EP1274961B1

EP1274961B1 - A process for the incineration of solid combustible material

Info

Publication number: EP1274961B1
Application number: EP00918617A
Authority: EP
Inventors: Hendrik Seghers
Original assignee: Seghers Keppel Technology Group
Current assignee: Keppel Seghers Holdings Pte Ltd
Priority date: 2000-04-21
Filing date: 2000-04-21
Publication date: 2006-06-14
Anticipated expiration: 2020-04-21
Also published as: DE60028833T2; PT1274961E; CN1460167A; EP1274961A1; AU2000239507A1; DE60028833D1; ES2265927T3; WO2001081827A1; ATE330177T1; CN1217128C

Abstract

This invention relates to a method for incinerating solid combustible material in an incineration zone in an incineration reactor. The method of this invention comprises the steps of adjusting at least one of the charging to or the feeding of the combustible material through the incineration zone so as to maintain the amount of material in the incineration zone substantially constant, comprising the steps of (1) measuring an over-all gas pressure P<i> in the incineration zone, (2) measuring a primary gas pressure below the carrier for the combustible material P<g>, (3) determining DELTA P<r> = P<i> - P<g> (4) determining DELTA P<ro> which is the pressure difference over the carrier that corresponds to the optimum amount of material in the incineration zone, (5) calculating the difference DELTA P between DELTA P<ro> and DELTA P<r>, (6) minimising DELTA P by adjusting the speed of the charging or the feeding of the combustible material to or through the incineration zone.

