Power plants – Motive fluid energized by externally applied heat – Process of power production or system operation
Reexamination Certificate
1999-01-13
2001-03-20
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Process of power production or system operation
C060S651000, C060S671000
Reexamination Certificate
active
06202418
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the selection and conditioning of materials to avoid brittleness caused by NITRIDING. More specifically, the present invention relates to selection and conditioning of materials exposed to an environment containing ammonia, such as materials exposed to ammonia/water working fluids within a Kalina cycle power generation plant.
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 systems' 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 systems pulverized-coal is ignited in a set 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 the 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.).
Waterwalls are formed of tubes which serve as flow passages for the working fluid. Hence, the waterwalls must be capable of being subjected to the pressure loads generated by the working fluid throughout the cycle. Typically, the waterwalls must also be capable of being subjected to other loads. For example, in many cases the waterwalls must be self supporting. It is also common for the waterwalls to have mounted in supported relation thereon other system elements, such as burners, a lower drum, and/or sootblowers. Accordingly, it is important that the waterwalls have the structural integrity to withstand the required loadings throughout a desired design life.
The waterwall tubes are conventionally made of steel. In a typical Rankine cycle power system, the waterwall tubes in those portions of the system which are subjected to lower temperatures may be of one type of steel while the waterwall tubes in higher temperature portions of the system are of a different type steel. Thus, the waterwall tubes in the lower temperature areas may be formed of low alloy steel, commonly referred to as ferritic steel, for example, having 2½Cr to 16Cr. Waterwall tubes in the higher temperature areas may be formed of high alloy steel, commonly referred to as austenitic or stainless steel, for example having 18Cr and 8Ni.
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, Conn. 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 boiler
142
is formed of tubular walls
142
a
and the superheater
144
is formed of tubular walls
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
.
FIG. 1A
depicts an expanded view of the boiler tubular walls
142
a
through which the working fluid flows. As shown, the tubular walls
142
a
are formed of steel tubes
150
. As is customary in Rankine cycle power systems, the tubes
150
have milled inner surfaces
155
.
FIG. 1B
depicts an expanded view of the superheater tubular walls
144
a
through which the vaporized working fluid flows. As shown, the tubular walls
144
a
are formed of steel tubes
160
. The tubes
160
also have conventional milled inner surfaces
165
. Those skilled in the art will recognize that the tubes similar to those forming the tubular walls are also utilized to transport the working fluid in other components of the VSS
110
, the TGSS
130
and the DCSS
100
.
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 by liquid stream FS
7
from the DCSS
100
. The working fluid is vaporized, i.e. boiled, in the tubular walls
142
a
of the boiler
142
. The vaporized working fluid from the boiler
142
, along with working fluid vaporized in the RHE
140
, is further heated in the tubular walls
144
a
of the superheater
144
. The superheated vapor, identified as FS vapor
40
is directed to and powers the TGSS
130
so that electrical power
131
is generated to meet the load requirement.
The expanded working fluid FS extraction
11
egresses from the TGSS
130
, e.g., from a low pressure (LP) turbine (not shown) within the TGSS
130
, and is directed to the DCSS
100
. The expanded working fluid is, in part, condensed in the DCSS
100
. Condensed working fluid, as described above, forms feed stream FS
7
to the boiler
142
. The DCSS
100
also separates the expanded working fluid into an ammonia rich working fluid flow FS rich
20
and an ammonia lean working fluid flow FS lean
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
20
,
30
respectively, are fed to the RHE
140
. Another somewhat less expanded hot working fluid FS extraction
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
1
Gabrielli Frank
Gibbons Thomas B.
Goodstine Stephen L.
O'Neill James K.
ABB Combustion Engineering
Nguyen Hoang
Stadnicki Alfred A.
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