhaust gases fan 60 is sized to overcome the pressure drop introduced
by first heat exchanger 55 under the maximum capacity (maximum flow) of the system
and for the suction of the exhaust gases from slack 35. In case of a shut down, exhaust
gases fan 60 is stopped so that the gases stop circulating through first heat exchanger 55.
The heat source medium used by heat exchanger 55 is a liquid, such as water, water and
30 glycol mix, thermal oil or equivalent, since these types of fluids have a larger thermal
capacity than exhaust gases and allow efficient transfer of heat to Organic Rankine Cycle
(ORC) system 130 within its acceptable working temperature range. First temperature
sensor and transmitter 75 is located at the input of tertiary exhaust gas stream 50 into first
heat exchanger 55 and measures the temperature of entering hot gases. Second
35 temperature sensor and transmitter 80 monitors the temperature of liquid exiting first heat
4
5 exchanger 55. The temperature data measured by the two sensors is transmitted to
controller 90 which may be a commercially available programmable logic controller
(PLC) or similar device and is used to regulate the temperature and flow of the heat source
liquid by changing the speed target of first VFD 70 which controls first electric motor 65.
The heat source liquid circuit incorporates heat source liquid circulating pump 95
10 which maintains the proper flow of liquid through ORC system 130 and may be of either a
fixed or variable speed type. Second electric motor 100, which may be either a fixed or
variable speed electric motor, is coupled to liquid circulating pump 95 and is controlled by
second VFD 105 in the case of a variable speed pump. Second VFD 105 is, in turn,
regulated by controller 90. This system is properly sized to overcome the maximum
15 pressure drop expected under the maximum possible flow of the heat source fluid. The
heat source liquid circuit incorporates heat source liquid expansion tank 115 which is
pressurized with inert gas 120 such as is typically available at a steel mill in which this
invention may be used and includes pressure relief valve 110 connected to the expansion
tank 115. Third sensor 125 is a pressure sensor located in the high temperature side of the
20 heat source circuit and functions to monitor the pressure. Evaporator 132, which is part of
ORC system 130, completes the heat source liquid circuit.
Steel plants typically have a plant water supply kept at a controlled temperature for
cooling purposes. Part of this water supply 160 can be diverted and incorporated into heat
sink circuit 134 which is part of ORC 130. In the event that a variable speed heat source
25 liquid circulation pump 95 is used rather than a fixed speed one, additional temperature
sensor and transmitter, such as fourth sensor 165, is required to measure the temperature
of the cooling medium. This temperature is required to calculate a reference for second
VFD 105 to regulate the speed of heat source liquid circulating pump 95. This additional
sensor can be included as a part of the ORC system or added externally. Based on the
30 values of this temperature variable and the heat source liquid target temperature, controller
90 modifies the pump speed reference in order to maintain the maximum possible output
power and efficiency of the system. When the temperature of the ORC system 130
cooling media andlor the target temperature for the heat source liquid changes, the system
will modify the flow of the heat source liquid in an attempt to maintain the power
35 generated and the ORC eficiency at the maximum possible values.
5 ORC system 130 used in this invention can be any one of several presently
commercially available ORC systems. Expander 135 of such a system is coupled to
generator 140 which is itself connected to the steel mill plant electrical distribution system
through properly sized electrical feeder 145 and corresponding circuit breaker 150. The
electrical power output of ORC system 130 is monitored by electrical active power
10 transducer 155 and the resulting data is transmitted to controller 90. The purpose of power
transducer 155 is to function as a protective device. Different protection levels can be set.
For example, in case of excessive power being generated by the system, controller 90 can
be programmed to reduce the speed of exhaust gases fan 60 in order lo reduce the heat
transferred or to stop the operation of exhaust gases fan 60 completely under pre-
15 designated circumstances. Some commercially available ORC systems also incorporate a
by-pass valve for the heat source fluid as a protection. In the went an upstream electrical
interruption occurs, such as through tripping of a circuit breaker, and generator 140 is
disconnected from the distribution network, protection would also be required. In this
case, active power transducer 155 will indicate zero power and a stop exhaust gases fan 60
20 sequence will also be initiated. If the liquid pressure exceeds a predetermined certain
value, detected by third sensor 125, the target reference of first VFD 70 for exhaust gases
fan 60 will be reduced as a measure to slow down the heat transfer that could be
contributing to high pressure. In the event of sensing of a predetermined greatly excessive
pressure, pressure relief valve 110 will actuate and the corresponding signal will be used
25 to shut down the system, by reducing the speed target of first VFD 70 for exhaust gases
Ian 60 to zero.
