What do you mean by Regenerative system in power plants???

 

Thermal power plants efficiency is in the range of 30 to 40%, the improvement of thermal cycle efficiency can be done either by increasing the inlet steam pressure & temperature or decreasing the turbine exhaust pressure. But improvement of Boiler parameters & decreasing exhaust pressure lead to increase in cost & also have limitations related to metallurgy & risk.

Another way is to increase the thermal efficiency is by using regenerative cycle. This cycle is more efficient than Rankine cycle.

What do you mean by Regenerative process or cycle???

In this process, steam is extracted from turbine at one or more points during steam expansion. This pressure is high, medium & low. Steam after some expansion cycle gets feed water heating ability. Such extracted steam is utilized to heat the feed water going to the Boilers nearer to its saturation temperature. Heating the Boiler feed water temperature ultimately increases the overall thermal efficiency.

How does the increase in feed water temperature increase the overall thermal efficiency??

Increase in feed water temperature at economizer inlet reduces the work done by boiler to generate the steam & hence consumes less fuel. As a thumb rule, on every 6-7 degree C rise in feed water temperature reduces Boiler fuel consumption by 1%.

What are the advantages of Regenerative cycle???

Regenerative cycle helps to increase in power plant thermal efficiency

Amount of steam condensed in steam condenser per KW decreases

Cooling water consumption decreases

Condenser size reduces

Auxiliary power consumption of cooling system reduces

Heat rate of the plant drastically reduces

Due to less fuel consumption load on fuel handling, fuel feeding & Boiler fans decreases & hence saving in plant auxiliary power consumption.

What are the major disadvantages of Regenerative cycle or process?

There are no much disadvantages except the requirement of HP, LP heaters, relating piping & controlling equipments.

What are the major parts of Regenerative cycle?

HP heaters, LP heaters & Deaerator.

What are the HP heaters?

HP heaters are the shell & tube type of heat exchangers situated between Boiler feed pumps & economizer.

The main design purpose of the HP heater is to heat the feed water coming from Boiler feed pump.

 

Why the name HP heater?

Because it I situated in high pressure zone that is at Boiler feed pump discharge feed water circuit

What are the heat transfer areas present in HP heaters?

Main heat transfer zones are

De-super heating zone

Condensing zone

Sub-cooling zone

What is the function of de-super heating zone in HP heaters?

It is separate heat exchanger placed within the shell, its main function is to remove the super heat from extracted steam

What is the function of sub-cooling zone in HP heaters?

It is another separate counter flow heat exchanger placed within the HP heater shell, its main function is to sub cool the condensate formed in condensing zone

What are LP heaters & where they are placed?

The condensate formed in the surface condenser is pre heated to elevated temperature before it goes to deaerator are called LP heaters.

LP heaters are placed between deaerator & ejector or CEP

LP heaters are also having 3 zones as like HP heaters

Why the name LP heater?

LP heaters are placed at low pressure zone from CEP to deaerator hence called LP heaters

Schematic diagram of power plant regenerative system

 

How do you prove that, regenerative cycle will increase the thermal power plant efficiency?

This can be explained by taking an example

Sl No.	Particular	UOM	Boiler-1	Boiler-2
1	Boiler steam generation	TPH	100	100
2	Steam pressure	Kg/cm2	87	87
3	Steam temperature	Deg C	515	515
4	Boiler efficiency	%	69	69
5	Fuel GCV	Kcal/kg	4300	4300
6	HP heater available	YES/NO	Yes	No
7	Feed water temperature at economizer inlet	Deg C	160	110

 

Looking at the above example, both boilers seem to be safe, except Boiler-1 has HP heater that is feed water heater & Boiler-2 has no HP heater.

Based on this we shall calculate fuel consumption of both the Boilers.

Enthalpy of steam at above parameters Hg = 818 kcal/kg

Enthalpy of feed water at temperature 110 deg C, Hf1 = 111kcal/kg

Enthalpy of feed water at temperature 160 deg C, Hf2 = 162kcal/kg

Now we shall calculate the fuel consumption of Boiler-1

Boiler1 = Steam flow X (Steam enthalpy-Feed water enthalpy) / (Fuel GCV X Boiler efficiency)

Boiler 1 =100 X (818-160) / (4300 X 0.69)

Boiler 1 fuel consumption = 22.17 TPH

Boiler2 = Steam flow X (Steam enthalpy-Feed water enthalpy) / (Fuel GCV X Boiler efficiency)

Boiler 2=100 X (818-110) / (4300 X 0.69)

Boiler 2 fuel consumption = 23.86 TPH

Looking at the fuel consumption of both the Boilers, Boiler 1 consumes less fuel as it has HP heater & hence more feed water temperature than Boiler-2

 Less fuel consumption in the sense less heat rate & less heat rate is nothing but more efficiency of the plant

 

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How do you calculate the Deaerator & HP heaters steam consumption???

