FULTON RBC1250 - Boiler Start-Up (from Cold)-All Models

RB-RBC-IOMM-2015-1
Fulton Ltd
Page 24
OPERATION - 3
3.5 BOILER START-UP (FROM COLD) ALL MODELS
When starting up the boiler, it is prudent to minimise the thermal and mechanical stress caused
by differential expansion of various parts of the boiler as they reach working temperature.
The shell temperature is determined by the contained water/steam temperature. The furnace
temperature which is higher is determined by the heat transfer/furnace wall loading and gas
temperature. The tube temperature lies between the shell and furnace temperatures, but is nearer
the shell temperature. Since all these components are virtually the same length, they expand
longitudinally by different amounts causing mechanical and thermal stress. Whilst this is catered
for in the mechanical design of the pressure vessel, the life expectancy of the boiler can be
affected if the boiler is frequently heated too quickly from cold.
When starting from cold the furnace approaches its design temperature shortly after start-up,
whereas the tube and shell temperatures are delayed by the time taken to bring the contained
water up to temperature. As a result, the thermal expansion is at its greatest. Additionally, the
temperature gradient which exists between the bottom and the top of the boiler is exaggerated.
This can be reduced by blowing the boiler down during the heat-up period.
In practical terms, the ideal solution would be to gradually raise the temperature and pressure in
theboilerprogressivelybyringtheboileronlowreforafewminutesandleavingitto‘soak’
(e.g. allowing the temperatures in the boiler and water to even out by diffusion) for 20 to 30
minutes,blowingdowntheboiler,ringtheboileragainforalittlelongerandsoakingforless,and
so on.
Start-Up (from cold) Procedure
1. Fill the boiler as described in Section 3.3.
2. Ensure the main steam valve is SHUT.
3. OPEN feedwater valves to the economiser and CLOSE the feedwater bypass valve (where
economiseristted),seegureFigure. 17 on page 26.
CAUTION
The system should be raised to temperature slowly to allow for expansion and to avoid thermal shock
and water hammer.
!
CAUTION
Where an economiser is tted, a constant ow of water through the economiser is required when the
boiler is running to prevent pressure build-up.
!
4. Open all the valves in the gas train/oil supply. It is assumed that the fuel supply lines have
been purged prior to attempting to start the boiler/burner.
5. Turn the Pump Only/Off/Pump & Burner On Switch to the PUMP & BURNER ON position.
6. Switch the burner mounted Burner On/Off/Reset Switch to the ON position. The 2nd Low
Water and High Pressure Alarm/Reset switches will illuminate and alarms will sound due to the
power restoration interlock, (refer to Section 3.2.3 - Pump Only/Off/Pump & Burner On switch
description).
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