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A turbine in which the steam leaving passes into a condenser operating at a pressure below atmospheric.



Related Terms

TURBINE RELIEF VALVE

The turbine casing is fitted with spring-loaded relief valves to prevent damage by excessive steam pressure at the low-pressure end if the exhaust valve is closed accidentally. Some casings on smaller turbines are fitted with a sentinel valve, which serves only to warn the operator of over-pressure of the exhaust end. A spring-loaded relic valve is needed to relieve high pressure.

REACTION TURBINE

A reaction turbine utilizes a jet of steam that flows from a nozzle on the rotor. Actually, the steam is directed into the moving blades by fixed blades designed to expand the steam. The result is a small increase in velocity over that of the moving blades. These blades form a wall of moving nozzles that further expand the steam. The steam flow is partially reversed by the moving blades, producing a reaction on the blades. Since the pressure drop is small across each row of nozzles (blades), the speed is comparatively low. Therefore, more rows of moving blades are needed than in an impulse turbine.

MULTI-PORT GOVERNOR VALVE

In large turbines, a valve controls steam flow to groups of nozzles. The number of open valves controls the number of nozzles in use according to the load. A bar-lift or cam arrangement operated by the governor opens and closes these valves in sequence. Such a device is a multi-port valve. Using nozzles at full steam pressure is more efficient than throttling the steam.

REHEATING CYCLE

In the reheating cycle, superheated steam is expanded in a high-pressure turbine and then returned to the boiler's re-heater to raise the temperature of the steam to the inlet temperature, usually to around 537°C; it is then returned to the turbine to be expanded through intermediate-pressure turbines. In some cases, the steam is again returned for re-heating in the boiler and then expanded in the lower- pressure sections of the turbine. The main purpose of re-heating the steam on large turbo-generators is to avoid condensation in the lower-pressure sections of the turbine, which can rapidly cause blade erosion problems from wet steam.

FLUE GAS EXPANDER

In a petroleum processing system, a turbine for recovering energy at the point where combustion gases are discharged under pressure to the atmosphere; the reduction in pressure drives the turbine impeller.

HELICAL-FLOW TURBINE

A steam turbine in which the steam is directed tangentially and radially inward by nozzles against buckets milled in the wheel rim; the steam flows in a helical path, reentering the buckets one or more times. Also known as tangential helical-flow turbine.

HIGH-PRESSURE BOILER

A boiler in which steam or vapor is generated at a pressure exceeding 15 psig.

BLEEDING CYCLE

A steam cycle in which steam is drawn from the turbine at one or more stages and used to heat the feedwater. Also known as regenerative cycle.

COMBINED CYCLE

Where heat from the exhaust gases of a gas turbine is used to generate steam to drive a steam turbine.

DIFFERENTIAL PIECE-RATE SYSTEM

A wage plan based on a standard task time whereby the worker receives increased or decreased piece rates as his or her production varies from that expected for the standard time. following pressure reduction. differential steam calorimeter

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