Waste Heat Recovery Units

[mechhou]

Hello:

Do excuse me if this posting does not belong to this particular group. I just chose the one I thought would be the most appropriate.

We are preparing a proposal for a client on Waste Heat Recovery Units (WHRUs - recovering waste heat from gas turbine exhaust to heat up oil running through tubes) on the Gas Turbine Exhaust Stacks. Using dampers and guillotines we need to make the WHRU module 'man-safe' so that the operator can access it while the Gas Turbine is running. How can it be accomplished and is there a standard governing the 'man-safe' requirements? Project is in Australia and USA

 

[rmw]

I can tell you how it is done, but I can't tell you what your local jurisdiction regulatory codes are.

To make it man safe, you can use double guillotines or double bladed guillotines or possible double louver dampers with a fan charging the zone between the damper blades at a higher pressure than the exhaust on the GT side.

If you use louvers, they should be the very low leakage type that is capable of holding the sealing air pressure of the fan above GT exhaust pressure. It is doubtful that that type of damper would be well suited for a GT exhaust environment, so you may be stuck with guillotines. The more I think about it, the less I like louvers in GT exhaust service even though I have seen this done on boilers before. So guillotines it is.

rmw

 

[unclesyd]

rmw,
What do you think about using dampers.

On two installations I've seen dampers use both to isolate and vent the exhaust. These were gear operated dampers. i believe that they were setup to where the exhaust vent had to be opened first. I still trying tot recall if they allowed personnel entry around the heater with the turbine online. I don't' think they did. These were low pressure steam generators.

 

[bhushan76]

You must be having a by-pass stack in your heat recovery system,to help GT running even when your recovery system is down.
In one of the project we had used coupled louver dampers , one at base of by-pass stack and second one before guillotine in main duct.When heat recovery coil bundle was down for maintenance or was not required,by-pass stack louver was open at 100% resulting in coupled louver 100% closed and guillotine closed as well.
There was one more guillotine in main stack (operating in horizontal plane) above the heat recovery bundle,to prevent any leakage of flue gases.
In spite of all above whenever there was man entry the GTG was shut down and there was some minimum cooling period before man entry was allowed.

 

[rmw]

Unclesyd,

The key to man-safe entry is the ability to absolutely guarantee that there can be no leakage from the exhaust gas side to the WHRU. This can be done with dampers, but they would have to be of a high pedigree type, tip seals, blade end seals, etc, and they would have to be able to maintain tight enough closure so that positive pressure (or pressure above the exhaust pressure) can be maintained while men are in the WHRU.

Dampers would work and I have seen and used the types I described above that had the pedigree to do so. However, that said, GT exhausts are typically brutal service environments. Temperatures hover around 1000F, and it is typically a very pulsating or excited area. Things tend to get beat to pieces in GT exhausts. So I fear that a multi-blade damper, no matter how good the pedigree would have a hard time surviving and being available to serve when called on to provide man-safe isolation. The benefit of Guillotines is that they are out of the gas flow until called on to be inserted. They are not subject to the ravages of the environment 24/7.

I would not hesitate, and have used dampers as described above in heaters and boilers, but the exhaust environment was in the 300F to 500F range, and the flow was fairly steady and stable.

rmw