Distributed system for optimizing the performance of a plurality of multi-stage steam turbines using function blocks

A system for optimizing the performance of a plurality of energy conversion devices is disclosed. Measurements of fluid flow into and out of the energy conversion devices, the efficiencies of the conversion devices and the power produced by the conversion devices are used as inputs to function blocks in a logic arrangements. The function blocks cause a decrease in load demand to be applied to the energy conversion device having the lowest efficiency and an increase in load demand to be applied to the energy conversion device having the highest efficiency.

TECHNICAL FIELD 
The present invention relates generally to a system for optimizing the 
performance of a plurality of energy conversion devices, such as turbines, 
and more particularly to a system which optimizes the operation of these 
devices by means of fixed function blocks. 
BACKGROUND ART 
Typically, optimization of the performance of a plurality of energy 
conversion devices, such as turbines, is achieved only through the use of 
computers and extensive computer programs. Such computer systems have some 
inherent disadvantages. For example, the computer programs usually use a 
"high level" language which requires expensive hardware and software to 
implement. Such a "high level" language usually results in a relatively 
long processing time for determining operation optimization. In addition, 
such computer systems typically require highly trained personnel to 
program and operate same. Thus, the computer system that is required for 
the optimization calculations is very costly to install and operate, and 
may not react to changes in the operation of the turbines as rapidly as 
desired. 
Because of the foregoing, it has become desirable to develop a system for 
optimizing the operation of a plurality of turbines or other energy 
conversion devices without the use of a computer system. 
SUMMARY OF THE INVENTION 
The present invention solves the aforementioned problems associated with 
the prior art as well as other problems by utilizing function blocks 
having fixed functional relations to provide the calculating features, 
which are generally only available through the use of computers, to 
determine the manner in which the turbines should be loaded to effect 
optimization of the overall system. Measurements of fluid flow into and 
out of the turbines, the power produced by the turbines, and the 
efficiencies of the turbine stages are processed through the use of 
function blocks to determine the efficiencies of the extraction flows. 
When there is a decrease in load demand, the load is assigned to the 
extraction flow with the lowest overall efficiency, whereas when there is 
an increase in load demand, the load is assigned to the extraction flow 
with the highest efficiency. In this manner, the efficiency of the overall 
system is optimized.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings where the illustrations are for the purpose 
of describing the preferred embodiment of the present invention and are 
not intended to limit the invention thereto, FIG. 1 is a schematic diagram 
of a pair of multi-stage turbines 10, 12 showing their respective 
connections to an input steam supply conduit 14, extraction flow conduits 
16, 18, and to a steam condenser conduit 20. By-pass valves 22, 24 are 
provided between the supply conduit 14 and extraction flow conduit 16, and 
between the extraction flow conduits 16 and 18, respectively. In one 
instance the objective is to optimize performance of the turbines 10, 12 
based upon steam demand. In this case, the demands of the extraction flows 
X.sub.m and X.sub.l of conduits 16 and 18 are specified and the power 
outputs W.sub.1 and W.sub.2 of the respective turbines 10, 12 are 
optimized so as to achieve the maximum output power (W=W.sub.1 +W.sub.2) 
therefrom. In this instance, during normal operating conditions the 
extraction flow X.sub.c through conduit 20 and the steam flows X.sub.pm 
and X.sub.pl through valves 22 and 24, respectively should be zero. When 
the extraction flows from the turbines 10, 12 reach their limits, any 
additional steam demands are met by the opening of the by-pass valves 22 
and 24. In the other instance, the objective is to optimize performance of 
the turbines 10, 12 based upon megawatt demand. In this case, the megawatt 
demand W=W.sub.1 +W.sub.2 is specified and the overall steam usage is 
minimized while the steam needs of X.sub.m and X.sub.l of conduits 16 and 
18 are satisfied. In this instance, during normal operating conditions the 
steam flows X.sub.pm and X.sub.pl through valves 22 and 24, respectively 
should be zero. Here again, when the extraction flows from the turbines 
10, 12 reach their limits, any additional steam demands are satisfied by 
the opening of the valves 22 and 24. 
