STEAM TURBINES

ANDAPPLICATIONS

One of the most versatile and oldest prime mover technologies in application for about 100 years

Steam utilised earlier to drive Reciprocating Steam Engines used as prime movers

Steam Turbines replaced Reciprocating Steam Engines due to inherent technical and economical advantages

Steam Turbines – Versatile Rotating Equipment

Industries, wherein large quantity of steam generated at high pressure and temperature and utilised for various process applications at 2-3 lower different pressures and temperatures by directly reducing these parameters through “Pressure reducing and de-superheating stations (PRDS)” or “De-superheating station”, i.e. pharmaceutical units with chilling plants, etc.

Industries having Heat:Power ratio greater than 3:1 depending on consumption pattern of electrical energy and steam, i.e. paper manufacturing units.

Industries wherein the waste heat energy generated during chemical process available in good quantum to generate high grade steam through waste heat recovery boiler utilising the waste heat, i.e. furnaces, sulphuric acid plants, incinerators, etc.

Feasibility of Steam Turbines for enhancement of Resource Utilisation Effectiveness in Industries

Efficiency of Typical Steam Distribution System

FUEL INPUT 100%

BOILER

BOILER LOSSES 15%

BOILER LOSSES 15% FOR STEAM GENERATION LOSSES 17.5% FOR 35% HP STEAM DRAWL FOR PROCESS THRO PRDS OVERALL THERMAL EFFICIENCY OF STEAM SYSTEM 67.5%

PRDS

BOILER EFFICIENCY

85% HP STEAM

100%

HP STEAM 35%

PRDS LOSSES

50%

LP STEAM TO PROCESS 35%

HP STEAM DIRECTLY UTILISED 65%

Efficiency of Typical Steam Distribution System with Steam Turbine

FUEL INPUT 100%

BOILER

BOILER LOSSES 15%

BOILER LOSSES 15% FOR STEAM GENERATION LOSSES 7.5% FOR 35% HP STEAM DRAWL FOR PROCESS THRO BACK-PRESSURE TURBINE OVERALL THERMAL EFFICIENCY OF STEAM SYSTEM 77.5%

ELECTRIC POWER

BOILER EFFICIENCY

85% HP STEAM

100%

HP STEAM 35% TO

BACK PRESSURE

STEAM TURBINE

TURBINE LOSSES 20%

LP STEAM TO PROCESS 35%

HP STEAM DIRECTLY UTILISED 65%

Typical Waste Heat Recovery from Process and Use for Steam Turbine

ELECTRIC POWER

HP STEAM TO CONDENSING

STEAM TURBINE

LP STEAM TO CONDENSER

CHEMCIAL PROCESS/ REACTION

PROCESS RAW

MATERIAL INPUT

WASTE HEAT

RECOVERY BOILER

HIGH TEMP GASES FROM

PROCESS

Back-pressure steam turbines

Extraction-cum-back-pressure steam turbines Single Extraction-cum-back-pressure steam

turbines Double Extraction-cum-back-pressure steam

turbines

Extraction-cum-condensing back-pressure steam turbines

Single Extraction-cum-condensing steam turbines

Double Extraction-cum-condensing steam turbines

Straight condensing steam turbines

Types of Steam Turbines

Steam Turbine Technology

• ab - feed water supplied to boiler at medium to high pressure – some heat added• bc – feed water heated in boiler to boiling temp corresponding to pressure, then converted into steam, superheated steam – heat added • cd - isentropic expansion of pressurized steam in steam turbine to lower pressure – heat utilised in turbine for work like power generation • da – steam finally exhausted either to condenser at vacuum conditions in condensing steam turbines – heat rejected from exhaust steam in condenser steam supplied at intermediate temperature/pressure to steam distribution system to deliver to industrial or commercial application in extraction/back pressure turbines - heat utilised in process

a d

cb

S

T

T1

T2

Sim ple Rankine CycleTem perature Entro py Diagram

Back-pressure Steam Turbine Cycle

Entire quantity of steam injected into steam turbine exhausted at parameters as required by process

Enthalpy difference between inlet and outlet steam utilised for power generation through a generator coupled with the turbine

No wastage of energy contained by steam as no direct condensation of high pressure, high temperature steam

Due to optimum utilisation of energy, highest system efficiency achieved among all types of Cogeneration systems

Back-pressure Steam Turbines -Merits and Demerits

Merits of back-pressure steam turbine system Simple configuration with few components Avoidance of the costs of expensive low pressure stages of the

turbine Low capital investment for steam turbine No need of cooling water for steam condensing, and less

cooling water requirement only for lube-oil cooling system Very high system thermal efficiency because of no heat

rejection through a condenser

Demerits of back-pressure steam turbine system Size of turbine larger for the same power output because of its

operation under comparatively lower enthalpy difference of steam

Dependence of steam mass flow rate through turbine on the thermal load, consequently power generated by steam put into turbine controlled by thermal load resulting into little or no flexibility in directly matching electrical output to electrical load

