METHOD OF HEAT INSULATING A SURFACE OF A HIGH TEMPERATURE

Abstract: A method of heat insulating surfaces of a high temperature comprising mounting a shell at a distance from the surface to be insulated and packing the space between the surface and the shell with separate insulation elements, each element consisting of a cover of a heat resistant material and containing loose mineral fiber material.

Description: Method of heat insulating a surface of a high temperature This invention relates to a method of heat insulating a surface of a high temperature, e.g. the surface of a power turbine, comprising the use of mineral fibres as insulation material. Without insulation the surface temperature of a turbine may rise to 500°C during operation. The object of insulating a power turbine housing is to maintain the surface temperature of the turbine housing at a sufficiently low value, e.g. 40°C, to allow the operators to work comfortably in proximity to the turbine and to maintain a high turbine efficiency and obtain a satisfactory heat economy. Furthermore, it is desirable to maintain a constant temperature in order to avoid undesired stress in the material. In a known method of heat insulating power turbines, a layer of mortar containing mineral fibres , i.e. a mixture of mineral fibres, cement and water, is sprayed onto the turbine housing to obtain a layer of a thickness of e.g. 150 mm. Due to the vibrations it is sometimes necessary to reinforce the layer thus formed with a wire netting. A power turbine is ordinarily dismantled and checked at suitable intervals, e.g 3rd or 4th year. Such a check-up typically takes about 8 weeks, one week for removing the mortar layer, 5 weeks for the actual check-up and necessary repairs, if any, and the last 2 weeks for re-establishing the layer of mortar. Because of the large sums invested in turbines for power stations it is essential that the stand still is as short as possible. Therefore, there is a need for reducing as much as possible the time required to remove and to re-establish the insulation layer on the turbine housing. As mentioned above the use of a mortar insulation requires a relatively long period for removing and re-establishing the insulation layer, and furthermore the removal of the layer causes contamination of the building in which the turbine is located. These operations therefore require the construction of a tent surrounding the turbine. The re-establishment of the mortar layer is a time consuming operation because the new mortar layer often has to be sprayed on to the turbine in steps with intervening drying periods. Besides, it may be difficult to avoid that the mortar layer cracks or falls off just as it may be difficult to make the mortar layer fit tightly to the turbine housing due to its poor adhesion. The object of this invention is to avoid or substantially reduce the drawbacks of the above mentioned prior art insulating method. This object is obtained with the method of the invention which method comprises mounting a shell at a distance from the surface to be insulated and packing the space between said shell and said surface with separate insulation elements, each comprising a cover of a heat resistant material and containing loose mineral fiber material . The method according to the invention presents the advantage that the construction of the shell and the filling of the space thus formed with insulation elements may take place gradually thereby making it possible to check at suitable intervals that the insulation elements are packed properly and that an efficient insulation is obtained. A further advantage offered by the insulation formed by the method of the invention is that it is strongly sound absorbing thereby eliminating the need for providing a separate outer sound shell when insulating e.g. turbines. The shell in question serves only to delimit a space surrounding the surface to be insulated and, therefore, it should only be capable of resisting the pressure exerted by the relatively light insulation elements. Thus, the shell may consist of a relatively thin and readily workable material, e.g. a thin metal sheet. The shell is preferably made from plate-shaped elements in cases where it is desired to provide an insulation having a smooth surface. In a particularly preferred embodiment of the method of the invention a shell is used consisting of sandwich elements having a mineral wool core with a metal sheet, such as a steel sheet, attached to each side of the core by means of a binder Thus, a dobble insulation is obtained, i.e. an inner insulation layer formed by the insulation elements which are placed in the space between the surface to be insulated and the shell, and an outer insulation layer formed by said sandwich elements. The outer insulation layer will thus work as a safety insulation layer in case of defects in the ' inner insulation layer. However, the shell may also consist of a rigid netting provided the mesh size of the netting is such that the insulation elements are retained in the netting. After the above mentioned shell has been established, the space between the surface to be insulated and the shell is readily filled with insulation elements. Since these elements are readily deformed the insulation elements can be closely packed in connection with the filling of said space so that no holes are left in the insulation. In cases where the surface to be insulated comprises protruding anchor bolts, which is often the case with turbine housings, spacers for supporting the surrounding shell may be attached to said anchor bolts. A well defined space between the surface to be insulated and the surrounding shell is thereby obtained. When the insulation layer is to be dismantled, optionally after dismantling of the shell, the insulation elements are removed. These elements will ordinarily remain intact and can therefore be re-used when an efficient heat insulation is to be re-established after a check, if any, has been completed. Thus, it is unnecessary to take special precautions to protect the surroundings, such as the construction of a tent, when the insulation layer is dismantled and re-established. Because of the possibility of re-using the insulation elements, the costs of materials can be kept at a minimum. German published patent specification No. 36 44 531 Al discloses a method of providing a fire proof filling of shielding holes in walls and floors, and particularly holes with cable inlets. In this known method bags of yarn of ceramic fibres and containing a light refractory material, such as ceramic granules, are placed in the holes and around the cable or cables. Dutch patent application No. 8400351 discloses a method of insulating cellar space by means of an insulation material in the form of e.g. mineral wool contained in bags or sacks. None of these prior art methods relates to high temperature insulation and no space defining elements are mounted at a distance from the surface to be insulated. As mentioned above the insulation elements used consist of a cover of a heat resistant material which cover contains loose mineral fibres. "Heat resistant" used herein means that the material can be heated to a temperature of at least 100°C without melting or decomposing. The covers used preferably consist of a woven or non-woven fibre material, e.g. nylon fibres, glass fibres, coal fibres, ceramic fibres and/or aramide fibres. The cover may also consist of other materials, e.g. a thin perforated metal foil. Covers of such perforated metal foil offer the advantage of also being heat reflecting to some degree. By varying the size of the holes of the perforated foil and the density of the woven or non-woven fibre material it is also possible to control the release of dust from the insulation elements. The elements preferably have a thickness of a few cm and surface dimensions ranging from a few cm up to 50-100 cm. For a given insulation task, insulation elements of different sizes are preferably used in order to allow the insulation elements to be packed as closely as possible. The mineral fibre material contained in the covers preferably contains no binder as several binders tend to decompose and to give off large amounts of gas under high temperature conditions. Preferred mineral fibres are rock wool fibres, glass fibres, carbon fibres and ceramic fibres. Rock wool fibres are particularly preferred because they are heat resistant at temperatures up to 1100°C and because they are relatively inexpensive. v Although the method of the invention primarily has been described with reference to the heat insulation of power turbines it should be understood that it is also suitable for use in the insulation of e.g. furnaces and boilers, including boilers for use in district heating plants and steam boilers. The invention will now be described in further detail with reference to the drawing in which Fig. 1 shows a cross sectional view of a turbine housing provided with heat insulation prepared by a preferred embodiment of a method of the invention and Fig. 2 shows part of the cross sectional view according to Fig. 1 on an enlarged scale. The drawing shows a steam turbine housing 1 having externally protruding bolts 2. The free end 3 of each bolt 2 has a thread, and said end is attached to one end of a spacer 5 by means of nuts 4, the opposite end of said spacer being connected with a shell 6 surrounding the steam turbine housing 1. The space between the steam turbine housing 1 and the shell 6 is filled with a large number of a insulation elements 7, each consisting of a cover of a heat resistant material and containing a mineral fibre material.

