Operator Generic Fundamentals

Operator Generic Fundamentals
Components – Heat Exchangers and Condensers

Heat Exchangers and Condensers
Principles of Operation Transfer heat from one fluid to another Fluids must be at different temperatures Fluids must come into thermal contact Heat flows from hotter to cooler fluid Maintains separation between the two fluids TLO 1 - Intro

Terminal Learning Objectives
At the completion of this training session, the trainee will demonstrate mastery of this topic by passing a written exam with a grade of ≥ 80% on the following areas: Describe the purpose, construction, and principles of operation for each major type of heat exchanger. Describe the purpose, construction, and principles of operation of condensers. Intro

Heat Exchanger Construction & Operation
TLO 1 – Describe the purpose, construction, and principles of operation for each major type of heat exchanger. Heat exchangers transfer heat from higher energy to lower energy system Conduction and convection heat transfer methods Allows systems to maintain physical separation of processes Heat exchangers use different flow designs, including counter and cross flow TLO 1

Enabling Learning Objectives for TLO 1
Describe the construction, effectiveness, and operation of the following types of heat exchangers and their components (tubes, tube sheets, baffles and shells): Tube and shell Plate Describe hot and cold fluid flow paths in the following types of heat exchangers: Parallel flow Counter flow Cross flow Describe the difference between the following types of heat exchangers: Single-pass versus multipass heat exchangers Regenerative versus nonregenerative heat exchangers TLO 1

Describe the operation of a typical heat exchanger to include the following: Startup and shutdown Control of temperature Effects and control of fouling Given the necessary data, calculate flow rates, and temperatures for various types of heat exchangers. Explain the consequences of heat exchanger tube failure. TLO 1

Types of Heat Exchangers
ELO 1.1 – Describe the construction, effectiveness, and operation of the following types of heat exchangers and their components (tubes, tube sheets, baffles, and shells): tube and shell and plate. Heat exchanger construction falls into one of two categories: Tube and shell Plate Each type has advantages and disadvantages Related KA K1.06 Components of a heat exchanger (tubes, shells, plates, etc.) ELO 1.1

Tube and Shell Most basic and most common type Consists of tubes in a container called a shell Fluid is separated from the shell-side fluid by the tube sheet(s) Tubes can withstand higher pressures than shells Support plates act as baffles, directing the flow of fluids 1. U-tube, 2. Shell, 3. Tube, 4. Support/baffle, 5. Vent connection, 6. Tube side inlet 7. Tube sheets, 8. Shell-side drain, 9. Shell-side inlet plenum Figure: Tube and Shell Heat Exchanger ELO 1.1

Plate Heat Exchanger Consists of plates instead of tubes to separate the hot and cold fluids Fluids alternate between each of the plates Baffles direct the flow of fluid between the plates Plates have a large surface area and provide each of the fluids with an extremely large heat transfer area Figure: Plate Heat Exchanger ELO 1.1

Heat Exchanger Applications
Heat exchangers are found in most chemical or mechanical systems Common applications are: Ventilation and air conditioning (HVAC) systems Radiators on internal combustion engines Boilers Condensers Preheaters or coolers ELO 1.1

Preheaters and Feedwater Heaters
Some heaters, such as feedwater, heat in stages verses all heat transfer in one large heat exchanger Increases the plant's efficiency Minimizes thermal shock stress to components compared to injecting ambient temperature liquid into a boiler (reactor) or other device that operates at high temperatures In a steam system, a portion of the processed steam is tapped off and used as heat source to preheat the feedwater in preheater stages ELO 1.1

Preheaters and Feedwater Heaters
Below is an example of construction and internals of a U-tube feedwater heat exchanger found in a preheater stage of a power plant Figure: Feedwater Heater ELO 1.1

Radiator A heat exchanger is any device that transfers heat from one fluid to another. Some equipment uses air-to-liquid heat exchangers An example of an air-to-liquid heat exchanger is a car radiator Coolant flowing in engine picks up heat from engine block and carries it to radiator Hot coolant flows into tube side of radiator (heat exchanger) Relatively cool air flowing over the outside of the tubes picks up the heat, reducing temperature of coolant Fins on the outside of the tubes increase surface area for heat transfer and maximize heat transfer efficiency ELO 1.1

AC Evaporator and Condenser
AC units contain at least two heat exchangers, usually called evaporator and condenser In each of these, refrigerant fluid flows into heat exchanger and transfers heat, either gaining or releasing it to cooling medium, which is commonly air or water In the condenser, the hot, high-pressure refrigerant gas condenses to a subcooled liquid In evaporator,subcooled refrigerant flows into heat exchanger, heat flow is reversed, cool refrigerant absorbs heat from hotter air flowing on the outside of tubes Cools the air and boils refrigerants ELO 1.1

Condenser Condenser is a type of heat exchanger used to condense a substance from a gaseous state to a liquid state by cooling. Condenser removes latent heat from the condensing fluid and transfers it to coolant Normally, tube and shell heat exchanger serves as a condenser Baffles usually added at inlet to prevent tube impingement from incoming gas or steam Frequently use large steam condensers as heat sinks for steam system ELO 1.1

