Description

The present invention relates to an incineration plant for solid material such as waste or biomass , the incineration plant having a combustion material inlet through which the solid material is to be introduced, a combu stion chamber into which the solid material is introduced and in which the solid material is combusted, whereby flue gases are produced, at least one empty pass downstream of the combustion chamber, a heat recovery steam generator (pas s) downstream of the empty pas s and a flue gas purification device (pass) downstream of the heat recovery steam generator.

The incineration plant usually comprises a combustion grate arranged within a lower section of the combustion chamber with which the solid material and combusted solid material can be conveyed through the combustion chamber from the combustion material inlet to a slag container. Primary air is usually supplied from below the combu stion grate to the solid material arranged on the combustion grate, so that the solid material arranged on the combustion grate is combu sted with the primary air.

Additionally, nozzles may be provided above the combustion grate with which secondary air, tertiary air for afterburning and/or an oxygen poor carrier gas can be provided to the flue gases .

The at least one empty pas s may be arranged vertically or horizontally , wherein the flue gases flow from the combustion chamber through the at least one empty pass to the heat recovery steam generator. In particular, two, three or more parallel empty passes may be embodied .

The heat recovery steam generator may be arranged (in sections) vertically and/or horizontally, wherein also an oblique orientation is po ssible.

The walls of the combustion chamber and the empty pass (es) are usually equipped with heat exchangers (i.e. tubes) , wherein the heat exchange medium of the heat exchangers is in particular provided to one common boiler drum.

The flue gas purification device may comprise elements for dedusting , scrubbing and desulfurization (such as SC R or SNCR) of the flue gas . A chimney may by arranged downstream of the flue gas purification device.

The heat recovery steam generator comprises heat exchangers (i.e. tubes) , which come into (thermal) contact with the flue gases , wherein a heat exchange medium (i.e. water or steam) provided through the heat exchangers transfers the exchanged heat to a boiler drum or similar.

During operation of such an incineration plant, contaminations in the flue gas deposit within the heat recovery steam generator on the heat exchangers or on the inner walls of the heat recovery steam generator, whereby the heat transfer efficiency from the flue gas to the heat transfer medium is reduced.

In order to remove such depositions in the heat recovery steam generator the whole incineration plant has to be run down, the heat recovery system generator needs to be cooled down and then the depo sitions can be removed manually. Afterwards it takes a relatively long time to run the incineration plant to full load. Accordingly, there is a long downtime of the incineration plant for cleaning the heat recovery steam generator.

EP 0 806 236 A 1 discloses an incineration plant which has a gas flow diverter ahead of two waste gas lines in order to control the waste gas temperature for a subsequent denox reactor.

In view of this , it is an object of the present invention to provide an

incineration plant which heat recovery system generator can be cleaned without the need to shut down the whole incineration plant.

This obj ect is achieved by an incineration plant with the features of the independent claim and by a method for operating the incineration plant.

Preferred embodiments of the invention are described in the sub claims and in the whole description, wherein single features of the preferred embodiments can be combined with each other in a technically meaningful manner.

The object is achieved in particular in that the heat recovery steam generator has a first heat recovery flow path and at least one, in particular one, two or even three second heat recovery flow path(s), each heat recovery flow path connecting the empty pass to the flue gas purification device, wherein at least one inflow shut off device is provided, so that a flue gas flow into each heat recovery pass is interruptible individually. In particular, one inflow shut off device is assigned to each heat recovery flow path.

With other words , the present invention suggests to provide the heat recovery steam generator with two fluidically parallel heat recovery flow paths, wherein each heat recovery flow path can be disconnected from the flue gas flow . This way the disconnected (closed) heat recovery flow path can be cleaned during operation of the incineration plant, wherein the flue gas is conducted through the open heat recovery flow path(s) .

It is also suggested to operate the incineration plant with a method

comprising the following steps : Combusting solid material (i.e. waste or biomass) in the combustion chamber with a first rate,

Reducing the combustion of the solid material in the combustion chamber to a second rate, for example the second rate being no more than 60% of the maximum combustion rate or preferable no more than 50% or 40% of the maximum combustion rate,

Closing at least one inflow shut off device for the first heat recovery flow path, so that the flow of flue gas into the closed first heat recovery flow path is interrupted,

Manually maintaining the closed first heat recovery flow path, for example with a manually operated high pressure water blaster, while solid material is combusted at the second rate and at least one non- closed second heat recovery flow path is flown through by flue gas .

According to the invention it is not neces sary to shut down the incineration plant in order to clean and/or maintain the heat recovery flow path of the heat recovery steam generator.

In particular it is suggested that during maintenance of the interrupted heat recovery flow path an overpres sure of ambient air is provided in the

interrupted heat recovery flow path, so that no flue gas may enter the interrupted heat recovery flow path.

In one embodiment, also the at least one empty pas s may comprise one first empty flow path and at least one second empty flow path, wherein each empty flow path connects the combustion chamber or one common upstream empty pas s to one heat recovery flow path . Accordingly, according to this

embodiment the at least one empty pas s has at least two fluidically parallel empty flow paths , each of which conduct the flue gas to a respective heat recovery flow path . In this embodiment the number of the empty flow paths may be the same as the number of heat recovery flow paths . Of course, the at least one empty pas s may have only one single path, through which the flue gas is conducted to the multiple heat recovery flow paths .

In an even further embodiment, also the flue gas purification device may comprise a first flue gas purification flow path and at least one second flue gas purification flow path, wherein each flue gas purification flow path is assigned to a respective heat recovery flow path . Accordingly, in this embodiment the number of the flue gas purification flow paths may be the same as the number of heat recovery flow paths . Of course, the flue gas purification device may have only one single path, into which the flue gas from the multiple heat recovery flow paths is conducted.