Description

The present invention relates to a process for incinerating solid combustible material, in particular solid combustible refuse, as described in the preamble of the first claim. In the following description with the wording refuse, solid combustible material in general is referred to as well as solid refuse material in particular.
In general, an incineration process in which the combustion of solid combustible material can be controlled on a permanent basis is highly desirable for a number of reasons. First of all, a stable combustion facilitates meeting the emission standards imposed by law for exhaust gasses, flue dust and ashes. Furthermore, by limiting temperature variations within the incinerator, energy costs for maintaining the optimal combustion conditions can be minimised. Finally, by limiting temperature variations within the incinerator also the variations in thermal and mechanical loads to which the incinerator is subjected can be minimised, which in turn will lead to an extended lifetime of the incinerator, in particular of the feeding and combustion grate.
However, the operation of a refuse incinerator may be complicated by variations occurring in a.o. size and density of the refuse which is mostly supplied in the form of more or less dense packs, and variations in the composition of the refuse, for example its water content, which lead to variations in the calorific value of the refuse. Variations in these parameters may largely complicate the process and its control system, in particular in case the control system aims at constant steam production output, wherein a steam controller controls the refuse combustion rate.
In a first known system aiming at constant steam production, the steam controller controls the amount of primary combustion air supplied to the incinerator, based on the steam output. The primary combustion air is responsible for the maintenance of the combustion process. This kind of system however is often burdened with the problem of an overloaded combustion grate system and incompletely burned ashes. Namely as steam output decreases, additional primary combustion air is supplied to the incinerator. This often leads to a further reduction of the combustion chamber temperature instead of an increase thereof. Cooling of the combustion chamber especially occurs in case the primary air is not capable of penetrating the refuse, for instance because the waste is too dense, or a big heap of wet refuse is formed. As the combustion rate decreases and the primary air supply is nevertheless increased, the oven cools down. Simultaneously the oxygen concentration in the flue gases increases.
In a second known system that aims at constant steam output, the latter is controlled by controlling the amount of refuse supplied to the incinerator. Thereto, the speed of the grate supplying the refuse to the oven is varied. Such a system often entails the problem of involving an overloaded combustion grate system, especially in case the refuse is rather dense and the primary air is hardly capable of penetrating the refuse. As a result, the refuse may be incompletely burned, even when supplying a large amount of primary air.
A solution to the problem of the varying operation of a refuse incinerator is given in US-A-5.398.623. In the method disclosed in US-A-5.398.623 an attempt is made to stabilise the operation of the refuse incinerator by keeping the amount of refuse on the combustion grate system approximately constant, regardless of the calorific value or the density of the refuse. This is done by varying the speed of the combustion grate system, i.e. the speed with which the refuse is advanced through the incinerator. The amount of refuse present on the combustion grate system is determined by monitoring the resistance exerted to the hydraulic drive mechanism which drives the combustion grate system. This resistance Is measured as the hydraulic pressure in the hydraulic drive mechanism.
The method disclosed in US-A-5.398.623 has the disadvantage that the system with which the amount of refuse on the combustion grate system is monitored and controlled is one and the same system, i.e. the hydraulic drive mechanism that drives the combustion grate system. The speed of the combustion grate system is controlled by adjusting the flow rate of the hydraulic liquid in the hydraulic drive mechanism. However, by varying the flow rate of the hydraulic liquid to vary the speed of the combustion grate system, the hydraulic pressure as such in the drive system is varied and the hydraulic pressure measured will no longer correspond to the amount of refuse present on the combustion grate system. As a consequence, the method disclosed in US-A-5.398.623 cannot be used to control the amount of refuse on the combustion grate system, unless the hydraulic system is not controlled, i.e. the speed of the combustion grate system is not controlled by the hydraulic drive mechanism.
EP-A-0 9 55 499 discloses a method for the incineration of solid combustible material in an incineration reator according to the preamble of claim 1 in which the rate of flow of primary air to combustion zones in the incinerator is adjusted based on measurement devices located within the combustion zones. Patent Abstracts of Japan, Vol 008, No 258 (M-340) in respect of JP 59129316 A. describes a process for drying dust in which a dust feeder is controlled in response to sensed values of pressure below the drying grids and the volume of air to be fed below the drying grids. Neither devices nor methods disclosed obtain reliable measurement readings owing fouling and inaccurate readings from the sensors. Consequently, combustion or drying is inefficient.
There is thus a need to find a method with which the amount of refuse supplied to the incinerator can be determined and controlled, independent of the hydraulic system that is responsible for the displacement of the combustion grate system.
It is the aim of the present invention to provide a method with which the amount of refuse supplied to the incinerator can be determined in a reliable manner and the incinerator can be operated in a stable manner.
This is achieved with the present invention with the features of the characterising part of the first claim.
According to the method of this invention, 1) first ΔP^ro is determined. ΔP^ro is the optimum gas pressure difference over the refuse bed on the carrier, which corresponds to an optimum incineration process and is representative for the optimum amount of refuse on the carrier. As the refuse on the carrier constitutes a resistance which hinders the passage of the primary combustion air from a position below the carrier to the incineration zone above the carrier, ΔP^ro is representative for the optimum amount of refuse on the carrier

2) the actual gas pressure Pⁱ in the incinerator is measured at a position above the carrier
3) the actual gas pressure P^g of the primary combustion air at the position of the inlet in the incinerator, below the carrier carrying the refuse is measured
4) the difference ΔP^r = P^g - Pⁱ is calculated. The difference ΔP^r is proportional to the resistance sensed by the gas, when flowing from the primary air inlet through the refuse towards the incineration zone and gives an indication of the amount of refuse on the carrier
5) ΔP^r - ΔP^ro = ΔP is calculated. ΔP^ro corresponds to the pressure difference over the carrier that corresponds to an optimum combustion process. ΔP is the difference between an actual pressure difference over the carrier and the optimum pressure difference over the carrier
6) at least one of the speed of the charging of the combustible material to the incineration zone or the feeding of the combustible material through the incineration zone is adjusted to minimise ΔP.

