EP1399695A1

EP1399695A1 - Flue gas purification device for an incinerator

Info

Publication number: EP1399695A1
Application number: EP02754776A
Authority: EP
Inventors: Hendrik Seghers
Original assignee: SEGHERS KEPPEL TECHNOLOGY GROU; Seghers Keppel Technology Group NV
Current assignee: Keppel Seghers Holdings Pte Ltd
Priority date: 2001-06-29
Filing date: 2002-06-27
Publication date: 2004-03-24
Anticipated expiration: 2022-06-27
Also published as: DE60226137D1; DE60226137T2; EP1399695B1; CN1266416C; ES2305274T3; ATE392590T1; CN1543552A; WO2003002912A1

Abstract

An incineration device for integrated heat recovery and flue gas purification is provided, comprising at least the following substantially integrated sections: (a) an incineration chamber or incinerator; (b) a heat recovery section; (c) one or more sections for the removal of acid; (d) one or more DeNOx sections; (e) a stepped dedusting section; (f) one or more sections for the removal of chlorinated hydrocarbons; (g) an adapted measuring and control section for the control of the different steps of flue gas purification and heat recovery. The invention further comprises the use of such an integrated incineration device for the incineration of contaminated combustibles, like waste, for instance domestic and industrial waste.

Description

FLUE GAS PURIFICATION DEVICE FOR AN INCINERATOR

Field of the invention

The present invention relates to an incineration device with integrated heat recovery and flue gas purification and particularly to an incineration device for the incineration of waste, such as domestic and industrial waste. The invention further relates to the use of such a device for the incineration or thermal treatment - like gasification, pyrolysis or drying - of waste and waste products of the residual fraction of alternative processing techniques for the processing of waste, biomass and also contaminated combustibles of industrial, agricultural or fossil origin. These combustibles can be denoted by the collective name 'contaminated combustibles' or 'secondary combustibles'.

Background ofrthe invention

Over the past years, a substantial progress has been made in improving the control of the incineration process in (waste) incineration installations, such as with respect to temperature control, air management, and the manipulation of the burning waste layer. Due to this progress, for example, the concentration of carbon monoxide and unburned hydrocarbons in flue gasses is reduced to levels far below the present standards that have been issued by the governments.

The most important contaminants present in the flue gasses of incineration installations for incinerating contaminated combustibles - like waste, biomass, residual products or carbons with a high sulphur content - are carbon monoxide, unburned hydrocarbons, sulphur oxides (SOx), hydrochloric acid (HCI) and other haloid acids (HF, HBr), nitrogen oxides (NOx), heavy metals (dust), polychlorobiphenyls (PCB's), polychlorodibenzodioxins (PCDD's), polychlorodibenzofurans (PCDF's) and other halogenated aromatic and aliphatic hydrocarbons.

The purification of flue gasses, combustion gasses and/or gasses of the thermal treatment of contaminated combustibles, hereafter both individually and collectively also referred to as 'flue gas' or 'flue gasses', usually requires the following main steps: a. Limitation of the emission of carbon monoxide and unburned hydrocarbons; b. Dedusting and removal or neutralisation of heavy metals; c. Removal of nitrogen oxides; d. Desulphurization and removal of haloid acids; e. Removal of dioxins and other organic trace elements.

All of these steps are known from the literature and practice individually and partially also together and will be described in short hereafter.

a. Limitation of the emission of carbon monoxide and unburned hydrocarbons

First of all, in order to limit the emission of carbon monoxide and unburned hydrocarbons, an optimal control of the incineration process is needed. This issue is known and the control principles are generally accepted. Consequently, the new generation of incinerators come up to the norm defined at present without any problems. The present invention therefore comprises as such no measures for preventing the formation of these contaminations. The interactions between the control principles of the incineration process and actions for preventing the emission of other contaminants, however, form part of the invention.

b. Dedusting and removal or neutralisation of heavy metals

US-A-5.501.161 describes a process for the thermal treatment of dusty and/or finely divided solids, which occur in the purification of flue gasses. The thermal treatment can serve to destroy halogenated, especially aromatic hydrocarbons and to remove ammonia and/or other volatile substances. The solids are supplied along a pre-set route to a filter device by means of a gas stream, the gas having at least the temperature of the thermal treatment. The solids can be subjected to a thermal post-treatment after filtration.

EP-A-0.5.501.161 describes a device for the production of a homogeneously divided and directed stream of flue gas, whereby the vertical stream of gas is bent off by the terminal walls in a plural drain tank and by a cascade of two or more blades (S1 , S2, ...Sn) to separate the dust from the flue gas. The blades are positioned and dimensioned in such a way that the stream path of the flue gasses makes sharp bends. This sudden change in stream direction allows the deposition of the ash, which is entrained along with the flue gasses, in the lower part of the kettle house.

c. Removing nitrogen oxides ('DeNOxinq')

Flue gasses usually contain large amounts of nitrogen oxides (NO_x), especially nitrogen monoxide (NO), which oxides are formed in the air upon incineration of waste or fossil fuel. When the flue gasses are released into the atmosphere before being subjected to a purification process, they cause several problems such as:

- The greenhouse effect. The greenhouse effect is partially caused by N₂O, which indeed is present in a much lower amount than CO₂, yet its effect per molecule N₂O over a period of 100 years is 290 times as high. NOx also contributes to the production of ozone, which is an important greenhouse gas, in the lower troposphere.

- The formation and exhaustion of ozone. As stated above, NOx can form ozone in the lower troposphere, thereby contributing to the greenhouse effect and the formation of photochemical smog. NOx can also react with ozone in the higher troposphere/stratosphere, thereby contributing to the exhaustion of the protecting ozone layer. NOx is responsible in a direct and indirect way for half of the exhaustion.

