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20 Explanations of Professional Terms for Industrial Steam Turbine
Created on 10.30
A practical guide to steam turbine terminology for plant owners, engineers and procurement teams
Understanding steam turbine terminology makes it easier to evaluate technical proposals, compare equipment and communicate project requirements. Similar-looking specifications can describe different operating conditions or measurement boundaries, which can affect equipment selection and expected performance.
This guide explains 20 common industrial steam turbine terms and their relevance to applications such as palm oil processing, sugar production, pulp and paper, chemicals and biomass power generation.
1. Industrial Steam Turbine
An industrial steam turbine converts energy carried by steam into rotating mechanical power. Its shaft can drive an electrical generator or industrial machinery such as a pump or compressor.
The turbine receives steam from a separate source, typically a boiler or heat recovery system. Fuel is not burned inside the steam turbine itself.
2. Combined Heat and Power — CHP
Combined heat and power, also called cogeneration, produces electricity or mechanical power together with useful heat.
In a steam turbine CHP system, exhaust or extraction steam serves industrial heating processes after generating power. Overall energy utilisation depends on how much of that heat is usefully consumed.
3. Back-Pressure Steam Turbine
A back-pressure turbine discharges steam into a downstream process steam system instead of a vacuum condenser.
Its exhaust pressure is selected to meet heating requirements. Electrical output is therefore closely connected to available steam flow and the required process steam pressure.
4. Condensing Steam Turbine
A condensing turbine exhausts steam into a condenser, normally operating below atmospheric pressure.
This permits further steam expansion for power generation. The configuration requires a condenser, vacuum equipment and a suitable cooling arrangement.
5. Extraction-Condensing Steam Turbine
An extraction-condensing turbine supplies part of its steam to industrial processes at an intermediate pressure. The remaining steam continues expanding toward the condenser.
Controlled extraction can help match process steam requirements, within the turbine’s operating limits. Selection requires a combined assessment of electricity demand, steam demand and cooling conditions.
6. Inlet Steam Pressure
Inlet steam pressure is the pressure at the specified turbine inlet measurement point. It is commonly expressed in MPa or bar.
The pressure available at the turbine may differ from the boiler outlet pressure because of losses through piping, valves and other equipment. A technical enquiry should identify both the pressure value and its measurement location.
7. Inlet Steam Temperature
Inlet steam temperature describes the temperature of steam entering the turbine, normally expressed in °C.
Together with pressure, it determines the inlet steam's thermodynamic state. It also influences material selection, thermal expansion and operating procedures. Customers should provide normal, minimum and maximum operating temperatures where available.
8. Exhaust Steam Pressure
Exhaust steam pressure is the pressure where steam leaves the turbine.
For a back-pressure turbine, it must match the downstream steam system, including relevant piping losses. For a condensing turbine, exhaust pressure is associated with condenser conditions. Performance comparisons must use the same exhaust pressure basis.
9. Steam Mass Flow Rate
Steam mass flow rate is the mass of steam passing through a specified point per unit of time, commonly expressed in t/h or kg/s.
For turbine selection, the steam actually available at the turbine inlet matters more than the boiler’s nameplate capacity. Process consumption, other steam users and changes in production can reduce the available flow.
10. Gauge Pressure and Absolute Pressure
Gauge pressure is measured relative to local atmospheric pressure. Absolute pressure is measured relative to a perfect vacuum.
Their relationship is:
Absolute pressure = Gauge pressure + Local atmospheric pressure
At standard atmospheric pressure, 1.0 MPa(g) is approximately 1.1013 MPa(a). Specifications should clearly identify the pressure basis, especially for exhaust and condenser conditions.
11. Superheated Steam
Superheated steam has a temperature above the saturation temperature corresponding to its pressure.
It is commonly used in steam turbines to provide suitable expansion conditions and help limit moisture formation. The required degree of superheat depends on the turbine design and operating conditions. A pressure value alone cannot define the state of superheated steam; temperature is also required.
