Indsamling og genanvendelse af SF6 fra elsektoren
Summary and conclusions
| 1.4 | Charting |
| 1.5 | Regeneration of SF6 |
| 1.6 | Collection system |
1.4 Charting
In this project the danish electricity sector has been charted, illustrating SF6 consumption in the branch in detail. In co-operation with Danish Energy stations Association (DEF) 97 companies in electricity sector have been identified as enterprises, who potentially use and handle SF6. By means of questionnaire inquiry, obtained the respond percentage at 100, SF6 consumption of the companies was charted and that made the best working foundation imaginable for development of collection system.
It appears from the inquiry that 42 companies in the electricity sector have SF6 breakers, where drawing off and handling of SF6 can be necessary. The total installed amount at these companies is approx. 39 tons SF6 out of roughly 56 tons, which is total installed amount of SF6 in the Danish electricity sector. From these 42 companies 17 companies have an installed amount at above 100 kg SF6 pr. company. A system, where SF6 is collected and regenerated at the companies, is estimated first of all to be relevant for those 17 companies.
In 1999 SF6 gas drawing off is occurred only at less than 20 of the 97 DEF members. Ca. 70 have outright refused SF6 drawing off at the company. The total installed SF6 amounts range between 0,2 and 8 tons, at those respondents, who has drawing off, as well as drawing off only cover SF6 -breakers from 50 - 400 kV along with GIS-arrangement. Drawing off is generally carried out by company itself, and to minor extent by externals such as suppliers/technical staff.
1.5 Regeneration of SF6
There has been developed a cleaning concept, which can clean gas polluted with moister, particles, sulphur, fluorides and other relevant pollution components. The fundamental principle for cleaning is an aluminiumbased molecylarfilter to remove humidity and fluoride-impurities from the gas.
During test running at the plant SF6 was cleaned from a bottle contained above 50% air. It brought on a very long turn-around time with clean velocity at 0,1-0,3 kg/h and relatively heavy SF6 loss. At the regeneration by means of bottle, contained 1,4% air, clean velocity was 7,1 kg/h. This air concentration is expected to be representative for gas correctly drawn off from power supply companies. Based on these experiences it is essential to put in claims how the gas is drawn off at the companies provided against a disproportionate big amount of air in the contaminated gas. In view of clean time and resource consumption air content should not exceed that turn-around time for the clean process is 5 kg/h as minimum.
Cleaned SF6, produced during the tests of plant, was qualitative analysed by an extern laboratory and quantitative analysed at the plants built-in O2 and H2O-analysator. Analyse results can be roughly summed up as follows bellow.
 | All the cleaned bottles with SF6 contain beyond SF6 contamination air (O2, N2), H20 and CO2. |
| H2O is quantitative analysed by own laboratory and here appear analyse values from 3 ppm till 28 ppm (demand< 15 ppm). H2O-value in the cleaned SF6 particularly depends on high pressure vessels preparation. |
| O2, also quantitative analysed, obtain values at 50 ppm till 90 ppm. This corresponds to an air content at 250 ppm till apr. 450 ppm (demand< 500 ppm) |
Other pollutions are qualitative identified by EIC-analyser (standard method). It applies to all these impurities, that very small amounts were noted near to detection limits, why it's on this basis expected to could meet purity demand which is an clean degree objective about > 99,9%.
Based on the accomplished test results the conclusion is, that regeneration of SF6 to a clean degree at > 99,9% of pollution components is possible with the clean technique elaborated in the project. The cleaned SF6 will meet current qualitative requirements to SF6 gas, valid for effect breakers, and constitutes therefore a commercial alternative to new SF6 gas.
1.6 Collection system
The direct potential for collecting of regenerated gas is 200-400 kg/y. This is only a minor amount of that gas, which is really consumed in the electricity sector per annum for the filling of new plants or for refilling of existing plants in connection with revisions or operationinterruptions. This consumption amounts to 1.500-2000 kg/y except for filling of new-installed GIS-arrangements.
In terms of this the demand for SF6 gas in the electricity sector is estimated to be min. 1.500 kg/y, and this amount can in principle be covered with regenerated gas via a collection system. It presumes however, that within the collection system there will be delivered min. 1.500 kg SF6 for regeneration pr year.
There are some few basic assumptions, which should be present making it possible technically and practically to collect and regenerate the gas.
The technical and practical assumptions for a collection system are as follows:
It’s assessed as the most appropriate, that it will be reached a framework agreement between DEF and a supplier from a collection– and recycling system, where the agreement basis is described so the same guidelines refer to all participated companies.
The collection order alone should comprise collection, regeneration and distribution of regenerated gas. The collection order should not include gas drawing off in connection with revision etc. from the several plants, partly due to safety grounds, partly due to supply companies responsibility for revisions, drawing off etc. what belongs to their daily running.
The gas should be kept in high pressure vessels, suitable for transportation. A standard packing, which is handy, f. ex. 10 or 20 kg bottles, to be used. It's estimated that there is no need for bottles with bigger volume, since some breakers seldom contain more than 20 kg pr. breaker. However GIS-arrangement can contain up to 100 kg in every chamber. So there should be an opportunity for installation of bottles with bigger volume, e.g. 50 kg in occasion of special bottling. If the gas is drought off to a tank, it has to be mobile and to bee carried and also to be provided with standard collections, so it is possible to draw off the gas to high pressure vessels. This is necessary for the elaborated regeneration set-up, which can't regenerate direct from a pressure-tank. But direct bottling to high pressure vessels is to be preferred because of SF6 loss due to drawing off and moreover it implies an increased time consumption caused of overloading from tank to bottles.
The bottled gas has to be kept safe at the plants measured up to guidelines for handling of high pressure vessels.
Considered the clean process the gas has to be bottled, provided that least possible air mixed with the gas. If the concentration of air exceeds a certain percent part the customer should have a possibility to reserve the right to refuse the gas. If ever specifications can be delivered to companies participated in collection system, indicated how the gas should to be bottled from the effect breaker, so the gas quality is optimal.
In the collection system a bottle system should be established consisted of too bottle pools – one for contaminated bottled gas and one for regenerated gas. Thereby expenses for bottle cleaning and rinsing at every regeneration will not be needed as clean/contaminated gas is always kept separated. Thereby it could be viable also to limit the needed bottle pool as much as possible. The demand is expected to be ca. 150 bottles in the bottle pool, because every company has capacity to draw off, keep and rebottle long time consumption at expected normal loading. It can also be a buffer at the supplier, who understands collection system so operation time during regeneration can be optimised.
It's presumed that the bottle pool live up to quality demands made to high pressure vessels, hereunder pressure testing, valve replacement and general maintenance. This should the supplier be responsible for.