Systems and methods for controlling a valve for directing an exhaust gas stream through an exhaust duct having a first after treatment device and a second after treatment device in an exhaust system. The method includes receiving sensor signals from a sensor coupled to the second after treatment device. The method includes processing the sensor signals to determine a temperature of the second after treatment device, and determining a position for the valve based on whether the temperature exceeds a pre-defined threshold for the temperature of the second after treatment device. The method includes outputting a control signal to move the valve to a first position in which the exhaust gas stream flows through a first portion of the first after treatment device or a second position in which the exhaust gas stream flows through a second portion of the first after treatment device based on the temperature.

Embodiments of emission reduction system including various embodiments of an emission filters for a power plant including a gas turbine are disclosed. The system includes: an emission filter; and a retraction system operably coupled to an exhaust passage of the gas turbine. The exhaust passage defines an exhaust path of exhaust from the gas turbine. The retraction system selectively moves the emission filter between a first location within the exhaust path and a second location out of the exhaust path. In a combined cycle power plant, the first location is upstream of a heat recovery steam generator (HRSG). The systems and filters described allow for temporary positioning of emission filter(s) just downstream of a gas turbine exhaust outlet, or upstream of an HRSG, where provided, for emission reduction at low loads or startup conditions, and removal of the emission filter(s) once operations move to higher loads.

A valve unit comprises a valve (7) having a valve shaft (30) with a rotational axis, an actuator (6) for, the actuator having an actuator shaft (20) with a rotational axis, a mechanical coupler (1) for rotational coupling of the actuator shaft (20) and the valve shaft (30), the mechanical coupler (1) comprising a rotational axis (10) coinciding with the rotational axis of the actuator shaft (20) and the rotational axis of the valve shaft (30), a first rotational member (2) coupled to the actuator shaft (20) and a second rotational member (3) coupled to the valve shaft (30), and a bridge element (4), the first and the second rotational members (2, 3) having slots (21, 31) for receiving engagement pins (41) of the bridge element (4). The bridge element (4) has a planar shape extending from the first rotational member (2) to the second rotational member (3), and the planar bridge element (4) has a body (42) and at least two engagement pins (41) projecting from the body (42) at each of two of opposite ends of the body (42) of the planar bridge element (4) in a parallel direction to the rotational axis (10) of the mechanical coupler (1). The engagement pins (41) are engaging with the corresponding slots (21, 31) in the rotational members (2, 3). The planar bridge element (4) comprises at least one through-hole (43) traversing the plane of the body (42) of the planar bridge element (4) extending from the first rotational member (2) to the second rotational member (3).