PPE chaapter 6.pptxPower Plant Engineering

Power Plant Engineering

1. Waste Heat Recovery Power Plant Engineering

2. Program: Diploma (Mechanical) Class: TY (ME) Semester: V Course: Power Plant Engineering Code: 22566 Unit : 4. Waste Heat Recovery

3. Unit IV: Waste Heat Recovery UNIT OUTCOMES (UOs) :- 4a. Explain the need of Waste Heat Recovery of the given Thermal Power Plants. 4b. Explain with sketches working principle of Co- generation and Tri- generation in the given Thermal Power Plant.

4. Unit IV: Waste Heat Recovery Waste heat found in the exhaust gas of various processes or even from the exhaust stream of a conditioning unit can be used to preheat the incoming gas . This is one of the basic methods for recovery of waste heat. Many steel making plants use this process as an economic method to increase the production of the plant with lower fuel demand. 4.1: WASTE HEAT RECOVERY: Introduction A Waste Heat Recovery Unit (WHRU) is an energy recovery heat exchanger that transfers heat from process outputs at high temperature to another part of the process for some purpose , usually to increase the efficiency. Waste heat may be extracted from sources such as hot flue gases from a diesel generator , steam from cooling towers , or even waste water from cooling processes such as in steel cooling . Waste heat is heat, which is generated in a process by way of fuel combustion or chemical reaction, and then The essential quality of heat is not the amount but rather its “value”. Waste heat found in the exhaust gas of various processes or even from the exhaust stream of a conditioning unit can be used to preheat the incoming gas . This is one of the basic methods for recovery of waste heat . Many steel making plants use this process as an economic method to increase the production of the plant with lower fuel demand.

5. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: IN A NUTSHELL • “Dumped” heat that can still be reused • “Value” (quality) more important than quantity • Waste heat recovery saves fuel and increases thermal efficiency • An effective way to increase • • • energy efficiency is to recover waste heat “Dumped” heat that can still be reused “Value” (quality) more important than quantity Waste heat recovery saves fuel and increases thermal efficiency An effective way to increase energy efficiency is to recover waste heat

6. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: SOURCE AND QUALITY OF WASTE HEAT S. No Source of Waste Heat Quality of Waste Heat 1 Heat in flue gases The higher the temperature, the greater the potential value for heat recovery 2 Heat in vapour streams As above but when condensed, latent heat also recoverable 3 Convective & radiant heat lost from exterior of equipment Low grade – if collected may be used for space heating or air preheats 4 Heat losses in cooling water Low grade – useful gains if heat is exchanged with incoming fresh water 5 Heat losses in providing chilled water or in the disposal of chilled water High grade if it can be utilized to reduce demand for refrigeration Low grade if refrigeration unit used as a form of Heat pump 6 Heat stored in products leaving the process Quality depends upon temperature 7 Heat in gaseous & liquid effluents leaving process Poor if heavily contaminated & thus requiring alloy heat exchanger

7. Unit IV: Waste Heat Recovery Low Temperature Heat Recovery High Temperature Heat Recovery Medium Temperature Heat Recovery 4.1: WASTE HEAT RECOVERY: CLASSIFICATION BASED ON TEMPERATURE RANGES Waste Heat Recovery Systems (WHRS) Heat comes from direct fuel fired processes . Heat comes from the exhaust of directly fired process units. Low temperature waste heat may be useful in a supplementary way for preheating purposes.

8. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: A) High Temperature Heat Recovery Types of Devices Temperature ( C) Nickel refining furnace 1370 – 1650 Aluminium refining furnace 650 –760 Zinc refining furnace 760 – 1100 Copper refining furnace 760 – 815 Steel heating furnace 925 – 1050 Copper reverberatory furnace 900 – 1100 Open hearth furnace 650 – 700 Cement kiln (Dry process) 620 – 730 Glass melting furnace 1000 – 1550 Hydrogen plants 650 – 1000 Solid waste incinerators 650 – 1000 Fume incinerators 650 – 1450 Table: Typical waste heat temperature at high temperature range from various sources

9. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: B) Medium Temperature Heat Recovery Types of Devices Temperature ( C) Steam boiler exhaust 230 – 480 Gas turbine exhaust 370 – 540 Reciprocating engine exhaust 315 – 600 Reciprocating engine exhaust (turbo charged) 230 – 370 Heat treatment furnace 425 – 650 Drying & baking ovens 230 – 600 Catalytic crackers 425 – 650 Annealing furnace cooling systems 425 – 650 Table: Typical waste heat temperature at Medium temperature range from various sources

10. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: C) Low Temperature Heat Recovery Heat Source Temperature C Process steam condensate 55- 88 Cooling water from: Furnace doors 32- 55 Injection molding machines 32- 88 Annealing furnaces 66- 230 Forming dies 27- 88 Air compressors 27- 50 Pumps 27- 88 Internal combustion engines 66- 120 Air conditioning and refrigeration condensers 32–43 Liquid still condensers 32- 88 Drying, baking and curing ovens 93- 230 Hot processed liquids 32- 232 Hot processed solids 93- 232

11. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: Types of Commercial Equipments 1.Recuperators Heat exchange occurs between flue gases and the air through metallic/ceramic walls. Ducts/tubes carry combustion air to be preheated in the combustion chamber; the other side contains waste heat stream. Inlet air from atmosphere Types of Recuperators:- 1. Convective Recuperator Metallic Recuperator Hybrid Recuperator Ceramic Recuperator Self- recuperative Burners Outside ducting Tune plate Preheated air Centre tube plate Exhaust gas from process

12. Unit IV: Waste Heat Recovery : WASTE HEAT RECOVERY: Types of Recuperators 1. Convective Recuperator: Hot gas through number of parallel small diameter tubes. Tubes can be baffled twice or thrice to allow gas to pass over them again. Baffling increases heat exchange but more expensive exchanger is needed.

13. Unit IV: Waste Heat Recovery : WASTE HEAT RECOVERY: Types of Recuperators 2. Metallic Recuperator: The radiation recuperator consists of two concentric lengths of metal tubing. The inner tube carries the hot exhaust gases, while the external annulus carries the combustion air from the atmosphere to the air inlets of the furnace burners. The radiation heat transfer is most effective at high temperature- - usually above 1,400°F (760°C)

14. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: Types of Recuperators 3. Hybrid Recuperator: For maximum effectiveness of heat transfer, hybrid recuperators are used. These are combinations of radiation and convective designs, with a high-temperature radiation section followed by a convective section. These are more expensive than simple metallic radiation recuperators, but are less bulky.

15. Unit IV: Waste Heat Recovery : WASTE HEAT RECOVERY: Types of Recuperators 4. Ceramic Recuperator: They have been developed to overcome the temperature limitations of metal recuperators as metal recuperators are normally used for temperatures from 1,600°–1,800°F (870° to 980°C) New Design have following features :- Reduced leakage rates. Air pre- heat temperature < 700°C Cannot be used for gases that contain particulates, corrosive gases, and condensable vapors. Requires high maintenance due to potential for air leaks.

16. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: Types of Recuperators 5. Self- recuperative Burners: A special class of recuperators, known as self-recuperative burners, is now offered by several burner suppliers. In this system, the recuperator is integrated with the burner itself, so there is no need to have hot air piping from the recuperator to the burners resulting in substantial cost advantage. The self-recuperative burners cannot give the same heat transfer rate or heat transfer efficiency; hence the fuel savings are limited to 30%–60%

17. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: Types of Commercial Equipments 2.Regenerators They are widely used in glass and steel melting furnaces to recover heat from high- temperature exhaust gases, normally above 2,500 ° F (1,370 ° C). They are made from high- temperature refractory bricks or specially designed ceramic shapes. The efficiency of the regenerator depends on the size of the regenerator; the time span between reversals; and the thickness, conductivity, and heat storage ratio of the brick. Accumulation of dust and slag on the surfaces reduce efficiency of heat transfer.

18. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: Types of Commercial Equipments 3. Heat Wheels / Thermal Wheels / Rotary Heat exchangers Applications in low- to medium- temperature waste heat recovery systems, usually limited to about 600 ° F (315 ° C). The wheel itself is a sizable porous disk, fabricated with material having a fairly high heat capacity. It rotates between two side- by- side ducts: one is a cold gas duct, the other a hot gas duct. The axis of the disk is located parallel and on the partition between the two ducts.

19. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: Types of Commercial Equipments Heat Pipe Exchangers (HPHE) It is a thermal energy absorbing and transferring system that has no moving parts and therefore requires minimal maintenance . Transfer up to 100 times more thermal energy than copper. It Consist of Three elements: Sealed container Capillary wick structure Working fluid Works with evaporation and condensation. The heat pipe is mainly used in space, process or air heating.

20. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: Types of Commercial Equipments Heat Pipe Exchangers (HPHE) Typical applications Process to space heating : Transfers thermal energy from process exhaust for building heating Process to process : Transfers recovered waste thermal energy from the process exhaust to the incoming process air HVAC applications : Cooling and heating by recovering thermal energy

21. Unit IV: Waste Heat Recovery 4.1: WASTE HEAT RECOVERY: Types of Commercial Equipments Economizers Used with a boiler system to pre- heat the boiler feed water with the flue gas heat or, in an air pre- heater, to pre- heat the combustion air. 1% fuel savings if 60 ° C rise of feed water temp through economizer. 200 ° C rise in combustion air temp through air preheater.

22. Unit IV: Waste Heat Recovery 4.1.1: NEED OF WASTE HEAT RECOVERY Recovery of waste heat has a direct effect on the efficiency of the process. This is reflected by reduction in the utility consumption, costs and process cost. Reduction in pollution : A number of toxic combustible wastes such as carbon monoxide gas, sour gas, etc, releasing to atmosphere if/when burnt in the incinerators serves dual purpose i.e. recovers heat and reduces the environmental pollution levels. Reduction in equipment sizes : Waste heat recovery reduces the fuel consumption, which leads to reduction in the flue gas produced. This results in reduction in equipment sizes of all flue gas handling equipment. Reduction in auxiliary energy consumption : Reduction in equipment sizes gives additional benefits in the form of reduction in auxiliary energy consumption like electricity for fans, pumps etc. To make huge savings and earn high profit: By switching to the most energy- efficient technology available, companies can make huge savings and significantly reduce environmental impact.

23. Unit IV: Waste Heat Recovery 4.1.2: OPPORTUNITIES OF WASTE HEAT RECOVERY: Iron and Steel Industry Waste Heat Source Heat Recovery Opportunities Blast furnace gas (BFG) Maintaining heating value to reduce or eliminate use of supplementary fuel, such as natural gas. Coke oven gas (COG) Use of sensible heat and chemical heat of COG— elimination of need to cool or quench the COG as discharged from the coke oven batteries. Steam from liquid steel refining area Recovery of steam heat and condensate return. Hot coke discharged from coke ovens Recovery of high-grade (temperature) sensible heat from hot coke. Hot products discharged from various furnaces Recovery of heat from high-temperature (1,300°–2,200°F) (700°–1,200°C) steel products. Contd …… .

24. Unit IV: Waste Heat Recovery 4.1.2: OPPORTUNITIES OF WASTE HEAT RECOVERY: Iron and Steel Industry Waste Heat Source Heat Recovery Opportunities Waste heat from recuperator or a regenerative burner system used on various heating or heat treating furnaces Recovery of sensible and latent heat from fly-use gases. Low-grade heat available in the form of hot water used in cooling systems for various operations (e.g., caster, reheat furnaces, and roll cooling) Recovery of heat from low-temperature water (usually less than 125°F or 52°C). Radiation – convection heat loss from furnace walls Recovery of heat for use within the plant. EAF exhaust gases Recovery of chemical and sensible heat.

25. Unit IV: Waste Heat Recovery 4.1.3: PRESENT PRACTICES OF WASTE HEAT RECOVERY Many sectors of industry have very good potential for Waste heat recovery. Industrial units in following sectors have WHRS installed and used effectively: Aluminum – Primary Production Aluminum – Recycling and Secondary Melting Steel – Integrated Steel Mill Steel – Mini Mill or EAF Mill Glass – Fiberglass Manufacturing Chemicals and Petroleum Refining – Major Operations Paper – Paper Mill Food – Food (Snack) Manufacturing Cement – Dry Process and Shaft Furnaces Coatings – Vinyl Coating Mill

26. U n i t I V : W a s t e H e a t R e c o v e r y - C o g e n e r a t i o n 4.2: COGENERATION OR COMBINED HEAT AND POWER (CHP) : Introduction It may be defined as, "the sequential generation of two different forms of useful energy from a single primary energy source , typically mechanical energy and thermal energy. Cogeneration (the alternative name for CHP) simply means that the electricity and heat are made at t h e s a m e t i m e . T h e o v e r a l l e ff i c i e n c y o f e n e r g y u s e i n cogeneration mode can be up t o 8 5 p e r c e n t a n d a b o v e i n s o m e cases.

