Most, if not all, steam systems have potential for energy savings.
These can be expressed in terms of steam, heat or fuel, or of course their dollar cost.
Further savings come via a reduction in CO2 emissions and water consumption.
As an example of the savings that can be made, and to quantify them, we have taken a plant generating 4000 kg/h of steam at 700 kPa in a gas-fired boiler, operating 16 hours/day, 5 days/week, 50 weeks/year.
The classic energy saver in a steam system is to fix or replace leaking steam traps. A Steam Trap Audit typically finds that around 10 per cent of installed traps are leaking, wasting steam that can easily account for around 1 per cent or more of the annual fuel bill.
Now this might not sound much, but usually the cost of finding and fixing these traps is much less, such that the payback period is just a few months, or even weeks. And the reduction in CO2 emissions can be quite impressive – around 30 tonnes less for the plant mentioned. Another classic energy saver is condensate recovery.
Condensate is hot water that will require little or no water treatment, so its place is in the boiler feed tank, not down the drain. If it does go down the drain, the waste is immense – 16,000 kilolitres a year, which would all be recycled if the condensate were recovered, saving up to $32,000 or more a year in fresh water costs.
And because the fresh water will be at say 20°C instead of the probable 95°C for returned condensate, 314 kilojoules of heat (via the boiler) needs to be input into every litre (kg).
Condensate recovery saves this, and it amounts to a staggering 5024 GJ of heat per year (1 GJ = 1 million kJ), wasting over 12 per cent of the annual fuel bill, and adding almost 370 unnecessary tonnes of CO2 to the atmosphere.
There’s also the cost of treating the fresh water, which is unnecessary if condensate is
Flash steam loss is another waster. Flash steam forms naturally when condensate is discharged by a trap, caused by the fact that the pressure and temperature conditions at a trap’s inlet are invariably much higher than at its outlet (usually atmospheric pressure or close to it).
“Flash steam” is the result and it’s usually highly visible as an unsightly steam loss from vents on receivers and feed tanks. Proper recovery of this flash steam (to heat or pre-heat water or air) typically reduces the annual fuel (and water) bill by about 10 per cent or more, so the savings (of fuel, water and CO2) are similar to those mentioned above for condensate recovery.
The potential for heat recovery from boiler blowdown is much overlooked. It shouldn’t be, because it can easily account for 1.5 per cent or more of the annual fuel bill, and 45 tonnes of CO2 (based on a typical blowdown rate of 6 per cent of the boiler’s actual output).
Because the blowdown is hot water at steam temperature, the easiest and best way of
recovering heat from it is to collect and use the flash steam from it, similar to flash steam recovery from condensate.
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