EP3122844B1

EP3122844B1 - Electrical power generation system

Info

Publication number: EP3122844B1
Application number: EP15720425.6A
Authority: EP
Inventors: Paolo GAGGERO; Luca CANEVARO; Francesco LEGROTTAGLIE
Original assignee: Mini Green Power Sas
Current assignee: Mini Green Power Sas
Priority date: 2014-03-24
Filing date: 2015-03-23
Publication date: 2020-11-11
Anticipated expiration: 2035-03-23
Also published as: WO2015145328A3; EP3122844A2; WO2015145328A2

Description

The present invention relates to an electrical power generation system which comprises at least one fuel supply device, for supplying fuel to at least one gasifier.
The gasifier is connected to at least one supply fluid generation unit of an electrical power generation device.
A waste product disposal circuit is further disclosed. Particularly, the disclosure relates to biomass energy generation systems.
Such systems are known and widely used in power plants that utilize biomass-derived renewable energy using various techniques: energy may be obtained by direct biomass combustion, with particular efficiency-improving measures, by pyrolysis and by obtaining synthesis gas through gasification.
Biomass combustion gases are generally used in combination with the so-called Organic Ranking Cycle (ORC) systems, i.e. systems that use heat to drive a turbine connected to a transformer for electrical power generation.
Biomass energy generation may have very high efficiencies, depending on the combustion technology in use.
Efficiency may be further improved by taking advantage of one of the qualities of biomass power plants, i.e. continuous power delivery: this promotes an additional advantage, i.e. the possibility of using power plants for cogeneration of heat to be used in remote domestic heating: the heat generated during the process, that would be otherwise lost, is thus used.
Finally, like any combustion process, biomass plant processes generate air pollutants and other polluting agents, although these are considerably reduced due to the use of prior art high-efficiency technologies in combustion, for preventing and substantially reducing undesired emissions.
In spite of the above mentioned advantages, the use of biomasses also involves certain drawbacks.
First, as compared with fossil fuels, biomass fuels have a low specific calorific value.
Furthermore, biomasses have a very high residual moisture content, and preliminary drying and densification treatments are required before starting combustion, pyrolysis or gasification processes.
Obviously, all these drawbacks directly impinge on the efficiency of biomass plants, thereby causing reduced electrical power generation.
Thus, prior art biomass plants cannot optimize the efficiency of each component of the plant according to the characteristics of the biomass or according to the different conditions under which the various processes of a biomass power generation plant are carried out.
Furthermore, there is an increasing demand among private users for the use of plant biomasses to produce synthesis gases suitable for use as engine fuel, and particularly for electrical power generation, or for various other uses.
This process, which is known as gasification, consists in the thermochemical conversion of biomass, shredded to chips, into a fuel gas, and is currently carried out by gasifier systems, as described above.
An example of fuel gas generated by gasification is biosyngas, in which biomass is entirely converted into H2 e CO, and also into CO2 and H2O.
Biosyngas is very similar in chemical nature to fossil-derived syngas, and may replace it in any application.
The various steps that lead to biomass gasification take place in various areas of the gasifier.
In the drying step, the water content of biomass is removed by evaporation, when biomass is introduced into the reaction chamber.
In the pyrolysis step, the biomass is decomposed, upon exposure to high temperatures in the absence of oxygen. Pyrolysis products are gases composed of CO, H2, CO2, CH4 and trace hydrocarbons.
In the oxidation step, exothermic combustion reactions occur.
In the reduction step, endothermic reduction reactions occur, to provide gas constituents such as biosyngas.
These steps are strongly influenced by fluid dynamic conditions in the combustion chamber, and particularly by the introduction of secondary air and primary air.
Unfortunately, the configuration of prior art gasifiers does not allow adjustment of air introduction, with the exception of some changes to the flow rate of inlet members, which do not afford accurate and careful control of the combustion and gasification processes that occur in the combustion chamber.
The promotion of gasification over combustion is a particularly important aspect, because it allows the gasifier behavior to be adapted to the fuel.
Therefore, there exists a need, yet unfulfilled in prior art systems, for an electrical power generation system that obviates the above drawbacks and maintains an adequate efficiency of each component regardless of the biomass type and process variables.
The present invention meets the above mentioned needs by providing an electrical power generation system as described above, in which a control unit is provided for controlling the operation of at least one components of the system.
The control unit includes a detection system for detecting parameters indicative of the operation of one or more components of the system as well as processor means for processing data obtained by the detection system.
The detection system may consist of sensors provided in combination with one or more of the components of the system.
This will provide a series of field probes controlled by the control unit, which has an acquisition and management system for monitoring and optimizing the generation system.
Therefore, a number of devices may be provided, which detect different parameters and are operable to control the operation of the whole system.
The control may be carried out manually, with the supervision of a user: in this case the control unit shall have control input interfaces and interfaces for providing a feedback to a user about the instantaneous operation of the system.
The processor means are adapted to execute a logic program, whose execution allows automatic control of the operation of at least one of the components of the system.
Here, the execution of the logic program allows the control unit to detect the operation of one or more components of the system on an instant-by-instant basis, and and to control such operation such that, for example, their efficiency will fall within a preset range of values.
The two control modes, i.e. the automatic and manual modes may be also provided together.
It will be apparent from the description of the various components of the system that each component may be controlled: for example, the amount of supplied biomass may be decreased or increased, the temperature and pressure may be changed, the opening and closing degree of system valves may be adjusted, etc.
The gasifier comprises an outer body which delimits a combustion chamber, which combustion chamber comprises at least one grate upon which fuel is placed and at least one fuel input compartment below the grate, as well as flame ignition means.
Furthermore, at least one outlet port is provided in the combustion chamber for the gases obtained therein, primary air inlet members being provided for introducing air into the combustion chamber below the grate.
The combustion chamber has a plurality of holes formed in the thickness of its walls, secondary air inlet members being provided for introducing air into the combustion chamber above the grate through said one or more holes.
The gasifier includes secondary air flow adjustment means, which comprise closing/opening means for closing/opening the holes, each hole being adapted to be opened/closed independently of the others, to change the amount of secondary air introduced into the combustion chamber.
Obviously, the closing/opening means are controlled by the control unit.
The gasifier is the component the most influences the efficiency of the whole system because the characteristics and amount of operating fluid that is used downstream from the gasifier for electrical power generation depend on the adjustment of secondary air and fuel supply.
Therefore, the control unit may be used to control the variables of the system as the operating regimes of the gasifier change.
The flow adjustment means may consist of any member adapted to change the secondary air flow, and may comprise, for example means for changing the sizes of the holes.
By adjusting the introduction of secondary air, gasification or combustion can be promoted according to the number of open holes, which allows the behavior of the gasifier to be adapted to particular requirements.
