Performance Management Of Boiler, Turbine , Cycle#l4

Performance management of Boiler, Turbine , Cycle Efficiency and other performance Parameters.

Goal: To generate electricity from heat input!!!

Carnot Power Cycle

Carnot Power Cycle

Practical Problems Associated with A Carnot Cycle • Maximum temperature limitation for a cycle. • Quality of steam at later stages of expansion in a turbine or engine. • Feasibility of Compression of wet steam.

The Rankine Cycle: An Alternate Ideal Thermodynamic Model

Ideal Rankine Cycle

How about a modified cycle - A Rankine cycle • To avoid transporting and compressing two-phase fluid, try to condense all fluid exiting from the turbine into saturated liquid before compressed it by a pump. • when the saturated vapor enters the turbine, its temperature and pressure decrease and liquid droplets will form by condensation. • These droplets can produce significant damages to the turbine blades due to corrosion and impact. • One possible solution: superheating the vapor. • It can also increase the thermal efficiency of the cycle.

Equivalent Carnot Model of Rankine Model

Tm,in

Tm,out

smin

smax

REMARKS ON STEAM RANKINE CYCLE In fossil -power plants, an increase in thermodynamic efficiency of 0.1% can be worth crores of rupees per year. There is a continued quest for higher efficiencies in thermal power plants, which has resulted in some innovative modifications to the basic steam-power cycle . Among these, there is the regenerative cycle, where the temperature of feedwater is raised from that on leaving the condenser to the final feedwater temperature using steam extracted from various stages of the turbines. The determination of the optimal fraction of mass flow rate to be extracted from each stage of the turbines is a complex optimization problem. In the regenerative cycle, a fraction of the steam that could have been used to produce work in the turbine is used to heat the feedwater instead. There is a gain of efficiency by one side, there is loss by the other.

Efficiency in Power Generation • Efficiency = Output/ Input = (Input – losses)/ Input.

• Types of losses • Exit heat loss • Radiation loss • Condenser loss • Auxiliary power loss.

Efficiency in Power Generation How to minimise the losses? • Heat exchanger • Insulation • Vacuum • Efficient auxiliaries and optimization.

Energy Conservation Why? • Mother earth has limited resources. • Energy production leads to environmental degradation.

Energy Conservation How? • Changing attitude and practices. • Creating awareness. • Optimisation. • Using energy efficient devices.

NEED • Almost Rs. 4.00 Crore Per MW • Cost Savings • Resource Saving • Life of Plant

Concepts • Cycle Efficiency is the efficiency of whole cycle and can be improved by particular set of steam condition employed • Turbine Efficiency is the efficiency of turbo alternator converting the available energy in the cycle into electrical energy. • Boiler Efficiency is effectiveness of combustion and heat transfer • Auxiliary Power efficiency depends on the ratio of Electricity sent out to Electricity Produced.

Requirement of Boiler • Should be able to produce at required parameters over • Compatible with feed water conditions which changes with turbine loads • Capable of following changes in demand for steam without excessive pressure swing • Reliable

BOILER SYSTEM • Feed Water System Makeup Water System Condensate System • Steam System • Fuel System

DPNL SHTR

Platen SHTR

Drum

Reheater S C R E E n Gooseneck

LTSH

Chimney

Downcomer waterwall

Fireball

Economiser

ID fan

APH Bottom Ash

ESP

210 MW Boiler: Water and Steam Circuit

LTSH

Final SH. Platen SH. 500-540C

330-375C

375C-425C Economizer Water Wall 240-310C 310C

FOCUS • Assess Boiler Efficiency by Direct and Indirect Method • Calculate and Optimize Boiler Blow Down Identify and Implement energy efficiency measures

Direct Method Where energy gain of the working fluid (Water & Steam) is compared with the energy content of the boiler fuel. Heat Output Boiler Efficiency=