Knowledge Check In a tube and shell heat exchanger, the fluid flowing ________ the tubes is called the tube-side fluid and the fluid flowing _________ of the tubes is the shell-side fluid. around; inside around; outside inside; outside outside; inside Correct answer is C. Correct answer is C. ELO 1.1

Heat Exchanger Classification
ELO 1.2 – Describe hot and cold fluid flow paths in the following types of heat exchangers: parallel flow, counter flow, and cross flow. Parallel Flow Tube-side and shell-side fluid flow in the same direction Fluids enter from same end with large temperature difference Heat transfers from hotter to cooler Temperatures of two fluids approach each other Hottest cold-fluid temperature is always less than the coldest hot-fluid temperature Related KAs K1.05 Flow paths for the heat exchanger (counterflow and U-types) 1.8* 1.9* K1.07 Control of heat exchanger temperatures Figure: Parallel-Flow Heat Exchanger ELO 1.2

Counter Flow Fluids flow in opposite directions and enter at opposite ends Cooler fluid will approach inlet temperature of the hot fluid Generally most efficient type of heat exchanger Hottest cold-fluid temperature can actually be greater than the coldest hot-fluid temperature Figure: Counter-Flow Heat Exchanger ELO 1.2

Cross Flow Fluid flows perpendicular Usually used when one of the fluids changes phase Large volumes of vapor may be condensed Most efficient when comparing heat transfer rate per unit surface area Average difference in temperature (∆T) between two fluids over the length of the heat exchanger is maximized Figure: Cross-Flow Heat Exchanger ELO 1.2

Heat Exchanger Comparison
Compare average temperature difference across heat exchanger Heat exchanger with largest average temperature difference is more efficient Mean (average) temperature for a heat exchanger calculated using this equation: ∆𝑇 𝑙𝑚 = ∆𝑇 2 − ∆𝑇 1 𝑙𝑛 ∆𝑇 2 ∆𝑇 1 ELO 1.2

When the values for Δ 𝑇 𝑙𝑚 are determined, rate of heat transfer ( ) in a heat exchanger is calculated using: Where: 𝑄 = heat transfer rate (BTU/hr) Uo = overall heat transfer coefficient (BTU/hr-ft2-°F) Ao = cross-sectional heat transfer area (ft2) ∆Tlm = log mean temperature difference (°F) 𝑄 = 𝑈 𝑜 𝐴 𝑜 ∆𝑇 𝑙𝑚 Consider the following example of a heat exchanger operated under identical conditions as a counter flow and then a parallel flow heat exchanger. T1 = represents the hot fluid temperature T1, in = 200°F T1, out = 145°F Uo = 70 BTU/hr-ft2-°F Ao = 75ft2 T2 = represents the cold fluid temperature T2in = 80°F T2out = 120°F ELO 1.2

Consider the following example of a heat exchanger operated under identical conditions as a counter-flow and then a parallel-flow heat exchanger. 𝑇 1 = hot fluid temperature 𝑇 1 𝑖𝑛 = 200°F 𝑇 1 𝑜𝑢𝑡 = 145°F 𝑈 0 = 70 BTU/hr - ft2 - °F 𝐴 0 = 75 ft2 𝑇 2 = cold fluid temperature 𝑇 2 𝑖𝑛 = 80°F 𝑇 2 𝑜𝑢𝑡 = 120°F ELO 1.2

Counter flow: ∆T lm = (200℉−120℉)−(145℉−80℉) 200℉−120℉ 145℉−80℉ =72℉ ∆T lm = 72 ℉ Parallel flow: ∆T lm = (200℉−80℉)−(145℉−120℉) 200℉−80℉ 145℉−120℉ =61℉ ∆T lm = 61℉ ELO 1.2

Inserting values from previous calculation into heat transfer equation for counter-flow heat exchanger yields: Q= 70 BTU ℎ𝑟− 𝑓𝑡 2 −℉ 𝑓𝑡 ℉ Q =3.8×10 5 BTU/hr Inserting values from previous calculation into heat transfer equation for parallel-flow heat exchanger yields: Q =3.2×10 5 BTU/hr ELO 1.2

Classification by Flowpath
Knowledge Check Refer to the drawing of a lube oil heat exchanger below. The heat exchanger is operating with the following parameters: 𝑇 𝑜𝑖𝑙 𝑖𝑛 = 174°F 𝑇 𝑜𝑖𝑙 𝑜𝑢𝑡 = 114°F 𝐶 𝑝 𝑜𝑖𝑙 = 1.1 𝑚 𝑜𝑖𝑙 = 4 x 104 lbm/hr 𝑇 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 = 85°F 𝑇 𝑤𝑎𝑡𝑒𝑟 𝑜𝑢𝑡 = 115°F 𝐶 𝑝 𝑜𝑖𝑙 = 1.0 𝑚 𝑤𝑎𝑡𝑒𝑟 = ? What is the mass flow rate of cooling water? 8.8 x 104 lbm/hr 7.3 x 104 lbm/hr 2.2 x 104 lbm/hr 1.8 x 104 lbm/hr Correct answer is A. 8.8 x 104 lbm/hr Correct answer is A. ELO 1.2

