Power plants – Combustion products used as motive fluid
Reexamination Certificate
1999-06-22
2001-03-13
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
Reexamination Certificate
active
06199362
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of power plant engineering. It pertains to a method of controlling and regulating a power plant, in which power plant thermal power is generated in a combustion chamber from a gaseous fuel and the thermal power is at least partially converted into electrical power in conversion equipment, and in which power plant the fuel for the combustion chamber is produced in a fuel producer from a feed product with the application of thermal and/or electrical power, which is removed at the outlet from the conversion equipment, and said fuel is passed on to the combustion chamber.
The present invention also relates to a power plant for implementing the method.
2. Discussion of Background
In view of the fact that environmental protection legislation is becoming increasingly more strict, it is becoming increasingly more difficult to dispose of waste products from refinery processes. For this reason, processes which convert such waste products into fuels which can subsequently be used in a power plant to generate electrical and/or thermal power are becoming profitable.
A typical plant for the conversion of waste materials into electrical energy comprises a gasification plant which converts the tar accumulating as refinery waste into so-called “Syngas”, a combustible mixture of various gases. The Syngas is then burned in a gas turbine, which at least partially converts the thermal energy of the hot gases produced into electrical energy (Integrated Fuel and Power Generation IFPG). In this case, the gas turbine is usually part of a combined process (with a gas and steam turbine), in order to increase the overall efficiency of the conversion of Syngas into electrical power. Some of the power generated is fed back (in the form of steam and/or electrical power) into the gasification plant, in order to effect the production of the Syngas. There is, therefore, close coupling between the Syngas producer (gasification plant) and the Syngas consumer (gas turbine or power plant block). In particular, stable, steady-state operation of these closely interwoven parts of the plant can be achieved only if the production and consumption of the Syngas are in harmony with each other. To this end, it is necessary for a control and regulation method to be developed which takes account of the special features of an IFPG plant and differs considerably from the operation of an autonomous power plant (Standalone Power Plant SAPP), in which the fuel is obtained from a store in the form of a gas or oil tank.
The typical construction of a power plant
10
in the form of a conventional SAPP plant is reproduced in schematic form in
FIG. 1. A
fuel supply device
12
(e.g. a pump) removes the fuel from a fuel store
11
and compresses or decompresses (expands) said fuel to a specific predefined pressure p
f1
. The fuel supply to the combustion chamber
16
is controlled by a control valve
14
. A fuel distribution system
15
distributes the fuel mass flow fed in to one or more burners arranged inside the combustion chamber
16
. The thermal power from the combustion chamber
16
is then converted, in subsequent conversion equipment
17
(gas turbine, waste-heat recovery boiler, steam turbine) into electrical power and/or steam, for example in a combined cycle. The basic strategy for controlling and regulating such a plant has two objectives: (a) the production of any desired, time-variable output power profiles within the limits of the operating range of the plant, and (b) ensuring the necessary fuel supply without significant delays.
Objective (a) is typically achieved by a power control loop, which brings the tracking error
dP(
t
)=P
c
(
t
)−P
m
(
t
)
to zero during steady-state operation. P
c
(t) designates the possibly time-variable set point for the power, and P
m
(t) is, according to
FIG. 1
, the measured output power. An overview of the SAPP plant with the principal control loops is illustrated in FIG.
1
.
A significant component of the control system is the power controller
20
. The power controller
20
may contain further control loops internally (for example temperature controllers, pressure regulators etc.), which are necessary to keep the internal states of the power plant within the prescribed operating limits. The power controller may optionally regulate the thermal power (steam) output by the conversion equipment
17
at the outlet
18
, or the electrical power output at the output
19
. On the input side, the power controller
20
has applied to it the difference between P
c
and P
m
, which is formed in a subtracter
21
. On the output side, said power controller
20
outputs a signal which corresponds to the required fuel mass flow {dot over (m)}
fc
. The output signal from the power controller
20
is converted, in a subsequent fuel/valve position converter
22
, into a valve position signal h
c
for the control valve
14
(or a corresponding variable of another fuel control member, such as the desired speed of a variable-speed fuel pump). The fuel mass flow through the control valve
14
depends on the pressures p
f1
and p
f2
upstream and downstream of the valve, the measured values of these pressures also being input into the fuel/valve position converter
22
for the purpose of calculating h
c
. For an inlet pressure p
f1
within the limiting curves a and b illustrated in
FIG. 2
, and within the operating limits of the control valve
14
, it is thus possible for any desired fuel mass flow to be set, virtually without delay, by suitable selection of the valve position signal h
c
. The significant limitation in the dynamics of the mass flow is imposed by the dynamics of the control valve
14
. The valve must therefore be designed such that it satisfies all the requirements for achieving the abovementioned objective (a). In order to achieve the abovementioned objective (b) (a precondition for the objective (a)), the fuel supply device
12
must ensure that the input pressure pfl is kept within the limiting curves a and b illustrated in FIG.
2
. To this end, according to
FIG. 1
a pressure control loop for p
f1
is provided, and is composed of the fuel supply device
12
and a pressure regulator
13
. It should be noted at this point that the fuel supply device
12
is typically a fuel delivery pump, a gas compressor or a pressure reducing valve.
By comparison with the structure of an SAPP plant shown in
FIG. 1
, an IFPG plant, in which the fuel is produced exclusively within the plant itself, and on which the method of the present invention is based, has the basic structure reproduced in FIG.
3
. Such a power plant
30
is characterized by a fuel producer
31
, a reducing device
32
(in some cases this may also be a controllable compression device) and a power plant block as has already been described in connection with FIG.
1
and which comprises a control valve
33
, a fuel distribution system
34
, a combustion chamber
35
and conversion equipment
36
having an outlet
37
for thermal power (steam) and an outlet
38
for electrical power. The reducing device
32
may be a controllable pressure-reducing valve or any other controllable pressure-reducing device. From the outlets
37
and
38
of the conversion equipment
36
(for example gas turbine, waste-heat recovery boiler and steam turbine), a steam feedback line
391
and a power feedback line
392
for electrical power provide the fuel producer
31
with the energy necessary for fuel production. Via the supply
393
, an appropriate feed product (for example tar) is fed into the fuel producer
31
, to be converted into fuel.
The control and regulation of the IFPG plant according to
FIG. 3
differs in principle from the control and regulation of the SAPP plant from
FIG. 1
, since, in the IFPG plant, the fuel producer
31
must be controlled in such a way that, within the operating limits of the power plant, it is adapted to the fuel consumption of the conversion equipment
36
. The setting of the objective for the control
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P
Rodriguez William
Thorpe Timothy S.
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