The Costs of steam boiler blowdown
The cost of steam boiler blowdown encompasses several factors, including energy loss, water and chemical treatment, and potentially heat recovery system costs. Minimising blowdown is crucial for cost savings, but a certain amount is necessary to maintain boiler efficiency and prevent issues like scaling.
factors influencing blowdown costs
Energy Loss
Blowdown involves discharging hot water from the boiler, resulting in energy loss that needs to be replenished by the boiler.
Heat Recovery
Heat recovery systems can capture some of the energy from blowdown water, reducing overall energy costs. These systems, however, involve an initial investment.
Operating Costs
Blowdown also impacts operational costs by requiring more fuel to heat makeup water and potentially increasing maintenance and repair costs due to scaling or carryover if blowdown is insufficient.
Water and Chemical Treatment
The water used in boilers needs to be treated to prevent scaling and corrosion. Blowdown removes these impurities, but also removes the treated water, requiring more water and chemicals to be added and treated.
cost reduction strategies
Optimising Blowdown Rate
A balance must be struck between removing impurities (reducing scaling and corrosion) and minimising energy loss.
Water Treatment
Well designed water treatment can reduce the amount of dissolved solids entering the boiler, potentially lowering the required blowdown rate.
Heat Recovery Systems
Installing heat recovery systems can capture waste heat from blowdown water, reducing energy consumption.
quantifying costs
Fuel Costs
The cost of fuel can be directly related to the heat loss from blowdown
Water and Chemical Costs
The costs of make-up water and treatment chemicals can be significant, particularly if blowdown rates are high.
Energy Savings
Heat recovery systems can lead to significant energy savings, potentially paying for themselves within a relatively short time.
calculations
Blowdown Rate = Feedwater TDS (ppm) x Steam Generation Rate (kg/hr)
Boiler Water TDS (ppm) – Feedwater TDS (ppm)
Example 1
10000 kg/hr boiler with maximum TDS of 3500 ppm
Feedwater TDS of 350ppm
= 350 x 10000
3500 – 350
= 1,111 kg/hr or 11.11%
Example 2
In this example, the feedwater TDS has been reduced by 90%. This could be achieved by installing a Reverse Osmosis system (more info here)
10000 kg/hr boiler with maximum TDS of 3500 ppm
Feedwater TDS of 35ppm
= 35 x 10000
3500 – 35
= 101 kg/hr or 1.01%
For every 1% reduction in boiler blowdown 0.19% reduction in fuel is achievable when operating the boilers at 7BarG.
