Power plants – Motive fluid energized by externally applied heat – Process of power production or system operation
Reexamination Certificate
1999-01-13
2001-07-24
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Process of power production or system operation
C060S651000, C060S671000, C060S673000
Reexamination Certificate
active
06263675
ABSTRACT:
FIELD OF THE INVENTION
The present invention is in the field of power generation. In particular, the present invention is related to control of multi-component working fluid vapor generation systems.
BACKGROUND OF THE INVENTION
In recent years, industrial and utility concerns with deregulation and operational costs have strengthened demands for increased power plant efficiency. The Rankine cycle power plant, which typically utilizes water as the working fluid, has been the mainstay for the utility and industrial power industry for the last 150 years. In a Rankine cycle power plant, heat energy is converted into electrical energy by heating a working fluid flowing through tubular walls, commonly referred to as waterwalls, to form a vapor, e.g., turning water into steam. Typically, the vapor will be superheated to form a high pressure vapor, e.g., superheated steam. The high pressure vapor is used to power a turbine/generator to generate electricity.
Conventional Rankine cycle power generation systems can be of various types, including direct-fired, fluidized bed and waste-heat type systems. In direct fired and fluidized bed type systems', combustion process heat is generated by burning fuel to heat the combustion air which in turn heats the working fluid circulating through the system's waterwalls. In direct-fired Rankine cycle power generation systems the fuel, commonly pulverized-coal, gas or oil, is ignited in burners located in the waterwalls. In bubbling fluidized bed Rankine cycle, power generation system pulverized-coal is ignited in a bed located at the base of the boiler to generate combustion process heat. Waste-heat Rankine cycle power generation systems rely on heat generated in another process, e.g., incineration for process heat to vaporize, and if desired superheat, the working fluid. Due to metallurgical limitations, the highest temperature of the superheated steam does not normally exceed 1050° F. (566° C.). However, in some “aggressive” designs, this temperature can be as high as 1100° F. (593° C.).
Over the years, efficiency gains in Rankine cycle power systems have been achieved through technological improvements which have allowed working fluid temperatures and pressures to increase and exhaust gas temperatures and pressures to decrease. An important factor in the efficiency of the heat transfer is the average temperature of the working fluid during the transfer of heat from the heat source. If the temperature of the working fluid is significantly lower than the temperature of the available heat source, the efficiency of the cycle will be significantly reduced. This effect, to some extent, explains the difficulty in achieving further gains in efficiency in conventional, Rankine cycle-based, power plants.
In view of the above, a departure from the Rankine cycle has recently been proposed. The proposed new cycle, commonly referred to as the Kalina cycle, attempts to exploit the additional degree of freedom available when using a binary fluid, more particularly an ammonia/water mixture, as the working fluid. The Kalina cycle is described in the paper entitled: “Kalina Cycle System Advancements for Direct Fired Power Generation”, co-authored by Michael J. Davidson and Lawrence J. Peletz, Jr., and published by Combustion Engineering, Inc. of Windsor, Connecticut.
Efficiency gains are obtained in the Kalina cycle plant by reducing the energy losses during the conversion of heat energy into electrical output.
A simplified conventional direct-fired Kalina cycle power generation system is illustrated in
FIG. 1
of the drawings. Kalina cycle power plants are characterized by three basic system elements, the Distillation and Condensation Subsystem (DCSS)
100
, the Vapor Subsystem (VSS)
110
which includes the boiler
142
, superheater
144
and recuperative heat exchanger (RHE)
140
, and the turbine/generator subsystem (TGSS)
130
. The DCSS
100
and RHE
140
are sometimes jointly referred to as the Regenerative Subsystem (RSS)
150
. The boiler
142
is formed of tubular walls
142
a
and the superheater
144
is of tubular walls and/or banks of fluid tubes
144
a
. A heat source
120
provides process heat
121
. A portion
123
of the process heat
121
is used to vaporize the working fluid in the boiler
142
. Another portion
122
of the process heat
121
is used to superheat the vaporized working fluid in the superheater
144
.
