Why there is no exhaust (duct) back pressure high protection for Frame9E GT (MarkIV control in my case)?

We have also Siemens & Fiat GTs at our plant & they both have this protection. I think that it's a very critical protection.

Our GTs run in combined cycle mode.

 

Different packagers of GE-design heavy duty gas turbines had different philosophies regarding unit protection, and both GE and the packagers also had to accommodate Customer preferences when building a unit. In general, GE-design Frame 9E heavy duty gas turbines can tolerate some exhaust back pressure, though it will reduce power output.

You didn't say if the exhaust runs through an HRSG (Heat Recovery Steam Generator), and if the HRSG has auxiliary duct burners or some kind of ammonia-based SCR (Static Catalytic Recovery), or if the Siemens and Fiat units at the site have the same or different equipment. Leaking gas fuel duct burners or leaking ammonia injection piping, both of which can increase the exhaust duct back pressure, can have catastrophic or disastrous effects on the unit, the least of which is decreasing power output because of increased back pressure. Also, if there is some kind of diverter damper to control or block the flow of exhaust gases into a bypass stack or some other process which could fail or become stuck is another reason for having exhaust duck back pressure protection. There are many; it depends on the application and the Customer's desires and the turbine packager's philosophy regarding machine protection at the time of the sale/installation.

Because, that makes the most difference. When there is a potential for something to cause an increased back pressure on the unit that was usually the governing factor in deciding to use exhaust duct back-pressure protection in that era. Also, in the Mark IV days, sometimes the I/O capacity was limited, and sensors were more expensive (relatively) than they are today.

So, there are a lot of things to consider when trying to compare one machine versus another. I've even seen Customers NOT want exhaust back pressure protection because they want to keep the unit running at all costs.

As has been said here many times before: When the unit is out of warranty, owners and operators are free to do whatever they deem appropriate to protect their turbines. I've seen insurance companies come in and dictate additional protection, also. Just remember to include some operational reliability in any decision to implement any additional trips (redundant sensors; where the sensor(s) is (are) connected; etc.).

 

Thanks CSA for your answer.

I have mentioned in my previous post that all our GTs run in combined cycle mode (they exhaust in a HRSG & HRSG has no auxiliary duct burners or some kind of ammonia-based SCR).

On GE turbines, we have BYpass dampers (BYD) & Boiler inlet dampers (BID) & we have exactly same configuration of power pack system (Hydraulic damper system) at Fiat & Siemens turbines. And also HRSGs on Siemens & GE turbines are almost the same (HRSGs installed at Siemens units have greater mass flow though as compared to GE units). Moreover, HRSGs on Siemens & Fiat Units (& hence back pressure protection) were installed almost two years earlier than GE.

But there is a one difference which I would like to mention. HRSGs on Siemens & Fiat units are installed such that flue gases are entering straight in to HRSG. While on GE units there is a 90 degree angle (maybe not exactly 90 degrees but very much close to it) at which flue gases had to turn before entering HRSG. Could this be reason for no back pressure protection?