Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2002-05-16
2004-02-24
Koczo, Michael (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S746000
Reexamination Certificate
active
06694745
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for running up a gas turbine plant according to the preamble of claim
1
.
BACKGROUND OF THE INVENTION
Gas turbines are increasingly equipped with multiple burners employing the lean premix technique. In this case, the fuel and the combustion air are premixed as uniformly as possible and only then fed to the flame. When this is carried out with a high air excess, relatively low flame temperatures are obtained and there is therefore an insignificant formation of nitrogen oxides.
In accordance with the geometry of gas turbines, the plurality of burners are often arranged annularly in the form of annular combustion chambers. Such annular gas turbine combustion chambers are known, for example, from EP-B1-0 597 138, U.S. Pat. No. 4,100,733, U.S. Pat. No. 5,303,542, U.S. Pat. No. 5,402,634, EP-A2-802,310 or EP-A1-976,982. The liquid or gaseous fuels are in this case fed via fuel feed rings to the burners arranged in single and multiple rings, where they are injected into the annular combustion chamber and burnt.
When gaseous fuel is used, different operating modes of the individual burners may be more or less advantageous, depending on the load state, on the number of burners in operation and on the emission values or similar characteristics of the gas turbine. In the case of double-cone burners, for example in what is known as pilot mode, the gaseous fuel may be admixed in the center, at the base of the double-cone burner, by what may be referred to as the pilot-gas piercing of the combustion air. The burners operated in this way are distinguished by a very stable flame with a high flame temperature, which, on the other hand, however, also entails unfavorable emission values. In what is known as the premix mode, on the other hand, in double-cone burners the gaseous fuel is admixed in the cone region by the lateral premix-gas piercing of the combustion air. The flames of burners in the premix mode are distinguished by a low flame temperature and the associated favorable emission values. However, they are appreciably less stable than burners operated in the pilot mode. A double-cone burner may, in principle, be constructed in such a way that it can be operated in both operating modes mentioned above, in succession and in parallel. Depending on the operating mode, the gaseous fuel is injected by means of one piercing or the other.
At the operating point of the gas turbine or in the upper load range, the burners have to operate at high firing temperatures and with low NO
x
emissions. The extinguishing limit of the burners in the premix mode is therefore necessarily near very high firing temperatures. For start-up and the part-load mode of the gas turbine and at the associated lower firing temperatures, therefore, additional pilot-gas injection of the burners is necessary. Stable diffusion combustion at low temperatures is thereby ensured. During the run-up of the gas turbine and when the latter is under load, there consequently has to be a changeover from the pilot mode (that is to say, diffusion combustion) to the premix mode by means of adjusting and regulating valves. The changeover must take place at a correct temperature of the flame within a narrow interval.
When a gas turbine of the type initially mentioned is run up from the idling mode into the load mode, undesirable effects often arise. Inter alia, in particular phases of the run-up and in the part-load mode, that is to say during the pilot mode, a pronounced generation of smoke and nitrogen oxides is possible, burners may be extinguished, and, moreover, an unfavorable pulsation of the gas turbine may occur. For these reasons, in the pilot mode, the burners should not be operated at flame temperatures which are too low or too high and which make it necessary to engage the gas turbine protection. On the other hand, a premature changeover from the pilot mode to the premix mode at a flame temperature which is too low leads to the extinguishing of the flame in the premix mode.
A reliable changeover from the pilot mode to the premix mode should take place at a constant flame temperature. Unfortunately, the flame temperature cannot be measured directly with sufficient accuracy. The measurement of the NO
x
emissions, as an indicator of the flame temperature, is also not sufficiently accurate in this case. Instead, the temperature of the exhaust gas is measured and the changeover is initiated when the mean exhaust-gas temperature measured reaches a specific fixed value. Unfortunately, even this solution may lead only to an approximate flame temperature, since the relationship between the flame temperature and the measured exhaust-gas temperature may vary. This depends, inter alia, on the ambient conditions, the internal air balance, the status of seals, the plays in the gas turbine plant, the ageing and heat penetration of the machine and other factors.
SUMMARY OF THE INVENTION
The object on which the invention is based is, therefore, to specify a method, by means of which both a run-up and a part-load mode of a gas turbine operated with the gaseous fuel are possible in a reliable, uncomplicated and low-pollutant way and an optimum point for the changeover from the pilot mode to the premix mode can be found, while harmful pulsations in the combustion chamber of the gas turbine plant are to be avoided.
The object is achieved, according to the invention, by means of a method according to the preamble of claim 1, in that
(a) the changeover time point from the pilot mode to the premix mode depends on a variable changeover temperature T
SWO
and this changeover temperature T
SWO
is determined from pulsations occurring in the flame of the combustion chamber, while
(b) the gas turbine plant is run up at a constant load gradient DL and the changeover is initiated without the occurrence of pulsations, in so far as an upper maximum changeover temperature T
SWOhot
is reached, and,
(c) when pulsations occur, the load gradient DL is lowered and the changeover is initiated, in so far as a lower minimum changeover temperature T
SWOcold
is reached, and,
(d) when further pulsations occur, at a specific exhaust-gas temperature T
pulslimit
, the changeover is initiated, as soon as a variable changeover temperature T
SWO
exceeds the lower minimum changeover temperature T
SWOcold
, the variable changeover temperature T
SWO
being determined from the exhaust-gas temperature T
pulslimit
by reduction by a specific amount DT
SWO
, and,
(e) in so far as the variable changeover temperature T
SWO
does not reach the lower minimum changeover temperature T
SWOcold
, the gas turbine plant is operated for a specific time at an exhaust-gas temperature below the exhaust-gas temperature T
pulslimit
at which pulsations occur, and, thereafter,
(f) the gas turbine plant is further acted upon at the lowered load gradient DL according to (c).
By means of intelligent process management with the aid of a variable definition of the changeover temperature, secondary effects, which influence the measurement of the exhaust-gas temperature and make it difficult or even impossible (transients) to determine the actual flame temperature, are ruled out in a simple way. This process management allows safe loading of the combustion chamber, without long-lasting, high and therefore harmful pulsations, along with the shortest possible warm-up time of the gas turbine plant, and also a reliably controllable changeover from the pilot mode to the premix mode, this having a positive effect on the availability of the plant.
The lowered load gradient from steps (c) and (f) may advantageously be determined indirectly via an increase in the exhaust-gas temperature DT
1
within a time interval. This gradient of the exhaust-gas temperature DT
1
may be determined variably as a function of the difference between the lower minimum changeover temperature T
SWOcold
and the exhaust-gas temperature T
pulslimit
at which pulsations occur. The variable changeover temperature T
SWO
is advantageously lowered in step (d) by less than
Knoepfel Hans Peter
Kueenzi Thomas
Rebhan Dieter
Stalder Marcel
Alstom Technology Ltd
Burns Doane Swecker & Mathis L.L.P.
Koczo Michael
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