Referring now to FIG. 2, which is a schematic diagram of the logic utilized 
to effect optimization of the operation of the turbines, measurements of 
steam flow X and power output W are used as inputs to a limit setting 
module 26. The function blocks comprising this module 26 are shown in FIG. 
3. In this Figure, flow transmitters 28 are provided to measure the output 
flows X.sub.1m, X.sub.2m . . . from each stage of the turbines 10, 12 and 
power transmitters 30 are provided to measure the respective output power 
W.sub.1, W.sub.2 produced by each of these turbines. In addition, flow 
transmitters 32 and 34 are provided to measure the flow into the turbines 
and through the by-pass valves, respectively. Considering only the turbine 
10, the output flow from the first stage thereof, i.e., output flow 
X.sub.1m, as measured by flow transmitter 28, is applied to the negative 
input to a subtraction function block 36. The other input to the 
subtraction function block 36, which is applied to the positive input 
thereto, is a preset maximum limit for output flow from this turbine 
stage. The output of this subtraction function block 36 is used as the 
input to a function generator 38 which produces an output signal F.sub.1m 
(.DELTA.), as shown in FIG. 4, equal to zero when the output of the 
subtraction function block 36 is negative, thus indicating that the output 
flow from the first turbine stage is above the preset maximum limit, and 
produces an output signal F.sub.1m (.DELTA.) equal to positive one when 
the output of the function block 36 is positive, this indicating that the 
output flow from the first turbine stage is below the preset maximum 
limit. 
The output flow from the first stage of turbine 10, i.e., output flow 
X.sub.1m, as measured by flow transmitter 28, is also applied to the 
positive input to a subtraction function block 40. The other input to this 
function block 40 is a preset minimum limit for output flow from this 
turbine stage, and this minimum limit is applied to the negative input to 
this function block 40. The output of this function block is used as the 
input to a function generator 42 which produces an output signal F.sub.1m 
(.DELTA.), as shown in FIG. 4, equal to a large positive number G when the 
output of the subtraction function block 40 is negative, this indicating 
that the output flow from the first turbine stage is below the preset 
minimum limit, and produces an output signal F.sub.1m (.DELTA.) equal to 
positive one when the output of the function block 40 is positive, thus 
indicating that the output flow from the first turbine stage is above the 
preset minimum limit. 
Again considering only turbine 10, the input flow thereto, i.e., X.sub.1t, 
as measured by the flow transmitter 32, is applied to the negative input 
to a subtraction function block 44. The other input to this function block 
44, which is applied to the positive input thereto, is a preset maximum 
limit for input flow into this turbine. The output of this function block 
44 is used as the input to a function generator 46 which produces an 
output signal F.sub.1t (.DELTA.), as shown in FIG. 4, equal to zero when 
the output of the subtraction function block 46 is negative, thus 
indicating that the input flow into the turbine 10 is above the preset 
maximum limit, and produces an output signal F.sub.1t (.DELTA.) equal to 
positive one when the output of the function block 46 is positive, thus 
indicating that the input flow to the turbine 10 is below the preset 
maximum limit. 
The input flow to the turbine 10, i.e., X.sub.1t, as measured by the flow 
transmitter 32, is also applied to the positive input to a subtraction 
function block 48. The other input to this function block 48 is a preset 
minimum limit for input flow to this turbine 10, and this minimum limit is 
applied to the negative input to this function block 48. The output of 
this function block 48 is used as the input to a function generator 50 
which produces an output signal F.sub.1t (.DELTA.), as shown in FIG. 4, 
equal to a large positive number G when the output of the subtraction 
function block 48 is negative, thus indicating that the input flow into 
the turbine 10 is below the preset minimum limit, and produces an output 
signal F.sub.1t (.DELTA.) equal to positive one when the output of the 
function block 48 is positive, thus indicating that the input flow into 
the turbine is above the preset minimum limit. 