DEAERATORS:

What is the function of Deaerator?

Functions of deaerator

To remove the dissolved oxygen from deaerator & bringing down to <0.005 ppm

To heat the feed water

To provide NPSH to Boiler feed pumps

Acts as surge for feed water storage device

2-Which steam is used for deaerator?

Saturated steam having pressure from 0.3 to 3 kg/cm2 and temperature 130 deg C to 200 deg C

3-What are the pipe lines connected to Deaerator & storage tank?

Inlet lines:

Make up water line

Condensate water line from CEP

Return condensate water from process

Recirculation water line from BFP

Balance leak off water lines from BFP

Condensate water from HP & LP heaters

Steam line from turbine extraction or PRDSH

Out let lines:

Feed water line to BFP suction

Deaerator overflow line

Deaerator storage tank drain line

Understanding with examples.

1-Calculate the steam consumption of deaerator based on following given data

Sl No.	Particular	UOM	Value
1	LP steam flow to deaerator at pressure 1.5kg/cm2G & temperature 135 deg C t	TPH	?
2	Feed water outlet temperature from deaerator	0C	105
3	Feed water outlet flow from deaerator	TPH	125
4	CEP water flow to deaerator at temperature 50 deg C flow	TPH	120
5	Make up water to deaerator at temperature 25 deg C	TPH	5

        

 

 

 

 

 

 

 

 

 

Solution:

Enthalpy of steam at pressure 1.5 kg/cm2 & temperature 135 deg C = 653 kcal/kg

Enthalpy of CEP water at temperature 50 deg C = 50 kcal/kg

Enthalpy of makeup water at temperature 25 deg C = 25 kcal/kg

Enthalpy of deaerator outlet feed water = 106 kcal/kg

Mass of steam = (Feed water flow X Enthalpy –CEP flow X Enthalpy-Makeup water X Enthalpy) / (Enthalpy of steam-Enthalpy of deaerator outlet water)

Mass of steam      = 125 X 106 -120 X 50 -5 X 25 / (653-106)

Mass of steam = 13.02 MT

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2-Calculate the steam consumption of deaerator based on following given data

Sl No.	Particular	UOM	Value
1	LP steam flow to deaerator at pressure 2.5 kg/cm2G & temperature 150 deg C t	TPH	?
2	Feed water outlet temperature from deaerator	0C	128
3	Feed water outlet flow from deaerator	TPH	210
4	CEP water flow to deaerator at temperature 45 deg C flow	TPH	30
5	Make up water to deaerator at temperature 25 deg C	TPH	20
6	Process return condensate at temperature 95 deg C	TPH	160

        

 

 

 

 

 

 

 

 

 

 

 Solution:

Enthalpy of steam at pressure 2.5 kg/cm2 & temperature 150 deg C = 658.4 kcal/kg

Enthalpy of CEP water at temperature 45 deg C = 45 kcal/kg

Enthalpy of makeup water at temperature 25 deg C = 25 kcal/kg

Enthalpy of deaerator outlet feed water = 129 kcal/kg

Enthalpy of return condensate water = 96 kcal/kg

Mass of steam = (Feed water flow X Enthalpy –CEP flow X Enthalpy-Makeup water X Enthalpy-Return condensate X Enthalpy) / (Enthalpy of steam-Enthalpy of deaerator outlet water)

Mass of steam      = (210 X 129 -30 X 45 -20 X 25-160 X 96) / (658.4-129)

Mass of steam = 18.66 MT

HP & LP heaters:

1-What are the applications of HP & LP heaters?

HP & LP heaters are used to heat the feed water & to improve the cycle efficiency

 

2-What are the various pipe lines connected to HP heaters?

Inlet lines:

1-Feed water inlet line

2-Bleed steam line from Turbine

Outlet lines:

1-Feed water outlet line

2-Condensate outlet line

Understanding with examples.

A HP heater is used to heat the 105 TPH feed water from 105 °C to 150 °C by using turbine bleed steam at 8 kg/cm2 and 200 °C. The condensate returning from heater is at 125 °C, calculate the quantity of steam used.

 Given that,

Qf = 105 TPH

Tf1 = 105 °C

Tf2 = 150 °C

Hg at pressure 8 kg/cm2 & temperature 200 °C =677 kcal/kg

Enthalpy of condensate water Hf = 126 kcal/kg

Heat lost by the steam = Heat gained by feed water

Ms X (Hg-Hf) = Mw X (Tf2-Tf1)

Ms X (677-126) = 105 X (150-105)

Ms = 8.57 TPH

 

