Switching or air blowers in a fired heater.

[ris2]

There are two blowers on the fired heater at our facility. To switch the blowers the heater must be shut down and the standby blower then started. The standby blower cannot be started with the online blower in operation. Once the discharge valve on the standby blower is opened the heater trips and the motor of the standby blower usually spins backwards. There are no check valves on the discharge line which is common to both blowers. What design can be done to prevent having to shut down the heater to switch these blowers.

 

[Montemayor]

ris2:

The best and safest way I've designed direct-fired heaters - like crude oil treaters - to switch burners & blowers during production without shutting down or missing a lick, is to design the heater to have two burners, each with its own blower and shut down one burner/blower independently of the other.

This allows for ease of start-up, shut-downs, and also permits dual operation if need be. More importantly for the operations crew, if furnishes real-life standby capacity and spare reliability. I've found that the cost of the additional burner at the outset is of minor incremental cost compared with the ease of operation and controls.

Art Montemayor
Spring, TX

 

[ris2]

Montemayor, do you think that placing a check valve on the discharge line or fabricating an exhaust pipe upstream of the discharge valve of the blowers is possible. I believe that this would elimimnate opening the discharge valve prior to starting because the standby blower could be started even with the other blower in operation.

 

[Montemayor]

ris2:

No.

I would not place any faith on the check valve operating in the manner you desire, 100% of the time. A check valve cannot be relied upon inherently. I guarantee you that the faith you place on a check valve's function will not pass the test during the mandatory HazOp that you have to have (in the USA) prior to installation.

Besides the above, I doubt if you can convince anyone that a check valve will function properly with inches of water pressure as typically occurs within a firebox.

Art Montemayor
Spring, TX

 

[smckennz]

Hi Ris2

whats the problem with starting the standby blower with its discharge valve closed, slowly opening, and slowly closing the duty blower valve? Surge issues?

Cheers

Steve