Energy & Power Generation Consulting,
Engineering & Management Services

1-888-705-0072

equipment

53.6 MW condensing steam turbine @ used within a combined cycle unit process


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.

RESULTS


• Completed a thorough evaluation of the equipment, piping, control logic, and operational process, of the turbine steam gland system. Detemined the causes of instabilities and provided formal recommendations for correcting.