AU597910B2

AU597910B2 - Device for reducing the quantity of pollutant gas during the operation of firing plants

Info

Publication number: AU597910B2
Application number: AU63669/86A
Authority: AU
Inventors: Erich Dipl.-Ing Kraft; Hans-Gunther Raths; Siegried Dipl.-Ing. Schluter
Original assignee: Apparatebau Rothemuehle Brandt and Kritzler GmbH
Current assignee: Apparatebau Rothemuehle Brandt and Kritzler GmbH
Priority date: 1985-10-22
Filing date: 1986-10-08
Publication date: 1990-06-14
Anticipated expiration: 2006-10-08
Also published as: AU6366986A; EP0226731A1; JPS6295120A; DE3668981D1; DE3537478A1; ES2012752B3; EP0226731B1

Description

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AUSTRALIA

PATENTS ACT 1952 COMPLETE SPECIFICATION Form

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Aprlication Number: G'5s G" Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: This document contains the amendments made under Section 49 and is correct for printing.

Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: APPARATEBAU ROTHEMUHLE BRANDT KRITZLER GMBH WILDENBURGER STRASSE 5963 WENDEN

ROTHEMUHLE

GERMANY

CLEMENT HACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

Actual Inventor: Address for Service: Complete Specification for the invention entitled: DEVICE FOR REDUCING THE QUANTITY OF POLLUTANT GAS DURING THE OPERATION OF FIRING PLANTS The following statement is a full description of this invention including the best method of performing it known to me:-

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ursijKaiu acT-Da tv-enen-- -I1I-J.Ltirn ucty ut.L_ jL-L z Rothemihle Apparatebau Rothemuhle Brandt Kritzler Gesellschaft mit beschrankger Haftung Dip.-Inq. G. Kritzler Geschaftsfthrer I 2 Device for Reducing the Quantity of Pollutants Gas During the Operation of Firing Plants The invention relates to flue gas scrubbing in firing plants, that is to secondary measures, which contributes in the case of firing plants of conventional design to a reduction in the quantity of SO 2 and NO x emissions.

The object of the invention is a device for reducing the quantity of pollutant gas duri:-g the operation of firing plants, for example for steam generation, which can be used for the removal of not only SO2, but also NO x from flue gas.

A known device for reducing the quantity of pollutant gas during the operation of firing plants comprises wet- and/or dry-operating reactors and regenerative heat exchanges associated with these, the regenerative heat exchangers being used either for the cooling and reheating or for the preheating and recooling of the flow of flue gas.

In the case of a so-called multi-flow regenerative heat exchanger, the storage mass of the heat exchanger is divided concentrically in such a way that the heat-transmitting and the heat-absorbing media can be passed through the storage mass in two separate, parallel flows. Thus, in devices for reducing the quantity of pollutant gas during the operation of firing 3 plants, the use cf multi-flow regenerative heat exchangers allows separate adjustability of the temperatures and quantities of the primary and secondary air.

In such a multi-flow regenerative heat exchanger design, the regulatable heating of the primary and secondary air is achieved by passing the two streams of air concentrically in relation to each other through separate chambers in the storage mass and regulating the temperatures and pressures of the streams independently of each other.

As can be seen from the paper entitled "Flue Gas Scrubbing in Large Firing Plants", by H. Juntgen and E.

Richter, Essen, pages 8 to 20 of "Dokumentation Rauchgasreinigung", VDI-Verlag, it is necessary not only to remove sulphur oxides from flue gases but also to bring about a reduction in the quantity of nitric oxides.

While the removal of SO 2 from flue gases of firing plants can be accomplished by scrubbing methods, such as for example with gypsum, or the so-called spray absorption method, hitherto, the removal of NOx from flue gases has been accomplished by catalytic reduction using NH 3 in so-called SCR reactors.

Typically, the SCR reactors are installed in the firing plants of steam generators either between the economizer and the air preheater, i.e. before the desulphurization of the flue gas or the removal of S02, or after the flue gas desulphurization or SO 2 removal, i.e. before the chimney.

4 In wet desulphurization, the flue gas is cooled by untreated gas before scrubbing and after this is reheated as clean gas.

In reducing the quantity of nitric oxides (after desulphurization of the flue gas) it is necessary to heat the flue gas before the SCR reactor and then to cool it again before entry into the chimney.

For this purpose, regenerative heat exchangers have been used. In regenerative heat exchangers of this kind there is the danger of a blockage of the heat storage bodies by deposits, which in the case of desulphurization of flue gases consist of lime compounds and fly ash, while in the case of the SRC reactor comprise ammonium bisulphate, i.e. NH4SO4.