Classification by Flowpath
Knowledge Check – NRC Bank The rate of heat transfer between two liquids in a heat exchanger will increase if the… (Assume specific heats do not change.) inlet temperature of the hotter liquid decreases by 20°F. inlet temperature of the colder liquid increases by 20°F. flow rates of both liquids decrease by 10 percent. flow rates of both liquids increase by 10 percent. Correct answer is D. Bank P1432 Correct answer is D. ELO 1.2

Other Heat Exchanger Characteristics
ELO 1.3 – Describe the difference between the following types of heat exchangers: single-pass versus multipass heat exchangers and regenerative versus nonregenerative heat exchangers. Most large heat exchangers are not purely parallel-flow, counter-flow, or cross-flow Combination types maximize heat exchanger efficiency Having two fluids pass each other several times within a single heat exchanger increases efficiency KA K1.05, Flow paths for the heat exchanger (counter flow and U-types) 1.8* 1.9* ELO 1.3

Single-pass heat exchanger Fluids pass each other once Multipass heat exchanger Fluids pass each other more than once Reverses flow in the tubes by use of one or more sets of U-bends in the tubes Baffles on the shell side of the heat exchanger direct fluid back and forth across the tubes to achieve the multipass effect Figure: Single-Pass and Multipass Heat Exchangers ELO 1.3

Heat exchangers are classified by their function Regenerative Nonregenerative Regenerative heat exchanger One fluid is both the cooling fluid and the cooled fluid Usually found in high-temperature systems Improves efficiency Nonregenerative heat exchanger Hot fluid is cooled by fluid from a separate system Energy (heat) removed is not returned to the system ELO 1.3

Regenerative and Nonregenerative Heat Exchanger Comparison
As previously stated: Regenerative heat exchanger – one fluid is both the cooling fluid and the cooled fluid Usually found in high-temperature systems Improves efficiency Nonregenerative heat exchanger – hot fluid is cooled by fluid from a separate system Energy (heat) removed is not returned to the system Figure: Regenerative Heat Exchanger Figure: Nonregenerative Heat Exchanger ELO 1.3

Knowledge Check In a ________________ heat exchanger, heat from the main process flow is ______________ the system. regenerative; rejected from regenerative; returned to nonregenerative; stored in nonregenerative; returned to Correct answer is B. - regenerative; returned to Correct answer is B. ELO 1.3

Heat Exchanger Startup & Operation
ELO 1.4 – Describe the operation of a typical heat exchanger to include startup and shutdown, control of temperature, and the effects and control of fouling. Startup Filled with fluid on both sides Cold fluid first Hot fluid slowly to minimize thermal shock Vent air and noncondensable gases (these can effectively reduce surface area and heat transfer) KA K1.01, K1.01 Startup/shutdown of a heat exchanger K1.02 Proper filling of a tube-and-shell heat exchanger K1.04 Effects of heat exchanger flow rates that are too high or too low and methods of proper flow adjustment K1.07 Control of heat exchanger temperatures K1.12 Effects of tube fouling and tube failure scaling on heat exchanger operation ; K1.14 Reasons for non-condensable gas removal Thermal shock will be discussed in detail later in this lesson. ELO 1.4

Shutdown Hot fluid normally stopped first Cold fluid stopped Never isolate from overpressure protection (either a discharge valve left open or a relief valve installed) ELO 1.4

Temperature Control Control the flow of either the cooled fluid or cooling fluid Example – Cooling fluid flow reduced: Cooling flow rate slowed, less heat transfer, heat exchanger outlet is higher (less cooling of system fluid) Figure: Operating Water Cleanup System ELO 1.4

Temperature Control Refer to the drawing:
Valves are identical and are initially 50 percent open To raise the temperature at point 7, the operator can adjust valve D (the cooling water throttle valve) in the closed or shut direction Figure: Operating Water Cleanup System ELO 1.4

Temperature Control Cooled fluid
Increasing cooled fluid flow will lower the outlet temperature Reverse will happen if the cooling fluid flow is slowed ELO 1.4

Fouling of Heat Exchange Surfaces
Foreign material (algae, scale, or debris) accumulates in a heat exchanger Lowers the efficiency Removal by Hydrolancing Chemical cleaning Backwashing Maintaining minimum flow through heat exchanger can prevent deposits Turbulent flow aids in heat transfer by agitating laminar film Chemicals can be added ELO 1.4

Knowledge Check Refer to the drawing of an operating lube oil heat exchanger below. Increasing the oil flow rate through the heat exchanger will cause the oil outlet temperature to _________ and the cooling water outlet temperature to __________. (Assume cooling water flow rate remains the same.) decrease; decrease decrease; increase increase; decrease increase; increase Correct answer is D. increase; increase Correct answer is D. ELO 1.4

