PROJECT: Combined Cycle Power Plant Steam Drain System Improvement Project

This facility was a 147 MW combined cycle generation unit using two gas turbines each with their own Heat Recovery Steam Generators (HRSG's) and one steam turbine/generator unit. At the time of this project, the plant had been recently commissioned within the last two years and was still ironing out some of the left over operational design issues.

The typical loading schedule for the plant was nightly shutdowns with a subsequent restart the following morning. The plant had incorporated many design features for this type of loading schedule. One of these designs was the method by which the high and low pressure main steam piping utilized a drain system to prevent the accumiliation of condensate during the warm up process. This was necessary to prevent the condensate from flashing resulting in potential piping hammering or water induction to the steam turbine.

The plant had a history of compliants registered from the nearby residential neighborhoods resulting from the noise created by the warm up steam releases even though the design of the warm up steam drain system used a flashtank with a very large silencer.

The engineering service was able to conduct a thorough evaluation of the system, used extensive compressible multi-phase steam flow modelling, and redesign the piping, valves, exhaust system sizes, and control logic to completely eliminate all steam drain system noise.

PROJECT: Turbine Gland Steam Controls Upgrade Project

This facility was a 147 MW combined cycle generation unit using two gas turbines each with their own Heat Recovery Steam Generators (HRSG's) and one steam turbine/generator unit. At the time of this project, this plant had been recently commissioned within the last two years and was still ironing out some of the left over operational design issues.

The Mitsubishi 53.6 MW condensing steam turbine was supplied with a pneumatic stand-alone gland steam supply system. At lower loads, the gland steam supply required a stable source of 60 psig, 510F supply steam for providing sufficient sealing steam to the two ends of the steam turbine rotating shaft. This steam was supplied by the "1st Stage Pressure Reduction & Desuperheating Station". At higher loads, the turbine was "self-sealing" and excess pressure was dumped to the steam condenser via a sparger system.

The "2nd Stage Pressure Reduction & Desuperheating Station" design utilized a common pneumatic pressure controller stand-alone system with the attemperation supply valve for the low pressure end of the turbine shaft controlled by the ABB DCS system. This pressure controller controlled both the steam supply and steam dump valves.

The purpose of this project was to diagnose the current causes of instabilities, recommend cost affective upgrade solutions, and conduct the approved modifications. Engineering services found that the primary cause of instabilities was the use of stand-alone controllers. It was common for one steam system to continue supplying steam while another controller was dumping to the condenser. Engineering services designed fully dependant control logic in the ABB DCS and had all necessary process inputs and outputs also transferred to the DCS.