In the field of district-heating - especially for higher temperatures, aggressive and hazardous media and /or difficult geographic positions - double-walled, vacuum-insulated tubes (the so-called 'Stahl-Mantel-Rohr' = SMR in German / 'Steel-in-Steel' Pipelines = SIS in English) are successfully used since many years. Current SIS are equipped with shaped insulation-elements out of rock wool bonded with organic binder. The ring-space /insulation is constantly evacuated to a residual gas-pressure of about 3 mbar. Under these conditions lambda-values in the range of 0,035 W/(m K) or slightly better can be reached at a mean-temperature of 80 deg.C (at ambient pressure the same insulation would lead to lambda = 0,048 W/(m K). New applications and stronger requirements make better insulations in SIS necessary. In Cryogenic Applications - e.g. Transportation- Pipelines for LNG - the media-temperature will be -163 deg.C, which has to be insulated against ambient temperatures up to 60 deg.C. Especially for tubes passing in the earth or under the sea very low heat-losses must be strictly adhered to avoid freezing of the ambience of the pipeline. The operating conditions at loading units for LNG are characterized by permanent temperature-changes between -163 deg.C and ambient temperature. In solar power-plants - for example the Andasol-complex in southern Spain - there is a big need for insulated tubes as connecting line between the collectors, the collector-fields and the power-station. Today, we are talking about temperatures of the heat transfer medium of about 400 deg.C at high pressures to some extent. With some new developments it is sought for even higher temperatures up to 500 deg.C and more. By means of the intermittently operating and the cooling down during the nights considerable starting-delays and -losses are caused. Such dissipation-losses lower the effectiveness of the power-plant. Dissipation could be reduced drastically by piping with high efficient insulation. It is well known that very good insulation-characteristics can be achieved with micro-porous fillers in evacuated insulations. The knowledge from other vacuum-insulations only partly can be transferred to SIS, because of special boundary conditions. Ongoing molded fiber-elements (rock-wool with organic binder; density rho = 100 kg/m3) are used as filler in SIS. The specific heat-transfer-rate of actually lambda = 0,035 W/ (m K) (at p = 3 mbar and a mean temperature of about 80 deg.C) might be reduced to lambda = 0,015 W/ (m K), if an evacuating to p << 0,1 mbar would be possible because of the condition of the involved surfaces and the extension of the insulation-volume this is impossible within passable duration!
Newly designed vacuum-insulation for big pipes and pipelines
2007
13 Seiten, 11 Bilder, 2 Tabellen, 4 Quellen
Conference paper
Storage medium
English
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