Paul Mayoh, Technical Manager at Spirax Sarco, offers five easy tips to get the most from your entire steam and condensate system, from treating boiler feedwater to condensate recovery.
Steam systems are generally efficient and reliable. Even so, many users are not utilising these valuable assets as hard as they might be. There are five basic strategies that everyone could be applying to increase productivity and achieve more ‘bang for their buck’.
Water treatment
A clean water supply is the basic starting point for any efficient steam system. Raw water can contain a whole range of impurities, and any number of these can have a negative impact on the performance of steam systems. The most common impurities in raw water include dissolved solids and gases, suspended solids and scum-forming substances.
The damage they cause typically falls into three categories. Corrosion is the biggest issue with dissolved gases, especially oxygen and carbon dioxide in the form of carbonic acid. In fact, if carbonic acid and oxygen are present, then the rate of corrosion rises by about 10%.
Deposits are another challenge and tend to build up if the alkalinity of the feedwater is not controlled. For example, a layer of deposits just one millimetre thick can reduce boiler efficiency by 10%, disrupting effective heat transfer.
Foaming can be caused by a build-up of total dissolved solids (known as TDS) in the boiler. This initially causes problems in the boiler, where it makes it tricky to gauge the water level, but it can also lead to carryover of boiler water into the steam distribution system, where it can interfere with heat transfer and cause waterlogging.
Effective water treatment tackles these problems at source. The traditional approach uses water softening supplemented by chemical treatment. More recently, reverse osmosis (RO) is also becoming increasingly popular. RO forces water through a semi-permeable membrane to strip out nearly all the contaminants. The resulting pure water will have had 98-99% of its salts removed.
An example of RO is action is at the Westons Cider in Ledbury. It is saving around £42,000 per year in fuel and water costs, as a new RO system has cut the amount of boiler blowdown and water needed. Accurate metering of fuel oil and water has pinpointed the savings, including 3,800 litres of oil saved over a 15-day period. What’s more, future savings are likely to be even higher than these measurements suggest because of reduced CO2 emissions and a lower Climate Change Levy (CCL).
Boiler control
Having the right controls is a crucial ingredient in the optimisation of any steam system. For example, the primary function of level controls is to ensure sufficient water is fed to the boiler to meet demand. If the water level falls too low, the heating surfaces could become exposed and the boiler would overheat. Too high, and water could be sucked into the steam, leading to poor quality steam that could impair heating or production efficiency and increase the risk of waterhammer.
Not every user experiences extreme difficulties, but better boiler controls can still deliver major savings, especially in the area of boiler blowdown. Boiler blowdown periodically ejects water from a boiler to prevent the build-up of contaminants in the boiler. It’s essential to deliver clean, dry steam, but it’s potentially very wasteful. Switching from manual opening of the blowdown valves to automatic blowdown controls can deliver a rapid return on investment.
Heat transfer
Effective heat transfer is a key driver for almost every installation, so using the most efficient heat exchangers should therefore be a priority for all steam users.
Traditional shell-and-tube calorifiers used to be the workhorses of steam, but plate heat exchangers are so much smaller that they typically improve energy efficiency by around 6-10% by reducing radiation heat losses from their surfaces. In addition, these compact systems can be so responsive that some of them, such as Spirax Sarco’s EasiHeat systems, can tailor their output on-demand. The recent addition of the Spirax Intelligent Management System (SIMS) to the EasiHeat package promises to save up to a further 10% by optimising the control and monitoring of energy use.
Condensate recovery
Next to steam, condensate is the most valuable resource available to any steam system operator. Condensate contains about 20% of the energy of the steam from which it came, which is why most steam system operators recognise condensate as being a particularly valuable resource. In reality, many UK sites already have condensate recovery systems in place, although nearly all could be enhanced by the latest techniques.
Most systems could be achieving a condensate recovery rate of 75-80%, so returning condensate to the boiler can save thousands of pounds per year in energy alone. Using hot condensate to heat the boiler feedwater means the boiler has less to do in converting the water to steam. In fact, every 6°C temperature boost in boiler feed water knocks 1% off a typical boiler energy bill. What’s more, any condensate returned to the boiler feed tank reduces the need for blowdown and thus helps to reduce the energy lost during the blowdown process.
On the other hand, any condensate not re-used must be replaced with fresh water, which in turn needs to be treated by costly chemicals. Furthermore, there may be issues associated with disposing of the effluent at the end of the process. For example, in the UK, effluent above 43°C cannot be returned to the public sewer so must be cooled first.
When it comes to condensate recovery, each steam system is different and only a technical assessment and cost saving calculation can determine the payback of a particular project. However, typically the payback is between one and two years, with some measures paying for themselves in weeks.
Service and support
Whatever business they’re in, another thing that steam system users tend to have in common is that steam is not their core area of expertise. And with the much-discussed skills gap affecting many organisations and in-house estates and maintenance personnel facing increasing demands on their time, calling in specialists to provide service and support for the steam system can be the most realistic, cost effective way of keeping things running at their optimum.
From steam system audits and water treatment to project management and training, there are a wide range of support services available from external suppliers.
In many cases the benefits will be immediate. For example, a steam trap management contract is projected to save AB World Foods 236 tonnes of carbon dioxide a year over a three year period. The Lancashire site uses steam for a variety of applications to produce its range of Pataks sauces, such as process hot water, sterilisation and Cleaning-In-Place. The deal sees Spirax Sarco specialists surveying and maintaining the site’s steam trap population every six months, and the investment looks set to pay for itself in only eight months thanks to improved energy efficiency.
Don’t miss out
Many of the measures described here are low or no-cost, and even those that require a significant upfront investment should start delivering benefits in the short or medium term. Steam system users are already sitting on large investments, so productivity is really all about making the most of their existing assets – and who can afford to miss a trick like that?