FIG. 3 is a block diagram of the method used to implement an industrial energy
recovely system. The system uses software code stored in controller 90 to calculate speed
targets of first VFD 70 for exhaust gases fan 60 and of second VFD 105 for heat source
30 liquid circulating puii~9l~5 which will inaximize the generated power and ~nainlaiilth e
process temperatures and flows within the design parameters of the components of the
system. The temperature of the exhaust gases and the corresponding flow are a direct
result of the fuel consumption of furnace 10. When the furnace changes from idle to full
load operation or vice versa, there is a time delay before the temperature of the exhaust
35 gases reaches the steady state temperature. This information is included in the model that
calculates the temperature target T* for the heat source liquid. This temperature target T*,
6
5 the corresponding temperature feedback of the heat source liquid Tho obtained from
lemperature sensor 80 located at the outlet of heat exchanger 55 and the flow of the heat
source liquid, which is calculated fiom the speed target n* of second VFD 105 for heat
source liquid circulating pump 95, are used to calculate the speed target of first VFD 70
for exhaust gases fan 60. Furnace controller 40 can provide furnace fuel consumption
10 data, Fuel-C. If so, that data is retrieved and transmitted to controller 90 at 305. A
determination is made at 300 whether furnace 10 has been operating for a sufficiently long
period of time. This data along with the initial target temperature TI* (a parameter stored
in controller 90) are used to calculate the optimum heat source liquid target temperature at
310 using the formula T* = KO(Thg,Fuel-C) + T1 * in which T* is the optimum target
15 temperature for the heat source liquid, KO(Thg.Fue1-C) is an interpolation block or a
function having as input variables the temperature feedback of hot gases entering the
system (Thg.) and the furnace fuel consumption (Fuel-C) which may or may not be
available, and TI * is the heat source liquid initial target temperature TI * stored as a
parameter in controller 90. As the temperature ofthe gases or fuel consumption rise, KO
20 will assume higher values until it reaches a preset limit. If either the furnace fuel
consumption data or temperature feedback of hot gases entering the system (Thg) or both
are not available, KO will be simplified accordingly. If furnace 10 fuel consumption data
is not available, then the optimal temperature T* is calculated at 320 based on the formula
T* = KO(Thg) + TI *. Using the calculated optimal temperature, T*, the desired speed
25 feed forward command of first VFD 70 for exhaust gases fan 60 is hrther calculated at
325 using the formula F*ff = KI(T*,n*) where F*ff is the exhaust gases fan speed
expressed as a feed-forward command and K I (T*,n*) is obtained from an interpolation
block or function having as input variables the calculated optimal heat source liquid
temperature, T* and the target speed reference n* for second VFD 105 of heat source
30 liquid circulating pump 95. The atnount of the speed adjustment is calci~laleda t 335
according to the formula F*c = (Kp + Ki/s).(T*-Tho) where F*c is the exhaust gases fan
speed target compensation, Tho is the heat source liquid temperature as measured by
second sensor 80 of liquid leaving heat exchanger 55 and Kp and Ki are the proportional
and integral gains of the exhaust gases fan speed regulator which correspond to a typical
35 proportional and integral (PI) regulator although other types of regulators may also be
used for this purpose. The term 11s is an operator known in the art that corresponds to an
7
5 integrator and is derived from applying the Laplace transformation to the solution of
differential equations. After the compensation F*c is calculated, the target speed F* of
first VFD 70 for exhaust gases fan 60 is set at 340 according to the formula F* = F*ff -t
F*c, and the maximum allowable speed F*max of first VFD 70 for exhaust gases fan 60 is
calculated according to the Sormula F*max = K2(T*,P,Pr) where F*max is the maximum
10 allowable fan speed reference of the VFD 70 and K2(T*,P,Pr) is an interpolation block or
function having as input variables the heat source liquid target temperature T*, the output
power feedback of the ORC system in kilowatts P as measured by transducer 155 and a
feedback signal from third sensor 125 representing the pressure Pr of the heat source
liquid. The funclion K2 can be simplified in case the P or Pr variables are not available. It
15 is desirable to know F*max in order to avoid running the exhaust gases fan at an excessive
speed and to prevent excessive heat source liquid pressure in the system. A comparison of
F* with F*max at 350 establishes whether the exhaust fan speed target is too high. If so,
the exhaust gas fan speed target is adjusted at 355 so that F* = F*max. Afterwards,
processing continues at 360 where the speed target n* of second VFD 105 for heat source
20 liquid circulating pump 95 is calculated according to the formula n* = K3(T*,Tc) + n I *
where K3(T*,Tc) is obtained from an interpolation block or a function based on the input
variables T*, for heat source liquid target temperature at the outlet of the heat exchanger
as calculated at 310 and Tc for the temperature of the ORC system cooling fluid based on
a feedback signal from fourth sensor 165 and where n 1 * is the base speed target of second
25 VFD 105 for heat source liquid circulating pump 95. When the ORC cooling fluid
temperature andlor the target temperature of the liquid heat source liquid change, K3 will
change in order to maintain the power generated and the efficiency of the ORC system 130
at the maximum possible values. The maximum allowed speed target of second VFD 105
Sor heat source liquid circulating pump 95 is calculated at 365 according to the formula
30 n*max = K4(P) where K4(P) is an interpolation block or a funclion for which the only
input variable is the output power of ORC 130 as measured at transducer 155. If the target
pump speed n* exceeds the maximum permissible pump speed n*max as determined at
370, a limit is imposed on the speed target of second VFD 105 for circulating pump 95 at
375 to reduce that speed. This method represents a control loop which is in constant use
35 when the furnace is running.
