EP2216598A2 - Method for reducing the polluting potential of waste gases and residues of combustion installations - Google Patents

Abstract

The method involves guiding a main fuel flow (10) and an additional fuel flow (7) for combustion in a combustion chamber (3). A fuel mixture with constant load is formed at a toxic raw material e.g. chlorine compound, and chlorine content is formed in exhaust gas during combustion. Adjustment of chlorine content is performed by control of supply of the additional fuel flow, based on chlorine content measurement by a sensor (12) in the exhaust gas. The additional fuel flow is supplied in the form of refuse.

Description

The invention relates to a method for reducing the pollutant potential in exhaust gases and residues of incinerators according to the first claim.

Incineration plants incinerate fuels in a fuel stream. Liquid or gaseous fuels are readily mixable and therefore homogenizable. They can thus be fed into a fuel stream with very small fluctuation margins in the composition, calorific value or pollutant content of the combustion.

On the other hand, solid fuels are fundamentally less compatible, which means that their combustion requires larger fluctuation margins of the aforementioned type. Has a fixed amount of fuel, such as If, in addition, there is an inhomogeneous composition of fuel particles of different sizes, the possible fluctuation margins increase considerably. In particular, the inhomogeneous composition of fuel streams from household waste with widely varying calorific values (calorific values) and pollutant source contents and consequently varying combustion characteristics complicate operation in comparison to other industrial combustion processes.

A pollutant source of particular importance for incineration includes chlorine and chlorine compounds. This substance group leads to combustion of hydrogen chloride (HCl) or other chlorine compounds and is considered to be the major cause of, for example, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD / F) in the flue gas. Chlorine is a basic component of many plastics in particular, such as PVC, and is equally selective in household waste and industrial waste individual waste components, but nevertheless integrally in large quantities.

Hydrogen chloride is a toxic and corrosive substance for which legislators in the Federal Republic of Germany (such as the TA-Luft) or other countries have set emission levels from incinerators and other technical equipment.

Due to their toxicity, the legislator in the Federal Republic of Germany has set a limit value for emissions of these compounds from waste incineration plants of 0.1 ng TEQ / Nm ³ (TEQ = toxicity equivalent) in the 17th Federal Immission Control Ordinance (17.BImSchV). According to current knowledge, this limit value for PCDD / F in combustion exhaust gas can not be met by solely optimizing the firing conditions. The concentration of the PCDD / F in the combustion exhaust gas must therefore be reduced below the prescribed limit with an additional combustion gas downstream of the combustion, for example with the aid of wet scrubbers with absorption components.

In the WO 02/064235 A2 For this purpose, the use of a material for absorption components of the aforementioned type for the retention of polyhalogenated compounds (PCDD / F) is proposed, consisting of carbon particles in a matrix of a polyolefin.

Alternatively, the emissions of PCDD / F in the flue gas can be reduced by means of sulfur oxides in the flue gas or the introduction of sulfur compounds into the combustion.

In the US 4,793,270 In addition to sulfur-containing coal, CS ₂ , CaS and SO _{2 are also introduced} into the combustion process to reduce the dioxin formation rate in the context of waste incineration.

Likewise, under the DE 199 53 418 A1 For the reduction of dioxins in the exhaust gas of chemical processes proposed addition of amidosulfonic acids and sulfamide to the fuel.

In addition, chlorine in the technical operation of incinerators due to the formation of e.g. hydrochloric acid but also significant corrosion damage. In addition, as a constituent of the flue gas, chlorine plays a key role in corrosion processes in the boiler sector, which increase operating costs through downtimes and time-consuming repairs. Because of this problem of corrosion, therefore, certain waste fractions with high chlorine contents are incinerated by operators of large-scale waste incineration plants only at relatively high costs.

A reduction of the corrosion problems promise, for example, protective coatings in the relevant areas, especially the boiler. In addition, high SO ₂ concentrations in the raw gas or high sulphate contents in flyashes reduce the corrosion problems.

In the DE 198 49 022 A1 Sulfur-containing chemicals such as SO ₂ and MgSO _{4 are introduced} into the fuel gas to reduce corrosion.

