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(11) | EP 1 006 313 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A boiler lining system |
| (57) A method of lining a heat recovery boiler for hot exhaust gases and a boiler so lined
are described. The method includes:-
(a) fitting at least one backing layer of thermal insulating material to the casing of the boiler; and (b) fitting an acoustic insulation facing material comprising a porous high temperature woven fabric over the backing layer. |
[0001] The present invention relates to a boiler lining system and, in particular, a boiler lining system for heat recovery boilers such as are used for heat recovery from hot exhaust gases.
[0002] The majority of gas turbine power generation installations above 50MW incorporate a Heat Recovery Steam Generator (HRSG). A boiler of this type produces steam via heat recovery from the hot exhaust gas. The steam produced drives a steam turbine, generating electricity in parallel with that generated directly from the gas turbine. This enables the combined cycle gas turbine plant (CCGT) to achieve a higher level of efficiency than a simple cycle gas turbine plant (SCGT).
[0003] A major requirement of HRSG construction is effective thermal insulation of the boiler wall casings.
[0004] In a typical HRSG, hot exhaust gas from the turbine enters the boiler via flared ductwork, enabling the velocity of the gas to be reduced from circa 60m/sec to circa 20m/sec. Interaction of the exhaust gas with the heat exchanger tubes then cools the gas, further reducing velocity to circa 10m/sec, and thereby maximising the retention time of the exhaust gas over the heat exchanger. Internal temperatures within the boiler typically range from circa 575°C at the inlet to circa 110°C at the outlet stack. The outer casing of the boiler is a structural component and typically comprises carbon steel of thickness up to 9mm. To ensure that the carbon steel is not subjected to excessive heat the outer casing temperature is usually restricted to circa 65°C emphasising the importance of the thermal insulation material. The thermal insulation is located on the inside of the structural outer casing, and is traditionally covered over by an inner protective liner of thin overlapping sheets of plain stainless steel.
[0005] Such internally lined HRSG boilers are usually insulated with either refractory ceramic fibre or a combination of refractory ceramic fibre and mineral wool. In the case of the latter, the relative proportions of the two materials depend upon their location within the boiler and the degree of insulation required. The insulation is installed as fibrous blankets or resin bonded panels and relies heavily on the inner lining sheets of plain stainless steel to protect against the erosion and loss of fibrous material into the exhaust gas flow. Consequences of fibre loss are the failure of insulation of the boiler outer casing and resulting pollution of the environment.
[0006] An alternative approach is the insulation of the boiler using pre-compressed blocks made from refractory ceramic fibre. Such blocks may be made more resistant to erosion and fibre loss by pre-treatment with an inorganic silicate binder. Specifically, after fixing the insulating blocks to the inside of the outer casing, typically by rods which pass through the blocks, the insulation is consolidated by spraying the internal surface of the blocks with the inorganic silicate binder. Although it has been possible to omit the inner stainless steel liner using this type of insulation system, a lack of tolerance to thermal-related movement within the boiler structure and the dusting-off of silicate material render this method unattractive.
[0007] The hot exhaust gases produced by the gas turbine plant travel through the boiler at high velocities and the noise generated by the exhaust gases is considerable. Accordingly, the outlet of the boiler is fitted with an appropriate silencer to reduce the noise levels in the exiting gas to meet environmental and safety requirements. The necessity for silencing capabilities at the outlets of boilers increases the costs associated with the process.
[0008] According to a first aspect of the present invention there is provided:-
a method of lining a heat recovery boiler for hot exhaust gases comprising the steps of:
(a) fitting at least one backing layer of thermal insulating material to the outer casing of the boiler;
(b) fitting an acoustic insulation facing material comprising a porous high temperature woven fabric over the backing layer.
[0009] Preferably, the facing material is overlaid with a further layer of gas permeable stainless steel sheet. The gas permeable stainless steel layer may be in the form of a mesh or a perforated sheet.
[0011] Preferably, the facing material comprises a core of a thermal insulating layer contained within an envelope of the porous high temperature woven fabric. A thermal shock protection layer may overlay the inner or hot face of the core material.
[0012] Preferably, the porosity of the woven fabric falls within the net range of 15,000 mks rayls per metre to 60,000 mks rayls per metre, more preferably, 15,000 mks rayls per metre to 45,000 mks rayls per metre, most preferably, 20,000 mks rayls per metre to 30,000 mks rayls per metre.
