Abstract:
A method for operating a refuse incineration plant and to a regulating system, in which, after the fire has been fanned, the generation of heat is made more uniform by regulating at least one of the following operating parameters: refuse metering; residence time on a grate; quantitative supply of primary air; and quantitative preheating of primary air. To match the operating parameters to a varying calorific value of the refuse, the calorific value of the refuse is recorded as well as the standard regulating variables and is used to adapt the regulating device. The measure used for the calorific value is, for example, the moisture content of the flue gas generated during the incineration. Consequently, there is no need for the operator to estimate the calorific value and manually adapt the operating parameters accordingly.

Description:
PRIORITY CLAIM 
     This is a U.S. national stage of application No. PCT/CH01/00630, filed on Oct. 24, 2001. Priority is claimed on that application: 
     Country: Switzerland, Application No.: 2000 2398/00, Filed: Dec. 8, 2000. 
    
    
     The invention relates to a method for operating a refuse incineration plant. The method further relates to a regulating system for regulating at least one of the operating parameters of a refuse incineration plant, and to a refuse incineration plant having a regulating system of this type. 
     The operation and in particular the uniform generation of heat in oil-fired or coal-fired power plants does not cause problems. This uniform generation of heat is achieved by uniform metering of the fuel, the quality of which is constant and known. The main aim of refuse incineration plants too is to keep the heat output constant. In addition, the flue gas has to comply with certain statutory regulations with regard to quality and quantity. The heat output cannot be controlled simply by metering the refuse supplied, since the calorific value of the refuse, on account of its differing composition and the varying water content, may fluctuate considerably. Accordingly, it is already difficult to maintain a constant quantity of heat. Additional optimization of the other parameters causes even more problems. 
     EP-B-0 499 976 has disclosed a method for operating a refuse incineration plant in which, to make the amount of heat which is generated more uniform, the supply of refuse, i.e. the movement of the metering ram, the conveying of refuse on the grate, i.e. movement or lifting frequency of the grate parts, and the supply of primary air is regulated by means of a cascaded regulating system. The quantity of steam which is generated is recorded with a slight delay and is used as the main regulating variable. The value for the oxygen content of the flue gas, which is rapidly available, is used as an auxiliary regulating variable. With this firing capacity regulation, it is possible for the refuse incineration plant to be substantially automatically matched to slightly changing properties of refuse and therefore to minor fluctuations in calorific value. However, the grate frequency, ram movement and primary air supply are always increased or reduced in the same direction. Consequently, this fire capacity regulation does not sufficiently compensate for relatively substantial changes in the condition or calorific value of the refuse which require the operating parameters to be changed in opposite directions. This is the case, for example, when switching over to wet, highly compacted refuse, in which case the ram velocity should be lowered in order to reduce the supply of refuse and the grate frequency should be increased in order to split or break up the refuse. In the known process, although the fluctuation in calorific value is compensated for in the short term by fanning or retarding the firing intensity and in the longer term by means of the metered quantity of refuse, the automatic fire capacity regulation takes no account of the correct incineration profile over the grate length. 
     In practice, such changes in the calorific value are usually compensated for by an operator by visual assessment of the condition of the refuse or the state of the fire. The operator then manually adjusts individual operating parameters; for example, in the case of wet refuse, the primary air preheating is often increased. A problem of this is that it is complicated to adjust the operating parameters, on account of the wide range of possible actions and interactions, and the adjustments are not always selected optimally. Furthermore, success is very dependent on the experience of the operator. The regulating process has an extremely long delay time, and consequently the full effects of an intervention can only be assessed after about an hour. 
     SUMMARY OF THE INVENTION 
     Therefore, the invention is based on the object of simplifying operation of a refuse incineration plant, in particular of providing a method for operating a refuse incineration plant in which the operating parameters are to a large extent automatically adapted to changing refuse properties, in particular fluctuations in the calorific value. 