The at least one inflow shut off device is arranged in such a manner that the flue gas flow into each heat recovery flow path can be interrupted

individually. For example, in case the empty pas s comprises multiple parallel paths, the inflow shut off device may be arranged at the upstream side or within the respective empty flow path. Preferable, one inflow shut off device is assigned to each heat recovery flow path, wherein the inflow shut off device is in particular arranged between the single path or multiple paths of the empty pas s and the respective heat recovery flow path .

In a further embodiment, an outflow shut off device is assigned to each heat recovery flow path, wherein preferably one outflow shut off device is assigned to each heat recovery flow path and is preferably arranged between the heat recovery steam generator and the downstream flue gas purification device. In case that also the heat recovery steam generator is embodied with multiple paths , the outflow shut off device may be arranged at the

downstream end of the respective flue gas purification flow path . This way it can be avoided that during maintenance of the interrupted heat recovery flow path flue gases enter into the respective heat recovery flow path . The at least one (inflow and/or outflow) shut off device may be embodied as linearly movable flue gas blade or as pivotable flue gas flap . In case the shut off device is embodied as linearly movable flue gas blade the blade may be entered from the bottom, the side or the top (guillotine damper) into the respective flow path. If the shut off device is embodied as pivotable flue gas flap the flap is arranged at the top , bottom or side in its initial state and can be pivoted in particular about a horizontal or vertical pivot axis into the respective flow path.

In one embodiment, the heat recovery flow path s extend also geometrically parallel to each other and are arranged with a distance to each other, so that the heat recovery flow path s do not have a common wall. This way, the heat transfer from one heat recovery flow path to a neighboring heat recovery flow path is reduced . In particular, a thermal insulating material may be arranged between the outer walls of two neighboring heat recovery flow paths .

Preferably, each heat recovery flow path comprises a superheater heat exchanger, an evaporator heat exchanger and an economizer heat exchanger which can be operated independently from respective heat exchangers of the parallel heat recovery flow paths . Accordingly, the heat transfer medium supplied to a heat exchanger of the first heat recovery flow path is not directly provided to a respective heat exchanger of the second heat recovery flow path.

In an embodiment, the heat exchangers arranged in the heat recovery flow paths are connected to one common boiler drum, so that the one boiler drum can be operated at any time, independently of which heat recovery flow path is interrupted.

Each heat recovery flow path comprises at least one separate door to enter the respective heat recovery flow path , when the respective heat recovery flow path is disconnected from the flue gas stream. This way the heat recovery flow paths are accessible independently of each other for the maintenance personal .

According to a further embodiment the incineration plant may comprise multiple (two, three or more) parallel incineration plant lines , each

incineration plant line comprising one combustion chamber with a combustion material inlet, at least one empty pass and a heat recovery steam generator according to the invention, wherein each incineration plant line may comprise one flue gas purification device or wherein two or more incineration plant lines are connected to one (common) flue gas purification device.

The invention and the technical background will now be explained with regard to the figures , which show an exemplary embodiment of the invention. The figures show schematically

Figure 1 : a side view of a part of an incineration plant and

Figure 2 : a perspective view of a heat recovery steam generator of the

incineration plant shown in figure 1 .

The incineration plant comprises a combustion chamber 2 with a combustion material inlet 1 , through which solid combustion material such as waste can be introduced in the combustion chamber 2. At the bottom of the combustion chamber 2 a combustion grate 3 is embodied, with which the solid material and combusted material (ashes) can be transported towards a slag outlet 4.

The flue gases produced in the combu stion chamber 2 are supplied into vertically extending empty pas ses 5. Downstream of the empty passes 5 a horizontally extending heat recovery steam generator 6 is arranged. As can be seen from the perspective view of figure 2 the heat recovery steam generator 6 comprises a first heat recovery flow path 7. 1 and a parallelly extending second heat recovery flow path 7.2. At the inlet to the first heat recovery flow path 7. 1 a first inflow shut off device 8. 1 embodied as guillotine damper is arranged, while a second inflow shut o ff device 8.2 is arranged at the inlet of the second heat recovery flow path 7.2.

In the first heat recovery flow path 7. 1 a first superheater heat exchanger 10. 1 and in the second heat recovery flow path 7.2 a second superheater heat exchanger 10.2 is arranged. As only indicated in figure 1 , in each of the heat recovery flow paths 7. 1 and 7.2 an evaporator heat exchanger 1 1 and an economizer heat exchanger 12 are additionally arranged, which are all connected to one common boiler drum 13.

At the outlet of each heat recovery flow paths 7. 1 and 7.2 an outflow shut off device 9 is arranged.

In case the internal elements (such as heat exchangers or walls) of the heat recovery flow paths 7. 1 and 7.2 need to be cleaned, the combustion rate of solid material is reduced and one of the inflow shut off devices 8. 1 and 8.2 is closed, so that the flue gas is completely conducted through the open heat recovery flow path .

After the closed heat recovery flow path is cooled down, an overpres sure of ambient air is applied to the respective heat recovery flow path, so that cleaning staff can enter the respective heat recovery flow path and can clean the respective components, while the incineration plant is still operating . Thereby it is avoided that the whole incineration plant needs to be shut down in order to clean the heat recovery steam generator 6. Reference sings

combustion material inlet combustion chamber

combustion grate

slag outlet

empty pas s

heat recovery steam generator fist heat recovery flow path second heat recovery flow path first inflow shut off device second inflow shut off device outflow shut off device

, 10. 1 , 10.2 superheater heat exchanger evaporator heat exchanger economizer heat exchanger boiler drum