Making the subtraction ΔP^r = P^g - Pⁱ is in fact a first correction which minimises the influence of non-process parameters on the primary air pressure below the carrier. By this first correction the influence of non-process parameters on the adjusting of at least one of the speed of the charging of the combustible material to the incineration zone or the feeding of the combustible material through the incineration zone can be minimised.
With this first correction in particular the influence of a varying pressure in the incineration zone can be minimised. Such pressure variations can for example be due to a varying flue gas production in the incinerator, especially with sudden changes in the physical properties or the heating value of the refuse. By the above described correction it is possible to prevent that the feeding or transporting speed of the refuse is constantly adapted to pressure fluctuations which have nothing to do with the amount of refuse on the carrier itself.
In the method of this invention, the speed of the carrier for the refuse is controlled by adjusting the hydraulic pressure of the mechanism which drives the carrier. The amount of refuse present on the carrier on the other hand is determined by measuring the gas pressure difference over the carrier in the incinerator. In that way the driving of the carrier is uncoupled from the measurement of the amount of refuse on the carrier, so that interference of both phenomena can be prevented and a reliable measurement of the amount of refuse on the carrier can be done.
This uncoupling of both mechanisms entails the advantage that the carrier can be driven in a continuous manner and operated at varying speed, and still allow a reliable measurement of the amount of refuse on the carrier.
Moreover, with the method of this invention the speed of the grate can be controlled in a continuous manner. The movement of the carrier can namely be described as a repeated alternating, slow, back and forth sliding in an approximately continuous manner, to advance the refuse over the carrier. Because the carrier can be driven in an approximately continuous manner, there is no necessity to provide dead times between the back and forth sliding of the carrier and the speed with which the carrier is displaced can be kept rather low. In that way not only a more constant steam production can be achieved, but also dust production can be reduced and sudden changes in the release of pollutants in the flue gasses can be avoided, thus leading to a more stable operation of a flue gas treatment plant provided after the incinerator.
As a carrier often use is made of a combustion grate system, but other carriers generally known in the art may also be used. According to the invention, ΔP is divided by the square of the volumetric primary air flow rate v² _pa (m³/s) through the carrier, as a pressure difference over a duct. i.c. a combustion grate element, is always proportional to the square of the flow through that duct. With this correction the influence of varying primary combustion air flow rate on ΔP, thus on the speed of the combustion grate system can be minimised.
Furthermore, in order to allow an optimum control of the incineration of the refuse over the entire incinerator and to ensure that the incineration process proceeds as complete as possible, the incineration zone is divided into a plurality of individual combustion zones, primary combustion air being supplied to each Individual zone, the primary combustion air supply flow rate being adjusted for each individual air supply or incineration zone. Thereto, the actual gas pressure P^g _z at each primary combustion air Inlet device and the actual pressure Pⁱ _z above the carrier in each individual incineration zone z is measured and ΔP^r _z is calculated for each zone. However, since the pressure differences between the individual incinerating zones above the carrier for the refuse are mostly small, the values of Pⁱ _z can be approximated to reasonable accuracy by a single measurement of Pⁱ in the incinerator. Preferably also the flow rate V_pa is measurable and adjustable for each zone.
Primary combustion air is supplied to the incinerator through a primary combustion air supply device. The primary combustion air supply device comprises an inlet through which primary combustion air is supplied to the primary combustion air supply device and an outlet through which primary combustion air is supplied from the primary combustion air supply device to an incineration zone of the incinerator. The flow rate of the primary combustion air in each individual zone is measured by determining

the pressure of the primary combustion air at the inlet and outlet of the primary combustion air supply device,
determining the pressure difference between the inlet and outlet,
calculating the flow rate corresponding to the measured pressure difference.

With known techniques, primary combustion air flow measurements per combustion zone are often not reliable as the air supply pipes are too short to accommodate the required instruments and as the applied instruments are often drifting since they get dirty by the dust present in the airflow. The inventor has now solved these problems by determining the primary air flow rate as follows:

the pressure of the primary combustion air is measured at the inlet and outlet of the air supply device. The pressure difference between inlet and outlet is calculated,
each air supply device has a characteristic curve from which the flow rate corresponding to the pressure difference between the inlet and outlet of the primary combustion air supply device can be determined.