Changes in temperature which occur when the firing plant is operating under part-load also have an adverse effect during flue gas desulphurization, since the water budget is adversely affected by the drop in the untreated gas entry temperature in the scrubber.

A method of avoiding these disadvantages in devices for reducing the quantity of pollutant gas during the operation of firing plants involves the use of two regenerative heat exchangers operating independently of each other, normally parallel, but able to be stopped individually and independently of each other when it is necessary to remove deposits by washing or when the firing plant is operating only under a part load.

Although each of these separately operating Sregenerative heat exchangers needs only to be designed

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C: ii)i r so that its storage bodies are adjusted to half the capacity of the gas-scrubbing plant in question, it is clear that the cost of the plant is considerable due to the necessity for two regenerative heat exchangers. Not only are there constructional and opera'ing costs associated with two regenerative heat exchangers, but there is a corresponding increase in the space requirements for the plant in question.

A disadvantage of a gas-scrubbing plant with two regenerative heat exchangers operating in parallel is also the fact that on operating under partial load, with the disconnection of one heat exchanger, the inflow into the other heat exchanger has an asymmetrical temperature profile.

The aim of the invention is not only to reduce the plant cost for firing installations which assure a reduction in the quantity of pollutant gases by flue gas desulphurization or removal of SO 2 and by the separation of nitric oxides and removal of NOx. It is also a matter of ensuring a high availability of gas-scrubbing plant by wet or thermal cleaning of the regenerative heat exchangers during the operation of the plant and also achieving a regulation of the gas temperatures to nominal values during operation under partial load and symmetrical temperature profiles in the outflowing media in each case.

According to the present invention there is provided an apparatus for reducing the amount of pollutants in a flue gas produced during the operation of a hydrocarbon fired plant comprising, wet- and/or p.A, dry-operating reactors, and associated regenerative

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p. 11

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-6heat-exchangers for cooling and re-heating or for preheating and subsequent cooling of the flue gas, each regenerative heat exchanger comprising: a storage mass having a vertical axis and opposed upper :ud lower inlet/outlet openings, the storage mass concentrically subdivided with respect to the axis into at least a first and second zones such that a heat transfer medium and a heat absorption medium are each able to be passed in two separate streams through the zones; a first medium supply hood connected to the 4 first zone and a second medium supply hood connected to Sr the second zone at one of the inlet/outlet openings and a medium discharge hood connected to both zones at the other of the inlet/outlet openings; a first medium discharge hood connected to the first zone and a second medium discharge hood connected to the second zone at the said one of the inlet/outlet openings and a medium supply hood connected to both the zones at the said other of the inlet/outlet I openings; and control means operable to vary or shut down altogether the flow of heat transfer medium and heat absorption medium through each of the first and second medium supply hoods and the first and second medium discharge hoods.

It is preferred the apparatus further comprises a cleaning device to clean the first and second zones, and said cleaning device is operable in use to clean one Cp.LIA

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-7of the zones when the flow of heat absorption media and heat transmitting media through the zone has been shut down altogether by the control means.

It is preferred that the storage means is subdivided so that, for each of the two parallel flows of the heat-transmitting medium and the heat-absorbing medium, half the capacity of these is available so that, during a complete shut down and scrubbing of one zone, operation with 60 to 65% of the nominal load in the other zone is possible.

The wet cleaning may be carried out in such a way that the appropriate zone is first separated from the hot medium of the cooling and then, after additional shutting off from the cold medium, washed with water.

The zone is then run up to operating temperature by opening the corresponding throttle valve.

Thermal cleaning is carried out by overheating or supercooling the storage mass in relation to the normal operating state. Through this, in both cases, a change in the aggregation state of the deposit which is present, for example, in the form of ammonium bisulphate

(NH

4

SO

4 occurs so that as a result the heating surfaces can be thoroughly cleaned. After the cleaning process the storage mass is again filled with heat-exchanging medium and resumes normal operation.

It is preferred that the control means comprises a throttle and/or butterfly valve located upstream of the first and second medium supply hoods and downstream of the first and second medium discharge hoods.

-8- In one arrangement, it is preferred that the storage mass is arranged for rotation about the axis.

In another arrangement, it is preferred that the storage mass is stationary, the medium discharge hood is located within the medium supply hood and is arranged for rotation about the axis, the second medium discharge hood is fixed, and the first and second medium supply hoods and the first medium discharge hood are located with the second medium discharge hood for rotation about the axis.