Claims: P A T E N T C L A I M S 1. A method of heat insulating a surface of a high temperature comprising the use of mineral fibres as insulation material, comprising the steps of mounting a shell at a distance from the surface to be insulated and packing the space between said shell and said surface with separate insulation elements, each element comprising a cover of at heat resistant material and containing loose mineral fibre material. 2. A method according to claim 1, comprising the use of a shell consisting of a thin metal sheet. 3. A method according to claim 1, comprising the use of a shell consisting of sandwich elements made from a mineral wool core and a metal sheet attached to each side of the core by means of a binder. 4. A method according to claims 1, 2 or 3 for insulating a surface provided with protruding anchoring means, comprising attaching the shell to the anchoring means by means of spacers. 5. A method according to any of the preceding claims, wherein the covers of the insulation elements consist of a woven or non-woven fibre material. 6. A method according to any of the preceding claims, wherein the insulation elements are of different sizes. 7. A method according to any of the preceding claims, wherein the mineral fibre material consists of binder-free rock wool.

Inventors: KAMSTRUP-LARSEN JOERGEN, KAMSTRUP-LARSEN, JOERGEN
Applicants: ROCKWOOL INT, ROCKWOOL INTERNATIONAL A/S
Application year: 1989
Main classification: F01B31
IPC codes: F16L59