P21
Recommendations on water treatment from the Danish District Heating Association The Danish District Heating Association recommends minimizing (and where possible fully avoiding) the use of chemicals – especially for removal of oxygen in the water, where new technologies have been developed. Chemicals clearly add to the salt content in district heating water, resulting in increased conductivity and thereby causing risks for corrosion. Chemicals add to the operational costs (OPEX), while they are also causing a health and safety issue for storage and handling. Finally, it makes sense that a sustainable heating system is operated through use of sustainable components/ technologies. Twentyfive years ago, most Danish district heating companies produced make-up water frommunicipal tap water by softening to remove hardness in water, then added chemicals for pH- adjustment and oxygen removal. In addition to softening today, the recommendation calls for removal of salts through membrane technology (RO) or ion exchange technology in order to produce demineralized water with low conductivity. These steps are then followed by oxygen removal, e.g. through membrane technology (membrane degassing) without the use of chemicals. The last step is adjustment of pH (9,8 +/- 0,2) by means of sodium hydroxide: The only chemical required. However, the general picture is that chemicals historically have been added to try to remedy a problem of more fundamental character with inadequate water chemistry. The water treatment recommended by the Danish District Heating Association takes the basic conditions of corrosion into account and approaches the problem without the use of chemicals. This may be considered as a professional way to handle the real issue before it becomes a problem. Looking back, use of demineralized water and removal of oxygen without chemicals were often not economically feasible – now this has changed due to new technologies available on the market. On top of that, chemicals are expensive so investments in new technology to remove oxygen without chemicals represent a short return on investment.
Water savings as well as energy savings can also be related to the positive impacts of proper water treatment.
It is quite clear that pipe corrosion (as a result of incorrect water treatment) can cause water leakages – by which the district heating company loses treated water - and energy - as the water has first been heated, then pumped out in the distribution network. Intrusion of untreated water often leads to pollution in the network that can further add to problems like corrosion and precipitations. Therefore, such undesired water needs to be treated. Experience has shown that if water intrusion into the network is not addressed properly, the cost impact will be significantly higher due to advanced corrosion and further water leakage. This issue represents a much higher cost compared to addressing the problem correctly by implementing partial stream filtration. When the district heating company repairs leakages/corroded pipes, this will often cause interruption of supply for its customers. This can also result in lost revenue as well as image issues for the district heating company. Finally, the cost for the repair as well as replacement pipes/joints needs to be included in the cost calculation for incorrect water treatment.
Example of corrosion in a district heating pipe.
Most of the make-up water lost every year leaks out into nature or enters into installations at the residential buildings. Thus, there are good reasons to keep chemicals in water treatment at an absolute minimum. A well-maintained plant through proper water chemistry is therefore also a safety issue in the daily operation as well as an economical and environmental gain.
www.dbdh.dk
A N N I V E R S A R Y I S S U E 2 0 1 8
Made with FlippingBook Converter PDF to HTML5