Dampers and expansion joints in any duct system often get very little credit for the work they do, but they are important behind-the-scenes players in making sure power and industrial processes operate efficiently and safely.
Expansion joints come in a variety of materials… for instance they can be a bellows type where they are formed from a single piece of metal and allow movement of the ducting. They tend to be expensive and are used for very specialized applications such as in high-pressure conditions.
Non-metallic expansion joints on the other hand are made with single or multiple layers of engineered fabrics such as EPDM, VITON or PTFE coated cloths to isolate ducting from vibrational equipment and allow for movement of the duct as expansion and contraction occurs due to changes in temperature.
There is a science and an art to designing expansion joints for each individual application. Depending upon the corrosive and/or erosive gases and temperatures a selection of material and the layers must be made in order to give the expansion joint a suitably long life under very demanding conditions. These include high heat, wide swings in temperature, and erosion and corrosive gases, all while staying within the budget allowed.
Dampers on the other hand allow control of the gas for stream within the ductwork. There are a wide variety of dampers and each one has their own special niche.
For instance, in a simple cycle power generation system one will see a tail-end expansion joint on the back of the gas turbine. This expansion joint must be designed to take the high heat and erosive nature of the hot gas exiting the turbine. Additionally, one might see a stack damper at the exit of the stack.
If at some point in the future there is a decision to go from simple cycle to combined cycle, then a diverter damper would have to be added.
A diverter damper in a combined cycle power station is a complex piece of equipment designed to divert the flow from the heat recovery steam generator (HRSG) to the stack or back from the stack to the HRSG.
Tremendous forces from the exiting gas turbine impinge upon the diverter damper. This is an extremely demanding application for a damper and it must be designed to be able to seal tightly as well as move under the high heat conditions and stresses imposed by the exiting gas turbine exhaust.
Some combined cycle power stations require the diverter to be able to move while the gas turbine is operating to allow modulation going into the HRSG. This adds another level of complexity to the controls and to the design of the diverter.
Diverter dampers are one of many dampers that are supplied to the industrial and power sector. We will continue with our next article talking about some of the others such as butterfly and knife gate dampers.