Iri., Further characteristics and advantages of the invention are explained in detail below with reference to the accompanying drawings in whicht Fig. 1 is an axial section of an essential part of a device for the reduction of the quantity of pollutant gas during the operation of large firing plants in accordance with the invention; and •Figs. 2 and 3 show two different designs of large firing plants which include a device according to the invention for reducing the quantity of pollutant gas.

In Fig. 1 of the drawings there is shown the construction of a so-called multi-flow regenerative heat exchanger 1 which contains, in a stationary housing 2, a plurality of storage bodies 3 with heating surfaces in vertical arrangement.

Inside the housing 2 the storage bodies of the L regenerative heat exchanger are divided by an inbuilt

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separating wall 4 concentrically into two storage body areas 3a and 3b, each of which covers 50% of the heating surfaces.

To one end, for example the lower end, of the stationary housing are connected two medium-feed hoods and 6 and two medium discharge hoods 7 and 8. The medium feed hoods 5 and 6 are connected to two separate fee channels 9 and 10, while two separate channels 11 and 12 are connected to the medium discharge hoods 7 and 8.

A medium feed hood 13 and a medium discharge hood 14 are associated with the other end of the stationary housing, the former connected to a channel and the latter connected to a channel 16.

The two medium feed hoods 5 and 6 and the medium discharge hood 14 are in the form of rotary hoods of annular sector shape mounted for rotational driving by a shaft 17. In use, the feed hood 5 brushes over the inner storage body annular region 3b and the medium feed hood 6 moves along the outer storage body region 3a.

The medium discharge hood 14 which is located as a rotary hood on the opposite side of the stationary housing 2 brushes simultaneously over the two storage body regions 3a and 3b arranged concentrically one inside the other.

The medium discharge hood 7 and the medium feed hood 13 are stationary, and the part 8a of the medium discharge hood 8 associated with the storage bodies 3 in the region of the concentric separating wall 4 is connected to the two medium feed hoods 5 and 6 for P1 rotational movement. A stationary section 8b of the

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i ~U 10 medium discharge hood 8 is connected to the rotatable section by means of coaxially overlapping sealing aprons 18a and 18b.

The medium feed hood 13 covers the entire upwardly directed face of the storage body regions 3a and 3b. The medium discharge hood 7 is associated only with the lower face of the storage body region 3a, and the medium discharge hood 8 covers the downwardly directed face of the storage body region 3b. The medium feed hoods 5 and 6 and the section 8a of the medium discharge hood 8 are received for rotational movement t inside the stationary medium discharge hood 7, and the A medium discharge hood 14 rotates within the stationary medium feed hood 13.

44~t~ 4r tr t By means of coaxially overlapping sealing aprons 19a and 19b and 20a and 20b the two stationary medium feed channels 9 and 10 are connected to the rotatable medium feed hoods 5 and 6, the channels arranged c concentrically one within the other. Throttle and/or butterfly valves 21 and 22, which can be operated St independently of each other, are incorporated into the medium feed channels 9 and 10 upstream of the rotatable medium feed hood 6 in the direction of flow of the media. In this way, through the throttle and/or butterfly valves 21, the medium feed channel 9 can be opened and closed as required thereby to vary the effective through cross-section. In a corresponding manner, the medium feed channel 10 can also be opened or closed by the throttle and/or butterfly valves 22 thereby to vary the effective through cross-section.

The rotatable medium discharge hood 14 is also joined by means of coaxially overlapping sealing aprons -a~sc i rar.e i t a.

I( I '4 a 44 11 to the stationary medium discharge channel 16.

The medium discharge channels 11 and 12, which are in fluid communication with the two medium discharge hoods 7 and 8, are also provided, downstream of the medium discharge hoods 7 and 8, with butterfly and/or throttle valves 24 and 25, by means of which the through cross-section can be opened and closed as required.

Downstream of the throttle and/or butterfly valves 24 and 25 the two medium discharge channels 11 and 12 open into a common flue gas duct 26, said flue gas duct 26 possibly leading to the chimney of the firing plant.

It is clear that by means of the design of the regenerative heat exchanger described above it is possible in each case to direct two parallel streams of the heat-transmitting medium and the heat-absorbing medium separately through the heat-storage bodies 3, namely on the one hand through the storage body region 3a and on the other hand through the storage body region 3b.