Heat Exchanger Calculations
ELO 1.5 – Given the necessary data, calculate flow rates and temperatures for various types of heat exchangers. Heat transfer in a heat exchanger is by conduction and convection. The rate of heat transfer ( Q ) is calculated using: 𝑄 =𝑈 𝑜 𝐴 𝑜 ∆𝑇 𝑙𝑚 Where: 𝑄 = heat transfer rate 𝑈 𝑜 = heat transfer coefficient 𝐴 𝑜 = area ∆𝑇 𝑙𝑚 = mean temperature Related KAs K1.07 Control of heat exchanger temperatures K1.08 Relationship between flow rates and temperatures K1.14 Reasons for non-condensable gas removal ELO 1.5

Heat Exchanger Heat Balance Heat exchanger heat balance is dependent on mass flow, specific heat capacity of the fluids, and change in temperature Where: 𝑚 1 = mass flow rate Cp = specific heat capacity ΔT = temperature change across heat exchanger Using this heat balance equation, it is possible to calculate change in mass flow rate or temperature of either fluid in a heat exchanger. 𝑚 1 𝐶 𝑝1 ∆ 𝑇 1 = 𝑚 2 𝐶 𝑝2 ∆ 𝑇 2 ELO 1.5

Use the following table to determine flow or temperature difference of heat exchanger fluids: Action Formula Determine heat transferred across heat exchanger to or from one of the fluids 𝑄 = 𝑈 𝑜 𝐴 𝑜 ∆ 𝑇 𝑙𝑚 or 𝑄 =𝑚 𝑐 𝑝 ∆𝑇 Determine log mean temperature difference between two fluids if necessary ∆𝑇 𝑙𝑚 = ∆𝑇 2 − ∆𝑇 1 𝑙𝑛 ∆𝑇 2 ∆𝑇 1 Once heat transfer is known, solve for flow or temperature difference of other fluid 𝑚 1 𝐶 𝑝1 ∆ 𝑇 1 = 𝑚 2 𝐶 𝑝2 ∆ 𝑇 2 ELO 1.5

Refer to drawing of a lube oil heat exchanger. The heat exchanger is operating with the following parameters: 𝑇 𝑜𝑖𝑙 𝑖𝑛 = 165°F 𝑇 𝑜𝑖𝑙 𝑜𝑢𝑡 = 110°F 𝐶 𝑝 𝑜𝑖𝑙 = 1.1 BTU/lbm – °F 𝑚 𝑜𝑖𝑙 = 3.0 x 104 lbm/hr 𝑇 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 = 65°F 𝑇 𝑤𝑎𝑡𝑒𝑟 𝑜𝑢𝑡 = 95°F 𝐶 𝑝 𝑤𝑎𝑡𝑒𝑟 = 1.0 BTU/lbm – °F 𝑚 𝑤𝑎𝑡𝑒𝑟 = ? What is the mass flow rate of the cooling water? ELO 1.5

Heat Exchanger Demonstration
Step Formula Solution Solve for Q oil Q oil = m oil C p oil ∆ T oil Q = 3.0× 𝑙𝑏𝑚 ℎ𝑟 𝐵𝑇𝑈 𝑙𝑏𝑚 −℉ 55℉ Q =1.815× 𝐵𝑇𝑈 ℎ𝑟 Solve for m water m water C p water ∆T water = m oil C p oil ∆T oil 1.185× 𝐵𝑇𝑈 ℎ𝑟 = m water 𝐵𝑇𝑈 𝑙𝑏𝑚 −℉ 30℉ 1.185× 𝐵𝑇𝑈 ℎ𝑟 𝐵𝑇𝑈 𝑙𝑏𝑚 −℉ 30℉ = m water 6.05× 𝑙𝑏𝑚 ℎ𝑟 = m water ELO 1.5

Refer to the drawing of an operating lube oil heat exchanger below. Given the following information: 𝑚 𝑜𝑖𝑙 = 2.0 x 104 lbm/hr 𝑚 𝑤𝑎𝑡𝑒𝑟 = 3.0 x 104 lbm/hr 𝐶 𝑝 𝑜𝑖𝑙 = 1.1 BTU/lbm – °F 𝐶 𝑝 𝑤𝑎𝑡𝑒𝑟 = 1.0 BTU/lbm – °F 𝑇 𝑐𝑜𝑜𝑙𝑖𝑛𝑔 𝑤𝑎𝑡𝑒𝑟 𝑖𝑛 = 92°F 𝑇 𝑐𝑜𝑜𝑙𝑖𝑛𝑔 𝑤𝑎𝑡𝑒𝑟 𝑜𝑢𝑡 = 125°F 𝑇 𝑜𝑖𝑙 𝑖𝑛 = 180°F 𝑇 𝑜𝑖𝑙 𝑜𝑢𝑡 = ? Which one of the following is the temperature of the oil exiting the heat exchanger ( 𝑇 𝑜𝑖𝑙 𝑜𝑢𝑡 )? Correct answer is A. – 135F 135°F 140°F 145°F 150°F Correct answer is A. ELO 1.5

