Purpose of the OT-HRSG is to use the hot exhaust gases from the gas turbine as well as supplementary firing from the duct burner to heat up the boiler feed water and to convert it to saturated steam. The saturated steam is delivered to the steam header, which deliver steam for injection in the oil fields.
The LP feed water is first pre-heated in the HT Blow down cooler after which it can be mixed with recycled and cooled blow down water. The HP boiler feed water pumps discharge the feed water to the boiler.
The exhaust gas flow in the OT-HRSG is horizontal.
OT-HRSG produces steam with exhaust gas from the Gas turbines.
Between gas turbine and the OT-HRSG a diverter damper is installed this enable us to operate turbines in simple cycle mode as well as combined cycle. Also used for a gradual start-up of the OT-HRSG.
OT-HRSG installation receives LP feed water from the MVC units and is fed through a set of HP boiler feed water pumps.
LP feed water is pre-heated by cooling the hot blow down water from the boiler.
Fuel gas from the Gas Pressure Reducing Station is supplied to the duct burners.
Schematic of OT-HRSG
Gas Pressure reducing Station
The GPRS is handling the fuel gas from the SSOGL/Government Gas Line (OGL) for the duct burner. The dusct burner has 12 vertical burner elements.The main function of the station is to reduce the fuel pressure to an acceptable pressure for control by the duct burners.
The fuel gas is heated by a heating unit to prevent plugging problems due to hydrate formation and icing.
A knockout drum is installed to make sure that the fuel gas is clean from debris and condensed liquids.
An automatic level control opens to discharge liquids to a condensate tank.
The flue gas from the turbine passes the evaporator 1 before it enters the duct burner which cools and straightens the flue gas flow profile. The duct burner can be fired up to 1562ºF (850 ºC).
A diverter damper and bypass stack are incorporated in mukhaizna OTSRG combined cycle.
The installation can be converted to simple cycle operation using the diverter damper.
With the exhaust gas diverter damper, it is possible to guide the exhaust gas from the GT to the by-pass stack or to the OT-HRSG. During simple cycle operation (OT_HRSG is out of operation) the GT exhaust is guided via the by-pass stack to the atmosphere.
With the OT-HRSG in operation the exhaust gas from the GT oulet is directed through the heat transfer sections of the OTHRSG, as well as through the duct burner, via the stack to the atmosphere.
Energy to move the diverter is supplied by a hydraulic pump unit (HPU).
During start-up and shutdown, the diverter will be positioned in several intermediate steps for a gradual start-up and shut down.
Expansion Joints ducting
Expansion joints in the dusting are installed to absorb movements of the ductwork as a result of thermal expansion.
Differences in expansion occurs in several situations:
- if the installation warms up during start up the various ducting parts will expand.
- while switching from simple cycle mode to combined mode.
- the wind loads on the stack and boiler cause lateral movements.
There are four expansion joints.
- Between GT diffuser outlet and inlet of the diverter box.
- Between diverter box and bypass stack.
- Between the diverter box and the inlet duct of the HRSG casing.
- Between HRSG outlet duct and the stack.