Increased turbulence in heat exchangers for improved efficiency of electric power plants and combined heat and power plants
Use of Drag Reducing Additives, DRA, in circulating district heating water can reduce network pressure losses significantly. However, a serious obstacle to the practical implementation of this concept is the fact that, as an unwanted side-effect of lowered degree of fluid flov turbulence, significant heat transfer reduction can take place in heat exchangers of the district heating network.
The purpose of the project is to identify optimal pipe geometries of water cooled heat condensers in steam power plants, in particular plants for combined heat and power production. Such optimal geometries will improve heat transfer significantly, while keeping unavoidable increases in pressure losses at a minimum. The improved heat transfer can be utilised for a lower condenser vacuum, resulting in greater electric output from the turbo-alternator. The optimisation will be made both for pure cooling water and for cooling water containing a friction reducing additive with the purpose of reducing pressure losses in district heating piplines
Especially in the case of shell-and-tube type steam condensers of combined heat and power plants such heat transfer reduction can cause serious retraction from plant performance. The present study presents an investigation of various methods of restoring heat transfer in steam condenser tubes by various methods of turbulence enhancement, as well as assessments of the viability of each of the methods in terms of heat transfer enhancement vs. pressure drop increase penalty, both directly and from an entire district heating systems performance point of view. A laboratory test rig was designed to measure DRA-related performance parameters in a single condenser tube of full-scale diameter and length. It was found that by increasing vater velocity inside pipes from a conventional design value of 2 m/s to 4-5 m/s, the DRA effect could be more or less eliminated. In special cases such flov velocity increase might be viable in practice. Application of upstream shearing flow obstructions, such as orifice plates, at entrance to pipes, can effectively break down the DRA effect, but a gradual restoration of the effect, hampering heat transfer, develops along the pipe, especially at higher temperatures. Insertion of helical springs inside tubes can be used when rather big pressure loss increases can be considered acceptable. Our investigation of this method mainly confirmed previous work done by others, both in terms of obtained measurement values, and viability of a mechanical method for mounting the springs. During our work a US-study was published which showed that use of fluted, helical tubes instead of smooth tubes, promises of very good heat transfer enhancement vs. pressure drop penalty. We translated the results of this study to conditions prevailing in steam condensers
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Category
Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Energinet | ||
| Bruun og Sørensen Energiteknik A/S | ||
| VESTEGNENS KRAFTVARMESELSKAB I/S |
Contact
P.O. Box 118
S-221 00 Lund, Sverige
Frederiksen, Svend (forskningschef, techn.dr.), 46462229280, Svend.Frederiksen@lth.se
Øvr. Partnere: Elsamprojekt A/S; Bruun og Sørensen Energiteknik A/S; Akto Nobel AB (SE); Vestegnens Kraftvarmeselskab I/S (VEKS)
