DE3139209A1 - "METHOD FOR OPERATING A COMBINED GAS-VAPOR TURBINE PLANT AND PLANT FOR CARRYING OUT THE METHOD - Google Patents

Description

Process for operating a combined gas-steam turbine system and system for carrying out the process

The invention relates to a method for operating a combined Gas-steam turbine system according to the preamble of the claim The invention also relates to a gas-steam turbine system for Implementation of the procedure.

A gas-steam turbine system to which the invention relates, consists of a gas turbine part and a steam turbine part. Both parts are shared by a fluidized bed chamber Energy supplied. The fluidized bed combustion chamber works under pressure and it supplies one or more steam turbines with steam and several gas turbines with propellant gas. The combustion takes place under pressure in a fluidized bed, from which the combustion gases are sent to the Gas turbines are directed. Coiled tubes for cooling the bed are arranged in the fluidized bed. In these coils is which generates steam for the steam turbines.

In combined systems, the type must be observed in the regulation, that the cooling effect of the pipe coils is essentially constant and can only be controlled with difficulty, but that on

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on the other hand, the air flow in the combustion air compressor is decreasing The ambient temperature rises because the density of the air increases as the temperature falls. When the air temperature falls, stands thus a larger amount of combustion air is available. If you try to use this available air, by adding more fuel to the combustion chamber while maintaining an optimal excess air factor, the temperature rises of the fluidized bed to an impermissible value. The best way to limit the bed temperature is to do this keeps constant by the excess air factor with larger fuel supply is increased. This control method has the consequence that the combustion efficiency due to the increasing excess of air becomes smaller that the combustion capacity of the combustion chamber is not fully utilized at a low ambient temperature and that when the ambient temperature is low, it is not possible to extract the maximum power from all parts of the system.

The invention is based on the object of creating a method for operating a combined gas-steam turbine system in which all system parts can be used to the maximum _{even at temperatures below the so-called design temperature T n.} Design temperature is the highest ambient temperature at which a certain specified power is to be achieved in a gas turbine. Usually the design temperature is + 30 ⁰ C.

To solve this problem, a method according to the preamble of claim 1 is proposed, which in the characterizing

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Part of claim 1 has mentioned features.

Advantageous further developments of the invention are set out in the subclaims called.

A combined gas-steam turbine system for carrying out the method is according to the invention by those mentioned in claim A. Features marked.

In a combined gas-steam turbine system according to the invention a maximum power extraction below the design temperature of the gas turbine for all system parts and thus achieved in the whole system that the fuel supply and the excess air factor can be controlled such that a maximum combustion capacity is utilized. To prevent that the bed and the gas turbine are overheated, the bed temperature and thus the gas temperature become at the same time due to the injection regulated by water or steam in the bed. The mass flow through the gas turbine and thus also the power are on the one hand by the increased fuel supply and on the other hand by the Increased water or steam supply to bed. The larger gas flow also results in a slightly larger amount of steam from an exhaust gas boiler, so that the steam turbine output is also somewhat greater;

The combustion chamber of the system contains sensors for determining the bed temperature and the excess air factor. The transmitter for determining the excess air factor is connected to a control device that controls a fuel valve when using liquid fuel. The transmitter for determining the bed temperature is on

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Connected control device that controls the water supply to the bed. The control devices contain elements which compare the measured actual values with setpoint values and control the fuel or water supply as a function of the deviations from the setpoint / actual value differences. The system also contains the usual control devices that are used for power control in power plants. The fuel supply is increased with greater air access and falling ambient temperature in such a way that the excess air factor Λ essentially in the vicinity of the smallest permissible value T ^. is kept constant. The risk of corrosion for the steam generator pipes in the fluidized bed determine the value for "} \ .. The following applies:

G = amount of air available (kg / s) m _n - amount of air in kg that is required to add 1 kg of fuel

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B = amount of fuel (kg / s).

The smallest permissible value ^ \. is calculated. He is dependent on the combustion chamber design, the fuel, the bed material, etc. Normally Ά> 1.5. Water can be added to the fluidized bed with. Fuel are supplied. Carbon or peat powder can slurried in water to form a so-called "slurry" and fluidized Bed can be fed through mouthpieces provided for this purpose.