Heat Exchanger Tube Failure
ELO 1.6 – Explain the consequences of heat exchanger tube failure. Most common failure is a breach of the pressure boundary Tubes can be worn or eroded over time due to: High flow rates Particulate in the fluids passing through Vibration Caused by irregular flow pattern or flow is throttled Related KA K1.03 Basic heat transfer in a heat exchanger K1.13 Consequences of heat exchanger tube failure ELO 1.6

Heat Exchanger Failure
Vibration could compromise seal between tubes and tube sheet or sealing surfaces between fluids Failure of the heat exchanger will allow two fluids to mix Higher-pressure fluid forces into lower-pressure system Contaminated fluid is generally of low-pressure side Instrumentation shows an equalization of fluid temperatures at some mid-temperature Lower-pressure system level should rise and increase the level in an expansion tank and the higher-pressure system level should decrease ELO 1.6

Heat Exchanger Failure Example
Refer to the drawing of an operating cooling water system below. What occurs when a tube fails in the heat exchanger? Figure: Cooling Water System ELO 1.6

Heat Exchanger Failure Example
Refer to the drawing of an operating cooling water system below. What occurs when a tube fails in the heat exchanger? High-pressure fluid from the tubes would force into shell- side of heat exchanger Low-pressure system pressure would rise and high-pressure system surge tank level would lower as fluid lost High-pressure fluid being cooled would also add heat to low-pressure system Figure: Cooling Water System ELO 1.6

Knowledge Check – NRC Bank Borated water is flowing through the tubes of a heat exchanger being cooled by fresh water. The shell-side pressure is less than tube-side pressure. What will occur as a result of a tube failure? Shell-side pressure will increase and the borated water system will be diluted. Shell-side pressure will decrease and the borated water inventory will be depleted. Shell-side pressure will increase and the borated water inventory will be depleted. Shell-side pressure will decrease and the borated water system will be diluted. Correct answer is C. Correct answer is C. ELO 1.6

TLO 1 Summary Now that you have completed this TLO, you should be able to do the following: Describe the purpose, construction, and principles of operation for each major type of heat exchanger. TLO 1

TLO 1 Summary Some important points concerning heat exchangers are as follows: Two methods of constructing heat exchangers are plate type and tube type Heat exchangers can be classified by the following types of flow: Parallel flow — hot fluid and coolant flow in same direction Counter flow — hot fluid and coolant flow in opposite directions Cross flow — hot fluid and coolant flow perpendicularly The four heat exchanger parts are as follows: Tubes/plates Tube sheet Shell Baffles TLO 1

TLO 1 Summary Single-pass heat exchangers have fluids that pass each other once Multipass heat exchangers have fluids that pass each other more than once by using U-tubes and/or baffles Heat exchangers should be vented when starting Colder fluid is supplied first to a shutdown heat exchanger Regenerative heat exchangers use same fluid for heating and cooling Nonregenerative heat exchangers use separate fluids for heating and cooling Heat exchangers are often used in the following applications: Preheater Radiator Air conditioning evaporator and condenser Steam condenser TLO 1

NRC Exam Examples Refer to the drawing of an operating water cleanup system. All valves are identical and are initially 50 percent open. To lower the temperature at point 7, the operator can adjust valve __________ in the open direction. A B C D Correct answer is D. One click to reveal correct answer. TLO 1

NRC Exam Examples Refer to the drawing of an operating lube oil heat exchanger. Increasing the oil flow rate through the heat exchanger will cause the oil outlet temperature to __________ and the cooling water outlet temperature to __________. increase; increase increase; decrease decrease; increase decrease; decrease Correct answer is A. One click to reveal correct answer. TLO 1

NRC Exam Examples Refer to the drawing of an operating water cleanup system. Valves A, B, and C are fully open. Valve D is 80 percent open. If valve D is throttled to 50 percent, the temperature at point... 3 will decrease. 4 will increase. 5 will increase. 6 will decrease. Correct answer is B. One click to reveal correct answer. TLO 1

TLO 1 Summary Now that you have completed this TLO, you should be able to do the following: Describe the construction, effectiveness, and operation of the following types of heat exchangers and their components (tubes, tube sheets, baffles and shells): tube and shell, and plate. Describe hot and cold fluid flow paths in the following types of heat exchangers: parallel flow, counter flow, and cross flow. Describe the difference between the following types of heat exchangers: single-pass versus multipass heat exchangers and regenerative versus nonregenerative heat exchangers. Describe the operation of a typical heat exchanger to include the following: Startup and shutdown Control of temperature Effects and control of fouling Given the necessary data, calculate flow rates and temperatures for various types of heat exchangers. Explain the consequences of heat exchanger tube failure. TLO 1