As noted in FIG. 3, the foregoing approach can be used to find F.sub.2m 
(.DELTA.) and F.sub.2m (.DELTA.) for the output flow from the first stage 
of turbine 12, F.sub.2t (.DELTA.) and F.sub.2t (.DELTA.) for the input 
flow to turbine 12, F.sub.pm (.DELTA.) and F.sub.pm (.DELTA.) for the flow 
through by-pass valve 22, F.sub.w1 (.DELTA.) and F.sub.w1 (.DELTA.) for 
the power produced by turbine 10, and F.sub.w2 (.DELTA.) and F.sub.w2 
(.DELTA.) for the power produced by turbine 12. In each case, if the 
parameters are within the preset limits, the foregoing output signals are 
equal to positive one. 
Referring to FIG. 2, the foregoing output signals produced by the limit 
setting module 26 are applied as inputs to a limit sequence module 52. The 
function blocks comprising this limit sequence module 52 are shown in FIG. 
5. As shown in this Figure, the output signal F.sub.1m (.DELTA.) produced 
by the function generator 42 is used as an input to a multiplication 
function block 54 whose other input is the output signal F.sub.1t 
(.DELTA.) produced by the function generator 50. The output signal 
produced by the multiplication function block 54 is used as an input to a 
multiplication function block 56 whose other input is the signal F.sub.w1 
(.DELTA.) which represents the low limit for the power produced by the 
turbine 10. Similarly, the output signal F.sub.1m (.DELTA.) produced by 
the function generator 38 is used as an input to a multiplication function 
block 58 whose other input is the output signal F.sub.1t (.DELTA.) 
produced by the function generator 46. The output signal produced by the 
multiplication function block 58 is used as an input to a multiplication 
function block 60 whose other input is the signal F.sub. w1 (.DELTA.) 
which represents the high limit for the power produced by the turbine 10. 
Assuming that the input flow to the turbine and the power produced by the 
turbine are within the preset maximum and minimum limits, i.e., input 
signals F.sub.1t (.DELTA.), F.sub.1t (.DELTA.), F.sub.w1 (.DELTA.) and 
F.sub.w1 (.DELTA.) are all equal to a positive one, then the output 
signals produced by multiplication function blocks 56 and 60 are as 
follows: 
______________________________________ 
Output of Function 
Output of Function 
Block 56 [F.sub.1m (.DELTA.)] 
Block 60 [F.sub.1m (.DELTA.)] 
Condition 
______________________________________ 
G 1 X.sub.1m .ltoreq. X.sub.1m 
1 1 X.sub.1m &lt; X.sub.1m &lt; X.sub.1m 
1 0 X.sub.1m .gtoreq. X.sub.1m 
______________________________________ 
It should be noted that the foregoing analysis, with similar results, can 
be obtained for F.sub.2m (.DELTA.) and F.sub.2m (.DELTA.) for the output 
flow from the first stage of the turbine 12. 
As shown in FIG. 2, the foregoing output signals produced by the limit 
sequence module 52 are used as inputs to a load limit module 62. The 
function blocks comprising this load limit module 62 are shown in FIG. 6. 
As shown in this Figure, the output signal F'.sub.1m (.DELTA.) produced by 
the multiplication function block 56 is used as an input to a 
multiplication function block 64 whose other input is the efficiency 
.eta..sub.t1m of the first stage of the turbine 10 causing a signal 
n'.sub.t1m to be produced at the output thereof. Similarly, the output 
signal F'.sub.2m (.DELTA.) is used as an input to a multiplication 
function block 66 whose other input is the efficiency .eta..sub.t2m of the 
first stage of the turbine causing a signal .eta.'.sub.t2m to be produced 
at the output thereof. And lastly, the signal F.sub.pm (.DELTA.) is used 
as an input to a multiplication function block 68 whose other input is the 
efficiency .eta..sub.pm of the by-pass valve 22 causing a signal 
.eta.'.sub.pm to be produced at the output thereof. The foregoing output 
signals .eta.'.sub.t1m, .eta.'.sub.t2m, and .eta.'.sub.pm , represent load 
decrease limiters on demand decrease. 
