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Contenuto archiviato il 2022-12-27

SEASONAL STORAGE OF RESIDUAL HEAT FROM A COMBINED HEAT AND POWER INSTALLATION IN AN AQUIFER ON THE SITE OF THE UNIVERSITY

Obiettivo

The aim is to demonstrate the practical applicability of heat storage in aquifers, in combination with combined heat and power installations, in order to augment the useful exploitation of these installations. The installations were regulated on the basis of the heat requirement of the buildings of the university complex which meant that at a reduced heat demand during summer the installations are running at part load to avoid unprofitable production of excess heat. This will lead to a lower total yield of the heat and power installations and additional electricity would also have to be purchased. By using heat storage the number of operating hours of the CHP installations is increased in summer, whereby the residual heat in the form of water at a temperature of 90?C is stored in an aquifer and the produced electricity will be used in the university complex. The stored residual heat is used in winter for the heating of a few buildings of the complex.
In the period November 1987 until December 1988 the design of the installations was prepared, following which the assembly took place. In November 1990 a beginning was made with testing, controlling and starting up the system . The system was first tested in a cold condition for charging and discharging. Subsequently the system was tested in the same manner at a charge temperature of approx. 15 deg. C, approx. 40 deg. C, approx. 65 deg. C and approx. 90 deg. C. As from May 10, 1991 the system was regulated completely automatic and charging took place at a temperature of 60 deg.C and as from August 29, 1991 at 90 deg. C. Injection at this temperature was carried out until week 43 (1991). During week 44 a start was made with retrieval. The temperature of the retrieved water was 83 deg. C. In week 14 (1992) retrieval was stopped and the retrieval temperature had then dropped to 51 deg. C. In April 1992 the second cycle was started. The charge temperature was then approx. 90 deg. C. Discharging started from October 1992. The temperature of the retrieved water at the beginning was 83 deg. C and at the end of the year, on December 31, 1992 it was 67 deg. C. In the feasibility study a thermal result of 65 to 75% in the third year was estimated. At the realization of the heat storage additional data of the soil structure were obtained. With these data the soil structure could be better represented diagrammatically. On that basis new calculations were performed. The calculated thermal results are respectively 13, 38, 48 and 52% for the first to the fourth cycle. Subsequently the model for the computer calculations was calibrated by means of the data derived from the measuring programme. The measured result for the first cycle is 16.8%. After calibration this result was closely approximated. The calibrated model was used to calculate that the results in the first, second and third cycle were respectively 40, 51 and 56.5 %.

During the first cycle 78% of the planned quantity of water was injected (78,121 m3). During the second cycle 38% of the planned water quantity was injected (37,817 m3). The reason for this low water quantity was malfunctions of the heat and power units.

During the charge period of the second cycle (from April 1992) 8,874 GJ was charged. On December 31, 1992 2,367 GJ was discharged (26.6% of the quantity charged). The objectives of the project:

- increasing the utilization of the combined heat and power installations at the site of the University of Utrecht;
- acquiring experience in the design and implementation of heat storage in general;
- checking the operation and the results of the system on the basis of the appropriate design;
- determination of the behaviour and the environmental effects of heat storage in an aquifer at a high temperature level.

In all these respects it can be claimed that the project was successful. At this time the entire installation operates without problem.
This project is an innovative system for the storage of residual heat in an aquifer at the University of Utrecht. This residual heat comes from two combined heat and power installations and it is produced mainly during summer. The total capacity of the combined cycle heat and power installations is 10.2 MW thermal and 7.5 MW electric. The combined heat and power installations are linked by means of site pipelines to the heat storage. Through using heat storage the number of operating hours of the heat and power installation during the summer period is increased because the heat produced can be usefully employed. The stored heat is used during winter for space heating. As a consequence during the winter months less gas has to be used for space heating and during summer less electricity will have to be purchased. The degree of utilisation of the heat and power installations is increased, while the primary energy consumption is reduced . For the storage system two sources were employed: one 'cold' source, maximum rate of flGW 100 m3/h and a 'warm' source, with a maximum rate of flow of 50 m3/h. The table below shows some technical identification numbers of the project.
load release
(summer) (winter)
thermal capacity MW 6.0 2.6
energy amount MWh 6,000 3,600
temperature hot source ?C 85-95 90-50
temperature cold source ?C max. 50 max. 50
maximum rate of flow m3/h 100 50
water displacement m3 100,000 130,000
depth m 210-260 210-260
The advantages of the project are:
- During winter less natural gas has to be burned for heating of the buildings.
- During summer less electricity has to be purchased.
- The useful exploitation of the combined heat and power installations is increased.
- The primary energy consumption is reduced.
Furthermore, an important objective is determining the behaviour and the ecological effects of heat storage in an aquifer at a high temperature level. In addition, during the construction and operation practical experience is gained and collected.

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Meccanismo di finanziamento

DEM - Demonstration contracts

Coordinatore

BREDERO ENERGY SYSTEM BV
Contributo UE
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Indirizzo
RUNNENBURG 13 P.O. BOX 95
3980 CB BUNNIK
Paesi Bassi

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