27. U n i t I V : W a s t e H e a t R e c o v e r y - C o g e n e r a t i o n 4 . 2 : C OG E N E R A T I O N : I n T h e r m a l P o w e r P la n t A conventional power plant makes electricity by a fairly inefficient process. A fossil fuel such as oil, coal, or natural gas is burned in a giant furnace to release heat energy. The heat is used to boil water and make steam, the steam drives a turbine, the turbine drives a generator, and the generator makes electricity. Instead of letting heat escape uselessly up cooling towers, the CHP systems is used to capture the heat that would normally be wasted and supply it to local buildings as well.

28. U n i t I V : W a s t e H e a t R e c o v e r y - C o g e n e r a t i o n 4 . 2 : C OG E N E R A T I O N : I n T h e r m a l P o w e r P la n t Where a conventional power plant makes electricity and wastes the heat it makes as a byproduct, a CHP power plant makes both electricity and hot water and supplies both to consumers. Cogeneration (the alternative name for CHP) simply m e a n s t h a t t h e e l e c tr i c i t y a n d h e a t a r e m a de a t t h e s a m e t i m e .

29. U n i t I V : W a s t e H e a t R e c o v e r y - C o g e n e r a t i o n 4 . 2 . 1 : N EE D OF C OG E N E R A T I ON Increased efficiency of energy conversion and use. Cogeneration is the most effective and efficient form of power generation. Lower emissions to the environment, in particular of CO2 , the main greenhouse gas. Cogeneration is the single biggest solution to the Paris Agreement goals. Large cost savings , providing additional competitiveness for industrial and commercial users, and offering affordable heat for domestic users. Improved local and general security of supply – local generation, through cogeneration, can reduce the risk of consumers being left without supplies of electricity and/or heating. In addition, the reduced need for fuel resulting from cogeneration reduces import dependency – helping to tackle a key challenge for future.

30. U n i t I V : W a s t e H e a t R e c o v e r y - C o g e n e r a t i o n 4 . 2 . 2 : OP P OR T U N I T I E S OF C OG E N E R A T I ON An opportunity to move towards more decentralized forms of electricity generation , where plants are designed to meet the needs of local consumers , providing high efficiency, avoiding transmission losses and increasing flexibility of system use. An opportunity to increase the diversity of generation plant , and provide competition in generation. Increased employment – a number of studies have now concluded that the development of CHP systems is a generator of jobs in following sectors:- Cities/Municipalities I n d u s t r i a l P r e m i s e s C o mm e r c i a l / R e t a i l s e c t o r Gas stations

31. U n i t I V : W a s t e H e a t R e c o v e r y - C o g e n e r a t i o n : PRESENT PRACTICES OF COGENERATION Co-generation is well proven technology , recognized worldwide as a cleaner alternative to traditional centralized power and it is highly energy efficient. Many sectors of industry have very good potential for cogeneration. Industrial units in following sectors c a n t a k e a d v a n t a g e : Sugar Paper Oil Extraction Rice Milling Chemical Fertilizers Textiles-Cotton & Synthetic Food Processing Rubber Industries Metallurgical Industries Urban Waste Treatment

32. Unit IV: Waste Heat Recovery- Trigeneration 4.3: TRIGENERATION OR COMBINED COOLING, HEAT AND POWER (CCHP) : Trigeneration can be defined as, "the simultaneous process of cooling , heating and power generation from only one fuel input ".

33. Unit IV: Waste Heat Recovery- Trigeneration 4.3: TRIGENERATION OR COMBINED COOLING, HEAT AND POWER (CCHP) : Trigeneration can be defined as, "the simultaneous process of cooling , heating and power generation from only one fuel input ".