[0013] Preferably, the facing modules have a net flow resistivity of between 10,000 and 60,000 mks rayls per metre, more preferably, 20,000 to 40,000 mks rayls per metre, most preferably, 30,000 to 35,000 mks rayls per metre.
[0014] Preferably, the thermal insulating backing and core material has a net flow resistivity in the range 5,000 to 40,000 mks rayls per metre, more preferably, 12,000 to 25,000 mks rayls per metre, most preferably, 12,000 to 15,000 mks rayls per metre.
[0015] Preferably, the density of the backing material and the facing material is of sufficient density to provide locational stability during use. Preferably, the density of the backing material and the facing modules is in the range between 110 & 160 kg.M-3, more preferably, between 120 & 145 kg.M-3, most preferably, between 125 & 130kg.M-3.
[0016] Preferably, the woven fabric weight is in the range 200 - 1000 g.m-2, more preferably, the woven fabric weight is in the range 400 - 800 g.m-2, most preferably, the woven fabric weight is in the range 500 - 700 g.m-2.
[0017] Preferably, the facing modules are rectilinear and, preferably, have a base flap on at least two adjacent sides thereof which, in use, extends under adjacent modules to thereby provide a continuous, i.e. gap free, barrier of woven fabric over the backing layer.
[0018] According to a second aspect of the present invention there is provided a heat recovery boiler lining system for hot exhaust gases comprising:-
at least one backing layer of thermal insulating material;
and at least one acoustic insulating facing layer over the backing layer comprising a porous high temperature woven fabric.
[0019] The woven fabric may be made from a suitable high temperature yarn such as treated glass yarn or silica yarn. Preferably, the glass yarn is coated with a suitable high temperature coating. Glass yarn is preferred to silica yarn due to its higher abrasion resistance. Other suitable yarns known to those skilled in the art may also be employed.
[0020] Preferably, the facing layer is overlaid with a further layer of gas permeable stainless steel sheet. The gas permeable stainless steel layer may be in the form of a mesh or a perforated sheet.
[0022] Preferably, the facing material comprises a core of a thermal insulating layer contained within an envelope of the porous high temperature woven fabric. A thermal shock protection layer may overlay the inner or hot face of the core material.
[0023] Preferably, the facing material comprises a core of a thermal insulating layer contained within an envelope of the porous high temperature woven fabric. A thermal shock protection layer may overlay the inner or hot face of the core material.
[0024] Preferably, the porosity of the woven fabric falls within the net range of 15,000 mks rayls per metre to 60,000 mks rayls per metre, more preferably, 15,000 mks rayls per metre to 45,000 mks rayls per metre, most preferably, 20,000 mks rayls per metre to 30,000 mks rayls per metre.
[0025] Preferably, the facing modules have a net flow resistively of between 10,000 and 60,000 mks rayls per metre, more preferably, 20,000 to 40,000 mks rayls per metre, most preferably, 30,000 to 35,000 mks rayls per metre.
[0026] Preferably, the thermal insulating backing and core material has a net flow resistivity in the range 5,000 to 40,000 mks rayls per metre, more preferably, 12,000 to 25,000 mks rayls per metre, most preferably, 12,000 to 15,000 mks rayls per metre.
[0027] Preferably, the density of the backing material and the facing material is of sufficient density to provide locational stability during use. Preferably, the density of the backing material and the facing modules is in the range between 110 & 160 kg.M-3, more preferably, between 120 & 145 kg.M-3, most preferably, between 125 & 130kg.M-3.
[0028] Preferably, the woven fabric weight is in the range 300 - 1000 g.m-2, more preferably, the woven fabric weight is in the range 450 - 850 g.m-2, most preferably, the woven fabric weight is in the range 500 - 800 g.m-2.
[0029] Preferably, the facing modules are rectilinear. Preferably, the facing modules have a base flap which, in use, extends under adjacent modules to thereby provide a continuous, i.e. gap free, barrier of woven fabric over the backing layer. Preferably, the flap extends on at least two adjacent sides of a rectilinear facing module.
[0030] Preferably, the thermal insulating layer may comprise basalt stainless steel wired mattresses, refractory ceramic fibre, a combination of refractory ceramic fibre and mineral wool, pre-compressed blocks of ceramic fibre pre-treated with inorganic silicate binder or other suitable thermal insulating material known to those skilled in the art. Preferably, however, a non-ceramic thermal insulating material is used such as basalt fibre which is, preferably, in the form of a stainless steel wired mattress.
