STEJASA - Dampers and Exhaust Bypass Systems

Since 1974, STEJASA has been a leading supplier of dampers and complete bypass systems that are able to operate in the worst working conditions: multilouver, tandem, guillotine, diverter and stack dampers, and expansion joints for CCPP, DESOX and DENOX.

Exhaust bypass systems

Exhaust gas systems are designed according to GT and plant characteristics in simple cycle power plant or combined cycle. A bypass system presents many advantages as power generation during boiler erection or boiler maintenance. Exhaust flow can be controlled with a diverter blade reducing boiler thermal stresses at start-up and emergency shut-down HRSG.

Exhaust gas systems generally include: diffuser, bypass dampers or elbow, stack, silencer, expansion joints, ladders and platforms. Air craft warning lights and emission test ports are supplied optionally. Hot silencer baffles reduce sound emissions according to installation requirements.

Gas distributors

A gas distributor is a T-shaped flanged housing with one gas input and two outputs. It has two blades, one at each gas outlet, with opposing movement. This simultaneous movement of the blades (one opens and the other closes) is achieved with an external linkage system that offers the benefit of flow regulation over diverter damper. The most common method of damper actuation is pneumatic actuation. Electric actuation can be provided on request. Gas distributors can be designed with metal-metal or elastic seal systems according to required tightness (up to 100% with seal air system).

Diverter dampers

STEJASA has designed and manufactured diverter dampers since 1986, offering minimum pressure drop compared with multiple blade dampers. Diverters can be manufactured in modules for easy shipping and field assembly. Seals are mounted around the periphery on both sides of the blade providing a sealing efficiency of 99.95% on the duct sectional area. Material seals are Inconel 625 or similar and designed to absorb gaps between the blade and the contact surface in all conditions.

For 100% sealing efficiency a double seal row shall be fitted. The cavity formed by the seals and the landing bars is pressurised by a small fan in order to provide an effective air barrier, resulting in zero cross blade leakage or 100% tightness. The sizing of the actuator is one of the most critical tasks in the design of a diverter. For any of the solutions used, direct shaft or toggle system drive, the following parameters must be considered: blade weight load, pressure duct loads and blade seal loads.

Guillotine dampers

Generally used in gas turbine installations, the STB blanking plate allows safe access to HRSG. In normal operation the blanking plate is hanging from a supporting structure and blocked by clamps. The plate is inserted by unbolting the flange at the expansion joint which is then compressed to allow the plate to be inserted.

The STR repair guillotine includes a frame, a blade and its support. The frame is suitable for bolting to adjacent ducting and is provided with a removable cover that remains closed when the plate is in or out of the gas stream. Blade actuation can be done by using a manual or electric drive.

The frame of the STS process guillotine is suitable for bolting to adjacent ducting. STS guillotine's bonnet ensures that there is no leakage from the damper to the atmosphere under all conditions. Options for STEJASA guillotine dampers (special cases) include: seal air system for 100% tightness; external or internal insulation; manual and pneumatic actuators.

Multilouver dampers and butterfly dampers

STEJASA designs and supplies fully manufactured butterfly and multilouver dampers for all industrial applications. They can be circular or rectangular. They can be designed with external or internal insulation (ceramic fibre, mineral wool or refractory insulation). Depending on the application's temperature, we can use carbon steels, alloys steels or stainless steels.

Multilouver dampers are equivalent to butterfly dampers but have two or more blades. All accessories and drives are mounted on the casing. Our blade design creates a very low pressure drop and an efficient flow control. Butterfly and multilouver dampers are designed with metal-metal or elastic seal systems. Flatness and strict manufacturing ensures optimal sealing. The actuator can be electric, pneumatic, hydraulic or manual. They can either be on-off or modulating.