Internal Economiser (If Fitted) - FULTON RB Series Installation, Operation And Maintenance Manual

OPERATION - 3
3.7

INTERNAL ECONOMISER (IF FITTED)

Feedwater from a constantly running modulating pump is passed through the economiser before
entering the boiler.
Heat is extracted from the boiler exhaust gases by the economiser which in turn heats the
feedwater to temperatures that can exceed 100 °C.
Back flow is prevented by non-return valve in the feedwater pipework on the inlet of the
economiser.
The economiser is designed to reduce the boiler exhaust temperature to approximately 140 °C,
if the temperature falls significantly below this figure condensation will occur which can lead to
corrosion.
The economiser is fitted with inlet and outlet temperature gauges for both feedwater and exhaust
gas. These gauges should be used to monitor the condition and performance of the economiser.
Note: Sudden changes in temperature should be reported immediately as they could indicate a blockage of the
economiser water ways, or a malfunction of the modulating feedwater control valve.
In general a 10 °C increase in feedwater temperature will give an efficiency improvement of 2%.
Because the boiler feedwater modulating control valve and the burner are both proportioned
to the steam load, the burner heat input and cooling water flow rate to the economiser are in
balance throughout the burner firing range.
A DN20 spill back line with a pneumatically operated piston valve is installed in the feedwater
pipework in the discharge from the pump, the outlet from this valve must be piped back to the
feedwater tank. The purpose of the spill back line is to prevent the constant running feedwater
pump from overheating should the water level reach the maximum working level. An orifice
plate is fitted in the spill back line in addition to the pneumatically operated piston valve, with a
manually operated/adjustable globe valve for making small adjustments to the spill back water
flow rate.
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Internal economisor
Boiler feedwater
economiser outlet valve
Boiler feedwater
economiser inlet valve
Boiler feedwater
economiser bypass valve
Boiler feedwater inlet
Figure. 17 - Typical Internal Economiser
Fulton Ltd
RB-RBC-IOMM-2015-1