X 100 Heat Input

Q x ( h g – hf ) Boiler Efficiency (ή )=

X100 q x GCV

Q : Qty of Stm generated in Kg/Hr q : Qty of Fuel Used in Kg/Hr hg: Enthalpy of Saturated Stm in KCal/Kg of Stm hf: Enthalpy of Feed Water KCal/Kg of Water GCV: Gross calorific Value of Fuel in Kcal/KG of Fuel

Advantages of Direct Method • Evaluation is quick • Requires Few parameters for Computation • Needs Few Instrument for monitoring

Disadvantages of Direct Method • No Clue to the operator • Does not calculate various losses accountable for low efficiency

Indirect Method • The efficiency is the difference between the losses and the energy input. • Loss Method • Boiler Efficiency (ή )= 100% - Losses

Types of Losses • Loss of Heat due to • Loss of Heat due to and combustion air • Loss of Heat due to Hydrogen • Loss of Heat due to • Loss of Heat due to

Dry Flue gases Moisture in Fuel Combustion of Radiation Unburnt

Data Required • Ultimate Analysis of Fuel i.e. H2, O2, S, C, Moisture & Ash Content • %age of O2 or CO2 in Flue Gas • Flue Gas Temperature • Ambient Temperature • Humidity of Air • GCV of Fuel • Percentage of Combustibles in ash • GCV of ash

Dry Flue gas Losses • Excess Air • Air Heater gas Outlet temperature

Air Heater gas Outlet temperature • Lack of Soot Blowing • Deposits on Boiler Heat Transfer Surface • High Excess Air (Causes less heat generation in Furnace and more in SH) • Higher Elevation burners in service at low load • Defective baffles and bypass dampers, causing gas short circuiting • Improper Combustion • Poor Milling Plant Performance • Air recirculation

Wet Flue Gas Loss • Moisture in Fuel • Moisture in Combustion • Moisture in Air

Carbon in Ash Loss • High Carbon in Ash • Low Carbon in Ash

High Carbon in Ash • Coarse Grinding • Mal adjustment of flame • Unequal loading of different Mills • Incorrect PA air temperature

Low Carbon in Ash • Exhauster speed too low • Mill Adjustment • Rich Fuel / Air Mixture • Separator ( Classifier) speed too high

Boiler Blow Down • Lower Pretreatment Cost • Less make up water consumption • Reduce maintenance downtime • Increased Boiler life • Lower consumption of treatment chemicals

BLOW DOWN CALCULATION Feed Water TDS x % Make up water Blow Down(%)= Max. Permissible TDS in Boiler Water TDS: Total Dissolved Solids Blow Down Rate = Boiler Evaporation rate X Blow Down(%)

Energy Efficiency Opportunity • Stack Temperature • Feed Water Preheating using Economiser • Combustion Air Preheat • Incomplete Combustion • Excess Air Control • Radiation and Convection Heat Losses

Energy Efficiency Opportunity …….Contd.

• Reduction in Scaling and Soot Losses • VFDs for Fans, Blowers and Pumps • Proper Boiler Scheduling • Milling plant performance • ESP performance

SIMPLE RANKINE CYCLE • LOW INITIAL COST

HEAT GAIN IN THE BOILER

• LOW CYCLE EFFICIENCY • HIGH MOISTURE AT TURBINE OUTLET • LIMITATION ON MAXIMUM PRESSURE BFP

• LIMITATION ON CONDENSER PRESSURE

MODIFIED RANKINE CYCLE • HIGHER CYCLE EFFICIENCY • LOW MOISTURE AT TURBINE OUTLET (LP TURBINE DESIGN EASIER) • NO LIMITATION ON MAXIMUM PRESSURE • NO LIMITATION ON CONDENSER PRESSURE • HIGHER INITIAL COST

 FOR 200 MW UNITS •

INITIAL STEAM PR- 150 Kg/Sq. CM (abs.)

•

INITIAL STEAM TEMPERATURE - 537 Deg C

•

REHEAT STEAM TEMPERATURE - 537 Deg C



FOR 500 MW UNITS (SUB CRITICAL UNITS)

•

INITIAL STEAM PR- 170 Kg/Sq. CM (abs.)