     To operate a refuse incineration plant, after the fire has been fanned, the generation of heat is made more uniform (fire capacity regulation) in a manner known per se by regulating a plurality of operating parameters, including at least one of the operating parameters: refuse metering; residence time on a grate and quantitative supply of primary air, as a function of a plurality of measured variables, including at least one of the measured variables: oxygen content in the flue gas and quantity of steam generated. By way of example, the method which is known from EP-B 0 499 976 is used. According to the invention, a calorific value parameter, which is a measure of the calorific value of the metered refuse or the change in this value, is derived from a measured variable. As a modification to the known control techniques, at least one of the operating parameters is adjusted at least in part as a function of the calorific value parameter. 
     The calorific value or the change in this value is automatically recorded by analyzing suitable measured variables. The calorific value parameter is used to influence the regulation of at least one operating parameter in accordance with a predetermined plan which is, for example, empirically determined or drawn up using model calculations. Ideally, therefore, no manual intervention is required, but rather the intervention takes place automatically on the basis of objective criteria, and the plant can in principle be left to run itself. 
     In addition, it is also possible to provide the option of manual intervention. To this end, the calorific value or the change in this value is estimated by an operator, for example by observing the fire position. The process control unit is used to input as calorific value parameter a variable which indicates, for example, the extent to which the estimated calorific value deviates from the nominal calorific value assumed when dimensioning the firing installation. 
     The measured variable for the calorific value parameter is recorded automatically. In an advantageous refinement of the method, the moisture content of the flue gas is used as a measure for the calorific value. This is based on the fact that the calorific value of the refuse is substantially determined by its water content. Since the water contained in the refuse begins to evaporate as soon as it is fed into the furnace, the measured moisture content reproduces changes in the refuse composition without a major time delay. A corresponding signal is then immediately available in order for the operating parameters or the regulation thereof to be matched to the changed calorific value. The moisture content of the flue gas can be measured directly by means of a humidity sensor. Preferably, however, the flue gas is saturated with water, and the readily measurable temperature of the saturated flue gas is used as a measure of the moisture content and therefore of the calorific value. The extraction of heat through evaporation is greater if less water was present in the flue gas from the outset. The temperature of the water-enriched flue gas is therefore a measure of the original water content of the refuse and therefore of the calorific value. Since in many refuse incineration plants a water injection means and a scrubber are present, this variant can be implemented particularly easily. The temperature is preferably measured downstream of the water injection means, in the sump of the scrubber or at the scrubber outlet. 
     The calorific value parameter is used to automatically determine at least one correction variable which modifies at least one of the setting values from the fire capacity regulation and/or one of the variables used for fire capacity regulation, e.g. input variables or amplifications of regulators involved. Preferably, a plurality of operating parameters are influenced in such a way, so that, by means of an intervention or on the basis of the automatically recorded calorific value, the characteristic diagram of the entire plant can be shifted and optimally matched to the changed calorific value. Correction variables are determined, for example, on the basis of model calculations or are based on empirical values. 
     The correction variable is used, for example, to shift the setting range or working point of an individual regulator, while the capacity regulation otherwise keeps the heat output constant in a known way. 
     In a further advantageous refinement of the invention, the correction variable determined from the calorific parameter value is used to modify the regulator amplification of at least one regulator. In this way, the operating range of this regulator is adapted to the changed calorific value. In addition, corresponding correction variables determined from the same calorific value parameter can also be used to adapt the setting value and/or the desired value of this regulator or of other regulators. 
     Preferably, the following operating parameters are adjusted as a function of the calorific value parameter: sum of primary air and secondary air, ratio of primary air to secondary air, zone flap position, primary air, refuse metering, residence time on the grate, desired oxygen value, primary air preheating. 
     The regulating system according to the invention for regulating at least one of the operating parameters of a refuse incineration plant has at least one regulator which, on the basis of at least one regulating variable supplied as an input signal and/or at least one desired value, generates an output signal which is fed as a setting value to one of the actuators for the ram, grate, primary air flaps or primary air preheater. According to the invention, there is a first measuring device for recording a measured variable from which a calorific value parameter, which is a measure of the calorific value of the refuse or the change in this value, is derived. Furthermore, there is a calorific value correction unit which, on the basis of the calorific value parameter, generates at least one correction variable, which is used to modify at least one desired value and/or setting value and/or a regulator amplification of the at least one regulator. 
     The regulating system is used in particular to carry out the method according to the invention. 