The first stage efficiency .eta..sub.t1m of the turbine 10 is also used as 
an input to a multiplication function block 70 whose other input is the 
output signal F'.sub.1m (.DELTA.) produced by the multiplication function 
block 60 causing a signal .eta.".sub.t1m to be produced at the output 
thereof. Similarly, the first stage efficiency .eta.'.sub.t2m of the 
turbine 12 is also used as an input to a multiplication function block 72 
whose other input is the signal F'.sub.2m (.DELTA.) causing a signal 
.eta.".sub.t2m to be produced at the output thereof. And lastly, the 
efficiency .eta.'.sub.pm of the by-pass valve 22 is also used as an input 
to a multiplication function block 74 whose other input is the signal 
F.sub.pm (.DELTA.) causing a signal .eta.".sub.pm to be produced at the 
output thereof. The foregoing output signals .eta.".sub.t1m, 
.eta.".sub.t2m and .eta.".sub.pm, represent load increase limiters on 
demand increase. 
Again referring to FIG. 2, the foregoing output signals produced by the 
load limit module 62 are used as inputs to a low and high selector and 
load allocation module 76. The function blocks comprising this low and 
high selector and load allocation module 76 are shown in FIG. 7. As 
illustrated in this Figure, the output signals .eta.'.sub.t1m, 
.eta.'.sub.t2m and .eta.'.sub.pm produced by multiplication function 
blocks 64, 66 and 68, respectively are used as inputs to a low limit 
function block 78 which produces an output signal equal to the smallest of 
the foregoing input signals. This output signal is then applied to the 
negative inputs to subtraction function blocks 80, 82 and 84 whose 
positive inputs are connected to the outputs of multiplication function 
blocks 64, 66 and 68, respectively. In this manner, the value of the 
smallest of the foregoing input signals, .eta.'.sub.t1m, .eta.'.sub.t2m 
and .eta.'.sub.pm, is subtracted from each of these input signals to 
produce a signal 1'.sub.m, 2'.sub.m and pm' at the output of subtraction 
function blocks 80, 82 and 84, respectively. Inasmuch as the value of the 
smallest input signal is subtracted from each of the input signals, one of 
the output signals, 1'.sub.m, 2'.sub.m and pm', will be zero, while the 
other two output signals will be positive. The output signal which is zero 
will be associated with the turbine stage or by-pass valve having the 
lowest efficiency. Similarly, the output signals .eta.".sub.t1m, 
.eta.".sub.t2m and .eta.".sub.pm produced by multiplication function 
blocks 70, 72 and 74, respectively are used as inputs to a high limit 
function block 86 which produces an output signal equal to the largest of 
the foregoing input signals. This output signal is then applied to the 
positive inputs to subtraction function blocks 88, 90 and 92 whose 
negative inputs are connected to the outputs of multiplication function 
blocks 70, 72 and 74, respectively. In this manner, each of the input 
signals, .eta.".sub.t1m, .eta." .sub.t2m and .eta.".sub.pm, is subtracted 
from the largest of these signals to produce a signal 1m", 2m" and pm" at 
the output of subtraction function blocks 88, 90 and 92, respectively. 
Inasmuch as each of the input signals is subtracted from the largest of 
the input signals, one of the output signals, 1m", 2m" or pm", will be 
zero while the other two output signals will be positive. The output 
signal which is zero will be associated with the turbine stage or by-pass 
valve having the highest efficiency. 
The low and high selector and load allocation module 76 also includes an 
optimum loading module 94, and the foregoing output signals, 1m', 2m', 
pm', 1m", 2m" and pm" are used as inputs thereto. The function blocks 
comprising this optimum loading module 94 are shown in FIG. 8. As shown in 
this Figure, each of the foregoing input signals is used as an input to a 
separate function generator 96 which produces an output as shown in FIG. 