[0031] Preferably, at least two thermal insulating layers are provided for the backing, more preferably, at least three such layers.
[0032] Preferably, the thermal shock protection layer may be selected from E-glass needlemat, silica needlemat, silica woven fleece, stainless steel needlefelt or other suitable material known to those skilled in the art.
[0033] Preferably, the method of lining the boiler comprises the steps of:-
(a) placing a facing module having at least two base flaps along the bottom and side edge thereof over the backing layer and
(b) subsequently placing a further module either below or adjacent thereto and overlapping the respective flap and
(c) repeating step (b) to build up a modular facing layer.
[0034] Preferably, the backing layer is fixed to the inside of the boiler casing by impaling the layer over suitable studs protruding from the casing. Preferably, the studs are threaded and tapered at the ends thereof. The facing layer may be similarly impaled over the ends of the studs protruding through the backing layer. Preferably, the facing layer may be further secured by pin fixing which may also be used to secure the gas permeable stainless-steel inner lining material to the facing material.
[0035] Advantageously, by lining the inside of the boiler in accordance with the invention, the boiler takes on at least some of the characteristics of a muffler tube and thus the need for silencing capabilities at the outlet is greatly reduced or removed altogether. The invention is applicable to all heat recovery boilers which utilise the heat from hot exhaust gases. It is particularly advantageous in the HRSG of CCGT power generation plants and in steam production from combined heat and power (CHP) boilers in heating and production facilities.
[0036] Thus, according to a further aspect of the present invention there is provided a heat recovery boiler, preferably, a hot exhaust gas heat recovery boiler, comprising a gas inlet connected to a hot exhaust gas source, a gas outlet, a boiler casing defining a passage for the hot exhaust gas having the said inlet and outlet, the casing being lined with at least one backing layer of thermal insulating material and a gas facing material over the said backing layer, wherein the facing material comprises a porous high temperature woven fabric.
[0037] The invention extends to a method of lining a heat recovery boiler comprising the steps of:-
(a) fitting at least one backing layer of thermal insulation material to the casing of the boiler;
(b) fitting an acoustic insulation facing material comprising a porous high temperature woven fabric over the backing layer.
[0038] In a method according to the invention, the facing and backing material may be assembled to each other first and then fitted to the said casing. The facing material may envelope the backing material or other material so that the backing material or other material is sandwiched therebetween and so that the facing material faces onto the gas on the inward facing side with respect to the gas passageway and onto the casing or further backing layers on the outward facing side.
[0039] By lining the inside of the hot exhaust gas passageway casing with a porous high temperature woven fabric, the noise and vibrations emanating from the gas are damped and absorbed directly as the facing material acts as an acoustic absorbing material. Advantageously, the gas is prevented from setting up primary vibrations through direct contact with a casing and it is therefore not necessary to line the outside of the casing as the cause of the primary vibrations is absorbed directly.
[0041] Accordingly, preferably, in use, the said woven fabric is in direct contact with the exhaust gases. A further gas permeable lining may be located over the woven fabric, preferably, typically, to protect the woven fabric but such would be designed to allow the gas to come into direct contact with the woven fabric after permeating the gas permeable lining.
[0042] Preferably, the warp of the fabric includes steel wire reinforcement, preferably, the weft of the fabric includes steel wire reinforcement. The warp and/or weft yarn may include several steel wires which may be incorporated in the yarn prior to or during fabric weaving. Preferably, there are less than ten wires per yarn in the woven fabric, more preferably, less than five, most preferably, less than three. In an especially preferred embodiment there is a single wire(s)/yarn. The warp yarn and weft yarn may have the same number of wire/yarn or a different number. Preferably, stainless steel is used for the wire. By high temperature woven fabric is meant a fabric that will withstand temperatures,preferably in excess of 250°C, more preferably 450°C, most preferably 650°C. Especially preferred is a fabric which may be resistant to 750°C.
[0043] Preferably, the yarn is treated with a high temperature resistant coating. The coating is, preferably, resistant to temperatures in excess of 250°C, more preferably in excess of 450°C, most preferably in excess of 650°C. In an especially preferred embodiment, the coating provides temperature resistance in excess of 750°C.
[0044] For high temperature applications, woven silica fabric may be used, preferably, woven fused silica fabric. Preferably, the silica yarn comprises over 70% silicon dioxide, more preferably, over 80% silicon dioxide, most preferably over 90% silicon dioxide. The woven silica may have temperature resistance in excess of 750°C, more preferably 900°C, most preferably 1000°C. The woven silica may or may not be coated.