- Acid deposition. The deposition, c.q. the precipitation of acid chemicals, for example nitrates, nitrites, sulphates, sulphites on the surface of the earth, on the land or in the water, under the influence of rain, snow, fog, clouds and even of dry particles. These deposits acidify the soil and the water, harm the ecosystems, the soil, the plants and cause corrosion and erosion.

- Health. The formation of photochemical smog and the exhaustion of the ozone layer have a detrimental effect on the health of people and animals and are also harmful for many plants, for instance crops.

Various processes are known for the separation of nitrogen oxides from waste gasses are known. In the most frequently used processes, ammonia is used for this purpose. Therefore, ammonia is introduced into the stream of waste gas, where it reacts with nitrogen oxides, thereby reducing the latter to elementary nitrogen (N₂). The dominant overall chemical reaction proceeds as follows:

4 NO + 4 NH₃ + O₂ — ► 4 N₂ + 6 H₂O (1)

4 NO₂ + 8 NH₃ + 2 O₂ _ 6N₂ + 12 H₂O (2)

Further, the following side reactions occur: 4 NH₃ + 3 O₂ — ► 2 N₂ + 6 H₂O (3)

4 NH₃ + 5 O₂ —► 4 NO + 6 H₂O (4)

2 SO₂ + O₂ — ► 2 SO₃ (5)

NH₃ + SO₃ + H₂O — _► NH₄HSO₄ (6)

2 NH₃ + SO₃ + H₂O — ► (NH₄)₂SO₄ (7)

In principle, there are two possibilities to decrease the emission of NOx: a selective non-catalytic reduction (SNCR) and a selective catalytic reduction (SCR) of NOx to N₂.

The SNCR-process is the thermal reaction, in which reducing chemicals are used to reduce NOx to nitrogen (gas) in the absence of a catalyst. The most frequently used embodiment consists of the injection of ammonia, urea or another ammonia forming substance into the incinerator or burner, at a temperature between approximately 700°C and 1100°C, depending on which reducing agent is used. Through the radical reaction between NO* and NH₂», N₂ and H₂O are formed. See for example EP-A-0.079.171.

A SNCR-installation of the DeNOx section typically consists of a storage module for the reagent, dosage modules and injection lances. The reagent is pumped from the storage module into the dosage modules. In the dosage module, the reagent, the pressurised air and the injection water are dosed in function of the relevant parameters. Reagent, pressurised air and/or water are preferably injected into the flue gasses by means of injection lances, preferably into the first draught of the kettle.

In the SCR-process, for example described in US-A- 3.970.739, in principle the same reducing agent is injected, although at a temperature range between approximately 150 and 700°C, depending on the composition of the flue gas. The ammonia forming substance typically is mixed with the waste gas in a reaction chamber, which is provided with suitable catalysts. Through the reaction of NH₃ on the catalyst surface, NO is converted into N₂. Through the occurrence of the side reactions 3 and 4, the actual consumption of ammonia is usually somewhat higher than stoichiometrically. If the amount of SO₂ is high, ammonium hydrogen sulphate is formed by the cascading effect of the last three reactions. This compound can block and de-activate the catalyst at a temperature of 230-270°C (depending on the supplier and the specific process conditions). Therefore, the temperature always needs to be kept sufficiently high.

A SCR-installation of the DeNOx section typically consists of a storage module for the reagent, a dosage module, injection lances or an injection grit, and a catalytic reactor. Possibly, the furnace gasses need to be heated again to the desired temperature, for instance by means of a gas burner, steam battery, heat exchangers and the like. In occurring instances, the furnace gasses need to be cooled by means of heat exchangers, and the like.

The reagent is pumped from the storage module into the dosage modules. In the dosage module, the reagent, pressurised air and the injection water are dosed in function of the relevant parameters. Reagent, pressurised air, and/or water are preferably injected or sprayed into the furnace gasses. Injection of the reagent into the furnace gasses is preferably carried out by means of a plurality of sprinkler heads, followed by a static mixer in the flue duct or by means of a grit that is introduced into the flue duct. A SCR-installation is typically introduced after a flue gas purification and at least after a first dedusting of the flue gasses (for example in an electrofilter).

It is known that not the whole amount of the ammonia reacts with the nitrogen oxides, both in the SNCR-process as well as in the SCR- process. US-A-5.069.886 describes a process whereby nitrogen oxides, present in waste gasses, are reduced with ammonia to elementary nitrogen and whereby the ammonia is recirculated to the incinerator, such that the amount ammonia that is released into the atmosphere, is reduced.

Further, combined SNCR-SCR processes for the reduction of nitrogen oxides are described in various references; see for instance US-A-4.978.514, US-A-5.465.690, US-A-5.853.683, WO 96/27428, EP-0.583.771 , EP-0.866.395, EP-0.803.278 and EP-0.803.278.

d. Desulphurisation and removal of haloid acids (especially hydrochloric acid)

The formation of sulphur oxides cannot be prevented because the basic components are part of the combustible. However, these acids can be captured in an early stage by the introduction of adsorbents and/or absorbents, hereinafter collectively denoted as absorbents. Suitable and known absorbents are for instance lime, calcium hydroxide, sodium bicarbonate, zeolites and clay minerals.

The capturing of SOx by means of lime has been applied in power stations burned with coal in the years 60-70 until approximately the beginning of the years 80. Since then, the effectiveness was further improved because lime products with a much higher specific surface and a higher reactivity, as compared to 10 years ago, appeared on the market. Moreover, alternative reagents for chemisorption of acids, such as sodium bicarbonate and zeolites, have been developed.