Condenser Construction and Operation
TLO 2 – Describe the purpose, construction, and principles of operation of condensers. Type of heat exchanger that condenses substance from a gaseous state to a liquid state by cooling Removes latent heat from condensing fluid and transfers it to the coolant Tube and shell heat exchanger normally used as condenser Baffles added at inlet, prevents tube impingement from incoming gas or steam Industrial plants frequently employ large steam condensers as heat sinks for steam system TLO 2

State the purpose of a condenser. State the definitions of hotwell and condensate depression. State the reason(s) why condensers in large steam cycles operate at a vacuum. State the definition of thermal shock. Describe the relationship between condenser vacuum and backpressure. Explain the process of forming a vacuum within a condenser. TLO 2

Purpose of a Condenser Main Condenser
ELO 2.1 – State the purpose of a condenser. Main Condenser Steam condenser is a major component of steam cycle in power generation facilities Purpose of the condenser is to: Provide a heat sink for turbines to exhaust to give up latent heat of vaporization Operating in a vacuum provides lowest heat sink, maximizing available heat energy transfer Deareates condensate and feedwater, improving corrosion protection Related KA K1.10 Principle of operation of condensers ELO 2.1

Purpose of a Condenser Gives up latent heat of vaporization
Converts used steam into water for return to S/G Increases cycle's efficiency, allowing largest possible ΔT and ΔP between heat source and heat sink Figure: Single-Pass Condenser ELO 2.1

Purpose of Condenser – Thermo Review
Called latent heat of condensation Specific volume decreases drastically Creates a low pressure, maintaining vacuum Increases plant efficiency Figure: Condenser ELO 2.1

Purpose of Condenser – Thermo Review
Thermodynamic Cycle Liquid delivered to condensate pump, then feed pump where its pressure is raised (point 1) to the saturation pressure corresponding to steam generator temperature High-pressure liquid is delivered to steam generator where cycle is repeated Figure: Thermodynamic Cycle ELO 2.1

Purpose of a Condenser Condensed steam (saturated liquid) continues to transfer heat as it falls to the bottom of the condenser, called subcooling Subcooling prevents condensate pump cavitation Too much subcooling lowers efficiency Typically uses a single-pass, cross-flow condenser ELO 2.1

Purpose of a Condenser Knowledge Check
Condensers increase cycle efficiency by... allowing the cycle to operate with the largest possible ΔT. allowing the cycle to operate with the smallest possible ΔT. allowing the condensate to operate with the largest possible ΔT. allowing the condensate to operate with the smallest possible ΔT. Correct answer is A. Correct answer is A. ELO 2.1

Condenser Terms ELO 2.2 – State the definitions of hotwell and condensate depression. No Related KAs to this ELO Figure: Condenser Cross-Section ELO 2.2

Condenser Hotwell As steam comes in contact with tubes, it cools and condenses Series of baffles redirects steam to minimize direct impingement on the cooling water tubes Condensed steam falls to the bottom of condenser Bottom area is a reservoir where condensate collects and is called the hotwell ELO 2.2

Condensate Depression
As the condensate falls towards the hotwell, it subcools (goes below TSAT) as it comes in contact with tubes lower in the condenser Amount of subcooling is “condensate depression” TSAT – THOTWELL = the amount of condensate depression ANSWER: D. Figure: T-v Diagram for Typical Condenser ELO 2.2

Knowledge Check After the steam condenses, the saturated liquid continues to transfer heat to the cooling water as it falls to the bottom of the condenser, or hotwell. This is called ____________ and is _______________. subcooling; desirable subcooling; undesirable latent heat; desirable latent heat; undesirable Correct answer is A. Correct answer is A. ELO 2.2

Condenser Vacuum ELO 2.3 – State why condensers in large steam cycles are operated at a vacuum. Steam's latent heat of condensation is passed to water flowing through tubes Condenser usually operated at a vacuum Vacuum helps increase plant efficiency by extracting more work from the turbine Related KA K1.14 Reasons for noncondensable gas removal , K1.10 Principle of operation of condensers ELO 2.3

Condenser Vacuum Steam turbines designed to exhaust into a condenser that operates within a specific vacuum range If pressure increases above these limits, physical damage will occur to turbine blades When exhausted steam is condensed, its specific volume decreases, which helps maintain vacuum If condensate level is allowed to rise over lower tubes of condenser, fewer tubes are exposed for heat transfer, reducing heat transfer area If condenser is operating near design capacity, a reduction in effective surface area results in difficulty maintaining condenser vacuum Temperature and flow rate of cooling water through condenser control temperature of condensate This in turn controls saturation pressure (vacuum) of condenser Related KA K1.14 Reasons for noncondensable gas removal ELO 2.3

Condenser & Noncondensable Gases
If noncondensable gases are allowed to build up in condenser, vacuum decreases and saturation temperature at which steam condenses increases Noncondensable gases also blanket tubes of condenser, thus reducing surface area for heat transfer in condenser Reduction in heat transfer surface has same effect as a reduction in cooling water flow ELO 2.3