[0045] Preferably, the woven fabric is texturised to increase porosity by creating an open weave without loss of warp/weft stability. Preferably, the fabric is texturised to the extent necessary to give the required final porosity.
[0046] Preferably, the passageway defined by the casing is wider than the said inlet and outlet. Preferably, the inlet and outlet are located at opposed ends of the passageway.
[0047] Preferably, the inlet is substantially centrally disposed at one end of the passageway and the outlet is centrally disposed at the other end of the passageway.
[0048] Preferably, the passageway is of a conventional cylindrical design but is not limited to such a shape.
[0049] For the avoidance of doubt "lining" is to be taken in its ordinary sense of providing a material between the casing or other lined entity and the passageway defined by the casing.
[0050] Generally the outer casing of a heat recovery boiler also defines the passageway and is its only casing so that inner casing and outer casing may be synonymous in respect of such boilers.
[0051] Preferably, the facing modules are substantially rectangular but it will be appreciated that various shapes are possible without departing from the invention as defined.
[0052] Preferably, each facing module is substantially aligned with the adjacent facing module in the same row and the mating ends of such adjacent facing modules are, preferably, staggered with respect to corresponding mating ends of facing modules of adjacent rows so that a staggered arrangement of facing modules is formed.
[0053] By aligning the facing modules in rows, the flaps are able to overlap with adjacent facing modules to minimise the loss of fibre through the gaps between the mating ends of adjacent modules. At the same time, the modular arrangement allows greater flexibility and ease of placement of the lining compared with a continuous sheet.
[0054] The staggering of the rows provides additional security and prevents lines of weakness being formed. It is possible for overlapping flaps to be found on all sides of each module but it is more economical to have a flap on only two sides which are perpendicular to provide the required overlap with modules in the same row and in adjacent rows.
[0055] Preferably, the woven fabric is temperature resistant to at least 600°C, more preferably, 700°C.
[0056] An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:-
figure 1 is a perspective view showing the structure of the lining system in accordance with the present invention; and figure 2 is a side schematic view of a lining system showing alternative fixing arrangements in accordance with the present invention.
[0057] Referring to figure 1, the partial section of the structural steel outer casing of a boiler wall 2 has fitted on its internal face 4 a lining system comprising a backing layer or blanket of backing material 6 and facing modules 8 laid over the internal surface of the backing material 6. In the embodiment shown, the backing material comprises a blanket of basalt stainless steel wired mattress which has been impaled on spaced fixings 10 which are mounted on the steel outer casing 2 at spaced intervals and which protrude internally perpendicularly therefrom to provide a means of impaling the backing material 6 onto the internal face 4 of the steel outer case 2. The fixings 10 are sufficiently long to protrude inwardly beyond the internal surface 12 of the wired mattress 6 and thereby also provide a means of impaling the facing modules 8 onto the internal surface 12 of the backing layer 6.
[0058] Each facing module 8 comprises a substantially rectangular pillow having a safety flap along the right hand and lower edge thereof. The safety flap is an extension to the outer face or base of the facing module (ie the face which lies against the inner surface 12 of the backing material 6). By aligning the facing modules in a row and staggering successive rows so that the mating ends of successive rows are staggered, the overlapping flaps complete a gap free network which protects the underlying thermal layer 6 from exposure to the hot high velocity gases and subsequent erosion.
[0059] The facing modules 8 are arranged in staggered rows to prevent the formation of lines of weakness which would, in time, allow fibre to escape from the underlying thermal layer 6. Each facing module 8 is arranged on the boiler so that its respective perpendicular flaps are all configured in the same manner. In the embodiment shown, the flaps are arranged so as to be found on the right hand and lower edge of each facing module 8. By starting at the upper left hand area, the facing modules may be arranged in aligned rows with each successive row staggered a half width of the facing module to prevent the formation of lines of weakness.
[0060] Referring to figure 2, each facing module 16 comprises a high temperature woven fabric outer envelope 18 and a thermal shock protection layer 20 which lies over the internal facing surface of the core material 22 which comprises a basalt stainless steel wired mattress. The thermal shock protection layer comprises E-glass needlemat and the seams of the high temperature woven fabric are stitched with heavy duty high temperature thread. The flaps 24 on the right hand and lower edge of each facing module are also formed from the high temperature woven fabric and may be stitched onto the facing module or may comprise an extension of the base surface 26 of the facing module envelope.