A large number of processes and devices for the desulphurisation of flue gasses and improvements thereof, often combined with the removal of nitrogen oxides, have been described in the patent literature; see for instance US-A-4.149.858, DE-34.07.277, DE-35.44.367, DE-36.12.142, DE- 36.12.143, EP-0.276.363, EP-0.623.047, US-A-5.585.081 , US-5.567.394 and many other references.

e. Removal of dioxins and other organic trace compounds

Based upon elaborated scientific studies it has been established that dioxins and related or similar compounds, for example PCB's, PCDD's and PCDF's, are already present in the domestic waste that is incinerated in the waste incineration devices, but also that they are destroyed during the incineration. Upon cooling down of the flue gasses, however, new dioxins are formed, especially at a temperature range between 450-250°C. The formation of the dioxins is enhanced by a number of parameters, such as:

- the amount of dust in the flue gasses,

- the load of, among others, heavy metals, chlorides and carbon in the dust,

- the oxygen and moisture content of the flue gasses, and

- the presence of precursors.

Similar parameters also apply to PCB's.

According to the state of the art, the emission of dioxins, furans and similar compounds is prevented by contacting the flue gasses with an absorbent, namely active carbon, and/or with a catalyst (for the latter, see for example US-5.512.259). The adsorption preferably occurs at lower temperatures (T<150°C), whereas the catalytic reaction preferably is carried out at temperatures between 150° and 500°C.

Although plenty of literature exists about the different individual process steps for the purification of flue gasses, as given above, almost no literature exists about completely integrated purification systems, and especially not in combination with an incinerator. The company Von Roll however describes a '4D' filter system, whereby, through the addition of specific additives to the flue gas stream after the kettle and upwardly of the filter, the following four steps are carried out in one single filter: the removal of dust (Dedusting), the removal of nitrogen oxides (DeNOxing), the removal of dioxins (Dedioxination) and sulphur (Desulphurisation by dry absorption).

Summary of the invention

The object of the present invention is to provide an incineration device with integrated heat recovery and flue gas purification, suitable for the incineration of contaminated combustibles, such as waste, for example domestic and industrial waste, whereby the incineration, the recovery of energy and at least the following purification steps:

- dedusting and removing or neutralisation of heavy metals

- removal of nitrogen oxides

- desulphurization and removal of haloid acids

- removal of dioxins and other organic trace elements are substantially performed in one integrated system.

The incineration device of the invention hereto comprises at least the following sections:

- an incineration chamber or an incinerator ;

- a heat recovery section which is integrated in the incinerator or combustion chamber ;

- one or more sections for removing acids, the said section or sections being integrated in the incinerator, incineration chamber and/or heat recovery section; one or more DeNOx sections integrated in the incinerator, incineration chamber, heat recovery section and/or other sections for flue gas purification ; a stepped dedusting section comprising one or more sections integrated in the incinerator, the incineration chamber, the heat recovery section and/or other sections for flue gas purification ; one or more sections for the removal of chlorinated hydrocarbons integrated in the incinerator, the incineration chamber, the heat recovery section and/or other sections for flue gas purification an adapted measuring and control section for controlling the different steps of flue gas purification and heat recovery, suitable for incinerating contaminated combustibles.

According to an embodiment of the device of the invention, the different sections of the integrated incineration device may operate separately or overlap with each other, whereby in one section a plurality of contaminants are treated or are simultaneously present.

According to another embodiment of the device of the invention, the different actions of the sections can be carried out in one single part of the device.

The invention further comprises the use of an integrated incineration device, as herein described and defined, for the incineration of contaminated combustibles, such as waste, for example domestic and industrial waste.

These and other aspects, such as preferred embodiments of the invention, are described in a detailed way by means of the following description and drawing.

Short description of the drawing

Figure 1 shows a schematic perspective view to an embodiment of the device of the invention. In this scheme, the incinerator, heat recovery in the form of an integrated steam kettle, and also the different sections for flue gas purification are indicated.

Detailed description of the invention The present invention provides an incineration device, comprising an incinerator with integrated heat recovery, for example in the form of a steam kettle, a thermal oil kettle or a gas-gas heat exchanger, a therein completely or partially integrated flue gas purification device, which flue gas purification device comprises primary or secondary means for preventing the formation and emission of contaminants, whereby the capturing and the destruction of contaminants occurs in a stage as early as possible in the process of incineration/recovery of energy.

In this description, by 'primary means', means are understood that directly interfere with the incineration process. 'Secondary means' are means, which limit the re-formation of contaminants or catch and/or destroy formed contaminants. Hereto, according to the invention, the flue gas purification is integrated as much as possible in the incinerator installation with integrated heat recovery (hereafter also referred to as "incinerator-kettle"). This integration has led to an entire new concept for an incinerator-kettle device, by which a very low amount of contaminants in the flue gasses can be obtained. This integration allows the installation for flue gas purification, connected in series, to operate as a safety filter or "police filter", meaning that it operates as a second step which captures eventual emission peaks, such that no exceeding of emission occurs, even when process failures occur.

In this description, by 'draughts', the different parts of the device which can be separated from each other each time the flue gas stream changes its direction (for example a turning of 90° or 180°), are understood. In Figure 1 , three empty draughts and an horizontal draught are indicated.

By 'economiser', that part of the steam kettle is understood where the water is heated by heat exchange with the hot flue gasses, without however evaporating (this occurs in the evaporators).

The most important sections of the flue gas purification, integrated in the incineration device, will be described in a detailed manner here below.

a. The incineration chamber or incinerator The incineration chamber or incinerator, which is used in the device of the invention, is usually of the conventional type. The incineration chamber or incinerator substantially consists of a carrier for the combustible, a space for the incineration of volatile substances and an after- incineration chamber. According to the invention, preferably a grate incinerator, a fluid bed incinerator or a static incinerator is used as incinerator, without, however, excluding other types of incinerators known to a person skilled in the art. The after-incineration chamber is a space that is connected in series with the described incinerator or incineration chamber. This space serves, by the supply of additional incineration air or supporting combustible or not, for the complete incineration (oxidation) of the gasses coming from the thermal treatment, like gasification, pyrolysis or drying.