Vacuum & Noncondensable Gases
Condenser vacuum should be maintained as close to 29 inches of Mercury (Hg) as practical Allows maximum expansion of steam and therefore maximum work If condenser perfectly airtight and no air or noncondensable gases present in exhaust steam, only necessary to condense steam and remove condensate to create and maintain vacuum Figure: Condenser Cross-Section ELO 2.3

Vacuum & Noncondensable Gases
Sudden reduction in steam volume as it condenses creates a vacuum Pumping water from condenser as fast as it forms maintains vacuum Not possible to prevent entrance of air and other noncondensable gases into condenser Some method also needed to create initial vacuum in condenser Necessitates use of an air ejector and vacuum pump to establish and help maintain condenser vacuum ELO 2.3

Condenser Vacuum Knowledge Check
During normal nuclear power plant operation, a main condenser develops an air leak that decreases vacuum at a rate of 1 inch of Hg/minimum. Which of the following will increase because of this condition? Extraction steam flow rate Condenser hotwell temperature Low-pressure turbine exhaust steam moisture content Steam cycle efficiency Correct answer is B. Correct answer is B. ELO 2.3

Thermal Shock ELO 2.4 – State the definition of thermal shock.
Thermal shock is the severe stress produced in a material upon experiencing a sudden, unequally distributed change in temperature. Heat exchangers and condensers experience pressure stress and thermal stress due to function of transferring heat To reduce effects of these stresses, condensers should be as close as possible to operating temperatures prior to admitting steam from main turbine If equipment is not properly preheated, severe damage can occur to condenser tubes and the turbine Related KA K1.09 Definition of thermal shock ELO 2.4

Thermal Shock Prevention
Large temperature differences between two fluids in a heat exchanger or between a fluid and vapor in a condenser are good from a thermodynamic perspective However, they should be controlled in the system to prevent thermal shock to components Prevention Hotter fluids or vapors should be slowly admitted When out of service, heat exchangers are maintained, filled, and pressurized Condensers steam side vented, waterside filled ELO 2.4

Thermal Shock Prevention
Main condensers must be at operating pressures (vacuum) prior to admitting steam Colder fluid should be supplied to heat exchanger first, followed by hotter fluid When securing a heat exchanger or condenser hot fluid, vapor is stopped first Colder fluid is allowed to operate for a period of time to cool down component(s) and reduce stress ELO 2.4

Thermal Shock Heat exchangers and condensers should not be isolated in such a manner that they do not have relief valve protection Liquid isolated within the heat exchanger could warm up due to surrounding air temperature Increased temperature would lead to expansion of liquid and damage to heat exchanger if not protected from overpressure ELO 2.4

Thermal Shock Knowledge Check
The major thermodynamic concern resulting from rapidly cooling a reactor vessel is... thermal shock. stress corrosion. loss of shutdown margin. loss of subcooling margin. Correct answer is A. Correct answer is A. ELO 2.4

Vacuum Versus Backpressure
ELO 2.5 – Describe the relationship between condenser vacuum and backpressure. Pressure and Vacuum Relationship If pressure is below that of atmosphere as in case of a condenser, it is a vacuum Vacuum, although a negative pressure, is normally expressed as a positive value Related KAs K1.11 Relationship between condenser vacuum and backpressure 2.1* 2.1* ELO 2.5

Pressure is a measure of force exerted per unit area on boundaries of a substance (or system) Collisions of molecules of substance with boundaries of system cause force Pressure is frequently expressed in units of lbf/in2 (psi) in the English system of measurement Pressure can also be measured using equivalent columns of liquid, such as water (H2O) or mercury (Hg) These scales use units of inches of H2O or Hg Height of column of liquid provides a certain pressure that can be directly converted to force per unit area ELO 2.5

Perfect vacuum would correspond to absolute zero pressure Gauge pressures are positive if they are above atmospheric pressure and negative if they are below atmospheric pressure Vacuum, although a negative pressure, is normally expressed as a positive value Related KAs K1.11 Relationship between condenser vacuum and backpressure 2.1* 2.1* ELO 2.5

Pressure and Vacuum Relationship Figure: Comparison of Pressure Ranges ELO 2.5

Pressure and Vacuum Relationship P abs =P atm + P gauge P abs =P atm − P vac Where: P abs = absolute pressure P atm = atmospheric pressure P gauge = gauge pressure P vac = vacuum pressure ELO 2.5

Table shows the relationship between pressure measurements associated with a condenser 29.9 inches of Hg pressure equals zero (0) inches of mercury vacuum (HgV) and zero (0) inches of Hg equals 29.9 inches of HgV PSIA PSIG Inches of HgV Inches of Hg 14.7 29.90 13.7 -1.0 2.03 27.87 12.7 -2.0 4.06 25.84 11.7 -3.0 6.09 23.81 ELO 2.5

Given that a condenser pressure is 3 inches of Hg, determine the corresponding vacuum by: 29.9 – 3 = 26.9 inches of Hg vacuum ELO 2.5