As part of the DE 602 11 476 T2 (from the WO 02/059526 ) an addition of a sulfur-containing chemical such as (NH ₄ ) ₂ SO ₄ , NH ₄ HSO ₄ , H ₂ SO ₄ or FeSO _{4 is} proposed for corrosion reduction.

DE 101 31 464 B4 proposes a process for the co-incineration of high-halogenated waste with low levels of corrosion and emissions in waste incineration plants with the addition of sulfur or sulfur-containing chemicals.

Also the DE 198 02 274 C2 discloses a method for reducing corrosion in the operation of a boiler of a waste incineration plant, wherein sulfur or sulfur compounds are introduced into the furnace or the hot exhaust gases before reaching the corrosion-prone heating surfaces.

Also in the WO 06/134227 A1 will be like in the WO 06/124772 A2 For corrosion reduction of steam boilers, it is proposed to add Fe (SO ₄ ) or Al ₂ (SO ₄ ) ₃ or SO ₂ , SO ₃ , H ₂ SO ₄ , sulfur or sulfur salts.

Basically, the co-combustion of sulfur, sulfur compounds or sulfur-containing fuels (eg municipal sewage sludge, waste tires or sulfur-containing coal) or metered addition of SO ₂ / SO ₃ , H ₂ SO ₄ or other sulfur-containing compounds such as (NH ₄ ) ₂ SO ₄ into the exhaust gas before entering the boiler.

Further, the DE 103 38 752 B9 a process-integrated SO ₂ cycle in the context of a waste incineration, which requires no external addition of sulfur or sulfur compounds. This method requires a flue gas cleaning with wet SO ₂ separation by means of at least one wet scrubber.

All methods are based on the fact that with increasing SO ₂ and / or SO ₃ concentration in the flue gas, the sulfation and thus the reduction of the chloride content of the air and boiler ash deposits is achieved. However, almost all processes require an excess of sulfur compounds in the waste incineration to ensure reduced dioxin formation or corrosion reduction.

In addition to the reduced PCDD / F formation and the positive effects on corrosion processes, the additional sulfur compounds added to the combustion lead to higher sulfur oxide concentrations in the flue gas, which must be separated for compliance with the relevant emission limit values with larger amounts of neutralizing agent. The higher need for neutralizing agents additionally causes a higher amount of residues, which must be disposed of cost-effectively as special waste.

On this basis, the object of the invention is to propose a method for reducing the pollutant potential in exhaust gases and residues of incinerators when using solid fuels with greatly varying chlorine loading that manages without higher residue levels and is also applicable to dry and quasi-dry flue gas cleaning systems. In addition, a more even distribution of chlorine in combustion residues (eg, ashes), flue dust and flue gas cleaning pressures is to be achieved.

The object is achieved by a method having the features of the first patent claim. Subclaims give advantageous embodiments of the invention again.

To solve the problem measures to adjust to be implemented on an industrial scale consistently occurring combustion proposed. This is aimed at a constant pollutant formation and Ausbrandgüte.

As a measure for generating a combustion proceeding consistently, it is proposed to feed at least one second fuel stream with at least one second fuel in parallel to the combustion, in addition to the first fuel stream discharging into the combustion with the abovementioned solid fuel having inhomogeneous pollutant contents. The feed takes place in such a way that the summed influx of pollutant starting material, but optionally in addition to calorific value and / or composition homogeneous or in the combustion in Homogeneous occurs at a narrow interval. The second and optionally further fuel streams serve to compensate for one or more material inhomogeneities in the first fuel stream and consequently require individual regulation of their material flow, preferably volumetric flow. Preferably, the fuels are present in these second and possibly subsequent fuel streams for the purpose of better controllability in a homogenized and readily transportable and portionable form, for example as a liquid, suspension or particle bed.

