Boiler house Heat recovery systems
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Operation Boiler water at saturation temperature is blown down from the boiler through a valve to the flash vessel. A percentage of this blowdown water will flash to steam as its pressure is reduced typically to 0.2 bar g. The flash steam is allowed to separate in the flash vessel and is then directly introduced into the feedtank through a steam distributor. This increases the temperature within the feedtank thus reducing heating requirements and driving off corrosion-causing dissolved oxygen. Also reduced is the quantity of expensive treated water required to replenish the feedtank. Residual blowdown from the flash vessel flows through a float trap to the heat exchanger where its heat content is used to raise the temperature of water from the cold, treated water storage tank. The circulating pump is thermostatically controlled to ensure that it only runs when the system receives blowdown and there is useful heat to be recovered.
Maintenance Daily There are no specific checks to be carried out daily on this system.
Weekly Take a boiler water sample and check the TDS. Adjust the blowdown controller accordingly. Observe the system under operating conditions for any system faults. Open the flash vessel drain valve whilst there is flow from the TDS system and check that the vessel drain is clear. Operate the isolating valves throughout the system to ensure that they do not seize. Check that the residual blowdown discharge rate increases as the blowdown valve opens. When the valve closes check that the residual blowdown discharged to drain eventually stops. Annually Examine the blowdown valve for any damage and replace parts as required. Normally it is not necessary to open a heat exchanger until it is so dirty that its function is impaired. When required open the heat exchanger according to the manufacturers dismantling instructions and clean each plate separately. Cleaning with the plates in the frame is recommended. Clean the plates using a water jet not an abrasive brush. If removed the exchanger plates must be numbered to ensure that they are assembled correctly after cleaning. Inspect the float trap on the flash vessel drain and clear out any deposits checking for any wear of the internals and free movement in all components. Re-commission the system. For the maintenance instructions of TDS systems refer to separate literature.
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AI-P404-07 AB Issue 7
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Boiler Blowdown Heat Recovery Systems - Installation, Operation and Maintenance
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