The waste or the combustible is introduced onto the grate, into the fluid bed or into the static incinerator, respectively, by means of an adapted feeding mechanism. Once the waste or the combustible is introduced into the incinerator, different processes occur, namely: the drying of the waste, degasification of the waste, gasification of the waste leading to the formation of volatile substances which flow to the empty incinerator space and after-incineration chamber, pyrolysis of the solid compounds and the incineration of the gasses.

The composition of the flue gasses is strongly influenced by the control of the 'incineration process'. Parameters, for example the amount of air that is conducted through the waste layer or the bed, the temperature in the waste layer or the fluid bed, and the speed of the air in the waste layer or through the fluid bed are contributing to the form and concentration of for instance heavy metals in the flue gasses, the composition of the fly ashes, the amount of NOx in the flue gasses, the potential for the dioxin formation of the fly ashes and the like. Moreover, the formation of contaminants in flue gasses can be controlled by the addition of reagents in the waste.

The invention also relates to other thermal processes - like gasification, pyrolysis, drying - by which the solid, pasty, liquid or gaseous - contaminated combustibles are converted to gasses considerably. b. Heat recovery section

The heat recovery section, which is used in the device of the invention, generally is of the conventional type and is completely or partially integrated in the incinerator or (after)-incineration chamber. The heat recovery section consists of a heat exchanging surface with fitting dimensions, which contacts the gasses from the thermal process, such that the available energy is transferred to another medium. According to the invention, preferably a steam kettle, a kettle on thermal oil or an organic fluid or a gas- gas heat exchanger is used, without, however, excluding other types of heat exchangers known to a person skilled in the art or otherwise.

A typical embodiment comprises a steam kettle, whereby the incinerator and the after-incineration chamber are completely integrated in the kettle. Different sections can be discriminated in the kettle, depending on whether the kettle is defined from the gas side or the water side.

From the gas phase, substantially the following parts can be discriminated:

- A radiation section, in which the heat transfer between the media of the flue gasses and water substantially is realised by means of radiation. Given the high temperatures of the gas in this radiation part, this part for contaminated combustibles usually is carried out as an empty space ('draught') with walls, which are built up as a heat exchanging surface. This means that these walls, in case of a steam kettle, consist of tubes through which a mixture of water and steam flows.

- A convection part, in which the heat transfer between the media of the flue gasses and water substantially is realised by means of convection. The temperatures are substantially lower in this part. The convection part usually comprises a collection of tubes, through which a mixture of water and stream flows. The walls are usually built up in the same way as in the radiation part of the kettle.

From the water phase, the following parts can be discriminated:

- An economiser: the kettle feed water is heated herein to a particular temperature, such that the water not yet evaporates and thus no vapour arises. In some embodiments, vapour can be formed in the economiser at certain thermal loads of the kettle.

- A drum: the water coming from the economisers is collected in a drum or a similar means and flows from here to the different evaporators of the kettle. The water-vapour mixture of the evaporators also flows back to the drum. If desired, a facility is installed through which the vapour subsequently flows from the upper part section of the drum (or a similar means) to the overheaters.

- Evaporators: the water coming from the drum flows to the evaporators, in which the water is converted in (saturated) steam.

- The overheater: the saturated steam coming from the drum is heated in the overheater to a temperature above the saturation temperature.

A characterising feature of the invention is that the incinerator and the (after)-incineration chamber preferably are part of the heat recovery section. The extent of integration is also determined by the caloric value of the contaminated combustible, whereby it needs to be understood that the heat recovery section is only partially or not at all integrated in the incinerator or the (after)-incineration chamber for a combustible with a low caloric value.

c. Section for the removal of acid

The reaction between sulphur oxides and haloid acids (HCI, HBr, HF) on the one hand, and an absorbent, for example unslaked lime, calciumhydroxide, lime stone and sodium carbonate, on the other hand, strongly depends on the temperature. Absorbents also comprise, as defined here before, adsorbents. Moreover, the yield of the reaction is also dependent on the temperature. An optimal consumption of one or more absorbents is achieved when they can react with the acid components in the flue gasses in one or more temperature windows.

The invention provides the injection of one or more absorbents into the after-incineration chamber, at a temperature which is preferably in the range between 900° and 1050°C. The reagent and the reaction products are removed from the flue gasses at a substantially lower temperature (T>100°C), such that a substantial temperature range is covered and a sufficient long contacting period between the reagents at different optimal temperatures is achieved. Further, the composition of the flue gasses in waste incineration installations is different as compared to installations that are burned with fossil fuels. Therefore, the use of absorbents at high temperature according to the invention in waste incineration is a substantial progress as compared to existing technologies.

The injection of absorbents in the flue gasses and the formation of sulphur oxides and halogen containing salts in the flue gasses lead to a different composition of the kettle ashes as compared to that which is typical for incineration installations. The purification mechanism of the kettle, the development of the temperature in the kettle - both from the gas side as from the water side - and the geometry of the kettle therefore need to be adapted to the changed composition of the fly ashes in order to minimise the deposition of fly ashes and to prevent corrosion of the kettle tubes.

The reduction of emissions of SOx in the incineration device of the invention can be achieved by one or more of the following steps:

- the injection of one or more aborbents, for example unslaked lime, calciumhydroxide, sodium carbonate and/or lime stone, at high temperature, such that SOx and haloid compounds are captured in a stage as early a possible. The sulphate salts are captured together with the fly ashes;

- the introduction, preferably by injecting, of one or more absorbents at low temperature. This injection can be considered as a second step, by which a high removal yield and a low consumption can be combined;

- the injection of one or more absorbents together with the reducing agent before the NOx reduction (see hereafter);

- the injection of one or more absorbents, for example clay minerals and natural and/or synthetic zeolites;

- the introduction of a device filled with one or more absorbents, for example a static bed, moving bed or fluid bed reactor, in the flue gas stream.

d. The DeNOx section

First, the formation of NOx during the incineration process can be limited by an adjusted temperature control and air management in such a way that a stepped incineration is achieved. Already for a long time, these measures are part of the incinerator control of modern installations. If desired, a recirculation of flue gas can be provided in order to further prevent the formation of NOx. By these primary measures, the concentration of NOx in the flue gasses of waste incineration installations can be limited to approximately 200-400 mg/Nm³ (11% oxygen, dry).