The invention is to be explained in more detail with the aid of the figures. Show it

Fig. 1 schematically shows an embodiment of a gas-steam

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Turbine system according to the invention,

2 shows an exemplary embodiment of a turbine system for the gas-steam turbine according to the invention belonging fluidized bed combustion chamber,

3 shows a stack diagram for the fluidized bed temperature,

4 shows a diagram of the relationship between the excess air factor / \ in the combustion chamber and the ambient temperature, if the system is not operated in accordance with the invention,

Fig. 5 shows the relationship between the. Ambient temperature and that of the combined gas-steam turbine system Power.

In Figures 1 and 2, 1 denotes a pressure vessel, the one Combustion chamber 2 with a fluidized bed 3 surrounds. In this there is a coil 4, which is surrounded by the bed material.

The gas turbine part of the system contains a high pressure turbine 6, which drives a high-pressure compressor 5 and is connected in terms of flow to a low-pressure turbine 7 connected in series, which in turn drives a low-pressure compressor 8. A starting motor 10 is connected to the high pressure compressor.

In the line 11 between the low-pressure compressor 8 and the high-pressure compressor 5 is an intercooler 12. Furthermore, one is Power turbine 13 is present, which drives a generator 19. The high pressure compressor 5 is connected to the pressure vessel via a line 14 1 connected. The combustion chamber 2 is on its exit side via a Leitui-.g 15 with the high-pressure turbine 6

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bound. A line is located between lines IA and 15 16 with a valve 17, through which compressor air with combustion gases to control or regulate the performance of the Plant can be mixed. The high-pressure turbine 6 and the low-pressure turbine 7 are connected to one another via the line 18. The low-pressure turbine 7 is connected to the power turbine 13 via a line 20.

The steam turbine part contains a steam turbine 21, which is a generator 22 drives. Condensate from the condenser 22a - the turbine 21 is from the feed water pump 23 through the line 24 to the feed water preheater 25 and then passed through line 26 to coil A in combustion chamber 2. Steam is generated here, which flows through line 27 to turbine 21. The exhaust gases from the power turbine 13 are passed through line 28 to the feedwater preheater 25 headed.

The combustion chamber 2 (Figure 2) divides the pressure vessel 1 into two separate spaces 30 and 31. The lower space 30 is supplied with compressed air from the high pressure compressor. The air gets through mouthpieces 32 is blown into the combustion chamber 2 and holds the bed material in the fluidized bed 3 in the fluidized state. Fuel is supplied through line 33. The fuel supply from an oil tank is regulated by the regulating device 51 and the valve 52 as a function of the excess air factor λ. This is provided by an encoder 53 measured. The measured current .Istwert is compared with a target value in a signal processing element 5A. Dependent on The fuel supply is regulated according to the difference between the setpoint and the actual value. When coal is used as fuel, the control

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is used as an actuator, for example, a screw conveyor for the supply of fuel. A pressurized water tank 34 is connected to the mouthpieces 37 via a line 35 in which a control valve 36 is located, through which water is directly fed into the fluidized bed can be injected, the water cooling the fluidized bed as it evaporates. The water injection is in Regulated as a function of the bed temperature. A sensor 38 measures the bed temperature, and the measured value is sent to the control unit via line 41 40 supplied. In the signal processing element 42, the measured value is compared with a nominal value, and as a function the target-actual value difference is the valve 36 and thus the amount of water, which is fed to the bed is controlled. The transmitter 38 can be placed in or above the fluidized bed 3, since combustion gases that leave bed 3, have about the same temperature as the bed.

An advantage of a combined gas-steam cycle system of the type described with combustion in a fluidized bed at increased pressure (10-16 bar) is its high efficiency. An overall efficiency of the system of over 40 % can be achieved. Another advantage is that the combustion can take place at a low temperature, 800 - 850 ° C, so that melt ash can be avoided. Particles that are entrained by the combustion gases from the bed are "dry" and therefore do not tend to stick in a cleaning system, for example of the cyclone type. Effective cleaning that is sufficient for gas turbines can be achieved, and there is only a low risk of deposits on turbine blades . Another advantage is that sulfur occurring in the fuel with a suitably selected bed mass

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material, such as dolomite, can react "dry" and is therefore absorbed by this with the formation of gypsum and removed together with the fuel ash and the used bed material. A spread of sulfur impurities together with the flue gases can therefore be prevented. A particularly great advantage is that coal * Yoü at a temperature as low as - can have 8 [3O ⁰ C completely burned.