As an air supply device use can be made of devices that are generally known in the art, for example an air fan or an air supply valve. In case use is made of an air fan, if so desired, the calculation may be corrected for variations In the rotation speed of the fan. Determination of the flow rate of the primary combustion air per combustion zone is also possible when primary air is supplied through the existing technique of one single fan, from which the primary combustion air is distributed towards the individual incineration zones through gas control valves, for example butterfly or register valves. In that case the pressure difference over the control valve is measured, and a calculation is done based on the characteristic curve of the control valve instead of the characteristic curve of the fan.
In a second preferred embodiment of this invention, ΔP/v² _pa is measured at predetermined time intervals and averaged as a function of time. This is preferably done by determining and averaging ΔP^r in a continuous manner, in particular by measuring P^g and Pⁱ and calculating the difference ΔP^r = P^g - Pⁱ in a continuous manner. In that way it can be avoided that the feeding or transporting speed of the refuse is adjusted in an unstable manner, due to quick pressure variations which are not important to the combustion process. In this way in fact a filtering of the noise on the pressure difference signal is carried out. An example of pressure variations that are not important to the incineration process as such, is in case the carrier comprises a plurality of subsequent grate elements, the dropping of an amount of refuse from one element on the next element.
The present invention also relates to a device for incinerating solid combustible material, the device comprising an incineration reactor with at least one incineration zone for combusting the combustible material, a carrier for carrying the combustible material and feeding the combustible material through the at least one incineration zone, a device for supplying combustion air below the carrier and means for adjusting the amount of combustible material in the incineration zone.
One embodiment of the present invention is a device for incinerating solid combustible material in an Incineration zone In an incineration reactor such that an optimum amount of material is present in the incineration zone, comprising:

an incinerator reactor with at least one incineration zone for combusting the combustible material,
a carrier for carrying the combustible material and feeding the combustible material through the at least one incineration zone,
a means for supplying combustion air below the carrier and
means for adjusting the amount of combustible material in the incineration zone, whereby the means for adjusting the amount of combustible material in the incineration zone comprise means for:

measuring an over-all gas pressure Pⁱ the incineration zone,
measuring a primary gas pressure below the carrier for the combustible material P^g,
determining a pressure difference over the carrier ΔP^r = Pⁱ - P^g,
determining ΔP^ro which is the pressure difference over the carrier that corresponds to the optimum amount of material in the incineration zone,
calculating the difference ΔP between ΔP^ro and ΔP^r,
minimising ΔP by adjusting at least one of the speed of the charging of the combustible material to the Incineration zone or the feeding of the combustible material through the incineration zone, characterised in that
each incineration zone is divided into a plurality of Individual combustion zones, the device comprising separate air supply devices to supply primary air to each individual combustion zone and comprising means to adjust primary air supplied to each individual combustion zone,
the device comprises a means for adjusting the speed of said feeding or charging of the combustible material based on ΔPlv² _pa, wherein v_pa is the flow rate of the primary combustion air, and
the device comprises means for measuring the flow rate of the primary combustion air in each individual zone, comprising:
- means for determining a pressure of the primary combustion air at an inlet through which primary combustion air is supplied to the primary combustion air supply device,
- means for determining a pressure of the primary combustion air at an outlet of the primary combustion air supply device through which primary combustion air is supplied to the incinerator.
- means for determining the pressure difference between the inlet and outlet of the primary combustion air supply device,
- means for calculating the flow rate corresponding to the pressure difference between the inlet and outlet of the primary combustion air supply device.

