Boost steam system centre efficiency
Condensate contains about a quarter of the energy of the steam from which it came. That’s a significant amount of heat available to a steam system. Ensuring that existing condensate recovery systems are as efficient as possible is, therefore, vital for reducing steam system costs. Paul Mayoh, Product Manager at Spirax Sarco, looks at ways to ensure as much condensate as possible is re-used.
In today’s straitened economic climate with capital budgets being squeezed, the focus of many energy managers has shifted away from significant capital expenditure projects. Instead, relatively low cost and easy to implement upgrades and enhancements to existing installations are in the spotlight, especially ones that can improve steam system efficiency. Making the most of existing plant is the order of the day.
For many steam using operators, the boiler house is a major source of operational costs and any improvements here can quickly repay themselves. In particular, it’s vital that steam systems run at optimum efficiency. Condensate recovery is a juicy target for upgrades because although steam systems will almost all have condensate recovery systems in place, often they can be improved relatively easily to achieve rapid payback.
Condensate is the hot, treated water produced as steam releases its heat energy. It’s a valuable resource that contains around 25% of the useful energy in the original steam. It makes sense to return it to the boiler, instead of dumping it to drain. It may be impractical to return all of the condensate to the boiler for various reasons, but in most applications a goal of 75-80% condensate return is reasonable.
Condensate recovery offers several benefits. It reduces fuel costs and saves energy, reduces water charges and chemical treatment costs and brings down effluent charges.
Returning hot condensate to the boiler feedtank can save thousands of pounds per year in energy alone. Using condensate to heat the boiler feedwater leaves the boiler with less to do to convert water to steam. In other words, less fuel is needed to produce steam from hot water rather than cold water. Using returned condensate to raise boiler feedwater temperature by 6°C gives a fuel saving of 1%.
Condensate is distilled water with little total dissolved solids (TDS). Condensate returned to the feedtank reduces the need for boiler blowdown, which reduces the concentration of dissolved solids in the boiler. This therefore reduces the energy lost from the boiler during the blowdown process. In addition any condensate that is not returned and re-used must be replaced by fresh water, incurring additional water charges.
In the UK, water above 43°C cannot be returned to the public sewer because it is detrimental to the environment and may damage earthenware pipes. Condensate above this temperature must be cooled if discharged, which could incur extra costs. Similar restrictions apply in most countries and effluent charges and fines may be imposed by water suppliers for non-compliance.
Steam systems that allow condensate to flash to steam can also create visible plumes, potentially presenting a poor image to the outside world of an organisation that is not environmentally friendly.
Each steam system is different and only a technical assessment and cost saving calculation can determine the payback of a particular enhancement project. However, it’s typically between one and two years, making it an attractive proposition for healthcare organisations.
At sites where the payback is longer than two years, it may still be a worthwhile project offering substantial cost savings in the longer term. However, many healthcare organisations may find it difficult to invest upfront in these projects, even though they could be saving them money. Help is at hand with the rising availability of rental options that can enable organisations to carry out projects sooner and reap the benefits of eliminating wasted energy immediately. The resulting savings effectively make many projects self-funding.
The role of steam traps
There are several essential steps in effective condensate recovery. In order to recover and re-use condensate it is first necessary to remove it from the steam system. The steam trap is the most important link in the condensate loop because it connects steam usage with condensate return by retaining steam within the process for maximum utilisation of heat, while releasing condensate and incondensable gases at the appropriate time.
Steam condenses as it gives up its heat. The resulting condensate must be purged from the system or it will lead to poor heat transfer and possible problems with waterhammer. Waterhammer is a risk in a poorly drained steam main, where condensate collects and forms a slug of water. This water is incompressible (unlike steam) and can cause damage when carried along by the high speed steam.
Air and other non-condensable gases must also be purged or they can lead to poor heat transfer and corrosion problems.
Commission a survey
A good start point in any project to improve condensate recovery and one of the most cost effective measures is to commission a professional steam trap survey to identify where improvements could be achieved. Such a survey will also give an estimate of the potential financial gains through upgrades – providing information to help justify maintenance expenditure.
A steam trap survey will help to keep a system running smoothly and will almost certainly reveal impressive savings through reduced fuel consumption, fuel emissions, water and effluent charges. For example, an analysis of 50 Spirax Sarco steam trap surveys revealed potential annual energy savings of £28,400 per survey on average.
The average payback time on each survey, including the cost of replacement products and their installation, is about two months, when all upgrade work is completed.
It is important to ‘walk the plant’, looking for tell-tale signs of escaping flash steam and checking that the condensate recovery system is working properly. It is best to engage a steam system expert to do this initial inspection as experience goes a long way in identifying opportunities for improvement.
From here it is possible to put together a detailed project proposal with full costings to identify payback periods and energy savings. Surveys cover a wide range of equipment including steam traps, high limit control equipment and condensate pumps. The most popular survey is the steam trap survey. Once the survey is complete and the steam trap population is brought up to peak operating efficiency, Spirax Sarco’s steam trap management service can save money and effort by taking responsibility for keeping steam traps running at maximum efficiency year after year.