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Power plant & Calculations

Codes & standards of practice for thermal power plant equipments

Sl No.	Particular	Code/standards of practice
A	Boilers
1	Code of practice for Constructions in steel	IS 800
2	Rules for construction of power boilers	ASME Section I
3	IBR materials	ASME BPVC SEC-II
4	Construction of heating boilers	ASME BPVC SEC-IV
5	Non-destructive testing	ASME BPVC SEC-V
6	Code of practice for design loads for buildings structures.	IS 875
7	Criteria for Earthquake Resistant – Design of Structures	IS 1893
8	Code for unfired pressure vessels	IS 2825
9	Indian Boiler Regulation	IBR 1950
10	Welding and Brazing Qualifications	ASME Section IX
11	Power piping	ASME B 31.1
12	Construction of pressure vessels	ASME BPVC SEC-VIII
13	Acceptance test for steam generator	DIN 1942
14	APH performance test code	ASME PTC 4.3
15	Boiler performance test	ASME PTC 4.1
16	Deaerator performance test code	ASMEPTC 12.3
17	Specification for wrought aluminium and aluminium alloys sheet and strip (For General Engineering Purpose)	IS 737
18	Design & construction of RCC chimney	IS 4998-1992
B	REFRACTORY & INSULATION
1	Moderate heat duty fire clay refractories Group-A	IS:6
2	High heat duty fire clay refractories	IS:8
3	Insulating bricks	IS : 2042
4	Method of determination of thermal conductivity of thermal insulation material	IS3346
5	Code of practice for storage and handling of insulating materials	IS10556
6	Industrial application and finishing of thermal insulting materials at temperatures above 80 deg C and up to 700 Deg. C	IS14164
7	Specification for Bonded Mineral Wool	IS: 8183
8	Hexagonal wire netting for general purpose	IS 2150
9	Methods of test for mineral Wool Thermal Insulation Material	IS3144
C	STEAM TURBINE & AUXILARIES
1	Duplex oil coolers design	ASME SEC-VIII, TEMA “C”
2	Steam ejector design	ASME SEC-VIII, DIV-1,TEMA “C”
3	Steam condenser design	HEI-IX EDITION
4	Thermal acceptance test for steam turbine	DIN 1943
5	Steam turbine performance test	ASME PTC 6
6	Surface condenser performance test codes	ASME PTC 12.2
7	Overall plant performance	ASMEPTC 46
D	WTP
1	Chemical dosing tanks design	BS 4994 1987
2	DM water storage  tank	IS 803
3	WTP vessels design	IS 2825
E	PUMPS ,COMPRESORS & FANS
1	Centrifugal pumps performance test code	ASME PTC 8.2
2	Design of Pumping Systems that use Centrifugal Pumps	PIP RECP001
3	Design of ASME B73.1 and General Purpose pump Base plates	PIP RESP002
4	Seal Flush and Lubrication Guidelines for Centrifugal Pumps	PIP REEP001
5	Compressors  performance test codes	ASMEPTC 10
6	Guide for selection installation and maintenance of air Compressor up to 10 bars.	IS 6206
7	Code of practice for testing of positive air displacement type Compressors and exhausters	IS 5456
8	Air receivers for compressed air installation	IS: 7938
9	Fans  performance test codes	ASMEPTC 11
F	BELT CONVEYORS
1	Specification for troughed belt conveyors	IS: 1891
2	Code of practice for conveyor safety	IS: 4776
3	Specification for pulleys for belt conveyors	IS: 7403
4	Specification for idlers for belt conveyors	IS8598
G	MAINTENANCE
1	Bars and Keyways for Flexible couplings	AGMA 9002
2	Pipe Threads, General Purpose	ASME B1.20.1
3	Cast Iron Pipe Flanges and Flanged Fittings	ASME B16.1
4	Pipe flanges and flanged fittings	ASME B 16.5
5	Roller Bearings –Dynamic Load Ratings and Rating Life – Part 1 : Calculation Methods.	ASME STD 9
6	Specification  for  Forgings,  Carbon  steel,  for  Piping Components	ASTM  A105
7	Specification for Seamless Carbon Steel Pipe for High Temperature Service.	ASTM A106
H	ELECTRICAL & INSTRUMENTATION
1	Design of Power transformer	IS 2026
2	Code of practice for earthing.	IS: 3043 - 1987
3	Guide for safety procedures and practices in electrical work: General.	IS: 5216(Part-1)-1982
4	General requirements for switchgear and control gear for voltages not exceeding 1000 V AC or 1200 V DC	IS:4237 - 1983
5	Air break switches, air break dis-connectors, air-break switch disconnectors and fuse-combination units for voltages not exceeding 1000 V AC or 1200 DC : General requirements	IS:4064(Part-1)-1978
6	Miniature air break circuit breakers for voltages not exceeding 1000 volt	IS: 8828 - 1978
7	Residua current operated circuit breakers.	IS:12640 - 1988
8	Contactors for voltages not exceeding 1000 V AC or 1200 V DC.	IS:2959 - 1985
9	PVC Insulated cables for working voltages up to and including 1100 V.	IS:694 - 1990