In a waste incineration, said second and optional further fuel streams preferably consist of comminuted or liquefied, ie an eligible refuse one or predominantly a waste fraction (waste) comprising eg wood, plastics, waste oils, cellulose, chemicals, composites or sorting residues. These waste fractions are characterized by a particularly pronounced property such as a high calorific value or a quick ignitability or a high content of a certain fuel source such as
Chlorine, so that even a small second or further fuel stream makes even stronger inhomogeneities in the (first) fuel flow compensated. It is essential that the second and optionally further fuel stream comprises a fuel with known or predominantly known fuel composition (and optionally calorific value). The fuel streams are preferably passed separately into the combustion chamber for combustion or mixed before combustion to a common fuel stream and passed into the combustion.

A setting of a constant chlorine content in the exhaust gas of the combustion is preferably carried out via a Hinzudosierung a chlorine-containing fuel, for example via a granulate of chlorine-containing plastics such as PVC in the second fuel stream.

For continuous combustion adjustment (e.g., via additional optional steam production, calorific value and / or composition control), controlled addition of, preferably, a highly flammable fuel such as cellulose, solvent or waste is suitable. A consistent, i. Continuous combustion without fluctuations in emission and burnout promotes consistent pollutant formation and continuous burnout during combustion.

The regulation of the second and optionally further fuel flow is a volume or mass flow control. For the determination of the controlled variables, sensors are provided for selective detection of the pollutants, in particular of HCl, into the combustion chamber and / or the afterburning zone (boiler) and / or raw gas duct. The additional control of the supply of a second or further fuel and thus the combustion takes place via data from the steam production or temperature at fixed measuring points in the combustion chamber, rust, in the combustion or afterburning zone. These measured values are compared in a process computer with corresponding setpoint values and converted into manipulated variables for the control.

The initial goal is not to reduce the emissions at the chimney, but to achieve a constant pollutant formation and / or combustion on a scale. The proposed measures according to the invention effect advantageously a realizable on an industrial scale constant concentration of corrosive pollutants such as HCl, H ₂ SO ₄ or other pollutants. In addition, they counteract the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD / F) in the flue gas in an advantageous manner.

A constant concentration of pollutants in the exhaust favors the operation of an exhaust gas purification. In contrast to fluctuating concentrations with discrete concentration peaks, a lower excess of neutralizing agent for the separation of HCl or other pollutants, such as e.g. Sulfur oxides required. Furthermore, a constant pollutant formation rate in a preferably even combustion promotes uniform burnout and thus combustion residues, in particular slag of constant composition, which simplifies recycling or landfilling of these residues.

In particular, corrosion problems caused by chlorine and the high consumption of neutralizing agents in the dry or quasi-dry flue gas cleaning can be reduced by a uniform and controlled chlorine concentration in the flue gas.

The invention is explained in more detail below with reference to figures, wherein illustrated features are disclosed as examples of the invention. This shows

Fig.1 the basic structure of a grate combustion system for solid fuels such as garbage.

A rust incinerator gem. Fig.1 includes the furnace 1 with combustion grate 2, combustion chamber 3 and a secondary combustion chamber arranged thereabove 4. The afterburning chamber is connected downstream of a heat transfer area 5, for example, one or more heat exchanger of a boiler or boiler. Further, a fuel supply 6 is provided in the combustion chamber 3 , comprising in the example a supply of additional fuel 7 via a conveyor 8 from its own silo 9 and a first main fuel stream 10 for the solid fuel directly into the combustion chamber.

For a uniform and controlled chlorine concentration in the flue gas, a continuous and synchronous control 11 of the conveyor 8 is proposed. The control is preferably based on empirically determined relationships between the measured chlorine concentration in the flue gas and the conveying speed of the second or further fuel, in opposite sense in opposite directions to each other in a first approximation. With a sensor 12 , the chlorine concentration in Rohgaskanal 13 between the heat exchanger region 5 and downstream spray or dry absorber 14 is determined and fed as a measurement signal via a measuring line 15 of the control 11 . The measurement signal is compared in the controller 11 with a setpoint. A control signal generated therefrom is forwarded via a control line 16 to the conveying device.

The supply of additional fuel 7 is controlled from the silo 9, preferably exclusively based on the measured chlorine concentrations in the flue gas. Optionally, the main fuel stream 10 is also controlled in the combustion chamber, preferably limited to a throttling when exceeding a predetermined chlorine concentration in the flue gas at the sensor 12 more preferably after the reduction of the supply of additional fuels . 7

For measuring the chlorine concentration in the exhaust gas, it is also possible to use sensors at a plurality of measuring points, preferably in the region of the heat exchanger regions 5 or the raw gas channel 13 .