For example, the change of the fluid dynamic conditions in the combustion chamber allows efficient burning of materials such as chicken droppings, whose combustion for energy production has poor results.
The closing/opening means may be formed in any known manner, for instance using valves, particularly poppet valves.
Likewise, both primary and secondary air inlet means may consist of any device known in the art, such as fans or the like.
According to the invention, the holes are arranged along the walls of the combustion chamber at least at two different heights relative to the grate and at least at two different angles relative to the axis of the outlet port.
With this arrangement, secondary air can be adjusted according to both the amount and the velocity of air introduced into the combustion chamber.
Thus, the air generated by the inlet means will obviously enter the combustion chamber at different velocities according to the holes through which it flows, and by adjusting the opening/closing state of a hole located higher than or at a different angle from another, the secondary air velocity may be increased and reduced, thereby directly affecting material combustion.
The opening/closing means may be actuated manually, preferably by transmitting controls through a control unit.
Advantageously, sensors may be provided, for detecting at least the amount of secondary air introduced into the combustion chamber.
Such detection provides important feedback for adjustment of the closing/opening means.
For this reason, sensors may be provided for detecting all parameters that influence the combustion process, such as primary air amount sensors, temperature sensors for sensing temperature at one or more areas of the combustion chambers, etc.
The use of sensors affords the provision of an automatic hole opening/closing system: the sensors may measure the conditions in the combustion chamber at each instant and change the opening/closing state of the holes to obtain preset and predetermined parameters.
A particular important aspect, which has effects on the efficiency of the gasifier, is the presence of waste products deriving from the combustion process.
The above described gasifier configuration allows heat to be concentrated in a small space, which affords efficient combustion and reduced generation of waste products, which may anyway be expelled during the process, i.e. before solidification thereof, without affecting proper execution of the process.
This will also allow combustion of very wet fuel, using any prior art fixed grate.
Nevertheless, improved removal of waste products may be obtained using a grate that facilitates expulsion of such waste products from the combustion chamber.
According to a first embodiment, the grate may be composed of at least two portions, at least one of which is supported to rotate relative to at least one axis, such that this portion can be rotated toward the fuel input compartment.
Thus, rotation of this portion allows the waste products to be discharged toward the input compartment.
As more clearly shown by certain examples, the grate preferably has more than one rotatably supported portion.
As an alternative to the above described variant, the grate may be designed to have a support structure, which support structure has grate moving means.
As described below, as the grate is moved it causes combustion waste products to fall by gravity.
Finally, according to a possible embodiment, additional air inlet means may be provided, level with the fuel input compartment.
These means generate an air flow from the outside toward the housing compartment and prevent any backflow of flue gas or backfire.
According to a preferred embodiment, the gasifier is preferably connected to the supply fluid generation unit of the electrical power generation device through a post-combustion connection tube.
Furthermore, tertiary air inlet means may be provided in combination with the connection tube.
Preferably, the electrical power generation system consists of a turbine connected to a transformer device for electrical power generation.
The turbine is driven by the gases produced by the supply fluid generation unit.
Thus, different types of systems may be defined according to the supply fluid generation unit, as this unit may use the gasifier output products to provide the operating fluid to drive the turbine.
According to a first embodiment, the operating fluid may consist of hot or superheated water.
In this case, the supply fluid generation unit of the electrical power generation device comprises an superheated water generator.
Alternatively, the operating fluid may consist of the hot flue gas resulting from combustion/gasification in the gasifier.
In this case, the system includes one or more components in the device that operates the electrical power generation device for treating such hot flue gas before conveying them to an evaporator, for evaporation of a liquid which expands in the turbine thereby generating power.
The addition of each component is obviously aimed at optimizing hot flue gas treatment to maximize efficiency thereof, thereby increasing electrical power generation.
According to a first embodiment, the supply fluid generation unit of the electrical power generation device comprises at least one attemperator device for controlling the temperature of the flue gas leaving the gasifier.
Controlling the temperature of the gasifier flue gas output is a critical aspect, both for system efficiency and safety and for protection of the components downstream from the gasifier.
Furthermore, the attemperator device also affords first flue gas dedusting and stabilization of reactions in and downstream from the device.
In order to improve the quality of flue gas for electrical power generation, its treatment may be optimized by connecting the attemperator device to a flue-gas dedusting and mixing device for the flue gas leaving the attemperator device.
According to a further embodiment, the supply fluid generation unit of at least one electrical power generation device comprises a recirculation circuit for recirculating the waste products of the electrical power generation device, such that at least part of the waste products are introduced into the dedusting and mixing device.
It shall be noted that waste products preferably consist of the heat depleted flue gas that leaves the evaporator.
This recirculation circuit provides obvious advantages, in that it allows reuse of at least some of the waste products and the energy contained therein.
In a preferred variant embodiment of the system of the present invention, the dedusting and mixing device is connected to the electrical power generation device and to the waste product disposal circuit.
A valve system supervises such connection and changes its configuration.
Thus, according to the data detected by the detection system, the configuration of the system, and particularly the connection of the dedusting and mixing device may be changed.
For example, the flue gas may be prevented from driving the turbine for power generation, based on its temperature. This is found to be a highly beneficial aspect, which reduces the wear of components by preventing their use under harsh conditions, such as high temperature.
Also, this feature is of utmost importance for safety of the system, as it prevents the use of certain components at critical temperatures.
The present application further discloses a biomass gasifier comprising an outer body which delimits a combustion chamber, which includes at least one grate upon which fuel is placed and at least one fuel input compartment below the grate, as well as flame ignition means.
Furthermore, at least one outlet port is provided in the combustion chamber for the gases obtained therein, primary air inlet members being provided for introducing air into the combustion chamber below the grate.
A plurality of holes are also formed in the thickness of the walls of the combustion chamber, secondary air inlet members being further provided for introducing air into the combustion chamber above the grate through said one or more holes.
The gasifier particularly includes secondary air flow adjustment means, which comprise closing/opening means for closing/opening said holes, each hole being adapted to be opened/closed independently of the others, to change the amount of secondary air introduced into the combustion chamber.
Advantageously, the gasifier may have one or more of the above described features concerning the system of the hovercraft of the present invention.
Finally, the present application also discloses a heat generation system, comprising:

at least one fuel supply device,
at least one gasifier,
at least one superheated water generator.