According to the invention, lower emission standards can be achieved by the use of a DeNOx section in the incineration device. This section reduces the nitrogen oxides present in the flue gasses to nitrogen gas by the injection of a reducing agent, for example ammonia or a nitrogen containing organic compound such as urea, or unsaturated hydrocarbons.

According to an aspect of the invention, a two- stepped DeNOx installation is integrated in the incinerator-kettle part of the incineration device. In this configuration, the NOx is reduced in a first step starting from the initial value to a pre-set value by means of the SNCR principle. This occurs in the after-incineration chamber. A catalyst volume is provided at the exit of the steam kettle, preferably between the evaporator bindles and the economiser, the catalyst volume eventually being preceded by an additional injection of the reducing agent. NOx is further reduced to the pre-set emission value in this second step.

The invention also comprises a combined injection of reducing agent with adsorbents and absorbents, for example lime and zeolite. Such a combined injection has the following advantages: a higher reactivity of the reagent by a higher degree of molecular collisions (reducing agent in suspension of lime and zeolite), simplification of the device, simplified process control, enhanced efficiency (lower consumption of reagents).

The lowering of NOx emissions in the incinerator device of the invention is thus achieved by means of one or more of the following steps:

- the addition, preferably by means of injection, of one or more reducing agents, for example urea, ammonia or unsaturated hydrocarbons, as well as of absorbents, for example lime, for capturing and neutralising acid components, in order to allow a more efficient reaction between NOx and NH₃; the reducing agent can be injected in the incineration chamber (SNCR location) or just before the catalyst; - the application of one or more SCR DeNOx catalysts in non-purified or partially purified flue gasses; the catalyst preferably is provided with a purification mechanism or is self-purifying;

- a two-stepped DeNOx installation, comprising a combination of SNCR and SCR DeNOx, substantially as known from the state of the art. The SNCR DeNOx installation can operate with a high amount of ammonia sludge and with a high reduction yield, through which the necessary volume of the SCR DeNOx catalyst, connected in series with the SNCR DeNOx installation, is optimised;

- oxidation of NO to NO₂, followed by injection of adsorbents for NO₂, for example clay minerals, natural zeolites, synthetic zeolites, Al₂O₃, SiO₂, AI₂O₃- MgO, TiO₂, SnO₂ and/or ZrO₂ at a suitable adsorption temperature, by which the NOx-compounds are destroyed in the furnace by the recirculation of the loaded adsorbent to the furnace;

- oxidation of NO to NO₂ can for instance occur by means of a solid catalyst, comprising a monolithically structure, a solid catalyst applied on a part of the heat recovery section, a solid catalyst applied on a carrier material and/or a catalyst which is injected into the gasses as a powder or suspension.

e. The dedusting section

According to the invention, the formation of dust in the incinerator c.q. the incineration process or the thermal conversion process is limited by one or more of the following measures:

- The lowering of the ratio of primary air to the total incineration air. The primary air is blown beneath the waste bed in the incinerator and is consequently one^' of the major reasons for the formation of dust. By stepped incineration (drying and gasification on the grate, complete incineration in the after-incineration chamber) lowers the amount of primary incineration air. By controlling each injection point for incineration air separately (for example by means of separate ventilators per part of the grate), the incineration process is controlled very accurately, such that the amount of primary air can be minimised (for example no air beneath the last grate if the incineration of the waste is good, meaning that there must be a minimum of organic carbon in the ashes). - Avoiding sudden movements of the burning waste layer. This can be achieved by adjusting the grate control (for example by using proportionally controlled valves). Preferably a SEGHERS® grate is used, whereby the horizontal (sliding) and vertical (fire hook) movement are controlled independent from each other, such that, with this grate, in contrast to with other commercially available grates, it is possible to control the movement of the burning waste layer in function of the incineration behaviour of the waste. In other words, the stirring of the waste can be controlled, as well with respect to speed as frequency - in function of the necessity to obtain a good incineration.

- The use of such a kettle design, allowing the separation of dust from the flue gasses before the temperature drops below 450°C as much as possible.

- The use of a purification system, which is as efficient as possible, of the convection parts of the kettle.

- The installation of mechanical beaters, and

- Selecting a horizontally executed kettle, such that the dust can be separated in an efficient and fast way.

- Limiting the evaporation of metals and metal compounds by limiting the temperature of the burning waste layer (gasification instead of incineration) and/or by a favourable differentiation in the formation of metal oxides, metal chlorides, metal sulphates and eventually other salts.

Given the importance of a temporary dedusting for preventing the formation of PCDD, PCDF, PCB and similar compounds, different dedusting technologies are evaluated at different working conditions (temperature). The following measures appeared efficient and they, both separately as in various combinations, are part of the invention:

- integration of multi(cyclones) in the kettle at temperatures between 450 and 650°C,

- integration of a ceramic filter consisting of top-filters or ceramic cloths,

- integration of a moving bed filter consisting of a (inert) filling which slowly falls down from the top to the bottom between two perforated walls. The filling and the captured dust are collected at the bottom of the filter, filtered, and again transported to the top. - integration of a filter, comprising filter cloths and top-filters, preferably made of metal or a metal alloy.

- adjustments of the kettle geometry, such that a maximal dedusting is obtained in the empty draughts (at temperatures above 450°C)

- injection of inert particles, functioning as a condensation surface for the formation of larger particles that can be separated much more easily.