5 In FIG. 4, an alternative arrangement of the functional elements of the system of
this invention is presented in a schematic diagram form. In this arrangement, exhaust
gasses fan 60, first electric motor 65 and first variable frequency drive 70 are eliminated.
Instead, valve 170 is incorporated at exhaust gas tap 45 where a portion of the exhaust
gases exiting recuperator 15 are first diverted into the energy recovery system, heat
10 exchanger 55. Valve 170 is regulated by controller 90 so as to change the flow of exhaust
gases into the energy recovery system in a manner similar to that described above for
providing a fan speed target of VFD 70 for exhaust gases fan 60.
The foregoing invention has been described in terms of a preferred embodiment.
However, it will be apparent to those skilled in the art that various modifications and
15 variations can be made to the disclosed apparatus and method without departing from the
scope or spirit of the invention and that this invention has applicability to many other
industrial processes besides steel manufacturing in which hot exhaust gases are produced,
such as, for example, cement plants and power generation. The specification and
examples are exemplary only, while the true scope of the invention is defined by the
20 following claims.

AMENDED CLAIMS
received by the International Bureau on 06 December 2010 (06.12.2010)
10 I. A sysbnl for converting excess energy gcncrated as a byproducl of a fucl-
'powered industrial process in the form of heated exhaust gases directed to an exhaust
structure into electrical energy comprising:
a heat exchanger located outside of the exhaust structure having a gas input
arid a gas output, each connected to the exhaust structure, and having further a heat source
15 liquid input and a hcat source liquid output; ,
nn orgahic Rankine cycie (OW) system having a fi'lrst input connected to'
the heat source liquid output of said heat exchanger and a first output connected to the heat
source liquid input of said heat exchanger, said ORC system further having a gcneratur
delivering electric power to a second output of said ORC systcm;
20 gas circulating means tor regulating the temperature of the liquid heat
source by diverting a portion of the exhaust gases out of and away from the exhaust
structure towards said heat exchanger and by changing the amount of gases circulated
between the exhaust structure and the gas input and the gas output of said heat exchanger;
and
25 heat source liquid circujating means for reeulating the hcat transfer to said
ORC system by changing the arnou~o~ft liquid circulated between mid OKC system and
.wid heat exchanger.
2. A system for converting excess energy generated as a byproduct of a fuel-
30 powered industrial process in the form of heated exhaust gws directed to an exhaust
structure into electrical cnergy comprising:
a heat exchanger located outside of the exhaust structure having s gas input,
a gas output, a heat source liquid input and a heat source liquid output;
first means for diverting ;r part of the heated exhaust gases out of and away
35 from the exhaust structure into the gas input of said heat exchanger;
'18
AMENDED SHEET (ARTICLE 19)
5 second means connected to the gas output of said heat exchanger for
regulating the circulation through and exit of the exhaust gases from said heat exchanger
through a vent back into the exhaust structure ;
third mealis for supplying and regulating the flow of heat source liquid to
the heat source liquid input of said heat exchanger; and
10 an organic Hankine cycle (ORC) system having n tirst input connected to
the heat source liquid output orsaid heat exchanger and a first output connected to the heat
source liquid input of said heat exchanger through said third means, said ORC system
further httving s generator delivering electric power to a second output of said ORC
system.