Need of grid connection for purchasing electricity to meet short-fall in electricity generation as mentioned above

Extraction-cum-Condensing Steam Turbine Cycle

Part of total high pressure steam injected into steam turbine drawn out by extraction at parameters as required by process

One or two extractions with condensing or one or two extractions with back pressure feature possible if steam required at two different levels

Efficiency lower than back pressure turbine in extraction-cum-condensing mode due to condensation of part steam

Efficiency marginally lower than back pressure turbine in extraction-cum-back pressure mode due to steam taken out from turbine at higher pressure and temperature levels

Extraction-cum-Condensing Steam Turbines – Merits and Demerits

Merits of extraction-cum condensing steam turbine system Possible to meet variable electric power and heat load by

regulating the extraction steam from the turbine No need of maintaining grid connection for purchasing

electricity, or minimum gird support to meet unforeseen eventuality in the CPP

Demerits of extraction-cum-condensing steam turbine system Configuration not as simple as that of back-pressure steam

turbine Lower system thermal efficiency due to heat rejection in part

steam condensing Higher capital investment for steam turbine due to condensing

stage More requirement of cooling water for circulating in the

steam condenser Dependence of steam mass flow rate through turbine on the

thermal load, consequently power generated by steam put into turbine controlled by thermal load resulting into little or no flexibility in directly matching electrical output to electrical load

Feasibility of Steam Turbine and Performance IndicesFor industry with steam supply from stand alone boiler for utilisation at different operating parameters

Determination of existing steam generation & distribution system

Heat losses in = Steam flow, kg/hr x (Enthalpy, kJ/kg – Enthalpy, kJ/kgPRDS, kJ/hr at inlet at outlet)

Losses in utilisation = Steam flow, kg/hr x Heat content in steam at end of process, kJ/kgTotal heat input to boiler, kJ/hr = Fuel flow rate, kg/hr x Gross calorific value, kJ/kg Boiler losses to be determined as already discussed separately

%boiler toinput heat Total

losses) system SteamlossesBoiler (boiler toinput heat Totalefficiency Thermal

steam of kJ/kg kg/hr genetared, Steam

kJ/hr boiler, toinput heat Total generation steamfor of RateHeat

Feasibility of Steam Turbine and Performance IndicesFor industry with steam supply from stand alone boiler for utilisation at different operating parameters

Determination of power generation potential from Steam Turbine

kW 4.19

kJ/kg outlet),at Enthalpy -inlet at (Enthalpy kg/hrx flow Steam generationPower

Overall Cogen Efficiency after introducing Steam Turbine

%boiler toinput heat Total

utilised steam ofheat Net kJ/hr generated,power Electricefficiency cogen Overall

Convert electric energy from kWh to kJ/hr by applying conversion factor 1kWh = 3600 kJ

Overall Cogen Heat Rate after introducing Steam Turbine

kJ/kWh kWh output,power Electrical

gen. steamfor required would Fuel-kJ/hr boiler, toheat Total RateHeat Cogen

Fuel would required – Fuel deemed to be required for process steam for steam gen. assuming the same boiler efficiency

kJ/kWhkWh generated,Power

kJ/kg) outlet,at Enthalpy kJ/kg inet,at (Enthalpy x kg input, SteamASR

kJ/kWh rate, steam lTheoreticakJ/kWh rate, steam Actual

Efficiency Turbine

Actual Steam Rate [ASR] : Quantity of heat energy required to generate one kWh of electric energy

Theoretical Steam Rate : Theoretical quantity of heat [TSR] energy required to generate one kWh of electric energy [Enthalpy to be taken from Mollier Charts for calculating TSR]

Determination of Steam Turbine Efficiency

kJ/kg turbine, in dropEnthaly kg/hr x input, Steamheat] to[Convert 4.19 x kWh generated,Power

Efficiency Electrical

Feasibility of Steam Turbine and Performance Indices

Steam Turbine Performance

Efficiency of steam turbine ∞ Steam pressure drop through the turbine

means - greater steam pressure drop across turbine result

into more power output reduction in steam turbine exhaust steam pressure

result into more power generation than an increase in pressure of steam at turbine inlet

specific steam consumption depend on the absolute pressure ratio of the turbine

Feasibility of Steam Turbine and Performance IndicesFor industry with potential of steam generation from Process Waste Heat

Determination of steam generation potential from WHRB

Steam flow from WHRB )h(h

)t(txCxWW

1112

ppepegs

Ws = steam rate, kg/secWeg = exhaust gas flow rate, kg/secCp = ave. value of specific heat of exhaust gas, kJ/kg0Cte = exhaust gas temperature, 0Ctpp = pinch point temperature, 0C (manufacturer’s data)h11 = feed water enthalpy at boiler drum inlet, kJ/kg h12 = steam enthalpy at boiler drum outlet, kJ/kg