In one example, a flow of the heat-transmitting medium passing upwardly through the medium feed channel 9 and the medium feed hood 5 acts on the storage body region 3b of the stationary storage bodies 3, and a stream of heat-transmitting medium passing upwardly through the medium feed channel 10 and the medium feed hood 6 acts on the storage body region 3a. Both flows of heat-transmitting medium are then received at the upper end of the stationary storage bodies 3 by the rotatable medium discharge hood 14 and directed by this into the medium discharge channel 16. The other medium

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3 <z~'LLn 12 passes downwardly through the medium feed channel into the stationary medium feed hood 13 to the upper end of the heat storage bodies 3 and is there divided by the concentric dividing wall 4 on passing through the heat storage bodies 3 into two separate flows of medium, one of these passing through the storage body region 3a and the other through the storage body region 3b. On the way to the lower end of the storage bodies 3, the two separate flows of media are each engaged in heat exchange with the storage body region 3a or the storage body region 3b, before passing separately into the annular space of the medium discharge hood 7 and into the medium discharge hood 8 respectively and from there into the medium discharge channels 11 and 12.

By means of the throttle and/or butterfly valve 21, the flow of the heat-transmitting medium through the storage body region 3b can be opened or shut off as required, and the throughput thereby varied. Through the throttle and/or butterfly valves 22, on the other hand, the flow of the heat-transmitting medium through the storage body region 3a can be shut off and opened as required and thereby throttled with respect to flow rate.

It is possible, on the other hand, by operating the shut-off valve 25 selectively to shut off the flow of the heat-absorbing medium through the storage body region 3a and to open it up and regulate the flow rate of the heat-absorbing medium. In a corresponding manner, however, through the throttle and/or butterfly valves 24, the passage of the heat-absorbing medium through the storage body region 3b can be selectively Uc, I™ 13shut off or opened up and the flow rate regulated, although the separation of the flow of the heat-absorbing medium does not take place until inside the storage bodies 3, namely by the separating wall 4 between the storage body regions 3a and 3b.

With regard to the construction, it is preferable that the flows of both the heat-transmitting medium and the heat-absorbing medium are effected on opposite ends of the regenerative heat exchanger 1 by appropriately designed hoods 5 and 6 and 7 and 8 and channels 9 and 10 and 11 and 12, and the total flows of both the heat-transmitting and the heat-absorbing medium are equal.

S* Cleaning or washing devices 28a and 28b are r disposed on the upper end of the regenerative heat tt exchanger I to wash or clean the two storage body regions 3a and 3b of the heat storage bodies 3 separately in each case, thereby to remove tho undesirable deposits formed in the storage bodies, these possibly (depending on the arrangement of the regenerative heat exchanger 1 in the gas-scrubbing plant system) being composed either or lime compounds and fly ash or additionally of ammonium bisulphate.

The washing and/or cleaning devices 28a, 28b, are disposed to advantage outside the rotatable medium discharge hood 14, but inside the medium feed hood 13, in such a way that they rotate together with the medium discharge hood 14 inside the medium feed hood 13 and, through this, brush over the entire face of the heat storage bodies 3 in the course of their movement. It is of advantage that a separating wall or a plate 29 is provided in each case in the region of the installation i 14of the washing and/or cleaning devices 28a, 28b, the wall or plate adjoining the concentric separating wall 4 in the housing 1 and through this screening the regions of action of the washing and/or cleaning devices 28a, 28b from each other.

The washing and/or cleaning devices 28a or 28b are operable on the one of the storage body regions 3a or 3b which has been shut-down.

It can be seen that the design of a regenerative heat exchanger described above may also remain in operation during the washing or cleaning operation on one of the two storage body regions 3a and 3b, with the other storage body region 3b or 3a, respectively, being acted on with 60 to 65% of the rated load. The gas-scrubbing plant does not, therefore, need to be reduced to a partial load corresponding to only half the rated load during a cleaning process.

Since, on the other hand, each individual storage body region 3a and 3b of the regenerative heat exchanger 1 can be varied within broad limits with regard to the action on it of both the heat-transmitting and the heat-absorbing medium, a regulation of the media temperatures to nominal values can be achieved which are optimally adjusted to the most widely differing partial-load operating conditions of the firing plant.

In every possible case of operation of the regenerative heat exchanger, rotationally symmetrical temperature profiles are obtained in the storage bodes 3 or in the storage body regions 3a and 3b, so that the correct adjustment of the sealing systems at any time is assured.

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t I- I 4 *l p I It would obviously also be possible within the scope of the invention to divide the storage bodies 3 into more than two concentrically arranged storage body regions and then to associate with these a corresponding number of medium feed and discharge hoods, at least on the hot side. The medium feed and discharge hoods associated with the central storage body region may in this case be so designed that the central storage body region can be connected as required with the inner or outer storage body region. While in each case one region of the storage bodies 3 is subjected to a washing or cleaning process, the other storage body regions can then remain in operation, with more than 65% of the rated load of the gas-scrubbing plant in question then also being possible. The cleaning process in the central switchable storage body region can still be carried out in this case when the large-scale firing plant is operating under partial load which amounts at the most to 50% of the nominal load.

