METHOD FOR CONTROLLING A COMBUSTION DEVICE

Abstract

A method for controlling a combustion process in a gas turbine wherein a combustion chamber, a control device storing a calculation model of the combustion process, and an exhaust air measurement device are used. A permissible limit value for nitrogen oxides and for carbon monoxide as pollutants is set. The actual value of at least one of the two pollutants is measured continuously in the exhaust air. When a signal to reduce the power of the gas turbine to a lowest possible value is given, then a minimum fuel supply at which the limit values are complied with is calculated. The fuel supply is then reduced either until the calculated minimum fuel supply is reached or until the continuously measured proportion of the pollutant reaches the permissible limit value.

Claims

1. A method for controlling a combustion process in a combustion device, comprising a combustion chamber, in which fuel is burnt with supply air, and at least one burner, which delivers the fuel and/or the supply air into the combustion chamber, and a control device, in which a calculation model of the combustion process is stored, and an exhaust air measurement device, which detects the actual proportion of nitrogen oxides; the method comprising: setting a permissible limit value for the proportion of nitrogen oxides and determining a target value as a limit value minus a tolerance; setting a permissible limit value for the proportion of carbon monoxide and determining a target value as a limit value minus a tolerance; continuously recording the actual proportion of nitrogen oxides in the exhaust air; acquiring a signal for setting a minimum power; calculating a minimum fuel supply, using the calculation model, at which the expected proportion of carbon monoxide reaches the target value; while continuously monitoring the actual proportion of nitrogen oxides in the exhaust air, reducing the fuel supply as far as the calculated minimum fuel supply or until the target value for nitrogen oxides is reached.

2. A method for controlling a combustion process in a combustion device, comprising a combustion chamber, in which fuel is burnt with supply air, and at least one burner, which delivers the fuel and/or the supply air into the combustion chamber, and a control device, in which a calculation model of the combustion process is stored, and an exhaust air measurement device, which detects the actual proportion of carbon monoxide; the method comprising: setting a permissible limit value for the proportion of nitrogen oxides and determining a target value as a limit value minus a tolerance; setting a permissible limit value for the proportion of carbon monoxide and determining a target value as a limit value minus a tolerance; continuously detecting the actual proportion of carbon monoxide in the exhaust air; acquiring a signal for setting a minimum power; calculating a minimum fuel supply, using the calculation model, at which the expected proportion of nitrogen oxides reaches the target value; while continuously monitoring the actual proportion of carbon monoxide in the exhaust air, reducing the fuel supply as far as the calculated minimum fuel supply or until the target value for carbon monoxide is reached.

3. A method for controlling a combustion process in a combustion device, comprising a combustion chamber, in which fuel is burnt with supply air, and at least one burner, which delivers the fuel and/or the supply air into the combustion chamber, and a control device, in which a calculation model of the combustion process is stored, and an exhaust air measurement device, which detects the actual proportion of nitrogen oxides and the actual proportion of carbon monoxide; the method comprising: setting a permissible limit value for the proportion of nitrogen oxides and determining a target value as a limit value minus a tolerance; setting a permissible limit value for the proportion of carbon monoxide and determining a target value as a limit value minus a tolerance; continuously detecting the actual proportion of nitrogen oxides and the actual proportion of carbon monoxide in the exhaust air; acquiring a signal for setting a minimum power; calculating a minimum total fuel supply, using the calculation model, at which the expected proportion of carbon monoxide and the expected proportion of nitrogen oxides, respectively, reach the target value; while continuously monitoring the actual proportion of nitrogen oxides and the actual proportion of carbon monoxide in the exhaust air, reducing the fuel supply as far as the calculated minimum fuel supply or until the respective target value for nitrogen oxides and carbon monoxide is reached.

4. The method as claimed in claim 3, wherein the calculation is carried out repeatedly, wherein the fuel supply is increased when exceeding of one of the limit values is detected, and the fuel supply is further reduced when undershooting of both target values minus a respective process tolerance is detected.

5. The method as claimed in claim 4, wherein the calculation is carried out at regular intervals; or wherein the calculation is carried out as soon as a specified difference between the measured actual proportion of a pollutant in the exhaust air and the target value given therefor is exceeded.

6. The method as claimed in claim 3, wherein the combustion device comprises at least one main burner and at least one secondary burner, which each delivers fuel and/or supply air into the combustion chamber; further comprising: when calculating the minimum fuel supply, determining a distribution of the fuel between the main burner and the secondary burner at which the expected proportion of carbon monoxide and the expected proportion of nitrogen oxides, respectively, reach the target value; reducing the fuel supply, taking into account the previously calculated distribution of the fuel between the main burner and the secondary burner.

7. The method as claimed in claim 6, wherein the secondary burner is a pilot burner.

8. The method as claimed in claim 6, wherein, when there is a relatively large difference between the target value and the calculated or measured actual proportion of carbon dioxide and a relatively small difference between the target value and the calculated or measured actual proportion of nitrogen oxides, the distribution of the fuel is changed, with a higher proportion for the main burner and a smaller proportion for the secondary burner; wherein the fuel supply is subsequently further reduced when undershooting of both target values is detected.

9. The method as claimed in claim 6, wherein, when there is a relatively large difference between the target value and the calculated or measured actual proportion of nitrogen oxides and a relatively small difference between the target value and the calculated or measured actual proportion of carbon dioxide, the distribution of the fuel is changed, with a higher proportion for the secondary burner and a smaller proportion for the main burner; wherein the fuel supply is subsequently further reduced when undershooting of both target values is detected.

