EP0352619A2 - Process for regulating the firing power in combustion plants - Google Patents

Abstract

The process for regulating the firing power in combustion plants, in particular in refuse combustion plants, in which process the measured O2-moist content of the flue gas is used as higher-order set point controlled variable for regulating the fuel supply and the measured steam flow rate as lower-order set point controlled variable (10) for regulating the primary air supply, provides, in accordance with a first variant, for the specified O2-moist set point (7) to be varied as a function of the combustion chamber temperature (6) measured in the flue gas. This varied controlled variable (9) is fed to a regulator (13) which influences the fuel feed and/or the grate drive. …<IMAGE>…

Description

The invention relates to a method for controlling the fire output in incineration plants, in particular waste incineration plants, in which the O ₂ moisture content measured in the flue gas as the higher-level setpoint control variable for controlling the fuel supply and optionally the measured steam mass flow or the combustion chamber temperature measured in the combustion gas is used as a subordinate setpoint control variable for controlling the primary air supply.

In a known method of this type, the connection of thermal measured values, e.g. B. furnace temperature and steam mass flow, and material measurements, z. B. O ₂ moisture content, keeping the fire output constant on the one hand, ie keeping the steam mass flow constant and minimizing pollutant emissions on the other hand, ie reducing the pollutants contained in the flue gas such as carbon monoxide, dust, hydrocarbons and nitrogen oxides. The use of the O ₂ moisture content as a higher-level control variable within such a control concept results in a quickly responsive control.

A disadvantage of this method is the fact that the O ₂ moisture content does not provide any definite information about the O _{2 dry} content and thus about the true excess air. However, the measurement of the O _{2 dry} content of the combustion gas is too sluggish and too uncertain under the existing operating conditions.

If the O ₂ moisture content is kept constant as the higher-level setpoint and the steam mass flow is kept constant, there is a shift in the combustion chamber temperature in the event of fluctuations in the moisture content of the flue gases. However, these fluctuations in the moisture content of the flue gases cannot be avoided due to the rapidly changing fuel composition in waste incineration plants. This can lead to a deterioration in the emission values for the set and desired performance.

If, on the other hand, the combustion chamber temperature is kept constant as a higher target value while the O ₂ moisture content is kept constant, there is a change in the steam mass flow in the event of fluctuations in the moisture content of the flue gases, which can lead to a deterioration in the thermal utilization of the overall system.

Because of the importance of low emission values for the environment, the material size, ie the O ₂ moisture content, dominates over the thermal values, namely the steam mass flow and the combustion chamber temperature.

The object of the invention is to optimize both the emission values and the fire performance based on the two variants of the known methods mentioned at the outset.

This task can be accomplished in two ways.

The solution to the problem is based on a process in which the O ₂ moisture content measured in the flue gas is used as the higher-level setpoint control variable for controlling the fuel supply and the measured steam mass flow as lower-level setpoint control variable for the control of the primary air supply that the specified O ₂ humidity setpoint is changed as a function of the combustion chamber temperature measured in the flue gas.

If, on the other hand, one proceeds from a process in which the O ₂ moisture content measured in the flue gas is used as the higher-level setpoint control variable for controlling the fuel supply and the combustion chamber temperature measured in the flue gas is used as the lower-level setpoint control variable for controlling the primary air supply The solution to the problem is that the predetermined O _{2 wet} setpoint is changed as a function of the measured steam mass flow.

When the first variant of the method is carried out, two temperature points are defined as limit values, the O _{2 moist} setpoint being increased when the upper temperature value is exceeded, while the value is increased when the temperature falls below the lower temperature limit O _{2 wet} setpoint is lowered. In the first case the "apparent" excess air is increased, while in the second case the "apparent" excess air is reduced. As long as the combustion chamber temperature is within the selected limit values, there is no influence on the O ₂ humidity setpoint.

A similar procedure is used for the second variant, with two steam mass flow limit values being selected instead of two temperature limit values, the O ₂ moisture setpoint being increased or decreased when they are exceeded or undershot. Because of the particular importance of the emission values for the environment, priority is also given to the material values, ie the O _{2 wet} setpoint, in the method according to the invention.

An even better control accuracy is achieved according to a preferred embodiment of the method in that the rate of change of the measured temperature or steam mass flow value is taken into account when changing the O _{2 moist} setpoint. In this embodiment, the differential of the temperature change or the change in steam mass flow over time is taken into account, so that a change in the O _{2 moist} setpoint can be carried out before the limit values are reached, as a result of which the combustion system operates even more evenly because the regulation is more sensitive.