According to the invention, the dedusting preferably occurs in two steps: a first dedusting in the empty draughts (radiation part) of the kettle or before the transition between the empty draughts and the overheater bindles, followed by a final dedusting at the exit of the kettle, for example by means of a classical cloth filter. The first step is new and constitutes, especially in combination with the second step, a substantial improvement as compared to the state of the art. The second step as such is known and is for the moment used as such in the majority of HVI's. By using the new technology, concentrations of dust below 2 mg/Nm³ can be achieved.

The following additional measures also are part of the invention:

- primary measures for preventing the formation of dust, for example limiting the manipulations of the waste layer, limiting the flow rate and/or the speed of the primary incineration air and the like.

- capturing of dust at the transition between the second and the third empty draught of the kettle by adjusting the flow pattern in the funnel below the second and third empty draught.

- artificially increasing the dust load shortly before the dedusting (funnel, cyclone, filter) of the crude flue gasses at a temperature above 450 °C, whereby volatile (heavy) metals may condense on the dust surface, thereby forming larger particles, such that an increased efficiency of the dedusting is achieved..

- introducing one or more of the above mentioned dust separators in the kettle at a temperature below 450 °C or below the lowest 'deformation' temperature of the dust.

f. The dedioxination section According to the invention, the emissions of PCDD, PCDF, PCB and other halogenated aromatic or aliphatic hydrocarbons are reduced by one or more of the following steps:

- catalytic oxidation of PCDD, PCDF and similar compounds at such a temperature that these compounds cannot be formed again;

- controlling possible present heavy metals in the course of the condensation of the volatile heavy metals or metal compounds on the dust particles, whereby the condensation preferably takes place at higher temperature by providing suitable contact compounds or wherein the heavy metals are de-activated at a suitable temperature with nitrogen or sulphur containing inhibitors;

- providing an air management in the incinerator which is adapted such that the excess of oxygen is minimised, the temperature in the waste layer is limited as a consequence of which less heavy metals arrive in the vapour phase and the amount of unburned carbon which is withdrawn with the flue gas flow, may be decreased;

- optimising the residence time of the flue gasses in the different temperature profiles, the residence time at temperatures above 600°C being prolonged and the residence time at temperatures between approximately 200 and 450°C being reduced;

- injecting absorbents inhibiting the formation of dioxins, such as the injection of lime in an after-incineration chamber, because for example these compounds concentrate dioxins and/or precursors thereof on the surface of the injected absorbents or absorb one or more dioxin building blocks, such as chlorine;

- artificially increasing the dust load, shortly before the dust filter of the crude flue gasses at a temperature of approximately 200°C, formation of dioxin being absent, adsorption of metal compounds on fly ash particles taking place.

In a flue gas purification which is integrated in the incinerator-kettle, according to this invention features are provided, which prevent or limit the re-formation of PCDD, PCDF, PCB and similar compounds. These features comprise one or more of the following embodiments:

- dedusting flue gasses at high temperature (above 450°C);

- capturing precursors through injection of absorbents;

- reducing the catalytic action of the fly ashes by injecting inhibitors

- optimising the incinerator control to limit the oxygen content and - reducing the carbon content of the fly ashes by prolonging the residence time at higher temperature.

The oxidation of PCDD, PCDF and PCB (and CO, CxHy) by an oxidant which is present in the flue gasses or is added to the flue gasses over a catalyst, constitutes a part of the present invention. The latter technology is proven technology for several years in the field of waste incinerating devices, however in these cases the oxidation catalyst (a classical SCR catalyst) being positioned at the end of the classical flue gas purification device, i.e. in the clean flue gasses. According to the present invention, the catalyst is now positioned in less purified flue gasses, as a consequence of which features are required with which for example the deposition of salts on the catalyst surface, poisoning of the catalyst by alkali metals and sulphur and deposition of dust may be avoided or the consequences thereof be compensated. These features include according to the invention, one or more of the following steps:

- Dedusting the flue gasses at high temperature;

- Desulphurising the flue gasses in the incinerator-kettle by means of one of the above described techniques (DeSOx);

- Treating the catalyst with an abrasive resistant coating or a protective coating which diminishes salt deposition or facilitates regeneration of the catalyst;

- Providing a purification of the catalyst with steam, air, flue gasses, water or (sound) waves.

g. Measuring and control section.

Since the different processes take place in the gas phase and the reagents are injected in the moving, cooling flue gas stream, a correct control of the flue gas parameters (temperature, speed, composition) in the different phases of the purification is of utmost importance.

In known waste power stations, pollutants are only measured in the fireplace, possibly a limited number of compounds is measured before or after one of the flue gas purification steps (e.g. oxygen at the exit of the kettle, HCI before the half wet reactor, dust after the sleeve filter , etc.).

An essential part of the present invention consists of implementing different measuring principles and control theories. Therewith, parameters such as usability at high temperature, interference of dust or other chemical components, possibility of measuring values in one plane in stead of a point, have been evaluated. Also the most suitable control philosophy has been determined.

With the present invention a measuring and control section is provided, which comprises one or more of the steps described hereafter:

- Controlling the injection of the reagents of the DeNOx step based on NO/NO₂ measurements, NH₃ measurements, O₂ measurements, H₂O measurements, flow rate measurements and/or temperature measurements at one or more positions in and/or after the kettle;

- Controlling the injection of the reagents for the desulphurisation step based on SOχ and/or HCI measurements, O₂ measurements, H₂O measurements, flow rate measurements and/or temperature measurements at one or more positions in and/or after the kettle;

- Determining a suitable operating temperature of the catalyst based on the SO₂ concentration before or after the catalyst, the moisture content, and the ammonia sludge;

Determining a suitable operating and/or cleaning temperature of the catalyst based on the NOx removal, the injection flow rate of the reagents and the amount of ammonia sludge.

