Feature Heat transfer


All you need to know about phosphate W


It’s a largely unrecognised problem that could be adding thousands of pounds to your annual fuel bill. Spirax Sarco’s Mike Griffin reveals what every boiler owner needs to know about phosphate


ater utilities routinely dose their water supplies with phosphate to inhibit lead from old pipes leaching into


drinking water. Great news for anyone drinking the treated water, but if it reaches an industrial steam boiler, it can cause the phosphate to precipitate to form scale.


This layer of scale forms a barrier against effective heat transfer and can reduce the energy efficiency of boilers, forcing owners to burn more fuel to raise the same amount of steam. A layer of scale just one millimetre thick can reduce boiler efficiency by 10%. Unfortunately there is widespread fail- ure of the water treatment industry to recognise this issue.


Phosphate was added to the water supply to meet the limits on lead imposed by the 1998 European Drinking Water Directive. However, new legislation to minimise the pres- ence of lead in drinking water to a tougher limit of just 10mg/litre, is to be introduced by December 2013. Despite some lead pipelines being replaced, it’s doubtful whether lead will be totally eliminated in the foresee- able future. So it looks like phosphate dosing is here to stay.


Hard and soft water areas The phosphate situation varies across the UK due to areas of hard and soft water. For example, soft water tends to dissolve the most lead, leaving suppli- ers in these areas relying on phosphate dosing more heavily than suppliers in hard water areas. Steam system opera- tors could have an issue with phos- phate unless they keep on top of the situation.


The fact is that many water treatment Non-toxic refrigerant for process cooling


eat transfer fluid manufacturer, Hydratech, has introduced CoolFlow DTX, a non-toxic sec- ondary refrigerant for the protection of process cooling, refrigeration and air conditioning systems. The efficient antifreeze ensures optimum flow, is biodegradable and has BS6580 cor- rosion control.


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CoolFlow DTX, based on ethylene glycol blended with patented DeTox additive, exploits the advantages of ethylene glycol over propylene glycol; a lower volume will give the same freeze protection, and it is easier to pump, especially at lower temperatures. The refrigerant is said to be less expensive per litre than other RAC process cooling fluids. It has been tested and classi- fied as Non-Toxic - ‘Relatively Harmless’ - by an EPA (Environmental Protection Agency) certi- fied laboratory.


In collaboration with Evans Cooling Systems Inc., Hydratech has eliminated the dilemma of having to choose between the high performance but toxic properties of ethylene glycol and the safer but less efficient propylene glycol. Also, the DeTox additive contains corrosion, scale and biological inhibitors, thus promoting long operational life and high thermal efficiency. Hydratech


T: 01792 586800 Process & Control JULY/AUGUST 2013 www.hydratech.co.uk


Water quality varies from region to region, with soft water areas relying more heavily on phosphate dosing


can prevent it precipitating and becom- ing a problem. Phosphate causes scal- ing when it reacts with calcium or magnesium in the boiler water, deposit- ing scale onto the boiler tubes, and reducing efficiency.


Managing alkalinity Avoiding this situation involves con- stantly and consistently managing the alkalinity of the water in the boiler, adding chemical dispersants and ensur- ing that the level of dissolved solids is kept in check through regular boiler blowdown.


companies simply do not test the raw incoming water, and if they are not aware of the potential for trouble, prob- lems can arise. Ironically, close exami- nation of phosphate levels used to be more widespread because dosing with phosphate is one way to condition other scale-forming salts. However, this method of treatment has declined and has been replaced by polymer-based dispersants. This is resulting in many boiler operators no longer monitoring phosphate levels in make-up water as a matter of routine.


If the presence of phosphate is recog- nised when checking the levels in the main water supply, the right treatment


Avoiding scale build-up, caused by phosphate in the water, involves con- stantly and consis- tent managing the alkalinity of the water in the boiler


Alternatively, reverse osmosis (RO) is becoming increasingly popular for treating incoming water. This mem- brane-based approach will eliminate 98% of anything dissolved in the water, including phosphate. This enables steam system users to start with a clean slate and add in only the chemicals that they want.


If an initial investigation reveals a build-up of scale, there are two approaches to getting rid of it. The “quick-fix” option is to strip down the boiler and descale the affected surfaces with acid; meaning the boiler should regain its full energy efficiency as soon as it resumes operations. However it does put the boiler completely out of action for a prolonged period of time. Online cleaning is a more gradual process over several months that dis- solves the scale, or softens and loosens it so that it drops to the bottom of the boiler. The process involves running the boiler at a higher alkalinity, with extra-low levels of dissolved solids and higher levels of chemical dispersants. The boiler can carry on generating steam throughout the process. However the extra boiler blowdown needed to keep dissolved solids at bay and to remove the additional sludge from the bottom of the boiler means losing even more energy, in addition to the extra money spent on treatment chemicals. As most boiler owners don’t have the skills and knowledge to optimise their water treatment and steam system con- ditioning regimes, specialist companies should provide whatever support the end user needs to make those checks possible. The recommendation is to carry out weekly testing, so any changes in the system chemistry can be identified and dealt with immediately.


Enter 206


Spirax Sarco T: 01242 521361


www.spiraxsarco.com/uk/ 7 Enter 207


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