Double pinch criterion for optimization of regenerative rankine cycles

Patent metadata

Field	Value
Publication number	US-9719379-B2
Application number	US-201514749399-A
Country	US
Kind code	B2
Filing date	Jun 24, 2015
Priority date	May 20, 2011
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

Systems and methods axe disclosed herein that generally involve a double pinch criterion for optimization of regenerative Rankine cycles. In some embodiments, operating variables such as bleed extraction pressure and bleed flow rate are selected such that a double pinch is obtained in a feedwater heater, thereby improving the efficiency of the Rankine cycle. In particular, a first pinch point is obtained at the onset of condensation of the bleed and a second pinch point is obtained at the exit of the bleed from the feedwater heater. The minimal approach temperature at the first pinch point can be approximately equal to the minimal approach temperature at the second pinch point. Systems that employ regenerative Rankine cycles, methods of operating such systems, and methods of optimizing the operation of such systems are disclosed herein in connection with the double pinch criterion.

First claim

What is claimed is:

1. A method of designing a power generation system, comprising:
using a processor, receiving a plurality of input design parameters and storing the input design parameters in a memory coupled to the processor;
using the processor, based on the received input design parameters, calculating an output design parameter comprising at least one of a bleed extraction pressure and a bleed mass flow rate for a feedwater heater, the feedwater heater being configured to preheat a feed of working fluid using a bleed extracted from a turbine; and
outputting the calculated output design parameter;
wherein the output design parameter is calculated to produce a double pinch in the feedwater heater, the double pinch comprising a first pinch point at an onset of condensation of the bleed and a second pinch point at a bleed outlet of the feedwater heater.

2. The method of claim 1 , wherein the input design parameters include at least one of a flow rate of a main stream through the turbine, a steam generator temperature, a steam generator pressure, and a condenser operating pressure.

3. The method of claim 1 , further comprising constructing the power generation system according to the output design parameter.

4. The method of claim 1 , wherein the output design parameter is further calculated such that a minimal approach temperature at the first pinch point is approximately equal to a minimal approach temperature at the second pinch point.

5. The method of claim 1 , wherein the output design parameter comprises the bleed extraction pressure (P B ) and the bleed mass flow rate ({dot over (m)} B ) which are approximately calculated for a given feedwater heater heat duty transfer ({dot over (Q)}) by:

m
.

B

=

m
.

F

⁢

h

g
,
sat

⁡

(

P
B

)

-

h
l

⁡

(

T

F
,
i

+

Δ
MITA

⁢
T

,

P
B

)

h
l

⁡

(

T
sat

⁡

(

P
B

)

-

Δ
MITA

⁢
T

,

P
F

)

-

h
l

⁡

(

T

F
,
i

,

P
F

)

and
{dot over (Q)}={dot over (m)} B ( h T ( P B )− h ( T F,i +Δ MITA T,P B )).

6. The method of claim 1 , wherein the output design parameter comprises the bleed extraction pressure calculated as the smallest extraction pressure that allows for a pinch at the bleed outlet of the feedwater heater.

7. The method of claim 1 , wherein the output design parameter comprises the bleed mass flow rate calculated as the smallest mass flow rate that allows for a pinch at the onset of condensation of the bleed.

8. The method of claim 1 , wherein the output design parameter is determined by an iterative calculation and a double pinch criterion in the feedwater heater is imposed during each iteration of the calculation.

9. A power generation system, comprising:
a steam generator in which a working fluid is heated;
a turbine in fluid communication with the steam generator and configured to be turned by the heated working fluid, the working fluid forming a feed after exiting the turbine; and
at least one feedwater heater configured to heat the feed using a bleed extracted from the turbine, the feedwater heater being configured to exchange heat between a first flow path through which the feed flows and a second flow path through which the bleed flows;
wherein at least one of a mass flow rate of the bleed and an extraction pressure of the bleed is selected such that a double pinch is obtained in the feedwater heater, the double pinch comprising a first pinch point at an onset of condensation of the bleed and a second pinch point at a bleed outlet of the feedwater heater.

10. The power generation system of claim 9 , wherein the feed is heated in the steam generator after it exits the feedwater heater.

11. The

Assignees

• Massachusetts Inst Technology

Inventors

• Zebian Hussam
• Mitsos Alexander

Classifications

• F01K17/06

  Returning energy of steam, in exchanged form, to process, e.g. use of exhaust steam for drying solid fuel or plant · CPC title

• F01K7/22

  the turbines having inter-stage steam heating · CPC title

• F01K7/24

  Control or safety means specially adapted therefor · CPC title

• F05D2270/66

  Mechanical actuators (F05D2270/62 takes precedence) · CPC title

• F05D2260/221

  Improvement of heat transfer · CPC title