Boiler Blowdown Considerations
Boilers require periodic blowdown in order to maintain effective operation, provide for good equipment life, and reduce maintenance time and expense. "Blowdown” refers to the removal of boiler water in order to maintain an acceptable level of Total Dissolved Solids (TDS). Blowdown has an economic impact because the water that is removed has been heated and chemically treated and the energy used to heat this water comes from the fuel burned in the boiler. In most cases, blowdown with a Clayton Steam Generator is significantly less than with conventional boilers and this reduction results in significant fuel savings.
Blowing down is the process of removing boiler water that has a maximum acceptable level of concentration. The water that is blown down is replaced by make-up water that has a much lower TDS level. This dilutes, or lowers, the concentration in the boiler water. The higher the TDS level in the blow down water the lower the amount of water that must be removed.
The amount of water that must be blown down for any given application depends upon:
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The TDS level in the make-up water – the higher the level the greater the amount of blowdown.
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The amount of make-up water vs. the amount of condensate returned – the greater the percent of make-up the greater the amount of blowdown.
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The maximum acceptable TDS level in the boiler water – the lower the level the greater the amount of blowdown.
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The TDS in the blowdown water – the higher the TDS, the lower the amount of blowdown.
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The average load level for the boiler (BHP / kW or lbs /kg. of steam per hour).
As can be seen from the above, applications with high make-up levels, high TDS in the make-up water and extended operation at high load levels result in high levels of blowdown.
The TDS of the blowdown water is significant because the higher the TDS, the lower the volume of water that must be removed.
Clayton Steam Generators provide a fuel savings, from reduced blowdown, because of two factors:
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First, since the Steam Generator is a forced circulation boiler it can tolerate relatively high TDS levels in the feedwater – as high as 8550 ppm.
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Second, water that is blown down is separator trap return water that has been concentrated to 4 to 5 times that of the feedwater level.
(See How We Make Steam for an explanation of the Clayton system and trap return water.)
Considering these two factors, blowdown water for a Clayton Steam Generator, typically, has a concentration of 24,000 to 40,000 ppm. That compares to values for conventional boilers in the range of 2,500 to 3,500 ppm. Since our blowdown water has TDS concentrations that are 7 to 16 times higher than conventional boilers, the volume of blowdown water with Clayton is 1/16 to 1/7 that of a conventional boiler. As will be shown, this can amount to a major savings in fuel cost.
In addition to the factors that determine the volume of blowdown water, the economic impact, depends upon:
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The temperature of the condensate and make-up water – the lower the temperatures the greater the economic impact.
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The steam pressure – the higher the pressure, and thus the temperature, the greater the economic impact.
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The cost of fuel – obviously, the higher the fuel cost the greater the economic impact.
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The number of hours of operation.
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The efficiency of the boiler.
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The cost of chemicals.
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The cost of water.
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The cost of disposal of blowdown water.
As noted, savings with a Clayton Steam Generator that result from reduced blowdown can be significant. These savings are application dependent. Please contact us if you would like an estimate for your application or use our online calculator.
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