In the system, the gasifier is also connected to the superheated water generator via a post-combustion connection tube, tertiary air inlet means being provided in combination with the connection tube.
The connection tube is mainly designed for the combustion of the carbon monoxide so formed.
According to a possible embodiment, the gasifier of the system includes one or more of the above described characteristics.
These and other features and advantages of the present invention will appear more clearly from the following description of a few embodiments, illustrated in the annexed drawings, in which:

Fig. 1 shows a schematic diagram of the electrical power generation system of the present invention;
Figs. 2a to 2f show different embodiments of the gasifier that is part of the system of the present invention;
Figs. 3a to 3d show a variant embodiment of the grate in the gasifier of the present invention;
Figs. 4a to 4d show a variant embodiment of the grate in the gasifier of the present invention;
Figs. 5a to 5c show an embodiment of the system of the present invention;
Figs. 6a and 6b show a perspective view and a functional diagram of an embodiment of the system of the present invention respectively;
Figs. 7a to 7m show various components of the system of Figures 6a and 6b of the present invention;
Fig. 8 shows a chart representing the operation logic implemented by the control unit for controlling the system of the present invention.

It shall be understood that, while the figures annexed to the present patent application show certain embodiments of the system of the present invention, these embodiments shall be intended by way of illustration of and without limitation to the inventive principle of the present invention.
The inventive principle concerns the possibility of controlling the operation of the system of the present invention to optimize its efficiency and electrical power generation.
Particularly referring to Figure 2, the electrical power generation system of the present invention comprises:

a fuel supply device 1,
a gasifier 2,
a supply fluid generation unit 3,
an electrical power generation device 4,
a waste product disposal circuit 5.

Like in prior art systems, the supply device 1 supplies biomass to the gasifier 2.
The gasifier 2 is connected to the supply fluid generation unit 3 which uses the hot flue gas generated by the gasifier 2 to drive an electrical power generation device.
The electrical power generation device 4 may consist of a turbine connected to a transformer device for electrical power generation, the turbine being driven by the gases generated by the supply fluid generation unit 3.
According to the characteristics of the system, the supply fluid generation unit 3 may consist of any device known in the art.
Certain possible variants of this unit are respectively shown in Figures 5a and 6a and 6b.
The waste products of the electrical power generation process are finally ejected through the waste product disposal circuit 5.
The system of the present invention includes a control unit 6, for controlling the operation of at least one of the components of the system.
The control unit includes a detection system for detecting parameters indicative of the operation of one or more components of the system as well as processor means for processing data obtained by the detection system.
In the particular case of Figure 1, the control unit 6 is connected to the gasifier 2 only, but it may be obviously have connections to one or more of the components of the system.
This means that each component may have sensors of the detection system of the control unit 6, such that the control unit 6 may control any component of the system.
Thus, the detection system of the control unit 6 may include, for instance, sensors for measuring biomass moisture, pressure, temperature and flow rate in each component, pressure and temperature at the connections between components, and for detecting identification parameters of the operating fluids that circulate in the system and are adapted to drive the power generation device.
As better explained below, the processor means are adapted to execute a logic program, whose execution allows automatic control of the operation of at least one of the components of the system.
Figure 2a shows a possible embodiment of the gasifier 2 that is part of the system of the present invention.
The gasifier 2 of the present invention comprises an outer body that delimits a combustion chamber 2.
The combustion chamber 2 includes at least one grate 21 upon which fuel is placed, at least one fuel input compartment 22 being provided below the grate 21 and flame ignition means 23.
Also, at least one outlet port being is provided in the combustion chamber 2 for exhausting the gases and flue gas so obtained.
Primary air inlet members 24 are also provided for introducing air into the combustion chamber 2 below the grate 21.
The illustrated gasifier has a plurality of holes 25 formed in the thickness of the walls of the combustion chamber.
Secondary air inlet members 26 are also provided for introducing air into the combustion chamber 2 above the grate 21 through said one or more holes 25.
The gasifier also includes secondary air flow adjustment means.
According to the variant as shown in Figure 2a, these adjustment means comprise closing/opening means 27 for closing/opening the holes 25, each hole 25 being adapted to be opened/closed independently of the others, to change the amount of secondary air introduced into the combustion chamber 2.
Particularly, the closing/opening means 27 may be adjusted through the control unit 6 to change the amount of secondary air and obtain the right supply of gases and flue gas at the outlet port to optimize electrical power generation.
For example, if the opening/closing means 27 consist of valves for closing the orifices of the holes 25, the control unit 6 may be arranged to act upon single, independent actuation of each valve.
In addition to or instead of this characteristic, sensors may be used to detect at least the amount of secondary air introduced into the combustion chamber 2.
As shown in Figures 2a and 2c, the holes 25 are arranged along the walls of the combustion chamber 2 at least at two different heights relative to the grate 21 and at least at two different angles relative to the axis of the outlet port 24.
As mentioned above, sensors may be used, for detecting at least the amount of secondary air introduced into the combustion chamber 2.
These sensors 28, as shown in Figure 2b, may be sensors designed for sensing temperature in the combustion chamber 2.
Figure 2b shows a first embodiment of the grate 21, including an inlet area 211 for receiving the fuel, which is then placed on the side walls 212 of the grate 21 that surround the inlet area 211.
The inlet area 211 communicates with the fuel input compartment 22.
Figures 3a to 3d show an embodiment of the grate 21 in the gasifier of the present invention, in which the grate 21 is composed of at least two portions, at least one of which is supported to rotate relative to at least one axis, such that this portion can be rotated toward the fuel input compartment 22.
Particularly referring to the figures, the grate 21 is composed of three separate portions 213, 214, 215, which are adapted to be rotated to thereby create empty areas for the discharge of combustion waste products.
This type of grate is derived from the fixed grate design of such systems, which is "cut" into multiple folding sections 213, 214, 215, supported by horizontal spindles 223, 224, 225, allowing the rotation of the individual portions of the grate 21.
This will facilitate intermittent ash discharge into the under-grate compartment, which is equipped with an ash removal system, such as a motor-driven screw, having an automatic and air-tight operation, to prevent the ingress of false air in the system.
The use of a multi-section grate requires an automated procedure, whose timing is designed according to the type of biomass being burned.
The actuation frequency depends on the biomass type and the difficulty of burning it. The sections 212, 213 and 214 of the grate 21 are actuated at different times, such that embers are allowed to remain for a given time in the combustion chamber, for easy restart of the system.
The timing of the discharge process includes different and successive steps.
The screw temporarily stops for a given time for unimpeded discharge to occur. During this period, the biomass on the grate 21 continues to burn to extinction, for optimized operation and minimized losses from burning residues. This rest period is a compromise between full combustion of the material in the burner and reduced thermal properties of the operating fluid. At the end of the rest period, the portions 213, 214 and 215 of the grate are opened, simultaneously or separately, for ash discharge.
Alternatively, Figures 4a to 4d show a variant embodiment of the grate 21.
According to this variant the grate 21 has a support structure, which support structure has means for moving said grate 21.
Preferably, the movements of the grate 21 are vibrations induced by the support structure.
In this case, the vibrating grate 21 consists of a circular perforated plate, upon which the biomass is placed with primary air being blown from below. The grate 21 is coupled to a rigid cylindrical support structure 216, with two vibrating motors imparting a shaking motion and a centrifugal circular motion to the opposite ends of its circumference. Such motors are arranged with different coaxial orientations, and the effect thereof, in combination with the vibration amplitude controlled by inverters according to the characteristics of the biomass being treated, i.e. its density and particle size, causes the residue to be expelled, whereas the biomass introduced into the grate continues its combustion process.
According to a possible embodiment, the two motors are mounted through connection flanges at the ends of the rigid cylindrical support structure 216, such that they remain outside the latter and allow ashes to be collected in the under-grate compartment 22.
The support structure 216 may in turn rest on a spring assembly, according to the weights of the system, which are accommodated in the under-grate compartment 22. For this reason the springs are made of a special material capable of withstanding temperatures as high as 180/200°C.
Vibration frequencies, permanence times and feeding rates are controlled by appropriate calibration of the inverters, according to the characteristics of the biomass being burned. With this adjustment, a longer initial permanence time may be set, through a low feeding rate, for the fresh biomass that has just been introduced into the grate, to allow gasification thereof, whereas its product may be accelerated toward the periphery of the grate 21 in view of completing its transformation by combustion and final residue expulsion. The frequency values are calibrated based on the knowledge of the time that the biomass must spend in the gas generator to complete its gasification, combustion and conversion into ash. Thus permanence time is divided into three parts, with the resulting time representing the time required for the biomass to complete a single centrifugal circular rotation on the vibrating grate 21, thereby running one third of its radius. Therefore, three full rotations are required for the biomass, converted into ash, to be on the outer expulsion channel.
Thus, the ashes are conveyed toward a circular channel at the edge of the grate 21 and fall by gravity therefrom through the slits 217, into a frustoconical section, and are removed from the system by means of a screw feeder.
The construction of the system includes vibrating motors rigidly joined to a box-like member which is connected to the circular rigid structure. The latter has folded edges which increase its stiffness and transfer the vibrating motion to the grate 21. For this purpose, the interior of the box-like member also has stiffening ribs.
As mentioned above, the above described grate embodiments provide advantages for ash discharge into the area that underlies the grate 21 of the gasifier.
Now, ashes may be removed from the gasifier with any method known in the art, a main difference being found between methods for wet ash removal and dry ash removal.
For wet ashes, a loop seal is used, in association with a Redler conveyor.
Conversely, dry ashes are removed through frustoconical section of the under-grate, in combination with a compartment with a discharge screw feeder through a flap valve or a rotary valve.
In order to maintain the desired air flows introduced into the gasifier through primary and secondary air inlet means, ashes are removed from the frustoconical collection section underlying the grate by opening a flap valve or a rotary valve, which have the purpose of maintaining the interior of the gasifier well separated from the outside. Here, ashes slide on the walls of the frustoconical collection section by the action of a vibrating motor, which is rigidly joined to the housing structure of the gasifier.
Figure 5a shows a first embodiment of the electrical power generation system of the present invention, in which the system comprises a fuel supply device 1, at least one gasifier 2 and at least one superheated water generator 31.
Furthermore, the gasifier 2 is connected to the superheated water generator 31 via a post-combustion connection tube 311, tertiary air inlet means 312 being provided in combination with the connection tube 311.
Particularly, the system as shown in Figure 5a comprises:

a fuel supply screw system 1 with a mixer 11;
a seal/primary air fan on the screw 7;
a primary air fan 24 under the grate;
a fan for preheated secondary air 25 in the combustion chamber;
tertiary air or post-combustion fan 311;
a three-pass superheated water generator 31;
an electrical power generation device 4.

Thus in this case the supply fluid generation unit 3 of the electrical power generation device is the three-pass superheated water generator 31.
In this particular system, the detection system of the control unit 6 may perform, for instance, the following measurements:

biomass moisture content of the part introduced into the gasifier 2, with automatic specific weight compensation;
flow rate of the primary, secondary and tertiary air inlet means;
oxygen content in the combustion chamber and at the outlet 311;
temperature at various locations of the system;
the flow rate of water in the closed loop for exchange with the cooling fluid of the ORC by means of an electromagnetic flow meter (if the electrical power generation device is an ORC-type device);
polluting emissions from combustion products.

EXEMPLARY EMBODIMENT

An example of an embodiment of the system according to the present invention is described below, particularly referring to Figures 5a to 5c, as well as a process that led to the definition of the characteristics as described for the gasifier of the present invention.
This system comprises:

a fuel supply screw system 1 with a mixer 11;
a seal/primary air fan on the screw 7;
a primary air fan 24 under the grate;
a fan for preheated secondary air 27 in the combustion chamber;
tertiary air or post-combustion fan 312;
a three-pass superheated water generator 31;
dedusting system and flue gas extraction fan 32.

DESCRIPTION OF THE PROCESS AND QUALITATIVE-QUANTITATIVE MODEL

In order to define a useful model for determining by first-order approximation the compositions and temperatures at particular points of interest for conduction of the gas generation, the ligneous biomass transformation process should be briefly described. For convenience, the combustion chamber 2 of the gasifier will be separated into three areas, as shown in Figure 5c.