The present invention also relates to a device as described above, wherein the carrier for the combustible material comprises a plurality of individual grate elements for advancing the combustible material through the incineration zone, an air supply device being provided below each grate element
The present invention also relates to a device as described above, wherein the carrier for the combustible material comprises a plurality of first individual combustion grate elements, the first grate elements being slideably mounted in forward and backward direction for transporting the refuse from a former combustion zone to a next combustion zone.
The present invention also relates to a device as described above, wherein the combustion grate system comprises a plurality of second grate elements, the first grate elements alternating with the second grate elements, the second grate elements being mounted In such a way that they can be tumbled to improve the intensity of the combustion.
The present invention also relates to a device as described above, wherein the combustion grate system comprises between the second grate element and a subsequent first grate element, a third grate element, the third grate element being stationary mounted.
The present invention also relates to a device as described above, wherein the first and second elements are individually controllable.
The present invention also relates to a device as described above, wherein the device comprises means for controlling the speed of the first and second grate elements in a continuous manner.
The carrier for the combustible material preferably comprises a plurality of individual grate elements for advancing the combustible material through the incineration zone, a primary combustion air supply device being provided below each grate element to allow an improved control of the incineration process. The most used technique for supplying primary combustion air to the incinerator at this moment makes use of one single air fan. From the air fan primary combustion air distribution over and along the different combustion grate elements is controlled by means of butterfly or register valves. By dividing the incineration zone in a number of individual zones and controlling the primary combustion air supply in each individual zone, an improved control of the incineration process can be achieved.
The device further preferably comprises a bum out control device to ensure that the solid combustible material has been completely bumed before it is removed from the incinerator.
The invention is further elucidated in the attached figures and description of the figures.

Figure 1 shows a cross section through a reactor for the incineration of refuse.
Figure 2 shows a detail of a combustion grate system for use in the method of this invention.

The incinerator shown in figure 1 comprises overhead cranes 1 for transferring solid combustible material, for example refuse 2 to a reactor feed hopper and a loading chute 3. The chute in fact functions as an air seal for the top of the incinerator, but is also provided for distributing the refuse 5 to a refuse supply device 6 with which the refuse is supplied to a carrier 7 for transporting the combustible material through the incinceration zone where it is combusted. The carrier 7 can be any carrier known to those skilled in the art, but preferably comprises a combustion grate system. The combustion grate system is further provided for drying the combustible material, igniting and burning it in the gasification and combustion zone. To support the combustion, primary combustion air is supplied to the incinerator through a primary combustion air supply device 8 which is preferably located below the combustion grate system. The primary combustion air supply device 8 may for example comprise an air supply fan or valve or any other primary combustion air supply device known in the art. The incineratore further preferably comprises a bum out control device to ensure that the solid combustible material is completely burnt out before it leaves the incinerator.
As can be seen from figure 2, the combustion grate system 7 used in the incinerator of this invention preferably comprises a plurality of combustion grate elements (11-16). The combustion grate elements 11-16 further function as a means for transporting and mixing the combustible material 1 from the feed hopper 3 to a former to a next combustion grate element, and finally to an ash discharge 6.
In a preferred embodiment, an air supply device is provided below each group of grate element 11-16 to provide an improved control of the combustion process. As an air supply device preferably use is made of a valve or a fan, but other air supply devices known in the art may also be used. Each air supply device comprises an inlet through which primary combustion air is supplied and an outlet through which the primary combustion air leaves the air supply device towards the incinerator. Means are provided for determining the air flow rate at the outlet of the primary air supply device. This can be done by actually measuring the pressure at the inlet and outlet of the primary combustion air supply device and determining the corresponding flow from the characteristic curve of the air supply device.
The combustion grate system 7 preferably comprises a plurality individual grate elements, preferably a plurality of sliding tiles, 11, 14 with which the layer of the combustible material is displaced over the combustion grate. The sliding movement of the tiles is preferably a slow, continuous movement, so as to avoid dust generation in the incinerator and increase the life time of the incinerator. Besides this, when continuously moving the tiles 11, 14 a virtually continuous steam production and consequently a virtually continuous electricity production can be ensured. The sliding tiles 11, 14 determine the thickness of the layer of the combustible material, the residence time of the combustible material in each combustion zone and the combustion quality
The combustion grate system 7 further preferably comprises a plurality of tumbling tiles (12, 15), which disentangle and aerate the refuse. This is important for drying and ignition of the refuse, to activate the combustion where and if necessary and to obtain a complete bum-out of the ashes. This combination of horizontal throughput action (sliding) and vertical aeration action (tumbling) allows the incinerator to adapt to short and long term fluctuations in the composition of the refuse. Thereby preferably, the throughput (sliding) and aeration (tumbling) can be controlled for each individual zone (combustion grate element). In addition to this an independent control of the two motions, i.e. the sliding and tumbling is highly desirable. Of course, the tumbling action is stopped automatically because of the increased risk of dust production when disentangling and more intense aeration of the refuse is not necessary.
Upon combustion of the refuse, flue gases are generated, which are mostly withdrawn from the incinerator through a fan. A refuse incinerating reactor is often coupled to a waste heat boiler wherein the thermal energy contained in the flue gases is converted into steam. This steam can in turn be used for electricity production purposes, combustion air preheating, industrial processes, hot water supply etc.
In the method of this invention, first the optimum amount of combustible material to be present in the incineration zone is determined. Solid combustible material is fed to the incineration reactor and transported to and through the incineration zone at a transport speed by means of the carrier. The amount of combustible material in the incineration zone correspond to

