Most gas turbine air pollution control equipment is designed to operate with an even velocity profile in the exhaust gas stream so that the contact between gas and catalyst or scrubbing agent is maximized. In practice, however, the velocity profile is often mal-distributed, usually because of the complex ducting rapidly expanding the gas stream into the Heat Recovery Steam Generator and catalysts for CO and NOx reduction. Inlet conditioning is often required to adjust temperature distributions--cooling for improved efficiency or heating to avoid icing problems. When there is complicated ducting, velocity distributions can be a problem for gas turbine inlets, as well.
Alden’s Gas Flow Systems Engineering team has grown out of the Acentech DynaFlow business, which Alden purchased in 2001. The group has guided utilities and engineering firms in optimizing the fluid dynamics associated with air pollution control systems for gas-fired, oil-fired, and coal-fired units. Much of this consulting work has employed physical and numerical modeling of the systems, including multiphase fluid dynamics.
Typical gas turbine exhaust optimization projects involve the use of CFD (Computational Fluid Dynamics) and/or scaled physical flow modeling to address the challenges listed above. Cooling air lance, mixer, AIG, silencer, and inlet ducting geometry are usually included explicitly, while perforated plates and catalyst modules are generally modeled as momentum sinks in CFD, and with a flow resistance device in physical models. Heat exchangers can be modeled either explicitly, or as a combined heat and momentum sink.
Chemistry, temperature, and velocity contours are reported from the models at selected planes, and pressure drops are indicated. Modifications for improved performance are suggested and simulated. Optimizing performance through modeling in this manner saves countless hours and dollars by avoiding problems after construction.