Area 1 - Pyrolysis and start of gasification

The chips are loaded into the combustion chamber 2 by means of the dosing screw 1 at the center of the static grate 21 located within the refractory-lined chamber of the gasifier. Then, the fuel spreads symmetrically at both sides of the outlet flange. Any backflow of flue gas or backfire is prevented due to the presence of the fan 7 on the casing of the scree and adjacent to the outer wall of the gasifier. The air of this fan 7 will be considered as part of the primary air, by assuming that its supply will first be used to dry the material entering the combustion chamber 2.
The grate 21 has an under-grate compartment from which gasification/combustion ashes are intermittently removed, and from which primary air is blown into the combustion chamber 2 through the fan 24.
The balance of primary, secondary and tertiary air characterizes the thermochemical process in the areas 1 and 2.
Considering the thickness of the refractory lining in the chamber and the presence of a free flame located approximately on the median plane of the outlet port, most of the incoming material is assumed to be instantaneously dried and to start pyrolysis. The term pyrolysis is intended as the release of volatile materials by heating, resulting in a weight loss. For lignocellulosic biomass this process involves a considerable weight loss which may even be 90% considering the dry material.
The material that remains on the grate shall be considered as chip char, or similar to charcoal. In this respect, under steady operating conditions and with proper management of airs and supply, a non-negligible unburned carbon content is expected to be found in the "ashes" recovered from the grate. The exact amount of this unburned carbon is a function of the time during which the char remains on the grate (depending on manual ash removal times), of the oxygen content (depending on the primary air that has been blown), and of the temperature of the ash bed (depending on flame radiation and on the exchange with the grate and the blown air).

Area 1 and Area 2 interface - Completion of gasification

The volatile materials and the fine-size fuel that is entrained by the slight negative pressure in the combustion chamber 2 undergo suspension gasification due to the radiation of the flame in the Area 2, which is generated by the oxygen suppled by the fan 27. The gasification products are mainly water, CO, H2, CO2. The nitrogen introduced with air is deemed to be "inert" during gasification, whereas any trace of sulfur and chlorine remains in reduced form in the gasification area and are partly oxidized to SOx and HCl in the flame of Area 2.
In the case of wood chips with the following composition (TAB 1) the presence of SOx and HCl shall not be deemed to be relevant for the purposes of emissions to the atmosphere: Tab. 1 Reference composition of dry chips

Element % s.s.

Carbon 48.00

Hydrogen 6.00

Nitrogen 0.17

Chlorine 0.01

Sulfur 0.03

Oxygen 45.00

Slag 0.79

TOTAL 100
The composition of Table 1 will be used as a reference composition for the next calculations.

Simplified gasification model

During the gasification process, various simultaneous chemical reactions occur, also concerning the char.
The influence of the various reactions and whether a thermodynamic balance is established is still matter of debate, considering the heterogeneity of fuel in terms of:

Size
Moisture
Composition

The role of fluid dynamic and mass transfer conditions in the chamber of the burner cannot be excluded. The only certainty is that the Water-Gas Shift (WGS) reaction has a key role and substantially comes to equilibrium.
The WGS reaction is as follows:

Water Gas Shift CO+H₂O → H₂ + CO₂ ΔH^R = -40,9 KJ/mol
As agreed by various authors the following simplifying hypothesis may be simply considered for the purposes of this study:

The only equilibrium is reached by WGS;
the following chemical species will be considered:
- N2, H2, CO, CO2, H2O, O2;
- Only moisture changes are admitted in fuel composition;
- The entire calorific power of the fuel will contribute to gasification, any under-grate char loss being negligible;
- The reactor is well-mixed with no bypass of dead volumes;
- The refractory lining is an "infinite" thermal flywheel, whereby secondary air will be always preheated: (Heat regeneration)
- The fan 6 will not participate in the total of airs, as it will be adjusted to ensure a minimum negative pressure, without allowing ingress of false air.

Area 2 Syngas combustion

In the Area 2, a quasi-planar jet of secondary air for combustion impinges on the synthesis products of gasification products (CO and H2).
The secondary air is sucked into the room in which the system is installed, by the fan 41, is preheated by swirling around within the refractory lining of the burner and is blown into the chamber through the holes 25 arranged on the half-circle that is symmetric to the connection tube 31 with the pressurized water generator 3 and on the median plane thereof. The coplanar arrangement of the holes 25 and their angular distance that causes the pitch-to-diameter ratio to be approximately 4-5 ensures an effect that is similar to planar jets, thereby allowing good turbulence and suction of gasification products, for combustion.

Area 3 Tertiary air injection with flame extinction

In the connection tube the fan 312 may have a dual purpose. When gasification prevails, the introduced oxygen completes the combustion of carbon monoxide, thereby considerably increasing temperatures and acting as a post-combustor. On the other hand, if the combustion process prevails, which is mostly completed in the combustion chamber 2 by the primary and secondary air inlet members, the oxygen percent remains in the oxidizing range, and contributes tto flame cooling, thereby preventing damages to the pressurized water generator.
Nevertheless it shall be noted that, both in time and space, not only one of the thermochemical processes as described above occurs, but the combustion chamber may have various areas defined therein, which are characterized by the prevalence of one mechanism relative to another. Of course, the process is controlled by the balance and ratios of combustion airs.
The above described process has been used to obtain the characteristics of the gasifier as described above, particularly referring to Figures 2a to 2f.
Particularly, the gasifier has a compact cylindrical shape having a height and a diameter with comparable values and a grate diameter ranging from 1000 mm and 160 mmm, preferably of 1300 mm.
The height ranges from 1500 mm and 2100 mm, and is preferably 1800 mm.
The grate 21 is placed above an ash compartment 22, in which a slide is also placed for moving the biomass upwards to the combustion chamber 2. The under-grate compartment is also the volume in which primary (or gasification) air is blown through the fan 24.
The grate 21 is located in an environment surrounded by a refractory lining, preferably having a thickness of 20 cm.
The upper portion of the combustion chamber, Area 2, has the holes 25 for receiving the secondary air introduced by the fan 27, as required for combustion of the syngas formed in the lower portion of the combustion chamber 2, Area 1.
The holes 25 preferably have a diameter of 100 mm.
The fan 27 pushes air into a plenum chamber formed between the outer side of the refractory lining 25 and an outer wall of the outer body 11 (Fig. 2a). The plenum chamber is formed with the holes 25, that may be adjusted by poppet valves.
The holes 25 are in front of the flame channel, which has a diameter of about 450 mm, and is the channel that emits the flame and the flue gas generated by both biomass combustion and syngas combustion.
Sensors may be further provided on each fan, for measuring the flow rates of the introduced air; the detections of such sensors are controlled by a control logic PID (derivative integral proportional control) to ensure the desired air-flue ratio.
Furthermore, the gasifier has such an overall length as to prevent undesired, uncontrolled bypasses of carbon monoxide from the combustion chamber 2 to the flame channel. This has further afforded an increase of the volume available for combustion and of the permanence times therein.
This study has determined the methods of quantitative control of carbon monoxide in the post-combustion section, i.e. the connection tube 31.
Thus, the various holes 25 have been placed at different heights and at different angles, to optimize the amount of secondary air to be introduced into the combustion chamber 2.
Figures 2c to 2f show a possible configuration:
Figure 2c shows a side view of the gasifier, with the holes 25 arranged at three different heights, and for each height level each hole 25 is placed with a different angle relative to the longitudinal axis of the outlet port 24, as shown in Figures 2d, 2e and 2f respectively.
With the above changes the process occurring in the flame channel may be controlled to generate:

CO post-combustion with temperature increase;
Elimination of flue gas, with flame cooling in case of excessively high temperatures in the post-combustion channel.

Figs. 6a and 6b show a further embodiment of the system of the present invention, namely as a perspective view and a functional block diagram.
The system of Figures 6a and 6b may have the same features as the system of Figure 5a, with the exception of a different embodiment of the supply fluid generation unit 3 of the electrical power generation device 4.
Particularly, in Figure 5a this unit 3 was a three-pass superheated water generator 31, whereas in Figures 6a and 6b the supply fluid generation unit 3 consists of a plurality of components and connections, as described below.
Particularly referring to the figures, the gasifier 2 is connected to an attemperator device 32 for controlling the temperature of the flue gas leaving the gasifier 2.
The attemperator device 32 is connected to a flue-gas dedusting and mixing device 33 for the flue gas leaving the attemperator device 31.
The dedusting and mixing device 33 is connected to the electrical power generation device 4 and to the waste product disposal circuit 5.
Here, the flue gas that leaves the gasifier 2 after undergoing the treatments associated with the attemperator device 32 and the dedusting and mixing device 33, may be used by the electrical power generation device 4 or be introduced into the waste product disposal circuit 5, according to given criteria.
A by-pass circuit 35 is thus provided, whereby the electrical power generation device 4 may be bypassed.
Therefore, a valve system is provided between the dedusting and mixing device 33 and the electrical power generation device 4 and the waste product disposal circuit 5.
This valve system is preferably controlled by the control unit 6 as shown in Figure 1.
According to the variant as shown in Figures 6a and 6b, the electrical power generation device 4 is a turbine or preferably an ORC (Organic Rankine Cycle) device 41, which is provided in combination with an evaporator 42 for evaporating the operating fluid that expands in the turbine, thereby generating power.
At least part of the waste flue gas that leaves the evaporator 42 or the by-pass circuit 35 may be reused, instead of being expelled out of the waste product disposal circuit 5.
Thus the illustrated embodiment includes a recirculation circuit 34 for the waste products of the electrical power generation device 4, which is adapted to introduce at least part of the waste products into the dedusting and mixing device 33 for reuse.
The recirculation circuit 34 connects the outlet of the evaporator 42 and the bypass circuit 35 to the outlet of the attemperator device 32 and may include pneumatic control systems 341 for opening or closing the circuit 34.
Like the other valves of the system of the present invention, these pneumatic control systems 341 may be also controlled by the control unit 6.
A possible embodiment of the components of the system of Figures 6a and 6b is shown in the next figures 7a to 7o.
Figure 7a shows the post-combustion connection tube 311.
Post-combustion occurs in a refractory-lined connection tube, which extends horizontally, i.e. parallel to the axis of the outlet of the gasifier 2 and interposed between the gasifier 2 and the attemperator device 32.
The tube 311 may have a length ranging from 2 m to 5 m.
The lining consists of a first inner layer of about 50 cm in contact with the flue gas, which is composed of alkaline earth silicate wool mized with inorganic and organic binders to obtain rigid tables having excellent insulation and stability properties at high temperatures. The second lining consists of a calcium magnesium silicate sheet, which imparts excellent thermal and physical stability. The last layer consists of about 125 mm bauxite-based concrete, with operating temperatures of 1600°C, and anchored to the covering structure.
Tertiary air is injected in this section, preferably in a swirl flow, using tertiary air inlet means 312, as shown in Figure 5a, which inject air through holes formed in the thickness of the wall of the connection tube 311.
Preferably there are three concentric holes arranged at 120° from each other.
As described above, two processes may occur in this section, i.e.:

Post-combustion of the CO that comes from the combustion chamber
Flame quenching.

Figures 7b and 7c show two views of the attemperator device 32 according to a possible embodiment.
The attemperator device 32 consists of a refractory-lined cylindrical body having an inlet conduit 321 at the bottom and an outlet conduit 322 on a plane near the cover 323.
The inlet 321 and outlet 322 are on different planes and are tangential and non-radial to the cylindrical geometry, to obtain a swirl flow.
The cover 323, which is also refractory-lined with calcium silicate, has a series of inlet holes on its bottom inner surface, for receiving air from the fan 324 installed on the cover 323.
The attemperator device 32 has multiple functions:

Attempering and uniforming the temperature of flue gas;
Performing preliminary rough flue gas dedusting (plenum chamber function);
Safety function, since it may introduce more quenching air through the fan 324 located on its "cover" 323 or act as a prechamber for an emergency stack.
Acting as a reference component for the process trough measurement with probes for detecting the amount of oxygen, CO, temperature and pressure (the system operating at negative pressure), which have a system controlling function.