The need to keep the temperature in the fluidized bed within narrow limits poses certain problems which, however, can be solved by the invention. This is illustrated in FIG. 3. The temperature of bed 3 must be kept in the interval AB. Although combustion can be maintained within the interval BC, the absorption of sulfur decreases, the turbine output decreases and the efficiency decreases, ash melts above level 4, which can form lumps which clog the air and fuel nozzles or which Drops can form, which are carried along by the combustion gases and settle in cleaners and on turbine blades. When the ambient temperature falls below the so-called design temperature T _n and the density of the air and thus the mass flow through the compressors are greater, the amount of oxygen available for combustion increases. This oxygen can only be used to a very small extent for the combustion of a larger amount of fuel if the cooling of the bed cannot be increased. The cooling capacity of the steam coil is by and large constant, so that "greater combustion" results in the temperature of the bed quickly reaching an inadmissible level. The excess air factor increases as shown in the figure

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illustrated. The excess air factor A is plotted on the ordinate and the outside air temperature T on the abscissa. The so-called design point T _Q is +30 C. At the design point, X = 1.5. If λ falls below 1.5, the atmosphere in the bed becomes reducing and corrosion occurs on the pipes in the bed.! X = 1.5 is thus the lowest excess air factor that can be permitted. Without increased cooling the supply of fuel cannot be increased proportionally to the amount of oxygen that is available at temperatures below T ". The value of A increases, as shown by the inclined, solid line AB. At temperatures above T, the fuel supply must be reduced so that Λ does not fall below, for example, Λ · = 1..5. A reduced power is obtained both in the gas turbine part and in the steam turbine part.

FIG. 5 shows the power delivered by the combined turbine system, ie the power output by the steam turbine 21 and the power turbine 13 of the gas turbine part. The steam turbine 21 is a substantially constant power between ~ 30 ° C and +30 ⁰ C.. After that, the performance decreases as the ambient temperature rises. See curve ABC. In the event that the invention is not used in the operation of the plant, the power gas turbine 13 outputs a power which is equal to the difference between the curves DEF and ABC. If the ambient temperature falls below the design temperature T _Q = +30 ⁰ C, the power increases somewhat due to the greater air mass flow. Above T "decreases d. '. E power because a smaller amount of oxygen for combustion is available, and the fuel feed mu ^ be lower, thus% non-un' he

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the permitted value decreases. In the case in which the invention at Operation of the system is used, the power turbine outputs a power which is equal to the difference between the curves GEF and ABC is. The grant benefit that can be obtained using the invention is the difference between the parts of the curve GE and DE. This grant comes from the fact that the water supplied to bed 3 cools the bed as it evaporates, and a larger supply of fuel with unchanged bed temperature enables. The desired mass flow through water and fuel feed and the increased energy input from larger combustion result in the desired output power.

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Claims (4)

Patent claims: [1J Method for operating a combined gas-steam turbine system, in which gas for the gas turbine and steam for the steam turbine are generated in a common fluidized bed combustion chamber and in which the combustion chamber of the gas turbine is adapted during operation at the so-called design temperature (design temperature) in such a way that the correct amount of gas at the selected design temperature results in full power utilization of the turbine, characterized in that that the excess air factor (Py) with falling ambient temperature and thus increasing air density and greater air flow is regulated by increasing the fuel supply and that at the same time the bed temperature is controlled by injecting water or steam into the fluidized bed (3) so that an impermissible Rise in the fluidized bed temperature as a result of the larger fuel supply is prevented. 2. The method according to claim 1, characterized in that water is supplied in such an amount that the excess air factor (/ \) and maintaining the fluidized bed temperature at a substantially unchanged level with increased fuel input. 3. The method according to claim 1, characterized in that the, the Bed (3) contains water fed in water slurried fuel. . ·. · · ::: * :: 23 O19 P 4. Combined gas-steam turbine system for carrying out the process according to claim 1 with a common fluidized bed combustion chamber for generating gas for a gas turbine (13) and steam for a steam turbine (21), the combustion chamber (1) of the gas turbine (13) being adapted in such a way that the combustion chamber is that for the gas turbine (13) required amount of gas for a given power at a certain temperature, usually + 30 C, results from this characterized in that a first transmitter (53) for measuring the excess air factor (Λ) is present in the combustion chamber, that control elements (51, 54) are present, which determine the fuel supply to the fluidized bed as a function of the difference in the measured Actual value and a set value of the excess air factor control that a second transmitter (38) for measuring the fluidized bed temperature is present and that regulating members' (40, 42) are present in which the actual value of the bed temperature is compared with a target value and which the injection when the target value is exceeded induce water or steam into the fluidized bed (3). / 3