In figure 1 , an embodiment of an incinerating device of this invention is shown, in which the incinerator with after-incineration chamber (which may also be part of the first draught or of the radiation part of the recuperation kettle), the recuperation kettle consisting of a radiation part and convection part, as well as the various sections for the purification of the flue gasses are indicated with a few of the corresponding preferred temperature profiles. In this scheme, the flue gas stream flows subsequently through a desulphurisation section (DeSOx) and neutralisation of hydrogen-halogen compounds, a section for the removal of nitrogen oxides (DeNOx), a section for dedusting and removal of heavy metals (DeDust) and a section for removing dioxins and compounds related thereto (DeDiox). Also the formation of CO and unburned hydrocarbons (CxHy) is limited to a minimum by controlling the gasification - incineration process, as described above. It will be clear to the man skilled in the art that the sequence of the purification steps may be changed and that a modification of the optimum temperature profiles should be taken into account.

The present invention is not limited to the embodiments described above, but includes all variations based on this description, whether or not in combination with the state of the art, and which are within the knowledge of the man skilled in the art. Such embodiments are also included in the present invention. The claimed rights are determined by the claims given hereafter.

Claims

1. An incineration device, suitable for the incineration of contaminated combustibles, for example waste, characterised in that the incineration, recovery of energy, and at least the following purification steps:

- dedusting and removing or neutralisation of heavy metals

- removal of nitrogen oxides

- desulphurization and removal of haloid acids

- removal of dioxins and other organic trace compounds are substantially performed in one integrated system.

2. An integrated incineration device according to claim 1 , characterised in that the device at least comprises the following sections:

- an incineration chamber or an incinerator ;

- one or more sections for removing acids, the said section or sections being integrated in the incinerator, incineration chamber and/or heat recovery section;

- one or more DeNOx sections integrated in the incinerator, incineration chamber, heat recovery section and/or other sections for flue gas purification ;

- a stepped dedusting section comprising one or more sections integrated in the incinerator, the incineration chamber, the heat recovery section and/or other sections for flue gas purification ;

- one or more sections for the removal of chlorinated hydrocarbons integrated in the incinerator; the incineration chamber, the heat recovery section and/or other sections for flue gas purification ;

- an adapted measuring and control section for controlling the different steps of flue gas purification and heat recovery, suitable for incinerating contaminated combustibles.

3. An integrated incineration device according to claim 1 or 2, characterised in that the different sections operate separately or overlap with each other, whereby in one section a plurality of contaminants are treated or present simultaneously.

4. An integrated incineration device according to any one of the preceding claims, characterised in that various sections are carried out in one simple part of the device.

5. An integrated incineration device according to any one of the preceding claims, characterised in that the device comprises means for supplying oxygen containing air to the incineration chamber or incinerator, whereby, when operating the device, oxygen containing air is conducted through the waste layer in a sub-stoichiometric amount (0,5 < λ < 0,99) and whereby at the transition between the incineration chamber and the first vertical draught of the device secondary oxygen containing air is introduced in such a way that the air factor is increased to 1 ,3 < λ < 1 ,5.

6. An integrated incineration device according to claim 5, whereby one or more absorbents are introduced in the after-incineration chamber together with the secondary air, the temperature of the flue gas being between approximately 800 and 1200°C.

7. An integrated incineration device according to any one of the preceding claims, characterised in that one or more reducing agents, for example ammonia or an ammonia forming substance or unsaturated hydrocarbons, are introduced into the radiation part of the device above the secondary air inlet points.

8. An integrated incineration device according to claim 7, characterised in that when supplying ammonia or an ammonia forming substance, the temperature of flue gas is between approximately 820 and 1050°C.

9. An integrated incineration device according to any one of the preceding claims, characterised in that the dedusting section comprises one or more narrowings and/or blades to affect the flow direction of the flue gasses and the flue gasses are separated from dust and fly ash following the change of the flow direction.

10. An integrated incineration device according to claim 9, characterised in that the maximum temperature of the flue gasses in the dedusting section is 450°C.

11. An integrated incineration device according to any one of the preceding claims, characterised in that the device also comprises an economiser section in which halogenated hydrocarbons, like PCDD, PCDF and PCB are catalytically oxidised.

12. An integrated incineration device according to claim 11 , characterised in that the catalyst is selected from the group comprising synthetic zeolites, AI₂O₃, SiO₂, AI₂O₃-MgO, TiO₂, SnO₂ en ZrO₂, or mixtures thereof and the oxidation is carried out at a temperature ranging from 150°C to 350°C.

13. An integrated incineration device according to claim 11 , characterised in that the catalyst is selected from a precious metal and the oxidation is carried out at a temperature ranging from 150°C to 550°C.

14. An integrated incineration device according to any one of the preceding claims, characterised in that the process is controlled in such a way that

- the amount of primary air needed is calculated based on the amount of oxygen above in the empty draught and the flow rate of the secondary air that has been blown in ;

- the amount of secondary air is calculated as percentage of the total amount of combustion air, with a minimum of 0% and a maximum of 50%, and is controlled by the deviation between the process setpoint and the process value of the steam flow rate, as defined herein, whereby the process setpoint is defined as the pre-set value to which the process control is directed, and the 'process value' is the real actual value as observed in the process.

- the amount of absorbent is controlled based on the deviation between the process setpoint and the process value of the HCI value, as measured at 450°C, after dedusting ; and

- the amount of reducing reagent is controlled based on the deviation between the process setpoint and the process value of the NOx value as measured at 450°C, after the dedusting.

15. An integrated incineration device according to any one of the preceding claims, characterised in that the absorbent is selected from the group comprising unslaked lime (CaO), calciumhydroxide (Ca(OH)₂), sodiumbicarbonate (NaHCO₃), sodiumcarbonate (Na₂CO₃), caliumcarbonate (CaCO₃), clay minerals, natural zeolites, synthetic zeolites, diatomaceous earth, C, AI₂O₃, SiO₂, AI₂O₃-Mg0, TiO₂, SnO₂, WO₃ and/or ZrO₂or mixtures thereof.