[0061] A number of alternative fixing devices may be used to secure the backing 30 and facing layers 16 to the boiler casing 28. The alternative fixing devices are shown schematically in figure 2 and comprise fixing type A, B and C. Type A comprises a single pin which is mounted in the outer casing 28 and extends inwardly, perpendicularly therefrom and is of sufficient length to allow the impalement of both the thermal backing layer 30 and the acoustic facing layer 16. The facing module may be secured to the pin 34 using a conventional nut and washer arrangement 6. The type B method of fixation comprises a heavy duty carrier pin which extends inwardly and perpendicularly from the outer casing 28 to the back of the facing module 16. The thermal layer 30 is secured to the pin by means of an elongate 'U' shaped bar 40 which has securing holes 44 formed therein to permit securement by means of a conventional nut and washer arrangement 42. Further pins 44 extend inwardly and perpendicularly from the securing bar 40 so that the facing module 46 can be impaled thereon and secured in the same manner as previously described with respect to fixing type A. Fixing type C comprises a smaller number of heavy duty pins 50 which extend through the full depth of the thermal layer 30 and acoustic layer 16 and support a 'U' shaped securing bar 52. Each securing bar 52 is fitted with holes 54 at either end thereof to receive the heavy duty pins 50 so that they may be secured thereto by a conventional nut and washer arrangement 56. The rear of the 'U' shaped securing bar 52 is fitted with light weight facing pins 58 which extend outwardly and perpendicularly therefrom to give further securement for the facing module 16. The light weight pins extend partially into the backing material 30 to provide such securement.
[0062] It will be appreciated that the relative thicknesses of the various layers may be varied to suit the specific requirements of the boiler lining to provide the appropriate thermal and acoustic protection required.
[0063] Although not shown in figure 1 and figure 2, the facing pillows may be overlaid with a metal mesh or perforated stainless steel liner.
[0064] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
[0065] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
[0066] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
1. A heat recovery boiler comprising a gas inlet connected to a hot exhaust gas source,
a gas outlet, a boiler casing defining a passage for the hot exhaust gas having the
said inlet and outlet, the casing being lined with at least one backing layer of thermal
insulating material and a gas facing material over the said backing layer, wherein
the facing material comprises a porous high temperature woven fabric.
2. A boiler according to claim 1, wherein the facing material envelopes the backing material
so that the backing material is sandwiched therebetween to form a core.
3. A boiler according to any preceding claim, wherein in use, the said woven fabric is
in direct contact with the exhaust gases.
4. A boiler according to any preceding claim, wherein a further gas permeable lining
is located over the woven fabric.
5. A boiler according to any preceding claim, wherein the woven fabric is designed to
withstand temperatures in excess of 250°C.
6. A boiler according to any preceding claim, wherein the woven fabric is texturised
to increase porosity by creating an open weave without loss of warp/weft stability.
7. A boiler according to any of claims 1-6, wherein the facing material is modular.
8. A boiler according to any preceding claim, wherein the porosity of the woven fabric
falls within the net range of 15,000 mks rayls per metre to 60,000 mks rayls per metre.
9. A boiler according to any preceding claim, wherein the woven fabric weight is in the
range 200 - 1000 g.m-2.
10. A heat recovery boiler lining system for hot exhaust gases comprising:-
at least one backing layer of thermal insulating material;
and at least one acoustic insulating facing layer over the backing layer comprising a porous high temperature woven fabric.
11. A method of lining a heat recovery boiler comprising the steps of:-
(a) fitting at least one backing layer of thermal insulation material to the casing of the boiler;
(b) fitting an acoustic insulation facing material comprising a porous high temperature woven fabric over the backing layer.
12. The method of lining the boiler according to claim 11 which comprises the steps of:-
(a) placing a facing module having at least two base flaps along the bottom and side edge thereof over the backing layer and
(b) subsequently placing a further module either below or adjacent thereto and overlapping the respective flap and
(c) repeating step (b) to build up a modular facing layer.
13. A method or boiler according to any of claims 7-9 or 12, wherein each facing module
is substantially aligned with the adjacent facing module in the same row.
14. A method or boiler according to any of claims 7-9 or 12 or 13, wherein the mating
ends of such adjacent facing modules are staggered with respect to corresponding mating
ends of facing modules of adjacent rows so that a staggered arrangement of facing
modules is formed.