     A refuse incineration plant having a regulating system of this type has all the advantages of the regulating system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are illustrated in the figures and described below. In the figures: 
     FIG. 1 diagrammatically depicts a flow diagram of a refuse incineration plant; 
     FIG. 2 diagrammatically depicts an example of a regulating means according to the invention; 
     FIG. 3 a  diagrammatically depicts examples for characteristic curves of a servo regulator for the grate at different calorific values; 
     FIG. 3 b  diagrammatically depicts examples for characteristic curves of a servo regulator for the air supply at different calorific values; 
     FIG. 4 diagrammatically depicts an example of a regulator circuit for the servo regulator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a flow diagram of a refuse incineration plant. Refuse is fed to the combustion chamber  101  by means of a ram (not shown here). The refuse which is metered in passes onto a driven incineration grate (not shown here), where it is dried, degassed and incinerated. The incineration sequence is influenced by the supply of primary air, secondary air and the grate movement. The hot flue gases  102  pass from the combustion chamber  101  into a boiler (not shown here), where they are used for steam generation. The flue gas then passes through a water injection means or quench device  103 , in which the flue gas  102  is saturated with water  104 . The saturated flue gas  105  is then fed to the flue-gas cleaning stage  106 . 
     A temperature-measuring device  108  measures the temperature of the water-saturated flue gas  105 . The measured value is fed to a processing unit  109 , which generates a calorific value parameter  110 . The processing unit  109  comprises, for example, a PI regulator. By way of example, the deviation of the instantaneous temperature of the sliding temperature mean is taken as a measure of the calorific value or the calorific value deviation. The temperature of the flue gas which is used for regulation purposes may be measured downstream of the quench device  103 , in the sump of the scrubber  106  or in the region of the scrubber outlet. 
     To determine the calorific value parameter  110 , it is also possible to measure the moisture content of the unsaturated flue gas  102  using a humidity-measuring device  107  and for this measurement to be evaluated in the processing unit  109 . This is recommended in particular for plants without a quench device  103 . 
     In a manner which is known per se, the regulating system shown in FIG. 2 has measuring devices  201 ,  202  for measuring the oxygen content of the flue gas and the quantity of steam. The operating parameters are regulated as follows: refuse metering by influencing the actuator “ram”  209 , residence time on the grate by influencing the actuator “grate”  210 , primary air preheating by influencing the corresponding actuator  208  and further parameters of the primary and secondary air supply and distribution by influencing the functional unit “air”  211 , which may include further regulators. The functional unit “air”  211  is used to influence, for example, actuators which are not shown here for the total air quantity, primary air quantity, secondary air quantity, air supply to the individual grate zones. 
     The measured value for the quantity of steam  222  is fed as input signal to a main or lead regulator  203 . This is preferably a slow-operation PI regulator. Its output signal  223  is fed to three downstream auxiliary or servo regulators  204 ,  205 ,  206 , which are preferably quick-operation P regulators. The desired value of the auxiliary regulators  204 ,  205 ,  206  is adjusted by the output signal  223  of the main regulator  203  on the basis of the measured steam values. The measured value for the oxygen content  224  is fed to the auxiliary regulators  204 ,  205 ,  206  as a further input signal. The predetermined desired value for the oxygen content  213  is used as a third input signal for all three auxiliary regulators  204 ,  205 ,  206 . The outputs of the auxiliary regulators  204 ,  205 ,  206  are connected to the actuators ram, grate and air  209 ,  210 ,  211 . 
     A control unit  214  is used to determine the basic setting of the actuators  209 ,  210 ,  211  on the basis of a predetermined desired steam value  212 . Corresponding signals  226  are fed to the actuators  209 ,  210 ,  211  as basic setting values. These basic setting values are modified by the output signals from the auxiliary regulators  204 ,  205 ,  206 , which are added, for example, to the basic setting values  226 . 