During normal operation of the Kalina cycle power system of
FIG. 1
, the ammonia/water working fluid is fed to the boiler
142
from the RHE
140
by liquid stream FS
5
and from the DCSS
100
by liquid stream FS
7
. The working fluid is vaporized, i.e., boiled, in the tubular walls
142
a
of the boiler
142
. The rich working fluid stream FS
20
from the DCSS
100
is also vaporized in the heat exchanger(s) of the RHE
140
.
In one implementation, the vaporized working fluid from the boiler
142
along with the vaporized working fluid FS
9
from the RHE
140
, is further heated in the tubular walls/fluid tube bank
144
a
of the superheater
144
. The superheated vapor as vapor FS
40
from the superheater
144
is directed to, and powers, the TGSS
130
so that electrical power
131
is generated to meet the load requirement. In an alternative implementation, the RHE
140
not only vaporizes but also superheats the rich stream FS
20
. In such a case, the superheated vapor flow FS
9
′ from the RHE
140
is combined with the superheated vapor from the superheater
144
to form vapor flow FS
40
to the TGSS
130
.
The expanded working fluid extraction FS
11
egresses from the TGSS
130
, e.g., from an intermediate pressure (IP) or a low it pressure (LP) turbine (not shown) within the TGSS
130
, and is directed to the DCSS
100
. This expanded working fluid is, in part, condensed in the DCSS
100
. Working fluid condensed in the DCSS
100
, as described above, forms feed fluid FS
7
to the boiler
142
. Another key feature of the DCSS
100
is the separation of the working fluid egressing from TGSS
130
into ammonia rich and ammonia lean streams for use by the VSS
110
. In this regard, the DCSS
100
separates the expanded working fluid into an ammonia rich working fluid flow FS
20
and an ammonia lean working fluid flow FS
30
. Waste heat
101
from the DCSS
100
is dumped to a heat sink, such as a river or pond.
The rich and lean flows FS
20
, FS
30
, respectively are fed to the RHE
140
. Another somewhat less expanded hot working fluid extraction FS
10
egresses from the TGSS
130
, e.g., from a high pressure (HP) turbine (not shown) within the TGSS
130
, and is directed to the RHE
140
. Heat is transferred from the expanded working fluid extraction FS
10
and the working fluid lean stream FS
30
to the rich working fluid flow FS
20
, to thereby vaporize the rich flow FS
20
and condense, at least in part, the expanded working fluid extraction FS
10
and lean working fluid flow FS
30
, in the RHE
140
. As discussed above, the vaporized rich flow is fed to either the superheater
144
, along with vaporized fluid from the boiler
142
, or is combined with the superheated working fluid from the superheater
144
and fed directly to the TGSS
130
. The condensed expanded working fluid from the RHE
140
forms part of the feed flow, i.e., flow FS
5
, to the boiler
142
, as has been previously described.
FIG. 2
details a portion of the RHE
140
of VSS
110
of FIG.
1
. As shown, the RHE
140
receives ammonia-rich, cold high pressure stream FS
20
from DCSS
100
. Stream FS
20
is heated by ammonia-lean hot low pressure stream FS
3010
. The stream FS
3010
is formed by combining the somewhat lean hot low pressure extraction stream FS
10
from TGSS
130
with the lean hot low pressure stream FS
30
from DCSS
100
, these flows being combined such that stream FS
30
dilutes stream FS
10
resulting in a desired concentration of ammonia in stream FS
3010
.
Heat energy
125
, is transferred from stream FS
3010
to rich stream FS
20
. As discussed above, this causes the transform
Hansen Paul L.
Kuczma Paul D.
Palsson Jens O.
Simon Jonathan S.
ABB Alstom Power Inc.
Nguyen Hoang
Warnock Russell W.
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