Boilerhouse managers and operators are constantly battling with rising energy prices. With pressure to remain competitive and reduce these costs, the search to combat energy consumption is top of the wish list. Chris Coleman, Boilerhouse National Specialist at Spirax Sarco, argues that truly efficient condensate recovery can boost productivity and improve regulation, at a much lower cost to steam users than we might imagine.
It’s no longer enough to strike a good deal on energy supplies or achieve high levels of productivity: now we are expected to do both, while complying with a complex web of regulation. Striking the right balance can make that crucial, tangible contribution to your company’s revenue flow, but, with ageing equipment and economic uncertainty coming into play, the potential to achieve precisely that is virtually impossible. That is, until we consider our use of condensate and the heat we may have otherwise wasted.
The value of condensate
To put it simply, condensate is the hot water that forms when steam passes from a vapour to a liquid state. While it is widely known that condensate is hot, it’s only when we consider how this translates to heat energy that we realise how useful it is as a resource. The condensate generated by the steam heating system will normally have about 25% of the energy that the steam had, and contains little to no dissolved solids.
If the condensate is merely discharged from the system and disposed of, that valuable energy resource is thrown away with it. That is an easily avoidable waste that few of us can afford.
Draining condensate, rather than re-using it, can trigger water and effluent management costs, which can be significant. Similarly, draining condensate can make it harder for us to comply with the regulatory standards around environmental effluent. In many countries, including the UK, condensate often has to be cooled before it can be drained which, again, will often come at an extra cost.
Put bluntly, those who are disposing of their condensate are throwing money away. Recovering and re-using as much of it as possible can have huge financial advantages.
The uses of condensate
We might now realise that condensate – and the heat energy it carries – is too valuable to be tipped down the drain, but how can it be put to better use?
- Boiler feedwater
If condensate is not used as feedwater, the boiler must be topped up continually with cold water. This is costly in terms of both water and energy because the cold feedwater must be heated. In contrast, condensate is already hot, which reduces the need for (and cost of) fresh water and treatment chemicals. It also requires much less energy than cold make-up water does to be ready for use.
- Flash steam recovery
Flash steam can be harvested and re-used. This is formed when high pressure condensate is exposed to a large pressure drop, often created during the blowdown process. A flash vessel is just one method that can be used to recover energy by separating flash steam from condensate. As condensate enters the flash vessel, flash steam is produced and can be piped from the top of the vessel to the feedtank through the deaerator.
We can fit float traps to the outlet of the flash vessel where residual blowdown water will be drained. The water will still be hot at this point and is allowed to pass into the plated heat exchanger, where it gives up its heat to the circulating cold make-up water. In other words, if we recover the heat energy from the hot water coming from the flash vessel.
The use of both a flash vessel and plated heat exchanger pack will allow you to recover up to 80% of the energy from the rejected Total Dissolved Solids (TDS) water, which can also result in fuel savings, a reduction in carbon dioxide emissions, and the elimination of unsightly plumes of steam.
Concerns that contaminates may enter the boiler are only natural, but this is a challenge that can be overcome. Conductivity or turbidity meters can be used with an existing condensate return system to detect contamination and dump the condensate before it reaches the boiler.
The recovery process
As you’re well aware by now, steam is usually generated for most industrial and process industries. How it is recovered can broadly be summarised in three important steps.
- Steam traps are used to remove condensate from the steam system. A steam trap survey can often offer some invaluable insight into the performance of a given system, and will almost certainly reveal impressive savings potential through reduced fuel consumption, fuel emissions, water, and effluent charges.
- Pumps are used to return any condensate not captured by steam traps to the boiler feedtank.
- Condensate is mixed with other types of feedwater to heat it within the feedtank.
This may outline the basic process, but there are other points to bear in mind.
- The flash steam released from hot condensate when the pressure drops can be recovered using a flash steam system before it goes back into the feedwater tank.
- Pressurised low-loss condensate recovery can deliver huge savings in annual fuel and water costs, resulting in payback times of less than a year in some cases.
Condensate recovery is one process that is genuinely capable of boosting boiler efficiency, saving energy, enhancing equipment lifespan and complying with legislation – all of which can, in turn, generate substantial savings to those who use steam systems.
Rising energy costs are having a major impact on all types of businesses across every industry. Saving energy from condensate is a simple, yet highly effective technique. It may not be the protagonist or the leading role in the steam system, but it is undeniably the unsung hero of the boilerhouse.
Spirax Sarco’s full report, The unsung hero of boiler house efficiency: How condensate recovery can transform steam system performance is available to download from http://sxscom.uk/boilerhouseefficiency.