Objective
To use geothermal energy to cover 85% of the heating requirements (estimated at 34,000 MW/yr) for 8 to 10 hectares of new glasshouses. A 2,000 m3 control tank will be installed at the head of the well; the tank will also be used to recover some of the salts once the gas has been removed from the fluid. The heat will be transferred by means of inox heat exchangers
(discharge temperature : 22 deg. C).
The geothermal fluid will be extracted from the 80 m thick inframolassic formations at around 1,500 m and, perhaps, from the subjacent Paleocene limestones. A flow-rate of 200 m3/h of brine at 62 deg. C and 0.5 g/l salinity is expected. No reinjection wells are planned unless the salinity proves too high or there is a loss of pressure in the reservoir. According to estimate : the project will save a total of between 4,800 and 5,150 TOE per year.
Three hectares of greenhouses (2 garden and 1 horticultural) have been installed since winter 1982 and operated for three consecutive heating seasons in a very successful way, despite extremely difficult climatic conditions (e.g. in January 1985 exterior temperature - 18 deg. C., temperature in the glasshouses + 10 deg. C. without back-up). This good technical performance has been combined with a high reliability of the equipment with the exception of the submerged pump which may also give some problems in the future.
The basic technical principle involved is the maximum economic use of the available geothermal energy. Three techniques have been harnessed in order to achieve this :
- Heat supply regulation
- Combination of the geothermal energy with another energy source (LPG)
- High performance through a soil-free, hydroponic production and control of
climatic effects.
Although the project has been technically very successful (and has already started reimbursing a part ofthe Community support), it has not yet reached its optimum commercial exploitation (8 hectares). This is due to economic difficulties, (not linked with geothermal energy) met by the exploiters of the well, notably with respect to the high cost of the investment. Once completed, 50% savings can be expected over an equivalent heavy fuel oil system, to give a therm cost price of 0,09 FF and a 18% internal rate of return. The payback period on the extra investment will be in the order of 5 - 7 years. The full use of the Lamazere geothermal complex will lead to savings of more than 4,000 TOE per year.
The production well was drilled down to a maximum depth of 1,750 m in June and July 1981 without reaching the Paleocene limestone. Lussagnet sands traversed between 1,622 and 1,697 m and sandstone containing nummulites between 1,700 and 1,750 m. Hole widened to 15" and lined between 1,630 to 1,671 m with gravel pack in order to be able to tap the Lussagnet sands. Characteristics : net pay of aquifer : 38 m.
Porosity : 17 to 25 %.
Transmissivity : 30 D.m.
Temperature : sbet
Salinity : 0.4 g/litre.
The upper layer of sandstone containing nummulites (1,707 to 1,713 m; net pay of aquifer : 6.5 m., porosity : 23 to 25 %) was not completed although its potential is substantial. Operating flow-rate : between 150 and 200 m3/h for a drawdown of 180 and 250 m respectively and an estimated temperature on the surface of 57 deg. C.
The geothermal water is driven to a regulating tank; distribution to the greenhouses is carried out by a variable pump and heat is released in the greenhouses by means of stainless steel plate heat exchangers
(1 per greenhouse).
In addition each greenhouse is equipped with a LPG fired independant boiler which provides back-up and emergency heating. As the temperature (57 deg. C.) was too low for a traditional heating system capacity (thermosiphon) to satisfy the needs of the plants with cooling water, the latest heat-exchange processes had to be applied.
The garden glasshouses consist of several parts, each one 6.40 m long, oriented NW-SE and set out into two groupings covering 10,000 m2 each. They are equipped with heat screens possessing a combined spray and dropwise fertilizing irrigation system.
The heating is carried out by way of radiant pipes through which the hot water is circulated at the desired temperature (these pipes connected with other flexible pipes can be raised and hooked up during cultivation work at ground level). The water is then used in the radiantmatling (tubular sheath of EPDM) which intermittantly is in contact with the ground across the rows of plants (cultivation). Another, horticultural, glasshouse of 10,000 m2 consists of 8 parts, each one 16 m long. Radiant pipes are located under and, if necessary, above the shelf surfaces. But most of the heating is supplied by the slabs themselves since they are constructed around coils of serpentine alveolar PVC piping with a high heat exchange surface.
Due to the very low salinity, the geothermal water, is discharged into the river. Discharge is governed by a temperature control thereby permitting the mix of water and elimination of waste heat.
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Coordinator
65001 TARBES
France
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