The importance of the drying process in dry-cleaning shops
Summary and conclusions
This project addresses the residues of chemicals in dry-cleaned textiles, focussing on the importance of the drying process in hydrocarbon dry-cleaning shops. The project, which is financed by the development programme of the Danish Environmental Protection Agency, includes the following activities:
 | An identification of the parameters influencing the residue: fibre types, choice of chemicals, charge sorting, drying temperature, drying time, etc. |
| A description of state of the art and optimisation possibilities for hydrocarbon dry-cleaning machines. |
| Exchange of knowledge at a meeting of representatives from the dry-cleaning trade, to identify and discuss the most promising possibilities for optimisation. |
| Discussion of the project results and preparation of an information folder for the dry-cleaning shops in Denmark. |
On the basis of the first two items, 14 different optimisation possibilities were identified. These possibilities were not aimed at the drying process only; they also included all relevant processes in the dry-cleaning shop. The optimisation possibilities are:
| Registration of the operation conditions |
| Improved charge sorting |
| Reduced charge size |
| Reduction of the number and quantity of chemicals |
| Improved distillation |
| Improved spin-drying |
| Extended drying time / increased drying temperature |
| Optimum drum rotation during the drying process |
| More stringent stop criteria (to lower drum concentration before opening drum door) |
| Ioning/shaping all textiles |
| Keeping the textiles without bag in the dry-cleaning shop |
| Keeping the textiles in heating cabinet |
| Control measurement of residue |
| Voluntary eco-labelling procedure |
At the knowledge exchange meeting, these 14 optimisation possibilities were discussed.
So far, no investigation results have been published that could contribute to a detailed assessment of the advantages and disadvantages of individual optimisation possibilities in relation to other optimisation scenarios. However, the project has identified some optimisations that can be initiated immediately in the dry-cleaning shops.
Generally, the most environmentally and economically appropriate solutions related to the pre-treatment and the processes in the dry-cleaning machine, and not the shaping and finishing treatment processes. The reason is that the processes are optimised exactly where the undesired chemicals are introduced.
It is found that the following actions are the most efficient:
- Registration of the conditions of operations with regard to:
| Registration of charge time |
| Consumption of chemicals per quantity of dry-cleaned textile |
| Periodic registration of amount of waste produced, such as distillation residue and contact water |
| Nature, scale and time for remedial adjustments |
- Improved charge sorting, i.e. identical textile types and textile thickness are
dry-cleaned in the same charge.
- Shaping all textiles.
- Dialogue with the installers on optimisation of the dry-cleaning machines as regards:
| Improved spin-drying, for instance interval spin-drying. |
| Optimised drying through optimised drying time, drying temperature, drying process and stop criteria. |
| Optimisation of the dry-cleaning programmes, securing a low residue for the given textile types. |
- Dialogue with the producers of dry-cleaning machines and chemicals for the dry-cleaning trade, to provide additional data describing the optimisation possibilities, especially within the following areas:
| Improved spin-drying. |
| Optimised drying by increased drying time and drying temperature as well as more stringent stop criteria in relation to lower drum concentration or condensation speed, allowing the drum door to be opened. |
| Optimisation of the dry-cleaning programmes for the textile types and requirements for low residues. |
| Identification of chemicals that do not or only to a limited extent contain components that are undesirable in the environment, and identification of chemical compositions resulting in low well-defined residues. |
It is estimated that the owners of the dry-cleaning shops may benefit from initiating optimisation possibilities A, B, C and D right away.
At present, suitable and cheap methods do not exist to demonstrate the effect of a given initiative on the residue. It is therefore recommended that the dry-cleaning trade develops and tests a measurement method. Until such a method is available, it is recommended that the content of chemicals in the drum air is measured as part of the optimisation measures.
It is estimated that – in order to have the best results - initiatives related to optimisation possibility E should taken through cooperation between installers, dealers and professional organisations or trade chains, for instance in cooperation with other European or international professional organisations.
Furthermore, the dialogue about eco-labelling of chemicals - and eventually the dry-cleaned textiles at the dry-cleaning shops - should be initiated. The eco-labelling may for instance follow the principles of "the Nordic Swan" or the "EU flower". Alternatively, criteria for voluntary trade labelling could be established, managed by the dry-cleaning trade itself. This trade regulation could for instance include periodic measurements of the residue. Such regulation implies the above-mentioned method for measurement of the residue, and the regulation could include a specified measurement frequency and a specified measurement method, as well as trade marginal values for permissible residue levels in a given textile. If the dry-cleaning shop is able to comply with the regulation, the shop may be allowed to publish the result.
The results of the project are presented briefly in an information folder that has been distributed to all Danish dry-cleaning shops. For further information about the project, see this folder and the reading instructions in section 2.
The project report is published on the Danish Environmental Protection Agency homepage, www.mst.dk.