15
3. 'Ihe system of clailn 2 wherein said first means comprises a tap connected at its
input to the exhaust structure and at its output to the gas input of said heat exchanger.
4. The system of claim 2 wherein said second means comprises;
20 an exhaust gases fan connected to the vent;
a tirst electric motor connected to said exhaust gases fan;
a first variable frequency drive connected to said first clectric motor; and
first controller means connected to said first variable frequency drive for
monitoring and regulating said tirst variable frequency drive.
25
5. The system of claim 4 wherein said second means further cornpriscs:
sccohd controlier means wnnected to said first controlier means for
monitoring fuel consumption data of the industrial process and transmitting that dala to
said first controller means;
30 first sensor means connected to the gas input of said hcat exchanger for
measuring thc temperature of the exhaust gases at that point and for transmitting that data
to said first controller means;
second sensor means connected to the heat source liquid output of said heat
exchanger far measuring the temperature of the liquid at that point and for transmitting
35 that data to said first controller mcans;
11
AMENDED SHEET (ARTICLE 19)
5 third sensor means connected to the heat source liquid output of said heat
cxchanyer for measuring the pressure of the heat source liquid at that point and for
transmitting that data to said first controller tneans; and
o protective power transducer connected between the second output of said
ORC system and said tirst controller means.
10
6. The system of claim 5 whercin said third mews comprises:
a pressurized heat source liquid expansiotl tank;
a pressure relief valve connected to said expansioti tank and to said first
controller meatis;
15 variable speed circulating pump means connected at its input to said
expansion tank and at its output to the heat source liquid input of said heat exchanger for
changing the flow ofthe heat source liquid in order to control the heat transferred from the
heat source liquid to the ORC;
a second electric motor con~~ectetod said pump;
20 a sccond variable frequency drive connected to said second electric motor;
and
tburth scnsor means connected to said ORC for measuring the temperature
of the cooling mcdium used by said ORC,
and wherein further said second variable frequency drive is further connected to said first
25 controller means.
7. The system of claim 5 wherein said third means cornprism:
a pressurized heat source liquid expansion tank;
a pressure relief valve connected to said expansion tank and to said first
30 controller mans;
a tixcd sped circulating pump connected at its input to said cxpnsion tank
ahd at its aulput to the hcat source liquid input of said heat exchanger; and
a second electric motor connected to said pump.
35 8, The system of claim 3 wherein said first means w~npriscsa n adjustable valve
connected to said tap, the movement of which is controlled by a first controller.
m
AMENDED SHEET (ARTICLE 19)
5
9. A method for regulating the generation of electricdl power from h ?ated waste
gases emitted from a fuel-puwcrcd industrial device into an exhaust st~uctu:i u sing a hcat
exchanger located away fmm the cxhaust structure having a gas input conneir~edto the
exhaust slructurc: and a gas output connected to a variable speed exhaust fan w. ich is itself
10 conned to the exheust structure and having further an organic Rankine cycle (ORc;
systeln with an evaporator having a heat source liquid input connected to a liquid outp~ot f
the hent exchanger and a heat source liquid output wnneckd to a pressurized source of
liquid further cohnwted to a pump and thereafter to a liquid input of the hent exchanger
wherein the ORC incorporates an expnnder coupled to a generator having an electrical
15 output connected to a trnnsducer comprising:
diverting a portion of the waste gases away from the exhaust structure into
the gas input of the heat exchanger;
regulding the heat source iiquid remprature by changing the amount of
the waste gases so diverted by vsrying the speed of the exhaust fan;
20 controlling the amount of heat transferred from the heat source liquid to the
ORC by changing the flow of the liquid circulated between the ORC system and the heat
exchanpr by managing the operation of the pump; and
monitoring at the transducer the amount of electricity guncrated by the
generator at the electrical output tbr purposes of either or both controlling the maximum
25 speed of the exhaust fan and protecting the generator and the ORC system.
10. The mcthod of claim 9 wherein the pump may be either a variable speed or a
fixed speed pump.