measuring an over-all gas pressure Pⁱ in the incineration zone,
measuring a primary gas pressure below the carrier for the combustible material P^g,
determining a pressure difference over the carrier ΔP^r= Pⁱ - P^g,
determining ΔP^ro which is the pressure difference over the carrier that corresponds to the optimum amount of combustible material in the incineration zone,
calculating the difference ΔP between ΔP^ro and ΔP^o.

To improve the incineration process the speed of the charging of the combustible material to the incineration zone or the feeding of the combustible material through the incineration zone is adjusted to minimise ΔP. The speed of the feeding of the combustible material is adjusted to ΔP/v² _pa, wherein v_pa is the flow rate of the primary combustion air. ΔP/v² _pa is measured at predetermined time intervals and averaged as a function of time or ΔP/v² _pa is filtered.
The primary air flow rate in each individual combustion zone is measured by determining a pressure of the primary air pressure at the inlet and outlet of the air supply device, determining the pressure difference between the inlet and outlet, calculating the flow rate corresponding to the measured pressure difference.

Claims

A method for incinerating solid combustible material in an incineration zone in an incineration reactor, this method comprising the steps of determining an optimum amount of material to be present in the incineration zone, feeding combustible material to the Incineration reactor, transporting the combustible material to and through the incineration zone at a transport speed by means of a carrier therefor, supplying primary combustion air to the incineration zone with a flow rate, through an air inlet located below the carrier, incinerating the combustible material in the incineration reactor to produce ashes and exhaust gases, determining the amount of combustible material in the incineration zone, adjusting the amount of combustible material in the incineration zone by adjusting at least one of the charging to or the feeding of the combustible material through the incineration zone so as to maintain the amount of material in the incineration zone substantially constant, whereby the adjusting of the amount of combustible material in the incineration zone comprises the steps of
- measuring an over-all gas pressure Pⁱ the incineration zone,

- measuring a primary gas pressure below the carrier for the combustible material P^g,

- determining a pressure difference over the carrier ΔP^r= Pⁱ- P^g,

- determining ΔP^ro which is the pressure difference over the carrier that corresponds to the optimum amount of material in the incineration zone,

- calculating the difference ΔP between ΔP^ro and ΔP^r,

- minimising AP by adjusting at least one of the speed of the charging of the combustible material to the incineration zone or the feeding of the combustible material through the incineration zone,
characterised in that
- the incineration zone is divided into a plurality of individual combustion zones, primary air being supplied to each individual combustion zone through a separate air supply device and adjusted for each individual combustion zone.