16. An integrated incineration device according to claim 15, characterised in that the absorbent is added as a powder or as granules, which are injected into the flue gasses and is subsequently separated from the flue gasses in the dedusting zone, whereby also a partial removal of NOx is achieved.

17. An integrated incineration device according to claim 16, characterised in that after the addition of the absorbent a reducing agent is introduced for further removal of NOx.

18. An integrated incineration device according to any one of the preceding claims, characterised in that the ammonia forming substance is selected from the group comprising ammonia, urea, vapours of a sludge drying device, vapours of a manure processing device, waste water from a manure processing device and humid nitrogen containing substances like sludge.

19. An integrated incineration device according to any one of the preceding claims, characterised in that the amount of absorbent is controlled based on the deviation between the 'process setpoint' and the process value of the SOx or SO₂ or SO₃ value instead of HCL value, as measured at 450°C, after dedusting.

20. An integrated incineration device according to any one of the preceding claims, characterised in that the economiser is a controlled economiser, in which the operating temperature of the catalyst is controlled in a temperature range of 50°C.

21. An integrated incineration device according to any one of the preceding claims, characterised in that the released fly ashes are cooled down (T<300°C) and recirculated over the empty draughts of the kettle in order to create terminal condensation surfaces for volatile heavy metals.

22. An integrated incineration device according to any one of the preceding claims, characterised in that the absorbent is injected at the transition between the first and second empty draught of the kettle or at one or more locations in the empty draughts of the kettle in order to create condensation surfaces for volatile heavy metals and to also allow a second reaction between the remaining acid components and the lime absorbing agent.

23. An integrated incineration device according to claim 1 , characterised in that one or more absorbing and reducing agents are introduced in the after-incineration chamber, preferably as a suspension, by means of an injection with pressurised air or steam, and preferably at a temperature between approximately 850 and 950°C.

24. An integrated incineration device according to one or more of the preceding claims, characterised in that the DeNOx removal comprises the following steps:

- incineration in the incinerator at low air excess in order to reduce the formation of NOx ;

- a first NOx removal by applying the SNCR principle;

- an additional NOx removal, whereby an additional amount of ammonia or ammonia forming substance is injected after dedusting and at a temperature below 450°C ;

- the introduction of a DeNOx catalyst in the economiser section of the kettle ;

- the on-line purification of the catalyst by means of the injection of steam, pressurised air, purified flue gasses or (sound) waves above the catalyst surface.

25. An integrated incineration device according to claim 24, characterised in that the catalyst is maintained in the following temperature window:

- titanium oxide based catalyst 200-450°C

- zeolite based catalyst 200-450°C

- iron oxide based catalyst 350-450°C

- activated carbon/coke 100-150°C

26. An integrated incineration device according to claims 24 and 25, characterised in that the DeNOx section is constructed in such a way that at least 50% of the NOx present in the flue gasses reacts with ammonia and maximally 50% of the NOx reacts with ammonia on/in the catalyst.

27. An integrated incineration device according to any one of the claims 24-26, characterised in that the catalyst is purified by means of ultrasonic waves.

28. An integrated incineration device according to any one of the claims 24-26, characterised in that the catalyst is purified by means of a temporary raise of the catalyst temperature.

29. An integrated incineration device according to claim 28, characterised in that the temperature raise is enforced externally.

30. An integrated incineration device according to claim 29, characterised in that the temperature raise is enforced internally by an exothermic reaction arising from the accumulation in the absence of carbon and unburned hydrocarbons on the catalyst surface and which are oxidised by an oxidising agent.

31. An integrated incineration device according to any one of the preceding claims, characterised in that the blades are cooled by water.

32. In integrated incineration device according to any one of the preceding claims, characterised in that the blades are hung loosely, such that they can be cleaned by vibrations and the collected dust can be removed from the cooling surface.

33. An integrated incineration device according to any one of the preceding claims, characterised in that the incineration device comprises an incinerator of one of the following types:

- a fluid bed ;

- a moving grate;

- a static grate.

34. An integrated incineration device according to any one of the preceding claims, characterised in that the additional dedusting is realised by means of a multicyclone, a ceramic filter or a metallic filter, preferably at a temperature <450°C, whereby the dedusting is preferably completely integrated in the recuperation kettle in the convection part of the kettle.

35. An integrated incineration device according to any one of the preceding claims, characterised in that an absorbent is contacted with the flue gas stream in a part of the device in a controlled way such that entraining of the absorbent along with the flue gasses is avoided.

36. An integrated incineration device according to claim 35, characterised in that the absorbent is contacted with the flue gasses by means of a series of moving bed filters.

37. An integrated incineration device according to claims 35 or 36, characterised in that the absorbent is contacted with the flue gasses at different temperatures.

38. An integrated incineration device according to any one of the preceding claims, characterised in that a plurality of flue gasses are contacted with the flue gasses, each at a particular temperature, which may be the same or may be different.

39. An integrated incineration device according to any one of the preceding claims, characterised in that the filters are selected from a group comprising:

- perforated plates

- lamellae positioned at a pre-defined angle

- lamellae and perforated plates

- cambric, mounted on a frame or not.

40. An integrated incineration device according to any one of the preceding claims, characterised in that also an oxidising catalyst is introduced in the flue gasses, at a temperature between 250°C and 550°C, for the oxidation of NO to NO₂, of SO₂ to SO₃ and of CO to CO₂.

41. An integrated incineration device according to any one of the preceding claims, characterised in that the device is suitable for the incineration of waste, such as domestic or industrial waste, industrial by- or rest- products, impure fossil fuels, biomass of vegetable and/or animal origin like wood, straw, energetic crops, manure, bone meal.

42. Process for the incineration of waste, such as domestic or industrial waste, industrial by- or residual products, impure fossil fuels, biomass of vegetable and/or animal origin like wood, straw, energetic crops, manure, bone meal, characterised in that the incineration is carried out in a device as defined in any one of claims 1-41.