30 I I . A method for egulating the production of electrical power from heated waste
gases generated as a byproduct of a fucl-powered industrial device wherein a part of the
waste gases are diverted at a ternperaturc measured by a first sensor into a gas input of a
heat exchanger before being expelled from a gas output of the first heat exchanger into an
exhaust structure, thc circulation of the waste gases through the heat exchanger being
35 regulated by at1 exhaust gases fan driven by a first electric motor the sped of which is
conlwlled by a first variable frequency drivc (VFD) itself further controlled by a first
B
AMENDED SHEET (ARTICLE 19)
5 controller incorporating a Proportional-Integral rcgulator, said tirst controller hing
connected to a second controller further connected to the fuel-powered device for
monitoring fuel consumption and to the first sensor and wherein further a heat source
liquid is delivcrcd to a liquid input of the hcat exchanger before being expelled fmm a
liquid output of the heat exchanger into a heat source liquid circuit at a temperature
10 measured by o second sensor and a pressure measured by o third sensor both of which
sensors bcing connected to the first controller, the circulation of the heal source liquid
through the heat exchanger being regulated by a pump driven by a sccond electric motor
the speed of which is controlled by a second variable frequertcy drive (VFD) itself further
controlled by the first controller, while the heat so11rr;e liquid pump inlet is also connected
15 to a liquid expansion tank subject to pressurization with inert gas, the pressure of which is
monitored by the third sensor, the expansion tank also including a pressure relief valve
monitored by the first controller, the heat source liquid expelled from thc liquid output
being then dircctcd through an cvilporator located in an organic Rankine cycle (ORC)
system incorporating a hetit sink circuit having a fourth sensor connected to the tirst
20 controller tbr measuring the bmpemture of the ORC cooling medium, an expander
connected to a generator and a power transducer connected between the generator and the
second controller comprising:
ascertaining tlrst whether data representing the fuel consumption of the fuel
powered industrial device is available from the first controller;
25 if so, calculating an optinlum target temperature for the heat source
liquid according tu the fornlula T* = KO(Thg,Fuel-C) t. TI* whew KOCl'hy.Fue1-C) is an
interpolation block or a function hnving as inpul variables the temperature feedback of
healod gases entering the gas input (Thg.) and the device fuel consumption (Fuel-C), and
TI * is the heat source liquid initial target temperature stored as a variable in the second
30 controller;
otherwise calculating an optimal target temperature for the hcat
source liquid according to the formula T* = KO(Thy) + TI *;
*
further colculnting a desired speed feed forward command for the tirst
variable frequency drive according to the formula FSff = KI(Tb,n*) where F*fT Is the
35 exhaust gases fati speed expre-d as a feed-forward command and K I(T*,nY) is an
interpolation block or function having as input variables the calculated optimal heat source
4Y
AMENDED SHEET (ARTICLE 19)
5 liquid temperature, T* and a target speed ieference n* for the second variable frequency
drive;
yet titrther calculating a speed adjuslrnant nccording to the formula F*c =
(Kp + Ki/s),(T"Tho) where FYc is the exhaust gases fan speed target compensation, Tho
is the hcat source liquid temperature as measured by the second sensor and Kp and Ki are,
10 respectively, the proportional and integral gains of the Proprotional-Integral regulator;
setting the target speed of the tirst variable frequency drivc according to the
formula F* = F*ff + F*c;
further setting the maximum ollowablc speed of the first variable frequency
drive according to the tbrmula F'max = K2(Tf,P,Pr) where KZ(T*,P,Pr) is an
15 interpolatiot~b lock or function having as input variables the hcat source liquid target
temperature T*, the output power feedback of the ORC system in kilowrrtts P as measured
by the transducer and Pr is a feedback signal from the third sensor representing the
pmssure of the heat source liquid circuit;
detennining whether F* > Famax;
20 if so, limiting the exhaust fan speed such that F*=F*rnax;
otherwise, calculating additionally thc target speed n* for the second
vnriable frequency drive according to the formula n* = K3(TS,Tc) I- n I where K3(T*,Tc)
is an interpolation block or a function based on the input variables TS representing the heat
source liquid target temperature at the outlet of the heat exchanger and Tc representing the
25 temperature of the ORC system cooling fluid based on a feedback signal from thc fourth
sensor and where n 1 * is the base speed target of the second VFL);
further determining the maximum allowable specd for the second VPD
according to tho formula n*mw = K4(P) where K4{P) is an interpotation block or a
function for which the input variable is the output power P of the ORC as measured by the
30 tratisducer;
ascertaining further whuther n*>n*rnax;
ifso, limiiing the pump sped such that n* = nqmax; and
&erwiw, until the fuel powered device is no longer in operation, returning
Dated this 12/06/20 12
ATTORNEY FOR THE APPL ~ T [ S I