Knowledge Check A turbine has a design backpressure of 5 inches of Hg. The main condenser is operating at 28 inches of HgV. What is the margin to design for the turbine? 24.9 inches of Hg 3 inches of Hg 3.1 inches of Hg 24.9 inches of HgV Correct answer is C. Correct answer is C. ELO 2.5

Drawing a Vacuum ELO 2.6 – Explain the process of forming a vacuum within a condenser. To prepare plant for startup, a vacuum must be drawn in the main condenser Allows recirculation of feedwater and condensate in order to clean up and deaerate these systems Allows warming of the main turbine Allows identification of any condenser tube leaks prior to placing the turbine in service Related KA K1.10 Principle of operation of condensers ELO 2.6

Drawing a Vacuum Vacuum is a condition where all molecules are removed
Allows steam cycle to exhaust to lowest possible heat sink, providing largest enthalpy drop through the main turbine Consists of isolating air in-leakage paths, establishing cooling water flow, then removing air from the condenser shell Mechanical vacuum pump initially removes air from condenser, then shifts to air ejectors Air removal during operation is essential for efficient operation If air leaks into the condenser, pressure increases, temperature increases, and plant efficiency decreases because the turbine exhaust enthalpy increases ELO 2.6

Drawing a Vacuum Action Step How Discussion Establish cooling flow
Startup support cooling systems Startup circulation water system Startup condensate system Various systems provide cooling for components necessary for vacuum pull (condensate pumps, air compressors, mechanical vacuum pumps) Isolate all air inleakage paths to the main condenser Complete valve lineup checks Close vacuum breakers Establish steam seal on turbines All possible leakage paths must be isolated to prevent loss of condenser pressure and temperature control. Air leakage across turbine shaft seals is removed via gland exhaust system. Establish turbine seals Startup steam sealing system Startup gland exhaust system Turbine shafts are sealed using labyrinth seals and low-pressure steam to prevent high-pressure steam from leaking out and air from leaking in. Remove air from the condenser Startup the mechanical vacuum pump (also known as a hogger) Shift to the air ejectors when vacuum reaches approximately 26 inches of HgV Mechanical vacuum pump removes air out of main condenser. As air molecules are removed, pressure decreases. ELO 2.6

Drawing a Vacuum Knowledge Check
During normal nuclear power plant operation, why does air entry into the main condenser reduce the thermodynamic efficiency of the steam cycle? The rate of steam flow through the main turbine increases. The condensate subcooling in the main condenser increases. The enthalpy of the low-pressure turbine exhaust increases. The air mixes with the steam and enters the condensate. Correct answer is C. Correct answer is C. ELO 2.6

TLO 2 Summary Now that you have completed this TLO, you should be able to do the following: Describe the purpose, construction, and principles of operation of condensers. TLO 2

TLO 2 Summary Condenser is type of heat exchanger used to condense a substance from a gaseous state to a liquid state by cooling Condenser removes latent heat from fluid and transfers it to coolant Condenser removes latent heat of vaporization, condensing vapor into liquid Hotwell is at the bottom of condenser where condensed steam is collected and pumped back into feedwater Condensate depression is amount condensate is cooled below saturation (degrees subcooled) Condensers operate at a vacuum to ensure temperature (thus the pressure) of steam is as low as possible, maximizing ΔT and ΔP between source and heat sink, ensuring highest cycle efficiency Thermal shock is stress produced in a body or in a material as a result of undergoing a sudden change in temperature TLO 2

TLO 2 Summary Now that you have completed this TLO, you should be able to do the following: State the purpose of a condenser. State the definitions of hotwell and condensate depression. State the reason(s) why condensers in large steam cycles operate at a vacuum. State the definition of thermal shock. Describe the relationship between condenser vacuum and backpressure. Explain the process of forming a vacuum. TLO 2

Heat Exchangers & Condensers Summary
This module covered types of heat exchangers and condensers, their applications and advantages, proper methods for operation, and system responses. Heat Exchangers The type of flow classifies different heat exchangers Parallel flow — hot fluid and coolant flow in same direction Counter flow — hot fluid and coolant flow in opposite directions Cross flow — hot fluid and coolant flow perpendicularly Single-pass heat exchangers have fluids that pass each other once Multipass heat exchangers have fluids that pass each other more than once through using U-tubes and/or baffles Regenerative heat exchangers use same fluid for heating and cooling Nonregenerative heat exchangers use separate fluids for heating and cooling

Condensers perform an important function in any heat cycle. They provide a heat sink that allows the cycle to operate at maximum efficiency. Condensers remove latent heat of vaporization, condensing vapor into a liquid Condensers operate at a vacuum to ensure temperature (thus pressure) of steam is as low as possible, maximizing ΔT and ΔP between source and heat sink, ensuring highest cycle efficiency

Now that you have completed this module, you should be able to do the following: Describe the purpose, construction, and principles of operation for each major type of heat exchanger. Describe the purpose, construction, and principles of operation of condensers.

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