- the speed of said feeding or charging of the combustible material is adjusted based on ΔP/v² _pa wherein V_pa is the flow rate of the primary combustion air, and

- the flow rate of the primary combustion air in each individual zone is measured by

- determining a pressure of the primary combustion air at an Inlet through which primary combustion air is supplied to the primary combustion air supply device,

- determining a pressure of the primary combustion air at an outlet of the primary combustion air supply device through which primary combustion air is supplied to the incinerator,

- determining the pressure difference between the inlet and outlet of the primary combustion air supply device,

- calculating the flow rate corresponding to the pressure difference between the inlet and outlet of the primary combustion air supply device.
A method according to claim 1 wherein ΔP/v² _pa is measured at predetermined time intervals and averaged as a function of time or ΔP/v² _pa is filtered.
A device for incinerating solid combustible material in an incineration zone in an incineration reactor such that an optimum amount of material is present in the incineration zone, comprising:
- an incinerator reactor with at least one incineration zone for combusting the combustible material,

- a carrier for carrying the combustible material and feeding the combustible material through the at least one incineration zone,

- means for supplying combustion air below the carrier and

- means for adjusting the amount of combustible material in the incineration zone, whereby the means for adjusting the amount of combustible material in the incineration zone comprise means for:

- measuring an over-all gas pressure Pⁱ the incineration zone,

- measuring a primary gas pressure below the carrier for the combustible material P^g,

- determining a pressure difference over the carrier ΔP^r = Pⁱ - P^g,

- determining ΔP^ro which is the pressure difference over the carrier that corresponds to the optimum amount of material in the incineration zone,

- calculating the difference ΔP between ΔP^ro and ΔP^r,

- minimising ΔP by adjusting at least one of the speed of the charging of the combustible material to the incineration zone or the feeding of the combustible material through the incineration zone, characterised in that

- each incineration zone is divided into a plurality of individual combustion zones, the device comprising separate air supply devices to supply primary air to each individual combustion zone and comprising means to adjust primary air supplied to each individual combustion zone,

- the device comprises means for adjusting the speed of said feeding or charging of the combustible material based on ΔP/v² _pa, wherein v_pa is the flow rate of the primary combustion air, and

- the device comprises means for measuring the flow rate of the primary combustion air in each individual zone, comprising: .

- means for determining a pressure of the primary combustion air at an inlet through which primary combustion air is supplied to the primary combustion air supply device,

- means for determining a pressure of the primary combustion air at an outlet of the primary combustion air supply device through which primary combustion air is supplied to the incinerator,

- means for determining the pressure difference between the inlet and outlet of the primary combustion air supply device,

- means for calculating the flow rate corresponding to the pressure difference between the inlet and outlet of the primary combustion air supply device.
A device according to claim 3, wherein the carrier for the combustible material comprises a plurality of individual grate elements for advancing the combustible material through the incineration zone, an air supply device being provided below each grate element.
A device according to claims 3 or 4, wherein the carrier for the combustible material comprises a plurality of first individual combustion grate elements, the first grate elements being slideably mounted in forward and backward direction for transporting the refuse from a former combustion zone to a next combustion zone.
A device according to claim 5, wherein the combustion grate system comprises a plurality of second grate elements, the first grate elements alternating with the second grate elements, the second grate elements being mounted in such a way that they can be tumbled to improve the intensity of the combustion.
A device according to claim 6, wherein the combustion grate system comprises between the second grate element and a subsequent first grate element, a third grate element, the third grate element being stationary mounted.
A device according to claim 7, wherein the first and second elements are individually controllable.
A device as according to claim 8, wherein the device comprises means for controlling the speed of the first and second grate elements in a continuous manner.