10. The method as claimed in claim 3, wherein a supply air measurement device determines at least one property of the supply air, wherein the property is taken into account in the control device when calculating the fuel supply and/or distribution of the fuel.

11. The method as claimed in claim 3, wherein the calculation parameters and available state data, comprising one or more of actual states of the combustion device and/or the type and/or quality of the fuel and/or the temperature and/or air humidity of the supply air and/or the actual proportion of nitrogen oxides and/or carbon monoxide in the exhaust air, are/is continuously stored, and regular or continuous adaptation of the calculation model is carried out on the basis of the stored data.

12. The method as claimed in claim 3, wherein the fuel is gaseous.

13. The method as claimed in claim 1, wherein the combustion device comprises a gas turbine.

14. The method as claimed in claim 2, wherein the combustion device comprises a gas turbine.

15. The method as claimed in claim 3, wherein the combustion device comprises a gas turbine.

16. The method as claimed in claim 10, wherein the at least one property of the supply air comprises temperature and/or air humidity.

17. The method as claimed in claim 11, wherein the regular or continuous adaptation of the calculation model is carried out on the basis of the stored data by methods of self-learning.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] A combustion device and a time sequence are outlined schematically in the following figures. More specifically:

[0040] FIG. 1 shows a schematic illustration of a combustion device according to the invention;

[0041] FIG. 2 shows a schematic illustration of one possible profile of parameters over time when using the method according to the invention.

DETAILED DESCRIPTION OF INVENTION

[0042] FIG. 1 schematically outlines a combustion device 01 according to the invention. First of all, this comprises the combustion chamber 02 with the main burner 03 arranged thereon and the secondary burner 04. Fuel 23 and supply air 21 can be fed to the burners 03, 04. Exhaust air 25, i.e. flue gas, emerges from the combustion chamber 02.

[0043] To control the method, there is a control device 11, in which a calculation model 12 is stored and which, in this exemplary embodiment, comprises a data memory 13. Various characteristic quantities are transmitted to the control device 11. On the one hand, the maximum proportion of nitrogen oxides 16 and the maximum proportion of carbon monoxide 17 are specified as fixed values. These may be the respectively permissible limit value or the target value. In the first case, the target value can be calculated by the control device. It is likewise possible to transmit both the permissible limit value and the respective target value to the control device 11 as stipulated values.

[0044] It is furthermore necessary for the type or quality 24 of the fuel 23 to be known in the calculation model. For this purpose, provision is made, by way of example, for this type or quality 24 to be continuously detected and transmitted to the control device 11. Provision is furthermore made in this exemplary embodiment for the temperature and the air humidity 22 of the supply air 21 to be measured and transmitted to the control device 11.

[0045] It is furthermore essential for the method according to the invention that the actual proportion of nitrogen oxides 26 and/or the actual proportion of carbon monoxide 27 in the exhaust air 25 be continuously measured and transmitted to the control device 11.

[0046] The method according to the invention is triggered by a signal for running up to a minimum power, for which purpose the respectively required setpoint power 15 is transmitted to the control device 11.

[0047] When the method is carried out in the control device 11 on the basis of the calculation model 12 stored there, the minimum fuel supply and, at the same time, the optimum distribution between the main burner 03 and the secondary burner 04 are calculated. On the basis of the calculation result, a correspondingly associated main valve 05 for controlling the fuel flow to the main burner 03 and a correspondingly associated secondary valve 06 for controlling the fuel flow to the secondary burner 04 are actuated by the control device 11.

[0048] FIG. 2 illustrates, by way of example a possible method sequence with various characteristic quantities over time. Starting from a normal power of the combustion device, the signal to run up to a minimum power P.sub.soll was output at time T1. A minimum power or minimum fuel supply at which the specified limit values for the proportion of nitrogen oxides and the proportion of carbon monoxide are maintained (i.e. at least one target value is reached) is then calculated in the control device 11 on the basis of the calculation model 12. In this case, the target value NOx.sub.max is specified in the control device. In accordance with the calculation, the fuel supply and thus the power P.sub.ist is now reduced. As a rule, the reduction in the power is accompanied by an increase in the proportion of pollutants, i.e. in this case the proportion of nitrogen oxides NOx.sub.ist, and the proportion of carbon monoxide (not illustrated here)—see time T2.

[0049] Now, it may be, for example, that the target value for carbon monoxide has already been reached in the calculation, whereas there is still a relatively large difference between the target value for nitrogen oxides and the measured value NOx.sub.ist. This leads to the advantageous method of changing the fuel distribution, such that there is also a difference between the target value for carbon monoxide and the calculated value, this being accompanied by a reduction of the difference between the target value for nitrogen oxides and the measured value NOx.sub.ist—see time T3. Here, a renewed reduction of the fuel quantity can be performed until the target values NOx.sub.max corresponding to the calculation or the respective measurement are substantially reached—see time T4.

[0050] Now, there may be a stabilization of the process, in which the proportion of pollutants decreases in the course of time—see time T5. By virtue of the continuous monitoring of at least one pollutant, it is possible to trigger a new calculation if a difference arises, thus allowing renewed lowering of the fuel supply and thus of the power P.sub.ist—see time T6.