Figure 7d shows the channel that connects the attemperator device 32 to the recirculation node, or the the attemperator device 32 to the recirculation circuit 34.
A T-joint 342 is provided for such connection, which is used to mix the primary flue gases directly obtained from the combustion of exhaust gas leaving the evaporator 42 of the ORC device 41, which are at 180/200°C. Due to such high temperatures, this section has a 120 mm inner refractory layer, consisting of a single bauxite-based concrete cast.
As clearly shown in Figure 6b, an additional straight section is provided downstream from the T-joint 342, for the two streams of flue gas at different temperatures to be mixed as homogeneously as possible.
The inlet of the dedusting and mixing device 33 is downstream from this section, which may have various lengths depending on space availability in the installation site.
The dedusting and mixing device 33, as shown in Figures 7e and 7f, preferably consists of a cyclone or multicyclone for high temperatures, which influences the choice of the length of the upstream section. Since this segment is the first high-temperature segment, the pipe material in use is AISI 309 or the like. The cyclone/multicyclone has the purpose of dedusting the hot gas flow and mixing it as thoroughly as possible such that low dust contents, as well as consistent inlet temperatures and heat outputs are found at the inlet of the exchanger of the ORC cycle. This purpose is achieved using a heat insulation with a ceramic fiber mat having a thickness of 25 mm and a second mineral wool layer having a thickness of 100 mm.
As mentioned above, the system of the present invention may include a by-pass circuit 35 for bypassing the evaporator 42.
The hot flue gas that comes from the evaporator 42, under certain operating conditions or in certain transients with temperature peaks, may be diverted into the by-pass circuit 35, which consists of a pipe section directly downstream from the dedusting cyclone 33. As shown in Figures 6b and 7g, the by-pass circuit 35 is controlled by 2 basic elements consisting of 2 valves, a control valve 351 and a double-flap forced-air valve 352.
The control valve 351 preferably consists of a heavy-construction single-flap butterfly valve for demanding uses, made of AISI 316L. Its purpose is to control the amount of flue gas into the evaporator 42; if the heating load is higher than requested, then the control valve 351 opens and diverts part of the flue gas into the by-pass, thereby maintaining the requested load. Under steady operation conditions, the valve 351 remains closed and allows the flue gas to run through the section 354 at the inlet of the evaporator 42.
The safety of the evaporator 42 and the obstruction of its inlet is afforded by the provision of a double-flap butterfly valve 352, also operated by pneumatic control and having a seal air fan, with air being blown into the space between the two flaps.
The system ensures 100% tightness with the fan working.
If the flue gas bypass the evaporator 42, a high temperature flow is found directly downstream from the outlet of the evaporator 42. The flue gas may be diverted into the bypass in either of the following modes: full-flow bypass, partial-flow bypass.
In both cases, the flue gas must be cooled to prevent the downstream components to be exposed to high thermal stresses; this function is accomplished by a butterfly control valve 355, which is inserted in a 90° bypass circuit section 35, as shown in Figure 5h. In the case of partial-flow bypass, the valve 355 will open in proportion to the temperature that is sensed downstream from the section. Outside air is sucked in by the negative pressure in the line and shall allow temperature to remain under 270°C.
Figures 7i and 7l show a possible embodiment of the power generation device 4, which consist of an ORC device 41 in combination with an evaporator 42.
The evaporator 42 consists of a tube bundle with the operating fluid flowing therein and with the heat exchange between the flue gas and the fluid occurring within its covering structure. The flue gas that flows into the connecting structure at the top flows through the entire body of the component and comes out of the bottom via a trapezoidal square-round connection. The construction is completed by a 100 mm mineral wool and ceramic fiber insulation, for proper exchange, an ash removal system which may consist of a double flap valve or an inclined screw feeder and a rotary valve, and a hydraulic system for cleaning the bundle in the case of the evaporator 42 by steel brushes.
As described above, the system of the present invention is equipped with a system for thermal recovery of the sensible heat of hot gases that leave the evaporator 42, which consists of the recirculation circuit 34, to increase to overall efficiency of the system.
Furthermore, the recirculation circuit 34 is also particularly useful to control temperature at the inlet of the evaporator.
The flue gas is extracted by a dedicated centrifugal fan between having a belt drive between the motor and the fan; the gases fall in the temperature range from 180 to 200°C, and may be mixed with outside air by the action of a valve block 341, as shown in Figure 5m, which is composed of:

An ON-OFF butterfly valve on the recirculation node side;
A control butterfly valve for false air intake;
An ON-OFF butterfly valve on the fan suction side.

Particularly referring to Figure 5m, the valve block 341 is connected both to the recirculation circuit and to the waste product disposal circuit 5.
According to a further embodiment, a control valve similar to the above described control valve may be provided downstream from the valve block 341, i.e. between the valve block 341 and the disposal circuit 5, for controlling the passage of outside air to be mixed with high-temperature gases.
The disposal circuit 5 preferably consists of a waste product carrying duct 5, which connects a filter section 52 to a stack 53.
Particularly, the flue gas that leaves the evaporator 42 has undergone two special dedusting treatments by the attemperator device 32 and the cyclone/multicyclone 33, and a last indirect treatment once it has flown past the tube bundle of the evaporator 42. In order to comply with pollutant content limits prescribed by regulations, the system is equipped with different flue gas treatment systems according to the biomass or byproduct introduced into the combustion process:

High-efficiency multicyclone
Bag filter
Hydrated lime and activated carbon injection system.

The flue gas can be later vented through a circular double-walled stack 53 having a high-density heat insulation. The construction has been conceived to minimize condensation and maintain a high flue gas velocity, with an adequate rain cap at its end, to limit the formation of dirty plumes.
Finally, in a further variant embodiment, an additional fan may be provided, both for the system of Figure 3 and for the system of Figures 4a and 4b, for sucking in the flue gas produced by combustion and ensuring that a negative pressure is maintained in the flue gas line.
This fan is preferably a high-temperature resistant belt-driven centrifugal fan, with fabric expansion joints at both suction and delivery sides.
A possible operation of the system of the present invention will be now described by way of example, and particularly the logic used by the control unit 6 to control the operation of the system of the present invention will be illustrated.
As mentioned above, the control unit 6 has processor means for executing a logic program.
It can also comprise input/output interfaces and at least one display interface, for a user to monitor the operation of the system and possibly control it.
The following technical terms will be used in this description:

UF1: the fan for introducing primary air into the area underlying the grate 21;
OV1: the fan for introducing secondary air into the area overlying the grate 21;
OV2: the fan for introducing tertiary air into the final portion of the flame profile ("flame base"), i.e. in the post-combustion tube;
Tflame: flame temperature (in the gasifier)
CO: carbon monoxide

CASE a - system of Figure 5a, i.e. gasifier 2 connected to a boiler 31.
Tout: temperature at the outlet of the boiler 31;
Tin: temperature at the inlet of the boiler 31;
Torc in: temperature of the operating fluid at the inlet of the ORC system;
Torc out: temperature of the operating fluid at the outlet of the ORC system;
The logic is divided into two states: STATE ONE is defined as "heating", and STATE TWO is defined as "steady operation".