9. If the input signal into the generator 96 is zero, the generator 
produces a positive one output signal, however, if the input signal is 
positive, the generator produces a zero output signal. Thus, because of 
the previous logic employed, the smallest of the input signals, 1m', 2m' 
and pm', will cause a positive one to be produced at the output of the 
respective function generator 96 while the remaining input signals will 
cause a zero to be produced at the output of the respective function 
generator 96. Similarly, because of the logic employed, the largest of the 
input signals, 1m", 2m" and pm", will cause a positive one to be produced 
at the output of the respective function generator 96 while the remaining 
two input signals will cause a zero to be produced at the output of the 
respective function generators 96. 
Referring again to FIG. 7, a pressure transmitter 98 is provided to measure 
the pressure of the extraction flow conduit 16. The output of the pressure 
transmitter 98 is connected to the negative input to a subtraction 
function block 100 whose positive input is connected to a preset desired 
pressure. The output (.DELTA.p) of the function block 100 becomes positive 
on a steam demand increase and negative on a steam demand decrease. This 
output (.DELTA.p) of block 100 is connected to the input to the high and 
low limiters 102 and 104, shown in FIG. 8. High and low limiter 102 
permits the input .DELTA.p as output for a negative .DELTA.p and limits 
the output to zero for other values of .DELTA.p input representing a steam 
demand decrease. In contrast, high and low limiter 104 permits the input 
.DELTA.p as output for a positive .DELTA.p input and limits the output to 
zero for other values of input .DELTA.p representing a steam demand 
increase. The output of limiter 102 is connected to the inputs to 
multiplication function blocks 106, 108 and 110 which are connected to the 
function generators 96 for the input signals 1m', 2m' and pm'. Similarly, 
the output of limiter 104 is connected to the inputs to multiplication 
function blocks 112, 114 and 116 which are connected to the function 
generators 96 for the input signals 1m", 2m", and pm". In this manner, the 
smallest of the input signals, 1m', 2m' and pm', will cause a positive 
.DELTA.p to be produced at the output of the multiplication function block 
(106, 108 or 110) to which it is the input while a zero is produced at the 
output of the two remaining function blocks. Similarly the smallest of the 
input signals, 1m", 2m" and pm", will cause a positive .DELTA.p to be 
produced at the output of the multiplication function block (112, 114 or 
116) to which it is the input while a zero is produced at the output of 
the two remaining function blocks. As shown in FIG. 7, output signals 1m' 
and 1m" produced by multiplication function blocks 106 and 112, 
respectively are used as inputs to a summation function block 118 which 
produces a signal 1m at its output; output signals 2m' and 2m" produced by 
multiplication function blocks 108 and 114, respectively are used as 
inputs to a summation function block 120 which produces a signal 2m at its 
output; and output signals pm' and pm" produced by multiplication function 
blocks 110 and 116, respectively are used as inputs to a summation 
function block 122 which produces a signal pm at its output. The foregoing 
output signals, 1m, 2m and pm, are subsequently used as biases for the 
extraction flows from the turbines 10 and 12 and through the by-pass valve 
22. From the foregoing, it is apparent, that in the case of a decrease in 
load demand, the load is assigned to the extraction flow with the lowest 
overall efficiency, whereas in the case of an increase in load demand, the 
load is assigned to the extraction flow with the highest efficiency. The 
foregoing analysis was based on optimization on steam demand, however, a 
similar analysis can be undertaken based on megawatt demand with analogous 
results other than the resulting bias signals will be used to regulate the 
flow of fluid through the condenser. 
Certain modifications and improvements will occur to those skilled in the 
art upon reading the foregoing. It will be understood that all such 
improvements and modifications have been deleted herein for the sake of 
conciseness and readability, but are properly within the scope of the 
following claims.