•

INITIAL STEAM TEMPERATURE - 537 Deg C

•

REHEAT STEAM TEMPERATURE - 537 Deg C

 FOR 660 MW UNITS (SUPER CRITICAL UNITS) •

INITIAL STEAM PR- 246 Kg/Sq. CM (abs.)

•

INITIAL STEAM TEMPERATURE - 537 Deg C

•

REHEAT STEAM TEMPERATURE - 565 Deg C

• IMPULSE TURBINES

• REACTION TURBINES

Turbine Efficiency output Efficiency =

Kwh =

Input Input 1 Kwh = 3600 K J output Efficiency = x 100 % Heat Input

Turbine Efficiency Contd.

……

Heat rate: 210MW LMW Turbine= 2040 K Cal/kWh ή = 42.15% 500 MW = 7940 K Cal/kWh ή = 45.3%

Degree of Reaction (R) Enthalpy Drop in Moving Blade R= Enthalpy Drop in Stages

Factors Affecting Operation  Effect of Load  Throttle Governing  Nozzle Governing  Overload (By Pass) Governing

Terminal Conditions  Effects of Vacuum  Effects of MS and RH Temperature  Effects of MS and RH Pressure  Pressure Drop through Reheaters

Effect of Heater Efficiency Gland Wear Feed Pump Power

Turbine Losses  Internal  Friction in Nozzle, Blades & Disc  Diaphragm gland and blade tip leakage  Partial Admission  Wetness  Exhaust

 External  Shaft Gland Leakage  Journal and Thrust Bearing  Governor and Oil Pump

Condenser Performance • Back Pressure » CW Pumping Power »Leaving Loss »Reduced Condensed Temperature/ Increased Blade steam »Wetness of Steam

Energy Saving Opportunities in Steam System • Monitoring Steam Traps • Avoiding Steam Leakages • Providing Dry Steam for Processes • Utilising Steam at the lowest Acceptable Pressure for the process • Proper Utilisation of Directly Injected Steam

Energy Saving Opportunities in Steam System ……. Contd • Minimizing Heat Transfer Barriers • Proper Air Venting • Condensate Recovery » Financial Reasons » Effluent Restriction » Maximizing Boiler output » Boiler Feed Quality

• Insulation of Steam Pipelines and Hot Process Equipments • Flash Steam Recovery

Control & Instrumentation • Data Acquisition System

• Distributed Digital Control Monitoring Information System

Functions • Data Acquisitions • Data Monitoring and Status Reporting • Alarm Monitoring & Status Reporting • SOE Recording • Mimics and Guidance's • Long Term data storage Retrieval and Statistical Analysis

Functions

…….. Contd.

• Better Human Machine Interface • Online Performance Monitoring • Report Generation • Pre and Post Trip Analysis

Factors for Unit Performance • Planned maintenance loss • Thermal Efficiency factors • Plant Load Factor • Forced Outages • Plant Availability Factor

• Availability and Efficiency has a direct relationship • Higher availability leads to higher efficiency • Efficient Unit leads to better availability due to better combustion control conditions, better fluid dynamic condition and better heat transfer condition

Conclusion • Performance Improvement

• Efficiency Improvement

• Effective Capacity Utilisation • Investment Cost • Lower Cost of Generation

• Lower Cost of Generation • Saving in Resources • Increased Life of Plant

INDIAN POWER SECTOR COAL : GAS : OIL : HYDRO: NUCLEAR: RENEWABLE TOTAL

69450 13582 1202 34110 3900 6191 128435

COST IMPLICATION •69450* 0.73= 50698.5 MW •18751.5 MW •Rs. 75006 Crore

Classification • Impulse • Impulse – Reaction

• • • •

Simple Impulse Velocity Compounded Pressure Compounded Pressure- Velocity Compounded

NOZZLE • All turbine have nozzles in which the pressure of the steam is reduced and the velocity increased. • In Impulse Turbine the nozzles are stationary which is stationary Blade. • In Impulse-Reaction turbine both the fixed and moving blades are nozzles.