The invention is explained below with reference to the diagrams shown in the drawing tert.

• Fig. 1 ein Regelschema bekannter Art;
• Fig. 2 eine erste Regelvariante nach der Erfindung; und
• Fig. 3 eine zweite Regelvariante nach der Erfindung

In this show:

• 1 shows a control scheme of a known type;
• 2 shows a first control variant according to the invention; and
• Fig. 3 shows a second control variant according to the invention

1 explains the known method described at the outset. Thereafter, the O ₂ moisture content measured in the flue gas 2 is used as the higher-level control variable 7, which is fed to a controller 3, which, if this control variable deviates from a specific range of guide values, is used to regulate the fire output of a combustion system 1 consisting of the furnace and boiler acts to feed the furnace with fuel and / or acts on the grate drive.

At the same time, the steam mass flow ṁ _D emerging from the boiler is measured and this control variable 10 is fed to a further controller 5 which, if the measured value deviates from a predetermined range of guide values for the steam mass flow, to the devices provided for setting the amount of combustion air, such as, for. B. acts fan drive and control flaps in the air distribution system.

The disadvantages of this control method have been explained at the beginning.

In a first variant of the control procedure according to According to the invention, which is shown in FIG. 2, both the combustion chamber temperature as controlled variable 6 and the O ₂ moisture content, which is designated as measured value 7, are determined in the flue gas 2 emerging from the combustion system 1. Both values 6 and 7 are fed to a controller 8. On the basis of an operating mode to be regarded as particularly favorable or optimal, the measured O ₂ moisture content is regarded as the target value. If there is a change in the combustion chamber temperature, this change having to be above a predetermined tolerance limit, the O _{2 wet} setpoint is changed by the controller 8. If the upper tolerance limit of the temperature value is exceeded, the O _{2 wet} setpoint is increased, while if the lower temperature tolerance limit is undershot, the O _{2 moist} setpoint is lowered. This modified O _{2 moist} setpoint is then fed as a control variable 9 to the controller 3, which changes the fuel supply by acting on the feed device and / or changes the grate speed by acting on the grate drive. In contrast to the known method shown in FIG. 1, the controller 3 is therefore not acted on with the measured O _{2 moist} value, but rather with an O _{2 moist} setpoint corrected as a function of the furnace temperature.

At the same time, at 4, as is also the case in the method explained in FIG. 1, the measured steam mass flow ṁ _{D is} fed as control variable 10 to the controller 5, which monitors the combustion air supply, as in the known method.

In the second variant of the control method according to the invention, which is explained in FIG. 3, the measured O ₂ -measured measured value is also used as the target value, starting from an operating state which is considered to be optimal. This measured value is also recorded in the flue gas 2, which leaves the combustion system 1 consisting of the furnace and the boiler. This measured value 6 is fed to the controller 8. At the same time, the controller 8 receives the steam mass flow ṁ _D measured at 4 as the control variable 10. The controller 8 now changes the control variable 6 when the steam mass flow leaves a predetermined range of guide values, namely when the upper steam mass flow limit value is exceeded, the O _{2 moist} setpoint is increased and when the lower steam mass flow limit value is undershot, the O _{2 moist} Setpoint value lowered and supplied as a corrected control variable 11 to the controller 3, which makes a change in the fuel supply and / or the combustion grate speed in the event of a corresponding deviation in the O _{2 moist} setpoint value. The combustion chamber temperature measured in the flue gas is fed as a subordinate control variable 12 to the controller 5, which monitors the amount of combustion air supplied.

Claims (3)

1.Procedure for controlling the fire output in incineration plants, in particular waste incineration plants, in which the O ₂ moisture content measured in the flue gas is used as the higher-level setpoint control variable for controlling the fuel supply and the measured steam mass flow is used as subordinate setpoint control variable for controlling the primary air supply is characterized in that the predetermined O _{2 moist} setpoint is changed depending on the combustion chamber temperature measured in the combustion gas. 2.Procedure for controlling the fire output in incineration plants, in particular waste incineration plants, in which the O ₂ moisture content measured in the flue gas as the higher-level setpoint control variable for controlling the fuel supply and the flue gas temperature measured in the flue gas as lower-level setpoint control variable for controlling the Primary air supply is used, characterized in that the predetermined O _{2 moist} setpoint is changed depending on the measured steam mass flow. 3. The method according to claim 1 or 2, characterized in that the rate of change of the measured temperature or steam mass flow value is taken into account when changing the O _{2 wet} setpoint.

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