Comparison of Steam Turbine Performance

Type ofSteam

Turbine

Power:Heat Ratio

TypicalElectrical Efficiency

Typical OverallThermal

Efficiency

Remarks

CondensingSteam Turbine

Notapplicable

Maximum 15 – 40% • Best for only power generation applications, suitable for combined cycle plants with GT

• Not suitable for CHP application• Power output sensitive to

ambient conditions

Back-pressureSteam Turbine

1:3to

1:10

7 – 20% 70 – 85% • Best option for industrial cogen applications

• Reduction in thermal energy demand reduce power output

Extraction-cum-CondensingSteam Turbine

1:3to1:8

10 – 25% 50 – 75% • Better option for industrial cogen applications

• Excellent operating flexibility with regulated extraction

Extraction-cum-Back-pressureSteam Turbine

1:3to1:8

10 – 20% 60 – 80% • Best option for industrial cogen applications

• Moderate operating flexibility• Reduction in thermal energy

demand reduce power output

Optimising Steam Turbine Performance at Operating Stage Best operational mode Power or heat operated - Depending on total power load of

industry, number of steam turbines to be arranged on one line so that one or more steam turbines available for service according to demand of power

Running of turbine close to its optimal operating range possible with such philosophy of operation

Steam conditions Input steam conditions to be fixed between 30 - 70 bar and live

steam temperature to be fixed between 400 – 500 0C to obtain desired steam turbine performance in case of 1 to 10 MW decentralised cogeneration power plants of low and medium output

Steam quality Maintaining of steam quality injected into a steam turbine as per

specified parameters extremely vital for performance of steam turbine

Quality of DM water and boiler feed water sent to boiler - determining factor for quality of steam generated by boiler and sent to steam turbine

On-line monitoring of steam conductivity a must as a part of instrumentation to get the data for any impurity going to steam turbine

Analysis of steam and water samples separately at least once in eight hours to ascertain the quality

Optimising Steam Turbine Performance at Operating Stage with Control and Monitoring Control for Steam Turbines Throttle valve to be installed in front of the steam turbine

to control pressure of steam flowing from steam line to individual turbine as well as output from each one

Nozzle group control may be provided in individual turbine to permit individual nozzles before first blade wheel (control wheel) to switch in or off to control mass flow rate of other stages as well as to regulate output

Monitoring for Steam Turbines Continuous of on-line monitoring of following parameters

extremely vital to avoid fall in steam turbine performance – Conductivity of steam to ensure silica content in steam,

turbine output adversely affected by silica deposits on blades

– Axial differential expansion, eccentricity, vibrations, etc. providing suitable microprocessor based instrumentation.

– Pressure and temperature of lube-oil circulation in bearings along with continuous cleaning of lube-oil through centrifuge

Optimising Steam Turbine Performance with Preventive Maintenance

Yearly Preventive Maintenance Program Inspection of steam turbines and steam pipelines to be

carried out at least once a year for observing irregularities Checking of turbine bearings during yearly maintenance Cleaning of steam pipeline from boiler up to turbine inlet

along with boiler Checking various control valve settings and calibrating as

recommended Calibration of various local gauges, electronic and

microprocessor instruments, on-line monitoring systems for accuracy

Testing of turbine protections by simulating possible fault conditions after maintenance

Five Yearly Preventive Maintenance Program Thorough inspection by dismantling casing, lifting nozzles,

rotors, bearings, etc. and complete overhauling to be resorted to every 5 years calling Service Personnel from the turbine manufacturers

Why Steam Turbine?

Higher electrical efficiencies in power generation applications Wide array of designs and complexity to match the desired

application and/or performance specifications Lower costs capital and maintenance costs Better reliability and availability, life extremely long with

proper operation and maintenance Low maintenance costs, major overhaul after longer service Capacities available for power generation from 50 kW to

several hundred MW Suitability for combined heat and power applications Better suitability as prime movers for pumps, compressors Suitability for wide range of Power:Heat ratio Separation of functions enabling Steam Turbine system to

operate with enormous variety of fuels to be fired in the Boiler for high pressure steam generation

Fossil Fuels Natural gas, Coal, Lignite, Fuel oil, LSHS, Residual fuel oil Bio-waste Fuels Bagasse (waste from crushed sugar cane)

Rice husk (waste from rice mills), Bio-gas, Municipal waste, Wood waste

Versatile Technology for Cogeneration Applications

Electrical energy generated normally as byproduct of heat (steam) generation in Steam Turbine based cogeneration system

Energy transfer from the Boiler to Steam Turbine through high pressure steam utilised first to rotate Steam Turbine and Generator, and then supplied to process

Steam at lower pressure extracted from steam turbines used directly or converted to other forms of thermal energy in process and CHP applications

Designed to match steam parameters as required by process along with optimum electrical efficiency while providing desired thermal energy output, even feasible to supply steam at different levels

Tailor made designs available to suit specific cogeneration applications

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