     According to the invention, the control system which has been described hitherto and is known per se is expanded by a feature allowing the regulation to be automatically adapted to changing calorific values. For this purpose, there is a measuring device  217  for providing a measured variable from which a measure of the calorific value or its change can be derived, for example the temperature of the water-saturated flue gas. A calorific value parameter  228 , which is fed as input variable to a calorific value correction unit  215 , is generated from this measured variable in a unit  216 . This correction unit uses the calorific value parameter to determine a plurality of correction variables  218 ,  219 ,  220 ,  221 , which are used to modify the regulation of the operating parameters. Firstly, the calorific value correction unit  215  generates an oxygen desired-value correction variable  218 , which is used to match the oxygen desired value  213  fed to the auxiliary regulators as input variable  225  to the changed calorific value, for example by adding the correction variable to the desired value. Setting-value correction variables  219  are used to modify the setting value  227  fed to the actuators  209 ,  210 ,  211 . By way of example, the setting value  227  used is the sum of the output signal from the auxiliary regulators  204 ,  205 ,  206 , the corresponding basic setting value  226  and the corresponding correction variable  219 . By suitably assigning correction variables  219  to the individual actuators, it is possible, by means of a single, automatically executed intervention, to optimally match the operating parameters to the current calorific value. By way of example, in the event of a transition to wet, highly compacted refuse (lower calorific value), the ram velocity is reduced (negative correction variable for actuator ram  209 ) and the grate lifting frequency is increased (positive correction variable for actuator grate  210 ). 
     In a preferred refinement of the invention, the calorific value correction unit  215  generates further correction variables  220 , which are used to modify the amplification of the auxiliary regulators  204 ,  205 ,  206 . By way of example, at high calorific values the amplification of the auxiliary regulator  205  which regulates the actuator grate  210  is increased and the amplification of the auxiliary regulator  206  which regulates the functional unit air  211  is reduced. At the same time, the basic setting values are adapted using correction variables  219 . This is based on the discovery that different refuse calorific values require different regulator responses (amplifications) for the same regulator deviation. Furthermore, the burn-off behavior of the refuse on the grate is dependent on the calorific value and therefore requires measures which ensure the optimum grate coverage for any condition of refuse (adaptation of the basic setting values). By way of example, at high calorific values the plant is preferably operated with a grate bias, i.e. with a short residence time on the grate, and at low calorific values the plant is preferably operated with an air bias. This can be achieved by modifying the regulator amplification in accordance with the invention. 
     The calorific value correction unit  215  generates a further control variable  221  which serves directly as a setting value for the primary air preheating actuator  208 . 
     FIGS. 3 a  and  3   b  in each case show two examples of characteristic curves of a servo regulator for the grate and for the air supply and the setting variables of the corresponding actuators for high calorific values (dashed line) and low calorific values (dotted line). FIG. 3 a  shows the grate lifting frequency f R  as a function of the measured oxygen content or the deviation of the servo regulator. If the control deviation is zero, the setting value x1, x2 is given by the basic variable which has been determined by the control unit  214  and corrected on the basis of the recorded calorific value. Accordingly, the basic setting x1 for a high calorific value is lower than the basic setting x2 for a low calorific value. The increase in the characteristic curves is determined by the regulator amplification, which is higher for a high calorific value than for a low calorific value. In the case of the primary air supply PL, the regulation of which is illustrated in FIG. 3 b , the basic setting X1, X2 and regulator amplification are lower for a high calorific value than for a low calorific value. 
     FIG. 4 shows an example of a regulator circuit for the servo regulators  205  or  206  from FIG.  2 . Correction variables  218 ,  219 ,  220  are generated from the calorific value parameter  228  in the calorific value correction unit  215 . The association takes place on the basis of predetermined functions, which are symbolized in FIG. 4 by nonlinear curves in the unit  215 . The oxygen desired value  213 , with the output signal  223  from the steam regulator, which indicates the oxygen desired value shift, and the desired value correction variable  218 , is fed to an adder. The difference with respect to the current oxygen measured value  224  is amplified or attenuated, the proportionality factor being determined by the regulator amplification correction variable  220 . The basic variable  226  for the setting value  227  and a setting-value correction variable  219  is added to this regulator amplification correction variable  220 . The basic variable  226  for the setting value  227  is generated in the control unit  214  by multiplication and addition using predetermined variables from the preset steam desired value  212 . The actuator  209  or  210  is actuated using the setting value  227  generated in this way.