AFBC BOILER HOT/WARM STARTUP PROCEDURE
In this article we discussed about the AFBC boiler hot startup and cold startup of boiler .in the power sector boiler may be tripped due to lots of resins like plant black out (grid supply goes ), any pump , fan , drive , tube punctured or other electrically or mechanically issues . After these condition we recovered the boiler his original running condition, these conditions are depending upon the time period of abnormality and his recovery time. And also depending upon the bed temperature so this condition may be explained in the terms of HOT / WARM boiler startup. These terms are explained in this article briefly. the starting procedure for different types of boilers is different . In this article proper care has been taken to cover starting procedure hot/warm of the boiler. Boiler operation manual supplied by boiler manufacturer may be most helpful. Boiler operator is required to familiar with boiler system he should have idea about safe operating limits or different parameters during startup of the boiler.
HOT START UP AFBC BOILER
When the boiler is restarted after a short duration of outage, it is called as hot startup in this condition boiler is already in pressurized condition and hot condition.
In hot startup condition the average bed temperature should be 760°C or above the auto ignition temperature of fuel being fired. After boiler tripping boiler can be started directly with solid fuel feeding. However, a fuel feeding at lower bed temperature is permitted, provided the temperature has been verified through test or actual experience as being capable of igniting the fuel. In no case solid fuel is allowed to introduce when average bed temperature is less than 500˙C. in that condition it’s a chance of overfeeding or it may be furnace get jammed.
“Windbox needs to be purged with steam as per the Windbox steam purging procedure”. However air purging is not required if average bed temperature is 760˙C.”
Following steps should be followed to bring back the boiler into service during hot startup:
- After completion of wind box steam purging, normalize the Dampers in air and gas circuit. Maintain the sufficient air flow according to the fuel feeding condition.
- Normalize the drum level it disturbed during the boiler tripping; insure that drum level should be maintain 50%.
- Bring back the entire Fan and fuel feeder drives to the minimum speed setting before starting insures that the all drivers are healthy from electrical side.
- Start the ID Fan, PA Fan and SA fan as per fan start-up sequence described in boiler cold start up procedure .Ensure minimum 30% air flow and maintained draft.
- Open the start up vent valve; ensure that minimum 20% MCR steam flow beacuse of maintain the flow through superheaters.
- Adjust the PA Air to wind box to start bed fluidization, ensure the air flow through windbox is above purge air flow requirement.
- Start the fuel feeders.
- Gradually increase the fuel and airflow, observing the rise in bed temperature.
- Adjust the fuel feeding and airflow to raise the boiler pressure to the rated pressure as per pressurization curve.
10 . Charge the main steam line as per the line charging procedure. Load the boiler as per loading procedure
WARM START UP OF AFBC BOILER
Warm startup of boiler is carried out when the boiler is stopped due to any fault it’s from electrical side or mechanical side but fault seems to restore in short interval of time then boiler operator hot box up the boiler for maintaining the bed temperature . When the fault is restored after that we can startup the boiler according the hot startup procedure. this type of startup is called the warm startup of the boiler .for warm startup of boiler following conditions are should be full filled . Average Bed Temperature of boiler should be < 760°C or below auto ignition temperature of fuel being fired or Average Bed Temperature 200°C After boiler tripping, if average bed temperature is < 760˙C or below the auto ignition temperature of Fuel being fired, boiler can not be started directly with solid fuel feeding.
“Windbox needs to be purged with steam as per the Winbox steam purging procedure”. Apart from steam purging, air purging also need to be carried out as per “Air Purging Procedure”.
>Following sequence may be followed to bring back the boiler into service:-
- After completion of wind box steam purging, normalize the Dampers in air and gas circuit.
- Start the ID Fan, PA Fan and SA fan as per fan start-up sequence described in boiler cold start up procedure. Ensure minimum 30% air flow and maintained draft.
- Carry out furnace air purge as per air purging procedure. Normalize the Dampers in air and gas circuit.
- Normalize the drum level. it disturbed during the boiler tripping, insure that drum level should be maintain 50%.
- Open the start up vent valve. Because of maintain the flow through superheaters.
- Start the over bed burner as burner start up procedure.
- Adjust the fuel feeding and airflow to raise the bed temperature.
- Once the required bed temperature is attained, initiate the solid fuel firing as per the procedure.
- Raise the boiler pressure as per start up curve.
- Whenever the boiler rated pressure is attained, charge the main steam line as per the line charging procedure. Load the boiler as per loading procedure with help of main steam stop valve may be opened and start up vent may be closed.
Whenever boiler tripped in power plant due to any resin its may be electrically or mechanically tripped boiler may be get back in his original running condition but before starting the boiler it should be know about the condition of boiler it is in cold startup condition or hot/warm startup condition , and also know about the tripping condition and his recovery time .when boiler axillaries power is restored then we insured light up condition of boiler through manually walk down check of boiler then start up the boiler according to the manufacturer guideline .
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