In Figs. 2 and 3 there is shown schematically two firing plants of different design which include in each case a device according to the invention for reducing the quantity of pollutant gas.

In both firing plants an economizer 31 is connected to a boiler In the firing plant shown in Fig. 2 the economizer 31 is followed by a SCR reactor 32 for the removal of nitric oxides and NO. To this is then connected an air preheater 33 for the combustion air of the boiler 30. Behind the air preheater 33 is installed n 16 a dust removal plant 34 and a flue gas blower 35. After the flue gas blower there is the regenerative heat exchanger 1 designed and operable according to the invention, this being operable to cool the flue gas before the flue gas enters the flue gas desulphurization plant 36 for the removal of SO 2 and then to preheat the flue gas leaving the flue gas desulphurization plant.

The large-scale firing plant shown in Fig. 3 differs from that shown in Fig. 2 firstly in that the SCR reactor 32 for the reduction of the quantity of nitric oxides or NOx is installed after the flue gas desulphurization plant 36, while the regenerative heat exchanger 1 according to the invention is located after the flue gas desulphurization plant 36. The regenerative heat exchanger 1 is operable to preheat the flue gas coming from the desulphurization plant 36 before entering the SCR reactor 32 and for cooling the flue gas coming from the SCR reactor 32 prior to passing to the chimney of the firing plant.

In the case of the firing plant shown in Fig. 3, a further regenerative heat exchanger 37 may also be installed before flue gas desulphurization, this possibly being of the same design and operation of the regenerative heat exchanger 1. The regenerative heat exchanger 37 is operable to preheat the flue gas before entering the flue gas desulphurization plant 36 and to cool the flue gas from the SCR reactor 32.

Claims

7-E 17 THE CLATMS DEFINING THE INVENTION ARE AS FOLLOWS: J. An apparatus for reducing the amount of pollutants in a flue gas produced during the operation of a hydrocarbon fired plant comprising, wet- and/or dry-operating reactors, and associated regenerative heat-exchangers for cooling and re-heating or for preheating and subsequent cooling of the flue gas, each regenerative heat exchanger comprising: a storage mass having a vertical axis and opposed upper and lower inlet/outlet openings, the storage mass concentrically subdivided with respect to o° 2 the axis into at least a first and second zones such that a heat transfer medium and a heat absorption medium are each able to be passed in two separate streams through the zones; t* tn a first medium supply hood connected to the first zone and a second medium supply hood connected to the second zone at one of the inlet/outlet openings and a medium discharge hood connected to both zones at the ppodI uother of the inlet/outlet openings, a first medium discharge hood connected to the first zone and a second medium discharge hood connected to the second zone at the said one of the inlet/outlet openings and a medium supply hood connected 4 to both the zones at the said other of the inlet/outlet openings; and control means operable to vary or shut down altogether the flow of heat transfer medium and heat UIAAp, absorption medium through each of the first and second (zl i L dry-operating reactors, and associated regenerative 18 medium supply hoods and the first and second medium discharge hoods. 2. The device as defined in claim i, further comprising a cleaning device to clean the first and second zones, and said cleaning device is operable in use to clean one of the zones when the flow of heat absorption media and heat transmitting media through the H zone has been shut down altogether by the control means. 3. The device defined in claim 1 or 2, wherein the control means comprises a throttle and/or butterfly valve located upstream of the first and second medium supply hoods and downstream of the first and second medium discharge hoods. 4. The device defined in any one of the preceding claims, wherein the storage mass is arranged for rotation about the axis. The device defined in any one of claims 1 to 3, wherein the storage mass is stationary, the medium discharge hood is located within the medium supply hood and is arranged for rotation about the axis, the second medium discharge hood is fixed, and the first and second medium supply hoods and the first medium discharge hood are located with the second medium discharge hood for rotation about the axis. 6. An apparatus for reducing the amount of pc itants in a flue gas produced during the operation of a hydrocarbon fired plarzt substantially as described aIu1 sala cleaning device is operable in use to clean one i' ,1 19 herein with reference to the accompanying drawings. Dated this 26th day of March, 1990 APPARATEBAU ROTHEMUHLE BRANDT KRITZLER GmbH By Its Patent Attorneys GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia. t 'I I