Steam: Strategies to boost productivity

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 that can have a negative impact on the performance of steam systems, such as 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.

•  Deposits are another challenge and tend to build up if the alkalinity of the feedwater is not controlled.

•  Foaming can be caused by a build-up of total dissolved solids (TDS) in the boiler. If carried over to the boiler foam 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 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.

Boiler control

Having the right controls is a crucial ingredient in the optimisation of any steam system and can 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 can tailor their output on-demand. 

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. 

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.

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

Something that most steam system users tend to have in common is that steam is not their core area of expertise. Calling in specialists to provide service and support for the steam system can be the most 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.

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 existing assets – and who can afford to miss a trick like that?