What is heat rate?

 

In general heat rate is defined as ratio of heat input to power output in a system, in other way requirement of heat energy to generate one unit of power.

In case of power plant cycle , output is electrical power and input is any kind of energy in fuel .If we consider steam turbine heat rate , input energy to turbine is in the form of steam energy i.e enthalpy corresponds to pressure and temperature. Different cases for steam turbine are considered as follows:

Steam Turbine Heat Rate:

CASE1:

This is the calculation for closed cycle, single cylinder, condensing type of turbine where steam inlet to turbine at point no1 is expanded to point 2 as per below fig:

Turbine Heat rate:

M= Mass flow rate of steam inlet to turbine, kg/hr

                                                 H1= Enthalpy of steam. Kcal/kg

                                                  H4=Enthalpy of feed water at Economiser inlet, Kcal/kg

                                                  Gkw=Power Generation, kw

Heat Rate in diffent design conditions:

·        Make up or boiler blow down water:

FW flow will increase by same percentage and increase HR

·        Turbine inlet steam flow=Main steam flow(MSSV outlet) – sealing steam – Ejector Steam

·        VWO- Valve wide open- Best HR condition

·        TMCR- Turbine maximum continuous rating

·        Loading – 80%, 60%, 40%

Plant Heat rate:

CASE2:

For Reheat Cycle:

 This is for reheat type of turbine consists of HP Turbine, cold reheat -CRH , Hot reheat  -HRH steam, IP turbine, LP Turbine and condensing type with regenerative feed heating cycle.

 Heat Rate is :

Hf= Enthalpy at point 1 , steam inlet to turbine

Hfw= Enthalpy at Feed water inlet to economiser.

Hhrt= Hot reheat enthalpy

Hcrt= Cold reheat enthalpy

HPH Extraction Flow =

Q_fw =Feed Water Flow

M= Mass flow rate of main steam at point 1

Ho= Enthalpy at FW outlet

Hi= Enthalpy at FW outlet of HPH

H_ext= HPH Ext enthalpy

H_drip= HPH drip enthalpy

M_rh= M-Q_hph+Q_rh

Q_rh= Reheater spray

CASE3:

For Co-generation Cycle:

In case of cogeneration cycle make up water requirement is very hi because the steam is supplied to process plant , The return condensate from process is less than the supplied steam and sometimes it got contaminated so it is rejected as make up water to power cycle. Plant heat rate is defined as

M= Fuel flow rate

m1 =  mass flow rate of makeup water

h1= enthalpy of makeup water

m2= mass flow rate of return condensate

h2=Enthalpy of return condensate

m3, m4= mass flow rate of steam supplied to process

h3,h4= enthalpy of steam supplied to process in different pr & temp.

Comparison of Turbine Heat Rate:

`

` Steam Parameters Turbine heat rate, Kcal/kwh 1 100ata, 510 Deg.C, Feed water temp=165Deg.C, 25MW set 2508 2 94ata,530 Deg.C, Final FW temp=235 Deg.C, 20MW set 2273 3 139 ata,535 Deg.C, Final FW temp=253 Deg.C, 210mw set 2065 4 170ata, 535/565Deg.C, 500MW 1895-1935 5 247ata, 537/565Deg.C,F FW Temp=280 Deg.C, 660MW 1860-1900 6 247ata, 565/593Deg.C,F FW Temp= Deg.C, 800MW 1810-1850

7            WHRB for cement plant, 12ata,        3323 kcal/kwh

              425deg.C,  107TPH, T-inlet

              Injection steam 3ata, 200 Deg,C

             7.1tph, 22.5MW FW temp-130 deg.C

                

Standards for Turbine Performance Calculation

1.     ASME PTC-6:

2.     DIN 1943

3.     BSEN 60953

4.     IEC953