STATE ONE

In the attemperator 32, until a value of 1100°C of Tflame is reached at the inlet:

the feeding screw follows the growth according to the frequency that has been set by automation control, until a flame temperature of 1100°C is objectively reached; during the growth of the T flame at the inlet of the attemperator, if the limit threshold of one of the following parameters, in the following order of importance, is exceeded:
1. 1. heat output reached at the flue gas or water,
2. 2. water temperature,
3. 3. oxygen,
4. 4. CO
the automation control will adjust the speed of the feeding screw and hence the fuel introduction speed, to fall within the safety and design specifications for the above values, as prescribed for the gasifier-heat exchanger system off the ORC.

Also, until a value of 1100°C of Tflame is reached at the inlet of the attemperator:
UF1 follows and adapts the amount of air introduced into the area underlying the grate 21 according to the oxygen content detected at the flue gas, by "leaning", i.e. by increasing the amount of air if the 4.5% oxygen target has not been reached, or by "enriching", i.e. reducing the introduction of air if the same 4.5% oxygen target has been exceeded at the flue gas.
OV1 and OV2 will be proportional to UF1, and follow the experimental lines as shown in Figure 8.

STATE TWO

Once the value of 1100°C of Tflame is reached at the inlet of the attemperator:
"steady operation" is started, in which Tflame at the inlet of the attemperator has reached 1100°C, the heat output is about 900 kWt, and the following changes occur in combustion management:
if the heat output has actually reached its steady value of 900 [kWt], then a. the new setpoint (SP) for Tflame at the inlet of the attemperator shall be 1080 °C and this value shall be maintained by the speed of the feeding screw that introduces the fuel, b. the new oxygen SP will be 5.5%, c. the air flow rates for OV1 and OV2 are set to SPs of 1300 [m3/h] each, to be attained within 10 minutes, d. a minimum flow rate of 250 [m3/h] is set for the fan UF1.
If the heat output has not reached the steady value of 900 [kWt], then the SP for Tflame at the inlet of the attemperator is set to 1150 °C, to increase the speed of the screw and reach the steady operation power. As soon as this SP of 1150°C for Tflame is attained, it will be maintained.
Should this Tflame at the inlet of the attemperator fall below 900 [°C], then the system will return to the automatic configuration of STATE ONE, to try again a temperature and power increase.
If the CO value exceeds the first threshold of 250 mg/m3, then: UF1 will be adjusted with the above described method, whereas OV1 will change the amount of air to be introduced if the CO threshold defined as "first threshold", of 250 mg/m3, is exceeded; the lower limit for OV1 is equal to 1/3 of the minimum value that has been set for the minimum operating state of the system.
If the second CO threshold of 500 mg/m3 is exceeded, when the above described minimum limit of 1/3 for OV1 is also reached, then the automation will adjust the speed of the fan OV2, which will start to change the amount of air to be introduced, i.e. to reduce it; the limit therefor is free and might tend to zero.
Finally, as mentioned above, the control unit 6 has a system for detecting the identification parameters of the various components of the system of the present invention.
The provision of such detection system allows system operation monitoring and alarming.
Therefore, the control unit will be able to generate alarm signals if the detected parameters do not meet certain threshold values.
These alarm signals may be of any known type; they may be, for instance, audible alarm signals, or notices via SMS, e-mail or the like.
Obviously, the operation logic of the control unit may assign a priority to alarms, for automatic lock or adjustment of each component of the system.

Claims

An electrical power generation system comprising:
at least one fuel supply device (1),

at least one gasifier (2),

the gasifier (2) being connected to at least one supply fluid generation unit (3) of an electrical power generation device (4),

a waste product disposal circuit (5) being further provided,

a control unit (6) being provided, for controlling the operation of at least one of the components of the system,

the control unit (6) including a detection system for detecting parameters indicative of the operation of one or more components of the system as well as processor means for processing data obtained by said detection system,

being the processor means adapted to execute a logic program, whose execution allows automatic control of the operation of at least one of the components of the system,

the gasifier (2) comprising an outer body (20) that delimits a combustion chamber, said combustion chamber comprising at least one grate (21) upon which fuel is placed, at least one fuel input compartment (22) being provided below the grate (21) and flame ignition means (23), at least one outlet port being provided in said combustion chamber for exhausting the gases so obtained,

primary air inlet members (24) being provided for introducing air into the combustion chamber below the grate (21),

characterized in that

a plurality of holes (25) are formed in the thickness of the walls of the combustion chamber,

secondary air inlet members (26) being provided for introducing air into the combustion chamber above the grate (21) through said one or more holes (25), secondary air flow adjustment means being further provided, said adjustment means comprising closing/opening means (27) for closing/opening said holes (25), each hole (25) being adapted to be opened/closed independently of the others, to change the amount of secondary air introduced into the combustion chamber, said holes (25) being arranged along the walls of the combustion chamber at least at two different heights relative to said grate (21) and at least at two different angles relative to the axis of the outlet port (24).
A system as claimed in claim 1, wherein said grate (21) is composed of at least two portions, at least one portion whereof is supported to rotate relative to at least one axis, such that said portion can be rotated toward the fuel input compartment (22) .
A system as claimed in claim 1, wherein said grate (21) has a support structure (216), which support structure (216) has means for moving said grate (21).
A system as claimed in claim 1, wherein said gasifier (2) is connected to the supply fluid generation unit (3) of the electrical power generation device through a post-combustion connection tube (311),
tertiary air inlet means (312) being provided in combination with said connection tube (311).
A system as claimed in claim 1, wherein said supply fluid generation unit (3) of the electrical power generation device comprises an superheated water generator (31).
A system as claimed in claim 1, wherein said supply fluid generation unit (3) of the electrical power generation device comprises at least one attemperator device (32) for controlling the temperature of the flue gas leaving said gasifier (2) .
A system as claimed in one or more of the preceding claims, wherein said attemperator device (32) is connected to a flue-gas dedusting and mixing device (33) for the flue gas leaving said attemperator device (32).
A system as claimed in claim 7, wherein said supply fluid generation unit (3) of at least one electrical power generation device comprises a recirculation circuit (34) for recirculating the waste products of said electrical power generation device (4), such that at least part of said waste products are introduced into said dedusting and mixing device (33).
A system as claimed in claim 7, wherein said dedusting and mixing device (33) is connected to said electrical power generation device (4) and to said waste product disposal circuit (5),
a valve system being provided for controlling the connection to the electrical power generation device (4) and to the waste product disposal circuit (5).