12. Steam Quality — Dryness Fraction
For a saturated liquid–vapour mixture, dryness fraction describes the proportion of the total mass present as water vapour.
A dryness fraction of 0.98 means 98% vapour and 2% liquid water by mass. This is a moisture measurement, rather than a measure of chemical purity. Dryness fraction is not normally used to describe superheated steam.
13. Enthalpy Drop
Specific enthalpy, normally expressed in kJ/kg, is a thermodynamic property used in steam energy calculations. Enthalpy drop is the difference between the inlet and outlet specific enthalpies.
This difference is central to calculating turbine power. For a simple turbine without extraction, the steam flow and actual enthalpy drop establish the available power before the relevant mechanical and electrical losses are applied.
14. Isentropic Efficiency
Isentropic efficiency compares actual turbine expansion with an ideal, constant-entropy expansion between the same inlet state and outlet pressure.
It indicates how effectively the turbine converts the ideal expansion opportunity into actual work. It differs from generator efficiency and overall CHP efficiency. Comparisons should use consistent definitions and equivalent operating conditions.
15. Specific Steam Consumption — SSC
Specific steam consumption is the mass of steam required to produce one unit of work or electrical energy, commonly expressed in kg/kWh.
For an electrical-output basis:
SSC = Steam mass flow rate (kg/h) ÷ Electrical power output (kW)
For example, 20,000 kg/h divided by 2,000 kW gives 10 kg/kWh.
A lower value is favourable only when inlet conditions, exhaust pressure, extraction duty, load and output boundaries are comparable.
16. Gross Power Output and Net Power Output
Gross electrical output is the power produced at the generator terminals. Net output deducts the auxiliary consumption included within an agreed system boundary.
These auxiliaries may include pumps, cooling equipment and other operating systems. A quotation should state which loads are deducted so that customers can assess the power available for their factory or grid connection.
17. Rated Speed
Rated speed is the specified rotational speed for rated operation, expressed in revolutions per minute, or rpm.
Turbine speed and generator speed are not necessarily identical. A reduction gearbox can connect a higher-speed turbine to a lower-speed generator. For example, a four-pole synchronous generator operates at 1,500 rpm on a 50 Hz system.
18. Digital Electro-Hydraulic Control — DEH
DEH combines digital control functions with hydraulic actuation to regulate turbine steam valves.
Depending on its configuration, it can support start-up, speed control, load control and steam pressure regulation. Control modes must match the application: an isolated generating system has different requirements from a unit operating in parallel with a large electrical grid.
19. Emergency Trip System — ETS
The emergency trip system initiates rapid turbine shutdown when defined protective conditions occur.
Trip inputs may include overspeed, low lubricating oil pressure or other conditions specified for the machine. The protection design should establish sensor requirements, trip logic and valve actions. Normal governing and protective shutdown have distinct functions and must be coordinated.
20. Turbine Supervisory Instrumentation — TSI
TSI monitors the mechanical condition and behaviour of the turbine.
Depending on the machine, measurements may include shaft vibration, axial position, speed, eccentricity and differential expansion. These measurements support condition assessment, alarms and protective actions. The required instrumentation should be selected for the turbine's size, construction and service requirements.
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Turning Technical Terms into a Clear Project Specification
A reliable turbine proposal starts with consistent information. Before requesting a quotation, confirm:
· Inlet steam pressure, temperature and available flow.
· Required exhaust or extraction conditions.
· Normal operating load and annual operating hours.
· Required electrical output, voltage and frequency.
· Grid-connected or isolated operation.
· Cooling conditions, where applicable.
· Equipment scope and performance measurement boundaries.
These details allow suppliers to assess the complete operating duty and help customers compare proposals on an equivalent basis.
Discuss Your Industrial Steam Turbine Requirements with YTS
YTS provides industrial steam turbine solutions for power generation and combined heat and power applications. Share your steam conditions, process heating requirements and electrical demand with our team to discuss a suitable configuration and clearly defined supply scope.
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