WET News

18 WET NEWS AUGUST 2014 INSIGHT Raw water quality is key in selecting a treatment plant. Spirax's Mike Griffin explains. A solution: It pays to have the right water treatment regime I t is easy to see why the wrong water quality can add up to a real headache for boiler and steam system operators. None of these problems are insurmount- able however, it just takes the right water treatment regime. Deciding on the optimum water treatment system is not always straightforward. Raw water quality can be variable and getting the wrong systems in place can mean pay- ing more than necessary for treatment chemicals or perhaps even failing to prevent the potential problems. Water supplies and steam systems are extremely dynamic and their chemistry can vary day by day. The quality of raw water is obviously an important factor when choosing a water treatment plant. Although dissolved solids levels will affect the perfor- mance of the boiler operation, other issues, such as total alka- linity or silica content can some- times be more important and then dominate the selection process for water treatment equipment. Expert input can be the best approach for many steam sys- tem users, perhaps even out- sourcing the water treatment entirely to a third party. Whether the treatment regime is devised in-house or outsourced, raw water needs to be treated before being fed to the boiler. The major water treatment processes include: • Water so€ening supple- mented by chemical treat- ment in which various chemicals are added to the boiler feedwater in order to reduce the effect of deposits, corrosion and chemical attack within the system. Chemicals should generally only be added to the boiler feedwater in accordance with accepted standards, such as BS 2486: 1997 or BS EN 12953 –10 2003. Following the guidance in the standards should help prevent exces- sive dosing and provide an effective programme of trouble-prevention. • Reverse osmosis – a pro- cess in which the water to be treated is forced through a semi-permeable membrane to strip out nearly all the contami- nants, leaving behind a concentrated solution of impurities, which is rejected to waste. The pure water, or "permeate", will have had 98-99% of its salts removed. • Carbon filtration – if the water is heavily chlorin- ated, carbon filtration may also be required either between the water so€ener and the Reverse Osmosis plant or before the water so€ener itself. This is nec- essary to remove chlorine from the water, which oth- erwise could be highly corrosive. There are also important aspects of the day-to-day opera- tion of the boiler itself that can have a big impact on water qual- ity. For instance, heating the water in the boiler feed tank will reduce the concentration of dis- solved oxygen and other gases. This minimises the oxygen- scavenging chemicals required and fewer chemicals means that less bottom blow-down is needed, which saves energy. In-house checks Most boiler owners recognise that they do not possess the in- depth knowledge and skills in-house to optimise their water treatment and steam system conditioning regimes. If they opt to bring in specialist help, the contract should specify no more than a month between visits. Even so, it may be prudent to carry out in-house checks between visits from the experts, and the specialist company should provide whatever sup- port the end user needs to make those checks possible. For example, Spirax Sarco not only provides testing kits and water treatment engineers, but also makes sure that steam plant owners have all the train- ing they need to use them properly. The recommendation on most sites is to carry out testing several times a week, so any changes in the system chemis- try can be identified and dealt with immediately. The benefits of a correctly designed water treatment pro- gramme include: • Faster steam system warm-up times • Reduced downtime • Fewer product rejects because steam reaches the point of use in the correct condition • Maximising heat transfer throughout the steam system • Minimising chemical, water and energy use • Reducing energy waste and carbon emissions • Lower fuel bills through improved energy efficiency • Compliance with water treatment guidelines (EN 12953/BS2486) Implementing an effective water treatment regime may seem like a complex and daunt- ing prospect. But in these days of rising energy bills and austerity, steam users simply cannot afford to have suboptimal systems eating into their utility bills and main- tenance budgets. There is plenty of help out there from responsible suppliers and any initial outlay with soon deliver healthy cost and perfor- mance improvements. n If companies opt to bring in specialist help, the contract should specify no more than a month between visits Water quality can vary tremen- dously from one region to another The correct dosage points for water treatment chemicals

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