34. Unit IV: Waste Heat Recovery- Trigeneration

35. Unit IV: Waste Heat Recovery- Trigeneration 4.3: TRIGENERATION OR COMBINED COOLING, HEAT AND POWER (CCHP) : EFFICIENCY

36. Unit IV: Waste Heat Recovery- Trigeneration : BENEFITS OF TRIGENERATION OR (CCHP) : H i g h e ff i c i e n c y When waste heat is used for heating and cooling, thermal efficiency can reach up to 90 percent. This is ideal for facilities such as 24-hour industrial parks, certain commercial building blocks, or even hospitals that operate all day. 2 . E n e r g y S u r e t y Tri-generation is also useful in areas prone to brownouts. O p e r a t i o n s c a n c o n t i nu e t h r o u g h e rr a t i c w e a t h e r p a t t e r n s t h a t o f t e n w o u l d a f f e c t e l e c t ri c i t y transmission from a centralized power station. 3 . E c o n o m i c a ll y So u n d Tri-generation can be an off-the-grid solution. This can help businesses scale back on the cost of electricity, as well as costs from heating and cooling requirements .

37. Unit IV: Waste Heat Recovery- Trigeneration 4.3.1: BENEFITS OF TRIGENERATION OR (CCHP) : 4 . C u t o u t t h e t r a n s m i ss i on c o s t s Localizing energy transmission means electricity does not need to be transported over a long distance to reach consumers. I t r ed u c e s t h e b u r de n o n a u t i l i t y ’ s t r a n s m i ss i o n i n f r a s t r u c t u r e . 5. More suitable Air Conditioning and Lower Heating Bills Tri-generation also enables an opportunity for efficient repurposing of waste heat, producing heating and cooling for customers nearby. 6 . R e d u c e d e m i ss i on Combining electricity, heating and cooling production from one source reduces carbon emissions significantly and beneficial to environment all aspects.

38. Unit IV: Waste Heat Recovery- Trigeneration 4.3.2: OPPORTUNITIES OF TRIGENERATION OR (CCHP) : The government has reinforced the need for efficiency at all stages of the energy value chain. To meet its targets, the Indian government has begun developing smart electric power infrastructure . These are built to deliver power combining conventional grid components with new storage and information communication technology. Tri-generation also provides India with significant opportunities to improve energy efficiency and reduce greenhouse gas emissions.

39. Unit IV: Waste Heat Recovery- Trigeneration 4.3.3: PRESENT PRACTICES OF TRIGENERATION OR (CCHP) : Many sectors of industry have very good potential for Trigeneration. Industrial units in following sectors c a n t a k e a d v a n t a g e : 1 . D a t a c e n t e r s . 3 . M a n u f a c t u r i n g u n i t s . 5 . M i l i t a r y c o m p l e x e s . 7 . O ff i c e b u i l d i n g s . 9 . M a n u f a c t u r i n g p l a n t s . 2 . F oo d p r o c e ss i n g i n d u s t r i e s . 4 . C o ll e g e s a n d u n i v e r s i t i e s . 6 . S c h oo l s , c o ll e g e s . 8 . S h o pp i n g c e n t e r s & S u p e r m a r k e t s . 1 . R e f r i g e r a t e d w a r e h o u s e s . 1 2 . A i r p o r t s . 1 4 . C a s i n o s . 11 . T h e a t r e s . 13 . G o l f / c o u n t r y c l u b s . 15 . R e s o r t s .

40. Unit IV: Waste Heat Recovery- Trigeneration 4 . 4 : C OG E N E R A T I O N V S T R I G E N E R A T I ON S r. N o . Parameter Co-generation Trigeneration 1 Definition P r ocess of s i m u l t a n eo u s g e n e r a ti on of h eat a n d p ower f r om s ing l e f u el S o u r ce. P r ocess of s i m u l t a n eo u s g e n e r a ti on of cooling, heating and power from single fuel Source. 2 A l t e r n a ti ve N ame C om bin ed H eat a n d P ower ( CH P ) Combined Heating, Cooling and Power (CCHP). 3 F o r m s of En e r gi es E l ec t r i c it y a n d H ea tin g E l ec t r i c it y, H ea tin g a n d C oo l ing . 4 Efficiency 80 % 90 % 5 Absorption R ef r ig e r a ti on s y s t em N ot N ee d ed Needed