If the chlorine concentration in the waste and thus in the flue gas drops, additional fuel can be added from the separate silo 9 . The fuel can preferably be metered directly into the firebox on the good bed or in the waste feed area.

If the chlorine concentration in the flue gas increases too much, the additional dosage can be reduced or switched off.

The controlled chlorine concentration in the raw gas leads in particular to a uniform choke load in the flue gas. Concentration peaks and drops of the crude gas chlorine charge are detected immediately by the sensor immediately after formation and adjusted by the aforementioned control of the fuel flows at a predetermined concentration level. The concentration level must be adjusted so that a corrosion attack, especially on the boiler, can be tolerated. Optionally, in particular the main fuel supply can be reduced if the chlorine concentration level is exceeded. Consequently, highly corrosive deposits with greatly increased chlorine concentrations in the boiler area can be avoided.

Due to the aforementioned measures enters the field of flue gas cleaning a flue gas with significantly lower concentration fluctuations of chlorine compounds. The lower concentration variations allow operation of the flue gas purification system with a lower neutralizer excess such that downstream purification steps comprising addition of dusty calcium hydroxide, calcium carbonate, sodium bicarbonate, carbonaceous adsorbents and / or coke 17 (dissolved or suspended in water or with separate water supply) into the exhaust. In the subsequent further separation of the pollutants in the abovementioned spray or dry absorber 14 and in a fabric filter 18 , a residue stream 19 is formed with toxic dusts from the flue gas cleaning system, which is lower due to the lower concentration fluctuations. Consequently, only a smaller amount of residue is to be disposed of. The purified exhaust gas is then discharged via a chimney 20 . The addition of dusty calcium hydroxide and coke 17 in the spray or dry absorber and / or in the exhaust gas is preferably carried out likewise regulated as a function of the chlorine loading, preferably via the control 11.

The measures, in particular comprising the supply control of the main fuel stream 10 are not only suitable for ensuring a constant formation of chlorine compounds or a homogeneous combustion, but also to a particular extent to stabilize the nitrogen oxide formation rate.

LIST OF REFERENCE NUMBERS

1

heating

2

burning rust

3

combustion chamber

4

afterburner chamber

5

Wärmeübrertragungsbereiche

6

fuel supply

7

additional fuel

8th

conveyor

9

silo

10

Main fuel flow

11

regulation

12

sensor

13

raw gas

14

Spray or dry absorber

15

Measurement line

16

control line

17

Calcium hydroxide, calcium carbonate, sodium bicarbonate, carbonaceous adsorbents and / or coke

18

fabric filters

19

residue stream

20

fireplace

Claims (5)

Method for reducing the pollutant potential in exhaust gases and residues of incinerators, wherein a) at a combustion of a first fuel stream (6, 10) solid fuel with changing loading as content of a pollutant source additionally at least a second fuel stream (7) in the form of eligible waste or a refuse fraction with a constant loading of the pollutant source fed into the combustion becomes, b) the pollutant source is chlorine or a chlorine compound, c) the fuel streams are passed to the combustion in a combustion chamber (3) , that a fuel mixture with a constant load on the pollutant starting material and a constant chlorine content in the exhaust gas of the combustion is formed, d) an adjustment of the constant chlorine content via a control of the addition of the second fuel stream (7) , based on the at least one sensor (12) measured chlorine content in the exhaust gas. A method according to claim 1, characterized in that the fuel mixture is brought together prior to feeding into the combustion to a common fuel stream. Method according to one of the preceding claims, characterized in that after the combustion, a measurement of the pollutant loading in the exhaust gas made and supplied as a measurement signal of a control (11) of the volume or mass flow for the second fuel flow. A method according to claim 3, characterized in that the measurements are a carbon monoxide concentration or oxygen measurement via absorption measurements or emission measurements include. Method according to one of the preceding claims, characterized in that a second or further fuel flow is fed directly into the combustion chamber (3) .

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